Conservation of the phase-space density of photons plus Lorentz invariance requires that the cosmological luminosity distance be larger than the angular diameter distance by a factor of $(1+z)^2$, where $z$ is the redshift. Because this is a fundamental symmetry, this prediction--known sometimes as the "Etherington relation" or the "Tolman test"--is independent of world model, or even the assumptions of homogeneity and isotropy. It depends, however, on Lorentz invariance and transparency. Transparency can be affected by intergalactic dust or interactions between photons and the dark sector. Baryon acoustic feature and type Ia supernovae measures of the expansion history are differently sensitive to the angular diameter and luminosity distances and can therefore be used in conjunction to limit cosmic transparency. At the present day, the comparison only limits the change $\Delta\tau$ in the optical depth from redshift 0.20 to 0.35 at visible wavelengths to $\Delta\tau < 0.13$ at 95-percent confidence. In a model with a constant comoving number density $n$ of scatterers of constant proper cross-section $\sigma$, this limit implies $n \sigma< 2\times10^{-4} h \Mpc^{-1}$. These limits depend weakly on cosmological world model. Within the next few years, the limits could extend to redshifts $z\approx2.5$ and improve to $n \sigma<1.1 \times10^{-5} h \Mpc^{-1}$. Cosmic variance will eventually limit the sensitivity of any test using the baryon acoustic feature at the $n \sigma\sim 4\times10^{-7} h \Mpc^{-1}$ level. Comparison with other measures of the transparency are provided; no other measure in the visible is as free of astrophysical assumptions.
All the physical processes involved in the formation, merging, and accretion history of massive black holes along the hierarchical build--up of cosmic structures are likely to leave an imprint on the gravitational waves detectable by future space--borne missions, such as LISA. We report here the results of recent studies, carried out by means of dedicated simulations of black hole build--up, aiming at understanding the impact on LISA observations of two ingredients that are crucial in every massive black hole formation scenario, namely: (i) the nature and abundance of the first black hole seeds and (ii) the large gravitational recoils following the merger of highly spinning black holes. We predict LISA detection rates spanning two order of magnitude, in the range 3-300 events per year, depending on the detail of the assumed massive black hole seed model. On the other hand, large recoil velocities do not dramatically compromise the efficiency of LISA observations. The number of detections may drop substantially (by ~60%), in scenarios characterized byabundant light seeds, but if seeds are already massive and/or relatively rare, the detection rate is basically unaffected.
Recent Cerenkov observations of the two BL Lac objects PKS 2155-304 and Mkn 501 revealed TeV flux variability by a factor ~2 in just 3-5 minutes. Even accounting for the effects of relativistic beaming, such short timescales are challenging simple and conventional emitting models, and call for alternative ideas. We explore the possibility that extremely fast variable emission might be produced by particles streaming at ultra-relativistic speeds along magnetic field lines and inverse Compton scattering any radiation field already present. This would produce extremely collimated beams of TeV photons. While the probability for the line of sight to be within such a narrow cone of emission would be negligibly small, one would expect that the process is not confined to a single site, but can take place in many very localised regions, along almost straight magnetic lines. A possible astrophysical setting realising these conditions is magneto-centrifugal acceleration of beams of particles. In this scenario, the variability timescale would not be related to the physical dimension of the emitting volume, but might be determined by either the typical duration of the process responsible for the production of these high energy particle beams or by the coherence length of the magnetic field. It is predicted that even faster TeV variability - with no X-ray counterpart - should be observed by the foreseen more sensitive Cerenkov telescopes.
(abridged) Non-ionizing stellar continua are a source of photons for continuum pumping in the hydrogen Lyman transitions. In the environments where these transitions are optically thick, deexcitation occurs through higher series lines, so that the flux in these lines has a fluorescent contribution in addition to recombination; in particular, Balmer emissivities are systematically enhanced above case B. The effectiveness of such mechanism in HII regions and the adequacy of photoionization models as a tool to study it are the two main focuses of this work. We find that photoionization models of H II regions illuminated by low-resolution population synthesis models significantly overpredict the fluorescent contribution to the Balmer lines. Conversely, photoionization models in which the non-ionizing part of the continuum is omitted or is not transferred underpredict the fluorescent contribution to the Balmer lines, producing a bias of similar amplitude in the opposite direction. In this paper, we carry out realistic estimations of the fluorescent Balmer intensity and discuss the variations to be expected as the simulated observational setup and the stellar population's parameters are varied. In all the cases explored, we find that fluorescent excitation provides a significant contribution. We also show that differential fluorescent enhancement may produce line-of-sight differences in the Balmer decrement, mimicking interstellar extinction. Fluorescent excitation emerges from our study as a small but important mechanism for the enhancement of Balmer lines, which should be taken into account in the abundance analysis of photoionized regions, particularly in the case of high-precision applications such as the determination of primordial helium.
We investigate the stellar populations in a sample of 89 faint (M*+2 to M*+4) red galaxies in the Coma cluster, using high S/N spectroscopy from the MMT. Our sample is drawn from two 1-degree fields, one centred on the cluster core and the other located a degree to the south west of the cluster centre. For a comparison sample we use published high-S/N data for red-sequence galaxies in the Shapley Supercluster. We use state-of-the-art stellar population models to infer the SSP-equivalent age and metallicity (Fe/H) for each galaxy, as well as the abundances of the light elements Mg, Ca, C and N. The ages of the Coma dwarfs span a wide range from <2 Gyr to >10 Gyr, with a strong environmental dependence. The oldest galaxies are found only in the core, while most of the galaxies in the outer south-west field have ages ~3 Gyr. The galaxies have a metallicity range -1.0 < [Fe/H] < 0.0, and follow the same age-metallicity-mass plane as high-mass galaxies, but with increased intrinsic scatter. The Mg/Fe abundance ratios are on average slightly super-solar, and span a range -0.1 < [Mg/Fe] < +0.4. The highest Mg enhancements are found only in the cluster core, while solar ratios predominate in the outskirts. Depending on the assumed star-formation history (quenched versus burst-dominated), the number of dwarf galaxies on the red sequence in the Coma core has doubled since z~0.4-0.7. These estimates bracket the red-sequence growth timescales found by direct studies of distant clusters. In the south-west field, the red sequence was established only at z~0.1-0.2. Our observations confirm previous indications of very recently quenched star formation in this part of the cluster. Our results support the picture in which much of the cluster passive dwarf population was generated by environment-driven transformation of infalling late-type galaxies.
The presence of large amounts of WIMP dark matter in stellar cores has been shown to have significant effects upon models of stellar evolution. We present a series of detailed grids of WIMP-influenced stellar models for main sequence stars, computed using the DarkStars code. We describe the changes in stellar structure and main sequence evolution which occur for masses ranging from 0.3 to 2.0 solar masses and metallicities from Z = 0.0003-0.02, as a function of the rate of energy injection by WIMPs. We then go on to show what rates of energy injection can be obtained using realistic orbital parameters for stars near supermassive black holes, including detailed considerations of dark matter halo velocity and density profiles. Capture and annihilation rates are strongly boosted when stars follow elliptical rather than circular orbits, causing WIMP annihilation to provide up to 100 times the energy of hydrogen fusion in stars at the Galactic centre.
We present commissioning data for the POLISH instrument obtained on the Hale 5-m telescope. The goal of this high precision polarimeter is to constrain orbital inclination of high mass X-ray binaries and to therefore obtain independent mass estimates for their black hole companions. We have obtained photon shot noise limited precision on standard stars, and we have measured the polarization of bright stars at the part per million level on a nightly basis. Systematic effects have been reduced to less than 1% of the measured polarization for polarized sources and to the part per million level for weakly polarized sources. The high sensitivity of this instrument to asymmetry suggests that valuable contributions will be made in many other fields, including studies of extrasolar planets, debris disks, and stellar astrophysics.
We resolve the kinematic distance ambiguity for 266 inner Galaxy HII regions out of a sample of 291 using existing HI and 13CO sky surveys. Our sample contains all HII regions with measured radio recombination line (RRL) emission over the extent of the 13CO Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey (18 deg, < l < 55 deg. and |b| < 1) and contains ultra compact, compact, and diffuse HII regions. We use two methods for resolving the distance ambiguity for each HII region: HI emission/absorption (HIEA) and HI self-absorption (HISA). We find that the HIEA and HISA methods can resolve the distance ambiguity for 72% and 87% of our sample, respectively. When projected onto the Galactic plane, this large sample appears to reveal aspects of Galactic structure, with spiral arm-like features at Galactocentric radii of 4.5 and 6 kpc, and a lack of HII regions within 3.5 kpc of the Galactic center. Our HII regions are approximately in the ratio of 2 to 1 for far verses near distances. The ratio of far to near distances for ultra-compact HII regions is 2.2 to 1. Compact HII regions are preferentially at the near distance; their ratio of far to near distances is 1.6 to 1. Diffuse HII regions are preferentially at the far distance; their ratio of far to near distances is 3.8 to 1. This implies that the distinction between ultra compact and compact HII regions is due largely to distance, and that the large angular size of diffuse HII regions is not due solely to proximity to the Sun.
We present 0.2" resolution near-infrared integral field spectroscopy of H-alpha emission from six star forming galaxies at z~1.6 (look-back time of ~9.6 Gyr). These observations were obtained with OSIRIS using the Keck Laser Guide Star Adaptive Optics system. All sources have a compact spatial extent of ~1", with an average half light radius of r=2.9 kpc and average dereddened star formation rate of 22 Msolar per year. Based on H-alpha kinematics we find that these six galaxies are dynamically distinguishable, and we classify them as either merger or disk candidate systems. We find three merger systems (HDF-BX1287, HDF-BX1315, and Q1623-BX491) with varying geometries and dynamical properties. Three galaxies (HDF-BMZ1299, Q2343-BX344, and Q2343-BM145) are well-fit by an inclined-disk model with low velocity residuals (20 to 46 km/sec). An average plateau velocity of v_p=185 km/sec is achieved within 1.0 kpc. The majority of observed velocity dispersions (~88 km/sec) can be explained by the residual seeing halo, and are not intrinsic to our sources. However, one merger and one disk candidate have high velocity dispersions (> 200 km/sec) that cannot be solely explained by beam smearing. For two disk candidates, we detect [NII] emission and are able to map the [NII]/H-alpha ratio on kiloparsec scales. In both cases, [NII] emission is more concentrated than H-alpha emission (< 0.2"), and peak ratios are best explained by the presence of an AGN. These are among the weakest known AGN at high redshift, however their emission is strong enough to impact high redshift metallicity studies that use nebular ratios. All disk candidates have likely completed only a few orbital periods, and if left unperturbed are excellent candidates to become present-day spiral galaxies.
We introduce the Dichroic-Mirror Camera (DMC), an instrument developed at the University of Tokyo which is capable of performing simultaneous imaging in fifteen bands. The main feature of the DMC is the dichroic mirrors, which split incoming light into red and blue components. Combination of dichroic mirrors split light from the telescope focus into fifteen intermediate-width bands across 390 -- 950 nm. The fifteen bands of DMC provide measurements of the object's spectral energy distribution (SED) at fifteen wavelength points. During May -- June 2007 and March 2008, observing run of the DMC was carried out at Higashi-Hiroshima Observatory, Japan. We observed several objects i.e. planets, asteroids, standard stars & star clusters, planetary nebulae, galaxies, and supernovae. We describe several early scientific results from the DMC.
We have examined the dust photoelectric heating in the intergalactic medium (IGM). The heating rate in a typical radiation field of the IGM is represented by $\Gamma_{\rm pe} = 1.2\times10^{-34}$ erg s$^{-1}$ cm$^{-3}$ $({\cal D}/10^{-4})(n_{\rm H}/10^{-5} {\rm cm^{-3}})^{4/3} (J_{\rm L}/10^{-21} {\rm erg s^{-1} cm^{-2} Hz^{-1} sr^{-1}})^{2/3} (T/10^4 {\rm K})^{-1/6}$, where ${\cal D}$ is the dust-to-gas mass ratio, $n_{\rm H}$ is the hydrogen number density, $J_{\rm L}$ is the mean intensity at the hydrogen Lyman limit of the background radiation, and $T$ is the gas temperature, if we assume the new X-ray photoelectric yield model by Weingartner et al. (2006) and the dust size distribution in the Milky Way by Mathis, Rumpl, & Nordsieck (1977). This heating rate dominates the HI and HeII photoionization heating rates when the hydrogen number density is less than $\sim10^{-6}$ cm$^{-3}$ if ${\cal D}=10^{-4}$ which is 1% of that in the Milky Way, although the heating rate is a factor of 2--4 smaller than that with the old yield model by Weingartner & Draine (2001). The grain size distribution is very important. If only large ($\ge0.1$ $\mu$m) grains exist in the IGM, the heating rate is reduced by a factor of $\simeq5$. Since the dust heating is more efficient in a lower density medium relative to the photoionization heating, it may cause an inverted temperature--density relation in the low density IGM suggested by Bolton et al. (2008). Finally, we have found that the dust heating is not very important in the mean IGM before the cosmic reionization.
Hierarchical Lambda CDM models provide a successful paradigm for the growth of dark matter on large scales, but they face important challenges in predicting how the baryonic components of galaxies evolve. I present constraints on two aspects of this evolution: (1) The interaction history of galaxies over the last 7 Gyr and the impact of interactions on their star formation properties, based on Jogee et al. (2008a,b); (2) Constraints on the origin of bulges in hierarchical models and the challenge posed in accounting for galaxies with low bulge-to-total ratios, based on Weinzirl, Jogee, Khochar, Burkert, and Kormendy (2008, hereafter WJKBK08)
As predicted by quantum chromodynamics, around $T\sim 100$ GeV in the early universe, the electroweak phase transition (EPT) occurs during which the primordial magnetic field (PMF) is produced. Since the PMF would give rise to an anisotropic stress that serving as a source of the equation of relic gravitational wave (RGW) lasting for a period, the spectrum of RGW would be greatly modified. Extending our previous analytical calculation of the spectrum of RGW, we explore the consequences caused by the PMF that is produced at the EPT. It is found that, for a scale of galactic cluster $\lambda=1$ Mpc, PMF would not markedly affect the spectrum of RGW, unless its amplitude is stronger than $B_{\lambda} \geq 10^{-9}$ Gauss. Moreover, by comparing with the sensitivity curve of laser interferometer GW detections, including LIGO and LISA, we find that for a scale of galactic cluster $\lambda=1$ Mpc, the amplitude of PMF, that produced by the EPT, has to be weaker than $B_{\lambda} \leq 1\times 10^{-6}$ Gauss; and for a scale of supercluster $\lambda=100$ Mpc, the amplitude of PMF has to be weaker than $B_{\lambda} \leq 0.6\times 10^{-9}$ Gauss. In this manner, gravitational wave observation has potential to make interesting contributions to the study of the origin of cosmic magnetic field.
The metallicity distribution in the intracluster medium of the NGC 5044 group was studied up to 0.3 r_180 using the XIS instrument on board the Suzaku satellite. Abundances of O, Mg, Si, S, and Fe were measured with high accuracy. The region within a radius of 0.05 r_180 from the center shows approximately solar abundances of Mg, Si, S, and Fe, while the O/Fe ratio is about 0.5--0.6 in solar units. In the outer region, the Fe abundance gradually drops to 0.3 solar. Radial abundance profiles of Mg, Si and S are similar to that of Fe, while that of O seems to be flatter. At r>0.05 r_180, the mass density profile of O differs from that of Fe, showing a shoulder-like structure that traces the luminosity density profile of galaxies. The mass-to-light ratios for O and Fe in NGC 5044 are one of the largest among groups of galaxies, but they are still smaller than those in rich clusters. These abundance features probably reflect the metal enrichment history of this relaxed group hosting a giant elliptical galaxy in the center.
Massive star formation exhibits an extremely rich chemistry. However, not much evolutionary details are known yet, especially at high spatial resolution. Therefore, we synthesize previously published Submillimeter Array high-spatial-resolution spectral line observations toward four regions of high-mass star formation that are in various evolutionary stages with a range of luminosities. Estimating column densities and comparing the spatially resolved molecular emission allows us to characterize the chemical evolution in more detail. Furthermore, we model the chemical evolution of massive warm molecular cores to be directly compared with the data. The four regions reveal many different characteristics. While some of them, e.g., the detection rate of CH3OH, can be explained by variations of the average gas temperatures, other features are attributed to chemical effects. For example, C34S is observed mainly at the core-edges and not toward their centers because of temperature-selective desorption and successive gas-phase chemistry reactions. Most nitrogen-bearing molecules are only found toward the hot molecular cores and not the earlier evolutionary stages, indicating that the formation and excitation of such complex nitrogen-bearing molecules needs significant heating and time to be fully developed. Furthermore, we discuss the observational difficulties to study massive accretion disks in the young deeply embedded phase of massive star formation. The general potential and limitations of such kind of dataset are discussed, and future directions are outlined. The analysis and modeling of this source sample reveals many interesting features toward a chemical evolutionary sequence. However, it is only an early step, and many observational and theoretical challenges in that field lie ahead.
The high energy emission of microquasars is thought to originate from high
energy particles. Depending on the spectral state, the distribution of these
particles can be thermal with a high temperature (typically 100 keV) or
non-thermal and extending to even higher energy. The properties of high energy
plasmas are governed by a rich microphysics involving particle-particle
collisions and particles-photons interactions.
We present a new code developed to address the evolution of relativistic
plasmas. This one-zone code focuses on the microphysics and solves the coupled
kinetic equations for particles and photons, including Compton scattering,
synchrotron emission and absorption, pair production and annihilation,
bremsstrahlung emission and absorption, Coulomb interactions, and prescriptions
for additional particle acceleration and heating. It can in particular describe
mechanisms such a thermalisation by synchrotron self-absorption and Coulomb
collisions.
Using the code, we investigate whether various acceleration processes, namely
thermal heating, non-thermal acceleration and stochastic acceleration, can
reproduce the different spectral states of microquasars. Premilinary results
are presented.
Accreting sources such as AGN, X-ray binaries or gamma-ray bursts are known
to be strong, high energy emitters. The hard emission is though to originate
from plasmas of thermal and/or non-thermal high energy particles. Not only does
this emission allow to probe the unique properties of the matter in an extreme
environment, but it also has a crucial backreaction on the energetics and the
dynamics of the emitting medium itself. Understanding interactions between
radiation and matter has become a key issue in the modelling of high energy
sources. Although most cross sections are well known, they are quite complex
and the way all processes couple non-linearly is still an open issue.
We present a new code that solves the local, kinetic evolution equations for
distributions of electrons, positrons and photons, interacting by radiation
processes such as self-absorbed synchrotron and brems-strahlung radiation,
Compton scattering, pair production/annihilation, and by Coulomb collisions.
The code is very general and aimed to modelled various high energy sources. As
an application, we study the spectral states of X-ray binaries, including
thermalization by Coulomb collisions and synchrotron self-absorption. It is
found that the low-hard and high-soft states can be modelled with different
illumination but the same non-thermal acceleration mechanism.
Statistical analyses of several Delta Scuti stars (FG Vir, 44 Tau, BL Cam and others) show that the photometrically observed frequencies cluster around the frequencies of the radial modes over many radial orders. The observed regularities can be partly explained by modes trapped in the stellar envelope. This mode selection mechanism was already proposed by Dziembowski & Krolikowska (1990) and was shown to be efficient for l=1 modes. New pulsation model calculations confirm the observed regularities. We present the s-f diagram, which compares the average separation of the radial frequencies (s) with the frequency of the lowest unstable radial mode (f). The diagram provides an estimate for the log g value of the observed star, if we assume that the centers of the observed frequency clusters correspond to the radial mode frequencies. This assumption is confirmed by examples of well-studied Delta Scuti variables in which radial modes were definitely identified.
There have been attempts to fit the abundance patterns of extremely metal-poor stars with supernova nucleosynthesis models for the lighter elements than Zn. On the other hand, observations have revealed that the presence of EMP stars with peculiarly high ratio of "weak r-process elements" Sr, Y and Zr. Although several possible processes were suggested for the origin of these elements, the complete solution for reproducing those ratios is not found yet. In order to reproduce the abundance patterns of such stars, we investigate a model with neutron rich matter ejection from the inner region of the conventional mass-cut. We find that explosive nucleosynthesis in a high energy supernova (or "hypernova") can reproduce the high abundances of Sr, Y and Zr but that the enhancements of Sr, Y and Zr are not achieved by nucleosynthesis in a normal supernova. Our results imply that, if these elements are ejected from a normal supernova, nucleosynthesis in higher entropy flow than that of the supernova shock is required.
Although $f(R)$ modified gravity models can be made to satisfy solar system and cosmological constraints, it has been shown that they have the serious drawback of the nonexistence of stars with strong gravitational fields. In this paper, we discuss whether or not higher curvature corrections can remedy the nonexistence consistently. The following problems are shown to arise as the costs one must pay for the $f(R)$ models that allow for neutrons stars: (i) the leading correction must be fine-tuned to have the typical energy scale $\mu \lesssim 10^{-19}$ GeV, which essentially comes from the free fall time of a relativistic star; (ii) the leading correction must be further fine-tuned so that it is not given by the quadratic curvature term. The second problem is caused because there appears an intermediate curvature scale and laboratory experiments of gravity will be under the influence of higher curvature corrections. Our analysis thus implies that it is a challenge to construct viable $f(R)$ models without very careful and unnatural fine-tuning.
We provide low temperature opacity data that incorporate varied abundances of the elements carbon and nitrogen. In the temperature range that we focus at, molecules are the dominant opacity source. Our dataset spans a large metallicity range and shall deliver the necessary input data for stellar evolution models as well as other applications. We conduct chemical equilibrium calculations in order to evaluate the partial pressures of neutral atoms, ions and molecules. Based on a large dataset containing atomic line and continuum data, and, most importantly, a plethora of molecular lines, we subsequently calculate Rosseland mean opacity coefficients. This is done not only for a number of different metallicities, but also for varied abundances of the isotopes 12C and 14N at each metallicity. The molecular data comprise the main opacity sources at either an oxygen-rich or carbon-rich chemistry. We tabulate the opacity coefficients as a function of temperature and, basically, density. Already within a certain chemistry regime an alteration in the carbon abundance causes, due to the special role of the CO molecule, considerable changes in the Rosseland opacity. The transition from a scaled solar (i. e. oxygen-rich) mixture to the carbon-rich regime results in opacities that can, at low temperatures, be orders of magnitude different compared to the initial situation. The reason is that different molecular absorbers make up the mean opacity in either case. A varying abundance of nitrogen has less pronounced effects but, nevertheless, cannot be neglected. [abridged]
We present an analysis of deep mid- to far-infrared (MFIR) Spitzer
photometric observations of the southern 2Jy sample of powerful radio sources
(0.05 < z < 0.7), conducting a statistical investigation of the links between
radio jet, AGN, starburst activity and MFIR properties. This is part of an
ongoing extensive study of powerful radio galaxies that benefits from both
complete optical emission line information and a uniquely high detection rate
in the far-infrared (far-IR). We find tight correlations between the MFIR and
[OIII] emission luminosities, which are significantly better than those between
MFIR and extended radio luminosities, or between radio and [OIII] luminosities.
Since [OIII] is a known indicator of intrinsic AGN power, these correlations
confirm AGN illumination of the circum-nuclear dust as the primary heating
mechanism for the dust producing thermal MFIR emission at both 24 and 70
microns. We demonstrate that AGN heating is energetically feasible, and
identify the narrow line region clouds as the most likely location of the cool,
far-IR emitting dust. Starbursts make a major contribution to the heating of
the cool dust in only 15-28% of our targets.
We also investigate the orientation dependence of the continuum properties,
finding that the broad- and narrow-line objects in our sample with strong
emission lines have similar distributions of MFIR luminosities and colours.
Therefore our results are entirely consistent with the orientation-based
unified schemes for powerful radio galaxies. However, the weak line radio
galaxies (WLRG) form a separate class of objects with intrinsically low
luminosity AGN in which both the optical emission lines and the MFIR continuum
are weak.
