Intergalactic MgII absorbers are known to have structures down to scales ~ 10^{2.5} pc, and there are now indications that they may be fragmented on scales <~ 10^{-2.5} pc (Hao et al., astro-ph/0612409). I show that quasar microlensing can effectively probe MgII and other absorption "cloudlets" with sizes ~ 10^{-4.0} - 10^{-2.0} pc by inducing significant spectral variability on the timescales of months to years. With numerical simulations, I demonstrate the feasibility of applying this method to Q2237+0305, and I show that high-resolution spectra of this quasar in the near future would provide a clear test of the existence of such metal absorbing "cloudlets".
Numerical simulations of turbulent, magnetized, differentially rotating flows driven by the magnetorotational instability are often used to calculate the effective values of alpha viscosity that is invoked in analytical models of accretion discs. In this paper we use various dynamical models of turbulent magnetohydrodynamic stresses as well as numerical simulations of shearing boxes to show that angular momentum transport in accretion discs cannot be described by the alpha model. In particular, we demonstrate that turbulent magnetorotational stresses are not linearly proportional to the local shear and vanish identically for angular velocity profiles that increase outwards.
For a number of reasons, the properties of integrated stellar populations are distributed. Traditional synthesis models usually return the mean value of such distribution, and a perfect fitting to observational data is sought for to infer the age and metallicity of observed stellar populations. We show here that, while this is correct on average, it is not in individual cases because the mean may not be representative of actual values. We present a simple mathematical formalism to derive the shape of the population's luminosity distribution function (pLDF), and an abridged way to estimate it without computing it explicitly. This abridged treatment can be used to establish whether, for a specific case, the pLDF is Gaussian and the application of Gaussian tools, such as the chi^2 test, is correct. More in general, our formalism permits to compute weights to be attributed to different properties (spectral features or band luminosities) in the fitting process. We emphasize that our formalism does not supersede the results of traditionaly synthesis models, but permits to reinterpret and extend them into more powerful tools. The reader is referred to the original paper for further details.
We present a new hybrid code for large volume, high resolution simulations of cosmic reionization, which utilizes a N-body algorithm for dark matter, physically motivated prescriptions for baryons and star formation, and an adaptive ray tracing algorithm for radiative transfer of ionizing photons. Two test simulations each with 3 billion particles and 400 million rays in a 50 Mpc/h box have been run to give initial results. Halos are resolved down to virial temperatures of 10^4 K for the redshift range of interest in order to robustly model star formation and clumping factors. This is essential to correctly account for ionization and recombination processes. We find that the halos and sources are strongly biased with respect to the underlying dark matter, re-enforcing the requirement of large simulation boxes to minimize cosmic variance and to obtain a qualitatively correct picture of reionization. We model the stellar initial mass function (IMF), by following the spatially dependent gas metallicity evolution, and distinguish between the first generation, Population III (PopIII) stars and the second generation, Population II (PopII) stars. The PopIII stars with a top-heavy IMF produce an order of magnitude more ionizing photons at high redshifts z>10, resulting in a more extended reionization. In our simulations, complete overlap of HII regions occurrs at z~6.5 and the computed mass and volume weighted residual HI fractions at 5<z<6.5 are both in good agreement with high redshift quasar absorption measurements from SDSS. The values for the Thomson optical depth are consistent within 1-sigma of the current best-fit value from third-year WMAP.
The two statistical studies of spectra from multiple heavy element transitions in quasar absorption systems report conflicting results on a varying fine-structure constant, alpha. Re-analysis of Srianand et al. [Phys. Rev. Lett. 92, 121302 (2004); also Chand et al., Astron. Astrophys. 417, 853 (2006)] reveals flawed parameter estimation methods. These caused errors to be underestimated by a factor of about 3 and may contribute to an existing strong bias in Delta(alpha)/alpha towards zero. Their spectra and absorption profile models actually imply a larger error and smaller alpha than their reported Delta(alpha)/(alpha)=(-0.06+/-0.06)x10^{-5}. Our revised value is (-0.44+/-0.16)x10^{-5} but we note that the published models may require detailed revision to derive a reliable measurement.
With an extinction-corrected V-band peak absolute magnitude of about -22.2, supernova (SN) 2006gy is probably the brightest SN ever observed. We report on multi-wavelength observations of this SN and its environment. The optical spectra and the slow light-curve evolution resemble those of members of the hybrid IIn/Ia SN class, also called type-IIa SNe. The total radiated energy in the first two months is about 1.2 x 10^51 erg, comparable to the total mechanical energy release of a type-Ia SN. If the engine behind SN2006gy is a type-Ia SN, the rapid conversion of mechanical energy to radiation requires a very dense circumstellar medium, which in turns implies an extreme mass loss rate for the progenitor, ~10^-2 solar mass per year over a period of ~100 yr prior to explosion. Such a mass-loss rate is a challenging requirement for most proposed models of type-IIa SN. Unlike the four previously known type-IIa SNe, the host galaxy NGC 1260 is not a star-forming galaxy, but rather an S0 galaxy dominated by an old stellar population, which probably has a relatively high metallicity. However, our high resolution adaptive optics images reveal a dust lane in this galaxy, passing about 300 pc (projected) from the SN position. These observations add more questions as to the origin of the enigmatic IIa supernovae.
We report on the discovery of strongly variable MgII and FeII absorption lines seen at z=1.48 in the spectra of the z=4.05 GRB 060206 obtained between 4.13 to 7.63 hours after the burst. In particular, the FeII line equivalent width (EW) decayed rapidly from 1.72+-0.25 AA to 0.28+-0.21 AA, only to increase to 0.96+-0.21 AA in a later date spectrum. The MgII doublet shows even more complicated evolution: the weaker line of the doublet drops from 2.05+-0.25 AA to 0.92+-0.32 AA, but then more than doubles to 2.47+-0.41 AA in later data. The ratio of the EWs for the MgII doublet is also variable, being closer to 1:1 (saturated regime) when the lines are stronger and becoming closer to 2:1 (unsaturated regime) when the lines are weaker, consistent with expectations based on atomic physics. We have investigated and rejected the possibility of any instrumental or atmospheric effects causing the observed strong variations. The possibility of variable intervening absorption in GRB spectra was recently predicted by Frank et al. (astro-ph/0605676). Our discovery of clearly variable intervening FeII and MgII lines lends very strong support to their scenario, in which the characteristic size of intervening patches of MgII ``clouds'' is comparable to the GRB beam size, i.e, about 10^16 cm. We discuss various implications of this discovery, including the nature of the MgII absorbers, the physics of GRBs, and measurements of chemical abundances from GRB and quasar absorption lines.
We examine the amplitude of the rotation velocity that can be attributed to the dark matter halos of disk galaxies, focusing on well measured intermediate radii. The data for 60 galaxies spanning a large range of mass and Hubble types, taken together, are consistent with a dark halo velocity log(Vh) = C + B log(r) with C = 1.47 (+0.15, -0.19) and B = 1/2 over the range 1 < r < 74 kpc. The range in C stems from different choices of the stellar mass estimator, from minimum to maximum disk. For all plausible choices of stellar mass, the implied densities of the dark halos are lower than expected from structure formation simulations in LCDM, which anticipate C > 1.6. This problem is not specific to a particular type of galaxy or to the innermost region of the halo (cusp or core); the velocity attributable to dark matter is too low at all radii.
High resolution spectra of the hot central star of the planetary nebula (CSPN) M27, acquired with the Far Ultraviolet Spectroscopic Explorer (\FUSE), have revealed an unusually rich set of narrow molecular hydrogen absorption features. This object is also unique in that the velocity of nebular absorption features are cleanly separated from the velocity of the intervening interstellar medium. These features blend with and in many cases obscure atomic features. We have developed a continuum model of the CSPN including atomic and molecular hydrogen absorption. Using this model we have identified and tabulated the metal lines as arising from either photospheric, nebular and/or non-nebular velocity systems. We find the nebular outflow and ionization balance to be stratified with high ionization states favored at low velocity and low ionization states favored at high velocity. Neutrals and molecules are found at a velocity that marks the transistion between these two regimes. These observations are a challenge to the interacting wind model of PN evolution. Mappings at high resolution of the line profiles for \ion{C}{1} \ion{-}{4}, \ion{N}{1} \ion{-}{3}, \ion{O}{1}, \ion{O}{6}, \ion{Si}{2} \ion{-}{4}, \ion{P}{2} \ion{-}{5}, \ion{S}{2} \ion{-}{4}, \ion{Ar}{1} \ion{-}{2} and \ion{Fe}{2} \ion{-}{3} within the \FUSE and STIS bandpasses are presented. The digitial spectra of the stars and the model are freely available on the H$_2$ools website. They will be useful for photospheric analyses seeking to determine the metallicity of the central star and for absorption line based atomic and molecular abundance determination of the nebular outflow.
Recent Spitzer infrared measurements of hot Jupiter eclipses suggest that eclipse mapping techniques could be used to spatially resolve the day-side photospheric emission of these planets using partial occultations. As a first step in this direction, we simulate ingress/egress lightcurves for the three brightest known eclipsing hot Jupiters and evaluate the degree to which parameterized photospheric emission models can be distinguished from each other with repeated, noisy eclipse measurements. We find that the photometric accuracy of Spitzer is insufficient to use this tool effectively. On the other hand, the level of photospheric details that could be probed with a few JWST eclipse measurements could greatly inform hot Jupiter atmospheric modeling efforts. A JWST program focused on non-parametric eclipse map inversions for hot Jupiters should be actively considered.
Physical conditions in the atmospheres of tidally-locked, slowly-rotating hot Jupiters correspond to dynamical circulation regimes with Rhines scales and Rossby deformation radii comparable to the planetary radii. Consequently, the large spatial scales of moving atmospheric structures could generate significant photospheric variability. Here, we estimate the level of thermal infrared variability expected in successive secondary eclipse depths, according to hot Jupiter turbulent ``shallow-layer'' models. The variability, at the few percent level or more in models with strong enough winds, is within the reach of Spitzer measurements. Eclipse depth variability is thus a valuable tool to constrain the circulation regime and global wind speeds in hot Jupiter atmospheres.
The mean pulsation period of ZZ Ceti stars increases with decreasing
effective temperature as we traverse from the blue to the red edge of the
instability strip. This well-established correlation between the mean period
and spectroscopic temperature suggests that the mean period could be utilized
as a tool to measure the relative temperature of the star independent of
spectroscopy. Measuring the pulsation periods of a ZZ Ceti star is a simple,
model-independent, and straight forward process as opposed to a spectroscopic
determination of its temperature.
Internal uncertainties in determining the spectroscopic temperature of a ZZ
Ceti star are at least 200K, 15% of the 1350K width of the instability strip.
The uncertainties in determining the mean period arise mostly from amplitude
modulation in the pulsation spectrum and are smaller than 100s for 91% of the
ZZ Ceti stars, <8% of the 1300s width of the instability strip. In principle
this implies that for 90% of the ZZ Ceti stars, the average uncertainty in
determining the location of a ZZ Ceti star within the instability strip
decreases by a factor of two in utilizing the mean period of the ZZ Ceti star
as a temperature indicator rather than conventional spectroscopy. Presently we
only claim that the relative temperatures of ZZ Ceti stars derived by using the
mean pulsation period are certainly as good as and perhaps about 15% better
than spectroscopy.
Here we test the idea that new globular clusters (GCs) are formed in the same gaseous ("wet") mergers or interactions that give rise to the young stellar populations seen in the central regions of many early-type galaxies. We compare mean GC colors with the age of the central galaxy starburst. The red GC subpopulation reveals remarkably constant mean colors independent of galaxy age. A scenario in which the red GC subpopulation is a combination of old and new GCs (formed in the same event as the central galaxy starburst) can not be ruled out; although this would require an age-metallicity relation for the newly formed GCs that is steeper than the Galactic relation. However, the data are also well described by a scenario in which most red GCs are old, and few, if any, are formed in recent gaseous mergers. This is consistent with the old ages inferred from some spectroscopic studies of GCs in external systems. The event that induced the central galaxy starburst may have therefore involved insufficient gas mass for significant GC formation. We term such gas-poor events "damp" mergers.
Space motions are given for 38 RR Lyrae (RRL) stars and 79 blue horizontal
branch (BHB) stars in a ~200 deg2 area around the North Galactic Pole (NGP)
using a homogeneous distance scale consistent with (m-M)0=18.52 for the LMC.
The kinematics of the 26 RRL and 52 BHB stars in the 10.4 cubic kpc volume
that have Z<8 kpc are not homogeneous. Our BHB sample (like that of Sirko et
al. 2004b) has a zero galactic rotation (V_phi) and roughly isotropic velocity
dispersions. The RRL sample shows a definite retrograde rotation (V_phi =
-95+/-29 km/s) and non-isotropic velocity dispersions. The combined BHB and RRL
sample has a retrograde galactic rotation (V) that is similar to that found by
Majewski (1992) for his sample of subdwarfs in SA 57. The velocity dispersion
of the RRL stars that have a positive W motion is significantly smaller than
the dispersion of those "streaming down" with a negative W.
One component of our sample (rich in RRL's) shows retrograde rotation and the
streaming motion that we associate with the accretion process. The other
(traced by the BHB stars) shows essentially no rotation and less evidence of
streaming. These two components have HB morphologies that suggest that they may
be the field star equivalents of the young and old halo globular clusters
respectively.
Longitudinal distributions of the photospheric magnetic field studied on the base of National Solar Observatory (Kitt Peak) data (1976 - 2003) displayed two opposite patterns during different parts of the 11-year solar cycle. Heliolongitudinal distributions differed for the ascending phase and the maximum of the solar cycle on one hand, and for the descending phase and the minimum on the other, depicting maxima around two opposite Carrington longitudes (180 deg. and 0/360 deg.). Thus the maximum of the distribution shifted its position by 180 deg. with the transition from one characteristic period to the other. Two characteristic periods correspond to different situations occurring in the 22-year magnetic cycle of the Sun, in the course of which both global magnetic field and the magnetic field of the leading sunspot in a group change their sign. During the ascending phase and the maximum (active longitude 180 deg.) polarities of the global magnetic field and those of the leading sunspots coincide, whereas for the descending phase and the minimum (active longitude 0/360 deg.) the polarities are opposite. Thus the observed change of active longitudes may be connected with the polarity changes of Sun's magnetic field in the course of 22-year magnetic cycle.
Sys-Rem (Tamuz, Mazeh & Zucker 2005) is a detrending algorithm designed to remove systematic effects in a large set of lightcurves obtained by a photometric survey. The algorithm works without any prior knowledge of the effects, as long as they appear in many stars of the sample. This paper presents the basic principles of Sys-Rem and discusses a parameterization used to determine the number of effects removed. We assess the performance of Sys-Rem on simulated transits injected into WHAT survey data. This test is proposed as a general scheme to assess the effectiveness of detrending algorithms. Application of Sys-Rem to the OGLE dataset demonstrates the power of the algorithm. We offer a coded implementation of Sys-Rem to the community.
Aims: The measurement of the redshift of a lensing galaxy that produces
multiple images of a background quasar is essential to any subsequent modeling,
whether related to the determination of the Hubble constant H0 or to the mass
profile of the lensing galaxy. We present the results of our ongoing
spectroscopic observations of gravitationally lensed quasars in order to
measure the redshift of their lensing galaxies. We report on the determination
of the lens redshift in seven gravitationally lensed systems.
Methods: Our deep VLT/FORS1 spectra are spatially deconvolved in order to
separate the spectrum of the lensing galaxies from the glare of the much
brighter quasar images. Our observing strategy involves observations in
Multi-Object-Spectroscopy (MOS) mode which allows the simultaneous observation
of the target and of several crucial PSF and flux calibration stars. The
advantage of this method over traditional long-slit observations is that it
allows a much more reliable extraction and flux calibration of the spectra.
Results: We obtain the first reliable spectra of the lensing galaxies in six
lensed quasars: FBQ 0951+2635 (z=0.260), BRI 0952-0115 (z=0.632), HE 2149-2745
(z=0.603), Q 0142-100 (z=0.491), SDSS J0246-0825 (z=0.723), and SDSS J0806+2006
(z=0.573). The last three redshifts also correspond to the MgII doublet seen in
absorption in the quasar spectra at the lens redshift. Finally, we reanalyse
the blue side of our previously published spectra of Q 1355-2257 and find MgII
in absorption at z=0.702, confirming our previous redshift estimate. The
spectra of all lenses are typical of early-type galaxies.
We present an analysis of recent XMM-Newton and HST archive data of the ultraluminous X-ray source NGC 1313 X-2. Quasi-simultaneous observations taken with XMM-Newton, HST and VLT allow us to study both the X-ray light curve and its correlation with the optical emission of the two proposed ULX counterparts. At the end of December 2003 the source experienced a short, but intense flare, reaching a maximum luminosity of ~10^40 erg/s. At the same time, the optical flux of both the suggested counterparts did not show pronounced variations (<30%). Assuming that the ULX emission is isotropic and taking X-ray reprocessing into account, the optical data for one of the proposed counterparts are consistent with it being an early type, main sequence star of about 10-18 Msun losing matter through Roche-lobe overflow onto a ~120 Msun black hole at an orbital separation corresponding to a period of about 2 days.
In radio bands, the study of compact radio sources can be affected by propagation effects through the Interstellar Medium. These are usually attributed to the presence of turbulent intervening plasma along the line of sight. Here, two of such effects are presented. The line of sight of B 2005+403 passes through the heavily scattered region of Cygnus, which causes substantial angular broadening of the source images obtained at frequencies between 0.6 GHz and 8 GHz. At higher frequencies, however the intrinsic source structure shines through. Therefore, multi-frequency VLBI observations allow to study the characteristics of the intervening material, the source morphology and the "coupling" of them in forming the observed image.
The size and time of formation of the first gravitationally bound objects in the Universe is set by the microphysical properties of the dark matter. It is argued that observations seem to favour cold and thermal candidates for the main contribution to the dark matter. For that type of dark matter, the size and time of formation of the first halos is determined by the elastic cross sections and mass of the CDM particles. Consequently, the astrophysics of CDM might allow us to measure some of the fundamental parameters of CDM particles. Essential for observations is the survival rate and spatial distribution of the very first objetcs, which are currently under debate.
N--body + hydrodynamical simulations of formation and evolution of galaxy groups in a LambdaCDM cosmology have been performed. The properties of the galaxy populations in 12 groups are here discussed, with focus on the colour-magnitude relation in both normal and fossil groups.
Particle acceleration at non-relativistic shocks can be very efficient, leading to the appearance of non-linear effects due to the dynamical reaction of the accelerated particles on the shock structure and to the non-linear amplification of the magnetic field in the shock vicinity. The value of the maximum momentum $p_{max}$ in these circumstances cannot be estimated using the classical results obtained within the framework of test particle approaches. We provide here the first attempt at estimating $p_{max}$ in the cosmic ray modified regime, taking into account the non-linear effects mentioned above.
We describe our recent progress in modeling supernova-fallback disks and
neutron star (NS) atmospheres.
We present a first detailed spectrum synthesis calculation of a SN-fallback
disk composed of iron. We assume a thin disk with a radial structure described
by the alpha-disk model. The vertical structure and emission spectrum are
computed self-consistently by solving the structure equations simultaneously
with the radiation transfer equations under non-LTE conditions. We describe the
properties of a specific disk model and discuss various effects on the emergent
UV/optical spectrum.
We investigate Compton scattering effects on the thermal spectrum of NSs. In
addition, we constructed a new generation of metal line-blanketed non-LTE model
atmospheres for NSs. It is compared to X-ray burst spectra of EXO0748-676. It
is possible that the gravitational redshift, deduced from absorption lines, is
lower (z=0.24) than hitherto assumed (z=0.35). Accordingly, this would result
in NS mass and radius lower limits of M>1.63Msun and R>13.8 km.
It is well known that the radiative cooling time of the hot X-ray emitting gas in the cores of most clusters of galaxies is less than 10^10 yr. In many clusters the gas temperature also drops towards the centre. If we draw a causal connection between these two properties then we infer the presence of a cooling flow onto the central galaxy. High spectral resolution XMM-Newton data and high spatial resolution Chandra data, show however a lack of X-ray emitting gas below about one third of the cluster virial temperature. The explanation is that some form of heating balances cooling. The smoothness and similarity of the cooling time profiles and the flatness of the required heating profiles all indicate that we must seek a relatively gentle, quasi-continuous (on timescales <10^8 yr), distributed heat source. The likely such source is the central black hole and its powerful jets which create bubble-like cavities in the inner hot gas. We briefly review the general heating and cooling statistics in an X-ray bright sample of cluster before we discuss the detailed situation in the Perseus cluster, the X-ray brightest cluster in the Sky.
The nucleosynthesis of nature's rarest isotope 180Ta depends sensitively on the temperature of the astrophysical environment because of depopulation of the long-living isomeric state via intermediate states to the short-living ground state by thermal photons. Reaction rates for this transition have been measured in the laboratory. These ground state rates understimate the stellar rates dramatically because under stellar conditions intermediate states are mainly populated by excitations from thermally excited states in 180mTa. Full thermalization of 180Ta is already achieved for typical s-process temperatures around kT = 25 keV. Consequently, for the survival of 180Ta in the s-process fast convective mixing is required which has to transport freshly synthesized 180Ta to cooler regions. In supernova explosions 180Ta is synthesized by photon- or neutrino-induced reactions at temperatures above T9 = 1 in thermal equilibrium; independent of the production mechanism, freeze-out from thermal equilibrium occurs at kT approx 40 keV, and only 35 +- 4 % of the synthesized 180Ta survive in the isomeric state.
Surveys of distant galaxies with the Hubble Space Telescope and from the ground have shown that there is only mild evolution in the relationship between radial size and stellar mass for galactic disks from z~1 to the present day. Using a sample of nearby disk-dominated galaxies from the Sloan Digital Sky Survey (SDSS), and high redshift data from the GEMS (Galaxy Evolution from Morphology and SEDs) survey, we investigate whether this result is consistent with theoretical expectations within the hierarchical paradigm of structure formation. The radius-mass relation for virialized dark matter halos in the concordance LCDM model evolves by about a factor of two over this interval. However, high resolution N-body simulations have shown that dark matter halos in hierarchical models build up from the inside out, so that the inner part of the halo, where the baryons are concentrated, changes very little over this interval. We compute the expected disk size-stellar mass distribution, accounting for this evolution in the internal structure of dark matter halos and the adiabatic contraction of the dark matter by the self-gravity of the collapsing baryons. We find that the predicted evolution in the mean size at fixed stellar mass since z~1 is about 15-20 percent, in good agreement with the observational constraints from GEMS. At redshift z~2, the model predicts that disks at fixed stellar mass were on average only 60 percent as large as they are today. This is somewhat stronger evolution than the available observations indicate, but is consistent with the data within the uncertainties.
We summarize the optical, UV, and X-ray properties of double-peaked emitters -- AGN with double-peaked Balmer emission lines believed to originate in the AGN accretion disk. We focus on the X-ray spectroscopic results obtained from a new sample of the 16 broadest Balmer line AGN observed with Chandra and Swift.
The presence of methyl alcohol or methanol (CH$_3$OH) in several astrophysical environments has been characterized by its high abundance that depends on both the production rate and the destruction rate. In the present work, the photoionization and photodissociation processes of methanol have been experimentally studied, employing soft X-ray photons (100-310 eV) from a toroidal grating monochromator (TGM) beamline of the Brazilian Synchrotron Light Laboratory (LNLS). Mass spectra were obtained using the photoelectron photoion coincidence (PEPICO) method. Kinetic energy distribution and abundances for each ionic fragment have been obtained from the analysis of the corresponding peak shapes in the mass spectra. Absolute photoionization and photodissociation cross sections were also determined. We have found, among the channels leading to ionization, about 11-16% of CH$_3$OH survive the soft X-rays photons. This behavior, together with an efficient formation pathways, may be associated with the high column density observed in star-forming regions. The three main photodissociation pathways are represented by COH$^+$ (or HCO$^+$) ion release (with ejection of H$_2$ + H), the dissociation via C-O bond rupture (with strong charge retention preferentially on the methyl fragment) and the ejection of a single energetic (2-4 eV) proton. Since methanol is very abundant in star forming regions, the produced protons could be an alternative route to molecular hydrogenation or a trigger for secondary dissociation processes or even to promote extra heating of the environment.
Phase-resolved high resolution optical spectroscopy has revealed narrow N III and He II emission lines from the soft X-ray transient Aquila X-1 during its 2004 outburst that move as a function of the orbit consistent with the phasing of the donor star. Under the assumption that these lines come from the irradiated side of the donor star, we can constrain its K_2 velocity to >247+/-8 km/s, and derive a mass function of f(M_1)>1.23+/-0.12M_sun. Estimates for the rotational broadening based on the emission components suggest a possible massive neutron star of >1.6M_sun (at 95% confidence). However, an updated ephemeris and additional high resolution spectroscopy of Aql X-1 during a future outburst are warranted in order to confirm that the narrow lines indeed originate on the donor star surface, and reliably characterise the system parameters of this important X-ray binary. Spectra taken during the end of the outburst show that the morphology of the emission lines changed dramatically. No donor star signature was present anymore, while the presence of narrow low-velocity emission lines became clear, making Aql X-1 a member of the slowly growing class of low-velocity emission line sources.
The binary nature of the bright (V = 4.2 mag) Mercury-Manganese star Phi Her has been known since 1976 and it was considered a low-amplitude single-lined SB. In a recent study we found evidence for lines of the secondary star. Other recent results from interferometry provide a good measure of the light ratio. It is very plausible that the secondary is a late main-sequence A star. We find the rotational velocity of the secondary to be ~42 +/- 5 km/s.
The F5 IV-V star Procyon A (\alpha CMi) was observed in January 2001 by means of the high resolution spectrograph SARG operating with the TNG 3.5m Italian telescope (Telescopio Nazionale Galileo) at Canary Islands, exploiting the iodine cell technique. The time-series of about 950 spectra carried out during 6 observation nights and a preliminary data analysis were presented in Claudi et al. 2005. These measurements showed a significant excess of power between 0.5 and 1.5 mHz, with ~ 1 ms^-1 peak amplitude. Here we present a more detailed analysis of the time-series, based on both radial velocity and line equivalent width analyses. From the power spectrum we found a typical p-mode frequency comb-like structure, identified with a good margin of certainty 11 frequencies in the interval 0.5-1400 mHz of modes with l=0,1,2 and 7< n < 22, and determined large and small frequency separations, Dn = 55.90 \pm 0.08 muHz and dnu_02=7.1 \pm 1.3 muHz, respectively. The mean amplitude per mode (l=0,1) at peak power results to be 0.45 \pm 0.07 ms^-1, twice larger than the solar one, and the mode lifetime 2 \pm 0.4 d, that indicates a non-coherent, stochastic source of mode excitation. Line equivalent width measurements do not show a significant excess of power in the examined spectral region but allowed us to infer an upper limit to the granulation noise.
We find a new Tully-Fisher-like relation for spiral galaxies holding at different galactocentric radii. This Radial Tully-Fisher (RTF) relation allows us to investigate the distribution of matter in the optical regions of spiral galaxies. This relation, applied to three different samples of rotation curves of spiral galaxies, directly proves that: 1) the rotation velocity of spirals is a good measure of their gravitational potential and both the RC's amplitudes and profiles are well predicted by galaxy luminosity 2) the existence of a dark component, less concentrated than the luminous one, and 3) a scaling law, according to which, inside the disk optical size: $ M_{dark}/M_{lum} = 0.5 (L_B/10^{11}L_{B\odot})^{-0.7}$.
Accreting black holes often show iron line emission in their X-ray spectra. When this line emission is very broad or variable then it is likely to originate from close to the black hole. The theory and observations of such broad and variable iron lines are briefly reviewed here. In order for a clear broad line to be found, one or more of the following have to occur: high iron abundance, dense disk surface and minimal complex absorption. Several excellent examples are found from observations of Seyfert galaxies and Galactic Black Holes. In some cases there is strong evidence that the black hole is rapidly spinning. Further examples are expected as more long observations are made with XMM-Newton, Chandra and Suzaku. The X-ray spectra show evidence for the strong gravitational redshifts and light bending expected around black holes.
