The ability to test the nature of dark mass-energy components in the universe through large-scale structure studies hinges on accurate predictions of sky survey expectations within a given world model. Numerical simulations predict key survey signatures with varying degrees of confidence, limited mainly by the complex astrophysics of galaxy formation. As surveys grow in size and scale, systematic uncertainties in theoretical modeling can become dominant. Dark energy studies will challenge the computational cosmology community to critically assess current techniques, develop new approaches to maximize accuracy, and establish new tools and practices to efficiently employ globally networked computing resources.
The Dark Energy Survey (DES) will use a new imaging camera on the Blanco 4-m telescope at CTIO to image 5000 square degrees of sky in the South Galactic Cap in four optical bands, and to carry out repeat imaging over a smaller area to identify and measure lightcurves of Type Ia supernovae. The main imaging area overlaps the planned Sunyaev-Zel'dovich survey of the South Pole Telescope. The idea behind DES is to use four distinct and largely independent methods to probe the properties of dark energy: baryon oscillations of the power spectrum, abundance and spatial distribution of clusters, weak gravitational lensing, and Type Ia supernovae. This white paper outlines, in broad terms, some of the theoretical issues associated with the first three of these probes (the issues for supernovae are mostly different in character), and with the general task of characterizing dark energy and distinguishing it from alternative explanations for cosmic acceleration. A companion white paper discusses the kind of numerical simulations and other theoretical tools that will be needed to address the these issues and to create mock catalogs that allow end-to-end tests of analysis procedures. Although we have been thinking about these problems in the specific context of DES, many of them are also relevant to other planned dark energy studies.
Nearly all proposed tests for the nature of dark energy measure some combination of four fundamental observables: the Hubble parameter H(z), the distance-redshift relation d(z), the age-redshift relation t(z), or the linear growth factor D_1(z). I discuss the sensitivity of these observables to the value and redshift history of the equation of state parameter w, emphasizing where these different observables are and are not complementary. Demonstrating time-variability of w is difficult in most cases because dark energy is dynamically insignificant at high redshift. Time-variability in which dark energy tracks the matter density at high redshift and changes to a cosmological constant at low redshift is {\it relatively} easy to detect. However, even a sharp transition of this sort at z_c=1 produces only percent-level differences in d(z) or D_1(z) over the redshift range 0.4 < z < 1.8$, relative to the closest constant-w model. Estimates of D_1(z) or H(z) at higher redshift, potentially achievable with the Ly-alpha forest, galaxy redshift surveys, and the CMB power spectrum, can add substantial leverage on such models, given precise distance constraints at z < 2. The most promising routes to obtaining sub-percent precision on dark energy observables are space-based studies of Type Ia supernovae, which measure d(z) directly, and of weak gravitational lensing, which is sensitive to d(z), D_1(z), and H(z).
In a large scale view of the universe, galaxies are the basic unit of structure. A typical bright galaxy may contain 100 billion stars and span tens of thousands of light years, but the empty expanses between the galaxies are much larger still. Galaxies are not randomly distributed in space, but instead reside in groups and clusters, which are themselves arranged in an intricate lattice of filaments and walls, threaded by tunnels and pocked with bubbles. Two ambitious new surveys, the Two-Degree Field Galaxy Redshift Survey (2dFGRS) and the Sloan Digital Sky Survey (SDSS), have mapped the three-dimensional distribution of galaxies over an unprecedented range of scales. Astronomers are using these maps to learn about conditions in the early universe, the matter and energy contents of the cosmos, and the physics of galaxy formation.
Many of the known extrasolar planets are ``hot Jupiters,'' giant planets with orbital periods of just a few days. We use the observed distribution of hot Jupiters to constrain the location of the ``inner edge'' and planet migration theory. If we assume the location of the inner edge is proportional to the Roche limit, then we find that this edge is located near twice the Roche limit, as expected if the planets were circularized from a highly eccentric orbit. If confirmed, this result would place significant limits on migration via slow inspiral. However, if we relax our assumption for the slope of the inner edge, then the current sample of hot Jupiters is not sufficient to provide a precise constraint on both the location and power law index of the inner edge.
We present an astrometric analysis of the binary systems ABDorA /ABDorC and
ABDorBa / ABDorBb. These two systems of well-known late-type stars are
gravitationally associated and they constitute the quadruple ABDoradus system.
From the astrometric data available at different wavelengths, we report: (i)
a determination of the orbit of ABDorC, the very low mass companion to ABDorA,
which confirms the mass estimate of 0.090Msun reported in previous works; (ii)
a measurement of the parallax of ABDorBa, which unambiguously confirms the
long-suspected physical association between this star and ABDorA; and (iii)
evidence of orbital motion of ABDorBa around ABDorA, which places an upper
bound of 0.4Msun on the mass of the pair ABDorBa / ABDorBb (50% probability).
Further astrometric monitoring of the system at all possible wavelengths would
determine with extraordinary precision the dynamical mass of its four
components.
New insights into the history of the inner solar system are derived from the impact cratering record of the Moon, Mars, Venus and Mercury, and from the size distributions of asteroid populations. Old craters from a unique period of heavy bombardment that ended $\sim$3.8 billion years ago were made by asteroids that were dynamically ejected from the main asteroid belt, possibly due to the orbital migration of the giant planets. The impactors of the past $\sim$3.8 billion years have a size distribution quite different from the main belt asteroids, but very similar to the population of near-Earth asteroids.
New 13CO data from the BU-FCRAO Milky Way Galactic Ring Survey (GRS) are analyzed to understand the shape and internal motions of molecular clouds. For a sample of more than five hundred molecular clouds, we find that they are preferentially elongated along the Galactic plane. On the other hand, their spin axes are randomly oriented. We therefore conclude that the elongation is not supported by internal spin but by internal velocity anisotropy. It has been known that some driving mechanisms are necessary to sustain the supersonic velocity dispersion within molecular clouds. The mechanism for generating the velocity dispersion must also account for the preferred elongation. This excludes some driving mechanisms, such as stellar winds and supernovae, because they do not produce the systemic elongation along the Galactic plane. Driving energy is more likely to come from large scale motions, such as the Galactic rotation.
We have completed a 1.1 mm continuum survey of 7.5 sq deg of the Perseus Molecular Cloud using Bolocam at the Caltech Submillimeter Observatory. This represents the largest millimeter or submillimeter continuum map of Perseus to date. Our map covers more than 30,000 31" (FWHM) resolution elements to a 1 sigma RMS of 15 mJy/beam. We detect a total of 122 cores above a 5 sigma point source mass detection limit of 0.18 M_sun, assuming a dust temperature of 10 K, 60 of which are new millimeter or submillimeter detections. The 1.1 mm mass function is consistent with a broken power law of slope -1.3 (0.5 M_sun<M<2.5 M_sun) and -2.6 (M>2.5 M_sun), similar to the local initial mass function slope. No more than 5% of the total cloud mass is contained in discrete 1.1 mm cores, which account for a total mass of 285 M_sun. We suggest an extinction threshold for millimeter cores of Av~5 mag, based on our calculation of the probability of finding a 1.1 mm core as a function of Av. Much of the cloud is devoid of compact millimeter emission; despite the significantly greater area covered compared to previous surveys, only 5-10 of the newly identified sources lie outside previously observed areas. The two-point correlation function confirms that dense cores in the cloud are highly structured, with significant clustering on scales as large as 2e5 AU. These 1.1 mm results, especially when combined with recently acquired c2d Spitzer Legacy data, will provide a census of dense cores and protostars in Perseus and improve our understanding of the earliest stages of star formation in molecular clouds.
Gravitational waves generated by the final merger of double neutron star (DNS) binary systems are a key target for the gravitational wave (GW) interferometric detectors, such as LIGO, and the next generation detectors, Advanced LIGO. The cumulative GW signal from DNS mergers in interferometric data will manifest as "geometrical noise": a non-continuous stochastic background with a unique statistical signature dominated by the spatial and temporal distribution of the sources. Because geometrical noise is highly non-Gaussian, it could potentially be used to identify the presence of a stochastic GW background from DNS mergers. We demonstrate this by fitting to a simulated distribution of transients using a model for the DNS merger rate and idealized Gaussian detector noise. Using the cosmological "probability event horizon" concept and recent bounds for the Galactic DNS merger rate, we calculate the evolution of the detectability of DNS mergers with observation time. For Advanced LIGO sensitivities and a detection threshold assuming optimal filtering, there is a 95% probability that a minimum of one DNS merger signal will be detectable from the ensemble of events comprising the stochastic background during 12-211 days of observation. For initial LIGO sensitivities, we identify an interesting regime where there is a 95% probability that at least one DNS merger with signal-to-noise ratio > unity will occur during 4-68 days of observation. We propose that there exists an intermediate detection regime with pre-filtered signal-noise-ratio less than unity, where the DNS merger rate is high enough that the geometrical signature could be identified in interferometer data.
We are carrying out sensitive X-ray observations with Chandra and XMM of type II quasars selected from the Sloan Digital Sky Survey based on their optical emission line properties. We present observations of four objects at redshifts 0.4 < z < 0.8 and an analysis of the archival data for four additional objects in the same redshift range. Six of the eight were detected in X-rays; five of them have sufficient signal to derive spectral information. All of the detected sources have intrinsic luminosities L(2-10 keV) > 5 x 10^43 erg s^-1. The five with sufficient counts for spectral fitting show evidence for significant absorption (N_H >~ a few x 10^22 cm^-2). At least three of the objects likely have N_H > 10^23 cm^-2; some may be Compton-thick (N_H > 10^{24} cm^-2). In the five objects for which we could fit spectra, the slopes tend to be significantly flatter than is typically observed in AGN; it is possible that this is due either to reprocessing of the nuclear emission or to a line of sight that passes through patchy absorption.
It is shown here that the so-called spinning Black Hole Candidates (BHCs) must be spinning HOT Magnetospheric Eternally Collapsing Objects (MECOs). The question would then arise why the spinning BHCs do not reveal their spin pulsation unlike spinning COLD Neutron Stars (NSs). Even for magnetized NSs, there may be no observed spin pulsation if the dipole axis and spin direction are exactly same. However, spinning MECOs do not show spin pulsation because their surface gravitational red shift is extremely high, z ~10^{7-8}. In contrast NSs have z ~ 0.1 -0.3. The time profile of any periodic signal generated on the surface of a spinning MECO gets extremely distorted due to extreme general relativistic frame dragging effect as it traverses through extremely steep gravitational field. However, if any radiation is formed in the MECO magnetosphere sufficiently away from the surface like in the pulsar ``outer slots'' (which may happen for isolated spinning MECOs), such a radiation might be pulsed one.
Although some of the properties of the caustics in planetary microlensing have been known, our understanding of them is mostly from scattered information based on numerical approaches. In this paper, we conduct a comprehensive and analytic analysis of the properties of the planetary caustics, which are one of the two sets of caustics in planetary microlensing, those located away from the central star. Under the perturbative approximation, we derive analytic expressions for the location, size, and shape of the planetary caustic as a function of the star-planet separation and the planet/star mass ratio. Based on these expressions combined with those for the central caustic, which is the other set of caustics located close to the central star, we compare the similarities and differences between the planetary and central caustics. We also present the expressions for the size ratio between the two types of caustics and for the condition of the merging of the two types of caustics. These analytic expressions will be useful in understanding the dependence of the planetary lensing behavior on the planet parameters and thus in interpreting the planetary lensing signals
The situation that a scalar field provides the source of the accelerated expansion of the universe while rolling down its potential is common in both the simple models of the primordial inflation and the quintessence-based dark energy models. Motivated by this point, we address the possibility of causing the current acceleration via the primordial inflation using a simple model based on hybrid inflation. We trigger the onset of the motion of the quintessence field via the transition field, and find that the fate of the universe depends on the true vacuum energy determined by choosing the parameters. We also briefly discuss the variation of the equation of state and the possible implementation of our scenario in supersymmetric theories.
In scalar-tensor theories of gravity, the equation of state of dark energy, w, can become smaller than -1 without violating any energy condition. The value of w today is tied to the level of deviations from general relativity which, in turn, is constrained by solar system and pulsars timing experiments. The conditions on these local constraints for w to be significantly less than -1 are established. It is demonstrated that this requires to consider theories that differ from the Jordan-Fierz-Brans-Dicke theory and that involve either a steep coupling function or a steep potential. It is also shown how a robust measurement of w could probe scalar-tensor theories.
We present the results of an XMM-Newton observation of the young (~2-4 Myr) cluster around the hot star sigma Orionis. In a previous paper we presented the analysis of the RGS spectrum of the central hot star; here we discuss the results of the analysis of the full EPIC field. We have detected 175 X-ray sources, 88 of which have been identified with cluster members, including very low-mass stars down to the substellar limit. We detected eleven new possible candidate members from the 2MASS catalogue. We find that late-type stars have a median log L_X/L_bol ~ -3.3, i.e. very close to the saturation limit. We detected significant variability in ~40% of late-type members or candidates, including 10 flaring sources; rotational modulation is detected in one K-type star and possibly in another 3 or 4 stars. Spectral analysis of the brightest sources shows typical quiescent temperatures in the range T_1 ~ 0.3-0.8 keV and T_2 ~ 1-3 keV, with subsolar abundances Z ~ 0.1-0.3 Z_sun, similar to what is found in other star-forming regions and associations. We find no significant difference in the spectral properties of classical and weak-lined T Tauri stars, although classical T Tauri stars tend to be less X-ray luminous than weak-lined T Tauri stars.
We study galaxy correlations from samples extracted from the 2dFGRS final release. Statistical properties are characterized by studying the nearest neighbor probability density, the conditional density and the reduced two-point correlation function. The result is that the conditional density has a power-law behavior in redshift space described by an exponent \gamma=0.8 \pm 0.2 in the interval from about 1 Mpc/h, the average distance between nearest galaxies, up to about 40 Mpc/h, corresponding to radius of the largest sphere contained in the samples. These results are consistent with other studies of the conditional density and are useful to clarify the subtle role of finite-size effects on the determination of the two-point correlation function in redshift and real space
We present a new picture for the central regions of Black Hole X-ray Binaries. In our view, these central regions have a multi-flow configuration which consists in (1) an outer standard accretion disc down to a transition radius r_J, (2) an inner magnetized accretion disc below r_J driving (3) a non relativistic self-collimated electron-proton jet surrounding, when adequate conditions for pair creation are met, (4) a ultra relativistic electron-positron beam. This accretion-ejection paradigm provides a simple explanation to the canonical spectral states, from radio to X/gamma-rays, by varying the transition radius r_J and disc accretion rate independently. Large values of r_J and low accretion rate correspond to Quiescent and Hard states. These states are characterized by the presence of a steady electron-proton MHD jet emitted by the disc below r_J. The hard X-ray component is expect to form at the jet basis. When r_J becomes smaller than the marginally stable orbit r_i, the whole disc resembles a standard accretion disc with no jet, characteristic of the Soft state. Intermediate states correspond to situations where r_J ~ r_i. At large accretion rate, an unsteady pair cascade process is triggered within the jet axis, giving birth to flares and ejection of relativistic pair blobs. This would correspond to the luminous intermediate state, with its associated superluminal motions.
It is shown that, contrary to the widespread opinion, particle collisions considerably increase accretion rate from the cosmological background onto 5D primordial black holes formed during the high-energy phase of the Randall-Sundrum Type II braneworld scenario. This accretion rate leads to new much tighter constraints on initial PBH mass fraction following from critical density limit and measurements of high-energy diffuse photon background and antiproton excess.
A population of X-ray dominated gamma-ray bursts (GRBs) observed by Ginga, BeppoSax and Hete-2 should be represented in the BATSE data as presumably soft bursts. We have performed a search for soft GRBs in the BATSE records in the 25--100 keV energy band. A softness of a burst spectrum can be a reason why it has been missed by the on-board procedure and previous searches for untriggered GRBs tuned to 50--300 keV range. We have found a surprisingly small number (~20/yr down to 0.1 ph cm$^{-2}$ s$^{-1}$) of soft GRBs where the count rate is dominated by 25--50 keV energy channel. This fact as well as the analysis of HETE-2 and common BeppoSAX/BATSE GRBs indicates that the majority of GRBs with a low Epeak has a relatively hard tail with the high-energy power-law photon index >-3. An exponential cutoff in GRB spectra below 20 keV may be a distinguishing feature separating non-GRB events.
We present a comparison of dynamical model atmospheres with mid-infrared (~11 micron) interferometric and spectroscopic observations of the Mira variable o Cet. The dynamical model atmospheres of Mira variables pulsating in the fundamental mode can fairly explain, without assuming ad-hoc components, the seemingly contradictory mid-infrared spectroscopic and interferometric observations of o Cet: the 11 micron sizes measured in the bandpass without any salient spectral features are about twice as large as those measured in the near-infrared. Our calculations of synthetic spectra show that the strong absorption due to a number of optically thick H2O lines is filled in by the emission of these H2O lines originating in the geometrically extended layers, providing a possible physical explanation for the picture proposed by Ohnaka (2004a) based on a semi-empirical modeling. This filling-in effect results in rather featureless, continuum-like spectra in rough agreement with the observed high-resolution 11 micron spectra, although the models still predict the H2O lines to be more pronounced than the observations. The inverse P-Cyg profiles of some strong H2O lines observed in the 11 micron spectra can also be reasonably reproduced by our dynamical model atmospheres. The presence of the extended H2O layers manifests itself as mid-infrared angular diameters much larger than the continuum diameter. The 11 micron uniform-disk diameters predicted by our dynamical model atmospheres are in fair agreement with those observed with the Infrared Spatial Interferometer (ISI), but still somewhat smaller than the observed diameters. We discuss possible reasons for this discrepancy and problems with the current dynamical model atmospheres of Mira variables.
A variety of terrestrial planets with different physical parameters and exotic atmospheres might plausibly exist outside our Solar System, waiting to be detected by the next generation of space-exploration missions. Some of these planets might transit their parent star. We present here the first study of atmospheric signatures of transiting Earth-size exoplanets. We focus on a limited number of significant examples, for which we discuss the detectability of some of the possible molecules present in their atmospheres, such as water, carbon dioxide, ozone or molecular oxygen. To this purpose, we developed a model to simulate transmission spectra of Earth-size exoplanets from the ultraviolet to the near infrared. According to our calculations, the signatures of planetary atmospheres represent an absorption of a few parts-per-million (ppm) in the stellar flux. The atmospheres of a few Earth-like planets can be detected with a 30-40m telescope. The detection of the extensive atmospheres of tens of small satellites of giant exoplanets and hundreds of hypothetical ocean-planets can be achieved with 20-30m and 10-20m instruments, respectively, provided all these planets are frequent and they are efficiently surveyed. We also found that planets around K stars are favored, mainly because these stars are more numerous and they are smaller compared to G or F stars. While not addressed in this study, limitations might come from the stellar photometric micro-variability.
We show that the extinction of quasar absorbers increases exponentially with the logarithmic column density of any volatile metal (e.g. zinc), with a charateristic turning point above which the quasars are severely dimmed. We derive the relation between extinction, HI column density, metallicity and fraction of iron in dust in Damped Lyman alpha (DLA) systems. We use this relation to estimate the effect of dust obscuration on the statistical distributions of N(HI) and metallicity measured in magnitude-limited surveys of DLAs. In the redshift range where the measurements of zinc column densities have sufficient statistics (1.8 </= z </= 3) we find that the obscuration bias affects the shapes of the observed distributions. The metallicity distribution is particularly affected by the bias, which hampers the detection of DLA galaxies with near solar metallicity. Our results perfectly reproduce, without tuning the dust parameters, the DLA observational threshold log N(ZnII) </~ 13.15 found by Boisse' and collaborators in 1998, in terms of a rapid rise of the obscuration. Our predictions of the effects of the bias on the statistics of DLAs are consistent with observational results obtained from unbiased surveys of radio-selected quasars.
We have carried out a Chandra observation of the globular cluster M54. We detected 7 sources located within the half-mass radius of M54, at a flux limit of 1.5x10^-15 erg/s/cm in the 0.3-8 keV energy band. The spatial distribution and the colour/spectral properties of the 7 sources suggest that they are likely to be cataclysmic variables or LMXBs in the globular cluster. M54 shows the largest number of X-ray sources with luminosities greater than 10^32 ergs/s compared to other globular clusters observed using Chandra and XMM-Newton. We searched for a correlation between the number of sources above this luminosity level with globular cluster parameters. We found evidence that the number of sources peaks at a King concentration parameter c~1.7-1.9, with globular clusters which are core-collapsed or have low-c values having a smaller number of sources. We speculate on possible reasons for this.
The GLIMPSE and MSX surveys have been used to examine the mid-infrared properties of a statistically complete sample of 6.7 GHz methanol masers. The GLIMPSE point sources associated with methanol masers are clearly distinguished from the majority, typically having extremely red mid-infrared colors, similar to those expected of low-mass class 0 young stellar objects. The intensity of the GLIMPSE sources associated with methanol masers is typically 4 magnitudes brighter at 8.0 micron than at 3.6 micron. Targeted searches towards GLIMPSE point sources with [3.6]-[4.5] > 1.3 and an 8.0 micron magnitude less than 10 will detect more than 80% of class II methanol masers. Many of the methanol masers are associated with sources within infrared dark clouds (IRDC) which are believed to mark regions where high-mass star formation is in its very early stages. The presence of class II methanol masers in a significant fraction of IRDC suggests that high-mass star formation is common in these regions. Different maser species are thought to trace different evolutionary phases of the high-mass star formation process. Comparison of the properties of the GLIMPSE sources associated with class II methanol masers and other maser species shows interesting trends, consistent with class I methanol masers tracing a generally earlier evolutionary phase and OH masers tracing a later evolutionary phase.
We present a study of the internal kinematics and stellar populations of early-type galaxies in the Fornax cluster based on integral-field spectroscopic observations with Gemini South GMOS and VLT-VIMOS. Seven galaxies in a luminosity range of -21.3 < M_B < -17.7 have been observed with these integral field units (IFU). As first results, velocity and line strength maps are presented for NGC 1427 and NGC 1419.
Local correlation tracking techniques are used to measure proper motions in a series of high angular resolution (~0.1 arcsec) penumbra images. If these motions trace true plasma motions, then we have detected converging flows that arrange the plasma in long narrow filaments co-spatial with dark penumbral filaments. Assuming that these flows are stationary, the vertical stratification of the atmosphere and the conservation of mass suggest downflows in the filaments of the order of 200 m/s. The association between downflows and dark features may be a sign of convection, as it happens with the non-magnetic granulation. Insufficient spatial resolution may explain why the estimated vertical velocities are not fast enough to supply the radiative losses of penumbrae.
We present a unifying empirical description of the structural and kinematic properties of all spheroids embedded in dark matter halos. We find that the stellar spheroidal components of galaxy clusters, which we call cluster spheroids (CSphs) and which are typically one hundred times the size of normal elliptical galaxies, lie on a "fundamental plane" as tight as that defined by ellipticals (rms in effective radius of ~0.07), but that has a different slope. The slope, as measured by the coefficient of the log(sigma) term, declines significantly and systematically between the fundamental planes of ellipticals, brightest cluster galaxies (BCGs), and CSphs.We attribute this decline primarily to a continuous change in M_e/L_e, the mass-to-light ratio within the effective radius r_e, with spheroid scale. The magnitude of the slope change requires that it arises principally from differences in the relative distributions of luminous and dark matter, rather than from stellar population differences such as in age and metallicity. By expressing the M_e/L_e term as a function of sigma in the simple derivation of the fundamental plane and requiring the behavior of that term to mimic the observed nonlinear relationship between log(M_e/L_e) and log(sigma), we simultaneously fit a 2-D manifold to the measured properties of dwarf ellipticals, ellipticals, BCGs, and CSphs. The combined data have an rms scatter in log(r_e) of 0.114 (0.099 for the combination of Es, BCGs, and CSphs), which is modestly larger than each fundamental plane has alone, but which includes the scatter introduced by merging different studies done in different filters by different investigators. This ``fundamental manifold'' fits the structural and kinematic properties of spheroids that span a factor of 100 in sigma and 1000 in r_e. (ABRIDGED)
Given a large-scale mixture of self-interacting dark matter (SIDM) particles and baryon matter distributed in the early Universe, we advance here a two-phase accretion scenario for forming supermassive black holes (SMBHs) with masses around $\sim 10^9 M_{\odot}$ at high redshifts $z (\gsim 6)$. The first phase is conceived to involve a rapid quasi-spherical and quasi-steady Bondi accretion of mainly SIDM particles embedded with baryon matter onto seed black holes (BHs) created at redshifts $z\lsim 30$ by the first generation of massive Population III stars; this earlier phase rapidly gives birth to significantly enlarged seed BH masses of $M_{\hbox{\tiny BH},t_1}\backsimeq 1.4\times 10^6\ M_\odot \sigma_0/(1\hbox{cm}^2\hbox{g}^{-1})(C_s/30\hbox{km s}^{-1})^4$ during $z\sim 20-15$, where $\sigma_0$ is the cross section per unit mass of SIDM particles and $C_s$ is the velocity dispersion in the SIDM halo referred to as an effective "sound speed". The second phase of BH mass growth is envisaged to proceed primarily via baryon accretion, eventually leading to SMBH masses of $M_{\hbox{\tiny BH}}\sim 10^9 M_\odot$; such SMBHs may form either by $z\sim 6$ for a sustained accretion at the Eddington limit or later at lower $z$ for sub-Eddington mean accretion rates. We intend to account for the reported detections of a few SMBHs at early epochs, e.g., SDSS 1148+5251 and so forth, without necessarily resorting to either super-Eddington baryon accretion or very frequent BH merging processes. Only extremely massive dark SIDM halos associated with rare peaks of density fluctuations in the early Universe may harbour such early SMBHs or quasars. Observational consequences are discussed.