Coronagraphic techniques are required to detect exoplanets with future
Extremely Large Telescopes. One concept, the Apodized Pupil Lyot Coronagraph
(APLC), is combining an apodizer in the entrance aperture and a Lyot opaque
mask in the focal plane. This paper presents the manufacturing and tests of a
microdots apodizer optimized for the near IR.
The intent of this work is to demonstrate the feasibility and performance of
binary apodizers for the APLC. This study is also relevant for any coronagraph
using amplitude pupil apodization.
A binary apodizer has been designed using a halftone dot process, where the
binary array of pixels with either 0% or 100% transmission is calculated to fit
the required continuous transmission, i.e. local transmission control is
obtained by varying the relative density of the opaque and transparent pixels.
An error diffusion algorithm was used to optimize the distribution of pixels
that best approximates the required field transmission. The prototype was
tested with a coronagraphic setup in the near IR.
The transmission profile of the prototype agrees with the theoretical shape
within 3% and is achromatic. The observed apodized and coronagraphic images are
consistent with theory. However, binary apodizers introduce high frequency
noise that is a function of the pixel size. Numerical simulations were used to
specify pixel size in order to minimize this effect, and validated by
experiment.
This paper demonstrates that binary apodizers are well suited for being used
in high contrast imaging coronagraphs. The correct choice of pixel size is
important and must be adressed considering the scientific field of view.
SAX J1818.6-1703 has been characterised as a Supergiant Fast X-ray Transient system on the basis of several INTEGRAL/IBIS detections since the original BeppoSAX Wide Field Camera detection. Using IBIS/ISGRI, Swift/BAT and archival observations, we show that in fact SAX J1818.6-1703 exhibits emission on a period of 30 +/- 0.1 days, with a high degree of recurrence. SAX J1818.6-1703 is therefore the second SFXT shown to exhibit periodic outbursts, but with a considerably shorter period than the other known system, IGR J11215-5952.
We present infrared (IR) to X-ray spectral energy distributions (SEDs) for 44 red AGN selected from the 2MASS survey on the basis of their red J-K$_S$ color (>2 mag) and later observed by Chandra. In comparison with optically-, radio-, and X-ray selected AGN, their median SEDs are red in the optical and near-IR with little/no blue bump. It thus seems that near-IR color selection isolates the reddest subset of AGN that can be classified optically. The shape of the SEDs is generally consistent with modest absorption by gas (in the X-ray) and dust (in the optical-IR). The levels of obscuration, estimated from X-rays, far-IR and our detailed optical/near-IR color modeling are all consistent implying N_H < few*10^{22} cm^{-2}. We present SED models that show how the AGN optical/near-IR colors change due to differing amounts of reddening, AGN to host galaxy ratio, redshift and scattered light emission and apply them to the sources in the sample. We find that the 2MASS AGN optical color, B-R, and to a lesser extent the near-IR color, J-K$_S$, are strongly affected by reddening, host galaxy emission, redshift, and in few, highly polarized objects, also by scattered AGN light. The obscuration/inclination of the AGN allows us to see weaker emission components which are generally swamped by the AGN.
We summarise some basic issues relevant to the optimisation and design of space-based experiments for the observation of the Extensive Air Showers produced by Ultra-High Energy Cosmic Particles interacting with the atmosphere. A number of basic relations is derived and discussed with a twofold goal: defining requirements for the experimental apparatus and estimating the exptected performance.
We analyze the spectral energy distributions (SEDs) and emission line properties of the red (J-K$_S$ > 2) 2MASS AGN observed by Chandra using principle component analysis. The sample includes 44 low redshift AGN with low or moderate obscuration (N_H < 10^{23} cm^{-2}) as indicated by X-rays and SED modeling. The obscuration of the AGN allows us to see weaker emission components (host galaxy emission, AGN scattered light) which are usually outshone by the AGN. The first four eigenvectors explain 70% of the variance in the sample. The dominant cause of variance in the sample (eigenvector 1) is the L/Ledd ratio strengthened by intrinsic absorption. Eigenvector 2 is related to host galaxy (relative to the observed AGN) emission and eigenvectors 3 and 4 distinguish between two sources of obscuration: host galaxy absorption and circumnuclear absorption. Although our analysis is consistent with unification schemes where inclination dependent obscuration is important in determining the AGN SEDs, the L/Ledd ratio is the most important factor, followed by host galaxy emission.
We study the time variability and spectral evolution of the Black Hole Candidate source XTE J1650-500 using the BeppoSax wide energy range (0.12-200 keV) observations performed during the 2001 X-ray outburst. The source evolves from a low/hard state (LHS) toward a high/soft state (HSS). In all states the emergent photon spectrum is described by the sum of Comptonization and soft (disk) blackbody components. In the LHS, the Comptonization component dominates in the resulting spectrum. On the other hand, during the HSS the soft (disk) component is already dominant. In this state the Comptonization part of the spectrum is much softer than that in the LHS (photon index is ~ 2.4 in the HSS vs. that is ~1.7 in the LHS). In the BeppoSAX data we find a strong signature of the index saturation with the mass accretion rate which can be considered as an observational evidence of the converging flow (black hole) in XTE J1650-500. We derive power spectra (PS) of the source time variability in different spectral states as a function of energy band. When the source undergoes a transition to softer states, the PS as a whole is shifted to higher frequencies which can be interpreted as a contraction of the Compton cloud during hard-soft spectral evolution. It is worthwhile to emphasize a detection of a strong low-frequency red noise component in the HSS PS which can be considered a signature of the presence of the strong extended disk in the HSS. Also as a result of our data analysis, we find a very weak sign of K_alpha line appearance in these BeppoSAX data. This finding does not confirm previous claims by Miniutti et al. on the presence of a broad and strongly relativistic iron emission line in this particular set of the BeppoSAX data.
While current atmospheric Cherenkov installations consist of only a few telescopes each, future installations will be far more complex. Monte Carlo simulations have become an essential tool for the design and optimisation of such installations. The CORSIKA air-shower simulation code and the sim_telarray code for simulation of arrays of Cherenkov telescopes have been used to simulate several candidate configurations of the future Cherenkov Telescope Array (CTA) in detail. Together with other detailed and simplified simulations the resulting data provide the basis for the ongoing optimisation of CTA over a wide energy range. In this paper, the simulation methods are outlined and preliminary results on a number of configurations are presented. It is demonstrated that the initial goals of the CTA project can be achieved with available technology, at least in the medium and high energy range (about 100 GeV to 100 TeV).
We present results from numerical modeling of emerging flux regions on the solar surface. The modeling was carried out by means of 3D radiative MHD simulations of the rise of buoyant magnetic flux tubes through the convection zone and into the photosphere. Due to the strong stratification of the convection zone, the rise results in a lateral expansion of the tube into a magnetic sheet, which acts as a reservoir for small-scale flux emergence events at the scale of granulation. The interaction of the convective downflows and the rising magnetic flux undulates it to form serpentine field lines emerging into the photosphere. Observational characteristics including the pattern of emerging flux regions, the cancellation of surface flux and associated high speed downflows, the convective collapse of photospheric flux tubes, the appearance of anomalous darkenings, the formation of bright points and the possible existence of transient kilogauss horizontal fields are discussed in the context of new observations from the Hinode Solar Optical Telescope. Implications for the local helioseismology of emerging flux regions are also discussed.
The nearby transiting system GJ 436b offers a unique opportunity to probe the structure and atmosphere of an extra-solar "hot Neptune". In this Letter, we present the main results of observations covering two transit events with the NICMOS camera on the Hubble Space Telescope. The data consist in high-cadence time series of grism spectra covering the 1.1-1.9 micron spectral range. We find Rpl=4.04 +- 0.10 R_earth and R_*= 0.446 +- 0.011 R_sun for the planet and star radius, confirming and improving earlier measurements with ground-based photometry and a Spitzer lightcurve at 8 microns, as opposed to a much higher value obtained with the Fine Guidance Sensor on the Hubble Space Telescope. We measure no departure from strict periodicity in the transits to the level of ~7 seconds. This strongly disfavours the proposed explanation of the orbital eccentricity of GJ 436b in terms of the perturbation by another close-by planet. We measure a flat transmission spectrum at the level of a few parts per 10'000 in flux, with no significant signal in the 1.4-micron water band to a level comparable to the maximum amplitude of the effect predicted by planetary atmosphere models.
Radio Interferometry is an essential method for astronomical observations. Self-calibration techniques have increased the quality of the radio astronomical observations (and hence the science) by orders of magnitude. Recently, there is a drive towards sensor arrays built using inexpensive hardware and distributed over a wide area acting as radio interferometers. Calibration of such arrays poses new problems in terms of computational cost as well as in performance of existing calibration algorithms. We consider the application of the Space Alternating Generalized Expectation Maximization (SAGE) \cite{Fess94} algorithm for calibration of radio interferometric arrays. Application to real data shows that this is an improvement over existing calibration algorithms that are based on direct, deterministic non linear optimization. As presented in this paper, we can improve the computational cost as well as the quality of the calibration using this algorithm.
We aim at reproducing the mass- and sigma-[alpha/Fe] relations in the stellar populations of early-type galaxies by means of a cosmologically motivated assembly history for the spheroids. We implement a detailed treatment for the chemical evolution of H, He, O and Fe in GalICS, a semi-analytical model for galaxy formation which successfully reproduces basic low- and high-redshift galaxy properties. The contribution of supernovae (both type Ia and II) as well as low- and intermediate-mass stars to chemical feedback are taken into account. We find that this chemically improved GalICS does not produce the observed mass- and sigma-[alpha/Fe] relations. The slope is too shallow and scatter too large, in particular in the low and intermediate mass range. The model shows significant improvement at the highest masses and velocity dispersions, where the predicted [alpha/Fe] ratios are now marginally consistent with observed values. We show that this result comes from the implementation of AGN (plus halo) quenching of the star formation in massive haloes. A thorough exploration of the parameter space shows that the failure of reproducing the mass- and sigma-[alpha/Fe] relations can partly be attributed to the way in which star formation and feedback are currently modelled. The merger process is responsible for a part of the scatter. We suggest that the next generation of semi-analytical model should feature feedback (either stellar of from AGN) mechanisms linked to single galaxies and not only to the halo, especially in the low and intermediate mass range. The integral star formation history of a single galaxy determines its final stellar [alpha/Fe] as it might be expected from the results of closed box chemical evolution models. (abridged)
As predicted by quantum chromodynamics(QCD), around $T\sim 190$ MeV in the early universe, the QCD transition occurs during which the quarks are combined into the massive hadrons. This process reduces the effective relativistic degree of freedom, and causes a change in the expansion behavior of the universe. Similarly, the $e^+e^-$ annihilation occurred around $T\sim 0.5$ Mev has the same kind of effect. Besides, the dark energy also drives the present stage accelerating expansion. We study these combined effects on the relic gravitational waves (RGWs). In our treatment, the QCD transition and the $e^+e^-$ annihilation, each is respectively represented by a short period of expansion inserted into the radiation era. Incorporating these effects, the equation of RGWs is analytically solved for a spatially flat universe, evolving from the inflation up to the current acceleration, and the spectrum of RGWs is obtained, covering the whole range of frequency $>10^{-19}$ Hz. It is found that the QCD transition causes a reduction of the amplitude of RGWs by $\sim 20%$ in the range $>10^{-9} $ Hz, and the $e^+e^-$ annihilation causes a reduction $\sim 10%$ in the range $>10^{-12} $ Hz. In the presence of the dark energy, the combination of the QCD transition and the $e^+e^-$ annihilation, causes a larger reduction of the amplitude by $\sim 30% $ for the range $>10^{-9} $ Hz, which covers the bands of operation of LIGO and LISA. By analysis, it is shown that RGWs will be difficult to detect by the present LIGO, but can be tested by LISA for certain inflationary models.
We propose a novel inflationary scenario in string theory in which the inflaton field is a 'Wilson line' degree of freedom in the worldvolume of a probe Dp-brane, in a warped flux compactification. Kinetic terms for Wilson line fields on the world volume of a D-brane take a nonstandard Dirac-Born-Infeld (DBI) form. Thus, we work in the framework of DBI inflation. This extends the original slow roll Wilson line inflationary scenario, where only the quadratic piece was considered. Warped DBI Wilson line inflation offers an attractive alternative to ordinary (position field) DBI inflation, inasmuch as observational and theoretical constraints get considerably relaxed. Besides the standard large non-Gaussianities in DBI scenarios, it is also possible to achieve an observable amount of gravitational waves.
We extend our previous work on the cosmology of Coleman-de Luccia bubble collisions. Within a set of approximations we calculate the effects on the cosmic microwave background (CMB) as seen from inside a bubble which has undergone such a collision. We find that the effects are always qualitatively similar--an anisotropy that depends only on the angle to the collision direction--but can produce a cold or hot spot of varying size, as well as power asymmetries along the axis determined by the collision. With other parameters held fixed the effects weaken as the amount of inflation which took place inside our bubble grows, but generically survive order 10 efolds past what is required to solve the horizon and flatness problems. In some regions of parameter space the effects can survive arbitrarily long inflation.
We present a simple model in which dark matter couples to the standard model through a light scalar intermediary that is itself unstable. We find this model has several notable features, and allows a natural explanation for a surplus of positrons, but no surplus of anti-protons, as has been suggested by early data from PAMELA and ATIC. Moreover, this model yields a very small nucleon coupling, well below the direct detection limits. In this paper we explore the effect of this model in both the early universe and in the galaxy.
Being able to safely distinguish astrophysical from potential dark matter (DM) annihilation signals is of utmost importance for indirect DM searches. To this end, one has to rely on distinctive -- and unique -- spectral signatures to look for. Internal bremsstrahlung (IB), unavoidable in the presence of charged annihilation products, provides such a signature. In fact, as it generically dominates the gamma-ray spectrum expected from DM annihilations, at high energies, it may well turn out to be more important for indirect DM searches than the traditionally looked-for line signals. As illustrated in some detail, the observation of IB signatures would even allow to distinguish between different DM candidates or to constrain significantly the parameter space of, e.g., neutralino DM. The gamma-ray contributions reported here are therefore of great interest for the already launched Fermi/GLAST satellite and the upcoming new generation of Air Cherenkov Telescope systems like CTA -- which are most sensitive at the high energies where these effects are particularly important. Finally, radiative corrections may even significantly alter the positron spectrum from DM annihilations; an intriguing positron excess recently found by the PAMELA satellite might turn out to be an indication of the peculiar spectral signature expected in that case.
Lattice refinement in LQC, its meaning and its necessity are discussed. The r\^ole of lattice refinement for the realisation of a successful inflationary model is explicitly shown. A simple and effective numerical technique to solve the constraint equation for any choice of lattice refinement model is briefly illustrated. Phenomenological and consistency requirements leading to a particular choice of lattice refinement model are presented, while it is subsequently proved that only this choice of lattice refinement leads to a unique factor ordering in the Wheeler-De Witt equation, which is the continuum limit of LQC.
The radion stability and radion mass are calculated in the setup of Lucak {\em et al} in the framework of the HW heterotic M-Theory on $S^{1}/Z_{2}$, by using the Goldberger-Wise mechanism. It is shown explicitly that the radion is stable and the radion mass can be of order of TeV. It is also shown that the gravity is localized in the visible brane located at $Y = Y_{c} > 0$, and the corrections to the 4D Newtonian potential from the higher order of the gravitational KK modes are exponentially suppressed. Applying such a setup to cosmology, we find the general generalized Friedmann equations on each of the two branes. Fitting the model to the reduced Union compilation of 307 SNe supernova data and the BAO measurement from the SDSS data, we find the best fitting value of the matter, among others, is $\Omega^{(0)}_m=0.22^{+0.03}_{-0.03}$. With these best fitting values as the initial conditions, we numerically integrate the field equations, and find that the late transient acceleration of the universe is a generic feature of the HW heterotic M Theory on $S^{1}/Z_{2}$.
The theory for the selection of the initial state of the universe from the landscape multiverse predicts superhorizon inhomogeneities induced by nonlocal entanglement of our Hubble volume with modes and domains beyond the horizon. Here we show these naturally give rise to a bulk flow with correlation length of order horizon size. The modification to the gravitational potential has a characteristic scale $L_{1} \simeq 10^{3} H^{-1}$, and it originates from the preinflationary remnants of the landscape. The 'tilt' in the potential induces power to the lowest CMB multipoles, with the dominant contribution being the dipole and next, the quadrupole. The induced multipoles $l \le 2$ are aligned with an axis normal to their alignment plane being oriented along the preferred frame determined by the dipole. The preferred direction is displayed by the velocity field of the bulk flow relative to the expansion frame of the universe. The parameters are tightly constrained thus the derived modifications lead to robust predictions for testing our theory. The 'dark' flow was recently discovered by Kashlinsky et al. to be about $700 km/s$ which seems in good agreement with our predictions for the induced dipole of order $3 \mu K$. Placed in this context, the discovery of the bulk flow by Kashlinsky et al. becomes even more interesting as it may provide a probe of the preinflationary physics and a window onto the landscape multiverse.
Motivated by the galactic positron excess seen by PAMELA and ATIC/PPB-BETS, we propose that dark matter is a TeV-scale particle that annihilates into a pseudoscalar "axion." The positron excess and the absence of an anti-proton or gamma ray excess constrain the axion mass and branching ratios. In the simplest realization, the axion is associated with a Peccei-Quinn symmetry, in which case it has a mass around 360-800 MeV and decays into muons. We present a simple and predictive supersymmetric model implementing this scenario, where both the Higgsino and dark matter obtain masses from the same source of TeV-scale spontaneous symmetry breaking.
Gravitational parity violation is inherent in string theory, one effective model of which is Chern-Simons modified gravity. This effective theory introduces a parity-violating modification to the Einstein equations, whose magnitude depends on derivatives of the Chern-Simons coupling. In the dynamical formulation, this coupling is an evolving field that is sourced by spacetime curvature. We here calculate the Chern-Simons modification to the orbital evolution of a binary system of spinning compact objects in the weak-field. The ratio of the Chern-Simons correction to perigee precession to the general relativistic prediction is found to scale quadratically with the semi-major axis and inversely with the square of the object's radius. Binary pulsar systems are ideal to test this theory, since perigee precession can be measured with sub-degree accuracies and the semi-major axis is millions of times larger than the stellar radius. We find that observations of perigee precession from the double binary pulsar PSR J 0737-3039 A/B dramatically constrain the Chern-Simons coupling, M_(CS) := |\dot{\theta}|^(-1) > 50 meV, approximately a hundred billion times better than Solar System tests.
Links to: arXiv, form interface, find, astro-ph, recent, 0811, contact, help (Access key information)
The eccentricity evolution of multiple planet systems can provide valuable constraints on planet formation models. Unfortunately, the inevitable uncertainties in the current orbital elements can lead to significant ambiguities in the nature of the secular evolution. Integrating any single set of orbital elements inadequately describes the full range of secular evolutions consistent with current observations. Thus, we combine radial velocity observations of HD 12661 with Markov Chain Monte Carlo sampling to generate ensembles of initial conditions for direct n-body integrations. We find that any mean motion resonances are quite weak and do not significantly impact the secular evolution, and that current observations indicate circulation or large amplitude libration of the periapses. The eccentricity of the outer planet undergoes large oscillations for nearly all of the allowed two-planet orbital solutions. This type of secular evolution would arise if planet c had been impulsively perturbed, perhaps due to strong scattering of an additional planet that was subsequently accreted onto the star. Finally, we note that the secular evolution implied by the current orbital configuration implies that planet c spends ~96% of the time following an orbit more eccentric than that presently observed. Either this system is being observed during a relatively rare state, or additional planets are affecting the observed radial velocities and/or the system's secular eccentricity evolution.
Recent high-resolution spectra of the Type Ia SN 2006X have revealed the presence of time-variable and blueshifted Na I D features, interpreted by Patat et al. as originating in circumstellar material within the progenitor system. The variation seen in SN 2006X induces relatively large changes in the total Na I D equivalent width (\Delta EW ~ 0.5 A in just over two weeks), that would be detectable at lower resolutions. We have used a large data set comprising 2400 low-resolution spectra of 450 Type Ia supernovae (SNe Ia) obtained by the CfA Supernova Program to search for variable Na I D features. Out of the 31 SNe Ia (including SN 2006X) in which we could have detected similar EW variations, only one other (SN 1999cl) shows variable Na I D features, with an even larger change over a similar ~10-day timescale (\Delta EW = 1.66 +/- 0.21 A). Interestingly, both SN 1999cl and SN 2006X are the two most highly-reddened objects in our sample, raising the possibility that the variability is connected to dusty environments.
A recent optical monitoring campaign on the prominent quasar 3C279 revealed a period of a remarkably clean exponential decay of BVRI fluxes with time, with a time constant of 12.8 d, over about 14 days. This is clearly too long to be associated with radiative cooling. Here we propose that this may be the signature of deceleration of the synchrotron emitting jet component. We develop a model analogous to the relativistic blast wave model for GRBs, including radiative energy losses and radiation drag, to simulate the deceleration of a relativistically moving plasmoid in the moderately dense AGN environment. Synchrotron, SSC and external Compton emission are evaluated self-consistently. We show that the observed optical light curve decay can be successfully reproduced with this model. The decelerating plasmoid model predicts a delayed X-ray flare, about 2 - 3 weeks after the onset of the quasi-exponential light curve decay in the optical. A robust prediction of this model, which can be tested with Fermi and simultaneous optical monitoring, is that the peak in the gamma-ray light curve at ~ 100 MeV is expected to be delayed by a few days with respect to the onset of the optical decay, while the VHE gamma-rays are expected to track the optical light curve closely with a delay of at most a few hours.
Gas in galactic disks is collected by gravitational instabilities into giant atomic-molecular complexes, but only the inner, molecular parts of these structures are able to collapse to form stars. Determining what controls the ratio of atomic to molecular hydrogen in complexes is therefore a significant problem in star formation and galactic evolution. In this paper we use the model of H_2 formation, dissociation, and shielding developed in the previous paper in this series to make theoretical predictions for atomic to molecular ratios as a function of galactic properties. We find that the molecular fraction in a galaxy is determined primarily by its column density and secondarily by its metallicity, and is to good approximation independent of the strength of the interstellar radiation field. We show that the column of atomic hydrogen required to shield a molecular region against dissociation is ~10 Msun pc^-2 at solar metallicity. We compare our model to data from recent surveys of the Milky Way and of nearby galaxies, and show that the both the primary dependence of molecular fraction on column density and the secondary dependence on metallicity that we predict are in good agreement with observed galaxy properties.
A review of star formation in the Rho Ophiuchi molecular complex is presented, with particular emphasis on studies of the main cloud, L1688, since 1991. Recent photometric and parallax measurements of stars in the Upper Scorpius subgroup of the Sco-Cen OB association suggest a distance for the cloud between 120 and 140 parsecs. Star formation is ongoing in the dense cores of L1688 with a median age for young stellar objects of 0.3 Myr. The surface population appears to have a median age of 2-5 Myr and merges with low mass stars in the Upper Scorpius subgroup. Making use of the most recent X-ray and infrared photometric surveys and spectroscopic surveys of L1688, we compile a list of over 300 association members with counterparts in the 2MASS catalog. Membership criteria, such as lithium absorption, X-ray emission, and infrared excess, cover the full range of evolutionary states for young stellar objects. Spectral energy distributions are classified for many association members using infrared photometry obtained from the Spitzer Space Telescope.
