Photoelectric photometry on the extended Stromgren system (uvbyCa) is presented for 7 giants and 21 main sequence stars in the old open cluster, NGC 752. Analysis of the hk data for the turnoff stars yields a new determination of the cluster mean metallicity. From 10 single-star members, [Fe/H] = -0.06 +/- 0.03, where the error quoted is the standard error of the mean and the Hyades abundance is set at [Fe/H] = +0.12. This result is unchanged if all 20 stars within the limits of the hk metallicity calibration are included. The derived [Fe/H] is in excellent agreement with past estimates using properly-zeroed m1 data, transformed moderate-dispersion spectroscopy, and recent high dispersion spectroscopy.
We report extensive radio and X-ray observations of SN 2003bg whose spectroscopic evolution shows a transition from a broad-lined Type Ic to a hydrogen-rich Type II and later to a typical hydrogen-poor Type Ibc. We show that the extraordinarily luminous radio emission is well described by a self-absorption dominated synchrotron spectrum while the observed X-ray emission is adequately fit by Inverse Compton scattering of the optical photons off of the synchrotron emitting electrons. Our radio model implies a sub-relativistic ejecta velocity, v ~ 0.22c, at t_0 ~ 10 days after the explosion which emphasizes that broad optical absorption lines do not imply relativistic ejecta. We find that the total energy of the radio ejecta evolves as E ~ 3.1 x 10^{48} (t/t_0)^{0.4} erg assuming equipartition of energy between relativistic electrons and magnetic fields (e_e=e_B=0.1). The circumstellar density is well described by a stellar wind profile with modest (factor of ~2) episodic density enhancements which produce abrupt achromatic flux variations. We estimate a progenitor mass loss rate of M_dot ~ 4 x 10^{-5} solar masses per year, consistent with the observed values for Galactic Wolf-Rayet stars. Comparison with other events reveals that ~50% of radio supernovae show similar short timescale flux variations attributable to circumstellar density irregularities. Specifically, the radio light-curves of SN2003bg are strikingly similar to those of the Type IIb SN2001ig, suggestive of a common progenitor evolution. We conclude that their progenitors experienced quasi-periodic mass loss episodes just prior to the SN explosion. Finally, this study emphasizes that abrupt radio light-curve variations cannot be used as a reliable proxy for an engine-driven explosion, including off-axis gamma-ray bursts. [ABRIDGED]
The decline of the high mass X-ray transient V0332+53 during the Dec. 2004 to
Feb. 2005 outburst is analysed from the data recorded by INTEGRAL. The flux is
shown to decrease exponentially until 2005 Feb. 10, with a decay time scale of
\~30 days above 20 keV and ~20 days at lower energies, and to decrease linearly
thereafter.
The energy spectrum is well modelled throughout the decay by a power law with
a folding energy of ~7.5 keV, and with two cyclotron absorption features. The
folding energy does not vary significantly over the decay, but the spectrum
becomes harder with time. Most important, we show that the parameters
describing the fundamental cyclotron line do vary with time: its energy and
depth decrease (by about 18% for the energy in ~6 weeks), while its width
decreases. These changes of the cyclotron line parameters are interpreted as
resulting from a change in the extent of the cyclotron scattering region.
Two quasi-periodic oscillations are also observed at various times during the
observations, one at 0.05 Hz and another one near the pulsation frequency
around 0.23 Hz.
We seek to understand whether the stellar populations of galactic bulges show fingerprints of secular evolution triggered by the presence of the disc. For this purpose we re-analyse the sample of Proctor and Sansom, deriving stellar population ages and element abundances from absorption line indices. We obtain very consistent constraints on ages from the three Balmer indices Hbeta, Hgamma, and Hdelta, in good agreement with those of Proctor and Sansom based on a completely different method. Like other studies in the literature, we find that bulges have relatively low luminosity weighted ages, the lowest age derived for the smallest bulges being 1.3 Gyr. Hence bulges are not generally old but actually rejuvenated systems. We discuss evidence that this might be true also for the bulge of the Milky Way. We show that the smallest bulges, being the youngest with the lowest alpha/Fe ratios, must have experienced star formation events involving 10-30 per cent of their total mass in the past 1-2 Gyr. No significant correlations of the stellar population parameters with Hubble Type are found instead. We show that the relationships with sigma coincide perfectly with those of early-type galaxies. Hence, bulges are typically seen younger, metal-poorer and less alpha/Fe enhanced than early-type galaxies, only because of their smaller masses. At a given velocity dispersion, bulges and elliptical galaxies are indistinguishable as far as their stellar populations are concerned. These results favour an inside-out formation scenario and indicate that the discs in spiral galaxies of Hubble types Sbc and earlier cannot have a significant influence on the evolution of the stellar populations in the bulge component. The phenomenon of pseudobulge formation must be restricted to spirals of types later than Sbc.
We investigate the dependence of dark matter halo clustering on halo formation time, density profile concentration, and subhalo occupation number, using high-resolution numerical simulations of a LCDM cosmology. We confirm results that halo clustering is a function of halo formation time, and that this trend depends on halo mass. For the first time, we show unequivocally that halo clustering is a function of halo concentration and show that the dependence of halo bias on concentration, mass, and redshift can be accurately parameterized in a simple way: b(c,M|z) = b(M|z) b(c|M/M*). The scaling between bias and concentration changes sign with the value of M/M*: high concentration (early forming) objects cluster more strongly for M <~ M* while low concentration (late forming) objects cluster more strongly for rare high-mass halos, M >~ M*. We show the first explicit demonstration that host dark halo clustering depends on the halo occupation number (of dark matter subhalos) and discuss implications for halo model calculations of dark matter power spectra and galaxy clustering statistics. The effect of these halo properties on clustering is strongest for early-forming dwarf-mass halos, which are significantly more clustered than typical halos of their mass. Our results suggest that isolated low-mass galaxies (e.g. low surface-brightness dwarfs) should have more slowly-rising rotation curves than their clustered counterparts, and may have consequences for the dearth of dwarf galaxies in voids. They also imply that self calibrating richness-selected cluster samples with their clustering properties might overestimate cluster masses and bias cosmological parameter estimation.
The measurement of the Shapiro time delay in binary pulsar systems with highly inclined orbit can be affected both by the motion of the pulsar's companion because of the finite time it takes a photon to cross the binary, and by the gravitational light bending if the orbit is sufficiently edge-on relative to the line of sight. Here we calculate the effect of retardation due to the companion's motion on various time delays in pulsar binaries, including the Shaipro delay, the geometric lensing delay, and the lens-induced delays associated with the pulsar rotation. Our results can be applied to systems so highly inclined that near conjunction gravitational lensing of the pulsar radiation by the companion becomes important (the recently discovered double pulsar system J0737-3039 may exemplify such a system). To the leading order, the effect of retardation is to shift all the delay curves backward in time around the orbit conjunction, without affecting the shape and amplitude of the curves. The time shift is of order the photon orbit crossing time, and ranges from a second to a few minutes for the observed binary pulsar systems. In the double pulsar system J0737-3039, the motion of the companion may also affect the interpretation of the recent correlated interstellar scintillation measurements. Finally, we show that lensing sets an upper limit on the magnitude of the frame-dragging time delay caused by the companion's spin, and makes this delay unobservable in stellar-mass binary pulsar systems.
We examine the black hole mass - galaxy bulge relationship in high-redshift QSOs. Black hole masses are derived from the broad emission lines, and the host galaxy stellar velocity dispersion sigma is estimated from the widths of the radio CO emission lines. At redshifts z > 3, the CO line widths are narrower than expected for the black hole mass, indicating that these giant black holes reside in undersized bulges by an order of magnitude or more. The largest black holes (above 10^9 solar masses) evidently grow rapidly in the early universe without commensurate growth of their host galaxies. CO line widths offer a unique opportunity to study AGN host galaxy dynamics at high redshift.
We discuss millisecond period brightness oscillations and surface atomic spectral lines observed during type I X-ray bursts from a neutron star in a low mass X-ray binary system. We show that modeling of these phenomena can constrain models of the dense cold matter at the cores of neutron stars. We demonstrate that, even for a broad and asymmetric spectral line, the stellar radius-to-mass ratio can be inferred to better than 5%. We also fit our theoretical models to the burst oscillation data of the low mass X-ray binary XTE J1814-338, and find that the 90% confidence lower limit of the neutron star's dimensionless radius-to-mass ratio is 4.2.
Conservative numerical schemes for general relativistic magnetohydrodynamics (GRMHD) require a method for transforming between ``conserved'' variables such as momentum and energy density and ``primitive'' variables such as rest-mass density, internal energy, and components of the four-velocity. The forward transformation (primitive to conserved) has a closed-form solution, but the inverse transformation (conserved to primitive) requires the solution of a set of five nonlinear equations. Here we discuss the mathematical properties of the inverse transformation and present six numerical methods for performing the inversion. The first method solves the full set of five nonlinear equations directly using a Newton-Raphson scheme and a guess from the previous timestep. The other methods reduce the five nonlinear equations to either one or two nonlinear equations that are solved numerically. Comparisons between the methods are made using a survey over phase space, a two-dimensional explosion problem, and a general relativistic MHD accretion disk simulation. The run-time of the methods is also examined. Code implementing the schemes is available for download on the web.
Properly apodized pupils can deliver point spread functions (PSFs) free of Airy rings, and are suitable for high dynamical range imaging of extrasolar terrestrial planets (ETPs). To reach this goal, classical pupil apodization (CPA) unfortunately requires most of the light gathered by the telescope to be absorbed, resulting in poor throughput and low angular resolution. Phase-induced amplitude apodization (PIAA) of the telescope pupil (Guyon 2003) combines the advantages of classical pupil apodization (particularly low sensitivity to low order aberrations) with full throughput, no loss of angular resolution and little chromaticity, which makes it, theoretically, an extremely attractive coronagraph for direct imaging of ETPs. The two most challenging aspects of this technique are (1) the difficulty to polish the required optics shapes and (2) diffraction propagation effects which, because of their chromaticity, can decrease the spectral bandwidth of the coronagraph. We show that a properly designed hybrid system combining classical apodization with the PIAA technique can solve both problems simultaneously. For such a system, the optics shapes can be well within today's optics manufacturing capabilities, and the $10^{-10}$ PSF contrast at $\approx 1.5 \lambda/D$ required for efficient imaging of ETPs can be maintained over the whole visible spectrum. This updated design of the PIAA coronagraph maintains the high performance of the earlier design, since only a small part of the light is lost in the classical apodizer(s).
The decay rate of cosmological gravitational potential measures the deviation from Einstein-de Sitter universe and can put strong constraints on the nature of dark energy and gravity. Usual method to measure this decay rate is through the integrated Sachs-Wolfe (ISW) effect-large scale structure (LSS) cross correlation. However, the interpretation of the measured correlation signal is complicated by the galaxy bias and matter power spectrum. This severely degrades its power to constrain the nature of dark energy and gravity. But, combining the lensing-LSS cross correlation measurements, the decay rate of gravitational potential can be isolated. For any given narrow redshift bin of LSS, the ratio of the two cross correlations directly measures $[d\ln D_{\phi}/d\ln a]H(z)/W(\chi,\chi_s)$, where $D_{\phi}$ is the linear growth factor of the gravitational potential, $H$ is the Hubble constant at redshift $z$, $W(\chi,\chi_s)$ is the lensing kernel and $\chi$ and $\chi_s$ are the comoving angular diameter distance to lens and source, respectively. Such measurement can put robust constraints on the amount of dark energy and its equation of state. It also provides a powerful test of modified gravity and can distinguish the Dvali-Gabadadze-Porrati model from $\Lambda$CDM at $>2.5\sigma$ confidence level.
We describe several techniques developed by the High Resolution Fly's Eye experiment for measuring aerosol vertical optical depth, aerosol horizontal attenuation length, and aerosol phase function. The techniques are based on measurements of side-scattered light generated by a steerable ultraviolet laser and collected by an optical detector designed to measure fluorescence light from cosmic-ray air showers. We also present a technique to cross-check the aerosol optical depth measurement using air showers observed in stereo. These methods can be used by future air fluorescence experiments.
The current understanding of galaxy formation is that it proceeds in a 'bottom up' way, with the formation of small clumps of gas and stars that merge hierarchically until giant galaxies are built up. The baryonic gas loses the thermal energy by radiative cooling and falls towards the centres of the new galaxies, while supernovae (SNe) blow gas out. Any realistic model therefore requires a proper treatment of these processes, but hitherto this has been far from satisfactory. Here we report an ultra-high-resolution simulation that follows evolution from the earliest stages of galaxy formation through the period of dynamical relaxation. The bubble structures of gas revealed in our simulation ($< 3\times10^8$ years) resemble closely the high-redshift Lyman $\alpha$ emitters (LAEs). After $10^9$ years these bodies are dominated by stellar continuum radiation and look like the Lyman break galaxies (LBGs) known as the high-redshift star-forming galaxies at which point the abundance of elements heavier than helium ("metallicity") appears to be solar. After $1.3\times10^{10}$ years, these galaxies resemble present-day ellipticals.
The phenomena customly called Dark Matter or Modified Newtonian Dynamics (MOND) have been argued by Bekenstein (2004) to be the consequences of a covariant scalar field, controlled by a free function (related to the MOND interpolating function $\mut(g/a_0)$) in its Lagrangian density. In the context of this relativistic MOND theory (TeVeS), we examine critically the interpolating function in the transition zone between weak and strong gravity. Bekenstein's toy model produces too gradually varying $\mut$ and fits rotation curves less well than the standard MOND interpolating function $\mut(x)=x/\sqrt{1+x^2}$. However, the latter varies too sharply and implies an implausible external field effect (EFE). These constraints on opposite sides have not yet excluded TeVeS, but made the zone of acceptable interpolating functions very narrow. A surviving "toy" Lagrangian density function with simple analytical properties is singled out for future studies of TeVeS in galaxies. We also suggest how to extend the model to solar system dynamics and cosmology.
Future weak lensing measurements of cosmic shear will reach such high accuracy that second order effects in weak lensing modeling, like the influence of baryons on structure formation, become important. We use a controlled set of state of the art cosmological simulations to quantify this effect by comparing pure N-body dark matter runs with corresponding hydrodynamical simulations, carried out both in non-radiative, and in dissipative form with cooling and star formation. In both hydrodynamical simulations, the clustering of the gas is suppressed while that of dark matter is boosted at scales k>1 h/Mpc. Despite this counterbalance between dark matter and gas, the clustering of the total matter is suppressed by up to 1 percent at 1<k<10 h/Mpc, while for k~ 20 h/Mpc it is boosted, up to 2 percent in the non-radiative run and 10 percent in the run with star formation. The stellar mass formed in the latter is highly biased relative to the dark matter in the pure N-body simulation. Using our power spectrum measurements to predict the effect of baryons on the weak lensing signal at 100<l<10000, we find that baryons may change the lensing power spectrum by less than 0.5 percent at l<1000, but by 1 to 10 percent at 1000<l<10000. The size of the effect exceeds the predicted accuracy of future lensing power spectrum measurements and will likely be detected. Precise determinations of cosmological parameters with weak lensing, and studies of small-scale fluctuations and clustering, therefore rely on properly including baryonic physics.
The Lyman-alpha forest at z >~ 5.5 shows strong scatter in the mean transmission even when smoothed over very large spatial scales, >~ 50 Mpc/h. This has been interpreted as a signature of strongly fluctuating radiation fields, or patchy reionization. To test this claim, we calculate the scatter arising solely from density fluctuations, with a uniform ionizing background, using analytic arguments and simulations. This scatter alone is comparable to that observed. It rises steeply with redshift and is of order unity by z ~ 6, even on ~ 50 Mpc/h scales. This arises because: i) at z ~ 6, transmission spectra, which are sensitive mainly to rare voids, are highly biased (with a linear bias factor b >~ 4-5) tracers of underlying density fluctuations, and ii) projected power from small-scale transverse modes is aliased to long wavelength line-of-sight modes. Inferring patchy reionization from quasar spectra is therefore subtle and requires much more detailed modeling. Similarly, we expect order unity transmission fluctuations in the z ~ 3 HeII Lyman-alpha forest from density fluctuations alone, on the scales over which these measurements are typically made.
To test the existence of a possible radial gradient in oxygen abundances within the Local Group dwarf irregular galaxy NGC 6822, we have obtained optical spectra of 19 nebulae with the EFOSC2 spectrograph on the 3.6-m telescope at ESO La Silla. The extent of the measured nebulae spans galactocentric radii in the range between 0.05 kpc and 2 kpc (over four exponential scale lengths). In five H II regions (Hubble I, Hubble V, Kalpha, Kbeta, KD28e), the temperature-sensitive [O III] 4363 emission line was detected, and direct oxygen abundances were derived. Oxygen abundances for the remaining H II regions were derived using bright-line methods. The oxygen abundances for three A-type supergiant stars are slightly higher than nebular values at comparable radii. Linear least-square fits to various subsets of abundance data were obtained. When all of the measured nebulae are included, no clear signature is found for an abundance gradient. A fit to only newly observed H II regions with [O III] 4363 detections yields an oxygen abundance gradient of -0.14 +/- 0.07 dex/kpc. The gradient becomes slightly more significant (-0.16 +/- 0.05 dex/kpc) when three additional H II regions with [O III] 4363 measurements from the literature are added. Assuming no abundance gradient, we derive a mean nebular oxygen abundance 12+log(O/H) = 8.11 +/- 0.10 from [O III] 4363 detections in the five H II regions from our present data; this mean value corresponds to [O/H] = -0.55.
