We compute the Milky Way potential in different cold dark matter (CDM) based models, and compare these with the modified Newtonian dynamics (MOND) framework. We calculate the axis ratio of the potential in various models, and find that isopotentials are less spherical in MOND than in CDM potentials. As an application of these models, we predict the escape velocity as a function of the position in the Galaxy. This could be useful in comparing with future data from planned or already-underway kinematic surveys (RAVE, SDSS, SEGUE, SIM, GAIA or the hypervelocity stars survey). In addition, the predicted escape velocity is compared with the recently measured high proper motion velocity of the Large Magellanic Cloud (LMC). To bind the LMC to the Galaxy in a MOND model, while still being compatible with the RAVE-measured local escape speed at the Sun's position, we show that an external field modulus of less than $0.03 a_0$ is needed.
The discovery ten years ago that the expansion of the Universe is accelerating put in place the last major building block of the present cosmological model, in which the Universe is composed of 4% baryons, 20% dark matter, and 76% dark energy. At the same time, it posed one of the most profound mysteries in all of science, with deep connections to both astrophysics and particle physics. Cosmic acceleration could arise from the repulsive gravity of dark energy -- for example, the quantum energy of the vacuum -- or it may signal that General Relativity breaks down on cosmological scales and must be replaced. We review the present observational evidence for cosmic acceleration and what it has revealed about dark energy, discuss the various theoretical ideas that have been proposed to explain acceleration, and describe the key observational probes that will shed light on this enigma in the coming years.
Here we investigate some aspects of stochastic acceleration of ultrarelativistic electrons by magnetic turbulence. In particular, we discuss the steady-state energy spectra of particles undergoing momentum diffusion due to resonant interactions with turbulent MHD modes, taking rigorously into account direct energy losses connected with different radiative cooling processes. For the magnetic turbulence we assume a given power spectrum of the type $W(k) \propto k^{-q}$. In contrast to the previous approaches, however, we assume a finite range of turbulent wavevectors $k$, consider a variety of turbulence spectral indexes $1 =< q =< 2$, and concentrate on the case of a very inefficient particle escape from the acceleration site. We find that for different cooling and injection conditions, stochastic acceleration processes tend to establish a modified ultrarelativistic Maxwellian distribution of radiating particles, with the high-energy exponential cut-off shaped by the interplay between cooling and acceleration rates. For example, if the timescale for the dominant radiative process scales with the electron momentum as $\propto p^r$, the resulting electron energy distribution is of the form $n_e(p) \propto p^2 exp[ - (1 / a) (p / p_eq)^a]$, where $a = 2-q-r$, and $p_eq$ is the equilibrium momentum defined by the balance between stochastic acceleration and energy losses timescales. We also discuss in more detail the synchrotron and inverse-Compton emission spectra produced by such an electron energy distribution, taking into account Klein-Nishina effects. We point out that the curvature of the high frequency segments of these spectra, even though being produced by the same population of electrons, may be substantially different between the synchrotron and inverse-Compton components.
In this work we show observational evidence supporting a downward revision of the traditional Oxygen abundance on the Sun. We present results of a novel approach based on the analysis of spectro-polarimetric observations which is practically model-independent, and therefore, extremely robust. The asymmetry of the Stokes V profile of the 6300 A [O I] and Ni I blend is used as an indicator of the relative abundances of these two elements. The peculiar shape of the profile is only compatible with a set of values that rules out the traditional O abundance and provides unambiguous evidence in favor of the downward revision.
We explore the properties of the submillijansky radio population at 20 cm by
applying a newly developed optical color-based method to separate star forming
(SF) from AGN galaxies at intermediate redshifts (z<1.3). Although optical
rest-frame colors are used, our separation method is shown to be efficient, and
not biased against dusty starburst galaxies. This classification method has
been calibrated and tested on a local radio selected optical sample. Given
accurate multi-band photometry and redshifts, it carries the potential to be
generally applicable to any galaxy sample where SF and AGN galaxies are the two
dominant populations.
In order to quantify the properties of the submillijansky radio population,
we have analyzed ~2,400 radio sources, detected at 20 cm in the VLA-COSMOS
survey. 90% of these have submillijansky flux densities. We classify the
objects into 1) star candidates, 2) quasi stellar objects, 3) AGN, 4) SF, and
5) high redshift (z>1.3) galaxies. We find, for the composition of the
submillijansky radio population, that SF galaxies are not the dominant
population at submillijansky flux levels, as previously often assumed, but that
they make up an approximately constant fraction of 30-40% in the flux density
range of ~50 microJy to 0.7 mJy. In summary, based on the entire VLA-COSMOS
radio population at 20 cm, we find that the radio population at these flux
densities is a mixture of roughly 30-40% of SF and 50-60% of AGN galaxies, with
a minor contribution (~10%) of QSOs.
We study zCOSMOS-bright optical spectra for 609 Spitzer/MIPS 24 micron-selected galaxies with S(24um)> 0.30 mJy and I<22.5 (AB mag) over 1.5 sq. deg. of the COSMOS field. From emission-line diagnostics we find that: 1) star-formation rates (SFR) derived from the observed Halpha and Hbeta lines underestimate, on average, the total SFR by factors ~5 and 10, respectively; 2) both the Calzetti et al. and the Milky Way reddening laws are suitable to describe the extinction observed in infrared (IR) sources in most cases; 3) some IR galaxies at z<0.3 have low abundances, but many others with similar IR luminosities and redshifts are chemically enriched; 4) The average [OIII]/Hbeta ratios of nuLnu(24um)>10^11 Lsun galaxies at 0.6<z<0.7 are ~0.6 dex higher than the average ratio of all zCOSMOS galaxies at similar redshifts. Massive star formation and active galactic nuclei (AGN) could simultaneously be present in those galaxies with the highest ionising fluxes; 5) ~1/3 of the galaxies with metallicity measurements at 0.5<z<0.7 lie below the general mass-metallicity relation at the corresponding redshifts. The strengths of the 4000 Angstrom break and the Hdelta EW of our galaxies show that secondary bursts of star formation are needed to explain the spectral properties of most IR sources. The LIRG and ULIRG phases occur, on average, between 10^7 and 10^8 years after the onset of a starburst on top of underlying older stellar populations. These results are valid for galaxies of different IR luminosities at 0.6<z<1.0 and seem independent of the mechanisms triggering star formation.
We have already reported the first result on the all-particle spectrum around the knee region based on data from 2000 November to 2001 October observed by the Tibet-III air-shower array. In this paper, we present an updated result using data set collected in the period from 2000 November through 2004 October in a wide range over 3 decades between $10^{14}$ eV and $10^{17}$ eV, in which the position of the knee is clearly seen at around 4 PeV. The spectral index is -2.68 $\pm$ 0.02(stat.) below 1PeV, while it is -3.12 $\pm$ 0.01(stat.) above 4 PeV in the case of QGSJET+HD model, and various systematic errors are under study now.
This paper provides a concise summary of the current status of the research and future perspectives discussed in the Mini-Conference on Angular Momentum Transport in Laboratory and Nature. This Mini-conference, sponsored by the Topical Group on Plasma Astrophysics, was held as part of the American Physical Society's Division of Plasma Physics 2007 Annual Meeting (November 12--16, 2007). This Mini-conference covers a wide range of phenomena happening in fluids and plasmas, either in laboratory or in nature. The purpose of this paper is not to comprehensively review these phenomena, but to provide a starting point for interested readers to refer to related research in areas other than their own.
We present a census of circumstellar disks in the Chamaeleon I star-forming region. Using the Infrared Array Camera and the Multiband Imaging Photometer onboard the Spitzer Space Telescope, we have obtained images of Chamaeleon I at 3.6, 4.5, 5.8, 8.0, and 24 um. To search for new disk-bearing members of the cluster, we have performed spectroscopy on objects that have red colors in these data. Through this work, we have discovered four new members of Chamaeleon I with spectral types of M4, M6, M7.5, and L0. The first three objects are highly embedded (A_J~5) and reside near known protostars, indicating that they may be among the youngest low-mass sources in the cluster (<1 Myr). The L0 source is the coolest known member of Chamaeleon I. Its luminosity implies a mass of 0.004-0.01 M_sun, making it the least massive brown dwarf for which a circumstellar disk has been reliably detected. To characterize the disk population in Chamaeleon I, we have classified the infrared spectral energy distributions of the 203 known members that are encompassed by the Spitzer images. Through these classifications, we find that the disk fraction in Chamaeleon I is roughly constant at ~50% from 0.01 to 0.3 M_sun. These data are similar to the disk fraction of IC 348, which is a denser cluster at the same age as Chamaeleon I. However, the disk fraction at M>1 M_sun is significantly higher in Chamaeleon I than in IC 348 (65% vs. 20%), indicating longer disk lifetimes in Chamaeleon I for this mass range. Thus, low-density star-forming regions like Chamaeleon I may offer more time for planet formation around solar-type stars than denser clusters.
We construct a steady analytic accretion flow model for a finite rotating gas cloud that accretes material to a central gravitational object. The pressure gradients of the flow are considered to be negligible and so, the flow is ballistic. We also assumme a steady flow and consider the particles at the boundary of the spherical cloud to be rotating as a rigid body, with a fixed amount of inwards radial velocity. This represents a generalisation of the traditional infinite gas cloud model described by Ulrich (1976). We show that the fluid particles are no longer parabollic, instead they could be any conical section which depends on the specific initial boundary conditions of the flow. Naturally, the model predicts the formation of an equatorial accretion disc about the central object with a radius different from the one calculated by Ulrich (1976).
We present the results of a variable stars search in the field of the old open cluster NGC 2204. Five new variables were found, four of them being eclipsing binaries. The sample includes a detached binary located at the turnoff, a W UMa - type system, and an interesting detached low-mass binary with a period of 0.45d which, however, is a foreground object. We provide V-light curves and finder charts for all variables together with color-magnitude diagrams of the cluster. For four variables incomplete I-light curves are also provided.
Ram pressure stripping, i.e. the removal of a galaxy's gas disk due to its motion through the intracluster medium of a galaxy cluster, appears to be a common phenomenon. Not every galaxy, however, is completely stripped of its gas disk. If the ram pressure is insufficiently strong, only the outer parts of the gas disk are removed, and the inner gas disk is retained by the galaxy. One example of such a case is the Virgo spiral NGC 4402. Observations of NGC 4402 (Crowl et al. 2005) reveal structures at the leading edge of the gas disk, which resemble the characteristic finger-like structures produced by the Rayleigh-Taylor (RT) instability. We argue, however, that the RT instability is unlikely to be responsible for these structures. We demonstrate that the conditions under which a galaxy's disk gas experiences ram pressure stripping are identical to those that lead to RT instability. If the galaxy's gravity prevents ram pressure stripping of the inner disk, it also prevents the RT instability. In contrast, the stripped gas could still be subject to RT instability, and we discuss consequences for the stripped gas.
AIMS :The thermodynamic and magnetic field structure of the solar photosphere is analyzed by means of a novel 3-dimensional spectropolarimetric inversion and reconstruction technique. METHODS : On the basis of high-resolution, mixed-polarity magnetoconvection simulations, we used an artificial neural network (ANN) model to approximate the nonlinear inverse mapping between synthesized Stokes spectra and the underlying stratification of atmospheric parameters like temperature, line-of-sight (LOS) velocity and LOS magnetic field. This approach not only allows us to incorporate more reliable physics into the inversion process, it also enables the inversion on an absolute geometrical height scale, which allows the subsequent combination of individual line-of-sight stratifications to obtain a complete 3-dimensional reconstruction (tomography) of the observed area. RESULTS : The magnetoconvection simulation data, as well as the ANN inversion, have been properly processed to be applicable to spectropolarimetric observations from the Hinode satellite. For the first time, we show 3-dimensional tomographic reconstructions (temperature, LOS velocity, and LOS magnetic field) of a quiet sun region observed by Hinode. The reconstructed area covers a field of approximately 12000 by 12000 km and a height range of 510 km in the photosphere. An enormous variety of small and large scale structures can be identified in the 3-D reconstructions. The low-flux region (B_{mag} = 20G) we analyzed exhibits a number of "tube-like" magnetic structures with field strengths of several hundred Gauss. Most of these structures rapidly loose their strength with height and only a few larger structures can retain a higher field strength to the upper layers of the photosphere.
Here we discuss the effects of strong gravity that can be observed in electromagnetic spectra of active galactic nuclei (AGN). According to the unification model of an AGN, there is a supermassive black hole ($10^7 - 10^9 M_\odot$) in its center, surrounded by an accretion disk that radiates in the X-ray band. Accretion disks could have different forms, dimensions, and emission, depending on the type of central black hole (BH), whether it is rotating (Kerr metric) or nonrotating (Schwarzschild metric). We modeled the emission of an accretion disk around supermassive BH using numerical simulations based on a ray-tracing method in the Kerr metric. A broad emission line Fe K$\alpha$ at 6.4 keV with asymmetric profile (narrow bright blue peak and a wide faint red wing) has been observed in a number of type 1 AGN. The effects of strong gravitational field are investigated by comparison between the modeled and observed iron K$\alpha$ line profiles. The results of our modeling show that the parameters of the Fe K$\alpha$ line emitting region have significant influence on the line profile and thus, allow us to determine the space-time geometry (metric) in vicinity of the central BH of AGN, and also can give us information about the plasma conditions in these regions.
We present a theoretical model fit to the HST/STIS optical transit transmission spectra of HD209458b. In our fit, we use the sodium absorption line profile along with the Rayleigh scattering by H2 to determine the average temperature-pressure profile at the planetary terminator, and infer the abundances of atomic and molecular species. The observed sodium line profile spans an altitude range of ~3,500 km, corresponding to pressures between ~0.001 and 50 mbar in our atmospheric model. We find that the sodium line profile requires condensation at pressures lower than ~3 mbar, presumably into sodium sulfide, depleting atomic sodium only at high altitudes. The condensation of sodium is supported by an observed sudden abundance change, from 2 times solar abundance in the lower atmosphere to 0.2 in the upper atmosphere, within a low temperature region which falls below that of the chemical equilibrium condensation curve of sodium sulfide. Our findings also indicate the presence of a hot atmosphere near stratospheric altitudes corresponding to pressures of ~30 mbar, consistent with that of the observed dayside temperature inversion. In addition, we find a separate higher altitude temperature rise, corresponding to pressures around ~0.01 mbar. This higher altitude temperature rise indicates that absorption by atomic sodium can potentially probe the bottom of the thermosphere, and might possibly be sensitive to the temperature rise linked with atmospheric escape.
In our SCUBA survey of Perseus, we find that the fraction of protostellar cores increases towards higher masses and the most massive cores are all protostellar. In this paper we consider the possible explanations of this apparent mass dependence in the evolutionary status of these cores, and the implications for protostellar evolution and the mapping of the embedded core mass function (CMF) onto the stellar IMF. We consider the following potential causes: dust temperature; selection effects in the submillimetre and in the mid-infrared observations used for pre/protostellar classification; confusion and multiplicity; transient cores; and varying evolutionary timescales. We develop Core Mass Evolution Diagrams (CMEDs) to investigate how the mass evolution of individual cores maps onto the observed CMF. Two physical mechanisms -- short timescales for the evolution of massive cores, and continuing accumulation of mass onto protostellar cores -- best explain the relative excess of protostars in high mass cores and the rarity of massive starless cores. In addition, confusion both increases the likelihood that a protostar is identified within a core, and increases mass assigned to a core. The observed pre/protostellar mass distributions are consistent with faster evolution and a shorter lifetime for higher-mass prestellar cores. We rule out longer timescales for higher-mass prestellar cores. The differences in the prestellar and protostellar mass distributions imply that the prestellar CMF (and possibly the combined pre+protostellar CMF) should be steeper than the IMF. A steeper prestellar CMF can be reconciled with the observed similarity of the CMF and the IMF in some regions if a second opposing effect is present, such as the fragmentation of massive cores into multiple systems.
We have performed a spectroscopic study of globular clusters (GCs) in the giant elliptical NGC 5128 using the 2dF facility at the Anglo-Australian telescope. We obtained integrated optical spectra for a total of 254 GCs, 79 of which are newly confirmed on the basis of their radial velocities and spectra. In addition, we obtained an integrated spectrum of the galaxy starlight along the southern major axis. We derive an empirical metallicity distribution function (MDF) for 207 GCs (~14 of the estimated total GC system) based upon Milky Way GCs. This MDF is multimodal at high statistical significance with peaks at [Z/H]~-1.3 and -0.5. A comparison between the GC MDF and that of the stellar halo at 20 kpc (~4 Reff) reveals close coincidence at the metal-rich ends of the distributions. However, an inner 8 kpc stellar MDF shows a clear excess of metal-rich stars when compared to the GCs. We compare a higher S/N subsample (147 GCs) with two stellar population models which include non-solar abundance ratio corrections. The vast majority of our sample (~90%) appears old, with ages similar to the Milky Way GC system. There is evidence for a population of intermediate-age (~4-8 Gy) GCs (<15% of the sample) which are on average more metal-rich than the old GCs. We also identify at least one younger cluster (~1-2 Gy) in the central regions of the galaxy. Our observations are consistent with a picture where NGC 5128 has undergone at least two mergers and/or interactions involving star formation and limited GC formation since z=1, however the effect of non-canonical hot stellar populations on the integrated spectra of GCs remains an outstanding uncertainty in our GC age estimates.
2003 EL61 is the largest member of a group of TNOs with similar orbits and
'unique' spectra (neutral slope in the visible and the deepest water ice
absorption bands ever observed in the TNb). Studying the composition of the
surface of 2003 EL61 provides useful constrains on the origin of this
particular group of TNOs and on the outer Solar system's history.
We present visible and near-infrared spectra of 2003 EL61 obtained with the
4.2m WHT and the 3.6m TNG at the Roque de los Muchachos Observatory (Canary
Islands, Spain). Near infrared spectra were obtained at different rotational
phases covering almost one complete rotational period. Spectra are fitted using
Hapke scattering models and constraints on the surface composition are derived.
No significant variations in the spectral slope and in the depth of the water
ice absorption bands at different rotational phases are evident, suggesting
that the surface of 2003 EL61 is homogeneous. The scattering models show that a
1:1 intimate mixture of crystalline and amorphous water ice is the most
probable composition for the surface of this TNO, and constrain the presence of
other minor constituents to a maximum of 8%
The derived composition suggests that: a) cryovolcanism is unlikely to be the
main resurfacing process responsible for the high presence of water ice on the
surface of these bodies; b) the surface is older than 10^8 yr. Any catastrophic
event, like the collision suggested to be the origin of this population, had to
happen at least 10^8 yr ago; c) the surface of 2003 EL61 is depleted of carbon
chains. According to the orbital parameters of this population, this makes it a
possible source of carbon-depleted Jupiter family comets.
We study cosmological expansion in F(R) gravity using the trace of the field equations. High frequency oscillations in the Ricci scalar, whose amplitude increase as one evolves backward in time, have been predicted in recent works. We show that the approxmiations used to derive this result very quickly breakdown in any realistic model due to the non-linear nature of the underlying problem. Using a combination of numerical and semi-analytic techniques, we study a range of models which are otherwise devoid of known pathogolies. We find that high frequency asymmetric oscillations and a singularity at finite time appear to be present for a wide range of initial conditions. We show that this singularity can be avoided with a certain range of initial conditions, which we find by evolving the models forwards in time. In addition we show that the oscillations in the Ricci scalar are highly suppressed in the Hubble parameter and scale factor.
We construct a new reduced nuclear reaction network able to reproduce the energy production due to the photo-disintegration of heavy elements such as Ru, which are believed to occur during superbursts in mixed H/He accreting systems. We use this network to simulate a detonation propagation, inside a mixture of C/Ru. As our reference, we use a full nuclear reaction network, including 14758 reactions on 1381 nuclides. Until the reduced and full networks converge to a good level of accuracy in the energy production rate, we iterate between the hydrodynamical simulation, with a given reduced network, and the readjustment of a new reduced network, on the basis of previously derived hydrodynamical profiles. We obtain the thermodynamic state of the material after the passage of the detonation, and the final products of the combustion. Interestingly, we find that all reaction lengths can be resolved in the same simulation. This will enable C/Ru detonations to be more easily studied in future multi-dimensional simulations, than pure carbon ones. We underline the dependence of the combustion products on the initial mass fraction of Ru. In some cases, a large fraction of heavy nuclei, such as Mo, remains after the passage of the detonation front. In other cases, the ashes are principally composed of iron group elements.
In this paper I investigate the family of mixed three-point correlation functions <tau^q gamma^{3-q}>, q=0,1,2, between the integrated Sachs-Wolfe (iSW) temperature perturbation tau and the galaxy overdensity gamma as a tool for detecting the gravitational interaction of cosmic microwave background (CMB) photons with the potentials of nonlinearly evolving cosmological structures. Both the iSW-effect as well as the galaxy overdensity are derived in hyper-extended perturbation theory to second order and I emphasise the different parameter sensitivities of the linear and non-linear iSW-effect. I examine the configuration dependence of the relevant bispectra, quantify their sensitivities and discuss their degeneracies with respect to the cosmological parameters Omega_m, sigma_8, h and the dark energy equation of state parameter $w$. I give detection sigificances for combining PLANCK CMB data and the DUNE galaxy sample, by using a quadratic approximation for the likelihood with LambdaCDM as the fiducial cosmology: The combination of PLANCK with DUNE should be able to reach a cumulative signal to noise ratio of ~0.6sigma for the bispectrum <tau gamma^2> up to l=2000, where the most important noise source are the primary CMB fluctuations.
The detection of TeV gamma-rays from LS 5039 and the binary pulsar PSR B1259-63 by HESS, and from LS I +61 303 and the stellar-mass black hole Cygnus X-1 by MAGIC, provides a clear evidence of very efficient acceleration of particles to multi-TeV energies in X-ray binaries. These observations demonstrate the richness of non-thermal phenomena in compact galactic objects containing relativistic outflows or winds produced near black holes and neutron stars. I review here some of the main observational results on very high energy (VHE) gamma-ray emission from X-ray binaries, as well as some of the proposed scenarios to explain the production of VHE gamma-rays. I put special emphasis on the flare TeV emission, suggesting that the flaring activity might be a common phenomena in X-ray binaries.
The search for a luminosity function for galaxies both alternative or companion to a Schechter function is a key problem in the reduction of data from catalogs of galaxies. Two luminosity functions for galaxies can be built starting from two distributions of mass as given by the fragmentation. A first overall distribution function is the Kiang function that represents a useful description of the area and volume distribution of the Poisson Voronoi diagrams. The second distribution, that covers the case of low mass galaxies, is the truncated Pareto distribution : in this model we have a natural bound due to the minimum mass/luminosity observed and an upper bound (function of the considered environment) represented by the boundary with the observed mass/luminosity overall behaviour. The mass distribution is then converted into a luminosity distribution through a standard mass-luminosity relationship.
We construct a family of viable scalar-tensor models of dark energy (DE) which possess a phase of late-time acceleration preceded by a standard matter era, while at the same time satisfying the local gravity constraints (LGC). The coupling Q between the scalar field and the non-relativistic matter in the Einstein frame is assumed to be constant in our scenario, which is a generalization of f(R) gravity theories corresponding to the coupling Q=-1/sqrt{6}. We find that these models can be made compatible with local gravity constraints even when |Q| is of the order of unity through a chameleon mechanism, if the scalar-field potential is chosen to have a sufficiently large mass in the high-curvature regions. We show that these models generally lead to the divergence of the equation of state of DE, which occur at smaller redshifts as the deviation from the LambdaCDM model become more significant. We also study the evolution of matter density perturbations and employ them to place bounds on the coupling |Q| as well as model parameters of the field potential from observations of the matter power spectrum and the CMB anisotropies. We find that, as long as |Q| is smaller than the order of unity, there exist allowed parameter regions that are consistent with both observational and local gravity constraints.