In this paper, the physical conditions within the inhomogeneous solar atmosphere have been reconstructed by means of solving the inverse problem of Non Local Thermodynamic Equilibrium (NLTE) radiative transfer. The profiles of $\lambda=523.42$ nm FeI spectral line of high spatial and time resolution were used as observational data. The velocity field has been studied for the real solar granulation in superadiabatic layer and overshooting convection region. Also, we investigate the vertical structure of inhomogeneous solar photosphere and consider penetration of granules from convective region into upper layers of stable atmosphere. The microturbulent velocity appears to be minimal at the bottom of overshooting convection region and increases sharply through superadiabatic layer and upper photosphere. High-turbulent layers emerge either in the central part of a flow or at the boundary of an incipient flow with following drift toward the centre of the flow. Wide descending flows tend to disintegrate into structures having turbulence augmented, these structures correspond to the flows of matter. High microturbulence of the intensive flows provokes steep temperature depression in upper photosphere leading to the second inversion of temperature for the intergranules. The inversion of vertical velocities is observed to be frequent in the solar granulation. Some of the convective flows reach the minimum temperature region. Vertical convective velocities of the matter flows were found to be smaller in the middle and upper photosphere. Also, the effect of finite resolution on the spacial variations of the velocities in solar photosphere has been estimated.
The supergiant fast X-ray transient IGR J08408-4503 was discovered by INTEGRAL on May 15, 2006, during a bright flare. The source shows sporadic recurrent short bright flares, reaching a peak luminosity of 10^36 erg s^-1 within less than one hour. The companion star is HD 74194, an Ob5Ib(f) supergiant star located at 3 kpc in the Vela region. We report the light curves and broad-band spectra (0.1-200 keV) of all the three flares of IGR J08408-4503 detected up to now based on INTEGRAL and Swift data. The flare spectra are well described by a power-law model with a high energy cut-off at ~15 keV. The absorption column density during the flares was found to be ~10^21 cm^-2, indicating a very low matter density around the compact object. Using the supergiant donor star parameters, the wind accretion conditions imply an orbital period of the order of one year, a spin period of the order of hours and a magnetic field of the order of 10^13 G.
A unified evolutionary scheme that includes post-AGB systems, barium stars, symbiotics, and related systems, explaining their similarites as well as differences. Can we construct it? We compare these various classes of objects in order to construct a consistent picture. Special attention is given to the comparison of the barium pollution and symbiotic phenomena. Finally, we outline a `transient torus' evolutionary scenario that makes use of the various observational and theoretical hints and aims at explaining the observed characteristics of the relevant systems.
Change of sign of the LNRF-velocity gradient has been found for accretion discs orbiting rapidly rotating Kerr black holes with spin a > 0.9953 for Keplerian discs and a > 0.99979 for marginally stable thick discs. Aschenbach (2004) has identified the maximal rate of change of the orbital velocity within the "humpy" profile with a locally defined critical frequency of disc oscillations, but it has been done in a coordinate-dependent form. We define the critical "humpy" frequency H in general relativistic, coordinate independent form, and relate the frequency defined in the LNRF to distant observers. At radius of its definition, so-called "humpy" radius r_h, the "humpy" frequency H is compared to the radial (R) and vertical (V) epicyclic frequencies and the orbital frequency of the disc. For Keplerian thin discs, we show that the epicyclic resonance radii r_31 and r_41 (with V:R = 3:1 or 4:1) are located in vicinity of r_h where efficient triggering of oscillations with frequencies ~ H could be expected. Asymptotically (for 1-a < 10^(-4)) the ratio of the epicyclic and Keplerian frequencies and the humpy frequency is nearly constant, i.e., almost independent of spin, being for the radial epicyclic frequency R:H ~ 3:2. For thick discs the situation is more complex due to dependence on distribution of the specific angular momentum l determining the disc properties. For l = const tori and 1-a < 10^(-6) the frequency ratios of the humpy frequency and the orbital and epicyclic frequencies are again nearly constant and independent of both a and l, being for the radial epicyclic frequency R:H close to 4. In the limiting case of very slender tori (l ~ l_ms) the epicyclic resonance radius r_41 ~ r_h for spin 1-a < 2x10^(-4).
We investigate how current and proposed observations of neutron stars can lead to an understanding of the state of their interiors and the key unknowns: the typical neutron star radius and the neutron star maximum mass. A theoretical analysis of neutron star structure, including general relativistic limits to mass, compactness, and spin rates is made. We consider observations made not only with photons, ranging from radio waves to X-rays, but also those involving neutrinos and gravity waves. We detail how precision determinations of structural properties would lead to significant restrictions on the poorly understood equation of state near and beyond the equilibrium density of nuclear matter.
A recent study demonstrated that there is significant covariance structure in the noise on data from ground-based photometric surveys designed to detect transiting extrasolar planets. Such correlation in the noise has often been overlooked, especially when predicting the number of planets a particular survey is likely to find. Indeed, the shortfall in the number of transiting extrasolar planets discovered by such surveys seems to be explained by co-variance in the noise. We analyse SuperWASP (Wide Angle Search for Planets) data and determine that there is a significant amount of correlated systematic noise present. After modelling the potential planet catch, we conclude that this noise places a significant limit on the number of planets that SuperWASP is likely to detect; and that the best way to boost the signal-to-noise ratio and limit the impact of co-variant noise is to increase the number of observed transits for each candidate transiting planet.
In a transiting planetary system, the presence of a second planet will cause the time interval between transits to vary. These transit timing variations (TTV) are particularly large near mean-motion resonances and can be used to infer the orbital elements of planets with masses that are too small to detect by any other means. I present the results of a study of simulated data where I show the potential that this planet detection technique has to detect and characterize secondary planets in transiting systems. These results have important ramifications for planetary transit searches since each transiting system presents an opportunity for additional discoveries through a TTV analysis. I present such an analysis for 13 transits of the HD 209458 system that were observed with the Hubble Space Telescope. This analysis indicates that a putative companion in a low-order, mean-motion resonance can be no larger than the mass of the Earth and constitutes, to date, the most sensitive probe for extrasolar planets that orbit main sequence stars. The presence or absence of small planets in low-order, mean-motion resonances has implications for theories of the formation and evolution of planetary systems. Since TTV is most sensitive in these regimes, it should prove a valuable tool not only for the detection of additional planets in transiting systems, but also as a way to determine the dominant mechanisms of planet formation and the evolution of planetary systems.
Spitzer Infrared Spectrograph (IRS) observations of 3C radio galaxies and quasars shed new light on the nature of the central engines of AGN. Emission from silicate dust obscuring the central engine can be used to estimate the bolometric luminosity of an AGN. Emission lines from ions such as O IV and Ne V give another indication of the presence or lack of a hidden source of far-UV photons in the nucleus. Radio-loud AGN with relative-to-Eddington luminosity ratios of L/L_Edd < 3E-3 do not appear to have broad optical emission lines, though some do have strong silicate emission. Aromatic emission features from star formation activity are common in low-luminosity radio galaxies. Strong molecular hydrogen pure-rotational emission lines are also seen in some mid-IR weak radio galaxies, caused by either merger shocks or jet shocks in the interstellar medium.
We describe the results of the largest and most accurate three-dimensional field theory simulations of domain wall networks with junctions. We consider a previously introduced class of models which, in the limit of large number $N$ of coupled scalar fields, approaches the so-called `ideal' model (in terms of its potential to lead to network frustration). We consider values of $N$ between N=2 and N=20. In all cases we find compelling evidence for a gradual approach to scaling, with the quantitative scaling parameters having only a mild dependence on $N$. These results strongly support our no-frustration conjecture.
Cosmic infrared background fluctuations may contain measurable contribution from objects inaccessible to current telescopic studies, such as the first stars and other luminous objects in the first Gyr of the Universe's evolution. In an attempt to uncover this contribution we have analyzed the GOODS data obtained with the Spitzer IRAC instrument, which are deeper and cover larger scales than the Spitzer data we have previously analyzed. Here we report these new measurements of the cosmic infrared background (CIB) fluctuations remaining after removing cosmic sources to fainter levels than before. The remaining anisotropies on scales > 0.5 arcmin have a significant clustering component with a low shot-noise contribution. We show that these fluctuations cannot be accounted for by instrumental effects, nor by the Solar system and Galactic foreground emissions and must arise from extragalactic sources.
We present an analysis of UV and optical spectra of NGC 4151 obtained at high spectral and angular resolutions with the Hubble Space Telescope's (HST's) Space Telescope Imaging Spectrograph (STIS). We identify a kinematic component of the emission lines that has a width of 1170 km/s (FWHM), intermediate between those from the broad and narrow (emission) line regions (BLR and NLR). We present evidence that these emission lines arise from the same gas responsible for most of the high-column UV and X-ray absorption (component ``D+E'') that we see in outflow at a distance of ~0.1 pc from the central nucleus. The gas in this intermediate-line region (ILR) shields the NLR and has a global covering factor of ~0.4, based on the observed C IV fluxes, indicating mass outflow over a large solid angle centered on the accretion disk's axis. A large transverse velocity (> 2100$ km/s) compared to the radial velocity centroid (-490$ km/s) indicates that the kinematics is dominated by rotation at this distance, but has a significant outflow component. The mass outflow rate at 0.1 pc is ~0.16 solar masses/yr, which is about 10 times the accretion rate. Based on physical conditions in the gas and dynamical considerations, models that invoke magnetocentrifugal acceleration (e.g., in an accretion-disk wind) are favored over those that rely on radiation driving or thermal expansion as the principal driving mechanism for the mass outflow.
We discuss interpretation of the cosmic infrared background (CIB) anisotropies detected by us recently in the Spitzer IRAC based measurements. The fluctuations are approximately isotropic on the sky consistent with their cosmological origin. They remain after removal of fairly faint intervening sources and must arise from a population which has a strong CIB clustering component with only a small shot-noise level. We discuss the constraints the data place on the luminosities, epochs and mass-to-light ratios of the indvidual sources producing them. Assuming the concordance LambdaCDM cosmology the measurements imply that the luminous sources producing them lie at cosmic times < 1 Gyr and were individually much brighter per unit mass than the present stellar populations.
We present the results of 10 micron nulling interferometric observations of 13 Herbig Ae stars using the Magellan I (Baade) and the MMT 6.5 m telescopes. A portion of the observations was completed with the adaptive secondary at the MMT. We have conclusively spatially resolved 3 of the 13 stars, HD 100546, AB Aur, and HD 179218, the latter two recently resolved using adaptive optics in combination with nulling interferometry. For the resolved objects we find that the 10 $\mu$m emitting regions have a spatial extent of 15-30 AU in diameter. We also have some evidence for resolved emission surrounding an additional 2 stars (V892 Tau and R CrA). For those objects in our study with mid-IR SEDs classifications from Meeus et al. (2001), we find that the Group I objects (those with constant to increasing mid-IR flux) are more likely to be resolved, within our limited sample. This trend is evident in correlations in the inferred disk sizes vs. the sub-millimeter SED slope and disk size vs. fractional infrared luminosity of the systems. We explore the spatial distribution and orientation of the warm dust in the resolved systems and constrain physical models which are consistent with their observational signatures.
The comparison of the proper motions constructed from positions spanning a short (Hipparcos) or long time (Tycho-2) makes it possible to uncover binaries with periods of the order of or somewhat larger than the short time span, since the unrecognised orbital motion will then add to the proper motion. A list of candidate proper motion binaries is constructed from a chi^2 test evaluating the statistical significance of the difference between the Tycho-2 and Hipparcos proper motions for 103134 stars in common between the two catalogues (excluding components of visual systems). The paper focuses on the evaluation of the detection efficiency of proper-motion binaries, using different kinds of control data (mostly radial velocities). The detection rate for entries from the Ninth Catalogue of Spectroscopic Binary Orbits (SB9) is evaluated, as well as for stars like barium stars, which are known to be all binaries. Proper motion binaries are efficiently detected for systems with parallaxes in excess of ca. 20 mas, and periods in the range 1000 - 30000 d. The shortest periods in this range (1000 - 2000 d) may appear only as DMSA/G binaries (accelerated proper motion in the Hipparcos Double and Multiple System Annex). Proper motion binaries detected among SB9 systems having periods shorter than about 400 d hint at triple systems. A list of 19 candidate triple systems is provided. Binaries suspected of having low-mass (brown-dwarf-like) companions are listed as well. Among the 37 barium stars with parallaxes larger than 5 mas, only 7 exhibit no evidence for duplicity whatsoever (be it spectroscopic or astrometric). Finally, the fraction of proper-motion binaries shows no significant variation among the various (regular) spectral classes, when due account is taken for the detection biases.
Recent results indicate that the grain size and crystallinity inferred from observations of silicate features may be correlated with spectral type of the central star and/or disk geometry. In this paper, we show that grain size, as probed by the 10 um silicate feature peak-to-continuum and 11.3-to-9.8 um flux ratios, is inversely proportional to log L_star. These trends can be understood using a simple two-layer disk model for passive irradiated flaring disks, CGPLUS. We find that the radius, R_10, of the 10 um silicate emission zone in the disk goes as (L_star/L_sun)^0.56, with slight variations depending on disk geometry (flaring angle, inner disk radius). The observed correlations, combined with simulated emission spectra of olivine and pyroxene mixtures, imply a grain size dependence on luminosity. Combined with the fact that R_10 is smaller for less luminous stars, this implies that the apparent grain size of the emitting dust is larger for low-luminositysources. In contrast, our models suggest that the crystallinity is only marginally affected, because for increasing luminosity, the zone for thermal annealing (assumed to be at T>800 K) is enlarged by roughly the same factor as the silicate emission zone. The observed crystallinity is affected by disk geometry, however, with increased crystallinity in flat disks. The apparent crystallinity may also increase with grain growth due to a corresponding increase in contrast between crystalline and amorphous silicate emission bands.
We discuss here the spatial clustering of Seyferts and LINERs and consequences for their central engines. We show that Seyferts are less clustered than LINERs, and that this difference is not driven by the morphology-density relation, but it is related to the difference in clustering as a function of level of activity in these systems and the amount of fuel available for accretion. LINERs, which are the most clustered among AGN, show the lowest luminosities and obscuration levels, and relatively low gas densities, suggesting that these objects harbor black holes that are relatively massive yet weakly active or inefficient in their accretion, probably due to the insufficiency of their fuel supply. Seyferts, which are weakly clustered, are very luminous, show generally high gas densities and large quantities of obscuring material, suggesting that in these systems the black holes are less massive but abundantly fueled and therefore accrete quickly and probably efficiently enough to clearly dominate the ionization.
There is now strong observational evidence that the expansion of the universe is accelerating. The standard explanation invokes an unknown "dark energy" component. But such scenarios are faced with serious theoretical problems, which has led to increased interest in models where instead General Relativity is modified in a way that leads to the observed accelerated expansion. The question then arises whether the two scenarios can be distinguished. Here we show that this may not be so easy, demonstrating explicitely that a generalised dark energy model can match the growth rate of the DGP model and reproduce the 3+1 dimensional metric perturbations. Cosmological observations are then unable to distinguish the two cases.
Luminous extended emission-line regions (EELRs) on kpc scales surround a substantial fraction of steep-spectrum radio-loud QSOs. Although their existence has been known for over three decades, there are still major uncertainties on the physical processes responsible for their complex morphology and kinematics. We are obtaining deep integral field spectroscopy for a sample of EELRs around QSOs at z<0.5 with the Integral Field Unit (IFU) of the GMOS on the Gemini North telescope, aiming at extracting accurate kinematics of the EELRs, measuring important physical parameters (e.g., density, temperature, metallicity) and reliable intensity ratios of diagnostic emission lines from individual clouds that comprise an EELR. Here we present results from the observations of the EELR of quasar 4C 37.43. We show maps of gas kinematics measured from the [O III] 5007 line and line-ratio diagnostic diagrams comparing the data with predictions from ionization models. We find that the ionized gas shows rather complex global kinematics, while linear velocity gradients are often seen in individual clouds. Pure photoionization by the QSO continuum is the most likely ionization mechanism for most of the EELR clouds.
We report on deep spectroscopy using LRIS on Keck I and FORS2 on the VLT of a sample of 22 candidate z~6 Lyman Break galaxies (LBGs) selected by the i-z> 1.3 dropout criterion. Redshifts could be measured for eight objects. These redshifts are all in the range z = 5.5 - 6.1, confirming the efficiency of the i-z color selection technique. Six of the confirmed galaxies show Ly-alpha emission. Assuming that the 14 objects without redshifts are z~6 LBGs, but lack detectable Ly-alpha emission lines, we infer that the fraction of Ly-alpha emitting LBGs with Ly-alpha equivalent widths greater than 20 Angstroms among z~6 LBGs is ~30%, similar to that found at z~3. Every Ly-alpha emitting object in our sample is compact with r <= 0.14". Furthermore, all the Ly-alpha emitting objects in our sample are more compact than average relative to the observed size-magnitude relation of a large i-dropout sample (332 candidate z~6 objects). We can reject the hypothesis that the Ly-alpha emitting population is a subset of the rest of the z~6 LBG population at >97% confidence. We speculate the small sizes of Ly-alpha emitting LBGs are due to these objects being less massive than other LBGs at z~6.
We have observed a sample of 13 large, powerful Fanaroff-Riley type II radio galaxies with the Very Large Array in multiple configurations and at multiple frequencies. We have combined our measurements of spectral indices, rotation measures and structural parameters such as arm-length ratios, axial ratios and misalignment angles, with similar data from the literature and revisited some well-known radio galaxy correlations.
Recent observations of the luminosity-redshift in Type Ia supernovae suggest an accelerated inflation of the Universe (open Universe) as well as the observed matter density showed to be less than the critical one, suggesting that a large fraction of the energy density of the Universe is in the form of dark energy with negative pressure (to supply repulsive forces). We present here an alternative mechanism on the basis of the photon energy loss in the inter-galactic gravitational field, and it is close to the Shapiro effect. It is argue that the redshift observed in distant galaxies is a cumulativeprocess, a dominant redshift due to the Doppler effect plus a redshift due to photon energy loss in the intergalactic gravitational field. We show that the last mechanism when interpreted as Doppler effect, supplies a non lineal relationship among the speed of recession of the galaxies and their distances. The effect is very tiny, even so, it increases with the distance and can be the key to explain the anomalous redshift observed in distant supernovae without the accelerated inflation hypothesis
We analyze the observational constraints on the model where a pseudo-Nambu-Goldstone boson (pNGB) plays the role of dark energy. The constraints are derived by using the latest Gold set of 182 type Ia supernovae and the CMB shift parameter. We allow for both the initial value of the scalar field and the present value of the energy in the pNGB to vary. We find that - compared to previous analyses - the allowed parameter space has shrunk around the region where the pNGB does not evolve significantly.
Observations give strong support for the unification scheme of active galactic nuclei. Clumpiness of the toroidal obscuration is crucial for explaining the IR observations and has significance consequences for AGN classification: type 1 and type 2 viewing is an angle-dependent probability, not an absolute property. The broad line region (BLR) and the dusty torus are, respectively, the inner and outer segments, across the dust sublimation radius, of a continuous cloud distribution. Continuum X-ray obscuration comes mostly from the inner, BLR clouds. All clouds are embedded in a disk wind, whose mass outflow rate is diminishing as the accretion rate, i.e., AGN luminosity, is decreasing. The torus disappears when $L \la$ \E{42} erg/sec, the BLR at some lower, yet to be determined luminosities.
We have traced the Galactic thick disk to its, to date, highest metallicities. Based on high-resolution spectroscopic observations of 187 F and G dwarf stars that kinematically can be associated either with the thin disk (60 stars) or with the thick disk (127 stars), we find that the thick disk stars reach at least solar metallicities, and maybe even higher. This finding is independent of the U_LSR, V_LSR and W_LSR velocities of the stars.
In this paper, we bring together various of our published and unpublished findings from our recent 2D multi-group, flux-limited radiation hydrodynamic simulations of the collapse and explosion of the cores of massive stars. Aided by 2D and 3D graphical renditions, we motivate the acoustic mechanism of core-collapse supernova explosions and explain, as best we currently can, the phases and phenomena that attend this mechanism. Two major foci of our presentation are the outer shock instability and the inner core g-mode oscillations. The former sets the stage for the latter, which damp by the generation of sound. This sound propagates outward to energize the explosion and is relevant only if the core has not exploded earlier by some other means. Hence, it is a more delayed mechanism than the traditional neutrino mechanism that has been studied for the last twenty years since it was championed by Bethe and Wilson. We discuss protoneutron star convection, accretion-induced-collapse, gravitational wave emissions, pulsar kicks, the angular anisotropy of the neutrino emissions, a subset of numerical issues, and a new code we are designing that should supercede our current supernova code VULCAN/2D. Whatever ideas last from this current generation of numerical results, and whatever the eventual mechanism(s), we conclude that the breaking of spherical symmetry will survive as one of the crucial keys to the supernova puzzle.
Recent estimates of the Kerr parameters a for two binaries (Shafee et al. 2006), GRO J1655-40 (Nova Scorpii) and 4U 1543-47 (IL Lupi), facilitate a test of stellar evolution. We found that the measured Kerr parameters are consistent with those of Lee et al. (2002, denoted as LBW), in which they predicted the Kerr parameters of X-ray transient sources based on the common envelope evolution which begins at the He red-giant stage of black hole progenitors. Based on this evolution, we propose a model for the evolution of GRS 1915+105, in which the spinning up the black hole by the accretion from the donor star plays an essential role to nearly reach the observed a*>0.98 (McClintock et al. 2006).
The diffuse galactic EGRET gamma ray data show a clear excess for energies
above 1 GeV in comparison with the expectations from conventional galactic
models. This excess shows all the features expected from Dark Matter WIMP
Annihilation: a)it is present and has the same spectrum in all sky directions,
not just in the galactic plane, as expected for WIMP annihilation b) it shows
an interesting substructure in the form of a doughnut shaped ring at 14 kpc
from the centre of the galaxy, where a ring of stars indicated the probable
infall of a dwarf galaxy. From the spectral shape of the excess the WIMP mass
is estimated to be between 50 and 100 GeV, while from the intensity the halo
profile is reconstructed, which is shown to explain the peculiar change of
slope in the rotation curve at about 11 kpc (due to the ring of DM at 14 kpc).
Recently it was claimed by Bergstrom et al. that the DM interpretation of the
EGRET gamma ray excess is excluded by the antiproton fluxes, since in their
propagation model with isotropic diffusion the flux of antiprotons would be far
beyond the observed flux. However, the propagation can be largely anisotropic,
because of the convection of particles perpendicular to the disc and
inhomogeneities in the local environment. It is shown that anisotropic
propagation can reduce the antiproton yield by an order of magnitude, while
still being consistent with the B/C ratio.
Therefore it is hard to use antiprotons to search for {\it light} DM
particles, which yield a similar antiproton spectrum as the background, but the
antiprotons are a perfect means to tune the many degenerate parameters in the
propagation models.
We present results from ACS and WFPC observations in the low luminosity galaxy NGC 45. We identified 28 young star cluster candidates. While the exact values of age, mass, and extinction depend somewhat on the choice of SSP models, we find no young clusters with masses higher than a few 1000 Msun for any model choice. We derive the luminosity function of young star clusters and find a slope of alpha=-1.94+-0.28. We also identified 19 old globular clusters and we estimate a specific frequency of globular clusters of S_N=1.4-1.9 which is significantly higher than observed for other late-type galaxies (e.g. SMC, LMC, M33). Most of these globular clusters appear to belong to a metal-poor population, although they coincide spatially with the location of the bulge of NGC 45.
We study the structure and reveal the physical nature of the reversed granulation pattern in the solar photosphere by means of 3-dimensional radiative hydrodynamics simulations. We used the MURaM code to obtain a realistic model of the near-surface layers of the convection zone and the photosphere. The pattern of horizontal temperature fluctuations at the base of the photosphere consists of relatively hot granular cells bounded by the cooler intergranular downflow network. With increasing height in the photosphere, the amplitude of the temperature fluctuations diminishes. At a height of z=130-140 km in the photosphere, the pattern of horizontal temperature fluctuations reverses so that granular regions become relatively cool compared to the intergranular network. Detailed analysis of the trajectories of fluid elements through the photosphere reveal that the motion of the fluid is non-adiabatic, owing to strong radiative cooling when approaching the surface of optical depth unity followed by reheating by the radiation field from below. The temperature structure of the photosphere results from the competition between expansion of rising fluid elements and radiative heating. The former acts to lower the temperature of the fluid whereas the latter acts to increase it towards the radiative equilibrium temperature with a net entropy gain. After the fluid overturns and descends towards the convection zone, radiative energy loss again decreases the entropy of the fluid. Radiative heating and cooling of fluid elements that penetrate into the photosphere and overturn do not occur in equal amounts. The imbalance in the cumulative heating and cooling of these fluid elements is responsible for the reversal of temperature fluctuations with respect to height in the photosphere.
(abridged) We present new absolute trigonometric parallaxes and relative
proper motions for nine Galactic Cepheid variable stars: l Car, zeta Gem, beta
Dor, W Sgr, X Sgr, Y Sgr, FF Aql, T Vul, and RT Aur. We obtain these results
with astrometric data from Fine Guidance Sensor 1r, a white-light
interferometer on Hubble Space Telescope. We find absolute parallaxes with an
average sigma_pi/pi = 8%. Two stars (FF Aql and W Sgr) required the inclusion
of binary astrometric perturbations, providing Cepheid mass estimates. With
these parallaxes we compute absolute magnitudes in V, I, K, and Wesenheit
W_{VI} bandpasses corrected for interstellar extinction and Lutz-Kelker-Hanson
bias. Adding our previous absolute magnitude determination for delta Cep, we
construct Period-Luminosity relations for ten Galactic Cepheids.
We compare our new Period-Luminosity relations with those adopted by several
recent investigations, including the Freedman and Sandage H_0 projects.
Adopting our Period-Luminosity relationship would tend to increase the Sandage
H_$ value, but leave the Freedman H_0 unchanged. Comparing our Galactic Cepheid
PLR with those derived from LMC Cepheids, we find the slopes for K and W_{VI}
identical in the two galaxies within their respective errors. Our data lead to
a W_{VI} distance modulus for the Large Magellanic Cloud, m-M = 18.50\pm0.03,
uncorrected for any metallicity effects. Applying recently derived metalllcity
corrections yields a corrected LMC distance modulus of (m-M)_0=18.40\pm0.05.
Comparing our Period-Luminosity relationship to solar-metallicity Cepheids in
NGC 4258 results in a distance modulus, 29.28 \pm 0.08, which agrees with that
derived from maser studies.
The presence of the dust in the circumnuclear region strongly affects our view of the nucleus itself. The effect is strong in type 2 objects but weaker effect is likely to be present in type 1 objects as well. In these objects a correction to the observed optical/UV spectrum must be done in order to recover the intrinsic spectrum of a nucleus. The approach based on the extinction curve is convenient for that purpose so significant effort has been recently done in order to determine the extinction curve for the circumnuclear material. It seems clear that the circumnuclear dust is different from the average properties of the dust in the Interstellar Medium in our galaxy: the well known 2175 A feature is weak or absent in AGN nuclear dust, and the extinction curve at shorter wavelength does not seem to be rising as steeply. The circumnuclear dust is therefore more similar to SMC dust, or more likely, to the dust in very dense molecular clouds in our Galaxy. However, the exact shape of the extinction curve in the far UV is still a matter of debate, and various effects are difficult to disentangle.