We investigate the dependence of galaxy clustering on the galaxy intrinsic luminosity at high redshift, using the data from the First Epoch VIMOS-VLT Deep Survey (VVDS). The size (6530 galaxies) and depth (I_{AB}<24) of the survey allows us to measure the projected two-point correlation function of galaxies, w_p(r_p) for a set of volume-limited samples up to an effective redshift <z>=0. and median absolute magnitude -19.6< M_B < -21.3. Fitting w_p(r_p) with a single power-law model for the real-space correlation function xi(r)=(r/r_0)^{-gamma}, we measure the relationship of the correlation length r_0 and the slope gamma with the sample median luminosity for the first time at such high redshift. Values from our lower-redshift samples (0.1<z<0.5) are fully consistent with the trend observed by larger local surveys. In our high redshift sample (0.5<z<1.2), we find that the clustering strength is suddenly rising around M_B^*, apparently with a sharper turn than at low redshifts. Galaxies in the faintest sample (<M_B\right>=-19.6) have a correlation length r_0=2.7^{+0.3}_{-0.3} h^{-1} Mpc, compared to r_0=5.0^{+1.5}_{-1.6} h^{-1} Mpc at <M_B>=-21.3. Correspondingly the slope of the correlation function is observed to steepen significantly from \gamma=1.6^{+0.1}_{-0.1} to \gamma=2.4^{+0.4}_{-0.2}. This is not observed neither by large local surveys nor in our lower-redshift sample and seems to imply a significant change in the way luminous galaxies trace dark-matter halos at z~1 with respect to z~0. At our effective median redshift z~0.9 this corresponds to a strong difference of the relative bias, from b/b* < 0.7 for galaxies with L < L*, to b/b*~1.4 for galaxies with L > L*.
We report the discovery of the first trans-neptunian object, designated 2004 XR190, with a nearly-cirular orbit beyond the 2:1 mean-motion resonance. Fitting an orbit to 23 astrometric observations spread out over 12 months yields an orbit of a=57.2\pm0.4, e=0.08\pm0.04, and i=46.6 deg. All viable orbits have perihelia distances q>49 AU. The very high orbital inclination of this extended scattered disk object might be explained by several models, but its existence again points to a large as-yet undiscovered population of transneptunian objects with large orbital perihelia and inclination.
We have studied the unbarred Sb galaxy with a nuclear star-forming ring, NGC 7742, by means of 2D spectroscopy, long-slit spectroscopy, and imaging, and have compared the results with the properties of another galaxy of this type, NGC 7217, which is studied by us earlier. Both galaxies have many peculiar features in common: each has two global exponential stellar disks with different scalelengths, each possesses a circumnuclear inclined gaseous disk with a radius of 300 pc, and each has a global counterrotating subsystem, gaseous one in NGC 7742 and stellar one in NGC 7217. We suggest that past minor merger is the probable cause of all these peculiarities, including appearance of the nuclear star-forming rings without global bars; the rings might be produced as resonance features by tidally induced oval distortions of the global stellar disks.
The general aim of this work is to obtain the lateral distribution of atmospheric Cherenkov light in extensive air showers produced by different primary particles precisely by. protons, Helium, Iron, Oxygen, Carbon, Nitrogen, Calcium, Silicon and gamma quanta in wide energy range at high mountain observation level of Chacaltaya cosmic ray station. The simulations are divided generally in two energy ranges 10GeV-10 TeV and 10 TeV-10 PeV. One large detector has been used for simulations, the aim being to reduce the statistical fluctuations of the obtained characteristics. The shape of the obtained lateral distributions of Cherenkov light in extensive air showers is discussed and the scientific potential for solution of different problems as well.
We generalize the predictions for the CMB anisotropy patterns arising in Bianchi type VIIh universes to include a dark energy component. We consider these models in light of the result of Jaffe et al. (2005a,b) in which a correlation was found on large angular scales between the WMAP data and the anisotropy structure in a low density Bianchi universe. We find that by including a term Omega_L > 0, the same best-fit anisotropy pattern is reproduced by several combinations of cosmological parameters. This sub-set of models can then be further constrained by current observations that limit the values of various cosmological parameters. In particular, we consider the so-called geometric degeneracy in these parameters imposed by the peak structure of the WMAP data itself. Apparently, despite the additional freedom allowed by the dark energy component, the modified Bianchi models are ruled out at high significance.
Experimental conclusions from air shower observations on cosmic-ray photons above 10^19 eV are based on the comparison to detailed shower simulations. For the calculations, the photonuclear cross-section needs to be extrapolated over several orders of magnitude in energy. The uncertainty from the cross-section extrapolation translates into an uncertainty of the predicted shower features for primary photons and, thus, into uncertainties for a possible data interpretation. After briefly reviewing the current status of ultra-high energy photon studies, the impact of the uncertainty of the photonuclear cross-section for shower calculations is investigated. Estimates for the uncertainties in the main shower observables are provided. Photon discrimination is shown to be possible even for rapidly rising cross-sections. When photon-initiated showers are identified, it is argued that the sensitivity of photon shower observables to the photonuclear cross-section can in turn be exploited to constrain the cross-section at energies not accessible at colliders.
Corrections to the magnitudes of high redshift objects due to intergalactic attenuation are computed using current estimates of the properties of the intergalactic medium. The results of numerical simulations are used to estimate the contributions to resonant scattering from the higher order Lyman transitions. Differences of 0.5-1 magnitude from the previous estimate of Madau (1995) are found. Intergalactic k_IGM-corrections and colours are provided for high redshift starburst galaxies and Type I and Type II QSOs for several filter systems used in current and planned deep optical and infra-red surveys.
We review four mechanisms for forming brown dwarfs: (i) turbulent fragmentation (producing very low-mass prestellar cores); (ii) gravitational instabilities in discs; (iii) dynamical ejection of stellar embryos from their placental cores; and (iv) photo-erosion of pre-existing cores in HII regions. We argue (a) that these are simply the mechanisms of low-mass star formation, and (b) that they are not mutually exclusive. If, as seems possible, all four mechanisms operate in nature, their relative importance may eventually be constrained by their ability to reproduce the binary statistics of brown dwarfs, but this will require fully 3-D radiative magneto-hydrodynamic simulations.
The colours of high redshift Type II QSOs are synthesized from observations of moderate redshift systems. It is shown that Type II QSOs are comparable to starbursts in their success at matching the colours of z_850-dropouts and i_775-drops in the Hubble Ultra Deep Field, and more naturally account for the bluest objects detected. Type II QSOs may also account for some of the i_775-drops detected in the GOODS fields. It is shown that by combining imaging data from the Hubble Space Telescope and the James Webb Space Telescope, it will be possible to clearly separate Type II QSOs from Type I QSOs and starbursts based on their colours. Similarly, it is shown that the UKIDSS ZYJ filters may be used to discriminate high redshift Type II QSOs from other objects. If Type II QSOs are prevalent at high redshifts, then AGN may be major contributors to the re-ionization of the Intergalactic Medium.
We briefly discuss some open problems and recent developments in the investigation of the origin and propagation of ultra high energy cosmic rays (UHECRs).
Scattering processes in the cosmic microwave background limit the propagation of ultra high energy charged particles in our Universe. For extragalactic proton sources resonant photopion production results in the famous Greisen-Zatsepin-Kuzmin (GZK) cutoff at about 4x10^10 GeV expected in the spectrum observed on Earth. The faint flux of ultra high energy cosmic rays of less than one event per year and cubic kilometer and the large systematic uncertainties in the energy calibration of cosmic ray showers is a challenge for cosmic ray observatories and so far the GZK cutoff has not been unambiguously confirmed. We have investigated the possibility that the primaries of super-GZK events are strongly interacting neutrinos which are not subject to the GZK cutoff. For the flux of protons and neutrinos from extragalactic optically thin sources and a flexible parameterization of the neutrino-nucleon cross section we have analyzed the cosmic ray spectra observed at AGASA and HiRes taking also into account results from horizontal events at AGASA and contained events at RICE. We find that scenarios of strongly interacting neutrinos are still compatible with the data requiring a steep increase of the inelastic neutrino-nucleon cross section by four order of magnitude within one energy decade compared to the Standard Model predictions. We also discuss the impact of the preliminary cosmic ray spectrum observed by the Pierre Auger Observatory.
We report new simultaneous near-infrared/sub-millimeter/X-ray observations of the SgrA* counterpart associated with the massive 3-4x10**6 solar mass black hole at the Galactic Center. The main aim is to investigate the physical processes responsible for the variable emission from SgrA*. The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope and the ACIS-I instrument aboard the Chandra X-ray Observatory as well as the Submillimeter Array SMA on Mauna Kea, Hawaii, and the Very Large Array in New Mexico. We detected one moderately bright flare event in the X-ray domain and 5 events at infrared wavelengths.
We report XMM-Newton observations of the young open cluster NGC 2547 which allow us to characterise coronal activity in solar-type stars at an age of 30 Myr. X-ray emission peaks among G-stars at luminosities (0.3-3keV) of Lx~10^{30.5} erg/s and declines to Lx<=10^{29.0} erg/s among M-stars. Coronal spectra show evidence for multi-temperature differential emission measures and low coronal metal abundances (Z~0.3). The G- and K-type stars follow the same relationship between X-ray activity and Rossby number established in older clusters and field stars, although most solar-type stars in NGC 2547 exhibit saturated/super-saturated X-ray activity levels. Median levels of Lx and Lx/Lbol in the solar-type stars of NGC 2547 are similar to T-Tauri stars of the Orion Nebula cluster (ONC), but an order of magnitude higher than in the older Pleiades. The spread in X-ray activity levels among solar-type stars in NGC 2547 is much smaller than in older or younger clusters. Coronal temperatures increase with Lx, Lx/Lbol and surface X-ray flux. Active solar-type stars in NGC 2547 have coronal temperatures between those in the ONC and the most active older ZAMS stars. A flaring rate (for total flare energies [0.3-3keV] >10^{34} erg) of 1 every 350^{+350}_{-120} ks was found for solar-type stars, similar to rates found in the ONC and Pleiades. Comparison with ROSAT HRI data taken 7 years previously reveals that only 10-15 percent of solar-type stars or stars with Lx>3x10^{29} erg/s exhibit X-ray variability by more than a factor of two. The similar levels of X-ray activity and rate of occurrence for large flares in NGC 2547 and the ONC demonstrate that the X-ray radiation environment around young solar-type stars remains relatively constant over their first 30 Myr (abridged).
The current and prospective status of astronomical research in Ukraine is discussed. A brief history of astronomical research in Ukraine is presented and the system organizing scientific activity is described, including astronomy education, institutions and staff, awarding higher degrees/titles, government involvement, budgetary investments and international cooperation. Individuals contributing significantly to the field of astronomy and their accomplishments are mentioned. Major astronomical facilities, their capabilities, and their instrumentation are described. In terms of the number of institutions and personnel engaged in astronomy, and of past accomplishments, Ukraine ranks among major nations of Europe. Current difficulties associated with political, economic and technological changes are addressed and goals for future research activities presented.
We propose and test a new method based on Richardson-Lucy deconvolution to reconstruct three-dimensional gas density and temperature distributions in galaxy clusters from combined X-ray and thermal Sunyaev-Zel'dovich observations. Clusters are assumed to be axially symmetric and arbitrarily inclined with respect to the line-of-sight. No equilibrium assumption other than local thermal equilibrium is needed. We test the algorithm with synthetic observations of analytically modeled and numerically simulated galaxy clusters and discuss the quality of the density and temperature reconstructions in idealised situations and in presence of observational noise, deviations from axial symmetry and cluster substructure. We find that analytic and numerical gas density and temperature distributions can be accurately reconstructed in three dimensions, even if observational noise is present. We also discuss methods for determining the inclination angle from data and show that it can be constrained using X-ray temperature maps. For a realistic cluster and including observational noise the three-dimensional reconstructions reach a level of accuracy of about 15%.
Measurements of molecular hydrogen (H_2) column densities are presented for the first six rotational levels (J=0 to 5) for 73 extragalactic targets observed with FUSE. All of these have a final signal-to-noise ratio larger than \snlimit, and are located at galactic latitude |b|>20 deg. The individual observations were calibrated with the FUSE calibration pipeline CalFUSE version 2.1 or higher, and then carefully aligned in velocity. The final velocity shifts for all the FUSE segments are listed. H_2 column densities or limits are determined for the 6 lowest rotational (J) levels for each HI component in the line of sight, using a curve-of-growth approach at low column densities ~16.5), and Voigt-profile fitting at higher column densities. Detections include 73 measurements of low-velocity H_2 in the Galactic Disk and lower Halo. Eight sightlines yield non-detections for Galactic H_2. The measured column densities range from log N(H_2)=14 to log N(H_2)=20. Strong correlations are found between log N(H_2) and T_01, the excitation temperature of the H_2, as well as between log N(H_2) and the level population ratios (log (N(J')/N(J))). The average fraction of nuclei in molecular hydrogen (f(H_2)) in each sightline is calculated; however, because there are many HI clouds in each sightline, the physics of the transition from HI to H_2 can not be studied. Detections also include H2 in 16 intermediate-velocity clouds in the Galactic Halo (out of 35 IVCs). Molecular hydrogen is seen in one high-velocity cloud (the Leading Arm of the Magellanic Stream), although 19 high-velocity clouds are intersected; this strongly suggests that dust is rare or absent in these objects. Finally, there are five detections of H_2 in external galaxies.
Tegmark and Bostrom's provocative analysis of the chances of a "doomsday catastrophe" [Nature 438, 754 (2005)] sets out an interesting idea, but unfortunately contains a fundamental error which invalidates their conclusions. The essential problem with their argument can be seen by considering the assertion that "if [planet-destroying] catastrophes were very frequent, then almost all intelligent civilisations would have arisen much earlier than ours". This does not follow from Tegmark and Bostrom's assumptions.
We investigate the emission-line properties of galaxies with red rest-frame colors using spectra from SDSS DR2. Emission lines are detected in more than half of the red galaxies. We focus on the relationship between two emission lines commonly used as star formation rate indicators: Ha 6563 and [OII] 3727. There is a strong bimodality in [OII]/Ha ratio in the full SDSS sample which closely corresponds to the bimodality in rest-frame color. Nearly all of the line-emitting red galaxies have line ratios typical of various types of AGN -- most commonly LINERs, a small fraction of transition objects and, more rarely, Seyferts. The [OII]-Ha EW diagram reveals the continuity between quiescent galaxies with no detectable emission and galaxies with LINER-like line ratios, which altogether form a LINER/Quiescent sequence. A straight line in the [OII]-Ha EW plane divides these galaxies from the remainder. [OII] equivalent widths in LINER- and AGN-like galaxies can be as large as in star-forming galaxies. Thus, unless objects with AGN/LINER-like line ratios are excluded, [OII] emission cannot be used directly as a proxy for star formation rate. Lack of [OII] emission is generally used to indicate lack of star formation when post-starburst galaxies are selected at high redshift. Our results imply, however, that these samples have been cut on AGN properties as well as star formation, and therefore may provide seriously incomplete sets of post-starburst galaxies. Furthermore, post-starburst galaxies identifed in SDSS by requiring minimal Ha equivalent width generally exhibit weak but nonzero line emission with ratios typical of AGNs; few of them show residual star formation. This suggests that most post-starbursts harbor AGNs/LINERs.
We present the spectral and temporal radiative signatures expected within the "Supercritical Pile" model of Gamma Ray Bursts (GRB). This model is motivated by the need for a process that provides the dissipation necessary in GRB and presents a well defined scheme for converting the energy stored in the relativistic protons of the Relativistic Blast Waves (RBW) associated with GRB into radiation; at the same time it leads to spectra which exhibit a peak in the burst $\nu F_{\nu}$ distribution at an energy $E_p \simeq 1$ MeV in the observer's frame, in agreement with observation and largely independent of the Lorentz factor $\Gamma$ of the associated relativistic outflow. Futhermore, this scheme does not require (but does not preclude) acceleration of particles at the shock other than that provided by the isotropization of the flow bulk kinetic energy on the RBW frame. In the present paper we model in detail the evolution of protons, electrons and photons from a RBW to produce detailed spectra of the prompt GRB phase as a function of time from across a very broad range spanning roughly $4 log_{10} \Gamma$ decades in frequency. The model spectra are in general agreement with observations and provide a means for the delineating of the model parameters through direct comparison with trends observed in GRB properties.
