We have measured the fraction of bars in nearby spiral galaxies using near-infrared J, H, and K_s images of 151 spiral galaxies from 2MASS. This local sample provides an anchor for the study of the evolution of the bar fraction and bar properties with redshift. We identify bars by analyzing the full two-dimensional light distribution and requiring a combined ellipticity and position angle signature. The combined bar signature is found in 59% of the galaxies. The bar fraction increases to 67% when we include "candidate" bars, where only the ellipticity signature is present. We also measure the change in the bar fraction as a function of bar size; the bar fraction drops to 36% for bars with a semi-major axis larger than 4 kpc. We find that infrared bars typically extend to one-third of the galactic disk, with a deprojected relative size of <a_{bar}/R_{25}> ~ 0.3 +/- 0.2. Early-type spirals host significantly larger bars, consistent with earlier studies. The <a_{bar}/R_{25}> is two times larger in early-types than in late-types. The typical bar axial ratio (b/a) is \~0.5, with a weak trend of higher axial ratios for larger bars.
The intergalactic medium - the cosmic gas that fills the great spaces between
the galaxies - is affected by processes ranging from quantum fluctuations in
the very early universe to radiative emission from newly-formed stars. This
gives the intergalactic medium a dual role as a powerful probe both of
fundamental physics and of astrophysics. The heading of fundamental physics
includes conditions in the very early universe and basic cosmological
parameters. The astrophysics refers to chapters of the long cosmic history of
stars and galaxies that are being revealed through the effects of stellar
feedback on the cosmic gas. This review describes the physics of the
intergalactic medium, focusing on recent theoretical and observational
developments in understanding early cosmic history. In particular, radiation
from the earliest generation of stars is thought to have transformed the
universe, turning the surrounding atoms into free electrons and ions. Knowing
exactly when and how the reionization process happened is a primary goal of
cosmologists, because this would tell us when the early stars and black holes
formed and in what kinds of galaxies.
Cosmic reionization is beginning to be understood with the help of
theoretical models and computer simulations. A wide variety of instruments
currently under design will probe the first sources of light during an epoch in
cosmic history that has been largely unexplored so far. The new observations
and the challenges for theoretical models and numerical simulations will
motivate intense work in this field over the coming decade. (abridged)
I present detailed analysis of the near infrared spectrum of HD 3651B, a faint, co-moving wide companion to the nearby planet-hosting star HD 3651. These data confirm the companion as a brown dwarf with spectral type T8, consistent with the analysis of Luhman et al. Application of the semi-empirical technique of Burgasser, Burrows & Kirkpatrick indicates that HD 3651B has Teff = 790+/-30 K and log g = 5.0+/-0.3 for a metallicity of [M/H] = 0.12+/-0.04, consistent with a mass M = 0.033+/-0.013 M_sun and an age of 0.7-4.7 Gyr. The surface gravity, mass and age estimates of this source are all highly sensitive to the assumed metallicity; however, a supersolar metallicity is deduced by direct comparison of spectral models to the observed absolute fluxes. The age of HD 3651B is somewhat better constrained than that of the primary, with estimates for the latter ranging over ~2 Gyr to >12 Gyr. As a widely orbiting massive object to a known planetary system that could potentially harbor terrestrial planets in its habitable zone, HD 3651B may play the role of Nemesis in this system.
Trigonometric parallaxes of 16 nearby planetary nebulae are presented, including reduced errors for seven objects with previous initial results and results for six new objects. The median error in the parallax is 0.42 mas, and twelve nebulae have parallax errors less than 20 percent. The parallax for PHL932 is found here to be smaller than was measured by Hipparcos, and this peculiar object is discussed. Comparisons are made with other distance estimates. The distances determined from these parallaxes tend to be intermediate between some short distance estimates and other long estimates; they are somewhat smaller than estimated from spectra of the central stars. Proper motions and tangential velocities are presented. No astrometric perturbations from unresolved close companions are detected.
Spitzer images of the luminous blue variable (LBV) candidate HD168625 reveal the existence of a bipolar nebula several times larger than its previously-known equatorial dust torus. The outer nebula of HD168625 has a full extent of about 80 arcsec or 0.85 pc, and one of the lobes has a well-defined polar ring. The nebula is a near twin of the triple-ring system around SN1987A. Because of these polar rings, and accounting for stellar/progenitor luminosity, HD168625 is an even closer twin of SN1987A than the B supergiant Sher 25 in NGC3603. HD168625's nebula was probably ejected during a giant LBV eruption and not during a red supergiant phase, so its similarity to the nebula around SN1987A may open new possibilities for the creation of SN1987A's rings. Namely, the hypothesis that Sk-69 202 suffered an LBV-like eruption would avert the complete surrender of single star models for its bipolar nebula by offering an alternative to an unlikely binary merger scenario. It also hints that LBVs are the likely progenitors of some type II supernovae, and that HD168625's nebula is a good example of a pre-explosion environment.
Using models of the SN~IIP 2005cs, we show that detailed spectral analysis can be used to determine reddening and abundances.
Low frequency gravitational wave detectors, such as the Laser Interferometer Space Antenna (LISA), will have to contend with large foregrounds produced by millions of compact galactic binaries in our galaxy. While these galactic signals are interesting in their own right, the unresolved component can obscure other sources. The science yield for the LISA mission can be improved if the brighter and more isolated foreground sources can be identified and regressed from the data. Since the signals overlap with one another we are faced with a ``cocktail party'' problem of picking out individual conversations in a crowded room. Here we present and implement an end-to-end solution to the galactic foreground problem that is able to resolve tens of thousands of sources from across the LISA band. Our algorithm employs a variant of the Markov Chain Monte Carlo (MCMC) method, which we call the Blocked Annealed Metropolis-Hastings (BAM) algorithm. Following a description of the algorithm and its implementation, we give several examples ranging from searches for a single source to searches for hundreds of overlapping sources. Our examples include data sets from the first round of Mock LISA Data Challenges.
We present millimeter interferometric observations of the molecular envelope around the red supergiant VY CMa with the SubMillimeter Array (SMA). The high angular resolution (< 2'') allows us to derive the structure of the envelope as observed in the 1.3 mm continuum, 12CO(2-1), 13CO(2-1) and SO(6,5-5,4) lines emission. The circumstellar envelope is resolved into three components: a dense, compact and dusty central component, embedded in a more diffuse and extended envelope plus a high velocity component. We construct a simple model, consisting of a spherically symmetric slowly expanding envelope and bipolar outflows with a wide opening angle (~ 120 deg.) viewed close to the line of sight (i = 15 deg.). Our model can explain the main features of the SMA data and previous single-dish CO multi-line observations. An episode of enhanced mass loss along the bipolar direction is inferred from our modelling. The SMA data provide a better understanding of the complicated morphology seen in the optical/IR high resolution observations.
A large disruption in the main asteroid belt can cause a large flux, an "asteroid shower", on the terrestrial planets. We quantitatively examine the hypothesis that such an event was the cause of the lunar late heavy bombardment (LHB). We performed numerical integrations of about 20000 test particles starting in the vicinity of the nu6 secular resonance in the main asteroid belt. The purpose of these integrations is to calculate, for each of the terrestrial planets, the collision probability of asteroids coming from an asteroid break-up event in the inner part of the main belt. Compared with previous studies, we simulate nearly two orders of magnitude larger number of particles, and we include the orbital effects of the eight planets, Mercury to Neptune. We also examined in detail the orbital evolution of asteroid fragments once they enter the Earth's activity sphere, including the effect of the Earth-Moon orbit. We obtained the collision probability, the distributions of impact velocities, impact positions, and impact angles of asteroid fragments on the Moon. The collision probability with the Moon (~0.1%) suggests that a fairly large parent body, 1000-1500 km in diameter, is required if the LHB event is to be ascribed to a single asteroid disruption. An even larger parent body is required for less favorable initial conditions than we investigated here. We conclude that an asteroid disruption event is not a viable explanation for the LHB.
We present an analysis of the broadband UV/optical properties of z<3.4 quasars matched in the Galaxy Evolution Explorer (GALEX) General Data Release 1 (GR1) and the Sloan Digital Sky Survey Data Release 3 (SDSS DR3). Of the 6371 DR3 quasars covered by 204 GR1 tiles, 5380 have near-UV detections, while 3034 have both near-UV and far-UV detections using a matching radius of 7". Most of the DR3 sample quasars are detected in the near-UV until z~1.7, with the near-UV detection fraction dropping to ~50% by z~2. Statistical tests performed on the distributions of non-detections indicate that the optically-selected quasars missed in the UV tend to be optically faint or at high redshift. The GALEX positions are shown to be consistent with the SDSS astrometry to within an rms scatter of 0.6-0.7" in each coordinate, and empirically determined photometric errors from multi-epoch GALEX observations significantly exceed the Poissonian errors quoted in the GR1 object catalogs. The UV-detected quasars are well separated from stars in UV/optical color-color space, with the relative colors suggesting a marginally detected population of reddened objects due to line of sight absorption or due to dust associated with the quasar. The resulting rest-frame spectral energy distributions (SEDs) cover ~350-9000A, where the overall median SED peaks near the Ly-a emission line, as found in other UV quasar studies. The large sample size allows us to construct median SEDs in small bins of redshift and luminosity, and we find the median SED becomes harder at UV wavelengths for quasars with lower continuum luminosity. Tables containing the results of the matching and the overall median SED are available in the electronic edition of the journal.
We discuss the results of the monitoring programs of the X-ray binaries with relativistic jets studies. We carried out a multi-frequency (1-30 GHz) daily monitoring of the radio flux variability of the microquasars SS433, GRS1915+105, V4641 Sgr and Cyg X-3 with RATAN-600 radio telescope during the recent sets in 2002-2006. We detected a lot of bright short-time flares from GRS 1915+105 which could be associated with active X-ray events. In 2004 we have detected two flares from V4641 Sgr, which followed after recurrent X-ray activity of the transient. From September 2005 to May 2006 and then in July we have daily measured flux densities from Cyg X-3. In January 2006 we detected a drop down of its quiescent fluxes (from 100 to ~20 mJy), then the 1Jy-flare was detected on 2 February 2006 after 18 days of quenched radio emission. The daily spectra of the flare in the maximum were flat from 2 to 110 GHz, using the quasi-simultaneous observations at 110 GHz with the RT45m telescope and the NMA millimeter array of the Nobeyama Radio Observatory in Japan. Several bright radio flaring events (1-15 Jy) followed during the continuing state of very variable and intensive 1-12 keV X-ray emission (~0.5 Crab), which was monitored in the RXTE ASM program. We discuss the various spectral and temporal characteristics of the light curves from the microquasars. Thus we conclude that monitoring of the flaring radio emission is a good tracer of jet activity X-ray binaries.
Binary systems of compact objects are strong emitters of gravitational waves whose amplitude depends on the binary orbital parameters as the component mass, the orbital semi-major axis and eccentricity. Here, in addition to the famous Hulse-Taylor binary system, we have studied the possibility to detect the gravitational wave signal emitted by binary systems at the center of our galaxy. In particular, recent infrared observation of the galactic center have revealed the existence of a cluster of stars each of which appears to orbit the central black hole in $SgrA^*$. For the stars labelled as S2 and S14, we have studied the emitted spectrum of gravitational wave and compare it with the sensitivity threshold of space-based interferometers like Lisa and Astrod. Furthermore, following recent observations, we have considered the possibility that $SgrA^*$ is actually a binary system of massive black holes and calculated the emission spectrum as a function of the system parameters. The diffraction pattern of gravitational waves emitted by a binary system by a cluster of stars has been also analyzed. We remark that this is only a preliminary-theoretical work than can acquire more interest in view of the next-coming gravitational wave astronomy era.
The most massive black holes, lurking at the centers of large galaxies, must have formed less than a billion years after the big bang, as they are visible today in the form of bright quasars at redshift larger than six. Their early appearance is mysterious, because the radiation pressure, generated by infalling ionized matter, inhibits the rapid growth of these black holes from stellar-mass black holes. Here we show that the supermassive black holes may form timeously through the accretion of radiationless and densely packed neutrino dark matter onto stellar-mass black holes. Our symbiotic scenario relies on the formation of, first, supermassive degenerate sterile neutrino balls through gravitational cooling and, then, stellar-mass black holes through supernova explosions of massive stars at the center of the neutrino balls. The observed lower and upper limits of the supermassive black holes are explained by the corresponding mass limits of the preformed neutrino balls.
X-ray surveys facilitate investigations of the environment of AGNs. Deep Chandra observations revealed that the AGNs source surface density rises near clusters of galaxies. The natural extension of these works is the measurement of spatial clustering of AGNs around clusters and the investigation of relative biasing between active galactic nuclei and galaxies near clusters. The major aims of this work are to obtain a measurement of the correlation length of AGNs around clusters and a measure of the averaged clustering properties of a complete sample of AGNs in dense environments. We present the first measurement of the soft X-ray cluster-AGN cross-correlation function in redshift space using the data of the ROSAT-NEP survey. The survey covers 9x9 deg^2 around the North Ecliptic Pole where 442 X-ray sources were detected and almost completely spectroscopically identified. We detected a > 3 sigma significant clustering signal on scales s<50 h_70^-1 Mpc. We performed a classical maximum-likelihood power-law fit to the data and obtained a correlation length s_0=8.7^+1.2_-0.3 h70^-1 Mpc and a slope gamma=1.7^+0.2_-0.7 (1 sigma errors). This is a strong evidence that AGNs are good tracers of the large scale structure of the Universe. Our data were compared to the results obtained by cross-correlating X-ray clusters and galaxies. We observe, with a large uncertainty, a similar behaviour of the AGNs clustering around clusters similar to the clustering of galaxies around clusters.
We report on a comprehensive set of observations of Gamma Ray Burst 050716, detected by the Swift satellite and subsequently followed-up rapidly in X-ray, optical and near infra-red wavebands. The prompt emission is typical of long-duration bursts, with two peaks in a time interval of T90 = 68 seconds (15 - 350 keV). The prompt emission continues at lower flux levels in the X-ray band, where several smaller flares can be seen, on top of a decaying light curve that exhibits an apparent break around 220 seconds post trigger. This temporal break is roughly coincident with a spectral break. The latter can be related to the extrapolated evolution of the break energy in the prompt gamma-ray emission, and is possibly the manifestation of the peak flux break frequency of the internal shock passing through the observing band. A possible 3 sigma change in the X-ray absorption column is also seen during this time. The late-time afterglow behaviour is relatively standard, with an electron distribution power-law index of p = 2 there is no noticable temporal break out to at least 10 days. The broad-band optical/nIR to X-ray spectrum indicates a redshift of z ~> 2 for this burst, with a host-galaxy extinction value of E(B-V) ~ 0.7 that prefers an SMC-like extinction curve.
(Abridged) We present a detailed study of the host galaxy of GRB 011121 (at z = 0.36) based on high-resolution imaging in 5 broad-band, optical and near-infrared filters with HST and VLT/ISAAC. The surface brightness profile of this galaxy is best fitted by a Sersic law with index ~ 2 - 2.5 and a rather large effective radius (~ 7.5 kpc). Both the morphological analysis and the F450W - F702W colour image suggest that the host galaxy of GRB 011121 is either a disk-system with a rather small bulge, or one hosting a central, dust-enshrouded starburst. Hence, we modeled the integrated spectral energy distribution of this galaxy by combining stellar population and radiative transfer models, assuming properties representative of nearby starburst or normal star-forming, Sbc-like galaxies. A range of plausible fitting solutions indicates that the host galaxy of GRB 011121 has a stellar mass of 3.1 - 6.9 x10^9 Msun, stellar populations with a maximum age ranging from 0.4 to 2 Gyr, and a metallicity ranging from 1 to 29 per cent of the solar value. Starburst models suggest this galaxy to be nearly as opaque as local starbursts (with an A_V = 0.27 - 0.76 mag). Alternatively, normal star-forming Sbc-like models suggest a high central opacity whereas A_V = 0.12$ -- 0.57 mag along the line of sight. For this subluminous galaxy (with L_B/Lstar_B = 0.26), we determine a model-dependent SFR of 2.4 - 9.4 Msun/yr. The SFR per unit luminosity (9.2 - 36.1 Msun/yr/(L_B/Lstar_B)) is high compared to those of most GRB host galaxies, but consistent with those of most of the hosts at similar low redshift. Our results suggest that the host galaxy of GRB 011121 is a rather large disk-system in a relatively early phase of its star formation history.
Surveys provide a wealth of data to the astronomical community that are used well after their completion. In this paper, we propose a project that would take the maximum benefit of Dome C in Antarctica by performing two surveys, in the wavelength range from 1-5 micron, complementary to SNAP space surveys. The first one over 1000 sq. deg. (1 KdF) for 4 years and the second one over 15 sq. deg (SNAP-IR) for the next 4 years at the same time as SNAP 0.35-1.7 microns survey. By using a Ground-Layer Adaptive Optics system, we would be able to recover, at the ice level and over at least half a degree in radius, the 300 mas angular resolution available above the 30-m high turbulent layer. Such a survey, combining a high angular resolution with high sensitivities in the NIR and MIR, should also play the role of a pre-survey for JWST and ALMA.
Many Local Group dwarf spheroidal galaxies are found in the Galactic halo along great circles in the sky. Some of these stellar systems are thought to be the fragments of larger parent galaxies which have once intruded into and were torn apart by the tide of the Galaxy. Supporting evidences for tidal disruption are found in the form of stellar tidal bridges and tails along the orbits of some dwarf galaxies and globular clusters. In this study, we investigate the influence of mass-loss from star clusters or dwarf galaxies on the rate of their orbit decay due to the effect of dynamical friction. Using a series of numerical N-body simulations, we show that stars, which become unbound from their host-systems, but remain in their vicinity and share their orbits, still contribute to the mass responsible for the dynamical friction. As a rule-by-thumb, the magnitude of dynamical friction at any instance can be approximated by the bound mass plus half of the mass which has already become unbound during the proceeding Galactic orbit. Based on these results, we suggest the tidal disruption of relatively massive satellite stellar systems may be more abrupt than previously estimated.
To gain a better understanding of high-energy Galactic sources, we observed the Galactic X-ray binary and black hole candidate XTE J1720-318 in the optical and near-infrared, just after the onset of its X-ray outburst in January, 2003. These observations were obtained with the ESO/NTT as a Target of Opportunity, in February and April 2003. We performed an accurate astrometry and analysed photometrical observations. We then produced a colour-magnitude diagram, looked at the overall evolution of the multi-wavelength light curve, and analysed the spectral energy distribution. We discovered the optical counterpart in the R-band (R ~ 21.5) and confirmed the near-infrared counterpart. We show that, for an absorption between 6 and 8 magnitudes, XTE J1720-318 is likely to be an intermediate mass X-ray binary located at a distance between 3 and 10 kpc, hosting a main sequence star of spectral type between late B and early G. Our second set of observations took place simultaneously with the third secondary outburst present in X-ray and near-infrared light curves. The evolution of its spectral energy distribution shows that XTE J1720-318 entered a transition from a high-soft to a low-hard state in-between the two observations. We finally discuss the different phases of the outburst of this source in the general scheme of outbursts from microquasars.
The mid-infrared emission at the center of IRAS 21026+4104 is not that of a simple compact source, as one would expect from an isolated high mass protostellar object. Furthermore the central thermal infrared emission does not appear to be coming directly from a circumstellar disk as has been recently hypothesized from near-infrared observations. The mid-infrared structure is complex, but with the help of multiple wavelength information two plausible scenarios to explain the emission in the region are advanced. The first is that there is a tight cluster of young stellar objects here. The second is that the mid-infrared emission and masers are delineating the walls of the outflow cavities of a massive stellar source located in the center of the near- and mid-infrared dark lane.
Context. RU Lup is a Classical T Tauri star with unusually strong emission lines, which has been interpreted as manifestations of accretion. Recently, evidence has accumulated that this star might have a variable radial velocity. Aims. We intended to investigate in more detail the possible variability in radial velocity using a set of 68 high-resolution spectra taken at the VLT (UVES), the AAT (UCLES) and the CTIO (echelle). Methods. Using standard cross-correlation techniques, we determined the radial velocity of RU Lup. We analysed these results with Phasedispersion minimization and the Lomb-Scargle periodogram and searched for possible periodicities in the obtained radial velocities. We also analysed changes in the absorption line shapes and the photometric variability of RU Lup. Results. Our analysis indicated that RU Lup exhibits variations in radial velocity with a periodicity of 3.71 days and an amplitude of 2.17 km/s. These variations can be explained by the presence of large spots, or groups of spots, on the surface of RU Lup. We also considered a low-mass companion and stellar pulsations as alternative sources for these variations but found these to be unlikely.
We present the motivation, aims and preliminary result from the Swift/VLT legacy survey on gamma-ray burst host galaxies. This survey will produce a homogeneous and well-understood host sample covering more than 95% of the lookback time to the Big Bang, and allow us to characterize their fundamental properties.
We present a detailed analysis of Jupiter's X-ray (0.2-10 keV) auroral emissions as observed by XMM-Newton in Nov. 2003 and compare it with that of an Apr. 2003 observation. We discover the existence of an electron bremsstrahlung component in the aurorae, which accounts for essentially all the X-ray flux above 2 keV: its presence had been predicted but never detected for lack of sensitivity of previous X-ray missions. This bremsstrahlung component varied significantly in strength and spectral shape over the 3.5 days covered by the Nov. 2003 observation, displaying substantial hardening of the spectrum with increasing flux. This variability may be linked to the strong solar activity taking place at the time, and may be induced by changes in the acceleration mechanisms inside Jupiter's magnetosphere. As in Apr. 2003, the auroral spectra below 2 keV are best fitted by a superposition of line emission most likely originating from ion charge exchange, with OVII playing the dominant role. We still cannot resolve conclusively the ion species responsible for the lowest energy lines (around 0.3 keV), so the question of the origin of the ions (magnetospheric or solar wind) is still open. It is conceivable that both scenarios play a role in what is certainly a very complex planetary structure. High resolution spectra of the whole planet obtained with the XMM-Newton RGS in the range 0.5-1 keV clearly separate emission lines (mostly of Fe) originating at low latitudes on Jupiter from the auroral lines due to O. These are shown to possess very broad wings which imply velocities of ~5000 km/s. Such speeds are consistent with the energies at which precipitating and charge exchanging O ions are expected to be accelerated in Jupiter's magnetosphere. Overall we find good agreement between our measurements and the predictions of recent models.
Aims. We study the geometry and kinematics of the circumstellar environment of the Be star Kappa CMa in the Br gamma emission line and its nearby continuum. Methods. We use the VLTI/AMBER instrument operating in the K band which provides a spatial resolution of about 6 mas with a spectral resolution of 1500 to study the kinematics within the disk and to infer its rotation law. In order to obtain more kinematical constraints we also use an high spectral resolution Pa beta line profile obtain in December 2005 at the Observatorio do Pico do Dios, Brazil and we compile V/R line profile variations and spectral energy distribution data points from the literature. Results. Using differential visibilities and differential phases across the Br gamma line we detect an asymmetry in the disk. Moreover, we found that kappa CMa seems difficult to fit within the classical scenario for Be stars, illustrated recently by alpha Arae observations, i.e. a fast rotating B star close to its breakup velocity surrounded by a Keplerian circumstellar disk with an enhanced polar wind. Finally we discuss the possibility for kappa CMa to be a critical rotator with a Keplerian rotating disk and try to see if the detected asymmetry can be interpreted within the "one-armed" viscous disk framework.
The sensitivity of interferometers with linear polarizers to the CMB E and B mode are variant under the rotation of the polarizer frame, while interferometer with circular polarizers are equally sensitive to E and B mode. We present analytically and numerically that the diagonal elements of window functions for CMB E/B power spectra are maximized in interferometric measurement of linear polarization, when the polarizer frame is in certain rotation from the associated baseline. We also present the simulated observation to show that the 1-$\sigma$ errors on E/B mode power spectrum estimation are variant under the polarizer frame rotation in the case of linear polarizers, while they are invariant in the case of circular polarizers. Simulation of the configuration similar to the DASI shows that minimum 1-$\sigma$ error on B mode in interferometer measurement with linear polarizers is 26% of that in interferometric measurement with circular polarizers. The simulation also shows that the E/B mixing in interferometer measurement with linear polarizers can be as low as 23% of that in interferometric measurement with circular polarizers. It is not always possible to physically align the the polarizer frame with all the associated baselines in the case of an interferometer array (N$>$2). There exist certain linear combinations of visibilities, which are equivalent to visibilities of the optimal polarizer frame rotation. We present the linear combinations, which enables B mode optimization for an interferometer array (N$>$2).