(Abridged) This paper presents the data recently released for the XMM-Newton/WFI survey carried out as part of the ESO Imaging Survey (EIS) project. The aim of this survey is to provide optical imaging follow-up data in BVRI for identification of serendipitously detected X-ray sources in selected XMM-Newton fields. In this paper, fully calibrated individual and stacked images of 12 fields as well as science-grade catalogs for the 8 fields located at high-galactic latitude are presented. The data covers an area of \sim 3 square degrees for each of the four passbands. The median limiting magnitudes (AB system, 2" aperture, 5\sigma detection limit) are 25.20, 24.92, 24.66, and 24.39 mag for B-, V-, R-, and I-band, respectively. These survey products, together with their logs, are available to the community for science exploitation in conjunction with their X-ray counterparts. Preliminary results from the X-ray/optical cross-correlation analysis show that about 61% of the detected X-ray point sources in deep XMM-Newton exposures have at least one optical counterpart within 2" radius down to R \simeq 25 mag, 50% of which are so faint as to require VLT observations thereby meeting one of the top requirements of the survey, namely to produce large samples for spectroscopic follow-up with the VLT, whereas only 15% of the objects have counterparts down to the DSS limiting magnitude.
Coupled one-dimensional photochemical-climate calculations have been performed for hypothetical Earth-like planets around M dwarfs. Visible, near-infrared and thermal-infrared synthetic spectra of these planets were generated to determine which biosignature gases might be observed by a future, space-based telescope. Our star sample included two observed active M dwarfs, AD Leo and GJ 643, and three quiescent model stars. The spectral distribution of these stars in the ultraviolet generates a different photochemistry on these planets. As a result, the biogenic gases CH4, N2O, and CH3Cl have substantially longer lifetimes and higher mixing ratios than on Earth, making them potentially observable by space-based telescopes. On the active M-star planets, an ozone layer similar to Earth's was developed that resulted in a spectroscopic signature comparable to the terrestrial one. The simultaneous detection of O2 (or O3) and a reduced gas in a planet's atmosphere has been suggested as strong evidence for life. Planets circling M stars may be good locations to search for such evidence.
We investigate the effects of the addition of pre-main sequence evolution to star cluster simulations. We allowed stars to follow pre-main sequence tracks that begin at the deuterium burning birthline and end at the zero age main sequence. We compared our simulations to ones in which the stars began their lives at the zero age main sequence, and also investigated the effects of particular choices for initial binary orbital parameters. We find that the inclusion of the pre-main sequence phase results in a slightly higher core concentration, lower binary fraction, and fewer hard binary systems. In general, the global properties of star clusters remain almost unchanged, but the properties of the binary star population in the cluster can be dramatically modified by the correct treatment of the pre-main sequence stage.
Special-relativistic effects on the imaging by a non-point-like arbitrarily moving optical instrument are discussed. Special-relativistic reflection law for a mirror of arbitrary shape and motion is derived in the limit of geometrical optics. In application to Gaia the effects of that relativistically modified reflection law of the images produced by a rotating reflector are demonstrated.
(Abridged) We present an initial look at the far infrared-radio correlation within the star-forming disks of four nearby, nearly face-on galaxies (NGC 2403, NGC 3031, NGC 5194, and NGC 6946). Using Spitzer MIPS imaging and WSRT radio continuum data, observed as part of the Spitzer Infrared Nearby Galaxies Survey (SINGS), we are able to probe variations in the logarithmic 24mu/22cm (q_24) and 70mu/22cm (q_70) surface brightness ratios across each disk at sub-kpc scales. We find general trends of decreasing q_24 and q_70 with declining surface brightness and with increasing radius. The residual dispersion around the trend of q_24 and q_70 versus surface brightness is smaller than the residual dispersion around the trend of q_24 and q_70 versus radius, on average by ~0.1 dex, indicating that the distribution of star formation sites is more important in determining the infrared/radio disk appearance than the exponential profiles of disks. We have also performed preliminary phenomenological modeling of cosmic ray electron (CRe^-) diffusion using an image-smearing technique, and find that smoothing the infrared maps improves their correlation with the radio maps. Exponential kernels tend to work better than Gaussian kernels which suggests that additional processes besides simple random-walk diffusion in three dimensions must affect the evolution of CRe^-s. The best fit smoothing kernels for the two less active star-forming galaxies (NGC 2403 and NGC 3031) have much larger scale-lengths than those of the more active star-forming galaxies (NGC 5194 and NGC 6946). This difference may be due to the relative deficit of recent CRe^- injection into the interstellar medium (ISM) for the galaxies having largely quiescent disks.
We searched for anomalously long GRBs (GRBs) in the archival records of the Burst and Transient Sources Experiment (BATSE). Ten obvious superlong (>500 s) GRBs with almost continuous emission episodes were found. Nine of these events are known from the BATSE catalog, but five have no duration estimates; we found one burst for the first time. We also detected events with emission episodes separated by a long period of silence (up to 1000 s) with a total duration of 1000--2000 s. In the latter case, we cannot reach an unequivocal conclusion about a common origin of the episodes due to the BATSE poor angular resolution. However, for most of these pairs, the probability of a coincidence of independent GRBs is much lower than unity, and the probability that all of these are coincidences is 10E-8. All of the events have a hardness ratio (the ratio of the count rates in different energy channels) typical of GRBs, and their unique duration is unlikely to be related to their high redshifts. Superlong bursts do not differ in their properties from typical long (>2 s) GRBs. We estimated the fraction of superlong GRBs (>500 s) among the long GRBs in the BATSE sample with fluxes up to 0.1 ph cm^{-2} s^{-1} to be between 0.3 and 0.5%, which is higher than the estimate based on the BATSE catalog.
Based on multi-dimensional multi-group radiation hydrodynamic simulations of
core-collapse supernovae with the VULCAN/2D code, we study the physical
conditions within and in the vicinity of the nascent protoneutron star (PNS).
Conclusions of this work are threefold: First, as before, we do not see any
large-scale overturn of the inner PNS material. Second, we see no evidence of
doubly-diffusive instabilities in the PNS, expected to operate on diffusion
timescales of at least a second, but instead observe the presence of
convection, within a radius range of 10-20 km, operating with a timescale of a
few milliseconds. Third, we identify unambiguously the presence of gravity
waves, predominantly at 200-300 ms past core bounce, in the region separating
the convective zones inside the PNS and between the PNS surface and the shocked
region.
PNS convection is always confined to a region between 10 and 20 km, i.e.,
within the neutrinospheric radii for all neutrino energies above just a few
MeV. We find that such motions do not appreciably enhance the electron neutrino
luminosity, and that they can enhance the anti-electron and "mu" neutrino
luminosities by no more than ~15% and ~30%, respectively, during the first
post-bounce ~100 ms, after which the optical depth barrier between the inner
convection and the neutrinospheres effectively isolates one from the other,
terminating even this modest enhancement. PNS convection is thus found to be a
secondary feature of the core-collapse phenomenon, rather than a decisive
ingredient for a successful explosion. (abridged)
The standard solar model was so reliable that it could predict the existence of the massive neutrino. Helioseismology measurements were so precise that they could determine the depth of the convection zone. This agreement between theory and observation was the envy of all astrophysics -- until recently when sophisticated three-dimensional hydrodynamic calculations of the solar atmosphere reduced the metal content by a factor of almost two. Antia & Basu (2005) suggested that a higher value of the solar neon abundance, Ne/O = 0.52, would resolve this controversy. Drake & Testa (2005) presented strong evidence in favor of this idea from a sample of 21 Chandra stars with enhanced values of the neon abundance, Ne/O = 0.41. In this paper, we have analyzed solar active region spectra from the archive of the Flat Crystal Spectrometer on Solar Maximum Mission, a NASA mission from the 1980s, as well as full-Sun spectra from the pioneering days of X-ray astronomy in the 1960s. These data seem consistent with the standard neon-to-oxygen abundance value, Ne/O = 0.15 (Grevesse & Sauval 1998). If these results prove to be correct, than the enhanced-neon hypothesis will not resolve the current controversy.
Given the basic parameters of a cosmic shear weak lensing survey, how well can systematic errors due to anisotropy in the point spread function (PSF) be corrected? The largest source of error in this correction to date has been the interpolation of the PSF to the locations of the galaxies. To address this error, we separate the PSF patterns into components that recur in multiple exposures/pointings and those that vary randomly between different exposures (such as those due to the atmosphere). In an earlier study we developed a principal component approach to correct the recurring PSF patterns (Jarvis and Jain 2004). In this paper we show how randomly varying PSF patterns can also be circumvented in the measurement of shear correlations. For the two-point correlation function this is done by simply using pairs of galaxy shapes measured in different exposures. Combining the two techniques allows us to tackle generic combinations of PSF anisotropy patterns. The second goal of this paper is to give a formalism for quantifying residual systematic errors due to PSF patterns. We show how the main PSF corrections improve with increasing survey area (and thus can stay below the reduced statistical errors), and we identify the residual errors which do not scale with survey area. Our formalism can be applied both to planned lensing surveys to optimize instrumental and survey parameters and to actual lensing data to quantify residual errors.
Anomalous radio flux ratios in four-image gravitational lens systems can be explained by adding a clumpy cold dark matter (CDM) component to the potential of the lens galaxy. Evans & Witt (2003) recently suggested that smooth multipole perturbations can provide a reasonable alternative to CDM substructure in some but not all cases. We generalize their method in two ways so as to determine whether multipole models can explain highly anomalous systems. We carry the multipole expansion to higher order, and also include external tidal shear as a free parameter. Fitting for the shear proves crucial to finding a physical (positive-definite density) model. For B1422+231, working to order k = 5 (and including shear) yields a model that is physical but implausible. Going to higher order (k >~ 9) reduces global departures from ellipticity at the cost of introducing small scale wiggles near the bright images. These localized undulations are more pronounced in B2045+265, where k ~ 17 multipoles are required to smooth out large scale deviations from elliptical symmetry. Such modes surely cannot be taken at face value; they must indicate that the models are trying to reproduce some other sort of structure. Our formalism naturally finds models that fit the data exactly, but we use B0712+472 to show that measurement uncertainties have little effect on our results. Finally, we consider the system B1933+503, where two sources are lensed by the same foreground galaxy. The additional constraints provided by the images of the second source render the multipole model unphysical. We conclude that external shear must be taken into account to obtain plausible models, and that a purely smooth angular structure for the lens galaxy does not provide a viable alternative to the prevailing CDM clump hypothesis.
We describe the flattening of scientific CCD imaging data using a dome flat field system. The system uses light emitting diodes (LEDs) to illuminate a carefully constructed dome flat field screen. LEDs have several advantages over more traditional illumination sources: they are available in a wide range of output wavelengths, are inexpensive, have a very long source lifetime, and are straightforward to control digitally. The circular dome screen is made of a material with Lambertian scattering properties that efficiently reflects light of a wide range of wavelengths and incident angles. We compare flat fields obtained using this new system with two types of traditionally-constructed flat fields: twilight sky flats and nighttime sky flats. Using photometric standard stars as illumination sources, we test the quality of each flat field by applying it to a set of standard star observations. We find that the dome flat field system produces flat fields that are superior to twilight or nighttime sky flats, particularly for photometric calibration. We note that a ratio of the twilight sky flat to the nighttime sky flat is flat to within the expected uncertainty; but since both of these flat fields are inferior to the dome flat, this common test is not an appropriate metric for testing a flat field. Rather, the only feasible and correct method for determining the appropriateness of a flat field is to use standard stars to measure the reproducibility of known magnitudes across the detector.
We present hydrodynamical calculations carried out with the 3D yguazu-a code of a precessing jet model, which interacts with a plane parallel wind. This scenario describes an extragalactic jet, in which the jet source is in motion with respect to the surrounding intra-cluster medium. From the numerical results, synthetic emission maps and spectra in X-ray band were obtained. We compare these predictions with observations of the radio jets emanating from the radio-galaxy 4C 26.42 (in the Abell 1795 galaxy cluster). We find that the general morphology of the radio jets can be described by a point-symmetric precessing jet system interacting with a plane parallel wind (i.e., the intra-cluster medium flowing past the galaxy). We also find that our synthetic X-ray emission maps reproduce the observed large scale structures (with sizes of the order of tens of kpc).
Recent spectral observations by the Spitzer Space Telescope (SST) reveal that some discs around young ($\sim {\rm few} \times 10^6$ yr old) stars have remarkably sharp transitions to a low density inner region in which much of the material has been cleared away. It has been recognized that the most plausible mechanism for the sharp transition at a specific radius is the gravitational influence of a massive planet. This raises the question of whether the planet can also account for the hole extending all the way to the star. Using high resolution numerical simulations, we show that Jupiter-mass planets drive spiral waves which create holes on time scales $\sim 10$ times shorter than viscous or planet migration times. We find that the theory of spiral-wave driven accretion in viscous flows by Takeuchi et al. (1996) can be used to provide a consistent interpretation of the simulations. In addition, although the hole surface densities are low, they are finite, allowing mass accretion toward the star. Our results therefore imply that massive planets can form extended, sharply bounded spectral holes which can still accommodate substantial mass accretion rates. The results also imply that holes are more likely than gaps for Jupiter mass planets around solar mass stars.
Arecibo S-band (lambda=13cm) radar observations of Comet C/2001 A2 (LINEAR) on 2001 July 7-9 showed a strong echo from large coma grains. This echo was significantly depolarized. This is the first firm detection of depolarization in a grain-coma radar echo and indicates that the largest grains are at least lambda / 2 or 2 cm in radius. The grains are moving at tens of m/s with respect to the nucleus. The non-detection of the nucleus places an upper limit of 3 km on its diameter. The broad, asymmetric echo power spectrum suggests a fan of grains that have a steep (differential number ~ a^-4) size distribution at cm-scales, though the observed fragmentation of this comet complicates that picture.
We have created a framework to facilitate the construction of specialized target lists for radial velocity surveys that are biased toward stars that (1) possess planets and (2) are easiest to observe with current detection techniques. We use a procedure that uniformly estimates fundamental stellar properties of Tycho 2 stars, with errors, using spline functions of broadband photometry and proper motion found in Hipparcos/Tycho 2 and 2MASS. We provide estimates of temperature and distance for 2.4 million Tycho 2 stars that lack trigonometric distances. For stars that appear to be FGK dwarfs according to estimated temperature and absolute magnitude, we also derive [Fe/H] and identify unresolved binary systems with mass ratios between 1.25 and 3. Our spline function models are trained on the unique Valenti & Fischer (2005) set, composed of 1000 dwarfs with precise stellar parameters estimated from HIRES spectroscopy. For FGK dwarfs with V photometric error less than 0.05 magnitudes, or V < 9, our temperature model gives a one-sigma error of +58.7/-65.9 K and our metallicity model gives a one-sigma error of +0.13/-0.14 dex. Our estimates of distance and spectral type enable us to isolate 354,822 Tycho 2 dwarfs, 321,996 of which are absent from Hipparcos, with giant and subgiant contamination at 2.6% and 7.2%, respectively. 2,500 of these FGK dwarfs are bright (V < 9.0) and metal-rich ([Fe/H] > 0.2). Our metallicity estimates have been used to identify targets for N2K (Fischer et al. 2005), a large-scale radial velocity search for Hot Jupiters, which has published the detection of 4 Hot Jupiters with one transit. The broadband filtering outlined here is the first screening tier for N2K; the second tier is a low-resolution spectroscopy program headed by S.E. Robinson (astro-ph/0510150).
In this paper, we contrast an empirical pulse function of gamma-ray bursts with a theoretical model in order to provide a physical explanation to the parameters of the KRL function and directly relate parameters in both models. We find the ratio of the rise index r to the decay index d, derived when fitted by the KRL function, increases quickly first and then remains nearly invariant with the relative width of local pulses when the width exceeds 2. The rise and decay times of pulses are found to be related to the Lorentz factor by a power law, where the power law index associated with the rise time is less than that of the decay time, and both are close to -2. In addition, the mean asymmetry shows a slight trend of decreasing with Lorentz factors. In plots of decay indices versus asymmetry, there is a descending phase and after this phase there is a rising portion. We find that these long bursts of the KRL sample are mainly associated with those light curves arising from co-moving pulses with the relative width being larger than 0.1. We show that the effect of the co-moving pulse shape on the KRL function parameters of the resulting pulses is considerable and can be distinguished by the decay index d when the relative co-moving pulse width is less than 2.
The next generation of galaxy surveys will attempt to measure the baryon oscillations in the clustering power spectrum with high accuracy. These oscillations encode a preferred scale which may be used as a standard ruler to constrain cosmological parameters and dark energy models. In this paper we present simple analytical fitting formulae for the accuracy with which the preferred scale may be determined in the tangential and radial directions by future spectroscopic and photometric galaxy redshift surveys. We express these accuracies as a function of survey parameters such as the central redshift, volume, galaxy number density and (where applicable) photometric redshift error. These fitting formulae should greatly increase the efficiency of optimizing future surveys, which requires analysis of a potentially vast number of survey configurations and cosmological models. The formulae are calibrated using a grid of Monte Carlo simulations, which are analyzed by dividing out the overall shape of the power spectrum before fitting a simple decaying sinusoid to the oscillations. The fitting formulae reproduce the simulation results with a fractional scatter of 7% (10%) in the tangential (radial) directions over a wide range of input parameters. We also indicate how sparse-sampling strategies may enhance the effective survey area if the sampling scale is much smaller than the projected baryon oscillation scale.
We report 3.6 cm continuum observations taken with the Very Large Array (VLA) of the young binary system UY Aur. The binary consists of a T Tauri star, UY Aur A, and a so-called ``infrared companion'' (IRC), UY Aur B, separated by 0.''89. UY Aur is an interesting system because it shows observational features whose origin is not well understood. One of them is the unusual low spectral index found in the millimeter region. In our VLA study, we have detected centimeter continuum radiation that coincides with the reported positions at 1.3 and 2.7 mm and is consistent with the optical position of UY Aur. We conclude that the 3.6 cm emission is associated with the binary system. Furthermore, we suggest that the centimeter emission might be related to a previously reported bipolar outflow.
The jet formation is thought to be closely connected with the mass of central supermassive black hole in Active Galactic Nuclei. The radio luminosity commonly used in investigating this issue is merely an indirect measure of the energy transported through the jets from the central engine, and severely Doppler boosted in core-dominated radio quasars. In this work, we investigate the relationship between the jet power and black hole mass, by estimating the jet power using extrapolated extended 151 MHz flux density from the VLA 5 GHz extended radio emission, for a sample of 146 radio loud quasars complied from literature. After removing the effect of relativistic beaming in the radio and optical emission, we find a significant intrinsic correlation between the jet power and black hole mass. It strongly implies that the jet power, so as jet formation, is closely connected with the black hole mass.To eliminate the beaming effect in the conventional radio loudness, we define a new radio loudness as the ratio of the radio extended luminosity to the optical luminosity estimated from the broad line luminosity.In a tentatively combined sample of radio quiet with our radio loud quasars, the apparent gap around the conventional radio loudness R=10 is not prominent for the new-defined radio loudness. In this combined sample, we find a significant correlation between the black hole mass and new-defined radio loudness.
We estimate the detection rate of ultrahigh-energy cosmic rays on ground based arrays by assuming that the cosmic ray sources are active galactic nuclei. We analyse the cases of detection of clusters, several particles that arrived, within the error limits, from the same area of the sky. The adopted model is shown to explain the detection rate of clusters on the AGASA array.
Using the radio observations by FIRST and NVSS, we build a sample of 151 radio variable quasars selected from the Sloan Digital Sky Survey Data Release 3 (SDSS DR3). Six (probably another two) among them are classified as broad absorption line (BAL) quasars, with radio flux variations of a few 10 percent within 1.5-5 years. Such large amplitudes of the variations imply brightness temperatures much higher than the inverse Compton limits (10$^{12}$ K) in all the BAL quasars, suggesting the presence of relativistic jets beaming toward the observer. The angle between the outflow and the jet is constrained to be less than $\sim 20^{\circ}$. Such BAL quasars with polar outflows are beyond the simple unification models of BAL quasars and non-BAL quasars, which hypothesize that BAL quasars are normal quasars seen nearly edge-on.
The major axis and ellipse-fit intensity profiles of spiral galaxies larger than 0.3'' in the Hubble Space Telescope Ultra Deep Field (UDF) are generally exponential, whereas the major axis profiles in irregular disk galaxies, called clump-clusters in our previous studies, are clearly not. Here we show that the deprojected positions of star-forming clumps in both galaxy types are exponential, as are the deprojected luminosity profiles of the total emissions from these clumps. These exponentials are the same for both types when normalized to the outer isophotal radii. The results imply that clumps form or accrete in exponential radial distributions, and when they disperse they form smooth exponential disks. The exponential scale lengths for UDF spirals average 1.5 kpc for a standard cosmology. This length is smaller than the average for local spirals by a factor of 2. Selection effects that may account for this size difference among spirals are discussed. Regardless of these effects, the mere existence of small UDF galaxies with grand-design spiral arms differs significantly from the situation in local fields, where equally small disks are usually dwarf Irregulars that rarely have spiral arms. Spiral arms require a disk mass comparable to the halo mass in the visible region -- something local spirals have but local dwarfs Irregulars do not. Our UDF result then implies that galaxy disks grow from the inside out, starting with a dense halo and dense disk that can form spiral arms, and then adding lower density halo and disk material over time. Bars that form early in such small, dense, gas-rich disks should disperse more quickly than bars that form later in fully developed disks.
Simulations and observations of galactic bars suggest they do not commonly evolve into bulges, although it is possible that the earliest bars formed bulges long ago, when galaxies were smaller, denser, and had more gas. The most highly evolved of today's bars may become lenses over a Hubble time. Most galaxies in the early Universe are extremely clumpy, with 10^8-10^9 Msun blue clumps that resemble in color and magnitude the isolated field objects nearby. The presence of blue and irregular bars at high redshift suggests that some bars formed primarily in the gas phase accompanied by giant starbursts, rather than in pure stellar disks like most models. Secular and non-secular processes that cause galaxies to evolve are summarized.
In this paper, we employe a new statistical analysis technique, Ensemble Learning for Independent Component Analysis (EL-ICA), on the synthetic galaxy spectra from a newly released high resolution evolutionary model by Bruzual & Charlot. We find that EL-ICA can sufficiently compress the synthetic galaxy spectral library to 6 non-negative Independent Components (ICs), which are good templates to model huge amount of normal galaxy spectra, such as the galaxy spectra in the Sloan Digital Sky Survey (SDSS). Important spectral parameters, such as starlight reddening, stellar velocity dispersion, stellar mass and star formation histories, can be given simultaneously by the fit. Extensive tests show that the fit and the derived parameters are reliable for galaxy spectra with the typical quality of the SDSS.