Spectral methods are well suited for solving hydrodynamic problems in which the self-gravity of the flow needs to be considered. Because Poisson's equation is linear, the numerical solution for the gravitational potential for each individual mode of the density can be pre-computed, thus reducing substantially the computational cost of the method. In this second paper, we describe two different approaches to computing the gravitational field of a two-dimensional flow with pseudo-spectral methods. For situations in which the density profile is independent of the third coordinate (i.e., an infinite cylinder), we use a standard Poisson solver in spectral space. On the other hand, for situations in which the density profile is a delta function along the third coordinate (i.e., an infinitesimally thin disk), or any other function known a priori, we perform a direct integration of Poisson's equation using a Green's functions approach. We devise a number of test problems to verify the implementations of these two methods. Finally, we use our method to study the stability of polytropic, self-gravitating disks. We find that, when the polytropic index Gamma is <= 4/3, Toomre's criterion correctly describes the stability of the disk. However, when Gamma > 4/3 and for large values of the polytropic constant K, the numerical solutions are always stable, even when the linear criterion predicts the contrary. We show that, in the latter case, the minimum wavelength of the unstable modes is larger than the extent of the unstable region and hence the local linear analysis is inapplicable.
We survey a sample of 32 M5-M8 stars with distance < 40pc for companions with separations between 0.1 arcsec and 1.5 arcsec and with Delta m_i <5. We find five new VLM binaries with separations between 0.15 arcsec and 1.1 arcsec, including a candidate brown dwarf companion. The raw binary fraction is 16% +8/-4% and the distance bias corrected fraction is 7% +7/-3%, for companions within the surveyed range. No systems with contrast ratio Delta m_i>1 were found, even though our survey is sensitive to up to Delta m=5 (well into the brown dwarf regime). The distribution of orbital radii is in broad agreement with previous results, with most systems at 1-5AU, but one detected binary is very wide at 46.8+/-5.0AU. We also serendipitously imaged for the first time a companion to Ross 530, a metal-poor single-lined spectroscopic binary. We used the new Lucky Imaging system LuckyCam on the 2.5m Nordic Optical Telescope to complete the 32 very low mass star i' and z' survey in only 5 hours of telescope time.
The recently discovered substellar companion to GQ Lup possibly represents a
direct test of current planet formation theories.
We examine the possible formation scenarios for the companion to GQ Lup
assuming it is a $\sim$2 M$_{Jup}$ object. We determine that GQ Lup B most
likely was scattered into a large, eccentric orbit by an interaction with
another planet in the inner system.
If this is the case, several directly observable predictions can be made,
including the presence of a more massive, secondary companion that could be
detected through astrometry, radial velocity measurements, or scuplting in GQ
Lup's circumstellar disk. This scenario requires a highly eccentric orbit for
the companion already detected. These predictions can be tested within the next
decade or so. Additionally, we look at scenarios of formation if the companion
is a brown dwarf. One possible formation scenario may involve an interaction
between a brown dwarf binary and GQ Lup. We look for evidence of any brown
dwarfs that have been ejected from the GQ Lup system by searching the 2MASS
all-sky survey.
INTEGRAL and RXTE performed three simultaneous observations of the nearby radio galaxy Cen A in 2003 March, 2004 January, and 2004 February with the goals of investigating the geometry and emission processes via the spectral/temporal variability of the X-ray/low energy gamma ray flux, and intercalibration of the INTEGRAL instruments with respect to those on RXTE. When combined with earlier archival RXTE results, we find the power law continuum flux and the line-of-sight column depth varied independently, and the iron line flux was essentially unchanging. Taking X-ray spectral measurements from satellite missions since 1970 into account, we discover a variability in the column depth between 1.0x10^23 cm^-2 and 1.5x10^23 cm^-2, and suggest that variations in the edge of a warped accretion disk viewed nearly edge-on might be the cause.
Radioastronomical studies have indicated that the magnetic field in the central few hundred parsecs of our Milky Way Galaxy has a dipolar geometry and a strength substantially larger than elsewhere in the Galaxy, with estimates ranging up to a milligauss. A strong, large-scale magnetic field can affect the Galactic orbits of molecular clouds by exerting a drag on them, it can inhibit star formation, and it can guide a wind of cosmic rays away from the central region, so a characterization of the magnetic field at the Galactic center is important for understanding much of the activity there. Here, we report Spitzer Space Telescope observations of an unprecedented infrared nebula having the morphology of an intertwined double helix. This feature is located about 100 pc from the Galaxy's dynamical centre toward positive Galactic latitude, and its axis is oriented perpendicular to the Galactic plane. The observed segment is about 25 pc in length, and contains about 1.25 full turns of each of the two continuous, helically wound strands. We interpret this feature as a torsional Alfven wave propagating vertically away from the Galactic disk, driven by rotation of the magnetized circumnuclear gas disk. As such, it offers a new morphological probe of the Galactic center magnetic field. The direct connection between the circumnuclear disk and the double helix is ambiguous, but the MSX images show a possible meandering channel that warrants further investigation.
The delay in light travel time along the line of sight generates an anisotropy in the power spectrum of 21cm brightness fluctuations from the epoch of reionization. We show that when the fluctuations in the neutral hydrogen fraction become non-linear at the later stages of reionization, the light-cone anisotropy becomes of order unity on scales >50 comoving Mpc. During this period the density fluctuations and the associated anisotropy generated by peculiar velocities are negligible in comparison.
We propose that dark matter consists of collections of atoms encapsulated inside pieces of an alternative vacuum, in which the Higgs field vacuum expectation value is appreciably smaller than in the usual vacuum. The alternative vacuum is supposed to have the same energy density as our own. Apart from this degeneracy of vacuum phases, we do not introduce any new physics beyond the Standard Model. The dark matter balls are estimated to have a radius of order 20 cm and a mass of order $10^{11}$ kg. However they are very difficult to observe directly, but inside dense stars may expand eating up the star and cause huge explosions (gamma ray bursts). The ratio of dark matter to ordinary baryonic matter is estimated to be of the order of the ratio of the binding energy per nucleon in helium to the difference between the binding energies per nucleon in heavy nuclei and in helium. Thus we predict approximately five times as much dark matter as ordinary baryonic matter!
Seed black holes formed in the collapse of population III stars have been invoked to explain the presence of supermassive black holes at high redshift. It has been suggested that a seed black hole can grow up to $10^{5\sim 6}\sunm$ through highly super-Eddington accretion for a period of $\sim 10^{6\sim 7}$ yr between redshift $z=20\sim 24$. We studied the feedback of radiation pressure, Compton heating and outflow during the seed black hole growth. It is found that its surrounding medium fueled to the seed hole is greatly heated by Compton heating. For a super-critical accretion onto a $10^3\sunm$ seed hole, a Compton sphere (with a temperature $\sim 10^6$K) forms in a timescale of $1.6\times 10^3$yr so that the hole is only supplied by a rate of $10^{-3}$ Eddington limit from the Compton sphere. Beyond the Compton sphere, the kinetic feedback of the strong outflow heats the medium at large distance, this leads to a dramatical decrease of the outer Bondi accretion onto the black hole and avoid the accumulation of the matter. The highly super-critical accretion will be rapidly halted by the strong feedback. The seed black holes hardly grow up at the very early universe unless the strong feedback can be avoided.
We present an analysis of the rotation measures (RMs) of polarized extragalactic point sources in the Southern Galactic Plane Survey. This work demonstrates that the statistics of fluctuations in RM differ for the spiral arms and the interarm regions. Structure functions of RM are flat in the spiral arms, while they increase in the interarms. This indicates that there are no correlated RM fluctuations in the magneto-ionized interstellar medium in the spiral arms on scales larger than ~ 0.5 deg, corresponding to ~ 17 pc in the nearest spiral arm probed. The non-zero slopes in interarm regions imply a much larger scale of RM fluctuations. We conclude that fluctuations in the magneto-ionic medium in the Milky Way spiral arms are not dominated by the mainly supernova-driven turbulent cascade in the global ISM but are probably due to a different source, most likely H II regions.
Using a large sample of MgII absorbers with 0.4<z<2.2 detected by Nestor et al (2005) in the Early Data Release of the SDSS, we present new constraints on the physical properties of these systems based on two statistical analyses: (i) By computing the ratio between the composite spectra of quasars with and without absorbers, we measure the reddening effects induced by these intervening systems; and (ii) by stacking SDSS images centered on quasars with strong MgII absorption lines and isolating the excess light around the PSF, we measure the mean luminosity and colors of the absorbing galaxies. This statistical approach does not require any spectroscopic follow up and allows us to constrain the photometric properties of absorber systems.
We study the effects of an external magnetic helicity production on the evolution of the cosmic axion field. It is shown that a helicity larger than (10^{-15} \G)^2 Mpc, if produced at temperatures above a few GeV, is in contradiction with the existence of the axion, since it would produce too much of an axion relic abundance.
Having conducted a search for the 22 GHz water vapor line towards galaxies with nuclear activity, large nuclear column densities or high infrared luminosities, we present H_2O spectra for NGC2273, UGC5101 and NGC3393 with isotropic luminosities of 7, 1500, and 400 L_sun. The H_2O maser in UGC5101 is by far the most luminous yet found in an ultraluminous infrared galaxy. NGC3393 reveals the classic spectrum of a `disk maser', represented by three distinct groups of Doppler components. As in all other known cases except NGC4258, the rotation velocity of the putative masing disk is well below 1000 km/s. Based on the literature and archive data, X-ray absorbing column densities are compiled for the 64 galaxies with reported maser sources beyond the Magellanic Clouds. For NGC2782 and NGC5728, we present Chandra archive data that indicate the presence of an active galactic nucleus in both galaxies. The correlation between absorbing column and H_2O emission is analyzed. There is a striking difference between kilo- and megamasers with megamasers being associated with higher column densities. All kilomasers (L_H_2O < 10 L_sun) except NGC2273 and NGC5194 are Compton-thin, i.e. their absorbing columns are < 10^24 cm^-2. Among the H_2O megamasers, 50% arise from Compton-thick and 85% from heavily obscured (> 10^23 cm^-2) active galactic nuclei. These values are not larger but consistent with those from samples of Seyfert 2 galaxies not selected on the basis of maser emission. The similarity in column densities can be explained by small deviations in position between maser spots and nuclear X-ray source and a high degree of clumpiness in the circumnuclear interstellar medium.
We searched for steady PeV gamma-ray emission from the Monogem ring region with the Tibet air shower array from 1997 February to 2004 October. No evidence for statistically significant gamma-ray signals was found in a region 111$\degr$ $\leq$ R.A. $<$ 114$\degr$, 12$\fdg$5 $\leq$ decl. $<$ 15$\fdg$5 in the Monogem ring where the MAKET-ANI experiment recently claimed a positive detection of PeV high-energy cosmic radiation, although our flux sensitivity is approximately 10 times better than MAKET-ANI's. We set the most stringent integral flux upper limit at a 99% confidence level of 4.0 $\times$ 10$^{-12}$ cm$^{-2}$ s$^{-1}$ sr$^{-1}$ above 1 PeV on diffuse gamma rays extended in the 3$^{\circ}$ $\times$ 3$^{\circ}$ region.
We examine whether active galaxies obey the same relation between black hole mass and stellar velocity dispersion as inactive systems, using the largest published sample of velocity dispersions for active nuclei to date. The combination of 56 original measurements with objects from the literature not only increases the sample from the 15 considered previously to 88 objects, but allows us to cover an unprecedented range in both stellar velocity dispersion (30--268 km/s) and black hole mass (10^5-10^8.6 M_sun). In the M-sigma relation of active galaxies we find a lower zeropoint than the best-fit relation of Tremaine et al. (2002) for inactive galaxies, and an intrinsic scatter of 0.4 dex. There is also evidence for a flatter slope at low black hole masses. We discuss potential contributors to the observed offsets, including variations in the geometry of the broad-line region, evolution in the M-sigma relation, and differential growth between black holes and galaxy bulges.
(ABRIDGED) We present stellar velocity dispersion (sigma*) measurements for a significant sample of 40 broad-line (Type 1) active galaxies for use in testing the well-known relation between black hole mass and stellar velocity dispersion. The objects are selected to contain Ca II triplet, Mgb triplet, and Ca H+K stellar absorption features in their optical spectra so that we may use them to perform extensive tests of the systematic biases introduced by both template mismatch and contamination from the active galactic nucleus (AGN). We use the Ca II triplet as a benchmark to evaluate the utility of the other spectral regions in the presence of AGN contamination. Broad Fe II emission, extending from ~5050-5520 A, in combination with narrow coronal emission lines, can seriously bias sigma* measurements from the Mgb region, highlighting the need for extreme caution in its use. However, we argue that at luminosities constituting a moderate fraction of the Eddington limit, when the Fe II lines are both weak and smooth relative to the stellar lines, it is possible to derive meaningful measurements with careful selection of the fitting region. In particular, to avoid the contamination of coronal lines, we advocate the use of the region 5250--5820 A, which is rich in Fe absorption features. We lay the groundwork for an extensive comparison between black hole mass and bulge velocity dispersion in active galaxies, as described in a companion paper by Greene & Ho.
We present measurements of the redshift-space luminosity-weighted or `marked' correlation function in the SDSS. These are compared with a model in which the luminosity function and luminosity dependence of clustering are the same as that observed, and in which the form of the luminosity-weighted correlation function is entirely a consequence of the fact that massive halos populate dense regions. We do this by using mock catalogs which are constrained to reproduce the observed luminosity function and the luminosity dependence of clustering, as well as by using the language of the redshift-space halo-model. These analyses show that marked correlations may show a signal on large scales even if there are no large-scale physical effects--the statistical correlation between halos and their environment will produce a measureable signal. Our model is in good agreement with the measurements, indicating that the halo mass function in dense regions is top-heavy; the correlation between halo mass and large scale environment is the primary driver for correlations between galaxy properties and environment; and the luminosity of the central galaxy in a halo is different from (in general, brighter than) that of the other objects in the halo. Thus our measurement provides strong evidence for the accuracy of these three standard assumptions of galaxy formation models. These assumptions also form the basis of current halo-model based interpretations of galaxy clustering.
We explore the possibility that the rest frames of CMB, matter and dark energy differ one from another, i.e. they do not converge on very large scales. In such a case, the usual interpretation of the CMB dipole as being due to the relative motion of the observer with respect to the CMB rest frame is not appropriate. Instead, we find that the measured dipole is due to the observer motion relative to the cosmic center of mass rest frame. This means, in particular, that even an observer at rest with respect to the CMB radiation could measure a non-vanishing dipole anisotropy, provided dark energy/matter is moving with respect to the CMB. We also consider the consequences of moving dark energy for the determination of cosmic bulk flows.
We characterize the mass-dependent evolution of galaxies in a large sample of more than 8,000 galaxies using spectroscopic redshifts drawn from the DEEP2 Galaxy Redshift Survey in the range 0.4 < z < 1.4 and stellar masses calculated from K-band photometry obtained at Palomar Observatory. Using restframe (U-B) color and [OII] line widths, we distinguish star-forming from passive populations in order to explore the nature of "downsizing"--a pattern in which the sites of active star formation shift from high mass galaxies at early times to lower mass systems at later epochs. Over the redshift range probed, we identify a mass limit, M_Q, above which star formation appears to be quenched. The physical mechanisms responsible for downsizing can thus be empirically quantified by charting the evolution in this threshold mass. We find that M_Q decreases with time by a factor of ~5 across the redshift range sampled with a redshift dependence of (1+z)^4.5. To further constrain possible quenching mechanisms, we investigate how this downsizing signal depends on local galaxy environment. For the majority of galaxies in regions near the median density, there is no significant correlation between downsizing and environment. However, a weak trend is observed in the comparison between more extreme environments that are more than 3 times overdense or underdense. Here, we find that downsizing is accelerated in overdense regions which host higher numbers of early-type galaxies and fewer late-types as compared to the underdense regions. Our results significantly constrain recent suggestions for the origin of downsizing and indicate that the process for quenching star formation must, primarily, be internally drive. Our survey provides a valuable benchmark for models incorporating baryon physics. (Abridged)
We present MAMBO 1.2 mm observations of five BzK-pre-selected vigorous starburst galaxies at z~2. Two of these were detected at more than 99.5% confidence levels, with 1.2 mm fluxes around 1.5 mJy. These millimeter fluxes imply vigorous activity with star-formation rates (SFRs) approx. 500-1500 Msun/yr, confirmed also by detections at 24 microns with the MIPS camera on board of the Spitzer satellite. The two detected galaxies are the ones in the sample with the highest SFRs estimated from the rest-frame UV, and their far-IR- and UV-derived SFRs agree reasonably well. This is different from local ULIRGs and high-z submm/mm selected galaxies for which the UV is reported to underestimate SFRs by factors of 10-100, but similar to the average BzK-ULIRG galaxy at z~2. The two galaxies detected at 1.2 mm are brighter in K than the typical NIR-counterparts of MAMBO and SCUBA sources, implying also a significantly different K-band to submm/mm flux ratio. This suggests a scenario in which z~2 galaxies, after their rapid (sub)mm brightest phase opaque to optical/UV light, evolve into a longer lasting phase of K-band bright and massive objects. Targeting the most UV active BzKs could yield substantial detection rates at submm/mm wavelengths.