We present the first resolved-star photometry of VV124 (UGC4879) and find that this is the most isolated dwarf galaxy in the periphery of the Local Group. Based on imaging and spectroscopic follow up observations with the 6m BTA telescope, we resolve VV124 into 1560 stars down to the limiting magnitude levels of V~25.6 and I~23.9. The young blue stellar populations and emission gas are found near the core, but noticeably displaced from the center of the galaxy as traced by dominant evolved red stars. The mean radial velocity derived from the spectra of two Blue Supergiant stars, an HII region and unresolved continuum sources is -80+/-10 km/s. The evolved ``red tangle'' stellar populations, which contains the red giant branch (RGB), are identified at large galactocentric radii. We use the I-band luminosity function to determine the distance based on the Tip of RGB method, 1.1+/-0.1 Mpc. This is ~10 times closer than the values usually assumed in the literature, and we provide revised distance dependent parameters. From the mean (V-I) color of the RGB, we estimate the mean metallicity as [Fe/H]~-1.37 dex. Despite of its isolated location, the properties of VV124 are clearly not those of a galaxy in formation, but rather similar to a transitional dIrr/dSph type.
We have investigated multiband optical photometric variability and stability of the H$\alpha$ line profile of the transient X-ray binary IGR J01583+6713. We set an upper limit of 0.05 mag on photometric variations in the {\it V} band over a time scale of 3 months. The H$\alpha$ line is found to consist of non-Gaussian profile and quite stable for a duration of 2 months. We have identified the spectral type of the companion star to be B2 IVe while distance to the source is estimated to be $\sim$ 4.0 kpc. Along with the optical observations, we have also carried out analysis of X-ray data from three short observations of the source, two with the {\it Swift}--XRT and one with the {\it RXTE}--PCA. We have detected a variation in the absorption column density, from a value of 22.0 $\times$ 10$^{22}$ cm$^{-2}$ immediately after the outburst down to 2.6 $\times$ 10$^{22}$ cm$^{-2}$ four months afterwards. In the quiescent state, the X-ray absorption is consistent with the optical reddening measurement of E(B - V) = 1.46 mag. From one of the {\it Swift} observations, during which the X-ray intensity was higher, we have a possible pulse detection with a period of 469.2 s. For a Be X-ray binary, this indicates an orbital period in the range of 216--561 days for this binary system.
We use the HST ACS imaging of the two GOODS fields during Cycles 11, 12, and 13 to derive the Type Ia supernova rate in four redshift intervals in the range 0.2<z<1.8. Compared to our previous results based on Cycle 11 observations only, we have increased the coverage of the search by a factor 2.7, making the total area searched equivalent to one square degree. The sample now consists of 56 Type Ia supernovae. The rates we derive are consistent with our results based on the Cycle 11 observations. In particular, the few detected supernovae at z>1.4 supports our previous result that there is a drop in the Type Ia supernova rate at high redshift, suggesting a long time delay between the formation of the progenitor star and the explosion of the supernova. If described by a simple one-parameter model, we find a characteristic delay time of 2-3 Gyr. However, a number of recent results based on e.g., low redshift supernova samples and supernova host galaxy properties suggest that the supernova delay time distribution is bimodal. In this model, a major fraction of the Type Ia supernova rate is 'prompt' and follows the star formation rate, while a smaller fraction of the rate has a long delay time, making this channel proportional to mass. While our results are fully consistent with the bimodal model at low redshifts, the low rate we find at z>1.4 appears to contradict these results. Models that corrects for star formation hidden by dust may explain at least part of the differences. Here we discuss this possibility together with other ways to reconcile data and models.
Rotation and solar-type magnetic activity are closely related to each other in stars of G or later spectral types. Presence and level of magnetic activity depend on star's rotation and rotation itself is strongly influenced by strength and topology of the magnetic fields. Open clusters represent especially useful targets to investigate the connection between rotation and activity. The open cluster NGC2099 has been studied as a part of the RACE-OC project, which is aimed at exploring the evolution of rotation and magnetic activity in the late-type members of open clusters of different ages. Time series CCD photometric observations of this cluster were collected during January 2004. The relations between activity manifestations, such as the light curve amplitude, and global stellar parameters are investigated. We have discovered 135 periodic variables, 122 of which are candidate cluster members. Determination of rotation periods of G- and K-type stars has allowed us to better explore evolution of angular momentum at an age of about 500 Myr. A comparison with the older Hyades cluster (~625 Myr) shows that the newly determined distribution of rotation periods is consistent with the scenario of rotational braking of main-sequence spotted stars as they age. However, a comparison with the younger M34 cluster (~200 Myr) shows that the G8-K5 members of these clusters have the same rotation period distribution, that is G8-K5 members in NGC2099 seem to have experienced no significant braking in the age range from ~200 to ~500 Myr. Finally, NGC2099 members have a level of photospheric magnetic activity, as measured by light curve amplitude, smaller than in younger stars of same mass and rotation, suggesting that the activity level also depends on some other age-dependent parameters.
Radio, X-ray and gamma-ray observations provide us with strong evidence of particle acceleration to multi-TeV energies in various astrophysical sources. Diffusive Shock Acceleration is one of the most successful models to explain the presence of such high energy particles. We discuss the impact of inverse Compton losses on the shock acceleration of electrons which takes place in radiation dominated environments, i.e. in regions where the radiation energy density exceeds that of the magnetic field. We perform a numerical calculation, including an energy loss term in the transport equation of accelerated particles. We discuss the implications of this effect on the hard X-ray synchrotron and gamma-ray inverse Compton radiation, produced by shock accelerated electrons in young Supernova Remnants in the presence of large radiation fields (e.g. in the Galactic Center). We also discuss possible implications of our results for clusters of galaxies and gamma-ray binaries. We demonstrate that the inverse Compton losses of electrons, in the Klein-Nishina regime, lead to spectra of ultra-relativistic electrons which may significantly differ from classical Diffusive Shock Acceleration solution. The most prominent feature is the appearance of a pile up in the spectrum around the cutoff energy.
An asymmetry index is derived from ellipse-fitting to galaxy images, that gives weight to faint outer features and is not strongly redshift-dependent. These measures are made on a sample of 13 2MASS QSOs and their neighbour galaxies, and a control sample of field galaxies from the same wide-field imaging data. The QSO host galaxy asymmetries correlate well with visual tidal interaction indices previously published. The companion galaxies have somewhat higher asymmetry than the control galaxy sample, and their asymmetry is inversely correlated with distance from the QSO. The distribution of QSO-companion asymmetry indices is different from that for matched control field galaxies at the $\sim95%$ significance level. We present the data and discuss this evidence for tidal and other disturbances in the vicinity of QSOs.
In this paper we analyze the biasing effect of point sources, either thermal Sunyaev-Zeldovich clusters or standard radio sources, on the estimated strength of the non-Gaussianity in the Cosmic Microwave Background (CMB). We show that the biggest contribution comes from the cross--correlation of the CMB with the matter density rather than from the poisson term which is conventionally assumed in these calculations. For the three year WMAP data, we estimate that point sources could produce a non--Gaussian signature equivalent to a bias in $f_{NL}$ of 0.8 in the Ka band and no greater than 0.2 in the V or W bands. For Planck, we estimate the point source bispectra to contaminate the $f_{NL}$ estimator with a bias of 3 at 30 GHz and 0.6 at 100 GHz. These results significantly depend on the assumed redshift distribution of the point sources. The level of bias we find is largely insufficient to explain the very high f_{NL} values recently detected by Yadav and Wandelt. However, given the projected Planck sensitivity of \Delta f_{NL} \simeq 5 (95 % C.L.), a good estimate of point sources' properties including their number density and redshift distribution is essential before deriving strong conclusions on primordial non--Gaussianity.
Although much is known about the nature of winds from hot stars and giants and supergiants with spectral types earlier than K, t here is still much to be learned regarding the mass-loss process in cool, late-type stars. We will review the current state of r esearch, with particular reference to observations and modelling of mass-loss from giant stars in symbiotic systems.
We present the Class I protostellar binary separation distribution based on the data tabulated in the companion paper. We verify the excess of Class I binary stars over solar-type main-sequence stars, especially at separations beyond 500 AU. Although our sources are in nearby star forming regions distributed across the entire sky (including Orion), none of our objects are in a high stellar density environment. The binary separation distribution changes significantly during the Class I phase, and the binary frequency at separations greater than 1000 AU declines steadily with respect to spectral index. Despite these changes, the binary frequency remains constant until the end of the Class I phase, when it drops sharply. We propose a scenario to account for the changes in the Class I binary separation distribution. This scenario postulates that companions with a separation greater than ~1000 AU were ejected during the Class 0 phase, but remain gravitationally bound due to the mass of the envelope. As the envelope dissipates, these companions become unbound and the binary frequency at wide separations declines. This scenario predicts that a large number of Class 0 objects should be non-hierarchical multiple systems, and that many Class I YSOs with a widely separated companion should also have a very close companion. We also find that Class I protostars are not dynamically pristine, and have experienced dynamical evolution before they are visible as Class I objects. For the first time, evidence is presented showing that the Class I binary frequency and the binary separation distribution strongly depend on the star forming environment. The reason for this dependence remains unclear.
A detailed analysis of the evolution of the properties of core-jet systems within the VLBA Imaging and Polarimetry Survey (VIPS) is presented. We find a power-law relationship between jet intensity and width that suggests for the typical jet, little if any energy is lost as it moves away from its core. Using VLA images at 1.5 GHz, we have found evidence that parsec-scale jets tend to be aligned with the the direction of emission on kiloparsec scales. We also found that this alignment improves as the jets move farther from their cores on projected scales as small as ~50-100 pc. This suggests that realignment of jets on these projected scales is relatively common. We typically find a modest amount of bending (a change in jet position angle of ~5 deg.) on these scales, suggesting that this realignment may typically occur relatively gradually.
We present reduced and calibrated high resolution Lyman-alpha (Lya) images for a sample of six local star forming galaxies. Targets were selected to represent a range in luminosity and metallicity and to include both known Lya emitters and non-emitters. Far ultraviolet imaging was carried out with the Solar Blind Channel of the Advanced Camera for Surveys on Hubble Space Telescope in the F122M (Lya on-line) and F140LP (continuum) filters. The resulting Lya images are the product of careful modeling of both the stellar and nebular continua, facilitated by supporting HST imaging at lambda=2200, 3300, 4400, 5500, H-alpha and 8000AA, combined with Starburst 99 evolutionary synthesis models. In all, the resulting morphologies in Lya, Ha, and UV-continuum are qualitatively very different and we show that the bulk of Lya emerges in a diffuse component resulting from resonant scattering events. Lya escape fractions, computed from Ha luminosities and recombination theory, are found never to exceed 14%. Even after corrections for internal dust extinction, the highest escape fraction in the sample is found to be 40%, with the remainder falling significantly short of the case B ratio. The images presented have a physical resolution 3 orders of magnitude better than attainable at high redshifts from the ground with current instrumentation and our images may therefore serve as useful templates for comparing with observations and modeling of primeval galaxy formation. We therefore provide the reduced Lya, Ha, and continuum images to the community.
(Abridged) We are undertaking an imaging study of local star-forming galaxies in the Lyman-alpha (Lya) emission line using the Solar Blind Channel (SBC) of the ACS onboard HST. Observations have been obtained in Lya and H-alpha and six line-free continuum filters between ~1500 AA and the I-band. In a previous article Hayes et al. (2005) we demonstrated that the production of Lya line-only images (i.e. continuum subtraction) in the SBC-only data-set is non-trivial and that supporting data is a requirement. We here develop various methods of continuum subtraction and assess their relative performance for given input spectral energy distributions (SED). We show that simple assumptions about the behavior of the UV continuum consistently lead to results that are significantly in error, and determine that a spectral fitting approach is essential. Furthermore, fitting of a single component stellar or stellar+nebular spectrum is not always sufficient for realistic template SEDs and, in order to successfully recover the input observables, care must be taken to control the contribution of nebular gas and any underlying stellar population. Independent measurements of the metallicity must first be obtained, while details of the initial mass function play only a small role. We identify the need to bin together pixels to obtain signal--to--noise (S/N) ratios of around 10 in each band before processing. At S/N=10 we are able to recover Lya fluxes accurate to within ~30% for Lya lines with intrinsic equivalent width W(Lya) of 10AA. This accuracy improves to <~10% for W(Lya)=100 AA. We describe the image processing applied to the observations presented in \"Ostlin et al. (2008) and the associated data-release. We also present simulations for an observing strategy for a future low-z Lya imaging campaign using ACS/SBC.
We discuss selection of QSO candidates from the combined SDSS and GALEX catalogues. We discuss properties of QSOs within the combined sample, and note uncertainties in number counts and completeness, compared with other SDSS-based samples. We discuss colour and other properties with redshift within the sample and the SEDs for subsets. We estimate the numbers of faint QSOs that are classified as extended objects in the SDSS, and consequent uncertainties that follow.
We present a study of the radial distribution of RR Lyrae variables, which present a range of photometric and pulsational properties, in the dwarf spheroidal galaxy Tucana. We find that the fainter RR Lyrae stars, having a shorter period, are more centrally concentrated than the more luminous, longer period RR Lyrae variables. Through comparison with the predictions of theoretical models of stellar evolution and stellar pulsation, we interpret the fainter RR Lyrae stars as a more metal-rich subsample. In addition, we show that they must be older than about 10 Gyr. Therefore, the metallicity gradient must have appeared very early on in the history of this galaxy.
Broadband femtosecond-laser frequency combs are filtered to spectrographically resolvable frequency-mode spacing, and the limitations of using cavities for spectral filtering are considered. Data and theory are used to show implications to spectrographic calibration of high-resolution, astronomical spectrometers.
We study the multi-wavelength signal induced by pairs annihilations at the Galactic center (GC) of a recently proposed dark matter (DM) candidate. The weakly interacting massive particle (WIMP) candidate, named A_, is the first Kaluza-Klein mode of a five dimensional abelian gauge boson. Electroweak precision tests and the DM cosmological bound constrain its mass and pair annihilation rate in small ranges, leading to precise predictions of indirect signals from what concerns the particle physics side. The related multi-wavelength emission is expected to be faint, unless a significant enhancement of the DM density is present at the GC. We find that in this case, and depending on few additional assumptions, the next generation of gamma-ray and wide-field radio observations can test the model, possibly even with the detection of the induced monochromatic gamma-ray emission.
The sensitivity of the lightest supersymmetric particle relic density calculation to the variation of the cosmological expansion rate before nucleosynthesis is discussed. We show that such a modification, even extremely modest and with no consequence on the cosmological observations, can greatly enhance the calculated relic density, and therefore change the constraints on the SUSY parameter space drastically. Hence, it is unsafe to use the lower bound of the WMAP limits in order to constrain supersymmetry, and we suggest to use only the upper value Omega_{DM} h^2 < 0.12.
We investigate the independent points in the sky require to search the periodic gravitational wave, assuming the noise power spectral density to be flat. We have made an analysis with different initial azimuth of the Earth for a week data set. The analysis shows significant difference in the independent points in the sky for the search. We numerically obtain an approximate relation to make trade-off between computational cost and sensitivities. We also discuss the feasibility of the coherent search in small frequency band in reference to advanced LIGO.
We consider stability properties of spherically symmetric spacetimes of stars in metric f(R) gravity. We stress that these not only depend on the particular model, but also on the specific physical configuration. Typically configurations giving the desired $\gamma_{\rm PPN} \approx 1$ are strongly constrained, while those corresponding to $\gamma_{\rm PPN} \approx 1/2$ are less affected. Furthermore, even when the former are found strictly stable in time, the domain of acceptable static spherical solutions typically shrinks to a point in the phase space. Unless a physical reason to prefer such a particular configuration can be found, this poses a naturalness problem for the currently known metric f(R) models for accelerating expansion of the Universe.
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We present a complete sample of International Ultraviolet Explorer and Hubble Space Telescope ultraviolet (UV) spectra of Type Ia supernovae (SNe Ia) through 2004. We measure the equivalent width (EW) and blueshifted velocity of the minimum of the one strong UV feature, Fe II 3250. We also quantify the slope of the near-UV spectra using a new parameter, the ``UV ratio.'' We find that the velocity of the Fe II line does not correlate with light-curve shape, while the EW shows distinct behavior for the slow and fast-declining objects. Using precise Cepheid and surface brightness fluctuation distance measurements of 6 objects with UV spectra observed near maximum light (a total of 12 spectra), we determine that the UV ratio at maximum light is highly correlated with SN Ia luminosity. A larger sample of UV spectra is necessary to increase the statistical certainty of these luminosity indicators and whether they can be combined with light-curve shape to improve measured SN Ia distances.
We describe a scenario for large-scale magnetic field generation and particle
acceleration in a collisionless collision of cold plasma clouds. A
first-principle (i.e. using particles) numerical simulation of this process
might be possible. Our scenario is essentially 3D. We argue that {\it
large-scale} magnetic fields are not generated in 2D, even in collisionless
plasma.
We calculate and numerically simulate magnetic field generation by
relativistic collisionless Kelvin-Helmholtz instability in 2D. Collisionless
tangential discontinuity might be more important than collisionless shock,
because tangential discontinuity remains unstable even in the hydro limit, when
the shock stabilizes.
We present a new approach to gravitational lens massmap reconstruction. Our massmap solutions perfectly reproduce the positions, fluxes, and shears of all multiple images. And each massmap accurately recovers the underlying mass distribution to a resolution limited by the number of multiple images detected. We demonstrate our technique given a mock galaxy cluster similar to Abell 1689 which gravitationally lenses 19 mock background galaxies to produce 93 multiple images. We also explore cases in which far fewer multiple images are observed, such as four multiple images of a single galaxy. Massmap solutions are never unique, and our method makes it possible to explore an extremely flexible range of physical (and unphysical) solutions, all of which perfectly reproduce the data given. Each reconfiguration of the source galaxies produces a new massmap solution. An optimization routine is provided to find those source positions (and redshifts, within uncertainties) which produce the "most physical" massmap solution, according to a new figure of merit developed here. Our method imposes no assumptions about the slope of the radial profile nor mass following light. But unlike "non-parametric" grid-based methods, the number of free parameters we solve for is only as many as the number of observable constraints (or slightly greater if fluxes are constrained). For each set of source positions and redshifts, massmap solutions are obtained "instantly" via direct matrix inversion by smoothly interpolating the deflection field using a recently developed mathematical technique. Our LensPerfect software is straightforward and easy to use and is made publicly available via our website.
We use electromagnetic Particle-in-Cell codes to investigate the two-stream instability and Weibel instability when two beams of plasma collide head-on relativistically. We compare the dissipation of kinetic energies in the two cases. We also study the evolution of the resultant electron energy distribution function produced by such dissipation.
We report on a Cluster multi-spacecraft cusp observation lasting more than 100 minutes. We determine the cusp boundary motion and reveal the effect on the cusp size of the interplanetary magnetic field (IMF) changing from southward to northward. The cusp shrinks at the beginning of the IMF rotation and it re-expands at the rate of 0.50$^{o}$ ILAT per hour under stable northward IMF. Based on plasma signatures inside the cusp, such as counter-streaming electrons with balanced fluxes and quasi-periodic enhancement of ion fluxes with energy E$>$5keV, we propose that pulsed dual lobe reconnection operates during the time of interest. SC1 and SC4 observations suggest a long-term regular periodicity of the pulsed dual reconnection, which we estimate to be $\sim$ 1-5 minutes. Further, the distances from the spacecraft to the reconnection site are estimated based on observations from three satellites. The distance determined using SC1 and SC4 observations is $\sim$ 15 RE, and that determined from SC3 data is $\sim$ 8 RE. The large-scale speed of the reconnection site sunward motion is $\sim$ 16 km s$^{-1}$. We observe also a fast motion of the reconnection site by SC1, which provides new information about the transitional phase after the IMF rotation. Finally, a statistical study of the dependency of plasma convection inside the cusp on the IMF clock angle is performed. The relationship between the cusp stagnation, the dual lobe reconnection process and the IMF clock angle is discussed.
Silicon Carbide (SiC) optical constants are fundamental inputs for radiative
transfer models of astrophysical dust environments. However, previously
published values contain errors and do not adequately represent the bulk
physical properties of the cubic (beta) SiC polytype usually found around
carbon stars. We provide new, uncompromised optical constants for beta- and
alpha-SiC derived from single-crystal reflectance spectra and investigate
quantitatively whether there is any difference between alpha- and beta-SiC that
can be seen in infrared spectra and optical functions.
Previous optical constants for SiC do not reflect the true bulk properties,
and they are only valid for a narrow grain size range. The new optical
constants presented here will allow narrow constraints to be placed on the
grain size and shape distribution that dominate in astrophysical environments.
In addition, our calculated absorption coefficients are much higher than
laboratory measurements, which has an impact on the use of previous data to
constrain abundances of these dust grains.
We develop a new method to reconstruct the cosmic density field from the distribution of dark matter haloes above a certain mass threshold. Our motivation is that well-defined samples of galaxy groups/clusters, which can be used to represent the dark halo population, can now be selected from large redshift surveys of galaxies, and our ultimate goal is to use such data to reconstruct the cosmic density field in the local universe. Our reconstruction method starts with a sample of dark matter haloes above a given mass threshold. Each volume element in space is assigned to the domain of the nearest halo according to a distance measure that is scaled by the virial radius of the halo. The distribution of the mass in and around dark matter haloes of a given mass is modelled using the cross-correlation function between dark matter haloes and the mass distribution within their domains. We use N-body cosmological simulations to show that the density profiles required in our reconstruction scheme can be determined reliably from large cosmological simulations, and that our method can reconstruct the density field accurately using haloes with masses down to $\sim 10^{12}\msun$ (above which samples of galaxy groups can be constructed from current large redshift surveys of galaxies). Working in redshift space, we demonstrate that the redshift distortions due to the peculiar velocities of haloes can be corrected in an iterative way. We also describe some applications of our method.
Gas-phase processes were long thought to be the key formation mechanisms for complex organic molecules in star-forming regions. However, recent experimental and theoretical evidence has cast doubt on the efficiency of such processes. Grain-surface chemistry is frequently invoked as a solution, but until now there have been no quantitative models taking into account both the high degree of chemical complexity and the evolving physical conditions of star-forming regions. Here, we introduce a new gas-grain chemical network, wherein a wide array of complex species may be formed by reactions involving radicals. The radicals we consider (H, OH, CO, HCO, CH3, CH3O, CH2OH, NH and NH2) are produced primarily by cosmic ray-induced photodissociation of the granular ices formed during the colder, earlier stages of evolution. The gradual warm-up of the hot core is crucial to the formation of complex molecules, allowing the more strongly-bound radicals to become mobile on grain surfaces. This type of chemistry is capable of reproducing the high degree of complexity seen in Sgr B2(N), and can explain the observed abundances and temperatures of a variety of previously detected complex organic molecules, including structural isomers. Many other complex species are predicted by this model, and several of these species may be detectable in hot cores. Differences in the chemistry of high- and low-mass star-formation are also addressed; greater chemical complexity is expected where evolution timescales are longer.