We present Chandra, Very Large Array (VLA), and Very Long Baseline Array (VLBA) observations of the nucleus of NGC 4696, a giant elliptical in the Centaurus cluster of galaxies. Like M87 in the Virgo cluster, PKS 1246-410 in the Centaurus cluster is a nearby example of a radio galaxy in a dense cluster environment. In analyzing the new X-ray data we have found a compact X-ray feature coincident with the optical and radio core. While nuclear emission from the X-ray source is expected, its luminosity is low, <10^{40} erg/s. We estimate the Bondi accretion radius to be 30 pc and the accretion rate to be 0.01 M_sun/yr which under the canonical radiative efficiency of 10% would overproduce by 3.5 orders of magnitude the radiative luminosity. Much of this energy can be directed into the kinetic energy of the jet, which over time inflates the observed cavities seen in the thermal gas. The VLBA observations reveal a weak nucleus and a broad, one-sided jet extending over 25 parsecs in position angle -150 degrees. This jet is deflected on the kpc-scale to a more east-west orientation (position angle of -80 degrees).
We present the HI observations of 94 flat spiral galaxies from RFGC (the Revised Flat Galaxy Catalog) and 14 galaxies from 2MFGC (the 2MASS selected Flat Galaxy Catalog) performed with the 100-m radio telescope in Effelsberg (Germany). HI fluxes, heliocentric radial velocities, and HI line widths are given for 65 detected galaxies. We present a mosaic of HI profiles. We calculated some of the global parameters of the galaxies and analyzed the linear correlations between them. The ratios of the total (indicative) masses of the galaxies to their luminosities lie within the range 0.4 with a mean of 3.8 ($M_{\sun}/L_{\sun}$), and the mean mass fraction of neutral hydrogen is 13%. Upper limits are given for the radio fluxes from 43 undetected galaxies.
We present new calibrations of the widely used H_alpha, [OII], and UV luminosity vs. star formation rate (SFR) relations. Using our evolutionary synthesis code GALEV we compute the different calibrations for 5 metallicities, from 1/50 solar up to 2.5 solar. We find significant changes in the calibrations for lower metallicities compared to the standard calibrations using solar input physics.
In this work, the gas infall and the formation of outflows around low and high mass protostars are investigated. A radial self-similar approach to model the transit of the molecular gas around the central object is employed. We include gravitational and radiative fields to produce heated pressure-driven outflows with magneto-centrifugal acceleration and collimation. Outflow solutions with negligible or vanishing magnetic field are reported. They indicate that thermodynamics is a sufficient engine to generate an outflow. The magnetized solutions show dynamically significant differences in the axial region, precisely where the radial velocity and collimation are the largest. They compare quantitatively well with observations. The influence of the opacity on the transit solutions is also studied. It is found that, when dust is not the dominant coolant, such as in the primordial universe, mass infall rates have substantial larger values in the equatorial region. This suggests that star forming in a dust-free environment should be able to accrete much more mass and become more massive than present day protostars.It is also suggested that molecular outflows may be dominated by the global transit of material around the protostar during the very early stages of star formation, especially in the case of massive or dust-free star formation.
Cosmic ray particles are more rapidly accelerated in oblique shocks, with the magnetic field inclined with respect to the shock normal direction, than in parallel shocks, as a result of mirror reflection at the shock surface and slower diffusion in the shock normal direction. We investigate quantitatively how these effects contribute to reducing the acceleration time over the whole range of magnetic field inclinations. It is shown that, for quasi-perpendicular inclination, the mirror effect plays a remarkable role in reducing the acceleration time; whereas, at relatively small inclination, the anisotropic diffusion effect is dominant in reducing that time. These results are important for a detailed understanding of the mechanism of particle acceleration by an oblique shock in space and heliosphereic plasmas.
We have determined accurate values of the product of the mass-loss rate and the ion fraction of P^{4+}, Mdot q(P^{4+}), for a sample of 40 Galactic O-type stars by fitting stellar-wind profiles to observations of the P V resonance doublet obtained with FUSE, ORFEUS/BEFS, and Copernicus. When P^{4+} is the dominant ion in the wind, Mdot q(P^{4+}) approximates the mass-loss rate to within a factor of 2. Theory predicts that P^{4+} is the dominant ion in the winds of O7-O9.7 stars, though an empirical estimator suggests that the range from O4-O7 may be more appropriate. However, we find that the mass-loss rates obtained from P V wind profiles are systematically smaller than those obtained from fits to Halpha emission profiles or radio free-free emission by median factors of about 130 (if P^{4+} is dominant between O7 and O9.7) or about 20 (if P^{4+} is dominant between O4 and O7). These discordant measurements can be reconciled if the winds of O stars in the relevant temperature range are strongly clumped on small spatial scales. We use a simplified two-component model to investigate the volume filling factors of the denser regions. This clumping implies that mass-loss rates determined from "density squared" diagnostics have been systematically over-estimated by factors of 10 or more, at least for a subset of O stars. Reductions in the mass-loss rates of this size have important implications for the evolution of massive stars and quantitative estimates of the feedback that hot-star winds provide to their interstellar environments.
We have imaged the halo populations of a sample of nearby spiral galaxies using the Wide Field Planetary Camera 2 on broad the Hubble Space Telescope with the aim of studying the stellar population properties and relating them to those of the host galaxies. In four galaxies, the red-giant branch is sufficiently well populated to measure the magnitude of the tip of the red-giant branch (TRGB), a well-known distance indicator. Using both the Sobel edge-detection technique and maximum-likelihood analysis to measure the $I$-band magnitude of the red giant branch tip, we determine distances to four nearby galaxies: NGC 253, NGC 4244, and NGC 4945, NGC 4258. For the first three galaxies, the TRGB distance determined here is more direct, and likely to be more accurate, than previous distance estimates. In the case of NGC 4258, our TRGB distance is in good agreement with the the geometrical maser distance, supporting the the Large Magellanic Cloud distance modulus $(m-M)_0 = 18.50$ that is generally adopted in recent estimates of the Hubble constant.
Using the Hubble Space Telescope, we have resolved individual red-giant branch stars in the halos of eight nearby spiral galaxies. The fields lie at projected distances between 2 and 13 kpc along the galaxies' minor axes. The data set allows a first look at the systematic trends in halo stellar populations. We have found that bright galaxies tend to have broad red-giant branch star color distributions with redder mean colors, suggesting that the heavy element abundance spread increases with the parent galaxy luminosity. The mean metallicity of the stellar halo, estimated using the mean colors of red-giant branch stars, correlates with the parent galaxy luminosity. The metallicity of the Milky Way halo falls nearly 1 dex below this luminosity-metallicity relation, suggesting that the halo of the Galaxy is more the exception than the rule for spiral galaxies; i.e., massive spirals with metal-poor halos are unusual. The luminosity-halo stellar abundance relation is consistent with the scaling relation expected for stellar systems embedded in dominant halos, suggesting that the bulk of the halo stellar population may have formed in situ.
(Abriged) We report results of a campaign to image the stellar populations in the halos of highly inclined spiral galaxies, with the fields roughly 10 kpc (projected) from the nuclei. We use the F814W (I) and F606W (V) filters in the Wide Field Planetary Camera 2, on board the Hubble Space telescope. Extended halo populations are detected in all galaxies. The color-magnitude diagrams appear to be completely dominated by giant-branch stars, with no evidence for the presence of young stellar populations in any of the fields. We find that the metallicity distribution functions are dominated by metal-rich populations, with a tail extending toward the metal poor end. To first order, the overall shapes of the metallicity distribution functions are similar to what is predicted by simple, single-component model of chemical evolution with the effective yields increasing with galaxy luminosity. However, metallicity distributions significantly narrower than the simple model are observed for a few of the most luminous galaxies in the sample. It appears clear that more luminous spiral galaxies also have more metal-rich stellar halos. The increasingly significant departures from the closed-box model for the more luminous galaxies indicate that a parameter in addition to a single yield is required to describe chemical evolution. This parameter, which could be related to gas infall or outflow either in situ or in progenitor dwarf galaxies that later merge to form the stellar halo, tends to act to make the metallicity distributions narrower at high metallicity.
There is now good evidence linking short-hard GRBs with both elliptical and spiral galaxies at relatively low redshifts, redshift of about 0.2. This contrasts with the average redshift of about 2 of long-duration events, which also occur only in star-forming galaxies. The diversity of hosts is reminiscent of type Ia supernovae, which are widely (but not universally) believed to originate from the coalescence of white dwarfs. By analogy, it has been postulated that short-hard bursts originate from neutron star mergers. Mergers, as well as stellar core-collapse events (type II SNe and long-duration GRBs) are accompanied by long-lived sub-relativistic components powered by radioactive decay of unstable elements produced in the explosion. It is therefore interesting to explore whether short duration events also have ejecta powered by radioactivity (i.e. that are supernova-like). Observations already inform us that any supernova like component in the first few well studied short hard bursts must be fainter than those typical of type Ia or core-collapse supernovae. Rather than refer to weaker supernova-like component as ``mini-super nova'', an etymologically indefensible term, I use the term {\it macronova}. I investigate the observability of macronovae powered by neutron decay and by radioactive Nickel. Separately, I note that a macronova will reprocess energetic emission arising from a long lived central source. I find that surprisingly interesting limits on the basic parameters of macronovae can be obtained provided observations are obtained with current 10-m class telescopes over a range of one hour to one day following the burst.
We report the results of our Chandra observations of six QSOs at $z\sim 3$ from the Palomer Transit Grism Survey. Our primary goal is to investigate the possible systematic change of $\alpha_{ox}$ between $z>4$ and $z\sim 3$, between which a rapid rise of luminous QSO number density with cosmic time is observed. The summed spectrum showed a power-law spectrum with photon index of $\Gamma \approx 1.9$, which is similar to other unabsorbed AGNs. Combining our $z\sim 3$ QSOs with X-ray observations of QSOs at $z>4$ from literaure/archive, we find a correlation of $\alpha_{\rm ox}$ with optical luminosity. This is consistent with the fact that the luminosity function slope of the luminous end of the X-ray selected QSOs is steeper than that of optically-selected QSOs. We discuss an upper limit to the redshift dependence of $\alpha_{ox}$ using a Monte-Carlo simulation. Within the current statistical errors including the derived limits on the redshift dependence of $\alpha_{\rm ox}$, we found that the behaviors of the X-ray and optically-selected QSO number densities are consistent with each other.
Strong observational evidence for a fluctuating ultraviolet background (UVB) has been accumulating through a number of studies of the HI and HeII Lya forest as well as accurate IGM metallicity measurements. UVB fluctuations could arise both from the inhomogeneous distribution of the ionizing sources and/or from radiative transfer (RT) through the filamentary IGM. In this study we investigate, via numerical simulations, the role of RT effects such as shadowing, self-shielding and filtering of the ionizing radiation, in giving raise to a fluctuating UVB. We focus on possible detectable signatures of these effects on quantities derived from Lya forest spectra, as photoionization rate fluctuations, eta parameter (the HeII to HI column density ratio) distributions and the IGM temperature at redshift about 3. We find that RT induces fluctuations up to 60% in the UVB, which are tightly correlated to the density field. The UVB mean intensity is progressively suppressed toward higher densities and photon energies above 4 Ryd, due to the high HeII opacity. Shielding of overdense regions (Delta > 5) from cosmic HeII ionizing radiation, produces a decreaseing trend of eta with overdensity. Furthermore we find that the mean eta value inferred from HI-HeII Lya forest observations can be explained only by properly accounting for the actual IGM opacity. We outline and discuss several implications of our findings.
We have searched for Type Ia supernovae (SNe Ia) in the local (d < 60 Mpc) Universe using Northern Sky Variability Survey (NSVS) data collected from the nightly optical surveys of the Robotic Optical Transient Search Experiment} (ROTSE) Telescope. It was hoped that SNe Ia would provide a means to find previously-unknown low surface brightness (LSB) galaxies or displaced stars that would otherwise be very difficult to detect. The ROTSE data allowed us to survey 19,000 square degrees at declinations north of 0 degrees, but we did not find a single SN Ia in a period of time covering roughly one year. Using known SNe Ia rates in bright galaxies, we set an upper limit on the optical luminosity density, L_B, of LSBs in the local Universe. Using mean LSB baryonic and dynamical mass-to-light ratios, we find 95% upper limits for LSBs of L_B \le 2.53 x 10^8 L_{B, solar} Mpc^{-3}, Omega_b \le 0.0040, and Omega_m \le 0.036. We conclude that LSBs and displaced stars are not a major constituent of matter in the local Universe.
We present strong observational evidence for a relationship between the direction of a pulsar's motion and its rotation axis. We show carefully calibrated polarization data for 25 pulsars, 20 of which display linearly polarized emission from the pulse longitude at closest approach to the magnetic pole. Such data allow determination of the position angle of the linear polarisation which in turn reflects the position angle of the rotation axis. Of these 20 pulsars, 10 show an offset between the velocity vector and the polarisation position angle which is either less than 10\degr or more than 80\degr, a fraction which is very unlikely by random chance. We believe that the bimodal nature of the distribution arises from the presence of orthogonal polarisation modes in the pulsar radio emission. In some cases this orthogonal ambiguity is resolved by observations at other wavelengths so that we conclude that the velocity vector and the rotation axis are aligned at birth. Strengthening the case is the fact that 4 of the 5 pulsars with ages less than 3 Myr show this relationship, including the Vela pulsar. We discuss the implications of these findings in the context of the Spruit & Phinney (1998)\nocite{sp98} model of pulsar birth-kicks. We point out that, contrary to claims in the literature, observations of double neutron star systems do not rule out aligned kick models and describe a possible observational test involving the double pulsar system.
The study of neutral hydrogen emission and absorption in radio galaxies is giving new and important insights on a variety of phenomena observed in these objects. Such observations are helping to understand the origin of the host galaxy, the effects of the interaction between the radio jet and the ISM, the presence of fast gaseous outflows as well as jet-induced star formation. Recent results obtained on these phenomena are summarized in this review. Although the HI observations concentrate on nearby radio galaxies, the results also have relevance for the high-z objects as all these phenomena are important, and likely even more common, in high-redshift radio sources.
This paper describes a very general approach to the calculation of the Zeeman splitting effect produced by an external magnetic field on the rotational levels of diatomic molecules. The method is valid for arbitrary values of the total electronic spin and of the magnetic field strength -that is, it holds for molecular electronic states of any multiplicity and for both the Zeeman and incomplete Paschen-Back regimes. It is based on an efficient numerical diagonalization of the effective Zeeman Hamiltonian, which can incorporate easily all the contributions one may eventually be interested in, such as the hyperfine interaction of the external magnetic field with the spin motions of the nuclei. The reliability of the method is demonstrated by comparing our results with previous ones obtained via formulae valid only for doublet states. We also present results for molecular transitions arising between non-doublet electronic states, illustrating that their Zeeman patterns show signatures produced by the Paschen-Back effect.
We report the detection of fast (~ 1000 km/s), massive outflows of neutral gas observed -- using the WSRT -- as 21-cm HI absorption against the strong radio continuum of seven radio sources. The neutral outflows occur, in at least somes cases, at kpc distance from the nucleus, and they are most likely driven by the interactions between the expanding radio jets and the gaseous medium enshrouding the central regions. We estimate that the associated mass outflow rates are up to ~50 M_sun/yr, comparable (although at the lower end of the distribution) to the outflow rates found for starburst-driven superwinds in Ultra Luminous IR Galaxies (ULIRG). This suggests that massive, jet-driven outflows of neutral gas in radio-loud AGN can have as large an impact on the evolution of the host galaxies as the outflows associated with starbursts. A radio-loud phase of the AGN is likely a relatively common, albeit short, phase in the life of many (or even all) massive ellipticals. Jet-driven neutral outflows may represent one of the main feedback mechanisms in these galaxies.
Aims: To determine the neon-to-oxygen abundance in the quiet Sun, a proxy for
the photospheric abundance ratio.
Method: An emission measure method applied to extreme ultraviolet emission
lines of Ne IV-VI and O III-V ions observed by the Coronal Diagnostic
Spectrometer on the SOHO satellite.
Results: The average Ne/O abundance ratio in supergranule cell centre regions
is 0.18 +/- 0.05, while in supergranule network regions is 0.16 +/- 0.04. A
photospheric Ne/O ratio of 0.17 +/- 0.05 is suggested, in good agreement with
the most recent compilation of solar photospheric abundances, but discrepant
with a recent Ne/O ratio derived from stellar X-ray spectra and revised neon
abundances suggested from solar interior models.
Certain regions of the solar atmosphere are at sufficiently low temperatures to be only partially ionised. The lower chromosphere contains neutral atoms, the existence of which greatly increases the efficiency of the damping of waves due to collisional friction momentum transfer. More specifically the Cowling conductivity can be up to 12 orders of magnitude smaller than the Spitzer value, so that the main damping mechanism in this region is due to the collisions between neutrals and positive ions. Using values for the gas density and temperature as functions of height taken from the VAL C model of the quiet Sun, an estimate is made for the dependance of the Cowling conductivity on height and strength of magnetic field. Using both analytic and numerical approaches the passage of Alfven waves over a wide spectrum through this partially ionised region is investigated. Estimates of the efficiency of this region in the damping of Alfven waves are made and compared for both approaches. We find that Alfven waves with frequencies above 0.6Hz are completely damped and frequencies below 0.01 Hz unaffected.
Focusing on the well motivated aperture mass statistics $\Map$, we study the possibility of constraining cosmological parameters using future space based SNAP class weak lensing missions. Using completely analytical results we construct the covariance matrix for estimators based on two-point and three-point statistics. Our approach incorporates an accurate modelling of higher-order statistics to describe cosmic variance as well as various sources of discrete noise at small angular scales. These results are then fed into a Fisher matrix based analysis to study cosmological parameter degeneracies. Joint and independent analysis, with or without redshift binning, for various parameter combinations are presented. An analytical modelling of the covariance matrix opens up the possibility of testing various approximations which are often used in derivations of semi-analytical results. These include how inclusion of full non-Gaussian terms in covariance matrix affects parameter estimation. Inclusion of three-point information and how such information can enhance the accuracy with which certain parameters can be estimated is also studied in detail. It is shown that broad correlation structure among various angular scales in such circumstances implies reduction in number of available angular scales which carry completely independent information. On the other hand, the effect of theoretical inaccuracies, in modelling either the power-spectrum or bi-spectrum evolution, onto the measure of cosmological parameters from weak lensing surveys is also considered. Several cosmological parameters, $\Om$, $\sigma_8$, spectral index $n_s$, running of spectral index $\alpha_s$ and equation of state of the dark energy $\wde$ are included in the analysis.
Broad-band spectra of accreting X-ray binary pulsars can be fit by a phenomenological model composed by a power law with a high energy rollover above 10 keV, plus a blackbody component with a temperature of few hundred eV. While, at least qualitatively, the hard tail can be explained in terms of (inverse) Compton scattering, the origin of the soft component cannot find a unique explanation. Recently a qualitative picture able to explain the overall broad band-spectrum of luminous X-ray pulsars was carried out by taking into account the effect of bulk Comptonization in the accretion column. After a review on these recent theoretical developments, I will present a case study of how different modelization of the continuum affect broad features, in particular the cyclotron resonance features in Vela X-1.
This is the second of a series of three papers exploring the connection between the multiwavelength properties of AGN in nearby early-type galaxies and the characteristics of their hosts. In Capetti et al. (2005) we presented a study of the surface brightness profiles for the 65 objects with available archival HST images out of the 116 radio-detected galaxies. We classified early-type galaxies into ``core'' and ``power-law'' galaxies, discriminating on the basis of the slope of their nuclear brightness profiles. Here we focus on the 29 core galaxies (hereafter CoreG). We used HST and Chandra data to isolate their nuclear emission. The CoreG invariably host radio-loud nuclei, with an average radio-loudness parameter of Log R = 3.6. The optical and X-ray nuclear luminosities correlate with the radio-core power, smoothly extending the analogous correlations already found for low luminosity radio-galaxies. This supports the interpretation of a common non-thermal origin of the nuclear emission also for CoreG. The luminosities of the nuclear sources, most likely dominated by jet emission, set firm upper limits, as low as L/L_Edd = 10^{-9} in both the optical and X-ray band, on any emission from the accretion process. The similarity of CoreG and LLRG indicates that they are drawn from the same population of early-type galaxies. LLRG represent only the tip of the iceberg associated with (relatively) high activity levels, with CoreG forming the bulk of the population. A minimum black hole mass of M_{BH} = 10^8 M_sun is apparently associated with the radio-loud nuclei in both CoreG and LLRG, but this effect must be tested on a sample of less luminous galaxies, likely to host smaller black holes. ABRIDGED.
We have determined the morphological types of 2295 galaxies from the ESO Nearby Abell Cluster Survey (ENACS) from CCD images made with the Dutch telescope on La Silla. The reliability of our classification appears to be quite comparable to that of other classifiers. Recalibration of the ENACS spectral classification shows that early- and late- type galaxies can be distinguished from their spectra with 83% reliability. Ellipticals and S0 galaxies cannot be distinguished spectrally, while spectral classification of late spirals has a reliability of 70%. We derive average pseudo-colors and linestrengths from the ENACS spectra for the galaxies of different morphological types, considering bright (M <= -20) and faint (M > -20) subsets of the galaxies without emission lines (non-ELG) separately. We find a strong and significant correlation between the average color and the average strength of the metal absorption lines. The average metallicity decreases and the average color gets bluer towards later Hubble type. In each morphological class the faint galaxies are bluer and less metal-rich than the bright ones. This extends the well-established color-magnitude relation of early-type galaxies to (late) spirals. Bright early spirals may, on average, have somewhat stronger H-delta absorption than the other galaxies, which could be due to recent starformation. The galaxies with emission lines (ELG) have a bluer spectral continuum than the non-ELG, and the amount of blueing hardly depends on morphological type. The fraction of ELG depends strongly on morphological type but it varies very little with projected distance from the cluster center.
The X and gamma-ray observations of the source GRB 031203 by INTEGRAL are interpreted within our theoretical model. In addition to a complete space-time parametrization of the GRB, we specifically assume that the afterglow emission originates from a thermal spectrum in the co-moving frame of the expanding baryonic matter shell. By determining the two free parameters of the model and estimating the density and filamentary structure of the ISM, we reproduce the observed luminosity in the 20-200 keV energy band. As in previous sources, the prompt radiation is shown to coincide with the peak of the afterglow and the luminosity substructure are shown to originate in the filamentary structure of the ISM. We predict a clear hard-to-soft behavior in the instantaneous spectra. The time-integrated spectrum over 20 seconds observed by INTEGRAL is well fitted. Despite this source has been considered "unusual", it appears to us a normal low energetic GRB.
The observed enhancement of the Fe K$\alpha$ line in three gravitationally lensed QSOs (MG J0414+0534, QSO 2237+0305, H1413+117) is interpreted in terms of microlensing, even when equivalent X-ray continuum amplification is not observed. In order to interpret these observations, first we studied the effects of microlensing on quasars spectra, produced by straight fold caustic crossing over standard relativistic accretion disk. The disk emission was analyzed using the ray tracing method, considering Schwarzschild and Kerr metrics. When the emission is separated in two regions (an inner disk corresponding to the Fe K$\alpha$ line and an outer annulus corresponding to the continuum, or vice-versa) we find microlensing events which enhance the Fe K$\alpha$ line without noticeable amplification of the X-ray continuum, but only during a limited time interval. Continuum amplification is expected if a complete microlensing event is monitored. Second, we studied a more realistic case of amplification by caustic magnification pattern. In this case we could satisfactorily explain the observations if the Fe K$\alpha$ line is emitted from the innermost part of the accretion disk, while the continuum is emitted from a larger region. Also, we studied the chromatic effects of microlensing, finding that the radial distribution of temperature in the accretion disk, combined with microlensing itself, can induce wavelength dependent variability of $\sim$ 30% for microlenses with very small masses. All these results show that X-ray monitoring of gravitational lenses is a well suited method for studying of the innermost structure of AGN accretion disks.
Vast sound waves traveling through the relativistic plasma during the first million years of the universe imprint a preferred scale in the density of matter. We now have the ability to detect this characteristic fingerprint in the clustering of galaxies at various redshifts and use it to measure the acceleration of the expansion of the Universe. The Wide-Field Multi-Object Spectrograph (WFMOS) would use this test to shed significant light on the true nature of dark energy, the mysterious source of this cosmic acceleration. WFMOS would also revolutionise studies of the kinematics of the Milky Way and provide deep insights into the clustering of galaxies at redshifts up to z~4. In this article we discuss the recent progress in large galaxy redshift surveys and detail how WFMOS will help unravel the mystery of dark energy.
