In this review, we describe our current understanding of cluster formation: from the general picture of collapse from initial density fluctuations in an expanding Universe to detailed simulations of cluster formation including the effects of galaxy formation. We outline both the areas in which highly accurate predictions of theoretical models can be obtained and areas where predictions are uncertain due to uncertain physics of galaxy formation and feedback. The former includes the description of the structural properties of the dark matter halos hosting cluster, their mass function and clustering properties. Their study provides a foundation for cosmological applications of clusters and for testing the fundamental assumptions of the standard model of structure formation. The latter includes the description of the total gas and stellar fractions, the thermodynamical and non-thermal processes in the intracluster plasma. Their study serves as a testing ground for galaxy formation models and plasma physics. In this context, we identify a suitable radial range where the observed thermal properties of the intra-cluster plasma exhibit the most regular behavior and thus can be used to define robust observational proxies for the total cluster mass. We put particular emphasis on examining assumptions and limitations of the widely used self-similar model of clusters. Finally, we discuss the formation of clusters in non-standard cosmological models, such as non-Gaussian models for the initial density field and models with modified gravity, along with prospects for testing these alternative scenarios with large cluster surveys in the near future.
Chapman's (1957) conductive model of the solar corona is characterized by a temperature varying as r**(-2/7) with heliocentric distance r. The density distribution in this non-isothermal hydrostatic model has a minimum value at 123 RS, and increases with r above that altitude. It is shown that this hydrostatic model becomes convectively unstable above r = 35 RS, where the temperature lapse rate becomes superadiabatic. Beyond this radial distance heat conduction fails to be efficient enough to keep the temperature gradient smaller than the adiabatic lapse rate. We report the results obtained by Lemaire (1968) who showed that an additional mechanism is then required to transport the energy flux away from the Sun into interplanetary space. He pointed out that this additional mechanism is advection: i.e. the stationary hydrodynamic expansion of the corona. In other words the corona is unable to stay in hydrostatic equilibrium. The hydrodynamic solar wind expansion is thus a physical consequence of the too steep (superadiabatic) temperature gradient beyond the peak of coronal temperature that can be determined from white light brightness distributions observed during solar eclipses. The thermodynamic argument for the existence of a continuous solar wind expansion which is presented here, complements Parker's classical argument based on boundary conditions imposed to the solutions of the hydrodynamic equations for the coronal expansion: i.e. the inability of the mechanical forces to hold the corona in hydrostatic equilibrium. The thermodynamic argument presented here is based on the energy transport equation. It relies on the temperature distribution which becomes super-adiabatic above a certain altitude in the inner corona.
We investigate statistical and individual astrophysical properties of active galactic nuclei (AGN), such as parsec-scale flux density, core dominance, angular and linear sizes, maximum observed brightness temperatures of VLBI core components, spectral index distributions for core and jet components, and evolution of brightness temperature along the jets. Furthermore, we statistically compare core flux densities and brightness temperature as well as jet spectral indices of gamma-ray bright and weak sources. We used 19 very long baseline interferometry (VLBI) observing sessions carried out simultaneously at 2.3 and 8.6 GHz with the participation of 10 Very Long Baseline Array (VLBA) stations and up to 10 additional geodetic telescopes. The observations span the period 1998-2003. We present here single-epoch results from high-resolution radio observations of 370 AGN. VLBI images at 2.3 and 8.6 GHz as well as Gaussian models are presented and analyzed. At least one-fourth of the cores are completely unresolved on the longest baselines of the global VLBI observations. The VLBI core components are partially opaque with the median value of spectral index of alpha_core=0.3, while the jet features are usually optically thin alpha_jet=-0.7. Spectral index typically decreases along the jet ridge line due to the spectral aging, with a median value of -0.05 mas^-1. Brightness temperatures are found to be affected by Doppler boosting and reaching up to \sim10^13 K with a median of \sim2.5x10^11 K at both frequencies. The brightness temperature gradients along the jets typically follow a power law T_b\simr^-2.2 at both frequencies. 147 sources (40%) positionally associated with gamma-ray detections from the Fermi LAT Second Source Catalog are found to have higher core flux densities and brightness temperatures, and are also characterized by less steep radio spectrum of the optically thin jet emission.
We present a cosmography analysis of the Local Universe based on the recently released Two-Micron All-Sky Redshift Survey (2MRS). Our method is based on a Bayesian Networks Machine Learning algorithm (the Kigen-code) which self-consistently samples the initial density fluctuations compatible with the observed galaxy distribution and a structure formation model given by second order Lagrangian perturbation theory (2LPT). From the initial conditions we obtain an ensemble of reconstructed density and peculiar velocity fields which characterize the local cosmic structure with high accuracy unveiling nonlinear structures like filaments and voids in detail. Coherent redshift space distortions are consistently corrected within 2LPT. From the ensemble of cross-correlations between the reconstructions and the galaxy field and the variance of the recovered density fields we find that our method is extremely accurate up to k ~ 1 h Mpc^-1 and still yields reliable results up to k ~ 2 h Mpc^-1. The motion of the local group we obtain within ~ 80 h^-1 Mpc (v_LG=522+-86 km s^-1, l_LG=291^o +- 16^o, b_LG=34^o+-8^o) is in good agreement with measurements derived from the CMB and from direct observations of peculiar motions and is consistent with the predictions of LambdaCDM.
We used three sets of high-resolution spectra acquired with the multifiber facility FLAMES at the Very Large Telescope of the European Southern Observatory to investigate the chemical and kinematical properties of a sample of 42 horizontal branch (HB) stars, 18 Blue Straggler Stars (BSSs) and 86 main sequence turn-off and sub-giant branch stars in the nearby globular cluster NGC 6397. We measured rotational velocities and Fe, O and Mg abundances. All the unevolved stars in our sample turn out to have low rotational velocites (v sin i< 10\kms), while HB stars and BSSs show a broad distribution, with values ranging from 0 to 70 \kms. For HB stars with T<10500 K there is a clear temperature-oxygen anti-correlation, that can be understood if the star position along the HB is mainly determined by the He content. The hottest BSSs and HB stars (with temperatures T>8200 K and T> 10500 K, respectively) also show significant deviations in their iron abundance with respect to the cluster metallicity (as traced by the unevolved stars, [Fe/H]=-2.12). While similar chemical patterns have been already observed in other hot HB stars, this is the first evidence ever collected for BSSs. We interprete these abundance anomalies as due to the metal radiative levitation, occurring in stars with shallow or no convective envelopes.
We examine the distribution of transition discs as a function of mm flux. We confirm that as expected in any model in which most primordial discs turn into transition discs and in which mm flux declines with time, transition discs have lower mm fluxes on average than primordial discs. However, we find that the incidence of transition discs does not, as expected, fall monotonically towards large mm fluxes and we investigate the hypothesis that these mm bright transition discs may have a distinct physical origin. We find that mm bright transition discs occupy a separate region of parameter space. Transition discs in the bright mm sub-sample have systematically higher accretion rates and inner hole radii than those in the faint mm sub-sample, along with being systematically weighted to earlier spectral types.
Motivated by the observed connection between molecular hydrogen (H2) and star
formation, we present a method for tracking the non-equilibrium abundance and
cooling processes of H2 and H2-based star formation in Smoothed Particle
Hydrodynamic simulations. The local abundances of H2 are calculated by
integrating over the hydrogen chemical network. This calculation includes the
gas-phase and dust grain formation of H2, shielding of HI and H2, and
photodissociation of H2 by Lyman-Werner radiation from nearby stellar
populations. Because this model does not assume equilibrium abundances, it is
particularly well suited for simulations that model low-metallicity
environments, such as dwarf galaxies and the early Universe. We further
introduce an explicit link between star formation and local H2 abundance. This
link limits star formation to "star-forming regions," represented by areas with
abundant H2.
With this implementation, we determine the effect of H2 on star formation in
a cosmological simulation of a dwarf galaxy. This simulation is the first
cosmological simulation with non-equilibrium H2 abundances to be integrated to
a redshift of zero or to include efficient SN feedback. We find that our
simulations are consistent with the observed Tully-Fisher, global
Kennicutt-Schmidt, and resolved Kennicutt-Schmidt relations. We find that the
inclusion of shielding of both the atomic and molecular hydrogen and, to a
lesser extent, the additional cooling from H2 at temperatures between 200 and
5000 K increases the amount of cold gas in the galaxies. The changes to the ISM
result in an increased amount of cold, dense gas in the disk of the galaxy and
the formation of a clumpier interstellar media (ISM). The explicit link between
star formation and H2 and the clumpier ISM results in a bluer galaxy with a
greater spatial distribution of star formation at a redshift of zero.
(abridged)
We measure the evolution of the X-ray luminosity-temperature (L_X-T) relation since z~1.5 using a sample of 211 serendipitously detected galaxy clusters with spectroscopic redshifts drawn from the XMM Cluster Survey first data release (XCS-DR1). This is the first study spanning this redshift range using a single, large, homogeneous cluster sample. Using an orthogonal regression technique, we find no evidence for evolution in the slope or intrinsic scatter of the relation since z~1.5, finding both to be consistent with previous measurements at z~0.1. However, the normalisation is seen to evolve negatively with respect to the self-similar expectation: we find E(z)^{-1} L_X = 10^{44.67 +/- 0.09} (T/5)^{3.04 +/- 0.16} (1+z)^{-1.5 +/- 0.5}, which is within 2 sigma of the zero evolution case. We see milder, but still negative, evolution with respect to self-similar when using a bisector regression technique. We compare our results to numerical simulations, where we fit simulated cluster samples using the same methods used on the XCS data. Our data favour models in which the majority of the excess entropy required to explain the slope of the L_X-T relation is injected at high redshift. Simulations in which AGN feedback is implemented using prescriptions from current semi-analytic galaxy formation models predict positive evolution of the normalisation, and differ from our data at more than 5 sigma. This suggests that more efficient feedback at high redshift may be needed in these models.
LP 209-28 and LP 209-27 have similar proper motions as tabulated by several catalogues. Using seven astrometric epochs spanning 59 years, we confirm a common tangential velocity by measuring a constant angular separation of rho = 666.62+/-0.09 arcsec. Accurate SDSS and 2MASS photometry indicates that they are normal dwarfs of approximate spectral types K7 V and M3 V. However, from their apparent magnitudes, both LP 209-28 and LP 209-27 are located at 200-250 pc, from where one can deduce an astonishing projected physical separation of 0.6-0.8 pc. The system Koenigstuhl 6 AB represents another world record among the least-bound systems with low-mass star components.
Galaxy clustering data can be used to measure H(z), D_A(z), and \beta(z).
Here we present a method for using effective multipoles of the galaxy two-point
correlation function (\xi_0(s), \xi_2(s), \xi_4(s), and \xi_6(s), with s
denoting the comoving separation) to measure H(z), D_A(z), and \beta(z), and
validate it using LasDamas mock galaxy catalogs. Our definition of effective
multipoles explicitly incorporates the discreteness of measurements, and treats
the measured correlation function and its theoretical model on the same
footing. We find that for the mock data, \xi_0 + \xi_2 + \xi_4 captures nearly
all the information, and gives significantly stronger constraints on H(z),
D_A(z), and \beta(z), compared to using only \xi_0 + \xi_2.
We apply our method to the sample of LRGs from the SDSS DR7 without assuming
a dark energy model or a flat Universe. We find that \xi_4(s) deviates on
scales of s<60\,Mpc/h from the measurement from mock data (in contrast to
\xi_0(s), \xi_2(s), and \xi_6(s)), leading to a significant difference in the
measured mean values of H(z), D_A(z), and \beta(z) from \xi_0 + \xi_2 and \xi_0
+ \xi_2 + \xi_4, thus it should not be used in deriving parameter constraints.
We obtain {H(0.35),D_A(0.35),\Omega_mh^2,\beta(z)} = {79.6_{-8.7}^{+8.3}km
s^{-1}Mpc^{-1}, 1057_{-87}^{+88}Mpc, 0.103\pm0.015, 0.44\pm0.15} using \xi_0 +
\xi_2. We find that H(0.35)r_s(z_d)/c and D_A(0.35)/r_s(z_d) (where r_s(z_d) is
the sound horizon at the drag epoch) are more tightly constrained:
{H(0.35)r_s(z_d)/c, D_A(0.35)/r_s(z_d)} =
{0.0437_{-0.0043}^{+0.0041},6.48_{-0.43}^{+0.44}} using \xi_0 + \xi_2. We
conclude that the multipole method can be used to isolate systematic
uncertainties in the data, and provide a useful cross-check of parameter
measurements from the full correlation function.
We present an analysis of the papers published in the journals Nature and Science in the years from 2006 to 2010. During this period, a total of 7788 papers were published in the two journals. This includes 544 astronomy papers that comprise 7.0% of the papers in `all' research fields and 18.9% of those in the fields of `physical sciences'. The sub-fields of research of the astronomy papers are distributed, in descending order of number of papers, in Solar System, stellar astronomy, galaxies and the universe, the Milky Way Galaxy, and exoplanets. The observational facilities used for the studies are mainly ground-based telescopes (31.1%), spacecrafts (27.0%), and space telescopes (22.8%), while 16.0% of papers did not use any noticeable facilities and 1.7% used other facilities. Korean scientists have published 86 papers (33 in Nature and 53 in Science), which is 1.10% of all the papers (N=7788) in the two journals. The share of papers by Korean astronomers among the scientific papers by Koreans is 8.14%, slightly higher than the contribution of astronomy papers (7.0%) in both journals.
We have performed a near-infrared photometric monitoring of 39 galactic young star clusters and star-forming regions, known as {\em NIP of Stars}, between the years 2009--2011, using the Swope telescope at Las Campanas Observatory (Chile) and the RetroCam camera. The primary objective of the campaign is to perform a census of photometric variability of such clusters and to discover massive eclipsing binary stars. In this work, we describe the general idea, the implementation of the survey, and the first preliminary results of some of the observed clusters. This monitoring program is complementary to the Vista Variables in the V\'ia L\'actea (VVV), as the brightest sources observed in NIP of Stars are saturated in VVV.
By mid-19th century, astronomers strongly suspected that the Moon was largely dry and airless, based on the absence of any observable weather. In 1892, William H. Pickering made a series of careful occultation measurements that allowed him to conclude that the lunar surface's atmospheric pressure was less than 1/4000th of Earth's. Any number of strange ideas arose to contradict this. Respectable scientists realized that significant amounts of water on the Moon's surface would rapidly sublime into the vacuum. Since 2007, however, the field has started another revolution in thought, and we describe this, including some lesser known aspects.
In Part I we recount the history of observation and laboratory measurement culminating with the excavation of water from a permanently shadowed region near the lunar South Pole by the impact of the LCROSS mission in 2009. In this installment we consider what the current data imply about the nature of water and other volatile substances on and in the Moon.
For centuries some scientists have argued that there is activity on the Moon (or water, as recounted in Parts I & II), while others have thought the Moon is simply a dead, inactive world. The question comes in several forms: is there a detectable atmosphere? Does the surface of the Moon change? What causes interior seismic activity? From a more modern viewpoint, we now know that as much carbon monoxide as water was excavated during the LCROSS impact, as detailed in Part I, and a comparable amount of other volatiles were found. At one time the Moon outgassed prodigious amounts of water and hydrogen in volcanic fire fountains, but released similar amounts of volatile sulfur (or SO2), and presumably large amounts of carbon dioxide or monoxide, if theory is to be believed. So water on the Moon is associated with other gases. We review what is known (and touch on what is unknown) about outgassing of various gases from the Moon.
In this paper, we present the higher order spectra of a scalar field produced through the higher derivative interactions in the initially anisotropic universe. Although we ignore the backreaction of the scalar field on the geometry, our analysis should have much overlap with the quantum fluctuations of the inflaton field in the anisotropic universe. We also include the planar modes whose momenta are along the plane which is perpendicular to the primordial preferred direction, for which effects of the initial anisotropy are not suppressed. The presence of a negative frequency mode produces features distinguishable from the case of the de Sitter inflation. We also show that richer features appear in the trispectra due to the primordial anisotropy.
I describe the logical basis of the method that I developed in 1962 and 1963 to define a quantum operator corresponding to the observable particle number of a quantized free scalar field in a spatially-flat isotropically expanding (and/or contracting) universe. This work also showed for the first time that particles were created from the vacuum by the curved space-time of an expanding spatially-flat FLRW universe. The same process is responsible for creating the nearly scale-invariant spectrum of quantized perturbations of the inflaton scalar field during the inflationary stage of the expansion of the universe. I explain how the method that I used to obtain the observable particle number operator involved adiabatic invariance of the particle number (hence, the name adiabatic regularization) and the quantum theory of measurement of particle number in an expanding universe. I also show how I was led in a surprising way, to the discovery in 1964 that there would be no particle creation by these spatially-flat FLRW universes for free fields of any integer or half-integer spin satisfying field equations that are invariant under conformal transformations of the metric. The methods I used to define adiabatic regularization for particle number, were based on generally-covariant concepts like adiabatic invariance and measurement that were fundamental and determined results that were unique to each given adiabatic order.
We perform a comparative analysis of the chemical kinetics of CO and $\rm PH_3$ in Jupiter and Saturn to assess the full set of constraints available on the troposphere water abundance in the two giant planets. For carbon monoxide we employ both a widely used CO kinetic scheme from Yung et al, and a newly identified CO chemical scheme from Visscher and Moses. For $\rm PH_3$ chemical scheme, we use the same chemical scheme as in Visscher and Fegley. Yung's chemical scheme for CO yields a water enrichment of 0.95 - 23.0 times solar abundance on Jupiter, and an upper limit of 14.0 for Saturn. Visscher's chemical scheme in contrast produces a water enrichment of 0.24 - 2.6 times solar abundance in Jupiter, and for Saturn an upper limit for water enrichment of 8.0. From this scheme, which takes advantage of the most up-to-date kinetics, we preclude high water enrichments on Jupiter and Saturn, and show that the kinetics approach yields Jovian bulk abundance in which values of C/O elevated relative to solar are admissible. Our result is consistent with recent reinterpretation of Galileo Probe data in which Jupiter formed in a water-depleted portion of the protoplanetary disk (Mousis et al).
For the first time we study the Eastern nucleus in greater detail and search for the more extended emission in the molecular gas in different CO line transitions of the famous ULIRG Arp 220. Furthermore we present a model of the merger in Arp 220 on large scales with the help of the CO data and an optical and near-infrared composite HST image of the prototypical ULIRG. Using the Plateau de Bure Interferometer (PdBI) we obtained CO(2-1) and (1-0) data at wavelengths of 1 and 3 mm in 1994, 1996, 1997 and 2006 at different beam sizes and spatial resolutions. The simulations of the merger in Arp 220 were performed with the Identikit modeling tool. The model parameters that describe the galaxy merger best give a mass ratio of 1:2 and result in a merger of ~6x10^8 yrs. The low resolution CO(1-0) PdBI observations suggest that there are indications for emission ~10" towards the south, as well as to the north and to the west of the two nuclei.
The Korteweg-de Vries (KdV) equation is a non-linear wave equation that has played a fundamental role in diverse branches of mathematical and theoretical physics. In the present paper, we consider its significance to cosmology. It is found that the KdV equation arises in a number of important scenarios, including inflationary cosmology, the cyclic universe, loop quantum cosmology and braneworld models. Analogies can be drawn between cosmic dynamics and the propagation of the solitonic wave solution to the equation, whereby quantities such as the speed and amplitude profile of the wave can be identified with cosmological parameters such as the spectral index of the density perturbation spectrum and the energy density of the universe. The unique mathematical properties of the Schwarzian derivative operator are important to the analysis. A connection with dark solitons in Bose-Einstein condensates is briefly discussed.
Context: Accurate fundamental parameters of stars are essential for the asteroseismic analysis of data from the NASA Kepler mission. Aims: We aim at determining accurate atmospheric parameters and the abundance pattern for a sample of 82 red giants that are targets for the Kepler mission. Methods: We have used high-resolution, high signal-to-noise spectra from three different spectrographs. We used the iterative spectral synthesis method VWA to derive the fundamental parameters from carefully selected high-quality iron lines. After determination of the fundamental parameters, abundances of 13 elements were measured using equivalent widths of the spectral lines. Results: We identify discrepancies in log g and [Fe/H], compared to the parameters based on photometric indices in the Kepler Input Catalogue (larger than 2.0 dex for log g and [Fe/H] for individual stars). The Teff found from spectroscopy and photometry shows good agreement within the uncertainties. We find good agreement between the spectroscopic log g and the log g derived from asteroseismology. Also, we see indications of a potential metallicity effect on the stellar oscillations. Conclusions: We have determined the fundamental parameters and element abundances of 82 red giants. The large discrepancies between the spectroscopic log g and [Fe/H] and values in the Kepler Input Catalogue emphasize the need for further detailed spectroscopic follow-up of the Kepler targets in order to produce reliable results from the asteroseismic analysis.
We review the implementation of individual particle time-stepping for N-body dynamics. We present a class of integrators derived from second order Hamiltonian splitting. In contrast to the usual implementation of individual time-stepping, these integrators are momentum conserving and show excellent energy conservation in conjunction with a symmetrized time step criterion. We use an explicit but approximate formula for the time symmetrization that is compatible with the use of individual time steps. No iterative scheme is necessary. We implement these ideas in the HUAYNO (available online at www.amusecode.org) code and present tests of the integrators and show that the presented integration schemes shows good energy conservation, with little or no systematic drift, while conserving momentum and angular momentum to machine precision for long term integrations.
Our main purpose is to estimate the e?ect of assuming uniform density on the line-of-sight in PDR chemistry models, compared to a more realistic distribution for which total gas densities may well vary by several orders of magnitude. A secondary goal of this paper is to estimate the amount of molecular hydrogen which is not properly traced by the CO (J = 1 -> 0) line, the so-called "dark molecular gas". We use results from a magnetohydrodynamical (MHD) simulation as a model for the density structures found in a turbulent diffuse ISM with no star-formation activity. The Meudon PDR code is then applied to a number of lines of sight through this model, to derive their chemical structures. It is found that, compared to the uniform density assumption, maximal chemical abundances for H2, CO, CH and CN are increased by a factor 2 to 4 when taking into account density fluctuations on the line of sight. The correlations between column densities of CO, CH and CN with respect to those of H2 are also found to be in better overall agreement with observations. For instance, at N(H2) > 2.10^{20} cm-2, while observations suggest that d[log N(CO)]=d[log N(H2)] = 3.07 +/- 0.73, we find d[log N(CO)]=d[log N(H2)] =14 when assuming uniform density, and d[log N(CO)]=d[log N(H2)] = 5.2 when including density fluctuations.
We present new observational determination of the evolution of the rest-frame 70 and 160 micron and total infrared (TIR) galaxy luminosity functions (LFs) using 70 micron data from the Spitzer Wide-area Infrared Extragalactic Legacy Survey (SWIRE). The LFs were constructed for sources with spectroscopic redshifts only in the XMM-LSS and Lockman Hole fields from the SWIRE photometric redshift catalogue. The 70 micron and TIR LFs were constructed in the redshift range 0<z<1.2 and the 160 micron LF was constructed in the redshift range 0<z<0.5 using a parametric Bayesian and the vmax methods. We assume in our models, that the faint-end power-law index of the LF does not evolve with redshifts. We find the the double power-law model is a better representation of the IR LF than the more commonly used power-law and Gaussian model. We model the evolution of the FIR LFs as a function of redshift where where the characteristic luminosity, $L^\ast$ evolve as $\propto(1+z)^{\alpha_\textsc{l}}$. The rest-frame 70 micron LF shows a strong luminosity evolution out to z=1.2 with alpha_l=3.41^{+0.18}_{-0.25}. The rest-frame 160 micron LF also showed rapid luminosity evolution with alpha_l=5.53^{+0.28}_{-0.23} out to z=0.5. The rate of evolution in luminosity is consistent with values estimated from previous studies using data from IRAS, ISO and Spitzer. The TIR LF evolves in luminosity with alpha_l=3.82^{+0.28}_{-0.16} which is in agreement with previous results from Spitzer 24 micron which find strong luminosity evolution. By integrating the LF we calculated the co-moving IR luminosity density out to z=1.2, which confirm the rapid evolution in number density of LIRGs and ULIRGs which contribute ~68^{+10}_{-07} % to the co-moving star formation rate density at z=1.2. Our results based on 70 micron data confirms that the bulk of the star formation at z=1 takes place in dust obscured objects.
We introduce a new survey to map the radio continuum halos of a sample of 35
edge-on spiral galaxies at 1.5 GHz and 6 GHz in all polarization products. The
survey is exploiting the new wide bandwidth capabilities of the Karl G. Jansky
Very Large Array (i.e. the Expanded Very Large Array, or EVLA) in a variety of
array configurations (B, C, and D) in order to compile the most comprehensive
data set yet obtained for the study of radio halo properties. This is the first
survey of radio halos to include all polarization products.
In this first paper, we outline the scientific motivation of the survey, the
specific science goals, and the expected improvements in noise levels and
spatial coverage from the survey. Our goals include investigating the physical
conditions and origin of halos, characterizing cosmic ray transport and wind
speed, measuring Faraday rotation and mapping the magnetic field, probing the
in-disk and extraplanar far-infrared - radio continuum relation, and
reconciling non-thermal radio emission with high-energy gamma-ray models. The
sample size allows us to search for correlations between radio halos and other
properties, including environment, star formation rate, and the presence of
AGNs. In a companion paper (Paper II) we outline the data reduction steps and
present the first results of the survey for the galaxy, NGC 4631.
Symbiotic X-ray binaries (SyXBs) comprise a rare class of low-mass X-ray
binaries. We study the Galactic SyXBs, which we consider as detached binaries
composed of low-mass giants and wind-fed neutron star companions, by simulation
of the interaction of a magnetized neutron star (NS) with its environment and
utilizing a population synthesis code. We focus mainly on the parameters that
influence observational appearance of the SyXB: the donor wind velocity (vw)
and the angular momentum distribution in the shell of matter settling onto NS.
We estimate the birthrate of SyXB as $\sim 4.1\times 10^{-5}$ yr$^{-1}$ to $
\sim 6.6\times 10^{-6}$ yr$^{-1}$ and their number in the Galaxy as $\sim$(100
-- 1000). Assumed stellar wind velocity from cool giants is the input parameter
that influences the model SyXBs population most.
Among known SyXBs or candidate systems, 4U 1954+31 and IGR J16358-4724 in
which NS have very long spin periods may host quasi-spherically accreting NSs.
GX 1+4 has a peculiar long-term spin behaviour and it may also be a
quasi-spherical wind-accreting source. We cannot identify whether there are
wind-fed accretion disks in 4U 1700+24, Sct X-1, IRXS J180431.1-273932 and 2XMM
J174016.0-290337.
We numerically investigate the dynamics of rotation of several close-in terrestrial exoplanets candidates. In our model, the rotation of the planet is disturbed by the torque of the central star due to the asymmetric equilibrium figure of the planet. We use surfaces of section to explore numerically the rotation phase space of the systems adopting different sets of parameters and initial conditions close to the main spin-orbit resonant states. We show that, depending on some parameters of the system like the radius and mass of the planet, orbital eccentricity etc, the rotation can be strongly perturbed and a chaotic layer around the synchronous state may occupy a significant region of the phase space. 55 Cnc e is an example.
We suggest a new way of the determining abundances and electron temperatures in HII regions from strong emission lines. Our approach is based on the standard assumption that HII regions with similar intensities of strong emission lines have similar physical properties and abundances. A "counterpart" for a studied HII region may be chosen among HII regions with well-measured abundances (reference HII regions) by comparison of carefully chosen combinations of strong line intensities. Then the abundances in the investigated HII region can be assumed to be the same as that in its counterpart. In other words, we suggest to determine the abundances in HII regions "by precedent". To get more reliable abundances for the considered HII region, a number of reference HII regions is selected and then the abundances in the target HII region is estimated through extra-/interpolation. We will refer to this method of abundance determination as the counterpart method or, for brevity, the C method. We define a sample of reference HII regions and verify the validity of the C method. We find that this method produces reliable abundances. Finally, the C method is used to obtain the radial abundance distributions in the extended discs of the spiral galaxies M83, NGC4625 and NGC 628.
NGC1851 possibly shows a spread in [Fe/H], but the relation between this spread and the division in the SGB is unknown. We obtained blue (3950-4600 A) intermediate resolution (R~8,000) spectra for 47 stars on the bright and 30 on the faint SGB of NGC 1851 (b-SGB and f-SGB, respectively). The determination of the atmospheric parameters to extremely high internal accuracy leads to small errors when comparing different stars in the cluster. We found that the b-SGB is slightly more metal-poor than the f-SGB, with [Fe/H]=-1.227+/-0.009 and [Fe/H]=-1.162+/- 0.012, respectively. This implies that the f-SGB is only slightly older by ~0.6 Gyr than the b-SGB if the total CNO abundance is constant. There are more C-normal stars in the b-SGB than in the f-SGB. This is consistent with what is found for HB stars, if b-SGB are the progenitors of red HB stars, and f-SGB those of blue HB ones. The abundances of the n-capture elements Sr and Ba have a bimodal distribution, reflecting the separation between f-SGB (Sr and Ba-rich) and b-SGB stars (Sr and Ba-poor). In both groups, there is a clear correlation between [Sr/Fe] and [Ba/Fe], suggesting that there is a real spread in the abundances of n-capture elements. There is some correlation between C and Ba abundances, while the same correlation for Sr is much more dubious. We identified six C-rich stars, which have a moderate overabundance of Sr and Ba and rather low N abundances. This group of stars might be the progenitors of these on the anomalous RGB in the (v, v-y) diagram. These results are discussed within different scenarios for the formation of NGC1851. It is possible that the two populations originated in different regions of an inhomogeneous parent object. However, the striking similarity with M22 calls for a similar evolution for these two clusters. Deriving reliable CNO abundances for the two sequences would be crucial.
We present a detailed study of the two Sun-like stars KIC 7985370 and KIC 7765135, aimed at determining their activity level, spot distribution, and differential rotation. Both stars were discovered by us to be young stars and were observed by the NASA Kepler mission. The stellar parameters (vsini, spectral type, Teff, log g, and [Fe/H]) were derived from optical spectroscopy which allowed us also to study the chromospheric activity from the emission in the core of H\alpha\ and CaII IRT lines. The high-precision Kepler photometric data spanning over 229 days were then fitted with a robust spot model. Model selection and parameter estimation are performed in a Bayesian manner, using a Markov chain Monte Carlo method. Both stars came out to be Sun-like with an age of about 100-200 Myr, based on their lithium content and kinematics. Their youth is confirmed by the high level of chromospheric activity, comparable to that displayed by the early G-type stars in the Pleiades cluster. The flux ratio of the CaII-IRT lines suggests that the cores of these lines are mainly formed in optically-thick regions analogous to solar plages. The model of the light curves requires at least seven enduring spots for KIC 7985370 and nine spots for KIC 7765135 for a satisfactory fit. The assumption of longevity of the star spots, whose area is allowed to evolve in time, is at the heart of our approach. We found, for both stars, a rather high value of the equator-to-pole differential rotation (d\Omega~0.18 rad/day) which is in contrast with the predictions of some mean-field models of differential rotation for fast-rotating stars. Our results are instead in agreement with previous works on solar-type stars and with other models which predict a higher latitudinal shear, increasing with equatorial angular velocity.
In an attempt to study whether the formation of brown dwarfs (BDs) takes place as a scaled-down version of low-mass stars, we conducted IRAM30m/MAMBO-II observations at 1.2 mm in a sample of 12 proto-BD candidates selected from Spitzer/IRAC data in the B213-L1495 clouds in Taurus. Subsequent observations with the CSO at 350 micron, VLA at 3.6 and 6 cm, and IRAM30m/EMIR in the 12CO(1-0), 13CO(1-0), and N2H+(1-0) transitions were carried out toward the two most promising Spitzer/IRAC source(s), J042118 and J041757. J042118 is associated with a compact (<10 arcsec or <1400 AU) and faint source at 350 micron, while J041757 is associated with a partially resolved (~16 arcsec or ~2000 AU) and stronger source emitting at centimetre wavelengths with a flat spectral index. The corresponding masses of the dust condensations are ~1 and ~5 Mjup for J042118 and J041757, respectively. In addition, about 40 arcsec to the northeast of J041757 we detect a strong and extended submillimetre source, J041757-NE, which is not associated with NIR/FIR emission down to our detection limits, but is clearly detected in 13CO and N2H+ at ~7 km/s, and for which we estimated a total mass of ~75 Mjup, high enough to be gravitationally bound. In summary, our observational strategy has allowed us to find in B213-L1495 two proto-BD candidates and one pre-substellar core candidate, whose properties seem to be consistent with a scaled-down version of low-mass stars.