Jet driving and fragmentation process in collapsing primordial cloud are studied using three-dimensional MHD nested grid simulations. Starting from a rotating magnetized spherical cloud with the number density of n=10^3 cm^-3, we follow the evolution of the cloud up to the stellar density n=10^22 cm^-3. We calculate 36 models parameterizing the initial magnetic and rotational energies (\gamma_0, \beta_0). In the collapsing primordial clouds, the cloud evolutions are characterized by the ratio of the initial rotational to magnetic energy, \gamma_0/\beta_0. The Lorentz force significantly affects the cloud evolution when \gamma_0 > \beta_0, while the centrifugal force is more dominant than the Lorentz force when \beta_0 > \gamma_0. When the cloud rotates rapidly with angular velocity of \Omega_0 > 10^-17 (n/10^3 cm^-3)^2/3 s^-1 and \beta_0 > \gamma_0, fragmentation occurs before the protostar is formed, but no jet appears after the protostar formation. On the other hand, a strong jet appears after the protostar formation without fragmentation when the initial cloud has the magnetic field of B_0 > 10^-9 (n/10^3 cm^-3)^2/3 G and \gamma_0 > \beta_0. Our results indicate that proto-Population III stars frequently show fragmentation and protostellar jet. Population III stars are therefore born as binary or multiple stellar systems, and they can drive strong jets, which disturb the interstellar medium significantly, as well as in the present-day star formation, and thus they may induce the formation of next generation stars.
Calculations of spectral darkening and visibility functions for the brightness oscillations of the Sun resulting from global solar oscillations are presented. This has been done for a broad range of the visible and infrared continuum spectrum. The procedure for the calculations of these functions includes the numerical computation of depth-dependent derivatives of the opacity caused by p modes in the photosphere. A radiative-transport code was used for this purpose to get the disturbances of the opacities from temperature and density fluctuations. The visibility and darkening functions are obtained for adiabatic oscillations under the assumption that the temperature disturbances are proportional to the undisturbed temperature of the photosphere. The latter assumption is the only way to explore any opacity effects since the eigenfunctions of p-mode oscillations have not been obtained so far. This investigation reveals that opacity effects have to be taken into account because they dominate the violet and infrared part of the spectrum. Because of this dominance, the visibility functions are negative for those parts of the spectrum. Furthermore, the darkening functions show a wavelength-dependent change of sign for some wavelengths owing to these opacity effects. However, the visibility and darkening functions under the assumptions used contradict the observations of global p-mode oscillations, but it is beyond doubt that the opacity effects influence the brightness fluctuations of the Sun resulting from global oscillations.
With reasonable assumptions and approximations, we compute the velocity of the meridional flow $U$ in the convective envelope by modified Chandrasekhar's (1956) MHD equations. The analytical solution of such a modified equation is found to be $U(x,\mu) = \sum_{n=0}^\infty \bigl[u1_n x^n + u2_n x^{-(n+3)}\bigr] C_n^{3/2}(\mu)$, where $x$ is non-dimensional radius, $\mu = cos{\vartheta}$, ${\vartheta}$ is the co-latitude, $C_n^{3/2} {(\mu)}$ are the Gegenbaur polynomials of order 3/2, $u1_n$ and $u2_n$ are the unknown constants. The results show that meridional velocity flow from the surface appears to penetrates deep below base of the convective envelope and at outer part of the radiative zone. With such a deep flow velocity below the convective envelope and a very high density stratification in the outer part of the radiative zone with likely existence of a strong ($\sim$ $10^{4}$ G) toroidal magnetic field structure, the velocity of transport of meridional flow is considerably reduced. Hence, it is very unlikely that the return flow will reach the surface (with a period of solar cycle) as required by some of the flux transport dynamo models. On the other hand, deep meridional flow is required for burning of Lithium at outer part of the radiative zone supporting the observed Lithium deficiency at the surface.
We study the impact of a stochastic background of primordial magnetic fields on the scalar contribution of CMB anisotropies and on the matter power spectrum. We give the correct initial conditions for cosmological perturbations and the exact expressions for the energy density and Lorentz force associated to the stochastic background of primordial magnetic fields, given a power-law for their spectra cut at a damping scale. The dependence of the CMB temperature and polarization spectra on the relevant parameters of the primordial magnetic fields is illustrated.
We present ultravioliet (UV) observations of supernovae (SNe) obtained with the UltraViolet/Optical Telescope (UVOT) on board the Swift spacecraft. This is the largest sample of UV light curves from any single instrument and covers all major SN types and most subtypes. The UV light curves of SNe Ia are fairly homogenous while SNe Ib/c and IIP show more variety in their light curve shapes. The UV-optical colors clearly differentiate SNe Ia and IIP, particularly at early times. The color evolution of SNe IIP, however, makes their colors similar to SNe Ia at about 20 days after explosion. SNe Ib/c are shown to have varied UV-optical colors. The use of UV colors to help type SNe will be important for high redshift SNe discovered in optical observations. These data can be added to ground based optical and near infrared data to create bolometric light curves of individual objects and as checks on generic bolometric corrections used in the absence of UV data. This sample can also be compared with rest-frame UV observations of high redshift SNe observed at optical wavelengths.
Using interferometric data from BIMA observations, combined with detailed modeling in Fourier space of the physical structures predicted by models, we constrain the circumstellar envelope parameters for four Class 0 young stellar objects, as well as their embedded circumstellar disks. The envelopes of these objects are still undergoing collapse, and theoretical collapse models can be compared to the observations. Since it has been suggested in a previous study that both the Larson-Penston and Shu similarity solutions underestimate the age of the system, we adopt Tassis & Mouschovias' model of the collapse process, which includes all relevant magnetic fields effects. The results of the model fitting show a good consistency between theory and data; furthermore, no age problem exists since the Tassis & Mouschovias' model is age independent for the first 255 kyr. Although the majority of the continuum dust emission arises from the circumstellar envelopes, these objects have well known outflows, which suggest the presence of circumstellar disks. At the highest resolution, most of the large-scale envelope emission is resolved out by interferometry, but the small-scale residual emission remains, making it difficult to observe only the compact disk component. By modeling the emission of the envelope and subtracting it from the total emission, we constrain the disk masses in our four systems to be comparable to or smaller than the typical disk masses for T Tauri systems.
We present a new method to classify galaxies from large surveys like the Sloan Digital Sky Survey using inclination-corrected concentration, inclination-corrected location on the color-magnitude diagram, and apparent axis ratio. Explicitly accounting for inclination tightens the distribution of each of these parameters and enables simple boundaries to be drawn that delineate three different galaxy populations: Early-type galaxies, which are red, highly concentrated, and round; Late-type galaxies, which are blue, have low concentrations, and are disk dominated; and Intermediate-type galaxies, which are red, have intermediate concentrations, and have disks. We have validated our method by comparing to visual classifications of high-quality imaging data from the Millennium Galaxy Catalogue. The inclination correction is crucial to unveiling the previously unrecognized Intermediate class. Intermediate-type galaxies, roughly corresponding to lenticulars and early spirals, lie on the red sequence. The red sequence is therefore composed of two distinct morphological types, suggesting that there are two distinct mechanisms for transiting to the red sequence. We propose that Intermediate-type galaxies are those that have lost their cold gas via strangulation, while Early-type galaxies are those that have experienced a major merger that either consumed their cold gas, or whose merger progenitors were already devoid of cold gas (the ``dry merger'' scenario).
Only very few solar-type stars exhibiting an infrared excess and harbouring planets are known to date. Indeed, merely a single case of a star-planet-disk system has previously been detected at submillimeter (submm) wavelengths. Consequently, one of our aims is to understand the reasons for these poor statistics, i.e., whether these results reflected the composition and/or the physics of the planetary disks or were simply due to observational bias and selection effects. Finding more examples would be very significant. The selected target, q1 Eri, is a solar-type star, which was known to possess a planet, q1 Eri b, and to exhibit excess emission at IRAS wavelengths, but had remained undetected in the millimeter regime. Therefore, submm flux densities would be needed to better constrain the physical characteristics of the planetary disk. Consequently, we performed submm imaging observations of q1 Eri. The detected dust toward q1 Eri at 870 micron exhibits the remarkable fact that the entire SED, from the IR to mm-wavelengths, is fit by a single temperature blackbody function (60 K). This would imply that the emitting regions are confined to a narrow region (ring) at radial distances much larger than the orbital distance of q1 Eri b, and that the emitting particles are considerably larger than some hundred micron. However, the 870 micron source is extended, with a full-width-half-maximum of roughly 600 AU. Therefore, a physically more compelling model also invokes a belt of cold dust (17 K), located at 300 AU from the star and about 60 AU wide. The minimum mass of 0.04 Mearth (3 Mmoon) of 1 mm-size icy ring-particles is considerable, given the stellar age of about 1 Gyr. These big grains form an inner edge at about 25 AU, which may suggest the presence of an unseen outer planet (q1 Eri c).
The major multi-epoch VLBA programs are described and discussed in terms of
relativistic beaming models. Broadly speaking the observed kinematics are
consistent with models having a parent population which is only mildly
relativistic but with Lorentz factors extending up to about 30. While the
collimation and acceleration appears to mainly occur close to the central
engine, there is evidence of accelerations up to 1 kpc downstream. Generally
the motion appears to be linear, but in some sources the motion follows a
curved trajectory. In other sources, successive features appear to be ejected
in different directions possibly the result of a precessing nozzle.
The launch of GLAST in 2008 will offer new opportunities to study the
relation between radio and gamma-ray activity, and possibly to locate the
source of the gamma-ray emission. VSOP-2 will give enhanced resolution and will
facilitate the study of the two-dimensional structure of relativistic jets,
while RadioAstron will provide unprecedented resolution to study the fine scale
structure of the jet base.
This work gives an explicit exact expression for the Thomas precession
arising in the framework of Special Theory of Relativity as the spatial
rotation resulting from two subsequence Lorentz boosts. The final result for
the orthogonal matrix of the Thomas precession is given by Eqs. (21)-(25).
In the framework of Gaia the special-relativistic Thomas precession is an
important step in the derivation of an aberrational formula with the
Mansouri-Sexl parameters. The latter formula will be used to test the Local
Lorentz Invariance with Gaia data as will be explained elsewhere.
We present results from a time dependent gas phase chemical model of a hot core based on the physical conditions of G305.2+0.2. While the cyanopolyyne HC_3N has been observed in hot cores, the longer chained species, HC_5N, HC_7N, and HC_9N have not been considered typical hot core species. We present results which show that these species can be formed under hot core conditions. We discuss the important chemical reactions in this process and, in particular, show that their abundances are linked to the parent species acetylene which is evaporated from icy grain mantles. The cyanopolyynes show promise as `chemical clocks' which may aid future observations in determining the age of hot core sources. The abundance of the larger cyanopolyynes increase and decrease over relatively short time scales, ~10^2.5 years. We also discuss several sulphur bearing species. We present results from a non-LTE statistical equilibrium excitation model as a series of density, temperature and column density dependent contour plots which show both the line intensities and several line ratios. These aid in the interpretation of spectral line data, even when there is limited line information available.
Pulsars have been recognized as normal neutron stars or quark stars. Sub-millisecond pulsars, if detected, would play an essential and important role in distinguishing quark stars from neutron stars. A key question is how sub-millisecond pulsars could form. Both sub-Keplerian (for neutron and quark stars) and super-Keplerian cases (only for quark stars, which are bound additionally by strong interaction) have been discussed in this paper in order to investigate possible ways of forming sub-millisecond pulsars. In the sub-Keplerian case, the equilibrium periods of both neutron and quark stars could be as low as ~0.4 ms when they are spun up through accretion in binary systems. In the super-Keplerian case, pulsars could very likely have an initial period of ~0.1 ms if quark stars with different mass could be formed from accretion-induced collapse (AIC) of white dwarfs. The timescale for a sub-millisecond pulsar to keep its period <1 ms is restricted due to gravitational wave radiation. We found that the timescales of neutron stars within sub-millisecond periods are approximately ~10 yr, but the timescales estimated (>10 Myr) for low-mass quark stars could be long enough for us to detect.
Collapse calculations indicate that the hot newly born protoneutron stars (PNS) rotate differentially so that strong toroidal magnetic field components should exist in the outer crust where also the Hall effect appears to be important when the Hall parameter \hat\beta=\omega_B \tau is of order unity. The amplitudes of the induced toroidal magnetic fields are limited from above by the Tayler instability. An important characteristic of the Hall effect is its distinct dependence on the {\em sign} of the magnetic field. We find for fast rotation that positive (negative) Hall parameters essentially reduce (increase) the stability domain. It is thus concluded that the toroidal field belts in PNS induced by their differential rotation should have different amplitudes in both hemispheres which later are frozen in. Due to the effect of magnetic suppression of the heat conductivity also the brightness of the two hemispheres should be different. As a possible example for our scenario the isolated neutron star RBS 1223 is considered which has been found to exhibit different X-ray brightness at both hemispheres.
We report the discovery of 70.5 ms pulsations from the X-ray source AX J1838.0-0655 using the Rossi X-ray Timing Explorer} (RXTE). PSR J1838-0655 is a rotation-powered pulsar with spin-down luminosity Edot = 5.5E36 ergs/s, characteristic age tau = P/2Pdot = 23 kyr, and surface dipole magnetic field strength Bs = 1.9E12 G. It coincides with an unresolved INTEGRAL source and the extended TeV source HESS J1837-069. At an assumed distance of 6.6 kpc by association with an adjacent massive star cluster, the efficiency of PSR J1838-0655 converting spin-down luminosity to radiation is 0.8% for the 2-10 keV ASCA flux, 9% for the 20-300 keV INTEGRAL flux and ~2% for the >200 GeV emission of HESS J1837-069, making it a plausible power source for the latter. A Chandra X-ray observation resolves AX J1838.0-0655 into a bright point source surrounded by a ~2' diameter, centrally peaked nebula. The spectra of the pulsar and nebula are each well fitted by power laws, with photon indices Gamma = 0.5(0.3-0.7) and Gamma = 1.6(1.1-2.0), respectively. The 2-10 keV X-ray luminosities of the pulsar and nebula are L{PSR} = 4.6E34 d(6.6}^2 ergs/s and L(PWN) = 5.2E33 d(6.6)^2 ergs/s. A second X-ray source adjacent to the TeV emission, AX J1837.3-0652, is resolved into an apparent pulsar/PWN; it may also contribute to HESS J1837-069. The star cluster RSGC1 may have given birth to one or both pulsars, while fueling TeV emission from the extended PWN with target photons for inverse Compton scattering.
We suggest that the unique X-ray source 1E161348-5055 at the centre of the supernova remnant RCW 103 consists of a neutron star in close orbit with a low mass main sequence star. The time signature of 6.67 hr is interpreted as the neutron star's spin period. This requires the neutron star to be endowed with a high surface magnetic field of~10^15 G. Magnetic or/and material (propeller) torques are able to spin rapidly the young neutron star down to an asymptotic, equilibrium spin period in close synchronism with the orbital period, similarly to what happens in the Polar Cataclysmic Variables. 1E161348-5055 could be the first case of a magnetar born in a young low mass binary system.
Context. More than ten Centaurs are now known to have cometary activity at
large heliocentric distance (i.e. $\simeq$ 5-13 AU). Among these objects,
174P/Echeclus which showed cometary activity at 13 AU from the Sun, is a unique
case, because of: (i) the amplitude of its outburst, (ii) the source of
cometary activity that appears distinct from Echeclus itself.
Aims. This paper aims at investigating the physical conditions that have led
to this unusual outburst. The purpose is also to quantify this phenomenon and
to provide observational constraints for its modeling.
Methods. We use observations from different telescopes, performed before,
during, and after the outburst. We performed the main observations on March 23
and 30, 2006, with the 8.2-m ESO Very Large Telescope and FORS 1 instrument.
They consist of visible images and spectra.
Results. Our main results are: (i) a cometary source distinct from Echeclus
itself that presents a brightness distribution compatible with a diffuse
source; (ii) a total dust production rate Q_dust equal to about 86 kg.s^-1 and
a parameter Afrho equal to 10,000cm; (iii) no emission lines (CN and C_2) can
be detected in the visible range; (iv) the upper limits for the CN and C_2
production rates are about 3.8x10^25 and 10^26 molecules.s^-1 respectively; (v)
we detected no Echeclus' satellite before the outburst up to M_R equal to about
26; (vi) the upper limit for the object generating the coma is about 8 km in
diameter; (vii) and we detected no cometary activity one year later, in March
2007.
The variation of properties of Type Ia supernovae, the thermonuclear explosions of Chandrasekhar-mass carbon-oxygen white dwarfs, is caused by different nucleosynthetic outcomes of these explosions, which can be traced from the distribution of abundances in the ejecta. The composition stratification of the spectroscopically normal but rapidly declining SN2004eo is studied performing spectrum synthesis of a time-series of spectra obtained before and after maximum, and of one nebular spectrum obtained about eight months later. Early-time spectra indicate that the outer ejecta are dominated by oxygen and silicon, and contain other intermediate-mass elements (IME), implying that the outer part of the star was subject only to partial burning. In the inner part, nuclear statistical equilibrium (NSE) material dominates, but the production of 56Ni was limited to ~0.43 \pm 0.05 Msun. An innermost zone containing ~0.25 Msun of stable Fe-group material is also present. The relatively small amount of NSE material synthesised by SN2004eo explains both the dimness and the rapidly evolving light curve of this SN.
The Interstellar Medium seems to have an underlying fractal structure, which can be characterized through its fractal dimension (Df). However, several factors may affect the determination of Df, such as distortions due to projection, low image resolution, opacity of the cloud, and low signal-to-noise ratio. Here we use both simulated clouds and real molecular cloud maps to study these effects in order to estimate Df in a reliable way. Our results indicate in a self-consistent way that the fractal dimension of the Interstellar Medium is in the range 2.6 < Df < 2.8, which is significantly higher than the value Df = 2.3 usually assumed in the literature.
We are presenting an Internal Linear Combination (ILC) CMB map, where foreground is reduced through harmonic variance minimization. We have derived our method by converting a general form of pixel-space approach into spherical harmonic space, maintaining full correspondence. By working in spherical harmonic space, spatial variability of linear weights is incorporated in a self-contained manner and our linear weights are continuous functions of position over the entire sky. The full correspondence to pixel-space approach enables straightforward physical interpretation on our approach. In variance minimization of a linear combination map, the existence of a cross term between residual foregrounds and CMB makes the linear combination of minimum variance differ from that of minimum foreground. We have developed an iterative foreground reduction method, where perturbative correction is made for the cross term. Our CMB map derived from the WMAP data is in better agreement with the WMAP best-fit $\Lambda$CDM model than the WMAP team's Internal Linear Combination map. We find that our method's capacity to clean foreground is limited by the availability of enough spherical harmonic coefficients of good Signal-to-Noise Ratio (SNR).
The space astrometry mission GAIA will construct a dense optical QSO-based celestial reference frame. For consistency between the optical and radio positions, it will be important to align the GAIA frame and the International Celestial Reference Frame (ICRF) with the highest accuracy. Currently, it is found that only 10% of the ICRF sources are suitable to establish this link, either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we have initiated a VLBI survey dedicated to finding additional high-quality radio sources for aligning the two frames. The sample consists of about 450 sources, typically 20 times weaker than the current ICRF sources, which have been selected by cross-correlating optical and radio catalogues. The paper presents the observing strategy and includes preliminary results of observation of 224 of these sources with the European VLBI Network in June 2007.
The IAU/IUGG Working Group on "Nutation for a non-rigid Earth", led by V\'eronique Dehant, won the European Descartes Prize in 2003, for its work developing a new model for the precession and the nutations of the Earth. This model (MHB2000, Mathews et al. 2002) was adopted by the IAU (International Astronomical Union) during the General Assembly in Manchester, in 2000. It is based (i) on some improvements for the precession model (with respect to the previous one of Lieske et al. 1977) owing to the VLBI technique, and (ii) on a very accurate nutation model, close to the observations. With this prize, the Descartes nutation project could offer for international scientists some grants, to be used for further improvements of the precession-nutation Earth model. At the IGG (Institute of Geodesy and Geophysics), with the OCCAM 6.1 VLBI analysis software and the best data and models available, we re-analyzed the whole VLBI sessions available (from 1985 till 2005) solving for the Earth Orientation Parameters (EOP). In this paper we present the results obtained for the EOP and more particularly for the nutation series. We compare them with the other IVS analysis centers results, as well as with the IVS combined EOP series from the analysis coordinator. The series are in good agreement, except for the polar motion coordinates that show a shift with respect to the other ones and that we discuss here. Finally, we analyse the nutation series in the framework of the free core nutation (FCN) study and modelisation.
The consequences of a newly suggested value for the SN explosion energy 1.2x10^{51} erg are explored for the case of Tycho's supernova remnant (SNR). A nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs is employed to investigate the properties of Tycho's SNR and their correspondence to the existing experimental data. It is demonstrated that the large mean ratio between the radii of the contact discontinuity and the forward shock is consistent with the very effective acceleration of nuclear energetic particles at the forward shock. It is also argued that consistency of the value E_{sn} = 1.2x10^{51} erg with the gas dynamics, acceleration theory, and the existing gamma-ray measurements requires the source distance to be greater than 3.3 kpc. The corresponding ambient gas number density is lower than 0.4 cm^{-3}. Since the expected gamma-ray flux strongly depends on the source distance, F_{\gamma}\propto d^{-7}, a future experimental determination of the actual gamma-ray flux from Tycho's SNR will make it possible to determine the values of the source distance and of the mean ambient gas density. A simple inverse Compton model without a dominant population of nuclear CRs is not compatible with the present upper limit for the gamma-ray emission for any reasonable ambient interstellar B-field. Given the consistency between acceleration theory and overall, as well as internal, gas dynamics, a future gamma-ray detection would make the case for nuclear particle acceleration in Tycho's SNR incontrovertible in our view.
We study the thermal equilibrium and stability of isobaric, spherical structures having a radiation source located at its center. The thermal conduction coefficient, external heating and cooling rates are represented as power laws of the temperature. The internal heating decreases with distance from the source r approximately as exp(-tau)/(r**2), being tau the optical depth. We find that the influence of the radiation source is important only in the central region, but its effect is enough to make the system thermally unstable above a certain threshold central temperature. This threshold temperature decreases as the internal heating efficiency increases, but, otherwise, it does not depend on the structure size. Our results suggest that a solar-like star migrating into a diffuse interstellar region may destabilize the surrounding medium.
CONTEXT: Gaussianity will become a strong observational tool allowing to constrain viable inflationary models. AIMS: In this paper, we introduce and analyze a new method for testing SI and Gaussianity and apply it to the 3 years WMAP CMB data. METHODS: We use an original pixelization scheme to divide the sky into regions of varying size and shape. We then measure the first four moments of the one-point distribution within these regions and using their simulated spatial distributions we test the statistical isotropy and Gaussianity hypotheses. By randomly varying orientations of these regions, their angular size and shape, we sample the underlying CMB field in a new manner, that offers a richer exploration of data the content. In our analysis we account for all correlations between different regions and also show the impact on the results when these correlations are neglected. The statistical significance is assessed via comparison with realistic Monte-Carlo simulations of the observed data. RESULTS: We find the 3 years WMAP maps, to be well consistent with the isotropic, Gaussian field hypothesis at all probed scales (at CL <~ 90%). We find some hints of foreground contamination in the form a localized kurtosis excess (CL <~ 88%) in the all bands co-added map, which however is not statistically important if single band data are used. We report a strong dipole "excess" in the V band (of no cosmological consequences) and find that the reported large scale hemispherical asymmetry is not statistically significant using our statistic. We easily detect the residual foreground contaminations in cross-band difference maps at rms level <8\mu K (at scales >~ 6 deg) and limit the systematical uncertainties to <1.7\mu K (at scales >~ 30 deg) consistently with the previously estimated limits.
We have measured the angular diameters for a sample of 24 exoplanet host stars using Georgia State University's CHARA Array interferometer. We use these improved angular diameters together with Hipparcos parallax measurements to derive linear radii and to estimate the stars' evolutionary states.