Most inhomogeneities in the chemical composition of GC stars are due to primordial enrichment. The model today most credited is that the winds lost by high mass Asymptotic Giant Branch (AGB) stars, evolving during the first $\simlt$200Myr of the Clusters life, directly form a second generation of stars with abundance anomalies. The best indirect hint towards this suggestion is the recognition that some peculiarities in the Horizontal Branch (HB) stars distribution (blue tails, gaps, anomalous luminosity slope of the flat part of the HB) can be attributed to the larger helium abundance in the matter, processed through Hot Bottom Burning, from which these stars are born. The model has been reinforced by finding a peculiar main sequence distribution in the cluster NGC 2808, which also has a bimodal HB distribution and an extended blue tail: the excess of blue objects on the main sequence has been interpreted as stars with very high helium. We remark that the RR Lyr distribution may be affected by the helium spread, and this can be at the basis of the very long periods of the RRab variables of the metal rich clusters NGC 6388 and NGC 6441, longer than for the very metal poor Oosterhoff II clusters. These periods imply that the RR Lyr are brighter than expected for their metallicities, consistent with a larger helium abundance.
We present BVI photometry for poorly known southern hemisphere open clusters: NGC 2425, Haffner 10 and Czernik 29. We have calculated the density profile and established the number of stars in each cluster. The colour-magnitude diagrams of the objects show a well-defined main sequence. However, the red giant clump is present only in NGC 2425 and Haffner 10. For these two clusters we estimated the age as 2.5 +/- 0.5 Gyr assuming metallicity of Z=0.008. The apparent distance moduli are in the ranges 13.2<(m-M)_V<13.6 and 14.3<(m-M)_V<14.7, while heliocentric distances are estimated to be 2.9<d<3.8 kpc and 3.1<d<4.3 kpc, respectively for NGC 2425 and Haffner 10. The angular separation of 2.4 deg (150 pc at mean distance) may indicate a common origin of the two clusters.
A non-parametric statistical model is constructed to directly relate The distribution of observed microlens timescales to that of the mass Function of the population from which the lenses are drawn, corrected For observational selection based on timescales and event amplifications. Explicit distributions are derived for microlensing impact parameters and maximum amplifications; both are shown to be statistically independent of all other parameters in the problem, including lens mass. The model is used to demonstrate that the narrow range of microlens timescales observed toward the Large Magellanic Cloud (LMC) is probably not consistent with lensing by a widely distributed spheroidal population of large velocity dispersion, as expected of a dark halo; but is consistent with lensing within a rotating thick disk. Poor numerical conditioning on the statistical connection between lens masses and event timescales, and small number statistics, severely limit the mass function information obtainable from current microlensing surveys toward the LMC.
VLBA high spatial resolution observations of the disk structure of the active galactic nucleus NGC 1068 has recently revealed that the kinematics and geometry of this AGN is well characterized by an outer disk of H2O maser emission having a compact milliarcsecond (parsec) scale structure, which is encircling a thin rotating inner disk surrounding a ~10^7 M$_\sun$ compact mass, likely a black hole. A curious feature in this source is the occurrence of a misalignment between the inner and outer parts of the disk, with the galaxy's radio jet being orthogonal to the inner disk. We interpret this peculiar configuration as due to the Bardeen-Petterson effect, a general relativistic effect that warps an initially inclined (to the black hole equator) viscous disk, and drives the angular momentum vector of its inner part into alignment with the rotating black hole spin. We estimate the time-scale for both angular momenta to get aligned as a function the spin parameter of the Kerr black hole. We also reproduce the shape of the parsec and kiloparsec scale jets, assuming a model in which the jet is precessing with a period and aperture angle that decrease exponentially with time, as expected from the Bardeen-Petterson effect.
The black hole candidate V4641 Sgr (= SAX J1819.3-2525) went through a brief outburst during 2003 Aug 01 to Aug 08. During the outburst, activity was noted in optical, radio as well as X-rays. Here we present results of Spectral and Temporal analysis of a pointed Rossi X-ray Timing Explorer (RXTE) observation of the source during the outburst. During this pointing we observed flaring activities with associated X-ray luminosity variations over factors of 5 or more in timescales of few tens of seconds. The observed flares during are intrinsically different in their spectral and temporal properties. We see evidence of variable column density during one of the flares. The spectral and temporal analyses of the data suggest occasional outflow/mass ejection.
We present near infra-red (NIR) adaptive optics assisted spectroscopic
observations of the CO ($\Delta\mu=2$) absorption bands towards the centre of
the giant elliptical galaxy NGC 1399. The observations were made with
NAOS-CONICA (ESO VLT) and have a FWHM resolution of 0\farcs15 (14pc). Kinematic
analysis of the observations reveals a decoupled core and strongly non-Gaussian
line-of-sight velocity profiles (VPs) in the central 0.2 arcsec (19pc). NIR
imaging also indicates an asymmetric elongation of the central isophotes in the
same region.
We use spherical orbit-superposition models to interpret the kinematics,
using a set of orthogonal ``eigenVPs'' that allow us to fit models directly to
spectra. The models require a central black hole of mass
$1.2^{+0.5}_{-0.6}\times10^9M_\odot$, with a strongly tangentially biased orbit
distribution in the inner 40pc.
We report INTEGRAL/IBIS gamma-ray and VLA radio observations of G0.570-0.018, a diffuse X-ray source recently discovered by ASCA and Chandra in the Galactic center region. Based on its spectrum and morphology, G0.570-0.018 has been proposed to be a very young supernova remnant. In this scenario, the presence of gamma-ray lines coming from the short-lived radioactive nucleus 44Ti as well as synchrotron radio continuum emission are expected. The first could provide informations on nucleosynthesis environments in the interior of exploding stars, the latter could probe the interaction between the supernova blast wave and the circumstellar/interstellar matter. We have not detected 44Ti lines nor any conspicuous radio feature associated with this source down to the achieved sensitivities. From the derived upper limits we set constraints on the nature of G0.570-0.018.
We have used high spatial resolution data from the Hubble Space Telescope and wide-field ground-based observations to search for blue straggler stars (BSS) over the entire radial extent of the large stellar system omega Centauri. We have detected the largest population of BSS ever observed in any stellar system. Even though the sample is restricted to the brightest portion of the BSS sequence, more than 300 candidates have been identified. BSS are thought to be produced by the evolution of binary systems (either formed by stellar collisions or mass exchange in binary stars). Since systems like Galactic globular clusters (GGC) and omega Cen evolve dynamically on time-scales significantly shorter than their ages, binaries should have settled toward the center, showing a more concentrated radial distribution than the ordinary, less massive single stars. Indeed, in all GGCs which have been surveyed for BSS, the BSS distribution is peaked at the center. Conversely, in omega Cen we find that the BSS share the same radial distribution as the adopted reference populations. This is the cleanest evidence ever found that such a stellar system is not fully relaxed even in the central region. We further argue that the absence of central concentration in the BSS distribution rules out a collisional origin. Thus, the omega Cen BSS are the purest and largest population of non-collisional BSS ever observed. Our results allow the first empirical quantitative estimate of the production rate of BSS via this channel. BSS in omega Cen may represent the best local template for modeling the BSS populations in distant galaxies where they cannot be individually observed.
We study the morphology-radius (MR-) and morphology-density (MD-) relations for a sample of about 850 galaxies (with M <= -19.5) in 23 clusters from the ENACS (ESO Nearby Abell Cluster Survey). On the basis of their radial distributions we must distinguish: 1. brightest ellipticals (with M < -22), 2. late spirals, and 3. the ensemble of less bright ellipticals, S0 galaxies and early spirals. The latter have indistinguishable distributions of projected radial distance R. The brightest ellipticals are most centrally concentrated, the late spirals are almost absent from the central regions and the other classes are intermediate. Radial segregation of the ellipticals is due to the brightest ellipticals only, that of the spirals to the late spirals only. We derive the MD-relation with two measures of projected density: one using the 10 nearest neighbours (Sigma10) and another using only the nearest neighbour (Sigma1). The Sigma10 MD-relation only shows a significant difference between early- and late-type galaxies, but the different galaxy types within those classes are indistinguishable. However, The Sigma1 MD-relation shows that the normal 'ellipticals' (with M >= -22), the S0 galaxies and the early spirals have different Sigma1-distributions. The reason for this is that Sigma1 is much less correlated with R than is Sigma10, and thus has much less cross-talk from the (MR-) relation. On average, the 'normal' ellipticals populate environments with higher projected density than do the S0 galaxies while the early spirals populate even less dense environments. The segregation of the brightest ellipticals and the late spirals is driven mostly by global factors, while the segregation between 'normal' ellipticals, S0 galaxies and early spirals is driven primarily by local factors.
We present the results of L-band spectroscopical observations of local bright ULIRGs, performed with ISAAC at the VLT. We discuss the L-band spectral features of seven single sources, and the statistical properties of a complete sample of 15 sources obtained combining our observations with other published 3-4 micron spectra. Our main results are: 1. When a spectral indicator suggesting the presence of an AGN (low equivalent width of the 3.3 micron emission line, steep lambda-f_lambda spectrum, presence of an absorption feature at 3.4 micron) is found, the AGN is always confirmed by independent analysis at other wavelengths. Conversely, in all known AGNs at least one of the above indicators is present. 2. Two new diagnostic diagrams are proposed combining the above indicators, in which starbursts and AGNs are clearly and completely separated. 3. The above diagnostic techniques are possible with spectra of relatively low quality, which can be obtained for several tens of ULIRGs with currently available telescopes. This makes L-band spectroscopy the current best tool to disentangle AGNs and starbursts contributions in ULIRGs. 4. The L-band properties of ULIRGs are heterogeneous. However, we show that all the spectral differences among ULIRGs can be reproduced starting from pure intrinsic AGN and SB spectra and varying two parameters: the amount of dust extinction of the AGN component, and the relative AGN/SB contribution to the bolometric luminosity. 5. Using the above decomposition model, we show that AGNs in ULIRGs have a low dust-to-gas ratio and a dust extinction curve different from Galactic. 6. The estimate of the contribution of AGNs in a complete sample show that AGNs are hosted by ~2/3 of ULIRGs, but their energetic contribution is relevant only in ~20% of the sample.
Radio emission models of colliding wind binaries (CWBs) have been discussed by Dougherty et al. (2003). We extend these models by considering the temporal and spatial evolution of the energy distribution of relativistic electrons as they advect downstream from their shock acceleration site. The energy spectrum evolves significantly due to the strength of inverse-Compton (IC) cooling in these systems, and a full numerical evaluation of the synchrotron emission and absorption coefficients is made. We have demonstrated that the geometry of the WCR and the streamlines of the flow within it lead to a spatially dependent break frequency in the synchrotron emission. We therefore do not observe a single, sharp break in the synchrotron spectrum integrated over the WCR, but rather a steepening of the synchrotron spectrum towards higher frequencies. We also observe that emission from the wind-collision region (WCR) may appear brightest near the shocks, since the impact of IC cooling on the non-thermal electron distribution is greatest near the contact discontinuity (CD). We show that the thermal emission from a CWB can mimic a thermal plus non-thermal composite spectrum if the thermal emission from the WCR becomes comparable to that from the unshocked winds, and obtain a number of insights relevant to models of closer systems such as WR140. Finally, we apply our new models to the very wide system WR147. The acceleration of non-thermal electrons appears to be very efficient in our models of WR147, and we suggest that the shock structure may be modified by feedback from the accelerated particles. (Abridged).
The final stage in the formation of terrestrial planets consists of the
accumulation of ~1000-km ``planetary embryos'' and a swarm of billions of 1-10
km ``planetesimals.'' During this process, water-rich material is accreted by
the terrestrial planets via impacts of water-rich bodies from beyond roughly
2.5 AU. We present results from five high-resolution dynamical simulations.
These start from 1000-2000 embryos and planetesimals, roughly 5-10 times more
particles than in previous simulations.
Each simulation formed 2-4 terrestrial planets with masses between 0.4 and
2.6 Earth masses. The eccentricities of most planets were ~0.05, lower than in
previous simulations, but still higher than for Venus, Earth and Mars. Each
planet accreted at least the Earth's current water budget.
We demonstrate several new aspects of the accretion process: 1) The feeding
zones of terrestrial planets change in time, widening and moving outward. Even
in the presence of Jupiter, water-rich material from beyond 2.5 AU is not
accreted for several millions of years. 2) Even in the absence of secular
resonances, the asteroid belt is cleared of >99% of its original mass by
self-scattering of bodies into resonances with Jupiter. 3) If planetary embryos
form relatively slowly, following the models of Kokubo & Ida, then the
formation of embryos in the asteroid belt may have been stunted by the presence
of Jupiter. 4) Self-interacting planetesimals feel dynamical friction from
other small bodies, which has important effects on the eccentricity evolution
and outcome of a simulation.
The water content and habitability of terrestrial planets are determined
during their final assembly, from ~1000-km ``planetary embryos'' and a swarm of
billions of 1-10 km ``planetesimals.'' During this process, water-rich material
is accreted by terrestrial planets via impacts of water-rich bodies originating
beyond roughly 2.5 AU. We present analysis of water delivery and habitability
in five high-resolution simulations of terrestrial accretion first described in
Raymond, Quinn & Lunine (2006).
In five simulations, we have formed a total of 15 terrestrial planets,
including five potentially habitable planets. Each simulation formed 2-4
planets with masses from 0.4 to 2.6 Earth masses. Every planet from each
simulation accreted at least the Earth's current water budget; most accreted
several times that amount (assuming no impact depletion). Each planet accreted
at least five water-rich embryos and planetesimals from past 2.5 AU; most
accreted 10-20 water-rich bodies. We show that the process of water delivery to
Earth-like planets is less stochastic than previously thought. Terrestrial
planets accrete a large number of water-rich planetesimals in a statistically
robust way, and a few water-rich embryos in a stochastic, ``hit or miss''
process.
In one interesting case, two ~Earth-mass, potentially habitable planets
formed in one system, at the inner and outer edges of the habitable zone. The
eccentricities of both planets oscillate out of phase, with amplitudes of ~0.2.
At certain times, their eccentric orbits cause each planet's orbit to venture
either interioror exterior to the habitable zone.
Thanks to observations performed at the Haute-Provence Observatory, Bouchy et al. recently announced the detection of a 2.2-day orbital period extra-solar planet that transits the disk of its parent star, HD189733. With high level of confidence, we find that Hipparcos likely observed one transit of HD189733b in October 1991, and possibly two others in February 1991 and February 1993. Using the range of possible periods for HD189733b, we find that the probability that none of those events are due to planetary transits but are instead all due to artifacts is lower than 0.15%. Thanks to the 15-year temporal baseline available, we can measure the orbital period of the planet HD189733b with a particularly high accuracy. We obtain a period of 2.218574 (+0.000006/-0.000010) days, corresponding to an accuracy of ~1 second. Such accurate measurements might provide clues for companions presence.
We use numerical MHD to look at the stability of a possible poloidal field in neutron stars (Flowers & Ruderman 1977), and follow its unstable evolution, which leads to the complete decay of the field. We then model a neutron star after the formation of a solid crust of high conductivity. As the initial magnetic field we use the stable `twisted torus' field which was the result of our earlier work (Braithwaite & Nordlund 2005), since this field is likely to exist in the interior of the star at the time of crust formation. We follow the evolution of the field under the influence of diffusion, and find that large stresses build up in the crust, which will presumably lead to cracking. We put this forward as a model for outbursts in soft gamma repeaters.
We present the results of a spectroscopic analysis of the Trapezium cluster stars inside the Orion Nebula. The rotational velocities have been obtained using Fourier analysis method, finding agreement with values derived from the usual method, based on linewidth measurements. The rotational velocity derived for theta 1 Ori C through this method is consistent with the variability of some of its spectral features that have a period of 15.42 days. By means of the fit of H, HeI and HeII observed profiles with FASTWIND synthetic profiles, stellar parameters and wind characteristics have been derived. This methodology let us estimate the errors associated with these parameters. It is found that macroturbulence effects have to be included for a good fit to the HeI-II lines in the spectrum of theta 1 Ori C. By means of a very accurate study, oxygen abundances have been derived for the three B0.5V stars theta 1 Ori A, D and theta 2 Ori B. Final abundances are consistent with the nebular gas-phase results presented in Esteban et al. (2004) and are lower than those given by Cunha and Lambert (1994). Our results suggest a lower dust depletion factor of oxygen than previous estimations for the Orion nebula.
Planetary embryos embedded in a gas disc suffer a decay in semimajor axis -- type I migration -- due to the asymmetric torques produced by the interior and exterior wakes raised by the body (Goldreich & Tremaine 1980; Ward 1986). This presents a challenge for standard oligarchic approaches to forming the terrestrial planets (Kokubo & Ida 1998) as the timescale to grow the progenitor objects near 1 AU is longer than that for them to decay into the Sun. In this paper we investigate the middle and late stages of oligarchic growth using both semi-analytic methods (based upon Thommes et al. 2003) and N-body integrations, and vary gas properties such as dissipation timescale in different models of the protoplanetary disc. We conclude that even for near-nominal migration efficiencies and gas dissipation timescales of ~1 Myr it is possible to maintain sufficient mass in the terrestrial region to form Earth and Venus if the disc mass is enhanced by factors of ~2-4 over the minimum mass model. The resulting configurations differ in several ways from the initial conditions used in previous simulations of the final stages of terrestrial accretion (e.g. Chambers 2001), chiefly in (1) larger inter-embryo spacings, (2) larger embryo masses, and (3) up to ~0.4 Earth masses of material left in the form of planetesimals when the gas vanishes. The systems we produce are reasonably stable for ~100 Myr and therefore require an external source to stir up the embryos sufficiently to produce final systems resembling the terrestrial planets.
(Abridged) We present the first high-resolution (5.6''x5.1'') images of the emission of silicon monoxide (SiO) in the nearby spiral IC342, obtained with the IRAM Plateau de Bure Interferometer. We have mapped the emission of the SiO(2-1) and H13CO+(1-0) lines in a 0.9kpcx1.3kpc region around the nucleus of IC342. The bulk of the line emission comes from a 290pc spiral arm and a r~80pc nuclear ring. The distribution of SiO clouds is mostly anticorrelated with the continuum emission at 87GHz, dominated by thermal free-free bremsstrahlung. The SiO/H13CO+ intensity ratio increases by an order of magnitude from the nuclear ring to the spiral arm. Furthermore the gas kinematics show significant differences between SiO and H13CO+ over the spiral arm, where the linewidths of SiO are 2 times larger than that of H13CO+. The average abundance of SiO in the inner r~320pc, X(SiO)>2x10^{-10}, evidences that shock chemistry is at work in IC342. We have compared the emission of SiO with another tracer of molecular shocks: the emission of methanol (CH3OH). The significant difference of the X(SiO) measured between the spiral arm (~a few 10^{-9}) and the nuclear ring (~10^{-10}) is not echoed by a comparable variation in the SiO/CH3OH intensity ratio. This implies that the typical shock velocities should be similar in both regions. In contrast, the fraction of shocked molecular gas should be 5-7 times larger in the spiral arm (up to ~10% of the available molecular gas mass over the arm region) compared to the nuclear ring. We conclude that the large-scale shocks revealed by the SiO map of IC342 are mostly unrelated with star formation and arise instead in a pre-starburst phase. Shocks are driven by cloud-cloud collisions along the potential well of the IC342 bar. The general implications for the current understanding of galaxy evolution are discussed.
We study the ovi distribution in space and time in a representative section of the Galactic disk by 3D adaptive mesh refinement HD and MHD simulations of the ISM, including the disk-halo-disk circulation. The simulations describe a supernova driven ISM on large (10 kpc) and small (1.25 pc) scales over a sufficiently large timescale (400 Myrs) in order to establish a global dynamical equilibrium. The Ovi column density, N(Ovi), is monitored through lines of sight measurements at different locations in the simulated disk. One has been deliberately chosen to be inside of a hot bubble, like our own Local Bubble, while the other locations are random. We obtain a correlation between N(Ovi) and distance, which is independent of the observer's vantage point in the disk. In particular, the location of the observer inside a hot bubble does not have any influence on the correlation, because the contribution of an individual bubble (with a typical extension of 100 pc) is negligibly small. We find a remarkable agreement between the Ovi column densities (as a function of distance) and the averaged Ovi density (~1.8x10^{-8}$ cm$^{-3}$) in the disk from our simulations and the values observed with Copernicus, and FUSE. Our results strongly support the important r\^ole of turbulent mixing in the distribution of Ovi clumps in the ISM. Supernova induced turbulence is quite strong and unavoidable due to shearing motions in the ISM and operates on a large range of scales.
In this thesis different numerical methods, as well as applications of the methods to a number of current problems in relativistic astrophysics, are presented. In the first part the theoretical foundation and numerical implementation of a new general relativistic magnetohydrodynamics code is discussed. A new form of the equations of motion using global coordinates, but evolving the dynamical variables from the point of view of a local observer is presented. No assumptions are made about the background metric and the design is ready to be coupled with methods solving the full Einstein equations. In the second part of the thesis important results concerning the understanding of collisionless shocks, obtained from experiments with a relativistic charged particle code, are presented. Relativistic collisionless shocks are important in a range of astrophysical objects; in particular in gamma ray burst afterglows and other relativistic jets. It is shown that a strong small scale, fluctuating, and predominantly transversal magnetic field is unavoidably generated by a two-stream instability. The magnetic energy density reaches a few percent of equipartition. A new acceleration mechanism for electrons in ion-electron collisionless shocks is proposed. The mechanism is capable of creating a powerlaw electron distribution in a collisionless shocked region. The non-thermal acceleration of the electrons is directly related to the ion current channels generated by the two-stream instability and is local in nature. Thus the observed radiation field may be tied directly to the local conditions of the plasma and could be a strong handle on the physical processes. (abridged)
We use a principle component approach to contrast different kinds of probes of dark energy, and to emphasize how an array of probes can work together to constrain an arbitrary equation of state history w(z). Rather than using a particular parameterization, we define a prior on the degree of smoothness of w(z). We then examine how informative various experiments will be in constraining the evolution of dark energy given different choices for the prior.
We report the discovery of a debris system associated with the $\sim 30$ Myr old G3/5V star HD 12039 using {\it Spitzer Space Telescope} observations from 3.6 -- 160$\mu$m. An observed infrared excess (L$_{\rm IR}$/L$_{\ast} = 1\times10^{-4}$) above the expected photosphere for $\lambda \gtrsim 14\mu$m is fit by thermally emitting material with a color temperature of T$\sim 110$ K, warmer than the majority of debris disks identified to date around Sun-like stars. The object is not detected at 70$\mu$m with a 3$\sigma$ upper limit 6 times the expected photospheric flux. The spectrum of the infrared excess can be explained by warm, optically thin material comprised of blackbody-like grains of size $\gtrsim 7 \mu$m that reside in a belt orbiting the star at 4--6 AU. An alternate model dominated by smaller grains, near the blow-out size $a\sim 0.5\mu$m, located at 30-40AU is also possible, but requires the dust to have been produced recently since such small grains will be expelled from the system by radiation pressure in $\sim$ few $\times 10^{2}$yrs.
We present new spectroscopic observations of 13 H II regions in the Local Group spiral galaxy M33. The regions observed range from 1 to 7 kpc in distance from the nucleus. Of the 13 H II regions observed, the [O III] 4363 Angstrom line was detected in six regions. Electron temperatures were thus able to be determined directly from the spectra using the [O III] 4959,5007 A/4363 A line ratio. Based on these temperature measurements, oxygen and neon abundances and their radial gradients were calculated. For neon, a gradient of -0.016 +/- 0.017 dex/kpc was computed, which agrees with the Ne/H gradient derived previously from ISO spectra. A gradient of -0.012 +/- 0.011 dex/kpc was computed for O/H, much shallower than was derived in previous studies. The newly calculated O/H and Ne/H gradients are in much better agreement with each other, as expected from predictions of stellar nucleosynthesis. We examine the correlation between the WC/WN ratio and metallicity, and find that the new M33 abundances do not impact the observed correlation significantly. We also identify two new He II-emitting H II regions in M33, the first to be discovered in a spiral galaxy other than the Milky Way. In both cases the nebular He II emission is not associated with Wolf-Rayet stars. Therefore, caution is warranted in interpreting the relationship between nebular He II emission and Wolf-Rayet stars when both are observed in the integrated spectrum of an H II region.