The origin of the cosmic gamma-ray background (CGB) is a longstanding mystery in high-energy astrophysics. Possible candidates include ordinary astrophysical objects such as unresolved blazars, as well as more exotic processes such as dark matter annihilation. While it would be difficult to distinguish them from the mean intensity data alone, one can use anisotropy data instead. We investigate the CGB anisotropy both from unresolved blazars and dark matter annihilation (including contributions from dark matter substructures), and find that the angular power spectra from these sources are very different. We then focus on detectability of dark matter annihilation signals using the anisotropy data, by treating the unresolved blazar component as a known background. We find that the dark matter signature should be detectable in the angular power spectrum of the CGB from two-year all-sky observations with the Gamma Ray Large Area Space Telescope (GLAST), as long as the dark matter annihilation contributes to a reasonable fraction, e.g., >~ 0.3, of the CGB at around 10 GeV. We conclude that the anisotropy measurement of the CGB with GLAST should be a powerful tool for revealing the CGB origin, and potentially for the first detection of dark matter annihilation.
Self-consistent N-body simulations have been performed in order to study the effects of a central active galactic nucleus (AGN) on the dark matter profile of a typical giant elliptical galaxy. In our analysis, we assume that periodic bipolar outbursts from a central AGN can induce harmonic oscillatory motions on both sides of the gas core. Using realistic AGN properties, we find that the motions of the gas core, driven by such feedback processes, can flatten the dark matter and/or stellar profiles after 4-5 Gyr. Such results are consistent with observational studies such as those of Kormendy et al. (2006) which suggest that most giant elliptical galaxies have cores or ``missing light'' in their inner part. Since stars behave as a ``collisionless'' fluid similar to dark matter, the density profile both of stars and dark matter should be affected in a similar way, leading to an effective reduction in the central brightness.
The OmegaCAM wide-field imager will start operations at the ESO VLT Survey Telescope at Paranal, Chile, in 2007. The photometric calibration of OmegaCAM data depends on standard star measurements that cover the complete 1 square degree FoV of OmegeaCAM. A catalog fullfilling this requirement for eight Landolt equatorial fields, denoted the OmegaCAM Secondary Standards Catalog, will be constructed from OmegaCAM observations during the first year of operations. Here we present the 'Preliminary Catalog' which will be used to bootstrap the construction of the OmegaCAM Secondary Standards Catalog. Thus the Preliminary Catalog will be used to assess the performance of OmegaCAM+VST early-on. The catalog is based on WFC data from the INT at La Palma.
This proceedings contribution summarizes first results obtained from a systematic study of 2011 NLS1 galaxies, as presented in Zhou et al. (2006, ApJS 166, 128). The sample was compiled by examining the spectral parameters of galaxies and QSOs derived from SDSS DR3 data. We discuss some preliminary results on the statistic properties of the sample, such as the fraction of NLS1, the properties of broad and narrow emission lines, and emission in other wavebands. The black hole mass--velocity dispersion relation for NLS1s was re-examined using the velocity dispersion values estimated from the stellar absorption spectra of the host galaxies. Preliminary result from an X-ray study for a small subset using data obtained by XMM-Newton is briefly discussed.
We apply instance-based machine learning to the task of estimating photometric redshifts for 55,746 objects spectroscopically classified as quasars in the Fifth Data Release of the Sloan Digital Sky Survey, and compare the results obtained to those from an empirical color-redshift relation (CZR). In contrast to previously published results using CZRs, we find that the instance-based photometric redshifts are assigned with no regions of catastrophic failure. Remaining outliers are simply scattered about the ideal relation, in a similar manner to the pattern seen in the optical for normal galaxies at redshifts z < ~1. The instance-based algorithm is trained on a representative sample of the data and pseudo-blind-tested on the remaining unseen data. The variance between the photometric and spectroscopic redshifts is sigma = 0.123 +/- 0.002 (compared to sigma = 0.265 +/- 0.006 for the CZR), and 54.9 +/- 0.7%, 73.3 +/- 0.6%, and 80.7 +/- 0.3% of the objects are within delta z < 0.1, 0.2, and 0.3 respectively. We also match our sample to the Second Data Release of the Galaxy Evolution Explorer legacy data and the resulting 7,642 objects show a further improvement, giving a variance of sigma = 0.054 +/- 0.005, and 70.8 +/- 1.2%, 85.8 +/- 1.0%, and 90.8 +/- 0.7% of objects within delta z < 0.1, 0.2, and 0.3. We show that the improvement is indeed due to the extra information provided by GALEX, by training on the same dataset using purely SDSS photometry, which has a variance of sigma = 0.090 +/- 0.007. Each set of results represents a realistic standard for application to further datasets for which the spectra are representative.
We have conducted a systematic search of AGNs with IMBHs from the SDSS DR4. As results we found 245 candidates of broad-line AGN with M_{BH}<10^6 \Msun estimated from the luminosity and width of the broad Halpha component. Compared to the pioneer Greene & Ho (2004) sample of 19 IMBH AGNs, our sample has improved in covering a larger range of the Eddington ratio, as well as black hole mass and redshift, taking the advantage of our AGN-galaxy spectral decomposition algorithm. Among these, thirty-six have L_{bol}/L_{Edd} < 0.1, hinting that a significant fraction of IMBHs might exist with weak or no nuclear activity.
The model of Dark Matter is proposed in which the Dark Matter is a classical color field. The color fields are invisible as they may interact with colored elementary particles like 't Hooft - Polyakov monopole only. The comparison with the Universal Rotation Curve is carried out.
A model of wavelength-dependent lags in optical continuum variability of AGNs is proposed which avoids the problems of the popular ``lamp-post'' model. Rather than being due to reprocessing of high-energy radiation from a hypothetical source above the accretion disk, the wavelength-dependent delays observed from the B to I bands are instead due to contamination of an intrinsically coherently variable continuum with the Wien tail of the thermal emission from the hot dust in the surrounding torus. The new model correctly gives the size, wavelength dependence, and luminosity dependence of the lags, and quantitatively predicts observed color hysteresis. The model also explains how the measured delays vary with epoch of observation. There must also be contamination by scattered light and this can be detected by a lag in the polarized flux.
We compute f-mode sensitivity kernels for flows. Using a two-dimensional model, the scattered wavefield is calculated in the first Born approximation. We test the correctness of the kernels by comparing an exact solution (constant flow), a solution linearized in the flow, and the total integral of the kernel. In practice, the linear approximation is acceptable for flows as large as about 400 m/s.
We used FUSE to observe ultraviolet emission from diffuse O VI in the hot gas in the Galactic halo. By comparing our result with another, nearby observation blocked by an opaque cloud at a distance of 230~pc, we could subtract off the contribution from the Local Bubble, leading to an apparent halo intensity of I_{OVI} = 4680^{+570}_{-660} photons/cm^2/s/sr. A correction for foreground extinction leads to an intrinsic intensity that could be as much as twice this value. Assuming T ~ 3 x 10^5 K, we conclude that the electron density, n_e, is 0.01-0.02 /cm^3, the thermal pressure, p/k, is 7000-10,000 K/cm^3, and that the hot gas is spread over a length of 50-70 pc, implying a small filling factor for O VI-rich gas. ROSAT observations of emission at 1/4 keV in the same direction indicate that the X-rays are weaker by a factor of 1.1 to 4.7, depending on the foreground extinction. Simulated supernova remnants evolving in low density gas have similar O VI to X-ray ratios when the remnant plasma is approaching collisional ioinizational equilibrium and the physical structures are approaching dynamical ``middle age''. Alternatively, the plasma can be described by a temperature power-law. Assuming that the material is approximately isobaric and the length scales according to T^(beta) d(ln T), we find beta = 1.5+/-0.6 and an upper temperature cutoff of 10^{6.6(+0.3,-0.2)} K. The radiative cooling rate for the hot gas, including that which is too hot to hold O VI, is 6 x 10^{38} erg/s/kpc^2. This rate implies that ~70% of the energy produced in the disk and halo by SN and pre-SN winds is radiated by the hot gas in the halo.
Binary stars are important for a full understanding of stellar evolution. We present a summary of how predictions of the relative supernova rates varies between single and binary stars. We also show how the parameter space of different supernova types differs between single and binary stars. We then consider an important question of how to infer a supernova progenitor's properties from pre-explosion imaging and present rescent work of producing synthe tic colours for our stellar models to make a direct comparison with any detections or limits obtained on supernova progentiors from pre-explosion images.
A method of counts-in-cells analysis of galaxy distribution is investigated with arbitrary smoothing functions in obtaining the galaxy counts. We explore the possiblity of optimizing the smoothing function, considering a series of $m$-weight Epanechnikov kernels. The popular top-hat and Gaussian smoothing functions are two special cases in this series. In this paper, we mainly consider the second moments of counts-in-cells as a first step. We analytically derive the covariance matrix among different smoothing scales of cells, taking into account possible overlaps between cells. We find that the Epanechnikov kernel of $m=1$ is better than top-hat and Gaussian smoothing functions in estimating cosmological parameters. As an example, we estimate expected parameter bounds which comes only from the analysis of second moments of galaxy distributions in a survey which is similar to the Sloan Digital Sky Survey.
The space missions MOST, COROT and Kepler are going to provide us with high-precision optical photometry of solar-like stars with time series extending from tens of days to several years. They can be modelled to obtain information on stellar magnetic activity by fitting the rotational modulation of the stellar flux produced by the brightness inhomogeneities associated with photospheric active regions. The variation of the total solar irradiance provides a good proxy for those photometric time series and can be used to test the performance of different spot modelling approaches. We test discrete spot models as well as maximum entropy and Tikhonov regularized spot models by comparing the reconstructed total sunspot area variation and longitudinal distributions of sunspot groups with those actually observed in the Sun along activity cycle 23. Appropriate statistical methods are introduced to measure model performance versus the timescale of variation. The maximum entropy regularized spot models show the best agreement with solar observations reproducing the total sunspot area variation on time scales ranging from a few months to the activity cycle, although the model amplitudes are affected by systematic errors during the minimum and the maximum activity phases. The longitudinal distributions derived from the models compare well with the observed sunspot group distributions except during the minimum of activity, when faculae dominate the rotational modulation. The resolution in longitude attainable through the spot modelling is about 60 degrees.
We present high sensitivity observations of the complex organic molecules (COMs) CH3OH, C2H5OH, HCOOCH3, HCOOH and H2CO and of SiO toward the quiescent dark cloud L183 and the molecular outflow L1448-mm. We have not detected C2H5OH, HCOOCH3 and SiO in L183 and in the quiescent gas of L1448-mm. The abundances of CH3OH, H2CO and SiO are enhanced by factors 4-20 in the shock precursor component, and those of CH3OH and SiO by 3 and 4 orders of magnitude in the shocked gas, without substantial changes (< factor of 2) in the abundances of C2H5OH and HCOOCH3 relative to that of CH3OH. The large enhancements of SiO and CH3OH can be explained by the shock ejection of an important fraction of the grain mantle material into gas phase. Our upper limits to the C2H5OH/CH3OH and HCOOCH3/CH3OH ratios are consistent with the rather constant ratios measured in hot cores and Galactic center clouds. However, the upper limits to the HCOOCH3/CH3OH and the HCOOH/CH3OH ratios are at least one order of magnitude smaller than those found in"hot corinos" surrounding low mass protostars. We speculate that the observed abundances of COMs in different objects are consistent with a sort of "universal" grain mantle composition which is locally changed by the processes of low mass star formation.
The Red MSX Source (RMS) survey is a multi-wavelength programme of follow-up observations designed to distinguish between genuine massive young stellar objects (MYSOs) and other embedded or dusty objects, such as ultra compact (UC) HII regions, evolved stars and planetary nebulae (PNe), from a sample of ~2000 MYSOs candidates. These were identified by comparing the colours of objects from the MSX and 2MASS point source catalogues to those of known MYSOs, in order to develop colour selection criteria which have been used to produced the RMS sample of MYSOs candidates. Our ultimate aim is to produce a large unbiased sample of MYSOs (~500) with complementary multi-wavelength data with which to study their properties. Here we report the results of 826 radio continuum and 346 mid-IR imaging observations carried out using the Australia Telescope Compact Array and TIMMI2 on the ESO 3.6 m telescope respectively. These observations are aimed at identifying and removing contaminating sources.
We mapped the HH212 Class 0 outflow in SiO(2--1, 5--4) and continuum using the PdBI in its extended configurations. The unprecedented angular resolution (down to 0.34") allows accurate comparison with a new, deep H2 image obtained at the VLT. The SiO emission is confined to a highly-collimated bipolar jet (width 0.35") along the outflow axis. The jet can be traced down to within 500 AU of the protostar, in a region that is heavily obscured in H2 images. Where both species are detected, SiO shows the same overall kinematics and structure as H2, indicating that both molecules are tracing the same material. We find that the high-velocity SiO gas near the protostar is not tracing a wide-angle wind but is already confined to a flow inside a narrow cone of half-opening angle < 6 deg.
We present new imaging and spectroscopic observations of six ultra-compact dwarf (UCD) galaxies in the Virgo Cluster, along with re-analysed data for five Fornax Cluster UCDs. These are the most luminous UCDs: -14<Mv<-12 mag. Our HST imaging shows that most of the UCDs have shallow or steep cusps in their cores; only one UCD has a flat ``King'' core. None of the UCDs show tidal cutoffs down to our limiting surface brightness. Spectroscopic analysis shows that Virgo UCDs are older than 8 Gyr and have metallicities in the range [Z/H]=-1.35...+0.35 dex. Five Virgo UCDs have super-solar alpha/Fe abundance ratios typical of old stellar populations found in globular clusters and elliptical galaxies. Virgo UCDs have structural and dynamical properties similar to Fornax UCDs. The Virgo and Fornax UCDs all have masses ~2-9x10^7 Msun and mass-to-light ratios ~3-5 Msun/Lsun,v. The dynamical M/L values for Virgo UCDs are consistent with SSP model predictions: Virgo UCDs do not require dark matter to explain their mass-to-light ratios. We conclude that the internal properties of Virgo UCDs are consistent with them being the high-mass/high-luminosity extreme of known globular cluster populations. We refrain from any firm conclusions on Fornax UCD origins until accurate age, metallicity and alpha-abundance estimates are obtained for them. Some of our results, notably the fundamental plane projections are consistent with the formation of UCDs by the simple removal of the halo from the nuclei of nucleated dwarf galaxies. However the ages, metallicities and abundances for Virgo UCDs are not consistent with this simple stripping model. It might be consistent with more sophisticated models of the stripping process that include the effects of gas removal on the chemical evolution of the nuclei.
Aims. We determine masses and mass-to-light ratios of five ultra-compact dwarf galaxies and one dwarf elliptical nucleus in the Fornax cluster from high resolution spectroscopy. Methods. Velocity dispersions were derived from selected wavelength regions using a direct-fitting method. To estimate the masses of the UCDs a new modelling program has been developed that allows a choice of different representations of the surface brightness profile (i.e. Nuker, Sersic or King laws) and corrects the observed velocity dispersions for observational parameters (i.e. seeing, slit size). Results. The observed velocity dispersions range between 22 and 30 km/s. The resulting masses are between 1.8 and 9.5x10^7M_sun. These, as well as the central and global projected velocity dispersions, were derived from the generalized King model which turned out to give the most stable results. The masses of two UCDs, that are best fitted by a two-component profile, were derived from a combined King+Sersic model. The mass-to-light ratios of the Fornax UCDs range between 3 and 5 (M/L_V)_sun. Within 1-2 half-mass radii dark matter is not dominating UCDs. Conclusions. We show that the mass-to-light ratios of UCDs in Fornax are consistent with those expected for pure stellar populations. Thus UCDs seem to be the result of cluster formation processes within galaxies rather than being compact dark matter dominated substructures themselves. Whether UCDs gained their mass in super-star cluster complexes of mergers or in nuclear star cluster formation processes remains an open question. It appears, however, clear that star clusters more massive than about 5\times10^6M_sun exhibit a more complex formation history than the less massive `ordinary' globular clusters.
(abridged) The radio-quiet quasar PG1416-129 (z=0.129) exhibits atypical optical and X-ray properties. Between 1990 and 2000, in response to its optical continuum decrease, the ``classical'' broad component of Hbeta almost completely disappeared, with a factor of 10 decrease in the line flux. In the X-ray band, this object was observed by Ginga in 1988 to have the hardest quasar photon index, with Gamma=1.1+/-0.1. We present an XMM/EPIC observation of PG1416-129 performed in July 2004. We analyze the time-averaged pn spectrum of this quasar, as well as perform time-resolved spectroscopy. We find that during the present XMM observation, PG1416-129 still has a rather hard photon index, both in the soft and hard energy ranges, compared to radio-quiet quasars but compatible with the photon index value found for radio-loud quasars. This object also shows long-term luminosity variability over 16 years by a factor of three with a variation of photon index from ~1.2 to ~1.8. In the soft energy band (0.2-2keV), we found a very weak soft X-ray excess compared to other RQ quasars. The whole time averaged spectrum is fit very well either by X-ray ionized reflection from the accretion disk surface, by a warm absorber-emitter plus power-law, or by a smeared absorption/emission from a relativistic outflow. While no constant narrow FeK line at 6.4keV is observed, we find the possible presence of two non-simultaneous transient iron lines: a redshifted narrow iron line at about 5.5keV (96.4% confidence level according to multi-trial Monte-Carlo simulations) at the beginning of this observation and the appearance of a line at 6.3-6.4keV (99.1% c.l.) at the end of the observation. These variable lines could be generated by discrete hot-spots on the accretion disk surface.
We studied the behaviour of the optical afterglow lightcurves of a sample of 24 Gamma--Ray Bursts (GRBs) with known redshift and published estimates of the optical extinction in the source frame, detected before the SWIFT satellite launch. We found an unexpected clustering of the optical luminosities at 12 hours in the source frame. The distribution of the optical luminosities is narrower than the distribution of X-ray luminosities at the same time. Few (3) bursts stand apart from the main optical distribution, being fainter by a factor of about 15. We also analysed the optical luminosities of the SWIFT burst with known redshift finding that the luminosity distribution is similar to the pre SWIFT GRBs one, even if they have a different mean redshift. These results can suggest the existence of a family of intrinsically optically under--luminous dark GRBs.
We explore a possibility for the Universe to cross the cosmological constant barrier for the dark energy state parameter w=-1. Exact spatially homogeneous solutions to the Friedmann equations with one phantom scalar field and one usual scalar field are considered. We construct a cosmological model with the string theory inspired polynomial potential and find a two-parameter set of exact solutions. Some of these solutions correspond to w>-1 at late time, whereas others correspond to w<-1. We demonstrate that the superpotential method is very useful to seek new exact solutions in the explicit form and in quadratures. We also present a two-fields model with a polynomial potential and w crossing the cosmological barrier infinitely often.
We review the main properties of "warm mirrors" in obscured AGN, and discuss whether the scattering gas could be also responsible for "warm absorbers" commonly observed in unobscured AGN.
Using nonlinear hydrocodes we have calculated single mode saturation amplitudes for beta Cephei models. Predicted saturation amplitudes are systematically higher than amplitudes observed in beta Cephei variables, even in monoperiodic ones. We argue that collective saturation of the pulsation instability by a dozen or so acoustic modes brings the theoretical amplitudes to the observed level.
Multi-frequency 1.7, 5 and 8.4-GHz VLBA observations of a radio-loud broad absorption line (BAL) quasar 1045+352 are presented. It is a young compact steep spectrum (CSS) object and its asymmetric, two-sided morphology on a scale of several hundred parsecs, extending in two different directions, may suggest intermittent activity. The young age and unusual morphology of 1045+352 are arguments in favour of an evolution scenario for BAL quasars, in which the BAL features appear at a very early stage of their evolution.
We report on the first XMM-Newton observation of the bright Narrow-Line Seyfert 1 galaxy Mrk 110. We find a narrow Fe K fluorescent line, a broad component FWHM ~ 16500 km/s of the OVII triplet, either due to infall motions or gravitational redshift effects in the vicinity of the central black hole, a Comptonized accretion disc layer, and a strong starburst component. If the broad redshifted soft X-ray components are due to gravitational redshift effects, the distance of the line emitting regions ranges between about 0.2 and 1 light day with respect to the central black hole.
We investigate the newtonian stationary accretion of a polytropic perfect fluid onto a central body with a hard surface. The selfgravitation of the fluid and its interaction with luminosity is included in the model. We find that for a given luminosity, asymptotic mass and temperature of the fluid there exist two solutions with different cores.
Recent fully relativistic calculations of radiative rates and electron impact excitation cross sections for Fe {\sc xiii} are used to generate emission-line ratios involving 3s$^{2}$3p$^{2}$--3s3p$^{3}$ and 3s$^{2}$3p$^{2}$--3s$^{2}$3p3d transitions in the 170--225 \AA and 235--450 \AA wavelength ranges covered by the Solar Extreme-Ultraviolet Research Telescope and Spectrograph (SERTS). A comparison of these line ratios with SERTS active region observations from rocket flights in 1989 and 1995 reveals generally very good agreement between theory and experiment. Several new Fe {\sc xiii} emission features are identified, at wavelengths of 203.79, 259.94, 288.56 and 290.81 \AA. However, major discrepancies between theory and observation remain for several Fe {\sc xiii} transitions, as previously found by Landi (2002) and others, which cannot be explained by blending. Errors in the adopted atomic data appear to be the most likely explanation, in particular for transitions which have 3s$^{2}$3p3d $^{1}$D$_{2}$ as their upper level. The most useful Fe {\sc xiii} electron density diagnostics in the SERTS spectral regions are assessed, in terms of the line pairs involved being (i) apparently free of atomic physics problems and blends, (ii) close in wavelength to reduce the effects of possible errors in the instrumental intensity calibration, and (iii) very sensitive to changes in N$_{e}$ over the range 10$^{8}$--10$^{11}$ cm$^{-3}$. It is concluded that the ratios which best satisfy these conditions are 200.03/202.04 and 203.17/202.04 for the 170--225 \AA wavelength region, and 348.18/320.80, 348.18/368.16, 359.64/348.18 and 359.83/368.16 for 235--450 \AA.
We present observations of GRB 060124, the first event for which both the prompt and the afterglow emission could be observed simultaneously and in their entirety by the three Swift instruments and by Konus-Wind. Thanks to these exceptional circumstances, the temporal and spectral properties of the prompt emission could be studied in the optical, X-ray and gamma-ray ranges (up to 2 MeV). While the X-ray emission (0.2-10 keV) clearly tracks the gamma-ray burst, the optical component follows a different pattern, likely indicating a different origin, possibly the onset of external shocks. The prompt GRB spectrum shows significant spectral evolution, with both the peak energy and the spectral index varying. As observed in several long GRBs, significant lags are measured between the hard- and low-energy components, showing that this behaviour extends over 3 decades in energy. The GRB peaks are also much broader at soft energies. This is related to the temporal evolution of the spectrum, and can be accounted for by the softening of the electron spectral index with time. The burst energy (E_iso~5x10^{53} erg at z=2.297) and average peak energy (E_p~300 keV) make GRB 060124 consistent with the Amati relation. The X-ray afterglow is characterized by a decay which presents a break at t_b~10^5s.
The shell-type supernova remnant RX J0852.0-4622 was observed with the High Energy Stereoscopic System (H.E.S.S.) of Atmospheric Cherenkov Telescopes between December 2004 and May 2005 for a total observation time of 33 hours, above an average gamma-ray energy threshold of 250 GeV. The angular resolution of ~0.06 degree (for events triggering 3 or 4 telescopes) and the large field of view of H.E.S.S. ($5^{\circ}$ diameter) are well adapted to studying the morphology of the object in very high energy gamma-rays, which exhibits a remarkably thin shell very similar to the features observed in the radio range and in X-rays. The spectral analysis of the source from 300 GeV to 20 TeV is also presented. Finally, the possible origins of the very high energy gamma-ray emission (Inverse Compton scattering by electrons or the decay of neutral pions produced by proton interactions) are discussed, on the basis of morphological and spectral features obtained at different wavelengths.
The very high spatial resolution provided by Adaptive Optics assisted spectroscopic observations at 8m-class telescopes (e.g. with SINFONI at the VLT) will allow to greatly increase the number of direct black hole (BH) mass measurements which is currently very small. This is a fundamental step to investigate the tight link between galaxy evolution and BH growth, revealed by the existing scaling relations between $M_{BH}$ and galaxy structural parameters. I present preliminary results from SINFONI K-band spectroscopic observations of a sample of 5 objects with $M_{BH}$ measurements obtained with the Reverberation Mapping (RM) technique. This technique is the starting point to derive the so-called virial $M_{BH}$ estimates, currently the only way to measure $M_{BH}$ at high redshift. Our goal is to assess the reliability of RM by measuring $M_{BH}$ with both gas and stellar kinematical methods and to investigate whether active galaxies follow the same $M_{BH}$-galaxy correlations as normal ones.
Deep X-ray surveys provide the most efficient identification of Active Galactic Nuclei (AGN) activity. However, recent evidence has indicated that the current <10 keV surveys do not detect the most heavily obscured AGNs. Here we explore whether the X-ray undetected AGN population can be identified within the ultra-deep Spitzer survey of the GOODS-N field using X-ray stacking techniques. We find evidence for AGN activity in the Spitzer dataset and the strongest and hardest X-ray signal is produced by galaxies with starburst-like infrared spectral slopes and median properties of z~0.8 and L_IR~10^{11} L_solar. The stacked X-ray properties suggest that obscured AGN activity is present in these sources, with a median X-ray spectral slope of Gamma~1 and L_X~10^{42} erg/s. These overall properties are consistent with the obscured AGN population expected to produce the unresolved X-ray background.
We present a speckle analysis of the active galactic nucleus (AGN) inside the archetype Seyfert type 2 galaxy NGC 1068. This study is based on 12.8 microns images obtained with the burst mode of VISIR (the Very Large Telescope Imager and Spectrometer in the InfraRed). The interferometric processing allows to push the resolution far below the diffraction limit of a 8m telescope in the N-band and to trace two main contributions to the mid-IR flux inside the nucleus. It also allows to partially fill the lack of visibility points at low spatial frequencies. The confrontation with VLT/MIDI (the Mid-InfrareD Interferometer) data points helps to establish the link between dust in the vicinity of the central engine and inside the ionisation cone to get a multi-scale picture of mid-IR sources emitting in the nucleus of NGC 1068.
Deep SCUBA surveys have uncovered a population of dust-enshrouded star-forming galaxies at z~2. Using the ultra-deep 2 Ms Chandra Deep Field-North survey we recently showed that a large fraction of these systems are also undergoing intense black-hole growth. Here we provide further constraints on the properties of the black holes in SCUBA galaxies using the virial black-hole mass estimator. We show that typical SCUBA galaxies are likely to host black holes with M_BH~10^7-10^8 M_solar which are accreting at, or close to, the Eddington limit. These results provide qualitative support for our earlier conclusion that the growth of the black hole lags that of the host galaxy in these massive ultraluminous galaxies.
XMM-Newton observations of the O supergiant zeta Orionis (O9.7 Ib) extend knowledge of its high-resolution spectrum beyond the CVI line at 33.7 Angstroms and suggest a new framework for the interpretation of the X-ray spectra of single hot stars. All the lines are broad and asymmetric with similar velocity profiles. X-rays probably originate in the wind's terminal velocity regime in collisionless shocks controlled by magnetic fields rather than in cooling shocks in the acceleration zone. During post-shock relaxation, exchange of energy between ions and electrons is so slow that electron heating does not take place before hot gas is quenched by the majority cool gas. The observed plasma is not in equilibrium and the electron bremsstrahlung continuum is weak. Charge exchange, ionization and excitation are likely to be produced by protons. Fully thermalized post-shock velocities ensure high cross-sections and account for the observed line widths, with some allowance probably necessary for non-thermal particle acceleration. In general, the form of X-ray spectra in both single and binary stars is likely to be determined principally by the amount of post-shock electron heating: magnetically confined X-ray plasma in binary systems can evolve further towards the higher electron temperatures of equilibrium while in single stars this does not take place. The long mean-free path for Coulomb energy exchange between fast-moving ions may also inhibit the development of line-driven instabilities.