We describe the results of a mJy-sensitivity, VLA survey of roughly 1 square degree near the Galactic center at 6 and 20 cm. Catalogs of compact and filamentary structures are given and compared to previous surveys of the region. Eight of the unusual, nonthermal radio filaments are detected in 6 cm polarized emission; three of these are the first such detections, confirming their nonthermal nature. This survey found emission from a filament at (l,b)=(359.1,0.75), or a projected distance from Sgr A* of 200 pc, greatly extending the latitude range observed with such features. There is also new evidence for spatial gradients in the 6/20 cm spectral indices of some filaments and we discuss models for these gradients. In studying compact sources, the combination of spectral index and polarization information allows us to identify pulsar candidates and compact HII regions in the survey. There is also some evidence that the flux measurements of compact sources may be affected by electron scattering from the interstellar medium in the cent ral few hundred parsecs of the Galaxy.
The possibility is examined that a model based on space noncommutativity of linear type can explain why photons from distant sources with multi-TeV energies can reach earth. In particular within a model in which space coordinates satisfy the algebra of SU(2) Lie group, it is shown that there is the possibility that the pair production through the reaction of CMB and energetic photons would be forbidden kinematically.
A multi-imaging strategy is proposed and experimentally tested to improve the accuracy of photon counting with an electron multiplying charge-coupled device (EMCCD), by taking into account the random nature of its on-chip gain and the possibility of multiple photo-detection events on one pixel. This strategy is based on Bayesian estimation on each image, with a priori information given by the sum of the images. The method works even for images with large dynamic range, with more improvement in the low light level areas. In these areas, two thirds of the variance added by the EMCCD in a conventional imaging mode are removed, making the physical photon noise predominant in the detected image.
N-body simulations of dark matter halos show that the density is cusped near the center of the halo. The density profile behaves as $r^{-\gamma}$ in the inner parts, where $\gamma \simeq 1$ for the NFW model and $\gamma \simeq 1.5$ for the Moore's model, but in the outer parts, both models agree with each other in the asymptotic behavior of the density profile. The simulations also show the information about anisotropy parameter $\beta(r)$ of velocity distribution. $\beta\approx 0$ in the inner part and $\beta\approx 0.5$ (radially anisotropic) in the outer part of the halo. We provide some distribution functions $F(E,L)$ with the constant anisotropy parameter $\beta$ for the two spherical models of dark matter halos: a new generalized NFW model and a generalized Moore model. There are two parameters $\alpha$ and $\epsilon$ for those two generalized models to determine the asymptotic behavior of the density profile. In this paper, we concentrate on the situation of $\beta(r)=1/2$ from the viewpoint of the simulation.
In the framework of the "Groupe de Recherches de G\'eod\'esie Spatiale" (GRGS), a rigorous combination of the data from five space geodetic techniques (VLBI, GPS, SLR, LLR and DORIS) is routinely applied to simultaneously determine a Terrestrial Reference Frame (TRF) and Earth Orientation Parameters (EOP). This analysis is conducted with the software package GINS which has the capability to process data from all five techniques together. Such a combination at the observation level should ultimately facilitate fine geophysical studies of the global Earth system. In this project, Bordeaux Observatory is in charge of the VLBI data analysis, while satellite geodetic data are processed by other groups. In this paper, we present (i) details about the VLBI analysis undertaken with GINS, and (ii) the results obtained for the EOP during the period 2005-2006. We also compare this EOP solution with the IVS (International VLBI Service for geodesy and astrometry) analysis coordinator combined results. The agreement is at the 0.2 mas level, comparable to that of the other IVS analysis centers, which demonstrates the capability of the GINS software for VLBI analysis.
A rigorous approach to simultaneously determine a Terrestrial Reference Frame (TRF) and Earth Orientation Parameters (EOP) is now currently applied on a routine basis in a coordinated project within the Groupe de Recherches de G\'eod\'esie Spatiale (GRGS) in France. Observations of the various space geodetic techniques (VLBI, SLR, LLR, DORIS and GPS) are separately processed by different analysis centers with the software package GINS-DYNAMO, developed and maintained at the GRGS/CNES (Toulouse). This project is aimed at facilitating fine geophysical analyses of the global Earth system (GGOS project). In this framework, Bordeaux Observatory is in charge of the VLBI (Very Long Baseline Interferometry) analyses with GINS for combination with the data of the other space geodetic techniques at the observation level. In this paper, we present (i) the analyses undertaken with this new VLBI software, and (ii) the results obtained for the EOP from beginning 2005 until 2007. Finally, we compare this EOP solution with the IVS (International VLBI Service) Analysis Coordinator combined results. The agreement is at the 0.2 mas level, comparable to that of the other IVS Analysis Centers, which demonstrates the VLBI capability of the GINS software.
We aim to study the nature of Gomez's Hamburger (IRAS 18059-3211), a nebula
that has been proposed to be a post-AGB object. Such a classification is not
confirmed, instead we argue that it will be a key object in the study of disks
rotating around young stars.
We present high resolution SMA maps of CO J=2--1 in Gomez's Hamburger. The
data are analyzed by means of a code that simulates the emission of a nebula
showing a variety of physical conditions and kinematics.
Our observations clearly show that the CO emitting gas in Gomez's Hamburger
forms a spectacular disk in keplerian rotation. Model calculations undoubtly
confirm this result. The central (mainly stellar) mass is found to be high, ~ 4
Mo for a distance of 500 pc. The mass and (relatively low) luminosity of the
source are, independently of the assumed distance, very different from those
possible in evolved stars. Gomez's Hamburger is probably a transitional object
between the pre-MS and MS phases, still showing interstellar material around
the central star or stellar system.
We present the results of the X-ray spectral analysis of an
XMM-Newton-selected type II QSO sample with z>0.5 and 0.5-10 keV flux of 0.3-33
x 10^{-14} erg/s/cm^2. The distribution of absorbing column densities in type
II QSOs is investigated and the dependence of absorption on X-ray luminosity
and redshift is studied.
We inspected 51 spectroscopically classified type II QSO candidates from the
XMM-Newton Marano field survey, the XMM-Newton-2dF wide angle survey (XWAS),
and the AXIS survey to set-up a well-defined sample with secure optical type II
identifications. Fourteen type II QSOs were classified and an X-ray spectral
analysis performed. Since most of our sources have only ~40 X-ray counts
(PN-detector), we carefully studied the fit results of the simulated X-ray
spectra as a function of fit statistic and binning method. We determined that
fitting the spectra with the Cash-statistic and a binning of minimum one count
per bin recovers the input values of the simulated X-ray spectra best. Above
100 PN counts, the free fits of the spectrum's slope and absorbing hydrogen
column density are reliable.
We find only moderate absorption (N_H=(2-10) x 10^22 cm^-2) and no obvious
trends with redshift and intrinsic X-ray luminosity. In a few cases a
Compton-thick absorber cannot be excluded. Two type II objects with no X-ray
absorption were discovered. We find no evidence for an intrinsic separation
between type II AGN and high X-ray luminosity type II QSO in terms of
absorption. The stacked X-ray spectrum of our 14 type II QSOs shows no iron
K-alpha line. In contrast, the stack of the 8 type II AGN reveals a very
prominent iron K-alpha line at an energy of ~ 6.6 keV and an EW ~ 2 keV.
As a by-product of beta Cephei and delta Cephei radiative model surveys we have found interesting cases of multimode pulsation. In case of beta Cephei stars, we found two multimode domains with two or three modes being involved. The origin of the multimode pulsation can be traced to one of the two different mechanisms: either to the non-resonant coupling of the two excited modes (double-mode pulsation) or to the 2omega_1 = omega_0 + omega_2 parametric resonance (triple-mode pulsation). In case of delta Cephei models, a triple-mode pulsation domain, connected with the 2:1 resonance, 2omega_0 = omega_2, is found. These models are of theoretical interest only, since they do not obey a proper mass-luminosity relation.
The natural mass scale for an electroweak singlet coupling through the Higgs portal is m_S ~ m_h. Annihilation of a singlet in this mass range is dominated by proximity to the W, Z and Higgs peaks in the annihilation cross section. We find that the gamma-ray signal from electroweak singlet annihilation in the mass range 80 GeV < m_S < 1 TeV can reach the per mil level of the EGRET diffuse gamma-ray flux.
Tracks and isochrones have been computed in the range of initial masses 0.15 - 20 Mo for a grid of 39 chemical compositions with the metal content Z between 0.0001 and 0.070, and helium content Y between 0.23 and 0.46. The Padova stellar evolution code has been implemented with updated physics. New synthetic TP-AGB models allow the extension of stellar models and isochrones until the end of the thermal pulses along the AGB. Software tools for the bidimensional interpolation (in Y and Z) of the tracks have been tuned. This first paper presents tracks for low mass stars (from 0.15 to 2.5 Mo) with scaled-solar abundances and the corresponding isochrones from very old ages down to about 1 Gyr. Tracks and isochrones are made available in tabular form for the adopted grid of chemical compositions in the plane Z-Y. An interactive web interface will allow users to obtain isochrones of whatever chemical composition and also simulated stellar populations with different Y(Z) helium-to-metal enrichment laws.
Ultracool dwarfs exhibit a remarkably varied set of characteristics which hint at the complex physical processes acting in their atmospheres and interiors. Spectra of these objects not only depend upon their mass and effective temperature, but also their atmospheric chemistry, weather, and dynamics. As a consequence divining their mass, metallicity and age solely from their spectra has been a challenge. JWST, by illuminating spectral blind spots and observing objects with constrained masses and ages should finally unearth a sufficient number of ultracool dwarf Rosetta Stones to allow us to decipher the processes underlying the complex brown dwarf cooling sequence. In addition the spectra of objects invisible from the ground, including very low mass objects in clusters and nearby cold dwarfs from the disk population, will be seen for the first time. In combination with other ground- and space-based assets and programs, JWST will usher in a new golden era of brown dwarf science and discovery.
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We present a method for determining mean light-weighted ages and abundances of Fe, Mg, C, N, and Ca, from medium resolution spectroscopy of unresolved stellar populations. The method, pioneered by Schiavon (2007), is implemented in a publicly available code called EZ_Ages. The method and error estimation are described, and the results tested for accuracy and consistency, by application to integrated spectra of well-known Galactic globular and open clusters. Ages and abundances from integrated light analysis agree with studies of resolved stars to within +/-0.1 dex for most clusters, and to within +/-0.2 dex for nearly all cases. The results are robust to the choice of Lick indices used in the fitting to within +/-0.1 dex, except for a few systematic deviations which are clearly categorized. The realism of our error estimates is checked through comparison with detailed Monte Carlo simulations. Finally, we apply EZ_Ages to the sample of galaxies presented in Thomas et al. (2005) and compare our derived values of age, [Fe/H], and [alpha/Fe] to their analysis. We find that [alpha/Fe] is very consistent between the two analyses, that ages are consistent for old (Age > 10 Gyr) populations, but show modest systematic differences at younger ages, and that [Fe/H] is fairly consistent, with small systematic differences related to the age systematics. Overall, EZ_Ages provides accurate estimates of fundamental parameters from medium resolution spectra of unresolved stellar populations in the old and intermediate-age regime, for the first time allowing quantitative estimates of the abundances of C, N, and Ca in these unresolved systems. The EZ_Ages code can be downloaded at this http URL
Using the longest optical-interferometeric baselines currently available, we have detected strong near-infrared (NIR) emission from inside the dust-destruction radius of Herbig Ae stars MWC275 and AB Aur. Our sub-milli-arcsecond resolution observations unambiguously place the emission between the dust-destruction radius and the magnetospheric co-rotation radius. We argue that this new component corresponds to hot gas inside the dust-sublimation radius, confirming recent claims based on spectrally-resolved interferometry and dust evaporation front modeling.
Our 50 ks Chandra observation of the small radio supernova remnant (SNR) G1.9+0.3 shows a complete shell structure with strong bilateral symmetry, about $100''$ in diameter. The radio morphology is also shell-like, but about 17% smaller, based on observations made in 1985. We attribute the size difference to expansion between 1985 and our Chandra observations of 2007. Expansion is confirmed in comparing radio images from 1985 and 1989. We deduce that G1.9+0.3 is of order 100 years old -- the youngest supernova remnant in the Galaxy. Based on a very high absorbing column density of $5.5 \times 10^{22}$ cm$^{-2}$, we place G1.9+0.3 at the Galactic Center, at a distance of about 8.5 kpc, at which the mean remnant radius is about 2 pc, and the required expansion speed about $15,000$ km s$^{-1}$. The X-ray spectrum is featureless and well-described by the exponentially cut off synchrotron model {\tt srcut}. With the radio flux at 1 GHz fixed at 0.9 Jy, we find a spectral index of 0.65 and a rolloff frequency of $1.4 \times 10^{18}$ Hz, the highest value ever reported for a shell supernova remnant, and which implies a characteristic rolloff electron energy of about $95 (B/10 \mu{\rm G})^{-1/2}$ TeV. This high rolloff energy can easily be reached by standard diffusive shock acceleration, given the very high shock velocities; it can be well described by either age-limited or synchrotron-loss-limited acceleration. Not only is G1.9+0.3 the youngest known Galactic remnant, it is also only the fourth synchrotron-dominated shell supernova remnant.
In the course of conducting a deep (14.5 ~< r ~< 23), 20 night survey for transiting planets in the rich ~550 Myr old open cluster M37 we have measured the rotation periods of 575 stars which lie near the cluster main sequence, with masses 0.2 Msun ~< M ~< 1.3 Msun. This is the largest sample of rotation periods for a cluster older than 500 Myr. Using this rich sample we investigate a number of relations between rotation period, color and the amplitude of photometric variability. Stars with M >~ 0.8 Msun show a tight correlation between period and mass with heavier stars rotating more rapidly. There is a group of 4 stars with P > 15 days that fall well above this relation, which, if real, would present a significant challenge to theories of stellar angular momentum evolution. Below 0.8 Msun the stars continue to follow the period-mass correlation but with a broad tail of rapid rotators that expands to shorter periods with decreasing mass. We combine these results with observations of other open clusters to test the standard theory of lower-main sequence stellar angular momentum evolution. Notably we find that the rotation period of the Sun and the periods of solar mass stars in M37, and the Hyades do not follow the ``Skumanich law'', i.e. they cannot be related by a simple model invoking solid-body rotation with a standard wind angular momentum-loss law. We also find that for late-K through early-M dwarf stars in this cluster rapid rotators tend to be bluer than slow rotators in B-V but redder than slow rotators in V-I_{C}. This result supports the hypothesis that the significant discrepancy between the observed and predicted temperatures and radii of low-mass main sequence stars is due to stellar activity.
We present a formalism to infer the presence of merging by comparing the time derivative of the observed galaxy stellar mass function (MF) to the change of the MF expected from the star formation rate (SFR) in galaxies as a function of mass and time. We present the SFR in as a function of stellar mass and time spanning 9<logM<12 and 0<z<5. We show that at z>=3 the average SFR, is a power law of stellar mass (SFR~M^0.6). The average SFR in the most massive objects at this redshift is 100-500 Msun/yr. At z~3, the SFR starts to drop at the high mass end. As z decreases further, the SFR drops at progressively lower masses (downsizing), dropping most rapidly for high mass (logM>11) galaxies. The mass at which the SFR starts to deviate from the power-law form (break mass) progresses smoothly from logM~13 at z~5 to logM~10.9 at z~0.5. The break mass evolves with redshift as M(z)=2.7x10^10 (1+z)^2.1. We directly observe a relationship between SFH and mass. More massive galaxies have steeper and earlier onsets of SF, their SFR peaks earlier and higher, and the following decay has a shorter e-folding time. The SFR observed in high mass galaxies at z~4 is sufficient to explain their rapid increase in number density. Within large uncertainties, at most 0.8 major mergers per Gyr are consistent with the high-z data, yet enough to transform most high mass objects into ellipticals contemporaneously with their major star formation episode. In contrast, at z<1.5 and at logM>11, mergers contribute 0.1-0.2 Gyr^-1 to the relative increase in number density (~1 major merger per massive object at 1.5>z>0). At 10<logM<11, galaxies are being preferably destroyed in mergers at high z, while at later times the change in their numbers turns positive. This shows the top-down buildup of the red sequence suggested by other observations.
Weak gravitational lensing by foreground density perturbations generates a gradient mode in the shear of background images. In contrast, cosmological tensor perturbations induce a non-zero curl mode associated with image rotations. In this note, we study the lensing signatures of both primordial gravitational waves from inflation and second-order gravitational waves generated from the observed spectrum of primordial density fluctuations. We derive the curl mode for galaxy lensing surveys at redshifts of 1 to 3 and for lensing of the cosmic microwave background (CMB) at a redshift of 1100. We find that the curl mode angular power spectrum associated with secondary tensor modes for galaxy lensing surveys dominates over the corresponding signal generated by primary gravitational waves from inflation. However, both tensor contributions to the shear curl mode spectrum are below the projected noise levels of upcoming galaxy and CMB lensing surveys and therefore are unlikely to be detectable.
Self-calibration techniques for analyzing cluster counts rely on using the abundance and the clustering amplitude of clusters to simultaneously constrain cosmological parameters and the relation between halo mass and its observable mass tracer. It was recently discovered that the clustering amplitude of halos depends not only on halo mass, but also on various secondary variables such as halo formation time and concentration; these dependences are collectively termed ``assembly bias.'' Using a modified Fisher matrix formalism, we explore whether these secondary variables have a significant impact on studying the properties of dark energy with self calibration in current (SDSS) and near future (DES, SPT, and LSST) cluster surveys. We find that for an SDSS-like survey, secondary dependences of halo bias are insignificant given the expected large statistical uncertainties in dark energy parameters. For SPT- or DES-like survey volumes, we find that the dependence of halo bias on secondary variables is not a significant systematic provided the scatter in the observable--mass relation is 20 percent or lower, as expected for X-ray or SZ surveys. At higher scatter (e.g. values currently possible with optical surveys), significant systematic errors are possible, depending on how strongly the cluster observable correlates with the secondary variables at fixed mass. For an LSST-like survey volume, this systematic is likely to be important even for lower scatter values or for less correlated observables.
We present c2d Spitzer/IRAC observations of the Lupus I, III and IV dark clouds and discuss them in combination with optical and near-infrared and c2d MIPS data. With the Spitzer data, the new sample contains 159 stars, 4 times larger than the previous one. It is dominated by low- and very-low mass stars and it is complete down to M $\approx$ 0.1M$_\odot$. We find 30-40 % binaries with separations between 100 to 2000 AU with no apparent effect in the disk properties of the members. A large majority of the objects are Class II or Class III objects, with only 20 (12%) of Class I or Flat spectrum sources. The disk sample is complete down to ``debris''-like systems in stars as small as M $\approx$ 0.2 M$_\odot$ and includes sub-stellar objects with larger IR excesses. The disk fraction in Lupus is 70 -- 80%, consistent with an age of 1 -- 2 Myr. However, the young population contains 20% optically thick accretion disks and 40% relatively less flared disks. A growing variety of inner disk structures is found for larger inner disk clearings for equal disk masses. Lupus III is the most centrally populated and rich, followed by Lupus I with a filamentary structure and by Lupus IV, where a very high density core with little star-formation activity has been found. We estimate star formation rates in Lupus of 2 -- 10 M$_\odot$ Myr$^{-1}$ and star formation efficiencies of a few percent, apparently correlated with the associated cloud masses.
Eleven years after its perihelion, comet C/1995 O1 (Hale-Bopp) is still active. Between October 20--22, 2007, we detected a diffuse coma of 180x10^3$km in diameter with a slight elongation toward N/S direction. The integrated brightness was 20.04 mag in R_C, implying Af\rho=300 m and albedo x dust surface $a_RC$=4300 km^2. The coma was relatively red at V-R=0.66 mag, which is consistent with that of the dust in other comets. The observed properties and the overall fading in brightness between 10 AU and 26 AU follow the predicted behaviour of CO-driven activity (Capria et al. 2002). This is the most distant cometary activity ever observed.
We estimate the timescales for orbital decay of wide binaries embedded within dark matter halos, due to dynamical friction against the dark matter particles. We derive analytical scalings for this decay and calibrate and test them through the extensive use of N-body simulations, which accurately confirm the predicted temporal evolution. For density and velocity dispersion parameters as inferred for the dark matter halos of local dSph galaxies, we show that the decay timescales become shorter than the ages of the dSph stellar populations for binary stars composed of 1 $M_{\odot}$ stars, for initial separations larger than 0.1 pc. Such wide binaries are conspicuous and have been well measured in the solar neighborhood. The prediction of the dark matter hypothesis is that they should now be absent from stellar populations embedded within low velocity dispersion, high density dark mater halos, as currently inferred for the local dSph galaxies, having since evolved into tighter binaries. Relevant empirical determinations of this will become technically feasible in the near future, and could provide evidence to discriminate between dark matter particle halos or modified gravitational theories, to account for the high dispersion velocities measured for stars in local dSph galaxies.
We obtained new UBV photometry and spectroscopy of Blue Plume (BP) stars in fields near the center of the Canis Major Over-Density (CMa). We combined analysis of the color-color diagrams with a new comparison of the hydrogen Balmer-line profile to the reddening-free Q parameter to improve the reddening and extinction estimates for this low-latitude, differentially reddened, area of the sky. Results of our stellar parameter analysis for B/A spectral type stars associated with the BP show that the majority of the stars have main-sequence surface gravities placing them at an average heliocentric distance of <D> = 6.0 +/- 2.7 kpc. This distance is more consistent with membership in the intervening Perseus spiral arm and strongly suggests that the BP stars are not associated with the other stellar populations previously reported to make up the CMa. This result casts serious doubt on the proposed dwarf galaxy origin for the CMa.
We have used the Sydney University Stellar Interferometer (SUSI) to measure the angular diameter of alpha Cir. This is the first detailed interferometric study of a rapidly oscillating A (roAp) star, alpha Cir being the brightest member of its class. We used the new and more accurate Hipparcos parallax to determine the radius to be 1.967+-0.066 Rs. We have constrained the bolometric flux from calibrated spectra to determine an effective temperature of 7420+-170 K. This is the first direct determination of the temperature of an roAp star. Our temperature is at the low end of previous estimates, which span over 1000 K and were based on either photometric indices or spectroscopic methods. In addition, we have analysed two high-quality spectra of alpha Cir, obtained at different rotational phases and we find evidence for the presence of spots. In both spectra we find nearly solar abundances of C, O, Si, Ca and Fe, high abundance of Cr and Mn, while Co, Y, Nd and Eu are overabundant by about 1 dex. The results reported here provide important observational constraints for future studies of the atmospheric structure and pulsation of alpha Cir.
We investigate long-term X-ray behaviors from the Sgr B2 complex using archival data of the X-ray satellites Suzaku, XMM-Newton, Chandra and ASCA. The observed region of the Sgr B2 complex includes two prominent spots in the Fe I K-$\alpha$ line at 6.40 keV, a giant molecular cloud M 0.66$-$0.02 known as the ``Sgr B2 cloud'' and an unusual X-ray source G 0.570$-$0.018. Although these 6.40 keV spots have spatial extensions of a few pc scale, the morphology and flux of the 6.40 keV line has been time variable for 10 years, in contrast to the constant flux of the Fe XXV-K$\alpha$ line at 6.67 keV in the Galactic diffuse X-ray emission. This time variation is mostly due to M 0.66$-$0.02; the 6.40 keV line flux declined in 2001 and decreased to 60% in the time span 1994--2005. The other spot G 0.570$-$0.018 is found to be conspicuous only in the Chandra observation in 2000. From the long-term time variability ($\sim$10 years) of the Sgr B2 complex, we infer that the Galactic Center black hole Sgr A$^*$ was X-ray bright in the past 300 year and exhibited a time variability with a period of a few years.