Recent observational studies have revealed star-to-star abundance inhomogeneity among light elements (e.g., C, N, O, Na, and Al) of stars on the main sequence in the Galactic globular clusters (GCs). One of promising interpretations for this result is that the observed abundance inhomogeneity is due to the second generation of stars formed from ejecta of the first generation of evolved stars (e.g., AGB stars) within GCs. However it remains unclear whether and how this primordial pollution can occur within GCs. We here propose a new scenario in which primordial pollution of GCs is highly likely to occur if GCs are located in the central regions of high redshift dark matter subhalos that can host low-mass dwarf galaxies. In this scenario, gas ejected from the first generation of stars of GCs can be effectively trapped in the deep gravitational potential of their host halos and consequently can be consumed for the formation of the second generation of stars without losing a significant amount of gas by ram pressure stripping of interstellar and intergalactic medium. During merging of these halos with the proto-Galaxy, the halos are completely destroyed owing to the strong tidal field of the Galaxy. The self-polluted GCs located initially in the central regions of the halos can survive from tidal destruction owing to their compactness and finally become the Galactic halo GCs. In this scenario, ejecta of field stars surrounding the central GCs can be also converted into stars within their host dwarfs and finally become the second generation of stars of GCs. We also discuss the origin of the difference in the degree of abundance inhomogeneity between different GCs, such as $\omega$ Centauri and NGC 6752, in terms of the difference in physical properties between host halos from which GC originate.
The Euler equation has been accepted as the basic postulate of stellar physics long before the plasma physics was developed. The existence of electrical interaction between particles of interstellar plasma poses the question, how this interaction must be accounted for. We argue that the right way is in formulation of a new postulate. On the base of the new postulate, the theory of a hot star interior is developed. Using this theory we obtain the distribution of stars over their masses and mass-radius, mass-temperature and mass-luminosity dependencies. All these theoretical predictions are in a good agreement with the known measurement data, which confirms the validity of the new postulate.
Recently, the Galactic Center has been reported to be a source of very high energy (VHE) gamma-rays by the VERITAS, CANGAROO and HESS experiments. The energy spectra as measured by these experiments show substantial differences. In this Letter we present MAGIC observations of the Galactic Center, resulting in the detection of a differential gamma-ray flux consistent with a steady, hard-slope power law, described as dN/(dA dt dE) = (2.9+/-0.6)*10^{-12} (E/TeV)^{-2.2+/-0.2} cm^{-2}s^{-1}TeV^{-1}. The gamma-ray source is centered at (Ra, Dec)=(17h 45m 20s, -29deg 2'. This result confirms the previous measurements by the HESS experiment and indicates a steady source of TeV gamma-rays. We briefly describe the observational technique used, the procedure implemented for the data analysis, and discuss the results in the perspective of different models proposed for the acceleration of the VHE gamma-rays.
Context. A molecular survey recently performed ahead of HH~2 supports the idea that the observed molecular enhancement is due to UV radiation from the HH object. Aims. The aim of the present work is to determine whether all HH objects with enhanced HCO$^+$ emission ahead of them also exhibit the same enhanced chemistry as HH~2. We thus observed several molecular lines at several positions ahead of five Herbig-Haro objects where enhanced HCO$^+$ emission was previously observed. Methods. We mapped the five Herbig-Haro objects using the IRAM-30 m. For each position we searched for more than one molecular species, and where possible for more than one transition per species. We then estimated the averaged beam column densities for all species observed and also performed LVG analyses to constrain the physical properties of the gas. Results. The chemically richest quiescent gas is found ahead of the HH~7-11 complex, in particular at the HH~7-11 A position. In some regions we also detected a high velocity gas component. We find that the gas densities are always higher than those typical of a molecular cloud while the derived temperatures are always quite low, ranging from 10 to 25 K. The emission of most species seems to be enhanced with respect to that of a typical dense clump, probably due to the exposure to a high UV radiation from the HH objects. Chemical differentiation among the positions is also observed. We attempt a very simple chemical analysis to explain such differentiation.
We address the topic of the Intra-Night Optical Variability of the BL Lac object S5 0716+714. To this purpose a long term observational campaign was performed, from 1996 to 2003, which allowed the collection of a very large data set, containing 10,675 photometric measurements obtained in 102 nights. The source brightness varied in a range of about 2 mag, although the majority of observations were performed when it was in the range 13.0 < R < 13.75. Variability time scales were estimated from the rates of magnitude variation, which were found to have a distribution function well fitted by an exponential law with a mean value of 0.027 mag/h, corresponding to an e-folding time scale of the flux tau_F = 37.6 h. The highest rates of magnitude variation were around 0.10--0.12 mag/h and lasted less than 2 h. These rates were observed only when the source had an R magnitude < 13.4, but this finding cannot be considered significant because of the low statistical occurrence. The distribution of tau_F has a well defined modal value at 19 h. Assuming the recent estimate of the beaming factor delta about 20, we derived a typical size of the emitting region of about 5 times 10^{16}/(1 + z) cm. The possibility to search for a possible correlation between the mean magnitude variation rate and the long term changes of the velocity of superluminal components in the jet is discussed.
Following an earlier proposal by Choudhuri (2003) for the origin of twist in the magnetic fields of solar active regions, we model the penetration of a wrapped up background poloidal field into a toroidal magnetic flux tube rising through the solar convective zone. The rise of the straight, cylindrical flux tube is followed by numerically solving the induction equation in a comoving Lagrangian frame, while an external poloidal magnetic field is assumed to be radially advected onto the tube with a speed corresponding to the rise velocity. One prediction of our model is the existence of a ring of reverse current helicity on the periphery of active regions. On the other hand, the amplitude of the resulting twist depends sensitively on the assumed structure (diffuse vs. concentrated/intermittent) of the active region magnetic field right before its emergence, and on the assumed vertical profile of the poloidal field. Nevertheless, in the model with the most plausible choice of assumptions a mean twist comparable to the observations can result rather naturally. Our results indicate that the contribution of this mechanism to the twist can be quite significant, and under favourable circumstances it can potentially account for most of the current helicity observed in active regions.
We present a follow-up imaging study (HST + ground based observations) of the complex gravitational lens system RXS J113155.4-123155. The latter consists of a quadruply imaged QSO and of an Einstein ring. Thanks to the MCS deconvolution technique (Magain, Courbin, Sohy 1998), we retrieve accurate relative positions for the lensed QSO images and photometry in the Bessel B, V, R, I filters and in the J-SOFI, F160W and Ks filters. The HST frames unveil structures in the Einstein ring as well as an unidentified object in the vicinity of the lensing galaxy. We discuss the lightcurves and the chromatic flux ratio variations observed in this system and deduce that both intrinsic variability and microlensing took place during a span longer than one year. We also demonstrate that microlensing may easily account for the so called anomalous flux ratios presented in the discovery paper. However, the actual flux ratios are still poorly reproduced when modelling the lens potential with a Singular Isothermal Ellipsoid+shear. We argue that this disagreement can hardly be explained by milli-lensing due to substructures in the lensing galaxy. A solution proposed elsewhere (Claeskens et al. 2006) consists in a more complex lens model including an octupole term to the lens gravitational potential.
Various formation channels for the puzzling ultra-compact dwarf galaxies (UCDs) have been proposed in the last few years. To better judge on some of the competing scenarios, we present spectroscopic [Fe/H] estimates for a sample of 26 compact objects in the central region of the Fornax cluster, covering the magnitude range of UCDs and bright globular clusters. We find a break in the metallicity distribution of compact objects at M_V ~ -11 mag (~3*10^6 M_sun): for M_V<-11 mag the mean metallicity is [Fe/H]=-0.62 +/- 0.05 dex, 0.56 +/- 0.15 dex higher than for M_V>-11 mag. This metallicity break is accompanied by a change in the size-luminosity relation for compact objects, as deduced from HST-imaging: for M_V<-11 mag, r_h scales with luminosity, while for M_V>-11 mag, r_h is almost luminosity-independent. We therefore assume a limiting absolute magnitude of M_V=-11 mag between UCDs and globular clusters. The mean metallicity of five Fornax dE,N nuclei included in our study is about 0.8 dex lower than that of the UCDs, at 4.5 sigma significance. Because of this large metallicity discrepancy we disfavor the hypothesis that most of the Fornax UCDs are the remnant nuclei of tidally stripped dE,Ns. Our metallicity estimates for UCDs are closer to but slightly below those derived for young massive clusters (YMCs) of comparable masses. We therefore favor a scenario where most UCDs in Fornax are successors of merged YMCs produced in the course of violent galaxy-galaxy mergers. It is noted that in contrast to that, the properties of Virgo UCDs are more consistent with the stripping scenario, suggesting that different UCD formation channels may dominate in either cluster.
We present the Shapley Optical Survey, a photometric study covering a 2 deg^2 region of the Shapley Supercluster core at z ~ 0.05 in two bands (B and R). The galaxy sample is complete to B=22.5 (>M^*+6, N_{gal}=16588), and R=22.0 (>M^*+7, N_{gal}=28008). The galaxy luminosity function cannot be described by a single Schechter function due to dips apparent at B ~ 17.5 (M_B ~ -19.3) and R ~ 17.0 (M_R ~ -19.8) and the clear upturn in the counts for galaxies fainter than B and R ~18 mag. We find, instead, that the sum of a Gaussian and a Schechter function, for bright and faint galaxies respectively, is a suitable representation of the data. We study the effects of the environment on the photometric properties of galaxies, deriving the galaxy luminosity functions in three regions selected according to the local galaxy density, and find a marked luminosity segregation, in the sense that the LF faint-end is different at more than 3sigma confidence level in regions with different densities. In addition, the luminosity functions of red and blue galaxy populations show very different behaviours: while red sequence counts are very similar to those obtained for the global galaxy population, the blue galaxy luminosity functions are well described by a single Schechter function and do not vary with the density. Such large environmentally-dependent deviations from a single Schechter function are difficult to produce solely within galaxy merging or suffocation scenarios. Instead the data support the idea that mechanisms related to the cluster environment, such as galaxy harassment or ram-pressure stripping, shape the galaxy LFs by terminating star-formation and producing mass loss in galaxies at \~M^*+2, a magnitude range where blue late-type spirals used to dominate cluster populations, but are now absent.
We present variability and multi-wavelength photometric information for the 933 known quasars in the QUEST Variability Survey. These quasars are grouped into variable and non-variable populations based on measured variability confidence levels. In a time-limited synoptic survey, we detect an anti-correlation between redshift and the likelihood of variability. Our comparison of variability likelihood to radio, IR, and X-ray data is consistent with earlier quasar studies. Using already-known quasars as a template, we introduce a light curve morphology algorithm that provides an efficient method for discriminating variable quasars from periodic variable objects in the absence of spectroscopic information. The establishment of statistically robust trends and efficient, non-spectroscopic selection algorithms will aid in quasar identification and categorization in upcoming massive synoptic surveys. Finally, we report on three interesting variable quasars, including variability confirmation of the BL Lac candidate PKS 1222+037.
We present a suite of three dimensional radiative gravitational hydrodynamics models suggesting that binary stars may be quite capable of forming planetary systems similar to our own. The new models with binary companions do not employ any explicit artificial viscosity, and also include the third (vertical) dimension in the hydrodynamic calculations, allowing for transient phases of convective cooling. The calculations of the evolution of initially marginally gravitationally stable disks show that the presence of a binary star companion may actually help to trigger the formation of dense clumps that could become giant planets. We also show that in models without binary companions, which begin their evolution as gravitationally stable disks, the disks evolve to form dense rings, which then break-up into self-gravitating clumps. These latter models suggest that the evolution of any self-gravitating disk with sufficient mass to form gas giant planets is likely to lead to a period of disk instability, even in the absence of a trigger such as a binary star companion.
We present Submillimeter Array observations of the Herbig Ae star HD169142 in 1.3 millimeter continuum emission and 12CO J=2-1 line emission at 1.5 arcsecond resolution that reveal a circumstellar disk. The continuum emission is centered on the star position and resolved, and provides a mass estimate of about 0.02 solar masses for the disk. The CO images show patterns in position and velocity that are well matched by a disk in Keplerian rotation with low inclination to the line-of-sight. We use radiative transfer calculations based on a flared, passive disk model to constrain the disk parameters by comparison to the spectral line emission. The derived disk radius is 235 AU, and the inclination is 13 degrees. The model also necessitates modest depletion of the CO molecules, similar to that found in Keplerian disks around T Tauri stars.
We discuss the production of cosmogenic neutrinos on extragalactic infrared photons in a model of its cosmological evolution. The relative importance of these infrared photons as a target for proton interactions is significant, especially in the case of steep injection spectra of the ultrahigh energy cosmic rays. For an E$^{-2.5}$ cosmic ray injection spectrum, for example, the event rate of neutrinos of energy above 1 PeV is more than doubled.
We have conducted an archival XMM-Newton study of the bright X-ray point sources in 32 nearby galaxies. From our list of approximately 100 point sources, we attempt to determine if there is a low-state counterpart to the Ultraluminous X-ray (ULX) population, testing the specific predictions of the IMBH hypothesis. Indeed, 16 sources in our sample match the criteria we set for a low-state ULX, namely, L$_X > 10^{38}$ erg s$^{-1}$ and a spectrum well fit with a simple absorbed power law. Further, we find evidence for 26 ULXs which are well fit by a combined blackbody and a power law, similar to high-state Galactic black holes. As in Galactic black hole systems, the spectral indices, $\Gamma$, of the low-state objects, as well as the luminosities, tend to be lower than those of the high-state objects. The observed range of blackbody temperatures is 0.1-1 keV with the most luminous systems tending toward the lowest temperatures. We also find a class of object whose properties (luminosity, blackbody temperature, and power law slopes) are very similar to those of galactic stellar mass black holes. In addition, we find a subset of these objects that can be best fit by a Comptonized spectrum similar to that used for Galactic black holes in the ``very high'' state, when they are radiating near the Eddington limit.
We calculate the full second-order radiation transfer function for Cosmic Microwave Background anisotropies on large angular scales in a flat universe filled with matter and cosmological constant. It includes (i) the second-order generalization of the Sachs-Wolfe effect, and of (ii) both the early and late Integrated Sachs-Wolfe effects, (iii) the contribution of the second-order tensor modes, and is valid for a generic set of initial conditions specifying the level of primordial non-Gaussianity.
Cosmological N-body simulations were performed to study the evolution of the phase-space density Q = rho/sigma^3 of dark matter halos. No significant differences in the scale relations Q ~ sigma^(-2.1) or Q ~ M^(-0.82) are seen for "cold" or "warm" dark matter models. The follow up of individual halos from z = 10 up to the present time indicate the existence of two main evolutionary phases: an early and fast one (10 > z > 6.5), in which Q decreases on the average by a factor of 40 as a consequence of the randomization of bulk motions and a late and long one (6.5 > z > 0), in which Q decreases by a factor of 20 because of mixing induced by merger events. The study of these halos has also evidenced that rapid and positive variations of the velocity dispersion, induced by merger episods, are related to a fast decrease of the phase density Q.
We present the results of 37 nights of CCD unfiltered photometry of nova V2574 Oph (2004) from 2004 and 2005. We find two periods of 0.14164 d (~3.40 h) and 0.14773 d (~3.55 h) in the 2005 data. The 2004 data show variability on a similar timescale, but no coherent periodicity was found. We suggest that the longer periodicity is the orbital period of the underlying binary system and that the shorter period represents a negative superhump. The 3.40 h period is about 4% shorter than the orbital period and obeys the relation between superhump period deficit and binary period. The detection of superhumps in the light curve is evidence of the presence of a precessing accretion disk in this binary system shortly after the nova outburst. From the maximum magnitude - rate of decline relation, we estimate the decay rate t_2 = 17+/-4 d and a maximum absolute visual magnitude of M_Vmax = -7.7+/-1.7 mag.
A key science goal of upcoming dark energy surveys is to seek time evolution of the dark energy. This problem is one of {\em model selection}, where the aim is to differentiate between cosmological models with different numbers of parameters. However, the power of these surveys is traditionally assessed by estimating their ability to constrain parameters, which is a different statistical problem. In this paper we use Bayesian model selection techniques, specifically forecasting of the Bayes factors, to compare the abilities of different proposed surveys in discovering dark energy evolution. We consider six experiments -- supernova luminosity measurements by the Supernova Legacy Survey, SNAP, JEDI, and ALPACA, and baryon acoustic oscillation measurements by WFMOS and JEDI -- and use Bayes factor plots to compare their statistical constraining power. The concept of Bayes factor forecasting has much broader applicability than dark energy surveys.
Extended, soft X-ray emission from the halo of a very large disk galaxy has been detected out to r~20-40 kpc. The luminosity and surface brightness distribution is in very good agreement with predictions by recent, cosmological galaxy formation models. Predictions of Ly-alpha emission, associated with ``cold'' accretion of filamentary gas onto galaxies, are presented. In particular these predictions are compared to the properties of a recently detected Ly-alpha ``blob'', which shows no obvious continuum counter-part in any of 12 broad-bands, from X-rays (Chandra) to infrared (Spitzer). Finally, the predicted evolution of the Tully-Fisher relation, going from z=0 to 1, is discussed in relation to recent observations.