We investigate the accuracy to which we can retrieve the solar photospheric magnetic field vector using the Helioseismic and Magnetic Imager (HMI) that will fly onboard of the Solar Dynamics Observatory (SDO) by inverting simulated HMI profiles. The simulated profiles realistically take into account the effects of the photon noise, limited spectral resolution, instrumental polarization modulation, solar p modes and temporal averaging. The accuracy of the determination of the magnetic field vector is studied considering the different operational modes of the instrument.
We present our activity on making the Subaru Data Archive accessible through the Japanese Virtual Observatory (JVO) system. There are a lot of demand to use the archived Subaru data from various fields of astronomers. To be used by those who are not familiar with the way to reduce the Subaru data, the data reduction should be made before providing for them, or at least it should be easily done without precise knowledge about instrument's characteristic and environment where data are taken. For those purposes, data quality assessment system NAQATA is developed, which is presented in this meeting by Nakata et al. (2006), and the science-ready image data are provided for some of the SuprimeCam data at SMOKA data service which is presented by Enoki et al (2006). JVO portal will provide the way to access the reduce data, and also provides the way to reduce from raw data with very few efforts through the user-friendly web browser I/F. To provide such a CPU-intensive service, we have developed a GRID computing system. The architecture of this Subaru Data and Analysis system are discussed.
It has been long recognised that, besides being a formidable experiment to observe the primordial CMB anisotropies, Planck will also have the capability to detect galaxy clusters via their SZ imprint. In this paper constraints on cosmological parameters derivable from the Planck cluster candidate sample are examined for the first time as a function of cluster sample selection and purity obtained from realistic simulations of the microwave sky at the Planck observing frequency bands, observation process modelling and a cluster extraction pipeline. In particular, we employ a multi-frequency matched filtering (MFMF) method to recover clusters from mock simulations of Planck observations. Obtainable cosmological constraints under realistic assumptions of priors and knowledge about cluster redshifts are discussed. Just relying on cluster redshift abundances without making use of recovered cluster fluxes, it is shown that from the Planck cluster catalogue cosmological constraints comparable to the ones derived from recent primordial CMB power spectrum measurements can be achieved. For example, for a concordance $\Lambda$CDM model and a redshift binning of $\Delta z = 0.1$, the $1\sigma$ uncertainties on the values of $\Omega_m$ and $\sigma_8$ are $\Delta \Omega_m \approx 0.031$ and $\Delta \sigma_8 \approx 0.014$ respectively. Furthermore, we find that the constraint of the matter density depends strongly on the prior which can be imposed on the Hubble parameter by other observational means.
We examine disk and spherical stellar systems of nearly radial orbits with
retrograde orbit precession. Such systems are stable to the well known radial
orbit instability. If there is a loss cone at low angular momentum, an
instability similar to loss-cone instability in plasma may occur. Examples of
systems with loss cone are the centers of galaxies or star clusters containing
a massive black hole. The instability can cause an inward flux of stars to the
galactic center fuelling nuclear activity.
The study is based on simple characteristic equations describing small
perturbations in a disk or a sphere of stellar orbits highly elongated in
radius. These characteristic equations are derived from the linearized Vlasov
equations (combining the collisionless Boltzmann kinetic equation and the
Poisson equation), using the action - angle variables. We use two techniques
for analyzing the characteristic equations: the first one is based on
preliminary finding of neutral modes, and the second one employs a counterpart
of the plasma Penrose--Nyquist criterion for disk and spherical gravitational
systems.
The population of non magnetic cataclysmic variables evolving under the influence of a circumbinary disk is investigated for systems above the upper edge of the period gap at orbital periods greater than 2.75hr. For a fractional mass input rate into the disk, corresponding to 3e-4 of the mass transfer rate, the model systems exhibit a bounce at orbital periods greater than 2.75hr. The simulations reveal that (1) some systems can exist as dwarf nova type systems throughout their lifetime, (2) dwarf nova type systems can evolve into nova-like systems as their mass transfer rate increases with increasing circumbinary disk mass, and (3) nova-like systems can evolve back into dwarf nova systems during their postbounce evolution to longer orbital periods. Among these subclasses, nova-like cataclysmic variables would be the best candidates to search for circumbinary disks at wavelengths greater than 10 micron. The theoretical orbital period distribution of our population synthesis model is in reasonable accord with the combined population of dwarf novae and nova-like systems above the period gap, suggesting the possibility that systems with unevolved donors need not detach and evolve below the period gap as in the disrupted magnetic braking model. The resulting population furthermore reveals the possible presence of systems with small mass ratios (a property of systems exhibiting superhump phenomena at long orbital periods) and a preference of O/Ne/Mg white dwarfs in dwarf nova systems in comparison to nova-like systems. The importance of observational bias in accounting for the differing populations is examined, and it is shown that an understanding of these effects is necessary in order to confront the theoretical distributions with the observed ones in a meaningful manner. (abridged)
In this contribution we briefly describe our recent results on the properties of Lyman break galaxies at z~5 obtained from deep and wide blank field surveys using Subaru telescope, and through the comparison with samples at lower redshift ranges we discuss the evolution of star-forming galaxies in the early universe.
We present spatially resolved stellar rotation velocity and velocity dispersion profiles form Keck/LRIS absorption-line spectra for 25 galaxies, mostly visually classified ellipticals, in three clusters at z=0.5. We interpret the kinematical data and HST photometry using oblate axisymmetric two-integral f(E,Lz) dynamical models based on the Jeans equations. This yields good fits, provided that the seeing and observational characteristics are carefully modeled. The fits yield for each galaxy the dynamical M/L and a measure of the galaxy rotation rate. Paper II addresses the implied M/L evolution. Here we study the rotation-rate evolution by comparison to a sample of local elliptical galaxies of similar present-day luminosity. The brightest galaxies in the sample all rotate too slowly to account for their flattening, as is also observed at z=0. But the average rotation rate is higher at z=0.5 than locally. This may be due to a higher fraction of misclassified S0 galaxies (although this effect is insufficient to explain the observed strong evolution of the cluster S0 fraction with redshift). Alternatively, dry mergers between early-type galaxies may have decreased the average rotation rate over time. It is unclear whether such mergers are numerous enough in clusters to explain the observed trend quantitatively. Disk-disk mergers may affect the comparison through the so-called progenitor bias, but this cannot explain the direction of the observed rotation-rate evolution. Additional samples are needed to constrain possible environmental dependencies and cosmic variance in galaxy rotation rates. Either way, studies of the internal stellar dynamics of distant galaxies provide a valuable new approach for exploring galaxy evolution.
We have discovered 21 new Type Ia supernovae (SNe Ia) with the Hubble Space
Telescope (HST) and have used them to trace the history of cosmic expansion
over the last 10 billion years. These objects, which include 13
spectroscopically confirmed SNe Ia at z > 1, were discovered during 14 epochs
of reimaging of the GOODS fields North and South over two years with the
Advanced Camera for Surveys on HST. Together with a recalibration of our
previous HST-discovered SNe Ia, the full sample of 23 SNe Ia at z > 1 provides
the highest-redshift sample known. Combined with previous SN Ia datasets, we
measured H(z) at discrete, uncorrelated epochs, reducing the uncertainty of
H(z>1) from 50% to under 20%, strengthening the evidence for a cosmic jerk--the
transition from deceleration in the past to acceleration in the present. The
unique leverage of the HST high-redshift SNe Ia provides the first meaningful
constraint on the dark energy equation-of-state parameter at z >1.
The result remains consistent with a cosmological constant (w(z)=-1), and
rules out rapidly evolving dark energy (dw/dz >>1). The defining property of
dark energy, its negative pressure, appears to be present at z>1, in the epoch
preceding acceleration, with ~98% confidence in our primary fit. Moreover, the
z>1 sample-averaged spectral energy distribution is consistent with that of the
typical SN Ia over the last 10 Gyr, indicating that any spectral evolution of
the properties of SNe Ia with redshift is still below our detection threshold.
Anthropic probability distributions for the cosmological constant and for the sum of neutrino masses are updated using the WMAP-3 data release. The new distribution for Lambda is in a better agreement with observation than the earlier one. The typicality of the observed value, defined as the combined probability of all values less likely than the observed, is no less than 22%. We discuss the dependence of our results on the simplifying assumptions used in deriving the distribution for Lambda and show that the agreement of the anthropic prediction with the data is rather robust. The distribution for the sum of the neutrino masses is peaked at 1 eV, suggesting degenerate masses, but a hierarchical mass pattern is still marginally allowed at a 2 sigma level.
We have developed an analytical model for the evolution of anisotropic galactic outflows. These outflows follow the path of least resistance, and thus travel preferentially into low-density regions, away from cosmological structures where galaxies form. We show that anisotropic outflows can significantly enrich low-density systems, while reducing the enrichment of overdense regions.
With the mainstream adoption of references to datasets in astronomical
manuscripts, researchers today are able to provide direct links from their
papers to the original data that were used in their study. Following a process
similar to the verification of references in manuscripts, publishers have been
working with the NASA Astrophysics Data System (ADS) to validate and maintain
links to these datasets.
Similarly, many astronomical data centers have been tracking publications
based on the observations that they archive, and have been working with the ADS
to maintain links between their datasets and the bibliographic records in
question. In addition to providing a valuable service to ADS users, maintaining
these correlations allows the data centers to evaluate the scientific impact of
their missions.
Until recently, these two activities have evolved in parallel on independent
tracks, with ADS playing a central role in bridging the connection between
publishers and data centers. However, the ADS is now implementing the
capability for all parties involved to find out which data links have been
published with which manuscripts, and vice versa. This will allow data centers
to periodically harvest the ADS to find out if there are new papers which
reference datasets available in their archives. In this paper we summarize the
state of the dataset linking project and describe the new harvesting interface.
We have designed an analytical model for the evolution of anisotropic galactic outflows. These outflows follow the path of least resistance, and thus travel preferentially into low-density regions, away from cosmological structures where galaxies form. We show that anisotropic outflows can significantly enrich low-density systems with metals.
We study M/L evolution of early-type galaxies using dynamical modeling of resolved internal kinematics. This makes fewer assumptions than Fundamental Plane (FP) studies and provides a powerful new approach for studying galaxy evolution. We focus on the sample of 25 galaxies in clusters at z=0.5 modeled in Paper I. For comparison we compile and homogenize M/L literature data for 60 nearby galaxies that were modeled in comparable detail. The nearby sample obeys log(M/L)_B = Z + S log(sigma_eff/[200 km/s]), with Z = 0.896 +/- 0.010, S = 0.992 +/- 0.054, and sigma_eff the effective velocity dispersion. The z=0.5 sample follows a similar relation but with lower zeropoint. The implied M/L evolution is Delta log(M/L) / Delta z = -0.457 +/- 0.046(random) +/- 0.078(systematic), consistent with passive evolution following high-redshift formation. This agrees with the FP results for this sample by van Dokkum & van der Marel. This confirms that FP evolution tracks M/L evolution, which is an important verification of the assumptions that underly FP studies. However, while we find more FP evolution for galaxies of low sigma_eff (or low mass), the dynamical M/L evolution instead shows little trend with sigma_eff. We argue that this difference can be plausibly attributed to a combination of two effects: (a) evolution in structural galaxy properties other than M/L; and (b) the neglect of rotational support in studies of FP evolution. The results leave the question open whether the low-mass galaxies in the sample have younger population ages than the high-mass galaxies. This highlights the general importance in the study of population ages for complementing dynamical measurements with broad-band colors or spectroscopic population diagnostics.
We present analysis and photoionization modeling of the Chandra high resolution spectrum of Mrk~279. There is clear evidence of an absorbing outflow which is best fit by a two component model, one with a low ionization parameter and one with a higher ionization parameter. The column density of the X-ray warm absorber, about log N_H=20, is the smallest known of all AGNs in which X-ray absorbing outflows are observed. We find that the X-ray and UV/FUV absorbers are part of the same overall outflow. There is some evidence of super-solar carbon, nitrogen, oxygen and iron in the Chandra spectrum of Mrk 279. While this is not a robust result in itself, Chandra data in combination with the UV data and the pressure equilibrium between two phases of the outflow, support the scenario of super-solar abundances. This the first case where super-solar abundances are reported in the nucleus of a normal Seyfert galaxy.
We apply a recently developed theoretical model of helium emission to observations of both the Orion Nebula and a sample of extragalactic H II regions. In the Orion analysis, we eliminate some weak and blended lines and compare theory and observation for our reduced line list. With our best theoretical model we find an average difference between theoretical and observed intensities $<I_{predicted}/I_{observed}-1> = 6.5%$. We argue that both the red and blue ends of the spectrum may have been inadequately corrected for reddening. For the 22 highest quality lines, with $3499 {\AA}\le\lambda\le6678 {\AA}$, our best model predicts observations to an average of 3.8%. We also perform an analysis of the reported observational errors and conclude they have been underestimated. In the extragalactic analysis, we demonstrate the likelihood of a large systematic error in the reported data and discuss possible causes. This systematic error is at least as large as the errors associated with nearly all attempts to calculate the primordial helium abundance from such observations. Our Orion analysis suggests that the problem does not lie in the theoretical models. We demonstrate a correlation between equivalent width and apparent helium abundance of lines from extragalactic sources that is most likely due to underlying stellar absorption. Finally, we present fits to collisionless case-B He I emissivities as well as the relative contributions due to collisional excitations out of the metastable $2s {}^{3}S$ term.
It is commonly assumed that high-energy gamma-rays are made via either purely electromagnetic processes or the hadronic process of pion production, followed by decay. We investigate astrophysical contexts where a third process (A*) may dominate, namely the photo-disintegration of highly boosted nuclei followed by daughter de-excitation. Starbust regions such as Cygnus OB2 appear to be promising sites for TeV gamma-ray emission via this mechanism. A unique feature of the A* process is a sharp energy minimum ~ 10 TeV/(T/eV) for gamma-ray emission from a thermal region of temperature T. We also check that a diffuse gamma-ray component resulting from the interaction of a possible extreme-energy cosmic-ray nuclei with background radiation is well below the observed EGRET data.
TeV gamma-rays may provide significant information about high energy astrophysical accelerators. Such gamma-rays can result from the photo-de-excitation of PeV nuclei after their parents have undergone photo-disintegration in an environment of ultraviolet photons. This process is proposed as a candidate explanation of the recently discovered HEGRA source at the edge of the Cygnus OB2 association. The Lyman-alpha background is provided by the rich O and B stellar environment. It is found that (1) the HEGRA flux can be obtained if there is efficient acceleration at the source of lower energy nuclei; (2) the requirement that the Lorentz-boosted ultraviolet photons can excite the Giant Dipole resonance implies a strong suppression of the gamma-ray spectrum compared to an E_\gamma^{-2} behavior at energies \alt 1 TeV (some of these energies will be probed by the upcoming GLAST mission); (3) a TeV neutrino counterpart from neutron decay following helium photo-disintegration will be observed at IceCube only if a major proportion of the kinetic energy budget of the Cygnus OB2 association is expended in accelerating nuclei.
High-precision data from observation of the cosmic microwave background and the large scale structure of the universe provide very tight constraints on the effective parameters that describe cosmological inflation. Indeed, within a constrained class of LambdaCDM models, the simple lambda phi^4 chaotic inflation model already appears to be ruled out by cosmological data. In this paper, we compute constraints on inflationary parameters within a more general framework that includes other physically motivated parameters such as a nonzero neutrino mass. We find that a strong degeneracy between the tensor-to-scalar ratio r and the neutrino mass prevents lambda phi^4 from being excluded by present data. Reversing the argument, if lambda phi^4 is the correct model of inflation, it predicts a sum of neutrino masses at 0.3-0.5 eV, a range compatible with present experimental limits and within the reach of the next generation of neutrino mass measurements. We also discuss the associated constraints on the dark matter density, the dark energy equation of state, and spatial curvature, and show that the allowed regions are significantly altered. Importantly, we find an allowed range of 0.094 < Omega_c h^2 < 0.136 for the dark matter density, a factor of two larger than that reported in previous studies. This expanded parameter space may have implications for constraints on SUSY dark matter models.
The X-ray bright z=0.116 quasar PKS 2155-304 is frequently observed with Chandra for calibration purposes. Highly-ionized metal absorption lines, including numerous lines at z=0 and a putative OVIII K\alpha line at z=0.055, have been reported in past Chandra studies of this source. Using all available Chandra spectra and analysis techniques developed for such z=0 X-ray absorption along other sightlines, we revisit these previous detections. The 1\sigma ranges of OVII column density and Doppler parameter are consistent with those derived for Mrk 421 and within 2\sigma of the Mrk 279 absorption. Temperatures and densities are inferred from the relative OVII and other ionic column densities and found to be consistent with either the local warm-hot intergalactic medium or a Galactic corona. Unlike the local X-ray absorbers seen along other sightlines, a link with the low- or high-velocity far-ultraviolet OVI absorption lines cannot be ruled out. The z=0.055 OVIII absorption reported by Fang et al. is seen with 3.5\sigma confidence in the ACIS spectrum, but no other absorption lines are found at the same redshift.
[Abridged] Contex. Young open clusters provide important clues to the interface between the main sequence and pre-main-sequence phases of stellar evolution. The young and nearby open cluster IC 2391 is well-suited to studies of these two evolutionary phases. Aims. We establish a bona fide set of cluster members and then analyze this set in terms of binary frequency, projected rotational velocities, [Fe/H], and lithium abundance. In the wake of the Hipparcos distance controversy for the Pleiades, we compare the main-sequence fitting distance modulus to the Hipparcos mean parallax for IC 2391. Results. The proper-motion survey covers a 6 times larger sky area than the prior targeted searches for cluster members in IC 2391. A total of 66 stars are considered bona fide cluster members down to a mass equivalent to 0.5M_sun. A quarter of them have been newly identified with many in the F2-K5 spectral range, which is crucial for a main-sequence fit. We find a mean [Fe/H] value of +0.06+/-0.06, when a solar abundance of log epsilon (Fe)=7.45 is adopted. The main sequence fitting yields a distance modulus that is 0.19 mag larger than that derived from Hipparcos parallaxes; thus this offset nearly has the size of a similar offset found for the Pleiades. The Li abundance pattern is similar to the earlier findings and is typical for a 40 Myr old open cluster.
The high opacity of He I 10830 makes it an exceptionally sensitive probe of the inner wind geometry of accreting T Tauri stars. In this line blueshifted absorption below the continuum results from simple scattering of stellar photons, a situation which is readily modeled without definite knowledge of the physical conditions and recourse to multi-level radiative transfer. We present theoretical line profiles for scattering in two possible wind geometries, a disk wind and a wind emerging radially from the star, and compare them to observed He I 10830 profiles from a survey of classical T Tauri stars. The comparison indicates that subcontinuum blueshifted absorption is characteristic of disk winds in ~30% of the stars and of stellar winds in ~40%. We further conclude that for many stars the emission profile of helium likely arises in stellar winds, increasing the fraction of accreting stars inferred to have accretion-powered stellar winds to ~60%. Stars with the highest disk accretion rates are more likely to have stellar wind than disk wind signatures and less likely to have redshifted absorption from magnetospheric funnel flows. This suggests the possibility that when accretion rates are high, disks can extend closer to the star, magnetospheric accretion zones can be reduced in size and conditions arise that favor radially outflowing stellar winds.
The initial cluster mass function (ICMF) is a fundamental property of star formation in galaxies. To gauge its universality, we measure and compare the ICMFs in irregular and spiral galaxies. Our sample of irregular galaxies is based on thirteen nearby galaxies selected from a volume-limited sample from the fifth data release of the Sloan Digital Sky Survey (SDSS). The extinctions, ages, and masses were determined by comparing their u'g'i'z' magnitudes to those generated from starburst models. Completeness corrections were performed using Monte Carlo simulations in which artificial clusters were inserted into each galaxy. We analyzed three nearby spiral galaxies with SDSS data in exactly the same way to derive their ICMF based on a similar number of young, massive clusters as the irregular galaxy ICMF. We find that the ICMFs of irregular and spiral galaxies for masses >10^5 M_sun are statistically indistinguishable. For clusters more massive than 10^5 M_sun, the ICMF of the irregular galaxies is reasonably well fit by a power law dN(M)/dM ~ M^-a_M with a_M = 1.62 +/- 0.08. Similar results were obtained for the ICMF of the spiral galaxy sample, with a_M = 1.74 +/- 0.07. We discuss the implications of our result for theories of star cluster formation, which appears to be independent of metallicity and galactic shear rate.
We present age and metallicities determinations based on narrow band continuum colors for the galaxies in the rich clusters A1185 and Coma. Using a new technique to extract luminosity-weighted age and [Fe/H] values for non-star-forming galaxies, we find that both clusters have two separate populations based on these parameters. One population is old ($\tau >$ 11 Gyrs) with a distinct mass-metallicity relation. The second population is slightly younger ($\tau \approx$ 9 Gyrs) with lower metallicities and lower stellar masses. We find detectable correlations between age and galaxy mass in both populations such that older galaxies are more massive and have higher mean metallicities, confirming previous work with line indices for the same type of galaxies in other clusters (Kelson et al 2006, Thomas et al 2005). Our results imply shorter durations for higher mass galaxies, in contradiction to the predictions of classic galactic wind models. Since we also find a clear mass-metallicity relation for these galaxies, then we conclude that star formation was more efficient for higher mass galaxies, a scenario described under the inverse wind models (Matteucci 1994). With respect to cluster environmental effects, we find there is a significant correlation between galaxy mean age and distance from the cluster center, such that older galaxies inhabit the core. This relationship would nominally support hierarchical scenarios of galaxy formation (younger age in lower density regions); however, environmental effects probably have larger signature in the sample and present-day galaxies are remnants from an epoch of quenching of initial star formation, which would result in the same age gradients.
We present mid-infrared photometry of 124 white dwarf stars with Spitzer Space Telescope. Objects were observed simultaneously at 4.5 and 8.0um with sensitivities better than 1 mJy. This data can be used to test models of white dwarf atmospheres in a new wavelength regime, as well as to search for planetary companions and debris disks.
I describe the current state of our knowledge of the mapping between the initial masses of stars and the compact objects -- particularly neutron stars and black holes -- that they produce. Most of that knowledge is theoretical in nature, and relies on uncertain assumptions about mass loss through winds, binary mass transfer, and the amount of mass ejected during a supernovae. Observational constraints on the initial masses of stars that produce neutron stars and black holes is scarce. They fall into three general categories: (1) models of the stars that produced the supernova remnants associated with known compact objects, (2) scenarios through with high mass X-ray binaries were produced, and (3) associations between compact objects and coeval clusters of stars for which the minimum masses of stars that have undergone supernovae are known. I focus on the last category as the most promising in the near term. I describe three highly-magnetized neutron stars that have been associated with progenitors that had initial masses of $>$30\msun, and evaluate the prospects of finding further associations between star clusters and compact objects.
We have performed broadband color photometry of the twelve brightest irregular satellites of Saturn with the goal of understanding their surface composition, as well as their physical relationship. We find that the satellites have a wide variety of different surface colors, from the negative spectral slopes of the two retrograde satellites S IX Phoebe (S'=-2.5+/-0.4 %/100nm) and S XXV Mundilfari (S'=-5.0+/-1.9 %/100nm) to the fairly red slope of S XXII Ijiraq (S'=19.5+/-0.9 %/100nm). We further find that there exist a correlation between dynamical families and spectral slope, with the prograde clusters, the Gallic and Inuit, showing tight clustering in colors among most of their members. The retrograde objects are dynamically and physically more dispersed, but some internal structure is apparent.