Thanks to the high counting statistics provided by a recent XMM-Newton observation of RX J1856.5-3754, we have discovered that this isolated neutron star pulsates at a period of 7.055 s. This confirms that RX J1856.5-3754 is similar in nature to the the other six thermally emitting, nearby neutron stars discovered in soft X-rays with ROSAT. The pulsations are detected at consistent periods in several XMM-Newton observations spanning from April 2002 to October 2006, yielding an upper limit of Pdot<1.9x10e-12 s/s (90% c.l.) on the period derivative. This implies a surface magnetic field smaller than 1.2x10^14 G, under the usual assumption of vacuum dipole magnetic braking. The pulse profile is nearly sinusoidal with a pulsed fraction of only ~1.5%, the smallest ever seen in an isolated X-ray pulsar.
High resolution data in the region of the line Halpha have been obtained at the time of the light maximum and after it of the 2006 optical outburst of the symbiotic binary Z And. A blue-shifted absorption component indicating outflow velocity of about 1400 km/s as well as additional emission components with similar velocities, situated on the two sides of the main peak of the line were observed during that time. It is suggested that all of them are spectral signature of bipolar outflow, observed for the first time in the optical spectrum of this binary. The emission measure and the mass of the nebular part of the streams were estimated approximately.
We study the structure of protoneutron stars within the finite temperature Brueckner-Bethe-Goldstone many-body theory. If nucleons, hyperons, and leptons are present in the stellar core, we find that neutrino trapping stiffens considerably the equation of state, because hyperon onsets are shifted to larger baryon density. However, the value of the critical mass turns out to be smaller than the ``canonical'' value 1.44 $M_\odot$. We find that the inclusion of a hadron-quark phase transition increases the critical mass and stabilizes it at about 1.5--1.6 $M_\odot$.
The prompt optical emission of GRB 990123 was uncorrelated to the gamma-ray light-curve and exhibited temporal properties similar to those of the steeply-decaying, early X-ray emission observed by Swift at the end of many bursts. These facts suggest that the optical counterpart of GRB 990123 was the large-angle emission released during (the second pulse of) the burst. If the optical and gamma-ray emissions of GRB 990123 have, indeed, the same origin then their properties require that (i) the optical counterpart was synchrotron emission and the gamma-rays arose from inverse-Compton scatterings ("synchrotron self-Compton model"), (ii) the peak-energy of the optical-synchrotron component was at ~20 eV, and (iii) the burst emission was produced by a relativistic outflow moving at Lorentz factor > 450 and at a radius > 10^{15} cm, which is comparable to the outflow deceleration radius. Because the spectrum of GRB 990123 was optically thin above 2 keV, the magnetic field behind the shock must have decayed on a length-scale of <1% of the thickness of the shocked gas, which corresponds to 10^6-10^7 plasma skin-depths. Consistency of the optical counterpart decay rate and its spectral slope (or that of the burst, if they represent different spectral components) with the expectations for the large-angle burst emission represents the most direct test of the unifying picture proposed here for GRB 990123.
The dynamics of two massive black holes in a rotationally supported nuclear disc of 10^8 solar masses is explored using N-Body/SPH simulations. Gas and star particles are co-present in the disc. Described with a Mestel profile, the disc has a vertical support provided by turbulence of the gas, and by stellar velocity dispersion. A 4 million solar masses primary black hole is placed at the centre of the disc, while a secondary black hole is set initially on an eccentric co-rotating orbit in the disc plane. Its mass is in a 1 to 1, 1 to 4, and to 10 ratio, relative to the primary. With this choice, we mimic the dynamics of black hole pairs released in the nuclear region at the end of a gas-rich galaxy merger. It is found that, under the action of dynamical friction, the two black holes form a close binary in ~10 Myrs. The inspiral process is insensitive to the mass fraction in stars and gas present in the disc and is accompanied by the circularization of the orbit. We have revealed the occurrence of radial inflows around each individual black hole that can create small gaseous Keplerian disc weighing ~2 % of the black hole mass, and of size ~0.01 pc. The mass of the tightly (loosely) bound particles increases (decreases) with time as the black holes spiral into closer and closer orbits. Double AGN activity is expected to occur on an estimated timescale of ~10 Myrs, comparable to the inspiral timescale. The double nuclear point-like sources that may appear during dynamical evolution have typical separations of ~10 pc.
We report the observations of the clear sky fraction at the Concordia station during winter 2006, and derive from it the duty cycle for astronomical observations. Performance in duty cycle and observation duration promotes Dome C for efficient asteroseismic observations. This performance is analyzed and compared to network observation. For network observations, simulations were run considering the helioseismic network GONG as a reference. Observations with 1 site in Antarctica provide performance similar or better than with a 6-site network, since the duty cycle limited by meteorology is as high as 92%. On bright targets, a 100-day long time series with a duty cycle about 87% can be observed, what network observation cannot.
Carbon-oxygen white dwarfs contain neon-22 formed from alpha-captures onto nitrogen during core He burning in the progenitor star. In a white dwarf (type Ia) supernova, the neon-22 abundance determines, in part, the neutron-to-proton ratio and hence the abundance of radioactive nickel-56 that powers the lightcurve. The neon-22 abundance also changes the burning rate and hence the laminar flame speed. We tabulate the flame speedup for different initial carbon and neon-22 abundances and for a range of densities. This increase in the laminar flame speed--about 30% for a neon-22 mass fraction of 6%--affects the deflagration just after ignition near the center of the white dwarf, where the laminar speed of the flame dominates over the buoyant rise, and in regions of lower density ~ 10^7 g/cm3 where a transition to distributed burning is conjectured to occur. The increase in flame speed will decrease the density of any transition to distributed burning.
We investigate the existence and properties of equipotential surfaces and Lagrangian points in non-synchronous, eccentric binary star and planetary systems under the assumption of quasi-static equilibrium. We adopt a binary potential that accounts for non-synchronous rotation and eccentric orbits, and calculate the positions of the Lagrangian points as functions of the mass ratio, the degree of asynchronism, the orbital eccentricity, and the position of the stars or planets in their relative orbit. We find that the geometry of the equipotential surfaces may facilitate non-conservative mass transfer in non-synchronous, eccentric binary star and planetary systems, especially if the component stars or planets are rotating super-synchronously at the periastron of their relative orbit. We also calculate the volume-equivalent radius of the Roche lobe as a function of the four parameters mentioned above. Contrary to common practice, we find that replacing the radius of a circular orbit in the fitting formula of Eggleton (1983) with the instantaneous distance between the components of eccentric binary or planetary systems does not always lead to a good approximation to the volume-equivalent radius of the Roche-lobe. We therefore provide a generalized semi-analytical fitting formula for the volume-equivalent Roche lobe radius appropriate for non-synchronous, eccentric binary star and planetary systems.
A sample of 196 AGNs and ULIRGs observed by the Infrared Spectrograph (IRS) on Spitzer is analyzed to study the distribution of the strength of the 9.7 micron silicate feature. Average spectra are derived for quasars, Seyfert 1 and Seyfert 2 AGNs, and ULIRGs. We find that quasars are characterized by silicate features in emission and Seyfert 1s equally by emission or weak absorption. Seyfert 2s are dominated by weak silicate absorption, and ULIRGs are characterized by strong silicate absorption (mean apparent optical depth about 1.5). Luminosity distributions show that luminosities at rest frame 5.5 micron are similar for the most luminous quasars and ULIRGs and are almost 10^5 times more luminous than the least luminous AGN in the sample. The distributions of spectral characteristics and luminosities are compared to those of optically faint infrared sources at z~2 being discovered by the IRS, which are also characterized by strong silicate absorption. It is found that local ULIRGs are a similar population, although they have lower luminosities and somewhat stronger absorption compared to the high redshift sources.
The surface brightness fluctuations (SBF) method is a statistical method applied on image pixels in different bands. This contribution aims to distinguish between the observational (statistical) method and the theoretical (probabilistic) method based on stellar population synthesis and needed for the calibration of observational SBF. We find that the commonly used SBF theoretical definition as the "mean luminosity-weighted luminosity of the stellar population" is only compatible with the observational method under quite strong hypotheses, and that it is not compatible with stellar population theory results.
We examine the stellar populations of a sample of 98 redshift 4.5 Lyman alpha emitting galaxies using their broadband colors derived from deep photometry at the MMT. These galaxies were selected by narrowband excess from the Large Area Lyman Alpha survey. Twenty-two galaxies are detected in two or more of our MMT filters (g', r', i' and z'). By comparing broad and narrowband colors of these galaxies to synthetic colors from stellar population models, we determine their ages and stellar masses. The highest equivalent width objects have an average age of 4 Myr, consistent with ongoing star formation. The lowest EW objects show an age of 40 - 200 Myr, consistent with the expectation that larger numbers of stars are causing low EWs. We found masses ranging from 2e7 solar masses for the youngest objects in the sample to 2e9 solar masses for the oldest. It is possible that dust effects could produce large equivalent widths even in older populations by allowing the Lyman alpha photons to escape, even while the continuum is extinguished, and we present models for this scenario also.
We present an algorithm to identify the types of supernova spectra, and determine their redshift and phase. This algorithm, based on the correlation techniques of Tonry & Davis, is implemented in the SuperNova IDentification code (SNID). It is used by members of the ESSENCE project to determine whether a noisy spectrum of a high-redshift supernova is indeed of type Ia, as opposed to, e.g., type Ib/c. Furthermore, by comparing the correlation redshifts obtained using SNID with those determined from narrow lines in the supernova host galaxy spectrum, we show that accurate redshifts (with a typical error < 0.01) can be determined for SNe Ia for which a spectrum of the host galaxy is unavailable. Last, the phase of an input spectrum is determined with a typical accuracy of ~3 days.
High redshift galaxies selected on the basis of their strong Lyman-alpha emission tend to be young in age and small in mass and size. We show this by analyzing spectral Energy distribution of nine Lyman-alpha emitting (LAE) galaxies at redshifts from 4.1 to 5.7 in the Hubble Ultra Deep Field (HUDF). Restframe UV to optical (700 to 7500 Angstrom) luminosities (or upper limits) are used to constrain old stellar populations. We derive best fit, as well as maximally massive and maximally old, properties of all nine objects. We show that these objects are all very young, being most likely only a few millions years old, and not massive, the mass in stars being 1e6 to 1e8 solar masses. Deep Spitzer Infrared Array Camera (IRAC) observations of these objects, even in cases where objects were not detected, were crucial in constraining the masses of these objects. The space density of these objects, about 1.25e-4 per comoving cubic Mpc, is comparable to previously reported space density of LAEs at moderate to high redshifts. The Lyman-alpha galaxies show modest star formation rates of about 8 Msun/year, which is nevertheless strong enough to have allowed these galaxies to assemble their stellar mass in less than a few million years. These sources appear to have small physical sizes, usually smaller than 1 kpc, and are also rather concentrated. They are likely to be some of the least massive and youngest high redshift galaxies observed to date.
A new generation of upcoming space-based experiments will soon start to probe the spectrum of cosmic ray antiparticles with an unprecedented accuracy and, in particular, will open up a window to energies much higher than those accessible so far. It is thus timely to carefully investigate the expected antiparticle fluxes at high energies. Here, we perform such an analysis for the case of antiprotons. We consider both standard sources as the collision of other cosmic rays with interstellar matter, as well as exotic contributions from dark matter annihilations in the galactic halo. Up to energies well above 100 GeV, we find that the background flux in antiprotons is almost uniquely determined by the existing low-energy data on various cosmic ray species; for even higher energies, however, the uncertainties in the parameters of the underlying propagation model eventually become significant. We also show that if the dark matter is composed of particles with masses at the TeV scale, which is naturally expected in extra-dimensional models as well as in certain parameter regions of supersymmetric models, the annihilation flux can become comparable to -- or even dominate -- the antiproton background at the high energies considered here.
We present the results of a VLA search for HI emission in the circumstellar envelopes of five nearby AGB stars: RS Cnc, IRC+10216, EP Aqr, R Cas, and R Aqr. We have detected emission coincident in both position and velocity with RS Cnc, implying that the emission arises from its extended envelope. For R Cas, we detected weak emission that peaks at the stellar systemic velocity and overlaps with the location of its circumstellar dust shell and thus is probably related to the star. Toward IRC+10216 and EP Aqr, we detected multiple, arcminute-scale HI emission features at velocities consistent with the circumstellar envelopes, but spatially offset from the stellar positions; in these cases we cannot determine unambiguously if the emission is associated with the stars. In the case of IRC+10216, we were unable to confirm the detection of HI in absorption against the cosmic background previously reported by Le Bertre & Gerard. We detected our fifth target, R Aqr (a symbiotic binary), in the 1.4 GHz continuum.
Many Swift GRBs show an early phase of shallow decay in their X-ray afterglows, lasting from $t \sim 10^{2.5} $s to $\sim 10^4 $s after the GRB, where the flux decays as $\sim t^{-0.2}-t^{-0.8}$. This is perhaps the most mysterious of the new features discovered by Swift in the early X-ray afterglow, since it is still not clear what causes it. I discuss different possible explanations for this surprising new discovery, as well as their potential implications for the gamma-ray efficiency, the afterglow kinetic energy, and perhaps even for the physics of collisionless relativistic shocks.
Galaxies with stellar bulges are generically observed to host supermassive black holes (SMBHs). The hierarchical merging of galaxies should therefore lead to the formation of SMBH binaries. Merging of old massive galaxies with little gas promotes the formation of low-density nuclei where SMBH binaries are expected to survive over long times. If the binary lifetime exceeds the typical time between mergers, then triple-black-hole systems may form. Such systems can lead to the ejection of one of the black holes (BHs) at a speed exceeding 1000 km/s, far greater than attainable through gravitational radiation recoil. We study the statistics of close triple-SMBH encounters in galactic nuclei by computing a series of three-body orbits with physically-motivated initial conditions appropriate for giant elliptical galaxies. Our simulations include a smooth background potential consisting of a stellar bulge plus a dark matter halo, drag forces due to gravitational radiation and dynamical friction on the stars and dark matter, and a simple model of the time evolution of the inner density profile under heating and mass ejection by the SMBHs. We find that the binary pair coalesces as a result of repeated close encounters in ~85% of our runs. In about 40% of the runs the lightest BH is left wandering through the galactic halo or escapes the galaxy altogether, but escape of all three SMBHs is exceedingly rare. The triple systems typically scour out cores with mass deficits ~1-2 times their total mass, which can help to account for the large cores observed in some massive elliptical galaxies, such as M87. The high coalescence rate, prevalence of very high-eccentricity orbits, and gravitational radiation ``spikes'' during close encounters may provide interesting signals for the future Laser Interferometer Space Antenna (LISA).
Deep radio observations of a wide region centred on the Hubble Deep Field South have been performed, providing one of the most sensitive set of radio observations acquired on the Australia Telescope Compact Array to date. A central rms of ~10 microJy is reached at four frequencies (1.4, 2.5, 5.2 and 8.7 GHz). In this paper the full source catalogues from the 2.5, 5.2 and 8.7 GHz observations are presented to complement Paper II, along with a detailed analysis of image quality and noise. We produce a consolidated catalogue by matching sources across all four frequencies of our survey. Radio spectral indices are used to investigate the nature of the radio sources and identify a number of sources with flat or inverted radio spectra, which indicates AGN activity. We also find several other interesting sources, including a broadline emitting radio galaxy, a giant radio galaxy and three Gigahertz Peaked Spectrum sources.
We present the polarization images in the $J$, $H$, & $Ks$ bands of the Orion Molecular Cloud 1 South region. The polarization images clearly show at least six infrared reflection nebulae (IRNe) which are barely seen or invisible in the intensity images. Our polarization vector images also identify the illuminating sources of the nebulae: IRN 1 & 2, IRN 3, 4, & 5, and IRN 6 are illuminated by three IR sources, Source 144-351, Source 145-356, and Source 136-355, respectively. Moreover, our polarization images suggest the candidate driving sources of the optical Herbig-Haro objects for the first time; HH529, a pair of HH202 and HH528 or HH 203/204, HH 530 and HH269 are originated from Source 144-351, Source 145-356, and Source 136-355, respectively.
We present 70 micron properties of submillimeter galaxies (SMGs) in the Great Observatories Origins Deep Survey (GOODS) North field. Out of thirty submillimeter galaxies (S_850 > 2 mJy) in the central GOODS-N region, we find two with secure 70 micron detections. These are the first 70 micron detections of SMGs. One of the matched SMGs is at z ~ 0.5 and has S_70/S_850 and S_70/S_24 ratios consistent with a cool galaxy. The second SMG (z = 1.2) has infrared-submm colors which indicate it is more actively forming stars. We examine the average 70 micron properties of the SMGs by performing a stacking analysis, which also allows us to estimate that S_850 > 2 mJy SMGs contribute 9 +- 3% of the 70 micron background light. The S_850/S_70 colors of the SMG population as a whole is best fit by cool galaxies, and because of the redshifting effects these constraints are mainly on the lower z sub-sample. We fit Spectral Energy Distributions (SEDs) to the far-infrared data points of the two detected SMGs and the average low redshift SMG (z_{median}= 1.4). We find that the average low-z SMG has a cooler dust temperature than local ultraluminous infrared galaxies (ULIRGs) of similar luminosity and an SED which is best fit by scaled up versions of normal spiral galaxies. The average low-z SMG is found to have a typical dust temperature T = 21 -- 33 K and infrared luminosity L_{8-1000 micron} = 8.0 \times 10^11 L_sun. We estimate the AGN contribution to the total infrared luminosity of low-z SMGs is less than 23%.
We present a statistical study of several fundamental properties of radio sources in nearby clusters, including the radial distribution within clusters, the radio luminosity function (RLF), and the fraction of galaxies that is radio-active (radio active fraction, RAF). The analysis is carried out for a sample of 573 clusters detected in the X-ray and also observed at 1.4 GHz in the NVSS. K-band data from the 2MASS are used to identify the brightest cluster galaxies (BCGs), and to construct the K-band LF. Our main results include: (1) The surface density profile of radio-loud AGNs is much more concentrated than that of all galaxies, and can be described by the NFW profile with concentration~25. (2) A comparison of the RLFs in the clusters and in the field shows that the cluster AGN number density is about 5,700 times higher, corresponding to a factor of 6.8 higher probability of a galaxy being radio active in the cluster than in the field. We suggest that about 40-50% of radio-loud AGNs in clusters may reside in low mass galaxies (M_K>-23). (3) The RAFs of cluster galaxies of different stellar mass are estimated. About 5% of galaxies more luminous than the characteristic luminosity (M_K<M_*~-24) host radio-loud AGNs. The RAF for BCGs is >30%, and depends on the cluster mass. Compare to the field population, cluster galaxies have 5-10 times higher RAF. Combining the AGN RLF and spatial distribution within clusters, we estimate that they may inject an energy of ~0.13 keV per particle to the intracluster medium near the cluster center. We also investigate the degree of contamination by cluster radio sources on the yields of SZE cluster surveys, and estimate that as many as 10% of clusters detected at 150 GHz may host AGNs whose flux is comparable to the cluster SZE signal. (abridged)
We present high spatial resolution (0$\farcs$3) polarimetric images in the $H$ and $K$ bands and direct images in the $L'$ and $M'$ bands of the NGC 6334 V infrared nebulae. The images show complex structures including the multi-shells and various knots in the nebulae. The appearances and colors of the eastern and western nebulae differ considerably. Our polarization images also show differences between the illuminating sources of the nebulae: the eastern nebula is illuminated by a deeply embedded mid-infrared source, KDJ 4, and the western nebula by our newly detected near-infrared source, WN-A1. The degree of polarization of the nebulae is very large, up to 70% at $K$ and 60% at $H$, which is consistent with a single scattering of near-infrared radiation from each source at the walls of the mass outflows.
We collected a sample of 661 confirmed and 361 possible BL Lac candidates from the recent catalog of BL Lac objects (Veron-Cetty & Veron 2006). We searched these sources in the recent data release DR5 of the Sloan Digital Sky Survey (SDSS) and found spectra were available for 169 and 109 confirmed and possible BL Lac candidates respectively. We found 32 candidates from confirmed and 19 candidates from possible BL Lac lists have non featureless spectra and are thus possibly not BL Lac candidates. We report here the preliminary results from our analysis of a sample of 278 BL Lac objects.
We consider compressive viscosity and thermal conductivity to study the propagation and dissipation of long period slow longitudinal MHD waves in polar coronal holes. We discuss their likely role in the line profile narrowing, and in the energy budget for coronal holes and the solar wind. We compare the contribution of longitudinal MHD waves with high frequency Alfven waves.
The X-ray flares of NGC 5905, RX J1242.6-1119A, and RX J1624.9+7554 observed by Chandra in 2001 and 2002 have been suggested as the candidate tidal disruption events. The distinct features observed from these events may be used to determine the type of a star tidally disrupted by a massive black hole. We investigate these three events, focusing on the differences for the tidal disruption of a giant star and a main sequence, resulted from their different relation between the mass and the radius. We argue that their X-ray flare properties could be modeled by the partial stripping of the outer layers of a solar type star. The tidal disruption of a giant star is excluded completely. This result may be useful for understanding the growth of a supermassive black hole by capturing stars, versus the growth mode through continuous mass accretion.
We investigate the accretion flows onto the supermassive binary black holes (SMBBHs) from the circumbinary disk with the equal mass, eccentric binary on the subparsec scale, using Smoothed Particle Hydrodynamics (SPH) code. We find that the material can be supplied from circumbinary disk, which leads to the formation of two accretion disks around the SMBBHs. The mass accretion rates significantly modulate with the binary orbital motion. These could provide the observable diagnosis of the existence of the supermassive binary black holes (e.g. OJ287) on the subparsec scale in merged galactic nuclei.
We discuss some topical issues related to the Fe K emission lines in AGNs. We show remarkable agreement between non-contemporaneous ASCA and Chandra grating data and explain why there has been terrible confusion about the ASCA and post-ASCA results on the relativistic Fe K lines. We point out that in fact the number of sources (not the percentage) that have been reported to exhibit relativistic Fe K lines is now larger than it was in the ASCA era. Thus, the case for Constellation-X as a probe of strong gravity is even more compelling than it was a decade ago. One of the primary goals of these studies is to establish the foundation for future missions to map the spacetime metric around black holes. A prerequisite first step is to measure the black hole angular momentum in a robust manner that does not rely on assumptions about the accreting system. In addition, probing the Fe K lines out to high redshifts will pave the way for studying the accretion history and evolution of supermassive black holes. However, we point out some issues that need to be resolved, pertaining to the spin measurement and to the relativistic Fe K line emission found from AGN in deep surveys.
We present the basic features and the activities of Japanese VLBI network (JVN), a newly-established VLBI network with baselines ranging from 50 to 2560 km spreading across the Japanese islands, and capable of observing at 6.7, 8.4, and 22 GHz. We show a number of results of JVN observations: 8.4-GHz continuum images of a Giga-hertz Peaked Spectrum (GPS) source and radio-loud Narrow-Line Seyfert 1 galaxies (NLS1s), the spatial and velocity structures of water masers in NML Cygni as well as methanol masers in Cep A, and demonstrative observations with the bigradient phase referencing.
Ultraviolet observations using the Solar Blind Channel on the Hubble Space Telescope provide light curves and low resolution spectra of three pulsating white dwarfs in the cataclysmic variables SDSS013132.39-090122.3, SDSSJ161033.64-010223.3 and SDSSJ220553.98+115553.7. The UV light curves show enhanced pulsation amplitudes over those from simultaneous and previous optical photometry, while the UV-optical spectra are fit with white dwarf temperatures near 15,000K. These temperatures place the accreting white dwarfs outside the instability zone for non-interacting DAV white dwarfs and show that the instability strip is complex for accreting white dwarfs.
We present the GMRT 235 MHz images of three radio galaxies and 610 MHz images of two sources belonging to a complete sample of cD galaxies in rich and poor galaxy clusters. The analysis of the spectral properties confirms the presence of aged radio emission in two of the presented sources.
We present a progress report on the kinematical analysis of the entire SPY (ESO SN Ia Progenitor surveY) sample of about one thousand white dwarfs and hot subdwarfs. In a previous study (Pauli et al. 2003, 2006) 398 DA white dwarfs have been analysed already. Here we extend the study to 634 DA white dwarfs. We discuss kinematic criteria for a distinction of thin disk, thick disk and halo populations. This is the largest homogeneous sample of white dwarfs for which accurate 3D space motions have been determined. They have been derived from radial velocities, spectroscopic distances and proper motions from catalogues. Galactic orbits and further kinematic parameters were computed. Our kinematic criteria for assigning population membership are deduced from a sample of F and G stars taken from the literature for which chemical criteria can be used to distinguish between thin disk, thick disk and halo members. The kinematic population classification scheme is based on the position in the $VU$-velocity diagram, the position in the eccentricity-JZ diagram and the Galactic orbit. We combine this with age estimates and find 12 halo and 37 thick disk members amongst our DA white dwarfs. We were unable to determine the population membership of only nine of them. The remaining members of the sample of 632 stars belong to the thin disk population.
The nature of the progenitors of type Ia supernovae is still under controversial debate. KPD 1930+2752 is one of the best SN Ia progenitor candidates known today. The object is a double degenerate system consisting of a subluminous B star and a massive white dwarf. Maxted et al. 2000 conclude that the system mass exceeds the Chandrasekhar mass. This conclusion, however, rests on the assumption that the sdB mass is 0.5 Mo. However, recent binary population synthesis calculations suggest that the mass of an sdB star may range from 0.3 Mo to more than 0.7 Mo. It is therefore important to measure the mass of the sdB star simultaneously with that of the white dwarf. Since the rotation of the sdB star is tidally locked to the orbit the inclination of the system can be constrained. An analysis of the ellipsoidal variations in the light curve allows to tighten the constraints derived from spectroscopy. We derive the mass-radius relation for the sdB star from a quantitative spectral analysis. The projected rotational velocity is determined for the first time from high-resolution spectra. In addition a reanalysis of the published light curve is performed. The atmospheric and orbital parameters are measured with unprecedented accuracy. In particular the projected rotational velocity vrotsini = 92.3 +/- 1.5 km/s is determined. The mass of the sdB is limited between 0.45 Mo and 0.52 Mo. The total mass of the system ranges from 1.36 Mo to 1.48 Mo and hence is likely to exceed the Chandrasekhar mass. So KPD 1930+2752 qualifies as an excellent double degenerate supernova Ia progenitor candidate.
The masses of compact objects like white dwarfs, neutron stars and black holes are fundamental to astrophysics, but very difficult to measure. We present the results of an analysis of subluminous B (sdB) stars in close binary systems with unseen compact companions to derive their masses and clarify their nature. Radial velocity curves were obtained from time resolved spectroscopy. The atmospheric parameters were determined in a quantitative spectral analysis. Based on high resolution spectra we were able to measure the projected rotational velocity of the stars with high accuracy. The assumption of orbital synchronization makes it possible to constrain inclination angle and companion mass of the binaries. Five invisible companions have masses that are compatible with that of normal white dwarfs or late type main sequence stars. But four sdBs have very massive companions like heavy white dwarfs > 1 Mo, neutron stars or even black holes. Such a high fraction of massive compact companions is not expected from current models of binary evolution.
Aims: To constrain the ionization fraction in protoplanetary disks, we present new high-sensitivity interferometric observations of N$_2$H$^+$ in three disks surrounding DM Tau, LkCa 15, and MWC 480. Methods: We used the IRAM PdBI array to observe the N$_2$H$^+$ J=1-0 line and applied a $\chi^2$-minimization technique to estimate corresponding column densities. These values are compared, together with HCO$^+$ column densities, to results of a steady-state disk model with a vertical temperature gradient coupled to gas-grain chemistry. Results: We report two \ndhp detections for LkCa 15 and DM Tau at the $5 \sigma$ level and an upper limit for MWC 480. The column density derived from the data for LkCa 15 is much lower than previously reported. The [N$_2$H$^+$/HCO$^+$] ratio is on the order of 0.02--0.03. So far, HCO$^+$ remains the most abundant observed molecular ion in disks. Conclusions: All the observed values generally agree with the modelled column densities of disks at an evolutionary stage of a few million years (within the uncertainty limits), but the radial distribution of the molecules is not reproduced well. The low inferred concentration of N$_2$H$^+$ in three disks around low-mass and intermediate-mass young stars implies that this ion is not a sensitive tracer of the overall disk ionization fraction.