The most puzzling property of the extrasolar planets discovered by recent radial velocity surveys is their high orbital eccentricities, which are very difficult to explain within our current theoretical paradigm for planet formation. Current data reveal that at least 25% of these planets, including some with particularly high eccentricities, are orbiting a component of a binary star system. The presence of a distant companion can cause significant secular perturbations in the orbit of a planet. At high relative inclinations, large-amplitude, periodic eccentricity perturbations can occur. These are known as "Kozai cycles" and their amplitude is purely dependent on the relative orbital inclination. Assuming that every planet host star also has a (possibly unseen, e.g., substellar) distant companion, with reasonable distributions of orbital parameters and masses, we determine the resulting eccentricity distribution of planets and compare it to observations? We find that perturbations from a binary companion always appear to produce an excess of planets with both very high (e>0.6) and very low (e<0.1) eccentricities. The paucity of near-circular orbits in the observed sample implies that at least one additional mechanism must be increasing eccentricities. On the other hand, the overproduction of very high eccentricities observed in our models could be combined with plausible circularization mechanisms (e.g., friction from residual gas) to create more planets with intermediate eccentricities (e=0.1-0.6).
We have successfully used a new on-the-fly mapping technique with the Mopra radiotelescope to image G305.2+0.2 in transitions of 13CO, HCO+, N2H+, CH3CN and CH3OH. All these species appear to be concentrated towards the infrared-quiet methanol maser site G305A (G305.21+0.21). We suggest that this region contains an extremely deeply embedded site of massive star formation, with comparable qualities to the low mass Class 0 stage. The infrared-bright methanol maser site G305B (G305.21+0.20) also exhibits emission in all the mapped transitions, but always at a lower level. We suggest this is because it harbours a site of massive star formation older and more developed than G305.21+0.21. All transitions appear to be extended beyond the size of the Mopra beam (30"). 13CO and HCO+ line wings are suggestive of an outflow in the region, but the spatial resolution of these data is insufficient to identify the powering source. A narrow-lined (1.6 km/s compared to a typical line FWHM of 6.4 km/s) N2H+ source (G305SW) is found 90" to the south-west of the main star forming centres, which does not correspond to any CH3CN or CH3OH source, nor does it correspond well to 13CO or HCO+ emission in the vicinity. We suggest this may be a massive, cold, quiescent and possibly prestellar core.
We have used the Advanced Camera for Surveys on board the Hubble Space Telescope to obtain deep photometry of the NGC 300 spiral galaxy in the Sculptor group. The results have been used to derive an accurate distance determination based on the Tip of the Red Giant Branch distance estimator. Both edge-detection and maximum likelihood methods have been applied, to derive a distance modulus (m-M)_0=26.30 +/- 0.03 +/- 0.12 for edge-detection, and (m-M)_0=26.36 +/- 0.02 +/- 0.12 for maximum likelihood. These results are fully consistent with the recent distance estimate derived from near-IR photometry of Cepheids variable stars in the context of the Araucaria project, (m-M)_0= 26.37 +/- 0.05 +/- 0.03.
We present the results of a deep, wide-area, optical and near-IR survey of massive high-redshift galaxies. The Suprime-Cam on the Subaru telescope was used to obtain BRIz' imaging over 2x940 arcmin^2 fields, while JKs imaging was provided by the SOFI camera at the NTT for a subset of the area. In this paper, we report on the properties of K-band selected galaxies, identified from a total area of ~920 arcmin^2 to K_Vega=19, of which 320 arcmin^2 are complete to K_Vega=20. The BzK selection technique was used to assemble complete samples of about 500 candidate massive star-forming galaxies (sBzKs) and about 160 candidate massive passively evolving galaxies (pBzKs) at 1.4<z<2.5; and the R-K>5 color criterion was used to assemble a sample of about 850 extremely red objects (EROs). Both sBzKs and pBzKs are strongly clustered, at a level at least comparable to that of EROs, with pBzKs appearing more clustered than sBzKs. We estimate the reddening, star formation rates (SFRs) and stellar masses for the ensemble of sBzKs, confirming that to K~20 typical (median) values are M~10^{11}M_sun, SFR 190M_sun yr^{-1}, and E(B-V)~0.44. A correlation is detected such that the most massive galaxies at z~2 are also the most actively star-forming, an effect which can be seen as a manifestation of downsizing at early epochs. The space density of massive pBzKs at z~1.4-2 that we derive is $45\pm15$% that of similarly massive early-type galaxies at z~0. Adding this space density to that of our massive star forming class, sBzKs, in the same redshift range produces a closer comparison with the local early-type galaxy population, naturally implying that we are detecting star formation in a sizable fraction of massive galaxies at z>1.4, which has been quenched by the present day.
We made stereoscopic observations of the Vela Pulsar region with two of the 10 m diameter CANGAROO-III imaging atmospheric Cherenkov telescopes in January and February, 2004, in a search for sub-TeV gamma-rays from the pulsar and surrounding regions. We describe the observations, provide a detailed account of the calibration methods, and introduce the improved and bias-free analysis techniques employed for CANGAROO-III data. No evidence of gamma-ray emission is found from either the pulsar position or the previously reported position offset by 0.13 degree, and the resulting upper limits are a factor of five less than the previously reported flux from observations with the CANGAROO-I 3.8 m telescope. Following the recent report by the H.E.S.S. group of %We also obtained indication TeV gamma-ray emission from the Pulsar Wind Nebula, which is $\sim$0.5 degree south of the pulsar position, we examined this region and found supporting evidence for emission extended over $\sim$0.6 degree.
Using a sample of nearly 20,000 massive early-type galaxies selected from the Sloan Digital Sky Survey, we study the color-magnitude relation for the most luminous (L > 2.2 L^{*}) field galaxies in the redshift range 0.1<z<0.4 in several colors. The intrinsic dispersion in galaxy colors is quite small in all colors studied, but the 40 milli-mag scatter in the bluest colors is a factor of two larger than the 20 milli-mag measured in the reddest bands. While each of three simple models constructed for the star formation history in these systems can satisfy the constraints placed by our measurements, none of them produce color distributions matching those observed. Subdividing by environment, we find the dispersion for galaxies in clusters to be about 11% smaller than that of more isolated systems. Finally, having resolved the red sequence, we study the color dependence of the composite spectra. Bluer galaxies on the red sequence are found to have more young stars than red galaxies; the extent of this spectral difference is marginally better described by passive evolution of an old stellar population than by a model consisting of a recent trace injection of young stars.
Recently, with the goal to study multiplicity of chemically peculiar stars, we carried out a survey of 40 stars using diffraction limited near infrared (IR) imaging with NAOS-CONICA (NACO) at the VLT. Here, we announce the detection of 27 near IR companion candidates around 25 late B-type chemically peculiar stars exhibiting strong overabundances of the chemical elements Hg and Mn in their atmospheres. A key point for the understanding of the abundance patterns in these stars may be connected with binarity and multiplicity. It is intriguing that more than half of the sample of HgMn stars studied previously by speckle interferometry and recently using the adaptive optics system NACO belong to multiple systems.
Stars are sphere of hot gas whose interiors transmit acoustic waves very efficiently. Geologists learn about the interior structure of Earth by monitoring how seismic waves propagate through it and, in a similar way, the interior of a star can be probed using the periodic motions on the surface that arise from such waves. Matthews et al. claim that the star Procyon does not have acoustic surface oscillations of the strength predicted. However, we show here, using ground-based spectroscopy, that Procyon is oscillating, albeit with an amplitude that is only slightly greater than the noise level observed by Matthews et al. using spaced-based photometry.
We present new high resolution neutral hydrogen (H I) images of the Galactic supershell GSH 242-03+37. These data were obtained with the Parkes Radiotelescope as part of the Galactic All-Sky Survey (GASS). GSH 242-03+37 is one of the largest and most energetic H I supershells in the Galaxy with a radius of $565 \pm 65$ pc and an expansion energy of 3x10^{53} ergs. Our images reveal a complicated shell with multiple chimney structures on both sides of the Galactic plane. These chimneys appear capped by narrow filaments about 1.6 kpc above and below the Galactic mid-plane, confirming structures predicted in simulations of expanding supershells. The structure of GSH 242-03+37 is extremely similar to the only other Galactic supershell known to have blown out of both sides of the plane, GSH 277+00+36. We compare the GASS H I data with X-ray and H-alpha, finding no strong correlations.
In this paper, we describe the nonlinear outcome of spiral shocks in protoplanetary disks. Spiral shocks, for most protoplanetary disk conditions, create a loss of vertical force balance in the post-shock region and result in rapid expansion of the gas perpendicular to the disk midplane. This expansion has characteristics similar to hydraulic-jumps, which occur in incompressible fluids. We present a theory to describe the behavior of these hydraulic/shock-jump hybrids (hs-jumps) and then compare the theory to three-dimensional hydrodynamics simulations. We discuss the fully three-dimensional shock structures that hs-jumps produce and discuss possible consequences of hs-jumps for disk mixing, turbulence, and evolution of solids.
With the aim to investigate the overall evolution of UIR band features with hardening of UV radiation (increase of the star's effective temperature) we have analysed ISO spectra for 32 C-rich stars: 20 proto-planetary nebulae and 12 planetary nebulae with Wolf-Rayet central stars. In this contribution we discuss variations in the peak position of UIR bands among analysed objects, and demonstrate that variations in the ``7.7'' to 11.3 microns flux ratio are correlated with the effective temperature (probably due to an increase of the ionization state of their carriers).
Aims. This study focuses on very luminous Mbol<-6.0 mag AGB stars with
J-Ks>1.5 mag and H-Ks>0.4 mag in the LMC, SMC, M31, and M33 from 2MASS data.
Methods.The data were taken from the 2MASS All-Sky Point Source catalogue
archive. We used Virtual Observatory tools and took advantage of its
capabilities at various stages in the analysis.
Results. It is well known that stars with the colors we selected correspond
mainly to carbon stars. Although the most luminous AGBs detected here contain a
large number of carbon stars,they are not included in existing catalogues
produced from data in the optical domain, where they are not visible since they
are dust-enshrouded. A comparison of the AGB stars detected with combined near
and mid-infrared data from MSX and 2MASS in the LMC shows that 10% of the
bright AGB stars are bright carbon stars never detected before and that the
other 50% are OH/IR oxygen rich stars, whereas the 40% that remain were not
cross-matched.
Conclusions. The catalogues of the most luminous AGB stars compiled here are
an important complement to existing data. In the LMC, these bright AGB stars
are centrally located, whereas they are concentrated in an active
star-formation ring in M31. In the SMC and M33, there are not enough of them to
draw definite conclusions, although they tend to be centrally located. Their
luminosity functions are similar for the four galaxies we studied.
A short overview is presented of the role that Low and Intermediate mass stars play in Galactic Chemical Evolution; their action affects key elements and isotopes, like deuterium, He-3, Li-7, carbon and nitrogen, and s-process nuclei. In all those cases, critical uncertainties still remain and are briefly discussed here.
Our recent studies of Very Short Gamma Ray Bursts (VSB) of duration T_{90} \le 100 ms have indicated a significant angular asymmetry and a uniform V/V_{max} distribution from the BATSE data. Here we update these studies, and we extend our research to events observed with KONUS satellite which gives a new insight into the spectra not possible with the BATSE data. KONUS has observed 18 events with T_{90} \le 100 ms duration. These events display considerable numbers of photons with energies above 1 MeV and have photons above 5 MeV in all cases. These appear to be some of the most energetic photons observed from any classes of GRB to date.
In this paper we present the results of time-dependent simulations of dipolar axisymmetric magnetospheres of neutron stars carried out both within the framework of relativistic magnetohydrodynamics and within the framework of resistive force-free electrodynamics. The results of force-free simulations reveal the inability of our numerical method to accommodate the equatorial current sheets of pulsar magnetospheres and raise a question mark over the robustness of this approach. On the other hand, the MHD approach allows to make a significant progress. We start with a nonrotating magnetically dominated dipolar magnetospheres and follow its evolution as the stellar rotation is switched on. We find that the time-dependent solution gradually approaches the steady state that is very close to the stationary solution of the Pulsar Equation found by Contopoulos et al.(1999). This result suggests that other stationary solutions that have the y-point located well inside the light cylinder are unstable. The role of the particle inertia and pressure on the structure and dynamics of MHD magnetospheres is studied in details, as well as the potential implications of the dissipative processes in the equatorial current sheet. We argue that pulsars may have differentially rotating magnetospheres which develop noticeable structural oscillations and that this may help to explain the nature of the sub-pulse phenomena.
We present new Hubble Space Telescope (HST)-NIC3, near-infrared H-band photometry of globular clusters (GC) around NGC 4365 and NGC 1399 in combination with archival HST-WCPC2 and ACS optical data. We find that NGC 4365 has a number of globular clusters with bluer optical colors than expected for their red optical to near-infrared colors and an old age. The only known way to explain these colors is with a significant population of intermediate-age (2-8 Gyr) clusters in this elliptical galaxy. In contrast, NGC 1399 reveals no such population. Our result for NGC 1399 is in agreement with previous spectroscopic work that suggests that its clusters have a large metallicity spread and are nearly all old. In the literature, there are various results from spectroscopic studies of modest samples of NGC 4365 globular clusters. The spectroscopic data allow for either the presence or absence of a significant population of intermediate-age clusters, given the index uncertainties indicated by comparing objects in common between these studies and the few spectroscopic candidates with optical to near-IR colors indicative of intermediate ages. Our new near-IR data of the NGC 4365 GC system with much higher signal-to-noise agrees well with earlier published photometry and both give strong evidence of a significant intermediate-age component. The agreement between the photometric and spectroscopic results for NGC 1399 and other systems lends further confidence to this conclusion, and to the effectiveness of the near-IR technique.
Quasar absorption lines have long been recognized to be a sensitive probe of the abundances, physical conditions, and kinematics of gas in a wide variety of environments including low-density intergalactic regions that probably cannot be studied by any other means. While some pre-Hubble Space Telescope (HST) observations indicated that Mg II absorption lines arise in gaseous galactic halos with a large covering factor, many early QSO absorber studies were hampered by a lack of information about the context of the absorbers and their connections with galaxies. By providing access to crucial ultraviolet resonance lines at low redshifts, deployment of HST and the Far Ultraviolet Spectroscopic Explorer enabled detailed studies of the relationships between QSO absorbers and galaxies. The advent of large surveys such as the Sloan Digital Sky Survey (SDSS) has also advanced the topic by greatly improving the size of absorber and galaxy samples. This paper briefly reviews some observational results on absorber-galaxy connections that have been obtained in the HST/SDSS era, including Mg II absorbers, the low-z Lyman alpha forest, Lyman limit and damped Lyman alpha absorbers, and O VI systems.
New uvby-\beta data are provided for 442 high-velocity and metal-poor stars; 90 of these stars have been observed previously by us, and 352 are new. When combined with our previous two photometric catalogues, the data base is now made up of 1533 high-velocity and metal-poor stars, all with uvby-\beta photometry and complete kinematic data, such as proper motions and radial velocities taken from the literature. Hipparcos, plus a new photometric calibration for M_v also based on the Hipparcos parallaxes, provide distances for nearly all of these stars; our previous photometric calibrations give values for E(b-y) and [Fe/H]. The [Fe/H],V(rot) diagram allows us to separate these stars into different Galactic stellar population groups, such as old-thin-disk, thick-disk, and halo. The X histogram, where X is our stellar-population discriminator combining V(rot) and [Fe/H], and contour plots for the [Fe/H],V(rot) diagram both indicate two probable components to the thick disk. These population groups and Galactic components are studied in the (b-y)_o,M_v diagram, compared to the isochrones of Bergbusch & VandenBerg (2001), to derive stellar ages. The two thick-disk groups have the mean characteristics: ([Fe/H], V(rot), Age, \sigma_W') ~ (-0.7 dex, 120 km/s, 12.5 Gyr, 62.0 km/s), and ~(-0.4, 160, 10.0, 45.8). The seven most metal-poor halo groups, -2.31 <= [Fe/H] <= -1.31, show a mean age of 13.0 +/-0.2 (mean error) Gyr, giving a mean difference from the WMAP results for the age of the Universe of 0.7 +/- 0.3 Gyr. These results for the ages and components of the thick disk and for the age of the Galactic halo field stars are discussed in terms of various models and ideas for the formation of galaxies and their stellar populations.
Gamma-ray burst light curves show quite different patterns: from very simple to extremely complex. We present a temporal and spectral study of the light curves in three energy bands (2-5, 5-10, 10-26 keV) of ten GRBs detected by the Wide Field Cameras on board BeppoSAX. For some events the time profiles are characterized by peaks superposed on a slowly evolving pedestal, which in some cases becomes less apparent at higher energies. We describe this behaviour with the presence of two components (slow and fast) having different variability time scales. We modelled the time evolution of slow components by means of an analytical function able to describe asymmetric rising and decaying profiles. The residual light curves, after the subtraction of the slow components, generally show structures more similar to the original curves in the highest energy band. Spectral study of these two components was performed evaluating their hardness ratios, used also to derive photon indices. Slow components are found generally softer than the fast ones suggesting that their origin is likely different. Being typical photon indices lower than those of the afterglows there is no evidence that the emission processes are similar. Another interesting possibility is that slow components can be related to the presence of a hot photosphere having a thermal spectrum with kT around a few keV superposed to a rapid variable non-thermal emission of the fast component.
[Abridged] One of the most promising approaches to clarify the nature of SN
Ia progenitors consists in studying the delay time distribution (DTD) between
the formation of the progenitor star and its explosion as a SN. We use recent
observations of the evolution of the SN Ia rate with redshift, the dependence
of the SN Ia rate on the colours of the parent galaxiex, and the enhancement of
the SN Ia rate in radio-loud early-type galaxies to derive, for the first time
on robust empirical grounds, the DTD. We find it to be bimodal, in that about
50% of type Ia SNe (dubbed "prompt" SN Ia) explode soon after their stellar
birth, in a time of the order of 10^8 years, while the remaining 50% ("tardy"
SN Ia) have a much broader distribution, well described by an exponential
function with a decay time of about 3 Gyr. It appears that "prompt" SN Ia
originate from stellar progenitors more massive than 5.5 Msun, which have an
explosion efficiency about 3 times higher than that of less massive
progenitors. The bimodality of the DTD, coupled with the well established
systematics in the properties of SN Ia, strongly support the existence of two
classes of progenitors. Several theoretical models, based on both single- and
double-degenerate schemes, can reproduce the evolution of SN Ia rate with
redshift and the dependence on the colors of the hosts, while none can account
for the enhancement of the SN Ia rates in radio-loud Ellipticals.
Since the two classes of SNe dominate at different redshifts, the confident
use of the SN Ia as "standardizable" candles in the local and in the distant
universe requires a good understanding of the properties of the two classes.
We investigate the 50-year old hypothesis that the magnetic fields of the Ap stars are stable equilibria that have survived in these stars since their formation. With numerical simulations we find that stable magnetic field configurations indeed appear to exist under the conditions in the radiative interior of a star. Confirming a hypothesis by Prendergast (1956), the configurations have roughly equal poloidal and toroidal field strengths. We find that tori of such twisted fields can form as remnants of the decay of an unstable random initial field. In agreement with observations, the appearance at the surface is an approximate dipole with smaller contributions from higher multipoles, and the surface field strength can increase with the age of the star. The results of this paper were summarised by Braithwaite & Spruit (2004).
The review presents basic elements of the theory of electromagnetic emission by nonthermal particles propagating in stochastic media. In particular, general theory and a few special regimes of Diffusive Synchrotron Radiation (DSR)arising in the presence of random magnetic/electric fields are analyzed in detail. Possible applications of the DSR theory to astrophysical sources as well as other emission processes typical for the random media are discussed briefly.
We propose an alternative theoretical approach showing how the existence of an extra dimension in Randall-Sundrum model can estimate the correction in the horizon of Schwarzschild and Kerr black holes, and consequently its measurability in terms of the variation of quasar luminosity, which can be caused by a imprint of an extra dimension endowing the geometry of a brane-world scenario in an AdS5 bulk. The rotation effects cause a more prominent correction in Kerr horizon radius than in Schwarzschild (static black hole) radius, via brane-world effects, and the consequent bigger variation in the luminosity in Kerr black holes quasars. This paper is intended to investigate the variation of luminosity due to accretion of gas in Schwarzschild and Kerr black holes (BHs) in the center of quasars, besides also investigating the variation of luminosity in supermassive BHs by brane-world effects, using Randall-Sundrum model.
This paper reports the first full-Sun vacuum ultraviolet (VUV) emission line profile originating from the transition region from the chromosphere to the corona. It is based on a raster scan of the whole solar disk using SUMER/SOHO. The full-Sun spectrum has a spectral resolution which allows an investigation of details in the line profile as well as a thorough comparison to stellar spectra as obtained, e.g. with FUSE or STIS/HST. The full-Sun spectrum shows enhanced emission in the wings, and is well described by a double Gaussian fit with a narrow and a broad component. It is shown that the broad component is due to structures on the solar surface, especially those related to the magnetic chromospheric network. Thus it is proposed that the broad components of other solar-like stars are also a consequence of the mixture of surface structures, and not necessarily a signature of small-scale heating processes like explosive events, as it is commonly argued. A comparison to spectra of luminous cool stars shows that the line asymmetries of these stars might also be a surface structure effect and not or only partly due to opacity effects in their cool dense winds. These comparisons show the potential of high quality full-Sun VUV spectra and their value for the study of solar-stellar connections. As an example, this study proposes that alpha Cen A has a considerably higher amount of magnetic flux concentrated in the chromospheric magnetic network than the Sun.
The trigger system of the Surface Detector (SD) of the Pierre Auger Observatory is described, from the identification of candidate showers ($E>1$ EeV) at the level of a single station, among a huge background (mainly single muons), up to the selection of real events and the rejection of random coincidences at a higher central trigger level (including the reconstruction accuracy). Efficiency of a single station trigger is evaluated using real data , and the high performance of event selection hierarchy will be demonstrated.
After a brief review of galactic cosmic rays in the GeV to TeV energy range, we describe some current problems of interest for particles of very high energy. Particularly interesting are two features of the spectrum, the `knee' above $10^{15}$ eV and the `ankle' above $10^{18}$ eV. An important question is whether the highest energy particles are of extra-galactic origin and, if so, at what energy the transition occurs. A theme common to all energy ranges is use of nuclear abundances as a tool for understanding the origin of the cosmic radiation.
Customary two-dimensional flux transport models for the evolution of the magnetic field at the solar surface do not account for the radial structure and the volume diffusion of the magnetic field. When considering the long-term evolution of magnetic flux, this omission can lead to an unrealistic long-term memory of the system and to the suppression of polar field reversals. In order to avoid such effects, we propose an extension of the flux transport model by a linear decay term derived consistently on the basis of the eigenmodes of the diffusion operator in a spherical shell. A decay rate for each eigenmode of the system is determined and applied to the corresponding surface part of the mode evolved in the flux transport model. The value of the volume diffusivity associated with this decay term can be estimated to be in the range 50--100 km^2/s by considering the reversals of the polar fields in comparison of flux transport simulations with observations. We show that the decay term prohibits a secular drift of the polar field in the case of cycles of varying strength, like those exhibited by the historical sunspot record.
The CGRO/BATSE database includes many types of data such as the 16-channel continuous background or medium energy resolution burst data (CONT and MER data types). We have calculated some four hundred burst's medium energy resolution spectra and Principal Component Analysis has been applied. We found five components can describe GRBs' spectra.
We present numerical calculations of the photon-light-pseudoscalar-boson conversion in the recently discovered binary pulsar system J0737-3039. Light pseudoscalar bosons (LPBs) oscillate into photons in the presence of strong magnetic fields. In the context of this binary pulsar system, this phenomenon attenuates the light beam emitted by one of the pulsars, when the light ray goes through the magnetosphere of the companion pulsar. We show that such an effect is observable in the gamma-ray band since the binary pulsar is seen almost edge-on, depending on the value of the LPB mass and on the strenght of its two-photon coupling. Our results are surprising in that they show a very sharp and significant (up to 50%) transition probability in the gamma-ray ($>$ tens of MeV) domain. The observations can be performed by the upcoming NASA GLAST mission.