We present HI observations of 54 galaxies in the Pegasus cluster. The observations include single dish HI measurements, obtained with the Arecibo telescope for all 54 galaxies in the sample, as well as HI images, obtained with the VLA for 10 of these. The Arecibo profiles reveal an overall HI deficiency in the cluster, with ~40% of the galaxies in the core of the cluster showing modest deficiencies of typically a factor of 2-3. The HI morphology of some galaxies shows that the HI disk is smaller than the optical disk and slightly offset from the stars. We find a correlation between HI deficiency and the ratio of the HI disk size to optical disk size. More HI deficient galaxies have relatively smaller HI disks, a configuration that is usually attributed to an interaction between the ISM of the galaxy and the hot ICM. Such a result is surprising since the Pegasus cluster has a low level of X-ray emission, and a low velocity dispersion. The low velocity dispersion, coupled with the lack of a dense hot ICM indicate that ram pressure stripping should not play a significant role in this environment. In addition, two of the galaxies, NGC7604 and NGC7648, are morphologically peculiar. Their peculiarities indicate contradictory scenarios of what is triggering their unusual star formation. Halpha imaging, along with long-slit spectroscopy of NGC7648 reveal morphological features which point to a recent tidal interaction. On the other hand, Halpha imaging,along with VLA HI mapping, of NGC7604 reveal morphological features suggestive of a ram pressure event. Our data indicate that ISM-ICM interactions may play a role in a wider variety of environments than suggested by simple ram pressure arguments.
We argue, following our earlier works (the "CEBZMC model"), that the phenomenon of twin peak high frequency quasi-periodic oscillations (QPOs) observed in black hole X-ray binaries is caused by magnetic coupling (MC) between accretion disk and black hole (BH). Due to MC, two bright spots occur at two separate radial locations r_{in} and r_{out} at the disk surface, energized by a kind of the Blandford-Znajek mechanism (BZ). We assume, following the Kluzniak-Abramowicz QPO resonance model, that Keplerian frequencies at these two locations are in the 3:2 ratio. With this assumption, we estimate the BH spins in several sources, including GRO J1655-40, GRS 1915+105, XTE J1550-564, H1743-322 and Sgr A*. We give an interpretation of the "jet line" in the hardness-intensity plane discussing the parameter space consisting of the BH spin and the power-law index for the variation of the large-scale magnetic field in the disk. Furthermore, we propose a new scenario for the spectral state transitions in BH X-ray binaries based on fluctuation in densities of accreting plasma from a companion star.
For four well studied spiral galaxies (M33, M81, M100 and M101) we consider the dependencies of star formation rate (SFR) and star formation efficiency (SFE = SFR/M_{gas}) both on the radial distance R and on some kinematic parameters of galactic discs. To estimate SFR(R) we used a combined UV+FIR method based on the UV profiles corrected for the interstellar extinction presented by Boissier et al, 2004. It is demonstrated that the most tight correlation, similar for all four galaxies we considered, exists between the local SFE and the surface brightness (density) of discs at a given R (beyond their central regions). To account for the observed surface densities of discs in the frame of a simple conservative model of evolution of gas content (a toy model) it is necessary for the local parameter N in the Schmidt law for a disc (SFR \sim \sigma_{gas}^N) not to exceed unit. Only in this case it is possible to reconcile the observed dependencies \sigma_{gas}(R) and SFE(R) assuming a gas accretion, more intense in the inner regions of galaxies.
We present a light curve model for the super-Eddington luminosity phase of five classical novae observed with IUE. Optical and UV light curves are calculated based on the optically thick wind theory with a reduced effective opacity for a porous atmosphere. Fitting a model light curve with the UV 1455 \AA light curve, we determine the white dwarf mass and distance to be (1.3 M_sun, 4.4 kpc) for V693 CrA, (1.05 M_sun, 1.8 kpc) for V1974 Cyg, (0.95 M_sun, 4.1 kpc) for V1668 Cyg, (1.0 M_sun, 2.1 kpc) for V351 Pup, and (1.0 M_sun, 4.3 kpc) for OS And.
A new scheme for testing the nuclear matter (NM) equation of state (EoS) at high densities using constraints from compact star (CS) phenomenology is applied to neutron stars with a core of deconfined quark matter (QM). An acceptable EoS shall not to be in conflict with the mass measurement of 2.1 +/- 0.2 M_sun (1 sigma level) for PSR J0751+1807 and the mass-radius relation deduced from the thermal emission of RX J1856-3754. Further constraints for the state of matter in CS interiors come from temperature-age data for young, nearby objects. The CS cooling theory shall agree not only with these data, but also with the mass distribution inferred via population synthesis models as well as with LogN-LogS data. The scheme is applied to a set of hybrid EsoS with a phase transition to stiff, color superconducting QM which fulfills all above constraints and is constrained otherwise from NM saturation properties and flow data of heavy-ion collisions. We extrapolate our description to low temperatures and draw conclusions for the QCD phase diagram to be explored in heavy-ion collision experiments.
We apply a Cross-correlation (CC) method developed previously for detecting gamma-ray point sources to the WMAP first year data by using the Point-Spread Function of WMAP and obtain a full sky CC coefficient map. Analyzing this map, we find that the CC method is a powerful tool to examine the WMAP foreground residuals which can be further cleaned accordingly. Evident foreground signals are found in WMAP foreground cleaned maps and Tegmark cleaned map. In this process 101 point-sources are detected, and 26 of them are new sources besides the originally listed WMAP 208 sources. We estimate the flux of these new sources and verify them by another method. As a result, a revised mask file based on the WMAP first year data is produced by including these new sources.
This collection of proceedings to the TeV PA II Conference presents some of the latest results of the IceCube Collaboration.
VERITAS is an atmospheric Cherenkov telescope array sited in Tucson, Arizona. The array is nearing completion and consists of four, 12m diameter telescopes. The first telescope in the array has been operating since February 2005, while observations with the full array are expected to begin in January, 2007. We report here in some detail on the performance of the first VERITAS telescope, and briefly discuss the first stereo observations.
We detected X-ray emission from PSR B1800-21 and its synchrotron nebula with the Chandra X-ray Observatory. The pulsar's observed flux is (1.4+/-0.2) 10^{-14} ergs cm^{-2} s^{-1} in the 1-6 keV band. The spectrum can be described by a two-component PL+BB model, suggesting a mixture of thermal and magnetospheric emission. For a plausible hydrogen column density n_{H}=1.4 10^{22} cm^{-2}, the PL component has a slope Gamma=1.4+/-0.6 and a luminosity L_{psr}^{nonth}=4 10^{31}(d/4 kpc)^2 ergs s^{-1}. The properties of the thermal component (kT=0.1-0.3 keV, L^{bol}=10^{31}-10^{33} ergs s^{-1}) are very poorly constrained because of the strong interstellar absorption. The compact, 7''\times4'', inner pulsar-wind nebula (PWN), elongated perpendicular to the pulsar's proper motion, is immersed in a fainter asymmetric emission. The observed flux of the PWN is (5.5+/-0.6) 10^{-14} ergs cm^{-2} s^{-1} in the 1-8 keV band. The PWN spectrum fits by a PL model with Gamma=1.6+/-0.3, L=1.6 10^{32} (d/4 kpc})^2 ergs s^{-1}. The shape of the inner PWN suggests that the pulsar moves subsonically and X-ray emission emerges from a torus associated with the termination shock in the equatorial pulsar wind. The inferred PWN-pulsar properties (e.g., the PWN X-ray efficiency, L_{pwn}/\dot{E}~10^{-4}; the luminosity ratio, L_{pwn}/L_{psr}^{nonth}=4; the pulsar wind pressure at the termination shock, p_s=10^{-9} ergs cm^{-3}) are very similar to those of other subsonically moving Vela-like objects detected with Chandra (L_{pwn}/\dot{E}=10^{-4.5}-10^{-3.5}, L_{pwn}/L_{psr}^{nonth}~5, p_s=10^{-10}-10^{-8} ergs cm^{-1}).
* Aims. Identify optical counterparts, address uncertain identifications and measure previously unknown redshifts of the host galaxies of candidate GPS radio sources, and study their stellar populations. * Methods. Long slit spectroscopy and deep optical imaging in the B, V and R bands, obtained with the Very Large Telescope. * Results. We obtain new redshifts for B0316+161, B0407-658, B0904+039, B1433-040, and identify the optical counterparts of B0008-421 and B0742+103. We confirm the previous identification for B0316+161, B0407-658, B0554-026, and B0904+039, and find that the previous identification for B0914+114 is incorrect. Using updated published radio spectral information we classify as non GPS the following sources: B0407-658, B0437-454, B1648+015. The optical colors of typical GPS sources are consistent with single instantaneous burst stellar population models but do not yield useful information on age or metallicity. A new master list of GPS sources is presented.
In a recent publication, we have demonstrated that differentially rotating
stars admit new channels of black hole formation via fragmentation
instabilities. Since a higher order instability of this kind could potentially
transform a differentially rotating supermassive star into a multiple black
hole system embedded in a massive accretion disk, we investigate the dependence
of the instability on parameters of the equilibrium model. We find that many of
the models constructed exhibit non-axisymmetric instabilities with corotation
points, even for low values of T/|W|, which lead to a fission of the stars into
one, two or three fragments, depending on the initial perturbation.
At least in the models selected here, an m=1 mode becomes unstable at lower
values of T/|W|, which would seem to favor a scenario where one black hole with
a massive accretion disk forms. In this case, we have gained evidence that low
values of compactness of the initial model can lead to a stabilization of the
resulting fragment, thus preventing black hole formation in this scenario.
We report on interferometric AMBER/VLTI observations of the recurrent nova RS Oph five days after its outburst on 2006 Feb 12. Using three baselines from 44 to 86m, and a spectral resolution of 1500, we measured the extension of the emission in the K band continuum and in the BrG and HeI2.06 micron lines. The continuum visibilities were interpreted by fitting simple geometric models consisting of uniform and Gaussian ellipses, ring and binary models. The visibilities and differential phases in the BrG line were interpreted using skewed ring models aiming to perform a limited parametric reconstruction of the extension and kinematics of the line forming region. The limited uv coverage does not allow discrimination between filled models and rings. Binary models are discarded because the measured closure phase in the continuum is close to zero. The visibilities in the lines are at a low level compared to their nearby continuum, consistent with a more extended line forming region for HeI2.06 than BrG. The ellipse models for the continuum and for the lines are highly flattened and share the same position angle. Two radial velocity fields are apparent in the BrG line: a 'slow' expanding ring-like structure (v~1800km/s), and a 'fast' structure extended in the E-W direction (v~2500-3000km/s). These results confirm the basic fireball model, contrary to the conclusions of other interferometric observations conducted by Monnier et al. (2006).
Since the end of the 2005-2006 austral summer, the IceCube detector consists of an array of 9 strings, deployed between 1450 m and 2450 m of depth and containing 540 digital optical sensors and 16 IceTop surface stations with 64 sensors. With the integrated AMANDA-II experiment this is the world's largest neutrino telescope in operation. The construction status of IceCube is presented along with an update on physics performance study for the detection of high energy neutrinos. The potential of the full km^3-scale telescope in the search for astrophysical sources is also addressed.
Neutrino telescopes detect the emission of Cherenkov light resulting from the tracks and showers of charged and neutral current neutrino interactions. These tracks or showers are reconstructed using a corresponding probability density function (PDF) which depends on measured time and location of the detected photo-electrons. We call a composite event the mixed detector response due to the juxtaposition of more than one Cherenkov light source (track or shower). This paper presents the construction of a generic PDF corresponding to a composite hypothesis. This composite PDF is therefore useful to reconstruct an arbitrary event topology and to favor or discard a given event topology hypothesis.
The inward flow of matter through accretion disks is driven by MHD turbulence. Global general relativistic MHD simulations shed quantitative light on this process, revealing a number of aspects of accretion previously unrecognized. Among them are strong stresses in the marginally stable and plunging regions near the black hole and electromagnetically-dominated conical relativistic jets that can form spontaneously from the accretion flow. The energy release associated with both of these effects can significantly augment the classical energy-release estimates based on purely hydrodynamic models.
We have combined infrared data with HI, H2 and HII surveys in order to spatially decompose the observed dust emission into components associated with different phases of the gas. An inversion technique is applied. For the decomposition, we use the IRAS 60 and 100 micron bands, the DIRBE 140 and 240 micron bands, as well as Archeops 850 and 2096 micron wavelengths. In addition, we apply the decomposition to all five WMAP bands. We obtain longitude and latitude profiles for each wavelength and for each gas component in carefully selected Galactic radius bins.We also derive emissivity coefficients for dust in atomic, molecular and ionized gas in each of the bins.The HI emissivity appears to decrease with increasing Galactic radius indicating that dust associated with atomic gas is heated by the ambient interstellar radiation field (ISRF). By contrast, we find evidence that dust mixed with molecular clouds is significantly heated by O/B stars still embedded in their progenitor clouds. By assuming a modified black-body with emissivity law lambda^(-1.5), we also derive the radial distribution of temperature for each phase of the gas. All of the WMAP bands except W appear to be dominated by emission from something other than normal dust, most likely a mixture of thermal bremstrahlung from diffuse ionized gas, synchrotron emission and spinning dust. Furthermore, we find indications of an emissivity excess at long wavelengths (lambda > 850 micron) in the outer Galaxy (R > 8.9 kpc). This suggests either the existence of a very cold dust component in the outer Galaxy or a temperature dependence of the spectral emissivity index. Finally, it is shown that ~ 80% of the total FIR luminosity is produced by dust associated with atomic hydrogen, in agreement with earlier findings by Sodroski et al. (1997).
We examine volume-limited samples from the SDSS galaxies to look for relations among internal and collective physical parameters of galaxies as faint as M_r=- 17.5, which include morphology, luminosity, color, color gradient, concentration, size, velocity dispersion, equivalent width (EW) of H_alpha line,axis ratio, the luminosity and velocity dispersion functions. At fixed morphology and luminosity, we find that bright (M_r<-20) early-types show very small dispersions in color, color gradient, concentration, size, and velocity dispersion. These dispersions increase at fainter magnitudes, where the fraction of blue early-types increases. Late-types show wider dispersions in all physical parameters compared to early types at the same luminosity. Concentration indices of early-types are well-correlated with velocity dispersion, but are insensitive to luminosity and color for bright galaxies. The slope of the Faber-Jackson relation continuously changes from 4.6 +- 0.4 to 2.7+- 0.2 when luminosity changes from M_r = -22 to -20. The size of early- types is well-correlated with stellar velocity dispersion (for >100 km/s). We find that passive spirals are well-separated from star-forming late-types at EW (H_alpha) of about 4. An interesting finding is that many physical parameters of galaxies manifest different behaviors across the absolute magnitude of about M_* +- 1. The morphology fraction as a function of luminosity depends less sensitively on large scale structure than the luminosity function (LF) does, and thus seems to be more universal. The effects of internal extinction in late-types on the completeness of volume limited samples and on the LF and morphology fraction are found to be very important. (abridged)
The magnetar model and the solid quark star model for anomalous X-ray pulsars/soft gamma-ray repeaters (AXPs/SGRs) are discussed. The pulsar-like stars manifesting variously are speculated to have different ambience and/or inner structure (mass and strain) in the solid quark star scenario. Relevant arguments made by the author's group are briefly summarized too.
Low-mass stars, ~1-2 solar masses, near the Main Sequence are efficient at producing 3He, which they mix into the convective envelope on the giant branch and distribute into the Galaxy by way of envelope loss. This process is so efficient that it is difficult to reconcile the observed cosmic abundance of 3He with the predictions of Big Bang nucleosynthesis. In this paper we find, by modeling a red giant with a fully three-dimensional hydrodynamic code and a full nucleosynthetic network, that mixing arises in the supposedly stable and radiative zone between the hydrogen-burning shell and the base of the convective envelope. This mixing is due to Rayleigh-Taylor instability within a zone just above the hydrogen-burning shell. In this zone the burning of the 3He left behind by the retreating convective envelope is predominantly by the reaction 3He + 3He -> 4He + 2p, a reaction which, untypically for stellar nuclear reactions, {\it lowers} the mean molecular weight, leading to a local minimum. This local minimum leads to Rayleigh-Taylor instability, and turbulent motion is generated which will continue ultimately up into the normal convective envelope. Consequently material from the envelope is dragged down sufficiently close to the burning shell that the 3He in it is progressively destroyed. Thus we are able to remove the threat that 3He production in low-mass stars poses to the Big Bang nucleosynthesis of 3He. Some slow mixing mechanism has long been suspected, that connects the convective envelope of a red giant to the burning shell. It appears to be necessary to account for progressive changes in the 12C/13C and 14N/12C ratios on the First Giant Branch. We suggest that these phenomena are also due to the Rayleigh-Taylor-unstable character of the 3He-burning region.
We investigate the dependence of physical properties of galaxies brighter than M_r=-18.0 in the SDSS on environment, as measured by local density using an adaptive smoothing kernel. We find that variations of galaxy properties with environment are almost entirely due to the dependence of morphology and luminosity on environment. Because galaxy properties depend not only on luminosity but also on morphology, it is clear that galaxy properties cannot be determined solely by dark halo mass. When morphology and luminosity are fixed, other physical properties, such as color, color-gradient, concentration, size, velocity dispersion, and star formation rate, are nearly independent of local density. The only feature is the sharp decrease of late type fraction above the critical luminosity of about M_r=-21.3 in the morphology versus luminosity relation. Weak residual dependences on environment include that of the color of late-types (bluer at lower density) and of the L-sigma relation of early-types (larger dispersion at higher density for bright galaxies). The early-type fraction is a monotonically increasing function of local density and luminosity. The morphology-density- luminosity relation should be a key constraint on galaxy formation models. We demonstrate that the dependence on environment of the morphology of galaxie originates from variations in density on effective Gaussian smoothing scales much smaller than 12 h^{-1}Mpc. We find that galaxy morphology varies both with density measured on an effective Gaussian smoothing scale of 4.7 h^{-1} Mpc and on distance to the nearest bright galaxy (particularly, for about 0.2 h^{-1}Mpc). We propose a mechanism that the morphology of galaxies in galaxy systems is transformed by the tidal force.
We present JHKs near-infrared CCD photometric study for the Galactic open clusters NGC 1641 and NGC 2394. These clusters have never been studied before, and we provide, for the first time, the cluster parameters; reddening, distance, metallicity and age. NGC 1641 is an old open cluster with age 1.6 +/- 0.2 Gyr, metallicity [Fe/H] = 0.0 +/- 0.2 dex, distance modulus (m-M)_0 = 10.4 +/- 0.3 mag (d = 1.2 +/- 0.2 kpc), and reddening E(B-V) = 0.10 +/- 0.05 mag. The parameters for the other old open cluster NGC 2394 are estimated to be age = 1.1 +/- 0.2 Gyr, [Fe/H] = 0.0 +/- 0.2 dex, (m-M)_0 = 9.1 +/- 0.4 mag (d = 660 +/- 120 pc), and E(B-V) = 0.05 +/- 0.10 mag. The metallicities and distance values for these two old open clusters are consistent with the relation between the metallicities and the Galactocentric distances of other old open clusters. We find the metallicity gradient of 53 old open clusters including NGC 1641 and NGC 2394 to be Delta [Fe/H]/Delta R_gc = -0.067 +/- 0.009 dex/kpc.
We report $^{12}$CO($J=$3--2) observations of 15 nearby elliptical galaxies carried out with the ASTE telescope. Thirteen were selected without regard to the presence of other tracers of cold interstellar matter. CO emission was detected from three of the galaxies, two of which are undetected by IRAS at 100 microns, suggesting that cold ISM may be present in more ellipticals than previously thought. The molecular gas masses range from $2.2 \times 10^6$ to $4.3 \times 10^8$ $M_\odot$. The ratio of the CO(3--2) and (1--0) lines, $R_{31}$, has a lower value for elliptical galaxies than for spiral galaxies except for NGC 855, for which the value is close to the mean for spirals. The molecular gas in NGC 855 has a mean density in the range 300 -- 1000 cm$^{-3}$ adopting a temperature range of 15 -- 100 K.
We present the highest resolution VLBI imaging observations of Sgr A* made at both 7 and 3.5 mm. These data reveal wavelength-dependent intrinsic sizes with an intrinsic emitting region at 3.5 mm of about 1 AU (at a distance of 8 kpc to the Galactic Center). When combined with the lower limit on the mass of Sgr A*, these size measurements provide strong evidence that Sgr A* is a super-massive black hole. We also detected a structural variation which results in an intrinsically symmetrical structure that increases in its intrinsic size by more than 25% at 7 mm.
We investigate a phase-reference VLBI observation that was conducted at 15.4 GHz by fast switching VLBA antennas between the compact steep-spectrum radio source 3C 138 and the quasar PKS 0528+134 which are about 4$^\circ$ away on the sky. By comparing the phase-reference mapping with the conventional hybrid mapping, we demonstrate the feasibility of high precision astrometric measurements for sources separated by 4$^\circ$. VLBI phase-reference mapping preserves the relative phase information, and thus provides an accurate relative position between 3C 138 and PKS 0528+134 of $\Delta\alpha=-9^m46^s.531000\pm0^s.000003$ and $\Delta\delta=3^\circ6^\prime26^{\prime\prime}.90311\pm0^{\prime\prime}.00007$ (J2000.0) in right ascension and declination, respectively. This gives an improved position of the nucleus (component A) of 3C 138 in J2000.0 to be RA=$05^h 21^m 9^s.885748$ and Dec=$16^\circ 38' 22''.05261$ under the assumption that the position of calibrator PKS 0528+134 is correct. We further made a hybrid map by performing several iterations of CLEAN and self-calibration on the phase-referenced data with the phase-reference map as an input model for the first phase self-calibration. Compared with the hybrid map from the limited visibility data directly obtained from fringe fitting 3C 138 data, this map has a similar dynamic range, but a higher angular resolution. Therefore, phase-reference technique is not only a means of phase connection, but also a means of increasing phase coherence time allowing self-calibration technique to be applied to much weaker sources.
This article was co-authored by all invited speakers at the Joint Discussion on `Neutron Stars and Black Holes in Star Clusters,' which took place during the IAU General Assembly in Prague, Czech Republic, on August 17 and 18, 2006. Each section presents a short summary of recent developments in a key area of research, incorporating the main ideas expressed during the corresponding panel discussion at the meeting. Our meeting, which had close to 300 registered participants, was broadly aimed at the large community of astronomers around the world working on the formation and evolution of compact objects and interacting binary systems in dense star clusters, such as globular clusters and galactic nuclei. Great advances have occurred in this field during the past few years, including the introduction of fundamentally new theoretical paradigms for the formation and evolution of compact objects in binaries as well as countless new discoveries by astronomers that have challenged many accepted models. Some of the highlights include: a nearly complete census of all the millisecond pulsars in 47 Tuc; first detections of many new radio pulsars in other clusters, particularly Terzan 5; detailed studies of X-ray binary populations and their luminosity functions in many galaxies and extragalactic globular clusters; increasing evidence for intermediate-mass black holes in clusters and greatly improved theoretical understanding of their possible formation processes.
We present resolved NACO photometry of the close binary AB Dor B in H- and Ks-band. AB Dor B is itself known to be a wide binary companion to AB Dor A, which in turn has a very low-mass close companion named AB Dor C. These four known components make up the young and dynamically interesting system AB Dor, which will likely become a benchmark system for calibrating theoretical pre-main sequence evolutionary mass tracks for low-mass stars. However, for this purpose the actual age has to be known, and this subject has been a matter of discussion in the recent scientific literature. We compare our resolved photometry of AB Dor Ba and Bb with theoretical and empirical isochrones in order to constrain the age of the system. This leads to an age estimate of about 50 to 100 Myr. We discuss the implications of such an age range for the case of AB Dor C, and compare with other results in the literature.
We investigate the atomic and molecular interstellar medium and star formation of NGC 275, the late-type spiral galaxy in Arp 140, which is interacting with NGC 274, an early-type system. The atomic gas (HI) observations reveal a tidal tail from NGC 275 which extends many optical radii beyond the interacting pair. The HI morphology implies a prograde encounter between the galaxy pair approximately 1.5 x 10**8 years ago. The Halpha emission from NGC 275 indicates clumpy irregular star-formation, clumpiness which is mirrored by the underlying mass distribution as traced by the Ks-band emission. The molecular gas distribution is striking in its anti-correlation with the {HII regions. Despite the evolved nature of NGC 275's interaction and its barred potential, neither the molecular gas nor the star formation are centrally concentrated. We suggest that this structure results from stochastic star formation leading to preferential consumption of the gas in certain regions of the galaxy. In contrast to the often assumed picture of interacting galaxies, NGC 275, which appears to be close to merger, does not display enhanced or centrally concentrated star formation. If the eventual merger is to lead to a significant burst of star formation it must be preceded by a significant conversion of atomic to molecular gas as at the current rate of star formation all the molecular gas will be exhausted by the time the merger is complete.