X-ray absorption spectroscopy provides a potentially powerful tool in determining the metal abundances in various phases of the interstellar medium (ISM). We present a case study of the sight line toward 4U 1820-303 (Galactic coordinates l, b=2.79, -7.91 and distance = 7.6 kpc), based on Chandra Grating observations. The detection of OI, OII, OIII, OVII, OVIII, and NeIX Kalpha absorption lines allows us to measure the atomic column densities of the neutral, warm ionized, and hot phases of the ISM through much of the Galactic disk. By comparing these measurements with the 21 cm hydrogen emission and with the pulsar dispersion measure along the same sight line, we estimate the mean oxygen abundances in the neutral and total ionized phases as 0.3(0.2, 0.6) and 2.2(1.1, 3.5) in units of Anders & Grevesse (1989) solar value. This significant oxygen abundance difference is apparently a result of molecule/dust grain destruction and recent metal enrichment in the warm ionized and hot phases. We also measure the column density of neon from its absorption edge and obtain the Ne/O ratio of the neutral plus warm ionized gas as 2.1(1.3, 3.5) solar. Accounting for the expected oxygen contained in molecules and dust grains would reduce the Ne/O ratio by a factor of ~1.5. From a joint-analysis of the OVII, OVIII, and NeIX lines, we obtain the Ne/O abundance ratio of the hot phase as 1.4(0.9, 2.1) solar, which is not sensitive to the exact temperature distribution assumed in the absorption line modeling. These comparable ISM Ne/O ratios for the hot and cooler gas are thus considerably less than the value (2.85+-0.07; 1sigma) recently inferred from corona emission of solar-like stars (Drake & Testa 2005). (abridged)
We report on a large scale numerical study of networks of semilocal cosmic strings in flat space in the stable regime. We find a population of segments with an exponential length distribution and indications of a scaling network without significant loop formation. Very deep in the stability regime strings of superhorizon size grow rapidly and percolate through the box. We believe these should lead at late times to a population of infinite strings similar to topologically stable strings. However, the strings are very light; delocalized scalar gradients dominate the energy density and the network has thus a global texture-like signature. As a result, the observational constraints, at least from the temperature power spectrum of the CMB, on models predicting semilocal strings, should be closer to those on global textures or monopoles, rather than on topologically stable gauged cosmic strings.
Combination of high-precision photometry and spectroscopy allows the detailed study of the upper main sequence in open clusters. We are carrying out a comprehensive study of a number of clusters containing Be stars in order to evaluate the likelihood that a significant number of Be stars form through mass exchange in a binary. Our first results show that most young open clusters contain blue stragglers. In spite of the small number of clusters so far analysed, some trends are beginning to emerge. In younger open clusters, such as NGC 869 and NGC 663, there are many blue stragglers, most of which are not Be stars. In older clusters, such as IC 4725, the fraction of Be stars among blue stragglers is very high. Two Be blue stragglers are moderately strong X-ray sources, one of them being a confirmed X-ray binary. Such objects must have formed through binary evolution. We discuss the contribution of mass transfer in a close binary to the formation of both blue stragglers and Be stars
The Gamma-Ray Burst (GRB) prompt emission is believed to be from highly relativistic electrons accelerated in relativistic shocks. From the GRB high-energy power-law spectral indices \beta observed by the Burst and Transient Source Experiment (BATSE) Large Area Detectors (LAD), we determine the spectral index, $p$, of the electrons' energy distribution. Both the theoretical calculations and numerical simulations of the particle acceleration in relativistic shocks show that $p$ has a universal value \approx 2.2-2.3. We show that the observed distribution of $p$ during GRBs is not consistent with a delta-function distribution or an universal $p$ value, with the width of the distribution >= 0.55. The distributions of $p$ during X-ray afterglows are also investigated. But a "universality" of $p$ in X-ray afterglows cannot be ruled out because of the limited sample size. The $p$ distributions in blazars and pulsar wind nebulae are also broad, inconsistent with a delta-function distribution.
We present a series of numerical studies of the interaction of colliding radiative, hydrodynamic young stellar outflows. We study the effect of the collision impact parameter on the acceleration of ambient material and the degree to which the flow is isotropized by the collision as a mechanism for driving turbulence in the parent molecular cloud. Our results indicate that the high degrees of compression of outflow material, achieved through radiative shocks near the vertex of the interaction, prevents the redirected outflow from spraying over a large spatial region. Furthermore, the collision reduces the redirected outflow's ability to entrain and impart momentum into the ambient cloud. Consideration of the probabilities of outflow collisions leads us to conclude that individual low velocity fossil outflows are the principle coupling between outflows and the cloud.
We present new astrometry of Pluto's three satellites from images taken of the Pluto system during 2002-3 with the High Resolution Camera (HRC) mode of the Advanced Camera for Surveys (ACS) instrument on the Hubble Space Telescope. The observations were designed to produce an albedo map of Pluto but they also contain images of Charon and the two recently discovered satellites, S/2005 P1 and S/2005 P2. Orbits fitted to all three satellites are co-planar and, for Charon and P2, have eccentricities consistent with zero. The orbit of the outermost satellite, P1, has a significant eccentricity of 0.0052 +/- 0.0011. Orbital periods of P1, P2, and Charon are 38.2065 +/- 0.0014, 24.8562 +/- 00013, and 6.3872304 +/- 0.0000011 days, respectively. The total system mass based on Charon's orbit is 1.4570 +/- 0.0009 x 10^22 kg. We confirm previous results that orbital periods are close to the ratio of 6:4:1 (P1:P2:Charon) indiciative of mean-motion resonances, but our results formally preclude precise integer period ratios. The orbits of P1 and P2, being about the barycenter rather than Pluto, enable us to measure the Charon/Pluto mass ratio as 0.1165 +/- 0.0055. This new mass ratio implies a density of 1.66 +/- 0.06 g cm^-3 for Charon and 2.03 +/- 0.06 g cm^-3 for Pluto thus adding confirmation that Charon is somewhat under-dense relative to Pluto. Finally, by stacking all images, we can extract globally averaged photometry. P1 has a mean opposition magnitude of V=24.39 +/- 0.02 and color of (B-V) = 0.644 +/- 0.028. P2 has a mean opposition magnitude of V=23.38 +/- 0.02 and color of (B-V) = 0.907 +/- 0.031. The colors indicate that P1 is spectrally neutral and P2 is slightly more red than Pluto. The variation in surface color with radial distance from Pluto is quite striking (red, neutral, red, neutral) and begs further study.
$\beta$ Cet, 31 Com and $\mu$ Vel represent the main stages through which late-type giants evolve during their lifetime (the Hertzsprung gap (31 Com), the rapid braking zone ($\mu$ Vel) and the core helium burning ``clump'' phase ($\beta$ Cet)). An analysis of their high resolution {\it Chandra} X-ray spectra reveals similar coronal characteristics in terms of both temperature structure and element abundances for the more evolved stars ($\mu$ Vel and $\beta$ Cet) with slight differences for the `younger' giant (31 Com). The coronal temperature structure of 31 Com is significantly hotter showing a clear peak while $\beta$ Cet and $\mu$ Vel show a plateau. $\beta$ Cet and $\mu$ Vel show evidence for a FIP effect in which coronae are depleted in high FIP elements relative to their photospheres by a factor of $\sim 2$. In contrast, 31 Com is characterized by a lack of FIP effect. In other words, neither depletion nor enhancement relative to stellar photospheric values is found. We conclude that the structural changes during the evolution of late-type giants could be responsible for the observed differences in coronal abundances and temperature structure. In particular, the size of the convection zone coupled with the rotation rate seem obvious choices for playing a key role in determining coronal characteristics.
VOFilter is an XML based filter developed by the Chinese Virtual Observatory project to transform tabular data files from VOTable format into OpenDocument format. VOTable is an XML format defined for the exchange of tabular data in the context of the Virtual Observatory (VO). It is the first Proposed Recommendation defined by International Virtual Observatory Alliance, and has obtained wide support from both the VO community and many Astronomy projects. OpenOffice.org is a mature, open source, front office applications suite with the advantage of native support of industrial standard OpenDocument XML file format. Using the VOFilter, VOTable files can be loaded in OpenOffice.org Calc, a spreadsheet application, and then displayed and analyzed as other spreadsheet files. Here, the VOFilter acts as a connector, bridging the coming VO with current industrial office applications. Virtual Observatory and technical background of the VOFilter are introduced. Its workflow, installation and usage are presented. Existing problems and limitations are also discussed together with the future development plans.
An alternative way of explaining astrophysical observations without dark matter is proposed. In the braneworld scenario, where our universe is visualised as a 4-dimensional hypersurface embedded in a higher dimensional spacetime, the effective Einstein equation on the brane contains extra terms. We show that the astrophysical observations which are usually explained by particle dark matter, can be explained in this modified theory of gravity via those extra terms, without the need for dark matter. As specific example, we model X-ray profiles of clusters of galaxies and the galaxy rotation curves which are consistent with observations. Further, we investigate whether gravitational lensing can discriminate between the two possibilities. Significant differences between the values of the deflection angles are obtained, which can be tested in future observations.
Relativistic neutron-loaded outflows in gamma-ray bursts are studied at their early stages, before deceleration by a surrounding medium. The outflow has four components: radiation, electrons, protons and neutrons. The components interact with each other and exchange energy as the outflow expands. The presence of neutrons significantly changes the outflow evolution. Before neutrons decouple from protons, friction between the two components increases their temperatures by many orders of magnitude. After the decoupling, the gradual neutron decay inside the outflow has a drag effect on the protons and reduces their final Lorentz factor.
We present observations of the 2002 September 30 white-light flare, in which the optical continuum emission near the Halpha line is enhanced by ~10%. The continuum emission exhibits a close temporal and spatial coincidence with the hard X-ray (HXR) footpoint observed by RHESSI. We find a systematic motion of the flare footpoint seen in the continuum emission; the motion history follows roughly that of the HXR source. This gives strong evidence the this white-light flare is powered by heating of nonthermal electrons. We note that the HXR spectrum in 10-50 keV is quite soft with gamma being ~7 and there is no HXR emission above 50 keV. The magnetic configuration of the flaring region implies magnetic reconnection taking place at a relatively low altitude during the flare. Despite a very soft spectrum of the electron beam, its energy content is still sufficient to produce the heating in the lower atmosphere where the continuum emission originates. This white-light flare highlights the importance of radiative backwarming to transport the energy below when direct heating by beam electrons is obviously impossible.
Recent observations demonstrate that dwarf elliptical (dE) galaxies in clusters, despite their faintness, are likely a critical galaxy type for understanding the processes behind galaxy formation. Dwarf ellipticals are the most common galaxy type, and are particularly abundant in rich galaxy clusters. The dwarf to giant ratio is in fact highest in rich clusters of galaxies, suggesting that cluster dEs do not form in groups that later merge to form clusters. Dwarf ellipticals are potentially the only galaxy type whose formation is sensitive to global, rather than local, environment. The dominant idea for explaining the formation of these systems, through Cold Dark Matter models, is that dEs form early and within their present environments. Recent results suggest that some dwarfs appear in clusters after the bulk of massive galaxies form, a scenario not predicted in standard hierarchical structure formation models. Many dEs have younger and more metal rich stellar populations than dwarfs in lower density environments, suggesting processes induced by rich clusters play an important role in dE formation. Several general galaxy cluster observations, including steep luminosity functions, and the origin of intracluster light, are natural outcomes of this delayed formation.
The two-point autocorrelation function of ultra-high energy cosmic ray (UHECR) arrival directions has a broad maximum around 25 degrees, combining the data with energies above $4\times 10^{19}$ eV (in the HiRes energy scale) of the HiRes stereo, AGASA, Yakutsk and SUGAR experiments. This signal is not or only marginally present analyzing events of a single experiment, but becomes significant when data from several experiments are added. Both the energy dependence and the angular scale might be interpreted as first signature of the large-scale structure of UHECR sources and of intervening magnetic fields.
IAU Symposium 232 allows a snapshot of ELTs at a stage when design work in several critical mass projects has been seriously underway for two to three years. The status and som eof the main initial design choices are reviewed for the North American Giant Magellan Telescope (GMT) and the Thirty Meter Telescope (TMT) projects and the European Euro50 and the Overwhelmingly Large (OWL) projects. All the projects are drawing from the same "basket" of science requirements, although each project has somewhat different ambitions. The role of the project offices in creating the balance between project scope, timeline and cost, the "iron triangle" of project management, is emphasized with the OWL project providing a striking demonstration at this meeting. There is a reasonable case that the very broad range of science would be most effectively undertaken on several complementary telescopes.
Our understanding of the physical and chemical structure of pre-stellar cores, the simplest star-forming sites, has significantly improved since the last IAU Symposium on Astrochemistry (South Korea, 1999). Research done over these years has revealed that major molecular species like CO and CS systematically deplete onto dust grains at the interior of pre-stellar cores, while species like N2H+ and NH3 survive in the gas phase and can usually be detected towards the core centers. Such a selective behaviour of molecular species gives rise to a differentiated (onion-like) chemical composition, and manifests itself in molecular maps as a dichotomy between centrally peaked and ring-shaped distributions. From the point of view of star-formation studies, the identification of molecular inhomogeneities in cores helps to resolve past discrepancies between observations made using different tracers, and brings the possibility of self-consistent modelling of the core internal structure. Here I present recent work on determining the physical and chemical structure of two pre-stellar cores, L1498 and L1517B, using observations in a large number of molecules and Monte Carlo radiative transfer analysis. These two cores are typical examples of the pre-stellar core population, and their chemical composition is characterized by the presence of large freeze out holes in most molecular species. In contrast with these chemically processed objects, a new population of chemically young cores has started to emerge. The characteristics of its most extreme representative, L1521E, are briefly reviewed.
The all-sky survey of Faraday rotation, a Key Science Project of the planned Square Kilometre Array, will accumulate tens of millions of rotation measure measurements toward background radio sources and will provide a unique database for characterizing the overall magnetic geometry of magnetic fields in galaxies and in the intergalactic medium. Deep imaging of the polarized synchrotron emission from a large number of nearby galaxies, combined with Faraday rotation data, will allow us to test the primordial, flow and dynamo models for field origin and amplification. The SKA will find the first fields in young galaxies and determine the timescale for building up small-scale turbulent and large-scale coherent fields. The spectrum of dynamo modes, if existing, will be resolved. The direction of the present-day coherent field keeps memory of the direction of the seed field which can be used for mapping the structure of the seed field before galaxy formation.
In this paper we test the astrometric precision of VLT/FORS2 observations using a serie of CCD frames taken in Galactic bulge area. A special reduction method based on symmetrization of reference fields was used to reduce the atmospheric image motion. Positional precision of unsaturated R=16 mag star images at 17 sec exposure and 0.55 arcsec seeing was found to be equal to 300 microarcsec. The total error of observations was decomposed into components. It was shown that astrometric error depends largely on the photon centroiding error of the target (250 microarcsec for 16 mag stars) while the image motion is much less (110 microarcsec). At galactic latitudes to about 20 degrees, precision for a serie of frames with a 10 min total exposure is estimated to be 30-50 microarcsec for 14-16 mag stars providing the images are not overexposed and the filter R "special" is used. Error estimates for fields with smaller sky star density are given. We conclude that astrometric observations with large telescopes, under optimal reduction, are never atmospheric limited. The bias caused by differential chromatic refraction and residual chromatism of LADC is considered and expressions valid for correcting color effects in the measured positions are given.
We construct orbit-based axisymmetric dynamical models for the globular cluster M15 which fit groundbased line-of-sight velocities and Hubble Space Telescope line-of-sight velocities and proper motions. This allows us to constrain the variation of the mass-to-light ratio M/L as a function of radius in the cluster, and to measure the distance and inclination of the cluster. We obtain a best-fitting inclination of 60+/-15 degrees, a dynamical distance of 10.3+/-0.4 kpc and an M/L profile with a central peak. The inferred mass in the central 0.05 parsec is 3400 Msun, implying a central density of at least 7.4x10^6 Msun pc^-3. We cannot distinguish the nature of the central mass concentration. It could be an IMBH or it could be large number of compact objects, or it could be a combination. The central 4 arcsec of M15 appears to contain a rapidly spinning core, and we speculate on its origin.
We review some modern applications of the theory of few-body encounters between binaries and single stars. Then we focus on a new treatment of adiabatic encounters, in a regime which is of importance in encounters between a star and a planetary system in a star cluster.
[Abridged abstract] We have performed an abundance analysis for 176 F- and G-
dwarfs of the Galactic thick disk component. Using accurate radial velocities
combined with $Hipparcos$ astrometry, kinematics (U, V, and W) and Galactic
orbital parameters were computed. We estimate the probability for a star to
belong to the thin disk, the thick disk or the halo.
Abundances of C, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu,
Zn, Y, Ba, Ce, Nd, and Eu have been obtained. The abundances for thick disk
stars are compared with those for thin disk members from Reddy et al. (2003).
The ratios of $\alpha$-elements (O, Mg, Si, Ca and Ti) to iron for thick disk
disk stars show a clear enhancement compared to thin disk members in the range
$-0.3 <$ [Fe/H] $ < -1.2$. There are also other elements -- Al, Sc, V, Co, and
possibly Zn -- which show enhanced ratios to iron in the thick disk relative to
the thin disk. The abundances of Na, Cr, Mn, Ni, and Cu (relative to Fe) are
very similar for thin and thick disk stars. The dispersion in abundance ratios
[X/Fe] at given [Fe/H] for thick disk stars is consistent with the expected
scatter due to measurement errors, suggesting a lack of `cosmic' scatter. The
observed compositions of the thin and thick disks seem to be consistent with
models of galaxy formation by hierarchical clustering in a $\Lambda$CDM
universe. In particular, the distinct abundance patterns observed in the thin
and thick disks, and the chemical homogeneity of the thick disk at different
galactocentric distances favor a scenario in which the majority of thick-disk
stars were formed {\it in situ}, from gas rich merging blocks.