A sample of 16 blue compact dwarf galaxies (BCDs) in the Virgo Cluster has been imaged in the near-infrared (NIR) in $J$ and $K_s$ on the 2.1m telescope at OAN-SPM in Mexico. Isophotes as faint as $\mu_J$ = 24 mag arcsec$^{-2}$ and $\mu_{K_s}$ = 23 mag arcsec$^{-2}$ have been reached in most of the targets. Surface brightness profiles can be fitted across the whole range of radii by the sum of two components: a hyperbolic secant (sech) function, which is known to fit the light profiles of dIs, and a Gaussian component, which quantifies the starburst near the centre. Isophotal and total fitted NIR magnitudes have been calculated, along with semimajor axes at $\mu_J$ = 23 mag arcsec$^{-2}$ and $\mu_{K_s}$ = 22 mag arcsec$^{-2}$. The diffuse underlying component and the young starburst have been quantified using the profile fitting. Most color profiles show a constant color, between $J-K_s$=0.7 to 0.9 mag. The diffuse component represents the overwhelming majority of the NIR light for most BCDs, the starburst enhancing the flux by less than about 0.3 mag. Linear correlations were found between the sech scale length and the sech magnitude, and between the sech semimajor axis and the sech magnitude. Overall, galaxies with more luminous diffuse components are larger and brighter in the centre. The central burst correlates with the diffuse component, with brighter BCDs having stronger star-bursts, suggesting that more massive objects are forming stars more efficiently. BCDs lie on the ``fundamental plane'' defined by dwarf irregulars (dISs) in Paper I, following the same relation between sech absolute magnitude, sech central surface brightness, and the hydrogen line-width $W_{20}$, although the scatter is larger than for the dIs. [one sentence cut]
We report a multisite photometric campaign for the Beta Cephei star 12
Lacertae. 750 hours of high-quality differential photoelectric Stromgren,
Johnson and Geneva time-series photometry were obtained with 9 telescopes
during 190 nights. Our frequency analysis results in the detection of 23
sinusoidal signals in the light curves. Eleven of those correspond to
independent pulsation modes, and the remainder are combination frequencies. We
find some slow aperiodic variability such as that seemingly present in several
Beta Cephei stars. We perform mode identification from our colour photometry,
derive the spherical degree l for the five strongest modes unambiguously and
provide constraints on l for the weaker modes. We find a mixture of modes of 0
<= l <= 4. In particular, we prove that the previously suspected rotationally
split triplet within the modes of 12 Lac consists of modes of different l;
their equal frequency splitting must thus be accidental.
One of the periodic signals we detected in the light curves is argued to be a
linearly stable mode excited to visible amplitude by nonlinear mode coupling
via a 2:1 resonance. We also find a low-frequency signal in the light
variations whose physical nature is unclear; it could be a parent or daughter
mode resonantly coupled. The remaining combination frequencies are consistent
with simple light-curve distortions.
The range of excited pulsation frequencies of 12 Lac may be sufficiently
large that it cannot be reproduced by standard models. We suspect that the star
has a larger metal abundance in the pulsational driving zone, a hypothesis also
capable of explaining the presence of Beta Cephei stars in the LMC.
We carried out a statistical analysis of galaxy pairs in hydrodynamical
Lambda-CDM simulations. We focused on the triggering of star formation by
interactions and analysed the enhancement of star formation activity in terms
of orbital parameters. By comparing to a suitable sample of simulated galaxies
without a nearby companion, we find that close encounters (r<30 kpc/h) may
effectively induce star formation. However, our results suggest that the
stability properties of systems and the spatial proximity are both relevant
factors in the process of triggering star formation by tidal interactions. In
order to assess the effects of projection and spurious pairs in observational
samples, we also constructed and analysed samples of pairs of galaxies in the
simulations obtained in projection. We found a good agreement with
observational results with a threshold at rp ~ 25 kpc/h for interactions to
effectively enhance star formation activity.
For pairs within rp < 100 kpc/h, we estimated a ~27% contamination by spurious
pairs, reduced to ~19% for close systems. We also found that spurious pairs
affect more strongly high density regions with 17% of spurious pairs detected
for low density regions compared to 33% found in high density ones. Also, we
analysed the dependence of star formation on environment by defining the usual
projected density parameter for both pairs and isolated galaxies in the
simulations. We find the expected star formation-local density relation for
both galaxies in pairs and without a close companion, with a stronger density
dependence for close pairs which suggests a relevant role for interactions in
driving this relation.
Voids are a prominent feature of the galaxy distribution but their quantitative study is hindered by the lack of a precise definition of what constitutes a void. Here we propose a definition of voids in point distributions that uses methods of discrete stochastic geometry, in particular, Delaunay and Voronoi tessellations, and we construct a new void-finder. We then apply the void-finder to scaling point distributions. First, we find the voids of pure fractals with a transition to homogeneity and show that the rank ordering of the voids also scales (Zipf's law) and, in addition, shows the transition to homogeneity. However, a pure fractal is arguably not a good model of the galaxy distribution, so we construct from a cosmological $N$-body simulation a bifractal mock galaxy sample representing two galaxy populations, which we identify as "wall" and "field" galaxies. The wall galaxy distribution fits a pure fractal with a transition to homogeneity and, furthermore, the rank ordering of its voids shows a scaling range with the right slope plus a transition to homogeneity.
Aql X-1 was observed in a Low Intensity State (LIS), a state that is usually characterized by high optical but low X-ray flux. Our daily monitoring of the source using the 1.3m telescope in Cerro Tololo Inter-America Observatory operated by the Small and Moderate Aperture Research Telescope System (SMARTS) was used to trigger a series of target-of-opportunity (ToO) observations of the source using the Rossi X-ray Timing Explorer satellite (RXTE). The X-ray colors and temporal variability studies suggest that the source was in a powerlaw dominated state featuring high rms variability in the lightcurve and dominance of hard photons during this LIS. The ToO observations were continued until the source made a transition to the canonical thermal dominated or high/soft state.
The relationship between gas-rich galaxies and Ly-alpha absorbers is addressed in this paper in the context of the baryonic content of galaxy halos. Deep Arecibo HI observations are presented of two gas-rich spiral galaxies within 125 kpc projected distance of a Ly-alpha absorber at a similar velocity. The galaxies investigated are close to edge-on and the absorbers lie almost along their major axes, allowing for a comparison of the Ly-alpha absorber velocities with galactic rotation. This comparison is used to examine whether the absorbers are diffuse gas rotating with the galaxies' halos, outflow material from the galaxies, or intergalactic gas in the low redshift cosmic web. The results indicate that if the gas resides in the galaxies' halos it is not rotating with the system and possibly counter-rotating. In addition, simple geometry indicates the gas was not ejected from the galaxies and there are no gas-rich satellites detected down to 3.6 - 7.5 x 10^6 Msun, or remnants of satellites to 5-6 x 10^{18} cm^{-2}. The gas could potentially be infalling from large radii, but the velocities and distances are rather high compared to the high velocity clouds around the Milky Way. The most likely explanation is the galaxies and absorbers are not directly associated, despite the vicinity of the spiral galaxies to the absorbers (58-77 kpc from the HI edge). The spiral galaxies reside in a filament of intergalactic gas, and the gas detected by the absorber has not yet come into equilibrium with the galaxy. These results also indicate that the massive, extended dark matter halos of spiral galaxies do not commonly have an associated diffuse baryonic component at large radii.
We present results of high time resolution photometry of the eclipsing pre-cataclysmic variable NN Ser. We observed 13 primary eclipses of NN Ser using the high-speed CCD camera ULTRACAM and derived times of mid-eclipse, from fitting of light curve models, with uncertainties as low as 0.06 s. The observed rates of period change appear difficult to reconcile with any models of orbital period change. If the observed period change reflects an angular momentum loss, the average loss rate is consistent with the loss rates (via magnetic stellar wind braking) used in standard models of close binary evolution, which were derived from observations of much more massive cool stars. Observations of low-mass stars such as NN Ser's secondary predict rates of ~100 times lower than we observe. We show that magnetic activity-driven changes in the quadrupole moment of the secondary star (Applegate, 1992) fail to explain the period change by an order of magnitude on energetic grounds, but that a light travel time effect caused by the presence of a third body in a long (~ decades) orbit around the binary could account for the observed changes in the timings of NN Ser's mid-eclipses. We conclude that we have either observed a genuine angular momentum loss for NN Ser, in which case our observations pose serious difficulties for the theory of close binary evolution, or we have detected a previously unseen low-mass companion to the binary.
We investigate the connection between collisionless equilibria and the phase-space relation between density $\rho$ and velocity dispersion $\sigma$ found in simulations of dark matter halo formation, $\rho/\sigma^3 \propto r^{-\alpha}$. Understanding this relation will shed light on the physics relevant to collisionless collapse and on the subsequent structures formed. We show that empirical density profiles that provide good fits to N-body halos also happen to have nearly scale-free $\rho/\sigma^3$ distributions when in equilibrium. Since the mechanical equilibrium condition that characterizes the final systems does not by itself lead to such distributions, our findings prompt us to posit that dynamical collapse processes (such as violent relaxation) are responsible for the radial power-law nature of the $\rho/\sigma^3$ distributions of virialized systems.
We present a comparative study of the intensity contrast in synthetic CH-band and violet CN-band filtergrams computed from a high-resolution simulation of solar magnetoconvection. The underlying simulation has an average vertical magnetic field of 250 G with kG fields concentrated in its intergranular lanes, and is representative of a plage region. To simulate filtergrams typically obtained in CH- and CN-band observations we computed spatially resolved spectra in both bands and integrated these spectra over 1 nm FWHM filter functions centred at 430.5 nm and 388.3 nm, respectively. We find that the average contrast of magnetic bright points in the simulated filtergrams is lower in the CN-band by a factor of 0.96. This result strongly contradicts earlier semi-empirical modeling and recent observations, which both etimated that the bright-point contrast in the CN-band is \emph{higher} by a factor of 1.4. We argue that the near equality of the bright-point contrast in the two bands in the present simulation is a natural consequence of the mechanism that causes magnetic flux elements to be particularly bright in the CN and CH filtergrams, namely the partial evacuation of these elements and the concomitant weakening of molecular spectral lines in the filter passbands. We find that the RMS intensity contrast in the whole field-of-view of the filtergrams is 20.5% in the G band and 22.0% in the CN band and conclude that this slight difference in contrast is caused by the shorter wavelength of the latter. Both the bright-point and RMS intensity contrast in the CN band are sensitive to the precise choice of the central wavelength of the filter.
A new method of matrix template matching is presented in the context of pulsar timing analysis. Pulse arrival times are typically measured using only the observed total intensity light curve. The new technique exploits the additional timing information available in the polarization of the pulsar signal by modeling the transformation between two polarized light curves in the Fourier domain. For a number of millisecond pulsars, arrival time estimates derived from polarimetric data are predicted to exhibit greater precision and accuracy than those derived from the total intensity alone. Furthermore, the transformation matrix produced during template matching may be used to calibrate observations of other point sources.
The physical processes involved in diffusion of Galactic cosmic rays in the interstellar medium are addressed. We study the possibility that the nonlinear MHD cascade sets the power-law spectrum of turbulence which scatters charged energetic particles. We find that the dissipation of waves due to the resonant interaction with cosmic ray particles may terminate the Kraichnan-type cascade below wavelengths 10^13 cm. The effect of this wave dissipation has been incorporated in the GALPROP numerical propagation code in order to asses the impact on measurable astrophysical data. The energy-dependence of the cosmic-ray diffusion coefficient found in the resulting self-consistent model may explain the peaks in the secondary to primary nuclei ratios observed at about 1 GeV/nucleon.
The discovery of high-energy (TeV-PeV) neutrinos from gamma-ray bursts (GRBs) would shed light on their intrinsic microphysics by confirming hadronic acceleration in the relativistic jet; possibly revealing an acceleration mechanism for the highest energy cosmic rays. We describe an analysis featuring three models based upon confronting the fireball phenomenology with ground-based and satellite observations of GRB030329, which triggered the High Energy Transient Explorer (HETE-II). Contrary to previous diffuse searches, the expected discrete muon neutrino energy spectra for models 1 and 2, based upon an isotropic and beamed emission geometry, respectively, are directly derived from the fireball description of the prompt gamma-ray photon energy spectrum, whose spectral fit parameters are characterized by the Band function, and the spectroscopically observed redshift, based upon the associated optical transient (OT) afterglow. For comparison, we also consider a model (3) based upon averaged burst parameters and isotropic emission. Strict spatial and temporal constraints (based upon electromagnetic observations), in conjunction with a single, robust selection criterion (optimized for discovery) have been leveraged to realize a nearly background-free search, with nominal signal loss, using archived data from the Antarctic Muon and Neutrino Detector Array (AMANDA-II). Our preliminary results are consistent with a null signal detection, with a peak muon neutrino effective area of ~80 m^2 at ~2 PeV and a flux upper limit of ~0.150 GeV/cm^2/s for model 1. Predictions for IceCube, AMANDA's kilometer scale successor, are compared with those found in the literature. Implications for correlative searches are discussed
Radial velocity observations of K giants have revealed periodic variations for some of the stars. The periods range from approximately 180 to 1000 or more days with velocity amplitudes ranging from approximately 50 m/s to 500 m/s. Except for Iota Draconis (Frink et al. (2002)), all variations are nearly sinusoidal. Companions with zero orbital eccentricity as well as pulsations may cause these radial velocity variations. Additional high resolution spectra were taken in order to reveal which of these mechanisms is at work. No conclusions can be drawn from this work yet, although it seems likely that at least for some stars pulsations are the best explanation. A theoretical study is performed to investigate what kind of pulsations could cause these long period radial velocity variations.
We report on the identification of a soft gamma-ray source, IGR J17204-3554, detected with the IBIS imager on board the INTEGRAL satellite. The source has a 20-100 keV flux of ~3x10^-11 erg cm^-2 s^-1 and is spatially coincident with NGC 6334, a molecular cloud located in the Sagittarius arm of the Milky Way. Diffuse X-ray emission has been reported from this region by ASCA and interpreted as coming from five far-infrared cores located in the cloud. However, the combined ASCA spectrum with a 9 keV temperature was difficult to explain in terms of emission from young pre-main sequence stars known to be embedded in the star forming regions. Detection of gamma-rays makes this interpretation even more unrealistic and suggests the presence of a high energy source in or behind the cloud. Follow up observations with Swift and archival Chandra data allow us to disentangle the NGC6334 enigma by locating an extragalactic object with the proper spectral characteristics to explain the gamma-ray emission. The combined Chandra/IBIS spectrum is well fitted by an absorbed power law with index 1.2+/-0.1, NH=1.4+/-0.1x10^23 cm^-2 and an unabsorbed 2-10 keV flux of 0.5x10^-11 erg cm^-2 s^-1. This column density is in excess of the galactic value implying that we are detecting a background galaxy concealed by the molecular cloud and further hidden by material located either in the galaxy itself or between IGR J17204-3554 and the cloud.
We present the redshift evolution of the restframe galaxy luminosity function (LF) in the red r', i', and z' bands as derived from the FORS Deep Field (FDF). Using the deep and homogeneous I-band selected dataset of the FDF we are able to follow the red LFs over the redshift range 0.5 < z < 3.5. The results are based on photometric redshifts for 5558 galaxies derived from the photometry in 9 filters achieving an accuracy of Delta z / (z_spec+1) ~ 0.03 with only ~ 1 % outliers. Because of the depth of the FDF we can give relatively tight constraints on the faint-end slope alpha of the LF: The faint-end of the red LFs does not show a large redshift evolution and is compatible within 1 sigma to 2 sigma with a constant slope over the redshift range 0.5 < z < 2.0. Moreover, the slopes in r', i', and z' are very similar with a best fitting value of alpha= -1.33 +- 0.03 for the combined bands. There is a clear trend of alpha to steepen with increasing wavelength: alpha_(UV & u')=-1.07 +- 0.04 -> alpha_(g' & B)=-1.25 +- 0.03 -> alpha_(r' & i' & z')=-1.33 +- 0.03. We show that the wavelength dependence of the LF slope can be explained by the relative contribution of different SED-type LFs to the overall LF, as different SED types dominate the LF in the blue and red bands. Furthermore we also derive and analyze the luminosity density evolution of the different SED types up to z ~ 2. Based on the FDF data, we find only a mild brightening of M_star and decrease of phi_star with increasing redshift. Therefore, from <z> ~ 0.5 to <z> \~ 3 the characteristic luminosity increases by ~0.8, ~0.4 and ~0.4 magnitudes in the r', i', and z' bands, respectively. Simultaneously the characteristic density decreases by about 40 % in all analyzed wavebands. [abridged]
We study the broad band (3-100 keV) spectrum of Cygnus X-2 with INTEGRAL. We find that the spectrum is well fitted by a Comptonized component with a seed-photons temperature of ~1 keV, an electron temperature of ~3 keV and an optical depth tau ~ 8. Assuming spherical geometry, the radius of the seed-photons emitting region is ~17 km. The source shows no hard X-ray emission; it was detected only at a 3 sigma level above 40 keV. We also analyzed public ISGRI data of Cyg X--2 to investigate the presence of a hard X-ray component. We report the possible presence of hard X-ray emission in one data set.
The recent search for a stochastic background of gravitational waves with LIGO interferometers has produced a new upper bound on the amplitude of this background in the 100 Hz region. We investigate the implications of the LIGO result on pre-Big-Bang models of the early Universe. We find that in the minimal pre-Big-Bang scenario, LIGO is already beginning to explore interesting regions of the parameter space, although its reach is still weaker than the indirect bound from Big-Bang nucleosynthesis. Future searches by LIGO, in the coming year, and by Advanced LIGO (2009) should further constrain the parameter space, and in some parts even surpass the Big-Bang nucleosynthesis bound. It will be more difficult to constrain the parameter space in non-minimal pre-Big-Bang models, which are characterized by multiple cosmological phases in the yet not well understood stringy phase, and where the higher-order curvature and/or quantum-loop corrections in the string effective action should be included.
We investigate the relationship between the C18O column density and the visual extinction in Chamaeleon I and in a part of the Chamaeleon III molecular cloud. The C18O column densities, N(C18O), are calculated from J=1-0 rotational line data observed with the SEST telescope. The visual extinctions, Av, are derived using JHK photometry from the 2MASS survey and the NICER color excess technique. In contrast with the previous results of Hayakawa et al. (2001), we find that the average N(C18O) / Av ratios are similar in Cha I and Cha III, and lie close to values derived for other clouds, i.e. N(C18O) ~ 2 x 10^14 cm^-2 (Av - 2). We find, however, clear deviations from this average relationship towards individual clumps. Larger than average N(C18O) / Av ratios can be found in clumps associated with the active star forming region in the northern part of Ch a I. On the other hand, some regions in the relatively quiescent southern part of Cha I show smaller than average N(C18O) / Av ratios and also very shallow proportionality between N(C18O) and Av. The shallow proportionality suggests that C18O is heavily depleted in these regions. As the degree of depletion is proportional to the gas density, these regions probably contain very dense, cold cores, which do not stand out in CO mappings. A comparison with the dust temperature map derived from the ISO data shows that the most prominent of the potentially depleted cores indeed coincides with a dust temperature minimum. It seems therefore feasible to use N(C18O) and Av data together for identifying old, dense cores in large scale mappings.
We present new medium-band uvby Stromgren and broad-band VI photometry for the central regions of the globular cluster Omega Cen. From this photometry we have obtained differential reddening estimates relative to two other globular clusters (M13 and NGC288) using a metallicity-independent, reddening-free temperature index, [c]=(u-v)-(v-b) - 0.2(b-y), for hot horizontal-branch (HB) stars (T_e> 8,500K). We estimate color excesses of these hot HB stars using optical and near-infrared colors, and find clumpy extinction variations of almost a factor of two within the area of the cluster core. In particular, the greatest density of more highly reddened objects appears to be shifted along the right ascension axis when compared with less reddened ones. These findings complicate photometric efforts to investigate the star formation history of Omega Cen.
We present an overview of pulsating stars in close binaries, focusing on the question what role the dupliticity plays in triggering and/or modifying stellar oscillations and on how it can help us to interpret the oscillatory behaviour of (one of) the components. We give examples of characteristic types of oscillations observed in binaries: forced oscillations and free oscillations in both, short- and long-period binaries. The importance of studies of oscillations in eclipsing binaries is also pointed out. A list of line-profile and rapid light variables in close binaries with their basic properties is provided. No obvious relations among the orbital eccentricity, orbital frequency, rotational frequency and intrinsic frequencies of oscillations were found. The value and future prospects of asteroseismic studies of binary stars are briefly outlined while the complexity of the problem and its possible complications are also discussed.
The geometric calibration of the Planck satellite is investigated, specifically those parameters which require the use of the science data for their extraction. Methods for the recovery of these geometric-calibration parameters from point source detections in the science data are presented, together with the accuracies which may be achieved. These methods apply to the a posteriori evaluation of these parameters using all the mission data, and may be incorporated into the initial stages of the construction of the Planck final compact source catalogue. It is found that this process achieves the pointing requirements, provided that the geometric-calibration parameters vary only slowly in time. Indeed the errors in the pointing reconstruction due to the geometric calibration parameters may be seen to approach those due to the star tracker.
We describe the Dark Energy Survey (DES), a proposed optical-near infrared survey of 5000 sq. deg of the South Galactic Cap to ~24th magnitude in SDSS griz, that would use a new 3 sq. deg CCD camera to be mounted on the Blanco 4-m telescope at Cerro Telolo Inter-American Observatory (CTIO). The survey data will allow us to measure the dark energy and dark matter densities and the dark energy equation of state through four independent methods: galaxy clusters, weak gravitational lensing tomography, galaxy angular clustering, and supernova distances. These methods are doubly complementary: they constrain different combinations of cosmological model parameters and are subject to different systematic errors. By deriving the four sets of measurements from the same data set with a common analysis framework, we will obtain important cross checks of the systematic errors and thereby make a substantial and robust advance in the precision of dark energy measurements.
We develop a Ly-alpha radiative transfer (RT) Monte Carlo code for cosmological simulations.High resolution,along with appropriately treated cooling can result in simulated environments with very high optical depths.Thus,solving the Ly-alpha RT problem in cosmological simulations can take an unrealistically long time.For this reason,we develop methods to speed up the Ly-alpha RT.With these accelerating methods,along with the parallelization of the code,we make the problem of Ly-alpha RT in the complex environments of cosmological simulations tractable.We test the RT code against simple Ly-alpha emitter models,and then we apply it to the brightest Ly-alpha emitter of a gasdynamics+N-body Adaptive Refinement Tree (ART) simulation at z~8.We find that recombination rather than cooling radiation Ly-alpha photons is the dominant contribution to the intrinsic Ly-alpha luminosity of the emitter,which is ~2.3x10e44 ergs/s.The size of the emitter is pretty small,making it unresolved for currently available instruments.Its spectrum before adding the Ly-alpha Gunn-Peterson absorption (GP) resembles that of static media,despite some net inward radial peculiar motion.This is because for such high optical depths as those in ART simulations,velocities of order some hundreds km/s are not important.We add the GP in two ways.First we assume no damping wing,corresponding to the situation where the emitter lies within the HII region of a very bright quasar,and second we allow for the damping wing.Including the damping wing leads to a maximum line brightness suppression by roughly a factor of ~62.The line fluxes,even though quite faint for current ground-based telescopes,should be within reach for JWST.
Current phenomenology suggests the presence of a compact baryon-poor energy source to cosmological gamma-ray bursts reacting to high-density matter. The association of short and long gamma-ray bursts with hyper- and suspended accretion onto slowly and rapidly spinning black holes predicts weak X-ray afterglow emissions from short bursts, as in GRB050509B and GRB050709. Long gamma-ray bursts are probably the birth place of rapidly spinning high-mass black holes in core-collapse of massive stars, as in GRB030329 with supernova SN2003dh. This predicts a long-duration burst of gravitational radiation powered by the spin-energy of the black hole. In contrast to MeV-neutrino emissions, as in SN1987A, this can be tested by the advanced detectors LIGO and Virgo about once per year up to distances of about 100Mpc. Detection of the expected chirps and long-duration bursts of gravitational waves promises identification of Kerr black holes as the most luminous objects in the Universe.