The orbit and physical parameters of the previously unsolved SB2 EB V570 Per are derived using high resolution Asiago Echelle spectroscopy and B, V photo-electric photometry. The metallicity from chi^2 analysis is [M/H]=+0.02 +/- 0.03, and reddening from interstellar NaI and KI absorption lines is E(B-V) =0.023 +/- 0.007. The two components have masses of 1.449 +/- 0.006 and 1.350 +/- 0.006 Msun and spectral types F3 and F5, respectively. They are both still within the Main Sequence band (T_1 =6842 +/- 25 K, T_2 =6562 +/- 25 K from chi^2 analysis, R_1 =1.523 +/- 0.030, R_2 =1.388 +/- 0.019 Rsun) and are dynamically relaxed to co-rotation with the orbital motion (Vrot sin i_{1,2} =40 and 36 (+/-1) km/sec). The distance to V570 Per obtained from the orbital solution is 123 +/- 2 pc, in excellent agreement with the revised Hipparcos distance of 123 +/- 11 pc. The observed properties of V570 Per components are compared to BaSTI models computed on purpose for exactly the observed masses and varied chemical compositions. This system is interesting since both components have their masses in the range where the efficiency of convective core overshooting has to decrease with the total mass as a consequence of the decreasing size of the convective core during the central H-burning stage. Our numerical simulations show that, a small but not null overshooting is required, with efficiencies lambda_{OV} =0.14 and 0.11 for the 1.449 and 1.350 Msun components, respectively. This confirms the finding of Paper II on the similar system V505 Per. At the approx 0.8 Gyr age of the system, the element diffusion has reduced the surface metallicity of the models from the initial [M/H]=+0.17 to [M/H]=+0.02, in perfect agreement with the spectroscopically derived [M/H]=+0.02 +/- 0.03 value.
We present new XMM-Newton data of the high-redshift (z=1.883), Mpc-sized giant radio galaxy 6C 0905+39. The larger collecting area and longer observation time for our new data means that we can better characterise the extended X-ray emission, in particular its spectrum, which arises from cosmic microwave background photons scattered into the X-ray band by the energetic electrons in the spent synchrotron plasma of the (largely) radio-quiet lobes of 6C 0905+39. We calculate the energy that its jet-ejected plasma has dumped into its surroundings in the last 3 X 10^7 years and discuss the impact that similar, or even more extreme, examples of spent, radio-quiet lobes would have on their surroundings. Interestingly, there is an indication that the emission from the hotspots is softer than the rest of the extended emission and the core, implying it is due to synchrotron emission. We confirm our previous detection of the low-energy turnover in the eastern hotspot of 6C 0905+39.
Damped Lyman-alpha systems (DLAs) and sub-DLAs seen toward background quasars provide the most detailed probes of elemental abundances. Somewhat paradoxically these measurements are more difficult at lower redshifts due to the atmospheric cut-off, and so a few years ago our group began a programme to study abundances at z < 1.5 in quasar absorbers. In this paper, we present new UVES observations of six additional quasar absorption line systems at z < 1.5, five of which are sub-DLAs. We find solar or above solar metallicity, as measured by the abundance of zinc, assumed not to be affected by dust, in two sub-DLAs: one, towards Q0138-0005 with [Zn/H]=+0.28 +/- 0.16; the other towards Q2335+1501 with [Zn/H]=+0.07 +/- 0.34. Relatively high metallicity was observed in another system: Q0123-0058 with [Zn/H]=-0.45 +/- 0.20. Only for the one DLA in our sample, in Q0449-1645, do we find a low metallicity, [Zn/H]=-0.96 +/- 0.08. We also note that in some of these systems large relative abundance variations from component to component are observed in Si, Mn, Cr and Zn.
Spiral patterns are important agents of galaxy evolution. In this review, I describe how the redistribution of angular momentum by recurrent transient spiral patterns causes the random speeds of stars to rise over time, metallicity gradients to be reduced, and drives large-scale turbulence in the disk, which could be important for galactic dynamos. I also outline a possible mechanism for the recurrence of spiral instabilities and supporting evidence from solar neighborhood kinematics. Finally, I confirm that cloud scattering alone would predict the local velocity ellipsoid to be flattened, contrary to long-held expectations.
We update our previous constraints on two-component hot dark matter (axions and neutrinos), including the recent WMAP 5-year data release. Marginalising over sum m_nu provides m_a < 1.02 eV (95% C.L.) for the axion mass. In the absence of axions we find sum m_nu < 0.63 eV (95% C.L.).
Very-high-energy (>100 GeV) gamma-ray astronomy is emerging as an important discipline in both high energy astrophysics and astro-particle physics. This field is currently dominated by Imaging Atmospheric-Cherenkov Telescopes (IACTs) and arrays of these telescopes. Such arrays have achieved the best angular resolution and energy flux sensitivity in the gamma-ray domain and are still far from the fundamental limits of the technique. Here I will summarise some key aspects of this technique and go on to review the current status of the major instruments and to highlight selected recent results.
We present observations aimed at exploring both the nature of Lya emitting
nebulae (Lya blobs) at z=2.38 and the way they trace large scale structure
(LSS), by exploring their proximity to maximum starbursts through submillimeter
emission. Our most important objectives are to make a census of associated
submillimeter galaxies (SMGs), check their properties, and look for a possible
overdensity in the protocluster J2142-4426 at z=2.38.
We used the newly commissioned Large APEX Bolometer Camera (LABoCa) on the
Atacama Pathfinder EXperiment (APEX) telescope, in its Science Verification
phase, to carry out a deep 10'x10' map at 870 micron, and we performed multiple
checks of the quality of data processing and source extraction.
Our map, the first published deep image, confirms the capabilities of
APEX/LABoCa as the most efficient current equipment for wide and deep submm
mapping. Twenty-two sources were securely extracted with 870 micron flux
densities in the range 3-21 mJy, rms noise 0.8-2.4 mJy, and far-IR luminosities
probably in the range ~5-20 x 10(12) Lo. Only one of the four 50 kpc-extended
Lya blobs has a secure 870 micron counterpart. The 870 micron source counts in
the whole area are marginally higher than in the SHADES SCUBA survey, with a
possible over-density around this blob. The majority of the 3.6-24 micron SEDs
of the submillimeter sources indicate they are starburst dominated, with
redshifts mostly >2. However, there is evidence of a high-z AGN in ~30% of the
sources.
Although cosmic microwave background (CMB) anisotropy data alone cannot
constrain simultaneously the spatial curvature and the equation of state of
dark energy, CMB data provide a valuable addition to other experimental
results. However computing a full CMB power spectrum with a Boltzmann code is
quite slow; for instance if we want to work with many dark energy and/or
modified gravity models, or would like to optimize experiments where many
different configurations need to be tested, it is possible to adopt a quicker
and more efficient approach.
In this paper we consider the compression of the projected Planck CMB data
into four parameters, R (scaled distance to last scattering surface), l_a
(angular scale of sound horizon at last scattering), Omega_b h^2 (baryon
density fraction) and n_s (powerlaw index of primordial matter power spectrum),
all of which can be computed quickly. We show that, although this compression
loses information compared to the full likelihood, such information loss
becomes negligible when more data is added. We also demonstrate that the method
can be used for scalar field dark energy independently of the parametrisation
of the equation of state, and discuss how this method should be used for other
kinds of dark energy models.
The Galactic center is a hotbed of star formation activity, containing the most massive star formation site and three of the most massive young star clusters in the Galaxy. Given such a rich environment, it contains more stars with initial masses above 100 \Msun than anywhere else in the Galaxy. This review concerns the young stellar population in the Galactic center, as it relates to massive star formation in the region. The sample includes stars in the three massive stellar clusters, the population of younger stars in the present sites of star formation, the stars surrounding the central black hole, and the bulk of the stars in the field population. The fossil record in the Galactic center suggests that the recently formed massive stars there are present-day examples of similar populations that must have been formed through star formation episodes stretching back to the time period when the Galaxy was forming.
The first part of the paper discusses nuclear properties relevant to predict compound reactions. The second part addresses direct reactions with special emphasis on direct neutron capture.
As part of a large study to investigate the nature of the longer wavelength continuum emission of radio-loud AGN, we present new mid to far-infrared (MFIR) and high frequency radio observations for a complete sample of 2Jy powerful, southern radio galaxies at intermediate redshifts (0.05<z<0.7). Utilizing the sensitivity of the Spitzer Space Telescope, we have made deep MIPS observations at the wavelengths of 24, 70 and 160 microns, detecting 100% of our sample at 24 microns, and 90% at 70 microns. This high detection rate at MFIR wavelengths is unparallelled in samples of intermediate redshift radio galaxies. Complementing these results, we also present new high frequency observations (15 to 24Ghz) from the Australia Telescope Compact Array (ATCA) and the Very Large Array (VLA), which are used to investigate the potential contamination of the MFIR continuum by non-thermal synchrotron emission. With the latter observations we detect the compact cores in 59% of our complete sample, and deduce that non-thermal contamination of the MFIR continuum is significant in a maximum of 30% of our total sample. MFIR fluxes, radio fluxes and spectral energy distributions for the complete sample are presented here, while in a second paper we will analyse these data and discuss the implications for our understanding of the heating mechanism for the warm/cool dust, star formation in the host galaxies, and the unified schemes for powerful radio sources.
We report on a recent spectral line survey of the planetary nebula (PN) NGC 7027 using the Arizona Radio Observatory (ARO) 12m telescope and the Heinrich Hertz Submillimeter Telescope (SMT) at millimeter wavelengths. The spectra covering the frequency ranges 71--111GHz, 157--161GHz, and 218--267GHz were obtained with a typical sensitivity of rms<8mK. A total of 67 spectral lines are detected, 21 of which are identified with 8 molecular species, 32 with recombination lines from hydrogen and helium, and 14 remains unidentified. As the widths of emission lines from CO, other neutral molecules, molecular ions, as well as recombination of H+ and He+ are found to be different with each other, the line strengths and profiles are used to investigate the physical conditions and chemical processes of the neutral envelope of NGC 7027. The column densities and fractional abundances relative to H2 of the observed molecular species are calculated and compared with predictions from chemical models. We found evidence for overabundance of N2H+ and underabundance of CS and HNC in NGC 7027, suggesting that X-ray emission and shock wave may play an important role in the chemistry of the hot molecular envelope of the young PN.
We present the first colour-magnitude relation (CMR) of early-type galaxies in the central region of the Antlia cluster, obtained from CCD wide-field photometry in the Washington photometric system. Integrated (C -T1) colours, T1 magnitudes, and effective radii have been measured for 93 galaxies (i.e. the largest galaxies sample in the Washington system till now) from the FS90 catalogue (Ferguson & Sandage 1990). Membership of 37 objects can be confirmed through new radial velocities and data collected from the literature. The resulting colour-magnitude diagram shows that early-type FS90 galaxies that are spectroscopically confirmed Antlia members or that were considered as definite members by FS90, follow a well defined CMR (sigma_(C -T1) ~ 0.07 mag) that spans 9 magnitudes in brightness with no apparent change of slope. This relation is very tight for the whole magnitude range but S0 galaxies show a larger dispersion, apparently due to a separation of ellipticals and S0s. Antlia displays a slope of -13.6 in a T1 vs. (C -T1) diagram, in agreement with results for clusters like Fornax, Virgo, Perseus and Coma, which are dynamically different to Antlia. This fact might indicate that the build up of the CMR in cluster of galaxies is more related to galaxies internal processes than to the influence of the environment. Interpreting the CMR as a luminosity-metallicity relation of old stellar systems, the metallicities of the Antlia galaxies define a global relation down to Mv ~ -13. We also find, for early-type dwarfs, no clear relation between luminosity and effective radius, indicating a nearly constant mean effective radius of ~ 1 kpc. This value is also found in several samples of dwarf galaxies in Virgo and Coma.
We present the analysis of a total of 177h of high-quality optical time-series photometry of the helium atmosphere pulsating white dwarf (DBV) EC 20058-5234. The bulk of the observations (135h) were obtained during a WET campaign (XCOV15) in July 1997 that featured coordinated observing from 4 southern observatory sites over an 8-day period. The remaining data (42h) were obtained in June 2004 at Mt John Observatory in NZ over a one-week observing period. This work significantly extends the discovery observations of this low-amplitude (few percent) pulsator by increasing the number of detected frequencies from 8 to 18, and employs a simulation procedure to confirm the reality of these frequencies to a high level of significance (1 in 1000). The nature of the observed pulsation spectrum precludes identification of unique pulsation mode properties using any clearly discernable trends. However, we have used a global modelling procedure employing genetic algorithm techniques to identify the n, l values of 8 pulsation modes, and thereby obtain asteroseismic measurements of several model parameters, including the stellar mass (0.55 M_sun) and T_eff (~28200 K). These values are consistent with those derived from published spectral fitting: T_eff ~ 28400 K and log g ~ 7.86. We also present persuasive evidence from apparent rotational mode splitting for two of the modes that indicates this compact object is a relatively rapid rotator with a period of 2h. In direct analogy with the corresponding properties of the hydrogen (DAV) atmosphere pulsators, the stable low-amplitude pulsation behaviour of EC 20058 is entirely consistent with its inferred effective temperature, which indicates it is close to the blue edge of the DBV instability strip. (abridged)
Upcoming Weak Lensing (WL) surveys can be used to constrain Dark Energy (DE) properties, namely if tomographic techniques are used to improve their sensitivity. In this work, we use a Fisher matrix technique to compare the power of CMB anisotropy and polarization data with tomographic WL data, in constraining DE parameters. Adding WL data to available CMB data improves the detection of all cosmological parameters, but the impact is really strong when DE--DM coupling is considered, as WL tomography can then succeed to reduce the errors on some parameters by factors >10.
We present Very Large Array (VLA) observations of H2O and OH masers, as well as radio continuum emission at 1.3 and 18 cm toward three sources previously cataloged as planetary nebulae (PNe) and in which single-dish detections of H2O masers have been reported: IRAS 17443-2949, IRAS 17580-3111, and IRAS 18061-2505. Our goal was to unambiguously confirm their nature as water-maser-emitting PNe, a class of objects of which only two bona-fide members were previously known. We detected and mapped H2O maser emission toward all three sources, while OH maser emission is detected in IRAS 17443-2949 and IRAS 17580-3111 as well as in other two objects within the observed fields: IRAS 17442-2942 (unknown nature) and IRAS 17579-3121 (also cataloged as a possible PN). We found radio continuum emission associated only with IRAS 18061-2505. Our results confirm IRAS 18061-2505 as the third known case of a PN associated with H2O maser emission. The three known water-maser-emitting PNe have clear bipolar morphologies, which suggests that water maser emission in these objects is related to non-spherical mass-loss episodes. We speculate that these bipolar PNe would have ``water-fountain'' Asymptotic Giant Branch (AGB) and post-AGB stars as their precursors. A note of caution is given for other objects that have been classified as OHPNe (objects with both OH maser and radio continuum emission, that could be extremely young PNe) based on single-dish observations, since interferometric data of both OH masers and continuum are necessary for a proper identification as members of this class.
We derive a new peak lag vs. peak luminosity relation in gamma-ray burst (GRB) pulses. We demonstrate conclusively that GRB spectral lags are pulse rather than burst properties and show how the lag vs. luminosity relation determined from CCF measurements of burst properties is essentially just a rough measure of this newly derived relation for individual pulses. We further show that most GRB pulses have correlated properties: short-lag pulses have shorter durations, are more luminous, and are harder within a burst than long-lag pulses. We also uncover a new pulse duration vs. pulse peak luminosity relation, and indicate that long-lag pulses often precede short-lag pulses. Although most pulse behaviors are supportive of internal shocks (including long-lag pulses), we identify some pulse shapes that could result from external shocks.
We present the observational results of a near-infrared survey of a large sample of Class I protostars designed to determine the Class I binary separation distribution from ~100 AU to ~5000 AU. We have selected targets from a new sample of 267 nearby candidate Class I objects. This sample is well understood, consists of mostly Class I young stellar objects (YSOs) within 1 kpc, has targets selected from the whole sky, and is not biased by previous studies of star formation. We have observed 189 Class I YSOs north of -40 degrees declination at H, K and L'-bands, with a median angular resolution of 0.33" at L'. We determine our detection limit for close binary companions by observing artificial binaries. We choose a contrast limit and an outer detection limit to minimize contamination and to ensure that a candidate companion is gravitationally bound. Our survey uses observations at L' rather than K-band for the detection of binary companions since there is less scattered light and better seeing at L'. This paper presents the positions of our targets, the near-IR photometry of sources detected in our fields at L', as well as the observed properties of the 89 detected companions (73 of which are newly discovered). Although we have chosen contrast and separation limits to minimize contamination, we expect that there are ~6 stars identified as binary companions that are due to contamination. Finder charts at L' for each field are shown to facilitate future studies of these objects.
Models of leptogenesis are constrained by the low reheat temperature at the end of reheating associated with the gravitino bound. However a detailed view of reheating, in which the maximum temperature during reheating, $\Tmax$, can be orders of magnitude higher than the reheat temperature, allows for the production of heavy Majorana neutrinos needed for leptogenesis. But then one must also consider the possibility of enhanced gravitino production in such scenarios. In this article we consider gravitino production during reheating, its dependence on $\Tmax$, and its relevance for leptogenesis. Earlier analytical studies of the gravitino abundance have only considered gravitino production in the post-reheating radiation dominated era. We find that the gravitino abundance generated during reheating is comparable to that generated after reheating. This lowers the upper bound on the reheat temperature by a factor of 4/3.
We consider the properties of stress-energy tensors compatible with a Null Big Bang, i.e., cosmological evolution starting from a Killing horizon rather than a singularity. For Kantowski-Sachs cosmologies, it is shown that if matter satisfies the Null Energy Condition (NEC), then (i) regular cosmological evolution can only start from a Killing horizon, (ii) matter is absent at the horizon, and (iii) matter can only appear in the cosmological region due to interaction with vacuum. The latter is understood phenomenologically as a fluid whose stress tensor is insensitive to boosts in a particular direction. We also argue that matter is absent in a static region beyond the horizon. All this generalizes the observations recently obtained for a mixture of dust and a vacuum fluid. If, however, we admit the existence of phantom matter, its certain special kinds (with the parameter $w \leq -3$) are consistent with a Null Big Bang without interaction with vacuum (or without vacuum fluid at all). Then in the static region there is matter with $w\geq -1/3$. Alternatively, the evolution can begin from a horizon in an infinitely remote past, leading to a scenario combining the features of a Null Big Bang and an emergent universe.
We propose an extension of the standard model with a B-L global symmetry that is broken softly at the TeV scale. The neutrinos acquire masses through a type-II seesaw while the lepton (L) asymmetry arises in the {\it singlet sector} but without B-L violation. The model has the virtue that the scale of L-number violation ($\Lambda$) giving rise to neutrino masses is independent of the scale of leptogenesis ($\Lambda'$). As a result the model can explain {\it neutrino masses, singlet scalar dark matter and leptogenesis at the TeV scale}. The stability of the dark matter is ensured by a surviving $Z_2$ symmetry, which could be lifted at the Planck scale and thereby allowing Planck scale-suppressed decay of singlet scalar dark matter particles of mass $\approx 3$ MeV to $e^+ e^-$ pairs in the Galactic halo. The model also predicts a few hundred GeV doubly charged scalar and a long lived charged fermion, whose decay can be studied at Large Hadron Collider (LHC) and International Linear Collider (ILC).
We perform a study of cosmic evolution with an equation of state parameter $\omega(t)=\omega_0+\omega_1(t\dot H/H)$ by selecting a phenomenological $\Lambda$ model of the form, $\dot\Lambda\sim H^3$. This simple proposition explains both linearly expanding and inflationary Universes with a single set of equations. We notice that the inflation leads to a scaling in the equation of state parameter, $\omega(t)$, and hence in equation of state. In this approach, one of its two parameters have been pin pointed and the other have been delineated. It has been possible to show a connection between dark energy and Higgs-Boson.
We investigate the cosmological evolution of the system of a Dirac-Born-Infeld field plus a perfect fluid. We analyze the existence and stability of scaling solutions for the AdS throat and the quadratic potential. We find that the scaling solutions exist when the equation of state of the perfect fluid is negative and in the ultra-relativistic limit.
In this paper we preliminarily explore the possibility of designing a dedicated satellite-based mission to measure the general relativistic gravitomagnetic Lense-Thirring effect in the gravitational field of Mars. The focus is on the systematic error induced by the multipolar expansion of the areopotential and on possible strategies to reduce it. It turns out that the major sources of bias are the Mars'equatorial radius R and the even zonal harmonics J_L, L = 2,4,6... of the areopotential. An optimal solution, in principle, consists of using two probes at high-altitudes (a\approx 9500-9600 km) and different inclinations, and suitably combining their nodes in order to entirely cancel out the bias due to \delta R. The remaining uncancelled mismodelled terms due to \delta J_L, L = 2,4,6,... would induce a bias \lesssim 1%, according to the present-day MGS95J gravity model, over a wide range of admissible values of the inclinations. The Lense-Thirring out-of-plane shifts of the two probes would amount to about 10 cm yr^-1.
I propose a new volume-weighted probability measure for cosmological "multiverse" scenarios involving eternal inflation. The "reheating-volume (RV) cutoff" calculates the distribution of observable quantities on a portion of the reheating hypersurface that is conditioned to be finite. The RV measure is gauge-invariant, does not suffer from the "youngness paradox," and is independent of initial conditions at the beginning of inflation. In slow-roll inflationary models with a scalar inflaton, the RV-regulated probability distributions can be obtained by solving nonlinear diffusion equations. I discuss possible applications of the new measure to "landscape" scenarios with bubble nucleation.
We discuss the effect of curvature and matter inhomogeneities on the averaged scalar curvature of the present-day Universe. Motivated by studies of averaged inhomogeneous cosmologies, we contemplate on the question whether it is sensible to assume that curvature averages out on some scale of homogeneity, as implied by the standard concordance model of cosmology, or whether the averaged scalar curvature can be largely negative today, as required for an explanation of Dark Energy from inhomogeneities. We confront both conjectures with a detailed analysis of the kinematical backreaction term and estimate its strength for a multi-scale inhomogeneous matter and curvature distribution. Our main result is a formula for the spatially averaged scalar curvature involving quantities that are all measurable on regional (i.e. up to 100 Mpc) scales. We propose strategies to quantitatively evaluate the formula, and pinpoint the assumptions implied by the conjecture of a small or zero averaged curvature. We reach the conclusion that the standard concordance model needs fine-tuning in the sense of an assumed equipartition law for curvature in order to reconcile it with the estimated properties of the averaged physical space, whereas a negative averaged curvature is favoured, independent of the prior on the value of the cosmological constant.
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The stellar content of the S0 galaxy NGC 5102 is investigated. A modest population of bright main sequence stars and red supergiants (RSGs) is detected throughout the western portion of the disk, and the star formation rate (SFR) during the past ten million years is estimated to have been 0.02 solar masses per year. RGB stars are traced out to galactocentric distances of 10 kpc, which corresponds to ~ 14 disk scale lengths. A large population of bright asymptotic giant branch (AGB) stars are seen throughout the western portion of the disk, and it is concluded that (1) stars that formed within the past Gyr comprise ~ 20% of the total stellar disk mass, and (2) the SFR during intermediate epochs in the disk of NGC 5102 was at least 1.4 solar masses per year. It is suggested that NGC 5102 was a spiral galaxy that experienced a galaxy-wide episode of enhanced star formation that terminated a few hundred Myr in the past, and that much of its interstellar medium was ejected in an outflow.