We present a homogeneous set of stellar atmospheric parameters Teff, log g, [Fe/H] for MILES, a new spectral stellar library covering the range 3525 - 7500 angstrom at 2.3 angstrom (FWHM) spectral resolution. The library consists of 985 stars spanning a large range in atmospheric parameters, from super metal-rich, cool stars to hot, metal-poor stars. The spectral resolution, spectral type coverage and number of stars represent a substantial improvement over previous libraries used in population synthesis models. The atmospheric parameters that we present here are the result of a previous, extensive compilation from the literature. In order to construct a homogeneous dataset of atmospheric parameters we have taken the sample of stars of Soubiran, Katz & Cayrel, which has very well determined fundamental parameters, as the standard reference system for our field stars, and have calibrated and bootstrapped the data from other papers against it. The atmospheric parameters for our cluster stars have also been revised and updated according to recent metallicity scales, colour-temperature relations and improved set of isochrones.
Recent solar photospheric abundance analyses by Asplund et al. (2005) have led to a significant reduction of the metal abundances compared to the previous determinations by Grevesse & Noels (1993). The solar models computed with standard opacities and diffusion processes using these new abundances give poor agreement with helioseismic inversions for the sound-speed profile, the surface helium abundance and the convective zone depth. We attempt to obtain a good agreement between helioseismic inversions and solar models which present the Grevesse & Noels (1993) mixture in the interior and the Asplund et al. (2005) chemical composition in the convective zone. To reach this result, we assume an undermetallic accretion at the beginning of the main sequence. We compute solar models with the Toulouse-Geneva Evolution Code in which we simulate an undermetallic accretion in the early stages of the main sequence, in order to obtain the Asplund et al. (2005) mixture in the outer convective zone. We compare the sound-speed profile, the convective zone depth and the surface helium abundance with those deduced from helioseismology by Basu et al. (1997). The model with accretion but without any mixing process inside is in better agreement with helioseismology than the solar model with the new abundances throughout. There is however a spike under the convective zone which reaches 3.4%. Furthermore, the convective zone depth and the surface helium abundance are too low. Introducing undershooting below the convective zone allows to recover the good convective zone radius and the addition of rotation-induced mixing and tachocline allows to reconcile the surface helium abundance. But in any case the agreement of the sound-speed profile with helioseismic inference is worse than obtained with the old abundances.
Recent analyses of the intergalactic UV background by means of the HeII Lyman alpha forest assume that HeII and HI absorption features have the same line widths. We omit this assumption to investigate possible effects of thermal line broadening on the inferred HeII/HI ratio eta and to explore the potential of intergalactic HeII observations to constrain the thermal state of the IGM. Deriving a simple relation between the column density and the temperature of an absorber we develop a procedure to fit the parameters of a power law temperature-density relation and eta simultaneously. In an alternative approach the temperature of an absorber, eta, and the redshift scale of eta variations are estimated simultaneously. Tests with artificial data show that well-constrained results can be obtained only if the signal-to-noise ratio in the HeII forest is S/N > 20. Thus, it is impossible to give an estimate of the temperature-density relation with the HeII data available at present (S/N ~5). However, we find that only 45% of the lines in our sample favor turbulent line widths. Furthermore, the inferred eta values are on average about 0.05 dex larger if a thermal component is taken into account, and their distribution is 46% narrower in comparison to a purely turbulent fit. Therefore, variations of eta on a 10% level may be related to the presence of thermal line broadening. The apparent correlation between the strength of the HI absorption and the eta value, which has been found in former studies, essentially disappears if thermal broadening is taken into account. In the redshift range 2.58 < z < 2.74 towards the quasars HE2347-4342 and HS1700+6416 we obtain eta ~ 100. (abridged)
We report results from the XMM-Newton observation of IRAS 13197-1627, a luminous IR galaxy with a Seyfert 1.8 nucleus. The hard X-ray spectrum is steep and is absorbed by Compton-thin neutral gas. We detect an Fe emission line at 6.4 keV, consistent with transmission through the absorber. The most striking result of our spectral analysis is the detection of a dominant X-ray reflection component and broad Fe line from the inner accretion disc. The reflection-dominated hard X-ray spectrum is confirmed by the strong Compton hump seen in a previous BeppoSAX observation and could be the sign that most of the primary X-rays are radiated from a compact corona (or e.g. base of the jet) within a few gravitational radii from the black hole. We also detect a relatively strong absorption line at 6.81 keV which, if interpreted as Fe xxv resonant absorption intrinsic to the source, implies an outflow with velocity of about 5000 km/s. In the soft energy band, the high-resolution RGS and the CCD-resolution data show the presence of both photo-ionized gas and thermal plasma emission, the latter being most likely associated with a recent starburst of 15-20 solar masses per year.
(Abridged) Polarization measurements of the Galactic plane at lambda6 cm probe the interstellar medium (ISM) to larger distances compared to measurements at longer wavelengths, hence enable us to investigate properties of the Galactic magnetic fields and electron density. We are conducting a new lambda6 cm continuum and polarization survey of the Galactic plane covering 10degr < l < 230degr and |b|<5degr. Missing large-scale structures in the U and Q maps are restored based on extrapolated polarization K-band maps from the WMAP satellite. The lambda6 cm data are analyzed together with maps at other bands. We discuss some results for the first survey region, 7degr X 10degr in size, centered at (l,b)=(125.5degr, 0degr). Two new passive Faraday screens, G125.6-1.8 and G124.9+0.1, were detected. They cause significant rotation of background polarization angles but little depolarization. G124.9+0.1 was identified as a new faint HII region at a distance of 2.8 kpc. G125.6-1.8, with a size of about 46 pc, has neither correspondence in enhanced Halpha emission nor a counterpart in total intensity. A model combining foreground and background polarization modulated by the Faraday screen was developed. Using this model, we estimated the strength of the ordered magnetic field along the line of sight to be 3.9 microGauss for G124.9+0.1, and exceeding 6.4 microGauss for G125.6-1.8. We obtained an estimate of 2.5 and 6.3 mK/kpc for the average polarized and total synchrotron emissivity towards G124.9+0.1. The synchrotron emission beyond the Perseus arm is quite weak.
We investigate the corrections of the holographic dark energy to inflation paradigm. We study the evolution of the holographic dark energy in the inflationary universe in detail, and carry out a model-independent analysis on the holographic dark energy correction to the primordial scalar power spectrum. It turns out that the corrections generically make the spectrum redder. To be consistent with the experimental data, there must be a upper bound on the reheating temperature. We also discuss the corrections due to different choices of the infrared cutoff.
AIMS: A peculiar morphology of the hot gas was discovered at the center of
IC1262 with the ROSAT HRI. Sensitive Chandra and XMM-Newton data were requested
to investigate the characteristics of this structure to understand its nature.
METHODS: We have exploited the high resolution and sensitivity of Chandra's
ACIS-S to investigate the peculiar morphology and spectral characteristics of
hot gas in the group around IC1262. XMM-Newton data are only partially usable
due to very heavy high background contamination, but they are useful to confirm
and strengthen the results from Chandra.
RESULTS: The Chandra data show a quite dramatic view of the \object{IC1262}
system: a sharp discontinuity east of the central galaxy, with steep drops and
a relatively narrow feature over 100 kpc long, plus an arc/loop to the N, are
all indicative of a turmoil in the high energy component. Their morphologies
could suggest them to be tracers of shocked material caused either by peculiar
motions in the system or by a recent merger process, but the spectral
characteristics indicate that the structure is cooler than its surroundings.
The lack of evidence of significant structures in the velocity distribution of
the group members and the estimated scale of the phenomenon make the
interpretation of its physical nature challenging. We review a few possible
interpretations, in light of similar phenomena observed in clusters and groups.
The ram pressure stripping of a bright spiral galaxy, now near the center of
the group, is a promising interpretation for most of the features observed. The
relation with the radio activity requires a better sampling of the radio
parameters that can only be achieved with deeper and higher resolution
observations.
We examine the X-ray luminosity of galaxy groups in the CNOC2 survey, at redshifts 0.1 < z < 0.6. Previous work examining the gravitational lensing signal of the CNOC2 groups has shown that they are likely to be genuine, gravitationally bound objects. Of the 21 groups in the field of view of the EPIC-PN camera on XMM-Newton, not one was visible in over 100 ksec of observation, even though three of the them have velocity dispersions high enough that they would easily be visible if their luminosities scaled with their velocity dispersions in the same way as nearby groups' luminosities scale. We consider the possibility that this is due to the reported velocity dispersions being erroneously high, and conclude that this is unlikely. We therefore find tentative evidence that groups at intermediate redshift are underluminous relative to their local cousins.
This paper presents 452 new 21-cm neutral hydrogen line measurements carried out with the FORT receiver of the meridian transit Nan\c{c}ay radiotelescope (NRT) in the period April 2003 -- March 2005. This observational programme is part of a larger project aiming at collecting an exhaustive and magnitude-complete HI extragalactic catalogue for Tully-Fisher applications (the so-called KLUN project, for Kinematics of the Local Universe studies, end in 2008). The whole on-line HI archive of the NRT contains today reduced HI-profiles for ~4500 spiral galaxies of declination delta > -40° (this http URL). As an example of application, we use direct Tully-Fisher relation in three (JHK) bands in deriving distances to a large catalog of 3126 spiral galaxies distributed through the whole sky and sampling well the radial velocity range between 0 and 8000 km/s. Thanks to an iterative method accounting for selection bias and smoothing effects, we show as a preliminary output a detailed and original map of the velocity field in the Local Universe.
Difference imaging is a technique for obtaining precise relative photometry
of variable sources in crowded stellar fields and, as such, constitutes a
crucial part of the data reduction pipeline in surveys for microlensing events
or transiting extrasolar planets. The Optimal Image Subtraction (OIS) algorithm
permits the accurate differencing of images by determining convolution kernels
which, when applied to reference images of particularly good quality, provide
excellent matches to the point-spread functions (PSF) in other images of the
time series to be analysed. The convolution kernels are built as linear
combinations of a set of basis functions, conventionally bivariate Gaussians
modulated by polynomials. The kernel parameters must be supplied by the user
and should ideally be matched to the PSF, pixel-sampling, and S/N of the data
to be analysed. We have studied the outcome of the reduction as a function of
the kernel parameters using our implementation of OIS within the TRIPP package.
From the analysis of noise-free PSF simulations as well as test images from
the ISIS OIS package, we derive qualitative and quantitative relations between
the kernel parameters and the success of the subtraction as a function of the
PSF sizes and sampling in reference and data images and compare the results to
those of implementations in the literature. On this basis, we provide
recommended parameters for data sets with different S/N and sampling.
We present a unified picture to explain the spectral states of BH binaries based on the two-flow model. In our view, the central regions have a multi-flow configuration consisting in (1) an outer standard accretion disc (SAD) down to a transition radius $r_{tr}$, (2) an inner magnetized jet emitting disc (JED) below $r_{tr}$ driving (3) a self-collimated non relativistic MHD jet surrounding, when conditions for pair creation are met, (4) a ultra relativistic pair beam. Large values of $r_{tr}$ correspond to Hard states while small values correspond to Soft states. In between these extremes, in the high intermediate state, $r_{tr}$ can reach values that switch on a pair cascade process giving birth to ultra-relativistic pair blobs that explain the superluminal events. In this model the accretion rate but also the disc magnetization $\mu$ play important roles, the latter being necessarily in the range 0.1-1 for the MHD jet to exist. Then, with simple assumptions on $\mu$, we propose an explanation for the hysteresis behavior observed in microquasars during their outburst. We also discuss the nature, in our framework, of the X-ray corona and the origin of the X-ray variability in the hard state. Preliminary results are discussed.
We present an {\it XMM-Newton} EPIC observation of HE0450-2958 which may be a ``naked''quasar as suggested by Magain et al. The \xmm EPIC spectra show a substantial soft X-ray excess, a steep photon index, as well as marginal evidence for a weak Fe K$\alpha$ line. The X-ray absorption is consistent with the galactic level. The 0.3-10 keV EPIC spectra can be fitted by a power law plus a blackbody model, however, the fit by the relativistically blurred photoionized disc reflection is better. We estimate the black hole mass of $2^{+7}_{-1.3} \times 10^{7} M_{\odot}$ from the X-ray variability. This broadly agrees with the value derived from the optical \hb line width. These results support a high-state Seyfert galaxy of the source. HE0450-2958 shares similar properties of transitionary objects from ultra-luminous infrared galaxies to quasars. We suggest that HE0450-2958 is just in the beginning of an optical quasar window.
We have used R_C I_C CCD photometry from the Isaac Newton telescope and intermediate resolution spectroscopy from the Gemini North telescope to identify and characterise low-mass (0.15<M/M_sun<1.3) pre-main sequence stars in the young open cluster NGC 2169. Isochrone fitting to the high- and low-mass populations yields an intrinsic distance modulus of 10.13{+0.06}{-0.09} mag and a model-dependent age of 9+/-2 Myr. Compared with the nearby, kinematically defined groups of a similar age, NGC 2169 has a large low-mass population which potentially offers a more precise statistical investigation of several aspects of star formation and early stellar evolution. By modelling the distribution of low-mass stars in the I_C versus R_C-I_C diagram we find that any age spread among cluster members has a Gaussian full width at half maximum <=2.5 Myr. A young age and small age spread (<10 Myr) are supported by the lack of significant lithium depletion in the vast majority of cluster members. There is no clear evidence for accretion or warm circumstellar dust in the low-mass members of NGC 2169, bolstering the idea that strong accretion has ceased and inner discs have dispersed in almost all low-mass stars by ages of 10 Myr.
The enrichment of the Intra-Cluster Medium (ICM) with heavy elements is reviewed. There is now good observational evidence for enrichment including abundance ratios and metallicity distributions. Various processes involved in the enrichment process -- ram-pressure stripping, galactic winds, galaxy-galaxy interactions, AGN outflows and intra-cluster supernovae -- are described. Simulations of the ICM evolution taking into account metal enrichment are presented.
We analyze 19 bright variable X-ray sources detected in the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST), in order to characterize the variations with time of their coronal properties and to derive informations on the X-ray emitting structures. We performed time-resolved spectroscopy of the EPIC PN and MOS spectra of the XEST sources, using a model with one or two thermal components, and we used the time evolution of the temperatures and emission measures during the decay phase of flares to derive the size of the flaring loops. The light curves of the selected sources show different types of variability: flares, long-lasting decay or rise through the whole observation, slow modulation or complex flare-like variability. Spectral analysis shows typical quiescent plasma temperatures of 5-10 MK and 15-35 MK; the cool component generally remains constant, while the observed flux changes are due to variations of the hot component. During flares the plasma reaches temperatures up to 100 MK and luminosities up to $\sim 10^{31}$ erg s$^{-1}$. Loop sizes inferred from flare analysis are generally smaller than or comparable to the stellar radius.
We discuss the region of transition between galactic and extragalactic cosmic rays. The exact shapes and compositions of these two components contains information about important parameters of powerful astrophysical sources and the conditions in extragalactic space. Several types of experimental data, including the exact shape of the ultrahigh energy cosmic rays, their chemical composition and their anisotropy, and the fluxes of cosmogenic neutrinos have to be included in the solution of this problem.
We present a K-band atlas of 106 reflection nebulae, 41 of which are new discoveries. We observed these nebulae with the UH 2.2 m telescope in the course of an imaging survey of 197 objects that were selected to be nearby young Class I sources. K-band images and flux calibrated surface brightness contour plots of each nebula are presented. We found that the near-IR luminosities and physical sizes of the nebulae increase with the bolometric luminosity of the illuminating sources. Only 22 nebulae, about 10% of these candidate Class I sources, have indications of shocked H_2 emission. The great variety of nebulae that we observed prevented us from classifying them based on morphology. However, we note that as the spectral index decreases, the central star is more frequently visible at K-band and the flux from the central star tends to be dominant over the flux from the nebula. For objects that have a higher spectral index, most of the K-band flux is from the reflection nebula, and the central star is less frequently visible. The nebula around IRAS 05450+0019 has a unique morphology, and we speculate that it may be an example of a disk shadow being projected into the surrounding cloud. We present J, H, and K-band images of this object with surface brightness contours, as well as its SED from 1.2 microns to 100 microns.
We combine optical and X-ray data for eight low redshift ($z\sim 0.06$) poor groups of galaxies from the {\it XI}({\it XMM/IMACS}) Groups Project to study the AGN population in the group environment. Among $\sim 140$ group members, we identify five AGN based on their optical emission lines. None of these optically-selected AGN are detected by {\it XMM-Newton}. One additional AGN is discovered in the {\it XMM-Newton} observations. This X-ray detected AGN, which has no obvious AGN emission line signatures in its optical spectrum, is a member of the only X-ray luminous group in our sample. The lack of a significant population of X-ray bright, but optically dull AGN among less dynamically evolved groups is in stark contrast to the large fraction of such objects in rich clusters of galaxies (Martini et al. 2006). We suggest this result can be explained by a physical scenario for AGN accretion evolution: AGN activity is initially triggered by galaxy merging, leading to a high accretion rate and an optically dominant phase (via thin disk accretion). As the accretion rate drops in time, the AGN gradually enters an X-ray dominant low-accretion phase (via a radiative inefficient accretion flow). In this picture, optical- and X-ray-selected AGN are the same population of supermassive black holes observed at different epochs. Within the context of this scenario, the majority of AGN in poor groups are in the high-accretion optically dominant phase, while the AGN population in rich clusters is mostly in the low-accretion X-ray dominant phase.
This paper describes a high-resolution, infrared spectroscopic survey of young, low-mass stars designed to identify and characterize pre-main-sequence spectroscopic binaries. This is the first large infrared radial velocity survey of very young stars to date. The frequency and mass ratio distribution of the closest, low-mass binaries bear directly on models of stellar, brown dwarf, and planetary mass companion formation. Furthermore, spectroscopic binaries can provide mass ratios and ultimately masses, independent of assumptions, needed to calibrate models of young star evolution. I present the initial results from observations of a uniform sample of 33 T Tauri M stars in the Ophiuchus molecular cloud. The average mass of this sample is less than that of other young star radial velocity surveys of similar scope by a factor of ~2. Almost every star was observed at 3-4 epochs over 3 years with the 10 meter Keck II telescope and the facility infrared spectrometer NIRSPEC. An internal precision of 0.43 km/s was obtained with standard cross-correlation calibration techniques. Four of the targets are newly discovered spectroscopic binaries, one of which is located in a sub-arcsecond, hierarchical quadruple system. Three other sub-arcsecond visual binaries were also serendipitously identified during target acquisition. The spectroscopic multiplicity of the sample is comparable to that of earlier type, pre-main-sequence objects. Therefore, there is no dearth of young, low-mass spectroscopic binary stars, at least in the Ophiuchus region.
The enrichment of the intergalactic medium with heavy elements is a process that lies at the nexus of poorly-understood aspects of physical cosmology. We review current understanding of the processes that may remove metals from galaxies, the basic predictions of these models, the key observational constraints on enrichment, and how intergalactic enrichment may be used to test cosmological simulations.
We have conducted a large-scale survey of 120 planetary nebulae (PNe) to search for the near-infrared emission lines [Kr III] 2.199 and [Se IV] 2.287 microns. The neutron(n)-capture elements Se and Kr may be enriched in a PN if its progenitor star experienced s-process nucleosynthesis and third dredge-up. In order to determine Se and Kr abundances, we have added these elements to the atomic databases of the photoionization codes Cloudy and XSTAR, which we use to derive ionization correction factors (ICFs) to account for the abundances of unobserved Se and Kr ions. However, much of the atomic data governing the ionization balance of these two elements are unknown, and have been approximated from general principles. We find that uncertainties in the atomic data can lead to errors approaching 0.3 dex in the derived Se abundances, and up to 0.2--0.25 dex for Kr. To reduce the uncertainties in the Kr ionization balance stemming from the approximate atomic data, we have modeled ten bright PNe in our sample, selected because they exhibit emission lines from multiple Kr ions in their optical and near-infrared spectra. We have empirically adjusted the uncertain Kr atomic data until the observed line intensities of the various Kr ions are adequately reproduced by our models. Using the adjusted Kr atomic data, we have computed a grid of models over a wide range of physical parameters (central star temperature, nebular density, and ionization parameter), and derived formulae that can be used to compute Se and Kr ICFs. In the second paper of this series, we will apply these ICFs to our full sample of 120 PNe, which comprises the first large-scale survey of n-capture elements in PNe.
The Atacama Large Millimeter/Submillimeter Array (ALMA) is an international effort to construct an instrument capable of matching the exquisite imaging properties of optical space telescopes at millimeter and submillimeter wavelengths. ALMA science will transform our vision of the cold, dusty, and gaseous universe, from extrasolar planets to the youngest galaxies.
The CMB quadrupole and octupole, as well as being weaker than expected, align suspiciously well with each other. Non-trivial spatial topology can explain the weakness. Might it also explain the alignment? The answer, at least in the case of the Poincare dodecahedral space, is a resounding no.
The Large Scale Structure (LSS) found in galaxy redshift surveys and in computer simulations of cosmic structure formation shows a very complex network of galaxy clusters, filaments, and sheets around large voids. Here, we introduce a new algorithm, based on a Minimal Spanning Tree, to find basic structural elements of this network and their properties. We demonstrate how the algorithm works using simple test cases and then apply it to haloes from the Millennium Run simulation (Springel et al. 2005). We show that about 70% of the total halo mass is contained in a structure composed of more than 74,000 individual elements, the vast majority of which are filamentary, with lengths of up to 15 Mpc/h preferred. Spatially more extended structures do exist, as do examples of what appear to be sheet-like configurations of matter. What is more, LSS appears to be composed of a fixed set of basic building blocks. The LSS formed by mass selected subsamples of haloes shows a clear correlation between the threshold mass and the mean extent of major branches, with cluster-size haloes forming structures whose branches can extend to almost 200 Mpc/h - the backbone of LSS to which smaller branches consisting of smaller haloes are attached.
Relations between the observed quantities for a beamed radio jet, apparent transverse speed and apparent luminosity (beta_app,L), and the intrinsic quantities, Lorentz factor and intrinsic luminosity (gamma,L_o), are investigated. The inversion from measured to intrinsic values is not unique, but approximate limits to gamma and L_o can be found using probability arguments. Roughly half the sources in a flux density--limited, beamed sample have a value of gamma close to the measured beta_app. The methods are applied to observations of 119 AGN jets made with the VLBA at 15 GHz during 1994-2002. The results strongly support the common relativistic beam model for an extragalactic radio jet. The (beta_app,L) data are closely bounded by a theoretical envelope, an aspect curve for gamma=32, L_o= 10^25 W/Hz. This gives limits to the maximum values of gamma and L_o in the sample: gamma_max about 32, and L_o,max ~ 10^26 W/Hz. No sources with both high beta_app and low L are observed. This is not the result of selection effects due to the observing limits, which are flux density S>0.5 Jy, and angular velocity mu<4 mas/yr. Many of the fastest quasars have a pattern Lorentz factor gamma_p close to that of the beam, gamma_b, but some of the slow quasars must have gamma_p<<gamma_b. Three of the 10 galaxies in the sample have a superluminal feature, with speeds up to beta_app about 6. The others are at most mildly relativistic. The galaxies are not off-axis versions of the powerful quasars, but Cygnus A might be an exception.