Recent EUV spectroscopic observations indicate that slow magnetosonic waves are present in active region (AR) loops. Some of the spectral data were also interpreted as evidence of fast (~100-300 km/s) quasi-periodic flows. We have performed three-dimensional magnetohydrodynamic (3D MHD) modeling of a bipolar AR that contains impulsively generated waves and flows in coronal loops. The model AR is initiated with a dipole magnetic field and gravitationally stratified density, with an upflow driven steadily or periodically in localized regions at the footpoints of magnetic loops. The resulting flows along the magnetic field lines of the AR produce higher density loops compared to the surrounding plasma by injection of material into the flux-tubes and the establishment of siphon flow. We find that the impulsive onset of flows with subsonic speeds result in the excitation of damped slow magnetosonic waves that propagate along the loops and coupled nonlinearly driven fast mode waves. The phase speed of the slow magnetosonic waves is close to the coronal sound speed. When the amplitude of the driving pulses is increased we find that slow shock-like wave trains are produced. When the upflows are driven periodically, undamped oscillations are produced with periods determined by the periodicity of the upflows. Based on the results of the 3D MHD model we suggest that the observed slow magnetosonic waves and persistent upflows may be produced by the same impulsive events at the bases of ARs.
Images of the Crab Nebula have been obtained through custom interference filters which transmit emission from the expanding supernova remnant in HI, HeI, HeII, [CI], [NII], [OI], [SII], and [SIII] emission lines. We present both raw and flux-calibrated data. Arrays of 19,440 photoionization models, with extensive input abundance ranges, were matched pixel by pixel to the calibrated data in order to derive corresponding element abundance or mass-fraction distributions for helium, carbon, nitrogen, oxygen, and sulfur. These maps show distinctive structure, and they illustrate regions of gas in which various stages of nucleosynthesis have apparently occurred, including the CNO-cycle, helium-burning, carbon-burning, and oxygen-burning. It is hoped that the calibrated observations and chemical abundance distribution maps will be useful for developing a better understanding of the precursor star evolution and the supernova explosive process.
Recent proposals have been advanced to apply imaging air Cherenkov telescope arrays to stellar intensity interferometry (SII). Of particular interest is the possibility of model-independent image recovery afforded by the good (u, v)-plane coverage of these arrays, as well as recent developments in phase retrieval techniques. The capabilities of these instruments used as SII receivers have already been explored for simple stellar objects, and here the focus is on reconstructing stellar images with non-uniform radiance distributions. We find that hot stars (T > 6000 K) containing hot and/or cool localized regions (T \sim 500 K) as small as \sim 0.1 mas can be imaged at short wavelengths ({\lambda} = 400 nm).
We report on high-sensitivity and high-angular resolution archival Submillimeter Array (SMA) observations of the large ($\sim$15000 AU) putative circumstellar disk associated with the O-type protostar NGC 7538 S. Observations of the continuum resolve this putative circumstellar disk into five compact sources, with sizes $\sim$ 3000 AU and masses $\sim10 M_\odot$. This confirm the results of recent millimeter observations made with CARMA/BIMA towards this object. However, we find that from most of these compact sources eject collimated bipolar outflows, revealed by our silicon monoxide (SiO {\it J}=5-4) observations and confirm that these sources have a (proto)stellar nature. All outflows are perpendicular to the large and rotating dusty structure. We propose therefore that, rather than being a single massive circumstellar disk, NGC 7538 S could be instead a large and massive contracting or rotating filament that is fragmenting at scales of 0.1 to 0.01 pc to form several B-type stars, via the standard process involving outflows and disks. As in recent high spatial resolution studies of dusty filaments, our observations also suggest that thermal pressure does not seem to be sufficient to support the filament, so that either additional support needs to be invoked, or else the filament must be in the process of collapsing. An SPH numerical simulation of the formation of a molecular cloud by converging warm neutral medium flows produces contracting filaments whose dimensions and spacings between the stars forming within them, as well as their column densities, strongly resemble those observed in the filament reported here.
We have used the angular Autocorrelation Function (AcF) on the angular scale of a few arcminutes to detect and characterize the emission from the Warm-Hot Intergalactic Medium (WHIM) in a pointing with Chandra's ACIS-S instrument. We focused our attention on the energy bands 0.4-0.6 keV, where the WHIM emission is expected to be strongest, due to the redshifted O VII and O VIII lines, and 0.7-0.9 keV, where the WHIM emission is expected to be significantly smaller. After removing identified point sources, and any spurious signal due to detector background and unidentified point sources, in the lower energy band we found a clear AcF signal that we attribute to the WHIM, with a statistical significance of several sigmas (chi2=129, N=31). The attribution of the signal to the WHIM (and not to other spurious emissions, such as unresolved point sources) is confirmed by the higher energy band where the signal is compatible with zero.
Recent observations of isotropic diffuse backgrounds by Fermi and IceCube allow us to get more insight into distant very-high-energy (VHE) and ultra-high-energy (UHE) gamma-ray/neutrino emitters, including cosmic-ray accelerators/sources. First, we investigate the contribution of intergalactic cascades induced by gamma-rays and/or cosmic rays (CRs) to the diffuse gamma-ray background (DGB) in view of the latest Fermi data. We identify a possible VHE Excess from the fact that the Fermi data are well above expectations for an attenuated power law, and show that cascades induced by VHE gamma rays (above ~10 TeV) and/or VHECRs (below ~10^19 eV) may significantly contribute to the DGB above ~100 GeV. The relevance of the cascades is also motivated by the intergalactic cascade interpretations of extreme TeV blazars such as 1ES 0229+200, which suggest very hard intrinsic spectra. This strengthens the importance of future detailed VHE DGB measurements. Then, more conservatively, we derive general constraints on the cosmic energy budget of high-energy gamma rays and neutrinos based on recent Fermi and IceCube observations of extragalactic background radiation. We demonstrate that these multi-messenger constraints are useful and the neutrino limit is very powerful for VHE/UHE hadronic sources. Furthermore, we show the importance of constraints from individual source surveys by future imaging atmospheric Cherenkov telescopes such as Cherenkov Telescope Array, and demonstrate that the cascade hypothesis for the VHE DGB can be tested by searching for distant emitters of cascaded gamma rays.
We present single-dish and VLBI observations of an outburst of water maser emission from the young binary system Haro 6-10. Haro 6-10 lies in the Taurus molecular cloud and contains a visible T Tauri star with an infrared companion 1.3" north. Using the Very Long Baseline Array, we obtained five observations spanning 3 months and derived absolute positions for 20 distinct maser spots. Three of the masers can be traced over 3 or more epochs, enabling us to extract absolute proper motions and tangential velocities. We deduce that the masers represent one side of a bipolar outflow that lies nearly in the plane of the sky with an opening angle of ~45\deg. They are located within 50 mas of the southern component of the binary, the visible T Tauri star Haro 6-10S. The mean position angle on the sky of the maser proper motions (~220\deg) suggests they are related to the previously observed giant Herbig-Haro (HH) flow which includes HH410, HH411, HH412, and HH184A-E. A previously observed HH jet and extended radio continuum emission (mean position angle of ~190\deg) must also originate in the vicinity of Haro6-10S and represent a second, distinct outflow in this region. We propose that a yet unobserved companion within 150 mas of Haro6-10S is responsible for the giant HH/maser outflow while the visible star is associated with the HH jet. Despite the presence of H_2 emission in the spectrum of the northern component of the binary, Haro6-10N, none of outflows/jets can be tied directly to this young stellar object.
Herein we show that the historical records of mid-latitude auroras from 1700 to 1966 present oscillations with periods of about 9, 10-11, 20-21, 30 and 60 years. The same frequencies are found in proxy and instrumental global surface temperature records since 1650 and 1850, respectively and in several planetary and solar records. Thus, the aurora records reveal a physical link between climate change and astronomical oscillations. Likely, there exists a modulation of the cosmic ray flux reaching the Earth and/or of the electric properties of the ionosphere. The latter, in turn, have the potentiality of modulating the global cloud cover that ultimately drives the climate oscillations through albedo oscillations. In particular, a quasi 60-year large cycle is quite evident since 1650 in all climate and astronomical records herein studied, which also include an historical record of meteorite fall in China from 619 to 1943. These findings support the thesis that climate oscillations have an astronomical origin. We show that a harmonic constituent model based on the major astronomical frequencies revealed in the aurora records is able to forecast with a reasonable accuracy the decadal and multidecadal temperature oscillations from 1950 to 2010 using the temperature data before 1950, and vice versa. The existence of a natural 60-year modulation of the global surface temperature induced by astronomical mechanisms, by alone, would imply that at least 60-70% of the warming observed since 1970 has been naturally induced. Moreover, the climate may stay approximately stable during the next decades because the 60-year cycle has entered in its cooling phase.
We present the first detailed imaging and spatially resolved spectroscopic study of the Galactic supernova remnant G292.2-0.5, associated with the high-magnetic field radio pulsar J1119-6127, using Chandra and XMM-Newton. The high-resolution X-ray images reveal a partially limb-brightened morphology in the west, with diffuse emission concentrated towards the interior of the remnant unlike the complete shell-like morphology observed at radio wavelengths. The spectra of most of the diffuse emission regions within the remnant are best described by a thermal+non-thermal model. The thermal component is described by a plane-parallel, non-equilibrium ionization plasma model with a temperature ranging from 1.3 keV in the western side of the remnant to 2.3 keV in the east, a column density increasing from 1.0e22 cm^-2 in the west to 1.8e22 cm^-2 in the east, and a low ionization timescale ranging from 5.7e9 cm^-3 s in the SNR interior to 3.6e10 cm^-3 s in the western side - suggestive of expansion of a young remnant in a low-density medium. The spatial and spectral differences across the SNR are consistent with the presence of a dark cloud in the eastern part of the SNR, absorbing the soft X-ray emission. The spectra from some of the regions also show slightly enhanced metal abundances from Ne, Mg and Si, hinting at the first evidence for ejecta heated by the reverse shock. Comparing our inferred metal abundances to core-collapse nucleosynthesis models yields, we estimate a high progenitor mass of ~30 solar mass suggesting a type Ib/c supernova. We confirm the presence of non-thermal hard X-ray emission from regions close to the pulsar. We estimate an SNR age range between 4.2 kyr (free expansion phase) and 7.1 kyr (Sedov phase), a factor of a few higher than the measured pulsar's age upper limit of 1.9 kyr.
Assuming Newton's gravity and GR to be valid at all scales leads to the dark matter hypothesis as a requirement demanded by the observed dynamics and measured baryonic content at galactic and extragalactic scales. Alternatively, modified gravity scenarios where a change of regime appears at acceleration scales $a<a_{0}$ have been proposed. This modified regime at $a<a_{0}$ will generically be characterised by equilibrium velocities which become independent of distance. Here we identify a critical test in this debate and we propose its application to samples of wide binary stars. Since for $1 M_{\odot}$ systems the acceleration drops below $a_{0}$ at scales of around 7000 AU, a statistical survey of wide binaries with relative velocities and separations reaching $10^{4}$ AU and beyond should prove useful to the above debate. We apply the proposed test to the best currently available data. Results show a constant upper limit to the relative velocities in wide binaries which is independent of separation for over three orders of magnitude, in analogy with galactic flat rotation curves in the same $a<a_{0}$ acceleration regime. Our results are suggestive of a breakdown of Kepler's third law beyond $a \approx a_{0}$ scales, in accordance with generic predictions of modified gravity theories designed not to require any dark matter at galactic scales and beyond.
We investigate the shapes of \gamma-ray pulsar light curves using 3D pulsar magnetosphere models of finite conductivity. These models, covering the entire spectrum of solutions between vacuum and force-free magnetospheres, for the first time afford mapping the GeV emission of more realistic, dissipative pulsar magnetospheres. To this end we generate model light curves following two different approaches: (a) We employ the emission patterns of the slot and outer gap models in the field geometries of magnetospheres with different conductivity \sigma. (b) We define realistic trajectories of radiating particles in magnetospheres of different \sigma and compute their Lorentz factor under the influence of magnetospheric electric fields and curvature radiation-reaction; with these at hand we then calculate the emitted radiation intensity. The light curves resulting from these prescriptions are quite sensitive to the value of \sigma, especially in the second approach. While still not self-consistent, these results are a step forward in understanding the physics of pulsar \gamma-radiation.
We present the first results from the CHANG-ES survey, a new survey of 35
edge-on galaxies to search for both in-disk as well as extra-planar radio
continuum emission. The motivation and science case for the survey are
presented in a companion paper (Paper I). In this paper (Paper II), we outline
the observations and data reduction steps required for wide-band calibration
and mapping of EVLA data, including polarization, based on C-array test
observations of NGC 4631.
With modest on-source observing times (30 minutes at 1.5 GHz and 75 minutes
at 6 GHz for the test data) we have achieved best rms noise levels of 22 and
3.5 $\mu$Jy beam$^{-1}$ at 1.5 GHz and 6 GHz, respectively. New disk-halo
features have been detected, among them two at 1.5 GHz that appear as loops in
projection. We present the first 1.5 GHz spectral index map of NGC 4631 to be
formed from a single wide-band observation in a single array configuration.
This map represents tangent slopes to the intensities within the band centered
at 1.5 GHz, rather than fits across widely separated frequencies as has been
done in the past and is also the highest spatial resolution spectral index map
yet presented for this galaxy. The average spectral index in the disk is
$\bar\alpha_{1.5 GHz}\,=\,-0.84\,\pm\,0.05$ indicating that the emission is
largely non-thermal, but a small global thermal contribution is sufficient to
explain a positive curvature term in the spectral index over the band. Two
specific star forming regions have spectral indices that are consistent with
thermal emission. Polarization results (uncorrected for internal Faraday
rotation) are consistent with previous observations and also reveal some new
features. On broad scales, we find strong support for the notion that magnetic
fields constrain the X-ray emitting hot gas.
Scalar fields are crucial components in high energy physics and extensions of General Relativity. The fact they are not observed in the solar system may be due to a mechanism which screens their presence in high dense regions. We show how observations of the ellipticity of galaxy clusters can discriminate between models with and without scalar fields and even between different screening mechanisms. Using nowadays X-ray observations we put novel constraints on the different models.
New generation ground and space-based CMB experiments have ushered in discoveries of massive galaxy clusters via the Sunyaev-Zeldovich (SZ) effect, providing a new window for studying cluster astrophysics and cosmology. Many of the newly discovered, SZ-selected clusters contain hot intracluster plasma (kTe > 10 keV) and exhibit disturbed morphology, indicative of frequent mergers with large peculiar velocity (v > 1000 km s^{-1}). It is well-known that for the interpretation of the SZ signal from hot, moving galaxy clusters, relativistic corrections must be taken into account, and in this work, we present a fast and accurate method for computing these effects. Our approach is based on an alternative derivation of the Boltzmann collision term which provides new physical insight into the sources of different kinematic corrections in the scattering problem. By explicitly imposing Lorentz-invariance of the scattering optical depth, we also show that the kinematic corrections to the SZ intensity signal found in this work differ from previously obtained expressions. We briefly mention additional complications connected with kinematic effects that should be considered when interpreting future SZ data for individual clusters. One of the main outcomes of this work is SZpack, a numerical library which allows very fast and precise (<~0.001% at frequencies h{\nu} <~20kT{\gamma}) computation of the SZ signals up to high electron temperature (kTe \simeq 25 keV) and large peculiar velocity (v/c \simeq 0.01). The accuracy is well beyond the current and future precision of SZ observations and practically eliminates uncertainties related to more expensive numerical evaluation of the Boltzmann collision term. Our new approach should therefore be useful for analyzing future high-resolution, multi-frequency SZ observations as well as computing the predicted SZ effect signals from numerical simulations.
We present a search for microwave emission from air showers induced by ultra-high energy cosmic rays with the MIcrowave Detection of Air Showers (MIDAS) experiment. No events were found, ruling out a wide range of power flux and coherence of the putative emission, including those suggested by recent laboratory measurements.
We develop an estimator for the angular correlation function which, in the ensemble average, returns the shape of the correlation function, even for signals that have significant correlations on the scale of the survey region. We develop versions of the estimator for both diffuse and discrete signals, and apply them to Monte Carlo simulations of the diffuse X-ray background that include spatially inhomogeneous detector background events. The estimator is applied to data from the Chandra X-ray observatory in a companion paper, Galeazzi et al. 2012. We discuss applying the estimator to the averaging of correlation functions evaluated on several small fields, and to other cosmological applications.
In this paper, we explain how moments of the thermal Sunyaev-Zel'dovich (tSZ) effect can constrain both cosmological parameters and the astrophysics of the intracluster medium (ICM). As the tSZ signal is strongly non-Gaussian, higher moments of tSZ maps contain useful information. We first calculate the dependence of the tSZ moments on cosmological parameters, finding that higher moments scale more steeply with sigma_8 and are sourced by more massive galaxy clusters. Taking advantage of the different dependence of the variance and skewness on cosmological and astrophysical parameters, we construct a statistic, |<T^3>|/<T^2>^1.4, which cancels much of the dependence on cosmology (i.e., sigma_8) yet remains sensitive to the astrophysics of intracluster gas (in particular, to the gas fraction in low-mass clusters). Constraining the ICM astrophysics using this statistic could break the well-known degeneracy between cosmology and gas physics in tSZ measurements, allowing for tight constraints on cosmological parameters. Although detailed simulations will be needed to fully characterize the accuracy of this technique, we provide a first application to data from the Atacama Cosmology Telescope and the South Pole Telescope. We estimate that a Planck-like full-sky tSZ map could achieve a <1% constraint on sigma_8 and a 1-sigma error on the sum of the neutrino masses that is comparable to the existing lower bound from oscillation measurements.
We present constraints on how far single field inflation may depart from the familiar slow-roll paradigm. Considering a fast-roll regime while requiring a near-scale invariant power spectrum introduces large self-interactions for the field and consequently large and scale-dependent non-Gaussianities. Employing this signal, we use the requirement of weak-coupling together with WMAP constraints to derive bounds on generic $P(X,\phi)$ theories of single field inflation.
The LIGO detector is undergoing a major upgrade that will increase its sensitivity by a factor of 10, and extend its bandwidth from 40 Hz to 10 Hz on the lower frequency end, while also allowing for high-frequency operation due to its tunability. This advanced LIGO (aLIGO) detector will extend the mass range at which compact mass binaries may be detected by a factor of four or more at a fixed signal-to-noise ratio [1]. The inspirals of stellar-mass compact objects into intermediate-mass black holes (IMBHs) of 50-350 solar masses will lie in the frequency band of aLIGO [2]. GW searches for these type of events will provide conclusive evidence for the existence of IMBHs and explore the dynamics of cluster environments. To realize this science we need to develop waveform templates that accurately capture the dynamical evolution of these type of events before aLIGO begins observations. Implementing gravitational self-force (SF) corrections in templates for compact binaries with mass-ratios 1:10-1:1000 will be essential to decode the information contained in the GW signals emitted by these sources. However, these SF corrections have been computed for low-frequency events with extreme mass-ratios 1:10^4-1:10^7. We develop a waveform model that accurately reproduces the dynamical evolution of intermediate mass ratio inspirals, as predicted by the effective-one-body (EOB) model introduced in [3], and which enables us to shed some light on the form of the SF for events with mass-ratio 1:6, 1:10 and 1:100. To complement this study, we make use of SF results in the extreme-mass-ratio regime, and of predictions of the EOB model introduced in [3], to derive a prescription for the shift of the orbital frequency at the innermost stable circular orbit which consistently captures predictions from the extreme, intermediate and comparable mass-ratio regimes.
We have developed, produced and characterised integrated sensors, actuators and the related read-out and drive electronics that will be used for the control of the Advanced LIGO suspensions. The overall system consists of the BOSEMs (displacement sensor with integrated electro-magnetic actuator), the satellite boxes (BOSEM readout and interface electronics) and six different types of coil-driver units. In this paper we present the design of this read-out and control system, we discuss the related performance relevant for the Advanced LIGO suspensions, and we report on the experimental activity finalised at the production of the instruments for the Advanced LIGO detectors.
We explicitly derive the principal Lyapunov Exponent \emph{in terms of the
radial equation of ISCO}(Innermost Stable Circular Orbit) for Spherically
symmetry (Schwarzschild, Reissner Nordstr{\o}m) black-hole space-times. Using
it, we show that the ISCO occurs at $r_{ISCO}=4M$ for extremal Reissner
Nordstr{\o}m black-hole and $r_{ISCO}=6M$ for Schwarzschild black-hole. We
elucidate the connection between Lyapunov Exponent and \emph{Geodesic Deviation
Equation}.
We also compute the \emph{Kolmogorov-Sinai(KS)} entropy which measures the
rate of exponential divergence between two trajectories(geodesics)via Lyapunov
Exponent. We further prove that ISCO is characterized by the \emph{greatest}
possible orbital period i.e. $T_{ISCO}>T_{photon}$ among all types of circular
geodesics(both time-like and null, geodesic and non-geodesic) as measured by
the asymptotic observers. Therefore, ISCO provide the \emph{slowest way} to
circle the black hole.
The responsivity and noise of a voltage-biased superconducting transition-edge sensor depends strongly on the details of its thermal model, and the simplest theory for TES response assumes a single heat capacity connected to the heat bath. Here, analytical results are derived and discussed for the complex impedance, the responsivity and the noise of a transition-edge sensor, when the thermal model is not simple but consists of either two or three connected heat capacities. The implications of the differences of the models are discussed, as well.
In this review we discuss the connection between two seemingly disparate topics, macroscopic gravity on astrophysical scales and Hamiltonians that are not Hermitian but $PT$ symmetric on microscopic ones. In particular we show that the quantum-mechanical unitarity problem of the fourth-order derivative conformal gravity theory is resolved by recognizing that the scalar product appropriate to the theory is not the Dirac norm associated with a Hermitian Hamiltonian but is instead the norm associated with a non-Hermitian but $PT$-symmetric Hamiltonian. Moreover, the fourth-order theory Hamiltonian is not only not Hermitian, it is not even diagonalizable, being of Jordan-block form. With $PT$ symmetry we establish that conformal gravity is consistent at the quantum-mechanical level. In consequence, we can apply the theory to data, to find that the theory is capable of naturally accounting for the systematics of the rotation curves of a large and varied sample of 138 spiral galaxies without any need for dark matter. The success of the fits provides evidence for the relevance of non-diagonalizable but $PT$-symmetric Hamiltonians to physics.
String/M theory compactifications with low energy supersymmetry tend to predict that dark matter has two components: axions and WIMPs \cite{1004.5138,1204.2795}. In accord with this, we show that the tentative 130 GeV gamma-line signal reported in \cite{1204.2797} can be interpreted as arising from the annihilation of 145 GeV mass, Wino-like WIMPs into a Z-boson and a photon. In this context, the signal implies a second component of dark matter which we interpret as being composed of axions - the relative Wino/Axion abundances being approximately equal. Further predictions are implied: signals in both diffuse and monochromatic photons from dwarf spheroidal galaxies; monochromatic photons with energy 145 GeV; for the LHC, the Higgs boson mass has been predicted in this framework \cite{1112.1059}, and the current Higgs limits provide interesting constraints on the mass of the Gluino.
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We show that for high-magnification (Amax > 100) microlensing events, accurate microlens parallaxes can be obtained from three or fewer photometric measurements from a small telescope on a satellite in solar orbit at ~1 AU from Earth. This is 1--2 orders of magnitude less observing resources than are required for standard space-based parallaxes. Such microlens parallax measurements would yield accurate mass and distance measurements to the lens for all cases in which finite-source effects were observed from the ground over peak. This would include virtually all high-magnification events with detected planets and a substantial fraction of those without. Hence it would permit accurate estimates of the Galactic distribution of planets.
Mergers of two carbon-oxygen white dwarfs have long been suspected to be progenitors of Type Ia Supernovae. Here we present our modifications to the cosmological smoothed particle hydrodynamics code Gadget to apply it to stellar physics including but not limited to mergers of white dwarfs. We demonstrate a new method to map a one-dimensional profile of an object in hydrostatic equilibrium to a stable particle distribution. We use the code to study the effect of initial conditions and resolution on the properties of the merger of two white dwarfs. We compare mergers with approximate and exact binary initial conditions and find that exact binary initial conditions lead to a much more stable binary system but there is no difference in the properties of the actual merger. In contrast, we find that resolution is a critical issue for simulations of white dwarf mergers. Carbon burning hotspots which may lead to a detonation in the so-called violent merger scenario emerge only in simulations with sufficient resolution but independent of the type of binary initial conditions. We conclude that simulations of white dwarf mergers which attempt to investigate their potential for Type Ia supernovae should be carried out with at least 10^6 particles.
We present a new statistical method to determine the relationship between the stellar masses of galaxies and the masses of their host dark matter haloes over the entire cosmic history from z~4 to the present. This multi-epoch abundance matching (MEAM) model self-consistently takes into account that satellite galaxies first become satellites at times earlier than they are observed. We employ a redshift-dependent parameterization of the stellar-to-halo mass relation to populate haloes and subhaloes in the Millennium simulations with galaxies, requiring that the observed stellar mass functions at several redshifts be reproduced simultaneously. Using merger trees extracted from the dark matter simulations in combination with MEAM, we predict the average assembly histories of galaxies, separating into star formation within the galaxies (in-situ) and accretion of stars (ex-situ). The peak star formation efficiency decreases with redshift from 23% at z=0 to 9% at z=4 while the corresponding halo mass increases from 10^11.8M\odot to 10^12.5M\odot. The star formation rate of central galaxies peaks at a redshift which depends on halo mass; for massive haloes this peak is at early cosmic times while for low-mass galaxies the peak has not been reached yet. In haloes similar to that of the Milky-Way about half of the central stellar mass is assembled after z=0.7. In low-mass haloes, the accretion of satellites contributes little to the assembly of their central galaxies, while in massive haloes more than half of the central stellar mass is formed ex-situ with significant accretion of satellites at z<2. We find that our method implies a cosmic star formation history and an evolution of specific star formation rates which are consistent with those inferred directly. We present convenient fitting functions for stellar masses, star formation rates, and accretion rates as functions of halo mass and redshift.
The cold dark matter (DM) paradigm describes the large-scale structure of the universe remarkably well. However, there exists some tension with the observed abundances and internal density structures of both field dwarf galaxies and galactic satellites. Here, we demonstrate that a simple class of DM models may offer a viable solution to all of these problems simultaneously. Their key phenomenological properties are velocity-dependent self-interactions mediated by a light vector messenger and thermal production with much later kinetic decoupling than in the standard case.
Exoplanets which are detected using the radial velocity technique have a well-known ambiguity of their true mass, caused by the unknown inclination of the planetary orbit with respect to the plane of the sky. Constraints on the inclination are aided by astrometric follow-up in rare cases or, in ideal situations, through subsequent detection of a planetary transit. As the predicted inclination decreases, the mass of the companion increases leading to a change in the predicted properties. Here we investigate the changes in the mass, radius, and atmospheric properties as the inclination pushes the companion from the planetary into the brown dwarf and finally low-mass star regimes. We determine the resulting detectable photometric signatures in the predicted phase variation as the companion changes properties and becomes self-luminous. We apply this to the HD 114762 and HD 162020 systems for which the minimum masses of the known companions places them at the deuterium-burning limit.
Despite decades of studying the Sun, the coronal heating problem remains unsolved. One fundamental issue is that we do not know the spatial scale of the coronal heating mechanism. At a spatial resolution of 1000 km or more it is likely that most observations represent superpositions of multiple unresolved structures. In this letter, we use a combination of spectroscopic data from the Hinode EUV Imaging Spectrometer (EIS) and high resolution images from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory to determine the spatial scales of coronal loops. We use density measurements to construct multi-thread models of the observed loops and confirm these models using the higher spatial resolution imaging data. The results allow us to set constraints on the number of threads needed to reproduce a particular loop structure. We demonstrate that in several cases million degree loops are revealed to be single monolithic structures that are fully spatially resolved by current instruments. The majority of loops, however, must be composed of a number of finer, unresolved threads; but the models suggest that even for these loops the number of threads could be small, implying that they are also close to being resolved. These results challenge heating models of loops based on the reconnection of braided magnetic fields in the corona.
Recent x-ray observations of Mrk 766 suggest that broad emission line region clouds cross our line of sight and produce variable x-ray absorption. Here we investigate what optical/ultraviolet spectroscopic features would be produced by such "Intervening BLR Clouds" (IBC) crossing our line of sight to the accretion disk, the source of the optical/UV continuum. Although the emission spectrum produced by intervening clouds is identical to the standard BLR model, they may produce absorption features on the optical or UV continuum. Single clouds will have little effect on the optical/UV spectrum because BLR clouds are likely to be much smaller than the accretion disk. This is unlike the X-ray case, where the radiation source is considerably smaller. However, an ensemble of intervening clouds will produce spectroscopic features in the FUV including a strong depression between the Lyman limit and Ly{\alpha}. The amount of the depression will indicate the line-of-sight covering factor of clouds, an unknown quantity that is important for the ionization of the intergalactic medium and the energy budget of AGN. Comparison with observations suggests that the SED of Mrk 766 may be affected by intervening BLR clouds and IBC may exist in most of AGNs.
We present radial-velocity measurements obtained in a program to search for extrasolar planets with the spectrograph SOPHIE at the 1.93-m telescope of the Haute-Provence Observatory. Targets were selected from catalogs observed with ELODIE, mounted previously at the telescope, in order to detect long-period planets with an extended database close to 15 years. Two new Jupiter-analogue candidates are reported to orbit the bright stars HD150706 and HD222155 in 16.1 and 10.9 yr at 6.7 (+4.0,-1.4) and 5.1(+0.6,-0.7) AU. They respectively have minimum masses of 2.71 (+1.44,-0.66) and 1.90 (+0.67,-0.53) M_Jup. Using the measurements from ELODIE and SOPHIE, we refine the parameters of the long-period planets HD154345b and HD89307b, and publish the first reliable orbit for HD24040b. This last companion has a minimum mass of 4.01 +/- 0.49 M_Jup orbiting its star in 10.0 yr at 4.92 +/- 0.38 AU. Moreover, the data present evidence for a third bound object in the HD24040 system. With a surrounding dust debris disk, HD150706 is an active G0 dwarf for which we partially corrected the effect of the stellar spot on the SOPHIE radial-velocities. By contrast, HD222155 is an inactive G2V. In the SOPHIE measurements an instrumental effect could be characterized and partly corrected. Considering the work of Lovis et al. (2011b) and that we did not find significant correlation with the activity index in the SOPHIE data, the radial-velocity variations are not expected to come from stellar magnetic cycles. Finally, we discuss the main properties of this new population of long-period Jupiter-mass planets, for the moment, builds up of less than 20 candidates. These stars are preferential targets for direct-imaging or astrometry follow-up to constrain the system parameters and for higher precision radial-velocity to search for lower mass planets, aiming to find a Solar System twin.
We describe the physical and orbital properties of C/2011 W3. After surviving perihelion, the comet underwent major changes (permanent loss of nuclear condensation, formation of spine tail). The process of disintegration culminated with an outburst on December 17.6 (T+1.6 d) and this delayed response is inconsistent with the rubble pile model. Probable cause was thermal stress from the heat pulse into the nucleus after perihelion, which could also produce fragmentation of sungrazers far from the Sun. The spine tail was a synchronic feature, made up of dust released at <30 m/s. Since the nucleus would have been located on the synchrone, we computed the astrometric positions of the missing nucleus as the coordinates of the points of intersection of the spine tail's axis with lines of forced orbital-period variation, derived from orbital solutions based on preperihelion astrometry from the ground. The resulting osculating orbital period was 698+/-2 years, which proves that C/2011 W3 is the first major member of the predicted new, 21st-century cluster of bright Kreutz-system sungrazers. The spine tail's tip contained dust 1-2 mm in diameter. The bizarre appearance of the dust tail in images taken hours after perihelion with coronagraphs on SOHO and STEREO is readily understood. The disconnection of the comet's head from the preperihelion tail and the apparent activity attenuation near perihelion are both caused by sublimation of all dust at heliocentric distances smaller than ~1.8 solar radii. The tail's brightness is strongly affected by forward scattering of sunlight by dust. The longest-imaged grains had a radiation-pressure parameter beta ~ 0.6, probably submicron-sized silicate grains. The place of C/2011 W3 within the hierarchy of the Kreutz system and its genealogy via a 14th century parent suggest that it is indirectly related to the celebrated sungrazer X/1106 C1.
We present the first results from the V-FASTR experiment, a commensal search for fast transient radio bursts using the Very Long Baseline Array (VLBA). V-FASTR is unique in that the widely spaced VLBA antennas provide a discriminant against non-astronomical signals and a mechanism for the localization and identification of events that is not possible with single dishes or short baseline interferometers. Thus far V-FASTR has accumulated over 1300 hours of observation time with the VLBA, between 90 cm and 3 mm wavelength (327 MHz - 86 GHz), providing the first limits on fast transient event rates at high radio frequencies (>1.4 GHz). V-FASTR has blindly detected bright individual pulses from seven known pulsars but has not detected any single-pulse events that would indicate high redshift impulsive bursts of radio emission. At 1.4 GHz, V-FASTR puts limits on fast transient event rates comparable with the PALFA survey at the Arecibo telescope, but generally at lower sensitivities, and comparable to the "fly's eye" survey at the Allen Telescope Array, but with less sky coverage. We also illustrate the likely performance of the Phase 1 SKA dish array for an incoherent fast transient search fashioned on V-FASTR.