In previous work stable approximately axisymmetric equilibrium configurations for magnetic stars were found by numerical simulation. Here I investigate the conditions under which more complex, non-axisymmetric configurations can form. I present numerical simulations of the formation of stable equilibria from turbulent initial conditions and demonstrate the existence of non-axisymmetric equilibria consisting of twisted flux tubes lying horizontally below the surface of the star, meandering around the star in random patterns. Whether such a non-axisymmetric equilibrium or a simple axisymmetric equilibrium forms depends on the radial profile of the strength of the initial magnetic field. The results could explain observations of non-dipolar fields on stars such as the B0.2 main-sequence star tau-Sco or the pulsar 1E 1207.4-5209. The secular evolution of these equilibria due to Ohmic and buoyancy processes is also examined.
We compute Fourier-resolved X-ray spectra of the Seyfert 1 Markarian 766 to study the shape of the variable components contributing to the 0.3-10 keV energy spectrum and their time-scale dependence. The fractional variability spectra peak at 1-3 keV, as in other Seyfert 1 galaxies, consistent with either a constant contribution from a soft excess component below 1 keV and Compton reflection component above 2 keV, or variable warm absorption enhancing the variability in the 1-3 keV range. The rms spectra, which shows the shape of the variable components only, is well described by a single power law with an absorption feature around 0.7 keV, which gives it an apparent soft excess. This spectral shape can be produced by a power law varying in normalisation, affected by an approximately constant (within each orbit) warm absorber, with parameters similar to those found by Turner et al. for the warm-absorber layer covering all spectral components in their scattering scenario. The total soft excess in the average spectrum can therefore be produced by a combination of constant warm absorption on the power law plus an additional less variable component. On shorter time-scales, the rms spectrum hardens and this evolution is well described by a change in power law slope, while the absorption parameters remain the same. The frequency dependence of the rms spectra can be interpreted as variability arising from propagating fluctuations through an extended emitting region, whose emitted spectrum is a power law that hardens towards the centre. This scenario reduces the short time-scale variability of lower energy bands making the variable spectrum harder on shorter time-scales and at the same time explains the hard lags found in these data by Markowitz et al.
According to one model, high-frequency quasi-periodic oscillations (QPOs) can be identified with inertial waves, trapped in the inner regions of accretion discs around black holes due to relativistic effects. In order to be detected, their amplitudes need to reach large enough values via some excitation mechanism. We work out in detail a non-linear coupling mechanism suggested by Kato, in which a global warping or eccentricity of the disc has a fundamental role. These large-scale deformations combine with trapped modes to generate `intermediate' waves of negative energy that are damped as they approach either their corotation resonance or the inner edge of the disc, resulting in amplification of the trapped waves. We determine the growth rates of the inertial modes, as well as their dependence on the spin of the black hole and the properties of the disc. Our results indicate that this coupling mechanism can provide an efficient excitation of trapped inertial waves, provided the global deformations reach the inner part of the disc with non-negligible amplitude.
We present Multiband Imaging Photometer for Spitzer (MIPS) observations at 24
and 70 microns for 30 stars, and at 160 microns for a subset of 12 stars, in
the nearby (~30 pc), young (~12 Myr) Beta Pictoris Moving Group (BPMG). In
several cases, the new MIPS measurements resolve source confusion and
background contamination issues in the IRAS data for this sample. We find that
7 members have 24 micron excesses, implying a debris disk fraction of 23%, and
that at least 11 have 70 micron excesses (disk fraction of >=37%). Five disks
are detected at 160 microns (out of a biased sample of 12 stars observed), with
a range of 160/70 flux ratios. The disk fraction at 24 and 70 microns, and the
size of the excesses measured at each wavelength, are both consistent with an
"inside-out" infrared excess decrease with time, wherein the shorter-wavelength
excesses disappear before longer-wavelength excesses, and consistent with the
overall decrease of infrared excess frequency with stellar age, as seen in
Spitzer studies of other young stellar groups. Assuming that the infrared
excesses are entirely due to circumstellar disks, we characterize the disk
properties using simple models and fractional infrared luminosities. Optically
thick disks, seen in the younger TW Hya and eta Cha associations, are entirely
absent in the BPMG.
Additional flux density measurements at 24 and 70 microns are reported for
nine Tucanae-Horologium Association member stars. Since this is <20% of the
association membership, limited analysis on the complete disk fraction of this
association is possible.
We report the discovery of a compact supercluster structure at z=0.9. The structure comprises three optically-selected clusters, all of which are detected in X-rays and spectroscopically confirmed to lie at the same redshift. The Chandra X-ray temperatures imply individual masses of ~5x10^14 Msun. The X-ray masses are consistent with those inferred from optical--X-ray scaling relations established at lower redshift. A strongly-lensed z~4 Lyman break galaxy behind one of the clusters allows a strong-lensing mass to be estimated for this cluster, which is in good agreement with the X-ray measurement. Optical spectroscopy of this cluster gives a dynamical mass in good agreement with the other independent mass estimates. The three components of the RCS2319+00 supercluster are separated from their nearest neighbor by a mere <3 Mpc in the plane of the sky and likely <10 Mpc along the line-of-sight, and we interpret this structure as the high-redshift antecedent of massive (~10^15 Msun) z~0.5 clusters such as MS0451.5-0305.
We analyzed Chandra observations of three gravitational lenses, SBS0909+523, FBQS0951+2635, and B1152+199, to measure the differential X-ray absorption and the dust-to-gas ratio of the lens galaxies. We successfully detected the differential X-ray absorption in SBS0909+523 and B1152+199, and failed to detect it in FBQS0951+2635 due to the dramatic drop in its flux from the ROSAT epoch. These measurements significantly increase the sample of dust-to-gas ratio measurements in cosmologically-distant, normal galaxies. Using the larger sample, we obtain an average dust-to-gas ratio of E(B-V)/NH = (1.5\pm0.5)e-22 mag cm^2/atoms with an estimated intrinsic dispersion in the ratio of \simeq 40%. This average dust-to-gas ratio is consistent with our previous measurement, and the average Galactic value of 1.7e-22 mag cm^2/atoms and the estimated intrinsic dispersion is also consistent with the 30% observed in the Galaxy. A larger sample size is still needed to improve the measurements and to begin studying the evolution in the ratio with cosmic time. We also detected X-ray microlensing in SBS0909+523 and significant X-ray variability in FBQS0951+2635.
We present a detailed analysis of the XMM-Newton and Chandra observations of Abell 2626 focused on the X-ray and radio interactions. Within the region of the radio mini-halo (~70 kpc), there are substructures which are probably produced by the central radio source and the cooling core. We find that there is no obvious correlation between the radio bars and the X-ray image. The morphology of Abell 2626 is more complex than that of the standard X-ray radio bubbles seen in other cool core clusters. Thus, Abell 2626 provides a challenge to models for the cooling flow -- radio source interaction. We identified two soft X-ray (0.3--2 keV) peaks with the two central cD nuclei; one of them has an associated hard X-ray (2--10 keV) point source. We suggest that the two symmetric radio bars can be explained by two precessing jets ejected from an AGN. Beyond the central regions, we find two extended X-ray sources to the southwest and northeast of the cluster center which are apparently associated with merging subclusters. The main Abell 2626 cluster and these two subclusters are extended along the direction of the Perseus-Pegasus supercluster, and we suggest that Abell 2626 is preferentially accreting subclusters and groups from this large-scale structure filament. We also find an extended X-ray source associated with the cluster S0 galaxy IC 5337; the morphology of this source suggests that it is infalling from the west, and is not associated with the southwest subcluster, as had been previously suggested.
We examine the effects of turbulent intermittency on the deflagration to detonation transition (DDT) in Type Ia supernovae. The Zel'dovich mechanism for DDT requires the formation of a nearly isothermal region of mixed ash and fuel that is larger than a critical size. We primarily consider the hypothesis by Khokhlov et al. and Niemeyer and Woosley that the nearly isothermal, mixed region is produced when the flame makes the transition to the distributed regime. We use two models for the distribution of the turbulent velocity fluctuations to estimate the probability as a function of the density in the exploding white dwarf that a given region of critical size is in the distributed regime due to strong local turbulent stretching of the flame structure. We also estimate lower limits on the number of such regions as a function of density. We find that the distributed regime, and hence perhaps DDT, occurs in a local region of critical size at a density at least a factor of 2-3 larger than predicted for mean conditions that neglect intermittency. This factor brings the transition density to be much larger than the empirical value from observations in most situations. We also consider the intermittency effect on the more stringent conditions for DDT by Lisewski et al. and Woosley. We find that a turbulent velocity of $10^8$ cm/s in a region of size $10^6$ cm, required by Lisewski et al., is rare. We expect that intermittency gives a weaker effect on the Woosley model with stronger criterion. The predicted transition density from this criterion remains below $10^7$ g/cm$^3$ after accounting for intermittency using our intermittency models.
We report the first Very Long Baseline Array (VLBA) observations of 43 GHz v=1, J=1-0 SiO masers in the circumstellar envelope of the M-type semi-regular supergiant variable star AH Sco at 2 epochs separated by 12 days in March 2004. These high-resolution VLBA images reveal that the distribution of SiO masers is roughly on a persistent elliptical ring with the lengths of the major and minor axes of about 18.5 and 15.8 mas, respectively, along a position angle of 150^{\circ}. And the red-shifted masers are found to be slightly closer to the central star than the blue-shifted masers. The line-of-sight velocity structure of the SiO masers shows that with respect to the systemic velocity of -6.8 km/s the higher velocity features are closer to the star, which can be well explained by the simple outflow or infall without rotation kinematics of SiO masers around AH Sco. Study of proper motions of 59 matched features between two epochs clearly indicates that the SiO maser shell around AH Sco was undergoing an overall contraction to the star at a velocity of ~13 km/s at a distance of 2.26 kpc to AH Sco. Our 3-dimensional maser kinematics model further suggests that such an inward motion is very likely due to the gravitation of the central star. The distance to AH Sco of 2.26$\pm$0.19 kpc obtained from the 3-dimensional kinematics model fitting is consistent with its kinematic distance of 2.0 kpc.
We present 432 low-dispersion optical spectra of 32 Type Ia supernovae (SNe Ia) that also have well-calibrated light curves. The coverage ranges from 6 epochs to 36 epochs of spectroscopy. Most of the data were obtained with the 1.5m Tillinghast telescope at the F. L. Whipple Observatory with typical wavelength coverage of 3700-7400A and a resolution of ~7A. The earliest spectra are thirteen days before B-band maximum; two-thirds of the SNe were observed before maximum brightness. Coverage for some SNe continues almost to the nebular phase. The consistency of the method of observation and the technique of reduction makes this an ideal data set for studying the spectroscopic diversity of SNe Ia.
This paper presents a summary of a panel discussion to more directly confront theoretical models and observational constraints in massive star formation research. The panel was moderated by Hans Zinnecker, and panel members included Ian Bonnell, Chris McKee, Francesco Palla, Malcolm Walmsley, and Harold Yorke. Additional ample discussion with the audience is recorded.
Context: We present 31.2 days of nearly continuous MOST photometry of the roAp star 10Aql. Aims:The goal was to provide an unambiguous frequency identification for this little studied star, as well as to discuss the detected frequencies in the context of magnetic models and analyze the influence of the magnetic field on the pulsation. Methods: Using traditional Fourier analysis techniques on three independent data reductions, intrinsic frequencies for the star are identified. Theoretical non-adiabatic axisymmetric modes influenced by a magnetic field having polar field strengths Bp = 0-5kG were computed to compare the observations to theory. Results: The high-precision data allow us to identify three definite intrinsic pulsation frequencies and two other candidate frequencies with low S/N. Considering the observed spacings, only one (50.95microHz) is consistent with the main sequence nature of roAp stars. The comparison with theoretical models yields a best fit for a 1.95Msun model having solar metallicity, suppressed envelope convection, and homogenous helium abundance. Furthermore, our analysis confirms the suspected slow rotation of the star and sets new lower limits to the rotation period (Prot>1 month) and inclination (i>30\pm10deg.). Conclusions:The observed frequency spectrum is not rich enough to unambiguously identify a model. On the other hand, the models hardly represent roAp stars in detail due to the approximations needed to describe the interactions of the magnetic field with stellar structure and pulsation. Consequently, errors in the model frequencies needed for the fitting procedure can only be estimated. Nevertheless, it is encouraging that models which suppress convection and include solar metallicity, in agreement with current concepts of roAp stars, fit the observations best.
Quantitative constraints on the wind clumping of massive stars can be obtained from the study of the hard X-ray variability of SFXTs. In these systems, a large fraction of the hard X-ray emission is emitted in the form of flares with typical duration of 3 ksec, frequency of 7 days and luminosity of $10^{36}$ ergs/s. Such flares are most probably emitted by the interaction of a compact object orbiting at $\sim10$ R$_*$ with wind clumps ($10^{22-23}$ g). The density ratio between the clumps and the inter-clump medium is $10^{2-4}$ . The parameters of the clumps and of the inter-clump medium are in good agreement with macro-clumping scenario and line-driven instability simulations.
The Odin satellite has been used to search for the 118.75-GHz line of molecular oxygen (O2)in the Galactic centre. Odin observations were performed towards the Sgr A* circumnuclear disk (CND), and the Sgr A +20 km/s and +50 km/s molecular clouds using the position-switching mode. Supplementary ground-based observations were carried out in the 2-mm band using the ARO Kitt Peak 12-m telescope to examine suspected SiC features. A strong emission line was found at 118.27 GHz, attributable to the J=13-12 HC3N line. Upper limits are presented for the 118.75-GHz O2 (1,1-1,0) ground transition line and for the 118.11-GHz 3Pi2, J=3-2 ground state SiC line at the Galactic centre. Upper limits are also presented for the 487-GHz O2 line in the Sgr A +50 km/s cloud and for the 157-GHz, J=4-3, SiC line in the Sgr A +20 and +50 km/s clouds, as well as the CND. The CH3OH line complex at 157.2 - 157.3 GHz has been detected in the +20 and +50 km/s clouds but not towards Sgr A*/CND. A 3-sigma upper limit for the fractional abundance ratio of [O2]/[H2] is found to be X(O2) < 1.2 x 10exp(-7) towards the Sgr A molecular belt region.
We present preliminary results from the analysis of simultaneous multiwavelength observations of the black hole candidate Swift J1753.5-0127. The source is still continuing its outburst started in May 2005, never leaving the Low/Hard State. In the X-ray energy spectra we confirm evidence for a thermal component at a very low luminosity possibly extending close to but not at the innermost stable orbit. This is unusual for black hole candidates in the Low/Hard State. Furthermore, we confirm that its radio emission is significantly fainter than expected from the relation observed in other black hole candidates between the observed radio/X-ray fluxes.
Effects of rapid stellar rotation on acoustic oscillation modes are poorly understood. We study the dynamics of acoustic rays in rotating polytropic stars and show using quantum chaos concepts that the eigenfrequency spectrum is a superposition of regular frequency patterns and an irregular frequency subset respectively associated with near-integrable and chaotic phase space regions. This opens new perspectives for rapidly rotating star seismology and also provides a new and potentially observable manifestation of wave chaos in a large scale natural system.
We use Bayesian model selection tools to forecast the Planck satellite's ability to distinguish between different models for the reionization history of the Universe, using the large angular scale signal in the cosmic microwave background polarization spectrum. We find that Planck is not expected to be able to distinguish between an instantaneous reionization model and a two-parameter smooth reionization model, and if so then it will not be able to distinguish between different two-parameter models either. However Bayesian model averaging will be needed to obtain unbiased estimates of the optical depth to reionization. We also generalize our results to a hypothetical future cosmic variance limited microwave anisotropy survey. There the outlook is much more optimistic.
In 2005 March 22nd, the INTEGRAL satellite caught a type-I X-ray burst from the unidentified source XMMU J174716.1-281048, serendipitously discovered with XMM-Newton in 2003. Based on the type-I X-ray burst properties, we derived the distance of the object and suggested that the system is undergoing a prolonged accretion episode of many years. We present new data from a Swift/XRT campaign which strengthen this suggestion. AX J1754.2-2754 was an unclassified source reported in the ASCA catalogue of the Galactic Centre survey. INTEGRAL observed a type-I burst from it in 2005, April 16th. Recently, a Swift ToO allowed us to refine the source position and establish its persistent nature.
We have examined the correlations between the large-scale environment of
galaxies and their physical properties, using a sample of 28,354 nearby
galaxies drawn from the Sloan Digital Sky Survey, and the large-scale tidal
field reconstructed in real space from the 2Mass Redshift Survey and smoothed
over a radius of $\sim 6 h^{-1}$Mpc. The large-scale environment is expressed
in terms of the overdensity, the ellipticity of the shear and the type of the
large-scale structure. The physical properties analyzed include $r$-band
absolute magnitude $M_{^{0.1}r}$, stellar mass $M_\ast$, $g-r$ colour,
concentration parameter $R_{90}/R_{50}$ and surface stellar mass density
$\mu_\ast$.
Both luminosity and stellar mass are found to be statistically linked to the
large-scale environment, regardless of how the environment is quantified. More
luminous (massive) galaxies reside preferentially in the regions with higher
densities, lower ellipticities and halo-like structures. At fixed luminosity,
the large-scale overdensity depends strongly on parameters related to the
recent star formation history, that is colour and D(4000), but is almost
independent of the structural parameters $R_{90}/R_{50}$ and $\mu_\ast$. All
the physical properties are statistically linked to the shear of the
large-scale environment even when the large-scale density is constrained to a
narrow range. This statistical link has been found to be most significant in
the quasi-linear regions where the large-scale density approximates to an order
of unity, but no longer significant in highly nonlinear regimes with
$\delta_{\rm LS}\gg 1$.
We analysed simultaneous X-ray/radio observations of Circinus X-1 collected respectively with RXTE and ATCA in 2000 October and 2002 December and identified radio flares close to phase 0.0 and 0.5 of the orbital period. To date, there is only circumstantial evidence for radio flares near phase 0.5. Moreover, in our data set, we clearly associated both a radio flare and X-ray spectral timing changes with phase 0.0. While for black hole X-ray binaries the picture of the association between the X-ray and the radio bands is quite well understood, for neutron star X-ray binaries a clear and complete picture is still missing.
At low temperatures, the main coolant in primordial gas is molecular
hydrogen, H2. Recent work has shown that primordial gas that is not collapsing
gravitationally but is cooling from an initially ionized state forms hydrogen
deuteride, HD, in sufficient amounts to cool the gas to the temperature of the
cosmic microwave background. This extra cooling can reduce the characteristic
mass for gravitational fragmentation and may cause a shift in the
characteristic masses of population III stars. Motivated by the importance of
the atomic and molecular data for the cosmological question, we assess several
chemical and radiative processes that have hitherto been neglected: the
sensitivity of the low temperature H2 cooling rate to the ratio of ortho-H2 to
para-H2, the uncertainty in the low temperature cooling rate of H2 excited by
collisions with H, the effects of cooling from H2 excited by collisions with H+
and e-, and the large uncertainties in the rates of several of the reactions
responsible for determining the H2 fraction in the gas.
We show that the most important of the neglected processes is the excitation
of H2 by collisions with protons and electrons. This cools the gas more rapidly
at early times, and so it forms less H2 and HD at late times. This fact, as
well as several of the chemical uncertainties presented here, significantly
affects the thermal evolution of the gas. We anticipate that this may lead to
clear differences in future detailed 3D studies of first structure formation.
Finally, we show that although the thermal evolution of the gas is in principle
sensitive to the ortho-para ratio, in practice the standard assumption of a 3:1
ratio produces results that are almost indistinguishable from those produced by
a more detailed treatment. (abridged)
Quillen et al.(2007) presented an imaging survey with the {\it Spitzer Space Telescope} of 62 brightest cluster galaxies with optical line emission located in the cores of X-ray luminous clusters. They found that at least half of these sources have signs of excess infrared emission. Here we discuss the nature of the IR emission and its implications for cool core clusters. The strength of the mid-IR excess emission correlates with the luminosity of the optical emission lines. Excluding the four systems dominated by an AGN, the excess mid-infrared emission in the remaining brightest cluster galaxies is likely related to star formation. The mass of molecular gas (estimated from CO observations) is correlated with the IR luminosity as found for normal star forming galaxies. The gas depletion time scale is about 1 Gyr. The physical extent of the infrared excess is consistent with that of the optical emission line nebulae. This supports the hypothesis that the star formation occurs in molecular gas associated with the emission line nebulae and with evidence that the emission line nebulae are mainly powered by ongoing star formation. We find a correlation between mass deposition rates (${\dot M}_X$) estimated from the X-ray emission and the star formation rate estimated from the infrared luminosity. The star formation rates are 1/10 to 1/100 of the mass deposition rates suggesting that the re-heating of the ICM is generally very effective in reducing the amount of mass cooling from the hot phase but not eliminating it completely.
We show that grains have grown to ~mm size (sand sized) or larger in the terrestrial zone (within ~3 AU) of the protoplanetary disk surrounding the 3 Myr old binary star KH 15D. We also argue that the reflected light in the system reaches us by back scattering off the far side of the same ring whose near side causes the obscuration.
We consider hot accretion disk outflows from black hole - neutron star mergers in the context of the nucleosynthesis they produce. We find that at least a weak r-process is produced, and in some cases a main r-process as well. This result stems directly from the interactions of the neutrinos emitted by the disk with the free neutrons and protons in the outflow.
Primordial Quark Nuggets,remnants of the quark-hadron phase transition, may be hiding most of the baryon number in superdense chunks have been discussed for years always from the theoretical point of view. While they seemed originally fragile at intermediate cosmological temperatures, it became increasingly clear that they may survive due to a variety of effects affecting their evaporation (surface and volume) rates. A search of these objects have never been attempted to elucidate their existence. We discuss in this note how to search directly for cosmological fossil nuggets among the small asteroids approaching the Earth. ``Asteroids'' with a high visible-to-infrared flux ratio, constant lightcurves and devoid of spectral features are signals of an actual possible nugget nature. A viable search of very definite primordial quark nugget features can be conducted as a spinoff of the ongoing/forthcoming NEAs observation programmes.
During the operational life of BeppoSax, the Wide Field Camera observations covered almost the full sky at different epochs. The energy coverage, wide field of view and imaging capabilities share many commonalities with IBIS, the gamma-ray telescope onboard INTEGRAL satellite. We mosaicked all the available single pointing WFC observation images and then we searched the map for persistent and transient sources as has been done for the IBIS survey. This work represents the first unbiased source list compilation produced in this way from the overall WFC data set.
The merging galaxy cluster 1E 0657-56, known as the "bullet cluster," is one
of the hottest clusters known. The X-ray emitting plasma exhibits
bow-shock-like temperature and density jumps. The segregation of this plasma
from the peaks of the mass distribution determined by gravitational lensing has
been interpreted as a direct proof of collisionless dark matter. If the high
shock speed inferred from the shock jump conditions equals the relative speed
of the merging CDM halos, however, this merger is predicted to be such a rare
event in a LCDM universe that observing it presents a possible conflict with
the LCDM model.
We examined this question using high resolution, 2D simulations of gas
dynamics in cluster collisions to analyze the relative motion of the clusters,
the bow shock, and the contact discontinuity, and relate these to the X-ray
data for the bullet cluster. We find that the velocity of the fluid shock need
not equal the relative velocity of the CDM components. An illustrative
simulation finds that the present relative velocity of the CDM halos is 16%
lower than that of the shock. While this conclusion is sensitive to the
detailed initial mass and gas density profiles of the colliding clusters, such
a decrease of the inferred halo relative velocity would significantly increase
the likelihood of finding 1E 0657-56 in a LCDM universe.