Some of the properties of the globular clusters in NGC 5128 are compared to those of Galactic globular clusters. Assuming the color- metallicity relations that hold for Galactic globular clusters then the metal-poor clusters in NGC 5128 that have [Fe/H] < -1.80 are significantly fainter than are the more metal-rich globulars in that galaxy. No such metallicity dependent luminosity difference is observed among the globular clusters associated with the Milky Way. Furthermore the NGC 5128 cluster sample contains two objects that, on the basis of their observed colors, appear to be super metal-poor. It is speculated that many of these apparently faint and metal-poor clusters in NGC 5128 are actually objects resembling intermediate-age Galactic open clusters. It is also found that large clusters with FWHM > 10 pc are typically less luminous in NGC 5128 than are their more more compact counterparts. In this respect the NGC 5128 cluster system is similar to the Galactic globular cluster system. Finally, the present data may hint at the possibility that the NGC 5128 cluster system differs from that surrounding the Milky Way, in that the NGC 5128 objects do not seem to exhibit a clear cut gap between the regions of the FWHM vs M_v plane that are occupied by globular clusters and dwarf spheroidal galaxies.
(ABRIDGED) Motivated by the desire to reliably and automatically classify structure of thousands of COSMOS galaxies, we present ZEST, the Zurich Estimator of Structural Types. To classify galaxy structure, ZEST uses: (i) Five non-parametric diagnostics: asymmetry, concentration, Gini coefficient, 2nd-order moment of the brightest 20% of galaxy pixels, and ellipticity; and (ii) The exponent n of single--Sersic fits to the 2D surface brightness distributions. To fully exploit the wealth of information while reducing the redundancy present in these diagnostics, ZEST performs a principal component (PC) Analysis. We use a sample of ~56,000 I<24 COSMOS galaxies to show that the first three PCs fully describe the key aspects of the galaxy structure, i.e., to calibrate a three-dimensional classification grid of axis PC_1, PC_2, and PC_3. We demonstrate the robustness of the ZEST grid on the z=0 sample of Frei et al. (1996). The ZEST classification breaks most of the degeneracy between different galaxy populations that affects morphological classifications based on only some of the diagnostics included in ZEST. As a first application, we present the evolution since z~1 of the Luminosity Functions of COSMOS galaxies of early, disk and irregular galaxies and, for disk galaxies, of different bulge-to-disk ratios. Overall, we find that the LF up to a redshift z=1 is consistent with a pure-luminosity evolution (of about 0.95 magnitudes at z \~0.7). We highlight however two trends, that are in general agreement with a down-sizing scenario for galaxy formation: (1.) A deficit of a factor of about two at z~0.7 of MB>-20.5 structurally--classified early--type galaxies; and (2.) An excess of a factor of about three, at a similar redshift, of irregular galaxies.
We compute the 3-point correlation function for a general model of inflation driven by a single, minimally coupled scalar field. Our approach is based on the numerical evaluation of both the perturbation equations and the integrals which contribute to the 3-point function. Consequently, we can analyze models where the potential has a "feature", in the vicinity of which the slow roll parameters may take on large, transient values. This introduces both scale and shape dependent non-Gaussianities into the primordial perturbations. As an example of our methodology, we examine the ``step'' potentials which have been invoked to improve the fit to the glitch in the $<TT>$ $C_l$ for $l \sim 30$, present in both the one and three year WMAP data sets. We show that for the typical parameter values, the non-Gaussianities associated with the step are far larger than those in standard slow roll inflation, and may even be within reach of a next generation CMB experiment such as Planck. More generally, we use this example to explain that while adding features to potential can improve the fit to the 2-point function, these are generically associated with a greatly enhanced signal at the 3-point level. Moreover, this 3-point signal will have a very nontrivial shape and scale dependence, which is correlated with the form of the 2-point function, and may thus lead to a consistency check on the models of inflation with non-smooth potentials.
We present X-ray and 12CO(J=1-0) observations of the very-high-energy (VHE) gamma-ray source HESS J1813-178 with the aim of understanding the origin of the gamma-ray emission. Using this dataset we are able to undertake spectral and morphological studies of the X-ray emission from this object with greater precision than previous studies. NANTEN 12CO(J=1-0) data are used to search for correlations of the gamma-ray emission with molecular clouds which could act as target material for gamma-ray production in a hadronic scenario. The NANTEN 12CO(J=1-0) observations show a giant molecular cloud of mass 2.5 10^5 M$_{\sun}$ at a distance of 4 kpc in the vicinity of HESS J1813-178. Even though there is no direct positional coincidence, this giant cloud might have influenced the evolution of the gamma-ray source and its surroundings. The X-ray data show a highly absorbed non-thermal X-ray emitting object coincident with the previously known ASCA source AX J1813-178 showing a compact core and an extended tail towards the north-east, located in the centre of the radio shell-type Supernova remnant (SNR) G12.82-0.2. This central object shows morphological and spectral resemblance to a Pulsar Wind Nebula (PWN) and we therefore consider that the object is very likely to be a composite SNR. We discuss the scenario in which the gamma-rays originate in the shell of the SNR and the one in which they originate in the central object. We demonstrate, that in order to connect the core X-ray emission to the VHE gamma-ray emission electrons have to be accelerated to energies of at least 1 PeV.
Colliding winds of massive binaries have long been considered as potential sites of non-thermal high-energy photon production. This is motivated by the detection of non-thermal spectra in the radio band, as well as by correlation studies of yet unidentified EGRET gamma-ray sources with source populations appearing in star formation regions. This work re-considers the basic radiative processes and its properties that lead to high energy photon production in long-period massive star systems. We show that Klein-Nishina effects as well as the anisotropic nature of the inverse Compton scattering, the dominating leptonic emission process, likely yield spectral and variability signatures in the gamma-ray domain at or above the sensitivity of current or upcoming gamma ray instruments like GLAST-LAT. In addition to all relevant radiative losses, we include propagation (such as convection in the stellar wind) as well as photon absorption effects, which a priori can not be neglected. The calculations are applied to WR140 and WR147, and predictions for their detectability in the gamma-ray regime are provided. Physically similar specimen of their kind like WR146, WR137, WR138, WR112 and WR125 may be regarded as candidate sources at GeV energies for near-future gamma-ray experiments. Finally, we discuss several aspects relevant for eventually identifying this source class as a gamma-ray emitting population. Thereby we utilize our findings on the expected radiative behavior of typical colliding wind binaries in the gamma-ray regime as well as its expected spatial distribution on the gamma-ray sky.
We studied the problematic of uncertainties in the diffuse gamma radiation apparent in stacking analysis of EGRET data at low Galactic latitudes. Subsequently, we co-added maps of counts, exposure and diffuse background, and residuals, in varying numbers for different sub-categories of putatively and known source populations (like PSRs). Finally we tested for gamma-ray excess emission in those maps and attempt to quantify the systematic biases in such approach. Such kind of an analysis will help the classification processes of sources and source populations in the GLAST era.
A large fraction of the anticipated source detections by the Gamma-ray Large Area Space Telescope (GLAST-LAT) will initially be unidentified. We argue that traditional approaches to identify individuals and/or populations of gamma ray sources will encounter procedural limitations. Those limitations are discussed on the background of source identifications from EGRET observations. Generally, our ability to classify (faint) source populations in the anticipated GLAST dataset with the required degree of statistical confidence will be hampered by sheer source wealth. A new paradigm for achieving the classification of gamma ray source populations is discussed.
We present results for the chemical evolution of the Galactic bulge in the context of an inside-out formation model of the Galaxy. A supernova-driven wind was also included in analogy with elliptical galaxies. New observations of chemical abundance ratios and metallicity distribution have been employed in order to check the model results. We confirm previous findings that the bulge formed on a very short timescale with a quite high star formation efficiency and an initial mass function more skewed toward high masses than the one suitable for the solar neighbourhood. A certain amount of primary nitrogen from massive stars might be required to reproduce the nitrogen data at low and intermediate metallicities.
Based on three years of deep observations of the Galactic center with the Chandra X-ray Observatory, we report the discovery of changes in the intensities and morphologies of two hard X-ray nebulosities. The nebulosities are dominated by fluorescent iron emission, and are coincident with molecular clouds. The morphological changes are manifest on parsec scales, which requires that these iron features are scattered X-rays from a 2 or 3-year-long outburst of a point source (either Sgr A* or an X-ray binary) with a luminosity of at least 1e37 erg/s. The variability precludes the hypotheses that these nebulae either are produced by keV electrons bombarding molecular clouds, or are iron-rich ejecta from supernovae. Moreover, the morphologies of the reflection nebulae implies that the dense regions of the clouds are filamentary, with widths of ~0.3 pc and lengths of ~2 pc.
Gamma-ray astrophysics depends in many ways on multiwavelength studies. The Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) Collaboration has started multiwavelength planning well before the scheduled 2007 launch of the observatory. Some of the high-priority multiwavelength needs include: (1) availability of contemporaneous radio and X-ray timing of pulsars; (2) expansion of blazar catalogs, including redshift measurements; (3) improved observations of molecular clouds, especially at high galactic latitudes; (4) simultaneous broad-band blazar monitoring; (5) characterization of gamma-ray transients, including gamma ray bursts; (6) radio, optical, X-ray and TeV counterpart searches for reliable and effective sources identification and characterization. Several of these activities are needed to be in place before launch.
In a novel approach in observational high-energy gamma-ray astronomy, observations carried out by imaging atmospheric Cherenkov telescopes provide necessary templates to pinpoint the nature of intriguing, yet unidentified EGRET gamma-ray sources. Using GeV-photons detected by CGRO EGRET and taking advantage of high spatial resolution images from H.E.S.S. observations, we were able to shed new light on the EGRET observed gamma-ray emission in the Kookaburra complex, whose previous coverage in the literature is somewhat contradictory. 3EGJ1420-6038 very likely accounts for two GeV gamma-ray sources (E>1 GeV), both in positional coincidence with the recently reported pulsar wind nebulae (PWN) by HESS in the Kookaburra/Rabbit complex. PWN associations at VHE energies, supported by accumulating evidence from observations in the radio and X-ray band, are indicative for the PSR/plerionic origin of spatially coincident, but still unidentified Galactic gamma-ray sources from EGRET. This not only supports the already suggested connection between variable, but unidentified low-latitude gamma-ray sources with pulsar wind nebulae (3EGJ1420-6038 has been suggested as PWN candidate previoulsy), it also documents the ability of resolving apparently confused EGRET sources by connecting the GeV emission as measured from a large-aperture space-based gamma-ray instrument with narrow field-of-view but superior spatial resolution observations by ground-based atmospheric Cherenkov telescopes, a very promising identification technique for achieving convincing individual source identifications in the era of GLAST-LAT.
We use observations from the 9 square degree multiwavelength survey in Bootes to identify hundreds of obscured active galactic nuclei (AGN) with high redshifts (z > 0.7), luminosities (L_bol > 10^45 ergs/s), and moderate obscuring columns (N_H > 10^22 cm^-2), and to measure the clustering properties of X-ray AGN at z > 1. In the Bootes region, shallow (5 ks) Chandra X-ray observations have detected ~4,000 X-ray sources, and the same region has been mapped with deep optical imaging and by Spitzer IRAC, which detects ~300,000 point sources, of which ~30,000 have detections in all four IRAC bands, for which we can select AGN on the basis of their mid-IR colors. With the MMT/Hectospec we have obtained modest resolution optical spectra for about half the X-ray sources (out to z > 3) and ~20,000 galaxies (out to z = 0.7). With this multiwavelength data we select >400 AGN per square degree (compared to 12 per square degree from SDSS). Among a sample of IRAC-selected AGN we identify 641 candidate obscured objects based on their R band and IRAC luminosities. We use X-ray stacking techniques to verify that they are obscured AGN and measure their absorbing column densities. We also measure the three-dimensional two-point correlation function for X-ray selected AGN.
A comparison of a 19 GHz full-sky map with the WMAP satellite K band (23 GHz) map indicates that the bulk of the 20 GHz emission within 7 degrees of the Galactic plane has an inverted (rising) spectrum with spectral index alpha ~ 0.3. While such a spectrum is inconsistent with steep spectrum synchrotron (alpha ~ -0.7) and flat spectrum free-free (Bremsstrahlung) (alpha ~ -0.1) emission, it is consistent with various models of electric dipole emission from thermally excited spinning dust grains as well as models of magnetic dipole emission from ferromagnetic dust grains. A few regions in the plane, e.g., near the Cygnus arm, have spectra with even larger alpha. It appears that the bulk of the emission in the plane is correlated with the morphology of dust. Between 7 and 20 degrees from the Galactic plane the spectrum steepens to alpha ~ -0.3.
We have analysed publicly available MACHO observations of 6833 variable stars in the Large Magellanic Cloud, classified as eclipsing binaries. After finding that a significant fraction of the sample was misclassified, we redetermined periods and variability class for all stars, producing a clean sample of 3031 eclipsing binaries. We have investigated their distribution in the period-color-luminosity space, which was used, for example, to assign a foreground probability to every object and establish new period-luminosity relations to selected types of eclipsing stars. We found that the orbital period distribution of LMC binaries is very similar to those of the SMC and the Milky Way. We have also determined the rate of period change for every star using the O-C method, discovering about 40 eclipsing binaries with apsidal motion, 45 systems with cyclic period changes and about 80 stars with parabolic O-C diagrams. In a few objects we discovered gradual amplitude variation, which can be explained by changes in the orbital inclination caused by a perturbing third body in the system.
Assuming that supernovae type Ia (SNe Ia) are standard candles one could use them to test cosmological theories. The Hubble Space Telescope team analyzed 186 SNe Ia (Riess et al. (2004)) to test the standard cosmological model (SC) and evaluate its parameters. We use the same sample to determine parameters of Conformal Cosmological models (CC). We concluded, that really the test is extremely useful and allows to evaluate parameters of the model. From a formal statistical point of view the best fit of the CC model is almost the same quality approximation as the best fit of SC model with $\Omega_\Lambda=0.72, \Omega_m=0.28$. As it was noted earlier, for CC models, a rigid matter component could substitute the $\Lambda$-term (or quintessence) existing in the SC model.
We present four new exoplanets: HIP 14810 b & c, HD 154345 b, and HD 187123 c. The two planets orbiting HIP 14810, from the N2K project, have masses of 3.9 and 0.76 M_jup. We have searched the radial velocity time series of 90 known exoplanet systems and found new residual trends due to additional, long period companions. Two stars known to host one exoplanet have sufficient curvature in the residuals to a one planet fit to constrain the minimum mass of the outer companion to be substellar: HD 68988 c with 8 M_jup < M sini < 20 M_jup and HD 187123 c with 3 M_jup < msini < 7 M_jup$, both with P > 8 y. We have also searched the velocity residuals of known exoplanet systems for prospective low-amplitude exoplanets and present some candidates. We discuss techniques for constraining the mass and period of exoplanets in such cases, and for quantifying the significance of weak RV signals. We also present two substellar companions with incomplete orbits and periods longer than 8 y: HD 24040 b and HD 154345 b with M sini < 20 M_jup and M sini < 10 M_jup, respectively.
We propose to determine the mass and the radius of a neutron star (NS) using three measurable mass-radius relationships, namely the ``apparent'' radius inferred from neutron star thermal emission, the gravitational redshift inferred from the absorption lines, as well as the averaged stellar mass density inferred from the orbital Keplerian frequency derived from the kilohertz quasi periodic oscillation (kHz QPO) data. We apply the method to constrain the NS mass and the radius of the X-ray sources, 1E 1207.4-5209, Aql X-1 and EXO 0748-676.
SUMMARIZED ABSTRACT:
We present a study of the stellar populations and morphologies of galaxies in
the core of the galaxy cluster Abell 2218. Integral field spectroscopy was
obtained using PMAS/PPAK@3.5m CAHA to obtain a complete flux limited sample of
cluster members within its field-of-view (~74"X64"). In addition of 31 galaxies
with known redshifts in the outer regions, we built up a final sample of 59
spectroscopically confirmed cluster members. Multiban photometry and detailed
morphologies were obtained using deep images taken with the HST/ACS camera in
the BVRI and z-bands. The CM diagram shows that the E-type galaxies cover the
range of brighter and redder colors. A large fraction of spiral galaxies
($\sim$50%) is found. They cover a wide range in colors. This result, together
with the distributions of ages, metallicities and masses, indicates that E-type
galaxies are more massive and have older stellar populations, while L-type
galaxies are less massive and have a wider range of stellar Our results agree
with a proposed two-step scenario for the evolution of galaxies in clusters. In
addition, an extremely blue merging galaxy system is found at the core, with
the nominal redshift of the cluster.
A 52'X52' field in the Lupus Galactic plane was observed with the ANU 1m telescope for 53 nights during 2005 and 2006 in a search for transiting Hot Jupiter planets. A total of 2200 images were obtained. We have sampled 120,000 stars via differential photometry, of which ~26,000 have sufficient photometric accuracy (<=2.5%) with which to perform a search for transiting planets. Ongoing analysis has led to the identification of three candidates. We present an overview of the project, including the results of radial velocity analysis performed on the first candidate (Lupus-TR-1) with the 4m AAT telescope. The third candidate, Lupus-TR-3 (P=3.914d, V~16.5), is a particularly strong case for a giant planet of 1.0-1.2RJ orbiting a solar-like primary star with a near central transit. Further observations are planned to determine its nature.
Detached eclipsing binaries are very useful objects for calibrating theoretical stellar models and checking their predictions. Detached eclipsing binaries in open clusters are particularly important because of the additional constraints on their age and chemical composition from their membership of the cluster. I compile a list containing absolute parameters of well-studied eclipsing binaries in open clusters, and present new observational data on the B-type systems V1481 Cyg and V2263 Cyg which are members of the young open cluster NGC 7128.
NGC 362 is a bright southern globular cluster for which no extensive variability survey has ever been done. Time-series CCD photometric observations have been obtained. Light curves have been derived with both profile fitting photometry and image subtraction. We developed a simple method to convert flux phase curves to magnitudes, which allows the use of empirical light curve shape vs. physical parameters calibrations. Using the RR Lyrae metallicity and luminosity calibrations, we have determined the relative iron abundances and absolute magnitudes of the stars. The color-magnitude diagram has been fitted with Yale-Yonsei isochrones to determine reddening and distance independently. For five RR Lyrae stars we obtained radial velocity measurements from optical spectra. We found 45 RR Lyr stars, of which the majority are new discoveries. About half of the RR Lyraes exhibit light curve changes (Blazhko effect). The RR Lyrae-based metallicity of the cluster is [Fe/H]=-1.16 +/- 0.25, the mean absolute magnitude of the RR Lyrae stars is M_V=0.82 +/- 0.04 mag implying a distance of 7.9 +/- 0.6 kpc. The mean period of RRab stars is 0.585 +/- 0.081 days. These properties place NGC 362 among the Oosterhoff type I globular clusters. The isochrone fit implies a slightly larger distance of 9.2 +/- 0.5 kpc and an age of 11 +/- 1 Gyr. We also found 11 eclipsing binaries, 14 pulsating stars of other types, including classical Cepheids in the SMC and 15 variable stars with no firm classification.
We present a model which contains a new complex scalar field $\Psi$, interacting with a new real scalar field, $\chi$, and an effective potential whose symmetry is almost exact, being explicitly broken by Planck-scale effects. We study the possibility of relating {\em inflation} with the {\em dark matter} of the universe. We find that for exponentially small explicit breaking, the model accounts for a period of inflation in the early universe and gives a dark matter candidate particle.
Mkn 841 has been observed during 3 different periods (January 2001, January 2005 and July 2005) by XMM-Newton for a total cumulated exposure time of ~108 ks. We present in this paper a broad band spectral analysis of the complete EPIC-pn data sets. These observations confirm the presence of the strong soft excess and complex iron line profile known to be present in this source since a long time. They also reveal their extreme and puzzling spectral and temporal behaviors. Indeed, the 0.5-2 keV soft X-ray flux decreases by a factor 3 between 2001 and 2005 and the line shape appears to be a mixed of broad and narrow components, both variable but on differen timescales. The broad-band 0.5-10 keV spectra are well described by a model including a primary power law continuum, a blurred photoionized reflection and a narrow iron line, the blurred reflection fitting self-consistently the soft excess and the broad line component. The origin and nature of the narrow component is unclear.
We investigate torsional Alfv\'{e}n modes of relativistic stars with a global dipole magnetic field. It has been noted recently (Glampedakis et al. 2006) that such oscillation modes could serve as as an alternative explanation (in contrast to torsional crustal modes) for the SGR phenomenon, if the magnetic field is not confined to the crust. We compute global Alfv\'{e}n modes for a representative sample of equations of state and magnetar masses, in the ideal MHD approximation and ignoring $\ell \pm 2$ terms in the eigenfunction. We find that the presence of a realistic crust has a negligible effect on Alfv\'{e}n modes for $B > 4\times 10^{15}$ G. Furthermore, we find strong avoided crossings between torsional Alfv\'{e}n modes and torsional crust modes. For magnetar-like magnetic field strengths, the spacing between consecutive Alfv\'{e}n modes is of the same order as the gap of avoided crossings. As a result, it is not possible to identify modes of predominantly crustal character and all oscillations are predominantly Alfv\'{e}n-like. Interestingly, we find excellent agreement between our computed frequencies and observed frequencies in two SGRs, for a maximum magnetic field strenght in the range of (0.8--1.2)$\times 10^{16}$ G.
The occurrence of the inverse Compton catastrophe when the synchrotron brightness temperature exceeds a threshold value, usually estimated to be 10^{12} K, appears to be in contradiction with observation because: (i) the threshold is substantially exceeded by several intra-day variable radio sources, but the inverse Compton emission is not observed, (ii) powerful, extra-galactic radio sources of known angular size do not appear to congregate close to the predicted maximum brightness temperature. We re-examine the parameter space available to synchrotron sources using a population of monoenergetic electrons, in order to see whether the revised threshold temperature is consistent with the data. The electron distribution and the population of each generation of scattered photons are computed using spatially averaged equations. We confirm our previous finding that intrinsic brightness temperatures T_{\rm B}~10^{14} K can occur without catastrophic cooling. We show that substantially higher temperatures cannot be achieved either in transitory solutions or in solutions that balance losses with a powerful acceleration mechanism. Depending on the observing frequency, we find strong cooling can set in at a range of threshold temperatures and the imposition of the additional constraint of equipartition between particle and magnetic field energy is not warranted by the data. Postulating a monoenergetic electron distribution, which approximates one that is truncated below a certain Lorentz factor, \gamma_{min}, alleviates several theoretical difficulties associated with the inverse Compton catastrophe, including those mentioned above.
We study the correlations between the jet ejection event and changes in the continuum emission of the radio-loud galaxy 3C 390.3, using the archived monitoring data in radio, optical and X-ray. We present evidence for the link between the variable optical continuum and a stationary radio feature in the jet. The ejection of radio components happens during, or after, the dip in the X-ray light curve. Moreover, during the X-ray dip the flux variability is significantly reduced while the hardness ratio and its variance becomes harder. These findings strengthen the idea of similarity between active galactic nuclei (AGN) and microquasars, pointing towards a common physical mechanism acting in the disk-jet system. Other similarities are also discussed on the basis of comparision between 3C 390.3 and the microquasars GRS 1915+105 and Cyg X-1. If the analogy (based on linear mass scaling) between the ejection rates of the microquasar GRS 1915+105 and 3C 390.3 is correct, then the rate of ejections in 3C 390.3 should vary between ~(0.01 to 1) ejections per year on a time scale of thousand years.
We have investigated the obliquity evolution of terrestrial planets in habitable zones (at ~ 1AU) in extrasolar planetary systems, due to tidal interactions with their satellite and host star with wide varieties of satellite-to-planet mass ratio and initial obliquity, through numerical calculations and analytical arguments. The obliquity, the angle between planetary spin axis and its orbit normal, of a terrestrial planet is one of the key factors in determining the planetary surface environments. A recent scenario of terrestrial planet accretion implies that giant impacts of Mars-sized bodies determine the planetary spin and form satellites. With isotropic giant impacts, tilted spins are more likely to be produced than straight ones and satellites with various mass are formed. However, most of previous studies have focused on a particular case of the Earth-Moon systems or the two-body planar problem. We numerically integrated the evolution of planetary spin and a satellite orbit with various satellite mass and initial obliquity. We found that in the case of initially tiled spins, the satellite's orbit migrates outward until the orbit reaches the critical radius ~ 10-20 planetary radii, but then the migration is reversed to inward one with large-amplitude oscillation. The satellite eventually falls onto the planetary surface or it is captured at the synchronous state at several planetary radii. With the results of numerical integration and analytical arguments, we identified the parameter regions of qualitatively different evolution.