Although accretion onto supermassive black holes in other galaxies is seen to produce powerful jets in X-ray and radio, no convincing detection has ever been made of a kpc-scale jet in the Milky Way. The recently discovered pair of 10 kpc tall gamma-ray bubbles in our Galaxy may be a sign of earlier jet activity from the central black hole. In this paper, we identify a gamma-ray cocoon feature in the southern bubble, a jet-like feature along the cocoon's axis of symmetry, and another directly opposite the Galactic center in the north. Both the cocoon and jet-like feature have a hard spectrum with spectral index ~ -2 from 1 to 100 GeV, with a cocoon luminosity of (5.5 +/- 0.45) x 10^35 erg/s and luminosity of the jet-like feature of (1.8 +/- 0.35) x 10^35 erg/s at 1 to 100 GeV. If confirmed, these jets are the first resolved gamma-ray jets ever seen.
We use precise radial velocity measurements and photometric data to derive the frequency spacing of the p-mode oscillation spectrum of the planet-hosting star Beta Gem. This spacing along with the interferometric radius for this star is used to derive an accurate stellar mass. A long time series of over 60 hours of precise stellar radial velocity measurements of Beta Gem were taken with an iodine absorption cell and the echelle spectrograph mounted on the 2m Alfred Jensch Telescope. Complementary photometric data for this star were also taken with the MOST microsatellite spanning 3.6 d. A Fourier analysis of the radial velocity data reveals the presence of up to 17 significant pulsation modes in the frequency interval 10-250 micro-Hz. Most of these fall on a grid of equally-spaced frequencies having a separation of 7.14 +/- 0.12 micro-Hz. An analysis of 3.6 days of high precision photometry taken with the MOST space telescope shows the presence of up to 16 modes, six of which are consistent with modes found in the spectral (radial velocity) data. This frequency spacing is consistent with high overtone radial pulsations; however, until the pulsation modes are identified we cannot be sure if some of these are nonradial modes or even mixed modes. The radial velocity frequency spacing along with angular diameter measurements of Beta Gem via interferometry results in a stellar mass of M = 1.91 +/- 0.09 solar masses. This value confirms the intermediate mass of the star determined using stellar evolutionary tracks. Beta Gem is confirmed to be an intermediate mass star. Stellar pulsations in giant stars along with interferometric radius measurements can provide accurate determinations of the stellar mass of planet hosting giant stars. These can also be used to calibrate stellar evolutionary tracks.
[Abridged] Radio galaxies and quasars are among the largest and most powerful single objects known and are believed to have had a significant impact on the evolving Universe and its large scale structure. We explore the intrinsic and extrinsic properties of the population of FRII objects (kinetic luminosities, lifetimes, and the central densities of their environments). In particular, the radio and kinetic luminosity functions of FRIIs are investigated using the complete, flux limited radio catalogues of 3CRR and Best et al. We construct multidimensional Monte Carlo simulations using semi-analytical models of FRII radio source growth to create artificial samples of radio galaxies. Unlike previous studies, we compare radio luminosity functions found with both the observed and simulated data to explore the fundamental source parameters. We allow the source physical properties to co-evolve with redshift, and we find that all the investigated parameters most likely undergo cosmological evolution. Strikingly, we find that the break in the kinetic luminosity function must undergo redshift evolution of at least (1+z)^3. The fundamental parameters are strongly degenerate, and independent constraints are necessary to draw more precise conclusions. We use the estimated kinetic luminosity functions to set constraints on the duty cycles of these powerful radio sources. A comparison of the duty cycles of powerful FRIIs with those determined from radiative luminosities of AGN of comparable black hole mass suggests a transition in behaviour from high to low redshifts, corresponding to either a drop in the typical black hole mass of powerful FRIIs at low redshifts, or a transition to a kinetically-dominated, radiatively-inefficient FRII population.
We show that it is possible to use cosmic rays to constrain asymmetric Dark Matter models violating the lepton flavor symmetry. This is possible if we require the models to explain the anomalies in the charged cosmic rays measured by PAMELA, FERMI and HESS. We first perform combined fits to the cosmic rays anomalies and find that the current data allow for the possibility of flavor violation asymmetric Dark Matter. We then determine the constraints coming from the measurement of the isotropic gamma-ray background by FERMI for a complete set of lepton flavor violating primary modes and over a range of DM masses from 100 GeV to 10 TeV. We find that FERMI constraints rule out the flavor violating asymmetric Dark Matter interpretation of the charged cosmic ray anomalies.
We present the results of testing the commercial digital camera Nikon D90 with a CMOS sensor for high-speed photometry with a small telescope Celestron 11" on Peak Terskol. CMOS sensor allows to perform photometry in 3 filters simultaneously that gives a great advantage compared with monochrome CCD detectors. The Bayer BGR color system of CMOS sensors is close to the Johnson BVR system. The results of testing show that we can measure the stars up to V $\simeq$ 14 with the precision of 0.01 mag. Stars up to magnitude V $\sim$ 10 can shoot at 24 frames per second in the video mode.
Recent progress in observational cosmology, and especially the forthcoming PLANCK mission data, open new directions in so-called precision cosmology. In this paper we illustrate this statement considering the accuracy of cosmological determination of the two-quanta decay rate of 2s hydrogen atom state. We show that the PLANCK data will allow us to measure this decay rate significantly better than in the laboratory experiments.
The spin behaviour of the neutron star in the newly discovered young Be/X-ray long-period pulsar SXP 1062 is discussed. The star is observed to rotate with the period of 1062s, and spin-down at the rate ~ - 2.6 \times 10^{-12} Hz s^{-1}. I show that all of the conventional accretion scenarios encounter major difficulties explaining the rapid spin-down of the pulsar. These difficulties can be, however, avoided within the magnetic accretion scenario in which the neutron star is assumed to accrete from a magnetized wind. The spin-down rate of the pulsar can be explained within this scenario provided the surface magnetic field of the neutron star is B_* ~ 4 \times 10^{13} G. I show that the age of the pulsar in this case lies in the rage (2-4) \times 10^4 yr, which is consistent with observations. The spin evolution of the pulsar is briefly discussed.
We study the anisotropy of Ultra-High Energy Cosmic Ray (UHECR) events collected by the Telescope Array (TA) detector in the first 40 months of operation. Following earlier studies, we examine event sets with energy thresholds of 10 EeV, 40 EeV, and 57 EeV. We find that the distributions of the events in right ascension and declination are compatible with an isotropic distribution in all three sets. We then compare with previously reported clustering of the UHECR events at small angular scales. No significant clustering is found in the TA data. We then check the events with E>57 EeV for correlations with nearby active galactic nuclei. No significant correlation is found. Finally, we examine all three sets for correlations with the large-scale structure of the Universe. We find that the two higher-energy sets are compatible with both an isotropic distribution and the hypothesis that UHECR sources follow the matter distribution of the Universe (the LSS hypothesis), while the event set with E>10 EeV is compatible with isotropy and is not compatible with the LSS hypothesis at 95% CL unless large deflection angles are also assumed. We show that accounting for UHECR deflections in a realistic model of the Galactic magnetic field can make this set compatible with the LSS hypothesis.
For the past 25 years, BW Vulpeculae has been the topic of period analyses centered on a secular period change with a periodic variation superposed, presumed to be due to light time effects in a binary system. According to this paradigm, one would expect what seems like a period increase of about 0.5 s during or soon after the year 2001. I have continued photometric monitoring through the year 2012, adding 35 new timings of maximum and minimum light. This expected change in period did not occur, which rules out that interpretation of the period variation. As of 2012, the observed timings are about two hours early compared to those predicted by the quadratic ephemeris, but are very close to those predicted by the linear ephemeris. In fact, the period has remained constant for the last 32 years, indicating that the previous epochs of constant period are almost certainly the correct interpretation, though the cause of the period changes is still not clear. Continued photometric monitoring of BW Vul leads to the conclusion that the period changes are abrupt, followed by epochs of constant period lasting between 12 and at least 32 years.
Outbursting AM CVn stars exhibit outbursts similar to those observed in different types of dwarf novae. Their light-curves combine the characteristic features of SU UMa, ER UMa, Z Cam and WZ Sge-type systems but also show a variety of properties never observed in dwarf novae. The compactness of AM CVn orbits and their unusual chemical composition make these systems valuable test-beds for outburst models. Understanding the role of helium in the accretion disc instability mechanism, testing the model for dwarf novae outbursts in the case of AM CVn stars, and the explanation of the outburst light-curves of these ultra-compact binaries. We calculate the properties of the hydrogen-free AM CVn stars using the Hameury et al. (1998) numerical code adapted to the different chemical composition of these systems and supplemented with formulae accounting for mass transfer rate variations, additional sources of the disc heating and the primary's magnetic field. We find how helium-dominated discs react to the thermal-viscous instability and reproduce various features of the outburst cycles in the light-curves of AM CVn stars. The AM CVn outbursts can be explained by the suitably adapted dwarf-nova disc instability model but, as in case of its application to hydrogen-dominated cataclysmic variables, one has to resort to additional mechanisms to account for the observed superoutbursts, dips, cycling states and standstills. We show that enhanced mass-transfer rate, due presumably to variable irradiation of the secondary, must not only be taken into account but is a determinant factor that shapes AM CVn star outbursts. The cause of variable secondary's irradiation has still to be understood; the best candidate being the precession of a tilted/warped disc.
The distance between the pre-impact surface of Comet 9P/Tempel 1 and the upper border of the largest cavity excavated during ejection of material after the collision of the impact module of the Deep Impact spacecraft with the comet is estimated to be about 5-6 metres if the diameter of the DI transient crater was about 150-200 m. The estimated distance was 4 m at the diameter was 100 m. This result suggests that cavities containing dust and gas under pressure located a few metres below surfaces of comets can be frequent.
A core-collapse supernova will produce an enormous burst of neutrinos of all flavors in the few-tens-of-MeV range. Measurement of the flavor, time and energy structure of a nearby core-collapse neutrino burst will yield answers to many physics and astrophysics questions. The neutrinos left over from past cosmic supernovae are also observable, and their detection will improve knowledge of core collapse rates and average neutrino emission. This review describes experimental techniques for detection of core-collapse neutrinos, as well as the sensitivities of current and future detectors.
We performed simultaneous spectral analysis of 26.6 ksec of Chandra and 102.3 ksec of Suzaku X-ray data of the starburst galaxy NGC 3079. The spectra are extracted from four regions: 0.5' (2.25 kpc) circle, an inner 0.5'-1' (2.25--4.5 kpc) ring, and an outer 1'-2' (4.5--9 kpc) ring from Chandra, and 4' (18 kpc) circle from Suzaku, all centered on the nucleus. Fitting with thermal plasma models yields interstellar medium (ISM) temperatures of 0.65+0.05-0.04, 0.45+0.07-0.06, and 0.24+0.03-0.02 keV in the three regions, respectively. The combination of Chandra's high angular resolution and Suzaku's good spectral sensitivity enable us to spatially resolve and measure the abundances of the metals O, Ne, Mg, and Fe within the hot ISM. In particular, the abundance patterns of O/Fe, Ne/Fe, Mg/Fe, and Si/Fe in the central regions (<4.5 kpc) are consistent with the expectations from Supernovae (SN) II synthesis. On the other hand, the pattern in the region beyond 4.5 kpc is closer to solar. The central regions are also where copious polycyclic aromatic hydrocarbon infrared emission related to recent starburst activity is known to occur. This suggests that we are seeing starburst-related SN II metal enrichment in the hot X-ray--emitting nuclear ISM. The spatial extent of the SN II--like abundance patterns is consistent with NGC 3079 being in a relatively-early phase of starburst activity.
The nearby Type Ia supernova SN 2011fe in M101 (cz=241 km s^-1) provides a unique opportunity to study the early evolution of a "normal" Type Ia supernova, its compositional structure, and its elusive progenitor system. We present 18 high signal-to-noise spectra of SN 2011fe during its first month beginning 1.2 days post-explosion and with an average cadence of 1.8 days. This gives a clear picture of how various line-forming species are distributed within the outer layers of the ejecta, including that of unburned material (C+O). We follow the evolution of C II absorption features until they diminish near maximum light, showing overlapping regions of burned and unburned material between ejection velocities of 10,000 and 16,000 km s^-1. This supports the notion that incomplete burning, in addition to progenitor scenarios, is a relevant source of spectroscopic diversity among SNe Ia. The observed evolution of the highly Doppler-shifted O I 7774 absorption features detected within five days post-explosion indicate the presence of O I with expansion velocities from 11,500 to 21,000 km s^-1. The fact that some O I is present above C II suggests that SN 2011fe may have had an appreciable amount of unburned oxygen within the outer layers of the ejecta.
We study the torque acting on a planet embedded in an optically thick accretion disc, using global two-dimensional hydrodynamic simulations. The temperature of an optically thick accretion disc is determined by the energy balance between the viscous heating and the radiative cooling. The radiative cooling rate depends on the opacity of the disc. The opacity is expressed as a function of the temperature. We find the disc is divided into three regions that have different temperature distributions. The slope of the entropy distribution becomes steep in the inner region of the disc with the high temperature and the outer region of the disc with the low temperature, while it becomes shallow in the middle region with the intermediate temperature. Planets in the inner and outer regions move outward owing to the large positive corotation torque exerted on the planet by an adiabatic disc, on the other hand, a planet in the middle region moves inward toward the central star. Planets are expected to accumulate at the boundary between the inner and middle regions of the adiabatic disc. The positive corotation torque decreases with an increase in the viscosity of the disc. We find that the positive corotation torque acting on the planet in the inner region becomes too small to cancel the negative Lindblad torque when we include the large viscosity, which destroys the enhancement of the density in the horseshoe orbit of the planet. This leads to the inward migration of the planet in the inner region of the disc. A planet with 5 Earth masses in the inner region can move outward in a disc with the surface density of 100 g/cm^2 at 1 AU when the accretion rate of a disc is smaller than 2x10^{-8} solar mass/yr.
We report the discovery of an X-ray/UV stellar flare from the source LMC 335, captured by XMM-Newton in the field of the Large Magellanic Cloud. The flare event was recorded continuously in X-ray for its first 10 hours from the precursor to the late decay phases. The observed fluxes increased by more than two orders of magnitude at its peak in X-ray and at least one in the UV as compared to quiescence. The peak 0.1-7.0 keV X-ray flux is derived from the two-temperature APEC model to be ~(8.4 +/- 0.6) x 10^-12 erg cm-2 s-1. Combining astrometric information from multiple X-ray observations in the quiescent and flare states, we identify the NIR counterpart of LMC 335 as the 2MASS source J05414534-6921512. The NIR color relations and spectroscopic parallax characterize the source as a Galactic K7-M4 dwarf at a foreground distance of (100 - 264) pc, implying a total energy output of the entire event of ~(0.4 - 2.9) x 10^35 erg. This report comprises detailed analyses of this late-K / early-M dwarf flare event that has the longest time coverage yet reported in the literature. The flare decay can be modeled with two exponential components with timescales of ~28 min and ~4 hours, with a single component decay firmly ruled out. The X-ray spectra during flare can be described by two components, a dominant high temperature component of ~40-60MK and a low temperature component of ~10MK, with a flare loop length of about 1.1-1.3 stellar radius.
Dust is a major component of protoplanetary and debris disks as it is the main observable signature of planetary formation. However, since dust dynamics is size-dependent (because of gas-drag or radiation pressure) any attempt to understand the full dynamical evolution of circumstellar dusty-disks that neglect the coupling of collisional evolution with dynamical evolution is thwarted because of the feedback between these two processes. Here, a new hybrid lagrangian/eulerian code is presented that overcomes some of these difficulties. The particles representing "dust-clouds" are tracked individually in a lagrangian way. This system is then mapped on an eulerian spatial grid, inside the cells of which the local collisional evolutions are computed. Finally, the system is remapped back in a collection of discrete lagrangian particles keeping constant their number. An application example on dust growth in a turbulent protoplanetary disk at 1 AU is presented. First the growth of dust is considered in the absence of a dead-zone and the vertical distribution of dust is self-consistently computed. It is found that the mass is rapidly dominated by particles about a fraction of millimeter in size. Then the same case with an embedded dead-zone is investigated and It is found that coagulation is much more efficient and produces, in a short time scale, 1cm-10cm dust pebbles that dominate the mass. These pebbles may then be accumulated into embryos sized objects inside large-scale turbulent structures as shown recently (see e.g. Johansen et al., 2007).
We present spectral properties of 996 X-ray binary sources resolved in a sample of 23 dusty early-type galaxies selected from different environments. The combined X-ray luminosity function of all the 996 sources within optical D25 region of sample galaxies is well described by a broken power law, with a break at the Eddington luminosity for a 1.4 Msun neutron star. Out of the 996 discrete sources, about 33% of sources have their X-ray luminosities < few \times10^{37} erg/s; about 63% between few \times 10^{37} to 10^{39} erg/s; while the remainder 4% have luminosities greater than 10^{39} erg/s. All the sources with luminosities greater than few \times 10^{39} erg/s are defined as ULXs and host intermediate mass black holes as their accreting source. The difference in X-ray colors of the resolved sources in the sample galaxies were used to classify them in different classes, like, SNR, LMXBs, HMXBs and heavily absorbed AGNs. Comparison of the X-ray color plots for the resolved sources in elliptical and lenticular galaxies exhibit a significant difference in nature of the X-ray emitting sources, in the sense that, elliptical galaxies host an additional population of soft X-ray sources, while no such sources were evident in the lenticular galaxies. The composite X-ray spectra of the resolved sources within D25 region of each of the galaxy are best represented by a power law with the average photon spectral index close to 1.65. Contribution of the resolved sources to the total X-ray luminosity of their host is found to vary greatly in the sense that in galaxies like NGC 3379 XRB contribution is about 81%while for NGC 5846 it is only 2%. The combined X-ray luminosity of the resolved sources in a galaxy is found to correlated with star formation rate as well as Ks band luminosity and IR luminosity of the target galaxies.
We study and constraint Mass-Varying Neutrino models using present and future available data. In these models, dark energy is a self-interacting scalar field directly coupled to neutrinos. We investigate two different potentials and both positive and negative coupling parameter \beta. This corresponds to increasing or decreasing neutrino mass, respectively. We explore couplings up to |\beta|\lesssim 5. In the case of the exponential potential, we find upper limits on \omega_\nu<0.004 at 2-\sigma level. In the case of the inverse power law potential the null coupling can be excluded with more than 2-\sigma significance, the limits on the coupling being \beta>3 for the increasing neutrino mass and \beta<-1.5 for the decreasing mass case. This is a clear sign of a preference for higer couplings. When including a prior on the neutrino mass today the upper limits on the coupling become |\beta|<3 at 2-\sigma level for the exponential potential. Finally, we present Fisher forecast using the tomographic weak lensing from the Euclid-like experiment, also in combination with the CMB temperature and polarization spectra from the Planck-like mission. If considered alone, lensing data is very efficient in constraining \omega_\nu, giving a signal of a non-null neutrino mass with high significance. There is, however, a strong degeneracy in the \beta-\omega_\nu plane. When the two data sets are combined, the latter degeneracy remains, but the zero \beta value can be excluded at more than 2-\sigma.
By performing two-dimensional special relativistic (SR) magnetohydrodynamic simulations, we study possible signatures of gravitational waves (GWs) in the context of the collapsar model for long-duration gamma-ray bursts. In our SR simulations, the central black hole is treated as an absorbing boundary. By doing so, we focus on the GWs generated by asphericities in neutrino emission and matter motions in the vicinity of the hyperaccreting disks. We compute nine models by adding initial angular momenta and magnetic fields parametrically to a precollapse core of a $35 M_{\odot}$ progenitor star. As for the microphysics, a realistic equation of state is employed and the neutrino cooling is taken into account via a multiflavor neutrino leakage scheme. To accurately estimate GWs produced by anisotropic neutrino emission, we perform a ray-tracing analysis in general relativity by a post-processing procedure. By employing a stress formula that includes contributions both from magnetic fields and special relativistic corrections, we study also the effects of magnetic fields on the gravitational waveforms. We find that the GW amplitudes from anisotropic neutrino emission show a monotonic increase with time, whose amplitudes are much larger than those from matter motions of the accreting material. We show that the increasing trend of the neutrino GWs stems from the excess of neutrino emission in the direction near parallel to the spin axis illuminated from the hyperaccreting disks. We point out that a recently proposed future space-based interferometer like Fabry-Perot type DECIGO would permit the detection of these GW signals within $\approx$ 100 Mpc.
Classically oscillating massive fields can be used as "standard clocks" in the primordial universe. They generate features in primordial density perturbations that directly record the scale factor evolution a(t). Detecting and measuring these "fingerprint" signals is challenging but would provide a direct evidence for a specific primordial universe paradigm. In this paper, such a search is performed for the power spectrum of the Cosmic Microwave Background (CMB) anisotropies using the WMAP7 data. Although a good fit to the data privileges a scale around k=0.01 Mpc^(-1), we do not find statistical significance for, neither against, the presence of any feature. We then forecast the expected constraints a Planck-like CMB experiment can impose on the fingerprint parameters by using Markov-Chain-Monte-Carlo (MCMC) methods on mock data. We exhibit a high sensitivity zone for wavenumbers ranging from 0.01 Mpc^(-1) to 0.1 Mpc^(-1) in which fingerprints show up first on the posterior probability distribution of the wavenumber at which they occur, and then on the modulation frequency. Within the sensitivity zone, we show that the inflationary paradigm can be inferred from a single feature generating at least a 20% modulation of the primordial power spectrum. This minimal value sensitively depends on the modulation frequency.
The ongoing large spectroscopic surveys of the Milky Way such as SEGUE and RAVE have enabled us to take a fresh look at the structure of the Galactic thin and thick disks, and how their structure fits within the framework of structure formation via hierarchical clustering. In this article I will summarize some recent results mainly based in the RAVE survey with respect to the structure of the Galactic disks, their possible origin as well as indications of substructure and asymmetries.
We present an analysis of a high resolution (R \sim 30000) optical spectrum of the central region of the proto-planetary nebula CRL 2688. This object is thought to have recently moved off the AGB, and display abundance patterns of CNO and heavy elements that can provide us with important clues to understand the nucleosynthesis, dredge-up and mixing experienced by the envelope of the central star during its AGB stage of evolution. The analysis of the molecular features, presumably originated from the circumstellar matter provides further constraints on the chemistry and velocity of the expanding shell, expelled as a consequence of the strong mass loss experienced by the central star. We confirm that the central star shows a spectrum typical of an F-type supergiant with Teff=7250 K, log g=0.5 and [Fe/H]=-0.3 dex. We find that the abundance pattern of this object is characterized by enhancements of Carbon ([C/Fe]=0.6), Nitrogen ([N/Fe]=1.0) and Na ([Na/Fe]=0.7), similar to other previously known carbon-rich post-AGB stars. Yttrium is also enhanced while the [Ba/Y] ratio is very low (-1.0), indicating that only the light s-process elements are enhanced. The Zinc abundance is found to be normal, [Zn/Fe]=0.0, suggesting that there is no depletion of refractory elements. The Halpha, Na I and K I resonance lines show prominent emission components, whose helio-centric radial velocities are offsetted by -41 km/s relative to the photospheric metal-absorption lines. The molecular features of C_2 and CN also show emission components, whose velocities are consistent with the emission components of the Halpha, Na I, and K I lines. On the other hand, their absorption components are more highly blue shifted than the corresponding emission components, which suggests that the regions where the emission and absorption components arise are expanding at different velocities.
In high-redshift ($z>5$) quasars, a large amount of dust ($\textstyle\sim 10^{8} \mathrm{M}_{\sun}$) has been observed. In order to explain the large dust content, we focus on a possibility that grain growth by the accretion of heavy elements is the dominant dust source. We adopt a chemical evolution model applicable to nearby galaxies but utilize parameters adequate to high-$z$ quasars. It is assumed that metals and dust are predominantly ejected by Type II supernovae (SNe). We have found that grain growth strongly depends on the grain size distribution. If we simply use the size distribution of grains ejected from SNe, grain growth is inefficient because of the lack of small grains (i.e.\ small surface-to-volume ratio of the dust grains). However, if we take small grain production by interstellar shattering into consideration, grain growth is efficient enough to account for the rich dust abundance in high-$z$ quasars. Our results not only confirm that grain growth is necessary to explain the large amount of dust in high-$z$ quasars, but also demonstrate that grain size distributions have a critical impact on grain growth.
The detections of X-ray emission from the kiloparsec-scale jets of blazars and radio galaxies may imply the existence of high energy electrons in these extended jets, and these electrons could produce high energy emission through inverse Compton (IC) process. In this paper we study the non-variable hard TeV emission from a blazar. The multi-band emission consists of two components: one is the traditional synchrotron self-Compton (SSC) emission from the inner jet, and the other is the emission produced via SSC and IC scattering of cosmic microwave background (CMB) photons (IC/CMB) and extragalactic background light (EBL) photons (IC/EBL) by relativistic electrons in the extended jet under the stochastic acceleration scenario. Such a model is applied to 1ES 1101-232. The results indicate that (1) the non-variable hard TeV emission of 1ES 1101-232 can be reproduced well, which is dominated by IC/CMB emission from the extended jet, using three characteristic values of Doppler factor ($\delta_{\rm D}=5,10,15$) for the TeV emitting region in the extended jet; and (2) in the cases of $\delta_{\rm D}=15$ and 10, the physical parameters can achieve the equipartition (or quasi-equipartition) between the relativistic electrons and the magnetic field; In contrast, the physical parameters largely deviate from the equipartition for the case of $\delta_{\rm D}=5$. It is therefore concluded that the TeV emission region of 1ES 1101-232 in the extended jet should be moderately or highly beamed.
In this study we show that the skewness $S_3$ of the cosmic density field contains a significant and potentially detectable and clean imprint of Baryonic Acoustic Oscillations. Although the BAO signal in the skewness has a lower amplitude than second order measures like the two-point correlation function and power spectrum, it has the advantage of a considerably lower sensitivity to systematic influences. Because it lacks a direct dependence on bias if this concerns simple linear bias, skewness will be considerably less beset by uncertainties due to galaxy bias. Also, it has a weaker sensitivity to redshift distortion effects. We use perturbation theory to evaluate the magnitude of the effect on the volume-average skewness, for various cosmological models. One important finding of our analysis is that the skewness BAO signal occurs at smaller scales than that in second order statistics. For an LCDM spectrum with WMAP7 normalization, the BAO feature has a maximum wiggle amplitude of ~3% and appears at a scale of $\sim82\hmpc$. We conclude that the detection of BAO wiggles in future extensive galaxy surveys via the skewness of the observed galaxy distribution may provide us with a useful, and potentially advantageous, measure of the nature of Dark Energy.
We forecast constraints on cosmological parameters with primary CMB anisotropy information and weak lensing reconstruction with a future post-Planck CMB experiment, the Cosmic Origins Explorer (COrE), using oscillation data on the neutrino mass splittings as prior information. Our MCMC simulations in flat models with a non-evolving equation-of-state of dark energy w give typical 68% upper bounds on the total neutrino mass of 0.136 eV and 0.098 eV for the inverted and normal hierarchies respectively, assuming the total summed mass is close to the minimum allowed by the oscillation data for the respective hierarchies (0.10 eV and 0.06 eV). Including information from future baryon acoustic oscillation measurements with the complete BOSS, Type 1a supernovae distance moduli from WFIRST, and a realistic prior on the Hubble constant, these upper limits shrink to 0.118 eV and 0.080 eV for the inverted and normal hierarchies, respectively. Addition of these distance priors also yields percent-level constraints on w. We find tension between our MCMC results and the results of a Fisher matrix analysis, most likely due to a strong geometric degeneracy between the total neutrino mass, the Hubble constant, and w in the unlensed CMB power spectra. If the minimal-mass, normal hierarchy were realised in nature, the inverted hierarchy should be disfavoured by the full data combination at typically greater than the 2-sigma level. For the minimal-mass inverted hierarchy, we compute the Bayes' factor between the two hierarchies for various combinations of our forecast datasets, and find that the future probes considered here should be able to provide `strong' evidence (odds ratio 12:1) for the inverted hierarchy. Finally, we consider potential biases of the other cosmological parameters from assuming the wrong hierarchy and find that all biases on the parameters are below their 1-sigma marginalised errors.
We employ a state-of-the-art asteroseismological model of G117-B15A, the archetype of the H-rich atmosphere (DA) white dwarf pulsators (also known as DAV or ZZ Ceti variables), and use the most recently measured value of the rate of period change for the dominant mode of this pulsating star to derive a new constraint on the mass of axion, the still conjectural non-barionic particle considered as candidate for dark matter of the Universe. Assuming that G117-B15A is truly represented by our asteroseismological model, and in particular, that the period of the dominant mode is associated to a pulsation g-mode trapped in the H envelope, we find strong indications of the existence of extra cooling in this star, compatible with emission of axions of mass m_a \cos^2 \beta = 17.4^{+2.3}_{-2.7} meV.
Lenticular galaxies with M_B < -21.5 are almost exclusively unbarred, whereas both barred and unbarred objects occur at fainter luminosity levels. This effect is observed both for objects classified in blue light, and for those that were classified in the infrared. This result suggests that the most luminous (massive) S0 galaxies find it difficult to form bars. As a result the mean luminosity of unbarred lenticular galaxies in both B and IR light is observed to be ~0.4 mag brighter than than that of barred lenticulars. A small contribution to the observed luminosity difference that is found between SA0 and SB0 galaxies may also be due to the fact that there is an asymmetry between the effects of small classification errors on SA0 and SB0 galaxies. An E galaxy might be misclassified as an S0, or an S0 as an E. However, an E will never be misclassified an SB0, nor will an SB0 ever be called an E. This asymmetry is important because elliptical (E) galaxies are typically twice as luminous as lenticular (S0) galaxies. The present results suggest that the evolution of luminous lenticular galaxies may be closely linked to that of elliptical galaxies, whereas fainter lenticulars might be more closely associated with ram-pressure stripped spiral galaxies. Finally it is pointed out that fine details of the galaxy formation process might account for some of the differences between the classifications of the same galaxy by individual competent morphologists.
Recently, both the ATLAS and CMS experiments have observed an excess of events that could be the first evidence for a 125 GeV Higgs boson. We investigate an implication of the CP-even Higgs boson with mass around 125 GeV in the context of the minimal gauge mediated supersymmetry breaking (mGMSB). In mGMSB, gravitino is the lightest sparticle (LSP) and hence the dark matter candidate. We consider the so-called superWIMP scenario where the dark matter gravitino is non-thermally produced by the decay of the next-to-LSP (NLSP) bino-like neutralino after its freeze-out. For a given $\tan \beta$ and the number of the messengers ($N_m$) fixed, we find that the rest of the mGMSB parameters, the SUSY breaking parameter and the messenger scale, are completely fixed by the conditions of simultaneously realizing the observed dark matter abundance and the 125 GeV Higgs boson mass, leading to the NLSP neutralino mass around 1.5-2 TeV and the gravitino mass around 3-7 GeV, depending on the values of $\tan \beta$ and $N_m$. The lifetime of the NLSP is found to be shorter than 1 sec, so that the success of the big bang nucleosynthesis remains intact. The non-thermally produced gravitino behaves as the warm dark matter with the free-streaming scale found to be $\lambda_{\rm FS} \simeq 0.1$ Mpc, whose value is reasonable for observations of the power spectrum on both large and sub-galactic scales in the Universe.
In this paper two things are done. First, it is pointed out the existence of exact asymptotically flat, spherically symmetric black holes when a self interacting, minimally coupled scalar field is the source of the energy momentum of the Einstein equations in four dimensions. The scalar field potential is the recently found to be compatible with the hairy generalization of the Plebanski-Demianski solution of general relativity. This paper describes the spherically symmetric solutions that smoothly connect the Schwarzschild black hole with its hairy counterpart. The geometry and scalar field are everywhere regular except at the usual Schwarzschild like singularity inside the black hole. The scalar field energy momentum tensor satisfies the null energy condition in the static region of the spacetime. The first law holds when the parameters of the scalar field potential are fixed under thermodynamical variation. Secondly, it is shown that an extra, dimensionless parameter, present in the hairy solution, allows to modify the gravitational field of a spherically symmetric black hole in a remarkable way. When the dimensionless parameter is increased, the scalar field generates a flat gravitational potential, that however asymptotically matches the Schwarzschild gravitational field. Finally, it is shown that a positive cosmological constant can render the scalar field potential convex if the parameters are within a specific rank.