Photoionization heating from UV radiation incident on the atmospheres of hot Jupiters may drive planetary mass loss. We construct a model of escape that includes realistic heating and cooling, ionization balance, tidal gravity, and pressure confinement by the host star wind. We show that mass loss takes the form of a hydrodynamic ("Parker") wind, emitted from the planet's dayside during lulls in the stellar wind. When dayside winds are suppressed by the confining action of the stellar wind, nightside winds might pick up if there is sufficient horizontal transport of heat. A hot Jupiter loses mass at maximum rates of ~2 x 10^12 g/s during its host star's pre-main-sequence phase and ~2 x10^10 g/s during the star's main sequence lifetime, for total maximum losses of ~0.06% and ~0.6% of the planet's mass, respectively. For UV fluxes F_UV < 10^4 erg/cm^2/s, the mass loss rate is approximately energy-limited and is proportional to F_UV^0.9. For larger UV fluxes, such as those typical of T Tauri stars, radiative losses and plasma recombination force the mass loss rate to increase more slowly as F_UV^0.6. Dayside winds are quenched during the T Tauri phase because of confinement by overwhelming stellar wind pressure. We conclude that while UV radiation can indeed drive winds from hot Jupiters, such winds cannot significantly alter planetary masses during any evolutionary stage. Planetary winds never attain speeds of 100 km/s; in modelling the absorption signature of a wind, we cannot reproduce the claimed ~9-15% decrement in Lyman-alpha emission from HD 209458 at such large Doppler equivalent velocities--particularly the redshifted component--even when we account for natural broadening. Variability at such large Doppler shifts may instead reflect intrinsic stellar variability.
We analyze in detail the two-dimensional Kolmogorov-Smirnov test as a tool to learn about the distribution of the sources of the ultra-high energy cosmic rays. We confront in particular models based on AGN observed in X rays, on galaxies observed in HI and isotropic distributions, discussing how this method can be used not only to reject isotropy but also to support or reject specific source models, extending results obtained recently in the literature.
Eclipsing binary star systems provide the most accurate method of measuring both the masses and radii of stars. Moreover, they enable testing tidal synchronization and circularization theories, as well as constraining models of stellar structure and dynamics. With the recent availability of large-scale multi-epoch photometric datasets we were able to study eclipsing binary stars en masse. In this thesis, we analyzed 185,445 light curves from ten TrES fields, and 218,699 light curves from the OGLE II bulge fields. In order to manage such large quantities of data, we developed a pipeline with which we systematically identified eclipsing binaries, solved for their geometric orientations, and then found their components' absolute properties. Following this analysis we assembled catalogs of eclipsing binaries with their models, computed statistical distributions of their properties, and located rare cases for further follow-up, including T-Cyg1-03378, which has unusual eclipse timing variations. Of particular importance are low-mass eclipsing binaries, which are rare yet critical for resolving the ongoing mass-radius discrepancy between theoretical models and observations. To this end, we have discovered over a dozen new low-mass eclipsing binary candidates and spectroscopically confirmed the masses of five of them. One of these confirmed candidates, T-Lyr1-17236, is especially interesting because of its long orbital period. We examined T-Lyr1-17236 in detail and found that it is consistent with the magnetic disruption hypothesis. Both the source code of our pipeline and the complete list of our candidates are freely available.
The first stars fundamentally transformed the early Universe through their production of energetic radiation and the first heavy chemical elements. The impact on cosmic evolution sensitively depends on their initial mass function (IMF), which can be empirically constrained through detailed studies of ancient, metal-poor halo stars in our Galaxy. We compare the lowest magnesium and iron abundances measured in Galactic halo stars with theoretical predictions for the minimum stellar enrichment provided by Population III stars under the assumption of a top-heavy IMF. To demonstrate that abundances measured in metal-poor stars reflect the chemical conditions at their formation, and that they can thus be used to derive constraints on the primordial IMF, we carry out a detailed kinematic analysis of a large sample of metal-poor stars drawn from the SDSS survey. We assess whether interstellar accretion has altered their surface abundances. We find that accretion is generally negligible, even at the extremely low levels where the primordial IMF can be tested. We conclude that the majority of the first stars were very massive, but had likely masses below ~140 M.
High-mass X-ray binary systems are powered by the stellar wind of their donor stars. The X-ray state of Cygnus X-1 is correlated with the properties of the wind which defines the environment of mass accretion. Chandra-HETGS observations close to orbital phase 0 allow for an analysis of the photoionzed stellar wind at high resolution, but because of the strong variability due to soft X-ray absorption dips, simultaneous multi-satellite observations are required to track and understand the continuum, too. Besides an earlier joint Chandra and RXTE observation, we present first results from a recent campaign which represents the best broad-band spectrum of Cyg X-1 ever achieved: On 2008 April 18/19 we observed this source with XMM-Newton, Chandra, Suzaku, RXTE, INTEGRAL, Swift, and AGILE in X- and gamma-rays, as well as with VLA in the radio. After superior conjunction of the black hole, we detect soft X-ray absorption dips likely due to clumps in the focused wind covering >95 % of the X-ray source, with column densities likely to be of several 10^23 cm^-2, which also affect photon energies above 20 keV via Compton scattering.
We review here the effects of supernovae (SNe) explosions on the environment
of star-forming galaxies. Randomly distributed, clustered SNe explosions cause
the formation of hot superbubbles that drive either galactic fountains or
supersonic winds out of the galactic disk. In a galactic fountain, the ejected
gas is re-captured by the gravitational potential and falls back onto the disk.
From 3D non-equilibrium radiative cooling hydrodynamical simulations of these
fountains, we find that they may reach altitudes smaller than 5 kpc in the halo
and hence explain the formation of the so-called intermediate-velocity-clouds
(IVCs). On the other hand, the high-velocity-clouds (HVCs) that are observed at
higher altitudes (of up to 12 kpc) require another mechanism to explain their
production. We argue that they could be formed either by the capture of gas
from the intergalactic medium and/or by the action of magnetic fields that are
carried out to the halo with the gas in the fountains. Due to angular momentum
losses (of 10-15%) to the halo, we find that the fountain material falls back
to smaller radii and is not largely spread over the galactic disk, as
previously expected. This result is consistent with the metal distribution
derived from recent chemical models of the galaxy. We also find that after
about 150 Myr, the gas circulation between the halo and the disk in the
fountains reaches a steady state regime (abridged).
We examine the case for Quark-Novae as possible sources for the reionization of the universe. We find that dual-shock Quark-Nova events can produce enough photons to reionize Hydrogen in the entire Inter-Galactic medium (IGM) by z ~ 6. Such events can explain the large optical depth \tau_e ~ 0.17 as measured by WMAP, if the clumping factor of the material being ionized is small. We suggest a way in which a normal initial mass function (IMF) for the oldest stars can be reconciled with a large optical depth as well as the mean metallicity of the early IGM post reionization. We point out the main cosmological signatures and means of detection for Quark-Novae, and their interpretation as high redshift (z ~ 7-8) gamma-ray bursts.
In this paper we review some aspects of the theory of magnetic threaded
disks. We discuss in particular the equations that determine the position of
the inner disk boundary by using different prescriptions for the neutron
star-accretion disk interaction. We apply the results to several accretion
powered X-ray pulsars that showed both quasi-periodic oscillations in their
X-ray flux and spin-up/spin-down torque reversals. Under the hypothesis that
the beat-frequency model is applicable to the quasi-periodic oscillations, we
show that these sources provide an excellent opportunity to test models of the
disk-magnetosphere interaction. A comparison is carried out between the
magnetospheric radius obtained with all the prescriptions used in threaded disk
models; this shows that none of those prescriptions is able to reproduce the
combination of quasi-periodic oscillations and torque behaviour observed for
different X-ray luminosity levels in the X-ray pulsars in the present sample.
This suggests that the problem of accretion disk threading by stellar
magnetic field is still lacking a comprehensive solution. We discuss briefly an
outline of possible future developments in this field.
First, we describe a general procedure to produce high quality vector
magnetograms using the Imaging Vector Magnetograph (IVM) at Mees Solar
Observatory. At the spatial resolution 2"x2", the Stokes Q,U,V uncertainty
reaches 0.001-0.0005 in time-averaged data over 1-hour in the quiet Sun. When
vector magnetic fields are inferred from the time-averaged Stokes spectral
images of FeI 6302.5A, the resulting uncertainties are on the order of 10 G for
the longitudinal fields, 40 G for the transverse field strength and 9 degree
for the magnetic azimuth. The magnetic field inversion used in this work is the
"Triplet" code, which was developed and implemented in the IVM software package
by the late Barry J. LaBonte. The inversion code is described in detail in the
Appendix.
Second, we solve for the absolute value of the vertical electric current
density, |Jz|, accounting for the above IVM problems, for two different active
regions. One is a single sunspot region (NOAA 10001 observed on 20 June 2002)
while the other is a more complex, quadrupolar region (NOAA10030 observed on 15
July 2002). We use a calculation that does not require disambiguation of 180
degree in the transverse field directions. The |Jz| uncertainty is on the order
of 7.0 mA m^-2. The vertical current density increases with increasing vertical
magnetic field. The rate of increase is about 1 -2 times as large in the
quadrupolar NOAA 10030 region as in the simple NOAA 10001, and it is more
spatially variable over NOAA 10030 than over NOAA 10001.
Wide-field VLBI observations of the nearby starburst galaxy NGC 4945, obtained with the Australian LBA, have produced 2.3 GHz images over two epochs with a maximum spatial resolution of 0.3 pc. 15 sources were detected, 13 of which correspond to sources identified in higher frequency (3 cm and 12 mm) ATCA images. Four of the sources are resolved into shell-like structures ranging between 1.1 to 2.1 pc in diameter. From these data the spectra of 13 compact radio sources in NGC 4945 were modelled; nine were found to be consistent with free-free absorbed power laws and four with a simple power law spectrum. The free-free opacity is highest toward the nucleus but varies significantly throughout the nuclear region, implying that the overall structure of the ionised medium is clumpy. Of the 13 sources, 10 have steep intrinsic spectra associated with synchrotron emission from supernova remnants, the remaining sources have flat intrinsic spectra which may be associated with thermal radio emission. A non-thermal source with a jet-like morphology is detected ~1" from the assumed location of the AGN. A type II supernova (SN) rate upper limit of 15.3/yr is determined for the inner 250 pc region of the galaxy at the 95% confidence level, based on the lack of detection of new sources in observations spanning 1.9 years and a simple model for the evolution of supernova remnants. A type II SN rate of >0.1(v/1e4)/yr is implied from estimates of supernova remnant source counts, sizes and expansion rates, where v is the radial expansion velocity of the supernova remnant in km/s. A SFR of 2.4(v/1e4)<SFR(M>=5Msun)<370 Msun/yr has been estimated directly from the SN rate limits and is of the same order of magnitude as rates determined from integrated FIR and radio luminosities.
We present optical UBVRI photometric and spectroscopic data of the type Ibn supernova SN 2006jc, until the onset of the dust forming phase. The optical spectrum shows a blue continuum and is dominated by the presence of moderately narrow (velocity ~2500 km/s) He I emission lines superimposed over a relatively weak supernova spectrum. The helium lines are produced in a pre-existing He rich circumstellar shell. The observed helium line fluxes indicate the circumstellar shell is dense, with a density of ~10^9 - 10^{10} cm^{-3}. The helium mass in this shell is estimated to be <~0.07 Msun. The optical light curves show a clear signature of dust formation, indicated by a sharp decrease in the magnitudes around day 50, accompanied by a reddening of the colours. The evolution of the optical light curves during the early phase and that of the uvoir bolometric light curve at all phases is reasonably similar to normal Ib/c supernovae.
The analysis of INTEGRAL observations (2003-2008) of superaccreting galactic microquasar SS433 at precessional phases with the maximum disk opening angle is carried out. The shape and width of the primary X-ray eclipse is found to be strongly variable suggesting additional absorption in dense stellar wind and gas outflows from the optical A7I-component. The joint modeling of X-ray eclipse and precessional X-ray variability by a geometrical model suggests the binary mass ratio q=m_x/m_v=0.3, allowing an explnation of peculiarities of the optical variability of SS433, in particular, the substantial precessional variability at the primary optical eclipse minimum. For the mass function of the optical star f_v=0.268 M_\odot as derived from Hillwig and Gies (2008) data, the obtained q yields the masses of the components m_x=5 M_\odot, m_v=15 M_\odot, confirming the black hole nature of the relativistic object in SS433. The independence of the observed hard X-ray spectrum on the precession phase suggests that hard X-ray emission is formed in an extended hot corona. The Monte-Carlo simulations of the broadband X-ray spectrum of SS433 at the maximum disk opening precessional phases allowed us to determine physical parameters of the corona (temperature T_{cor}=20 keV, Thomson optical depth \tau=0.2), and to estimate the jet mass outflow rate \dot M_j=3\times 10^{19} g/s yielding the kinetic power of the jets \sim 10^{39} erg/s.
The coronal magnetic field above a particular photospheric region will vanish at a certain number of points, called null points. These points can be found directly in a potential field extrapolation or their density can be estimated from Fourier spectrum of the magnetogram. The spectral estimate, which assumes that the extrapolated field is random, homogeneous and has Gaussian statistics, is found here to be relatively accurate for quiet Sun magnetograms from SOHO's MDI. The majority of null points occur at low altitudes, and their distribution is dictated by high wavenumbers in the Fourier spectrum. This portion of the spectrum is affected by Poisson noise, and as many as five-sixths of null points identified from a direct extrapolation can be attributed to noise. The null distribution above 1500 km is found to depend on wavelengths that are reliably measured by MDI in either its low-resolution or high-resolution mode. After correcting the spectrum to remove white noise and compensate for the modulation transfer function we find that a potential field extrapolation contains, on average, one magnetic null point, with altitude greater than 1.5 Mm, above every 322 square Mm patch of quiet Sun. Analysis of 562 quiet Sun magnetograms spanning the two latest solar minimum shows that the null point density is relatively constant with roughly 10% day-to-day variation. At heights above 1.5 Mm, the null point density decreases approximately as the inverse cube of height. The photospheric field in the quiet Sun is well approximated as that from discrete elements with mean flux 1.0e19 Mx distributed randomly with density n=0.007 per square Mm.
We analyse the interaction between Dark Energy and Dark Matter from a thermodynamical perspective. By assuming they have different temperatures, we study the possibility of occurring a decay from Dark Matter into Dark Energy, characterised by a negative parameter $Q$. We find that, if at least one of the fluids has non vanishing chemical potential, for instance $\mu_x<0$ and $\mu_{dm}=0$ or $\mu_x=0$ and $\mu_{dm}>0$, the decay is possible, where $\mu_x$ and $\mu_{dm}$ are the chemical potentials of Dark Energy and Dark Matter, respectively. Using recent cosmological data, we find that, for a fairly general interaction, the Dark Matter decay is favoured with a probability of $\sim 87%$ over the Dark Energy decay.
In future microwave background polarization experiments, particularly those that aim to characterize the B component, careful attention will have to be paid to the mixing of E and B components due to finite sky coverage and pixelization. Any polarization map can be decomposed into "pure E," "pure B," and "ambiguous" components. In practice, since the B component is expected to be much weaker than the E component, nearly all of the recoverable $B$ information is contained in the pure B component. The amount of B information lost to ambiguous modes can be estimated in simple ways from the survey geometry and pixelization. Separation of any given map into pure and ambiguous components can be done by finding a basis of pure and ambiguous modes, but it is often more efficient to "purify" the map directly in real space by solving a certain differential equation to find the ambiguous component. This method may be useful in conjunction with power spectrum estimation techniques such as the pseudo-Cl method.
We present spectroscopic data for individual stars observed from 2004 March through 2008 August as part of our Michigan/MIKE Fiber System (MMFS) survey of four dwarf spheroidal (dSph) galaxies: Carina, Fornax, Sculptor and Sextans. Using MMFS at the Magellan/Clay Telescope at Las Campanas Observatory, we have acquired 8855 spectra from 7103 red giant candidates in these Galactic satellites. We list measurements of each star's line-of-sight velocity (median error +/- 2.1 km/s) and spectral line indices for iron and magnesium absorption features. We use globular cluster spectra to calibrate the indices onto standard [Fe/H] metallicity scales, but comparison of the resulting metallicities with published values suggests that the MMFS indices are best used as indicators of relative, not absolute metallicity. The empirical distributions of velocity and spectral indices also allow us to quantify the amount of contamination by foreground stars. In a companion paper we develop an algorithm that evaluates the membership probability for each star, showing that the present MMFS sample contains more than 5000 dSph members, including 774 Carina members, 2483 Fornax members, 1365 Sculptor members, and 441 Sextans members.
The simplest version of the daemon paradigm suggests the modulated 2-6-keV range events in DAMA/NaI and DAMA/LIBRA detectors are caused by the iodine ions knocked out elastically by the electrically neutral c-daemons moving with V = 30-50 km/s (c-daemon is a complex of negative daemon located in a remainder of formerly captured nucleus where the daemon decomposes nucleons one by one with ~10^-6 s mean interval). Furthermore, after the 2-6 keV event occurred, in subsequent ~10^-6 s, the c-daemon (which becomes negative during this time) recaptures new nucleus with resulting scintillations in ~10 MeV range! The last possibility was so far overlooked in the experiments as it did not stem from WIMP hypotheses. A modification of the NaI(Tl) experiments is suggested for revealing the effect described. Independently of the outcome, any obtained result will be important for refining the daemon paradigm further on.
Bars in spiral galaxies can weaken through gas inflow towards the center, and
angular momentum transfer. Several bar episodes can follow one another in the
life of the galaxy, if sufficient gas is accreted from the intergalactic medium
to revive young disks.
Pattern speeds of the successive bars are different, due to mass
concentration, or increased velocity dispersion of the remaining stellar
component. In the same time, the spiral galaxy evolves in morphological type.
Numerical simulations are presented, trying to correlate type and bar pattern
speeds.
We present development of the collimated bipolar jets from the symbiotic prototype Z And that appeared and disappeared during its 2006 outburst. In 2006 July Z And reached its historical maximum at U ~ 8.0. During this period, rapid photometric variations with Dm ~ 0.06 mag on the timescale of hours developed. Simultaneously, high-velocity satellite components appeared on both sides of the H-alpha and H-beta emission line profiles. They were launched asymmetrically with the red/blue velocity ratio of 1.2 - 1.3. From about mid-August they became symmetric. Their spectral properties indicated ejection of bipolar jets collimated within an average opening angle of 6.1 degrees. We estimated average outflow rate via jets to dM(jet)/dt ~ 2xE10-6(R(jet)/1AU)**(1/2) M(Sun)/year, during their August - September maximum, which corresponds to the emitting mass in jets, M(jet, emitting) ~ 6xE-10(Rjet)/1AU)^{3/2} M(Sun). During their lifetime, the jets released the total mass of M(jet, total) approx 7.4x1E-7 M(Sun). Evolution in the rapid photometric variability and asymmetric ejection of jets around the optical maximum can be explained by a disruption of the inner parts of the disk caused by radiation-induced warping of the disk.
We report the statistical properties of stars, brown dwarfs and multiple
systems obtained from the largest hydrodynamical simulation of star cluster
formation to date that resolves masses down to the opacity limit for
fragmentation (a few Jupiter masses). The simulation is essentially identical
to that of Bate, Bonnell & Bromm except that the initial molecular cloud is
larger and more massive. It produces more than 1250 stars and brown dwarfs,
providing unprecedented statistical information that can be compared with
observational surveys.
We find that hydrodynamical/sink particle simulations can reproduce many of
the observed stellar properties very well. Binarity as a function of primary
mass, the frequency of very-low-mass (VLM) binaries, general trends for the
separation and mass ratio distributions of binaries, and the relative orbital
orientations of triples systems are all in reasonable agreement with
observations. We also examine the radial variations of binarity, velocity
dispersion, and mass function in the resulting stellar cluster and the
distributions of disc truncation radii due to dynamical interactions. For VLM
binaries, we find that their frequency when using small accretion radii and
gravitational softening is similar to that expected from observational surveys
(approximately 20 percent). We also find that VLM binaries evolve from wide,
unequal-mass systems towards close equal-mass systems as they form. The two
main deficiencies of the calculations are that they over produce brown dwarfs
relative to stars and that there are too few unequal mass binaries with K and
G-dwarf primaries. [Abridged]
We describe features of the LSST science database that are amenable to scientific data mining, object classification, outlier identification, anomaly detection, image quality assurance, and survey science validation. The data mining research agenda includes: scalability (at petabytes scales) of existing machine learning and data mining algorithms; development of grid-enabled parallel data mining algorithms; designing a robust system for brokering classifications from the LSST event pipeline (which may produce 10,000 or more event alerts per night); multi-resolution methods for exploration of petascale databases; indexing of multi-attribute multi-dimensional astronomical databases (beyond spatial indexing) for rapid querying of petabyte databases; and more.
Circumbinary disks have been hypothesized to exist around a number of binary post-AGB stars. Although most of the circumbinary disks have been inferred through the near IR excess, a few of them are strong emitters of molecular emission. Here we present high angular resolution observations of the emission of $^{12}$CO and its isotopomer $^{13}$CO J=2--1 line from the circumstellar envelope around the binary post-AGB star IRAS 08544$-$4431, which is one of the most prominent members of this class of objects. We find that the envelope is resolved in our observations and two separate components can be identified: (a) a central extended and strong component with very narrow linewidth between 2 - 6 \kms; (b) a weak bipolar outflow with expansion velocity up to 8 \kms. The central compact component possesses low and variable $^{12}$CO/$^{13}$CO J=2--1 line ratio, indicating optically thick emission of the main isotope. We estimate a molecular gas mass of 0.0047 M$_\odot$ for this component based on the optically thinner $^{13}$CO J=2--1 line. We discuss the relation of the molecular envelope and the circumbinary disk inferred from near IR excess and compare with other known cases where the distribution of molecular gas has been imaged at high angular resolution.
Context: A planetary nebula (PN) candidate was discovered during FORS imaging of the Local Group dwarf galaxy Phoenix. Aims: Use this PN to complement abundances from red-giant stars. Methods: FORS spectroscopy was used to confirm the PN classification. Empirical methods and photoionization modeling were used to derive elemental abundances from the emission line fluxes and to characterize the central star. Results: For the elements deemed most reliable for measuring the metallicity of the interstellar medium (ISM) from which the PN formed, [O/H] ~ -0.46 and [Ar/H] ~ -1.03. [O/H] has lower measurement errors but greater uncertainties due to the unresolved issue of oxygen enrichment in the PN precursor star. Conclusions: Earlier than 2 Gyr ago (the lower limit of the derived age for the central star) the ISM had Z = 0.002--0.008, a range slightly more metal-rich than the one provided by stars. Comparing our PN-to-stellar values to surveys for other dwarf Local Group galaxies, Phoenix appears as an outlier.
In their study Bottke et al. (2007) suggest that a member of the Baptistina asteroid family was the probable source of the K/T impactor which ended the reign of the Dinosaurs 65 Myr ago. Knowledge of the physical and material properties pertaining to the Baptistina asteroid family are, however, not well constrained. In an effort to begin addressing the situation, data from an international collaboration of observatories were synthesized to determine the rotational period of the family's largest member, asteroid 298 Baptistina (P_r = 16.23+-0.02 hrs). Discussed here are aspects of the terrestrial impact delivery system, implications arising from the new constraints, and prospects for future work.
The outcome of collisions between small icy bodies, such as Kuiper belt objects, is poorly understood and yet a critical component of the evolution of the trans-Neptunian region. The expected physical properties of outer solar system materials (high porosity, mixed ice-rock composition, and low material strength) pose significant computational challenges. We present results from catastrophic small body collisions using a new hybrid hydrocode to $N$-body code computational technique. This method allows detailed modeling of shock propagation and material modification as well as gravitational reaccumulation. Here, we consider a wide range of material strengths to span the possible range of Kuiper belt objects. We find that the shear strength of the target is important in determining the collision outcome for 2 to 50-km radius bodies, which are traditionally thought to be in a pure gravity regime. The catastrophic disruption and dispersal criteria, $Q_D^*$, can vary by up to a factor of three between strong crystalline and weak aggregate materials. The material within the largest reaccumulated remnants experiences a wide range of shock pressures. The dispersal and reaccumulation process results in the material on the surfaces of the largest remnants having experienced a wider range of shock pressures compared to material in the interior. Hence, depending on the initial structure and composition, the surface materials on large, reaccumulated bodies in the outer solar system may exhibit complex spectral and albedo variations. Finally, we present revised catastrophic disruption criteria for a range of impact velocities and material strengths for outer solar system bodies.