We present an analysis of the Fe II, Ge II, Mg I, Mg II, S I, S II, Si II and Zn II interstellar lines for 63 stars. The column density of Mg II, S II, Si II and Zn II is well correlated with the distance. However, the column density -- distance relation should be used with care for the estimation of the distance to OB stars. For stars with large $f(H_2)$ this relation can lead to a large overestimation of the distance. Hydrogen -- normalised column densities of Mg II, Si II and Ge II (our largest samples of data) drop with the interstellar reddening E(B-V) as expected for elements that are incorporated into dust grains. The Ge II abundance (GeII/H) is lower in dense molecular clouds. The abundances of all analysed elements are generally lower than their Solar System values.
We report new constraints on the local escape speed of our Galaxy. Our analysis is based on a sample of high velocity stars from the RAVE survey and two previously published datasets. We use cosmological simulations of disk galaxy formation to motivate our assumptions on the shape of the velocity distribution, allowing for a significantly more precise measurement of the escape velocity compared to previous studies. We find that the escape velocity lies within the range $498\kms < \ve < 608 \kms$ (90 per cent confidence), with a median likelihood of $544\kms$. The fact that $\ve^2$ is significantly greater than $2\vc^2$ (where $\vc=220\kms$ is the local circular velocity) implies that there must be a significant amount of mass exterior to the Solar circle, i.e. this convincingly demonstrates the presence of a dark halo in the Galaxy. For a simple isothermal halo, one can calculate that the minimum radial extent is $\sim58$ kpc. We use our constraints on $\ve$ to determine the mass of the Milky Way halo for three halo profiles. For example, an adiabatically contracted NFW halo model results in a virial mass of $1.42^{+1.14}_{-0.54}\times10^{12}M_\odot$ and virial radius of $305^{+66}_{-45}$ kpc (90 per cent confidence). For this model the circular velocity at the virial radius is $142^{+31}_{-21}\kms$. Although our halo masses are model dependent, we find that they are in good agreement with each other.
Over the past two years, we used a series of GBT observations to uncover at least 33 millisecond pulsars in the globular cluster Terzan 5 located in the Galactic bulge. We now have 32 timing solutions for the pulsars which give us precise positions and dispersion measures (DMs) and indicate that the DMs are dominated by variations in the integrated electron density along the slightly different sight lines towards the pulsars. At a distance of ~8.7 kpc, angular separations between the pulsars range from 0.4"-100" and correspond to projected physical separations of 0.01-4 pc, giving us a unique probe into the ionized ISM properties on these scales. Our measurement of the DM structure function toward Terzan 5 is not inconsistent with Kolmogorov-like electron density fluctuations in the ISM on scales ranging from at least 0.2-2 pc.
Aims: We analyse a long XMM-Newton spectrum of the narrow-line Seyfert 1 galaxy Mrk 766, using the marked spectral variability on timescales >20ks to separate components in the X-ray spectrum. Methods: Principal components analysis is used to identify distinct emission components in the X-ray spectrum, possible alternative physical models for those components are then compared statistically. Results: The source spectral variability is well-explained by additive variations, with smaller extra contributions most likely arising from variable absorption. The principal varying component, eigenvector one, is found to have a steep (photon index 2.4) power-law shape, affected by a low column of ionised absorption that leads to the appearance of a soft excess. Eigenvector one varies by a factor 10 in amplitude on time-scales of days and appears to have broad ionised Fe K-alpha emission associated with it: the width of the ionised line is consistent with an origin at about 100 gravitational radii. There is also a strong component of near-constant emission that dominates in the low state, whose spectrum is extremely hard above 1 keV, with a soft excess at lower energies, and with a strong edge at Fe K but remarkably little Fe K-alpha emission. Although this component may be explained as relativistically-blurred reflection from the inner accretion disc, we suggest that its spectrum and lack of variability may alternatively be explained as either (i) ionised reflection from an extended region, possibly a disc wind, or (ii) a signature of absorption by a disc wind with a variable covering fraction. Absorption features in the low state may indicate the presence of an outflow.
We show that the radio emission of black hole (BH) and neutron star (NS) X-ray binaries (XRBs) follows the analytical prediction of a jet model where the jet carries a constant fraction of the accretion power. The radio emission can therefore be used as a tracer of the accretion rate. This measure is normalised with efficiently radiating objects. As it is independent of the X-ray fluxes, the measure allows us to compare the accretion rate dependency of the bolometric X-ray luminosity of BHs and NSs. For NSs, it scales linearly with accretion rate while the scaling for BHs is quadratic - as expected for inefficient accretion flows. We find the same behaviour in AGN. This new approach uses the jet power to obtain the accretion rate. Thus, we know both the jet power and the radiated power of an accreting BH. This allows us to show that some accretion power is likely to be advected into the black hole, while the jet power dominates over the bolometric luminosity of a hard state BH.
There is growing interest in the possible link between the growth of supermassive black holes and the effect of feedback from them on galaxy growth. There are three areas of significant uncertainty: (i) the physics of the feedback; (ii) the prevalence and effectiveness of feedback; (iii) the link between the growth of black holes and their hosts. The 2QZ optical QSO survey indicates that luminous QSOs are relatively short-lived, and it has recently been shown that the observed bolometric luminosity density from all AGN and its evolution can be reproduced if black holes grew coevally with their galaxies, implying but not requiring a causal link between galaxy growth and black hole growth. At low redshifts there is some evidence that black hole and galaxy growth are starting to decouple.
At temperatures below the critical temperature of superfluid phase transition baryonic matter emits neutrinos by breaking and recombination of Cooper pairs formed in the condensate. The strong interactions in the nuclear medium modify the weak interaction vertices and the associated neutrino loss rates. We study these modifications non-perturbatively by summing infinite series of particle-hole diagrams in the S-wave superfluid neutron matter. We argue that a consistent approach requires fulfillment of the dispersion relations for the polarization tensor, which insure the unitarity of the S-matrix. The pairing and particle-hole interactions in neutron matter are described in the framework of the BCS and Fermi-liquid theories derived from microscopic interactions. The neutrino loss rates in the vector channel are enhanced compared to the rates derived from free-space weak vertices in the temperature domain close to the critical temperature, T_c, but are suppressed by factors 5-10 for temperatures below 0.5 T_c. The vertex corrected axial vector current emission is suppressed by the ratio of the baryon to the neutrino velocity squared.
A three-dimensional Monte Carlo code for modelling radiation transport in Type Ia supernovae is described. In addition to tracking Monte Carlo quanta to follow the emission, scattering and deposition of radiative energy, a scheme involving volume-based Monte Carlo estimators is used to allow properties of the emergent radiation field to be extracted for specific viewing angles in a multi-dimensional structure. This eliminates the need to compute spectra or light curves by angular binning of emergent quanta. The code is applied to two test problems to illustrate consequences of multi-dimensional structure on the modelling of light curves. First, elliptical models are used to quantify how large scale asphericity can introduce angular dependence to light curves. Secondly, a model which incorporates complex structural inhomogeneity, as predicted by modern explosion models, is used to investigate how such structure may affect light curve properties.
Ice crystal clouds in the upper troposphere can generate polarisation signals at the uK level. This signal can seriously affect very sensitive ground based searches for E- and B-mode of Cosmic Microwave Background polarisation. In this paper we estimate this effect within the ClOVER experiment observing bands (97, 150 and 220 GHz) for the selected observing site (Llano de Chajnantor, Atacama desert, Chile). The results show that the polarisation signal from the clouds can be of the order of or even bigger than the CMB expected polarisation. Climatological data suggest that this signal is fairly constant over the whole year in Antarctica. On the other hand the stronger seasonal variability in Atacama allows for a 50% of clean observations during the dry season.
We consider simple semi-analytic models that relate the active galactic nuclei (AGN) evolution to the merging history of their host dark matter haloes and quantify their ability of matching the AGN luminosity function and its spatial clustering at low and intermediate redshifts. In particular, we focus on the recent determinations of the AGN luminosity function in the hard X-ray band at z~0 which constitutes the most stringent observational test for our models. Indeed, while we find an acceptable agreement between the model bolometric luminosity function and the data at 1<z<2 and for luminosities larger than 1e10 solar bolometric luminosities, no semi-analytic model is capable of reproducing the number density of faint X-ray sources in the local universe. Some improvement can be obtained by advocating energy feedback that we model through a time-dependent Eddington ratio. Even in this case, however, the number density of faint AGNs is significantly below observations. This failure indicates that major mergers cannot constitute the only trigger to accretion episodes in the local AGN population.
Rotation-powered radio pulsars are born with inferred initial rotation periods of order 300 ms (some as short as 20 ms) in core-collapse supernovae. In the traditional picture, this fast rotation is the result of conservation of angular momentum during the collapse of a rotating stellar core. This leads to the inevitable conclusion that pulsar spin is directly correlated with the rotation of the progenitor star. So far, however, stellar theory has not been able to explain the distribution of pulsar spins, suggesting that the birth rotation is either too slow or too fast. Here we report a robust instability of the stalled accretion shock in core-collapse supernovae that is able to generate a strong rotational flow in the vicinity of the accreting proto-neutron star. Sufficient angular momentum is deposited on the proto-neutron star to generate a final spin period consistent with observations, even beginning with spherically symmetrical initial conditions. This provides a new mechanism for the generation of neutron star spin and weakens, if not breaks, the assumed correlation between the rotational periods of supernova progenitor cores and pulsar spin.
Recent observations of the line of sight velocity profile of elliptical galaxies have furnished controversial results with some works favouring the presence of a large amount of dark matter in the outer regions and others arguing in favour of no dark matter at all. In order to shed new light on this controversy, we propose here a new phenomenological description of the total mass profile of galaxies. Under the hypothesis of spherical symmetry, we assume a double power-law expression for the global M/L ratio Upsilon(r)= Upsilon_0(r/r_0) ^{alpha}(1+r/r_0)^{beta}. In particular, Upsilon propto r^{alpha} for r/r_0<<1 so that alpha=0 mimics a constant M/L ratio in the inner regions, while, for (r/r_0>>1), Upsilon propto r^{alpha+beta} thus showing that models with alpha+beta=0 have an asymptotically constant M/L ratio. A wide range of possibilities is obtained by varying the slope parameters in the range we determine on the basis of physical considerations. Choosing a general expression for the luminosity density profile j(r), we work out an effective galaxy model that accounts for all the phenomenology observed in real elliptical galaxies. We derive the main dynamics and lensing properties of such an effective model. We analyze a general class of models, able to take into account different dynamical trends. We are able to obtain analytical expressions for the main dynamical and lensing quantities. We show that constraining the values of alpha+beta makes it possible to analyze the problem of the dark matter in elliptical galaxies. Indeed, positive values of alpha+beta would be a strong evidence for dark matter. Finally we indicate possible future approaches in order to face the observational data, in particular using velocity dispersion profiles and lensed quasar events.
Using the MIPS instrument on the Spitzer telescope, we have searched for infrared excesses around a sample of 82 stars, mostly F, G, and K main-sequence field stars, along with a small number of nearby M stars. These stars were selected for their suitability for future observations by a variety of planet-finding techniques. These observations provide information on the asteroidal and cometary material orbiting these stars - data that can be correlated with any planets that may eventually be found. We have found significant excess 70um emission toward 12 stars. Combined with an earlier study, we find an overall 70um excess detection rate of $13 \pm 3$% for mature cool stars. Unlike the trend for planets to be found preferentially toward stars with high metallicity, the incidence of debris disks is uncorrelated with metallicity. By newly identifying 4 of these stars as having weak 24um excesses (fluxes $\sim$10% above the stellar photosphere), we confirm a trend found in earlier studies wherein a weak 24um excess is associated with a strong 70um excess. Interestingly, we find no evidence for debris disks around 23 stars cooler than K1, a result that is bolstered by a lack of excess around any of the 38 K1-M6 stars in 2 companion surveys. One motivation for this study is the fact that strong zodiacal emission can make it hard or impossible to detect planets directly with future observatories like the {\it Terrestrial Planet Finder (TPF)}. The observations reported here exclude a few stars with very high levels of emission, $>$1,000 times the emission of our zodiacal cloud, from direct planet searches. For the remainder of the sample, we set relatively high limits on dust emission from asteroid belt counterparts.
We review recent PIC simulation results which show that double-sided irradiation of a thin over-dense plasma slab with ultra-intense laser pulses from both sides can lead to sustained comoving Poynting flux acceleration of electrons to energies much higher than the conventional ponderomotive limit. The result is a robust power-law electron momentum spectrum similar to astrophysical sources. We discuss future ultra-intense laser experiments that may be used to simulate astrophysical particle acceleration.
If dark matter consists of cold, neutral particles with a non-zero magnetic moment, then, in the presence of an external magnetic field, a measurable gyromagnetic Faraday effect becomes possible. This enables direct constraints on the nature and distribution of such dark matter through detailed measurements of the polarization and temperature of the cosmic microwave background radiation.
Inhomogeneous cosmological perturbation equations are derived in loop quantum gravity, taking into account corrections in particular in gravitational parts. This provides a framework for calculating the evolution of modes in structure formation scenarios related to inflationary or bouncing models. Applications here are corrections to the Newton potential and to the evolution of large scale modes which imply non-conservation of curvature perturbations possibly noticeable in a running spectral index. These effects are sensitive to quantization procedures and test the characteristic behavior of correction terms derived from quantum gravity.
At the most fundamental level, all digital images are just large arrays of numbers that can easily be manipulated by computer software. Specialized digital imaging software packages often use routines common to many different applications and fields of study. The freely available, platform independent, image-processing package ImageJ has many such functions. We highlight ImageJ's capabilities by presenting methods of processing sequences of images to produce a star trail image and a single high quality planetary image.
We present new far infrared maps of the Small Magellanic Cloud (SMC) at 24, 70, and 160 microns obtained as part of the Spitzer Survey of the Small Magellanic Cloud (S3MC,Bolatto et al. 2006). These maps cover most of the active star formation in the SMC Bar and the more quiescent Wing. We combine our maps with literature data to derive the dust surface density across the SMC. We find a total dust mass of Mdust = 3 10^5 Msun, implying a dust-to-hydrogen ratio over the region studied of log D/H = -2.86, or 1-to-700, which includes H_2. Assuming the dust to trace the total gas column, we derive H_2 surface densities across the SMC. We find a total H_2 mass M_H2 = 3.2 10^7 Msun in a distribution similar to that of the CO, but more extended. We compare profiles of CO and H_2 around six molecular peaks and find that on average H_2 is more extended than CO by a factor of \sim 1.3. The implied CO-to-H_2 conversion factor over the whole SMC is XCO = 13 +/- 1 10^21 cm^-2 (K km/s)^-1. Over the volume occupied by CO we find a lower conversion factor, XCO = 6 +/- 1 10^21 cm^-2 (K km/s)^-1, which is still a few times larger than that found using virial mass methods. The molecular peaks have H_2 surface densities \Sigma_H2 \approx 180 +/- 30 Msun pc^-2, similar to those in Milky Way GMCs, and correspondingly low extinctions, A_V \sim 1 - 2 mag. To reconcile these measurements with predictions by the theory of photoionization-regulated star formation, which requires A_V \sim 6, the GMCs must be \sim 3 times smaller than our 46 pc resolution element. We find that for a given hydrostatic gas pressure, the SMC has a 2 - 3 times lower ratio of molecular to atomic gas than spiral galaxies. Combined with the lower mean densities in the SMC this may explain why this galaxy has only 10% of its gas in the molecular phase.
Relativistic electron degeneracy effects are dominant in ultra-dense plasmas (UDP), such as those found in white dwarfs. These effects can be treated systematically by obtaining an expansion of the screening length in inverse powers of $\hbar^{2}$. In general, our theory leads to an ${\cal O}(10)$ effect on the enhancement of fusion rates in white dwarfs. Further, it is shown analytically for these stellar conditions that Bose statistics of nuclei have a negligible effect on the screening length, in consonance with Monte Carlo simulations found in literature.
We investigate aspects of the cosmological evolution of FR II radio galaxies, focusing first on the abilities of models to match data for linear-sizes, radio powers, redshifts and spectral indices. Here we consider modifications to the theoretical models we had treated earlier, primarily by accounting for the growth of the radius of hotspots with source size. Better fits to the distributions of most of the data in three low-frequency surveys can be found with sensible choices of model parameters but no model yet considered gives a good match to all of the survey data simultaneously, nor does any do a good job of producing the spectral index distributions. The observational datasets are too small to completely discriminate among the models. We calculate the volume fraction of the ``relevant universe'' cumulatively occupied by the expanding radio galaxy lobes over the quasar era, when these powerful radio galaxies were much more common, and when they have been argued to play an important role in triggering galaxy formation and spreading magnetic fields and metals. We found the cumulative relevant volume filling factor of radio galaxies to be $\sim 5 %$, so we conclude that these impacts are smaller than previously estimated but that they are still significant.
We present high-resolution spectroscopic observations of GRB 060418, obtained with VLT/UVES. These observations were triggered using the VLT Rapid-Response Mode (RRM), which allows for automated observations of transient phenomena, without any human intervention. This resulted in the first UVES exposure of GRB 060418 to be started only 10 minutes after the initial Swift satellite trigger. A sequence of spectra covering 330-670 nm were acquired at 11, 16, 25, 41 and 71 minutes (mid-exposure) after the trigger, with a resolving power of 7 km/s, and a signal-to-noise ratio of 10-15. This time-series clearly shows evidence for time variability of allowed transitions involving Fe II fine-structure levels, and metastable levels of both Fe II and Ni II, at the host-galaxy redshift z=1.490. We model the observed evolution of the level populations with three different excitation mechanisms: collisions, excitation by infra-red photons, and fluorescence following excitation by ultraviolet photons. Our data allow us to reject the collisional and IR excitation scenarios with high confidence. The UV pumping model, in which the GRB afterglow UV photons excite a cloud of atoms with a column density N, distance d, and Doppler broadening parameter b, provides an excellent fit, with best-fit values: log N(Fe II)=14.75+/-0.06, log N(Ni II)=13.8+/-0.02, d=1.7+/-0.2 kpc, and b=25+/-3 km/s. No significant amount of Fe II or Ni II is present at distances smaller than \~1.7 kpc, most likely because it is ionized by the GRB X-ray/UV flash. The UV pumping fit constrains two GRB afterglow parameters: the spectral slope, beta=-0.44+0.64-1.05, and the total rest-frame UV flux that irradiated the cloud since the GRB trigger, constraining the magnitude of a possible UV flash. [abridged]
The diffuse gamma radiation arising from the interaction of cosmic ray particles with matter and radiation in the Galaxy is one of the few probes available to study the origin of the cosmic rays. Milagro is a water Cherenkov detector that continuously views the entire overhead sky. The large field-of-view combined with the long observation time makes Milagro the most sensitive instrument available for the study of large, low surface brightness sources such as the diffuse gamma radiation arising from interactions of cosmic radiation with interstellar matter. In this paper we present spatial and flux measurements of TeV gamma-ray emission from the Cygnus Region. The TeV image shows at least one new source MGRO J2019+37 as well as correlations with the matter density in the region as would be expected from cosmic-ray proton interactions. However, the TeV gamma-ray flux as measured at ~12 TeV from the Cygnus region (after excluding MGRO J2019+37) exceeds that predicted from a conventional model of cosmic ray production and propagation. This observation indicates the existence of either hard-spectrum cosmic-ray sources and/or other sources of TeV gamma rays in the region.
This paper examines the consistency of the exact scaling laws for isotropic MHD turbulence in numerical simulations with large magnetic Prandtl numbers Pm and with Pm=1. The exact laws are used to elucidate the structure of the magnetic and velocity fields. Despite the linear scaling of certain third-order correlation functions, the situation is not analogous to the case of Kolmogorov turbulence. The magnetic field is adequately described by a model of stripy (folded) field with direction reversals at the resistive scale. At currently available resolutions, the cascade of kinetic energy is short-circuited by the direct exchange of energy between the forcing-scale motions and the stripy magnetic fields. This nonlocal interaction is the defining feature of isotropic MHD turbulence.
Neutral hydrogen observations towards the Bootes dwarf spheroidal galaxy, a very low luminosity metal-poor Galactic satellite, were obtained using the Parkes Radio Telescope. We do not detect any HI in or around Bootes to a 3sigma upper limit of 180 Msun within the optical half light radius and 8000 Msun within 1.6 kpc. Its HI mass-to-light ratio is less than 0.002 Msun/Lsun, making Bootes one of the most gas-poor galaxies known. Either reionisation severely inhibited gas infall onto the proto-Bootes, or large amounts of gas have been removed by ram pressure and/or tidal stripping. Since Bootes lies on the mass-metallicity fundamental line, this relation and the inefficiency of star formation at the faintest end of the galaxy luminosity function must be partly driven, or at least not disrupted, by extreme gas loss in such low luminosity galaxies. We also do not detect any HI associated with the leading tidal tail of the Sagittarius dSph galaxy, which fortuitously passes through the observed field, to a 3sigma column density limit of 2 x 10^17 cm^-2. This suggests that either the leading gaseous tail is ionised, or the gas in the trailing tail was removed before the current tidal disruption of the parent dSph began.
It is possible that the scale of gravity, parameterized by the apparent Planck mass, may obtain different values within different universes in an encompassing multiverse. We investigate the range over which the Planck mass may scan while still satisfying anthropic constraints. The window for anthropically allowed values of the Planck mass may have important consequences for landscape predictions. For example, if the likelihood to observe some value of the Planck mass is weighted by the inflationary expansion factors of the universes that contain that value, then it appears extremely unlikely to observe the value of the Planck mass that is measured within our universe. This is another example of the runaway inflation problem discussed in recent literature. We also show that the window for the Planck mass significantly weakens the anthropic constraint upon the cosmological constant when both are allowed to vary over a landscape.
We study a scenario for the very early universe in which there is a fast phase transition from a non-geometric, high temperature phase to a low temperature, geometric phase described by a classical solution to the Einstein equations. In spite of the absence of a classical metric, the thermodynamics of the high temperature phase may be described by making use of the holographic principle. The thermal spectrum of fluctuations in the high temperature phase manifest themselves after the phase transition as a scale invariant spectrum of fluctuations. A simple model of the phase transition confirms that the near scale invariance of the fluctuations is natural; but the model also withstands detailed comparison with the data.
We present an investigation of the propagation of Ultra High Energy Cosmic Rays (UHECRs) in extragalactic magnetic field (EGMF). We use the IRAS PSCz catalogue in order to reconstruct EGMF taking into account power-law dependence between the magnetic field and the infrared luminosity density. Contrary to the previous works [11] the normalization parameters have been estimated according to the observable values of magnetic field of the galaxy clusters (B_GC = 0.3 - 2 microG) and assessed values of field in the voids of the Local Universe (B_Void = 1 pG - 100 pG). We construct the full-sky maps of expected deflection angles of UHE protons with the arrival energies E = 100 EeV and E = 40 EeV in the reconstructed EGMF for two boundary cases of "strong" (B_GC=2 microG, B_Void = 100 pG) and "weak" (B_GC=0.3 microG, B_Void = 1 pG) magnetic fields. It is found that average deflections of protons with observable energies above 40 EeV and maximum energy in sources E_max = 10 ZeV are unimportant (comparable with the errors of modern detectors) only in the case of "weak" EGMF model.
We report the discovery of the wide L1.5+L4.5 binary 2MASS J15200224-4422419AB, identified during spectroscopic followup of high proper motion sources selected from the Two Micron All Sky Survey. This source was independently identified by Kendall et al. in the SuperCOSMOS Sky Survey. Resolved JHK photometry and low resolution near-infrared spectroscopy demonstrate that this system is composed of two well-separated (1"174+/-0"016) L dwarfs. Component classifications are derived using both spectral ratios and comparison to near-infrared spectra of previously classified field L dwarfs. Physical association for the pair is deduced from the large (mu = 0"73+/-0"03 /yr) common proper motion of the components and their similar spectrophotometric distances (19+/-2 pc). The projected separation of the binary, 22+/-2 AU, is consistent with maximum separation/total system mass trends for very low mass binaries. The 2MASS J1520-4422 system exhibits both large tangential (66+/-7 km/s) and radial velocities (-70+/-18 km/s), and its motion in the local standard of rest suggests that it is an old member of the Galactic disk population. This system joins a growing list of well-separated (>0"5), very low mass binaries, and is an excellent target for resolved optical spectroscopy to constrain its age as well as trace activity/rotation trends near the hydrogen-burning limit.