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The galaxy CXOC J100043.1+020637, also known as CID-42, is a highly unusual object. An apparent galaxy merger remnant, it displays signatures of both an inspiraling, kiloparsec-scale active galactic nucleus (AGN) pair and of a recoiling AGN with a kick velocity of at least 1300 km s^-1. Among recoiling AGN candidates, CID-42 alone has both spatial offsets (in optical and X-ray bands) and spectroscopic offsets. In order to constrain the relative likelihood of both scenarios, we develop models using hydrodynamic galaxy merger simulations coupled with radiative transfer calculations. Our gas-rich, major merger models are generally well matched to the galactic morphology and to the inferred stellar mass and star formation rate. We show that a recoiling supermassive black hole (SMBH) in CID-42 should be observable as an AGN at the time of observation. However, in order for the recoiling AGN to produce narrow-line emission, it must be observed shortly after the kick while it still inhabits a dense gaseous region, implying a large total kick velocity (greater than about 2000 km s^-1). For the dual AGN scenario, an unusually large broad-line offset is required, and the best match to the observed morphology requires a galaxy that is less luminous than CID-42. Further, the lack of X-ray emission from one of the two optical nuclei is not easily attributed to an intrinsically quiescent SMBH or to a Compton-thick galactic environment. While the current data do not allow either the recoiling or the dual AGN scenario for CID-42 to be excluded, our models highlight the most relevant parameters for distinguishing these possibilities with future observations. In particular, high-quality, spatially-resolved spectra that can pinpoint the origin of the broad and narrow line features will be critical for determining the nature of this unique source.
We build a sample of distant (D > 80 kpc) stellar halo stars with measured radial velocities. Faint ($20 < g <22$) candidate blue horizontal branch (BHB) stars were selected using the deep, but wide, multi-epoch Sloan Digital Sky Survey photometry. Follow-up spectroscopy for these A-type stars was performed using the VLT-FORS2 instrument. We classify stars according to their Balmer line profiles, and find 7 are bona fide BHB stars and 31 are blue stragglers (BS). Owing to the magnitude range of our sample, even the intrinsically fainter BS stars can reach out to D ~ 90 kpc. We complement this sample of A-type stars with intrinsically brighter, intermediate-age, asymptotic giant branch stars. A set of 4 distant cool carbon stars is compiled from the literature and we perform spectroscopic follow-up on a further 4 N-type carbon stars using the WHT-ISIS instrument. Altogether, this provides us with the largest sample to date of individual star tracers out to r ~ 150 kpc. We find that the radial velocity dispersion of these tracers falls rapidly at large distances and is surprisingly cold (sigma_r ~ 50-60 km/s) between 100-150 kpc. Relating the measured radial velocities to the mass of the Milky Way requires knowledge of the (unknown) tracer density profile and anisotropy at these distances. Nonetheless, by assuming the stellar halo stars between 50-150 kpc have a moderate density fall-off (with power-law slope alpha < 5) and are on radial orbits (sigma^2_t/sigma^2_r < 1), we infer that the mass within 150 kpc is less than 10^12 M_solar and suggest it probably lies in the range (5-10) x 10^11 M_solar. We discuss the implications of such a low mass for the Milky Way.
We report the discovery of a ring-like cluster complex in the starburst galaxy NGC 2146. The Ruby Ring, so named due to its appearance, shows a clear ring-like distribution of star clusters around a central object. It is located in one of the tidal streams which surround the galaxy. NGC 2146 is part of the Snapshot Hubble U-band Cluster Survey (SHUCS). The WFC3/F336W data has added critical information to the available archival Hubble Space Telescope imaging set of NGC 2146, allowing us to determine ages, masses, and extinctions of the clusters in the Ruby Ring. These properties have then been used to investigate the formation of this extraordinary system. We find evidence of a spatial and temporal correlation between the central cluster and the clusters in the ring. The latter are about 4 Myr younger than the central cluster, which has an age of 7 Myr. This result is supported by the H alpha emission which is strongly coincident with the ring, and weaker at the position of the central cluster. From the derived total H alpha luminosity of the system we constrain the star formation rate density to be quite high, e.g. ~ 0.47 Msun/yr/kpc^2. The Ruby Ring is the product of an intense and localised burst of star formation, similar to the extended cluster complexes observed in M51 and the Antennae, but more impressive because is quite isolated. The central cluster contains only 5 % of the total stellar mass in the clusters that are determined within the complex. The ring-like morphology, the age spread, and the mass ratio support a triggering formation scenario for this complex. We discuss the formation of the Ruby Ring in a "collect & collapse" framework. The predictions made by this model agree quite well with the estimated bubble radius and expansion velocity produced by the feedback from the central cluster, making the Ruby Ring an interesting case of triggered star formation.
BL Lacertae (Lac) objects that are detected at very-high energies (VHE) are of fundamental importance to study multiple astrophysical processes, including the physics of jets, the properties of the extragalactic background light and the strength of the intergalactic magnetic field. Unfortunately, since most blazars have featureless optical spectra that preclude a redshift determination, a substantial fraction of these VHE extragalactic sources cannot be used for cosmological studies. To assess whether molecular lines are a viable way to establish distances, we have undertaken a pilot program at the IRAM 30m telescope to search for CO lines in three BL Lac objects with known redshifts. We report a positive detection of M_H2 ~ 3x10^8 Msun toward 1ES 1959+650, but due to the poor quality of the baseline, this value is affected by a large systematic uncertainty. For the remaining two sources, W Comae and RGB J0710+591, we derive 3sigma upper limits at, respectively, M_H2 < 8.0x10^8 Msun and M_H2 < 1.6x10^9 Msun, assuming a line width of 150 km/s and a standard conversion factor alpha=4 M_sun/(K km/s pc^2). If these low molecular gas masses are typical for blazars, blind redshift searches in molecular lines are currently unfeasible. However, deep observations are still a promising way to obtain precise redshifts for sources whose approximate distances are known via indirect methods. Our observations further reveal a deficiency of molecular gas in BL Lac objects compared to quasars, suggesting that the host galaxies of these two types of active galactic nuclei (AGN) are not drawn from the same parent population. Future observations are needed to assess whether this discrepancy is statistically significant, but our pilot program shows how studies of the interstellar medium in AGN can provide key information to explore the connection between the active nuclei and the host galaxies.
We discuss the ability of the planned Euclid mission to detect deviations from General Relativity using its extensive redshift survey of more than 50 Million galaxies. Constraints on the gravity theory are placed measuring the growth rate of structure within 14 redshift bins between z=0.7 and z=2. The growth rate is measured from redshift-space distortions, i.e. the anisotropy of the clustering pattern induced by coherent peculiar motions. This is performed in the overall context of the Euclid spectroscopic survey, which will simultaneously measure the expansion history of the universe, using the power spectrum and its baryonic features as a standard ruler, accounting for the relative degeneracies of expansion and growth parameters. The resulting expected errors on the growth rate in the different redshift bins, expressed through the quantity f\sigma_8, range between 1.3% and 4.4%. We discuss the optimisation of the survey configuration and investigate the important dependence on the growth parameterisation and the assumed cosmological model. We show how a specific parameterisation could actually drive the design towards artificially restricted regions of the parameter space. Finally, in the framework of the popular "\gamma -parameterisation", we show that the Euclid spectroscopic survey alone will already be able to provide substantial evidence (in Bayesian terms) if the growth index differs from the GR value \gamma=0.55 by at least \sim 0.13. This will combine with the comparable inference power provided by the Euclid weak lensing survey, resulting in Euclid's unique ability to provide a decisive test of modified gravity.
We calculate the dust formed around AGB and SAGB stars of metallicity Z=0.008 by following the evolution of models with masses in the range 1M<M<8M throughthe thermal pulses phase, and assuming that dust forms via condensation of molecules within a wind expanding isotropically from the stellar surface. We find that, because of the strong Hot Bottom Burning (HBB) experienced, high mass models produce silicates, whereas lower mass objects are predicted to be surrounded by carbonaceous grains; the transition between the two regimes occurs at a threshold mass of 3.5M. These fndings are consistent with the results presented in a previous investigation, for Z=0.001. However, in the present higher metallicity case, the production of silicates in the more massive stars continues for the whole AGB phase, because the HBB experienced is softer at Z=0.008 than at Z=0.001, thus the oxygen in the envelope, essential for the formation of water molecules, is never consumed completely. The total amount of dust formed for a given mass experiencing HBB increases with metallicity, because of the higher abundance of silicon, and the softer HBB, both factors favouring a higher rate of silicates production. This behaviour is not found in low mass stars,because the carbon enrichment of the stellar surface layers, due to repeated Third Drege Up episodes, is almost independent of the metallicity. Regarding cosmic dust enrichment by intermediate mass stars, we ?nd that the cosmic yield at Z=0.008 is a factor 5 larger than at Z=0.001. In the lower metallicity case carbon dust dominates after about 300 Myr, but at Z=0.008 the dust mass is dominated by silicates at all times,with a prompt enrichment occurring after about 40 Myr, associated with the evolution of stars with masses M =7.5 -8M.
Using 3D MHD simulation with the effects of radiative cooling/heating, chemical reactions, and thermal conduction, we investigate the formation of molecular cloud in the ISM. We consider the formation of molecular cloud by accretion of the HI clouds as suggested in recent observations. The simulation shows that the initial HI medium is compressed and piled up behind the shock waves induced by the accretion flows. Since the initial medium is highly inhomogeneous as a consequence of the thermal instability, the formed molecular cloud becomes very turbulent owing to the development of the Richtmyer-Meshkov instability. The structure of the post shock region is composed of dense cold gas (T<100 K) and diffuse warm gas (T>1,000 K), which are spatially well mixed owing to the turbulence. Because the energy source of the turbulence is the accretion flows, the turbulence is highly anisotropic biased toward the direction of accretion flows. The kinetic energy of the turbulence dominates the thermal, magnetic, and gravitational energies in the total 10 Myr evolution. However, the kinetic energy measured by using the CO-fraction-weighted density is comparable to the other energies. This suggests that the true kinetic energy of turbulence in molecular cloud as a hole can be much larger than the kinetic energy of turbulence estimated by line-width of molecular emissions. The clumps in the molecular cloud show statistically homogeneous evolution as follows: The typical plasma beta of the clumps is roughly constant <beta>~ 0.4. The size-velocity dispersion relation show dv ~ 1.5 km s^{-1} (l/1 pc)^{0.5}, irrespective of the density. The clumps evolve toward magnetically supercritical, gravitationally unstable cores. The clumps seem to evolve into cores that satisfy the condition for fragmentation into binary. These statistical properties may provide the initial condition of star formation.
Machine learning, algorithms to extract empirical knowledge from data, can be used to classify data, which is one of the most common tasks in observational astronomy. In this paper, we focus on Bayesian data classification algorithms using the Gaussian mixture model and show two applications in pulsar astronomy. After reviewing the Gaussian mixture model and the related Expectation-Maximization algorithm, we present a data classification method using the Neyman-Pearson test. To demonstrate the method, we apply the algorithm to two classification problems. Firstly, it is applied to the well known period-period derivative diagram, where we find that the pulsar distribution can be modeled with six Gaussian clusters, with two clusters for millisecond pulsars (recycled pulsars) and the rest for normal pulsars. From this distribution, we derive an empirical definition for millisecond pulsars as $\frac{\dot{P}}{10^{-17}} \leq3.23(\frac{P}{100 \textrm{ms}})^{-2.34}$. The two millisecond pulsar clusters may have different evolutionary origins, since the companion stars to these pulsars in the two clusters show different chemical composition. Four clusters are found for normal pulsars. Possible implications for these clusters are also discussed. Our second example is to calculate the likelihood of unidentified \textit{Fermi} point sources being pulsars and rank them accordingly. In the ranked point source list, the top 5% sources contain 50% known pulsars, the top 50% contain 99% known pulsars, and no known active galaxy (the other major population) appears in the top 6%. Such a ranked list can be used to help the future follow-up observations for finding pulsars in unidentified \textit{Fermi} point sources.
A model for the formation and distribution of sedimentary rocks on Mars is proposed. The rate-limiting step is supply of liquid water from seasonal melting of snow or ice. The model is run for a O(10^2) mbar pure CO2 atmosphere, dusty snow, and solar luminosity reduced by 23%. For these conditions snow only melts near the equator, and only when obliquity >40 degrees, eccentricity >0.12, and perihelion occurs near equinox. These requirements for melting are satisfied by 0.01-20% of the probability distribution of Mars' past spin-orbit parameters. Total melt production is sufficient to account for aqueous alteration of the sedimentary rocks. The pattern of seasonal snowmelt is integrated over all spin-orbit parameters and compared to the observed distribution of sedimentary rocks. The global distribution of snowmelt has maxima in Valles Marineris, Meridiani Planum and Gale Crater. These correspond to maxima in the sedimentary-rock distribution. Higher pressures and especially higher temperatures lead to melting over a broader range of spin-orbit parameters. The pattern of sedimentary rocks on Mars is most consistent with a Mars paleoclimate that only rarely produced enough meltwater to precipitate aqueous cements and indurate sediment. The results suggest intermittency of snowmelt and long globally-dry intervals, unfavorable for past life on Mars. This model makes testable predictions for the Mars Science Laboratory rover at Gale Crater. Gale Crater is predicted to be a hemispheric maximum for snowmelt on Mars.
Notes from a series of 12 one hour (or more) lectures on Plasma Physics given
to Ramesh Narayan' research group at Harvard Center for Astrophysics, from
February to May 2012.
Lectures 1 to 5 cover various key Plasma Physics themes. Then, we go over the
Review Paper on "Multidimensional electron beam-plasma instabilities in the
relativistic regime" [Physics of Plasmas 17, 120501 (2010)].
We present the results from timing observations with the GMRT of the young pulsar J1833-1034, in the galactic supernova remnant G21.5-0.9. We detect the presence of 4 glitches in this pulsar over a period of 5.5 years, making it one of a set of pulsars that show fairly frequent glitches. The glitch amplitudes, characterized by the fractional change of the rotational frequency, range from 1 \times 10^-9 to 7 \times 10^-9, with no evidence for any appreciable relaxation of the rotational frequency after the glitches. The fractional changes observed in the frequency derivative are of the order of 10-5 . We show conclusively that, in spite of having significant timing noise, the sudden irregularities like glitches detected in this pulsar can not be modeled as smooth timing noise. Our timing solution also provides a stable estimate of the second derivative of the pulsar spin-down model, and a plausible value for the braking index of 1.857, which, like the value for other such young pulsars, is much less than the canonical value of 3.0. PSR J1833-1034 appears to belong to a class of pulsars exhibiting fairly frequent occurrence of low amplitude glitches. This is further supported by an estimate of the glitch activity parameter, Ag = 1.53 \times 10^-15 s^-2, which is found to be significantly lower than the trend of glitch activity versus characteristic age (or spin frequency derivative) that a majority of the glitching pulsars follow. We present evidence for a class of such young pulsars, including the Crab, where higher internal temperature of the neutron star could be responsible for the nature of the observed glitch activity.
This paper contains details on the algorithms implemented in the TEMPO2 pulsar timing software package and describes how the software is used. Information is given on how to download and install the software, use the various interfaces, simulate realistic data sets and develop the software. The use of TEMPO2 in predictive mode is also described.
PSRCHIVE is an open-source, object-oriented, scientific data analysis software library and application suite for pulsar astronomy. It implements an extensive range of general-purpose algorithms for use in data calibration and integration, statistical analysis and modeling, and visualisation. These are utilised by a variety of applications specialised for tasks such as pulsar timing, polarimetry, radio frequency interference mitigation, and pulse variability studies. This paper presents a general overview of PSRCHIVE functionality with some focus on the integrated interfaces developed for the core applications.
This is a status report on our endeavor to reveal the mechanism of core-collapse supernovae (CCSNe) by large-scale numerical simulations. Multi-dimensionality of the supernova engine, general relativisitic magnetohydrodynamics, energy and lepton number transport by neutrinos emitted from the forming neutron star as well as nuclear interactions there, are all believed to play crucial roles in repelling infalling matter and producing energetic explosions. These ingredients are nonlinearly coupled with one another in the dynamics of core-collapse, bounce, and shock expansion. Serious quantitative studies of CCSNe hence make extensive numerical computations mandatory. Since neutrinos are neither in thermal nor in chemical equilibrium in general, their distributions in the phase space should be computed. This is a six dimensional (6D) neutrino transport problem and quite a challenge even for those with an access to the most advanced numerical resources such as the "K computer". To tackle this problem, we have embarked on multi-front efforts. In particular we report in this paper our recent progresses in the treatments of multi-dimensional (multi-D) radiation-hydrodynamics. We are currently proceeding on two different paths to the ultimate goal; in one approach we employ an approximate but highly efficient scheme for neutrino transport and treat 3D hydrodynamics and/or general relativity rigorously; some neutrino-driven explosions will be presented and comparisons will be made between 2D and 3D models quantitatively; in the second approach, on the other hand, exact but so far Newtonian Boltzmann equations are solved in two and three spatial dimensions; we will show some demonstrative test simulations. We will also address the perspectives of exa-scale computations on the next generation supercomputers.
We estimate the diffuse supernova neutrino background (DSNB) using, for the first time, the most recent progenitor-dependent, long-term supernova simulations and including neutrino oscillations for several post-bounce times. Assuming multi-angle matter suppression of collective effects during the accretion phase, we find that oscillation effects are dominated by the matter-driven MSW resonances, while neutrino-neutrino collective effects contribute at the 5-10% level. The impact of the neutrino mass hierarchy, of the time-dependent neutrino spectra and of the diverse progenitor star population is 10% or less, small compared to the uncertainty of at least 25% of the normalization of the supernova rate. Therefore, assuming that the sign of the neutrino mass hierarchy will be determined within the next decade, the future detection of the DSNB will deliver approximate information on the MSW-oscillated neutrino spectra. With a reliable model for neutrino emission, its detection will be a powerful instrument to provide complementary information on the star formation rate and for learning about stellar physics.
Using HST/WFPC2 data, we have performed a comparative study of the Blue Straggler Star (BSS) populations in the central regions of the globular clusters AM 1, Eridanus, Palomar 3, and Palomar 4. Located at distances RGC > 50 kpc from the Galactic Centre, these are (together with Palomar 14 and NGC 2419) the most distant clusters in the Halo. We determine their colour-magnitude diagrams and centres of gravity. The four clusters turn out to have similar ages (10.5-11 Gyr), significantly smaller than those of the inner-Halo globulars, and similar metallicities. By exploiting wide field ground based data, we build the most extended radial density profiles from resolved star counts ever published for these systems. These are well reproduced by isotropic King models of relatively low concentration. BSSs appear to be significantly more centrally segregated than red giants in all globular clusters, in agreement with the estimated core and half-mass relaxation times which are smaller than the cluster ages. Assuming that this is a signature of mass segregation, we conclude that AM 1 and Eridanus are slightly dynamically more evolved than Pal 3 and Pal 4.
We investigate the growth index parameter \gamma and the time variation of the gravitational constant G_{eff} by using the currently available growth function f(z) data at different redshifts, consistently scaled to the fiducial \Lambda CDM model. We inquire the four different models of \gamma including a constant \gamma model. From a \chi^2 minimization, we constrain the parameter spaces of models and show that \Lambda CDM model is excluded by 1-\sigma level from current f(z) data. G_{eff} is different from the Newton's gravitational constant G_{N} in modified gravity theories and interestingly, the current data shows that G_{eff} \neq G_{N} at z \gtrsim 0.3 with 3-\sigma level. From these, we conclude that Einstein's General Relativity with \Lambda CDM is ruled out by 99 % confidence level from large scale structure (LSS) observations.
Surveys of the binary populations in the solar neighbourhood have shown that the periods of G- and M-type stars are log-normally distributed. However, observations of young binary populations suggest a log-uniform distribution. Clearly some process(es) change the period distribution over time. Most stars form in star clusters, in which two important dynamical processes occur: i) gas-induced orbital decay of embedded binary systems and ii) destruction of soft binaries in three-body interactions. The emphasis here is on orbital decay which has been largely neglected so far. Using a combination of Monte-Carlo and dynamical nbody modelling it is demonstrated here that the cluster dynamics destroys the number of wide binaries, but leaves short-period binaries basically undisturbed even for a initially log-uniform distribution. By contrast orbital decay significantly reduces the number and changes the properties of short-period binaries, but leaves wide binaries largely uneffected. Until now it was unclear whether the short period distribution of the field is unaltered since its formation. It is shown here, that orbital decay is a prime candidate for such a task. In combination the dynamics of these two processes, convert an initial log-uniform distribution to a log-normal period distribution. The probability is 94% that the evolved and observed period distribution were sampled from the same parent distribution. This means binaries can be formed with periods that are sampled from the log-uniform distribution. As the cluster evolves, short-period binaries are merged to single stars by the gas-induced orbital decay while the dynamical evolution in the cluster destroys wide binaries. The combination of these two equally important processes reshapes a initial log-uniform period distribution to the log-normal period distribution, that is observed in the field (abridged).
The mid-infrared spectra of ultraluminous infrared galaxies (ULIRGs) contain
a variety of spectral features that can be used as diagnostics to characterise
the spectra. However, such diagnostics are biased by our prior prejudices on
the origin of the features. Moreover, by using only part of the spectrum they
do not utilise the full information content of the spectra. Blind statistical
techniques such as principal component analysis (PCA) consider the whole
spectrum, find correlated features and separate them out into distinct
components.
We further investigate the principal components (PCs) of ULIRGs derived in
Wang et al.(2011). We quantitatively show that five PCs is optimal for
describing the IRS spectra. These five components (PC1-PC5) and the mean
spectrum provide a template basis set that reproduces spectra of all z<0.35
ULIRGs within the noise. For comparison, the spectra are also modelled with a
combination of radiative transfer models of both starbursts and the dusty torus
surrounding active galactic nuclei. The five PCs typically provide better fits
than the models. We argue that the radiative transfer models require a colder
dust component and have difficulty in modelling strong PAH features.
Aided by the models we also interpret the physical processes that the
principal components represent. The third principal component is shown to
indicate the nature of the dominant power source, while PC1 is related to the
inclination of the AGN torus.
Finally, we use the 5 PCs to define a new classification scheme using 5D
Gaussian mixtures modelling and trained on widely used optical classifications.
The five PCs, average spectra for the four classifications and the code to
classify objects are made available at: this http URL
Is it realistic to recover the 3D structure of galaxies from their images? To answer this question, we generate a sample of idealised model galaxies consisting of a disc-like component and a spheroidal component (bulge) with varying luminosities, inclination angles and structural parameters, and component density following the Einasto distribution. We simulate these galaxies as if observed in the SDSS project through ugriz filters, thus gaining a set of images of galaxies with known intrinsic properties. We remodel the galaxies with a 3D galaxy modelling procedure and compare the restored parameters to the initial ones in order to determine the uncertainties of the models. Down to the r-band limiting magnitude 18, errors of the restored integral luminosities and colour indices remain within 0.05 mag and errors of the luminosities of individual components within 0.2 mag. Accuracy of the restored bulge-to-disc ratios (B/D) is within 40% in most cases, and becomes even worse for galaxies with low B/D due to difficulties in reconstructing their bulge properties. Nevertheless, the general balance between bulges and discs is not shifted systematically. Inclination angle estimates are better for disc-dominated galaxies, with the errors remaining below 5deg for galaxies with B/D < 2. Errors of the recovered sizes of the galactic components are less than 10% in most cases. Axial ratios and the parameter N of Einasto's distribution (similar to the S\'ersic index) are relatively inaccurate, but can provide statistical estimates for large samples. In general, models of disc components are more accurate than models of bulge components for geometrical reasons.
Aims: We aim to perform the first long-term analysis of the system HS Hya. Methods: We performed an analysis of the long-term evolution of the light curves of the detached eclipsing system HS Hya. Collecting all available photometric data since its discovery, the light curves were analyzed with a special focus on the evolution of system's inclination. Results: We find that the system undergoes a rapid change of inclination. Since its discovery until today the system's inclination changed by more than 15{\deg}. The shape of the light curve changes, and now the eclipses are almost undetectable. The third distant component of the system is causing the precession of the close orbit, and the nodal period is about 631 yr. Conclusions: New precise observations are desperately needed, preferably this year, because the amplitude of variations is decreasing rapidly every year. We know only 10 such systems on the whole sky at present.
Microlensing detections of cool planets are important for the construction of an unbiased sample to estimate the frequency of planets beyond the snow line, which is where giant planets are thought to form according to the core accretion theory of planet formation. In this paper, we report the discovery of a giant planet detected from the analysis of the light curve of a high-magnification microlensing event MOA-2010-BLG-477. The measured planet-star mass ratio is $q=(2.181\pm0.004)\times 10^{-3}$ and the projected separation is $s=1.1228\pm0.0006$ in units of the Einstein radius. The angular Einstein radius is unusually large $\theta_{\rm E}=1.38\pm 0.11$ mas. Combining this measurement with constraints on the "microlens parallax" and the lens flux, we can only limit the host mass to the range $0.13<M/M_\odot<1.0$. In this particular case, the strong degeneracy between microlensing parallax and planet orbital motion prevents us from measuring more accurate host and planet masses. However, we find that adding Bayesian priors from two effects (Galactic model and Keplerian orbit) each independently favors the upper end of this mass range, yielding star and planet masses of $M_*=0.67^{+0.33}_{-0.13}\ M_\odot$ and $m_p=1.5^{+0.8}_{-0.3}\ M_{\rm JUP}$ at a distance of $D=2.3\pm0.6$ kpc, and with a semi-major axis of $a=2^{+3}_{-1}$ AU. Finally, we show that the lens mass can be determined from future high-resolution near-IR adaptive optics observations independently from two effects, photometric and astrometric.
We present the results of quantum calculations based on entirely ab initio methods for a variety of molecular processes and chemical reactions involving the LiHe$^+$ ionic polar molecule. With the aid of these calculations we derive accurate reaction rates and fitting expressions valid over a range of gas temperatures representative of the typical conditions of the pregalactic gas. With the help of a full chemical network, we then compute the evolution of the abundance of LiHe$^+$ as function of redshift in the early Universe. Finally, we compare the relative abundance of LiHe$^+$ with that of other polar cations formed in the same redshift interval.
Uniquely among the dwarf spheroidal (dSph) satellite galaxies of the Milky Way, Fornax hosts globular clusters. It remains a puzzle as to why dynamical friction has not yet dragged any of Fornax's five globular clusters to the centre, and also why there is no evidence that any similar star cluster has been in the past (for Fornax or any other dSph). We set up a suite of 2800 N-body simulations that sample the full range of globular-cluster orbits and mass models consistent with all existing observational constraints for Fornax. In agreement with previous work, we find that if Fornax has a large dark-matter core then its globular clusters remain close to their currently observed locations for long times. Furthermore, we find previously unreported behaviour for clusters that start inside the core region. These are pushed out of the core and gain orbital energy, a process we call 'dynamical buoyancy'. Thus a cored mass distribution in Fornax will naturally lead to a shell-like globular cluster distribution near the core radius, independent of the initial conditions. By contrast, CDM-type cusped mass distributions lead to the rapid infall of at least one cluster within \Delta t = 1-2Gyr, except when picking unlikely initial conditions for the cluster orbits (\sim 2% probability), and almost all clusters within \Delta t = 10Gyr. Alternatively, if Fornax has only a weakly cusped mass distribution, dynamical friction is much reduced. While over \Delta t = 10Gyr this still leads to the infall of 1-4 clusters from their present orbits, the infall of any cluster within \Delta t = 1-2Gyr is much less likely (with probability 0-70%, depending on \Delta t and the strength of the cusp). Such a solution to the timing problem requires that in the past the globular clusters were somewhat further from Fornax than today; they most likely did not form within Fornax, but were accreted.
By using various properties of the complete elliptic integrals, we have derived an alternative expression for the gravitational potential of axially symmetric bodies, which is free of singular kernel in contrast with the classical form. This is mainly a radial integral of the local surface density weighted by a regular "mean Green function" which depends explicitly on the body's vertical thickness. Rigorously, this result stands for a wide variety of configurations, as soon as the density structure is vertically homogeneous. Nevertheless, the sensitivity to vertical stratification | the Gaussian profile has been considered | appears weak provided that the surface density is conserved. For bodies with small aspect ratio (i.e. geometrically thin discs), a first-order Taylor expansion furnishes an excellent approximation for this mean Green function, the absolute error being of the fourth order in the aspect ratio. This formula is therefore well suited to studying the structure of self-gravitating discs and rings in the spirit of the "standard model of thin discs" where the vertical structure is often ignored, but it remains accurate for discs and tori of finite thickness. This approximation which perfectly saves the properties of Newton's law everywhere (in particular at large separations), is also very useful for dynamical studies where the body is just a source of gravity acting on external test particles.
Since their discovery by the Beppo-SAX satellite in 1997, gamma-ray burst afterglows have attracted an ever-growing interest. They have allowed redshift measurements that have confirmed that gamma-ray bursts are located at cosmological distances. Their study covers a huge range both in time (from one minute to several months after the trigger) and energy (from the GeV to radio domains). The purpose of this review is first to give a short historical account of afterglow research and describe the main observational results with a special attention to the early afterglow revealed by Swift. We then present the standard afterglow model as it has been developed in the pre-Swift era and show how it is challenged by the recent Swift and Fermi results. We finally discuss different options (within the standard framework or implying a change of paradigm) that have been proposed to solve the current problems.
The functional form of the nuclear symmetry energy in the whole range of densities relevant for the neutron stars is still unknown. Discrepancies concern both the low as well as the high density behaviour of this function. By use of Bezier curves three different families of the symmetry energy shapes, relevant for different density range were introduced. Their consequences for the crustal properties of neutron stars are presented.
V405 And is an ultrafast-rotating (P_rot ~ 0.46 days) eclipsing binary. The system consists of a primary star with radiative core and convective envelope, and a fully convective secondary. Theories have shown, that stellar structure can depend on magnetic activity, i.e., magnetically active M-dwarfs should have larger radii. Earlier light curve modelling of V405 And indeed showed this behaviour: we found that the radius of the primary is significantly larger than the theoretically predicted value for inactive main sequence stars (the discrepancy is the largest of all known objects), while the secondary fits well to the mass-radius relation. By modelling our recently obtained light curves, which show significant changes of the spotted surface of the primary, we can find further proof for this phenomenon.
We present the morphological properties of 161 star clusters in M33 using the Advanced Camera For Surveys Wide Field Channel onboard the Hubble Space Telescope using observations with the F606W and F814W filters. We obtain, for the first time, ellipticities, position angles, and surface brightness profiles for a significant number of clusters. On average, M33 clusters are more flattened than those of the Milky Way and M31, and more similar to clusters in the Small Magellanic Cloud. The ellipticities do not show any correlation with age or mass, suggesting that rotation is not the main cause of elongation in the M33 clusters. The position angles of the clusters show a bimodality with a strong peak perpendicular to the position angle of the galaxy major axis. These results support the notion that tidal forces are the reason for the cluster flattening. We fit King and EFF models to the surface brightness profiles and derive structural parameters including core radii, concentration, half-light radii and central surface brightness for both filters. The surface brightness profiles of a significant number of clusters show irregularities such as bumps and dips. Young clusters (Log age < 8) are notably better fitted by models with no radial truncation (EFF models), while older clusters show no significant differences between King or EFF fits. M33 star clusters seem to have smaller sizes, smaller concentrations, and smaller central surface brightness as compared to clusters in the MW, M31, LMC and SMC. Analysis of the structural parameters presents a age-radius relation also detected in other star cluster systems. The overall analysis shows differences in the structural evolution between the M33 cluster system and cluster systems in nearby galaxies. These differences could have been caused by the strong differences in these various environments.
We used the GEOS database to study the Blazhko effect of galactic RRab stars. The database is continuously enriched by maxima supplied by amateur astronomers and by a dedicated survey by means of the two TAROT robotic telescopes. The same value of the Blazhko period is observed at different values of the pulsation periods and different values of the Blazhko periods are observed at the same value of the pulsation period. There are clues suggesting that the Blazhko effect is changing from one cycle to the next. The secular changes in the pulsation and Blazhko periods of Z CVn are anticorrelated. The diagrams of magnitudes against phases of the maxima clearly show that the light curves of Blazhko variables can be explained as modulated signals, both in amplitude and in frequency. The closed curves describing the Blazhko cycles in such diagrams have different shapes, reflecting the phase shifts between the epochs of the brightest maximum and the maximum O-C. Our sample shows that both clockwise and anticlockwise directions are possible for similar shapes. The improved observational knowledge of the Blazhko effect, in addition to some peculiarities of the light curves, have still to be explained by a satisfactory physical mechanism.