We discuss an extended set of Tree+SPH simulations of galaxy clusters, with the goal of investigating the interplay between numerical resolution effects and star-formation/feedback processes. The simulated clusters span the mass range (0.1-2.3) 10^{15}Msun/h, with mass resolution varying by several decades. At the highest achieved resolution, we resolve the virial region of a Virgo-like cluster with more than 2 million gas particles and with at least as many dark-matter (DM) particles. Our resolution study confirms that, in the absence of an efficient feedback mechanism, runaway cooling leads to about 35 per cent of baryons in clusters to be locked up in long lived stars at our highest resolution, with no evidence of convergence. However, including feedback causes the fraction of cooled baryons to converge at about 15 per cent already at modest resolution. Feedback also stabilizes other gas-related quantities, such as radial profiles of entropy, gas density and temperature, against variations due to changes in resolution. We also investigate the influence of the gravitational force softening length, and that of numerical heating of the gas induced by two-body encounters between DM and lighter gas particles. We show that simulations where more DM than gas particles are used, show a significantly enhanced efficiency of star formation at z>3. Our results are important for establishing and delineating the regime of numerical reliability of the present generation of hydrodynamical simulations of galaxy clusters.
We explore whether stellar tidal streams can provide information on the secular, cosmological evolution of the Milky Way's gravitational potential and on the presence of subhalos. We carry out long-term (~t_hubble) N-body simulations of disrupting satellite galaxies in a semi-analytic Galaxy potential where the dark matter halo and the subhalos evolve according to a LCDM cosmogony. All simulations are constrained to end up with the same position and velocity at present. Our simulations account for: (i) the secular evolution of the host halo's mass, size and shape, (ii) the presence of subhalos and (iii) dynamical friction. We find that tidal stream particles respond adiabatically to the Galaxy growth so that, at present, the energy and angular momentum distribution is exclusively determined by the present Galaxy potential. In other words, all present-day observables can only constrain the present mass distribution of the Galaxy independent of its past evolution. We also show that, if the full phase-space distribution of a tidal stream is available, we can accurately determine (i) the present Galaxy's shape and (ii) the amount of mass loss from the stream's progenitor, even if this evolution spanned a cosmologically significant epoch.
A Monte Carlo simulation exploring uncertainties in standard stellar
evolution theory on the red giant branch of metal-poor globular clusters has
been conducted. Confidence limits are derived on the absolute V-band magnitude
of the bump in the red giant branch luminosity function (M_v,b) and the excess
number of stars in thebump, R_b. The analysis takes into account uncertainties
in the primordial helium abundance, abundance of alpha-capture elements,
radiative and conductive opacities, nuclear reaction rates, neutrino energy
losses, the treatments of diffusion and convection, the surface boundary
conditions, and color transformations.
The uncertainty in theoretical values for the red giant bump magnitude varies
with metallicity between +0.13/-0.12 mag at [Fe/H] = -2.4 and +0.23/-0.21 mag
at [Fe/H] = -1.0$. The dominant sources of uncertainty are the abundance of the
alpha-capture elements, the mixing length, and the low-temperature opacities.
The theoretical values of M_v,b are in good agreement with observations. The
uncertainty in the theoretical value of R_b is +/-0.01 at all metallicities
studied. The dominant sources of uncertainty are the abundance of the
alpha-capture elements, the mixing length, and the high-temperature opacities.
The median value of R_b varies from 0.44 at [Fe/H] = -2.4$ to 0.50 at [Fe/H] =
-1.0. These theoretical values for R_b are in agreement with observations.
Sterile neutrinos with masses in the keV range are viable candidates for the warm dark matter. We analyze existing data for the extragalactic diffuse X-ray background for signatures of sterile neutrino decay. The absence of detectable signal within current uncertainties of background measurements puts model-independent constraints on allowed values of sterile neutrino mass and mixing angle, which we present in this work.
We present a detailed chemical abundance analysis of the parent star of the transiting extrasolar planet TrES-1. Based on high-resolution Keck/HIRES and HET/HRS spectra, we have determined abundances relative to the Sun for 16 elements (Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, and Ba). The resulting average abundance of $<[$$X$/H$]>$ $= -0.02\pm0.06$ is in good agreement with initial estimates of solar metallicity based on iron. We compare the elemental abundances of TrES-1 with those of the sample of stars with planets, searching for possible chemical abundance anomalies. TrES-1 appears not to be chemically peculiar in any measurable way. We investigate possible signs of selective accretion of refractory elements in TrES-1 and other stars with planets, and find no statistically significant trends of metallicity [$X$/H] with condensation temperature $T_c$. We use published abundances and kinematic information for the sample of planet-hosting stars (including TrES-1) and several statistical indicators to provide an updated classification in terms of their likelihood to belong to either the thin disk or the thick disk of the Milky Way Galaxy. TrES-1 is found to be a very likely member of the thin disk population. By comparing $\alpha$-element abundances of planet hosts and a large control sample of field stars, we also find that metal-rich ([Fe/H]$\gtrsim 0.0$) stars with planets appear to be systematically underabundant in [$\alpha$/Fe] by $\approx 0.1$ dex with respect to comparison field stars. The reason for this signature is unclear, but systematic differences in the analysis procedures adopted by different groups cannot be ruled out.
Using recent spectroscopic observations, we show that the triple system AO Vel with an eclipsing BpSi primary is in fact a remarkable quadruple system formed by two double-lined spectroscopic binaries with components close to the ZAMS. All available data have been reanalyzed to derive proper orbital parameters for both binary systems and to calculate absolute parameters of the eclipsing system. For the first time, direct determination of the radius and the mass have been obtained for a BpSi star. The study of the physical parameters of this unique system is especially important since it can be used as a test of evolutionary models for very young stars of intermediate mass.
Stable lumps of quark matter may be present in cosmic rays at a flux level, which can be detected by high precision cosmic ray experiments sensitive to anomalous "nuclei" with high mass-to-charge ratio. The properties of these lumps, called strangelets, are described, and so is the production and propagation of strangelets in cosmic rays. Two experiments underway which are sensitive to a strangelet flux in the predicted range are briefly described. Finally it is summarized how strangelets circumvent the acceleration problem encountered by conventional candidates for ultra-high energy cosmic rays and move the Greisen-Zatsepin-Kuzmin cutoff to energies well above the observed maximum energies.
We propose to use a simple observable, the fractional area of "hot spots" in weak lensing mass maps which are detected with high significance, to determine background cosmological parameters. Because these high-shear regions are directly related to the physical non-linear structures of the universe, they derive cosmological information mainly from the non-linear regime of density fluctuations. We show that in combination with future cosmic microwave background (CMB) anisotropy measurements, this method can place constraints on cosmological parameters that are comparable to those from the redshift distribution of galaxy cluster abundances. In particular, adding the information from this simple shear statistic derived from an LSST-like survey to CMB anisotropy information from a Planck-like experiment improves the constraints on the dark energy parameters (energy density and equation of state) and the normalization of the matter power spectrum by over a factor of ten. The main advantage of the statistic proposed in this paper is that projection effects, normally the main source of uncertainty when determining the presence and the mass of a galaxy cluster, here serve as a source of information.
The ionized gas kinematics of the Virgo Cluster galaxy NGC 4254 (Messier 99) is analyzed by an harmonic decomposition of the velocity field into Fourier coefficients. The aims of this study are to measure the kinematical asymmetries of Virgo cluster galaxies and to connect them to the environment. The analysis reveals significant $m=1,2,4$ terms which origins are discussed.
Although it is widely accepted that most galaxies have supermassive black holes (SMBHs) at their centers^{1-3}, concrete proof has proved elusive. Sagittarius A* (\sgras)^4, an extremely compact radio source at the center of our Galaxy, is the best candidate for proof^{5-7}, because it is the closest. Previous Very Long Baseline Interferometry (VLBI) observations (at 7mm) have detected that \sgras is ~2 astronomical unit (AU) in size^8, but this is still larger than the "shadow" (a remarkably dim inner region encircled by a bright ring) arising from general relativistic effects near the event horizon^9. Moreover, the measured size is wavelength dependent^{10}. Here we report a radio image of \sgras at a wavelength of 3.5mm, demonstrating that its size is $\sim$1 AU. When combined with the lower limit on its mass^{11}, the lower limit on the mass density is 6.5x10^{21} Msun pc^{-3}, which provides the most stringent evidence to date that \sgras is an SMBH. The power-law relationship between wavelength and intrinsic size (size $\propto$ wavelength^{1.09}), explicitly rules out explanations other than those emission models with stratified structure, which predict a smaller emitting region observed at a shorter radio wavelength.
The H atoms inside minihalos (i.e. halos with virial temperatures T_vir < 10^4 K, in the mass range roughly from 10^4 M_sun to 10^8 M_sun) during the cosmic dark ages in a LambdaCDM universe produce a redshifted background of collisionally-pumped 21-cm line radiation which can be seen in emission relative to the cosmic microwave background (CMB). Previously, we used semi-analytical calculations of the 21-cm signal from individual halos of different mass and redshift and the evolving mass function of minihalos to predict the mean brightness temperature of this 21-cm background and its angular fluctuations. Here we use high-resolution cosmological N-body and hydrodynamic simulations of structure formation at high redshift (z>8) to compute the mean brightness temperature of this background from both minihalos and the intergalactic medium (IGM) prior to the onset of Ly-alpha radiative pumping. We find that the 21-cm signal from gas in collapsed, virialized minihalos dominates over that from the diffuse shocked gas in the IGM.
Two explanations exist for the short-lived radionuclides present in the solar system when the CAIs first formed. They originated either from the ejecta of a supernova or by the in situ irradiation of nebular dust by energetic particles. With a half-life of only 53 days, Beryllium-7 is then the key discriminant, since it can be made only by irradiation. We calculate the yield of Be-7. Within model uncertainties associated mainly with nuclear cross sections, we obtain agreement with the experimental value. Moreover, if Be-7 and Be-10 have the same origin, the irradiation time must be short. The x-wind model provides a natural astrophysical setting that gives the requisite conditions. The decoupling of the Al-26 and Be-10 observed in some rare CAIs receives a quantitative explanation when rare gradual events are considered. Finally, we show that the presence of supernova-produced Fe-60 in the solar accretion disk does not necessarily mean that other short-lived radionuclides have a stellar origin.
We demonstrate that the quasi-equilibrium state in self-gravitating $N$-body system after cold collapse are uniquely characterized by the local virial relation using numerical simulations. Conversely assuming the constant local virial ratio and Jeans equation for spherically steady state system, we investigate the full solution space of the problem under the constant anisotropy parameter and obtain some relevant solutions. Especially, the local virial relation always provides a solution which has a power law density profile in both the asymptotic regions $r\to 0$ and $\infty$. This type of solutions observed commonly in many numerical simulations. Only the anisotropic velocity dispersion controls this asymptotic behavior of density profile.
Members of the family of pulsar-like stars are distinguished by their different manifestations observed, i.e., radio pulsars, accretion-driven X-ray pulsars, X-ray bursts, anomalous X-ray pulsars/soft gamma-ray repeaters, compact center objects, and dim thermal neutron stars. Though one may conventionally think that these stars are normal neutron stars, it is still an open issue whether they are actually neutron stars or quark stars, as no convincing work, either theoretical from first principles or observational, has confirmed Baade-Zwicky's original idea that supernovae produce neutron stars. After introducing briefly the history of pulsars and quark stars, the author summarizes the recent achievements in his pulsar group, including quark matter phenomenology at low temperature, starquakes of solid pulsars, low-mass quark stars, and the pulsar magnetospheric activities.
We present high-resolution ($1\farcs8$ -- $4\farcs5$) CO data of the Virgo spiral galaxy NGC 4569, obtained using the Nobeyama Millimeter Array. We found that the molecular gas is highly concentrated in the circumnuclear region with two off-center peaks. A CO image with the highest angular resolution of $2\farcs0 \times 1\farcs8$ shows that six blobs likely form a circumnuclear elliptical ring (CER) with a semi-major axis radius of 720 pc. The CER shows a strongly twisted velocity field, and the position--velocity (PV) diagram shows significant forbidden velocity components. These kinetic features are understood as being non-circular motion due to a bar-potential. We found that the CER coincides with the H$\alpha$ bright central core and that the mass ratio of the molecular gas to the dynamical mass is about 18%. These results support a gaseous inflow scenario induced by a weak bar potential and self-gravity of the gas.
The Indo-US coud\'{e} feed stellar spectral library (CFLIB) made available to the astronomical community recently by Valdes et al. (2004) contains spectra of 1273 stars in the spectral region 3460 to 9464 \AA at a high resolution of 1 \AA FWHM and a wide range of spectral types. Cross-checking the reliability of this database is an important and desirable exercise since a number of stars in this database have no known spectral types and a considerable fraction of stars has not so complete coverage in the full wavelength region of 3460-9464 \AA resulting in gaps ranging from a few \AA to several tens of \AA. In this paper, we use an automated classification scheme based on Artificial Neural Networks (ANN) to classify all 1273 stars in the database. In addition, principal component analysis (PCA) is carried out to reduce the dimensionality of the data set before the spectra are classified by the ANN. Most importantly, we have successfully demonstrated employment of a variation of the PCA technique to restore the missing data in a sample of 300 stars out of the CFLIB.
We report results of multiband optical monitoring of two well known blazars, S5 0716+714 and BL Lacertae, carried out in 1996 and 2000-01 with an aim to study optical variations on time scales from minutes to hours and longer.The light curves were derived relative to comparison stars present on the CCD frames. Night to night flux variations of >0.1 mag were observed in S5 0716+714 during a campaign of ~2 weeks in 1996.A good correlation between the lightcurves in different optical bands was found for both inter-night and intra-night observations. Two prominent events of intra-night optical variability were detected in S5 0716+714.Each of these rapidly varying segments of the lightcurves trace an exponential flux profile whose rate of variation is the same in both cases. Our long-term monitoring data of S5 0716+714 showed a distinct flare around JD 2451875 which can be identified in the BVRI bands.This flare coincides with the brightest phase recorded during 1994-2001 in the long-term lightcurves reported by Raiteri et al.(2003). No evidence for the bluer when brighter trend was noticed on inter-night and intra-night time scales. On the other hand, our nearly simultaneous multiband observations of BL Lacertae in October 2001 showed flux variations that were not achromatic. This blazar was found to become bluer when brighter on intra-night time scales and there is a hint of the same trend on inter-night time scales. Based on five nights of observations during a week, BL Lacertae showed a peak night-to-night variability of ~0.6 mag in B. Thus, we found that the present observations of the two blazars, reveal a contrasting behaviour in terms of the dependence of spectral hardening with increasing brightness, at least on intra-night, and possibly also on inter-night, time scales.
The origin of Galactic CRs up the knee energy remains unanswered and provides strong motivation for the study of gamma-ray sources at energies above 10 TeV. We discuss recent results from ground-based gamma-ray Cherenkov imaging systems at these energies as well as future observational efforts in this direction. The exciting results of H.E.S.S. give clues as to the nature of Galactic CR accelerators, and suggest that there is a population of Galactic gamma-ray sources with emission extending beyond 10 TeV. A dedicated system of Cherenkov imaging telescopes optimised for higher energies appears to be a promising way to study the multi-TeV gamma-ray sky.
This paper presents a non-classic approach to narrow field astrometry that offers a significant improvement over conventional techniques due to enhanced reduction of atmospheric image motion. The method is based on two key elements: apodization of the entrance pupil and the enhanced virtual symmetry of reference stars. Symmetrization is implemented by setting special weights to each reference star. Thus a reference field itself forms a virtual net filter that effectively attenuates the image motion spectrum. Atmospheric positional error was found to follow a power dependency ~ R^{K \mu /2} D^{-K/2+1/3} on angular field size R and aperture D; here K is some optional even integer 2<=K<=sqrt{8N+1}-1 limited by a number N of reference stars, and \mu <= 1 is a term dependent on K and the magnitude and sky star distribution in the field. As compared to conventional techniques for which K=2, the improvement in accuracy increases by some orders. Limitations to astrometric performance of monopupil large ground-based telescopes are estimated. The total atmospheric and photon noise for at a 10 m telescope at good 0.4" seeing was found to be, depending on sky star density, 10 to 60 microarcsec per 10 min exposure in R band. For a 100 m telescope and FWHM=0.1" (low-order adaptive optics corrections) the potential accuracy is 0.2 to 2 microarcsec.
In this paper, we present a first comparison of different Adaptive Optics (AO) concepts to reach a given scientific specification for 3D spectroscopy on Extremely Large Telescope (ELT). We consider that a range of 30%-50% of Ensquarred Energy (EE) in H band (1.65um) and in an aperture size from 25 to 100mas is representative of the scientific requirements. From these preliminary choices, different kinds of AO concepts are investigated : Ground Layer Adaptive Optics (GLAO), Multi-Object AO (MOAO) and Laser Guide Stars AO (LGS). Using Fourier based simulations we study the performance of these AO systems depending on the telescope diameter.