We have continued our studies of the Classical Nova outburst by evolving TNRs on 1.25Msun and 1.35Msun WDs (ONeMg composition) under conditions which produce mass ejection and a rapid increase in the emitted light, by examining the effects of changes in the nuclear reaction rates on both the observable features and the nucleosynthesis during the outburst. In order to improve our calculations over previous work, we have incorporated a modern nuclear reaction network into our hydrodynamic computer code. We find that the updates in the nuclear reaction rate libraries change the amount of ejected mass, peak luminosity, and the resulting nucleosynthesis. In addition, as a result of our improvements, we discovered that the pep reaction was not included in our previous studies of CN explosions. Although the energy production from this reaction is not important in the Sun, the densities in WD envelopes can exceed $10^4$ gm cm$^{-3}$ and the presence of this reaction increases the energy generation during the time that the p-p chain is operating. The effect of the increased energy generation is to reduce the evolution time to the peak of the TNR and, thereby, the accreted mass as compared to the evolutionary sequences done without this reaction included. As expected from our previous work, the reduction in accreted mass has important consequences on the characteristics of the resulting TNR and is discussed in this paper.
(Abridged) We have performed a comprehensive multiwavelength analysis of a sample of 20 starburst galaxies that show the presence of a substantial population of massive stars. The main aims are the study of the massive star formation and stellar populations in these galaxies, and the role that interactions with or between dwarf galaxies and/or low surface companion objects have in triggering the bursts. We completed new deep optical and \NIR\ broad-band images, as well as the new continuum-subtracted H$\alpha$ maps, of our sample of Wolf-Rayet galaxies. We analyze the morphology of each system and its surroundings and quantify the photometric properties of all important objects. All data were corrected for both extinction and nebular emission using our spectroscopic data. The age of the most recent star-formation burst is estimated and compared with the age of the underlying older low-luminosity population. The \Ha-based star-formation rate, number of O7V equivalent stars, mass of ionized gas, and mass of the ionizing star cluster are also derived. We found interaction features in many (15 up to 20) of the analyzed objects, which were extremely evident in the majority. We checked that the correction for nebular emission to the broad-band filter fluxes is important in compact objects and/or with intense nebular emission to obtain realistic colors and compare with the predictions of evolutionary synthesis models. The estimate of the age of the most recent star-formation burst is derived consistently. With respect to the results found in individual objects, we remark the strong \Ha\ emission found in IRAS 08208+2816, UM 420, and SBS 0948+532, the detection of a double-nucleus in SBS 0926+606A, a possible galactic wind in Tol 9, and one (two?) nearby dwarf star-forming galaxies surrounding Tol 1457-437.
We present a study of the spectral, polarimetric, morphological and environmental properties of the diffuse radio source 0809+39 using observations taken with the Westerbork Synthesis Radio Telescope, the Very Large Array, and archival optical and X-ray data. The source has two distinct diffuse, steep-spectrum components, one in the north that is highly polarized, and a linear southern component undetected in polarization. We discuss several plausible origins for each component, and conclude that the northern bright polarized component is most likely a radio relic associated with a poor z$\sim$0.2 cluster of galaxies, with a radio/X-ray luminosity ratio two orders of magnitude above typical values. The southern component is aligned with a more extended filament of galaxies $\sim$5 Mpc long at z$\sim$0.04. Deep optical and X-ray follow-ups are still needed in order to confirm and understand the physical origins of the synchrotron emission. Whatever the details of these origins, 0809+39 highlights the utility of synchrotron radiation for illuminating the diffuse components of low density environments unrelated to rich clusters.
We explore the dependence of the subhalo mass function on the spectral index n of the linear matter power spectrum using scale-free Einstein-de Sitter simulations with n=-1 and n=-2.5. We carefully consider finite volume effects that call into question previous simulations of n<-2 power spectra. Subhaloes are found using a 6D friends-of-friends algorithm in all haloes above a resolution threshold originating from high-sigma peaks. The parameters of this algorithm are varied to examine systematics. We find that subhaloes become more triaxial, and less distinct with an increasingly ill defined boundary as n->-3. We examine the cumulative subhalo mass function and fit a power-law to compare with previous studies. We find that the index of the power-law alpha shows little or no dependence on the criteria used to find subhaloes at n=-1 and is consistent with previous results. At n=-2.5, the index does depend on the criteria used to find subhaloes and is generally shallower with alpha>=-0.75. We infer that although the subhalo mass function appears to be independent of n so long as n>=-2, it begins to flatten as n->-3. Thus, the common practice of using alpha=-1.0 may greatly overestimate the number of subhaloes at the smallest scales in the CDM hierarchy.
We investigate the formation and evolution of giant molecular clouds (GMCs) in a Milky-Way-like disk galaxy with a flat rotation curve. We perform a series of 3D adaptive mesh refinement (AMR) numerical simulations that follow both the global evolution on scales of ~20kpc and resolve down to scales ~<10pc with a multiphase atomic interstellar medium (ISM). In this first study, we omit star formation and feedback, and focus on the processes of gravitational instability and cloud collisions and interactions. We define clouds as regions with n_H>=100cm^-3 and track the evolution of individual clouds as they orbit through the galaxy from their birth to their eventual destruction via merger or via destructive collision with another cloud. After ~140Myr a large fraction of the gas in the disk has fragmented in clouds, with typical masses ~10^6Msun, similar to Galactic GMCs. The disk settles into a quasi steady state in which gravitational scattering of clouds keeps the disk near the threshold of global gravitational instability. The cloud collision time is found to be a small fraction, ~1/5, of the orbital time, and this is an efficient mechanism to inject turbulence into the clouds. This keeps the clouds only moderately gravitationally bound, with virial parameters of order unity. Many other observed GMC properties, such as mass surface density, angular momentum, velocity dispersion, and vertical distribution, can be accounted for in this simple model with no stellar feedback.
The Square Kilometre Array (SKA) is a planned multi purpose radio telescope with a collecting area approaching 1 million square metres. One of the key science objectives of the SKA is to provide exquisite strong-field tests of gravitational physics by finding and timing pulsars in extreme binary systems such as a pulsar-black hole binary. To find out how three preliminary SKA configurations will affect a pulsar survey, we have simulated SKA pulsar surveys for each configuration. We estimate that the total number of normal pulsars the SKA will detect, using only the 1-km core and 30 minutes integration time, is around 14000 normal pulsar and 6000 millisecond pulsars. We describe a simple strategy for follow-up timing observations and find that, depending on the configuration, it would take 1-6 days to obtain a single timing point for 14000 pulsars. Obtaining a single timing point for the high-precision timing projects of the SKA, will take less than 14 hours, 2 days, or 3 days, depending on the configuration. The presence of aperture arrays will be of great benefit here. We also study the computational requirements for beam forming and data analysis for a pulsar survey. Beam forming of the full field of view of the single-pixel feed 15-m dishes using the 1-km core of the SKA requires about 2.2*10^15 operations per second. The corresponding data rate from such a pulsar survey is about 4.7*10^11 bytes per second. The required computational power for a deep real time analysis is estimated to be 1.2*10^16 operations per second. For an aperture array or dishes equipped with phased array feeds, the survey can be performed faster, but the computational requirements and data rates will go up.
We study the full contribution of a stochastic background (SB) of primordial magnetic fields (PMF) on the anisotropies in temperature and polarization of the cosmic microwave background radiation (CMB). A SB of PMF modelled as a fully inhomogeneous component induces non-gaussian scalar, vector and tensor metric linear perturbations. We give the exact expressions for the Fourier spectra of the relevant energy-momentum components of such SB, given a power-law dependence parametrized by a spectral index $n_B$ for the magnetic field power spectrum cut at a damping scale $k_D$. For all the values of $n_B$ considered here, the full contribution to the CMB temperature pattern by such a SB is dominated by the scalar contribution and then by the vector one at higher multipoles. We also give an analytic estimate of the scalar contribution to the CMB temperature pattern.
We propose a star-quake model to understand X-ray flares of both long and short Gamma-ray bursts (GRBs) in a solid quark star regime. Two kinds of central engines for GRBs are available if pulsar-like stars are actually (solid) quark stars, i.e., the SNE-type GRBs and the SGR-type GRBs. It is found that a quark star could be solidified about 10^3 to 10^6 s later after its birth if the critical temperature of phase transition is a few MeV, and then a new source of free energy (i.e., elastic and gravitational ones, rather than rotational or magnetic energy) could be possible to power GRB X-ray flares.
We consider a modification of the Heisenberg algebra with the non-vanishing commutator of scalar field operators. We then identify the scalar field with the second quantized inflaton fluctuation and calculate effects of microcausality violation on the temperature anisotropy of cosmic microwave background radiation.
Growing evidence indicate supermassive black holes (SMBHs) in the mass range of $M_{\rm BH}$$\sim 10^6-10^{10}M_{\odot}$ lurking in central bulges of many galaxies. Extensive observations reveal fairly tight power laws of $M_{\rm BH}$ versus the mean stellar velocity dispersion $\sigma$ of the host bulge. The dynamic evolution of a bulge and the formation of a central SMBH should be physically linked by various observational clues. In this contribution, we reproduce the empirical $M_{\rm BH}-\sigma$ power laws based on a self-similar general polytropic quasi-static bulge evolution and a sensible criterion of forming a SMBH surrounding the central density singularity of a general singular polytropic sphere (SPS) \cite{loujiang2008}. Other properties of host bulges and central SMBHs are also examined. Based on our model, we discuss the intrinsic scatter of the $M_{\rm BH}-\sigma$ relation and a scenario for the evolution of SMBHs in different host bulges.
After more than 5.5 years of in flight lifetime, the ESA space observatory INTEGRAL is depicting a new scenario in the soft gamma Ray domain. With the observation and discovery of more than 400 hard X-Ray sources has changed our view of a moderately crowded and dark sky basically populated by "peculiar" and erratic sources. The new high energy sky is also composed by a large variety of "normal" though very powerful objects, characterized by new accretion and acceleration processes. Among the 421 sources detected in the energy range 17-100 keV the 3rd INTEGRAL/IBIS catalogue includes 41% galactic accreting system, 29% extragalactic objects, 8% of other types, and 26% not classified i.e. of unknown origin. If compared to to previous IBIS/ISGRI surveys it is clear that there is a continuous increase of the rate of discovery of HMXB, an increase in the number of AGN discovered, including a variety of distant QSOs, basically due to the increased exposure away from the Galaxy Plane, while the percentage of sources without an identification has remained constant. INTEGRAL, by the end of Y6, will complete the Core Programme observation due to provide an almost constant exposure of the whole Galaxy Plane and will be fully open to the scientific community for Open Time and Key Programme observations from the beginning of 2009. In this paper we shortly review the main outcome of the 3rd INTEGRAL/IBIS catalogue (cat3) including an excursus of the INTEGRAL high energy sky with particular regard to sources emitting at high energy, including Low and High Mass X-Ray Binaries (LMXB & HMXB), Supergiant Fast X-Ray Transients (SFXT), Pulsar Wind Nebulae (PWN) and Active Galactic Nuclei (AGN).
Post-starburst (E+A or k+a) spectra, characterized by their exceptionally strong Balmer lines in absorption and the lack of emission lines, belong to galaxies in which the star formation activity ended abruptly sometime during the past Gyr. We perform a spectral analysis of galaxies in clusters, groups, poor groups and the field at z=0.4-0.8 based on the ESO Distant Cluster Survey. The incidence of k+a's at these redshifts depends strongly on environment. K+a's reside preferentially in clusters and, unexpectedly, in a subset of the sigma = 200-400 km/s groups, those that have a low fraction of [OII] emitters. In these environments, 20-30% of the recently star-forming galaxies have had their star formation activity recently truncated. In contrast, there are proportionally fewer k+a's in the field, the poor groups and groups with a high [OII] fraction. The incidence of k+a galaxies correlates with the cluster velocity dispersion: more massive clusters have higher proportions of k+a's. Spectra of dusty starburst candidates, with strong Balmer absorption and emission lines, present a very different environmental dependence from k+a's. They are numerous in all environments at z=0.4-0.8, but they are especially numerous in all types of groups, favoring the hypothesis of triggering by a merger. Our observations are consistent with previous suggestions that cluster k+a galaxies are observed in a transition phase as massive S0 and Sa galaxies, evolving from star-forming later types to passively evolving early-type galaxies. The correlation between k+a fraction and cluster sigma supports the hypothesis that k+a galaxies in clusters originate from processes related to the intracluster medium, while several possibilities are discussed for the origin of the k+a frequency in low-[OII] groups.(abr.)
We investigate the relationship between Low Mass X-ray Binaries (LMXBs) and globular clusters (GCs) using UKIRT observations of M31 and existing Chandra, XMM-Newton, and ROSAT catalogues. By fitting King models to these data we have estimated the structural parameters and stellar collision rates of 239 of its GCs. We show a highly significant trend between the presence of a LMXB and the stellar collision rate of a cluster. The stellar collision rate is found to be a stronger predictor of which clusters will host LMXBs than the host cluster mass. We argue that our results show that the stellar collision rate of the clusters is the fundamental parameter related to the production LMXBs. This is consistent with the formation of LMXBs through dynamical interactions with little direct dependence on the neutron star retention fraction or cluster mass.
The parameter fit from a model grid is limited by our capability to reduce the number of models, taking into account the number of parameters and the non linear variation of the models with the parameters. The Local MultiLinear Regression (LMLR) algorithms allow one to fit linearly the data in a local environment. The MATISSE algorithm, developed in the context of the estimation of stellar parameters from the Gaia RVS spectra, is connected to this class of estimators. A two-steps procedure was introduced. A raw parameter estimation is first done in order to localize the parameter environment. The parameters are then estimated by projection on specific vectors computed for an optimal estimation. The MATISSE method is compared to the estimation using the objective analysis. In this framework, the kernel choice plays an important role. The environment needed for the parameter estimation can result from it. The determination of a first parameter set can be also avoided for this analysis. These procedures based on a local projection can be fruitfully applied to non linear parameter estimation if the number of data sets to be fitted is greater than the number of models.
The scientific impact of the research of 36 astronomy PhD granting departments is measured and ranked here. Because of the complex nature of Universities, this study looks at the Universities in two ways; first analyzing the impact of the published work over a 10 year period of the Department which grants the PhD and; second, looking at the impact of the published work as a whole including Laboratories, Centers, and Facilities. The Universities considered in the study are drawn from the 1992 NRC study on Programs of Research, Doctorate in Astrophysics and Astronomy with three Universities added. Johns Hopkins, Michigan State, and Northwestern all host substantial astronomical research within their Departments of Physics and Astronomy and so are included here. The first method of measuring impact concentrates on tenured and tenured track faculty, with the top quartile being 1. Caltech, 2. UC Santa Cruz, 3. Princeton, 4. Harvard, 5. U Colorado, Boulder, 6. SUNY, Stony Brook, 7. Johns Hopkins, 8. Penn State, and 9. U Michigan, Ann Arbor. The second method additionally includes "soft money" scientists in research and adjunct faculty positions, with the top quartile being 1. UC Santa Cruz, 2. Princeton, 3. Johns Hopkins 4. Penn State, 5. SUNY Stony Brook, 6. U Michigan, Ann Arbor, 7. New Mexico State, 8. UMass, Amherst, and 9. U Virginia. Both methods reveal important aspects of Universities, representing both the depth and the breadth of the science available at the University. Finally, a comparison is made of the total articles published in the 10 year period, both from the departments alone and from the larger universities. Three Universities have both impact index in the top quartile, and have more than 1000 publications in a decade; UC at Santa Cruz, Princeton, and Johns Hopkins.
abridged] A method to rapidly estimate the Fourier power spectrum of a point distribution is presented. This method relies on a Taylor expansion of the trigonometric functions. It yields the Fourier modes from a number of FFTs, which is controlled by the order N of the expansion and by the dimension D of the system. In three dimensions, for the practical value N=3, the number of FFTs required is 20. We apply the method to the measurement of the power spectrum of a periodic point distribution that is a local Poisson realization of an underlying stationary field. We derive explicit analytic expression for the spectrum, which allows us to quantify--and correct for--the biases induced by discreteness and by the truncation of the Taylor expansion, and to bound the unknown effects of aliasing of the power spectrum. We show that these aliasing effects decrease rapidly with the order N. The only remaining significant source of errors is reduced to the unavoidable cosmic/sample variance due to the finite size of the sample. The analytical calculations are successfully checked against a cosmological N-body experiment. We also consider the initial conditions of this simulation, which correspond to a perturbed grid. This allows us to test a case where the local Poisson assumption is incorrect. Even in that extreme situation, the third-order Fourier-Taylor estimator behaves well. We also show how to reach arbitrarily large dynamic range in Fourier space (i.e., high wavenumber), while keeping statistical errors in control, by appropriately "folding" the particle distribution.
In this paper we report on the improvements implemented in the cosmological radiative transfer code CRASH. In particular we present a new multi-frequency algorithm for spectra sampling which makes use of colored photon packets: we discuss the need for the multi-frequency approach, describe its implementation and present the improved CRASH performance in reproducing the effects of ionizing radiation with an arbitrary spectrum. We further discuss minor changes in the code implementation which allow for more efficient performance and an increased precision.
The World Space Observatory-Ultraviolet (WSO-UV) will provide access to the UV range during the next decade. The instrumentation on board will allow to carry out high resolution imaging, high sensitivity imaging, high resolution (R~55000) spectroscopy and low resolution (R~2500) long slit spectroscopy. In this contribution, we briefly outline some of the key science issues that WSO-UV will address during its lifetime. Among them, of special interest are: the study of galaxy formation and the intergalactic medium; the astronomical engines; the Milky Way formation and evol ution, and the formation of the Solar System and the atmospheres of extrasolar p lanets.
It is well known that the density and anisotropy profile in the inner regions of a stellar system with positive phase-space distribution function are not fully independent. Here we study the interplay between density profile and orbital anisotropy at large radii in physically admissible (consistent) stellar systems. The analysis is carried out by using two-component (n-gamma,gamma_1) spherical self-consistent galaxy models, in which one density distribution follows a generalized gamma profile with external logarithmic slope n, and the other a standard gamma_1 profile (with external slope 4). The necessary and sufficient conditions for phase-space consistency are determined analytically, also in presence of a dominant massive central black hole, and the analytical phase-space distribution function of (n-gamma,1) models, and of n-gamma models with a central black hole, is derived for gamma=0,1,2. It is found that the density slope in the external regions of a stellar system can play an important role in determining the amount of admissible anisotropy: in particular, for fixed density slopes in the central regions, systems with a steeper external density profile can support more radial anisotropy than externally flatter models. This is quantified by an inequality formally identical to the ``cusp slope-central anisotropy'' theorem (An & Evans 2006), relating at all radii (and not just at the center) the density logarithmic slope and the anisotropy indicator in all Osipkov-Merritt systems [Abridged].
Pulsar wind nebulae are a prominent class of very high energy (E > 0.1 TeV) Galactic sources. Their Gamma-ray spectra are interpreted as due to inverse Compton scattering of ultrarelativistic electrons on the ambient photons, whereas the X-ray spectra are due to synchrotron emission. We investigate the relation between the Gamma- and-X-ray emission and the pulsars' spin-down luminosity and characteristic age. We find that the distance-independent Gamma- to X-ray flux ratio of the nebulae is inversely proportional to the spin-down luminosity, (\propto \dot{E}^-1.9), while it appears proportional to the characteristic age, (\propto tau_c^2.2), of the parent pulsar. We interpret these results as due to the evolution of the electron energy distribution and the nebular dynamics, supporting the idea of so-called relic pulsar wind nebulae. These empirical relations provide a new tool to classify unidentified diffuse Gamma-ray sources and to estimate the spin-down luminosity and characteristic age of rotation powered pulsars with no detected pulsation from the X- and Gamma-ray properties of the associated pulsar wind nebulae. We apply these relations to predict the spin-down luminosity and characteristic age of four (so far unpulsing) candidate pulsars associated to wind nebulae.
The results of an Halpha photometric survey of 30 dwarf galaxies of various morphologies in the Centaurus A and Sculptor groups are presented. Of these 30, emission was detected in 13: eight are of late-type, two are early-type and three are of mixed-morphology. The typical flux detection limit of 2e-16 erg s-1 cm-2, translates into a Star Formation Rate (SFR) detection limit of 4e-6 M_sol yr-1 . In the light of these results, the morphology-density relation is reexamined: It is shown that, despite a number of unaccounted parameters, there are significant correlations between the factors determining the morphological type of a galaxy and its environment. Dwarf galaxies in high density regions have lower current SFR and lower neutral gas content than their low density counterparts, confirming earlier results from the Local Group and other denser environments. The effect of environment is also seen in the timescale formed from the ratio of blue luminosity to current SFR - dwarfs in higher density environments have larger values, indicating relatively higher past average SFR. The influence of environment extends very far and no dwarfs from our sample can be identified as 'field' objects.
We present time-series Doppler images of the rapidly-rotating active binary star EI Eri from spectroscopic observations collected during the MUSICOS multi-site campaign in 1998, since the critical rotation period of 1.947 days makes it impossible to obtain time-resolved images from a single site. From the surface reconstructions a weak solar-type differential rotation, as well as a tiny poleward meridional flow are measured.
We present the ultraviolet-optical-infrared spectral energy distribution of the low inclination novalike cataclysmic variable V592 Cassiopeiae, including new mid-infrared observations from 3.5-24 microns obtained with the Spitzer Space Telescope. At wavelengths shortward of 8 microns, the spectral energy distribution of V592 Cas is dominated by the steady state accretion disk, but there is flux density in excess of the summed stellar components and accretion disk at longer wavelengths. Reproducing the observed spectral energy distribution from ultraviolet to mid-infrared wavelengths can be accomplished by including a circumbinary disk composed of cool dust, with a maximum inner edge temperature of ~500 K. The total mass of circumbinary dust in V592 Cas (~10^21 g) is similar to that found from recent studies of infrared excess in magnetic CVs, and is too small to have a significant effect on the long-term secular evolution of the cataclysmic variable. The existence of circumbinary dust in V592 Cas is possibly linked to the presence of a wind outflow in this system, which can provide the necessary raw materials to replenish the circumbinary disk on relatively short timescales, and/or could be a remnant from the common envelope phase early in the formation history of the system.
We calculate the structure of a wake generated by, and the dynamical friction force on, a gravitational perturber travelling through a gaseous medium of uniform density and constant background acceleration g_ext, in the context of Modified Newtonian Dynamics (MOND). The wake is described as a linear superposition of two terms. The dominant part displays the same structure as the wake generated in Newtonian gravity scaled up by a factor mu^{-1}(g_ext/a_0), where a_{0} is the constant MOND acceleration and mu the interpolating function. The structure of the second term depends greatly on the angle between g_{ext} and and the velocity of the perturber. We evaluate the dynamical drag force numerically and compare our MOND results with the Newtonian case. We mention the relevance of our calculations to orbit evolution of globular clusters and satellites in a gaseous proto-galaxy. Potential differences in the X-ray emission of gravitational galactic wakes in MOND and in Newtonian gravity with a dark halo are highlighted.
Recent measurements of the spectrum and composition of ultrahigh energy cosmic rays suggest that their extragalactic sources may be accelerating heavy nuclei in addition to protons. This can suppress the cosmogenic neutrino flux relative to the usual expectation for an all-proton composition. Cosmic neutrino detectors may therefore need to be even larger than currently planned but conversely they will also be able to provide valuable information concerning astrophysical accelerators. Moreover measurement of ultrahigh energy cosmic neutrino interactions can provide an unique probe of QCD dynamics at high parton density.