We report a multisite photometric campaign for the Beta Cep stars V2052 Oph and V986 Oph. 670 hours of high-quality differential photoelectric Stromgren, Johnson and Geneva time-series photometry were obtained with eight telescopes on five continents during 182 nights. Frequency analyses of the V2052 Oph data enabled the detection of three pulsation frequencies, the first harmonic of the strongest signal, and the rotation frequency with its first harmonic. Pulsational mode identification from analysing the colour amplitude ratios confirms the dominant mode as being radial, whereas the other two oscillations are most likely l=4. Combining seismic constraints on the inclination of the rotation axis with published magnetic field analyses we conclude that the radial mode must be the fundamental. The rotational light modulation is in phase with published spectroscopic variability, and consistent with an oblique rotator for which both magnetic poles pass through the line of sight. The inclination of the rotation axis is 54o <i< 58o and the magnetic obliquity 58o <beta< 66o. The possibility that V2052 Oph has a magnetically confined wind is discussed. The photometric amplitudes of the single oscillation of V986 Oph are most consistent with an l=3 mode, but this identification is uncertain. Additional intrinsic, apparently temporally incoherent, light variations of V986 Oph are reported. Different interpretations thereof cannot be distinguished at this point, but this kind of variability appears to be present in many OB stars. The prospects of obtaining asteroseismic information for more rapidly rotating Beta Cep stars, which appear to prefer modes of higher l, are briefly discussed.
Encompasing a volume of ~1 km^3 of glacial ice at the South Pole, IceCube is currently the worlds largest neutrino detector. It consists of 5160 optical modules on 86 strings in a depth between 1450m and 2450m, as well as 324 optical modules arranged in 81 stations on the surface to detect charged cosmic rays. A large amount of data has already been acquired with smaller configurations throughout the installation period. Using this data the atmospheric neutrino spectrum in the northern hemisphere has been measured up to 100 TeV. No point sources have been identified in a set of more than 10^5 neutrino candidates from both hemispheres. Searches for transient sources have set stringent limits on neutrino emission from gamma-ray bursts, and are now accompanied by an extensive neutrino-triggered follow-up program. A very large statistics of cosmic ray events has revealed an anisotropy in the cosmic ray flux on the 10^-3 level in the 10-100 TeV range. While no sources of extra-terrestrial neutrinos have been found yet, the physics results obtained so far illustrate the very good performance of the detector.
Asteroseismology is the determination of the interior structures of stars by using their oscillations as seismic waves. Simple explanations of the astrophysical background and some basic theoretical considerations needed in this rapidly evolving field are followed by introductions to the most important concepts and methods on the basis of example. Previous and potential applications of asteroseismology are reviewed and future trends are attempted to be foreseen.
This paper presents a detailed and precise study of the characteristics of the Exoplanet Host Star and CoRoT main target HD 52265, as derived from asteroseismic studies. The results are compared with previous estimates, with a comprehensive summary and discussion. The basic method is similar to that previously used by the Toulouse group for solar-type stars. Models are computed with various initial chemical compositions and the computed p-mode frequencies are compared with the observed ones. All models include atomic diffusion and the importance of radiative accelerations is discussed. Several tests are used, including the usual frequency combinations and the fits of the \'echelle diagrams. The possible surface effects are introduced and discussed. Automatic codes are also used to find the best model for this star (SEEK, AMP) and their results are compared with that obtained with the detailed method. We find precise results for the mass, radius and age of this star, as well as its effective temperature and luminosity. We also give an estimate of the initial helium abundance. These results are important for the characterization of the star-planet system.
Oscillations from high energy photons into light pseudoscalar particles in an external magnetic field is expected to happen in some extensions of the Standard Model. It is usually assumed that those axionlike particles (ALPs) could produce a drop in the energy spectra of gamma ray sources and possibly decrease the opacity of the Universe for TeV gamma rays. We show here that these assumptions are in fact based on an average behavior that cannot happen in real observations of single sources. We propose a new method to search for photon-ALP oscillations, taking advantage of the fact that a single observation would deviate from the average expectation. Our method is based on the search for irregularities in the energy spectra of gamma ray sources. We predict features that are unlikely to be produced by known astrophysical processes and a new signature of ALPs that is easily falsifiable.
The Telescope Array Collaboration has observed a cosmic-ray event with estimated primary energy of 1.38*10^20 eV whose arrival direction coincides (see arxiv:1205.5984), given the angular resolution of 1.5 deg, with that of an event with estimated primary energy of 1.23*10^20 eV observed by the Pierre Auger Observatory. The total number of events with energies >10^20 eV published by both experiments is six. I estimate the statistical significance of the doublet, which is rather weak, and point out that the arrival directions of events in the doublet coincide with the Galactic X-ray source Aql X-1.
We model the production of OH+, H2O+, and H3O+ in interstellar clouds, using a steady state photodissociation region code that treats the freeze-out of gas species, grain surface chemistry, and desorption of ices from grains. The code includes PAHs, which have important effects on the chemistry. All three ions generally have two peaks in abundance as a function of depth into the cloud, one at A_V<~1 and one at A_V~3-8, the exact values depending on the ratio of incident ultraviolet flux to gas density. For relatively low values of the incident far ultraviolet flux on the cloud ({\chi}<~ 1000; {\chi}= 1= local interstellar value), the columns of OH+ and H2O+ scale roughly as the cosmic ray primary ionization rate {\zeta}(crp) divided by the hydrogen nucleus density n. The H3O+ column is dominated by the second peak, and we show that if PAHs are present, N(H3O+) ~ 4x10^{13} cm^{-2} independent of {\zeta}(crp) or n. If there are no PAHs or very small grains at the second peak, N(H3O+) can attain such columns only if low ionization potential metals are heavily depleted. We also model diffuse and translucent clouds in the interstellar medium, and show how observations of N(OH+)/N(H) and N(OH+)/N(H2O+) can be used to estimate {\zeta}(crp)/n, {\chi}/n and A_V in them. We compare our models to Herschel observations of these two ions, and estimate {\zeta}(crp) ~ 4-6 x 10^-16 (n/100 cm^-3) s^-1 and \chi/n = 0.03 cm^3 for diffuse foreground clouds towards W49N.
We study for the first time the environment of massive black hole (BH) seeds (~10^4-5 Msun) formed via the direct collapse of pristine gas clouds in massive haloes (>10^7 Msun) at z>6. Our model is based on the evolution of dark matter haloes within a cosmological N-body simulation, combined with prescriptions for the formation of BH along with both Pop III and Pop II stars. We calculate the spatially-varying intensity of Lyman Werner (LW) radiation from stars and identify the massive pristine haloes in which it is high enough to shut down molecular hydrogen cooling. In contrast to previous BH seeding models with a spatially constant LW background, we find that the intensity of LW radiation due to local sources, J_local, can be up to 10^6 times the spatially averaged background in the simulated volume and exceeds the critical value, J_crit, for the complete suppression of molecular cooling, in some cases by 4 orders of magnitude. Even after accounting for possible metal pollution in a halo from previous episodes of star formation, we find a steady rise in the formation rate of direct collapse (DC) BHs with decreasing redshift from 10^{-3}/Mpc^3/z at z=12 to 10^{-2}/Mpc^3/z at z=6. The onset of Pop II star formation at z~16 simultaneously marks the onset of the epoch of DCBH formation, as the increased level of LW radiation from Pop II stars is able to elevate the local levels of the LW intensity to J_local > J_crit while Pop III stars fail to do so at any time. The number density of DCBHs is sensitive to the number of LW photons and can vary by an order of magnitude at z=6 after accounting for reionisation feedback. Haloes hosting DCBHs are more clustered than similar massive counterparts that do not host DCBHs, especially at redshifts z>10. We also show that planned surveys with JWST should be able to detect the supermassive stellar precursors of DCBHs.
The first Search for Extra-Terrestrial Intelligence (SETI) conducted with Very Long Baseline Interferometry (VLBI) is presented. By consideration of the basic principles of interferometry, we show that VLBI is efficient at discriminating between SETI signals and human generated radio frequency interference (RFI). The target for this study was the star Gliese 581, thought to have two planets within its habitable zone. On 2007 June 19, Gliese 581 was observed for 8 hours at 1230-1544 with the Australian Long Baseline Array. The dataset was searched for signals appearing on all interferometer baselines above five times the noise limit. A total of 222 potential SETI signals were detected and by using automated data analysis techniques, were ruled out as originating from the Gliese 581 system. From our results we place an upper limit of 7 MW/Hz on the power output of any isotropic emitter located in the Gliese 581 system, within this frequency range. This study shows that VLBI is ideal for targeted SETI, including follow-up observations. The techniques presented are equally applicable to next-generation interferometers, such as the long baselines of the Square Kilometre Array (SKA).
Observations of high-redshift quasars at z>6 imply that supermassive black holes (SMBHs) with masses over 10^{9}M\odot were in place less than 1 Gyr after the Big Bang. If these SMBHs assembled from "seed" BHs left behind by the first stars, then they must have accreted gas at close to the Eddington limit during a large fraction (>50%) of the time. A generic problem with this scenario, however, is that the mass density in M\sim10^{6}M\odot SMBHs at z 6 already exceeds the locally observed SMBH mass density by several orders of magnitude. In order to avoid this overproduction, BH seed formation and growth must become significantly less efficient in less massive protogalaxies, while proceeding uninterrupted in the most massive galaxies that formed first. Using Monte-Carlo realizations of the merger and growth history of BHs, we show that X-rays from the earliest accreting BHs can provide such a feedback mechanism. Our calculations paint a self-consistent picture of black-hole-made climate change, in which the first miniquasars - among them the ancestors of the z 6 quasar SMBHs - globally warm the IGM and suppress the formation and growth of subsequent generations of BHs. We present two specific models with global miniquasar feedback that provide excellent agreement with recent estimates of the z=6 SMBH mass function. For each of these models, we estimate the rate of BH mergers at z>6 that could be detected by the proposed gravitational-wave observatory eLISA/NGO.
The evolution of a large-scale poloidal magnetic field in accretion discs is an important problem because of its role in the launching of jets and winds and in determining the intensity of turbulence. In this paper, we develop a formalism to calculate the transport magnetic flux in a thin accretion disc, thus determining its evolution on a viscous/resistive timescale. The governing equations are derived by performing an asymptotic expansion in the limit of a thin disc, in the regime where the magnetic field is dominated by its vertical component. Turbulent viscosity and resistivity are included, with an arbitrary vertical profile that can be adjusted to mimic the vertical structure of the turbulence. At a given radius and time, the rates of transport of mass and magnetic flux are determined by a one-dimensional problem in the vertical direction, in which the radial gradients of various quantities appear as source terms. We solve this problem to obtain the transport rates and the vertical structure of the disc. The present paper is then restricted to the idealised case of uniform diffusion coefficients, while a companion paper will study more realistic vertical profiles of these coefficients. We show the advection of weak magnetic fields to be significantly faster than the advection of mass, contrary to what a crude vertical averaging might suggest. This results from the larger radial velocities away from the mid-plane, which barely affect the mass accretion owing to the low density in these regions but do affect the advection of magnetic flux. Possible consequences of this larger accretion velocity include a potentially interesting time-dependence with the magnetic flux distribution evolving faster than the mass distribution. If the disc is not too thin, this fast advection may also partially solve the long-standing problem of too efficient diffusion of an inclined magnetic field.
Fermi-LAT has confirmed the excess in cosmic positron fraction observed by PAMELA, which could be explained by dark matter annihilating or decaying in the center of the galaxy. Most existing models postulate that the dark matter annihilates or decays into final states with two or four leptons, which would produce diffuse gamma ray emissions that are in tension with data measured by Fermi-LAT. We point out that the tension could be alleviated if the dark matter decays into three-body final states with a pair of leptons and a missing particle. Using the goldstino decay in a certain class of supersymmetric theories as a prime example, we demonstrate that simultaneous fits to the total e+ + e- and the fractional e+/e- fluxes from Fermi-LAT and PAMELA could be achieved for a 2 TeV parent particle and a 1 TeV missing particle, without being constrained by gamma-ray measurements. By studying different effective operators giving rise to the dark matter decay, we show that this feature is generic for three-body decaying dark matter containing a missing particle. Constraints on the hadronic decay widths from the cosmic anti-proton spectra are also discussed.
We consider neutrino oscillations in non-uniform matter in a quantum field theoretic (QFT) approach, in which neutrino production, propagation and detection are considered as a single process. We find the conditions under which the oscillation probability can be sensibly defined and demonstrate how the properly normalized oscillation probability can be obtained in the QFT framework. We derive the evolution equation for the oscillation amplitude and discuss the conditions under which it reduces to the standard Schr\"odinger-like evolution equation. It is shown that, contrary to the common usage, the Schr\"odinger-like evolution equation is not applicable in certain cases, such as oscillations of neutrinos produced in decays of free pions provided that sterile neutrinos with $\Delta m^2\gtrsim 1$ eV$^2$ exist.
Stable domain walls of light (pseudo)scalar fields permeating the entire Universe and persisting to the present epoch is a generic consequence of many extensions to the Standard Model. Currently the combination of gravitational and cosmological constraints provides the best limits on such a possibility. We show that if domain walls are generated by an axion-like field with a coupling to the spins of standard-model particles, and the galactic environment contains a network of such walls, terrestrial experiments aimed at detection of wall-crossing events are realistic. In particular, a geographically separated but time-synchronized network of sensitive atomic magnetometers can detect a wall crossing and probe a range of model parameters currently unconstrained by astrophysical observations and gravitational experiments.
Motivated by the couplings of the dilaton in four-dimensional effective actions, we investigate the cosmological consequences of a scalar field coupled both to matter and a Maxwell-type vector field. The vector field has a background isotropy-violating component. New anisotropic scaling solutions which can be responsible for the matter and dark energy dominated epochs are identified and explored. For a large parameter region the universe expands almost isotropically. Using that the CMB quadrupole is extremely sensitive to shear, we constrain the ratio of the matter coupling to the vector coupling to be less than 10^(-5). Moreover, we identify a large parameter region, corresponding to a strong vector coupling regime, yielding exciting and viable cosmologies close to the LCDM limit.
Astrophysical black hole candidates are thought to be the Kerr black hole predicted by General Relativity. In order to confirm the Kerr-nature of these objects, we need to probe the geometry of the space-time around them and see if the observations are consistent with the predictions of the Kerr metric. That can be achieved, for instance, by studying the properties of the electromagnetic radiation emitted by the gas in the accretion disk. The high-frequency quasi-periodic oscillations observed in the X-ray flux of some stellar-mass black hole candidates might do the job. As the frequencies of these oscillations depend only very weakly on the observed X-ray flux, it is thought they are mainly determined by the metric of the space-time. In this paper, I consider the resonance models proposed by Abramowicz and Kluzniak and I extend previous results to the case of non-Kerr space-times. The emerging picture is more complicated than the one around a Kerr black hole and there is a larger number of possible combinations between different modes. I then compare the bounds inferred from the twin peak high-frequency quasi-periodic oscillations observed in three micro-quasars (GRO J1655-40, XTE J1550-564, and GRS 1915+105) with the measurements from the continuum-fitting method of the same objects. For Kerr black holes, the two approaches do not provide consistent results. In a non-Kerr geometry, this conflict may be solved if the observed quasi-periodic oscillations are produced by the resonance $\nu_\theta : \nu_r = 3:1$, where $\nu_\theta$ and $\nu_r$ are the two epicyclic frequencies. It is at least worth mentioning that the deformation from the Kerr solution required by observations would be consistent with the one suggested in another recent work discussing the possibility that steady jets are powered by the spin of these compact objects.
f(T) gravity, a generally modified teleparallel gravity, has become very popular at recent times as it is able to reproduce the unification of inflation and late-time acceleration with no need of a dark energy component or an inflation field. In this present work, we investigate specifically the range of validity of Birkhoff's theorem and present a new spherically symmetric solution in the frame of $f(T)$ gravity upto the perturbative order. We also compare the results in the Jordan and the so-called Einstein frames via conformal transformation. The meaning of results respond to the physical equivalence between both frames, at least the perturbative order is discussed. This analysis obtains some conditions for Birkhoff's theorem to be hold in the modified gravity.
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We present new IRAM PdBI 1.3mm continuum observations at ~1.5" resolution of 28 SMGs previously discovered with the 870um bolometer LABOCA at APEX within the central 0.7deg2 of the COSMOS field. 19 out of the 28 LABOCA sources were detected with the PdBI at a >~3sigma level of ~1.4mJy/b. A combined analysis of this new sample with existing interferometrically identified SMGs in the COSMOS field yields the following results: 1) >~15%, and possibly up to ~40% of single-dish detected SMGs consist of multiple sources, 2) statistical identifications of multi-wavelength counterparts to the single-dish SMGs yield that only ~50% of these single-dish SMGs have real radio or IR counterparts, 3) ~18% of interferometric SMGs have only radio or even no multi-wavelength counterpart at all, and 4) ~50-70% of z>~3 SMGs have no radio counterparts down to an rms of 7-12uJy at 1.4GHz. Using the exact interferometric positions to identify proper multi-wavelength counterparts allows us to determine accurate photometric redshifts for these sources. The redshift distributions of the combined and the individual 1.1mm and 870um selected samples have a higher mean and broader width than the redshift distributions derived in previous studies. Our sample supports the previous tentative trend that on average brighter and/or mm-selected SMGs are located at higher redshifts. There is a tentative offset between the mean redshift for the 1.1mm (<z>=3.1+/-0.4) and 870um (<z>=2.6+/-0.4) selected samples, with the 1.1mm sources lying on average at higher redshifts. Based on our nearly complete sample of AzTEC 1.1mm SMGs within a uniform 0.15deg2 area we infer a higher surface density of z>~4 SMGs than predicted by current cosmological models. In summary, our findings imply that (sub-)millimeter interferometric identifications are crucial to build statistically complete and unbiased samples of SMGs.
The strength of gravity-sensitive absorption lines in the integrated light of old stellar populations is one of the few direct probes of the stellar initial mass function (IMF) outside of the Milky Way. Owing to the advent of fully depleted CCDs with little or no fringing it has recently become possible to obtain accurate measurements of these features. Here we present spectra covering the wavelength ranges 0.35 - 0.55 micron and 0.72 - 1.03 micron for the bulge of M31 and 34 early-type galaxies from the SAURON sample, obtained with the Low Resolution Imaging Spectrometer on Keck. The signal-to-noise ratio is >200 per Angstrom out to 1 micron, which is sufficient to measure gravity-sensitive features for individual galaxies and to determine how they depend on other properties of the galaxies. Combining the new data with previously obtained spectra for globular clusters in M31 and the most massive elliptical galaxies in the Virgo cluster we find that the dwarf-sensitive Na I doublet and the FeH Wing-Ford band increase systematically with velocity dispersion, while the giant-sensitive Ca II triplet decreases with dispersion. These trends are consistent with a varying IMF, such that galaxies with deeper potential wells have more dwarf-enriched mass functions. In a companion paper (Conroy & van Dokkum 2012) we use a comprehensive stellar population synthesis model to demonstrate that IMF effects can be separated from age and abundance variations and quantify the IMF variation among early-type galaxies.
We investigate the gravitational interactions between live stellar disks and their dark matter halos, using LCDM haloes similar in mass to that of the Milky Way taken from the Aquarius Project. We introduce the stellar disks by first allowing the haloes to respond to the influence of a growing rigid disk potential from z = 1.3 to z = 1.0. The rigid potential is then replaced with star particles which evolve self-consistently with the dark matter particles until z = 0.0. Regardless of the initial orientation of the disk, the inner parts of the haloes contract and change from prolate to oblate as the disk grows to its full size. When the disk normal is initially aligned with the major axis of the halo at z=1.3, the length of the major axis contracts and becomes the minor axis by z=1.0. Six out of the eight disks in our main set of simulations form bars, and five of the six bars experience a buckling instability that results in a sudden jump in the vertical stellar velocity dispersion and an accompanying drop in the m=2 Fourier amplitude of the disk surface density. The bars are not destroyed by the buckling but continue to grow until the present day. Bars are largely absent when the disk mass is reduced by a factor of two or more; the relative disk-to-halo mass is therefore a primary factor in bar formation and evolution. A subset of the disks is warped at the outskirts and contains prominent non-coplanar material with a ring-like structure. Many disks reorient by large angles between z=1 and z=0, following a coherent reorientation of their inner haloes. Larger reorientations produce more strongly warped disks, suggesting a tight link between the two phenomena. The origins of bars and warps appear independent: some disks with strong bars show no disturbances at the outskirts, while the disks with the weakest bars show severe warps.
The spectral absorption lines in early-type galaxies contain a wealth of information regarding the detailed abundance pattern, star formation history, and stellar initial mass function (IMF) of the underlying stellar population. Using our new population synthesis model that accounts for the effect of variable abundance ratios of 11 elements, we analyze very high quality absorption line spectra of 38 early-type galaxies and the nuclear bulge of M31. These data extend to 1\mu m and they therefore include the IMF-sensitive spectral features NaI, CaII, and FeH at 0.82\mu m, 0.86\mu m and 0.99\mu m, respectively. The models fit the data well, with typical rms residuals of 1%. Strong constraints on the IMF and therefore the stellar mass-to-light ratio, (M/L)_stars, are derived for individual galaxies. We find that the IMF becomes increasingly bottom-heavy with increasing velocity dispersion and [Mg/Fe]. At the lowest dispersions and [Mg/Fe] values the derived IMF is consistent with the Milky Way IMF, while at the highest dispersions and [Mg/Fe] values the derived IMF contains more low-mass stars (is more bottom-heavy) than a Salpeter IMF. Our best-fit (M/L)_stars values do not exceed dynamically-based M/L values. We also apply our models to stacked spectra of four metal-rich globular clusters in M31 and find an (M/L)_stars that implies fewer low-mass stars than a Milky Way IMF, again agreeing with dynamical constraints. We discuss other possible explanations for the observed trends and conclude that variation in the IMF remains the simplest and most plausible.
We have performed an analysis of the diffuse gamma-ray emission with the Fermi Large Area Telescope in the Milky Way Halo region searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal, constraints are presented. We consider both gamma rays produced directly in the dark matter annihilation/decay and produced by inverse Compton scattering of the e+e- produced in the annihilation/decay. Conservative limits are derived requiring that the dark matter signal does not exceed the observed diffuse gamma-ray emission. A second set of more stringent limits is derived based on modeling the foreground astrophysical diffuse emission using the GALPROP code. Uncertainties in the height of the diffusive cosmic-ray halo, the distribution of the cosmic-ray sources in the Galaxy, the index of the injection cosmic-ray electron spectrum and the column density of the interstellar gas are taken into account using a profile likelihood formalism, while the parameters governing the cosmic-ray propagation have been derived from fits to local cosmic-ray data. The resulting limits impact the range of particle masses over which dark matter thermal production in the early Universe is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic ray anomalies as annihilation of dark matter.
Non-axisymmetric components, such as spirals and central bars, play a major role in shaping galactic discs. An important aspect of the disc secular evolution driven by these perturbers is the radial migration of stars. It has been suggested recently that migration can populate a thick-disc component from inner-disc stars with high vertical energies. Since this has never been demonstrated in simulations, we study in detail the effect of radial migration on the disc velocity dispersion and disc thickness, by separating simulated stars into migrators and non-migrators. We apply this method to three isolated barred Tree-SPH N-body galaxies with strong radial migration. Contrary to expectations, we find that as stellar samples migrate, on the average, their velocity dispersion change (by as much as 50%) in such a way as to approximately match the non-migrating population at the radius at which they arrive. We show that, in fact, migrators suppress heating in parts of the disc. To confirm the validity of our findings, we also apply our technique to three cosmological re-simulations, which use a completely different simulation scheme and, remarkably, find very similar results. We believe the inability of migration to thicken discs is a fundamental property of internal disc evolution, irrespective of the migration mechanism at work. We explain this with the approximate conservation of the (average) vertical and radial actions rather than the energy. This "action mixing" can be used to constrain the migration rate in the Milky Way: estimates of the average vertical action in observations for different populations of stars should reveal flattening with radius for older groups of stars.
We perform observational tests of statistical isotropy using data from large-scale structure surveys spanning a wide range of wavelengths. Using data from 2MASS, 2MRS, and NVSS galaxies, and BATSE gamma-ray bursts, we constrain the amplitude and direction of dipolar modulations in the number count of sources projected along the line of sight. We pay particular attention to the treatment of systematic errors and selection effects, and carefully distinguish between different sources of dipole signal previously considered in the literature. Dipole signals detected in these surveys are consistent with the standard, statistically isotropic expectation, except for the NVSS result, which is likely biased by remaining systematics in the data. We place constraints on the amplitude of any intrinsic dipole driven by novel physics in the early universe.
Models of rotationally-driven dynamos in stellar radiative zones have suggested that magnetohydrodynamic transport of angular momentum and chemical composition can dominate over the otherwise purely hydrodynamic processes. A proper consideration of the interaction between rotation and magnetic fields is therefore essential. Previous studies have focused on a magnetic model where the magnetic field strength is derived as a function of the stellar structure and angular momentum distribution. We have adapted our one-dimensional stellar rotation code, RoSE, to model the poloidal and toroidal magnetic field strengths with a pair of time-dependent advection-diffusion equations coupled to the equations for the evolution of the angular momentum distribution and stellar structure. This produces a much more complete, though still reasonably simple, model for the magnetic field evolution. Our model reproduces well observed surface nitrogen enrichment of massive stars in the Large Magellanic Cloud. In particular it reproduces a population of slowly-rotating nitrogen-enriched stars that cannot be explained by rotational mixing alone alongside the traditional rotationlly-enriched stars. The model further predicts a strong mass-dependency for the dynamo-driven field. Above a threshold mass, the strength of the magnetic dynamo decreases abruptly and so we predict that more massive stars are much less likely to support a dynamo-driven field than less massive stars.
The galaxy cluster SPT-CL J0205-5829 currently has the highest spectroscopically-confirmed redshift, z=1.322, in the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey. XMM-Newton observations measure a core-excluded temperature of Tx=8.7keV producing a mass estimate that is consistent with the Sunyaev-Zel'dovich derived mass. The combined SZ and X-ray mass estimate of M500=(4.9+/-0.8)e14 h_{70}^{-1} Msun makes it the most massive known galaxy cluster at z>1.2 and the second most massive at z>1. Using optical and infrared observations, we find that SPT-CL J0205-5829 already had a strong red sequence of passive galaxies by the time the universe was <5 Gyr old, with stellar population ages >3 Gyr, and low rates of star formation (<0.5Msun/yr) in the central galaxies. We find that, despite the high redshift and mass, the existence of SPT-CL J0205-5829 is not surprising given a flat LambdaCDM cosmology with Gaussian initial perturbations. The a priori chance of finding a cluster of similar rarity (or rarer) in a survey the size of the 2500 deg^2 SPT-SZ survey is 69%.
It is expected on both evolutionary and empirical grounds that many merging neutron star (NS) binaries are composed of a highly magnetized NS in orbit with a relatively low magnetic field NS. I study the magnetic interactions of these binaries using the framework of a unipolar inductor model. The e.m.f. generated across the non-magnetic NS as it moves through the magnetosphere sets up a circuit connecting the two stars. The exact features of this circuit depend on the uncertain resistance in the space between the stars R_space. Nevertheless, I show that there are interesting observational and/or dynamical effects irrespective of its exact value. When R_space is large, electric dissipation as great as ~10^{46} erg/s (for magnetar-strength fields) occurs in the magnetosphere, which would exhibit itself as a hard X-ray precursor in the seconds leading up to merger. With less certainty, there may also be an associated radio transient, but this would be observed well past merger (~hrs) because of interstellar dispersion. When R_space is small, electric dissipation largely occurs in the surface layers of the magnetic NS. This can reach ~10^{49} erg/s during the final ~1 sec before merger, similar to the energetics and timescales of short gamma-ray bursts. In addition, for dipole fields greater than ~10^{12} G and a small R_space, magnetic torques spin up the magnetized NS. This drains angular momentum from the binary and accelerates the inspiral. A faster coalescence results in less orbits occurring before merger, which would impact matched-filtering gravitational-wave searches by ground-based laser interferometers and could create difficulties for studying alternative theories of gravity with compact inspirals.
The near-infrared colors of the planets directly imaged around the A star HR 8799 are much redder than most field brown dwarfs of the same effective temperature. Previous theoretical studies of these objects have concluded that the atmospheres of planets b, c, and d are unusually cloudy or have unusual cloud properties. Most studies have also found that the inferred radii of some or all of the planets disagree with expectations of standard giant planet evolution models. Here we compare the available data to the predictions of our own set of atmospheric and evolution models that have been extensively tested against observations of field L and T dwarfs, including the reddest L dwarfs. Unlike almost all previous studies we require mutually consistent choices for effective temperature, gravity, cloud properties, and planetary radius. This procedure thus yields plausible values for the masses, effective temperatures, and cloud properties of all three planets. We find that the cloud properties of the HR 8799 planets are not unusual but rather follow previously recognized trends, including a gravity dependence on the temperature of the L to T spectral transition--some reasons for which we discuss. We find the inferred mass of planet b is highly sensitive to whether or not we include the H and K band spectrum in our analysis. Solutions for planets c and d are consistent with the generally accepted constraints on the age of the primary star and orbital dynamics. We also confirm that, like in L and T dwarfs and solar system giant planets, non-equilibrium chemistry driven by atmospheric mixing is also important for these objects. Given the preponderance of data suggesting that the L to T spectral type transition is gravity dependent, we present an exploratory evolution calculation that accounts for this effect. Finally we recompute the the bolometric luminosity of all three planets.
40 years have passed since the first molecular detection outside our Galaxy. Since then, our knowledge on the distribution, kinematics and composition of the molecular material in the extragalactic ISM has built up significantly based not only on the carbon monoxide observations but also in the more than 50 molecular species detected. In particular, line surveys have been proven to be excellent tools to study the chemical composition in the nuclei of galaxies. Such studies have been favored by the increasing instantaneous bandwidth of current mm and sub-mm facilities. Here I will summarize the highlights of extragalactic molecular spectroscopy, mostly focusing in the results from molecular line surveys published in the last few years as well as the aims of still ongoing projects.
Rotation has a number of important effects on the evolution of stars. It
decreases the surface gravity, causes enhanced mass loss and leads to surface
abundance anomalies of various chemical isotopes. We have adapted the Cambridge
stellar evolution code to incorporate a number of different physical models for
rotation. We compare detailed grids of stellar evolution models along with
simulated stellar populations to identify the key differences between them.
Models of rotationally-driven dynamos in stellar radiative zones have
suggested that magnetohydrodynamic transport of angular momentum and chemical
composition can dominate over the otherwise purely hydrodynamic processes. We
have adapted our purely hydrodynamic model to include the evolution of the
magnetic field. We consider what effects this has on our populations of
rotating stars and how these relate to observational data.
Strong magnetic fields are also observed at the end of the stellar lifetime.
The surface magnetic field strength of white dwarfs is observed to vary from
very little up to 10^9G. We look at how the strongest magnetic fields in white
dwarfs may be generated by dynamo action during the common envelope phase of
strongly interacting binary stars.
We have performed an extensive search for planet candidates in the publicly available Kepler Long Cadence data from quarters Q1 through Q6. The search method consists of initial de-trending of the data, applying the trend filtering algorithm, searching for transit signals with the Box Least Squares fitting method in two frequency domains, visual inspection of the potential transit candidates, and in-depth analysis of the shortlisted candidates. In this paper we present 16 new periodic planet candidates and 8 single transit events.The periods of these planet candidates vary from ~0.968 day to ~440 day. Nine of the planet candidates have radii smaller than 3 Rearth. We also report seven newly identified false positives---systems that look like transiting planets, but are probably due to blended eclipsing binaries.
We compare high-resolution ultraviolet spectra of the Sun and thirteen solarmass main sequence stars with different rotational periods that serve as proxies for their different ages and magnetic field structures. In this the second paper in the series, we study the dependence of ultraviolet emission-line centroid velocities on stellar rotation period, as rotation rates decrease from that of the Pleiades star HII314 (Prot = 1.47 days) to Alpha Cen A (Prot = 28 days). Our stellar sample of F9 V to G5 V stars consists of six stars observed with the Cosmic Origins 1Guest Observer, NASA/ESA Hubble Space Telescope and User of the Data Archive at the Space Telescope Science Institute. Spectrograph on HST and eight stars observed with the Space Telescope Imaging Spectrograph on HST. We find a systematic trend of increasing redshift with more rapid rotation (decreasing rotation period) that is similar to the increase in line red shift between quiet and plage regions on the Sun. The fastest-rotating solar-mass star in our study, HII314, shows significantly enhanced redshifts at all temperatures above log T = 4.6, including the corona, which is very different from the redshift pattern observed in the more slowly-rotating stars. This difference in the redshift pattern suggests that a qualitative change in the magnetic-heating process occurs near Prot = 2 days. We propose that HII314 is an example of a solar-mass star with a magnetic heating rate too large for the physical processes responsible for the redshift pattern to operate in the same way as for the more slowly rotating stars. HII314 may therefore lie above the high activity end of the set of solar-like phenomena that is often called the "solar-stellar connection".