We present photometric data of the type II-P supernova (SN) 2004dj in NGC 2403. The multicolor light curves cover the SN from $\sim$ 60 to 200 days after explosion, and are measured with a set of intermediate-band filters that have the advantage of tracing the strength variations of some spectral features. The light curves show a flat evolution in the middle of the plateau phase, then decline exponentially at the late times, with a rate of 0.10$\pm$0.03 mag (10 days)$^{-1}$ in most of the filters. In the nebular phase, the spectral energy distribution (SED) of SN 2004dj shows a steady increase in the flux near 6600 \AA and 8500 \AA, which may correspond to the emission lines of H$\alpha$ and Ca II near-IR triplet, respectively. The photometric behavior suggests that SN 2004dj is a normal SN II-P. Compared with the light curves of another typical SN II-P 1999em, we estimate the explosion date to be June 10$\pm$21 UT, 2004 (JD 2453167$\pm$21) for SN 2004dj. We also estimate the ejected nickel mass during the explosion to be $M(^{56}\rm{Ni})$ = 0.023 $\pm$ 0.005 $M_{\odot}$ from two different methods, which is typical for a SN II-P. We derive the explosion energy $E \approx 0.75^{+0.56}_{-0.38}\times10^{51}$ erg, the ejecta mass $M \approx 10.0^{+7.4}_{-5.2}$ $M_{\odot}$, and the initial radius $R \approx 282^{+253}_{-122}$ $R_{\odot}$ for the presupernova star of SN 2004dj, which are consistent with other typical SNe II-P.
We consider the sample of weakly active galaxies situated in 'Local Universe'
collected in the paper of Pellegrini (2005) with inferred accretion
efficiencies from $10^{-2}$ to $10^{-7}$.
We apply a model of spherically symmetrical Bondi accretion for given
parameters ($M_{BH}$,$T_{\infty}$,$\rho_{\infty}$,) taken from observation. We
calculate spectra emitted by the gas accreting onto its central objects using
Monte Carlo method including synchrotron and bremsstrahlung photons as seed
photons. We compare our results with observed nuclear X-ray luminosities
$L_{X,nuc}$ (0.3-10 keV) of the sample. Model is also tested for different
external medium parameters ($\rho_{\infty}$ and $T_{\infty}$) and different
free parameters of the model. Our model is able to explain most of the observed
nuclear luminosities $L_X$ under an assumption that half of the compresion
energy is transfered directly to the electrons.
Heat conduction plays an important role in the balance between heating and cooling in many astrophysical objects, e.g. cooling flows in clusters of galaxies. Here we investigate the effect of heat conduction on the interaction between a cool disk and a hot corona around black holes. Using the one-radial-zone approximation, we study the vertical structure of the disk corona and derive evaporation and coronal mass flow rates for various reduced thermal conductivities. We find lower evaporation rates and a shift in the evaporation maxima to smaller radii. This implies that the spectral state transition occurs at a lower mass flow rate and a disk truncation closer to the black hole. Reductions of thermal conductivity are thought to be magnetically caused and might vary from object to object by a different configuration of the magnetic fields.
We present the results of a systematic search in 8.5 years of Rossi X-ray Timing Explorer All-Sky Monitor data for evidence of periodicities. The search was conducted by application of the Lomb-Scargle periodogram to the light curves of each of 458 actually or potentially detected sources in each of four energy bands (1.5-3 keV, 3-5 keV, 5-12 keV, and 1.5-12 keV). A whitening technique was applied to the periodograms before evaluation of the statistical significance of the powers. We discuss individual detections with focus on relatively new findings.
We continue the study of the effects of a strong magnetic field on the temperature distribution in the crust of a magnetized neutron star (NS) and its impact on the observable surface temperature. Extending the approach initiated in Geppert et al.(2004), we consider more complex and, hence, more realistic, magnetic field structures but still restrict ourselves to axisymmetric configurations. We put special emphasis on the heat blanketing effect of a toroidal field component. We show that asymmetric temperature distributions can occur and a crustal field consisting of dipolar poloidal and toroidal components will cause one polar spot to be larger than the opposing one. These two warm regions can be separated by an extended cold equatorial belt. We present an internal magnetic field structure which can explain both the X-ray and optical spectra of the isolated NS RXJ 1856-3754. We investigate the effects of the resulting surface temperature profiles on the observable lightcurve which an isolated thermally emitting NS would produce for different field geometries. The lightcurves will be both qualitatively (deviations from sinusoidal shape) and quantitatively (larger pulsed fraction for the same observational geometry) different from those of a NS with an isothermal crust. This opens the possibility to determine the interna} magnetic field strengths and structures in NSs by modeling their X-ray lightcurves and spectra. The striking similarities of our model calculations with the observed spectra and pulse profiles of isolated thermally emitting NSs is an indication for the existence of strong magnetic field components maintained by crustal currents.
We present the first time resolved medium resolution optical spectroscopy of the recently identified peculiar Intermediate Polar (IP) 1RXSJ154814.5-452845, which allows us to precisely determine the binary orbital period (Porb=9.87+/-0.03hr) and the white dwarf spin period Pspin=693.01+/-0.06s). This system is then the third just outside the purported 6-10hr IP orbital period gap and the fifth of the small group of long period IPs, which has a relatively high degree of asynchronism. From the presence of weak red absorption features, we identify the secondary star with a spectral type K2+/-2V, which appears to have evolved on the nuclear timescale. From the orbital radial velocities of emission and the red absorption lines a mass ratio q=0.65+/-0.12 is found. The masses of the components are estimated to be Mwd >= 0.5Msun and Msec=0.4-0.79Msun and the binary inclination 25deg < i <=58deg . A distance between 540-840pc is estimated. At this distance, the presence of peculiar absorption features surrounding Balmer emissions cannot be due to the contribution of the white dwarf photosphere and their spin modulation suggests an origin in the magnetically confined accretion flow. The white dwarf is also not accreting at a particularly high rate (Mdot<5x10**16g/s), for its orbital period. The spin-to-orbit period ratio Pspin/Porb=0.02 and the low mass accretion rate suggest that this system is far from spin equilibrium. The magnetic moment of the accreting white dwarf is found to be < 4.1x10**32 Gcm**3, indicating a low magnetic field system.
We provide a description of the SNSPH code--a parallel 3-dimensional radiation hydrodynamics code implementing treecode gravity, smooth particle hydrodynamics, and flux-limited diffusion transport schemes. We provide descriptions of the physics and parallelization techniques for this code. We present performance results on a suite of code tests (both standard and new), showing the versatility of such a code, but focusing on what we believe are important aspects of modeling core-collapse supernovae.
A catalogue of astrometric (positions, proper motions) and photometric (B, V, R, r', J) data of stars in fields with ICRF objects has been compiled at the Observatory of the National Academy of Sciences of Ukraine and the Kyiv University Observatory. All fields are located in the declination zone from 0 to +30 degrees; the nominal field size is 46' (right ascension) x 24' (declination). The observational basis of this work is 1100 CCD scans down to V=17 mag which were obtained with the Kyiv meridian axial circle in 2001-2003. The catalogue is presented in two versions. The version KMAC1-T contains 159 fields (104 796 stars) and was obtained with reduction to the Tycho2 catalogue. For another 33 fields, due to a low sky density of Tycho2 stars, the reduction was found to be unreliable. Transformation to the ICRF system in the second version of the catalogue (KMAC1-CU) was performed using the UCAC2 and CMC13 catalogues as a reference; it contains 115 032 stars in 192 fields and is of slightly better accuracy. The external accuracy of one catalogue position is about 50-90 mas for V < 15 mag stars. The average error of photometry is better than 0.1 mag for stars down to 16 mag.
We present high resolution spectro-astrometry of a sample of 28 Herbig Ae/Be and 3 F-type pre-main sequence stars. The spectro-astrometry is shown from both empirical and simulated data to be capable of detecting binary companions that are fainter by up to 6 magnitudes at separations larger than 0.1 arcsec. The nine targets that were previously known to be a binary are all detected. In addition, we report the discovery of 6 new binaries and present 5 further possible binaries. The resulting binary fraction of 68+/-11 per cent is the largest reported for any observed sample of Herbig Ae/Be stars, presumably because of the exquisite sensitivity of spectro-astrometry for detecting binary systems. The data hint that the binary frequency of the Herbig Be stars is larger than for the Herbig Ae stars. The appendix presents model simulations to assess the capabilities of spectro-astrometry and reinforces the empirical findings. Two objects, HD 87643 and Z CMa, display evidence for asymmetric outflows. Finally, the position angles of the binary systems have been compared with available orientations of the circumprimary disc and these appear to be co-planar. The alignment between the circumprimary discs and the binary systems strongly suggests that the formation of binaries with intermediate mass primaries is due to fragmentation as the alternative, stellar capture, does not naturally predict aligned discs. The aligment extends to the most massive B-type stars in our sample. This leads us to conclude that formation mechanisms that do result in massive stars, but predict random angles beween the binaries and the circumprimary disks, such as stellar collisions, are also ruled out for the same reason.
Dynamics of spiral galaxies derived from a given surface mass density has been derived by Toomre in a classic paper. We try to transform the singular elliptic function in the integral into a regular elliptic function. The result makes corresponding numerical evaluations and analytic analysis easier. It is applied to the study of the dynamics of Newtonian system and MOND as well. One shows clearly that careful treatment is needed in dealing with the cut-off of the input data. Explicit examples with simple models are also shown in this paper.
In this work, the relation between muon production in extensive air showers and features of hadronic multiparticle production at low energies is studied. Using CORSIKA, we determine typical energies and phase space regions of secondary particles which are important for muon production in extensive air showers and confront the results with existing fixed target measurements. Furthermore possibilities to measure relevant quantities of hadron production in existing and planned accelerator experiments are discussed.
We present 3-5 micron spectroscopy of the interacting system NGC 6240, showing the presence of two active galactic nuclei. The brightest (southern) nucleus shows up with a starburst-like emission, with a prominent 3.3 micron emission feature. However, the presence of an AGN is revealed by the detection of a broad Br alpha emission line, with a width of ~1,800 km/s. The spectrum of the faintest (northern) nucleus shows typical AGN features, such as a steep continuum and broad absorption features in the M-band. We discuss the physical properties of the dusty absorbers/emitters, and show that in both nuclei the AGN is dominant in the 3-5 micron band, but its contribution to the total luminosity is small (a few percent of the starburst emission).
The detection of compact sources embedded in a background is a very common problem in many fields of Astronomy. In these lecture notes we present a review of different techniques developed for the detection and extraction of compact sources, with a especial focus on their application to the field of the cosmic microwave background radiation. In particular, we will consider the detection of extragalactic point sources and the thermal and kinematic Sunyaev-Zeldovich effects from clusters of galaxies.
We performed a spectroscopic search for binaries among hot Horizontal Branch stars in globular clusters. We present final results for a sample of 51 stars in NGC6752, and preliminary results for the first 15 stars analyzed in M80. The observed stars are distributed along all the HBs in the range 8000 < Teff < 32000 K, and have been observed during four nights. Radial velocity variations have been measured with the cross-correlation technique. We carefully analyzed the statistical and systematic errors associated with the measurements in order to evaluate the statistical significance of the observed variations. No close binary system has been detected, neither among cooler stars nor among the sample of hot EHB stars (18 stars with Teff > 22000 K in NGC6752). The data corrected for instrumental effects indicate that the radial velocity variations are always below the 3sigma level of ~15 km/s. These results are in sharp contrast with those found for field hot subdwarfs, and open new questions about the formation of EHB stars in globular clusters, and possibly of the field subdwarfs.
We present a model for the accretion flow around the supermassive black hole in the LINER nucleus of NGC 1097 which fits the optical to X-ray spectral energy distribution (SED). The X-ray segment of the SED is based on observations with the Chandra X-Ray Observatory, which are reported here for the first time. The inner part of the flow is modeled as a radiatively inefficient accretion flow (RIAF) and the outer part as a standard thin disk. The value of the transition radius (~225 Schwarzschild radii) between the RIAF and outer thin disk was obtained from our previous fitting of the double-peaked Balmer emission line profile, which originates in the thin disk. The black hole mass was inferred from measurements of the stellar velocity dispersion in the host galaxy. When these parameters are used in the accretion flow model, the SED can be successfully reproduced, which shows that the line profile model and the accretion flow model are consistent with each other. A small remaining excess in the near-UV is accounted by the contribution of an obscured starburst located within 9 pc from the nucleus, as we reported in an earlier paper. The radio flux is consistent with synchrotron emission of a relativistic jet modeled by means of the internal shock scenario. In an appendix we also analyze the Chandra X-ray observations of the ~1 kpc circumnuclear star-forming ring and of an ultraluminous compact X-ray source located outside the ring.
We present ground-based mid-infrared observations of Class 0 protostars in LDN 1448. Of the five known protostars in this cloud, we detected two, L1448N:A and L1448C, at 12.5, 17.9, 20.8, and 24.5 microns, and a third, L1448 IRS 2, at 24.5 microns. We present high-resolution images of the detected sources, and photometry or upper limits for all five Class 0 sources in this cloud. With these data, we are able to augment existing spectral energy distributions (SEDs) for all five objects and place them on an evolutionary status diagram.
We present the absolute measurement of the unresolved 0.5-8 keV X-ray background in the Chandra Deep Fields (CDF) North and South, the longest observations with Chandra (2 Ms and 1 Ms, respectively). We measure the unresolved CXB intensity by extracting spectra of the sky, removing all point and extended sources detected in the CDF. To model and subtract the instrumental background, we use observations obtained with ACIS in stowed position, not exposed to the sky. The unresolved signal in the 0.5-1 keV band is dominated by diffuse Galactic and local thermal-like emission. In the 1-8 keV band, the unresolved spectrum is adequately described by a power law with a photon index 1.5. We find unresolved CXB background intensities of (1.05+/-0.14)x10^-12 ergs cm^-2 s^-1 deg^-2 for the 1-2 keV band and (3.5+/-1.7)x10^-12 ergs cm^-2 s^-1 deg^-2 for the 2-8 keV band. Our detected unresolved intensities in these bands significantly exceed the expected flux from sources below the CDF detection limits, if one extrapolates the logN/logS curve to zero flux. Thus these background intensities imply either a genuine diffuse component, or a steepening of the logN/logS curve at low fluxes, most significantly for energies <2 keV. Adding the unresolved intensity to the total contribution from sources detected in these fields and wider-field surveys, we obtain a total intensity of the extragalactic CXB of (4.6+/-0.2) x10^-12 ergs cm^-2 s^-1 deg^-2 for 1-2 keV and (1.7+/-0.2)x10^-11 ergs cm^-2 s^-1 deg^-2 for 2-8 keV. These totals correspond to a CXB power law normalization (for photon index 1.4) of 10.9 photons s^-1 keV^-1 sr^-1 at 1 keV. This corresponds to resolved fractions of 77+/-3% and 79+/-8% for 1-2 and 2-8 keV, respectively.
From a newly obtained VLT/UVES spectrum we have determined the oxygen abundance of HE 1327-2326, the most iron-poor star known to date. UV-OH lines yield a 1D LTE abundance of [O/Fe]_OH = 3.7 (subgiant case) and [O/Fe]_OH = 3.4 (dwarf case). Using a correction of -1.0 dex to account for 3D effects on OH line formation, the abundances are lowered to [O/Fe] = 2.8 and [O/Fe] = 2.5, respectively, which we adopt. Without 3D corrections, the UV-OH based abundance would be in disagreement with the upper limits derived from the OI triplet lines: [O/Fe]_trip < 2.8 (subgiant) and [O/Fe]_trip < 3.0 (dwarf). We also correct the previously determined carbon and nitrogen abundances for 3D effects. Knowledge of the O abundance of HE 1327-2326 has implications for the interpretation of its abundance pattern. A large O abundance is in accordance with HE 1327-2326 being an early Population II star which formed from material chemically enriched by a first generation supernova. Our derived abundances, however, do not exclude other possibilities such as a Population III scenario.
Our objective is to prove that integrated optics (IO) is not only a good concept for astronomical interferometry but also a working technique with high performance. We used the commissioning data obtained with the dedicated K-band integrated optics two-telescope beam combiner which now replaces the fiber coupler MONA in the VLTI/VINCI instrument. We characterize the behaviour of this IO device and compare its properties to other single mode beam combiner like the previously used MONA fiber coupler. The IO combiner provides a high optical throughput, a contrast of 89% with a night-to-night stability of a few percent. Even if a dispersive phase is present, we show that it does not bias the measured Fourier visibility estimate. An upper limit of 0.005 for the cross-talk between linear polarization states has been measured. We take advantage of the intrinsic contrast stability to test a new astronomical prodecure for calibrating diameters of simple stars by simultaneously fitting the instrumental contrast and the apparent stellar diameters. This method reaches an accuracy with diameter errors of the order of previous ones but without the need of an already known calibrator. These results are an important step of integrated optics and paves the road to incoming imaging interferometer projects.
I comment (in a review fashion) on a few selected topics in the field of extragalactic globular clusters with strong emphasis on recent work. The topics are: bimodality in the colour distribution of cluster systems, young massive clusters, and the brightest old clusters. Globular cluster research, perhaps more than ever, has lead to important (at least to astronomers) progress and problems in galaxy structure and formation.