Two-dimensional axisymmetric simulations have shown that the post-bounce accretion shock in core collapse supernovae is subject to the Spherical Accretion Shock Instability, or SASI. Recent three-dimensional simulations have revealed the existence of a non-axisymmetric mode of the SASI as well, where the postshock flow displays a spiral pattern. Here we investigate the growth of these spiral modes using two-dimensional simulations of the post-bounce accretion flow in the equatorial plane of a core-collapse supernova. By perturbing a steady-state model we are able to excite both one, two and three-armed spiral modes that grow exponentially with time, demonstrating that these are linearly unstable modes closely related to the original axisymmetric sloshing modes. By tracking the distribution of angular momentum, we show that these modes are able to efficiently separate the angular momentum of the accretion flow (which maintains a net angular momentum of zero), leading to a significant spin-up of the underlying accreting proto-neutron star.
The galaxy central mass $M_\mathrm{c}$ and central velocity dispersion $\sigma_\mathrm{c}$ have been found to correlate with large scale galaxy parameters for samples of galaxies with a limited range of characteristics. A scalar potential model (SPM) that derived from considerations of galaxy clusters, of redshift, of discrete redshift, of H{\scriptsize{I}} rotation curves (RCs) of spiral galaxies and of RC asymmetry is applied to central region parameters. The $\sigma_\mathrm{c}$ and $ M_\mathrm{c}$ are found to correlate to the host galaxy's and neighboring galaxy's B band luminosity. The sample included galaxies with rising, flat and declining RCs; galaxies with a wide range of characteristics; and galaxies excluded from samples of other studies of $\sigma_\mathrm{c}$ relationships. The equations have the same form as the SPM equations for the parameters of the H{\scriptsize{I}} RCs. Because the SPM is consistent with $M_\mathrm{c}$ and $\sigma_\mathrm{c}$ observations of the sample galaxies, the Sources and Sinks act as monopoles at the center of the galaxies around them. This suggests the outward scalar potential force of a Source holds the $M_\mathrm{c}$ from collapse into a supermassive black hole.
The WIMPs search project PICO-LON has been started with multilayer thin NaI(Tl) crystals. The thin (0.05cm) and wide area (5cmx5cm) NaI(Tl) crystals was successfully developed. The performances of thin NaI(Tl) scintillator was measured and they showed good energy resolution (20% at 60keV) and good position resolution (20% in 5cmx5cm wider area).
The generation of large-scale magnetic fields is studied in inflationary cosmology. We consider the violation of the conformal invariance of the Maxwell field by dilatonic as well as non-minimal gravitational couplings. We derive a general formula for the spectrum of large-scale magnetic fields for a general form of the coupling term and the formula for the spectral index. The result tells us clearly the (necessary) condition for the generation of magnetic fields with sufficiently large amplitude.
We present a new concept of nonlinear dynamics of incoherent superstrong radiation in plasmas. Recently we have disclosed a novel mechanism of the establishment of equilibrium between a photon and a dense photon bunch through the exchange of longitudinal photons (Tsintsadze 2004 Phys. Plasmas 11, 855). Based on this mechanism of the "Compton" scattering type, we have generalized Wigner-Moyal equation for the dense photon gas, including the collision integral for the occupation number of photons. In the geometric optics approximation the Wigner-Moyal type of equation reduces to the one particle Vlasov-Boltzmann equation for the photon gas. From this equation, which gives a microscopic description of the photon gas, we derive a set of fluid equations, and consider numerically the formation of 3D shock waves.
In this poster, we present an investigation of a new, preferred diagnostic tool for the determination of the sulphur abundance of disk stars, see also Ryde A&A (2006). We are in the process of analyzing a large set of stars both in the galactic disk and halo (Ryde et al. 2007, in prep.). This diagnostics, the forbidden sulphur line at 10821 A, is less sensitive to the assumed temperatures of the stars investigated and less prone to non-LTE effects than other tracers. It is an intercombination line, an M1 transition between the triplet ground-state and the first excited singlet state. The E2 transition is two orders of magnitude weaker. In the investigation presented here, we have studied a homogeneous set of sub-giant and giant stars ranging from spectral types of G5 to K4 (effective temperatures of 4000 - 5000 K). The reason why the [SI] has not been use before is that it lies beyond the reach of normal CCDs.
We present the low frequency (610 MHz) radio source counts of the VVDS-VLA field and investigate the radio spectral index properties of the sub-mJy population. We use new deep (r.m.s.$\simeq 50$ $\mu$Jy/beam) observations of the VVDS-VLA field obtained at 610 MHz with the GMRT and matched in resolution (6 arcsec) with already available VLA data at 1.4 GHz on the same field. We find evidence of a change of the dominant population of radio sources below 0.5 mJy (at 1.4 GHz): between 0.15 and 0.5 mJy the median spectral index is significantly flatter ($\alpha=-0.46\pm 0.03$) than that of brighter sources ($\alpha=-0.67\pm 0.05$). A relevant contribution below 0.5 mJy from a population of flat spectrum low luminosity compact AGNs and radio quiet QSOs could explain this effect. At even fainter flux density, between 0.10 and 0.15 mJy at 1.4 GHz, the median spectral index steepens again ($\alpha=-0.61\pm 0.04$) suggesting that the contribution of starburst galaxies becomes important below $\sim 0.2$ mJy. Finally we present a sample of 58 candidate ultra-steep sources with radio flux density from one to two orders of magnitude lower than any other sample of such objects.
The stellar populations in the outer Galactic disk are nowadays a subject of wide interest. To contribute to a better picture of this part of the Galaxy, we have studied the nature of five marginally investigated star clusters (Collinder 74, Berkeley 27, Haffner 8, NGC 2509, and VdB-Hagen 4) by means of accurate CCD photometry in the V and I pass-bands. These clusters are in fact located in the Third Galactic Quadrant. We aim to obtain the basic parameters of these objects, which in some cases are still disputed in the literature. In the case of VdB-Hagen 4 we provide the first estimate of its fundamental parameters, while for Haffner 8 we present the first CCD photometry. The analysis is based on the comparison between field stars decontaminated Color Magnitude Diagrams and stellar models. Particular care is devoted to the assessment of the data quality, and the statistical field stars decontamination. The library of stellar isochrones from Girardi et al. (2000) is adopted in this study. The analysis we carried out allowed us to solve a few inconsistencies in the literature regarding Haffner 8 and NGC 2509. Collinder 74 is found to be significantly older than reported before. VdB-Hagen 4 is a young open cluster located more than 20 kpc from the Galactic center. Such an extreme distance is compatible with the cluster belonging to the Norma-Cygnusarm.
This contribution gives an overview about various applications of (sub)mm interferometry in star formation research. The topics covered are molecular outflows, accretion disks, fragmentation and chemical properties of low- and high-mass star-forming regions. A short outlook on the capabilities of ALMA is given as well.
We follow the growth of baryonic structure in the presence of a magnetic field within an approximate cosmological magneto-hydrodynamic simulation, produced by adding an (isotropic) magnetic pressure related to the local gas pressure. We perform an ensemble of these simulations to follow the amplification of the field with time. By using a variety of initial field strengths and changing the slope of the power law that governs the way the field grows with increasing density we span the range of current observations and demonstrate the size of the effect realistic magnetic fields could have on the central density of groups and clusters. A strong magnetic field significantly reduces the central gas density which, in turn, reduces observable quantities such as the X-ray luminosity.
During the life of isolated neutron stars (NSs) their magnetic field passes through a variety of evolutionary phases. Depending on its strength and structure and on the physical state of the NS (e.g. cooling, rotation), the field looks qualitatively and quantitatively different after each of these phases. Three of them, the phase of MHD instabilities immediately after NS's birth, the phase of fallback which may take place hours to months after NS's birth, and the phase when strong temperature gradients may drive thermoelectric instabilities, are concentrated in a period lasting from the end of the proto--NS phase until 100, perhaps 1000 years, when the NS has become almost isothermal. The further evolution of the magnetic field proceeds in general inconspicuous since the star is in isolation. However, as soon as the product of Larmor frequency and electron relaxation time, the so-called magnetization parameter, locally and/or temporally considerably exceeds unity, phases, also unstable ones, of dramatic changes of the field structure and magnitude can appear. An overview is given about that field evolution phases, the outcome of which makes a qualitative decision regarding the further evolution of the magnetic field and its host NS.
Pumping routes of masers can in principle be recovered from a small matrix of master equations, at an advanced stage of elimination, by tracing back the coefficients to a set of unmodified all-process rate coefficients, drawn from those which appeared in the original set of master equations, prior to any elimination operations. The traceback is achieved by logging the operations carried out on each coefficient. There is no guarantee that a pumping scheme can be represented as a small set of important routes in this way. In the present work, the traceback method is applied to a model which is typical of a large volume of parameter space which produces very strong inversions in the main lines of the rotational ground state of OH, at 1665- and 1667-MHz. For both lines, the pumping scheme is largely restricted to the $^{2}\Pi_{3/2}$ stack of rotational levels, and it is possible to list a comparatively small set of routes (less than ten) which provide more than 80 per cent of the inversion. In both cases, the strongest, and simplest, route consists of a radiative upward stage, to the $^{2}\Pi_{3/2}, J=5/2$ rotational level, followed by a collisional de-excitation to the rotational ground state.
We present an approximate, analytical formulae for the computation of hadronically-produced gamma-ray luminosity in the innermost regions of stellar winds. We put this into the context of other recent research on regions of star formation as gamma-ray sources.
We derive a first order linear differential equation describing the shape of the probability density function of magnetic field strengths in the quiet Sun (PDF). The modeling is very schematic. It considers convective motions which continuously supply and withdraw magnetic structures. In addition, a magnetic amplification mechanism increases the field strength up to a threshold that cannot be exceeded. These three basic ingredients provide PDFs in good agreement with the PDFs produced by realistic numerical simulations of magneto convection, as well as with quiet Sun PDFs inferred from observations. In particular, the distribution is approximately lognormal, and it produces an excess of magnetic fields (i.e., a 'hump' in the distribution) right before the maximum field strength. The success of this simple model may indicate that only a few basic ingredients shape the quiet Sun PDF. Our approach provides a concise parametric representation of the PDF, as required to develop automatic methods of diagnostics.
We present a coarse-grained field theory of density fluctuations for a Newtonian self-gravitating many-body system and apply it to a homogeneous Universe with small density fluctuations. The theory treats the clustering of galaxies and clusters in terms of the field of density fluctuations. The Jeans length $\lambda_0$, a unique physical scale for a gravitating system, appears naturally as the characteristic scale underlying the large scale structure. Under Gaussian approximation the analytic expressions of $\xi(r)$ and $P(k)$ are obtained. The correlation amplitude is proportional to the galactic mass, and is oscillating over large scales $\sim 100$ $h^{-1}$ Mpc and damped to zero. The spectrum amplitude is inversely proportional to the galactic number density.The preliminary results qualitatively explain some pronounced features of large scale structures.
We present a partial analysis of a multi-wavelength study of the X-ray binary Cir X-1, a system harboring the most relativistic outflow in our galaxy so far. The data were taken (almost) simultaneously in radio and X ray during a survey carried out in October 2000 and December 2002. Cir X-1 was observed at the radio frequencies of 4.8 and 8.6 GHz with the Australia Telescope Compact Array (ATCA). In the X-ray spectral domain we used the Rossi X-Ray Timing Explorer (RXTE). We found strong evidence for flaring activity in radio not only at the periastron but also at the apoastron passages. A comparison of our data against different correlations between radio and X ray found in other neutron star systems shows that Cir X-1 does not seem to follow the general trend. However, the fact that Cir X-1 is an `exotic' X-ray binary makes any interpretation more complicated.
Using a samples of 61506 spiral galaxies selected from the SDSS DR2, we examine the luminosity function (LF) of spiral galaxies with different inclination angles. We find that the characteristic luminosity of the LF, $L^*$, decreases with increasing inclination, while the faint-end slope, $\alpha$, depends only weakly on it. The inclination-dependence of the LF is consistent with that expected from a simple model where the optical depth is proportional to the cosine of the inclination angle, and we use a likelihood method to recover both the coefficient in front of the cosine, $\gamma$, and the LF for galaxies viewed face-on. The value of $\gamma$ is quite independent of galaxy luminosity in a given band, and the values of $\gamma$ obtained in this way for the 5 SDSS bands give an extinction curve which is a power law of wavelength ($\tau\propto\lambda^{-n}$), with a power index $n=0.96\pm0.04$. Using the dust extinction for galaxies obtained by Kauffmann et al. (2003), we derive an `extinction-corrected' luminosity function for spiral galaxies. Dust extinction makes $M^*$ dimmer by about 0.5 magnitudes in the $z$-band, and about 1.2 magnitudes in the $u$- band. Since our analysis is based on a sample where selection effects are well under control, the dimming of edge-on galaxies relative to face-on galaxies is best explained by assuming that galaxy disks are optically thick in dust absorptions.
The comparison between observations of galaxy clusters thermo-dynamical properties and theoretical predictions suggests that non-gravitational heating needs to be added into the models. We implement an internally self-consistent heating scheme into GADGET-2 for the third (and fourth) run of the Millennium gas project (Pearce et al. in preparation), a set of four hydrodynamical cosmological simulations with N=2(5x10^8) particles and with the same volume (L=500 h-1 Mpc) and structures as the the N-body Millennium Simulation (Springel et al. 2005). Our aim is to reproduce the observed thermo-dynamical properties of galaxy clusters.
We report the discovery of oscillations at 1122 +/- 0.3 Hz in an X-ray burst from the X-ray transient XTE J1739-285. The signal has a peak Leahy power of 42.8 and, after consideration of the number of trials, has a chance probability of occurrence of 4E-5 equivalent to a 4.2 sigma detection. The oscillation frequency suggests that XTE J1739-285 contains the fastest rotating neutron star yet found. We also found millisecond quasiperiodic oscillations in the persistent emission with frequencies ranging from 757 Hz to 862 Hz. We detected seven X-ray bursts and derive an upper limit on the source distance of about 10.6 kpc from the brightest burst.
We propose to extract the charge information of high energy muons in very inclined extensive air showers by analyzing their relative lateral positions in the shower transverse plane. We calculate the muon lateral deviation under the geomagnetic field and compare it to dispersive deviations from other causes. By our criterion of resolvability, positive and negative muons with energies above $10^4$ GeV will be clearly separated into two lobes if the shower zenith angle is larger than $70^\circ$. Thus we suggest a possible approach to measure the $\mu^+ / \mu^-$ ratio for high energy muons.
I consider the nonaxisymmetric linear theory of an isothermal magnetohydrodynamic (MHD) shear flow. The analysis is performed in the shearing box, a local model appropriate for a thin disk geometry. Linear perturbations in this model can be decomposed in terms of shearing waves (shwaves), which appear spatially as plane waves in a frame comoving with the shear. The time dependence of these waves cannot in general be expressed in terms of a frequency eigenvalue as in a normal mode decomposition, and numerical integration of a set of first-order amplitude equations is required for a complete characterization of their behavior. Their generic time dependence, however, is oscillatory with slowly-varying frequency and amplitude, and one can construct accurate analytic solutions by applying the Wentzel-Kramers-Brillouin method to the full set of amplitude equations. For the bulk of wavenumber space, therefore, the shwaves are well-approximated as modes with time-dependent frequencies and amplitudes. The incompressive shwaves, which require a sub-thermal mean field, include the nonaxisymmetric extension of magneto-rotationally unstable modes. The compressive shwaves are the extension of the fast and slow magnetosonic modes to a shear flow; the validity of the latter requires a super-thermal mean field. The oscillatory nature of the incompressive shwaves breaks down for very weak fields, in which case their amplitudes can be expressed in terms of hypergeometric functions. The complete set of solutions constitutes a comprehensive linear test suite for numerical MHD algorithms that incorporate a background shear flow. I conclude with a brief discussion of possible astrophysical applications.
We present a study of the effects of clumping on the emergent spectral energy distribution (SED) from dusty supernova (SN) shells illuminated by a diffuse radiation source distributed throughout the medium. (...) The fully 3D radiation transport problem is solved using a Monte Carlo code, MOCASSIN, and we present a set of models aimed at investigating the sensitivity of the SEDs to various clumping parameters. We find that, contrary to the predictions of analytical prescriptions, the combination of an optical and IR observational data set is sufficient to constrain dust masses even in the case where optically thick clumps are present. Using both smoothly varying and clumped grain density distributions, we obtain new estimates for the mass of dust condensed by the Type II SN 1987A by fitting the optical and infrared spectrophotometric data of Wooden et al. (1993) at two epochs (day 615 and day 775). (...) From our numerical models we derive dust masses for SN 1987A that are comparable to previous analytic clumped graphite grain mass estimates, and at least two orders of magnitude below the 0.1-0.3 Msol that have been predicted to condense as dust grains in primordial core collapse supernova ejecta. This low condensation efficiency for SN 1987A is in contrast to the case of SN 2003gd, for which a dust condensation efficiency as large as 0.12 has recently been estimated. (Abridged)
The H.E.S.S. array of imaging Cherenkov telescopes has discovered a number of previously unknown gamma-ray sources in the very high energy (VHE) domain above 100 GeV. The good angular resolution of H.E.S.S. (~0.1 degree per event), as well as its sensitivity (a few percent of the Crab Nebula flux) and wide 5-degree field of view, allow a much better constrained search for counterparts in comparison to previous instruments. In several cases, the association of the VHE sources revealed by H.E.S.S. with pulsar wind nebulae (PWNe) is supported by a combination of positional and morphological evidence, multi-wavelength observations, and plausible PWN model parameters. These include the plerions in the composite supernova remnants G 0.9+0.1 and MSH 15-52, the recently discovered Vela X nebula, two new sources in the Kookaburra complex, and the association of HESS J1825-137 with PSR B1823-13. The properties of these better-established associations are reviewed. A number of other sources discovered by H.E.S.S. are located near high spin-down power pulsars, but the evidence for association is less complete. These possible associations are also discussed, in the context of the available multi-wavelength data and plausible PWN scenarios.
We present a method that uses disk models to determine stellar masses for Pre-Main sequence T Tauri stars from JHK photometry. We find that the infrared excess produced by the disk behaves in a similar way to the extinction vector when plotted on color-color and color-magnitude diagrams, but that it is linearly independent. Employing these vectors as a basis of a vector space we carry out a coordinate transformation that allows us to find the mass of a central star for a given age. To test this Principal Vectors (PV) method we compare the mass values (MPV) obtained for 14 T Tauri objects in the Taurus-Auriga region with mass values known by dynamical methods. Further on, we analyzed 4 systems with multiple components (GG Tau, FO Tau, FS Tau, and V733 Tau) and determined the mass for each component of the system. We analyzed the effect of using different evolutionary models and other parameter values.
We present new far infrared maps of the Small Magellanic Cloud (SMC) at 24, 70, and 160 microns obtained as part of the Spitzer Survey of the Small Magellanic Cloud (S3MC,Bolatto et al. 2006). These maps cover most of the active star formation in the SMC Bar and the more quiescent Wing. We combine our maps with literature data to derive the dust surface density across the SMC. We find a total dust mass of Mdust = 3 10^5 Msun, implying a dust-to-hydrogen ratio over the region studied of log D/H = -2.86, or 1-to-700, which includes H_2. Assuming the dust to trace the total gas column, we derive H_2 surface densities across the SMC. We find a total H_2 mass M_H2 = 3.2 10^7 Msun in a distribution similar to that of the CO, but more extended. We compare profiles of CO and H_2 around six molecular peaks and find that on average H_2 is more extended than CO by a factor of \sim 1.3. The implied CO-to-H_2 conversion factor over the whole SMC is XCO = 13 +/- 1 10^21 cm^-2 (K km/s)^-1. Over the volume occupied by CO we find a lower conversion factor, XCO = 6 +/- 1 10^21 cm^-2 (K km/s)^-1, which is still a few times larger than that found using virial mass methods. The molecular peaks have H_2 surface densities \Sigma_H2 \approx 180 +/- 30 Msun pc^-2, similar to those in Milky Way GMCs, and correspondingly low extinctions, A_V \sim 1 - 2 mag. To reconcile these measurements with predictions by the theory of photoionization-regulated star formation, which requires A_V \sim 6, the GMCs must be \sim 3 times smaller than our 46 pc resolution element. We find that for a given hydrostatic gas pressure, the SMC has a 2 - 3 times lower ratio of molecular to atomic gas than spiral galaxies. Combined with the lower mean densities in the SMC this may explain why this galaxy has only 10% of its gas in the molecular phase.
Relativistic electron degeneracy effects are dominant in ultra-dense plasmas (UDP), such as those found in white dwarfs. These effects can be treated systematically by obtaining an expansion of the screening length in inverse powers of $\hbar^{2}$. In general, our theory leads to an ${\cal O}(10)$ effect on the enhancement of fusion rates in white dwarfs. Further, it is shown analytically for these stellar conditions that Bose statistics of nuclei have a negligible effect on the screening length, in consonance with Monte Carlo simulations found in literature.
We investigate aspects of the cosmological evolution of FR II radio galaxies, focusing first on the abilities of models to match data for linear-sizes, radio powers, redshifts and spectral indices. Here we consider modifications to the theoretical models we had treated earlier, primarily by accounting for the growth of the radius of hotspots with source size. Better fits to the distributions of most of the data in three low-frequency surveys can be found with sensible choices of model parameters but no model yet considered gives a good match to all of the survey data simultaneously, nor does any do a good job of producing the spectral index distributions. The observational datasets are too small to completely discriminate among the models. We calculate the volume fraction of the ``relevant universe'' cumulatively occupied by the expanding radio galaxy lobes over the quasar era, when these powerful radio galaxies were much more common, and when they have been argued to play an important role in triggering galaxy formation and spreading magnetic fields and metals. We found the cumulative relevant volume filling factor of radio galaxies to be $\sim 5 %$, so we conclude that these impacts are smaller than previously estimated but that they are still significant.
We present high-resolution spectroscopic observations of GRB 060418, obtained with VLT/UVES. These observations were triggered using the VLT Rapid-Response Mode (RRM), which allows for automated observations of transient phenomena, without any human intervention. This resulted in the first UVES exposure of GRB 060418 to be started only 10 minutes after the initial Swift satellite trigger. A sequence of spectra covering 330-670 nm were acquired at 11, 16, 25, 41 and 71 minutes (mid-exposure) after the trigger, with a resolving power of 7 km/s, and a signal-to-noise ratio of 10-15. This time-series clearly shows evidence for time variability of allowed transitions involving Fe II fine-structure levels, and metastable levels of both Fe II and Ni II, at the host-galaxy redshift z=1.490. We model the observed evolution of the level populations with three different excitation mechanisms: collisions, excitation by infra-red photons, and fluorescence following excitation by ultraviolet photons. Our data allow us to reject the collisional and IR excitation scenarios with high confidence. The UV pumping model, in which the GRB afterglow UV photons excite a cloud of atoms with a column density N, distance d, and Doppler broadening parameter b, provides an excellent fit, with best-fit values: log N(Fe II)=14.75+/-0.06, log N(Ni II)=13.8+/-0.02, d=1.7+/-0.2 kpc, and b=25+/-3 km/s. No significant amount of Fe II or Ni II is present at distances smaller than \~1.7 kpc, most likely because it is ionized by the GRB X-ray/UV flash. The UV pumping fit constrains two GRB afterglow parameters: the spectral slope, beta=-0.44+0.64-1.05, and the total rest-frame UV flux that irradiated the cloud since the GRB trigger, constraining the magnitude of a possible UV flash. [abridged]
The diffuse gamma radiation arising from the interaction of cosmic ray particles with matter and radiation in the Galaxy is one of the few probes available to study the origin of the cosmic rays. Milagro is a water Cherenkov detector that continuously views the entire overhead sky. The large field-of-view combined with the long observation time makes Milagro the most sensitive instrument available for the study of large, low surface brightness sources such as the diffuse gamma radiation arising from interactions of cosmic radiation with interstellar matter. In this paper we present spatial and flux measurements of TeV gamma-ray emission from the Cygnus Region. The TeV image shows at least one new source MGRO J2019+37 as well as correlations with the matter density in the region as would be expected from cosmic-ray proton interactions. However, the TeV gamma-ray flux as measured at ~12 TeV from the Cygnus region (after excluding MGRO J2019+37) exceeds that predicted from a conventional model of cosmic ray production and propagation. This observation indicates the existence of either hard-spectrum cosmic-ray sources and/or other sources of TeV gamma rays in the region.