(Conference proceedings based on a poster at Bash Symposium 2007)
Sakai et al. have observed long-chain unsaturated hydrocarbons and cyanopolyynes in the low-mass star-forming region L1527, and have attributed this result to a gas-phase ion-molecule chemistry, termed ``Warm Carbon Chain Chemistry'', which occurs during and after the evaporation of methane from warming grains. The source L1527 is an envelope surrounding a Class 0/I protostar with regions that possess a slightly elevated temperature of ~30 K. The molecules detected by Sakai et al. are typically associated only with dark molecular clouds, and not with the more evolved hot corino phase. In order to determine if L1527 is chemically distinct from a dark cloud, we compute models including various degrees of heating. The results indicate that the composition of L1527 is somewhat more likely to be due to ``Warm Carbon Chain Chemistry'' than to be a remnant of a colder phase. If so, the molecular products provide a signature of a previously uncharacterized early phase of low mass star formation, which can be characterized as a ``lukewarm'' corino. We also include predictions for other molecular species that might be observed toward candidate lukewarm corino sources. Although our calculations show that unsaturated hydrocarbons and cyanopolyynes can be produced in the gas phase as the grains warm up to 30 K, they also show that such species do not disappear rapidly from the gas as the temperature reaches 200 K, implying that such species might be detected in hot corinos and hot cores.
28 hitherto neglected candidates for the Catalogue of Nearby Stars (CNS) were
investigated to verify their classification and to improve their distance
estimates. All targets had at least a preliminary status of being nearby dwarf
stars based on their large proper motions and relatively faint magnitudes.
Better photometric and/or spectroscopic distances were required for selecting
stars which are worth the effort of trigonometric parallax measurements.
Low-resolution spectra were obtained with NASPEC at the Tautenburg 2m
telescope and with CAFOS at the Calar Alto 2.2m telescope. The spectral types
of M-type stars were determined by direct comparison of the target's spectra
with those of comparison stars of known spectral types observed with the same
instrument. The classification of earlier types was done based on comparison
with published spectral libraries. The majority were classified as M dwarfs
including 11 stars within 25 pc. The fainter component of LDS 1365, previously
thought to form a nearby common proper motion pair, is according to our results
an unrelated high-velocity background star. For several other nearby common
proper motion pairs our distance estimates of the fainter components are in
good agreement with Hipparcos distances of the brighter components. (abridged)
This paper offers a new point of view on component separation, based on a model of additive components which enjoys a much greater flexibility than more traditional linear component models. This flexibility is needed to process the complex full-sky observations of the CMB expected from the Planck space mission, for which it was developed, but it may also be useful in any context where accurate component separation is needed.
INTEGRAL has two sensitive gamma-ray instruments that have detected 46 gamma-ray bursts (GRBs) up to July 2007. We present the spectral, spatial, and temporal properties of the bursts in the INTEGRAL GRB catalogue using data from the imager, IBIS, and spectrometer, SPI. Spectral properties of the GRBs are determined using power-law, Band model and quasithermal model fits to the prompt emission. Spectral lags, i.e. the time delay in the arrival of low-energy gamma-rays with respect to high-energy gamma-rays, are measured for 31 of the GRBs. The photon index distribution of power-law fits to the prompt emission spectra is consistent with that obtained by Swift. The peak flux distribution shows that INTEGRAL detects proportionally more weak GRBs than Swift because of its higher sensitivity in a smaller field of view. The all-sky rate of GRBs above ~0.15 ph cm^-2 s^-1 is ~1400 yr^-1 in the fully coded field of view of IBIS. Two groups are identified in the spectral lag distribution, one with short lags <0.75 s (between 25-50 keV and 50-300 keV) and one with long lags >0.75 s. Most of the long-lag GRBs are inferred to have low redshifts because of their long spectral lags, their tendency to have low peak energies and their faint optical and X-ray afterglows. They are mainly observed in the direction of the supergalactic plane with a quadrupole moment of Q=-0.225+/-0.090 and hence reflect the local large-scale structure of the Universe. The rate of long-lag GRBs with inferred low luminosity is ~25% of Type Ib/c supernovae. Some of these bursts could be produced by the collapse of a massive star without a supernova or by a different progenitor, such as the merger of two white dwarfs or a white dwarf with a neutron star or black hole, possibly in the cluster environment without a host galaxy.
We present results from K band slit scan observations of a ~20''x20'' region of the Galactic center (GC) in two separate epochs more than five years apart. The high resolution (R>=14,000) observations allow the most accurate radial velocity and acceleration measurements of the stars in the central parsec of the Galaxy. Detected stars can be divided into three groups based on the CO absorption band heads at ~2.2935 microns and the He I lines at ~2.0581 microns and ~2.112, 2.113 microns: cool, narrow-line hot and broad-line hot. The radial velocities of the cool, late-type stars have approximately a symmetrical distribution with its center at ~-7.8(+/-10.3) km/s and a standard deviation ~113.7(+/-10.3) km/s. Although our statistics are dominated by the brightest stars, we estimate a central black hole mass of 3.9(+/-1.1) million solar masses, consistent with current estimates from complete orbits of individual stars. Our surface density profile and the velocity dispersion of the late type stars support the existence of a low density region at the Galactic center suggested by earlier observations. Many hot, early-type stars show radial velocity changes higher than maximum values allowed by pure circular orbital motions around a central massive object, suggesting that the motions of these stars greatly deviate from circular orbital motions around the Galactic center. The correlation between the radial velocities of the early type He I stars and their declination offsets from Sagittarius A* suggests that a systematic rotation is present for the early-type population. No figure rotation around the Galactic center for the late type stars is supported by the new observations.
We present mid-infrared Spitzer spectra of eleven planetary nebulae in the Galactic Bulge. We derive argon, neon, sulfur, and oxygen abundances for them using mainly infrared line fluxes combined with some optical line fluxes from the literature. Due to the high extinction toward the Bulge, the infrared spectra allow us to determine abundances for certain elements more accurately that previously possible with optical data alone. Abundances of argon and sulfur (and in most cases neon and oxygen) in planetary nebulae in the Bulge give the abundances of the interstellar medium at the time their progenitor stars formed; thus these abundances give information about the formation and evolution of the Bulge. The abundances of Bulge planetary nebulae tend to be slightly higher than those in the Disk on average, but they do not follow the trend of the Disk planetary nebulae, thus confirming the difference between Bulge and Disk evolution. Additionally, the Bulge planetary nebulae show peculiar dust properties compared to the Disk nebulae. Oxygen-rich dust feature (crystalline silicates) dominate the spectra of all of the Bulge planetary nebulae; such features are more scarce in Disk nebulae. Additionally, carbon-rich dust features (polycyclic aromatic hydrocarbons) appear in roughly half of the Bulge planetary nebulae in our sample, which is interesting in light of the fact that this dual chemistry is comparatively rare in the Milky Way as a whole.
Atomic hydrogen escaping from the planet HD209458b provides the largest observational signature ever detected for an extrasolar planet atmosphere. However, the Space Telescope Imaging Spectrograph (STIS) used in previous observational studies is no longer available, whereas additional observations are still needed to better constrain the mechanisms subtending the evaporation process, and determine the evaporation state of other `hot Jupiters'. Here, we aim to detect the extended hydrogen exosphere of HD209458b with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST) and to find evidence for a hydrogen comet-like tail trailing the planet, which size would depend on the escape rate and the amount of ionizing radiation emitted by the star. These observations also provide a benchmark for other transiting planets, in the frame of a comparative study of the evaporation state of close-in giant planets. Eight HST orbits are used to observe two transits of HD209458b. Transit light curves are obtained by performing photometry of the unresolved stellar Lyman-alpha emission line during both transits. Absorption signatures of exospheric hydrogen during the transit are compared to light curve models predicting a hydrogen tail. Transit depths of (9.6 +/- 7.0)% and (5.3 +/- 10.0)% are measured on the whole Lyman-alpha line in visits 1 and 2, respectively. Averaging data from both visits, we find an absorption depth of (8.0 +/- 5.7)%, in good agreement with previous studies. The extended size of the exosphere confirms that the planet is likely loosing hydrogen to space. Yet, the photometric precision achieved does not allow us to better constrain the hydrogen mass loss rate.
In this talk I discuss properties of hot stellar matter at sub-nuclear densities which is formed in supernova explosions. I emphasize that thermodynamic conditions there are rather similar to those created in the laboratory by intermediate-energy heavy-ion collisions. Theoretical methods developed for the description of multi-fragment final states in such reactions can be used also for description of the stellar matter. I present main steps of the statistical approach to the equation of state and nuclear composition, dealing with an ensemble of nuclear species instead of one "average" nucleus.
Chern-Simons modified gravity comprises the Einstein-Hilbert action and a higher-derivative interaction containing the Chern-Pontryagin density. We derive the analog of the Gibbons-Hawking-York boundary term required to render the Dirichlet boundary value problem well-defined. It turns out to be a boundary Chern-Simons action for the extrinsic curvature. We address applications to black hole thermodynamics.
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We have measured the Zeeman splitting of OH megamaser emission at 1667 MHz from five (ultra)luminous infrared galaxies ([U]LIRGs) using the 305 m Arecibo telescope and the 100 m Green Bank Telescope. Five of eight targeted galaxies show significant Zeeman-splitting detections, with 14 individual masing components detected and line-of-sight magnetic field strengths ranging from ~0.5-18 mG. The detected field strengths are similar to those measured in Galactic OH masers, suggesting that the local process of massive star formation occurs under similar conditions in (U)LIRGs and the Galaxy, in spite of the vastly different large-scale environments. Our measured field strengths are also similar to magnetic field strengths in (U)LIRGs inferred from synchrotron observations, implying that milligauss magnetic fields likely pervade most phases of the interstellar medium in (U)LIRGs. These results provide a promising new tool for probing the astrophysics of distant galaxies.
This chapter is based on four lectures given at the Cambridge N-body school "Cambody". The material covered includes the IMF, the 6D structure of dense clusters, residual gas expulsion and the initial binary population. It is aimed at those needing to initialise stellar populations for a variety of purposes (N-body experiments, stellar population synthesis).
In prior work, {\it Chandra} and Gemini-North observations of the eclipsing X-ray binary M33 X-7 have yielded measurements of the mass of its black hole primary and the system's orbital inclination angle of unprecedented accuracy. Likewise, the distance to the binary is known to a few percent. In an analysis based on these precise results, fifteen {\it Chandra} and {\it XMM-Newton} X-ray spectra, and our fully relativistic accretion disk model, we find that the dimensionless spin parameter of the black hole primary is $a_* = 0.77 \pm 0.05$. The error includes all sources of observational uncertainty. Four {\it Chandra} spectra of the highest quality, which were obtained over a span of several years, all lead to the same estimate of spin to within statistical errors (2%), and this estimate is confirmed by 11 spectra of lower quality. There are two remaining uncertainties: (1) the validity of the relativistic model used to analyze the observations, which is being addressed in ongoing theoretical work; and (2) our assumption that the black hole spin is approximately aligned with the angular momentum vector of the binary, which can be addressed by a future X-ray polarimetry mission.
One of the plausible unification schemes in physics considers the observable universe to be a 4-dimensional surface (the "brane") embedded in a higher-dimensional curved spacetime (the "bulk"). In such braneworld gravity models with infinitely large extra dimensions, black holes evaporate through the emission of the additional gravitational degrees of freedom, resulting in lifetimes of stellar-mass black holes that are significantly smaller than the Hubble time. We show that the predicted evaporation rate leads to a change in the orbital period of X-ray binaries harboring black holes that is observable with current instruments. We obtain an upper limit on the rate of change of the orbital period of the binary A0620-00 and use it to constrain the asymptotic curvature radius of the extra dimension to a value comparable to the one obtained by table-top experiments.
M87 provides the best opportunity to study the base of a jet where it is collimated and accelerated. The size of that region scales with the mass of the black hole, and M87 has the best combination of high mass, proximity to the Earth, and presence of a bright jet. VLBI observations of M87 can probe regions under 100 gravitational radii where theoretical studies suggest that the jet formation and acceleration occurs. A one-year sequence of 43 GHz observations every 3 weeks on the VLBA is being used to study the structure and dynamics in this region. Initial results from that effort are reported here, including the observation of rapid motions - sufficiently rapid that more frequent observations are planned for early 2008. The contribution ends with a discussion of prospects for future VLBI observations of M87 with VSOP2. For VSOP2, a strong recommendation is made that a series of daily observations at 43 GHz be planned.
The atmospheres of close-in extrasolar planets absorb most of the incident stellar radiation, advect this energy, then reradiate photons in preferential directions. Those photons carry away momentum, applying a force on the planet. Here we evaluate the resulting secular changes to the orbit, known as the Yarkovsky effect. For known transiting planets, typical fractional changes in semi-major axis are about 1% over their lifetime, but could be up to ~5% for close-in planets like OGLE-TR-56b or inflated planets like TrES-4. We discuss the origin of the correlation between semi-major axis and surface gravity of transiting planets in terms of various physical processes, finding that radiative thrusters are too weak by about a factor of 10 to establish the lower boundary that causes the correlation.
The recently revised cosmological constraints from the Five-Year WMAP data ameliorate previous tension between cosmological constraints from the microwave background and from cluster abundances. We demonstrate that the revised estimates of cosmological parameters are in excellent agreement with the mass function of X-ray clusters in the Sloan Digital Sky Survey. Velocity segregation between galaxies and the underlying dark matter could cause virial mass estimates to be biased, causing the mass scale of the mass function to be offset from the true value. Modest velocity segregation ($\sigma_{gxy}/\sigma_{DM}$=1.13$^{+0.06}_{-0.05}$) is sufficient to match the mass function to the Five-Year WMAP results. When the new WMAP results are combined with constraints from supernovae and baryon acoustic oscillations, there is no need for velocity segregation ($\sigma_{gxy}/\sigma_{DM}$=1.05$\pm$0.05). This result agrees with expectations for velocity segregation from state-of-the-art numerical simulations of clusters. Together with the improved agreement between the new WMAP results and recent cosmic shear measurements, this result demonstrates that the amplitude of large-scale structure in the nearby universe matches that predicted from the structure seen in the microwave background. The new constraint we place on velocity segregation in clusters indicates that virial mass estimates for clusters are reasonably accurate. This result suggests that future cluster surveys will be able to probe both cosmological parameters and fundamental cluster physics.
We present science highlights and performance from the Swift X-ray Telescope (XRT), which was launched on November 20, 2004. The XRT covers the 0.2-10 keV band, and spends most of its time observing gamma-ray burst (GRB)afterglows, though it has also performed observations of many other objects. By mid-August 2007, the XRT had observed over 220 GRB afterglows, detecting about 96% of them. The XRT positions enable followup ground-based optical observations, with roughly 60% of the afterglows detected at optical or near IR wavelengths. Redshifts are measured for 33% of X-ray afterglows. Science highlights include the discovery of flaring behavior at quite late times, with implications for GRB central engines; localization of short GRBs, leading to observational support for compact merger progenitors for this class of bursts; a mysterious plateau phase to GRB afterglows; as well as many other interesting observations such as X-ray emission from comets, novae, galactic transients, and other objects.
The Lyman-alpha forest has opened a new redshift regime for cosmological investigation. At z > 2 it provides a unique probe of cosmic geometry and an independent constraint on dark energy that is not subject to standard candle or ruler assumptions. In Paper I of this series on using the Lyman-alpha forest observed in pairs of QSOs for a new application of the Alcock-Paczynski test, we present and discuss the results of a campaign to obtain moderate-resolution spectroscopy (FWHM ~ 2.5 Angstroms) of the Lyman-alpha forest in pairs of QSOs with small redshift differences (Delta z < 0.25, z > 2.2) and arcminute separations (< 5'). This data set, composed of seven individual QSOs, 35 pairs, and one triplet, is also well-suited for future investigations of the coherence of Lyman-alpha absorbers on ~ 1 Mpc transverse scales and the transverse proximity effect. We note seven revisions for previously published QSO identifications and/or redshifts.
The isotropy of the Lyman-alpha forest in real-space uniquely provides a measurement of cosmic geometry at z > 2. The angular diameter distance for which the correlation function along the line of sight and in the transverse direction agree corresponds to the correct cosmological model. However, the Lyman-alpha forest is observed in redshift-space where distortions due to Hubble expansion, bulk flows, and thermal broadening introduce anisotropy. Similarly, a spectrograph's line spread function affects the autocorrelation and cross-correlation differently. In this the second paper of a series on using the Lyman-alpha forest observed in pairs of QSOs for a new application of the Alcock-Paczynski (AP) test, these anisotropies and related sources of potential systematic error are investigated with cosmological hydrodynamic simulations. Three prescriptions for galactic outflow were compared and found to have only a marginal effect on the Lyman-alpha flux correlation (which changed by at most 7% with use of the currently favored variable-momentum wind model vs. no winds at all). An approximate solution for obtaining the zero-lag cross-correlation corresponding to arbitrary spectral resolution directly from the zero-lag cross-correlation computed at full-resolution (good to within 2% at the scales of interest) is presented. Uncertainty in the observationally determined mean flux decrement of the Lyman-alpha forest was found to be the dominant source of systematic error; however, this is reduced significantly when considering correlation ratios. We describe a simple scheme for implementing our results, while mitigating systematic errors, in the context of a future application of the AP test.
The influence of dark matter inhomogeneities on the angular size-redshift test is investigated for a large class of flat cosmological models driven by dark energy plus a cold dark matter component (XCDM model). The results are presented in two steps. First, the mass inhomogeneities are modeled by a generalized Zeldovich-Kantowski-Dyer-Roeder (ZKDR) distance which is characterized by a smoothness parameter $\alpha(z)$ and a power index $\gamma$, and, second, we provide a statistical analysis to angular size data for a large sample of milliarcsecond compact radio sources. As a general result, we have found that the $\alpha$ parameter is totally unconstrained by this sample of angular diameter data.
The temporal behaviour of the early optical emission from Gamma-Ray Burst afterglows can be divided in four classes: fast-rising with an early peak, slow-rising with a late peak, flat plateaus, and rapid decays since first measurement. The fast-rising optical afterglows display correlations among peak flux, peak epoch, and post-peak power-law decay index that can be explained with a structured outflow seen off-axis, but the shock origin (reverse or forward) of the optical emission cannot be determined. The afterglows with plateaus and slow-rises may be accommodated by the same model, if observer location offsets are larger than for the fast-rising afterglows, or could be due to a long-lived injection of energy and/or ejecta in the blast-wave. If better calibrated with more afterglows, the peak flux-peak epoch relation exhibited by the fast and slow-rising optical light-curves could provide a way to use this type of afterglows as standard candles.
We explore tidal interactions of a galactic disk with Toomre parameter Q ~ 2 embedded in rigid halo/bulge with a point mass companion moving in a prescribed parabolic orbit. Tidal interactions produce well-defined spiral arms and extended tidal features such as bridge and tail that are all transient, but distinct in nature. In the extended disks, strong tidal force is able to lock the perturbed epicycle phases of the near-side particles to the perturber, shaping them into a tidal bridge that corotates with the perturber. A tidal tail develops at the opposite side as strongly-perturbed, near-side particles overtake mildly-perturbed, far-side particles. The tail is essentially a narrow material arm with a roughly logarithmic shape, dissolving with time because of large velocity dispersions. Inside the disks where tidal force is relatively weak, on the other hand, a two-armed logarithmic spiral pattern emerges due to the kinematic alignment of perturbed particle orbits. While self-gravity makes the spiral arms a bit stronger, the arms never become fully self-gravitating, wind up progressively with time, and decay after the peak almost exponentially in a time scale of ~ 1 Gyr. The arm pattern speed varying with both radius and time converges to Omega-kappa/2 at late time, suggesting that the pattern speed of tidally-driven arms may depend on radius in real galaxies. We present the parametric dependences of various properties of tidal features on the tidal strength, and discuss our findings in application to tidal spiral arms in grand-design spiral galaxies. (Abridged)
X-ray spectra of dwarf novae in quiescence observed by Chandra and XMM-Newton provide new information on the boundary layers of their accreting white dwarfs. Comparison of observations and models allows us to extract estimates for the thermal conductivity in the accretion layer and reach conclusions on the relevant physical processes. We calculate the structure of the dense thermal boundary layer that forms under gravity and cooling at the white dwarf surface on accretion of gas from a hot tenuous ADAF-type coronal inflow. The distribution of density and temperature obtained allows us to calculate the strength and spectrum of the emitted X-ray radiation. They depend strongly on the values of thermal conductivity and mass accretion rate. We apply our model to the dwarf nova system VW Hyi and compare the spectra predicted for different values of the thermal conductivity with the observed spectrum. We find a significant deviation for all values of thermal conductivity that are a sizable fraction of the Spitzer conductivity. A good fit arises however for a conductivity of about 1% of the Spitzer value. This also seems to hold for other dwarf nova systems in quiescence. We compare this result with thermal conduction in other astrophysical situations. The highly reduced thermal conductivity in the boundary layer requires magnetic fields perpendicular to the temperature gradient. Locating their origin in the accretion of magnetic fields from the hot ADAF-type coronal flow we find that dynamical effects of these fields will lead to a spatially intermittent, localized accretion geometry at the white dwarf surface.
Recent suggestions for a modification of general relativity to provide an alternative approach to gravity in connection with the dark energy (matter) problem imply a long range vector component of the gravitational field. This could lead to emission of gravitational dipole emission from objects such as pulsars. Stringent observational limits on period changes of binary and millisecond pulsars and their consistency with general relativity impose severe limits on couplings of such forces. These bounds are tighter than those implied by lunar laser ranging experiments.
We report on an analysis of X- and $\gamma$-ray observations of PKS 1830-211, based on the long-term campaigns carried out by \emph{INTEGRAL} and COMPTEL. The \emph{INTEGRAL} data currently available present a $33\sigma$ significance detection in the 20-100 keV band, while the COMPTEL 6-years data provide a $5.2\sigma$ significance detection in the 1-3 MeV energy band. At hard X-rays, \emph{INTEGRAL} and supplementary \emph{SWIFT} observations show flux variability on timescales of months. At $\gamma$-rays, the source shows persistent emission over years. The hard X-ray spectrum is well represented by a power-law model, with $\Gamma \sim 1.3$ in the 20-250 keV band. This photon index is well consistent with the previous report of $\Gamma \sim 1.3$ obtained at $E > 3.5$ keV from the best fit of \emph{XMM-Newton} data with a broken power law model. The joint \emph{XMM-Newton}/\emph{INTEGRAL} spectrum presented here is then fit with a broken power-law model and the parameters are refined compared to the previous. The results show the photon index changes from $\sim 1.0$ to $\sim 1.3$ at a break energy $\sim 4$ keV. At MeV energies, the spectrum softens to $\Gamma \sim 2.2$. These results, together with the EGRET measurement at $E \ge 100$ MeV, constitute a broad-band spectrum containing the peak of the power output at MeV energies, similar to most high-luminosity $\gamma$-ray blazars. The measured spectral characterstics are then discussed in the framework of the gravitational lens effects.
We present a simple method for determination of the orbital parameters of binary pulsars, using data on the pulsar period at multiple observing epochs. This method uses the circular nature of the velocity space orbit of Keplerian motion and produces preliminary values based on two one dimensional searches. Preliminary orbital parameter values are then refined using a computationally efficient linear least square fit. This method works for random and sparse sampling of the binary orbit. We demonstrate the technique on (a) the highly eccentric binary pulsar PSR J0514-4002 (the first known pulsar in the globular cluster NGC 1851) and (b) 47 Tuc T, a binary pulsar with a nearly circular orbit.