We study the pressureless Navier--Stokes-Poisson equations of describing the evolution of the gaseous star in astrophysics. The isothermal blowup solutions of Yuen, to the Euler-Poisson equations in R2, can be extended to the pressureless Navier-Stokes-Poisson equations with density-dependent viscosity in R3. Besides some remarks, about the meaning of the blowup solutions and the applicability of such solutions to the the drift-diffusion model in semiconductors, are discussed in the end.
In the present paper we obtain the WIMP velocity distribution in our vicinity starting from spherically symmetric WIMP density profiles in a self consistent way by employing the Eddington approach. By adding a reasonable angular momentum dependent term in the expression of the energy, we obtain axially symmetric WIMP velocity distributions as well. We find that some density profiles lead to approximate Maxwell-Boltzmann distributions, which are automatically defined in a finite domain, i.e. the escape velocity need not be put by hand. The role of such distributions in obtaining the direct WIMP detection rates, including the modulation, is studied in some detail and, in particular, the role of the asymmetry is explored.
The NSF has chosen the site for the Deep Underground Science and Engineering
Laboratory (DUSEL) to be in Lead, South Dakota. In fact, the state of South
Dakota has already stepped up to the plate and contributed its own funding for
the proposed lab, see this http URL
The final decision by NSF for funding the Initial Suite of Experiments for
DUSEL will be made early in 2009. At that time the NSF Science Board must make
a decision.
Of order 200 experimentalists have already expressed an interest in
performing experiments at DUSEL. In order to assess the interest of the
theoretical community, the Center for Cosmology and Astro-Particle Physics
(CCAPP) at The Ohio State University (OSU) organized a 3-day DUSEL Theory
Workshop in Columbus, Ohio from April 4 - 6, 2008. The workshop focused on the
scientific case for six proposed experiments for DUSEL: long baseline neutrino
oscillations, proton decay, dark matter, astrophysical neutrinos, neutrinoless
double beta decay and N-Nbar oscillations.
The outcome of this workshop is the DUSEL Theory White paper addressing the
scientific case at a level which may be useful in the decision making process
for policy makers at the NSF and in the U.S. Congress. In order to assess the
physics interest in the DUSEL project we have posted the DUSEL Theory White
paper on the following CCAPP link this http URL . Please
read the white paper and, if you are interested, use the link to show your
support by co-signing the white paper.
In cascade inflation and some other string inflation models, collisions of mobile branes with other branes or orbifold planes occur and lead to interesting cosmological signatures. The fundamental M/string-theory description of these collisions is still lacking but it is clear that the inflaton looses part of its energy to some form of brane matter, e.g. a component of tensionless strings. In the absence of a fundamental description, we assume a general barotropic fluid on the brane, which absorbs part of the inflaton's energy. The fluid is modeled by a scalar with a suitable exponential potential to arrive at a full-fledged field theory model. We study numerically the impact of the energy transfer from the inflaton to the scalar on curvature and isocurvature perturbations and demonstrate explicitly that the curvature power spectrum gets modulated by oscillations which damp away toward smaller scales. Even though, the contribution of isocurvature perturbations decays toward the end of inflation, they induce curvature perturbations on scales that exit the horizon before the collision. We consider cases where the scalar behaves like radiation, matter or a web of cosmic strings and discuss the differences in the resulting power spectra.
Light sterile neutrinos might mix with the active ones and be copiously produced in the early Universe. In the present paper, a detailed multi-flavor analysis of sterile neutrino production is performed. Making some justified approximations allows us to consider not only neutrino interactions with the primeval medium and neutrino coherence breaking effects, but also oscillation effects arising from the presence of three light (mostly-active) neutrino states mixed with two heavier (mostly-sterile) states. First, we emphasize the underlying physics via an analytical description of sterile neutrino abundances that is valid for cases with small mixing between active and sterile neutrinos. Then, we study in detail the phenomenology of (3+2) sterile neutrino models in light of short-baseline oscillation data, including the LSND and MiniBooNE results. Finally, by using the information provided by this analysis, we obtain the expected sterile neutrino cosmological abundances and then contrast them with the most recent available data from Cosmic Microwave Background and Large Scale Structure observations. We conclude that (3+2) models are significantly more disfavored by the internal inconsistencies between sterile neutrino interpretations of appearance and disappearance short-baseline data themselves, rather than by the used cosmological data.
I discuss the essential features of the QCD axion: the strong CP solution and hence its theoretical necessity. I also review the axion and axino effects on astrophysics and cosmology, in particular with emphasis on their role in the dark matter component in the universe.
We investigate collision dynamics of two non-Abelian vortices and find that unlike Abelian vortices, they do not reconnect themselves but create a gluon rung between them. This affords direct evidence of networking structures among non-Abelian vortices. Our prediction can be tested experimentally in the cyclic phase of a spin-2 spinor Bose-Einstein condensate.
We consider the three-dimensional semi-relativistic Hartree model for fast quantum mechanical particles moving in a self-consistent field. Under appropriate assumptions on the initial density matrix as a (fully) mixed quantum state we prove, using Wigner transformation techniques, that its classical limit yields the well known relativistic Vlasov-Poisson system. The result holds for the case of attractive and repulsive mean-field interaction, with an additional size constraint in the attractive case.
A stable Dirac fermion with four-fermion interactions to leptons suppressed by a scale Lambda ~ 1 TeV is shown to provide a viable candidate for dark matter. The thermal relic abundance matches cosmology, while nuclear recoil direct detection bounds are automatically avoided in the absence of (large) couplings to quarks. The annihilation cross section in the early Universe is the same as the annihilation in our galactic neighborhood. This allows Dirac fermion dark matter to naturally explain the positron ratio excess observed by PAMELA with a minimal boost factor, given present astrophysical uncertainties. We use the Galprop program for propagation of signal and background; we discuss in detail the uncertainties resulting from the propagation parameters and, more importantly, the injected spectra. Fermi/GLAST has an opportunity to see a feature in the gamma-ray spectrum at the mass of the Dirac fermion. The excess observed by ATIC/PPB-BETS may also be explained with Dirac dark matter that is heavy. A supersymmetric model with a Dirac bino provides a viable UV model of the effective theory. The dominance of the leptonic operators, and thus the observation of an excess in positrons and not in anti-protons, is naturally explained by the large hypercharge and low mass of sleptons as compared with squarks. Minimizing the boost factor implies the right-handed selectron is the lightest slepton, which is characteristic of our model. Selectrons (or sleptons) with mass less than a few hundred GeV are an inescapable consequence awaiting discovery at the LHC.
Recently it was shown that the inclusion of higher signal harmonics in the inspiral signals of binary supermassive black holes (SMBH) leads to dramatic improvements in parameter estimation with the Laser Interferometer Space Antenna (LISA). In particular, the angular resolution becomes good enough to identify the host galaxy or galaxy cluster, in which case the redshift can be determined by electromagnetic means. The gravitational wave signal also provides the luminosity distance with high accuracy, and the relationship between this and the redshift depends sensitively on the cosmological parameters, such as the equation-of-state parameter $w=p_{\rm DE}/\rho_{\rm DE}$ of dark energy. With a single binary SMBH event at $z < 1$ having appropriate masses and orientation, one would be able to constrain $w$ to within a few percent. We show that, if the measured sky location is folded into the error analysis, the uncertainty on $w$ goes down by an additional factor of 2-3, leaving weak lensing as the only limiting factor in using LISA as a dark energy probe.
The physical properties of our universe at energy scales above the expansion rate during inflation can affect predictions for the ratio between the amplitudes of the primordial scalar and tensor fluctuations. In particular, we study here the effects of a breakdown of a locally Lorentz invariant description of nature at tiny space-time intervals. In some instances, these effects shift the amplitudes by a constant amount, altering the standard relation between this ratio and the slow-roll parameters. More generally, "trans-Planckian" effects introduce a modulation in the primordial power spectra which grows at shorter scales, making the value of the ratio sensitive to the scale at which it is defined. We also present a model where symmetries are broken at horizon scales during inflation. In this case, the power at large scales today could then be suppressed, relative to that at smaller scales.
Links to: arXiv, form interface, find, astro-ph, recent, 0811, contact, help (Access key information)
We present an analysis of a 50 orbit HST ACS observation of the M87 globular cluster system. We use the extraordinary depth of this dataset to test whether the colors and magnitudes show evidence for a mass-metallicity relation in globular cluster populations. We find only a weak or absent relation between the colors and magnitudes of the metal poor subpopulation of globular clusters. The weakness or absence of a color-magnitude relation is established over a wide range in luminosity from $M_V=-11$ to $M_V=-6$, encompassing most of the M87 globular clusters. The constancy of the colors of the metal-poor subpopulation seen in our 50 orbit observation is in contrast to suggestions from single orbit ACS data that the metal-poor globular clusters in M87 and several other galaxies show a "blue tilt." The formal best fit for the mass-metallicity relation for the metal-poor subpopulation in our much deeper data is $Z\propto M^{0.08\pm0.05}$. Our analysis of these data also shows a possible small "red tilt" in the metal-rich globular cluster subpopulation. While either of these small tilts may be real, they may also illustrate the limit to which mass-metallicity relations can be determined, even in such extraordinarily deep data. We specifically test for a wide range of systematic effects and find that while small tilts cannot be confirmed or rejected, the data place a strong upper limit to any tilt of $|0.20|\pm0.05$. This upper limit is much smaller than some earlier claims from single orbit data, and strongly limits self-enrichment within globular clusters. This mass-metallicity relation for globular clusters is also shallower than the relation for galaxies, suggesting that the formation mechanisms for these two types of objects are different.
Gravitational flexion has recently been introduced as a technique by which one can map out and study substructure in clusters of galaxies. Previous analyses involving flexion have measured the individual galaxy-galaxy flexion signal, or used either parametric techniques or a KSB-type inversion to reconstruct the mass distribution in Abell 1689. In this paper, we present an aperture mass statistic for flexion, and apply it to the lensed images of background galaxies obtained by ray-tracing simulations through a simple analytic mass distribution and through a galaxy cluster from the Millennium simulation. We show that this method is effective at detecting and accurately tracing structure within clusters of galaxies on sub-arcminute scales with high signal-to-noise even using a moderate background source number density and image resolution. In addition, the method provides much more information about both the overall shape and the small-scale structure of a cluster of galaxies than can be achieved through a weak lensing mass reconstruction using gravitational shear data. Lastly, we discuss how the zero-points of the aperture mass might be used to infer the masses of structures identified using this method.
With the prospect of measuring the fraction of arriving secondary photons, produced through photo-pion energy loss interactions of ultra high energy cosmic ray (UHECR) protons with the microwave background during propagation, we investigate how information about the local UHECR source distribution can be inferred from the primary (proton) to secondary (photon) ratio. As an aid to achieve this, we develop an analytic description for both particle populations as a function of propagation time. Through a consideration of the shape of the GZK cut-off and the corresponding photon fraction curve, we investigate the different results expected for both different maximum proton energies injected by the sources, as well as a change in the local source distribution following a perturbative deformation away from a homogeneous description. At the end of the paper, consideration is made as to how these results are modified through extra-galactic magnetic field effects on proton propagation. The paper aims to demonstrate how the shape of the cosmic ray flux in the cut-off region, along with the photon fraction, are useful indicators of the cutoff origin as well as the local UHECR source distribution.
Context: Only two planetary systems around old ms-pulsars are currently
known. Young radio pulsars and radio-quiet neutron stars cannot be covered by
the usually-applied radio pulse timing technique. However, finding substellar
companions around these neutron stars would be of great interest -- not only
because of the companion's possible exotic formation but also due to the
potential access to neutron star physics.
Aims: We investigate the closest young neutron stars to search for substellar
companions around them.
Methods: Young, thus warm substellar companions are visible in the Near
Infrared while the neutron star itself is much fainter. Four young neutron
stars are moving fast enough to enable a common proper motion search for
substellar companions within few years.
Results. For Geminga, RX J0720.4-3125, RX J1856.6-3754, and PSR J1932+1059 we
did not find any co-moving companion down to 12, 15, 11, 42 Jupiter masses for
assumed ages of 1, 1, 1, 3.1 Myrs and distances of 250, 361, 167, 361 pc,
respectively. Near Infrared limits are presented for these four as well as five
other neutron stars for which we currently have only observations at one epoch.
Conclusions: We conclude that young isolated neutron stars rarely have brown
dwarf companions.
We present initial results and source lists of variable sources in the Large Magellanic Cloud (LMC) for which we detect thermal infrared variability from the SAGE (Surveying the Agents of a Galaxy's Evolution) survey, which had 2 epochs of photometry separated by three months. The SAGE survey mapped a 7 degree by 7 degree region of the LMC using the IRAC and the MIPS instruments on board Spitzer. Variable sources are identified using a combination of the IRAC 3.6, 4.5, 5.8, 8.0 \micron bands and the MIPS 24 \micron bands. An error-weighted flux difference between the two epochs is used to assess the variability. Of the ~ 3 million sources detected at both epochs we find ~ 2,000 variable sources for which we provide electronic catalogs. Most of the variable sources can be classified as asymptotic giant branch (AGB) stars. A large fraction (> 66%) of the extreme AGB stars are variable and only smaller fractions of carbon-rich (6.1%) and oxygen-rich (2.0%) stars are detected as variable. We also detect a population of variable young stellar object candidates.
We developed CdTe double-sided strip detectors (DSDs or cross strip detectors) and evaluated their spectral and imaging performance for hard X-rays and gamma-rays. Though the double-sided strip configuration is suitable for imagers with a fine position resolution and a large detection area, CdTe diode DSDs with indium (In) anodes have yet to be realized due to the difficulty posed by the segmented In anodes. CdTe diode devices with aluminum (Al) anodes were recently established, followed by a CdTe device in which the Al anodes could be segmented into strips. We developed CdTe double-sided strip devices having Pt cathode strips and Al anode strips, and assembled prototype CdTe DSDs. These prototypes have a strip pitch of 400 micrometer. Signals from the strips are processed with analog ASICs (application specific integrated circuits). We have successfully performed gamma-ray imaging spectroscopy with a position resolution of 400 micrometer. Energy resolution of 1.8 keV (FWHM: full width at half maximum) was obtained at 59.54 keV. Moreover, the possibility of improved spectral performance by utilizing the energy information of both side strips was demonstrated. We designed and fabricated a new analog ASIC, VA32TA6, for the readout of semiconductor detectors, which is also suitable for DSDs. A new feature of the ASIC is its internal ADC function. We confirmed this function and good noise performance that reaches an equivalent noise charge of 110 e- under the condition of 3-4 pF input capacitance.
We analyze the sidereal daily variations observed between 1985 and 2006 at Matsushiro, Japan (MAT) and between 1993 and 2005 at Liapootah, Tasmania (LPT). These stations comprise the two hemisphere network (THN) of underground muon detectors in Japan and Australia. Yearly mean harmonic vectors at MAT and LPT are more or less stable without any significant change in phase and amplitude in correlation with either the solar activity- or magnetic-cycles. In this paper, therefore, we analyze the average anisotropy over the entire observation periods, i.e. 1985-2006 for MAT and 1993-2005 for LPT. We apply to the THN data a best-fitting analysis based on a model anisotropy in space identical to that adopted by Amenomori et al. (2007) for Tibet III data. The median energies of primary cosmic rays recorded are ~0.5 TeV for THN and ~5 TeV for the Tibet III experiment. It is shown that the intensity distribution of the best-fit anisotropy is quite similar to that derived from Tibet III data, regardless of the order of magnitude difference in energies of primary particles. This, together with the THN observations, confirms that the analysis by Amenomori et al. (2007) based on the Tibet III experiment in the northern hemisphere is not seriously biased. The best-fit amplitudes of the anisotropy, on the other hand, are only one third or less of those reported by the Tibet III experiment, indicating attenuation due to solar modulation. The rigidity dependence of the anisotropy amplitude in the sub-TeV region is consistent with the spectrum reported by Hall et al. (1999), smoothly extending to the Tibet III result in the multi-TeV region. The amplitude at higher energies appears almost constant or gradually decreasing with increasing rigidity.
Cool L- and T-type objects were discovered first as companions to stars in 1988 and 1995, respectively. A certain example of the yet cooler Y-type spectral class (Teff <~ 500K?) has not been seen. Recent infrared imaging observations of stars and brown dwarfs indicate that substellar companions with large semi-major axes and with masses less than the brown dwarf/giant planet dividing line (~13.5 Mj) are rare. Theoretical considerations of Jeans mass fragmentation of molecular clouds are consistent with this minimum mass cutoff and also with the semi-major axis (hundreds of AU) characteristic of the lowest mass imaged companions. As a consequence, Y-class companions with large semi-major axes should be scarce around stars <2Gyr old, and also around substellar primaries of all ages. By focusing on brown dwarf companions to young stellar primaries, it is possible to derive a first estimate of the brown dwarf IMF over the entire range of brown dwarf masses (13 Mj to 79 Mj) -- the number of companion brown dwarfs is proportional to mass to the -1.2+-0.2 power.
The basic concepts of gravitational microlensing are introduced. We start with the lens equation, and then derive the image positions and magnifications. The statistical quantities of optical depth and event rate are then described. We finish with a summary and a list of challenges and open questions. A problem set is given for students to practice.
Lac OB1 is a nearby OB association in its final stage of star formation. While the member stars suggest an expansion time scale of tens of Myr, the latest star formation episode, as manifested by the existence of massive and pre-main sequence stars, took place no more than a few Myr ago. The remnant molecular clouds in the region provide evidence of starbirth triggered by massive stars.
We present the results of the analysis of the AGN population in the deepest extragalactic hard X-ray survey. The survey is based on INTEGRAL observation of the 3C 273/Coma cluster region, and covers 2500 deg2 with a 20-60 keV flux limit 1.5 times lower than other surveys at similar energies, resolving about 2.5% of the cosmic hard X-ray background. Using this survey, we can constrain in an unbiased way the distribution of hydrogen column absorption up to Nh=10^25 cm-2. We put an upper limit of 24% to the fraction of Compton-thick objects. Compared to models of the AGN population selected in the 2-10 keV band, the Log N-Log S diagram is generally in good agreement, but the Nh distribution is significantly different, with significantly less unabsorbed sources (Nh<10^22 cm-2) at a given flux limit compared to the models. We also study the local hard X-ray luminosity function (LF), which is compatible with what is found in other recent hard X-ray surveys. The extrapolation of the 2-10 keV LF is lower than the hard X-ray LF. The discrepancy is resolved if AGN spectra typically present reflection humps with reflection fraction R~1. Finally, we use the population properties of this survey to show that a future ultra-deep INTEGRAL extragalactic survey can result in a quite large AGN sample with enough objects at redshifts larger than z=0.05 so that we can detect evolution in the hard X-ray LF.
Angular momentum loss (AML) mechanisms and dynamical evolution owing to magnetic braking and gravitational radiation in relativistic binary stars (RBS) are studied with use of physical parameters collected from the literature. We have calculated and compared AML time scales for the RBS with non-degenerate components and double degenerate (DD) systems.
We investigate to what extent the temperature dependence of the nuclear symmetry energy can affect the neutronization of the stellar core prior to neutrino trapping during gravitational collapse. To this end, we implement a one-zone simulation to follow the collapse until beta equilibrium is reached and the lepton fraction remains constant. Since the strength of electron capture on the neutron-rich nuclei associated to the supernova scenario is still an open issue, we keep it as a free parameter. We find that the temperature dependence of the symmetry energy consistently yields a small reduction of deleptonization, which corresponds to a systematic effect on the shock wave energetics: the gain in dissociation energy of the shock has a small yet non-negligible value of about 0.4 foe (1 foe = 10^51 erg) and this result is almost independent from the strength of nuclear electron capture. The presence of such a systematic effect and its robustness under changes of the parameters of the one-zone model are significative enough to justify further investigations with detailed numerical simulations of supernova explosions.
The space experiment CoRoT has recently detected transits by a hot Jupiter across the disc of an active G7V star (CoRoT-Exo-2a) that can be considered as a good proxy for the Sun at an age of approximately 0.5 Gyr. We present a spot modelling of the optical variability of the star during 142 days of uninterrupted observations performed by CoRoT with unprecedented photometric precision. We apply spot modelling approaches previously tested in the case of the Sun by modelling total solar irradiance variations. To model the light curve of CoRoT-Exo-2a, we take into account both the photometric effects of cool spots as well as those of solar-like faculae, adopting solar analogy. Two active longitudes initially on opposite hemispheres are found on the photosphere of CoRoT-Exo-2a with a rotation period of 4.522 $\pm$ 0.024 days. Their separation changes by approximately 80 degrees during the time span of the observations. From this variation, a relative amplitude of the surface differential rotation lower than about 1 percent is estimated. Individual spots form within the active longitudes and show an angular velocity about 1 percent smaller than that of the longitude pattern. The total spotted area shows a cyclic oscillation with a period of 28.9 $\pm$ 4.3 days, which is close to 10 times the synodic period of the planet as seen by the rotating active longitudes. The implications of such results for the internal rotation of CoRoT-Exo-2a are discussed on the basis of solar analogy. A possible magnetic star-planet interaction is suggested by the cyclic variation of the spotted area. Alternatively, the 28.9-d cycle may be related to Rossby-type waves propagating in the subphotospheric layers of the star.
Results of realistic simulations of solar surface convection on the scale of supergranules (96 Mm wide by 20 Mm deep) are presented. The simulations cover only 10% of the geometric depth of the solar convection zone, but half its pressure scale heights. They include the hydrogen, first and most of the second helium ionization zones. The horizontal velocity spectrum is a power law and the horizontal size of the dominant convective cells increases with increasing depth. Convection is driven by buoyancy work which is largest close to the surface, but significant over the entire domain. Close to the surface buoyancy driving is balanced by the divergence of the kinetic energy flux, but deeper down it is balanced by dissipation. The damping length of the turbulent kinetic energy is 4 pressure scale heights. The mass mixing length is 1.8 scale heights. Two thirds of the area is upflowing fluid except very close to the surface. The internal (ionization) energy flux is the largest contributor to the convective flux for temperatures less than 40,000 K and the thermal energy flux is the largest contributor at higher temperatures. This data set is useful for validating local helioseismic inversion methods. Sixteen hours of data are available as four hour averages, with two hour cadence, at steinr.msu.edu/~bob/96averages, as idl save files. The variables stored are the density, temperature, sound speed, and three velocity components. In addition, the three velocity components at 200 km above mean continuum optical depth unity are available at 30 sec. cadence.
Mass loss is a key process in the evolution of massive stars, and must be understood quantitatively to be successfully included in broader astrophysical applications. In this review, we discuss various aspects of radiation driven mass loss, both from the theoretical and the observational side. We focus on winds from OB-stars, with some excursions to the Luminous Blue Variables, Wolf- Rayet stars, A-supergiants and Central Stars of Planetary Nebulae. After reca- pitulating the 1-D, stationary standard model of line-driven wind, extensions accounting for rotation and magnetic fields are discussed. The relevance of the so-called bi-stability jump is outlined. We summarize diagnostical methods to infer wind properties from observations, and compare the results with theore- tical predictions, featuring the massloss-metallicity dependence. Subsequently, we concentrate on two urgent problems which challenge our present understanding of radiation driven winds: weak winds and wind- clumping. We discuss problems of measuring mass-loss rates from weak winds and the potential of NIR- spectroscopy. Wind-clumping has severe implications for the interpretation of observational diagnostics, as derived mass-loss rates can be overestimated by factors of 2 to 10 if clumping is ignored, and we describe ongoing attempts to allow for more uniform results. We point out that independent arguments from stellar evolution favor a moderate reduction of present- day mass-loss rates. We also consider larger scale wind structure, interpreted in terms of co-rotating interacting regions, and complete this review with a discussion of recent progress on the X-ray line emission from massive stars, highlighting as to how far the analysis of such X-ray line emission can give further clues regarding an adequate description of wind clumping. (Abridged abstract)
We present the results of a speckle interferometric survey of Galactic massive stars that complements and expands upon a similar survey made over a decade ago. The speckle observations were made with the KPNO and CTIO 4 m telescopes and USNO speckle camera, and they are sensitive to the detection of binaries in the angular separation regime between 0.03" and 5" with relatively bright companions (Delta V < 3). We report on the discovery of companions to 14 OB stars. In total we resolved companions of 41 of 385 O-stars (11%), 4 of 37 Wolf-Rayet stars (11%), and 89 of 139 B-stars (64%; an enriched visual binary sample that we selected for future orbital determinations). We made a statistical analysis of the binary frequency among the subsample that are listed in the Galactic O Star Catalog by compiling published data on other visual companions detected through adaptive optics studies and/or noted in the Washington Double Star Catalog and by collecting published information on radial velocities and spectroscopic binaries. We find that the binary frequency is much higher among O-stars in clusters and associations compared to the numbers for field and runaway O-stars, consistent with predictions for the ejection processes for runaway stars. We present a first orbit for the O-star Delta Orionis, a linear solution of the close, apparently optical, companion of the O-star Iota Orionis, and an improved orbit of the Be star Delta Scorpii. Finally, we list astrometric data for another 249 resolved and 221 unresolved targets that are lower mass stars that we observed for various other science programs.