Exoplanets, and in particular hot ones such as hot Jupiters, require a very significant quantities of molecular spectroscopic data to model radiative transport in their atmospheres or to interpret their spectra. This data is commonly provided in the form of very extensive transition line lists. The size of these line lists is such that constructing a single model may require the consideration of several billion lines. We present a procedure to simplify this process based on the use of cross sections. Line lists for water, H$_3^+$, HCN /HNC and ammonia have been turned into cross sections on a fine enough grid to preserve their spectroscopic features. Cross sections are provided at a fixed range of temperatures and an interpolation procedure which can be used to generate cross sections at arbitrary temperatures is described. A web-based interface (www.exomol.com/xsec) has been developed to allow astronomers to download cross sections at specified temperatures and spectral resolution. Specific examples are presented for the key water molecule.
Theoretical work has shown that intermediate mass (0.01Msun<M_He<0.1Msun) Helium shells will unstably ignite on the accreting white dwarf (WD) in an AM CVn binary. For more massive (M>0.8Msun) WDs, these helium shells can be dense enough (5x10^5 g/cc) that the convectively burning region runs away on a timescale comparable to the sound travel time across the shell; raising the possibility for an explosive outcome. The nature of the explosion (i.e. deflagration or detonation) remains ambiguous. In the case of detonation, this causes a laterally propagating front whose properties in these geometrically thin and low density shells we begin to study here. Our calculations show that the radial expansion time of <0.1 s leads to incomplete helium burning, in agreement with recent work by Sim and collaborators, but that the nuclear energy released is still adequate to realize a self-sustaining detonation propagating laterally at slower than the Chapman-Jouguet speed. Our simulations resolve the subsonic region behind the front and are consistent with a direct computation of the reaction structure from the shock strength. The ashes are typically He rich, and consist of predominantly Ti-44, Cr-48, along with a small amount of Fe-52, with very little Ni-56 and with significant Ca-40 in carbon-enriched layers. If this helium detonation results in a Type Ia Supernova, its spectral signatures would appear for the first few days after explosion. (abridged)
Tsinghua-NAOC (National Astronomical Observatories of China) Telescope (hereafter, TNT) is an 80-cm Cassegrain reflecting telescope located at Xinglong bservatory of NAOC, with main scientific goals of monitoring various transients in the universe such as supernovae, gamma-ray bursts, novae, variable stars, and active galactic nuclei. We present in this paper a systematic test and analysis of the photometric performance of this telescope. Based on the calibration observations on twelve photometric nights, spanning the period from year 2004 to year 2012, we derived an accurate transformation relationship between the instrumental $ubvri$ magnitudes and standard Johnson $UBV$ and Cousins $RI$ magnitudes. In particular, the color terms and the extinction coefficients of different passbands are well determined. With these data, we also obtained the limiting magnitudes and the photometric precision of TNT. It is worthwhile to point out that the sky background at Xinglong Observatory may become gradually worse over the period from year 2005 to year 2012 (e.g., $\sim$21.4 mag vs. $\sim$20.1 mag in the V band).
The vector magnetic field characteristics of superactive regions (SARs) hold the key for understanding why SARs are extremely active and provide the guidance in space weather prediction. We aim to quantify the characteristics of SARs using the vector magnetograms taken by the Solar Magnetic Field Telescope at Huairou Solar Observatory Station. The vector magnetic field characteristics of 14 SARs in solar cycles 22 and 23 were analyzed using the following four parameters: 1) the magnetic flux imbalance between opposite polarities, 2) the total photospheric free magnetic energy, 3) the length of the magnetic neutral line with its steep horizontal magnetic gradient, and 4) the area with strong magnetic shear. Furthermore, we selected another eight large and inactive active regions (ARs), which are called fallow ARs (FARs), to compare them with the SARs. We found that most of the SARs have a net magnetic flux higher than 7.0\times10^21 Mx, a total photospheric free magnetic energy higher than 1.0\times10^24 erg/cm, a magnetic neutral line with a steep horizontal magnetic gradient (\geq 300 G/Mm) longer than 30 Mm, and an area with strong magnetic shear (shear angle \geq 80\degree) greater than 100 Mm^2. In contrast, the values of these parameters for the FARs are mostly very low. The Pearson \c{hi}2 test was used to examine the significance of the difference between the SARs and FARs, and the results indicate that these two types of ARs can be fairly distinguished by each of these parameters. The significance levels are 99.55%, 99.98%, 99.98%, and 99.96%, respectively. However, no single parameter can distinguish them perfectly. Therefore we propose a composite index based on these parameters, and find that the distinction between the two types of ARs is also significant with a significance level of 99.96%. These results are useful for a better physical understanding of the SAR and FAR
In this paper we consider two outstanding intertwined problems in modern high-energy astrophysics: (1) the vertical thermal structure of an optically thick accretion disk heated by the dissipation of magnetohydrodynamic (MHD) turbulence driven by the magneto-rotational instability (MRI), and (2) determining the fraction of the accretion power released in the corona above the disk. For simplicity, we consider a gas-pressure-dominated disk and assume a constant opacity. We argue that the local turbulent dissipation rate due to the disruption of MRI channel flows by secondary parasitic instabilities should be uniform across most of the disk, almost up to the disk photosphere. We then obtain a self-consistent analytical solution for the vertical thermal structure of the disk, governed by the balance between the heating by MRI turbulence and the cooling by radiative diffusion. Next, we argue that the coronal power fraction is determined by the competition between the Parker instability, viewed as a parasitic instability feeding off of MRI channel flows, and other parasitic instabilities. We show that the Parker instability inevitably becomes important near the disk surface, leading to a certain lower limit on the coronal power. While most of the analysis in this paper focuses on the case of a disk threaded by an externally imposed vertical magnetic field, we also discuss the zero-net-flux case, in which the magnetic field is produced by the MRI dynamo itself, and show that most of our arguments and conclusions should be valid in this case as well.
Possible bulk compositions of the super-Earth exoplanets, CoRoT-7b, Kepler-9d, and Kepler-10b are investigated by applying a commonly used silicate and a non-standard carbon model. Their internal structures are deduced using the suitable equation of state of the materials. The degeneracy problems of their compositions can be partly overcome, based on the fact that all three planets are extremely close to their host stars. By analyzing the numerical results, we conclude: 1) The iron core of CoRoT-7b is not more than 27% of its total mass within 1 $\sigma$ mass-radius error bars, so an Earth-like composition is less likely, but its carbon rich model can be compatible with an Earth-like core/mantle mass fraction; 2) Kepler-10b is more likely with a Mercury-like composition, its old age implies that its high iron content may be a result of strong solar wind or giant impact; 3) the transiting-only super-Earth Kepler-9d is also discussed. Combining its possible composition with the formation theory, we can place some constraints on its mass and bulk composition.
This paper presents observations of a protoplanetary disk around Herbig Ae star HD 163296 in 12CO (J=1-0), 12CO (J=3-2), 13CO (J=1-0), and 13CO (J=3-2) emission lines. Double-peaked emission profiles originating from the rotating circumstellar disk were detected in all the lines. The disk parameters were estimated from model calculation in which the radial distribution of temperature or surface density inside the disk has a power-law form. The surface density should be sufficiently high so that the disk is optically thick for all the CO lines, as discussed in previous studies based on interferometric observations. The temperature and outer radius of the disk were also confirmed to be consistent with the previous results. Taking advantage of difference in position of the photosphere among the CO lines, we revealed temperature distribution in vertical direction. The temperature of 12CO (J=3-2) emitting region is about twice higher than that of any other CO emitting region; the former is about 59 K while the latter is about 31 K at 100 AU from the central star, suggesting that there are at least two distinct temperature regions. The best fit temperature for 13CO (J=1-0) that should trace the deepest region of the disk is even lower, implying that there is also a different temperature region in deep inside of the disk. Such vertical temperature distribution in a disk was identified both in T Tauri and Herbig Ae stars (e.g., DM Tau, AB Aur, and HD 31648), and this should be a common feature in protoplanetary disks.
We study the growth of structures in modified gravity models where the Poisson equation and the relationship between the two Newtonian potentials are modified by explicit functions of space and time. This parameterisation applies to the $f(R)$ models and more generally to screened modified gravity models. We investigate the linear and weakly nonlinear regimes using the "standard" perturbative approach and a resummation technique, while we use the spherical dynamics to go beyond low-order results. This allows us to estimate the matter density power spectrum and bispectrum from linear to highly nonlinear scales, the full probability distribution of the density contrast on weakly nonlinear scales, and the halo mass function. We analyse the impact of modifications of gravity on these quantities for a few realistic models. In particular, we find that the standard one-loop perturbative approach is not sufficiently accurate to probe these effects on the power spectrum and it is necessary to use resummation methods even on weakly nonlinear scales which provide the best observational window for modified gravity as relative deviations from General Relativity do not grow significantly on smaller scales where theoretical predictions become increasingly difficult.
We present a detailed analysis of the X-ray emission of HS 1700+6416, a high redshift (z=2.7348), luminous quasar, classified as a Narrow Absorption Line (NAL) quasar on the basis of its SDSS spectrum. The source has been observed 9 times by Chandra and once by XMM from 2000 to 2007. Long term variability is clearly detected, between the observations, in the 2-10 keV flux varying by a factor of three (~3-9x10^-14 erg s^-1 cm^-2) and in the amount of neutral absorption (Nh < 10^22 cm^-2 in 2000 and 2002 and Nh=4.4+-1.2x10^22 cm^-2 in 2007). Most interestingly, one broad absorption feature is clearly detected at 10.3+-0.7 keV (rest frame) in the 2000 Chandra observation, while two similar features, at 8.9+-0.4 and at 12.5+-0.7 keV, are visible when the 8 contiguous Chandra observations of 2007 are stacked together. In the XMM observation of 2002, strongly affected by background flares, there is a hint for a similar feature at 8.0+-0.3 keV. We interpreted these features as absorption lines from a high velocity, highly ionized (i.e. Fe XXV, FeXXVI) outflowing gas. In this scenario, the outflow velocities inferred are in the range v=0.12-0.59c. To reproduce the observed features, the gas must have high column density (Nh>3x10^23 cm^-2), high ionization parameter (log(xi)>3.3 erg cm s^-1) and a large range of velocities (Delta V~10^4 km s^-1). This Absorption Line QSO is the fourth high-z quasar displaying X-ray signatures of variable, high velocity outflows, and among these, is the only one non-lensed. A rough estimate of the minimum kinetic energy carried by the wind of up to 18% L(bol), based on a biconical geometry of the wind, implies that the amount of energy injected in the outflow environment is large enough to produce effective mechanical feedback.
The Poynting-Robertson Cosmic Battery proposes that the innermost part of the accretion disk around a black hole is threaded by a large scale dipolar magnetic field generated in situ, and that the return part of the field diffuses outward through the accretion disk. This is different from the scenario that the field originates at large distances and is carried inward by the accretion flow. In view of the importance of large scale magnetic fields in regulating the processes of accretion and outflows, we study the stability of the inner edge of a magnetized disk in general relativity when the distribution of the magnetic field is the one predicted by the Poynting-Robertson Cosmic Battery. We found that as the field grows, the inner edge of the disk gradually moves outward. In a fast spinning black hole with a>0.8M the inner edge moves back in towards the black hole horizon as the field grows beyond some threshold value. In all cases, the inner part of the disk undergoes a dramatic structural change as the field approaches equipartition.
The observational progress obtained by Fermi-GBM and Konus-Wind satellites is used to identify the new class of genuine short GRBs: short bursts with the same inner engine of the long GRBs but endowed with a severely low value of the Baryon load, B<~5x10^{-5}. The emission from these GRBs mainly consists in a first emission, the P-GRB, followed by a softer emission "squeezed" on the first one. The typical separation between the two components is expected to be smaller than 10^{-3}-10^{-2}s. Attention is given to the time-resolved spectral analysis of GRB090227B. From the 16ms time-binned light curves we find a significant thermal emission in the first 96ms, which we identify with the P-GRB. The subsequent emission is identified with the extended afterglow. We find a P-GRB with the highest temperature ever observed, kT=517keV. We estimate from our theoretical model the cosmological redshift z=1.61 and, consequently, we derive the total energy E^{tot}_{e^+e^-}=2.83x10^{53}ergs, the Baryon load B=4.13x10^{-5}, the Lorentz \Gamma factor at transparency \Gamma_{tr}=14365, and the intrinsic duration \Delta t'~0.35. We also determine the average density of the CircumBurst Medium (CBM), <n_{CBM}>=1.9x10^{-5}particles/cm^3. There is no evidence of beaming in the system. In view of the energetics and of the Baryon load of the source, as well as of the low interstellar medium and of the intrinsic time scale of the signal, we identify the GRB progenitor as a binary neutron star. From the recent developed theory of the neutron stars configuration, we estimate the masses of the stars, m_1=m_2=1.34M_\odot, their radii, R_1=R_2=12.24km, and the thickness of their crusts, ~0.47km, consistent with the above values of the Baryon load, of the energetics and of the time duration of the event.
Many pulsars are observed to "glitch", i.e. show sudden jumps in their rotational frequency $\nu$, some of which can be as large as $\Delta \nu/\nu\approx 10^{-6}-10^{-5}$ in a subset of pulsars known as giant glitchers. Recently Pizzochero (2011) has shown that an analytic model based on realistic values for the pinning forces in the crust and for the angular momentum transfer in the star can describe the average properties of giant glitches, such as the inter-glitch waiting time, the step in frequency and that in frequency derivative. In this paper we extend the model (originally developed in Newtonian gravity and for a polytropic equation of state) to realistic backgrounds obtained by integrating the relativistic equations of stellar structure and using physically motivated equations of state to describe matter in the neutron star. We find that this more detailed treatment still reproduces the main features of giant glitches in the Vela pulsar and allows us to set constraints on the equation of state. In particular we find that stiffer equations of state are favoured and that it is unlikely that the Vela pulsar has a high mass (larger than $M\approx 1.5 M_\odot$).
Following the recent theoretical interpretation of GRB 090618 and GRB 101023, we here interpret GRB 970828 in terms of a double episode emission: the first episode, observed in the first 40 s of the emission, is interpreted as the proto-black-hole emission; the second episode, observed after t$_0$+50 s, as a canonical gamma ray burst. The transition between the two episodes marks the black hole formation. The characteristics of the real GRB, in the second episode, are an energy of $E_{tot}^{e^+e^-} = 1.60 \times 10^{53}$ erg, a baryon load of $B = 7 \times 10^{-3}$ and a bulk Lorentz factor at transparency of $\Gamma = 142.5$. The clear analogy with GRB 090618 would require also in GRB 970828 the presence of a possible supernova. We also infer that the GRB exploded in an environment with a large average particle density $<n> \, \approx 10^3$ part/cm$^3$ and dense clouds characterized by typical dimensions of $(4 - 8) \times 10^{14}$ cm and $\delta n/n \propto 10$. Such an environment is in line with the observed large column density absorption, which might have darkened both the supernova emission and the GRB optical afterglow.
Interferometric calibration always yields non unique solutions. It is therefore essential to remove these ambiguities before the solutions could be used in any further modeling of the sky, the instrument or propagation effects such as the ionosphere. We present a method for LOFAR calibration which does not yield a unitary ambiguity, especially under ionospheric distortions. We also present exact ambiguities we get in our solutions, in closed form. Casting this as an optimization problem, we also present conditions for this approach to work. The proposed method enables us to use the solutions obtained via calibration for further modeling of instrumental and propagation effects. We provide extensive simulation results on the performance of our method. Moreover, we also give cases where due to degeneracy, this method fails to perform as expected and in such cases, we suggest exploiting diversity in time, space and frequency.
The existence of outflow and magnetic field in the inner region of hot accretion flows have been confirmed by observations and numerical magnetohydrodynamic simulations (MHD). We present self-similar solutions for radiation inefficiently accretion flows (RIAF) around black holes in the presence of outflow and global magnetic field. The influence of outflow is taken into account by adopting a radius dependent of mass accretion rate $ \dot{M} = \dot{M}_{0}(r/r_{0})^{s} $ with $ s > 0 $. Also we consider convection through a mixing length formalism to calculate convection parameter $ \alpha_{con} $. Moreover we consider the additional magnetic field parameters $ \beta_{r,\varphi,z}\big[= c^2_{r,\varphi,z}/(2 c^2_{s}) \big] $, where $ c^2_{r,\varphi,z} $ are the Alfv$\acute{e}$n sound speeds in three direction of cylindrical coordinate. Our numerical results show that by increasing all components of magnetic field, the surface density and rotational velocity increase although the sound speed and radial infall velocity of the disc decrease. Also we have found out that the existence of wind will lead to reduction of surface density as well as rotational velocity. Moreover the radial velocity, sound speed, advection parameter and the vertical thickness of the disc will increase when outflow becomes important in the radiation inefficiently accretion flow.
We employ high resolution filtergrams and polarimetric measurements from Hinode to follow the evolution of a sunspot for eight days starting on June 28, 2007. The imaging data were corrected for intensity gradients, projection effects, and instrumental stray light prior to the analysis. The observations show the formation of a light bridge at one corner of the sunspot by a slow intrusion of neighbouring penumbral filaments. This divided the umbra into two individual umbral cores. During the light bridge formation, there was a steep increase in its intensity from 0.28 to 0.7 I_QS in nearly 4 hr, followed by a gradual increase to quiet Sun (QS) values in 13 hr. This increase in intensity was accompanied by a large reduction in the field strength from 1800 G to 300 G. The smaller umbral core gradually broke away from the parent sunspot nearly 2 days after the formation of the light bridge rendering the parent spot without a penumbra at the location of fragmentation. The penumbra in the fragment disappeared first within 34 hr, followed by the fragment whose area decayed exponentially with a time constant of 22 hr. The depleted penumbra in the parent sunspot regenerated when the inclination of the magnetic field at the penumbra-QS boundary became within 40 deg. from being completely horizontal and this occurred near the end of the fragment's lifetime. After the disappearance of the fragment, another light bridge formed in the parent which had similar properties as the fragmenting one, but did not divide the sunspot. The significant weakening in field strength in the light bridge along with the presence of granulation is suggestive of strong convection in the sunspot which might have triggered the expulsion and fragmentation of the smaller spot. Although the presence of QS photospheric conditions in sunspot umbrae could be a necessary condition for fragmentation, it is not a sufficient one.
We present the results for a chemical abundance analysis between the planet host and non-host stars for 12 refractory elements for a total of 1111 nearby FGK dwarf stars observed within the context of the HARPS GTO programs. 109 of these stars are known to harbour high-mass planetary companions and 26 stars are hosting exclusively Neptunians and super-Earths. We found that the [X/Fe] ratios for Mg, Al, Si, Sc, and Ti both for giant and low-mass planet hosts are systematically higher than those of comparison stars at low metallicities ([Fe/H] < from -0.2 to 0.1 dex depending on the element). The most evident discrepancy between planet host and non-host stars is observed for Mg. Our data suggest that the planet incidence is greater among the thick disc population than among the thin disc for mettallicities bellow -0.3 dex. After examining the [alpha/Fe] trends of the planet host and non-host samples we conclude that a certain chemical composition, and not the Galactic birth place of the stars, is the determinative factor for that. The inspection of the Galactic orbital parameters and kinematics of the planet host stars shows that Neptunian hosts tend to belong to the "thicker" disc compared to their high-mass planet hosting counterparts. We also found that Neptunian hosts follow the distribution of high-alpha stars in the UW vs V velocities space, but they are more enhanced in Mg than high-alpha stars without planetary companions. Our results indicate that some metals other than iron may also have an important contribution to planet formation if the amount
The projected virial theorem is applied to the case of multiple stellar populations in the nearby dwarf spheroidal galaxies. As each population must reside in the same gravitational potential, this provides strong constraints on the nature of the dark matter halo. We derive necessary conditions for two populations with Plummer or exponential surface brightnesses to reside in a cusped Navarro-Frenk-White (NFW) halo. We apply our methods to the Sculptor dwarf spheroidal, and show that there is no NFW halo compatible with the energetics of the two populations. The dark halo must possess a core radius of ~ 120 pc for the virial solutions for the two populations to be consistent. This conclusion remains true, even if the effects of flattening or self-gravity of the stellar populations are included.
We study the dynamics of a homogeneous and isotropic Friedmann-Robertson-Walker universe in the context of the Eddington-inspired Born-Infeld theory of gravity. We generalize earlier results, obtained in the context of a radiation dominated universe, to account for the evolution of a universe permeated by a perfect fluid with an arbitrary equation of state parameter $w$. We show that a bounce may occur for $\kappa >0$, if $w$ is time-dependent, and we demonstrate that it is free from tensor singularities. We argue that Eddington-inspired Born-Infeld cosmologies may be a viable alternative to the inflationary paradigm as a solution to fundamental problems of the standard cosmological model.
The sunspot drawings of Johann Staudacher of 1749--1799 were used to determine the solar differential rotation in that period. These drawings of the full disk lack any indication of their orientation. We used a Bayesian estimator to obtain the position angles of the drawings, the corresponding heliographic spot positions, a time offset between the drawings and the differential rotation parameter \delta\Omega, assuming the equatorial rotation period is the same as today. The drawings are grouped in pairs, and the resulting marginal distributions for \delta\Omega were multiplied. We obtain \delta\Omega=-0.048 \pm 0.025 d^-1 (-2.75^o/d) for the entire period. There is no significant difference to the value of the present Sun. We find an (insignificant) indication for a change of \delta\Omega throughout the observing period from strong differential rotation, \delta\Omega\approx -0.07 d^-1, to weaker differential rotation, \delta\Omega\approx-0.04 d^-1.
We present an asymptotic theory that describes regular frequency spacings of pressure modes in rapidly rotating stars. We use an asymptotic method based on an approximate solution of the pressure wave equation constructed from a stable periodic solution of the ray limit. The approximate solution has a Gaussian envelope around the stable ray, and its quantization yields the frequency spectrum. We construct semi-analytical formulas for regular frequency spacings and mode spatial distributions of a subclass of pressure modes in rapidly rotating stars. The results of these formulas are in good agreement with numerical data for oscillations in polytropic stellar models. The regular frequency spacings depend explicitly on internal properties of the star, and their computation for different rotation rates gives new insights on the evolution of mode frequencies with rotation.
We analyzed the soft X-ray light curves from the {\sl Geostationary Operational Environmental Satellites (GOES)} over the last 37 years (1975-2011) and measured with an automated flare detection algorithm over 300,000 solar flare events (amounting to $\approx 5$ times higher sensitivity than the NOAA flare catalog). We find a powerlaw slope of $\alpha_F=1.98\pm0.11$ for the (background-subtracted) soft X-ray peak fluxes that is invariant through three solar cycles and agrees with the theoretical prediction $\alpha_F=2.0$ of the {\sl fractal-diffusive self-organized criticality (FD-SOC)} model. For the soft X-ray flare rise times we find a powerlaw slope of $\alpha_T =2.02\pm0.04$ during solar cycle minima years, which is also consistent with the prediction $\alpha_T=2.0$ of the FD-SOC model. During solar cycle maxima years, the powerlaw slope is steeper in the range of $\alpha_T \approx 2.0-5.0$, which can be modeled by a solar cycle-dependent flare pile-up bias effect. These results corroborate the FD-SOC model, which predicts a powerlaw slope of $\alpha_E=1.5$ for flare energies and thus rules out significant nanoflare heating. While the FD-SOC model predicts the probability distribution functions of spatio-temporal scaling laws of nonlinear energy dissipation processes, additional physical models are needed to derive the scaling laws between the geometric SOC parameters and the observed emissivity in different wavelength regimes, as we derive here for soft X-ray emission. The FD-SOC model yields also statistical probabilities for solar flare forecasting.
This paper explores the dynamic properties of the planar system of an ellipsoidal satellite in an equatorial orbit about an oblate primary. In particular, we investigate the conditions for which the satellite is bound in librational motion or when the satellite will circulate with respect to the primary. We find the existence of stable equilibrium points about which the satellite can librate, and explore both the linearized and non-linear dynamics around these points. Absolute bounds are placed on the phase space of the libration-orbit coupling through the use of zero-velocity curves that exist in the system. These zero-velocity curves are used to derive a sufficient condition for when the satellite's libration is bound to less than 90 degrees. When this condition is not satisfied so that circulation of the satellite is possible, the initial conditions at zero libration angle are determined which lead to circulation of the satellite. Exact analytical conditions for circulation and the maximum libration angle are derived for the case of a small satellite in orbits of any eccentricity.
This paper presents an analysis of core-collapse supernova distributions in isolated and interacting host galaxies, paying close attention to the selection effects involved in conducting host galaxy supernova studies. When taking into account all of the selection effects within our host galaxy sample, we draw the following conclusions: i) Within interacting, or 'disturbed', systems there is a real, and statistically significant, increase in the fraction of stripped-envelope supernovae in the central regions. A discussion into what may cause this increased fraction, compared to the more common type IIP supernovae, and type II supernovae without sub-classifications, is presented. Selection effects are shown not to drive this result, and so we propose that this study provides direct evidence for a high-mass weighted initial mass function within the central regions of disturbed galaxies. ii) Within 'undisturbed' spiral galaxies the radial distribution of type Ib and type Ic supernovae is statistically very different, with the latter showing a more centrally concentrated distribution. This could be driven by metallicity gradients in these undisturbed galaxies, or radial variations in other properties (binarity or stellar rotation) driving envelope loss in progenitor stars. This result is not found in 'disturbed' systems, where the distributions of type Ib and Ic supernovae are consistent.
Very Large Array observations of the extreme carbon star IRC+10216 at 7 mm wavelength with 40 milli-arcsecond resolution resolve the object's radio emission, which forms an almost round uniform disk of 83 milli arcseconds diameter, corresponding to 11 AU (for an assumed distance of 130 pc). We find a brightness temperature of 1635 K for the radio photosphere. Since the emission is optically thick, we can directly estimate IRC+10216's average luminosity, which is 8640 L\odot. This value is in excellent agreement with what is predicted from the period-luminosity relation for carbon-rich Miras. Assuming an effective temperature of 2750 K for IRC+10216, it implies an optical photospheric diameter of 3.8 AU. Our precise determination of IRC+10216's proper motion fits the picture presented by far-ultraviolet and far-infrared wavelength observations of its interaction region with the interstellar medium (its "astrosphere"): the star moves roughly in the direction expected from the morphology of the termination shock and its astrotail structures. Calculation of its three dimensional velocity and an analysis of the kinematics of its surrounding interstellar medium (ISM) suggest an appreciable relative velocity of 42 km s/s, which is about half the value discussed in recent studies. This suggests a lower (time-averaged) mass loss rate and/or a higher ISM density than previously assumed.
We report observations of Faraday rotation measures (RMs) for a sample of 191 extragalactic radio jets observed within the MOJAVE program. Multifrequency VLBA observations were carried out over twelve epochs in 2006 at four frequencies between 8 and 15 GHz. We detect parsec-scale Faraday RMs in 149 sources and find the quasars to have larger RMs on average than BL Lac objects. The median core RMs are significantly higher than in the jet components. This is especially true for quasars where we detect a significant negative correlation between the magnitude of the RM and the de-projected distance from the core. We perform detailed simulations of the observational errors of total intensity, polarization and Faraday rotation, and concentrate on the errors of transverse Faraday RM gradients in unresolved jets. Our simulations show that the finite image restoring beam size has a significant effect on the observed RM gradients, and spurious gradients can occur due to noise in the data if the jet is less than two beams wide in polarization. We detect significant transverse RM gradients in four sources (0923+392, 1226+023, 2230+114 and 2251+158). In 1226+023 the RM is for the first time seen to change sign from positive to negative over the transverse cuts, which supports the presence of a helical magnetic field in the jet. In this source we also detect variations in the jet RM over a time scale of three months, which are difficult to explain with external Faraday screens and suggest internal Faraday rotation. By comparing fractional polarization changes in jet components between the four frequency bands to depolarization models we find that an external purely random Faraday screen viewed through only a few lines of sight can explain most of our polarization observations but in some sources, such as 1226+023 and 2251+158, internal Faraday rotation is needed.
Recent analyses that include cosmic microwave background (CMB) anisotropy measurements from the Atacama Cosmology Telescope and the South Pole Telescope have hinted at the presence of a dark radiation component at more than two standard deviations. However, this result depends sensitively on the assumption of an HST prior on the Hubble constant, where $H_0=73.8\pm2.4$ km/s/Mpc at 68% c.l.. From a median statistics (MS) analysis of 537 non-CMB $H_0$ measurements from Huchra's compilation we derive $H_0=68 \pm2.8$ km/s/Mpc at 68% c.l., in good agreement with the results of a recent analysis of the full Huchra list of $H_0$ measurements. This result is also fully consistent with the value of $H_0=69.7\pm2.5$ km/s/Mpc at 68% c.l. obtained from CMB measurements under assumption of the standard $\Lambda$CDM model. We show that with the MS $H_0$ prior the evidence for dark radiation is weakened to $\sim 1.2$ standard deviations. Parametrizing the dark radiation component through the effective number of relativistic degrees of freedom $N_{eff}$, we find $N_{eff}=3.98\pm0.37$ at 68% c.l. with the HST prior and $N_{eff}=3.52\pm0.39$ at 68% c.l. with the MS prior.
Turbulence driven by magnetorotational instability (MRI) affects planetesimal formation by inducing diffusion and collisional fragmentation of dust particles. We examine conditions preferred for planetesimal formation in MRI-inactive "dead zones" using an analytic dead-zone model based on our recent resistive MHD simulations. We argue that successful planetesimal formation requires not only a sufficiently large dead zone (which can be produced by tiny dust grains) but also a sufficiently small net vertical magnetic flux (NVF). Although often ignored, the latter condition is indeed important since the NVF strength determines the saturation level of turbulence in MRI-active layers. We show that direct collisional formation of icy planetesimal across the fragmentation barrier is possible when the NVF strength is lower than 10 mG (for the minimum-mass solar nebula model). Formation of rocky planetesimals via the secular gravitational instability is also possible within a similar range of the NVF strength. Our results indicate that the fate of planet formation largely depends on how the NVF is radially transported in the initial disk formation and subsequent disk accretion processes.
Motivated by the cosmological constant and the coincidence problems, we consider a cosmological model where the cosmological constant $\Lambda_0$ is replaced by a cosmological term $\Lambda(t)$ which is allowed to vary in time. More specifically, we are considering that this dark energy term interacts with dark matter through the phenomenological decay law $\dot{\rho}_{\Lambda}=-Q\rho_{\Lambda}^{n}$. We have constrained the model for the range $n\in[0,10]$ using various observational data (SNeIa, GRB, CMB, BAO, OHD), emphasizing the case where $n=3/2$. This case is the only one where the late-time value for the ratio of dark energy density and matter energy density $\rho_{\Lambda}/\rho_{m}$ is constant, which could provide an interesting explanation to the coincidence problem. We obtain strong limits on the model parameters which however exclude the region where the coincidence or the cosmological constant problems are significantly ameliorated.
We present the results from a search of data from the first 33.5 days of the Kepler science mission (Quarter 1) for exoplanet transits by the Planet Hunters citizen science project. Planet Hunters enlists members of the general public to visually identify transits in the publicly released Kepler light curves via the World Wide Web. Over 24,000 volunteers reviewed the Kepler Quarter 1 data set. We examine the abundance of \geq 2 R\oplus planets on short period (< 15 days) orbits based on Planet Hunters detections. We present these results along with an analysis of the detection efficiency of human classifiers to identify planetary transits including a comparison to the Kepler inventory of planet candidates. Although performance drops rapidly for smaller radii, \geq 4 R\oplus Planet Hunters \geq 85% efficient at identifying transit signals for planets with periods less than 15 days for the Kepler sample of target stars. Our high efficiency rate for simulated transits along with recovery of the majority of Kepler \geq 4 R\oplus planets suggest suggests the Kepler inventory of \geq 4 R\oplus short period planets is nearly complete.
We present our successful program using Chandra for identifying the X-ray afterglow with sub-arcsecond accuracy for the short GRB 111117A discovered by Swift and Fermi. Thanks to our rapid target of opportunity request, Chandra clearly detected the X-ray afterglow, whereas no optical afterglow was found in deep optical observations. Instead, we clearly detect the host galaxy in optical and also in near-infrared bands. We found that the best fit photometric redshift of the host is $z=1.31_{-0.23}^{+0.46}$ (90% confidence), making it one of the highest redshift short GRBs. Furthermore, we see an offset of $1.0 \pm 0.2$ arcseconds, which corresponds to $8.4 \pm 1.7$ kpc assuming z=1.31, between the host and the afterglow position. We discuss the importance of using Chandra for obtaining sub-arcsecond localization of the afterglow in X-rays for short GRBs to study GRB environments in great detail.
We present MMT spectroscopic observations of HII regions in 42 low luminosity
galaxies in the LVL. For 31 galaxies, we measured the temperature sensitive [O
III] line at a strength of 4 sigma or greater, and thus determine direct oxygen
abundances. Our results provide the first direct estimates of oxygen abundance
for 19 galaxies. Oxygen abundances were compared to B-band and 4.5 micron
luminosities and stellar masses in order to characterize the
luminosity-metallicity (L-Z) and mass-metallicity (M-Z) relationships at
low-luminosity.