This paper examines the consistency of the exact scaling laws for isotropic MHD turbulence in numerical simulations with large magnetic Prandtl numbers Pm and with Pm=1. The exact laws are used to elucidate the structure of the magnetic and velocity fields. Despite the linear scaling of certain third-order correlation functions, the situation is not analogous to the case of Kolmogorov turbulence. The magnetic field is adequately described by a model of stripy (folded) field with direction reversals at the resistive scale. At currently available resolutions, the cascade of kinetic energy is short-circuited by the direct exchange of energy between the forcing-scale motions and the stripy magnetic fields. This nonlocal interaction is the defining feature of isotropic MHD turbulence.
Neutral hydrogen observations towards the Bootes dwarf spheroidal galaxy, a very low luminosity metal-poor Galactic satellite, were obtained using the Parkes Radio Telescope. We do not detect any HI in or around Bootes to a 3sigma upper limit of 180 Msun within the optical half light radius and 8000 Msun within 1.6 kpc. Its HI mass-to-light ratio is less than 0.002 Msun/Lsun, making Bootes one of the most gas-poor galaxies known. Either reionisation severely inhibited gas infall onto the proto-Bootes, or large amounts of gas have been removed by ram pressure and/or tidal stripping. Since Bootes lies on the mass-metallicity fundamental line, this relation and the inefficiency of star formation at the faintest end of the galaxy luminosity function must be partly driven, or at least not disrupted, by extreme gas loss in such low luminosity galaxies. We also do not detect any HI associated with the leading tidal tail of the Sagittarius dSph galaxy, which fortuitously passes through the observed field, to a 3sigma column density limit of 2 x 10^17 cm^-2. This suggests that either the leading gaseous tail is ionised, or the gas in the trailing tail was removed before the current tidal disruption of the parent dSph began.
It is possible that the scale of gravity, parameterized by the apparent Planck mass, may obtain different values within different universes in an encompassing multiverse. We investigate the range over which the Planck mass may scan while still satisfying anthropic constraints. The window for anthropically allowed values of the Planck mass may have important consequences for landscape predictions. For example, if the likelihood to observe some value of the Planck mass is weighted by the inflationary expansion factors of the universes that contain that value, then it appears extremely unlikely to observe the value of the Planck mass that is measured within our universe. This is another example of the runaway inflation problem discussed in recent literature. We also show that the window for the Planck mass significantly weakens the anthropic constraint upon the cosmological constant when both are allowed to vary over a landscape.
We study a scenario for the very early universe in which there is a fast phase transition from a non-geometric, high temperature phase to a low temperature, geometric phase described by a classical solution to the Einstein equations. In spite of the absence of a classical metric, the thermodynamics of the high temperature phase may be described by making use of the holographic principle. The thermal spectrum of fluctuations in the high temperature phase manifest themselves after the phase transition as a scale invariant spectrum of fluctuations. A simple model of the phase transition confirms that the near scale invariance of the fluctuations is natural; but the model also withstands detailed comparison with the data.
We present an investigation of the propagation of Ultra High Energy Cosmic Rays (UHECRs) in extragalactic magnetic field (EGMF). We use the IRAS PSCz catalogue in order to reconstruct EGMF taking into account power-law dependence between the magnetic field and the infrared luminosity density. Contrary to the previous works [11] the normalization parameters have been estimated according to the observable values of magnetic field of the galaxy clusters (B_GC = 0.3 - 2 microG) and assessed values of field in the voids of the Local Universe (B_Void = 1 pG - 100 pG). We construct the full-sky maps of expected deflection angles of UHE protons with the arrival energies E = 100 EeV and E = 40 EeV in the reconstructed EGMF for two boundary cases of "strong" (B_GC=2 microG, B_Void = 100 pG) and "weak" (B_GC=0.3 microG, B_Void = 1 pG) magnetic fields. It is found that average deflections of protons with observable energies above 40 EeV and maximum energy in sources E_max = 10 ZeV are unimportant (comparable with the errors of modern detectors) only in the case of "weak" EGMF model.
We report the discovery of the wide L1.5+L4.5 binary 2MASS J15200224-4422419AB, identified during spectroscopic followup of high proper motion sources selected from the Two Micron All Sky Survey. This source was independently identified by Kendall et al. in the SuperCOSMOS Sky Survey. Resolved JHK photometry and low resolution near-infrared spectroscopy demonstrate that this system is composed of two well-separated (1"174+/-0"016) L dwarfs. Component classifications are derived using both spectral ratios and comparison to near-infrared spectra of previously classified field L dwarfs. Physical association for the pair is deduced from the large (mu = 0"73+/-0"03 /yr) common proper motion of the components and their similar spectrophotometric distances (19+/-2 pc). The projected separation of the binary, 22+/-2 AU, is consistent with maximum separation/total system mass trends for very low mass binaries. The 2MASS J1520-4422 system exhibits both large tangential (66+/-7 km/s) and radial velocities (-70+/-18 km/s), and its motion in the local standard of rest suggests that it is an old member of the Galactic disk population. This system joins a growing list of well-separated (>0"5), very low mass binaries, and is an excellent target for resolved optical spectroscopy to constrain its age as well as trace activity/rotation trends near the hydrogen-burning limit.
Two-dimensional axisymmetric simulations have shown that the post-bounce accretion shock in core collapse supernovae is subject to the Spherical Accretion Shock Instability, or SASI. Recent three-dimensional simulations have revealed the existence of a non-axisymmetric mode of the SASI as well, where the postshock flow displays a spiral pattern. Here we investigate the growth of these spiral modes using two-dimensional simulations of the post-bounce accretion flow in the equatorial plane of a core-collapse supernova. By perturbing a steady-state model we are able to excite both one, two and three-armed spiral modes that grow exponentially with time, demonstrating that these are linearly unstable modes closely related to the original axisymmetric sloshing modes. By tracking the distribution of angular momentum, we show that these modes are able to efficiently separate the angular momentum of the accretion flow (which maintains a net angular momentum of zero), leading to a significant spin-up of the underlying accreting proto-neutron star.
The galaxy central mass $M_\mathrm{c}$ and central velocity dispersion $\sigma_\mathrm{c}$ have been found to correlate with large scale galaxy parameters for samples of galaxies with a limited range of characteristics. A scalar potential model (SPM) that derived from considerations of galaxy clusters, of redshift, of discrete redshift, of H{\scriptsize{I}} rotation curves (RCs) of spiral galaxies and of RC asymmetry is applied to central region parameters. The $\sigma_\mathrm{c}$ and $ M_\mathrm{c}$ are found to correlate to the host galaxy's and neighboring galaxy's B band luminosity. The sample included galaxies with rising, flat and declining RCs; galaxies with a wide range of characteristics; and galaxies excluded from samples of other studies of $\sigma_\mathrm{c}$ relationships. The equations have the same form as the SPM equations for the parameters of the H{\scriptsize{I}} RCs. Because the SPM is consistent with $M_\mathrm{c}$ and $\sigma_\mathrm{c}$ observations of the sample galaxies, the Sources and Sinks act as monopoles at the center of the galaxies around them. This suggests the outward scalar potential force of a Source holds the $M_\mathrm{c}$ from collapse into a supermassive black hole.
The WIMPs search project PICO-LON has been started with multilayer thin NaI(Tl) crystals. The thin (0.05cm) and wide area (5cmx5cm) NaI(Tl) crystals was successfully developed. The performances of thin NaI(Tl) scintillator was measured and they showed good energy resolution (20% at 60keV) and good position resolution (20% in 5cmx5cm wider area).
The generation of large-scale magnetic fields is studied in inflationary cosmology. We consider the violation of the conformal invariance of the Maxwell field by dilatonic as well as non-minimal gravitational couplings. We derive a general formula for the spectrum of large-scale magnetic fields for a general form of the coupling term and the formula for the spectral index. The result tells us clearly the (necessary) condition for the generation of magnetic fields with sufficiently large amplitude.
We present a new concept of nonlinear dynamics of incoherent superstrong radiation in plasmas. Recently we have disclosed a novel mechanism of the establishment of equilibrium between a photon and a dense photon bunch through the exchange of longitudinal photons (Tsintsadze 2004 Phys. Plasmas 11, 855). Based on this mechanism of the "Compton" scattering type, we have generalized Wigner-Moyal equation for the dense photon gas, including the collision integral for the occupation number of photons. In the geometric optics approximation the Wigner-Moyal type of equation reduces to the one particle Vlasov-Boltzmann equation for the photon gas. From this equation, which gives a microscopic description of the photon gas, we derive a set of fluid equations, and consider numerically the formation of 3D shock waves.
In this poster, we present an investigation of a new, preferred diagnostic tool for the determination of the sulphur abundance of disk stars, see also Ryde A&A (2006). We are in the process of analyzing a large set of stars both in the galactic disk and halo (Ryde et al. 2007, in prep.). This diagnostics, the forbidden sulphur line at 10821 A, is less sensitive to the assumed temperatures of the stars investigated and less prone to non-LTE effects than other tracers. It is an intercombination line, an M1 transition between the triplet ground-state and the first excited singlet state. The E2 transition is two orders of magnitude weaker. In the investigation presented here, we have studied a homogeneous set of sub-giant and giant stars ranging from spectral types of G5 to K4 (effective temperatures of 4000 - 5000 K). The reason why the [SI] has not been use before is that it lies beyond the reach of normal CCDs.
We present the low frequency (610 MHz) radio source counts of the VVDS-VLA field and investigate the radio spectral index properties of the sub-mJy population. We use new deep (r.m.s.$\simeq 50$ $\mu$Jy/beam) observations of the VVDS-VLA field obtained at 610 MHz with the GMRT and matched in resolution (6 arcsec) with already available VLA data at 1.4 GHz on the same field. We find evidence of a change of the dominant population of radio sources below 0.5 mJy (at 1.4 GHz): between 0.15 and 0.5 mJy the median spectral index is significantly flatter ($\alpha=-0.46\pm 0.03$) than that of brighter sources ($\alpha=-0.67\pm 0.05$). A relevant contribution below 0.5 mJy from a population of flat spectrum low luminosity compact AGNs and radio quiet QSOs could explain this effect. At even fainter flux density, between 0.10 and 0.15 mJy at 1.4 GHz, the median spectral index steepens again ($\alpha=-0.61\pm 0.04$) suggesting that the contribution of starburst galaxies becomes important below $\sim 0.2$ mJy. Finally we present a sample of 58 candidate ultra-steep sources with radio flux density from one to two orders of magnitude lower than any other sample of such objects.
The stellar populations in the outer Galactic disk are nowadays a subject of wide interest. To contribute to a better picture of this part of the Galaxy, we have studied the nature of five marginally investigated star clusters (Collinder 74, Berkeley 27, Haffner 8, NGC 2509, and VdB-Hagen 4) by means of accurate CCD photometry in the V and I pass-bands. These clusters are in fact located in the Third Galactic Quadrant. We aim to obtain the basic parameters of these objects, which in some cases are still disputed in the literature. In the case of VdB-Hagen 4 we provide the first estimate of its fundamental parameters, while for Haffner 8 we present the first CCD photometry. The analysis is based on the comparison between field stars decontaminated Color Magnitude Diagrams and stellar models. Particular care is devoted to the assessment of the data quality, and the statistical field stars decontamination. The library of stellar isochrones from Girardi et al. (2000) is adopted in this study. The analysis we carried out allowed us to solve a few inconsistencies in the literature regarding Haffner 8 and NGC 2509. Collinder 74 is found to be significantly older than reported before. VdB-Hagen 4 is a young open cluster located more than 20 kpc from the Galactic center. Such an extreme distance is compatible with the cluster belonging to the Norma-Cygnusarm.
This contribution gives an overview about various applications of (sub)mm interferometry in star formation research. The topics covered are molecular outflows, accretion disks, fragmentation and chemical properties of low- and high-mass star-forming regions. A short outlook on the capabilities of ALMA is given as well.
We follow the growth of baryonic structure in the presence of a magnetic field within an approximate cosmological magneto-hydrodynamic simulation, produced by adding an (isotropic) magnetic pressure related to the local gas pressure. We perform an ensemble of these simulations to follow the amplification of the field with time. By using a variety of initial field strengths and changing the slope of the power law that governs the way the field grows with increasing density we span the range of current observations and demonstrate the size of the effect realistic magnetic fields could have on the central density of groups and clusters. A strong magnetic field significantly reduces the central gas density which, in turn, reduces observable quantities such as the X-ray luminosity.
During the life of isolated neutron stars (NSs) their magnetic field passes through a variety of evolutionary phases. Depending on its strength and structure and on the physical state of the NS (e.g. cooling, rotation), the field looks qualitatively and quantitatively different after each of these phases. Three of them, the phase of MHD instabilities immediately after NS's birth, the phase of fallback which may take place hours to months after NS's birth, and the phase when strong temperature gradients may drive thermoelectric instabilities, are concentrated in a period lasting from the end of the proto--NS phase until 100, perhaps 1000 years, when the NS has become almost isothermal. The further evolution of the magnetic field proceeds in general inconspicuous since the star is in isolation. However, as soon as the product of Larmor frequency and electron relaxation time, the so-called magnetization parameter, locally and/or temporally considerably exceeds unity, phases, also unstable ones, of dramatic changes of the field structure and magnitude can appear. An overview is given about that field evolution phases, the outcome of which makes a qualitative decision regarding the further evolution of the magnetic field and its host NS.
Pumping routes of masers can in principle be recovered from a small matrix of master equations, at an advanced stage of elimination, by tracing back the coefficients to a set of unmodified all-process rate coefficients, drawn from those which appeared in the original set of master equations, prior to any elimination operations. The traceback is achieved by logging the operations carried out on each coefficient. There is no guarantee that a pumping scheme can be represented as a small set of important routes in this way. In the present work, the traceback method is applied to a model which is typical of a large volume of parameter space which produces very strong inversions in the main lines of the rotational ground state of OH, at 1665- and 1667-MHz. For both lines, the pumping scheme is largely restricted to the $^{2}\Pi_{3/2}$ stack of rotational levels, and it is possible to list a comparatively small set of routes (less than ten) which provide more than 80 per cent of the inversion. In both cases, the strongest, and simplest, route consists of a radiative upward stage, to the $^{2}\Pi_{3/2}, J=5/2$ rotational level, followed by a collisional de-excitation to the rotational ground state.
We present an approximate, analytical formulae for the computation of hadronically-produced gamma-ray luminosity in the innermost regions of stellar winds. We put this into the context of other recent research on regions of star formation as gamma-ray sources.
We derive a first order linear differential equation describing the shape of the probability density function of magnetic field strengths in the quiet Sun (PDF). The modeling is very schematic. It considers convective motions which continuously supply and withdraw magnetic structures. In addition, a magnetic amplification mechanism increases the field strength up to a threshold that cannot be exceeded. These three basic ingredients provide PDFs in good agreement with the PDFs produced by realistic numerical simulations of magneto convection, as well as with quiet Sun PDFs inferred from observations. In particular, the distribution is approximately lognormal, and it produces an excess of magnetic fields (i.e., a 'hump' in the distribution) right before the maximum field strength. The success of this simple model may indicate that only a few basic ingredients shape the quiet Sun PDF. Our approach provides a concise parametric representation of the PDF, as required to develop automatic methods of diagnostics.
We present a coarse-grained field theory of density fluctuations for a Newtonian self-gravitating many-body system and apply it to a homogeneous Universe with small density fluctuations. The theory treats the clustering of galaxies and clusters in terms of the field of density fluctuations. The Jeans length $\lambda_0$, a unique physical scale for a gravitating system, appears naturally as the characteristic scale underlying the large scale structure. Under Gaussian approximation the analytic expressions of $\xi(r)$ and $P(k)$ are obtained. The correlation amplitude is proportional to the galactic mass, and is oscillating over large scales $\sim 100$ $h^{-1}$ Mpc and damped to zero. The spectrum amplitude is inversely proportional to the galactic number density.The preliminary results qualitatively explain some pronounced features of large scale structures.
We present a partial analysis of a multi-wavelength study of the X-ray binary Cir X-1, a system harboring the most relativistic outflow in our galaxy so far. The data were taken (almost) simultaneously in radio and X ray during a survey carried out in October 2000 and December 2002. Cir X-1 was observed at the radio frequencies of 4.8 and 8.6 GHz with the Australia Telescope Compact Array (ATCA). In the X-ray spectral domain we used the Rossi X-Ray Timing Explorer (RXTE). We found strong evidence for flaring activity in radio not only at the periastron but also at the apoastron passages. A comparison of our data against different correlations between radio and X ray found in other neutron star systems shows that Cir X-1 does not seem to follow the general trend. However, the fact that Cir X-1 is an `exotic' X-ray binary makes any interpretation more complicated.
Using a samples of 61506 spiral galaxies selected from the SDSS DR2, we examine the luminosity function (LF) of spiral galaxies with different inclination angles. We find that the characteristic luminosity of the LF, $L^*$, decreases with increasing inclination, while the faint-end slope, $\alpha$, depends only weakly on it. The inclination-dependence of the LF is consistent with that expected from a simple model where the optical depth is proportional to the cosine of the inclination angle, and we use a likelihood method to recover both the coefficient in front of the cosine, $\gamma$, and the LF for galaxies viewed face-on. The value of $\gamma$ is quite independent of galaxy luminosity in a given band, and the values of $\gamma$ obtained in this way for the 5 SDSS bands give an extinction curve which is a power law of wavelength ($\tau\propto\lambda^{-n}$), with a power index $n=0.96\pm0.04$. Using the dust extinction for galaxies obtained by Kauffmann et al. (2003), we derive an `extinction-corrected' luminosity function for spiral galaxies. Dust extinction makes $M^*$ dimmer by about 0.5 magnitudes in the $z$-band, and about 1.2 magnitudes in the $u$- band. Since our analysis is based on a sample where selection effects are well under control, the dimming of edge-on galaxies relative to face-on galaxies is best explained by assuming that galaxy disks are optically thick in dust absorptions.
The comparison between observations of galaxy clusters thermo-dynamical properties and theoretical predictions suggests that non-gravitational heating needs to be added into the models. We implement an internally self-consistent heating scheme into GADGET-2 for the third (and fourth) run of the Millennium gas project (Pearce et al. in preparation), a set of four hydrodynamical cosmological simulations with N=2(5x10^8) particles and with the same volume (L=500 h-1 Mpc) and structures as the the N-body Millennium Simulation (Springel et al. 2005). Our aim is to reproduce the observed thermo-dynamical properties of galaxy clusters.
We report the discovery of oscillations at 1122 +/- 0.3 Hz in an X-ray burst from the X-ray transient XTE J1739-285. The signal has a peak Leahy power of 42.8 and, after consideration of the number of trials, has a chance probability of occurrence of 4E-5 equivalent to a 4.2 sigma detection. The oscillation frequency suggests that XTE J1739-285 contains the fastest rotating neutron star yet found. We also found millisecond quasiperiodic oscillations in the persistent emission with frequencies ranging from 757 Hz to 862 Hz. We detected seven X-ray bursts and derive an upper limit on the source distance of about 10.6 kpc from the brightest burst.
We propose to extract the charge information of high energy muons in very inclined extensive air showers by analyzing their relative lateral positions in the shower transverse plane. We calculate the muon lateral deviation under the geomagnetic field and compare it to dispersive deviations from other causes. By our criterion of resolvability, positive and negative muons with energies above $10^4$ GeV will be clearly separated into two lobes if the shower zenith angle is larger than $70^\circ$. Thus we suggest a possible approach to measure the $\mu^+ / \mu^-$ ratio for high energy muons.
I consider the nonaxisymmetric linear theory of an isothermal magnetohydrodynamic (MHD) shear flow. The analysis is performed in the shearing box, a local model appropriate for a thin disk geometry. Linear perturbations in this model can be decomposed in terms of shearing waves (shwaves), which appear spatially as plane waves in a frame comoving with the shear. The time dependence of these waves cannot in general be expressed in terms of a frequency eigenvalue as in a normal mode decomposition, and numerical integration of a set of first-order amplitude equations is required for a complete characterization of their behavior. Their generic time dependence, however, is oscillatory with slowly-varying frequency and amplitude, and one can construct accurate analytic solutions by applying the Wentzel-Kramers-Brillouin method to the full set of amplitude equations. For the bulk of wavenumber space, therefore, the shwaves are well-approximated as modes with time-dependent frequencies and amplitudes. The incompressive shwaves, which require a sub-thermal mean field, include the nonaxisymmetric extension of magneto-rotationally unstable modes. The compressive shwaves are the extension of the fast and slow magnetosonic modes to a shear flow; the validity of the latter requires a super-thermal mean field. The oscillatory nature of the incompressive shwaves breaks down for very weak fields, in which case their amplitudes can be expressed in terms of hypergeometric functions. The complete set of solutions constitutes a comprehensive linear test suite for numerical MHD algorithms that incorporate a background shear flow. I conclude with a brief discussion of possible astrophysical applications.
We present a study of the effects of clumping on the emergent spectral energy distribution (SED) from dusty supernova (SN) shells illuminated by a diffuse radiation source distributed throughout the medium. (...) The fully 3D radiation transport problem is solved using a Monte Carlo code, MOCASSIN, and we present a set of models aimed at investigating the sensitivity of the SEDs to various clumping parameters. We find that, contrary to the predictions of analytical prescriptions, the combination of an optical and IR observational data set is sufficient to constrain dust masses even in the case where optically thick clumps are present. Using both smoothly varying and clumped grain density distributions, we obtain new estimates for the mass of dust condensed by the Type II SN 1987A by fitting the optical and infrared spectrophotometric data of Wooden et al. (1993) at two epochs (day 615 and day 775). (...) From our numerical models we derive dust masses for SN 1987A that are comparable to previous analytic clumped graphite grain mass estimates, and at least two orders of magnitude below the 0.1-0.3 Msol that have been predicted to condense as dust grains in primordial core collapse supernova ejecta. This low condensation efficiency for SN 1987A is in contrast to the case of SN 2003gd, for which a dust condensation efficiency as large as 0.12 has recently been estimated. (Abridged)
The H.E.S.S. array of imaging Cherenkov telescopes has discovered a number of previously unknown gamma-ray sources in the very high energy (VHE) domain above 100 GeV. The good angular resolution of H.E.S.S. (~0.1 degree per event), as well as its sensitivity (a few percent of the Crab Nebula flux) and wide 5-degree field of view, allow a much better constrained search for counterparts in comparison to previous instruments. In several cases, the association of the VHE sources revealed by H.E.S.S. with pulsar wind nebulae (PWNe) is supported by a combination of positional and morphological evidence, multi-wavelength observations, and plausible PWN model parameters. These include the plerions in the composite supernova remnants G 0.9+0.1 and MSH 15-52, the recently discovered Vela X nebula, two new sources in the Kookaburra complex, and the association of HESS J1825-137 with PSR B1823-13. The properties of these better-established associations are reviewed. A number of other sources discovered by H.E.S.S. are located near high spin-down power pulsars, but the evidence for association is less complete. These possible associations are also discussed, in the context of the available multi-wavelength data and plausible PWN scenarios.
We present a method that uses disk models to determine stellar masses for Pre-Main sequence T Tauri stars from JHK photometry. We find that the infrared excess produced by the disk behaves in a similar way to the extinction vector when plotted on color-color and color-magnitude diagrams, but that it is linearly independent. Employing these vectors as a basis of a vector space we carry out a coordinate transformation that allows us to find the mass of a central star for a given age. To test this Principal Vectors (PV) method we compare the mass values (MPV) obtained for 14 T Tauri objects in the Taurus-Auriga region with mass values known by dynamical methods. Further on, we analyzed 4 systems with multiple components (GG Tau, FO Tau, FS Tau, and V733 Tau) and determined the mass for each component of the system. We analyzed the effect of using different evolutionary models and other parameter values.