We present a detailed abundance analysis of high-resolution ultraviolet echelle spectra of five subdwarf B stars obtained with HST-STIS The goal of our observations was to test the hypothesis that pulsations in sdBs are correlated to the surface abundances of iron-group elements. We study two pulsators and three non-pulsators and determined abundances for 25 elements including the iron group and even heavier elements such as tin and lead using LTE spectrum synthesis techniques. We find strong enrichments of heavy elements up to 2.9dex with respect to solar which are probably caused by atomic diffusion processes. No clear-cut correlation between pulsations and metal abundances becomes apparent. Abundances for lead isotopes are derived from very high resolution spectra using an UV line of triply ionised lead. As Pb terminates the s-process sequence Pb isotopic abundance ratios yield important constraints. It is very difficult to measure them in hot stars. For the first time we were able to measure them in two subluminous B stars and conclude that the 207Pb/208Pb is solar.
Variation of constants in the very early universe can generate inflation. We consider a scenario where the strong coupling constant was changing in time and where the gluon condensate underwent a phase transition ending the inflation.
We present results for the 2m spectroscopic part of the MultiSite Spectroscopic Telescope campaign, which took place in May/June 2002. In order to perform an asteroseismological analysis on the multiperiodic pulsating subdwarf B star PG 1605+072 we used over 150 hours of time resolved spectroscopy in order to search for and analyse line profile variations by using phase binning. We succeeded in finding variations in effective temperature and gravity for four modes. A pilot analysis using the \textit{BRUCE} and \textit{KYLIE} programs and assuming strong rotation and low inclination favours models with $l=1$ or $l=2$ with $m\leq0$.
Integral field spectrographs are major instruments to study the mechanisms involved in the formation and the evolution of early galaxies. When combined with multi-object spectroscopy, those spectrographs can behave as machines used to derive physical parameters of galaxies during their formation process. Up to now, there is only one available spectrograph with multiple integral field units, e.g. FLAMES/GIRAFFE on the VLT. However, current ground based instruments suffer from a degradation of their spatial resolution due to atmospheric turbulence. In this article we describe the performance of FALCON, an original concept of a new generation multi-object integral field spectrograph with adaptive optics for the ESO Very Large Telescope. The goal of FALCON is to combine high angular resolution (0.25 arcsec) and high spectral resolution (R > 5000) in J and H bands over a wide field of view (10x10 arcmin2) in the VLT Nasmyth focal plane. However, instead of correcting the whole field, FALCON will use multi-object adaptive optics (MOAO) to perform locally on each scientific target the adaptive optics correction. This requires then to use atmospheric tomography in order to use suitable natural guide stars for wavefront sensing. We will show that merging MOAO and atmospheric tomography allows us to determine the internal kinematics of distant galaxies up to z=2 with a sky coverage of 50%, even for objects observed near the galactic pole. The application of such a concept to Extremely Large Telescopes seems therefore to be a very promising way to study galaxy evolution from z = 1 to redshifts as high as z = 7.
We introduce a set of stellar models for massive stars whose evolution has been affected by mass transfer in a binary system, at a range of metallicities. As noted by other authors, the effect of such mass transfer is frequently more than just rejuvenation. We find that, whilst stars with convective cores which have accreted only H-rich matter rejuvenate as expected, those stars which have accreted He-rich matter (for example at the end stages of conservative mass transfer) evolve in a way that is qualitatively similar to rejuvenated stars of much higher metallicity. Thus the effects of non-conservative evolution depend strongly on whether He-rich matter is amongst the portion accreted or ejected. This may lead to a significant divergence in binary evolution paths with only a small difference in initial assumptions. We compare our models to observed systems and find approximate formulae for the effect of mass accretion on the effective age and metallicity of the resulting star.
Many ground-based photometric surveys are now under way, and five of them have been successful at detecting transiting exoplanets. Nevertheless, detecting transiting planets has turned out to be much more challenging than initially anticipated. Transit surveys have learnt that an overwhelming number of false positives and confusion scenarios, combined with an intermittent phase coverage and systematic residuals in the photometry, could make ground-based surveys rather inefficient in the detection of transiting planets. We have set up a working group on transiting planets to confront the experience of the different surveys and get a more complete understanding of these issues, in order to improve the observing strategies and analysis schemes for ongoing surveys, and to prepare for the coming Corot and Kepler space missions. This contribution presents the current results of our working group.
We report early photospheric-phase observations of the Type IIP Supernova (SN) 2005cs obtained by Swift's Ultraviolet-Optical and X-Ray Telescopes. Observations started within two days of discovery and continued regularly for three weeks. During this time the V-band magnitude remained essentially constant, while the UV was initially bright but steadily faded until below the brightness of an underlying UV-bright HII region. This UV decay is similar to SNe II observed by the International Ultraviolet Explorer. UV grism spectra show the P-Cygni absorption of MgII 2798A, indicating a photospheric origin of the UV flux. Based on non-LTE model atmosphere calculations with the CMFGEN code, we associate the rapid evolution of the UV flux with the cooling of the ejecta, the peak of the spectral energy distribution (SED) shifting from ~700A on June 30th to ~1200A on July 5th. Furthermore, the corresponding recombination of the ejecta, e.g., the transition from FeIII to FeII, induces considerable strengthening of metal line-blanketing at and above the photosphere, blocking more effectively this fading UV flux. SN2005cs was not detected in X-rays, and the upper limit to the X-ray luminosity yields a limit to the mass loss rate of the progenitor of about 10^-5 solar masses per year. Overall, Swift presents a unique opportunity to capture the early and fast evolution of Type II SNe in the UV, providing additional constraints on the reddening, the SED shortward of 4000A, and the ionization state and temperature of the photon-decoupling regions.
Microlensing promises to be a powerful tool for studying distant galaxies and quasars. As the data and models improve, there are systematic effects that need to be explored. Quasar continuum and broad-line regions may respond differently to microlensing due to their different sizes; to understand this effect, we study microlensing of finite sources by a mass function of stars. We find that microlensing is insensitive to the slope of the mass function but does depend on the mass range. For negative parity images, diluting the stellar population with dark matter increases the magnification dispersion for small sources and decreases it for large sources. This implies that the quasar continuum and broad-line regions may experience very different microlensing in negative-parity lensed images. We confirm earlier conclusions that the surface brightness profile and geometry of the source have little effect on microlensing. Finally, we consider non-circular sources. We show that elliptical sources that are aligned with the direction of shear have larger magnification dispersions than sources with perpendicular alignment, an effect that becomes more prominent as the ellipticity increases. Elongated sources can lead to more rapid variability than circular sources, which raises the prospect of using microlensing to probe source shape.
Scattering by dust grains in our Galaxy can produce X-ray halos, visible as expanding rings, around GRBs. This has been observed in three GRBs to date, allowing to derive accurate distances for the dust clouds as well as some constraints on the prompt GRB X-ray emission that was not directly observed. We developed a new analysis method to study dust scattering expanding rings and have applied it to all the XMM-Newton and Swift/XRT follow-up observations of GRBs.
We present 15 - 20 micron long-slit spectra, from the Infrared Spectrograph (IRS) on Spitzer, of NGC 7023. We observe recently-discovered interstellar emission features, at 15.9, 16.4, 17.0, 17.4, 17.8, and 18.9 microns, throughout the reflection nebula. The 16.4 micron emission feature peaks near the photodissociation front northwest of the star, as do the aromatic emission features (AEFs) at 3.3, 6.2 and 11.3 microns. The 16.4 micron emission feature is thus likely related to the AEFs and radiates by non-equilibrium emission. The new 18.9 micron emission feature, by contrast, decreases monotonically with stellar distance. We consider candidate species for the 18.9 micron feature, including polycyclic aromatic hydrocarbons, fullerenes, and diamonds. We describe future laboratory and observational research needed to identify the 18.9 micron feature carrier.
Aims. Understand the shape and implications of the multiband light curve of GRB 050408, an X-ray rich (XRR) burst. Methods. We present a multiband optical light curve, covering the time from the onset of the gamma-ray event to several months after, when we only detect the host galaxy. Together with X-ray, millimetre and radio observations we compile what, to our knowledge, is the most complete multiband coverage of an XRR burst afterglow to date. Results. The optical and X-ray light curve is characterised by an early flattening and an intense bump peaking around 6 days after the burst onset. We explain the former by an off-axis viewed jet, in agreement with the predictions made for XRR by some models, and the latter with an energy injection equivalent in intensity to the initial shock. The analysis of the spectral flux distribution reveals an extinction compatible with a low chemical enrichment surrounding the burst. Together with the detection of an underlying starburst host galaxy we can strengthen the link between XRR and classical long-duration bursts.
We analyze the near-infrared luminosity profiles and photometric parameters of the host galaxies of 3CR radio sources with z<0.3, to investigate their physical nature. Our sample includes 82 galaxies, of which 22 (27%) are FR Is and 60 (73%) are FR IIs. Using near-infrared data taken both with NICMOS onboard the Hubble Space Telescope and from the ground with the Telescopio Nazionale Galileo, we find that luminosity profiles are very well described by a single Sersic law in 52% of the cases and for the remaining objects (48%) it is necessary to include an exponential profile, which could indicate the presence of a disk. The average bulge to disk luminosity ratio for the galaxies is (b/d) ~ 1.1. The analysis of the photometric parameters of the sub samples indicates that FR Is and FR IIs show rather similar bulges in terms of effective surface magnitude, effective radius, and Sersic index. On the other hand, disks in FR Is and FR IIs hosts show, on average, different properties. Central surface magnitudes are dimmer and scale lengths are greater by a factor of 2 in FR Is when compared to FR IIs. We also estimate the black hole mass associated with each galaxy using two different methods that claim tight correlations between the black hole mass (M_BH) with the infrared bulge luminosity (L_bulge) and with the Sersic index (n). Our data indicate that masses obtained through these two methods show a high dispersion and M_BH obtained through L_bulge are systematically higher (by a factor of ~3) than those obtained using n. This result may reflect the fact that for our sample galaxies we do not find any correlation between L_bulge and n.
In March 2006, the Hubble Heritage Team obtained a large four-filter (B, V, I, and H-alpha) six-point mosaic dataset of the prototypical starburst galaxy NGC 3034 (M82), with the Advanced Camera for Surveys (ACS) onboard the Hubble Space Telescope (HST). The resulting color composite Heritage image was released in April 2006, to celebrate Hubble's 16th anniversary. Cycle 15 HST proposers were encouraged to submit General Observer and Archival Research proposals to complement or analyze this unique dataset. Since our M82 mosaics represent a significant investment of expert processing beyond the standard archival products, we will also release our drizzle combined FITS data as a High Level Science Product via the Multimission Archive at STScI (MAST) on December 31, 2006. This paper documents the key aspects of the observing program and image processing: calibration, image registration and combination (drizzling), and the rejection of cosmic rays and detector artifacts. Our processed FITS mosaics and related information can be downloaded from this http URL
The fast repositioning system of the MAGIC Telescope has allowed during its first data cycle, between 2005 and the beginning of year 2006, observing nine different GRBs as possible sources of very high energy gammas. These observations were triggered by alerts from Swift, HETE-II, and Integral; they started as fast as possible after the alerts and lasted for several minutes, with an energy threshold varying between 80 and 200 GeV, depending upon the zenith angle of the burst. No evidence for gamma signals was found, and upper limits for the flux were derived for all events, using the standard analysis chain of MAGIC. For the bursts with measured redshift, the upper limits are compatible with a power law extrapolation, when the intrinsic fluxes are evaluated taking into account the attenuation due to the scattering in the Metagalactic Radiation Field (MRF).
CCD photometry on the intermediate-band vbyCaHbeta system is presented for the metal-rich, old open cluster, NGC 6791. Preliminary analysis led to [Fe/H] above +0.4 with an anomalously high reddening and an age below 5 Gyr. A revised calibration between (b-y)_0 and [Fe/H] at a given temperature shows that the traditional color-metallicity relations underestimate the color of the turnoff stars at high metallicity. With the revised relation, the metallicity from hk and the reddening for NGC 6791 become [Fe/H] = +0.45 +/- 0.04 and E(b-y) = 0.113 +/- 0.012 or E(B-V) = 0.155 +/- 0.016. Using the same technique, reanalysis of the photometry for NGC 6253 produces [Fe/H] = +0.58 +/-0.04 and E(b-y) = 0.120 +/- 0.018 or E(B-V) = 0.160 +/- 0.025. The errors quoted include both the internal and external errors. For NGC 6791, the metallicity from m_1 is a factor of two below that from hk, a result that may be coupled to the consistently low metal abundance from DDO photometry of the cluster and the C-deficiency found from high dispersion spectroscopy. E(B-V) is the same value predicted from Galactic reddening maps. With E(B-V) = 0.15 and [Fe/H] = +0.45, the available isochrones predict an age of 7.0 +/- 1.0 Gyr and an apparent modulus of (m-M) = 13.60 +/- 0.15, with the dominant source of the uncertainty arising from inconsistencies among the isochrones. The reanalysis of NGC 6253 with the revised lower reddening confirms that on both the hk and m_1 metallicity scales, NGC 6253, while less than half the age of NGC 6791, remains at least as metal-rich as NGC 6791, if not richer.
We present subarcsecond-resolution mid-infrared images of the debris disk surrounding the 230 Myr- old A star Zeta Lep. Our data obtained with T-ReCS at Gemini South show the source to be unresolved at 10.4 microns but clearly extended at 18.3 microns. Quadratic subtraction of the PSF profile from that of Zeta Lep implies a characteristic radius for the dust disk of 3 AU, which is comparable in size to our solar system's asteroid belt. Simple models suggest that the 18 micron flux is well approximated by two contiguous annuli of mid-infrared-emitting dust from 2-4 and 4-8 AU with a 3:1 flux ratio for the annuli, respectively. We consider two scenarios for the collisions that must be resupplying the dust population: (1) continuous "steady state" grinding of planetesimals, and (2) an isolated cataclysmic collision. We determine that radiation pressure and subsequent collisions are the dominant determinants of the disk morphology in either case, and that Poynting-Robertson drag is comparatively insignificant.
Recent progress in realistic simulations of solar convection have given us an unprecedented opportunity to evaluate the robustness of solar interior structures and dynamics obtained by methods of local helioseismology. We present results of testing the time-distance method using realistic simulations. By computing acoustic wave propagation time and distance relations for different depths of the simulated data, we confirm that acoustic waves propagate into the interior and then turn back to the photosphere. This demonstrates that in the numerical simulations properties of acoustic waves (p-modes) are similar to the solar conditions, and that these properties can be analyzed by the time-distance technique. For the surface gravity waves (f-mode), we calculate perturbations of their travel times, caused by localized downdrafts, and demonstrate that the spatial pattern of these perturbations (representing so-called sensitivity kernels) is similar to the patterns obtained from the real Sun, displaying characteristic hyperbolic structures. We then test the time-distance measurements and inversions by calculating acoustic travel times from a sequence of vertical velocities at the photosphere of the simulated data, and inferring a mean 3D flow fields by performing inversion based on the ray approximation. The inverted horizontal flow fields agree very well with the simulated data in subsurface areas up to 3 Mm deep, but differ in deeper areas. Due to the cross-talk effects between the horizontal divergence and downward flows, the inverted vertical velocities are significantly different from the mean convection velocities of the simulation dataset.
We investigate the conditions for the presence of a magnetically inactive dead zone in protostellar disks, using 3-D shearing-box MHD calculations including vertical stratification, Ohmic resistivity and time-dependent ionization chemistry. Activity driven by the magnetorotational instability fills the whole thickness of the disk at 5 AU, provided cosmic ray ionization is present, small grains are absent and the gas-phase metal abundance is sufficiently high. At 1 AU the larger column density of 1700 g/cm^2 means the midplane is shielded from ionizing particles and remains magnetorotationally stable even under the most favorable conditions considered. Nevertheless the dead zone is effectively eliminated. Turbulence mixes free charges into the interior as they recombine, leading to a slight coupling of the midplane gas to the magnetic fields. Weak, large-scale radial fields diffuse to the midplane where they are sheared out to produce stronger azimuthal fields. The resulting midplane accretion stresses are just a few times less than in the surface layers on average.
Images obtained with the ESO VLT and FORS1 in [O III] 5007 on- and off-band as well as r_Gunn filters are analyzed to search for Planetary Nebula (PN) candidates in the dwarf irregular NGC 3109. In the continuum-subtracted [O III] 5007 on-band images, a large number of emission-line regions were detected. We describe the criteria employed in order to distinguish PN candidates from compact HII regions, finding that the sizes and the properties of the ionizing stars are the most unambiguous discriminators for separating the two classes. Based upon these criteria, we have found 20 PN candidates for which we present coordinates, nebular [O III] fluxes, and stellar magnitudes. The cumulative luminosity function for these PNe is discussed. A catalog of HII regions listing coordinates, nebular [O III] fluxes, stellar magnitudes and other characteristics is also presented. We find that HII regions are rather concentrated towards the disk of the galaxy, while PNe are found also above and below this structure, consistent with their belonging to an older stellar population.
We have observed selected Fraunhofer lines, both integrated over the Full Disk and for a small circular region near the center of the solar disk, on 1,215 days for the past 30 years. Full Disk results: Ca II K 393 nm nicely tracks the 11 year magnetic cycle based on sunspot number with a peak amplitude in central intensity of ~37%. The wavelength of the mid-line core absorption feature, called K3, referenced to nearby photospheric Fe, displays an activity cycle variation with an amplitude of 3 milli-Angstroms. Other chromospheric lines track Ca II K intensity with lower relative amplitudes. Low photosphere: Temperature sensitive CI 5380 nm appears constant in intensity to 0.2%. High photosphere: The cores of strong Fe I lines, Na D1 and D2, and the Mg I b lines, present a puzzling signal perhaps indicating a role for the 22 y Hale cycle. Solar minimum around 1985 was clearly seen, but the following minimum in 1996 was missing. This anomalous behavior is not seen in comparison atmospheric O2. Center Disk results: Both Ca II K and C I 538 nm intensities are constant, indicating that the basal quiet atmosphere is unaffected by cycle magnetism within our observational error. A lower limit to the Ca II K central intensity atmosphere is 0.040. The wavelength of Ca II K3 varies with the cycle by 6 milli-Angstroms, a factor of 2X over the full disk value. This may indicate the predominance of radial motions at Center Disk. This is not an effect of motions in plages since they are absent at Center Disk. This 11 y variation in the center of chromospheric lines could complicate the radial velocity detection of planets around solar-type stars. An appendix provides instructions for URL access to both the raw and reduced data.
Future microwave sky surveys will have the sensitivity to detect the kinematic Sunyaev-Zeldovich signal from moving galaxy clusters, thus providing a direct measurement of their line-of-sight peculiar velocity. We show that cluster peculiar velocity statistics applied to foreseeable surveys will put significant constraints on fundamental cosmological parameters. We consider three statistical quantities that can be constructed from a cluster peculiar velocity catalog: the probability density function, the mean pairwise streaming velocity, and the pairwise velocity dispersion. These quantities are applied to an envisioned data set which measures line-of-sight cluster velocities with normal errors of 100 km/s for all clusters with masses larger than $10^{14}$ solar masses over a sky area of up to 5000 square degrees. A simple Fisher matrix analysis of this survey shows that the normalization of the matter power spectrum and the dark energy equation of state can be constrained to better than 10 percent, and the Hubble constant and the primordial power spectrum index can be constrained to a few percent, independent of any other cosmological observations. We also find that the current constraint on the power spectrum normalization can be improved by more than a factor of two using data from a 400 square degree survey and WMAP third-year priors.
General relativistic kinematics and the cosmological principle alone imply a monotonicity constraint in the Hubble diagram, which we confront to present-day supernova data. We use the running gradient method of statistical inference by Hall & Heckman (2000). We find no significant departure from monotonicity. The method seems well adapted and we recommend its use with future data.
This paper describes a study to deduce fundamental parameters and magnetic field characteristics for all magnetic Ap/Bp stars with in a 100 parsec heliocentric radius volume. This study has allowed for the first time the determination of an effectively unbiased magnetic field distribution of a sample of intermediate mass stars. From published catalogues and other literature sources, we have identified 57 bone fide magnetic A and B stars in the volume, corresponding to 1.7% of all intermediate mass stars within 100 parsec of the Sun. The masses of Ap stars range from 1.5 to 6 solar masses, with the peak of the mass incidence distribution between 3.3 and 3.6 solar masses. Observations of 30 of the Ap/Bp stars were obtained using the MuSiCoS spectropolarimeter at the Telescope Bernard Lyot at Pic du Midi Observatory. These observations will be used to refine periods, and determine magnetic field strength and geometry.
We present a quantitative analysis of the morphologies for 199 nearby galaxies as parameterized with measurements of the concentration, asymmetry, and clumpiness (CAS) parameters at wavelengths from 0.15-0.85$\mu$m. We find that these CAS parameters depend on both galaxy type and the wavelength of observation. As such, we use them to obtain a quantitative measure of the "morphological k-correction", i.e., the change in appearance of a galaxy with rest-frame wavelength. Whereas early-type galaxies (E--S0) appear about the same at all wavelengths longward of the Balmer break, there is a mild but significantly-determined wavelength-dependence of the CAS parameters for galaxies types later than S0, which generally become less concentrated, and more asymmetric and clumpy toward shorter wavelengths. Also, as a merger progresses from pre-merger via major-merger to merger-remnant stages, it evolves through the CAS parameter space, becoming first less concentrated and more asymmetric and clumpy, and then returning towards the "locus" of normal galaxies. The final merger products are, on average, much more concentrated than normal spiral galaxies.
If the diffuse extragalactic gamma ray emission traces the large scale structures of the universe, peculiar anisotropy patterns are expected in the gamma ray sky. In particular, because of the cutoff distance introduced by the absorption of 0.1-10 TeV photons on the infrared/optical background, prominent correlations with the local structures within a range of few hundreds Mpc should be present. We provide detailed predictions of the signal based on the PSCz map of the local universe. We also use mock N-body catalogues complemented with the halo model of structures to study some statistical features of the expected signatures. The results are largely independent from cosmological details, and depend mostly on the index of correlation (or bias) of the sources with respect to the large scale distribution of galaxies. The predicted signal in the case of a quadratic correlation (as expected e.g. for a dark matter annihilation contribution to the diffuse gamma flux) differs substantially from a linear correlation case, providing a complementary tool to unveil the nature of the sources of the diffuse gamma ray emission. The chances of the present and future space and ground based observatories to measure these features are discussed.
We examine the properties of two galaxy "halos" at z ~ 0.7 in the TON 153 (z_em = 1.01) quasar field. The first absorber-galaxy pair (G1) is a z = 0.672, L_B = 4.3 L*_B, E/S0 galaxy probed at D = 58 kpc. G1 is associated with a remarkable five-component Ly-alpha complex having tau_LL < 0.4, W_r(Lya) = 2.8 A, and a velocity spread of v = 1420 km/s. We find no MgII, CIV, NV, nor OVI absorption in these clouds and infer metallicity upper limits of -3 < log(Z/Z_sun) < -1, depending upon assumptions of photoionized or collisionally ionized gas. The second absorber-galaxy pair (G2) is a z = 0.661, L_B = 1.8 L*_B, Sab galaxy probed at D = 103 kpc. G2 is associated with metal--enriched (log Z/Z_sun ~ -0.4) photoionized gas having N(HI) ~ 18.3 and a velocity spread of v = 200 km/s. The very different G1 and G2 systems both have gas-galaxy properties inconsistent with the standard luminosity dependent galaxy "halo" model commonly invoked for quasar absorption line surveys. We emphasize that mounting evidence is revealing that extended galactic gaseous envelopes in the regime of D < 100 kpc do not exhibit a level of homogeneity supporting a standardized halo model. Selection effects may have played a central role in the development of a simple model. We discuss the G1 and G2 systems in the context of Lambda-CDM models of galaxy formation and suggest that the heterogeneous properties of absorber-galaxy pairs is likely related to the range of overdensities from which galaxies and gas structures arise.
We explore the hardness-intensity correlations observed in several AXPs and SGRs within the framework of a thermally emitting magnetar model. Using our detailed atmosphere models and taking into account reprocessing of the surface emission by the magnetosphere, we show that the hardness of the surface spectra increases with increasing temperature and hence the changes in the effective temperatures of the outer layers of the star alone can account for the observed correlations. We conclude that the slow release of the heat deposited in the deep crust during a magnetar burst naturally accounts for the spectral changes during the afterglow. The correlations are further enhanced by changes in the structures of the magnetic currents during or following a burst. However, the additional hardening produced by scattering of the surface photons off the magnetospheric charges saturates at moderate values of the scattering optical depth.
Markarian 421 (Mrk 421) was the first blazar detected at gamma-ray energies above 300 GeV, and it remains one of only twelve TeV blazars detected to date. TeV gamma-ray measurements of its flaring activity and spectral variability have placed constraints on models of the high-energy emission from blazars. However, observations between 50 and 300 GeV are rare, and the high-energy peak of the spectral energy distribution (SED), predicted to be in this range, has never been directly detected. We present a detection of Mrk 421 above 100 GeV as made by the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) during a multiwavelength campaign in early 2004. STACEE is a ground-based atmospheric Cherenkov telescope using the wavefront sampling technique to detect gamma rays at lower energies than achieved by most imaging Cherenkov telescopes. We also outline a method for reconstructing gamma-ray energies using a solar heliostat telescope. This technique was applied to the 2004 data, and we present the differential energy spectrum of Mrk 421 above 130 GeV. Assuming a differential photon flux dN/dE proportional to E^-a, we measure a spectral index a = 2.1 +/- 0.2 (statistical) +0.2/-0.1 (systematic). Finally, we discuss the STACEE spectrum in the context of the multiwavelength results from the same epoch.
We present first results of XMM-Newton X-ray observations of the infrared cluster lying near the NGC 2071 reflection nebula in the Orion B region. This cluster is of interest because it is one of the closest regions known to harbor embedded high-mass stars. We report the discovery of hard X-ray emission from the dense central NGC 2071-IR subgroup which contains at least three high-mass young stellar objects (NGC 2071 IRS-1, IRS-2, and IRS-3). A prominent X-ray source is detected within 1 arcsecond of the infrared source IRS-1, which is thought to drive a powerful bipolar molecular outflow. The X-ray spectrum of this source is quite unusual compared to the optically thin plasma spectra normally observed in young stellar objects (YSOs). The spectrum is characterized by a hard broad-band continuum plus an exceptionally broad emission line at approximately 6.4 keV from neutral or near-neutral iron. The fluorescent Fe line likely originates in cold material near the embedded star (i.e. a disk or envelope) that is irradiated by the hard heavily-absorbed X-ray source.
We demonstrate that the X-ray and Gamma-ray spectra of Swift GRBs and their afterglows are dominated by emission characteristic of an expanding, relativistic fireball. The classical afterglow due to the impact of the fireball on the external medium is often not observed until one to several hours after the GRB. Focusing on GRBs 061121, 060614, and 060124, but generalizing to the full (>50 Msec XRT exposure) Swift sample up to and including GRB061210, we show that the emission in >90% of early afterglows has a characteristic nu*F_nu spectral energy E_peak which likely evolves from the Gamma-rays through the soft X-ray band on timescales of 10^2-10^4s after the GRB. The observed spectra are strongly curved and have often been incorrectly fitted in other studies with a time-varying soft X-ray absorption. The spectral evolution inferred from fitting instead models used to fit GRBs demonstrates a common evolution--a powerlaw hardness intensity correlation and hard to soft evolution--for GRBs and the early X-ray afterglows and X-ray flares. Combined with studies of short timescale variability, our findings indicate a central engine active for longer than previously suspected. The GRB spectra are observed to become very soft at late times due to an intrinsic spectral evolution and due to the surprising faintness of some afterglows. We re-interpret early afterglow studies prior to Swift and also discuss models for the early X-ray emission.