We present and analyze a "Combined Select" sample composed of 38 objects
(drawn from our parent sample and the literature) with direct oxygen abundances
and reliable distance determinations (TRGB or Ceph). Consistent with previous
studies, the B-band and 4.5 micron L-Z relationships were found to be
12+log(O/H)=(6.27+/-0.21)+(-0.11+/-0.01)M_B and
12+log(O/H)=(6.10+/-0.21)+(-0.10+/-0.01)M_[4.5] (sigma=0.15 and 0.14). For this
sample, we derive a M-Z relationship of
12+log(O/H)=(5.61+/-0.24)+(0.29+/-0.03)log(M*), which agrees with previous
studies; however, the dispersion (sigma=0.15) is not significantly lower than
that of the L-Z relationships. Because of the low dispersions in these
relationships, if an accurate distance is available, the luminosity of a
low-luminosity galaxy is often a better indicator of metallicity than that
derived using certain strong-line methods, so significant departures from the
L-Z relationships may indicate that caution is prudent in such cases. We also
revisit the 70/160 micron color metallicity relationship.
Additionally, we examine N/O abundance trends with respect to oxygen
abundance and B-V color. We find a positive correlation between N/O ratio and
B-V color for 0.05\lesssimB-V\lesssim0.75:
log(N/O)=(1.18+/-0.9)x(B-V)+(-1.92+/-0.08), with a dispersion of sigma=0.14,
that is in agreement with previous studies.
Recent indications of a 125 GeV Higgs boson are challenging for gauge-mediated supersymmetry breaking (GMSB), since radiative contributions to the Higgs boson mass are not enhanced by significant stop mixing. This challenge should not be considered in isolation, however, as GMSB also generically suffers from two other problems: unsuppressed electric dipole moments and the absence of an attractive dark matter candidate. We show that all of these problems may be simultaneously solved by considering heavy superpartners, without extra fields or modified cosmology. Multi-TeV sfermions suppress the EDMs and raise the Higgs mass, and the dark matter problem is solved by Goldilocks cosmology, in which TeV neutralinos decay to GeV gravitinos that are simultaneously light enough to solve the flavor problem and heavy enough to be all of dark matter. The implications for collider searches and direct and indirect dark matter detection are sobering, but EDMs are expected near their current bounds, and the resulting non-thermal gravitino dark matter is necessarily warm, with testable cosmological implications.
We present data from our investigation of the anomalous orange-colored afterglow that was seen in the GammeV Chameleon Afterglow Search (CHASE). These data includes information about the broad band color of the observed glow, the relationship between the glow and the temperature of the apparatus, and other data taken prior to and during the science operations of CHASE. While differing in several details, the generic properties of the afterglow from CHASE are similar to luminescence seen in some vacuum compounds. Contamination from this, or similar, luminescent signatures will likely impact the design of implementation of future experiments involving single photon detectors and high intensity light sources in a cryogenic environment.
We study the spin response of cold dense neutron matter in the limit of zero momentum transfer, and show that the frequency dependence of the long-wavelength spin response is well constrained by sum-rules and the asymptotic behavior of the two-particle response at high frequency. The sum-rules are calculated using Auxiliary Field Diffusion Monte Carlo technique and the high frequency two-particle response is calculated for several nucleon-nucleon potentials. At nuclear saturation density, the sum-rules suggest that the strength of the spin response peaks at $\omega \simeq$ 40--60 MeV, decays rapidly for $\omega \geq $100 MeV, and has a sizable strength below 40 MeV. This strength at relatively low energy may lead to enhanced neutrino production rates in dense neutron-rich matter at temperatures of relevance to core-collapse supernova.
Current neutrino oscillation data indicate that \theta_{13} is not strongly suppressed and \theta_{23} might have an appreciable deviation from \pi/4, implying that the 3 \times 3 neutrino mixing matrix V does not have an exact \mu-\tau permutation symmetry. We make a further study of the effect of \mu-\tau symmetry breaking on the democratic flavor distribution of ultrahigh-energy (UHE) cosmic neutrinos at a neutrino telescope, and find that it is characterized by |V_{\mu i}|^2 - |V_{\tau i}|^2 which would vanish if either \theta_{23} = \pi/4 and \theta_{13} = 0 or \theta_{23} = \pi/4 and \delta = \pm \pi/2 held. We observe that the second-order \mu-\tau symmetry breaking term \bar{\Delta} may be numerically comparable with or even larger than the first-order term \Delta in the flux ratios \phi^{T}_e : \phi^{T}_\mu : \phi^{T}_\tau \simeq (1- 2\Delta) : (1 + \Delta + \bar{\Delta}) : (1 + \Delta - \bar{\Delta}), if \sin (\theta_{23} - \pi/4) and \cos\delta have the same sign. The detection of the UHE \bar{\nu}_e flux via the Glashow-resonance channel \bar{\nu}_e e \to W^- \to anything is also discussed by taking account of the first- and second-order \mu-\tau symmetry breaking effects.
A global network of advanced gravitational wave interferometric detectors is under construction. These detectors will offer an order of magnitude improvement in sensitivity over the initial detectors and will usher in the era of gravitational wave astronomy. In this paper, we evaluate the benefits of relocating one of the advanced LIGO detectors to India.
We study for a dielectric particle with negative electron affinity the effect of surplus electrons on the anomalous scattering of light arising from the transverse optical phonon resonance in the particle's dielectric constant. Using the fact that the same phonon leads to the polarization-induced trapping of the surplus electrons and also limits the surface conductivity, we demonstrate that the surface charge shifts extinction resonances in the infrared. This offers an optical way to measure the charge of the particle and thus to use it in a plasma as a minimally invasive electric probe.
The computation of probabilities in an eternally inflating universe requires a regulator or "measure". The scale factor time measure truncates the universe when a congruence of timelike geodesics has expanded by a fixed volume factor. This definition breaks down if the generating congruence is contracting---a serious limitation that excludes from consideration gravitationally bound regions such as our own. Here we propose a closely related regulator which is well-defined in the entire spacetime. The New Scale Factor Cutoff restricts to events with scale factor below a given value. Since the scale factor vanishes at caustics and crunches, this cutoff always includes an infinite number of disconnected future regions. We show that this does not lead to divergences. The resulting measure combines desirable features of the old scale factor cutoff and of the light-cone time cutoff, while eliminating some of the disadvantages of each.
An exact expression for the rate of dragging of inertial frames (Lense-Thirring (LT) precession) in a general stationary spacetime, is derived without invoking the weak field approximation. This expression, when used for the Kerr metric, leads to the LT precession frequency in the strong gravity regime appropriate to compact gravitating objects like rotating neutron stars and black holes. Numerical values of the precession rate are computed for a few known cases of pulsars (including a double-pulsar) and compared to the precession rates in the weaker gravity regimes of the earth and the sun.
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We present a new probe of primordial non-Gaussianity via the 21cm radiation from minihalos at high redshifts. We calculate the fluctuations in the brightness temperature (measured against the cosmic microwave background) of the 21cm background from minihalos containing HI, and find a significant enhancement due to small non-Gaussianity with amplitude f_NL=O(1). This enhancement can be attributed to the nonlinear bias which is increased in the presence of non-Gaussianity. We show that our results are robust against changes in the assumed mass function and some physical aspects of minihalo formation, but are nevertheless sensitive to the presence of strong radiation sources within or around the minihalos. Our results are relevant for constraining and searching for small primordial non-Gaussianity with upcoming radio telescopes such as LOFAR and SKA.
We present 1.2mm MAMBO-2 observations of a field which is over-dense in Lyman Break Galaxies (LBGs) at z~5. The field includes seven spectroscopically-confirmed LBGs contained within a narrow (z=4.95+/-0.08) redshift range and an eighth at z=5.2. We do not detect any individual source to a limit of 1.6 mJy/beam (2*rms). When stacking the flux from the positions of all eight galaxies, we obtain a limit to the average 1.2 mm flux of these sources of 0.6mJy/beam. This limit is consistent with FIR imaging in other fields which are over-dense in UV-bright galaxies at z~5. Independently and combined, these limits constrain the FIR luminosity (8-1000 micron) to a typical z~5 LBG of LFIR<~3x10^11 Lsun, implying a dust mass of Mdust<~10^8 Msun (both assuming a grey body at 30K). This LFIR limit is an order of magnitude fainter than the LFIR of lower redshift sub-mm sources (z~1-3). We see no emission from any other sources within the field at the above level. While this is not unexpected given millimetre source counts, the clustered LBGs trace significantly over-dense large scale structure in the field at z = 4.95. The lack of any such detection in either this or the previous work, implies that massive, obscured star-forming galaxies may not always trace the same structures as over-densities of LBGs, at least on the length scale probed here. We briefly discuss the implications of these results for future observations with ALMA.
The Milky Way galaxy is observed to have multiple components with distinct properties, such as the bulge, disk, and halo. Unraveling the assembly history of these populations provides a powerful test to the theory of galaxy formation and evolution, but is often restricted due to difficulties in measuring accurate stellar ages for low mass, hydrogen-burning stars. Unlike these progenitors, the "cinders" of stellar evolution, white dwarf stars, are remarkably simple objects and their fundamental properties can be measured with little ambiguity from spectroscopy. Here I report observations of newly formed white dwarf stars in the halo of the Milky Way, and a separate analysis of archival data on white dwarfs in the well-studied 12.5 billion year old globular cluster Messier 4. From this, I measure the mass distribution of the remnants and invert the stellar evolution process to develop a new relation that links this final stellar mass to the mass of their immediate progenitors, and therefore to the age of the parent population. By applying this technique to a small sample of four nearby and kinematically-confirmed halo white dwarfs, I measure the age of local field halo stars to be 11.4 +/- 0.7 billion years. This age is directly tied to the globular cluster age scale, on which the oldest clusters formed 13.5 billion years ago. Future (spectroscopic) observations of newly formed white dwarfs in the Milky Way halo can be used to reduce the present uncertainty, and to probe relative differences between the formation time of the last clusters and the inner halo.
We present a method to select hot subdwarf stars with A to M-type companions using photometric selection criteria. We cover a wide range in wavelength by combining GALEX ultraviolet data, optical photometry from the SDSS and the Carlsberg Meridian telescope, near-infrared data from 2MASS and UKIDSS. We construct two complimentary samples, one by matching GALEX, CMC and 2MASS, as well as a smaller, but deeper, sample using GALEX, SDSS and UKIDSS. In both cases, a large number of composite subdwarf plus main-sequence star candidates were found. We fit their spectral energy distributions with a composite model in order to estimate the subdwarf and companion star effective temperatures along with the distance to each system. The distribution of subdwarf effective temperature was found to primarily lie in the 20,000 - 30,000 K regime, but we also find cooler subdwarf candidates, making up ~5-10 per cent. The most prevalent companion spectral types were seen to be main-sequence stars between F0 and K0, while subdwarfs with M-type companions appear much rarer. This is clear observational confirmation that a very efficient first stable Roche-lobe overflow channel appears to produce a large number of subdwarfs with F to K-type companions. Our samples thus support the importance of binary evolution for subdwarf formation.
The large majority of neutron stars (NSs) in low mass X-ray binaries (LMXBs) have never shown detectable pulsations despite several decades of intense monitoring. The reason for this remains an unsolved problem that hampers our ability to measure the spin frequency of most accreting NSs. The accreting millisecond X-ray pulsar (AMXP) HETE J1900.1--2455 is an intermittent pulsar that exhibited pulsations at about 377 Hz for the first 2 months and then turned in a non-pulsating source. Understanding why this happened might help to understand why most LMXBs do not pulsate. We present a 7 year long coherent timing analysis of data taken with the Rossi X-ray Timing Explorer. We discover new sporadic pulsations that are detected on a baseline of about 2.5 years. We find that the pulse phases anti-correlate with the X-ray flux as previously discovered in other AMXPs. We place stringent upper limits of 0.05% rms on the pulsed fraction when pulsations are not detected and identify an enigmatic pulse phase drift of ~180 degrees in coincidence with the first disappearance of pulsations. Thanks to the new pulsations we measure a long term spin frequency derivative whose strength decays exponentially with time. We interpret this phenomenon as evidence of magnetic field burial.
We present a study of close white dwarf and M dwarf (WD+dM) binary systems and examine the effect that a close companion has on the magnetic field generation in M dwarfs. We use a base sample of 1602 white dwarf -- main sequence binaries from Rebassa et al. to develop a set of color cuts in GALEX, SDSS, UKIDSS, and 2MASS color space to construct a sample of 1756 WD+dM high-quality pairs from the SDSS DR8 spectroscopic database. We separate the individual WD and dM from each spectrum using an iterative technique that compares the WD and dM components to best-fit templates. Using the absolute height above the Galactic plane as a proxy for age, and the H{\alpha} emission line as an indicator for magnetic activity, we investigate the age-activity relation for our sample for spectral types \leqM7. Our results show that early-type M dwarfs (\leqM4) in close binary systems are more likely to be active and have longer activity lifetimes compared to their field counterparts. However, at a spectral type of M5 (just past the onset of full convection in M dwarfs), the activity fraction and lifetimes of WD+dM binary systems becomes more comparable to that of the field M dwarfs. One of the implications of having a close binary companion is presumed to be increased stellar rotation through disk-disruption, tidal effects, or angular momentum exchange. Thus, we interpret the similarity in activity behavior between late-type dMs in WD+dM pairs and late-type field dMs to be due to a decrease in sensitivity in close binary companions (or stellar rotation), which has implications for the nature of magnetic activity in fully-convective stars. (Abridged)
We study the distribution of aluminum abundances among red giants in the peculiar globular cluster NGC 1851. Aluminum abundances were derived from the strong doublet Al I 8772-8773 A measured on intermediate resolution FLAMES spectra of 50 cluster stars acquired under the Gaia-ESO public survey. We coupled these abundances with previously derived abundance of O, Na, Mg to fully characterize the interplay of the NeNa and MgAl cycles of H-burning at high temperature in the early stellar generation in NGC 1851. The stars in our sample show well defined correlations between Al,Na and Si; Al is anticorrelated with O and Mg. The average value of the [Al/Fe] ratio steadily increases going from the first generation stars to the second generation populations with intermediate and extremely modified composition. We confirm on a larger database the results recently obtained by us (Carretta et al. 2011a): the pattern of abundances of proton-capture elements implies a moderate production of Al in NGC 1851. We find evidence of a statistically significant positive correlation between Al and Ba abundances in the more metal-rich component of red giants in NGC 1851.
The Small Magellanic Cloud (SMC) has surprisingly strong submm and mm-wavelength emission that is inconsistent with standard dust models, including those with emission from spinning dust. Here we show that the emission from the SMC may be understood if the interstellar dust mixture includes magnetic nanoparticles, emitting magnetic dipole radiation resulting from thermal fluctuations in the magnetization. The magnetic grains can be metallic iron, magnetite Fe3O4, or maghemite gamma-Fe2O3. The required mass of iron is consistent with elemental abundance constraints. The magnetic dipole emission is predicted to be polarized orthogonally to the normal electric dipole radiation if the nanoparticles are inclusions in larger grains. We speculate that other low-metallicity galaxies may also have a large fraction of the interstellar Fe in magnetic materials.
We have made the largest-volume measurement to date of the transition to large-scale homogeneity in the distribution of galaxies. We use the WiggleZ survey, a spectroscopic survey of over 200,000 blue galaxies in a cosmic volume of ~1 (Gpc/h)^3. A new method of defining the 'homogeneity scale' is presented, which is more robust than methods previously used in the literature, and which can be easily compared between different surveys. Due to the large cosmic depth of WiggleZ (up to z=1) we are able to make the first measurement of the transition to homogeneity over a range of cosmic epochs. The mean number of galaxies N(<r) in spheres of comoving radius r is proportional to r^3 within 1%, or equivalently the fractal dimension of the sample is within 1% of D_2=3, at radii larger than 71 \pm 8 Mpc/h at z~0.2, 70 \pm 5 Mpc/h at z~0.4, 81 \pm 5 Mpc/h at z~0.6, and 75 \pm 4 Mpc/h at z~0.8. We demonstrate the robustness of our results against selection function effects, using a LCDM N-body simulation and a suite of inhomogeneous fractal distributions. The results are in excellent agreement with both the LCDM N-body simulation and an analytical LCDM prediction. We can exclude a fractal distribution with fractal dimension below D_2=2.97 on scales from ~80 Mpc/h up to the largest scales probed by our measurement, ~300 Mpc/h, at 99.99% confidence.
Laporte et al. (2011) reported a very high redshift galaxy candidate: a lensed J-band dropout (A2667-J1). J1 has a photometric redshift of z=9.6-12, the probability density function for which permits no low or intermediate z solution. We here report new spectroscopic observations of this galaxy with VLT/XShooter, which show clear [OIII]5007AA, Ly-alpha, H-alpha, and H-beta emission and place the galaxy firmly at z=2.082. The oxygen lines contribute only ~25% to the H-band flux, and do not significantly affect the dropout selection of J1. After correcting the broadband fluxes for line emission, we identify two roughly equally plausible natures for A2667-J1: either it is young heavily reddened starburst, or a maximally old system with a very pronounced 4000AA break, upon which a minor secondary burst of star formation is superimposed. Fits show that to make a 3 sigma detection of this object in the B-band (V-band), imaging of depth AB=30.2 (29.5) would be required - despite the relatively bright NIR magnitude, we would need optical data of equivalent depth to the Hubble Ultra Deep Field to rule out the mid-z solution on purely photometric grounds. Assuming that this stellar population can be scaled to the NIR magnitudes of recent HST/WFC3 IR-selected galaxies, we conclude that infeasibly deep optical data AB~32 would be required for the same level of security. There is a population of galaxies at z~2 with continuum colours alone that mimic those of our z=7-12 candidates.
We present a study of the distribution of X-ray AGN in a representative sample of 26 massive clusters at 0.15<z<0.30, combining Chandra observations with highly complete spectroscopy of cluster members down to M_K*+2. In total we identify 48 X-ray AGN among the cluster members, with luminosities 2x10^41-1x10^44erg/s. In the stacked caustic diagram, the X-ray AGN appear to preferentially lie along the caustics, suggestive of an infalling population. They also appear to avoid the region with lowest cluster-centric radii and relative velocities (r_proj<0.4 r_500; |v-<v>|/sigma_v<0.8), which is dominated by the virialized population of galaxies accreted earliest into the clusters. Moreover the velocity dispersion of the 48 X-ray AGN is 1.51x that of the overall cluster population, which is consistent with the sqrt(2) ratio expected by simple energetic arguments when comparing infalling versus virialized populations. This kinematic segregation is significant at the 4.66-sigma level. When splitting the X-ray AGN sample into two according to X-ray or infrared (IR) luminosity, both X-ray bright and IR-bright sub-samples show higher velocity dispersions than their X-ray dim and IR-dim counterparts at >2sigma significance. This is consistent with the nuclear activity responsible for the X-ray and IR emission being slowly shut down as the host galaxies are accreted into the cluster. Overall our results provide the strongest observational evidence to date that X-ray AGN found in massive clusters are an infalling population, and that the cluster environment very effectively suppresses radiatively-efficient nuclear activity in its member galaxies. These results are consistent with the view that for galaxies to host an X-ray AGN they should be the central galaxy within their dark matter halo and have a ready supply of cold gas.
We use GALEX ultraviolet and WISE 22 micron observations to investigate the current star formation activity of the optically-red spirals recently identified as part of the Galaxy Zoo project. These galaxies were accurately selected from the Sloan Digital Sky Survey in order to be pure discs with low or no current star formation activity, representing one of the best optically-selected samples of candidate passive spirals. However, we show that these galaxies are not only still forming stars at a significant rate >= 1 M_sun/yr but, more importantly, their star formation activity is not different from that of normal star-forming discs of the same stellar mass (M* >= 10^10.2 M_sun). Indeed, these systems lie on the UV-optical blue sequence, even without any corrections for internal dust attenuation, and they follow the same specific star formation rate vs. stellar mass relation of star-forming galaxies. Our findings clearly show that, at high stellar masses, optical colours do not allow to discriminate between actively star-forming and truly quiescent systems.
Observations of non-thermal emission from several supernova remnants suggest
that magnetic fields close to the blastwave are much stronger than would be
naively expected from simple shock compression of the field permeating the
interstellar medium (ISM).
We present a simple model which is capable of achieving sufficient magnetic
field amplification to explain the observations. We propose that the cosmic-ray
pressure gradient acting on the inhomogeneous ISM upstream of the supernova
blastwave induces strong turbulence upstream of the supernova blastwave. The
turbulence is generated through the differential acceleration of the upstream
ISM which occurs as a result of density inhomogeneities in the ISM. This
turbulence then amplifies the pre-existing magnetic field.
Numerical simulations are presented which demonstrate that amplification
factors of 20 or more are easily achievable by this mechanism when reasonable
parameters for the ISM and supernova blastwave are assumed. The length scale
over which this amplification occurs is that of the diffusion length of the
highest energy non-thermal particles.
Context.- This paper is part of a series involving the AMIGA project (Analysis of the Interstellar Medium of Isolated GAlaxies) which identifies and studies a statistically-significant sample of the most isolated galaxies in the northern sky. Aims.- We present a catalogue of nuclear activity, traced by optical emission lines, in a well-defined sample of the most isolated galaxies in the local Universe, that will be used as a baseline for the study of the effect of the environment on nuclear activity. Methods.- We obtained spectral data from the 6th Data Release of the Sloan Digital Sky Survey, and these were inspected in a semi-automatic way. We subtracted the underlying stellar populations from the spectra (using the software Starlight) and modelled the nuclear emission features. Standard emission-line diagnostics diagrams were applied, using a new classification scheme that takes into account censored data, to classify the type of nuclear emission. Results.- We provide a final catalogue of spectroscopic data, stellar populations, emission lines and classification of optical nuclear activity for AMIGA galaxies. The prevalence of optical active galactic nuclei (AGN) in AMIGA galaxies is 20.4%, or 36.7% including transition objects. The fraction of AGN increases steeply towards earlier morphological types and higher luminosities. We compare these results with a matched analysis of galaxies in isolated denser environments (Hickson Compact Groups). After correcting for the effects of the morphology and luminosity, we find that there is no evidence for a difference in the prevalence of AGN between isolated and compact group galaxies, and we discuss the implications of this result. Conclusions.- We find that a major interaction is not a necessary condition for the triggering of optical AGN.
We review some results of the past 12 years derived from optical and infrared photometry of Type Ia supernovae. A combination of optical and infrared photometry allows us to determine accurately the extinction along the line of sight. The resulting distance measurements are much more accurate than can be obtained from optical data alone. Type Ia supernovae are very nearly standard candles in the near-infrared. Accurate supernova distances, coupled with other observational data available at present, allow us to determine the matter density in the universe and lead to evidence for the existence of Dark Energy. We can now address some questions on the grandest scale such as, "What is the ultimate Fate of the universe?"
Gale crater, the landing site of the Curiosity Mars rover, hosts a 5 kilometer high layered mound of uncertain origin which may represent an important archive of the planet's past climate. Although widely considered to be an erosional remnant of a once crater-filling unit, we combine structural measurements and a new model of formation to show how this mound may have grown in place near the center of the crater under the influence of topographic slope-induced winds. This mechanism implicates airfall-dominated deposition with a limited role for lacustrine or fluvial activity in the formation of the Gale mound, and is not favorable for the preservation of organic carbon. Slope-wind enhanced erosion and transport is widely applicable to a range of similar sedimentary mounds found across the Martian surface.
V393 Scorpii is a Double Periodic Variable characterized by a relatively stable non-orbital photometric cycle of 253 days. Mennickent et al. argue for the presence of a massive optically thick disc around the more massive B-type component and describe the evolutionary stage of the system. In this paper we analyze the behavior of the main spectroscopic optical lines during the long non-orbital photometric cycle. We study the radial velocity of the donor determining their orbital elements and find a small but significant orbital eccentricity (e = 0.04). The donor spectral features are modeled and removed from the spectrum at every observing epoch using the light-curve model given by Mennickent et al. We find that the line emission is larger during eclipses and mostly comes from a bipolar wind. We find that the long cycle is explained in terms of a modulation of the wind strength; the wind has a larger line and continuum emissivity on the high state. We report the discovery of highly variable chromospheric emission in the donor, as revealed by Doppler maps of the emission lines MgII 4481 and CI 6588. We discuss notable and some novel spectroscopic features like discrete absorption components, especially visible at blue-depressed OI 7773 absorption wings during the second half-cycle, Balmer double emission with V/R-curves showing "Z-type" and "S-type" excursions around secondary and main eclipse, respectively, and H_beta emission wings extending up to +- 2000 km/s. We discuss possible causes for these phenomena and for their modulations with the long cycle.
We present the first proper motion measurements for the galaxy M31. We obtained new V-band imaging data with the HST ACS/WFC and WFC3/UVIS of a spheroid field near the minor axis, an outer disk field along the major axis, and a field on the Giant Southern Stream. The data provide 5-7 year time baselines with respect to pre-existing deep first-epoch observations. We measure the positions of thousands of M31 stars and hundreds of compact background galaxies in each field. High accuracy and robustness is achieved by building and fitting a unique template for each individual object. The average proper motion for each field is obtained from the average motion of the M31 stars between the epochs with respect to the background galaxies. For the three fields, the observed proper motions (mu_W,mu_N) are (-0.0458, -0.0376), (-0.0533, -0.0104), and (-0.0179,-0.0357) mas/yr, respectively. The ability to average over large numbers of objects and over the three fields yields a final accuracy of 0.012 mas/yr. The robustness of the proper-motion measurements and uncertainties are supported by the fact that data from different instruments, taken at different times and with different telescope orientations, as well as measurements of different fields, all yield statistically consistent results. Papers II and III explore the implications for our understanding of the history, future, and mass of the Local Group. (Abridged)
We determine the velocity vector of M31 with respect to the Milky Way and use this to constrain the mass of the Local Group, based on HST proper-motion measurements presented in Paper I. We construct N-body models for M31 to correct the measurements for the contributions from stellar motions internal to M31. We also estimate the center-of-mass motion independently, using the kinematics of satellite galaxies of M31 and the Local Group. All estimates are mutually consistent, and imply a weighted average M31 heliocentric transverse velocity of (v_W,v_N) = (-125.2+/-30.8, -73.8+/-28.4) km/s. We correct for the reflex motion of the Sun using the most recent insights into the solar motion within the Milky Way. This implies a radial velocity of M31 with respect to the Milky Way of V_rad = -109.3+/-4.4 km/s, and a tangential velocity V_tan = 17.0 km/s (<34.3 km/s at 1-sigma confidence). Hence, the velocity vector of M31 is statistically consistent with a radial (head-on collision) orbit towards the Milky Way. We revise prior estimates for the Local Group timing mass, including corrections for cosmic bias and scatter. Bayesian combination with other mass estimates yields M_LG = M_MW(vir) + M_M31(vir) = (3.17 +/- 0.57) x 10^12 solar masses. The velocity and mass results imply at 95% confidence that M33 is bound to M31, consistent with expectation from observed tidal deformations. (Abridged)
We study the future orbital evolution and merging of the MW-M31-M33 system, using a combination of collisionless N-body simulations and semi-analytic orbit integrations. Monte-Carlo simulations are used to explore the consequences of varying the initial phase-space and mass parameters within their observational uncertainties. The observed M31 transverse velocity implies that the MW and M31 will merge t = 5.86 (+1.61-0.72) Gyr from now, after a first pericenter at t = 3.87 (+0.42-0.32) Gyr. M31 may (probability p=41%) make a direct hit with the MW (defined here as a first-pericenter distance less than 25 kpc). Most likely, the MW and M31 will merge first, with M33 settling onto an orbit around them. Alternatively, M33 may make a direct hit with the MW first (p=9%), or M33 may get ejected from the Local Group (p=7%). The MW-M31 merger remnant will resemble an elliptical galaxy. The Sun will most likely (p=85%) end up at larger radius from the center of the MW-M31 merger remnant than its current distance from the MW center, possibly further than 50 kpc (p=10%). The Sun may (p=20%) at some time in the next 10 Gyr find itself moving through M33 (within 10 kpc), but while dynamically still bound to the MW-M31 merger remnant. The arrival and possible collision of M31 (and possibly M33) with the MW is the next major cosmic event affecting the environment of our Sun and solar system that can be predicted with some certainty. (Abridged)
Plasmas of geometrically thick, black hole (BH) accretion flows in active galactic nuclei (AGNs) are generally collisionless for protons, and involve magnetic field turbulence. Under such conditions a fraction of protons can be accelerated stochastically and create relativistic neutrons via nuclear collisions. These neutrons can freely escape from the accretion flow and decay into protons in dilute polar region above the rotating BH to form relativistic jets. We calculate geometric efficiencies of the neutron energy and mass injections into the polar region, and show that this process can deposit luminosity as high as L_j ~ 2e-3 dot{M} c^2 and mass loading dot{M}_j ~ 6e-4 dot{M} for the case of the BH mass M ~ 1e8 M_sun, where dot{M} is mass accretion rate. The terminal Lorentz factors of the jets are Gamma ~ 3, and they may explain the AGN jets having low luminosities. For higher luminosity jets, which can be produced by additional energy inputs such as Poynting flux, the neutron decay still can be a dominant mass loading process, leading to e.g., Gamma ~ 50 for L_{j,tot} ~ 3e-2 dot{M}c^2.
(1) We find that comet 107P/WH was active in 1949, 1979, 1992, 2005, and 2009. (2) Its age can be measured. We find T-AGE=4700 comet years, WB-AGE=7800 cy. (3) This is a methuselah comet very near to its dormancy phase, being temporarily rejuvenated due to a diminution of its perihelion distance. (4) We measured the diameter as Deffe=3.67\pm0.06 km, and the rotational period, Prot=6.093\pm0.002 h. (5) We define the region of the graveyard of comets, and three comets belong to the graveyard: 107P/Wilson-Harrington, 133P/Elst-Pizarro and D/1891W1 Blanpain.
Galaxy formation and growth under the {\Lambda}CDM paradigm is expected to proceed in a hierarchical, bottom-up fashion by which small galaxies grow into large galaxies; this mechanism leaves behind large "classical bulges" kinematically distinct from "pseudobulges" grown by internal, secular processes. We use archival data (Spitzer 3.6 \mum wavelength, Hubble Space Telescope H-band, Two Micron All Sky Survey Ks-band, and Sloan Digital Sky Survey gri-band) to measure composite minor- and major-axis surface brightness profiles of the almost-edgeon spiral galaxy NGC 5746. These light profiles span a large range of radii and surface brightnesses to reveal an inner, high surface brightness stellar component that is distinct from the well-known boxy bulge. It is well fitted by S\'ersic functions with indices n = 0.99 \pm 0.08 and 1.17 \pm 0.24 along the minor and major axes, respectively. Since n < 2, we conclude that this innermost component is a secularly-evolved pseudobulge that is distinct from the boxy pseudobulge. This inner pseduobulge makes up 0.136 \pm 0.019 of the total light of the galaxy. It is therefore considerably less luminous than the boxy structure, which is now understood to be a bar seen nearly end-on. The infrared imagery shows further evidence for secular evolution in the form of a bright inner ring of inner radius 9.1 kpc and width 1.6 kpc. NGC 5746 is therefore a giant, pure-disk SB(r)bc galaxy with no sign of a merger-built bulge. We do not understand how such galaxies form in a {\Lambda}CDM universe.
The nearby M-dwarf AP Col was recently identified by Riedel et al. 2011 as a pre-main sequence star (age 12 - 50 Myr) situated only 8.4 pc from the Sun. The combination of its youth, distance, and intrinsically low luminosity make it an ideal target to search for extrasolar planets using direct imaging. We report deep adaptive optics observations of AP Col taken with VLT/NACO and Keck/NIRC2 in the L-band. Using aggressive speckle suppression and background subtraction techniques, we are able to rule out companions with mass m >= 0.5 - 1M_Jup for projected separations a>4.5 AU, and m >= 2 M_Jup for projected separations as small as 3 AU, assuming an age of 40 Myr using the COND theoretical evolutionary models. Using a different set of models the mass limits increase by a factor of ~2. The observations presented here are the deepest mass-sensitivity limits yet achieved within 20 AU on a star with direct imaging. While Doppler radial velocity surveys have shown that Jovian bodies with close-in orbits are rare around M-dwarfs, gravitational microlensing studies predict that ~17% of these stars host massive planets with orbital separations of 1-10 AU. Sensitive high-contrast imaging observations, like those presented here, will help to validate results from complementary detection techniques by determining the frequency of gas giant planets on wide orbits around M-dwarfs.