Many of the current anomalies reported in the Wilkinson Microwave Anisotropy Probe (WMAP) 1-year data disappear after `correcting' for the best-fit embedded Bianchi type VII_h component (Jaffe et al. 2005), albeit assuming no dark energy component. We investigate the effect of this Bianchi correction on the detections of non-Gaussianity in the WMAP data that we previously made using directional spherical wavelets (McEwen et al. 2005a). As previously discovered by Jaffe et al. (2005), the deviations from Gaussianity in the kurtosis of spherical Mexican hat wavelet coefficients are eliminated once the data is corrected for the Bianchi component. This is due to the reduction of the cold spot at Galactic coordinates (l,b)=(209^\circ,-57\circ), which Cruz et al. (2005) claim to be the source of non-Gaussianity introduced in the kurtosis. Our previous detections of non-Gaussianity observed in the skewness of spherical wavelet coefficients are not reduced by the Bianchi correction. Indeed, the most significant detection of non-Gaussianity made with the spherical real Morlet wavelet at a significant level of 98.4% remains (using a very conservative method to estimate the significance). We make our code to simulate Bianchi induced temperature fluctuations publicly available.
The young stellar object MWC 297 has been observed with the VLT interferometer equipped with the AMBER instrument. MWC 297 has been spatially resolved in the continuum with a visibility of 0.50 as well as in the Br gamma emission line where the visibility decrease to a lower value of 0.33. This change in the visibility with the wavelength can be interpreted by the presence of an optically thick disk responsible for the visibility in the continuum and of a stellar wind traced by Br gamma and whose apparent size is 40% larger. We validate this interpretation by building a model of the stellar environment that combines a geometrically thin, optically thick accretion disk model consisting of gas and dust, and a latitude-dependent stellar wind outflowing above the disk surface. The continuum emission and visibilities obtained from this model are fully consistent with the interferometric AMBER data. They agree also with existing optical, near-infrared spectra and other broad-band near-infrared interferometric visibilities. A picture emerges in which MWC 297 is surrounded by an equatorial flat disk that is possibly still accreting and an outflowing wind which has a much higher velocity in the polar region than at the equator. [abridged]
The Smithsonian Hectospec Lensing Survey (SHELS) combines a large deep complete redshift survey with a weak lensing map from the Deep Lens Survey (Wittman et al. 2002; 2005). We use maps of the velocity dispersion based on systems identified in the redshift survey to compare the three-dimensional matter distribution with the two-dimensional projection mapped by weak lensing. We demonstrate directly that the lensing map images the three-dimensional matter distribution obtained from the kinematic data.
First analyses of coincident data of the LOPES (LOfar PrototypE Station) radio antennas with the particle air shower experiment KASCADE-Grande show basic correlations in the observed shower parameters, like the strength of the radio signal and the particle number, or comparing the estimated shower directions. In addition, an improvement of the experimental resolution of the shower parameters reconstructed by KASCADE-Grande can be obtained by including the data of the radio antennas. This important feature will be shown in this article explicitely by an example event.
Radio emission in extensive air showers arises from an interaction with the geomagnetic field and is subject of theoretical studies. This radio emission has advantages for the detection of high energy cosmic rays compared to secondary particle or fluorescence measurement methods. Radio antennas like the LOPES30 antenna system are suited to investigate this emission process by detecting the radio pulses. The characteristic observable parameters like electric field strength and pulse length require a calibration which was done with a reference radio source resulting in an amplification factor representing the system behavior in the environment of the KASCADE-Grande experiment. Knowing the amplification factor and the gain of the LOPES antennas LOPES30 is calibrated absolutely for systematic analyses of the radio emission.
We present here the discovery and characterisation of a very light planet around HD4308. The planet orbits its star in 15.56 days. The circular radial-velocity variation presents a tiny semi-amplitude of 4.1 m/s that corresponds to a planetary minimum mass m2sin(i)=14.1 Earth masses. The planet was unveiled by high-precision radial-velocity measurements obtained with the HARPS spectrograph on the ESO 3.6-m telescope. The radial-velocity residuals around the Keplerian solution are 1.3 m/s, demonstrating the very high quality of the HARPS measurements. Activity and bisector indicators exclude any significant perturbations of stellar intrinsic origin, which supports the planetary interpretation. Contrary to most planet-host stars, HD4308 has a marked sub-solar metallicity ([Fe/H]=-0.31), raising the possibility that very light planet occurrence might show a different coupling with the parent star's metallicity than do giant gaseous extra-solar planets. Together with Neptune-mass planets close to their parent stars, the new planet occupies a position in the mass-separation parameter space that is constraining for planet-formation and evolution theories. The question of whether they can be considered as residuals of evaporated gaseous giant planets, ice giants, or super-earth planets is discussed in the context of the latest core-accretion models.
Using the method suggested in Ref.\cite{zhao} and the Cosmic Microwave Background Radiation (CMB) temperature anisotropy quadrupole observed by COBE, we find that $C_2^T/C_2^S=5.9\pm2.7$, where $C_2^T$ and $C_2^S$ are the CMB anisotropy quadrupole generated by tensor perturbation and scalar perturbation respectively. But if using the $C_2^S$ predicted by the standard inflation-$\Lambda$CDM models, we can find that $C_2^T/C_2^S=0.11\pm0.04$. This result consists with prediction of inflation models, it also consists with the upper limit of the tensor perturbation which got from Ref.\cite{tensor}. From this result, we find the contribution on the CMB anisotropy is not too small to be omitted. So it is necessary to reestimate the cosmological parameters after considering the effect of the tensor perturbation. This result also suggests that the much damping of the CMB anisotropy quadrupole may be only occurring on the contribution of scalar perturbation, but not on the tensor perturbation, this is a new character of this damping, and will be a very constraint on the explanation of it.
In this paper, we study the possibility of building Yang-Mills(YM) field dark
energy models with equation of state across -1. We find that it can not be
realized by a single YM field as the scalar field models, but can be easily
realized by two normal YM fields which gives rise to an equation of state
larger than -1 in the past and less than -1 at the present time. And we also
find that this change must be from $\omega>-1$ to $<-1$, and it also will go to
$\omega=-1$ with the expansion of the Universe.
In this paper the accelerating expansion of our universe at the late cosmic
evolution time in a generally modified (extended) \emph{Chaplygin gas} (Dark
Fluid) model is detailed, which is characterized by two parameters ($m$,
$\alpha$). Different choices to the parameters $m$ and $\alpha$ divide this
model into two main kinds of situation by different properties with
cosmological interests. With proper choices of parameters, we find that this
extended model can realize the phantom divide $w=-1$ (Equation Of State
parameter) crossing phenomenon with interesting ranges of the scale factor
value $a(t)$ corresponding to $w=-1$ and present value of state parameter $w$.
Additionally, through Taylor series expansion of the function $A(a)$ in the
extended Chaplygin gas model, a specific Equation of State is gained. Under the
framework of Friedman-Robertson-Walker cosmic model, it can successfully
explain the accelerating expansion of our universe. However, the value of $w$
in this case is large than -1, that is, indicating it like a quintessence fluid
and no $w=-1$ crossing occurs.
Multiband VRIJHK photometry of the Blazar PKS 0537-441 obtained with the REM telescope from December 2004 to March 2005 is presented. A major period of activity is found with more than four magnitudes variability in the V filter in 50 days and of 2.5 in 10 days. In intensity and duration the activity is similar to that of 1972 reported by Eggen (1973), but it is much better documented. No clear evidence of variability on time-scale of minutes is found. The spectral energy distribution is roughly described by a power-law, with the weaker state being the softer.
We reconsider constraints on Brans-Dicke theories arising from the requirement of successful Big Bang Nucleosynthesis. Such constraints typically arise by imposing that the universe be radiation-dominated at early times, and therefore restricting the contribution that a Brans-Dicke scalar could make to the energy budget of the universe. However, in this paper we show how the dynamics of the Brans-Dicke scalar itself can mimic a portion of the radiation contribution, thereby allowing successful nucleosynthesis with a sizable contribution to the total cosmic energy density. This possibility significantly relaxes the existing bounds on Brans-Dicke fields, and opens the door to new possibilities for early universe cosmology. The necessary fine tunings required by such an arrangement are identified and discussed.
Little is known about the content and distribution of dark matter in spiral galaxies. To break the degeneracy in galaxy rotation curve decompositions, which allows a wide range of dark matter halo density profiles, an independent measure of the mass surface density of stellar disks is needed. Here, we present our ongoing Disk Mass project, using two custom-built Integral Field Units, to measure the vertical velocity dispersion of stars in ~40 spiral galaxies. This will provide a kinematic measurement of the stellar disk mass required to break the degeneracy, enabling us to determine the dark matter properties in spiral galaxies with unprecedented accuracy. Here we present preliminary results for three galaxies with different central disk surface brightness levels.
SBS0335-052 is a well studied Blue Compact Dwarf galaxy with one of the lowest metallicities of any known galaxy. It also contains 6 previously identified Super Star Clusters. We combine archival HST NICMOS images in the Pa alpha line and the 1.6 micron continuum of the eastern component, SBS0335-052E, with other space and ground based data to perform a multi-wavelength analysis of the super star clusters. We concentrate on the southern most clusters, designated S1 and S2, which appear to be the youngest clusters and are the strongest emitters of Pa alpha, radio, and x-ray flux. Our analysis leads to a possible model for S1 and perhaps S2 as a cluster of very young, massive stars with strong stellar winds. The wind density can be high enough to absorb the majority of ionizing photons within less than 1000 AU of the stars, creating very compact HII regions that emit optically thick radiation at radio wavelengths. These winds would then effectively quench the photoionizing flux very close to the stars. This can delay the onset of negative feedback by photoionization and photodissociation on star formation in the clusters. This is significant since SBS0335-052E resembles the conditions that were probably common for high redshift star formation in galaxies near the epoch of reionization.
The Type Ib/c supernova SN 2001em was observed to have strong radio, X-ray, and Halpha emission at an age of about 2.5 yr. Although the radio and X-ray emission have been attributed to an off-axis gamma-ray burst, we model the emission as the interaction of normal SN Ib/c ejecta with a dense, massive (3 Msun) circumstellar shell at a distance about 7 x 10^{16} cm. We investigate two models, in which the circumstellar shell has or has not been overtaken by the forward shock at the time of the X-ray observation. The circumstellar shell was presumably formed by vigorous mass loss with a rate (2-10) x 10^{-3} Msun/yr at 1000-2000 yr prior to the supernova explosion. The hydrogen envelope was completely lost, and subsequently was swept up and accelerated by the fast wind of the presupernova star up to a velocity of 30-50 km/s. Although interaction with the shell can explain most of the late emission properties of SN 2001em, we need to invoke clumping of the gas to explain the low absorption at X-ray and radio wavelengths.
Rotation information for spiral galaxies can be obtained through the observation of different spectral lines. While the Halpha(6563 A) line is often used for galaxies with low to moderate redshifts, it is redshifted into the near-infrared at z>0.4. This is why most high redshift surveys rely on the [OII](3727 A) line. Using a sample of 32 spiral galaxies at 0.155 < z < 0.25 observed simultaneously in both Halpha and [OII] with the Hale 200 inch telescope, the relation between velocity widths extracted from these two spectral lines is investigated, and we conclude that Halpha derived velocities can be reliably compared to high z [OII] measurements. The sample of galaxies is then used along with VIMOS-VLT Deep Survey observations to perform the angular diameter - redshift test to find constraints on cosmological parameters. The test makes it possible to discriminate between various cosmological models, given the upper limit of disc size evolution at the maximum redshift of the data set, no matter what the evolutionary scenario is.
The braneworld model of Dvali, Gabadadze and Porrati (DGP) provides an intriguing modification of gravity at large distances and late times. By embedding a three-brane in an uncompactified extra dimension with separate Einstein-Hilbert terms for both brane and bulk, the DGP model allows for an accelerating universe at late times even in the absence of an explicit vacuum energy. We examine the evolution of cosmological perturbations on large scales in this theory. At late times, perturbations enter a DGP regime in which the effective value of Newton's constant increases as the background density diminishes. This leads to a suppression of the integrated Sachs-Wolfe effect, bringing DGP gravity into slightly better agreement with WMAP data than conventional LCDM. However, we find that this is not enough to compensate for the significantly worse fit to supernova data and the distance to the last-scattering surface in the pure DGP model. LCDM is, therefore, a better fit.
We provide the first age estimates for two recently discovered white dwarf-red subdwarf systems, LHS 193AB and LHS 300AB. These unusual systems provide a new opportunity for linking the reliable age estimates for the white dwarfs to the (measurable) metallicities of the red subdwarfs. We have obtained precise photometry in the $V_{J}R_{KC}I_{KC}JH$ bands and spectroscopy covering from 6000\AA to 9000\AA for the two new systems, as well as for a comparison white dwarf-main sequence red dwarf system, GJ 283 AB. Using model grids available in the literature, we estimate the cooling age as well as temperature, surface gravity, mass, progenitor mass and {\it total} lifetimes of the white dwarfs. The results indicate that the two new systems are probably ancient thick disk objects with ages of at least 6-9 Gyr. We also conduct searches of red dwarf and white dwarf compendia from SDSS data and the L{\'e}pine Shara Proper Motion (LSPM) catalog for additional common proper motion white dwarf-red subdwarf systems. Only seven new candidate systems are found, which indicates the rarity of these systems.
We investigate the question of whether ambipolar diffusion (ion-neutral drift) determines the smallest length and mass scale on which structure forms in a turbulent molecular cloud. We simulate magnetized turbulence in a mostly neutral, uniformly driven, turbulent medium, using a three-dimensional, two-fluid, magnetohydrodynamics (MHD) code modified from Zeus-MP. We find that substantial structure persists below the ambipolar diffusion scale because of the propagation of compressive slow MHD waves at smaller scales. Contrary to simple scaling arguments, ambipolar diffusion thus does not suppress structure below its characteristic dissipation scale as would be expected for a classical diffusive process. We have found this to be true for the magnetic energy, velocity, and density. Correspondingly, ambipolar diffusion leaves the clump mass spectrum unchanged. Ambipolar diffusion appears unable to set a characteristic scale for gravitational collapse and star formation in turbulent molecular clouds.
The details of ignition of Type Ia supernovae remain fuzzy, despite the
importance of this input for any large-scale model of the final explosion.
Here, we begin a process of understanding the ignition of these hotspots by
examining the burning of one zone of material, and then investigate the
ignition of a detonation due to rapid heating at single point.
We numerically measure the ignition delay time for onset of burning in
mixtures of degenerate material and provide fitting formula for conditions of
relevance in the Type Ia problem. Using the neon abundance as a proxy for the
white dwarf metallicity, we then find that ignition times can decrease by ~20%
with addition of even 5% of neon by mass. When temperature fluctuations that
successfully kindle a region are very rare, such a reduction in ignition time
can increase the probability of ignition by orders of magnitude.
We then consider the ignition of a detonation by an explosive energy input in
one localized zone, eg a Sedov blast wave leading to a shock-ignited
detonation. Building on previous work on curved detonations, we find that
surprisingly large inputs of energy are required to successfully launch a
detonation, leading to required matchheads of ~4500 detonation thicknesses -
tens of centimeters to hundreds of meters - which is orders of magnitude larger
than naive considerations might suggest. This is a very difficult constraint to
meet for some pictures of a deflagration-to-detonation transition, such as a
Zel'dovich gradient mechanism ignition in the distributed burning regime.
The optical afterglow spectrum of GRB 050401 (at z=2.8992+/-0.0004) shows the presence of a large damped Ly-alpha absorber (DLA), with log N(HI)=22.5+/-0.3. This is the highest column density DLA ever observed, and is nearly an order of magnitude larger than any DLA observed in QSO spectra. The X-ray spectrum shows absorption above Galactic of log N(H)=22.21^{+0.06}_{-0.08} (assuming solar abundances and a redshift z=2.8992). The comparison of the X-ray column density measurement, which is dominated by metal absorption, and the optical H(I) column, allows us to derive [X/H]=-0.3+/-0.3. From the optical spectrum, we infer a zinc abundance of [Zn/H] = -0.8+/-0.4. We can then derive [alpha/Zn] = 0.5+/-0.2, suggestive of an overabundance of alpha-elements in the absorber, consistent with alpha-element overabundances observed in DLAs with similar Fe-group metallicities. There is evidence of dust depletion in Fe, Si and Cr and the optical spectrum is very reddened. This can be well reproduced with an SMC extinction curve, with A_V=0.62+/-0.06. However the total extinction can also be constrained from the optical--X-ray SED, to be 0.5>A_V>4.5, independent of assumptions about the shape of the extinction curve. These limits are less than the A_V=9.1^{+1.4}_{-1.5} inferred from the soft X-ray absorption. This discrepancy implies a low dust-to-metals ratio. 'Grey' extinction cannot explain the discrepancy, even with an arbitrarily flat extinction curve (i.e. large absorption with little reddening), but a large alpha-element overabundance can. If such overabundance is common in afterglow absorbers it may explain the high X-ray column densities with little optical reddening observed in afterglow spectra, and would necessitate a cautious approach to dust content based on metallicity arguments in these environments.
We consider the distribution of local supermassive black hole Eddington ratios and accretion rates, accounting for the dependence of radiative efficiency and bolometric corrections on the accretion rate. We find that black hole mass growth, both of the integrated mass density and the masses of most individual objects, must be dominated by an earlier, radiatively efficient, high accretion rate stage, and not by the radiatively inefficient low accretion rate phase in which most local supermassive black holes are currently observed. This conclusion is particularly true of supermassive black holes in elliptical host galaxies, as expected if they have undergone merger activity in the past which would fuel quasar activity and rapid growth. We discuss models of the time evolution of accretion rates and show that they all predict significant mass growth in a prior radiatively efficient state. The only way to avoid this conclusion is through careful fine-tuning of the accretion/quasar timescale to a value that is inconsistent with observations. Our results agree with a wide range of observational inferences drawn from the quasar luminosity function and X-ray background synthesis models, but our approach has the virtue of being independent of the modeling of source populations. Models in which black holes spend the great majority of their time in low accretion rate phases are thus completely consistent both with observations implying mass gain in relatively short, high accretion rate phases and with the local distribution of accretion rates.
The Milky Way contains several distinct old stellar components that provide a fossil record of its formation. We can understand their spatial distribution and kinematics in a hierarchical formation scenario by associating the proto-galactic fragments envisaged by Searle and Zinn (1978) with the rare peaks able to cool gas in the cold dark matter density field collapsing at redshift z>10. We use hierarchical structure formation simulations to explore the kinematics and spatial distribution of these early star-forming structures in galaxy haloes today. Most of the proto-galaxies rapidly merge, their stellar contents and dark matter becoming smoothly distributed and forming the inner Galactic halo. The metal-poor globular clusters and old halo stars become tracers of this early evolutionary phase, centrally biased and naturally reproducing the observed steep fall off with radius. The most outlying peaks fall in late and survive to the present day as satellite galaxies. The observed radial velocity dispersion profile and the local radial velocity anisotropy of Milky Way halo stars are successfully reproduced in this model. If this epoch of structure formation coincides with a suppression of further cooling into lower sigma peaks then we can reproduce the rarity, kinematics and spatial distribution of satellite galaxies as suggested by Bullock et al. (2000). Reionisation at z=12+/-2 provides a natural solution to the missing satellites problem. Measuring the distribution of globular clusters and halo light on scales from galaxies to clusters could be used to constrain global versus local reionisation models. If reionisation occurs contemporary, our model predicts a constant frequency of blue globulars relative to the host halo mass, except for dwarf galaxies where the average relative frequencies become smaller.
We present new measurements of the quasar autocorrelation from a sample of \~80,000 photometrically-classified quasars taken from SDSS DR1. We find a best-fit model of $\omega(\theta) = (0.066\pm^{0.026}_{0.024})\theta^{-(0.98\pm0.15)}$ for the angular autocorrelation, consistent with estimates from spectroscopic quasar surveys. We show that only models with little or no evolution in the clustering of quasars in comoving coordinates since z~1.4 can recover a scale-length consistent with local galaxies and Active Galactic Nuclei (AGNs). A model with little evolution of quasar clustering in comoving coordinates is best explained in the current cosmological paradigm by rapid evolution in quasar bias. We show that quasar biasing must have changed from b_Q~3 at a (photometric) redshift of z=2.2 to b_Q~1.2-1.3 by z=0.75. Such a rapid increase with redshift in biasing implies that quasars at z~2 cannot be the progenitors of modern L* objects, rather they must now reside in dense environments, such as clusters. Similarly, the duration of the UVX quasar phase must be short enough to explain why local UVX quasars reside in essentially unbiased structure. Our estimates of b_Q are in good agreement with recent spectroscopic results, which demonstrate the implied evolution in b_Q is consistent with quasars inhabiting halos of similar mass at every redshift. Treating quasar clustering as a function of both redshift and luminosity, we find no evidence for luminosity dependence in quasar clustering, and that redshift evolution thus affects quasar clustering more than changes in quasars' luminosity. We provide a new method for quantifying stellar contamination in photometrically-classified quasar catalogs via the correlation function.
(abridged) We study the mass assembly history (MAH) of dark matter haloes. We compare MAHs obtained using (i) merger trees constructed with the extended Press-Schechter (EPS) formalism, (ii) numerical simulations, and (iii) the Lagrangian perturbation code PINOCCHIO. We show that the PINOCCHIO MAHs are in excellent agreement with those obtained using numerical simulations. Using a suite of 55 PINOCCHIO simulations, with 256^3 particles each, we study the MAHs of 12,924 cold dark matter haloes in a \LambdaCDM concordance cosmology. We show that haloes less massive than the characteristic non-linear mass scale establish their potential wells much before they acquire most of their mass. The time when a halo reaches its maximum virial velocity roughly divides its mass assembly into two phases, a fast accretion phase which is dominated by major mergers, and a slow accretion phase dominated by minor mergers. Each halo experiences about 3 \pm 2 major mergers since its main progenitor had a mass equal to one percent of the final halo mass. This major merger statistic is found to be virtually independent of halo mass. However, the average redshift at which these major mergers occur, is strongly mass dependent, with more massive haloes experiencing their major mergers later.
We have imaged the recently discovered stellar overdensity located approximately one core radius from the center of the Fornax dwarf spheroidal galaxy using the Magellan Clay 6.5m telescope with the Magellan Instant Camera (MagIC). Superb seeing conditions allowed us to probe the stellar populations of this overdensity and of a control field within Fornax to a limiting magnitude of R=26. The color-magnitude diagram of the overdensity field is virtually identical to that of the control field with the exception of the presence of a population arising from a very short (less than 300 Myr in duration) burst of star formation 1.4 Gyr ago. Coleman et al. have argued that this overdensity might be related to a shell structure in Fornax that was created when Fornax captured a smaller galaxy. Our results are consistent with this model, but we argue that the metallicity of this young component favors a scenario in which the gas was part of Fornax itself.
The scale lengths of the old stars and ionized gas distributions are compared for similar samples of Virgo Cluster members and field spiral galaxies via Halpha and broad R-band surface photometry. While the R-band and Halpha scale lengths are, on average, comparable for the combined sample, we find significant differences between the field and cluster samples. While the Halpha scale lengths of the field galaxies are a factor of 1.14 +- 0.07 longer on average than their R-band scale lengths, the Halpha scale lengths of Virgo Cluster members are on average 20% smaller than their R-band scale lengths. Furthermore, in Virgo, the scale length ratios are correlated with the size of the star-forming disk: galaxies with smaller overall Halpha extents also show steeper radial falloff of star formation activity. At the same time, we find no strong trends in scale length ratio as a function of other galaxy properties including galaxy luminosity, inclination, morphological type, central R--band light concentration, or bar type. Our results for Halpha emission are similar to other results for dust emission, suggesting that Halpha and dust have similar distributions. The environmental dependence of the Halpha scale length places additional constraints on the evolutionary process(es) that cause gas depletion and a suppression of the star formation rate in clusters of galaxies.
Measurements are reported on the fluorescence of air as a function of depth in electromagnetic showers initiated by bunches of 28.5 GeV electrons. The light yield is compared with the expected and observed depth profiles of ionization in the showers. It validates the use of atmospheric fluorescence profiles in measuring ultra high energy cosmic rays.
I review recent results on the spatial distribution of substructure in CDM halos. I show that the spatial distribution of subhalos is anisotropic and generally prolate with a long axis that is closely aligned with the long axis of the total mass distribution of the host halo. I show that the correlation between the subhalo distribution and the long axis of the host halo is strong both in dissipationless and dissipational gasdynamical simulations. More massive subhalos tend to be more strongly clustered along the major axis of the host halo reflecting filamentary accretion. The anisotropy of subhalos has potential implications for the interpretation of several observations in the Local Group and beyond. For example, I show that while the mean projected mass fraction in substructure in the central regions of CDM halos is fsub \approx 0.4%, fsub is a strong function of projection angle and is ~ 5 to 6 times higher for projections that are nearly collinear with the major axis of the host halo.