Astrophysical observations indicate that about 23% of the energy density of the universe is in the form of non-baryonic particles beyond the standard model of particle physics. One exciting and well motivated candidate is the lightest supersymmetric partner particle (LSP), which could be a weakly interacting massive particle (WIMP) left over from the Big Bang. To determine that the LSP is the dark matter, it is necessary both to measure the particle's properties at an accelerator and to detect the particle in the galaxy directly (or indirectly). Direct detection of these particles requires sophisticated detectors to defeat much higher-rate backgrounds due to radioactivity and other sources. Promising techniques identify individual interactions in shielded fiducial volumes and distinguish nuclear-recoil signal events from electron-recoil backgrounds, based on the timing, energy density, and/or the division of the energy into signals of ionization, scintillation, or phonons. I review the techniques of the dozens of experiments searching for WIMPs and summarize the most interesting results and prospects for detection.
We apply a new method to determine the magnetic field in coronal loops using observations of coronal loop oscillations. We analyze seven Doppler shift oscillation events detected by SUMER in the hot flare line Fe XIX to obtain oscillation periods of these events. The geometry, temperature, and electron density of the oscillating loops are measured from coordinated multi-channel soft X-ray imaging observations from SXT. All the oscillations are consistent with standing slow waves in their fundamental mode. The parameters are used to calculate the magnetic field of coronal loops based on MHD wave theory. For the seven events, the plasma $\beta$ is in the range 0.15-0.91 with a mean of 0.33$\pm$0.26, and the estimated magnetic field varies between 21-61 G with a mean of 34$\pm$14 G. With background emission subtracted, the estimated magnetic field is reduced by 9%-35%. The maximum backgroud subtraction gives a mean of 22$\pm$13 G in the range 12-51 G. We discuss measurement uncertainties and the prospect of determining coronal loop magnetic fields from future observations of coronal loops and Doppler shift oscillations.
The unexplained sunward acceleration $a_\mathrm{P}$ of the Pioneer 10 (P10) and the Pioneer 11 (P11) spacecraft remains a mystery. A scalar potential model (SPM) that derived from considerations of galaxy clusters, of redshift, and of H{\scriptsize{I}} rotation curves of spiral galaxies is applied to the Pioneer Anomaly. Matter is posited to warp the scalar potential $\rho$ field. The gradient of the $\rho$ field produces a force on matter and light. The changing $\rho$ along the light path causes the Pioneer Anomaly. The SPM is consistent with the general value of $a_\mathrm{P}$, with the annual periodicity, with the differing $a_\mathrm{P}$ between the spacecraft, with the slowly declining $a_\mathrm{P}$, with the low value of $a_\mathrm{P}$ immediately before the P11's Saturn encounter, with the high uncertainty in the value of $a_\mathrm{P}$ obtained during and after the P11's Saturn encounter, and with the cosmological connection suggested by $a_\mathrm{P} \approx cH_\mathrm{o}$. The effect of the $\rho$ field warp appears as the curvature of space proposed by general relativity.
We investigate the relationship between black hole mass and host galaxy velocity dispersion for QSOs in Data Release 3 of the Sloan Digital Sky Survey. We derive black hole mass from the broad Hbeta line width and continuum luminosity, and the bulge stellar velocity dispersion from the [OIII] narrow line width. At higher redshifts, we use MgII and [OII] in place of Hbeta and [OIII]. For redshifts z < 0.5, our results agree with the black hole mass - bulge velocity dispersion relationship for nearby galaxies. For 0.5 < z < 1.2, this relationship appears to show evolution with redshift in the sense that the bulges are too small for their black holes. However, we find that part of this apparent trend can be attributed to observational biases, including a Malmquist bias involving the QSO luminosity. Accounting for these biases, we find ~0.2 dex evolution in the black hole mass-bulge velocity dispersion relationship between now and redshift z ~ 1.
We search for viable f(R) theories of gravity, making use of the equivalence between such theories and scalar-tensor gravity. We find that models can be made consistent with solar system constraints either by giving the scalar a high mass or by exploiting the so-called chameleon effect. However, in both cases, it appears likely that any late-time cosmic acceleration will be observationally indistinguishable from acceleration caused by a cosmological constant. We also explore further observational constraints from, e.g., big bang nucleosynthesis and inflation.
In this contribution we report our recent investigation of the gas metallicity in active galactic nuclei and its dependence on luminosity and redshift. We compile large spectroscopic datasets of broad-line and narrow-line AGNs, and compare them with the results of our photoionization models. Through the analysis of both the broad and the narrow emission-line regions, we find that: (1) for a given luminosity, there is no redshift dependence of the gas metallicity; (2) for a given redshift, there is a significant correlation between gas metallicity and luminosity; (3) the luminosity-metallicity relation does no show any evolution in the redshift range 2 < z < 4.
We propose a factorizability ansatz for angular bispectra which permits fast algorithms for forecasting, analysis, and simulation, yet is general enough to encompass many interesting CMB bispectra. We describe a suite of general algorithms which apply to any bispectrum which can be represented in factorizable form. First, we present algorithms for Fisher matrix forecasts and the related problem of optimizing the factorizable representation, giving a Fisher forecast for Planck as an example. We show that the CMB can give independent constraints on the amplitude of primordial bispectra of both local and equilateral shape as well as those created by secondary anisotropies. We also show that the ISW-lensing bispectrum should be detected by Planck and could bias estimates of the local type of non-Gaussianity if not properly accounted for. Second, we implement a bispectrum estimator which is fully optimal in the presence of sky cuts and inhomogeneous noise, extends the generality of fast estimators which have been limited to a few specific forms of the bispectrum, and improves the running time of existing implementations by several orders of magnitude. Third, we give an algorithm for simulating random, weakly non-Gaussian maps with prescribed power spectrum and factorizable bispectrum.
The first detections of afterglows from short gamma-ray bursts (GRBs) have confirmed the previous suspicion that they are triggered by a different central engine than long bursts. In particular, the recent detections of short GRBs in galaxies without star formation lends support to the idea that an old stellar population is involved. Most prominent are mergers of either double neutron stars or of a neutron star with a stellar-mass black hole companion. Since the final identification of the central engine will only come from an integral view of several properties, we review the observable signatures that can be expected from both double neutron stars and neutron star black hole systems. We discuss the gravitational wave emission, the structure of the neutrino-cooled accretion disks, the resulting neutrino signal and possible mechanisms to launch a GRB. In addition, we address the speculative idea that in some cases a magnetar-like object may be the final outcome of a double neutron star merger. We also discuss possibilities to explain the late-time X-ray activity that has been observed in several bursts.
We present multi-frequency observational results for the Compact Steep-Spectrum (CSS) quasar 3C309.1. The observations were carried out with the VSOP at 1.6 and 4.8GHz and the VLBA at 15.4GHz. The source has a distorted, one-sided radio jet. Relativistics effects and physical properties are discussed. Comparing the predicted and observed X-ray fluxes in the framework of the synchrotron self-Compton model we derive the beaming factor for 3C309.1. The complex structure of the jet may be explained by a relativistic helical flow in a heterogeneous, clumpy ISM.
We report the discovery of fifteen previously unknown Wolf-Rayet (WR) stars
found as part of an infrared broad-band study of candidate WR stars in the
Galaxy. We have derived an empirically-based selection algorithm which has
selected ~5000 WR candidate stars located within the Galactic Plane drawn from
the GLIMPSE (mid-infrared) and 2MASS (near-infrared) catalogues. Spectroscopic
follow-up of 184 of these reveals eleven WN and four WC-type WR stars. Early WC
subtypes are absent from our sample and none show evidence for circumstellar
dust emission. Of the candidates which are not WR stars, ~120 displayed
hydrogen emission line features in their spectra. Spectral features suggest
that the majority of these are in fact B supergiants/hypergiants, ~40 of these
are identified Be/B[e] candidates.
Here, we present the optical spectra for six of the newly-detected WR stars,
and the near-infrared spectra for the remaining nine of our sample. With a WR
yield rate of ~7% and a massive star detection rate of ~65%, initial results
suggest that this method is one of the most successful means for locating
evolved, massive stars in the Galaxy.
We report the results of simultaneous multiwavelength observations of the X-ray transient source SWIFT J1753.5-0127 performed with INTEGRAL, RXTE, NTT, REM and VLA on 2005 August 10-12. The source, which underwent an X-ray outburst since 2005 May 30, was observed during the INTEGRAL Target of Opportunity program dedicated to new X-ray novae located in the Galactic Halo. Broad-band spectra and fast timing variability properties of SWIFT J1753.5-0127 are analyzed together with the optical, near infra-red and radio data. We show that the source was significantly detected up to 600 keV with Comptonization parameters and timing properties typical of the so-called Low/Hard State of black hole candidates. We build a spectral energy distribution and we show that SWIFT J1753.5-0127 does not follow the usual radio/X-ray correlation of X-ray binaries in the Low/Hard State. We give estimates of distance and mass. We conclude that SWIFT J1753.5-0127 belongs to the X-ray nova class and that it is likely a black hole candidate transient source of the Galactic Halo which remained in the Low/Hard State during its main outburst. We discuss our results within the context of Comptonization and jet models.
We report the first results from deep ACS imaging of ten classical globular clusters in the far outer regions (15 < R_p < 100 kpc) of M31. Eight of the clusters, including two of the most remote M31 globular clusters presently known, are described for the first time. Our F606W, F814W colour-magnitude diagrams extend ~ 3 magnitudes below the horizontal branch and clearly demonstrate that the majority of these objects are old (> 10 Gyr), metal-poor clusters. Five have [Fe/H] ~ -2.1, while an additional four have -1.9 < [Fe/H] < -1.5. The remaining object is more metal-rich, with [Fe/H] ~ -0.70. Several clusters exhibit the second parameter effect. Using aperture photometry, we estimate integrated luminosities and structural parameters for all clusters. Many, including all four clusters with projected radii greater than 45 kpc, are compact and very luminous, with -8.9 < M_V < -8.3. These four outermost clusters are thus quite unlike their Milky Way counterparts, which are typically diffuse, sub-luminous (-6.0 < M_V < -4.7) and more metal-rich (-1.8 < [Fe/H] < -1.3).
In this paper we use the complementary imaging capabilities of Spitzer (sensitivity) and Gemini-South/T-ReCS (spatial resolution) to study the mid-IR properties of local (d < 75Mpc) LIRGs. The T-ReCS 8-10micron imaging observations of LIRGs have allowed us to spatially resolve the nuclear emission (star formation and/or AGN) and that of HII regions in the central 3-7kpc regions of LIRGs. From the comparison of the 8micron/Pa-alpha ratios of the integrated vs. resolved HII regions of LIRGs, we infer the existence of an 8micron diffuse component, not directly related to the ionizing stars, that can be as luminous as that from the resolved HII regions. We conclude that although the mid-IR integrated luminosity of galaxies undergoing dusty, intense star formation is a good indicator of the star formation rate (SFR), the empirical calibrations should be based on the integrated emission of nearby galaxies, not that of HII regions alone. To this end we provide a calibration of the SFR in terms of the integrated 24micron luminosity that can be used for distant dusty galaxies.
We present a detailed investigation of the young stellar populations(YSP) in the radio-loud ultra luminous infrared galaxy (ULIRG) PKS1345+12, based on high resolution HST imaging and long slit spectra taken with the WHT. While the images clearly show bright knots suggestive of super star clusters(SSC), the spectra reveal the presence of YSP in the diffuse light across the full extent of the halo of the merging-double nucleus system. Spectral synthesis modelling has been used to estimate the ages of the YSP for both the SSC and the diffuse light sampled by the spectra. For the SSC we find ages t{SSC} < 6 Myr with reddenings 0.2 < E(B-V) < 0.5 and masses 10e6 < M{SSC} < 10e7 M{solar}. However, in some regions of the galaxy we find that the spectra of the diffuse light component can only be modelled with a relatively old post-starburst YSP (0.04 - 1.0 Gyr) or with a disk galaxy template spectrum. The results demonstrate the importance of accounting for reddening in photometric studies of SSC, and highlight the dangers of focussing on the highest surface brightness regions when trying to obtain a general impression of the star formation activity in the host galaxies of ULIRGs. The case of PKS1345+12 provides clear evidence that the star formation histories of the YSP in ULIRGs are complex. Intriguingly, our long-slit spectra show line splitting at the locations of the SSC, indicating that they are moving at up to 450km s-1 with respect to the local ambient gas. Given their kinematics, it is plausible that the SSC have been formed either in fast moving gas streams/tidal tails that are falling back into the nuclear regions as part of the merger process, or as a consequence of jet-induced star formation linked to the extended, diffuse radio emission detected in the halo of the galaxy
One primary difficulty in understanding the nature of the putative accretion disk in the central engine of AGNs is that some of its key intrinsic spectral signatures are buried under the emissions from the surrounding regions, i.e. the broad line region (BLR) and the obscuring torus. We argue here that these signatures can be revealed by using optical and near-IR polarization. At least in some quasars, the polarization is seen only in the continuum and is not shared by emission lines. In this case, the polarized flux is considered to show the intrinsic spectrum interior to the BLR, removing off the emissions from the BLR and torus. We have used this polarization to reveal the Balmer-edge feature and near-IR spectral shape of the central engine, both of which are important for testing the fundamental aspects of the models.
Astrophysical fluids under the influence of magnetic fields are often
subjected to single-fluid or two-fluid approximations. In the case of weakly
ionized plasmas however, this can be inappropriate due to distinct responses
from the multiple constituent species to both collisional and non-collisional
forces. As a result, in dense molecular clouds and proto-stellar accretion
discs for instance, the conductivity of the plasma may be highly anisotropic
leading to phenomena such as Hall and ambipolar diffusion strongly influencing
the dynamics.
Diffusive processes are known to restrict the stability of conventional
numerical schemes which are not implicit in nature. Furthermore, recent work
establishes that a large Hall term can impose an additional severe stability
limit on standard explicit schemes. Following a previous paper which presented
the one-dimensional case, we describe a fully three-dimensional method which
relaxes the normal restrictions on explicit schemes for multifluid processes.
This is achieved by applying the little known Super TimeStepping technique to
the symmetric (ambipolar) component of the evolution operator for the magnetic
field in the local plasma rest-frame, and the new Hall Diffusion Scheme to the
skew-symmetric (Hall) component.
The decay of the inflaton into radiation and particles during the slow-roll suggests that these may interact with each other and that the latter may also decay into subproducts before inflation is completed. As a consequence, the fluid is no longer perfect and a non-negligible bulk viscosity necessarily sets in. We write the corresponding equations as an autonomous system and study the asymptotic behavior, the conditions for the existence of scaling solutions, and show that the late time effect of fluid dissipation alleviates the depletion of matter and increases the duration of inflation.
We investigate the behavior and consequences of the reverse shock that terminates the supersonic expansion of the baryonic wind which is driven by neutrino heating off the surface of (non-magnetized) new-born neutron stars in supernova cores. To this end we perform long-time hydrodynamic simulations in spherical symmetry. In agreement with previous relativistic wind studies, we find that the neutrino-driven outflow accelerates to supersonic velocities and in case of a compact, about 1.4 solar mass (gravitational mass) neutron star with a radius of about 10 km, the wind reaches entropies of about 100 k_B per nucleon. The wind, however, is strongly influenced by the environment of the supernova core. It is decelerated and shock-heated abruptly by a termination shock that forms when the supersonic outflow collides with the slower preceding supernova ejecta. The radial position of this reverse shock varies with time and depends on the strength of the neutrino wind and the different conditions in progenitor stars with different masses and structure. Its basic properties and behavior can be understood by simple analytic considerations. We demonstrate that the entropy of matter going through the reverse shock can increase to a multiple of the asymptotic wind value. Seconds after the onset of the explosion it therefore can exceed 400 k_B per nucleon. The temperature of the shocked wind has typically dropped to about or less than 10^9 K, and density and temperature in the shock-decelerated matter continue to decrease only very slowly. Such conditions might strongly affect the important phases of supernova nucleosynthesis in a time and progenitor dependent way. (abridged)
We carried out a quantitative spectral analysis of 73 hot subluminous O-stars selected from the SDSS spectral database. While the helium deficient sdOs are scattered over a wide range of effective temperature and gravity, the helium enriched sdO stars are concentrated in a small intervall of 40kK to 50kK and log g = 5.5 ... 6.0. Comparing the distribution in the T_eff-log g-diagram with evolutionary tracks, we find the helium deficient sdOs to be the progeny of the sdB stars. The results for the helium enriched ones are less conclusive. Both the merger of two white dwarfs and the delayed helium core flash scenarios are viable options to be explored further.
The Vector SpectroMagnetograph (VSM) instrument has recorded full-disk photospheric vector magnetograms weekly since August 2003 as part of the Synoptic Optical Long-term Investigations of the Sun (SOLIS) project. After the full deployment of the VSM data processing system, a typical observing day will include three Fe I 630.2 nm full-disk photospheric vector magnetograms, one full-disk photospheric and three Ca II 854.2 nm chromospheric longitudinal magnetograms, along with three He I 1083 nm spectroheliograms. The photospheric vector magnetograms will be available over the Internet in two stages: first, as a quick-look product within minutes of data acquisition, and then as a Milne-Eddington inversion product within a day of each observation.
Nanoflares have been proposed as the main source of heating of the solar corona. However, detecting them directly has so far proved elusive, and extrapolating to them from the properties of larger brightenings gives unreliable estimates of the power-law exponent $\alpha$ characterising their distribution. Here we take the approach of statistically modelling light curves representative of the quiet Sun as seen in EUV radiation. The basic assumption is that all quiet-Sun EUV emission is due to micro- and nanoflares, whose radiative energies display a power-law distribution. Radiance values in the quiet Sun follow a lognormal distribution. This is irrespective of whether the distribution is made over a spatial scan or over a time series. We show that these distributions can be reproduced by our simple model.
The method of detection of dust in the stratosphere and mesosphere by the twilight sky background observations is being considered. The polarization measurements are effective for detection of the meteoric dust scattering on the background consisting basically of troposphere multiple scattering. The method is based on the observed and explained polarization properties of the sky background during different stages of twilight. It is used to detect the mesosphere dust after the Leonids maximum in 2002 and to investigate its evolution. The polarization method takes into account the multiple scattering and sufficient contribution of moonlight scattering background and turns out to be more sensitive than existing analogs used in the present time.
The anomalous X-ray pulsar 4U 0142+61 was recently detected in the mid infrared bands with the SPITZER Observatory (Wang, Chakrabarty & Kaplan 2006). This observation is the first instance for a disk around an AXP. From a reanalysis of optical and infrared data, we show that the observations indicate that the disk is likely to be an active disk rather than a passive dust disk beyond the light cylinder, as proposed in the discovering paper. Furthermore, we show that the irradiated accretion disk model can also account for all the optical and infrared observations of the anomalous X-ray pulsars in the persistent state.
To prepare for the unprecedented spatial and spectral resolution provided by ALMA and Herschel/HIFI, chemical models are being benchmarked against each other. It is obvious that chemical models also need well-constrained observations that can serve as references. Photo-dissociation regions (PDRs) are particularly well suited to serve as references because they make the link between diffuse and molecular clouds, thus enabling astronomers to probe a large variety of physical and chemical processes. At a distance of 400 pc (1" corresponding to 0.002 pc), the Horsehead PDR is very close to the prototypical kind of source (i.e. 1D, edge-on) needed to serve as a reference to models.
We test models for the generation of X-rays in accreting T Tauri stars (TTS), using X-ray data from the classical TTS T Tau. High-resolution spectroscopy from the Reflection Grating Spectrometers on XMM-Newton is used to infer electron densities, element abundances and the thermal structure of the X-ray source. We also discuss the ultraviolet light curve obtained by the Optical Monitor, and complementary ground-based photometry. A high-resolution image from Chandra constrains contributions from the two companions of T Tau N. The X-ray grating spectrum is rich in emission lines, but shows an unusual mixture of features from very hot (~30 MK) and very cool (1-3 MK) plasma, both emitted by similar amounts of emission measure. The cool plasma confirms the picture of a soft excess in the form of an enhanced OVII/OVIII Lya flux ratio, similar to that previously reported for other accreting TTS. Diagnostics from lines formed by this plasma indicate low electron densities (<~ 1E10 cm-3). The Ne/Fe abundance ratio is consistent with a trend in pre-main sequence stars in which this ratio depends on spectral type, but not on accretion. On the basis of line density diagnostics, we conclude that the density of the cool ``soft-excess'' plasma is orders of magnitude below that predicted for an accretion shock, assuming previously determined accretion rates of (3-6)E-8 M_sun/y. We argue that loading of magnetic field lines with infalling material suppresses the heating process in a part of the corona. We thus suggest that the X-ray production of T Tau is influenced by the accretion process although the X-rays may not form in the bulk of the accretion footpoints.
We report here results from a Chandra ACIS observation of the stellar populations in and around the Messier 17 H II region. The field reveals 886 sources, 771 of which have stellar counterparts in infrared images. In addition to comprehensive tables of X-ray source properties, several results are presented: * The X-ray Luminosity Function is calibrated to that of the Orion Nebula Cluster population to infer a total population of roughly 8000--10,000 stars * About 40% of the ACIS sources are heavily obscured with A_V > 10 mag. Some are concentrated around well-studied star-forming regions but most are distributed across the field. X-ray emission is detected from 64 of the hundreds of Class I protostar candidates that can be identified by near- and mid-infrared colors. These constitute the most likely protostar candidates known in M17. * The spatial distribution of X-ray stars is complex: we find a new embedded cluster, a 2 pc-long arc of young stars along the southwest edge of the M17 H II region, and 0.1 pc substructure within various populations. These structures may indicate that the populations are dynamically young. * All (14/14) of the known O stars but only about half (19/34) of the known B0--B3 stars in the M17 field are detected. Six of these stars exhibit very hard thermal plasma components (kT>4 keV) that may be due to colliding wind binaries. More than 100 candidate new OB stars are found, including 28 X-ray detected intermediate- and high-mass protostar candidates with infrared excesses. * Only a small fraction (perhaps 10%) of X-ray selected high- and intermediate- mass stars exhibit K-band emitting protoplanetary disks, providing further evidence that inner disks evolve very rapidly around more massive stars.
The majority of X-ray-detected rotation-powered millisecond pulsars (MSPs) appear to exhibit predominantly thermal emission, believed to originate from the heated magnetic polar caps of the pulsar. In the nearest MSP, J0437--4715 a faint PL is also observed at >3 keV, usually associated with magnetospheric emission processes. However, the hard emission in this and other similar MSPs may instead be due to weak Comptonization of the thermal polar cap emission by energetic electrons/positrons of small optical depth most likely in the pulsar magnetosphere. This spectral model implies that all soft X-rays are of purely thermal origin, which has important implications in the study of neutron stars.
We present the results of a 53 ks long Chandra observation of the dipping source XB 1254--690. During the observation neither bursts or dips were observed. From the zero-order image we estimated the precise X-ray coordinates of the source with a 90% uncertainty of 0.6\arcsec. Since the lightcurve did not show any significant variability, we extracted the spectrum corresponding to the whole observation. We confirmed the presence of the \ion{Fe}{xxvi} K$_\alpha$ absorption lines with a larger accuracy with respect to the previous XMM EPIC pn observation. Assuming that the line width were due to a bulk motion or a turbulence associated to the coronal activity, we estimate that the lines were produced in a photoionized absorber between the coronal radius and the outer edge of the accretion disk.
We investigate the relation between the X-ray nuclear emission, optical emission line, radio luminosity and black hole mass for a sample of nearby Seyfert galaxies. Strong linear correlations between the 2-10 keV and [OIII], radio luminosities have been found, showing the same slopes found in quasars and luminous Seyfert galaxies, thus implying independence from the level of nuclear activity displayed by the sources. Moreover, despite the wide range of Eddington ratios (L/L(Edd)) tested here (six orders of magnitude, from 0.1 down to 10^(-7), no correlation is found between the X-ray, optical emission lines, radio luminosities and the black hole mass. These results suggest that low luminosity Seyfert galaxies are a scaled down version of luminous AGN and probably are powered by the same physical processes.
We report on XMM-Newton observations of the Black Widow pulsar, PSR B1957+20. The pulsar's X-ray emission is non-thermal and best modeled with a single powerlaw spectrum of photon index 2.03^{+0.51}_{-0.36}. No coherent X-ray pulsations at the pulsar's spin-period could be detected, though a strong binary-phase dependence of the X-ray flux is observed for the first time. The data suggest that the majority of the pulsar's X-radiation is emitted from a small part of the binary orbit only. We identified this part as being near to where the radio eclipse takes place. This could mean that the X-rays from PSR B1957+20 are mostly due to intra-shock emission which is strongest when the pulsar wind interacts with the ablated material from the companion star.
We present X-ray and multi-frequency radio observations of the central radio sources in several X-ray cavity systems. We show that targeted radio observations are key to determining if the lobes are being actively fed by the central AGN. Low frequency observations provide a unique way to study both the lifecycle of the central radio source as well as its energy input into the ICM over several outburst episodes.
Optical novae have recently been identified as the major class of supersoft X-ray sources in M31 based on ROSAT and early XMM-Newton and Chandra observations. This paper reports on a search for X-ray counterparts of optical novae in M31 based on archival Chandra HRC-I and ACIS-I as well as XMM-Newton observations of the galaxy center region obtained from July 2004 to February 2005. We systematically determine X-ray brightness or upper limit for counterparts of all known optical novae with outbursts between November 2003 to the end of the X-ray coverage. In addition, we determine the X-ray brightnesses for counterparts of four novae with earlier outbursts. For comparison with the X-ray data we created a catalogue of optical novae in M31 based on our own nova search programs and on all novae reported in the literature. We collected all known properties and named the novae consistently following the CBAT scheme. We detect eleven out of 34 novae within a year after the optical outburst in X-rays. While for eleven novae we detect the end of the supersoft source phase, seven novae are still bright more than 1200, 1600, 1950, 2650, 3100, 3370 and 3380 d after outburst. One nova is detected to turn on 50 d, another 200 d after outburst. Three novae unexpectedly showed short X-ray outbursts starting within 50 d after the optical outburst and lasting only two to three months. The X-ray emission of several of the novae can be characterized as supersoft from hardness ratios and/or X-ray spectra or by comparing HRC-I count rates with ACIS-I count rates or upper limits. The number of detected optical novae at supersoft X-rays is much higher than previously estimated (>30%). We use the X-ray light curves to estimate the burned masses of the White Dwarf and of the ejecta.
Special relativistic and strong gravity effects are clearly seen in X-ray energy spectra from AGN. Most important here are the broad profiles of the Fe Kalpha line observed in a large fraction of sources. These indicate that X-ray generation and reprocessing takes place very close to the central black hole. Here we explore consequences of such effects on X-ray variability. We perform computations of a possible quasi-periodic signal from a Keplerian motion of primary X-ray source. We also study in some details the light-bending model of variability of the X-ray reprocessed component, extending previous work on the subject.
We present the first results of a large ACS Survey of Galactic globular clusters. This Hubble Space Telescope (HST) Treasury project is designed to obtain photometry with S/N > ~10 for main sequence stars with masses > ~0.2Msun in a sample of globulars using the Advanced Camera for Surveys (ACS) Wide Field Channel. Here we focus on clusters without previous HST imaging data. These include NGC 5466, 6779, 5053, 6144, Palomar 2, E 3, Lynga 7, Palomar 1, and NGC 6366. Our CMDs extend reliably from the horizontal branch to as much as seven magnitudes fainter than the main sequence turnoff and represent the deepest CMDs published to-date for these clusters. Using fiducial sequences for three standard clusters (M92, NGC 6752, and 47 Tuc) with well-known metallicities and distances, we perform main sequence fitting on the target clusters in order to obtain estimates of their distances and reddenings. These comparisons along with fitting the cluster main sequences to theoretical isochrones yield ages for the target clusters. We find that the majority of the clusters have ages that are consistent with the standard clusters at their metallicities. The exceptions are E 3 which appears ~2 Gyr younger than 47 Tuc, and Pal 1, which could be as much as 8 Gyr younger than 47 Tuc.