Two long gamma-ray bursts, GRB 060505 and GRB 060614, occurred in nearby galaxies at redshifts of 0.089 and 0.125 respectively. Due to their proximity and durations, deep follow-up campaigns to search for supernovae (SNe) were initiated. However none were found in either case, to limits more than two orders of magnitude fainter than the prototypical GRB-associated SN, 1998bw. It was suggested that the bursts, in spite of their durations (4 and 102 s), belonged to the population of short GRBs which has been shown to be unrelated to SNe. In the case of GRB 060614 this argument was based on a number of indicators, including the negligible spectral lag, which is consistent with that of short bursts. GRB 060505 has a shorter duration, but no spectral lag was measured. We present the spectral lag measurements of GRB 060505 using Suzakus Wide Area Monitor and the Swift Burst Alert Telescope. We find that the lag is 0.36+/- 0.05 s, inconsistent with the lags of short bursts and consistent with the properties of long bursts and SN-GRBs. These results support the association of GRB 060505 with other low-luminosity GRBs also found in star-forming galaxies and indicates that at least some massive stars may die without bright SNe.
The GALEX (Galaxy Evolution Explorer) spectroscopic survey mode, with a resolution of about 8 A in the FUV (1350 - 1750 A) and about 20 A in the NUV (1950 - 2750 A) is used for a systematic search of Ly-a emitting galaxies at low redshift. This aims at filling a gap between high-redshift surveys and a small set of objects studied in detail in the nearby universe. A blind search of 7018 spectra extracted in 5 deep exposures (5.65 sq.deg) has resulted in 96 Ly-a emitting galaxy candidates in the FUV domain, after accounting for broad-line AGNs. The Ly-a EWs (equivalent width) are consistent with stellar population model predictions and show no trends as a function of UV color or UV luminosity, except a possible decrease in the most luminous that may be due to small-number statistics. Their distribution in EW is similar to that at z about 3 but their fraction among star-forming galaxies is smaller. Avoiding uncertain candidates, a sub-sample of 66 objects in the range 0.2 < z < 0.35 has been used to build a Ly-a LF (luminosity function). The incompleteness due to objects with significant Ly-a emission but a UV continuum too low for spectral extraction has been evaluated. A comparison with H-a LF in the same redshift domain is consistent with an average Ly-a/H-a of about 1 in about 15 % of the star-forming galaxies. A comparison with high-redshift Ly-a LFs implies an increase of the Ly-a luminosity density by a factor of about 16 from z about 0.3 to z about 3. By comparison with the factor 5 increase of the UV luminosity density in the same redshift range, this suggests an increase of the average Ly-a escape fraction with redshift.
We study a small sample of z=0.1-0.6 core-collapse supernova (CCSN) host galaxies. Continuum observations at 250GHz have been performed with MAMBO at the IRAM-30m telescope. None of these sources has been detected and the error-weighted mean flux is 0.25+/-0.32 mJy. Upper limits on their dust masses are derived and the corresponding sample mean corresponds to 1.4 +/- 2.2 x 10^8 Msol. These results are comparable with previous submillimetre observations of SN-Ia hosts performed by Farrah et al. and by Clements et al. We conclude that CCSN hosts are not extreme at millimetre wavelengths, and as confirmed with the optical luminosities of a subset of our sample, they are typical of the local galaxy population.
We completed a new survey for H I emission for a large, well-defined sample of 154 nearby (z < 0.1) galaxies with type 1 AGNs. We make use of the extensive database presented in a companion paper to perform a comprehensive appraisal of the cold gas content in active galaxies and to seek new strategies to investigate the global properties of the host galaxies and their relationship to their central black holes (BHs). We show that the BH mass obeys a strong, roughly linear relation with the host galaxy's dynamical mass. BH mass follows a looser, though still highly significant, correlation with the maximum rotation velocity of the galaxy, as expected from the known scaling between rotation velocity and central velocity dispersion. Neither of these H I-based correlations is as tight as the more familiar relations between BH mass and bulge luminosity or velocity dispersion, but they offer the advantage of being insensitive to the glare of the nucleus and therefore are promising new tools for probing the host galaxies of both nearby and distant AGNs. We present evidence for substantial ongoing BH growth in the most actively accreting AGNs. In these nearby systems, BH growth appears to be delayed with respect to the assembly of the host galaxy but otherwise has left no detectable perturbation to its mass-to-light ratio or its global gas content. The host galaxies of type 1 AGNs, including those luminous enough to qualify as quasars, are generally gas-rich systems, possessing a cold interstellar medium reservoir at least as abundant as that in inactive galaxies of the same morphological type. This calls into question current implementations of AGN feedback in models of galaxy formation that predict strong cold gas depletion in unobscured AGNs. (Abridged)
[ABRIDGED] The unconditional mass function (UMF) of dark matter haloes has been determined accurately in the literature, showing excellent agreement with high resolution numerical simulations. However, this is not the case for the conditional mass function (CMF). We propose a simple analytical procedure to derive the CMF by rescaling the UMF to the constrained environment using the appropriate mean and variance of the density field at the constrained point. This method introduces two major modifications with respect to the standard re-scaling procedure. First of all, rather than using in the scaling procedure the properties of the environment averaged over all the conditioning region, we implement the re-scaling locally. We show that for high masses this modification may lead to substantially different results. Secondly, we modify the (local) standard re-scaling procedure in such a manner as to force normalisation, in the sense that when one integrates the CMF over all possible values of the constraint multiplied by their corresponding probability distribution, the UMF is recovered. In practise, we do this by replacing in the standard procedure the value delta_c (the linear density contrast for collapse) by certain adjustable effective parameter delta_eff. In order to test the method, we compare our prescription with the results obtained from numerical simulations in voids (Gottlober et al. 2003), finding a very good agreement. Based on these results, we finally present a very accurate analytical fit to the (accumulated) conditional mass function obtained with our procedure, which may be useful for any theoretical treatment of the large scale structure.
We consider the perihelion precession and bending of light in a class of Kaluza-Klein models and show that the "electric redshift" model, proposed in Zhang (2006) to explain the redshift of Quasars, does not agree with observations. As Zhang's model only considers the Jordan frame, we also compute the perihelion precession as seen in the Einstein frame and show that, to lowest order, the perihelion precession can only be consistent with observation in the Einstein frame. However, when we consider the corresponding "electric redshift" in the Einstein frame, we find that the redshift is significantly lower than for the Jordan frame and is therefore very unlikely to explain the redshift of quasars.
The connection between the long GRBs and Type Ic Supernovae (SNe) has revealed the interesting diversity: (i) GRB-SNe, (ii) Non-GRB Hypernovae (HNe), (iii) X-Ray Flash (XRF)-SNe, and (iv) Non-SN GRBs (or dark HNe). We show that nucleosynthetic properties found in the above diversity are connected to the variation of the abundance patterns of extremely-metal-poor (EMP) stars, such as the excess of C, Co, Zn relative to Fe. We explain such a connection in a unified manner as nucleosynthesis of hyper-aspherical (jet-induced) explosions Pop III core-collapse SNe. We show that (1) the explosions with large energy deposition rate, $\dot{E}_{\rm dep}$, are observed as GRB-HNe and their yields can explain the abundances of normal EMP stars, and (2) the explosions with small $\dot{E}_{\rm dep}$ are observed as GRBs without bright SNe and can be responsible for the formation of the C-rich EMP (CEMP) and the hyper metal-poor (HMP) stars. We thus propose that GRB-HNe and the Non-SN GRBs (dark HNe) belong to a continuous series of BH-forming stellar deaths with the relativistic jets of different $\dot{E}_{\rm dep}$.
It is argued that irradiation in low-mass X-ray binaries (LMXBs) caused by accretion-generated X-rays can not only change the optical appearance of LMXBs but also their outburst properties and possibly also their long-term evolution. Irradiation during an outburst of the outer parts of the accretion disc in a transient LMXB leads to drastic changes in the outburst properties. As far as the secular evolution of such systems is concerned, these changes can result in enhanced loss of mass and angular momentum from the system and, most important, in neutron star LMXBs in a much less efficient use of the transferred matter to spin up the neutron star to a ms-pulsar. Irradiation of the donor star can destabilize mass transfer and lead to irradiation-driven mass transfer cycles, i.e. to a secular evolution which differs drastically from an evolution in which irradiation is ignored. It is argued that irradiation-driven mass transfer cycles cannot occur in systems which are transient because of disc instabilities, i.e. in particular in long-period LMXBs with a giant donor. It is furthermore shown that for irradiating either the disc or the donor star, direct irradiation alone is insufficient. Rather, indirect irradiation via scattered accretion luminosity must play an important role in transient LMXBs and is, in fact, necessary to destabilize mass transfer in short-period systems by irradiating the donor star. Whether and to what extent irradiation in LMXBs does change their secular evolution depends on a number of unsolved problems which are briefly discussed at the end of this article.
Because of their large number of stars spread over the entire stellar mass spectrum, starburst clusters are highly suitable to benchmark and calibrate star formation models and theories. Among the handful of Galactic starburst clusters, Westerlund 1 with its estimated 150 O-stars, W-R stars, supergiants and hypergiants is the most massive young cluster identified to date in the Milky Way. While previous studies of Westerlund 1 focused largely on optical and X-ray observations of its evolved massive stellar population, we have analyzed near-infrared data, resulting in the first in depth study of the ``lower-mass'' main sequence and pre-main sequence cluster population, i.e., of stars in the mass range 0.4 to 30 solar masses. The derived properties of the cluster population allow us to test theoretical evolutionary tracks. By comparison of Westerlund 1's half-mass radius with younger starburst clusters like NGC 3603 YC and Arches, and somewhat older massive clusters like RSGC1 and RSGC2, we find evidence for a rapid dissolution of Galactic starburst clusters, which has interesting implications for the long-term survival of starburst clusters, and the question to which extent Galactic starburst clusters might mimic proto-globular clusters.
We explore the dynamics of cosmological models with two coupled dark components with energy densities $\rho_A$ and $\rho_B$. We assume that the coupling is of the form $Q=Hq(\rho_A,\rho_B)$, so that the dynamics of the two components turns out to be scale independent, i.e. does not depend explicitly on the Hubble scalar $H$. With this assumption, we focus on the general linear coupling $q=q_o+q_A\rho_A+q_B\rho_B$, which may be seen as arising from any $q(\rho_A,\rho_B)$ at late time and leads in general to an effective cosmological constant. In the second part of the paper we consider observational constraints on the form of the coupling from SN Ia data, assuming that one of the components is cold dark matter. We find that the constant part of the coupling function is unconstrained by SN Ia data and, among typical linear coupling functions, the one proportional to the dark energy density $\rho_{A}$ is preferred in the strong coupling regime, $|q_{A}|>1$. While phantom models favor a positive coupling function, in non-phantom models, not only a negative coupling function is allowed, but the uncoupled sub-case falls at the border of the likelihood.
Micrometeoroid or space debris impacts have been observed in the focal planes
of the XMM-Newton and Swift-XRT X-ray observatories. These impacts have
resulted in damage to, and in one case the failure of, focal-plane
Charge-Coupled Device (CCD) detectors.
We present a simple model for the propagation of micrometeoroids and space
debris particles into telescopes with grazing incidence X-ray optics. The risks
of future focal-plane impact events in three present (Swift-XRT, XMM-Newton,
and Chandra) and two future (SIMBOL-X and XEUS) X-ray observatories are then
estimated.
The probabilities of at least one impact occurring in the Swift-XRT,
XMM-Newton, and Chandra focal planes, in a one year period from the time of
writing in November 2007 are calculated to be ~5% and ~50% and ~3%. First-order
predictions of the impact rates expected for the future SIMBOL-X and XEUS X-ray
observatories yield probabilities for at least one focal-plane impact, during
nominal 5-year missions, of more than 94% and 99%, respectively.
Future X-ray observatories, with large collecting areas and long focal
lengths, may experience much higher impact rates on their focal-plane detectors
than those currently in operation. This should be considered in the design and
planning of future missions.
A thorough search for Ultraluminous X-ray source candidates within the Local Volume is made. The search spatially matches potential ULXs detected in X-ray images or cataloged in the literature with galaxies tabulated in the Catalog of Neighboring Galaxies compiled by Karachentsev et al. (2004). The specific ULX frequency (occurrence rate per unit galaxy mass) is found to be a decreasing function of host galaxy mass for host masses above $\sim10^{8.5}$ solar mass. There is too little mass in galaxies below this point to determine if this trend continues to lower galaxy mass. No ULXs have yet been detected in lower-mass galaxies. Systematic differences between dwarf and giant galaxies that may explain an abundance of ULXs in dwarf galaxies and what they may imply about the nature of ULXs are discussed.
The WD+MS channel of the single-degenerate scenario is currently favourable for progenitors of type Ia supernovae (SNe Ia). Incorporating the results of detailed binary evolution calculations for this channel into the latest version of a binary population synthesis code, I obtained the distributions of many properties of the companion stars at the moment of SN explosion. The properties can be verified by future observations.
The diagnostic age versus mass-to-light ratio diagram is often used in attempts to constrain the shape of the stellar initial mass function (IMF), and the stability and the potential longevity of extragalactic young to intermediate-age massive star clusters. Here, we explore its potential for Galactic open clusters. On the basis of a homogenised cluster sample we provide useful constraints on the dynamical state of the individual clusters, and also on the presence of significant binary fractions. Using the massive young Galactic cluster Westerlund 1 as a key example, we caution that stochasticity in the IMF introduces significant additional uncertainties. Therefore, the stability and long-term survival chances of Westerlund 1 remain largely inconclusive. We conclude that for an open cluster to survive for any significant length of time and in the absence of substantial external perturbations, it is a necessary but not a sufficient condition to be located close to or (in the presence of a significant binary population) somewhat BELOW the predicted photometric evolutionary sequences for "normal" simple stellar populations (although such a location may be dominated by a remaining "bound" cluster core and thus not adequately reflect the overall cluster dynamics).
We present the results of hydrodynamic simulations of the formation and subsequent orbital evolution of giant planets embedded in a circumbinary disc. We assume that a 20 earth masses core has migrated to the edge of the inner cavity formed by the binary where it remains trapped by corotation torques. This core is then allowed to accrete gas from the disc, and we study its orbital evolution as it grows in mass. For each of the two accretion time scales we considered, we performed three simulations. In two of the three simulations, we stop the accretion onto the planet once its mass becomes characteristic of that of Saturn or Jupiter. In the remaining case, the planet can accrete disc material freely in such a way that its mass becomes higher than Jupiter's. The simulations show different outcomes depending on the final mass m_p of the giant. For m_p=1 M_S (where M_S is Saturn's mass), we find that the planet migrates inward through its interaction with the disc until its eccentricity becomes high enough to induce a torque reversal. The planet then migrates outward, and the system remains stable on long time scales. For m_p > 1 M_J (where M_J is Jupiter's mass) we observed two different outcomes. In each case the planet enters the 4:1 resonance with the binary, and resonant interaction drives up the eccentricity of the planet until it undergoes a close encounter with the secondary star. The result can either be ejection from the system or scattering out into the disc followed by a prolonged period of outward migration. These results suggest that circumbinary planets are more likely to be quite common in the Saturn-mass range. Jupiter-mass circumbinary planets are likely to be less common because of their less stable evolution.
We have started a survey of M 33 in order to find variable stars and Cepheids in particular. We have obtained more than 30 epochs of g'r'i' data with the CFHT and the one-square-degree camera MegaCam. We present first results from this survey, including the search for variable objects and a basic characterization of the various groups of variable stars.
We present here an extensive analysis of the protostellar jet driven by IRAS 20126+4104, deriving the kinematical, dynamical, and physical conditions of the H2 gas along the flow. The jet has been investigated by means of near-IR H2 and [FeII] narrow-band imaging, high resolution spectroscopy of the 1-0S(1) line (2.12 um), NIR (0.9-2.5 um) low resolution spectroscopy, along with ISO-SWS and LWS spectra (from 2.4 to 200 um). The flow shows a complex morphology. In addition to the large-scale jet precession presented in previous studies, we detect a small-scale wiggling close to the source, that may indicate the presence of a multiple system. The peak radial velocities of the H2 knots range from -42 to -14 km s^-1 in the blue lobe, and from -8 to 47 km s^-1 in the red lobe. The low resolution spectra are rich in H_2 emission, and relatively faint [FeII] (NIR), [OI] and [CII] (FIR) emission is observed in the region close to the source. A warm H2 gas component has an average excitation temperature that ranges between 2000 K and 2500 K. Additionally, the ISO-SWS spectrum reveals the presence of a cold component (520 K), that strongly contributes to the radiative cooling of the flow and plays a major role in the dynamics of the flow. The estimated L(H2) of the jet is 8.2+/-0.7 L_sun, suggesting that IRAS20126+4104 has an accretion rate significantly increased compared to low-mass YSOs. This is also supported by the derived mass flux rate from the H2 lines (Mflux(H2)~7.5x10^-4 M_sun yr^-1). The comparison between the H2 and the outflow parameters strongly indicates that the jet is driving, at least partially, the outflow. As already found for low-mass protostellar jets, the measured H2 outflow luminosity is tightly related to the source bolometric luminosity.
Aims: We identify the source of fast-drifting decimetric-metric radio emission that is sometimes observed prior to the so-called flare continuum emission. Fast-drift structures and continuum bursts are also observed in association with coronal mass ejections (CMEs), not only flares. Methods: We analyse radio spectral features and images acquired at radio, H-alpha, EUV, and soft X-ray wavelengths, during an event close to the solar limb on 2 June 2003. Results: The fast-drifting decimetric-metric radio burst corresponds to a moving, wide emission front in the radio images, which is normally interpreted as a signature of a propagating shock wave. A decimetric-metric type II burst where only the second harmonic lane is visible could explain the observations. After long-lasting activity in the active region, the hot and dense loops could be absorbing or suppressing emission at the fundamental plasma frequency. The observed burst speed suggests a super-Alfvenic velocity for the burst driver. The expanding and opening loops, associated with the flare and the early phase of CME lift-off, could be driving the shock. Alternatively, an instantaneous but fast loop expansion could initiate a freely propagating shock wave. The later, complex-looking decametre-hectometre wave type III bursts indicate the existence of a propagating shock, although no interplanetary type II burst was observed during the event. The data does not support CME bow shock or a shock at the flanks of the CME as the origin of the fast-drift decimetric-metric radio source. Therefore super-Alfvenic loop expansion is the best candidate for the initiation of the shock wave, and this result challenges the current view of metric/coronal shocks originating either in the flanks of CMEs or from flare blast waves.
This work treats the matter deceleration in a magnetohydrodynamics radiative shock wave at the surface of a star. The problem is relevant to classical T Tauri stars where infalling matter is channeled along the star's magnetic field and stopped in the dense layers of photosphere. A significant new aspect of the present work is that the magnetic field has an arbitrary angle with respect to the normal to the star's surface. We consider the limit where the magnetic field at the surface of the star is not very strong in the sense that the inflow is super Alfv\'enic. In this limit the initial deceleration and heating of plasma (at the entrance to the cooling zone) occurs in a fast magnetohydrodynamic shock wave. To calculate the intensity of radiative losses we use "real" and "power-law" radiative functions. We determine the stability/instability of the radiative shock wave as a function of parameters of the incoming flow: velocity, strength of the magnetic field, and its inclination to the surface of the star. In a number of simulation runs with the "real" radiative function, we find a simple criterion for stability of the radiative shock wave. For a wide range of parameters, the periods of oscillation of the shock wave are of the order 0.02-0.2 sec.
We have conducted a new Arecibo survey for H I emission for 113 galaxies with broad-line (type 1) active galactic nuclei (AGNs) out to recession velocities as high as 35,000 km/s. The primary aim of the study is to obtain sensitive H I spectra for a well-defined, uniformly selected sample of active galaxies that have estimates of their black hole masses in order to investigate correlations between H I properties and the characteristics of the AGNs. H I emission was detected in 66 out of the 101 (65%) objects with spectra uncorrupted by radio frequency interference, among which 45 (68%) have line profiles with adequate signal-to-noise ratio and sufficiently reliable inclination corrections to yield robust deprojected rotational velocities. This paper presents the basic survey products, including an atlas of H I spectra, measurements of H I flux, line width, profile asymmetry, optical images, optical spectroscopic parameters, as well as a summary of a number of derived properties pertaining to the host galaxies. To enlarge our primary sample, we also assemble all previously published H I measurements of type 1 AGNs for which can can estimate black hole masses, which total an additional 53 objects. The final comprehensive compilation of 154 broad-line active galaxies, by far the largest sample ever studied, forms the basis of our companion paper, which uses the H I database to explore a number of properties of the AGN host galaxies.
We show that the exoplanet-host star iota Horologii, alias HD17051, which belongs to the so-called Hyades stream, was formed within the primordial Hyades stellar cluster and has evaporated towards its present location, 40 pc away. This result has been obtained unambiguously by studying the acoustic oscillations of this star, using the HARPS spectrometer in La Silla Observatory (ESO, Chili). Besides the fact that $\iota$ Hor belongs to the Hyades stream, we give evidence that it has the same metallicity, helium abundance, and age as the other stars of the Hyades cluster. They were formed together, at the same time, in the same primordial cloud. This result has strong implications for theories of stellar formation. It also indicates that the observed overmetallicity of this exoplanet-host star, about twice that of the Sun, is original and not caused by planet accretion during the formation of the planetary system.
We discuss Q-balls in the complex signum-Gordon model in d-dimensional space for d=1,2,3. The Q-balls have strictly finite radius. Their total energy is a power-like function of the conserved U(1) charge with the exponent equal to (d+2)/(d+3). In the cases d=1 and d=3 explicit analytic solutions are presented.
We analyze the origin of the quasiclassical realm from the no-boundary proposal for the universe's quantum state in a class of minisuperspace models. The models assume homogeneous, isotropic, closed spacetime geometries, a single scalar field moving in a quadratic potential, and a fundamental cosmological constant. The allowed classical histories and their probabilities are calculated to leading semiclassical order. We find that for the most realistic range of parameters analyzed a minimum amount of scalar field is required, if there is any at all, in order for the universe to behave classically at late times. If the classical late time histories are extended back, they may be singular or bounce at a finite radius. The ensemble of classical histories is time symmetric although individual histories are generally not. The no-boundary proposal selects inflationary histories, but the measure on the classical solutions it provides is heavily biased towards small amounts of inflation. However, the probability for a large number of efoldings is enhanced by the volume factor needed to obtain the probability for what we observe in our past light cone, given our present age. Our results emphasize that it is the quantum state of the universe that determines whether or not it exhibits a quasiclassical realm and what histories are possible or probable within that realm.
A phase of massive gravity free from pathologies can be obtained by coupling the metric to an additional spin-two field. We study the gravitational field produced by a static spherically symmetric body, by finding the exact solution that generalizes the Schwarzschild metric to the case of massive gravity. Besides the usual 1/r term, the main effects of the new spin-two field are a shift of the total mass of the body and the presence of a new power-like term, with sizes determined by the mass and the shape (the radius) of the source. These modifications, being source dependent, give rise to a dynamical violation of the Strong Equivalence Principle. Depending on the details of the coupling of the new field, the power-like term may dominate at large distances or even in the ultraviolet. The effect persists also when the dynamics of the extra field is decoupled.
It is shown how high energy neutrino beams from very distant sources can be utilized to learn about many properties of neutrinos such as lifetimes, mass hierarchy, mixing, minuscule pseudo-Dirac mass splittings; in addition, the production mechanism of neutrinos in astrophysical sources can also be elucidated.