We have fitted ~200 RXTE and INTEGRAL spectra of the neutron star LMXB GX 9+9 from 2002-2007 with a model consisting of a disc blackbody and another blackbody representing the spreading layer (SL), i.e. an extended accretion zone on the NS surface as opposed to the more traditional disc-like boundary layer. Contrary to theory, the SL temperature was seen to increase towards low SL luminosities, while the approximate angular extent had a nearly linear luminosity dependency. Comptonization was not required to adequately fit these spectra. Together with the ~70 degree upper bound of inclination implied by the lack of eclipses, the best-fitting normalization of the accretion disc blackbody component implies a distance of ~10 kpc, instead of the usually quoted 5 kpc.
Prompted by a high optical state in September 2007, the Whole Earth Blazar Telescope (WEBT) consortium organized an intensive optical, near-IR (JHK) and radio observing campaign on the intermediate BL Lac object 3C 66A throughout the fall and winter of 2007 -- 2008. The source remained in a high optical state throughout the observing period and exhibited several bright flares on time scales of ~ 10 days. This included an exceptional outburst around September 15 - 20, 2007, reaching a peak brightness at R ~ 13.4. Our campaign revealed microvariability with flux changes up to |dR/dt| ~ 0.02 mag/hr. Our observations do not reveal evidence for systematic spectral variability or spectral lags. We infer a value of the magnetic field in the emission region of B ~ 19 e_B^{2/7} \tau_h^{-6/7} D_1^{13/7} G. From the lack of systematic spectral variability, we can derive an upper limit on the Doppler factor, D <= 28 \tau_h^{-1/8} e_B^{3/16}. This is in agreement with superluminal motion measurements of \beta_{app} \le 27 and argues against models with very high Lorentz factors of \Gamma > 50, required for a one-zone SSC interpretation of some high-frequency-peaked BL Lac objects detected at TeV gamma-ray energies.
We present high resolution (0."4) observations of HNC J=3-2 with the SubMillimeter Array (SMA). We find luminous HNC 3-2 line emission in the western part of Arp220, centered on the western nucleus, while the eastern side of the merger shows relatively faint emission. A bright (36 K), narrow (60 km/s) emission feature emerges from the western nucleus, superposed on a broader spectral component. A possible explanation is weak maser emission through line-of-sight amplification of the background continuum source. There is also a more extended HNC 3-2 emission feature north and south of the nucleus. This feature resembles the bipolar OH maser morphology around the western nucleus. Substantial HNC abundances are required to explain the bright line emission from this warm environment. We discuss this briefly in the context of an X-ray chemistry and radiative excitation. We conclude that the luminous and possibly amplified HNC emission of the western nucleus of the Arp220 merger reflects the unusual, and perhaps transient, environment of the starburst/AGN activity there. The faint HNC line emission towards Arp220-east reveals a real difference in physical conditions between the two merger nuclei.
For about a decade, spectro-polarimetry of HeI 10830 has been applied to the magnetic diagnostics of the solar chromosphere. This resonance line is very versatile, as it is visible both on disk and in off-limb structures, and it has a good sensitivity to both the weak-field Hanle effect and the strong-field Zeeman effect. Recent observations of an active-region filament showed that the linear polarization was dominated by the transverse Zeeman effect, with very little or no hint of scattering polarization. This is surprising, since the HeI levels should be significantly polarized in a conventional scattering scenario. To explain the observed level of atomic depolarization by collisional or radiative processes, one must invoke plasma densities larger by several orders of magnitude than currently known values for prominences. We show that such depolarization can be explained quite naturally by the presence of an unresolved, highly entangled magnetic field, which averages to give the ordered field inferred from spectro-polarimetric data, over the typical temporal and spatial scales of the observations. We present a modeling of the polarized HeI 10830 in this scenario, and discuss its implications for the magnetic diagnostics of prominences and spicules, and for the general study of unresolved magnetic field distributions in the solar atmosphere.
Machine learning techniques are utilised in several areas of astrophysical
research today. This dissertation addresses the application of ML techniques to
two classes of problems in astrophysics, namely, the analysis of individual
astronomical phenomena over time and the automated, simultaneous analysis of
thousands of objects in large optical sky surveys. Specifically investigated
are (1) techniques to approximate the precise orbits of the satellites of
Jupiter and Saturn given Earth-based observations as well as (2) techniques to
quickly estimate the distances of quasars observed in the Sloan Digital Sky
Survey. Learning methods considered include genetic algorithms, particle swarm
optimisation, artificial neural networks, and radial basis function networks.
The first part of this dissertation demonstrates that GAs and PSOs can both
be efficiently used to model functions that are highly non-linear in several
dimensions. It is subsequently demonstrated in the second part that ANNs and
RBFNs can be used as effective predictors of spectroscopic redshift given
accurate photometry, especially in combination with other learning-based
approaches described in the literature. Careful application of these and other
ML techniques to problems in astronomy and astrophysics will contribute to a
better understanding of stellar evolution, binary star systems, cosmology, and
the large-scale structure of the universe.
Within the interstellar medium, supernovae are thought to be the prevailing agents in driving turbulence. Until recently, their effects on magnetic field amplification in disk galaxies remained uncertain. Analytical models based on the uncorrelated-ensemble approach predicted that any created field would be expelled from the disk before it could be amplified significantly. By means of direct simulations of supernova-driven turbulence, we demonstrate that this is not the case. Accounting for galactic differential rotation and vertical stratification, we find an exponential amplification of the mean field on timescales of several hundred million years. We especially highlight the importance of rotation in the generation of helicity by showing that a similar mechanism based on Cartesian shear does not lead to a sustained amplification of the mean magnetic field.
In this paper we introduce a new multiparametric technique that attempts to tackle simultaneously the problems of composition determination and hadronic interaction uncertainty. Employing simulations of a real world detector under its planned operational conditions, and disregarding systematics, we can asses that the present technique should be able to determine the composition of a binary mixture of p and Fe with a statistical confidence of few percent, in a way that is independent of the assumed hadronic interaction model. Moreover, the combination of real data with the tools developed and presented here should give an indication of the reliability of the various hadronic interaction models in current use in the area. We center our study in the region of the ankle, where composition carries critical astrophysical information, and use two main parameters: the number of muons at 600 m from the shower axis and the depth of the shower maximum obtained from the hybrid operation of the planned muon counters and high elevation fluorescence telescopes of the AMIGA and HEAT Auger enhancements.
We have monitored the benchmark L dwarf binary Kelu-1AB over the past 3 years to derive improved spectral types and luminosities for the individual components. The astrometric measurements enable us to compute the orbital parameters and result in the first dynamical mass estimate for the system. We obtained resolved high angular resolution, near-IR images with HST and the VLT/NACO adaptive optics instrument in the J, H and Ks bands. In addition we used NACO to achieve the first spatially resolved mid-resolution spectra in the H- and K-band for a precise spectral type determination. The near-IR spectrum of Kelu-1A reveals a distinct dip in the H-band providing evidence that Kelu-1 A itself is a spectroscopic binary. We derive spectral types of L0.5+- 0.5 for Kelu- 1 Aa and T7.5+-1 for Kelu-1 Ab. Kelu-1B is classified as spectral type L3pec +-1.5. From the relative orbit, we derive an orbital period of 38 +8 -6 years and a semi-major axis of 6.4+2.4 -1.3 AU. This yields the first dynamically determined total system mass of 177 +113 -55 Mjup for the Kelu-1AB system, with the uncertainties mainly attributed to the error of the system distance measurement and the yet missing apastron passage. The derived properties of Kelu-1AB allow us to test common theoretical models. The comparison of our results with color-magnitude diagrams based on evolutionary models yields a slightly revised age estimate (0.3 - 0.5 Gyr) and a discrepancy between dynamically and theoretically derived masses, stressing the importance for further dynamical mass determinations of brown dwarf binaries.
We study galaxy evolution from z=1 to z=0 as a function of velocity dispersion sigma for galaxies with sigma > 95 km/s based on the measured and Monte Carlo realised local velocity dispersion functions (VDFs) of galaxies and the revised statistical properties of 30 strongly-lensed sources from the Cosmic Lens All-Sky Survey (CLASS), the PMN-NVSS Extragalactic Lens Survey (PANELS) and the Hubble Space Telescope Snapshot survey. For the evolutionary behaviours of the VDFs we find that: (1) the number density of massive (mostly early-type) galaxies with sigma > 200 km/s evolves differentially in the way that the number density evolution is greater at a higher velocity dispersion, contradicting the "mass-downsizing" scenario suggested by several galaxy surveys unless the unlikely systematic variation of the mass profiles of massive galaxies occurs over cosmic time; (2) the number density of intermediate and low mass early-type galaxies (95 km/s < sigma < 200 km/s) is nearly constant;(3) the late-type VDF transformed from the Monte Carlo realised circular velocity function is consistent with no evolution in its shape or integrated number density consistent with galaxy survey results. These evolutionary behaviours are similar to the evolutions of the galaxy stellar mass functions predicted by Stringer et al. using the GALFORM semi-analytical model code based on the Millennium simulation. We consider several possible systematic errors for the lensing analysis and find that they are not likely to alter the conclusions. (abridged)
Understanding why the expansion of the universe is presently accelerating is one of the most important open questions in modern cosmology. In this work we show that the presence of a temporal electromagnetic field on cosmological scales generates an effective cosmological constant which could be responsible for the acceleration. Primordial electromagnetic quantum fluctuations produced during electroweak scale inflation could naturally explain the presence of this field and the measured value of the dark energy density. This mechanism could be discriminated from a true cosmological constant by observations of CMB and structure formation. In the same way as the presence of matter or radiation in the Universe breaks global Lorentz symmetry, the existence of dark energy could be signalling the breakdown of electromagnetic gauge invariance on cosmological scales.
Ground-based long-term optic variability of AM Her, covering the period between 2003-2008, has been conducted to study the features seen in both low and high states of the system. Low-state analysis shows the presence of short-term, low-amplitude light variations of about 0.02-0.03 mag with a mean power time between 16 s and 226 s. Brightness variations on the order of 0.7--2 mag, which could be due to the stellar activity of the component in the system, are also detected. A total of 30 years times of minimum light given in the literature are combined with nine times of minima obtained in this study. We represented the (observed--calculated) diagram by a parabolic curve and also by two broken lines. Under the assumption of a parabolic variation, we estimate an increase in period, dP/dt=7.5(1.2)x10^{-9} days yr^{-1}, with a mass transfer rate of dM/dt = 8(2)x10^{-9} M_{\odot} yr^{-1}, in agreement with the previous findings by a different method.
Multi-wavelength studies at radio, infrared, optical, X-ray, and TeV wavelengths have discovered probable counterparts to many Galactic sources of GeV emission detected by EGRET. These include pulsar wind nebulae, high mass X-ray binaries, and mixed morphology supernova remnants. Here we provide an overview of the observational properties of Galactic sources which emit across 19 orders of magnitude in energy. We also present new observations of several sources.
A summary of the current knowledge on hypervelocity stars (HVSs). HVSs are fascinating because their properties are linked to Sgr A* and the stellar environment of the Galactic Center. Observing the distribution of HVSs can address: 1) the nature of the black hole ejection mechanism, 2) the in-fall history of stars onto Sgr A*, 3) the types of stars orbiting Sgr A*, and 4) a unique measurement the shape of the Galaxy's dark matter potential. The challenge to observers is to find new HVSs and strengthen the connection between HVSs and the Galactic Center.
Hyper-velocity stars (HVSs) were first predicted by theory to be the result of the tidal disruption of a binary system by a super-massive black hole (SMBH) that accelerates one component to beyond the Galactic escape velocity (the Hills mechanism). Because the Galactic centre hosts such a SMBH it is the suggested place of origin for HVSs. However, the SMBH paradigm has been challenged recently by the young HVS HD271791 because its kinematics point to a birthplace in the metal-poor rim of the Galactic disc. Here we report the atmosphere of HD271791 to indeed show a sub-solar iron abundance along with an enhancement of the alpha-elements, indicating capture of nucleosynthesis products from a supernova or a more energetic hypernova. This implies that HD271791 is the surviving secondary of a massive binary system disrupted in a supernova explosion. No such run-away star has ever been found to exceed the Galactic escape velocity, hence HD271791 is the first hyper-runaway star. Such a run-away scenario is an alternative to the Hills mechanism for the acceleration of some HVSs with moderate velocities. The observed chemical composition of HD271791 puts invaluable observational constraints on nucleosynthesis in a supernova from the core-collapse of a very massive star (M_ZAMS >= 55 M_Sun), which may be observed as a gamma-ray burst of the long-duration/soft-spectrum type.
We present preliminary astrometric results for the closest known brown dwarf binary to the Sun: Epsilon Indi Ba, Bb at a distance of 3.626 pc. Via ongoing monitoring of the relative separation of the two brown dwarfs (spectral types T1 and T6) with the VLT NACO near-IR adaptive optics system since June 2004, we obtain a model-independent dynamical total mass for the system of 121 MJup, some 60% larger than the one obtained by McCaughrean et al. (2004), implying that the system may be as old as 5 Gyr. We have also been monitoring the absolute astrometric motions of the system using the VLT FORS2 optical imager since August 2005 to determine the individual masses. We predict a periastron passage in early 2010, by which time the system mass will be constrained to < 1 MJup and we will be able to determine the individual masses accurately in a dynamical, model-independent manner.
We report the results of a 3-weeks multi-wavelength campaign on the flat spectrum radio quasar 3C 273 carried out with the AGILE gamma-ray mission, covering the 30 MeV -50 GeV and 18-60 keV, the REM observatory (covering the near-IR and optical), Swift (near-UV/Optical, 0.2-10 keV and 15-50 keV), INTEGRAL (3 - 200 keV) and Rossi XTE (2-12 keV). This is the first observational campaign including gamma-ray data, after the last EGRET observations, more than 8 years ago. Our study was carried out using simultaneous light curves of the source flux from all the involved instruments, in the different energy ranges, in search for correlated variability. Then a time-resolved SED was used for a detailed physical modelling of the emission mechanisms. The source was detected in gamma-rays only in the second week of our campaign. We found indication of a possible anti-correlation between the emission at gamma-rays and at soft and hard X-rays, supported by the complete set of instruments. Instead, optical data do not show short term variability. Only in two EGRET observations (in 1993 and 1997) 3C 273 showed intra-observation variability in gamma-rays. The SED with almost simultaneous data, partially covers the regions of the synchrotron emission, the big blue bump, and the inverse-Compton. The soft X-ray emission is consistent with combined SSC and EC mechanisms, while hard X and gamma-ray emissions are compatible with EC from thermal photons of the disk. The time evolution of the SED is well interpreted and modelled in terms of an acceleration episode of the electrons population, leading to a shift in the IC peak towards higher energies.
There is an intimate link between supermassive black hole (SMBH) mass (M) and the stellar velocity dispersion (sigma) of the host bulge. This has a fundamental impact on our understanding of galaxy and SMBH formation and evolution. However, the scatter, slope and zero-point of the relation is a subject of some debate. For any progress to be made on this relation, the established values of M and sigma must be robust. Over 50% of current M estimates have been made using the technique of stellar dynamics. However, there is serious concern over this method that prompts their re-evaluation. In addition, it is not clear how best to define sigma. The aim of the M-Sigma Project is to use STIS long-slit spectroscopy, integral field spectroscopy and the latest stellar models, to best estimate the values of M and sigma in as many cases as possible. The project will determine the most appropriate properties of the M-Sigma relation itself.
We are conducting a large program with the NRAO Very Long Baseline Array (VLBA) to measure trigonometric parallaxes of massive star-forming regions across the Milky Way. Here we report measurement of the parallax and proper motion of methanol masers in S 252 and G232.6+1.0. The parallax of S 252 is 0.476 +/- 0.006 mas (2.10 [+0.027/-0.026] kpc), placing it in the Perseus spiral arm. The parallax of G232.6+1.0 is 0.596 +/- 0.035 mas (1.68 [+0.11/-0.09] kpc), placing it between the Carina-Sagittarius and Perseus arms, possibly in a Local (Orion) spur of the Carina-Sagittarius arm. For both sources, kinematic distances are significantly greater than their parallax distances. Our parallaxes and proper motions yield full space motions accurate to about 1 km/s. Both sources orbit the Galaxy about 13 km/s slower than circular rotation.
We calculate the decay rate of bottomonium to two-charm quark jets $\Upsilon \to c \bar c$ at the tree level and one-loop level including color-singlet and color-octet $b \bar b$ annihilations. We find that the short distance coefficient of the color-octet piece is much larger than the color-singlet piece, and that the QCD correction will change the endpoint behavior of the charm quark jet. The color-singlet piece is strongly affected by the one-loop QCD correction. In contrast, the QCD correction to the color-octet piece is weak. Once the experiment can measure the branching ratio and energy distribution of the two-charm quark jets in the $\Upsilon$ decay, the result can be used to test the color octet mechanism or give a strong constraint on the color-octet matrix elements.
We explain the PAMELA positron excess and the PPB-BETS/ATIC e+ + e- data using a simple two component dark matter model (2DM). The two particle species in the dark matter sector are assumed to be in thermal equilibrium in the early universe. While one particle is stable and is the present day dark matter, the second one is metastable and decays after the universe is 10^-8 s old. In this model it is simple to accommodate the large boost factors required to explain the PAMELA positron excess without the need for large spikes in the local dark matter density. We provide the constraints on the parameters of the model and comment on possible signals at future colliders.
We summarize recent results on the properties of near-horizon metrics in different spherically symmetric space-times, including Kantowski-Sachs cosmological models whose evolution begins with a horizon (the so-called Null Big Bang) and static metrics related to black holes. We describe the types of matter compatible with cosmological and black-hole horizons. It turns out, in particular, that a black hole horizon can be in equilibrium with a fluid of disordered cosmic strings ("black holes can have curly hair"). We also discuss different kinds of horizons from the viewpoint of the behavior of tidal forces acting on an extended body and recently classified as "usual", "naked" and "truly naked" ones; in the latter case, tidal forces are infinite in a freely falling reference frame. It is shown that all truly naked horizons, as well as many of those previously characterized as naked and even usual ones, do not admit an extension and therefore must be considered as singularities. The whole analysis is performed locally (in a neighborhood of a candidate horizon) in a model-independent manner. Finally, the possible importance of some of these models in generating dynamic, perturbatively small vacuum fluctuation contributions to the cosmological constant (within a cosmological Casimir-effect approach to this problem) is discussed.
We study analytically the fundamental resonances of near-extremal, slowly rotating Kerr-Newman black holes. We find a simple analytic expression for these black-hole quasinormal frequencies in terms of the black-hole physical parameters: omega=m Omega-2i pi T(l+1+n), where T and Omega are the temperature and angular velocity of the black hole. The mode parameters l and m are the spheroidal harmonic index and the azimuthal harmonic index of a co-rotating mode, respectively. This analytical formula is valid in the regime Im omega << Re omega <<1/M, where M is the black-hole mass.
The first and second cosmological coincidence problems are two most puzzles in the dark energy problem. In this letter, we investigate these two problems in the interacting Yang-Mills field dark energy models. The research shows that, if the attractor solution of the interacting system exists, the equation of-state of the dark energy must evolve from $w_y>0$ to $w_y<-1$, and the first and second cosmological coincidence problems are alleviated. At the same time, the total equation-of-state in the attractor solution is $w_{tot}=-1$, the universe is a de Sitter expansion, and the cosmic big rip is naturally avoided. These features are all independent of the interacting forms.
In this paper we revisit the formulation of scalar field theories on de Sitter backgrounds subject to the generalized uncertainty principle (GUP). The GUP arises in several contexts in string theory, but is most readily thought of as resulting from using strings as effective probes of geometry, which suggests an uncertainty relation incorporating the string scale $l_s$. After reviewing the string theoretic case for the GUP, which implies a minimum length scale $l_s$, we follow in the footsteps of Kempf and concern ourselves as to how one might write down field theories which respect the GUP. We uncover a new representation of the GUP, which unlike previous studies, readily permits analytical solutions for the mode functions of a scalar field on de Sitter backgrounds. We find that scalar fields cannot be quantized on inflationary backgrounds with a Hubble radius $H^{-1}$ smaller than the string scale, implying a potential sub-planckian cutoff on the scale of inflation resulting from the GUP. We also compute order $(H l_s)^2$ (as opposed to $(H l_{pl})^2$) corrections to the two point correlation function and comment on the future prospects of observing such corrections in the event our universe is described by a weakly coupled string theory.
We derive conditions under which f(G) dark energy models, whose Lagrangian densities f are written in terms of a Gauss-Bonnet term G, are cosmologically viable. The most crucial condition to be satisfied is that f_GG, the second derivative of f with respect to G, must be positive, which is required to ensure the stability of a late-time de-Sitter solution as well as the existence of standard radiation/matter dominated epochs. We present a number of explicit f(G) models in which a cosmic acceleration is followed by the matter era. We find that the equation of state of dark energy can cross the phantom divide before reaching the present Universe. The viable models are such that f_GG goes to +0 when |G| goes to infinity, in which case a rapid oscillation of perturbations occurs unless such an oscillating degree of freedom is suppressed relative to a homogeneous mode in the early universe. We also introduce an iterative method to avoid numerical instabilities associated with a large mass of the oscillating mode.
Acceleration of the universe is obtained from a model of non-relativistic particles with a short-range attractive interaction, at low enough temperature to produce a Bose-Einstein condensate. Conditions are derived for negative-pressure behavior. In particular, we show that a phantom-accelerated regime at the beginning of the universe solves the horizon problem, consistently with nucleosynthesis.
We review cosmology in non-minimal Yang-Mills/Maxwell theory, in which the Yang-Mills/electromagnetic field couples to a function of the scalar curvature. We show that power-law inflation can be realized due to the non-minimal gravitational coupling of the Yang-Mills field which may be caused by quantum corrections. Moreover, we study non-minimal vector model in the framework of modified gravity and demonstrate that both inflation and the late-time accelerated expansion of the universe can be realized. We also discuss the cosmological reconstruction of the Yang-Mills theory. Furthermore, we investigate late-time cosmology in non-minimal Maxwell-Einstein theory. We explore the forms of the non-minimal gravitational coupling which generate the finite-time future singularities and the general conditions for this coupling in order that the finite-time future singularities cannot appear.
The influence of the GUP and EUP on the thermodynamics of the FRW universe has been investigated. It is shown that the entropy of the apparent horizon of the FRW universe gets a correction if one considers the effect of the GUP or EUP. Moreover, starting with the corrected entropy and applying the first law of thermodynamics, $dE=TdS$, to apparent horizon of the FRW universe, we obtain the corrected Friedmann equations. The influence of the GUP or EUP on the thermodynamics of the FRW universe provides a deep insight into the understanding the quantum gravity or large length scale corrections to the dynamics of the FRW universe.