This paper proposes an explanation for the Pioneer anomaly: an unexplained Sunward acceleration of 8.74 +/- 1.33 x 10^-10 m s^-2 seen in the behaviour of the Pioneer probes. Two hypotheses are made: (1) Inertia is a reaction to Unruh radiation and (2) this reaction is weaker for low accelerations because some wavelengths in the Unruh spectrum do not fit within a limiting scale (twice the Hubble distance) and are disallowed: a process similar to the Casimir effect. When these ideas are used to model the Pioneer crafts' trajectories there is a slight reduction in their inertial mass, causing an anomalous Sunward acceleration of 6.9 +/- 3.5 x 10^-10 m s^-2 which agrees within error bars with the observed Pioneer anomaly beyond 10 AU from the Sun. This new scheme is appealingly simple and does not require adjustable parameters. However, it also predicts an anomaly within 10 AU of the Sun, which has not been observed. Various observational tests for the idea are proposed.
The contact binary AW UMa has an extreme mass ratio, with the more massive component close to the main sequence, while the low mass star at q ~ 0.1 has a much larger radius than a main sequence star of a comparable mass. We propose that the secondary has almost exhausted hydrogen in its center and is much more advanced in its evolution, as suggested by Stepien. Presumably the secondary lost most of its mass during its evolution with part of it transferred to the present primary. After losing a large fraction of its angular momentum, the binary will evolve into a system of FK Com type.
Working with the submillimetre continuum map of the Perseus molecular cloud (Hatchell et al. 2005), we aimed to determine the evolutionary stage of each submm core in Perseus, and investigate the lifetimes of these phases. We compile spectral energy distributions (SEDs) from 2MASS, Spitzer IRAC, Michelle, IRAS, SCUBA and Bolocam data. Sources are classified starless/protostellar on the basis of infrared and/or outflow detections and Class I/Class 0 on the basis of Tbol, Lbol/Lsmm and F_{3.6}/F_{850}. In order to investigate the dependence of these evolutionary indicators on mass, we construct radiative transfer models of Class 0 sources. Of the submm cores, 56/103 (54%) are confirmed protostars on the basis of infrared emission or molecular outflows. Of these, 22 are classified Class 1 on the basis of three evolutionary indicators, 34 are Class 0, and the remaining 47 are assumed starless. Perseus contains a much greater fraction of Class 0 sources than either Taurus or Rho Oph. Comparing the protostellar with the T Tauri population, the lifetime of the protostellar phase in Perseus is 0.25-0.67 Myr (95% confidence limits). The relative lifetime of the Class 0 and Class 1 phases are similar. We find that for the same source geometry but different masses, evolutionary indicators such as Tbol vary their value. It is therefore not always appropriate to use a fixed threshold to separate Class 0 and Class I sources. More modelling is required to determine the observational characteristics of the Class 0/Class I boundary over a range of masses.
The $^{13}C$ substitutions of molecule $HC_7N$ were observed in TMC-1 using
the J = 12 - 11, J = 13 - 12 rotational transitions in the frequency range 12.4
to 13.6 GHz. We present the first detection the $^{13}C$ isotopic species of
$HC_7N$ in the interstellar medium, based on the average of a number of weak
rotational transitions.
This paper describes the calibration and data averaging process that is also
used in a search for large cyanopolyyne molecules in TMC-1 using the 100m
Robert C. Byrd Green Bank Telescope (GBT). The capabilities of the GBT 11 to 15
GHz observing system are described along with a discussion of numerical methods
for averaging observations of a number of weak spectral lines to detect new
interstellar molecules.
Discovery of hot Jupiter exo-planets, those with anomalously inflated size and low density relative to Jupiter, has evoked much discussion as to possible sources of internal heat production. But to date, no explanations have come forth that are generally applicable. The explanations advanced typically involve presumed tidal dissipation and/or converted incident stellar radiation. The present, brief communication suggests a novel interfacial nuclear fission-fusion source of internal heat production for hot Jupiters that has been overlooked by theoreticians and which has potentially general applicability.
We present {\it Spitzer}/IRAC observations of the L5 dwarf, 2MASSI J1315309-264951 (2M1315). This ultracool dwarf is known to display strong emission in the H$\alpha$ line. The SED for this object does not show any IR excess, that would indicate the presence of an accretion disk. Although the IRAC colors for 2M1315 are consistent with other L dwarfs, they seem to be redder by $\sim$0.1 mag compared to the other L5 dwarfs, and more like the late-type L dwarfs. The existing six epochs of spectroscopy suggest that the emission in H$\alpha$ is not persistent, but shows long-term variability between a flare value of $\sim$100 $\AA$ and a quiescent value of $\sim$25 $\AA$. Chromospheric activity seems to be the most likely cause, which is also indicated by the detection of Na I D lines in emission (Fuhrmeister et al.). We have measured a proper motion of 0.79$\arcsec\pm$ 0.06$\arcsec$/yr, that corresponds to a tangential velocity of $\sim$81 km/s, at a distance of $\sim$22 pc. The high $V_{tan}$ for this object suggests an old age. Evolutionary models indicate lower limits of 3.3 Gyr (Chabrier et al.) or 1.4 Gyr (Burrows et al.) for this magnetically active L dwarf to be a stable hydrogen-burning star. There seem to be no observational differences between this old L dwarf that has H$\alpha$ emission and the other field L dwarfs without it.
In the past few years observations by high-resolution space imaging telescopes and spectrometers have confirmed that a great variety of MHD waves are supported in the solar corona of a low-beta plasma and fine structure. MHD waves are an important diagnostic tool for the determination of the physical parameters of coronal loops, dubbed {\em coronal seismology}. In this paper, I will review recent results of both propagating and standing waves observed with SOHO and TRACE, and discuss the wave damping and excitation mechanisms as well as some applications of coronal seismology based on recent numerical simulations and theories in relation to the observations.
Over 24 years of synoptic data from the NSO Kitt Peak Vacuum Telescope is used to investigate the coherency and source of the 27-day (synodic) periodicity that is observed over multiple solar cycles in various solar-related time series. A strong 27.03-day period signal, recently reported by Neugebauer et al. (2000), is clearly detected in power spectra of time series from integrated full-disk measurements of the magnetic flux in the 868.8 nm Fe I line and the line equivalent width in the 1083.0 nm He I line. Using spectral analysis of synoptic maps of photospheric magnetic fields, in addition to constructing maps of the surface distribution of activity, we find that the origin of the 27.03-day signal is long-lived complexes of active regions in the northern hemisphere at a latitude of approximately 18 degrees. In addition, using a new time series analysis technique which utilizes the phase variance of a signal, the coherency of the 27.03-day period signal is found to be significant for the past two decades. However, using the past 120 years of the sunspot number time series, the 27.03-day period signal is found to be a short-lived, no longer than two 11-year solar cycles, quasi-stationary signal.
Gamma-ray bursts are among the most powerful and remote events in the universe. It is commonly thought that these explosions originate inside fireballs expanding ultra-relativistically. Here we report a direct measurement of the relativistic expansion velocity of the fireball. Using the robotic telescope REM located in Chile we were able to catch the infrared afterglow of two gamma-ray bursts before the early maximum. By measuring the delay between the burst onset and the peak of the afterglow light curve, we determine the fireball initial Lorentz factor to be about 400, corresponding to a velocity >99.999% of the light speed.
The UKIRT Infrared Deep Sky Survey (UKIDSS) is the first of a new generation of hemispheric imaging projects to extend the work of the Two Micron All Sky Survey (2MASS) by reaching three magnitudes deeper in YJHK imaging, to K=18.2 (5-sigma, Vega) over wide fields. Better complementing existing optical surveys such as the Sloan Digital Sky Survey (SDSS), the resulting public imaging catalogues provide new photometry of rare object samples too faint to be reached previously. The first data release of UKIDSS has already surpassed 2MASS in terms of photons gathered, and using this new dataset we examine the near-infrared properties of 2837 quasars found in the SDSS and newly catalogued by the UKIDSS in ~189 square degrees. The matched quasars include the RA range 22hr to 4hr on the Southern Equatorial Stripe (SDSS Stripe 82), an area of significant future followup possibilities with deeper surveys and pointed observations. The sample covers the redshift and absolute magnitude ranges 0.08<z<5.03 and -29.5<M_i<-22.0, and 98 per cent of SDSS quasars have matching UKIDSS data. We discuss the photometry, astrometry, and various colour properties of the quasars. We also examine the effectiveness of quasar/star separation using the near-infrared passbands. The combination of SDSS ugriz photometry with the YJHK near-infrared photometry from UKIDSS over large areas of sky has enormous potential for advancing our understanding of the quasar population.
We describe the angular power spectrum of unresolved 3.6 micron IR light in Spitzer GOODS fields. The amplitude of the anisotropy spectrum decreases with decreasing flux threshold to which resolved sources are removed from images. When all pixels brighter than a Vega magnitude of 24.6 are removed, the amplitude of the power spectrum at arcminute angular scales can be described with an extra component of z>8 sources with a IRB contribution around 0.4 nW m^-2 sr-1. The shape of the power spectrum, however, is more consistent with that expected for unresolved, faint galaxies at lower redshifts with Vega magnitudes fainter than 23 with a total 3.6 micron intensity between 0.1 to 0.8 nW m^-2 sr^-1. We confirm this assumption by showing that large-scale power decreases rapidly when the unresolved clustering spectrum is measured from a processed HDF-N IRAC image where locations of faint ACS sources with no IR counterparts were also masked. Based on resolved counts and unresolved fluctuations, we find that, at most, about 7.0 nW m^-2 sr^-1 can be ascribed to galaxies.
We study the degree of chemical enrichment in the Broad Emission Line Regions (BELRs) of two QSOs with unusually strong nitrogen emission lines. The N V 1240/ C IV 1549 intensity ratio is often used as a metallicity indicator for QSOs. The validity of this approach can be tested by studying objects in which the N IV] and N III] lines, in addition to N V, are unusually strong and easily measurable. If all of these ionization states of nitrogen point to the same metallicity, it implies that the large N V strengths observed in most QSOs are not due to some peculiarity of the N V 1240 line. This test had previously been applied to Q0353-383, a QSO long known to have extremely strong N III] and N IV] lines, with the result supporting high metallicity in that object. Here we make the same check in two other QSOs with very strong nitrogen lines, as a step towards using such QSOs to better probe the early chemical enrichment histories of their host galaxies. J1254+0241 has a metallicity of about 10x solar, with good agreement between the abundance results from different line ratios. J1546+5253 has a more moderate metallicity, about 5x solar, but the abundances determined from different line ratios show a much wider scatter than they do for J1254+0241 or Q0353-383. This QSO also has an unusual low-ionization emission line spectrum similar to some low-ionization BAL QSOs and to the unusual AGN I Zw 1. We attribute the peculiarities in its spectrum to some combination of unusual structure and/or unusual physical conditions in its BELR. Our results further affirm the validity of the N V/C IV ratio as an abundance indicator in QSOs.
In braneworld gravity models with a finite AdS curvature in the extra dimension, the AdS/CFT correspondence leads to a prediction for the lifetime of astrophysical black holes that is significantly smaller than the Hubble time, for asymptotic curvatures that are consistent with current experiments. Using the recent measurements of the position, three-dimensional spatial velocity, and mass of the black hole XTE J1118+480, I calculate a lower limit on its kinematic age of 11 Myr (95% confidence). This translates into an upper limit for the asymptotic AdS curvature in the extra dimensions of 0.08 mm, which significantly improves the limit obtained by table-top experiments of sub-mm gravity.
We present deep near-infrared JHK imaging of four 10'x10' fields. The observations were carried out as part of the Multiwavelength Survey by Yale-Chile (MUSYC) with ISPI on the CTIO 4m telescope. The typical point source limiting depths are J~22.5, H~21.5, and K~21 (5sigma; Vega). The effective seeing in the final images is ~1.0". We combine these data with MUSYC UBVRIz imaging to create K-selected catalogs that are unique for their uniform size, depth, filter coverage, and image quality. We investigate the rest-frame optical colors and photometric redshifts of galaxies that are selected using common color selection techniques, including distant red galaxies (DRGs), star-forming and passive BzKs, and the rest-frame UV-selected BM, BX, and Lyman break galaxies (LBGs). These techniques are effective at isolating large samples of high redshift galaxies, but none provide complete or uniform samples across the targeted redshift ranges. The DRG and BM/BX/LBG criteria identify populations of red and blue galaxies, respectively, as they were designed to do. The star-forming BzKs have a very wide redshift distribution, a wide range of colors, and may include galaxies with very low specific star formation rates. In comparison, the passive BzKs are fewer in number, have a different distribution of K magnitudes, and have a somewhat different redshift distribution. By combining these color selection criteria, it appears possible to define a reasonably complete sample of galaxies to our flux limit over specific redshift ranges. However, the redshift dependence of both the completeness and sampled range of rest-frame colors poses an ultimate limit to the usefulness of these techniques.
The Baldwin Effect, a negative correlation between emission-line equivalent width and luminosity in active galactic nuclei, is still of interest as a diagnostic of accretion physics nearly thirty years after its discovery. This review examines recent developments in the study of correlations between line and continuum emission in AGNs, as measured both in ensembles and in individual sources.
Gigantic cosmological gamma-ray bursts have fallen into a dichotomy of long and short bursts, each with a very different origin. The discovery of an oddball burst calls for a rethink of that classification.
We investigate, in a set of 3D numerical simulations of driven, magnetized, isothermal, and self-gravitating molecular clouds (MCs), the statistical correlations between the energy ratios (thermal/gravity, and kinetic/gravity) of clumps and cores (CCs) identified in the simulations and gravitational binding indicators commonly used in observational studies such as the Jeans number, J_{c}, and the virial parameter, alpha_{vir}. In the energy ratios, we consider the surface energy terms which account for the effects of the environment on the clump gravitational boundedness. We find that: a) J_{c} and the thermal/gravitational energy ratios are well correlated, b) alpha_{vir} and the (thermal+kinetic)/gravity or kinetic/gravity energy ratios are poorly correlated, additionally affected by the ambiguity of the compressive or dispersive effect of the velocity field. This result suggest that the use of alpha_{vir} estimates in the observations is only useful to assess the kinetic+thermal energy content of a CC and not its gravitational boundedness. Finally, we discuss briefly the possibility of measuring the kinetic energy surface term directly in the observations.
We apply in this paper the statefinder parameters to the interacting phantom energy with dark matter. There are two kinds of scaling solutions in this model. It is found that the evolving trajectories of these two scaling solutions in the statefinder parameter plane are quite different, and that are also different from the statefinder diagnostic of other dark energy models.
Supernovae resulting from the deaths of massive stars span a wide range of peak luminosities, usually reached within 30 days after explosion. Their diversity depends on the star's initial mass and rate of mass loss during its lifetime. Stars born with initial masses above 40 times the mass of the Sun are expected to shed their hydrogen envelopes to expose their He core before they die, resulting in supernovae with little or no evidence for hydrogen gas observed in their spectrum. Here we report on our discovery and follow-up observations of SN 2006gy, which reveal that it reached a peak luminosity at least 3 times greater than any other supernova seen to date, and far greater than most others. We find that a large ejected mass of order 100 Solar masses is required to power its enormous total radiated luminosity, indicating a total kinetic energy of more than 10^52 ergs. This suggests that SN 2006gy marked the demise of an extremely massive star that, contrary to expectations, failed to shed its massive hydrogen envelope. A circumstellar shell that surrounded the progenitor star has a large mass and expansion speed, effectively ruling-out certain types of progenitor stars. Based on a number of lines of evidence, we suggest that the progenitor was a very massive evolved object like eta Carinae, which is the most luminous star known in the Milky Way. These observations suggest that the most massive stars can explode earlier than expected, and can create bright supernovae instead of dying ignominious deaths through direct collapse to a black hole. If such a fate is common, then supernovae from the first stars in the universe, which may have been extremely massive, will be more numerous than previously believed.
We report on a recent 90 cm wide-field VLBI survey of two 3.1 deg^2 fields using the VLBA, Westerbork and Jodrell Bank telescopes. In-beam calibration was used to calibrate each field, the process was simplified by imaging the calibrators in DIFMAP and transferring the calibration solutions to AIPS using the newly developed DIFMAP task - cordump. We detected and imaged 13 out of the 141 sources originally detected by the low resolution (54") WENSS survey of the same two fields. The sources were detected at 7-12 sigma levels above the image noise, had total flux densities ranging between 85-1640 mJy and were between 16'-58' from the phase centre of each field. This is the first systematic (and non-biased), deep, high resolution survey of the low frequency radio sky. These initial results suggest that new instruments such as LOFAR should detect many compact radio sources and that plans to extend these arrays to baselines of several thousand kilometres are warranted.
We have investigated the final accretion stage of terrestrial planets from Mars-mass protoplanets that formed through oligarchic growth in a disk comparable to the minimum mass solar nebula (MMSN), through N-body simulation including random torques exerted by disk turbulence due to Magneto-Rotational-Instability. For the torques, we used the semi-analytical formula developed by Laughlin et al.(2004). The damping of orbital eccentricities (in all runs) and type-I migration (in some runs) due to the tidal interactions with disk gas are also included. We found that the orbital eccentricities pumped up by the turbulent torques and associated random walks in semimajor axes tend to delay isolation of planets, resulting in more coagulation of planets than in the case without turbulence. The eccentricities are still damped after planets become isolated. As a result, the number of final planets decreases with increase in strength of the turbulence, while Earth-mass planets with small eccentricities are still formed. In the case of relatively strong turbulence, the number of final planets are 4-5 at 0.5-2AU, which is consistent with Solar system, for relatively wide range of disk surface density (~10^{-4}-10^{-2} times MMSN).
We have conducted J, H, and Ks imaging observations for the Coalsack Globule 2 with the SIRIUS infrared camera on the IRSF 1.4 m telescope at SAAO, and determined the color excess ratio, E(J-H)/E(H-Ks). The ratio is determined in the same photometric system as our previous study for the rho Oph and Cha clouds without any color transformation; this enables us to directly compare the near-infrared extinction laws among these regions. The current ratio E(J-H)/E(H-Ks) = 1.91 +- 0.01 for the extinction range 0.5 < E(J-H) <1.8 is significantly larger than the ratios for the rho Oph and Cha clouds (E(J-H)/E(H-Ks) = 1.60-1.69). This ratio corresponds to a large negative index alpha = 2.34 +- 0.01 when the wavelength dependence of extinction is approximated by a power law which might indicate little growth of dust grains, or larger abundance of dielectric non-absorbing components such as silicates, or both in this cloud. We also confirm that the color excess ratio for the Coalsack Globule 2 has a trend of increasing with decreasing optical depth, which is the same trend as the rho Oph and Cha clouds have.
We report simultaneous multicolor near-infrared (NIR) observations of the supernova associated with x-ray Flash 060218 during the first 16 days after the high energy event. We find that the light curve rises and peaks relatively fast compared to other SN Ic, with the characteristic broad NIR peak seen in all three bands. We find that the rise profile before the peak is largely independent of NIR wavelength, each band appearing to transition into a plateau phase around day 10--13. Since the light curve is in the plateau phase when our observations end at day 16, we can only place limits on the peak absolute magnitudes, but we estimate that SN 2006aj is one of the lowest NIR luminosity XRF/GRB associated SNe observed to date. The broad peaks observed in the {\em JHK$_s$} bands point to a large increase in the NIR contribution of the total flux output from days 10--16. This evolution can be seen in the broad color and SED diagrams constructed using {\em UBVRIJHK$_s$} monochromatic flux measurements for the first 16 days of the event. Ultimately, a 10-day rise time would make SN 2006aj an extremely fast rise SN Ic event, faster than SN 1998bw and SN 2003dh, which combined with its underluminous nature, indicates a lower amount of $^{56}$Ni ejected by the progenitor compared to other XRF/GRB-SNe. Furthermore, the lack of significant color change during the rise portion of the burst points to little or no spectral evolution over the first 10 days of activity in the NIR.
Aims. The properties of the early-type stars in the core of the Westerlund2
cluster are examined in order to establish a link between the cluster and the
very massive Wolf-Rayet binary WR20a as well as the HII complex RCW49.
Methods. Photometric monitoring as well as spectroscopic observations of
Westerlund2 are used to search for light variability and to establish the
spectral types of the early-type stars in the cluster core.
Results. The first light curves of the eclipsing binary WR20a in B and V
filters are analysed and a distance of 8kpc is inferred. Three additional
eclipsing binaries, which are probable late O or early B-type cluster members,
are discovered, but none of the known early O-type stars in the cluster
displays significant photometric variability above 1% at the 1-sigma level. The
twelve brightest O-type stars are found to have spectral types between O3 and
O6.5, significantly earlier than previously thought.
Conclusions. The distance of the early-type stars in Westerlund2 is
established to be in excellent agreement with the distance of WR20a, indicating
that WR20a actually belongs to the cluster. Our best estimate of the cluster
distance thus amounts to 8.0pm1.4kpc. Despite the earlier spectral types, the
currently known population of early-type stars in Westerlund2 does not provide
enough ionizing photons to account for the radio emission of the RCW49 complex.
This suggests that there might still exist a number of embedded early O-stars
in RCW49.
Observations of the optical afterglow of GRB 041006 with the Kiso Observatory 1.05 m Schmidt telescope, the Lulin Observatory 1.0 m telescope and the Xinglong Observatory 0.6 m telescope. Three-bands (B, V and R) of photometric data points were obtained on 2004 October 6, 0.025-0.329 days after the burst. These very early multi band light curves imply the existence of a color dependent plateau phase. The B-band light curve shows a clear plateau at around 0.03 days after the burst. The R band light curve shows the hint of a plateau, or a possible slope change, at around 0.1 days after the burst. The overall behavior of these multi-band light curves may be interpreted in terms of the sum of two separate components, one showing a monotonic decay the other exhibiting a rising and a falling phase, as described by the standard afterglow model.
Context: Existing SWAS observations and future HIFI/Herschel data require a clear sense of the information content of water emission and absorption lines. Aims: Investigate wether the ground-state transition of ortho-H2O, 1_(10)-1_(01), at 557GHz can be used to measure the column density throughout an interstellar cloud. Methods: We make use of a multi-zone escape probability code suitable for the treatment of molecular line emission. Results: For low abundances, i.e., X(H2O)=<10^(-9), the intensity of the 1_(10)-1_(01) transition scales with the total column of H2. However, this relationship breaks down with increasing abundance, i.e., optical depth, due to line trapping and -- for T_(dust)>=25K, X(H2O)=<10^(-8) and n~10^4 cm^(-3) -- absorption of the dust continuum. Conclusions: An observed decline in intensity per column, expected if H2O is a surface tracer, does not necessarily mean that the water is absent in the gas phase at large columns, but can be caused by line trapping and subsequent collisional de-excitation. To determine the amount of water vapour in the interstellar medium, multiple line measurements of optically thin transitions are needed to disentangle radiative transfer and local excitation effects.
AIMS: We develop an optimization principle for computing stationary MHD equilibria. METHODS: Our code for the self-consistent computation of the coronal magnetic fields and the coronal plasma uses non-force-free MHD equilibria. Previous versions of the code have been used to compute non-linear force-free coronal magnetic fields from photospheric measurements. The program uses photospheric vector magnetograms and coronal EUV images as input. We tested our reconstruction code with the help of a semi-analytic MHD-equilibrium. The quality of the reconstruction was judged by comparing the exact and reconstructed solution qualitatively by magnetic field-line plots and EUV-images and quantitatively by several different numerical criteria. RESULTS: Our code is able to reconstruct the semi-analytic test equilibrium with high accuracy. The stationary MHD optimization code developed here has about the same accuracy as its predecessor, a non-linear force-free optimization code. The computing time for MHD-equilibria is, however, longer than for force-free magnetic fields. We also extended a well-known class of nonlinear force-free equilibria to the non-force-free regime for purposes of testing the code. CONCLUSIONS: We demonstrate that the code works in principle using tests with analytical equilibria, but it still needs to be applied to real data.
Utilizing two Chandra High Resolution Camera (HRC-I) observations with an epoch separation of somewhat more than five years, we have measured the proper motion of the central compact object, RX J0822-4300, in the supernova remnant Puppis-A for the first time. The position of RX J0822-4300 is found to be different by 0.574 +/- 0.184 arcsec, implying a proper motion of 107.49 +/- 34.46 mas/yr with a position angle of 241 degree +/- 24 degree. For a distance of 2.2 kpc, this proper motion is equivalent to a recoil velocity of 1121.79 +/- 359.60 km/s. Both the magnitude and the direction of the proper motion are in agreement with the birth place of RX J0822-4300 being near to the optical expansion center of the supernova remnant. Although the positional shift inferred from the current data is significant at a ~ 3 sigma level only, one or more future HRC-I observations can obtain a much larger positional separation and further constrain the measurement.
It is widely believed that the heating of the chromosphere in quiet-Sun internetwork regions is provided by dissipation of acoustic waves that are excited by the convective motions close to the top of the convection zone and in the photospheric overshoot layer. This view lately became challenged by observations suggesting that the acoustic energy flux into the chromosphere is too low, by a factor of at least ten. Based on a comparison of TRACE data with synthetic image sequences for a three-dimensional simulation extending from the top layers of the convection zone to the middle chromosphere, we come to the contradicting conclusion that the acoustic flux in the model provides sufficient energy for heating the solar chromosphere of internetwork regions. The role of a weak magnetic field and associated electric current sheets is also discussed.
We report the discovery of an X-ray nebula associated with the nearby millisecond pulsar PSR J2124-3358. This is the first time that extended emission from a solitary millisecond pulsar is detected. The emission extends from the pulsar to the northwest by ~ 0.5 arcmin. The spectrum of the nebular emission can be modeled by a power law spectrum with photon index of 2.2 +/-0.4. This is inline with the emission being originated from accelerated particles in the post shock flow.
The neutrino-driven wind from a nascent neutron star at the center of a supernova expands into the earlier ejecta of the explosion. Upon collision with this slower matter the wind material is decelerated in a wind termination shock. By means of hydrodynamic simulations in spherical symmetry we demonstrate that this can lead to a large increase of the wind entropy, density, and temperature, and to a strong deceleration of the wind expansion. The consequences of this phenomenon for the possible r-process nucleosynthesis in the late wind still need to be explored in detail. Two-dimensional models show that the wind-ejecta collision is highly anisotropic and could lead to a directional dependence of the nucleosynthesis even if the neutrino-driven wind itself is spherically symmetric.
Thermal radiation from hot polar caps is examined in radio pulsars with drifting subpulses. It is argued that if these subpulses correspond to sparking discharges of the inner acceleration region right above the polar cap surface then a simple relationship between the observed subpulse drift rate in radio and thermal X-ray luminosity from the polar cap heated by sparks should exist. This relationship is derived and tested in pulsars for which an appropriate good quality data is available.
We present recent X-ray and radio observations of pulsar wind nebulae discovered in EGRET error boxes. Two XMM-Newton observations show the X-ray extent of the rapidly moving PWN associated with the variable gamma-ray source 3EG J1809-2328, and a trail coming from the new millisecond pulsar PSR J1614-2230 at high Galactic z. We also briefly discuss three PWN that are HESS TeV sources including a new HESS source we argue is associated with the Eel nebula in 3EG J1826-1302.
The High Energy Stereoscopic System (H.E.S.S.) is a system of four, imaging, atmospheric Cherenkov telescopes in Namibia, designed to detect very-high-energy gamma rays above ~ 100 GeV. During 2002--2003, H.E.S.S. collected data from two, young and energetic radio pulsars: the Crab and PSR B1706-44. We searched for pulsations at the lowest energies that H.E.S.S. is capable of detecting, aiming at a detection that would potentially differentiate between the two popular models of pulsar high-energy emission: the Polar Cap and the Outer Gap. No evidence for pulsed emission was found in the data, and upperlimits were derived to a 99.95% confidence level. Our assumptions and upper limit values for the two pulsars are reported.