The new solar composition, when applied to compute a model of the Sun, leads to serious disagreement between the predictions of the model and the observations obtained by helioseismology. New measurements of the coronal Ne/O abundance ratio in nearby stars using X-ray spectra typically find high values of Ne/O=0.4 rather than 0.15 normally adopted for the Sun. Drake & Testa (2005) suggest that this high Ne/O ratio is appropriate also for the Sun, which would bring the solar models back in agreement with the helioseismological observations. Here we present arguments why the high Ne/O ratio is unlikely to be applicable to the Sun.
The discovery of the highly relativistic neutron star (NS) binary (in which both NS's are pulsars) not only increases the estimated merging rate for the two NS's by a large factor, but also adds the missing link in the double helium star model of binary NS evolution. This model gives $\sim 20$ times more gravitational merging of low-mass black-hole (LMBH), NS binaries than binary NS's, whatever the rate for the latter is.
In the light of recent observations in which short $\gamma$-ray bursts are
interpreted as arising from black-hole, neutron-star or neutron-star,
neutron-star mergings we would like to review our research on the evolution of
compact binaries, especially those containing neutron stars. These were carried
out with predictions for LIGO in mind, but are directly applicable to short
$\gamma$-ray bursts in the interpretation above.
Most important in our review is that we show that the standard scenario for
evolving double neutron star binaries always ends up with a low-mass black
hole, neutron star binary. This is where the factor $\sim 20$ in the ratio of
these to double neutron star binaries comes from. In fact, the double neutron
star binaries can {\it only} be evolved if their two giant progenitors burn
helium at the same time. This requires the two progenitors to be within 4% of
each other in mass and it is this special requirement that results in the
double neutron star binaries being relatively scarce compared with the low-mass
black hole neutron star binaries.
Our scenario of double neutron star binaries as having been proceeded by a
double He-star binary is collecting observational support in terms of the
nearly equal neutron star masses within a given close binary.
Double neutrons are especially important because they give most accurate informations on the masses of neutron stars. Observations on double neutron stars show that all masses of the neutron stars are below 1.5$\msun$. Furthermore, two neutron stars in a given double pulsar are nearly equal in mass. With hypercritical accretion, we found that the probability of having companion mass $>1.5\msun$ is larger than 90%, while there is no observations on such systems. We believe that those companions with masses higher than $1.5\msun$ went into black holes, which is consistent with our preferred maximum neutron star mass $M_{NS}^{max} \approx 1.5\msun$ due to the kaon condensation. In this work, we point out that the black-hole neutron star binaries are 10 times more dominant than double neutron star binaries. As a result, black-hole, neutron star binaries can increase the LIGO detection rate by a factor 20.
The event of September 4th, 2005 (GRB 050904) was detected by the SWIFT/BAT experiment. The source was found to be at a redshift z = 6.29, corresponding to an age of the Universe which is only 7% of the present epoch. The 25 cm TAROT robotic telescope3 was able to catch the bright flare emitted by GRB 050904 at the time of the prompt high-energy event. In this letter we discuss the flux and the behaviour of the optical emission during the prompt high-energy emission and the early afterglow. We combine our data with simultaneous observations performed in X-rays and we analyze the broad-band spectrum. We show that the optical emission is too bright to have the same origin as the high energy photons. Both the temporal and spectral behaviour of the event are difficult to explain within the current internal or reverse shock models. These observations lead us to emphasize the similarity of GRB 050904 with GRB 990123, a remarkable gamma-ray burst whose optical emission reached 9th magnitude4. While GRB 990123 was, until now, considered as a unique event, our observations suggest the existence of a population of GRBs which have very large isotropic equivalent energies and extremely bright optical counterparts. The luminosity of these GRBs is such that they are easily detectable through the entire universe. Since we can detect them to very high redshift even with small aperture telescopes like TAROT, they will constitute powerful tools for the exploration of the high-redshift Universe and might be used to probe the first generation of stars.
The relation between the central mass and quasar luminosity (M_BH \propto L^{\alpha}FHWM^2) links a given Eddington ratio with a value of H_0, within a cosmology with fixed (\Omega_m,\Omega_{\Lambda}). We point out that because the relation is calibrated at low z using distance independent reverberation mapping to get the BLR size, the derived M_BH interestingly does not depend on H_0, while L/L_Edd is sensitive to H_0, but rather robust to changes of \Omega_{\Lambda} in the standard flat model. This means, e.g., that enough of extragalactic objects radiating at the Eddington limit could be used to study the global Hubble constant in a new way, bypassing the local distance ladder. The method could become practical when systematic errors in derived M_BH are understood and objects with L /leq L_Edd can be independently identified. As an illustration, if we take a sample of tranquil very luminous quasars in the redshift range 0.5 < z < 1.6, and assume that they are radiating with L_bol \leq L_Edd, then the usual numeric factors used for calculating M_BH and L_bol would lead to the result that the Hubble constant must be larger than 45 km/s/Mpc.
We propose a new kind of interferometric array that yields images of high dynamic range and large field. The numerous individual apertures in this array form a pattern related to a Fresnel zone plate. This array can be used for astrophysical imaging over a broad spectral bandwidth spanning from the U.V. (50 nanometers) to the I.R. (20 microns). Due to the long focal lengths involved, this instrument requires formation-flying of two space borne vessels. We present the concept and study the S/N ratio in different situations, then apply these results to probe the suitability of this concept to detect exoplanets.
We discuss a series of Earthshine spectra obtained with the NTT/EMMI instrument between 320nm and 1020nm with a resolution of R~450 in the blue and R~250 in the red. These ascending and descending Moon's Earthshine spectra taken from Chile give disk-averaged spectra for two different Earth's phases. The spectra show the ozone (Huggins and Chappuis bands), oxygen and water vapour absorption bands, and also the stronger Rayleigh scattering in the blue. Removing the known telluric absorptions reveals a spectral feature around 700nm which is attributed to the vegetation stronger reflectivity in the near-IR, so-called vegetation red-edge.
Based on 5344 quasar spectra taken from the SDSS Data Release 2, the dependences of various emission-line flux ratios on redshift and quasar luminosity are investigated in the ranges 2.0 < z < 4.5 and -24.5 > M_B > -29.5$. We show that the emission lines in the composite spectra are fitted better with power-law profiles than with double Gaussian or modified Lorentzian profiles, and in particular we show that the power-law profiles are more appropriate to measure broad emission-line fluxes than other methods. The composite spectra show that there are statistically significant correlations between quasar luminosity and various emission-line flux ratios, such as NV/CIV and NV/HeII, while there are only marginal correlations between quasar redshift and emission-line flux ratios. We obtain detailed photoionization models to interpret the observed line ratios. The correlation of line ratios with luminosity is interpreted in terms of higher gas metallicity in more luminous quasars. For a given quasar luminosity, there is no metallicity evolution for the redshift range 2.0 < z < 4.5. The typical metallicity of BLR gas clouds is estimated to be Z ~ 5 Z_sun, although the inferred metallicity depends on the assumed BLR cloud properties, such as their density distribution function and their radial distribution. The absence of a metallicity evolution up to z ~ 4.5 implies that the active star-formation epoch of quasar host galaxies occurred at z > 7.
The Standard Model Extension formulated by Colladay and Kosteleck\'y is reviewed in the framework of the $^4He$ primordial abundance. Upper bounds on coefficients for the Lorentz violation are derived using the present observational data.
In their survey paper of prestellar cores with SCUBA, Kirk et al. (2005) have discarded two of our papers on L183 (Pagani et al. 2003, 2004). However these papers bring two important pieces of information that they cannot ignore. Namely, the real structure of L183 and the very poor correlation between submillimeter and far infrared (FIR) dust emission beyond \Avb $\approx$ 15 mag. Making the erroneous assumption that it is the same dust that we are seeing in emission at both 200 and 850 $\mu$m, they derive constant temperatures which are only approximate, and column densities which are too low. In fact dust temperatures do decrease inside dark clouds and the FIR emission is only tracing the outer parts of the dark clouds (Pagani et al. 2004)
Recently an additional technique was applied to investigate the properties of kHz QPOS, i.e. the analysis of the distribution of frequency ratios or frequencies themselves. I review the results of such work on the data from ScoX-1: Abramowicz et al. (2003), which was later criticized by Belloni et al.(2005). I conclude that the findings of the latter paper are consistent with results presented earlier: kHz QPOs cluster around the value corresponding to the frequency ratio of 2/3. I also discuss the random walk model of kHz QPOs and possible future observations needed to verify it.
Recent high resolution numerical simulations have shown that the interstellar atomic hydrogen clouds have a complex two-phase structure. Since molecular clouds form through the contraction of HI gas, the question arises of whether this structure is maintained in the molecular phase or not. Here we investigate whether the warm neutral atomic hydrogen (WNM) can exist in molecular clouds. We calculate how far a piece of WNM which is not heated by the UV photons could penetrate into the cloud, and estimate that in the absence of any heating it is unlikely that large fraction of WNM exists inside molecular clouds. We then consider two possible heating mechanisms, namely dissipation of turbulent energy and dissipation of MHD waves propagating in the WNM inside the cloud. We find that the second one is sufficient to allow the existence of WNM inside molecular clouds. We speculate that channels of magnetized WNM permeatting the molecular clouds may allow to inject energy very efficiently allowing to sustain the internal turbulence which otherwise decay in a crossing time.
We report recent results of a WIMP dark matter search experiment using 310g of CaF2(Eu) scintillator at Kamioka Observatory. We chose a highly radio-pure crystal, PMTs and radiation shields, so that the background rate decreased considerably. We derived limits on the spin dependent WIMP-proton and WIMP-neutron coupling coefficients, a_p and a_n. The limits excluded a part of the parameter space allowed by the annual modulation observation of the DAMA NaI experiment.
We study the evolution of an embedded protoplanet in a circumstellar disk
using the 3D-Radiation Hydro code TRAMP, and treat the thermodynamics of the
gas properly in three dimensions. The primary interest of this work lies in the
demonstration and testing of the numerical method. We show how far numerical
parameters can influence the simulations of gap opening. We study a standard
reference model under various numerical approximations. Then we compare the
commonly used locally isothermal approximation to the radiation hydro
simulation using an equation for the internal energy. Models with different
treatments of the mass accretion process are compared. Often mass accumulates
in the Roche lobe of the planet creating a hydrostatic atmosphere around the
planet. The gravitational torques induced by the spiral pattern of the disk
onto the planet are not strongly affected in the average magnitude, but the
short time scale fluctuations are stronger in the radiation hydro models.
An interesting result of this work lies in the analysis of the temperature
structure around the planet. The most striking effect of treating the
thermodynamics properly is the formation of a hot pressure--supported bubble
around the planet with a pressure scale height of H/R ~ 0.5 rather than a thin
Keplerian circumplanetary accretion disk. We also observe an outflow of gas
above and below the planet during the gap opening phase.
Using the Effelsberg radio telescope at 4.85GHz and 8.35 GHz we discovered large symmetric lobes of polarized radio emission around the strongly HI deficient Virgo cluster spiral galaxy NGC4569. These lobes extend up to 24 kpc from the galactic disk. Our observations were complemented by 1.4 GHz continuum emission from existing HI observations. This is the first time that such huge radio continuum lobes are observed in a cluster spiral galaxy. The eastern lobe seems detached and has a flat spectrum typical for in-situ cosmic ray electron acceleration. The western lobe is diffuse and possesses vertical magnetic fields over its whole volume. The lobes are not powered by an AGN, but probably by a nuclear starburst producing >10^5 supernovae which occurred ~30 Myr ago. Since the radio lobes are symmetric, they resist ram pressure due to the galaxy's rapid motion within the intracluster medium.
We investigate the response of an accretion disk to the presence of a
perturbing protoplanet embedded in the disk through time dependent
hydrodynamical simulations. The disk is treated as a two-dimensional viscous
fluid and the planet is kept on a fixed orbit. We run a set of simulations
varying the planet mass, and the viscosity and temperature of the disk. All
runs are followed until they reach a quasi-equilibrium state.
We find that for planetary masses above a certain minimum mass, already 3
M_Jup for a viscosity of nu = 10^{-5}, the disk makes a transition from a
nearly circular state into an eccentric state. Increasing the planetary mass
leads to a saturation of disk eccentricity with a maximum value of around 0.25.
The transition to the eccentric state is driven by the excitation of an m=2
spiral wave at the outer 1:3 Lindblad resonance. The effect occurs only if the
planetary masses are large enough to clear a sufficiently wide and deep gap to
reduce the damping effect of the outer 1:2 Lindblad resonance. An increase in
viscosity and temperature in the disk, which both tend to close the gap, have
an adverse influence on the disk eccentricity.
In the eccentric state the mass accretion rate onto the planet is greatly
enhanced, an effect that may ease the formation of massive planets beyond about
5 M_Jup that are otherwise difficult to reach.
We report on a possible association of the recently discovered very high-energy $\gamma$-ray source HESS J1825--137 with the pulsar wind nebula (commonly referred to as G 18.0--0.7) of the $2.1\times 10^{4}$ year old Vela-like pulsar PSR B1823--13. HESS J1825--137 was detected with a significance of 8.1 $\sigma$ in the Galactic Plane survey conducted with the H.E.S.S. instrument in 2004. The centroid position of HESS J1825--137 is offset by 11\arcmin south of the pulsar position. \emph{XMM-Newton} observations have revealed X-ray synchrotron emission of an asymmetric pulsar wind nebula extending to the south of the pulsar. We argue that the observed morphology and TeV spectral index suggest that HESS J1825--137 and G 18.0--0.7 may be associated: the lifetime of TeV emitting electrons is expected to be longer compared to the {\it XMM-Newton} X-ray emitting electrons, resulting in electrons from earlier epochs (when the spin-down power was larger) contributing to the present TeV flux. These electrons are expected to be synchrotron cooled, which explains the observed photon index of $\sim 2.4$, and the longer lifetime of TeV emitting electrons naturally explains why the TeV nebula is larger than the X-ray size. Finally, supernova remnant expansion into an inhomogeneous medium is expected to create reverse shocks interacting at different times with the pulsar wind nebula, resulting in the offset X-ray and TeV $\gamma$-ray morphology.
From observations made with the ESPaDOnS spectropolarimeter, recently installed on the 3.6-m Canada--France--Hawaii Telescope, we report the discovery of a strong magnetic field in the Of?p spectrum variable HD 191612 -- only the second known magnetic O star (following theta1 Ori C). The stability of the observed Zeeman signature over four nights of observation, together with the non-rotational shape of line profiles, argue that the rotation period of HD 191612 is significantly longer than the 9-d value previously proposed. We suggest that the recently identified 538-d spectral-variability period is the rotation period, in which case the observed line-of-sight magnetic field of -220+-38 G implies a large-scale field (assumed dipolar) with a polar strength of about -1.5 kG. If confirmed, this scenario suggests that HD 191612 is, essentially, an evolved version of the near-ZAMS magnetic O star theta1 Ori C, but with an even stronger field (about 15 kG at an age similar to that of theta1Ori C). We suggest that the rotation rate of HD 191612, which is exceptionally slow by accepted O-star standards, could be due to angular-momentum dissipation through a magnetically confined wind.
The transition to a type II proton superconductor which is believed to occur in a cooling neutron star is accompanied by changes in the equation of hydrostatic equilibrium and by the formation of proton vortices with quantized magnetic flux. Analysis of the electron Boltzmann equation for this system and of the proton supercurrent distribution formed at the transition leads to the derivation of a simple expression for the transport velocity of magnetic flux in the liquid interior of a neutron star. This shows that flux moves easily as a consequence of the interaction between neutron and proton superfluid vortices during intervals of spin-down or spin-up in binary systems. The differences between the present analysis and those of previous workers are reviewed and an error in the paper of Jones (1991) is corrected.
We report on a survey of the inner part of the Galactic Plane in very high energy gamma-rays, with the H.E.S.S. Cherenkov telescope system. The Galactic Plane between +-30deg in longitude and +-3deg in latitude relative to the Galactic Centre was observed in 500 pointings for a total of 230 hours, reaching an average flux sensitivity of 2% of the Crab Nebula at energies above 200 GeV. Fourteen previously unknown sources were detected at a significance level greater than 4 sigma after accounting for all trials involved in the search. Initial results on the eight most significant of these sources were already reported elsewhere. Here we present detailed spectral and morphological information for all the new sources, along with a discussion on possible counterparts in other wavelength bands. The distribution in Galactic latitude of the detected sources appears to be consistent with a scale height in the Galactic disk for the parent population smaller than 100 pc, consistent with expectations for supernova remnants and/or pulsar wind nebulae.
What is the origin of the numerous population of diffuse elliptical galaxies
(dE) in clusters? These galaxies formed their stars several billion years ago
and lost their gas. Though the stellar winds resulting from star formation and
the interactions with the environment undoubedtly play a role, their respective
role and details of the mechanism of this evolution is still debated.
In this presentation we will review the first 3D spectroscopic observations
of a handful of dE galaxies. These data reveal complex kinematical structures,
with embedded discs and counter rotating cores, and they open extremely
promising perspectives for studying the history of the stellar population
throughout these various features.
The presence of disks, which was already known from detailed image analysis,
and of complex kinematics and the new constraints on the stellar population
enforce the hypothesis of the evolutionary connection between dEs and disk
galaxies.
The hypothesis that CAK-type line driving is responsible for the large observed Wolf-Rayet (W-R) mass-loss rates has been called into question in recent theoretical studies. The purpose of this paper is to reconsider the plausibility of line driving of W-R winds within the standard approach using the Sobolev approximation while advancing the conceptual understanding of this topic. Due to the multiple scattering required in this context, of particular importance is the role of photon frequency redistribution into spectral gaps, which in the extreme limit yields the statistical Sobolev-Rosseland (SSR) mean approximation. Interesting limits to constrain are the extremes of no frequency redistribution, wherein the small radii and corresponding high W-R surface temperature induces up to twice the mass-loss rate relative to cooler stars, and the SSR limit, whereby the reduced efficiency of the driving drops the mass flux by as much as an order of magnitude whenever there exist significant gaps in the spectral line distribution. To see how this efficiency drop might be sufficiently avoided to permit high W-R mass loss, we explore the suggestion that ionization stratification may serve to fill the gaps globally over the wind. We find that global ionization changes can only fill the gaps sufficiently to cause about a 25% increase in the mass-loss rate over the local SSR limit. Higher temperatures and more ionization stages (especially of iron) may be needed to achieve optically thick W-R winds, unless strong clumping corrections eliminate the need for such winds.
We present the results of our long-term monitoring of BD+53 2790, the optical counterpart to the X-ray source 4U~2206+54. Unlike previous studies that classify the source as a Be/X-ray binary, we find that its optical and infrared properties differ from those of typical Be stars: the variability of the V/R ratio is not cyclical; there are variations in the shape and strength of the H$\alpha$ emission line on timescales less than 1 day; and no correlation between the EW and the IR magnitudes or colors is seen. Our observations suggest that BD+53 2790 is very likely a peculiar O9.5V star. In spite of exhaustive searches we cannot find any significant modulation in any emission line parameter or optical/infrared magnitudes. Spectroscopy of the source extending from the optical to the K-band confirms the peculiarity of the spectrum: not only are the He lines stronger than expected for an O9.5V star but also there is no clear pattern of variability. The possibility that BD+53 2790 is an early-type analogue to He-strong stars (like theta^1 Ori C) is discussed.
M31 RV is a luminous red variable star that appeared for several months in
the bulge of M31 during 1988. Unlike classical novae, M31 RV was cool
throughout its outburst. Interest in this object has revived recently because
of its strong resemblance to V838 Mon, a luminous Galactic variable star that
appeared in 2002 and is illuminating a spectacular light echo, and has evolved
to ever-cooler surface temperatures. V4332 Sgr is a third object which was also
a red supergiant throughout its eruption.
We have examined archival Hubble Space Telescope (HST) images of the site
of M31 RV, obtained fortuitously in 1999 with the WFPC2 camera in parallel mode
during spectroscopic observations of the nucleus of M31. We located the site of
M31 RV in the HST frames precisely through astrometric registration with
ground-based CCD images, including several taken during the outburst. No light
echo is seen at the M31 RV site, implying that M31 RV is not surrounded by
circumstellar (or interstellar) dust similar to that around V838 Mon, or that
its extent is less than ~1.7 pc.
The stellar population at the outburst site consists purely of old red
giants; there is no young population, such as seen around V838 Mon. There are
no stars of unusual color at the site, suggesting that M31 RV had faded below
HST detectability in the 11 years since outburst, that it is an unresolved
companion of one of the red giants in the field, or that it is one of the red
giants. We suggest future observations that may help decide among these
possibilities.
We present the first results on variability of very low mass stars and brown dwarfs belonging to the 5 Myr Lambda Orionis cluster (Collinder 69). We have monitored almost continuously in the J filter a small area of the cluster which includes 12 possible members of the cluster during one night. Some members have turned to be short-term variable. One of them, LOri167, has a mass close to the planetary mass limit and its variability might be due to instabilities produced by the deuterium burning, although other mechanism cannot be ruled out.
Using XMM-Newton we have obtained the first X-ray observation covering a complete orbit of the longest period polar, V1309 Ori. The X-ray light curve is dominated by a short, bright phase interval with EPIC pn count rates reaching up to 15 cts/sec per 30 sec resolution bin. The bright phase emission is well described by a single blackbody component with kT_bb = (45 +- 3) eV. The absence of a bremsstrahlung component at photon energies above 1 keV yields a flux ratio F_bb/F_br > 6700. This represents the most extreme case of a soft X-ray excess yet observed in an AM Herculis star. The bright, soft X-ray emission is subdivided into a series of individual flare events supporting the hypothesis that the soft X-ray excess in V1309 is caused by accretion of dense blobs. In addition to the bright phase emission, a faint, hard X-ray component is visible throughout the binary orbit with an almost constant count rate of 0.01 cts/sec. Spectral modelling indicates that this emission originates from a complex multi-temperature plasma. At least three components of an optically thin plasma with temperatures kT= 0.065, 0.7, and 2.9 keV are required to fit the observed flux distribution. The faint phase emission is occulted during the optical eclipse. Eclipse ingress lasts about 15--20 min and is substantially prolonged beyond nominal ingress of the white dwarf. This and the comparatively low plasma temperature provide strong evidence that the faint-phase emission is not thermal bremsstrahlung from a post-shock accretion column above the white dwarf. A large fraction of the softer faint-phase emission could be explained by scattering of photons from the blackbody component in the infalling material above the accretion region. The remaining hard X-ray flux could be produced in the coupling region, so far unseen in other polars.
We present low-resolution VLT spectroscopy of the afterglow of the gamma-ray bursts (GRBs) 991216, 011211 and 021211. Our spectrum of GRB991216 is the only optical spectrum for this afterglow. It shows two probable absorption systems at z=0.80 and z=1.02, where the highest redshift most likely reflects the distance to the host galaxy. A third system may be detected at z=0.77. HST imaging of the field, obtained 4 months after the burst, has resulted in the detection of two amorphous regions of emission, one at the projected afterglow position, and the other 0.6" away. The spectrum shows a depression in flux in between 4000 A and 5500 A. This could be the result of a 2175 A-type extinction feature in the host of GRB991216, but at a rather red wavelength of 2360 A. If this interpretation is correct, it is the first time the extinction feature is seen in a GRB afterglow spectrum. It is centered at a wavelength similar to that of the ultra-violet (UV) bumps inferred from observations of a few UV-strong, hydrogen-poor stars in the Galaxy. All significant absorption lines (except for one) detected in the spectrum of GRB011211 are identified with lines originating in a single absorption system at z=2.142+-0.002, the redshift of the GRB011211 host galaxy. We also detect the Lyman alpha absorption line in the host, to which we fit a neutral hydrogen column density of log N(HI)=20.4+-0.2, which indicates that it is a damped Lyman alpha system. Using a curve-of-growth analysis, we estimate the Si, Fe and Al metallicity at the GRB011211 redshift. For GRB021211, we detect a single emission line in a spectrum obtained tens of days after the burst, which we identify as [OII] 3727 at z=1.006. The corresponding unobscured [OII] star-formation rate is 1.4 Msun/yr.