For more than a decade now, it has been controversial whether or not the high rate of giant gravitational arcs and the largest observed Einstein radii are consistent with the standard cosmological model. Recent studies indicate that mergers provide an efficient mechanism to substantially increase the strong lensing efficiency of individual clusters. Based on purely semi-analytic methods, we investigate the statistical impact of cluster mergers on the distribution of the largest Einstein radii and the optical depth for giant gravitational arcs of selected cluster samples. Analysing representative all-sky realizations of clusters at redshifts z < 1, we find that mergers increase the number of Einstein radii above 10 arcsec (20 arcsec) by ~ 35% (~ 55 %). Exploiting the tight correlation between Einstein radii and lensing cross sections, we infer that the optical depth for giant gravitational arcs with length-to-width ratio > 7.5 of those clusters with Einstein radii above 10 arcsec (20 arcsec) increases by ~ 45 % (~ 85 %). Our findings suggest that cluster mergers significantly influence in particular the statistical lensing properties of the strongest gravitational lenses. We conclude that semi-analytic studies must inevitably take these events into account before questioning the standard cosmological model on the basis of the largest observed Einstein radii and the statistics of giant gravitational arcs.
The recent progress in the understanding the physical nature of neutron star equilibrium configurations and the first observational evidence of a genuinely Short Gamma-Ray Burst, GRB 090227B, allows to give an estimate of the gravitational waves versus electromagnetic emission in a Gamma-Ray Burst.
We present high spatial resolution, medium spectral resolution near-infrared (NIR) H- and K-band long-slit spectroscopy for a sample of 29 nearby (z < 0.01) inactive spiral galaxies, to study the composition of their NIR stellar populations. These spectra contain a wealth of diagnostic stellar absorption lines, e.g. MgI 1.575 micron, SiI 1.588 micron, CO (6-3) 1.619 micron, MgI 1.711 micron, NaI 2.207 micron, CaI 2.263 micron and the 12CO and 13CO bandheads longward of 2.29 micron. We use NIR absorption features to study the stellar population and star formation properties of the spiral galaxies along the Hubble sequence, and we produce the first high spatial resolution NIR HK-band template spectra for low redshift spiral galaxies along the Hubble sequence. These templates will find applications in a variety of galaxy studies. The strength of the absorption lines depends on the luminosity and/or temperature of stars and, therefore, spectral indices can be used to trace the stellar population of galaxies. The entire sample testifies that the evolved red stars completely dominate the NIR spectra, and that the hot young star contribution is virtually nonexistent.
Within the framework of modified Newtonian dynamics (MOND) we investigate the kinematics of two dwarf spiral galaxies belonging to very different environments, namely KK 246 in the Local Void and Holmberg II in the M81 group. A mass model of the rotation curve of KK 246 is presented for the first time, and we show that its observed kinematics are consistent with MOND. We re-derive the outer rotation curve of Holmberg II, by modelling its HI data cube, and find that its inclination should be closer to face-on than previously derived. This implies that Holmberg II has a higher rotation velocity in its outer parts, which, although not very precisely constrained, is consistent with the MOND prediction.
We propose to measure the radii of the Penn State - Torun Planet Search (PTPS) exoplanet host star candidates using the CHARA Array. Stellar radii estimated from spectroscopic analysis are usually inaccurate due to indirect nature of the method and strong evolutionary model dependency. Also the so-called degeneracy of stellar evolutionary tracks due to convergence of many tracks in the giant branch decreases the precision of such estimates. However, the radius of a star is a critical parameter for the calculation of stellar luminosity and mass, which are often not well known especially for giants. With well determined effective temperature (from spectroscopy) and radius the luminosity may be calculated precisely. In turn also stellar mass may be estimated much more precisely. Therefore, direct radii measurements increase precision in the determination of planetary candidates masses and the surface temperatures of the planets.
Once formed in a supernova explosion, a neutron star cools rapidly via neutrino emission during the first 10^4-10^5 yrs of its life-time. Here we compute the axion emission rate from baryonic components of a star at temperatures below their respective critical temperatures T_c for normal-superfluid phase transition. The axion production is driven by a charge neutral weak process, associated with Cooper pair breaking and recombination. The requirement that the axion cooling does not overshadow the neutrino cooling puts a lower bound on the axion decay constant f_a > 7.4 10^{9} T_{c9}^{-1} GeV, with T_{c9} = T_c/10^{9} K. This translates into a upper bound on the axion mass m_a < 10^{-3}\, T_{c9} eV.
We investigate the accretion process in high-luminosity AGNs (HLAGNs) in the scenario of the disk evaporation model. Based on this model, the thin disk can extend down to the innermost stable circular orbit (ISCO) at accretion rates higher than $0.02\dot{M}_{\rm Edd}$; while the corona is weak since part of the coronal gas is cooled by strong inverse Compton scattering of the disk photons. This implies that the corona cannot produce as strong X-ray radiation as observed in HLAGNs with large Eddington ratio. In addition to the viscous heating, other heating to the corona is necessary to interpret HLAGN. In this paper, we assume that a part of accretion energy released in the disk is transported into the corona, heating up the electrons and thereby radiated away. We for the first time, compute the corona structure with additional heating, taking fully into account the mass supply to the corona and find that the corona could indeed survive at higher accretion rates and its radiation power increases. The spectra composed of bremsstrahlung and Compton radiation are also calculated. Our calculations show that the Compton dominated spectrum becomes harder with the increase of energy fraction ($f$) liberating in the corona, and the photon index for hard X-ray($2-10 \rm keV$) is $2.2 < \Gamma < 2.7 $. We discuss possible heating mechanisms for the corona. Combining the energy fraction transported to the corona with the accretion rate by magnetic heating, we find that the hard X-ray spectrum becomes steeper at larger accretion rate and the bolometric correction factor ($L_{\rm bol}/L_{\rm 2-10keV}$) increases with increasing accretion rate for $f<8/35$, which is roughly consistent with the observational results.
14 Ceti is a subgiant star of F spectral class that displays variations in the S-index of its CaII H & K lines and an X-ray emission that is stronger than the mean observed for its spectral class, which may be due to some magnetic activity. We attempt to Zeeman-detect and study the magnetic field of 14 Ceti and to infer its origin. We used the spectropolarimeter Narval at the Telescope Bernard Lyot, Pic du Midi Observatory, and the least squares deconvolution method to create high signal-to-noise ratio Stokes V profiles. We derived the surface-averaged longitudinal magnetic field Bl. We also measured the S-index, and the radial velocity for each observation. 14 Ceti is Zeeman-detected for the 30 observed dates spanning from August 2007 to January 2012. The average longitudinal magnetic field does not reverse its sign, reaches about -35 G, and shows some month-long-timescale variations in our 2008 and 2011-2012 observations. The S-index follows the same long-term trend as Bl. 14 Ceti is confirmed as a single star without H-K emission cores. The strength of the observed surface magnetic field of 14 Ceti is one order of magnitude greater than the observed one for late F main-sequence stars, and is comparable to the values measured in the active late F pre-main-sequence star HR 1817. On the other hand, taking into account the post-main-sequence evolution of an Ap star, an oblique rotator model can explain the strength of the magnetic field of 14 Ceti. The variations with a timescale of months observed for both the Bl and S-index could be due to the rotation. The most probable scenario to explain our observations appears to be that 14 Ceti is the descendant of a cool Ap star .
The origin of ultra-high-energy cosmic rays (UHECRs) is one of the most intriguing problems of modern cosmic ray physics. We briefly review the main astrophysical models of their origin and the forthcoming orbital experiments TUS and JEM-EUSO, and discuss how the new data can help one solve the long-standing puzzle.
We present the results of our UBVRI CCD photometry for the second brightest supernova of 2009, SN 2009nr, discovered during a sky survey with the telescopes of the MASTER robotic network. Its light and color curves and bolometric light curves have been constructed. The light-curve parameters and the maximum luminosity have been determined. SN 2009nr is shown to be similar in light-curve shape and maximum luminosity to SN 1991T, which is the prototype of the class of supernovae Ia with an enhanced luminosity. SN 2009nr exploded far from the center of the spiral galaxy UGC 8255 and most likely belongs to its old halo population. We hypothesize that this explosion is a consequence of the merger of white dwarfs.
We produce synthetic images and SEDs from radiation hydrodynamical simulations of radiatively driven implosion. The synthetically imaged bright rimmed clouds (BRCs) are morphologically similar to those observed in star forming regions. Using nebular diagnostic line-ratios, simulated Very Large Array (VLA) radio images, H{\alpha} imaging and SED fitting we compute the neutral cloud and ionized boundary layer gas densities and temperatures and perform a virial stability analysis for each model cloud. We determine that the neutral cloud temperatures derived by SED fitting are hotter than the dominant neutral cloud temperature by 1 - 2 K due to emission from warm dust. This translates into a change in the calculated cloud mass by 8-35 %. Using a constant mass conversion factor (C{\nu}) for BRCs of different class is found to give rise to errors in the cloud mass of up to a factor of 3.6. The ionized boundary layer (IBL) electron temperature calculated using diagnostic line ratios is more accurate than assuming the canonical value adopted for radio diagnostics of 10^4 K. Both radio diagnostics and diagnostic line ratios are found to underestimate the electron density in the IBL. Each system is qualitatively correctly found to be in a state in which the pressure in the ionized boundary layer is greater than the supporting cloud pressure, implying that the objects are being compressed. We find that observationally derived mass loss estimates agree with those on the simulation grid and introduce the concept of using the mass loss flux to give an indication of the relative strength of photo-evaporative flow between clouds. The effect of beam size on these diagnostics in radio observations is found to be a mixing of the bright rim and ambient cloud and HII region fluxes, which leads to an underestimate of the cloud properties relative to a control diagnostic.
We aim to characterize the nature of galaxies whose optical emission line diagnostics are consistent with star formation, but whose X-ray properties strongly point towards the presence of an AGN. Understanding these sources is of particular importance in assessing the completeness of AGN samples derived from large galaxy surveys, selected solely on the basis of their optical spectral properties.We construct a large sample of 211 NELGs, which have FWHMs Hb emission line <1200 km/s from the SDSS-DR7 galaxy spectroscopic catalogue, for which we are able to construct a classical diagnostic diagram, [OIII]/Hb versus [NII]/Ha (hence z<0.4), and that are also detected in the hard energy band and present in the 2XMM catalogue. This sample offers a large database by which to investigate potential mismatches between optical diagnostics and X-ray emission. Among these 211 objects, which based on our selection criteria are all at z<0.4, we find that 145 galaxies are diagnosed as AGNs, having 2-10 keV X-ray luminosities that span a wide range, from 10^40 erg/s to above 10^44 erg/s. Out of the remaining 66 galaxies, which are instead diagnosed as SF, we find a bimodal distribution in which 28 have X-ray luminosities in excess of 10^42 erg/s, large T (>1), and large X/O ratio (>0.1), while the rest are consistent with being simply SF galaxies. Those 28 galaxies exhibit the broadest Hb line FWHMs, from ~300 to 1200 km/s, and their X-ray spectrum is steeper than average and often displays a soft excess. We therefore conclude that the population of X-ray luminous NELGs with optical lines consistent with those of a starforming galaxy (which represent 19% of our whole sample) is largely dominated by NLS1s. The occurrence of such sources in the overall optically selected sample is small (<2%), hence the contamination of optically selected galaxies by NLS1s is very small.
We use samples of local main-sequence stars to show that the radial gradient of [Fe/H] in the thin disk of the Milky Way decreases with mean effective stellar temperature. Many of these stars are visiting the solar neighborhood from the inner and outer Galaxy. We use the angular momentum of each star about the Galactic center to determine the guiding center radius and to eliminate the effects of epicyclic motion, which would otherwise blur the estimated gradients. We interpret the effective temperature as a proxy for mean age, and conclude that the decreasing gradient is consistent with the predictions of radial mixing due to transient spiral patterns. We find some evidence that the trend of decreasing gradient with increasing mean age breaks to a constant gradient for samples of stars whose main-sequence life-times exceed the likely age of the thin disk.
Experiments showing a seasonal variation of the nuclear decay rates of a number of different nuclei, and decay anomalies apparently related to solar flares and solar rotation, have suggested that the Sun may somehow be influencing nuclear decay processes. Recently, Cooper searched for such an effect in $^{238}$Pu nuclei contained in the radioisotope thermoelectric generators (RTGs) on board the Cassini spacecraft. In this paper we modify and extend Cooper's analysis to obtain constraints on anomalous decays of $^{238}$Pu over a wider range of models, but these limits cannot be applied to other nuclei if the anomaly is composition-dependent. We also show that it may require very high sensitivity for terrestrial experiments to discriminate among some models if such a decay anomaly exists, motivating the consideration of future spacecraft experiments which would require less precision.
The presence of ferromagnetic or ferrimagnetic nanoparticles in the interstellar medium would give rise to magnetic dipole radiation at microwave and submm frequencies. Such grains may account for the strong mm-wavelength emission observed from a number of low-metallicity galaxies, including the Small Magellanic Cloud. We show how to calculate the absorption and scattering cross sections for such grains, with particular attention to metallic Fe, magnetite Fe3O4, and maghemite gamma-Fe2O3, all potentially present in the interstellar medium. The rate of Davis-Greenstein alignment by magnetic dissipation is also estimated. We determine the temperature of free-flying magnetic grains heated by starlight and we calculate the polarization of the magnetic dipole emission from both free-fliers and inclusions. For inclusions, the magnetic dipole emission is expected to be polarized orthogonally relative to the normal electric dipole radiation. Finally, we present self-consistent dielectric functions for metallic Fe, magnetite Fe3O4, and maghemite gamma-Fe2O3, enabling calculation of absorption and scattering cross sections from microwave to X-ray wavelengths.
We present an analysis of the maximum light, near ultraviolet (NUV; 2900-5500 A) spectra of 32 low redshift (0.001<z<0.08) Type Ia supernovae (SNe Ia), obtained with the Hubble Space Telescope (HST). We combine this spectroscopic sample with high-quality gri light curves obtained with robotic telescopes to measure photometric parameters, such as stretch, optical colour, and brightness. By comparing our data to a comparable sample of SNe Ia at intermediate-z (0.4<z<0.9), we detect modest spectral evolution (3-sigma), in the sense that our mean low-z NUV spectrum has a depressed flux compared to its intermediate-z counterpart. We also see a strongly increased dispersion about the mean with decreasing wavelength, confirming the results of earlier surveys. These trends are consistent with changes in metallicity as predicted by contemporary SN Ia spectral models. We also examine the properties of various NUV spectral diagnostics in the individual spectra. We find a general correlation between stretch and the velocity (or position) of many NUV spectral features. In particular, we observe that higher stretch SNe have larger Ca II H&K velocities, that also correlate with host galaxy stellar mass. This latter trend is probably driven by the well-established correlation between stretch and stellar mass. We find no trends between UV spectral features and optical colour. Mean spectra constructed according to whether the SN has a positive or negative Hubble residual show very little difference at NUV wavelengths, indicating that the NUV evolution and variation we identify do not directly correlate with Hubble residuals. Our work confirms and strengthens earlier conclusions regarding the complex behaviour of SNe Ia in the NUV spectral region, but suggests the correlations we find are more useful in constraining progenitor models than improving the use of SNe Ia as cosmological probes.
We report on the results from observations of the most recent outbursts of XTE J1739-302 and IGR J17544-2619, which are considered to be the prototypes of the supergiant fast X-ray transient (SFXT) class. They triggered the Swift/BAT on 2011 February 22 and March 24, respectively, and each time a prompt Swift slew allowed us to obtain the rich broad-band data we present. The XRT light curves show the descending portion of very bright flares that reached luminosities of ~2x10^{36} and ~5x10^{36} erg/s, respectively. The broad-band spectra, when fit with the usual phenomenological models adopted for accreting neutron stars, yield values of both high energy cut-off and e-folding energy consistent with those obtained from previously reported outbursts from these sources. In the context of more physical models, the spectra of both sources can be well fitted either with a two-blackbody model, or with a single unsaturated Comptonization model. In the latter case, the model can be either a classical static Comptonization model, such as COMPTT, or the recently developed COMPMAG model, which includes thermal and bulk Comptonization for cylindrical accretion onto a magnetized neutron star. We discuss the possible accretion scenarios derived by the different models, and we also emphasize the fact that the electron density derived from the Comptonization models, in the regions where the X-ray spectrum presumably forms, is lower than that estimated using the continuity equation at the magnetospheric radius and the source X-ray luminosity, and we give some possible explanations.
The transneptunian objects (TNOs) trapped in mean-motion resonances with Neptune were likely emplaced there during planet migration late in the giant-planet formation process. We perform detailed modelling of the resonant objects detected in the Canada-France Ecliptic Plane Survey (CFEPS) in order to provide population estimates and, for some resonances, constrain the complex internal orbital element distribution. Detection biases play a critical role because phase relationships with Neptune make object discovery more likely at certain longitudes. This paper discusses the 3:2, 5:2, 2:1, 3:1, 5:1, 4:3, 5:3, 7:3, 5:4, and 7:4 mean-motion resonances, all of which had CFEPS detections, along with our upper limit on 1:1 Neptune Trojans (which is consistent with their small population estimated elsewhere). For the plutinos (TNOs in the 3:2 resonance) we refine the orbital element distribution given in Kavelaars et al. (2009) and show that steep H-magnitude distributions (N(H) proportional to 10aH, with a=0.8-0.9) are favoured in the range Hg=8-9, and confirm that this resonance does not share the inclination distribution of the classical Kuiper Belt. We give the first population estimate for the 5:2 resonance and find that, to within the uncertainties, the population is equal to that of the 3:2 (13,000 TNOs with Hg < 9.16), whereas the 2:1 population is smaller by a factor of 3-4 compared to the other two resonances. We also measure significant populations inhabiting the 4:3, 5:3, 7:3, 5:4, 7:4, 3:1, and 5:1 resonances, with Hg < 9.16 (D >100 km) populations in the thousands. We compare our intrinsic population and orbital-element distributions with several published models of resonant-TNO production; the most striking discrepancy is that resonances beyond the 2:1 are in reality more heavily populated than in published models.
We present 16-GHz AMI SZ observations of 19 clusters with L_X >7x10^37 W (h50=1) selected from the LoCuS survey (0.142<z<0.295) and of A1758b, in the FoV of A1758a. We detect 17 clusters with 5-23sigma peak surface brightnesses. Cluster parameters are obtained using a Bayesian cluster analysis. We fit isothermal beta-models to our data and assume the clusters are virialized (with all the kinetic energy in gas internal energy). Our gas temperature, T_AMI, is derived from AMI SZ data, not from X-ray spectroscopy. Cluster parameters internal to r500 are derived assuming HSE. We find: (i) Different gNFW parameterizations yield significantly different parameter degeneracies. (ii) For h70 = 1, we find the virial radius r200 to be typically 1.6+/-0.1 Mpc and the total mass M_T(r200) typically to be 2.0-2.5xM_T(r500).(iii) Where we have found M_T X-ray (X) and weak-lensing (WL) values in the literature, there is good agreement between WL and AMI estimates (with M_{T,AMI}/M_{T,WL} =1.2^{+0.2}_{-0.3} and =1.0+/-0.1 for r500 and r200, respectively). In comparison, most Suzaku/Chandra estimates are higher than for AMI (with M_{T,X}/M_{T,AMI}=1.7+/-0.2 within r500), particularly for the stronger mergers.(iv) Comparison of T_AMI to T_X sheds light on high X-ray masses: even at large r, T_X can substantially exceed T_AMI in mergers. The use of these higher T_X values will give higher X-ray masses. We stress that large-r T_SZ and T_X data are scarce and must be increased. (v) Despite the paucity of data, there is an indication of a relation between merger activity and SZ ellipticity. (vi) At small radius (but away from any cooling flow) the SZ signal (and T_AMI) is less sensitive to ICM disturbance than the X-ray signal (and T_X) and, even at high r, mergers affect n^2-weighted X-ray data more than n-weighted SZ, implying significant shocking or clumping or both occur even in the outer parts of mergers.
The spectral distribution of field white dwarfs shows a feature called the "non-DA gap". As defined by Bergeron et al., this is a temperature range (5100K--6100K) where relatively few non-DA stars are found, even though such stars are abundant on either side of the gap. It is usually viewed as an indication that a significant fraction of white dwarfs switch their atmospheric compositions back and forth between hydrogen-rich and helium-rich as they cool. In this paper, we present a Monte Carlo model of the Galactic disk white dwarf population, based on the spectral evolution model of Chen and Hansen. We find that the non-DA gap emerges naturally, even though our model only allows white dwarf atmospheres to evolve monotonically from hydrogen-rich to helium-rich through convective mixing. We conclude by discussing the effects of convective mixing on the white dwarf luminosity function and the use thereof for Cosmochronology.
We present multi-wavelength observations of the afterglow of the short GRB111117A, and follow-up observations of its host galaxy. From rapid optical and radio observations we place limits of r \gtrsim 25.5 mag at \deltat \approx 0.55 d and F_nu(5.8 GHz) < 18 \muJy at \deltat \approx 0.50 d, respectively. However, using a Chandra observation at t~3.0 d we locate the absolute position of the X-ray afterglow to an accuracy of 0.22" (1 sigma), a factor of about 6 times better than the Swift-XRT position. This allows us to robustly identify the host galaxy and to locate the burst at a projected offset of 1.25 +/- 0.20" from the host centroid. Using optical and near-IR observations of the host galaxy we determine a photometric redshift of z=1.3 (+0.3,-0.2), one of the highest for any short GRB, and leading to a projected physical offset for the burst of 10.5 +/- 1.7 kpc, typical of previous short GRBs. At this redshift, the isotropic gamma-ray energy is E_{gamma,iso} \approx 3\times10^51 erg (rest-frame 23-2300 keV) with a peak energy of E_{pk} \approx 850-2300 keV (rest-frame). In conjunction with the isotropic X-ray energy, GRB111117A appears to follow our recently-reported E_x,iso-E_gamma,iso-E_pk universal scaling. Using the X-ray data along with the optical and radio non-detections we find that for a blastwave kinetic energy of E_{K,iso} \approx E_{gamma,iso}, the circumburst density is n_0 \sim 3x10^(-4)-1 cm^-3 (for a range of epsilon_B=0.001-0.1). Similarly, from the non-detection of a break in the X-ray light curve at t<3 d, we infer a minimum opening angle for the outflow of theta_j> 3-10 degrees (depending on the circumburst density). We conclude that Chandra observations of short GRBs are effective at determining precise positions and robust host galaxy associations in the absence of optical and radio detections.
The neutrino-driven explosion mechanism for core-collapse supernovae in its modern flavor relies on the additional support of hydrodynamical instabilities in achieving shock revival. Two possible candidates, convection and the so-called standing accretion shock instability (SASI), have been proposed for this role. In this paper, we discuss new successful simulations of supernova explosions that shed light on the relative importance of these two instabilities. While convection has so far emerged as the primary agent in self-consistent hydrodynamical models with multi-group neutrino transport, we here present the first such simulation in which the SASI grows faster while the development of convection is initially inhibited. We illustrate the features of this SASI-dominated regime using an explosion model of a 27 solar mass progenitor, which is contrasted with a convectively-dominated model of an 8.1 solar mass progenitor with subsolar metallicity, whose early post-bounce behavior is more in line with previous 11.2 and 15 solar mass explosion models. We analyze the conditions discriminating between the two different regimes, showing that a high mass-accretion rate and a short advection time-scale are conducive for strong SASI activity. We also briefly discuss some important factors for capturing the SASI-driven regime, such as general relativity, the progenitor structure, a nuclear equation of state leading to a compact proto-neutron star, and the neutrino treatment. Finally, we evaluate possible implications of our findings for 2D and 3D supernova simulations.
We present spectroscopic confirmation of a z=0.99 galaxy cluster discovered using data from the Wide-field Infrared Survey Explorer (WISE). This is the first z~1 cluster candidate from the Massive Distant Clusters of WISE Survey (MaDCoWS) to be confirmed. It was selected as a significant overdensity of probable z>~1 sources using the WISE catalog combined with relatively-shallow optical catalogs. Deep follow-up imaging data from Subaru and WIYN reveal the cluster to be a rich system of galaxies, and multi-object spectroscopic observations from Keck confirm five cluster members at z=0.99. The detection and confirmation of this cluster represents a first step towards constructing a uniformly-selected sample of distant, high-mass galaxy clusters over the full extragalactic sky using WISE data.
Parikh and Wilczek have shown that Hawking radiation's spectrum cannot be strictly thermal. Such a non-strictly thermal character implies that the spectrum is also not strictly continuous and thus generates a natural correspondence between Hawking radiation and black hole's quasinormal modes. This issue endorses the idea that, in an underlying unitary quantum gravity theory, black holes result highly excited states. We use this key point to re-analyze the spectrum of black hole's quasinormal modes by introducing a black hole's effective temperature. Our analysis changes the physical understanding of such a spectrum and enables a re-examination of various results in the literature which realizes important modifies on quantum physics of black holes. In particular, the formula of the horizon's area quantization and the number of quanta of area are modified becoming functions of the quantum "overtone" number n. Consequently, Bekenstein-Hawking entropy, its sub-leading corrections and the number of microstates, i.e. quantities which are fundamental to realize unitary quantum gravity theory, are also modified. They become functions of the quantum overtone number too. Previous results in the literature are re-obtained in the very large n limit.
Motivated by a recent work [arXiv:1111.0888], in this paper we have examined the validity of linear perturbation theory near bounce in covariant analysis. Some linearity parameters are defined to set up conditions for linear theory. Linear evolution of density perturbation and gravitational waves have been computed previously. We have calculated the vector and scalar induced part of the shear tensor. It has been shown for radiation-like and dust-like single fluid dominated collapsing FLRW background, that the linearity conditions are not satisfied near bounce.
Cosmological magnetic fields in open Friedmann universes can experience superadiabatic amplification within the realm of conventional electromagnetism. This is possible mathematically, despite the conformal invariance of Maxwell's equations, because Friedmann spacetimes with non-Euclidean spatial geometry are not globally conformal to Minkowski space. Physically, this means that even universes that are marginally open today can sustain large-scale magnetic fields that are substantially stronger than previously anticipated. In the present article, we investigate this purely geometric amplification mechanism in greater detail, focusing on the early evolution of the electromagnetic modes in inflationary Friedmann models with hyperbolic spatial geometry. This also allows us to refine the earlier numerical estimates and provide the current spectrum of the residual, superadiabatically amplified magnetic field.
Numerous claims in the literature suggest that gravity induced on a higher co-dimensional surface violates unitarity in the weak coupling regime. However, it remained unclear, why a conserved source localized on this surface and giving rise to an induced gravity term at low energies would absorb and emit the associated ghost, given a consistent source-free theory. In this article it is shown that the appearance of the induced Einstein Hilbert term does not threaten the unitarity of the theory. The physics arguments behind this statement are presented in a semi-covariant language, but the detailed proof is given using Dirac's constraint analysis. It is shown that the would-be ghost highlighted in previous works is non-dynamical and therefore not associated with a state in the Hilbert space. As a result of these investigations, brane induced gravity goes without a ghost, opening an exciting window of opportunity for consistent deformations of gravity at the largest observable distances.
Recent reports of a gamma-ray line feature at ~130 GeV in data from the Fermi Gamma-Ray Space Telescope have generated a great deal of interest in models in which dark matter particles annihilate with a sizable cross section to final states including photons. In this article, we take a model-independent approach, and discuss a number of possibilities for dark matter candidates which could potentially generate such a feature. While we identify several scenarios which could lead to such a gamma-ray line, these models are each fairly constrained. In particular, viable models require large couplings (g>1-3), and additional charged particles with masses in the range of approximately ~130-200 GeV. Furthermore, lower energy gamma-ray constraints from the Galactic Center force us to consider scenarios in which the dark matter annihilates in the early universe through velocity-suppressed processes, or to final states which yield relatively few gamma-rays (such as electrons, muons or neutrinos). An exception to these conclusions can be found in models in which the dark matter annihilates to heavy intermediate states which decay to photons to generate a line-like gamma-ray spectrum.
n-DBI gravity is a gravitational theory which yields near de Sitter inflation spontaneously at the cost of breaking Lorentz invariance by a preferred choice of foliation. We show that this breakdown endows n-DBI gravity with one extra physical gravitational degree of freedom: a scalar graviton. Its existence is established by Dirac's theory of constrained systems. Firstly, studying scalar perturbations around Minkowski space-time, we show that there exists one scalar degree of freedom and identify it in terms of the metric perturbations. Then, a general analysis is made in the canonical formalism, using ADM variables. It is useful to introduce an auxiliary scalar field, which allows recasting n-DBI gravity in an Einstein-Hilbert form but in a Jordan frame. Identifying the constraints and their classes we confirm the existence of an extra degree of freedom in the full theory, besides the two usual tensorial modes of the graviton. We then argue that, unlike the case of (the original proposal for) Horava-Lifschitz gravity, there is no evidence that the extra degree of freedom originates pathologies, such as vanishing lapse, instabilities and strong self-coupling at low energy scales.
The equation of state (EOS) of dense matter has been a long-sought goal of nuclear physics. Equations of state generate unique mass versus radius (M-R) relations for neutron stars, the ultra-dense remnants of stellar evolution. In this work, we determine the neutron star mass-radius relation and, based on recent observations of both transiently accreting and bursting sources, we show that the radius of a 1.4 solar mass neutron star lies between 10.4 and 12.9 km, independent of assumptions about the composition of the core. We show, for the first time, that these constraints remain valid upon removal from our sample of the most extreme transient sources or of the entire set of bursting sources; our constraints also apply even if deconfined quark matter exists in the neutron star core. Our results significantly constrain the dense matter EOS and are, furthermore, consistent with constraints from both heavy-ion collisions and theoretical studies of neutron matter. We predict a relatively weak dependence of the symmetry energy on the density and a value for the neutron skin thickness of lead which is less than 0.20 fm, results that are testable in forthcoming experiments.
The Casimir-Polder interaction potential is evaluated for a polarizable microparticle and a conducting wall in the geometry of a cosmic string perpendicular to the wall. The general case of the anisotropic polarizability tensor for the microparticle is considered. The corresponding force is a function of the wall-microparticle and cosmic string-microparticle distances. Depending on the orientation of the polarizability tensor principal axes the force can be either attractive or repulsive. The asymptotic behavior of the Casimir-Polder potential is investigated at large and small separations compared to the wavelength of the dominant atomic transitions. We show that the conical defect may be used to control the strength and the sign of the Casimir-Polder force.
Using a semi-analytical approach recently developed to model the tidal deformations of neutron stars in inspiralling compact binaries, we study the dynamical evolution of the tidal tensor, which we explicitly derive at second post-Newtonian order, and of the quadrupole tensor. Since we do not assume a priori that the quadrupole tensor is proportional to the tidal tensor, i.e. the so called "adiabatic approximation", our approach enables us to establish to which extent such approximation is reliable. We find that the ratio between the quadrupole and tidal tensors (i.e., the Love number) increases as the inspiral progresses, but this phenomenon only marginally affects the emitted gravitational waveform. We estimate the frequency range in which the tidal component of the gravitational signal is well described using the stationary phase approximation at next-to-leading post-Newtonian order, comparing different contributions to the tidal phase. We also derive a semi-analytical expression for the Love number, which reproduces within a few percentage points the results obtained so far by numerical integrations of the relativistic equations of stellar perturbations.
Although General Relativity (GR) has been tested extensively in the weak gravity regime, similar tests in the strong gravity regime are still missing. In this paper we explore the possibility to use X-ray spectropolarimetric observations of black holes in X-ray binaries to distinguish between the Kerr metric and the phenomenological metrics introduced by Johannsen and Psaltis (2011) (which are not vacuum solutions of Einstein's equation) and thus to test the no-hair theorem of GR. To this end, we have developed a numerical code that calculates the radial brightness profiles of accretion disks and parallel transports the wave vector and polarization vector of photons through the Kerr and non-GR spacetimes. We used the code to predict the observational appearance of GR and non-GR accreting black hole systems. We find that the predicted energy spectra and energy dependent polarization degree and polarization direction do depend strongly on the underlying spacetime. However, for large regions of the parameter space, the GR and non-GR metrics lead to very similar observational signatures, making it difficult to observationally distinguish between the two types of models.
The center-of-mass energy of two particles colliding near the horizon of a maximally rotating black hole can be arbitrarily high if the angular momentum of either of the incident particles is fine-tuned, which we call a critical particle. We study particle emission from such high-energy collision and reaction in the equatorial plane fully analytically. We show that the unconditional upper limit of the energy of the emitted particle is given by 218.6% of that of the injected critical particle, irrespective of the details of the reaction and this upper limit can be realized for massless particle emission. The upper limit of the energy extraction efficiency for this emission as a collisional Penrose process is given by 146.6%, which can be realized in the collision of two massive particles with optimized mass ratio. Moreover, we analyze perfectly elastic collision, Compton scattering, and pair annihilation and show that net positive energy extraction is really possible for these three reactions. The Compton scattering is most efficient among them and the efficiency can reach 134.3%. On the other hand, our result is qualitatively consistent with the earlier claim that the mass and energy of the emitted particle are at most of order the total energy of the injected particles and hence we can observe neither super-heavy nor super-energetic particle.
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