A few topics concerning the early chemical evolution of the Milky Way are critically discussed. In particular, it is argued that: 1) Observed abundance patterns of extremely metal poor stars (of Pop. II) do not constrain the mass range of the first generation (Pop. III) stars; the latter may well be normal massive stars (10-50 Msun) or very massive ones (140-1000 Msun) or a combination of the two classes. 2) The discrepancy between primordial Li abundance (after WMAP) and the observed ``Spite plateau'' cannot be due to astration by a generation of massive Pop. III stars, as recently suggested, unless if such stars eject negligible amounts of metals. 3) The observed halo metallicity disribution may well be understood in the framework of hierarchical galaxy formation, as shown here with a simple semi-analytical model. 4) Formation of the Milky Way's halo from a myriad of smaller sub-haloes may have important implications for our understanding of the abundance patterns of r-elements, the origin of which remains still unclear.
Observations of a strong and extended positron-electron annihilation line emission in the Galactic center (GC) region by the SPI/INTEGRAL are challenging to the existing models of positron sources in the Galaxy. In this paper, we study the possibility that pulsar winds from a millisecond pulsar population in the GC produce the 511 keV line. Our preliminary estimations predict that the e+/- annihilation rate in the GC is around 5 x 10E+42 sE-1, which is consistent with the present observational constraints. Therefore, the e+/- pairs from pulsar winds can contribute significantly to the positron sources in the Galactic center region. Furthermore, since the diffusion length of positrons is short in the magnetic field, we predict that the intensity distribution of the annihilation line should follow the distribution of millisecond pulsars, which should then correlate to the mass distribution in the GC.
The X-ray emission from quasars such as 3C273 is generally agreed to arise from Compton scattering of low energy seed photons by relativistic electrons in a relativistic jet oriented close to the line of sight. However there are a number of possible models for the origin of the seed photons. In Paper I (McHardy et al 1999) we showed that the X-ray and IR variability from 3C273 was highly correlated in 1997, with the IR flux leading the X-rays by ~0.75 +/- 0.25 days. The strong correlation, and lag, supports the Synchrotron Self-Compton (SSC) model, where the seed photons are synchroton photons from the jet itself. The previous correlation was based on one moderately well sampled flare and another poorly sampled flare, so the possibility of chance correlated variability exists. Here we report on further X-ray and IR observations of 3C273 which confirm the behaviour seen in Paper I. During a 2 week period of observations we see a flare of amplitude ~25%, lasting for ~5 days, showing a high correlation between IR and X-ray variations, with the X-rays lagging by ~1.45+/- 0.15 days. These observations were not scheduled at any special time, implying that the same mechanism - almost certainly SSC - dominates the X-ray emission on most occasions and that the structure of the emission region is similar in most small flares.
The space mission STEREO will provide images from two viewpoints. An
important aim of the STEREO mission is to get a 3D view of the solar corona.
We develop a program for the stereoscopic reconstruction of
3D coronal loops from images taken with the two STEREO spacecraft.
A pure geometric triangulation of coronal features leads to ambiguities
because the dilute plasma emissions complicates the association of features in
image 1 with features in image 2. As a consequence of these problems the
stereoscopic reconstruction is not unique and multiple solutions occur.
We demonstrate how these ambiguities can be resolved with the help of
different coronal magnetic field models (potential, linear and non-linear
force-free fields). The idea is that, due to the high conductivity in the
coronal plasma, the emitting plasma outlines the magnetic field lines.
Consequently the 3D coronal magnetic field provides a proxy for the
stereoscopy which allows to eliminate inconsistent configurations.
The combination of stereoscopy and magnetic modelling is more powerful than
one of these tools alone. We test our method with the help of a model active
region and plan to apply it to the solar case as soon as
STEREO data become available.
We present here the current status of pulsar simulations for the Large Area Telescope, the main instrument on the GLAST mission. We present "PulsarSpectrum", a pulsar simulator that can reproduce with high detail gamma-ray emission from pulsars. "PulsarSpectrum" takes into account advanced timing effects, e.g. period changes with time, barycentering effects and glitches. Other ancillary tools have been built to provide the simulator with a realistic population of pulsars and their ephemerides. All these tools are currently used in the GLAST collaboration for testing the LAT Science Analysis Tools and for studying LAT capabilities for pulsar science. They have been used also for generating a simulated pulsar population for the "Data Challenge 2 (DC2)", one of the most important milestones in the development of the GLAST software. During the DC2, scientists analyzed a set of 55 days of simulated data in order to validate LAT MonteCarlo, study instrument response functions, exercise analysis tools and study LAT capabilities. This contribution also contains results of some analysis performed during DC2 on EGRET pulsars.
We present results from the first 2+1 and 3+1 simulations of the collapse of rotating stellar iron cores in general relativity employing a finite-temperature equation of state and an approximate treatment of deleptonization during collapse. We compare full 3+1 and conformally-flat spacetime evolution methods and find that the conformally-flat treatment is sufficiently accurate for the core-collapse supernova problem. We focus on the gravitational wave (GW) emission from rotating collapse, core bounce, and early postbounce phases. Our results indicate that the GW signature of these phases is much more generic than previously estimated. In addition, we track the growth of a nonaxisymmetric instability of dominant m = 1 character in two of our models that leads to prolonged narrow-band GW emission at ~ 920-930 Hz over several tens of milliseconds.
Hanle-effect observations of forbidden coronal line transitions and recently also longitudinal Zeeman-effect measurements of coronal lines show quantitative signatures of the weak coronal magnetic field. The interpretation of these observations is, however, complicated by the fact that they are the result of line-of-sight integrations through the optically thin corona. We study by means of simulated observations the possibility of applying tomographic techniques in order to reconstruct the 3D magnetic field configuration in the solar corona from these observations. The reconstruction problem relates to a family of similar problems termed vector tomography. It is shown that Zeeman data and Hanle data alone obtained from vantage points in the ecliptic plane alone are sensitive only to certain magnetic field structures. For a full reconstruction it is necessary to combine the longitudinal Zeeman and Hanle effect data.
We investigate the role of massive perturbers, such as giant molecular clouds or stellar clusters, in supplying low-angular momentum stars that pass very close to the central massive black hole (MBH) or fall into it. We show that massive pe rturbers can play an important role in supplying both binaries and single stars to the vicinity of the MBH. We discuss possible implications for the ejection of high velocity stars; for the capture of stars on tight orbits around the MBH; for the emission of gravitational waves from low-eccentricity inspiraling stars; and for the origin of the young main sequence B stars observed very near the Gal actic MBH. Massive perturbers may also enhance the the growth rate of MBHs, and may accelerate the dynamical orbital decay of coalescing binary MBHs.
Knowledge regarding the coronal magnetic field is important for the understanding of many phenomena, like flares and coronal mass ejections. Because of the low plasma beta in the solar corona the coronal magnetic field is often assumed to be force-free and we use photospheric vector magnetograph data to extrapolate the magnetic field into the corona with the help of a non-linear force-free optimization code. Unfortunately the measurements of the photospheric magnetic field contain inconsistencies and noise. In particular the transversal components (say Bx and By) of current vector magnetographs have their uncertainties. Furthermore the magnetic field in the photosphere is not necessary force-free and often not consistent with the assumption of a force-free field above. We develop a preprocessing procedure to drive the observed non force-free data towards suitable boundary conditions for a force-free extrapolation. As a result we get a data set which is as close as possible to the measured data and consistent with the force-free assumption.
Observations of high-redshift supernovae indicate that the universe is accelerating at the present stage, and we refer to the cause for this cosmic acceleration as ``dark energy''. In particular, the analysis of current data of type Ia supernovae (SNIa), cosmic large-scale structure (LSS), and the cosmic microwave background (CMB) anisotropy implies that, with some possibility, the equation-of-state parameter of dark energy may cross the cosmological-constant boundary ($w=-1$) during the recent evolution stage. The model of ``quintom'' has been proposed to describe this $w=-1$ crossing behavior for dark energy. As a single-real-scalar-field model of dark energy, the generalized ghost condensate model provides us with a successful mechanism for realizing the quintom-like behavior. In this paper, we reconstruct the generalized ghost condensate model in the light of three forms of parametrization for dynamical dark energy, with the best-fit results of up-to-date observational data.
The availability of multi-wavelength high-quality data of gamma-ray burst afterglows in the Swift era, contrary to the expectations, did not allow us to fully confirm yet one of the most fundamental features of the standard afterglow picture: the presence of an achromatic break in the decaying light curve. We briefly review the most interesting cases identified so far.
We present Chandra and VLT observations of the X-Ray Flash XRF 040812. The X-ray analysis reveals with high precision the position of a hard, fading source. A careful analysis of our I-band VLT images taken starting 17 hours after the burst led to the discovery of the optical afterglow superimposed to a bright (I=21.5) host galaxy. The optical afterglow is seen decaying with an index of 1.1. We do not detect any jet break and supernova rebrightening in the optical light curve. The bright apparent luminosity of the host galaxy allows us to get a rough estimate of the redshift, comparing with a set of GRB/XRF host galaxies with known luminosity and redshift. Such comparison suggests a redshift of XRF 040812 in the range 0.3<z<0.7. This is also consistent with the lack of emission features in our spectrum. The low inferred redshift is in agreement with the idea that XRFs are low-luminosity, closer events.
We summarize the status of art of the secular evolution of low mass X-ray binaries (LMXBs) and take a close look at the orbital period distribution of LMXBs and of binary millisecond pulsars (MSP), in the hypothesis that this latter results from the LMXB evolution. The deficiency of systems below the period gap, which in cataclysmic binaries occurs between ~ 2 and 3 hr, points to a very different secular evolution of LMXBs with respect to their counterparts containing a white dwarf compact object. The presence of several ultrashort period LMXBs (some of which are also X-ray millisecond pulsars), the important fraction of binary MSPs at periods between 0.1 and 1 day, the periods (26 and 32hr) of two ``interacting'' MSPs in Globular Clusters are other pieces of the puzzle in the period distribution. We consider the possible explanations for these peculiarities, and point out that Grindlay's old proposal that all (most of) LMXBs in the field were originally born in globular clusters must be carefully reconsidered.
We performed imaging on 49 type 2 Seyfert galaxies in 6 near- and mid-infrared bands (1-10$\mu$m). We are separating the contribution of the torus from the host galaxy by radial profile fitting techniques and we will compare the observed spectral energy distributions with theoretical models of torus emission to constrain geometrical and physical parameters.
We present results from very high signal-to-noise spectropolarimetric observations of the Seyfert 1 galaxy NGC 3783. Position Angle (PA) changes across the Balmer lines show that the scatterer is resolving the Broad-Emission Line Region (BLR). A broad component seen in polarized light and located bluewards from the H$\beta$ line very likely corresponds to HeII$\lambda4686$. The lack of PA changes across this line suggests that the region responsible for this emission appears to the scatterer as unresolved as the continuum source, in agreement with the stratified BLR structure determined from reverberation mapping.
We present results of numerical 3D MHD simulations with radiative energy transfer of fine structure in a small sunspot of about 4 Mm width. The results show the development of filamentary structure with nearly field-free gaps, interlaced by concentrations of stronger magnetic field at the interface between the umbra and the outer field-free atmosphere. Calculated synthetic images show dark cores like those seen in the observations. They are the result of an elevated $\tau=1$ surface. The magnetic field in these cores is weaker and more horizontal than for adjacent brighter structures at the photosphere. Higher up in the atmosphere there are only small variations in field strength. Movies made show an inward migration of filamentary structures very similar to the patterns seen in observations of the inner penumbra. Although the filamentary structures in the simulations are too short compared to observations, most other aspects of the simulations appear consistent with observed penumbra filamentary structures.
We discuss some basic principles of stereoscopy and their relevance to the reconstruction of coronal loops. The aim of the paper is to make the solar physicist familiar with basic stereoscopy principles and to give hints how they may apply to the analysis of data from the forthcoming STEREO mission. We disucss the geometry of the solar coronal stereo problem, give the basic principles of a tie-point reconstruction algorithm and consider ambiguities and resolution errors. Finally we mention extensions to plain stereoscopy such as a third view, a tomography-like approach and how magnetic field information can be used to improve the reconstruction.
CONTEXT: As the coronal magnetic field can usually not be measured directly, it has to be extrapolated from photospheric measurements into the corona. AIMS: We test the quality of a non-linear force-free coronal magnetic field extrapolation code with the help of a known analytical solution. METHODS: The non-linear force-free equations are numerically solved with the help of an optimization principle. The method minimizes an integral over the force-free and solenoidal condition. As boundary condition we use either the magnetic field components on all six sides of the computational box in Case I or only on the bottom boundary in Case II. We check the quality of the reconstruction by computing how well force-freeness and divergence-freeness are fulfilled and by comparing the numerical solution with the analytical solution. The comparison is done with magnetic field line plots and several quantitative measures, like the vector correlation, Cauchy Schwarz, normalized vector error, mean vector error and magnetic energy. RESULTS: For Case I the reconstructed magnetic field shows good agreement with the original magnetic field topology, whereas in Case II there are considerable deviations from the exact solution. This is corroborated by the quantitative measures, which are significantly better for Case I. CONCLUSIONS: Despite the strong nonlinearity of the considered force-free equilibrium, the optimization method of extrapolation is able to reconstruct it; however, the quality of reconstruction depends significantly on the consistency of the input data, which is given only if the known solution is provided also at the lateral and top boundaries, and on the presence or absence of flux concentrations near the boundaries of the magnetogram.
The cosmic infrared background (CIB) consists of emission from distant, dusty, star-forming galaxies. Energetically, the CIB is very important as it contains as much energy as the extragalactic optical background. The nature and evolutionary status of the objects making up the background are, however, unclear. The CIB peaks at ~150 microns, and as such is most effectively studied from space. The limited apertures of space-borne telescopes set the angular resolution that can be attained, and so even Herschel, with its 3.5m diameter, will be confusion-limited at this wavelengths at ~5mJy. The bulk of the galaxies contributing to the CIB are fainter than this, so it is difficult to study them without interferometry. Here we present the results of a preliminary study of an alternative way of probing fainter than the continuum confusion limit using far-IR imaging spectroscopy. An instrument capable of such observations is being planned for SPICA - a proposed Japanese mission with an aperture equivalent to that of Herschel and more than 2 orders of magnitude more sensitive. We investigate the potential of imaging spectrometers to break the continuum confusion limit. We have simulated the capabilities of a spectrometer with modest field of view (2'x2'), moderate spectral resolution (R~1-2000) and high sensitivity. We find that such an instrument is capable of not only detecting line emission from sources with continuum fluxes substantially below the confusion limit, but also of determining their redshifts and, where multiple lines are detected, some emission line diagnostics. We conclude that 3-D imaging spectrometers on cooled far-IR space telescopes will be powerful new tools for extragalactic far-IR astronomy.
Radio, X-ray, and HESS gamma-ray observations of the Galactic Center (GC) composite supernova remnant SNR G0.9+0.1 are used to constrain a time-dependent injection model of the downstream electron spectrum responsible for the total multiwavelength spectrum. The effect of spindown power evolution aswell as nebular field evolution is employed to reproduce the present-day multiwavelength spectrum. Assuming a nebular magnetic field decay model of typical HESS-type pulsar wind nebulae (PWN), ending with a present-day field strength of 6muG, we obtain an initial spindown power of ~ 10E+38 ergs/s if we assume a birth period and age of 43ms and 6,500 yr respectively to reproduce the properties of the SNR shell. This gives a present-day spindown power of ~ 10E+37 ergs/s, which agrees well with the present-day spindown power derived from X-ray observations.
The Gold06 SnIa dataset recently released in astro-ph/0611572 consists of five distinct subsets defined by the group or instrument that discovered and analyzed the corresponding data. These subsets are: the SNLS subset (47 SnIa), the HST subset (30 SnIa), the HZSST subset (41 SnIa), the SCP subset (26 SnIa) and the Low Redshift (LR) subset (38 SnIa). These subsets sum up to the 182 SnIa of the Gold06 dataset. We use Monte-Carlo simulations to study the statistical consistency of each one of the above subsets with the full Gold06 dataset. In particular, we compare the best fit $w(z)$ parameters (w_0,w_1) obtained by subtracting each one of the above subsets from the Gold06 dataset (subset truncation), with the corresponding best fit parameters (w^r_0,w^r_1) obtained by subtracting the same number of randomly selected SnIa from the same redshift range of the Gold06 dataset (random truncation). We find that the probability for (w^r_0,w^r_1)=(w_0,w_1) is large for the Gold06 minus SCP (Gold06-SCP) truncation but is less than 5% for the Gold06-SNLS, Gold06-HZSST and Gold06-HST truncations. This result implies that the Gold06 dataset is not statistically homogeneous. By comparing the values of the best fit (w_0,w_1) for each subset truncation we find that the tension among subsets is such that the SNLS and HST subsets are statistically consistent with each other and `pull' towards LCDM (w_0=-1,w_1=0) while the HZSST subset is statistically distinct and strongly `pulls' towards a varying w(z) crossing the line $w=-1$ from below (w_0<-1,w_1>0). We also isolate six SnIa that are mostly responsible for this behavior of the HZSST subset.
The majority of the inhomogeneities in the chemical composition of Globular Cluster (GC) stars appear due to primordial enrichment. The most studied model today claims that the ejecta of Asymptotic Giant Branch (AGB) stars of high mass -those evolving during the first ~100Myr of the Clusters life- directly form a second generation of stars with abundance anomalies. In this talk, we review the status of the art with regard to this model, whose major problems are i) the modelling of the chemical anomalies is still not fully complete, and ii) it requires an IMF peculiarly enhanced in the intermediate mass stars. The model predicts enhanced helium abundance in the stars showing chemical anomalies, and the helium abundance distribution can be roughly derived from the morphology of the horizontal branch. Such distribution may possibly help to falsify the model for the first phases of evolution of GCs. As an illustration, we compare the results of the analysis of the HB morphology of some clusters.
Star clusters are formed in molecular clouds which are believed to be the birth places of most stars. From recent observational data, Lada & Lada(2003) estimated that only 4 to 7% of the proto-clusters have survived. Many factors could cause this high infant mortality. Galactic tidal forces, close encounters with molecular clouds and shock heating are among the possible causes but they have a longer timescale than typical lifetime of molecular clouds. Another possible reason is mass loss in very beginning of cluster evolution in the form of UV radiation, stellar winds or supernova explosions. Mass loss is the main factor we study in this work by using N-body simulations. We find that most proto-clusters survive for more than 40 Myr even when the mass loss rate is high.
We report experimental oscillator strengths for 88 Ti I transitions covering the wavelength range 465 to 3892 nm, 67 of which had no previous experimental values. Radiative lifetimes for thirteen energy levels, including the low energy levels 3d2 (3F) 4s4p (3P) z5Dj, have been measured using time resolved laser induced fluorescence. Intensity calibrated Ti I spectra have been measured using Fourier transform spectroscopy to determine branching fractions for the decay channels of these levels. The branching fractions are combined with the radiative lifetimes to yield absolute transition probabilities and oscillator strengths. Our measurements include 50 transitions in the previously unobserved infrared region lambda > 1000 nm, a region of particular interest to the analysis of cool stars and brown dwarfs.
Spectrum synthesis analysis of FUSE and STIS spectra of the cataclysmic variable IX Velorum successfully produces a system model. Light synthesis analysis of K band photometry shows that the accretion disk rim is vertically extended beyond the gravitational equilibrium value.
Using high-resolution spectra of nearby F and G dwarf stars, we have investigated the detailed abundance and age structure of the Hercules stream. We find that the stars in the stream have a wide range of stellar ages, metallicities, and element abundances. By comparing to existing samples of stars in the solar neighbourhood with kinematics typical of the Galactic thin and thick disks we find that the properties of the Hercules stream distinctly separate into the abundance and age trends of the two disks. Hence, we find it unlikely that the Hercules stream is a unique Galactic stellar population, but rather a mixture of thin and thick disk stars. This points toward a dynamical origin for the Hercules stream, probably caused by the Galactic bar.
We calculate neutrino and photon energy spectra in extragalactic space from evaporation of primordial black holes, assuming that the power spectrum of primordial density fluctuations has a strong bump in the region of small scales. The constraints on the parameters of this bump based on neutrino and photon cosmic background data are obtained.
We have modeled atmospheric effects, especially ozone depletion, due to a solar proton event which probably accompanied the extreme magnetic storm of 1-2 September 1859. We use an inferred proton fluence for this event as estimated from nitrate levels in Greenland ice cores. We present results showing production of odd nitrogen compounds and their impact on ozone. We also compute rainout of nitrate in our model and compare to values from ice core data.
We report on the temporal and spectral characteristics of the early X-ray emission from the Gamma Ray Burst 051117A as observed by Swift. The superb quality of the early X-ray light-curve and spectra of this source, one of the brightest seen by the X-ray Telescope at such early times, allows an unprecedented look at the spectral and temporal evolution of the prompt and early afterglow emission for this GRB and allows us to place stringent limits on the detection of lines. The X-ray light-curve at early times is characteristic of a shot-noise process, with individual shots well-modelled by a fast-rise and exponential decay spanning a broad range in rise-times and decay rates. A temporal spectral analysis of the early light-curve shows that the photon index and source intensity are highly correlated with the spectrum being significantly harder when brighter, consistent with the movement of the peak of the Band function to lower energies following individual flares. The high quality spectrum obtained from the first orbit of WT mode data, enables us to place a 3 sigma upper limit on the strength of any emission line features of EW < 15 eV, assuming a narrow emission-line of 100 eV at the peak of the effective area (abridged).
CMB anisotropies are modified by the weak lensing effect of intervening large scale structures on the photon path from the last scattering surface to the observer. This has to be accounted for when observational data of sensitive experiments are used to constrain cosmological models. A common approximation to analyze the CMB angular power spectra is to include only the gaussian part of the lensing correction and to ignore the non-gaussian terms in the error covariance matrix of the spectra. In order to investigate the validity of this approximation, we computed these non-gaussian terms by using a perturbative expansion method. We demonstrate that neglecting those terms is an accurate approximation for all polarizations but B, and it will remain so even for the analysis of very sensitive post-Planck experiments projects. For the B polarization, non-gaussian contributions up to order 4 must be taken into account.
Using the full three-dimensional potential of galaxy cluster halos (drawn from an N-body simulation of the current, most favored cosmology), the distribution of the X-ray emitting gas is found by assuming a polytropic equation of state and hydrostatic equilibrium, with constraints from conservation of energy and pressure balance at the cluster boundary. The resulting properties of the gas for these simulated redshift zero clusters (the temperature distribution, mass--temperature and luminosity-- temperature relations, and the gas fraction) are compared with observations in the X-ray of nearby clusters. The observed properties are reproduced only under the assumption that substantial energy injection from non-gravitational sources has occurred; AGN may be capable of providing this energy, which amounts to roughly 3 to 5 x10^{-5} of the rest mass in stars (assuming roughly ten percent of the gas initially in the cluster forms stars). With the method described here it is possible to generate realistic X-ray and Sunyaev-Zel'dovich cluster maps and catalogs from N-body simulations, with the distributions of internal halo properties (and their trends with mass, location, and time) taken into account.
The central engine of gamma-ray bursts (GRBs) is believed to be a hot and dense disk with hyperaccretion onto a few solar mass black hole. We investigate where magnetorotational instability (MRI) actively operates in the hyperaccretion disk, which can cause angular momentum transport in disks. The inner region of the hyperaccretion disk can become neutrino opaque, and the energy and momentum transports by the neutrino have great impacts on the feature of MRI. We find that the MRI is strongly suppressed by the neutrino viscosity at the region smaller than $\sim 20 r_s$ assuming reasonable disk models and the weak magnetic field $B \lesssim 10^{14} \rm{G}$. On the other hand, MRI grow actively in the outer neutrino transparent region regardless of the field strength. This suggests that the baryonic matter is accumulated into the inner dead zone where the MRI grows inactively and the angular momentum transport becomes inefficient. When the inner region gains the mass and becomes gravitationally unstable at some stage, the nonsteady and violent mass accretion onto the central black hole must be caused by the gravitational torque, and which can be the physical origin of the short-term variability in the prompt emission of GRBs. Finally, the origin of flaring activities in the X-ray afterglow is predicted in the context of our gravitational ignition scenario.
Massive stars can significantly modify the surrounding medium during their lifetime. When the stars explode as supernovae, the resulting shock wave expands within this modified medium and not within the interstellar medium. We explore the evolution of the medium around massive stars, and the expansion of the shock wave within this medium. We then apply these results to understanding the expansion of the shock wave in the ambient medium surrounding SN 1987A, and the evolution of the radio and X-ray emission in this case.
We present an updated version of the Multicolor Light Curve Shape method to measure distances to type Ia supernovae (SN Ia), incorporating new procedures for K-correction and extinction corrections. We also develop a simple model to disentangle intrinsic color variations and reddening by dust, and expand the method to incorporate U-band light curves and to more easily accommodate prior constraints on any of the model parameters. We apply this method to 133 nearby SN Ia, including 95 objects in the Hubble flow (cz >= 2500 km/s), which give an intrinsic dispersion of less than 7% in distance. The Hubble flow sample, which is of critical importance to all cosmological uses of SN Ia, is the largest ever presented with homogeneous distances. We find the Hubble flow supernovae with Hd >= 7400 km/s yield an expansion rate that is 6.5 +/- 1.8% lower than the rate determined from supernovae within that distance, and this can have a large effect on measurements of the dark energy equation of state with SN Ia. Peculiar velocities of SN Ia host galaxies in the rest frame of the Local Group are consistent with the dipole measured in the Cosmic Microwave Background. Direct fits of SN Ia that are significantly reddened by dust in their host galaxies suggest their mean extinction law may be described by R_V ~= 2.7, but optical colors alone provide weak constraints on R_V.
Weak gravitational lensing is responsible for the shearing and magnification of the images of high-redshift sources due to the presence of intervening matter. The distortions are due to fluctuations in the gravitational potential, and are directly related to the distribution of matter and to the geometry and dynamics of the Universe. As a consequence, weak gravitational lensing offers unique possibilities for probing the Dark Matter and Dark Energy in the Universe. In this review, we summarise the theoretical and observational state of the subject, focussing on the statistical aspects of weak lensing, and consider the prospects for weak lensing surveys in the future. Weak gravitational lensing surveys are complementary to both galaxy surveys and cosmic microwave background (CMB) observations as they probe the unbiased non-linear matter power spectrum at modest redshifts. Most of the cosmological parameters are accurately estimated from CMB and large-scale galaxy surveys, so the focus of attention is shifting to understanding the nature of Dark Matter and Dark Energy. On the theoretical side, recent advances in the use of 3D information of the sources from photometric redshifts promise greater statistical power, and these are further enhanced by the use of statistics beyond two-point quantities such as the power spectrum. The use of 3D information also alleviates difficulties arising from physical effects such as the intrinsic alignment of galaxies, which can mimic weak lensing to some extent. (Abridged)
We present a sequence of high resolution (R~20,000 or 15 km/s) infrared spectra of stars and brown dwarfs spanning spectral types M2.5 to T6. Observations of 16 objects were obtained using eight echelle orders to cover part of the J-band from 1.165-1.323 micron with NIRSPEC on the Keck II telescope. By comparing opacity plots and line lists, over 200 weak features in the J-band are identified with either FeH or H2O transitions. Absorption by FeH attains maximum strength in the mid-L dwarfs, while H2O absorption becomes systematically stronger towards later spectral types. Narrow resolved features broaden markedly after the M to L transition. Our high resolution spectra also reveal that the disappearance of neutral Al lines at the boundary between M and L dwarfs is remarkably abrupt, presumably because of the formation of grains. Neutral Fe lines can be traced to mid-L dwarfs before Fe is removed by condensation. The neutral potassium (K I) doublets that dominate the J-band have pressure broadened wings that continue to broaden from ~50 km/s (FWHM) at mid-M to ~500 km/s at mid-T. In contrast however, the measured pseudo-equivalent widths of these same lines reach a maximum in the mid-L dwarfs. The young L2 dwarf, G196-3B, exhibits narrow potassium lines without extensive pressure-broadened wings, indicative of a lower gravity atmosphere. Kelu-1AB, another L2, has exceptionally broad infrared lines, including FeH and H2O features, confirming its status as a rapid rotator. In contrast to other late T objects, the peculiar T6 dwarf 2MASS 0937+29 displays a complete absence of potassium even at high resolution, which may be a metallicity effect or a result of a cooler, higher-gravity atmosphere.