Recently we have shown that there are crucial similarities in the physics of cosmic microwave background radiation (CMBR) anisotropies and the flow anisotropies in relativistic heavy-ion collision experiments (RHICE). We also argued that, following CMBR anisotropy analysis, a plot of root-mean square values of the flow coefficients, $v_n^{rms}$, calculated in a lab fixed frame for RHICE can yield important information about the nature of initial state anisotropies and their evolution. Here we demonstrate the strength of this technique by showing that elliptic flow for non-central collisions can be directly probed from such a plot without any need for the determination of event-plane.
Results of a previous article with the same title are retrieved by a different method. A one-component plasma is bounded by a plane surface. The plasma is fully coupled to the electromagnetic field, therefore the charge correlations are retarded. The quantum correlation function of the surface charge densities, at times different by $t$, at asymptotical large distances $R$, at inverse temperature $\beta$, decays as $-1/(8\pi^2\beta R^3)$, a surprisingly simple result: the decay is independent of Planck's constant $\hbar$ and of the time difference $t$. The present paper is based on the analysis of the collective vibration modes of the system.
Links to: arXiv, form interface, find, astro-ph, recent, 0811, contact, help (Access key information)
We describe a method for determining the dispersion of magnetic field vectors about local mean fields in turbulent molecular clouds. The method is designed to avoid inaccurate estimates of MHD or turbulent dispersion - and hence to avoid inaccurate estimates of field strengths - due to large-scale, non-turbulent field structure when using the well-known method of Chandrasekhar and Fermi. Our method also provides accurate, independent estimates of the turbulent to mean magnetic field strength ratio. We discuss applications to the molecular clouds Orion, M17, and DR21.
Determinations of the solar oxygen content relying on the neutral forbidden transition at 630 nm depend upon the nickel abundance, due to a Ni I blend. Here we rederive the solar nickel abundance, using the same ab initio 3D hydrodynamic model of the solar photosphere employed in the recent revision of the abundances of C, N, O and other elements. Using 17 weak, unblended lines of Ni I together with the most accurate atomic and observational data available we find log epsilon_Ni = 6.17 +/- 0.05, a downwards shift of 0.06-0.08 dex relative to previous 1D-based abundances. We investigate the implications of the new nickel abundance for studies of the solar oxygen abundance based on the [O I] 630 nm line in the quiet Sun. Furthermore, we demonstrate that the oxygen abundance implied by the recent sunspot spectropolarimetric study of Centeno & Socas-Navarro needs to be revised downwards from log epsilon_O = 8.86 +/- 0.07 to 8.71 +/- 0.10. Determinations of the solar oxygen content relying on forbidden lines now appear to converge around log epsilon_O = 8.7.
The first stars in the universe, forming at redshifts z>15 in minihalos with masses of order 10^6 Msun, may leave behind black holes as their remnants. These objects could conceivably serve as "seeds" for much larger black holes observed at redshifts z~6. We study the growth of the remnant black holes through accretion including for the first time the emitted accretion radiation with adaptive mesh refinement cosmological radiation-hydrodynamical simulations. The effects of photo-ionization and heating dramatically affect the accretion flow from large scales, resulting in negligible mass growth of the black hole. We compare cases with the accretion luminosity included and neglected to show that the accretion radiation drastically changes the environment within 100 pc of the black hole, where gas temperatures are increased by an order of magnitude. The gas densities are reduced and million years of evolution we followed. These calculations show that even without the radiative feedback included most seed black holes do not gain mass as efficiently as has been hoped for in previous theories, implying that black hole remnants of Pop III stars that formed in minihalos are not likely to be the origin of miniquasars. Most importantly, however, these calculations demonstrate that if early stellar mass black holes are indeed accreting close to the Bondi-Hoyle rate with ten percent efficiency they have a dramatic local effect in regulating star formation in the first galaxies.
Dark matter annihilation into charged particles is necessarily accompanied by gamma rays, produced via radiative corrections. Internal bremsstrahlung from the final state particles can produce hard gamma rays up to the dark matter mass, with an approximately model-independent spectrum. Focusing on annihilation into electrons, we compute robust upper bounds on the dark matter self annihilation cross section, $<\sigma_A v >_{e^+e^-}$, using gamma ray data from the Milky Way spanning a wide range of energies, $\sim10^{-3} - 10^4$ GeV. We also compute corresponding bounds for the other charged leptons. We make conservative assumptions about the astrophysical inputs, and demonstrate how our derived bounds would be strengthened if stronger assumptions about these inputs are adopted. The fraction of hard gamma rays near the endpoint accompanying annihilation to $e^+e^-$ is only a factor of $\alt 10^2$ lower than for annihilation directly to monoenergetic gamma rays. The bound on $<\sigma_A v >_{e^+e^-}$ is thus weaker than that for $<\sigma_A v >_{\gamma\gamma}$ by this same factor. The upper bounds on the annihilation cross sections to charged leptons are compared with an upper bound on the {\it total} annihilation cross section defined by neutrinos.
We present a number of statistical tools for obtaining studying turbulence in molecular clouds and diffuse interstellar medium. For our tests we used of three-dimensional 512 cube compressible MHD isothermal simulations performed for different sonic and Alfvenic Mach numbers. We introduce the bispectrum, a new tool for statistical studies of the interstellar medium which, unlike an ordinary power spectrum of turbulence, preserves the phase information of the stochastic field. We show that the bispectra of the 3D stochastic density field and of column densities, available from observations, are similar. We use the bispectrum technique to define the role of non-linear wave-wave interactions in the turbulent energy cascade. We also obtained the bispectrum function for density and column densities with varying magnetic field strength. Larger values of sonic Mach number result in increased correlations for modes with different wavenumbers. This effect becomes more evident with increasing magnetic field intensity. In addition to the bispectrum, we calculated the 3rd and 4th statistical moments of density and column density, namely, skewness and kurtosis, respectively. We found a strong dependence of skewness and kurtosis with the sonic Mach number. In particular, as this number increases, so does the asymmetry of the density distribution. We also studied the correlations of 2D column density with dispersion of velocities and magnetic field, as well as the correlations of 3D density with magentic and kinetic energy and Alfven Mach number for comparison. Our results show that column density is linearly correlated with magnetic field for high sonic Mach number. This trend is independent of the turbulent kinetic energy and can be used to characterize inhomogeneities of physical properties in low density clumps in the ISM.
We present the redshift catalogs for the X-ray sources detected in the
Chandra Deep Field North (CDF-N), the Chandra Large Area Synoptic X-ray Survey
(CLASXS), and the Chandra Lockman Area North Survey (CLANS). The catalogs for
the CDF-N and CLASXS fields include redshifts from previous work, while the
redshifts for the CLANS field are all new. For fluxes above 10^-14 ergs cm^-2
s^-1 (2-8 keV) we have redshifts for 76% of the sources. We extend the redshift
information for the full sample using photometric redshifts. The goal of the
OPTX Project is to use these three surveys, which are among the most
spectroscopically complete surveys to date, to analyze the effect of spectral
type on the shape and evolution of the X-ray luminosity functions and to
compare the optical spectral types with the X-ray spectral properties.
We also present the CLANS X-ray catalog. The nine ACIS-I fields cover a solid
angle of ~0.6 square degrees and reach fluxes of 7x10^-16 ergs cm^-2 s^-1
(0.5-2 keV) and 3.5x10^-15 ergs cm^-2 s^-1 (2-8 keV). We find a total of 761
X-ray point sources. Additionally, we present the optical and infrared
photometric catalog for the CLANS X-ray sources, as well as updated optical and
infrared photometric catalogs for the X-ray sources in the CLASXS and CDF-N
fields.
The CLANS and CLASXS surveys bridge the gap between the ultradeep pencil-beam
surveys, such as the CDFs, and the shallower, very large-area surveys. As a
result, they probe the X-ray sources that contribute the bulk of the 2-8 keV
X-ray background and cover the flux range of the observed break in the
logN-logS distribution. We construct differential number counts for each
individual field and for the full sample.
We describe optical spectroscopic observations of the icy dwarf planet Eris
with the 6.5 meter MMT telescope and the Red Channel Spectrograph. We report a
correlation, that is at the edge of statistical significance, between blue
shift and albedo at maximum absorption for five methane ice bands. We interpret
the correlation as an increasing dilution of methane ice with another ice
component, probably nitrogen, with increasing depth into the surface.
We suggest a mechanism to explain the apparent increase in nitrogen with
depth. Specifically, if we are seeing Eris 50 degrees from pole-on (Brown and
Schaller, 2008), the pole we are seeing now at aphelion was in winter darkness
at perihelion. Near perihelion, sublimation could have built up atmospheric
pressure on the sunlit (summer) hemisphere sufficient to drive winds toward the
dark (winter) hemisphere, where the winds would condense. Because nitrogen is
more volatile and scarcer than methane, it sublimated from the sunlit
hemisphere relatively early in the season, so the early summer atmosphere was
nitrogen rich, and so was the ice deposited on the winter pole. Later in the
season, much of the nitrogen was exhausted from the summer pole, but there was
plenty of methane, which continued to sublimate. At this point, the atmosphere
was more depleted in nitrogen, as was the ice freezing out on top of the
earlier deposited nitrogen rich ice.
Astrophysical fluids, including interstellar and interplanetary medium, are magnetized and turbulent. Their appearance, evolution, and overall properties are determined by the magnetic turbulence that stirs it. We argue that examining magnetic turbulence at a fundamental level is vital to understanding many processes. A point that frequently escapes the attention of researchers is that magnetic turbulence cannot be confidently understood only using ``brute force'' numerical approaches. In this review we illustrate this point on a number of examples, including intermittent heating of plasma by turbulence, interactions of turbulence with cosmic rays and effects of turbulence on the rate of magnetic reconnection. We show that the properties of magnetic turbulence may vary considerably in various environments, e.g. imbalanced turbulence in solar wind differs from balanced turbulence and both of these differ from turbulence in partially ionized gas. Appealing for the necessity of more observational data on magnetic fields, we discuss a possibility of studying interplanetary turbulence using alignment of Sodium atoms in the tail of comets.
We study generic single-field dark energy models, by a parametrization of the most general theory of their perturbations around a given background, including higher derivative terms. In appropriate limits this approach reproduces standard quintessence, k-essence and ghost condensation. We find no general pathology associated to an equation of state w_Q < -1 or in crossing the phantom divide w_Q = -1. Stability requires that the w_Q < -1 side of dark energy behaves, on cosmological scales, as a k-essence fluid with a virtually zero speed of sound. This implies that one should set the speed of sound to zero when comparing with data models with w_Q < -1 or crossing the phantom divide. We summarize the theoretical and stability constraints on the quintessential plane (1+w_Q) vs. speed of sound squared.
We use a large set of high-resolution N-body simulations of a variety of structure formation models (scale-free, Lambda CDM, standard CDM, and open CDM) to study the mass accretion histories, the mass- and redshift-dependence of concentrations and the concentration evolution histories of dark matter halos. We show that the much-used empirical models in the literature all fail significantly to match our simulations. Based on our simulation results, we find that the mass accretion rate of a halo is tightly correlated with a combination of its mass, the redshift, parameters of the cosmology and the initial density fluctuation. We also find that the concentration of a halo is strongly correlated with the universe age when its progenitor on the mass accretion history first reaches 4% of its current mass. According to these correlations, we develop new empirical models for both the mass accretion histories and the concentration evolution histories of dark matter halos, and the latter can also be used to predict the mass- and redshift-dependence of halo concentrations. These models are accurate and universal: the same set of model parameters works well for different cosmological models and for halos of different masses at different redshifts. These models are also simple and easy to implement. We provide an appendix describing the step-by-step implementation of our models. A calculator which allows one to interactively generate data for any given cosmological model is provided at this http URL, together with a user-friendly code to make the relevant calculations and some tables listing the expected concentration as a function of halo mass and redshift in several popular cosmological models.
I examine the effectiveness of Kozai oscillations in the centres of galaxies and in particular the Galactic centre using standard techniques from celestial mechanics. In particular, I study the effects of a stellar bulge potential and general relativity on Kozai oscillations, which are induced by stellar discs. Lockmann et al (2008) recently suggested that Kozai oscillations induced by the two young massive stellar discs in the Galactic centre drives the orbits of the young stars to large eccentricity ($e\approx 1$). If some of these young eccentric stars are in binaries, they would be disrupted near pericentre, leaving one star in a tight orbit around the central SMBH and producing the S-star population. I find that the {\it spherical} stellar bulge suppresses Kozai oscillations, when its enclosed mass inside of a test body is of order the mass in the stellar disc(s). Since the stellar bulge in the Galactic centre is much larger than the stellar discs, Kozai oscillations {\it due to the stellar discs} are likely suppressed. Whether Kozai oscillations are induced from other nonspherical components to the potential (for instance, a flattened stellar bulge) is yet to be determined.
We present new X-ray imaging and spectroscopy of a composite supernova remnant G327.1-1.1 using the Chandra and XMM-Newton X-ray observatories. G327.1-1.1 has an unusual morphology consisting of a symmetric radio shell and an off center nonthermal component that indicates the presence of a pulsar wind nebula (PWN). Radio observations show a narrow finger of emission extending from the PWN structure towards the northwest. X-ray studies with ASCA, ROSAT, and BeppoSAX revealed elongated extended emission and a compact source at the tip of the finger that may be coincident with the actual pulsar. The high resolution Chandra observations provide new insight into the structure of the inner region of the remnant. The images show a compact source embedded in a cometary structure, from which a trail of X-ray emission extends in the southeast direction. The Chandra images also reveal two prong-like structures that appear to originate from the vicinity of the compact source and extend into a large bubble that is oriented in the north-west direction, opposite from the bright radio PWN. The emission from the entire radio shell is detected in the XMM data and can be characterized by a thermal plasma model with a temperature of 0.3 keV, which we use to estimate the physical properties of the remnant. The peculiar morphology of G327.1-1.1 may be explained by the emission from a moving pulsar and a relic PWN that has been disrupted by the reverse shock.
Recent advances in numerical relativity provide a detailed description of the waveforms of coalescing massive black hole binaries (MBHBs), expected to be the strongest detectable LISA sources. We present a preliminary study of LISA's sensitivity to MBHB parameters using a hybrid numerical/analytic waveform for equal-mass, non-spinning holes. The Synthetic LISA software package is used to simulate the instrument response and the Fisher information matrix method is used to estimate errors in the parameters. Initial results indicate that inclusion of the merger signal can significantly improve the precision of some parameter estimates. For example, the median parameter errors for an ensemble of systems with total redshifted mass of one million Solar masses at a redshift of one were found to decrease by a factor of slightly more than two for signals with merger as compared to signals truncated at the Schwarzchild ISCO.
We report the discovery of spatially-extended, non-thermal or hot, quasi-thermal emission components in Chandra X-ray spectra for five of a sample of seven massive, merging galaxy clusters with powerful radio halos: Abell 665, 2163, 2255, 2319, and 1E0657-56. The emission components can be fitted by power-law models with mean photon indices in the range 1.4 < Gamma < 2.0, or by bremsstrahlung emission from hot gas with kT > 20 keV. A control sample of regular, dynamically relaxed clusters without radio halos but with comparable thermal temperatures and luminosities shows no evidence for similar components in their Chandra spectra. Detailed X-ray spectral mapping reveals the complex thermodynamic states of the radio halo clusters. We report the discovery of a clear, large-scale shock front in Abell 2219. Our deepest observations, of the Bullet Cluster 1E0657-56, demonstrate a spatial correlation between the strongest power law X-ray emission, highest thermal pressure, and brightest 1.34GHz radio halo emission in this cluster. The integrated flux and mean spectral index of the power law X-ray emission from 1E0657-56 are in good agreement with constraints at harder X-ray energies from the Rossi X-ray Timing Explorer. We explore possible origins for the power law X-ray components which include inverse Compton scattering of cosmic microwave background photons by relativistic electrons in the clusters; quasi-thermal bremsstrahlung from supra-thermal electrons energized by Coulomb collisions with an energetic, non-thermal proton population; synchrotron emission associated with ultra-relativistic electrons; and spatially unresolved temperature structure e.g. due to hot gas associated with shocks driven by the ongoing merger activity.
Diffusive shock acceleration operating at expanding supernova remnant shells is by far the most popular model for the origin of galactic cosmic rays. Despite the general consensus received by this model, an unambiguous and conclusive proof of the supernova remnant hypothesis is still missing. In this context, the recent developments in gamma ray astronomy provide us with precious insights into the problem of the origin of galactic cosmic rays, since production of gamma rays is expected both during the acceleration of cosmic rays at supernova remnant shocks and during their subsequent propagation in the interstellar medium. In particular, the recent detection of a number of supernova remnants at TeV energies nicely fits with the model, but it still does not constitute a conclusive proof of it, mainly due to the difficulty of disentangling the hadronic and leptonic contributions to the observed gamma ray emission. In this paper, the most relevant cosmic-ray-related results of gamma ray astronomy are briefly summarized, and the foreseeable contribution of future gamma ray observations to the final solution of the problem of cosmic ray origin is discussed.
We discuss a long-standing problem of how turbulence can be studied using observations of Doppler broadened emission and absorption lines. The focus of the present review is on two new techniques, the Velocity-Channel Analysis (VCA), which makes use of the channel maps, and the Velocity Coordinate Spectrum (VCS), which utilizes the fluctuations measured along the velocity axis of the Position-Position Velocity (PPV) data cubes. Both techniques have solid theoretical foundations based on analytical calculations as well as on numerical testings. Among the two the VCS, which has been developed quite recently, has two unique features. First of all, it is applicable to turbulent volumes that are not spatially resolved. Second, it can be used with absorption lines that do not provide good spatial sampling of different lags over the image of the turbulent object. In fact, recent studies show that measurements of absorption line along less than 10 absorption directions are sufficient for a reliable recovering of the underlying spectrum of the turbulence. Moreover, both weak absorption lines and absorption lines in saturated regime can be used, which extends the applicability of the technique. Our comparison of the VCA and the VCS with a more traditional technique of Velocity Centroids shows that the former two techniques recover reliably the spectra of supersonic turbulence, while the Velocity Centroids may be used only for studying subsonic turbulence. We discuss spectra of astrophysical turbulence obtained with the VCA and the VCS techniques.
The ability of NICMOS to perform high accuracy polarimetry is currently hampered by an uncalibrated residual instrumental polarization at a level of 1.2-1.5%. To better quantify and characterize this residual we obtained observations of three polarimetric standard stars at three separate space-craft roll angles. Combined with archival data, these observations were used to characterize the residual instrumental polarization to enable NICMOS to reach its full polarimetric potential. Using these data, we calculate values of the parallel transmission coefficients that reproduce the ground-based results for the polarimetric standards. The uncertainties associated with the parallel transmission coefficients, a result of the photometric repeatability of the observations, dominate the accuracy of p and theta. However, the new coefficients now enable imaging polarimetry of targets with p~1.0% at an accuracy of +/-0.6% and +/-15 degrees.
Turbulent motions induce Doppler shifts of observable emission and absorption lines motivating studies of turbulence using precision spectroscopy. We provide the numerical testing of the two most promising techniques, Velocity Channel Analysis (VCA) and Velocity Coordinate Spectrum (VCS). We obtain an expression for the shot noise that the discretization of the numerical data entails and successfully test it. We show that the numerical resolution required for recovering the underlying turbulent spectrum from observations depend on the spectral index of velocity fluctuations, which makes low resolution testing misleading. We demonstrate numerically that, dealing with absorption lines, sampling of turbulence along just a dozen directions provides a high quality spectrum with the VCS technique.
We present a unified rotation curve of the Galaxy re-constructed from the existing data by re-calculating the distances and velocities for a set of galactic constants R_0=8 kpc and V_0=200 km/s. We decompose it into a bulge with de Vaucouleurs-law profile of half-mass scale radius 0.5 kpc and mass 1.8 x 10^{10}M_{sun}, an exponential disk of scale radius 3.5 kpc of 6.5 x 10^{10}M_{sun}, and an isothermal dark halo of terminal velocity 200 km/s. The r^{1/4}-law fit was obtained for the first time for the Milky Way's rotation curve. After fitting by these fundamental structures, two local minima, or the dips, of rotation velocity are prominent at radii 3 and 9 kpc. The 3-kpc dip is consistent with the observed bar. It is alternatively explained by a massive ring with the density maximum at radius 4 kpc. The 9-kpc dip is clearly exhibited as the most peculiar feature in the galactic rotation curve. We explain it by a massive ring of amplitude as large as 0.3 to 0.4 times the disk density with the density peak at radius 11 kpc. This great ring may be related to the Perseus arm, while no peculiar feature of HI-gas is associated.
We construct a Galacto-Local Group rotation curve, combining the Galactic rotation curve with a diagram, where galacto-centric radial velocities of outer globular clusters and member galaxies of the Local Group are plotted against their galacto-centric distances. The high-velocity ends of this pseudo rotation curve within a radius R ~ 150 kpc are well traced by a rotation curve calculated for the NFW (Navaro, Frenk, White) and Burkert dark halo models. The NFW model indicates that the Galaxy's mass within 385 kpc, half distance to M31, is ~ 4 x 10^{11}M_{sun}. High-velocity ends of the pseudo rotation curve for the entire Local Group up to 1.5 Mpc indicate isothermal nature with a terminal velocity of ~ 200 km/s. In order for the Local Group to be gravitationally bound, an order of magnitude larger mass than those of the Galaxy and M31 is required. This fact indicates that the Local Group contains dark matter of mass ~ 5 x 10^{12}M_{sun} filling the space between the Galaxy and M31. The mass density of the Galactic dark halo becomes equal to that of the Local Group's dark matter at R ~ 100 kpc, beyond which the intracluster dark matter dominates. If we define the Galaxy's radius at this distance, the enclosed Galactic mass is ~ 3 x 10^{11}M_{sun}.
Disk galaxies are common in our universe and this is a source of concern for hierarchical formation models like LCDM. Here we investigate this issue as motivated by raw merger statistics derived for galaxy-size dark matter halos from LCDM simulations. Our analysis shows that a majority (~70%) of galaxy halos with M = 10^12 M_sun at z=0 should have accreted at least one object with mass m > 10^11 M_sun ~ 3 M_disk over the last 10 Gyr. Mergers involving larger objects should have been rare, and this pinpoints m/M = 0.1 mass-ratio mergers as the most worrying ones for the survival of thin galactic disks. Motivated by these results, we use use high-resolution, dissipationless N-body simulations to study the response of stellar Milky-Way type disks to these common mergers and show that thin disks do not survive the bombardment. The remnant galaxies are roughly three times as thick and twice as kinematically hot as the observed thin disk of the Milky Way. Finally, we evaluate the suggestion that disks may be preserved if the mergers involve gas-rich progenitors. Using empirical measures to assign stellar masses and gas masses to dark matter halos as a function of redshift, we show that the vast majority of large mergers experienced by 10^12 M_sun halos should be gas-rich (f_gas > 0.5), suggesting that this is a potentially viable solution to the disk formation conundrum. Moreover, gas-rich mergers should become increasingly rare in more massive halos > 10^12.5 M_sun, and this suggest that merger gas fractions may play an important role in establishing morphological trends with galaxy luminosity.
Five planets are presently believed to orbit the primary star of 55 Cnc, but there exists a large 5 AU gap in their distribution between the two outermost planets. This gap has attracted considerable interest because it may contain one or more lower--mass planets whose existence is not contradicted by long-term orbit stability analyses, in fact it is expected according to the "packed planetary systems" hypothesis and an empirical Titius--Bode relation recently proposed for 55 Cnc. Furthermore, the second largest planet is just the second farthest and it orbits very close to the star. Its orbit, the most circular of all, appears to be nearly but not quite commensurable with the orbit of the third planet, casting doubt that any migration or resonant capture of the inner planets has ever occurred and lending support to the idea of "in--situ" giant planet formation by the process of core accretion. All of the above ideas will be tested in the coming years in this natural laboratory as more observations will become available. This opportunity presents itself in conjunction with a physical model that relates the orbits of the observed planets to the structure of the original protoplanetary disk that harbored their formation at the early stages of protostellar collapse. Using only the 5 observed planets of 55 Cnc, this model predicts that the surface density profile of its protoplanetary disk varied with distance $R$ precisely as $\Sigma (R)\propto R^{-3/2}$, as was also found for the minimum--mass solar nebula. Despite this similarity, the disk of 55 Cnc was smaller, heavier, and less rotationally supported than the solar nebula, so this system represents a different mode of multi--planet formation compared to our own solar system.
For r-process nucleosynthesis the beta decay rates of very neutron-rich nuclei are important ingredients. We consider the region around the neutron number N=82 and calculate the half-lives and rates for a number of nuclei. Forms for beta strength functions based on spectral distribution methods are used. The calculated half-lives are first compared to the observed values and then predictions are made for very neutron-rich nuclei close to drip line for which no experimental values are available.
We present a case study of the 13 July 2004 solar event, in which disturbances caused by eruption of a filament from an active region embraced a quarter of the visible solar surface. Remarkable are absorption phenomena observed in the SOHO/EIT 304 A channel; they were also visible in the EIT 195 A channel, in the H-alpha line, and even in total radio flux records. Coronal and Moreton waves were also observed. Multi-spectral data allowed reconstructing an overall picture of the event. An explosive filament eruption and related impulsive flare produced a CME and blast shock, both of which decelerated and propagated independently. Coronal and Moreton waves were kinematically close and both decelerated in accordance with an expected motion of the coronal blast shock. The CME did not resemble a classical three-component structure, probably, because some part of the ejected mass fell back onto the Sun. Quantitative evaluations from different observations provide close estimates of the falling mass, ~3 10^15 g, which is close to the estimated mass of the CME. The falling material was responsible for the observed large-scale absorption phenomena, in particular, shallow widespread moving dimmings observed at 195 A. By contrast, deep quasi-stationary dimmings observed in this band near the eruption center were due to plasma density decrease in coronal structures.
X-ray bursts are thermonuclear explosions on the surface of accreting neutron stars in low mass X-ray binaries. As most of the known X-ray bursters are frequently observed by INTEGRAL, an international collaboration have been taking advantage of its instrumentation to specifically monitor the occurrence of exceptional burst events lasting more than ~10 minutes. Half of the so-called intermediate long bursts registered so far have been observed by INTEGRAL. The goal is to derive a comprehensive picture of the relationship between the nuclear ignition processes and the accretion states of the system leading up to such long bursts. Depending on the composition of the accreted material, these bursts may be explained by either the unstable burning of a large pile of mixed hydrogen and helium, or the ignition of a thick pure helium layer. Intermediate long bursts are particularly expected to occur at very low accretion rates and make possible to study the transition from a hydrogen-rich bursting regime to a pure helium regime.
We address the problem of assessing the statistical significance of candidate periodicities found using the so-called `multi-harmonic' periodogram, which is being used for detection of non-sinusoidal signals, and is based on the least-squares fitting of truncated Fourier series. The recent investigation (Baluev 2008) made for the Lomb-Scargle periodogram is extended to the more general multi-harmonic periodogram. As a result, closed and efficient analytic approximations to the false alarm probability, associated with multi-harmonic periodogram peaks, are obtained. The resulting analytic approximations are tested under various conditions using Monte Carlo simulations. The simulations showed a suitable precision and robustness of these approximations.
We derive the equations of motion of test bodies for a theory with non-minimal coupling by means of a multipole method. The propagation equations for pole-dipole particles are worked out for a gravity theory with a very general coupling between the curvature scalar and the matter fields. Our results allow for a systematic comparison with the equations of motion of general relativity and other gravity theories.
We present a parameter study of self-consistent models of protoplanetary disks around Herbig AeBe stars. We use the code developed by Dullemond and Dominik, which solves the 2D radiative transfer problem including an iteration for the vertical hydrostatic structure of the disk. This grid of models will be used for several studies on disk emission and mineralogy in followup papers. In this paper we take a first look on the new models, compare them with previous modeling attempts and focus on the effects of various parameters on the overall structure of the SED that leads to the classification of Herbig AeBe stars into two groups, with a flaring (group I) or self-shadowed (group II) SED. We find that the parameter of overriding importance to the SED is the total mass in grains smaller than 25um, confirming the earlier results by Dullemond and Dominik. All other parameters studied have only minor influences, and will alter the SED type only in borderline cases. We find that there is no natural dichotomy between group I and II. From a modeling point of view, the transition is a continuous function of the small dust mass. We also show that moderate grain growth produces spectra with weak or no 1um feature, both for flaring (Group I) and non-flaring (Group II) sources. The fact that sources with weak features have been found mostly in Group I sources is therefore surprising and must be due to observational biases or evolutionary effects.
The Stromlo Missing Satellites (SMS) program is a critical endeavor to investigate whether cold dark matter cosmology is flawed in its ability to describe the matter distribution on galaxy scales or proves itself once again as a powerful theory to make observational predictions. The project will deliver unprecedented results on Milky Way satellite numbers, their distribution and physical properties. It is the deepest, most extended survey for optically elusive dwarf satellite galaxies to date, covering the entire 20,000 sq deg of the Southern hemisphere. 150TB of CCD images will be analysed in six photometric bands, 0.5-1.0 mag fainter than SDSS produced by the ANU SkyMapper telescope over the next five years. (For more details see: this http URL)
We have used the Submillimeter Array (SMA) to make the first interferometric observations (beam size ~1") of the 12CO J=6-5 line and 435 micron (690 GHz) continuum emission toward the central region of the nearby ULIRG Arp 220. These observations resolve the eastern and western nuclei from each other, in both the molecular line and dust continuum emission. At 435 micron, the peak intensity of the western nucleus is stronger than the eastern nucleus, and the difference in peak intensities is less than at longer wavelengths. Fitting a simple model to the dust emission observed between 1.3 mm and 435 micron suggests that dust emissivity power law index in the western nucleus is near unity and steeper in the eastern nucleus, about 2, and that the dust emission is optically thick at the shorter wavelength. Comparison with single dish measurements indicate that the interferometer observations are missing ~60% of the dust emission, most likely from a spatially extended component to which these observations are not sensitive. The 12CO J=6-5 line observations clearly resolve kinematically the two nuclei. The distribution and kinematics of the 12CO J=6-5 line appear to be very similar to lower J CO lies observed at similar resolution. Analysis of multiple 12CO line intensities indicates that the molecular gas in both nuclei have similar excitation conditions, although the western nucleus is warmer and denser. The excitation conditions are similar to those found in other extreme environments, including M82, Mrk 231, and BR 1202-0725. Simultaneous lower resolution observations of the 12CO, 13CO, and C18O J=2-1 lines show that the 13CO and C18O lines have similar intensities, which suggests that both of these lines are optically thick, or possibly that extreme high mass star formation has produced in an overabundance of C18O.
Recent progress in pushing the sensitivity of the Imaging Atmospheric Cherenkov Technique into the 10 mCrab regime has enabled first sensitive observations of the innermost few 100 pc of the Milky Way in Very High Energy (VHE; >100 GeV) gamma rays. These observations are a valuable tool to understand the acceleration and propagation of energetic particles near the Galactic Centre. Remarkably, besides two compact gamma-ray sources, faint diffuse gamma-ray emission has been discovered with high significance. The current VHE gamma-ray view of the Galactic Centre region is reviewed, and possible counterparts of the gamma-ray sources and the origin of the diffuse emission are discussed. The future prospects for VHE Galactic Centre observations are discussed based on order-of-magnitude estimates for a CTA type array of telescopes.
The timing properties of the 4.45 s pulsar in the Be X-ray binary system GRO J1750-27 are examined using hard X-ray data from INTEGRAL and Swift during a Type II outburst observed during 2008. The orbital parameters of the system are measured and agree well with those found during the last known outburst of the system in 1995. Correcting the effects of the doppler shifting of the period, due to the orbital motion of the pulsar, leads to the detection of an intrinsic spin-up that is well described by a simple model including Pdot and Pdotdot terms of -7.5E-10 ss^-1 and 1E-16 ss^-2 respectively. The model is then used to compare the time-resolved variation of the X-ray flux and intrinsic spin-up against the accretion torque model of Ghosh & Lamb (1979); this finds that GRO J1750-27 is likely located 12-22 kpc distant and that the surface magnetic field of the neutron star is ~2E12 G. The shape of the pulse and the pulsed fraction shows different behaviour above and below 20 keV indicating that the observed pulsations are the convolution of many complex components.
LS 5039 is an X-ray binary that presents non-thermal radio emission. The radiation at $\sim 5$ GHz is quite steady and optically thin, consisting on a dominant core plus an extended jet-like structure. There is a spectral turnover around 1 GHz, and evidence of variability at timescales of 1 yr at 234 MHz. We investigate the radio emitter properties using the available broadband radio data, and assuming two possible scenarios to explain the turnover: free-free absorption in the stellar wind, or synchrotron self-absorption. We use the relationships between the turnover frequency, the stellar wind density, the emitter location, size and magnetic field, and the Lorentz factor of the emitting electrons, as well as a reasonable assumption on the energy budget, to infer the properties of the low-frequency radio emitter. Also, we put this information in context with the broadband radio data. The location and size of the low-frequency radio emitter can be restricted to $\ga$ few AU from the primary star, its magnetic field to $\sim 3\times 10^{-3}-1$ G, and the electron Lorentz factors to $\sim 10-100$. The observed variability of the extended structures seen with VLBA would point to electron bulk velocities $\ga 3\times 10^8$ cm s$^{-1}$, whereas much less variable radiation at 5 GHz would indicate velocities for the VLBA core $\la 10^8$ cm s$^{-1}$. The emission at 234 MHz in the high state would mostly come from a region larger than the dominant broadband radio emitter. We suggest a scenario in which secondary pairs, created via gamma-ray absorption and moving in the stellar wind, are behind the steady broadband radio core, whereas the resolved jet-like radio emission would come from a collimated, faster, outflow.
We investigate what current cosmological data tells us about the cosmological
expansion rate in a model independent way. Specifically, we study if the
expansion was decelerating at high redshifts and is accelerating now, without
referring to any model for the energy content of the universe, nor to any
specific theory of gravity. This differs from most studies of the expansion
rate which, e.g., assumes some underlying parameterised model for the dark
energy component of the universe. To accomplish this, we have devised new
methods to probe the expansion rate without relying on such assumptions.
Using only supernova data, we conclude that there is little doubt that the
universe has been accelerating at late times. However, contrary to some
previous claims, we can not determine if the universe was previously
decelerating. For a variety of methods used for constraining the expansion
history of the universe, acceleration is detected from supernovae alone at >5
sigma, regardless of the curvature of the universe. Specifically, using a
Taylor expansion of the scale factor, acceleration today is detected at >12
sigma. If we also include the ratio of the scale of the baryon acoustic
oscillations as imprinted in the cosmic microwave background and in the large
scale distribution of galaxies, it is evident from the data that the expansion
decelerated at high redshifts, but only with the assumption of a flat or
negatively curved universe.
AX J1845.0-0433 is a transient high-mass X-ray binary discovered by ASCA. The
source displays bright and short flares observed recently with INTEGRAL. The
transient behaviour and the bright and short flares are studied in order to
understand the accretion mechanisms and the nature of the source. Public
INTEGRAL data and a pointed XMM-Newton observation are used to study in details
the flaring and quiescent phases.
AX J1845.0-0433 is a persistent X-ray binary with a O9.5I supergiant
companion emitting at a low 0.2-100 keV luminosity of ~1e35 erg/s with seldom
flares reaching luminosities of 1e36 erg/s. The most-accurate X-ray position is
R.A. (2000) =18h45m01s.4 and Dec. = -04deg33'57''.7 (uncertainty 2'').
Variability factors of 50 are observed on time scale as short as hundreds of
seconds. The broad-band high-energy spectrum is typical of wind-fed accreting
pulsars with an intrinsic absorption of NH=(2.6+/-0.2)e22 cm-2, a hard
continuum of Gamma=(0.7-0.9)+/-0.1 and a high-energy cutoff at Ecut=16+/-3 keV.
An excess at low energies is also observed fitted with a black body with a
temperature of kT=0.18+/-0.05 keV. Optically-thin and highly-ionised iron (Fe
XVIII-XIX) located near the supergiant star is detected during the quiescence
phase. The spectral shape of the X-ray continuum is constant. The flare
characteristics in contrast to the persistent quiescent emission suggest that
clumps of mass M~1e22 g are formed within the stellar wind of the supergiant
companion.
The aim of this paper is to investigate the environment of gamma ray bursts (GRBs) and the interstellar matter of their host galaxies. We use to this purpose high resolution spectroscopic observations of the afterglow of GRB050922C, obtained with UVES/VLT 3.5 hours after the GRB event. We found that, as for most high resolution spectra of GRBs, the spectrum of the afterglow of GRB050922C is complex. At least seven components contribute to the main absorption system at z=2.1992. The detection of lines of neutral elements like MgI and the detection of fine-structure levels of the ions FeII, SiII and CII allows us to separate components in the GRB ISM along the line of sight. Moreover, in addition to the main system, we have analyzed the five intervening systems between z = 2.077 and z = 1.5664 identified along the GRB line of sight. GRB afterglow spectra are very complex, but full of information. This can be used to disentangle the contribution of the different parts of the GRB host galaxy and to study their properties. Our metallicity estimates agree with the scenario of GRBs exploding in low metallicity galaxies
In this paper we summarize some aspects of the wind accretion theory in high mass X-ray binaries hosting a magnetic neutron star and a supergiant companion. In particular, we concentrate on the different types of interaction between the inflowing wind matter and the neutron star magnetosphere that are relevant when accretion of matter onto the neutron star surface is largely inhibited; these include inhibition by the centrifugal and magnetic barriers. We show that very large luminosity swings (~10^4 or more on time scales as short as hours) can result from transitions across different regimes. This scenario is then applied to the activity displayed by supergiant fast X-ray transients (SFXTs), a new class of high mass X-ray binaries in our galaxy recently discovered with INTEGRAL. According to this interpretation we argue that SFXTs which display very large luminosity swings and host a slowly spinning neutron star are expected to be characterized by magnetar-like fields. Supergiant fast X-ray transients might thus provide a unique opportunity to detect and study accreting magnetars in binary systems.
The ARGO-YBJ experiment has been in stable data taking since November 2007 at the YangBaJing Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l.). In this paper we report a few selected results in Gamma-Ray Astronomy (Crab Nebula and Mrk421 observations, search for high energy tails of GRBs) and Cosmic Ray Physics (Moon and Sun shadow observations, proton-air cross section and antiproton/proton preliminary measurements).
Recent revisions of the determination of the solar composition have resulted in solar models in marked disagreement with helioseismic inferences. The effect of the composition change on the model is largely caused by the change in the opacity. Thus we wish to determine an intrinsic opacity change that would compensate for the revision of the composition. By comparing models computed with the old and revised composition we determine the required opacity change. Models are computed with the opacity thus modified and used as reference in helioseismic inversions to determine the difference between the solar and model sound speed. An opacity increase varying from around 30 per cent near the base of the convection zone to a few percent in the solar core results in a sound-speed profile, with the revised composition, which is essentially indistinguishable from the original solar model. As a function of the logarithm of temperature this is well represented by a simple cubic fit. The physical realism of such a change remains debatable, however.
FERMI (formely GLAST) will shortly provide crucial information on relativistic particles in galaxy clusters. We discuss non-thermal emission in the context of general calculations in which relativistic particles (protons and secondary electrons due to proton-proton collisions) interact with MHD turbulence generated in the cluster volume during cluster mergers. Diffuse cluster-scale radio emission (Radio Halos) and hard X-rays are produced during massive mergers while gamma ray emission, at some level, is expected to be common in galaxy clusters.
Polarized microwave emission from dust is an important foreground that may contaminate polarized CMB studies unless carefully accounted for. Modeling of polarization from dust requires a quantitative understanding of grain alignment. I review the current status of grain alignment theory outlining recent advances in quantitative description of the alignment. In particular, I show that the grain-alignment theory is a predictive one, and its results nicely match observations. Those indicate that the most important process of alignment is related to radiative torques acting on irregular grains. The recently developed analytical model of radiative torque alignment has proven to be a very efficient tool for predicting the degree of grain alignment. We expect the alignment theory to further mature before CMBPol flight, which would ensure a better accounting for the dust-related polarization. At the same time, CMBPol should provide the additional testing of grain alignment, clarifying the reliability of polarimetry for tracing of magnetic field.
The complex relationship between the galaxy density field and the underlying matter field limits our ability to extract cosmological constraints from galaxy redshift surveys. Our approach is to use halos rather than galaxies to trace the underlying mass distribution. We identify Fingers-of-God (FOGs) and replace multiple galaxies in each FOG with a single halo object. This removes the nonlinear contributions of satellite galaxies, the one-halo term. We test our method on a large set of high-fidelity mock SDSS Luminous Red Galaxy (LRG) catalogs. We find that the aggressive FOG compression algorithm adopted in the LRG P(k) analysis of Tegmark et al. (2006) leads to a ~10% correction to the underlying matter power spectrum at k = 0.1 h/Mpc and ~40% correction at k=0.2 h/Mpc, thereby compromising the cosmological constraints. In contrast, the power spectrum of our reconstructed halo density field deviates from the underlying matter power spectrum by less than 1% for k less than 0.1 h/Mpc and less than 4% for k less than 0.2 h/Mpc. The reconstructed halo density field also removes the bias in the measurement of the redshift space distortion parameter beta induced by the FOG smearing of the linear redshift space distortions.
We investigate the effect of radiative feedback on the star formation process
using radiation hydrodynamical simulations. We repeat the previous
hydrodynamical star cluster formation simulations of Bate et al., and Bate &
Bonnell, but we use a realistic gas equation of state and radiative transfer in
the flux-limited diffusion approximation rather than the original barotropic
equation of state.
Whereas star formation in the barotropic simulations continued unabated until
the simulation was stopped, we find that radiative feedback essentially
terminates the production of new objects after roughly one local dynamical
time. Radiative feedback also dramatically decreases the propensity of massive
circumstellar discs to fragment and inhibits fragmentation of other dense gas
(e.g. filaments) close to existing protostellar objects. These two effects
decrease the numbers of protostars formed by a factor of approximately 4.
Whereas the original simulations produced more brown dwarfs than stars, the
radiative feedback results in a ratio of stars to brown dwarfs of approximately
5:1, in much better agreement with observations. Most importantly, we find that
although the characteristic stellar mass in the original calculations scaled
linearly with the initial mean Jeans mass, when radiative feedback is included
the characteristic stellar mass is indistinguishable for the two calculations.
We thus propose that the reason the observed initial mass function appears to
be universal is due to self-regulation of the star formation process by
radiative feedback. We present an analytic argument showing how a
characteristic mass may be derived that is relatively independent of initial
conditions such as the cloud's density. (Abridged)
Two practical spin-offs from the development of cryogenic dark matter detectors are presented. One in materials research, the other in biology.
We derive the constitutive equations of causal relativistic dissipative hydrodynamics ($d$-hydrodynamics) from perfect nonextensive hydrodynamics ($q$-hydrodynamics) using the nonextensive/dissipative correspondence (NexDC) proposed by us recently. The $q$-hydrodynamics can be thus regarded as a possible model for the $d$-hydrodynamics facilitating its application to high energy multiparticle production processes. As an example we have shown that applying the NexDC to the perfect 1+1 $q$-hydrodynamics, one obtains a proper time evolution of the bulk pressure and the Reynolds number.
There has been a recent stimulus in the study of alternative theories of gravity lately, mostly triggered from combined motivation coming from cosmology/astrophysics and high energy physics. Among the proposed theories, one that has attracted much attention is f(R) gravity. It is certainly debatable whether such a simplistic modification of General Relativity can constitute a viable alternative theory of gravitation. However, it is quite straightforward to see the merits of such a theory when viewed as a toy theory whose role is to help us understand the implications and difficulties of beyond-Einstein gravity. Under this perspective, I review some of the main lessons we seem to have learned from the study of f(R) gravity in the recent past.
The standard model (SM) plus a real gauge-singlet scalar field dubbed darkon (SM+D) is the simplest model possessing a weakly interacting massive particle (WIMP) dark-matter candidate. The upper limits for the WIMP-nucleon elastic cross-section as a function of WIMP mass from the recent XENON10 and CDMS-II experiments rule out darkon mass ranges from 10 to (50,70,75) GeV for Higgs-boson masses of (120,200,350) GeV, respectively. This may exclude the possibility of the darkon providing an explanation for the gamma-ray excess observed in the EGRET data. We show that by extending the SM+D to a two-Higgs-doublet model plus a darkon the experimental constraints on the WIMP-nucleon interactions can be circumvented due to suppression occurring at some values of the product tan(alpha)tan(beta), with alpha being the neutral-Higgs mixing angle and tan(beta) the ratio of vacuum expectation values of the Higgs doublets. We also comment on the implication of the darkon model for Higgs searches at the LHC.
In this second paper we complete the classical description of an isolated
system of "charged positive-energy particles, with Grassmann-valued electric
charges and mutual Coulomb interaction, plus a transverse electro-magnetic
field" in the rest-frame instant form of dynamics.
In particular we show how to determine a collective variable associated with
the internal 3-center of mass on the instantaneous 3-spaces, to be eliminated
with the constraints ${\vec {\cal K}}_{(int)} \approx 0$. Here ${\vec {\cal
K}}_{(int)}$ is the Lorentz boost generator in the unfaithful internal
realization of the Poincare' group and its vanishing is the gauge fixing to the
rest-frame conditions ${\vec {\cal P}}_{(int)} \approx 0$. We show how to find
this collective variable for the following isolated systems: a) charged
particles with a Coulomb plus Darwin mutual interaction; b) transverse
radiation field; c) charged particles with a mutual Coulomb interaction plus a
transverse electro-magnetic field.
Then we define the Dixon multipolar expansion for the open particle
subsystem. We also define the relativistic electric dipole approximation of
atomic physics in the rest-frame instant form and we find the a possible
relativistic generalization of the electric dipole representation.
The astronomer E.V. Pitjeva, by analyzing with the EPM2008 ephemerides a large number of planetary observations including also two years (2004-2006) of normal points from the Cassini spacecraft, phenomenologically estimated a statistically significant non-zero correction to the usual Newtonian/Einsteinian secular precession of the longitude of the perihelion of Saturn, i.e. \Delta\dot\varpi_Sat = -0.006 +/- 0.002 arcsec/cy; the formal, statistical error is 0.0007 arcsec/cy. It can be explained neither by any of the standard classical and general relativistic dynamical effects mismodelled/unmodelled in the force models of the EPM2008 ephemerides nor by several exotic modifications of gravity recently put forth to accommodate certain cosmological/astrophysical observations without resorting to dark energy/dark matter. Both independent analyses by other teams of astronomers and further processing of larger data sets from Cassini will be helpful in clarifying the nature and the true existence of the anomalous precession of the perihelion of Saturn.
We survey motivation, basic ideas and physical consequences of a theory where the underlying action involves terms both with the usual volume element $\sqrt{-g}d^{4}x$ and with the new one $\Phi d^{4}x={4!}d\varphi_{1}\wedge d\varphi_{2}\wedge d\varphi_{3}\wedge d\varphi_{4}$. The latter may be interpreted as the 4-form determined on the 4-D space-time manifold (not necessary Riemannian). Regarding the scalar fields $\varphi_{a} (a=1,...4)$ as new dynamical variables and proceeding in the first order formalism we realize the so-called Two Measures Theory which possesses a number of attractive features. We discuss new physical effects which arise from this theory and in particular strong gravity effect in high energy physics experiments.
Links to: arXiv, form interface, find, astro-ph, recent, 0811, contact, help (Access key information)