Orion's Veil is an absorbing screen that lies along the line of sight to the Orion H II region. It consists of two or more layers of gas that must lie within a few parsecs of the Trapezium cluster. Our previous work considered the Veil as a whole and found that the magnetic field dominates the energetics of the gas in at least one component. Here we use high-resolution STIS UV spectra that resolve the two velocity components in absorption and determine the conditions in each. We derive a volume hydrogen density, 21 cm spin temperature, turbulent velocity, and kinetic temperature, for each. We combine these estimates with magnetic field measurements to find that magnetic energy significantly dominates turbulent and thermal energies in one component, while the other component is close to equipartition between turbulent and magnetic energies. We observe molecular hydrogen absorption for highly excited v, J levels that are photoexcited by the stellar continuum, and detect blueshifted S III and P III. These ions must arise from ionized gas between the mostly neutral portions of the Veil and the Trapezium and shields the Veil from ionizing radiation. We find that this layer of ionized gas is also responsible for He I absorption in the Veil, which resolves a 40-year-old debate on the origin of He I absorption towards the Trapezium. Finally, we determine that the ionized and mostly atomic layers of the Veil will collide in less than 85,000 years.
We have performed a pilot Chandra survey of an off-center region of the Coma cluster to explore the X-ray properties and Luminosity Function of normal galaxies. We present results on 13 Chandra-detected galaxies with optical photometric matches, including four spectroscopically-confirmed Coma-member galaxies. All seven spectroscopically confirmed giant Coma galaxies in this field have detections or limits consistent with low X-ray to optical flux ratios (fX/fR < 10^-3). We do not have sufficient numbers of X-ray detected galaxies to directly measure the galaxy X-ray Luminosity Function (XLF). However, since we have a well-measured optical LF, we take this low X-ray to optical flux ratio for the 7 spectroscopically confirmed galaxies to translate the optical LF to an XLF. We find good agreement with Finoguenov et al. (2004), indicating that the X-ray emission per unit optical flux per galaxy is suppressed in clusters of galaxies, but extends this work to a specific off-center environment in the Coma cluster. Finally, we report the discovery of a region of diffuse X-ray flux which might correspond to a small group interacting with the Coma Intra-Cluster Medium (ICM).
Collisionless shocks are commonly argued to be the sites of cosmic ray (CR) acceleration. We study the influence of CRs on weakly magnetized relativistic collisionless shocks and apply our results to external shocks in gamma-ray burst (GRB) afterglows. The common view is that the transverse Weibel instability (TWI) generates a small-scale magnetic field which facilitates collisional coupling and thermalization in the shock transition. The TWI field is expected to decay rapidly, over a finite number of proton plasma skin depths from the transition. However, the synchrotron emission in GRB afterglows suggests that a strong and persistent magnetic field is present in the plasma that crosses the shock; the origin of this field is a key open question. Here we find that the common picture involving TWI demands revision. Namely, the CRs drive turbulence in the shock upstream on scales much larger than the skin depth. This turbulence generates a large-scale magnetic field that quenches TWI and produces a magnetized shock. The new field efficiently confines CRs and enhances the acceleration efficiency. The CRs modify the shocks in GRB afterglows at least while they remain relativistic. The origin of the magnetic field that gives rise to the synchrotron emission is plausibly in the CR-driven turbulence. We do not expect ultrahigh energy cosmic ray production in external GRB shocks.
We review the X-ray spectra of the cores of clusters of galaxies. Recent high resolution X-ray spectroscopic observations have demonstrated a severe deficit of emission at the lowest X-ray temperatures as compared to that expected from simple radiative cooling models. The same observations have provided compelling evidence that the gas in the cores is cooling below half the maximum temperature. We review these results, discuss physical models of cooling clusters, and describe the X-ray instrumentation and analysis techniques used to make these observations. We discuss several viable mechanisms designed to cancel or distort the expected process of X-ray cluster cooling.
We report on integral field spectrocopy observations, performed with the PPAK module of the PMAS spectrograph, covering a field-of-view of ~74''X64'' centered on the core of the galaxy cluster Abell 2218. A total of 43 objects were detected, 27 of them galaxies at the redshift of the cluster. We deblended and extracted the integrated spectra of each of the objects in the field using an adapted version of galfit for 3D spectroscopy (galfit3d). We use these spectra, in combination with morphological parameters derived from deep HST/ACS images, to study the stellar population and evolution of galaxies in the core of this cluster.
We present an analysis of the HD 82943 planetary system based on a radial velocity data set that combines new measurements obtained with the Keck telescope and the CORALIE measurements published in graphical form. We examine simultaneously the goodness of fit and the dynamical properties of the best-fit double-Keplerian model as a function of the poorly constrained eccentricity and argument of periapse of the outer planet's orbit. The fit with the minimum chi_{nu}^2 is dynamically unstable if the orbits are assumed to be coplanar. However, the minimum is relatively shallow, and there is a wide range of fits outside the minimum with reasonable chi_{nu}^2. For an assumed coplanar inclination i = 30 deg. (sin i = 0.5), only good fits with both of the lowest order, eccentricity-type mean-motion resonance variables at the 2:1 commensurability, theta_1 and theta_2, librating about 0 deg. are stable. For sin i = 1, there are also some good fits with only theta_1 (involving the inner planet's periapse longitude) librating that are stable for at least 10^8 years. The libration semiamplitudes are about 6 deg. for theta_1 and 10 deg. for theta_2 for the stable good fit with the smallest libration amplitudes of both theta_1 and theta_2. We do not find any good fits that are non-resonant and stable. Thus the two planets in the HD 82943 system are almost certainly in 2:1 mean-motion resonance, with at least theta_1 librating, and the observations may even be consistent with small-amplitude librations of both theta_1 and theta_2.
In this letter, we comment on the robustness of putative cool (kT ~ 0.2 keV) accretion disc components in the X-ray spectra of the most luminous (L ~ 10^40 erg/s) ultra-luminous X-ray sources (ULXs) in nearby normal galaxies. When compared to stellar-mass black holes, the low disc temperatures observed in some ULXs may imply intermediate-mass black hole primaries. Recent work has claimed that such soft excesses are unlikely to be actual disc components, based on the lack of variability in these components, and in the overall source flux. Other work has proposed that alternative phenomenological models, and complex Comptonisation models, rule-out cool disc components in ULX spectra. An inspection of the literature on Galactic stellar-mass black holes and black hole candidates demonstrates that the flux behaviours seen in specific ULXs are consistent with phenomena observed in well-known Galactic X-ray binaries. Applying Comptonisation models to simulated disc blackbody plus power-law spectra shows that at the sensitivity achieved in even the best ULX spectra, Comptonisation fits are highly model-dependent, and do not yield meaningful constraints on the accretion flow. In contrast, the need for a soft, thermal component does not appear to be model-dependent. As we have previously noted, soft thermal components in ULX spectra may not represent accretion discs, but present alternatives to this interpretation are not robust.
In this comment we question some arguments presented in astro-ph/0512048 to refuse the presence of an singular mass surface layer. In particular, incorrect expressions are used for the disk's surface mass density. We also point out that the procedure of removing the descontinuity on the $z=0$ plane with a region of continuous density gradient generates other two regions of descontinuities with singular mass surface layers making the model unrealistic.
We present numerical radiation-hydrodynamic simulations of the evolution of HII regions formed in an inhomogeneous medium resulting from turbulence simulations. We find that the filamentary structure of the underlying density distribution produces a highly irregular shape for the ionized region, in which the ionization front escapes to large distances in some directions within 80,000 years. In other directions, on the other hand, neutral gas in the form of dense globules persists within 1 parsec of the central star for the full duration of our simulation (400,000 years). Divergent photoablation flows from these globules maintain a root-mean-squared velocity in the ionized gas that is close to the ionized sound speed. Simulated images in optical emission lines show morphologies that are in strikingly detailed agreement with those observed in real HII regions.
We analyze several recently detected gamma-ray bursts (GRBs) with late X-ray flares in the context of late internal shock and late external shock models. We find that the X-ray flares in GRB 050421 and GRB 050502B originate from late internal shocks, while the main X-ray flares in GRB 050406 and GRB 050607 may arise from late external shocks. Under the assumption that the central engine has two periods of activities, we get four basic types of X-ray light curves. The classification of these types depends on which period of activities produces the prompt gamma-ray emission (Type 1 and Type 2: the earlier period; Type 3 and Type 4: the late period), and on whether the late ejecta catching up with the early ejecta happens earlier than the deceleration of the early ejecta (Type 1 and Type 3) or not (Type 2 and Type 4). We find that the X-ray flare caused by a late external shock is a special case of Type 1. Our analysis reveals that the X-ray light curves of GRBs 050406, 050421, and 050607 can be classified as Type 1, while the X-ray light curve of GRB 050502B is classified as Type 2. However, the X-ray light curve of GRB 050406 is also likely to be Type 2. We also predict a long-lag short-lived X-ray flare caused by the inner external shock, which forms when a low baryon-loading long-lag late ejecta decelerates in the non-relativistic tail of an outer external shock driven by an early ejecta.
A growing number of early Be stars discovered in X-ray surveys exhibit X-ray luminosities intermediate between those of normal stars and those of most Be/X-ray binaries in quiescence. Their X-ray spectra are also much harder than those of shocked wind OB stars and can be best fitted by a thin thermal plasma with T ~ 10^8 K, added to a cooler and much fainter thermal component. An iron line complex including a fluorescence component is detected in many cases. There is no evidence for coherent pulsations in any of these systems but strong variability on time scales as short as 100 s is usually observed. Large oscillations with quasi-periods of the order of one hour or more are detected in the X-ray light curves of several sources, but have so far failed to prove to be strictly periodic. The optical and X-ray properties of these new objects strikingly resemble those of the so far unique and enigmatic Be star Gamma-Cas and define a new class of X-ray emitters. We discuss the possible origin of the X-ray emission in the light of the models proposed for Gamma-Cas, magnetic disc-star interaction or accretion onto a compact companion object -- neutron star or white dwarf.
PPak is a new fiber-based Integral Field Unit (IFU), developed at the Astrophysical Institute Potsdam, implemented as a module into the existing PMAS spectrograph. The purpose of PPak is to provide both an extended field-of-view with a large light collecting power for each spatial element, as well as an adequate spectral resolution. The PPak system consists of a fiber bundle with 331 object, 36 sky and 15 calibration fibers. The object and sky fibers collect the light from the focal plane behind a focal reducer lens. The object fibers of PPak, each 2.7 arcseconds in diameter, provide a contiguous hexagonal field-of-view of 74 times 64 arcseconds on the sky, with a filling factor of 60%. The operational wavelength range is from 400 to 900nm. The PPak-IFU, together with the PMAS spectrograph, are intended for the study of extended, low surface brightness objects, offering an optimization of total light-collecting power and spectral resolution. This paper describes the instrument design, the assembly, integration and tests, the commissioning and operational procedures, and presents the measured performance at the telescope.
We have calculated the evolution of low-mass X-ray binaries that leads to the formation of the binary radio pulsars like PSR J1713+0747. We show that the mass transfer is most likely to be nonconservative, due to unstable disk accretion, to account for the mass of PSR J1713+0747, which is close to its initial value. We assume that part of the lost material from the binary may form a circumbinary disk, and find that it can significantly influence the mass transfer processes. We briefly discuss the implications of the circumbinary disks on the evolution of low-mass X-ray binaries and the formation of low-mass binary pulsars.
We present an analysis of an anomalously long X-ray burst from the low-mass X-ray binary system GX~3+1 observed by INTEGRAL on August 31, 2004. The burst is characterized by two distinct phases: an initial short spike of 6 s followed by an extended decay phase lasting more than 2000 s. Due to its uncommon duration this burst appears as intermediate between the normal type I X-ray bursts and the long superbursts. We see emission up to 30 keV energy during the first 5 s of the outburst where the bolometric burst peak luminosity approaches the Eddington limit. Indications of a radius expansion episode during the peak phase are thus not overruled. A time-resolved two-component spectral analysis of the total emission reveals similar results as a black-body modeling of the net burst emission. From the burst light curve and the derived burst parameters we conclude that we observed a type I X-ray burst of an unusual character. We discuss three alternative schemes to explain this peculiar X-ray burst: 1) unstable burning of a hydrogen/helium layer involving an unusually large amount of hydrogen, 2) pure helium ignition at an unusually large depth, but this seems unlikely in the present case, and 3) limited carbon burning at an unusually shallow depth triggered by unstable helium ignition.
We present a new analysis of the very first mid-infrared N-band long-baseline interferometric observations of an extragalactic source: the nucleus of the Seyfert 2 galaxy NGC 1068, obtained with MIDI (Mid-InfrareD Interferometer), the mid-infrared beamcombiner at the European Southern Observatory (ESO) Very Large Telescope Interferometer (VLTI). The resolution of 10 mas allows to study the compact central core of the galaxy between 8 and 13 microns. Both visibility measurements and MIDI spectrum are well reproduced with a simple radiative transfer model with two concentric spherical components. The derived angular sizes and temperatures are about 35 and 83 mas, and 361 K and 226 K for these two components respectively. Some other evidences strongly support such low temperatures. This modeling also provides the variation of optical depth as a function of wavelength for the extended component across the N-band pointing towards the presence of amorphous silicate grains. This shows that MIDI actually carried out the first direct observations of the distribution of dust around the central engine. Together with other observational pieces, we are able to move a step forward in the reconstruction of the picture drawn for AGNs.
Fragments from organic molecule dissociation (such as reactive ions and radicals) can form interstellar complex molecules like amino acids. The goal of this work is to experimentally study photoionization and photodissociation processes of acetic acid (CH$_3$COOH), a glycine (NH$_2$CH$_2$COOH) precursor molecule, by soft X-ray photons. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), employing soft X-ray photons from a toroidal grating monochromator (TGM) beamline (100 - 310 eV). 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, that only 4-6% of CH$_3$COOH survive the strong ionization field. CH$_3$CO$^+$, COOH$^+$ and CH$_3^+$ ions are the main fragments, and the presence of the former may indicate that the production-destruction process of acetic acid in hot molecular cores (HMCs) could decrease the H$_2$O abundance since the net result of this process converts H$_2$O into OH + H$^+$. The COOH$^+$ ion plays an important role in ion-molecule reactions to form large biomolecules like glycine.
Aims. We intend to spatially and spectrally resolve the [O I] emission region
in two nearby Herbig stars.
Methods. We present high-resolution (R = 80,000) VLT/UVES echelle spectra of
the [O I] 6300A line in the Herbig Ae/Be stars HD 97048 and HD 100546. Apart
from the spectral signature, also the spatial extent of the [O I] emission
region is investigated. For both stars, we have obtained spectra with the slit
positioned at different position angles on the sky.
Results. The [O I] emission region of HD 100546 appears to be coinciding with
the dust disk, its major axis located at 150+/-11 degrees east of north. The SE
part of the disk moves towards the observer, while the NW side is redshifted.
The [O I] emission region rotates counterclockwise around the central star. For
HD 97048, the position angle of the emission region is 160+/-19 degrees east of
north, which is the first determination of this angle in the literature. The
southern parts of the disk are blueshifted, the northern side moves away from
us. Our data support the idea that a gap is present at 10AU in the disk of HD
100546. Such a gap is likely planet-induced. We estimate the mass and orbital
radius of this hypothetical companion responsible for this gap to be 20 Jupiter
masses and 6.5 AU respectively.
Conclusions. Based on temporal changes in the [O I] line profile, we conclude
that inhomogeneities are present in the [O I] emission region of HD 100546.
These ``clumps'' could be in resonance with the suggested companion, orbiting
the central star in about 11 yr. If confirmed, these observations could point
to the existence of an object straddling the line between giant planet and
brown dwarf in a system as young as 10 million years.
We present a new 12CO(J=1-0)-line survey of the Andromeda galaxy, M31, covering the bright disk with the highest resolution to date (85 pc along the major axis), observed On-the-Fly (in italics) with the IRAM 30-m telescope. We discuss the distribution of the CO emission and compare it with the distributions of HI and emission from cold dust traced at 175mum. Our main results are: 1. Most of the CO emission comes from the radial range R=3-16 kpc, but peaks near R=10 kpc. The emission is con- centrated in narrow, arm-like filaments defining two spiral arms with pitch angles of 7d-8d. The average arm-interarm brightness ratio along the western arms reaches 20 compared to 4 for HI. 2. For a constant conversion factor Xco, the molecular fraction of the neutral gas is enhanced in the arms and decreases radially. The apparent gas-to-dust ratios N(HI)/I175 and (N(HI)+2N(H2))/I175 increase by a factor of 20 between the centre and R=14 kpc, whereas the ratio 2N(H2)/I175 only increases by a factor of 4. Implications of these gradients are discussed. In the range R=8-14 kpc total gas and cold dust are well correlated; molecular gas is better correlated with cold dust than atomic gas.
The hadronic interaction model BBL implements the ideas of gluon saturation due to large densities. When approaching the black body limit at high energies, leading partons acquire large transverse momenta which breaks up their coherence. This leads to a suppression of forward scattering, and is therefore important for air showers. We discuss some general aspects of this new approach and their influence on air shower properties as seen by fluorescence and surface detectors: The position of the shower maximum is reduced due to stronger absorption in the atmosphere. The lateral distribution functions become flatter for the same reason. Muons are produced abundantly due to high multiplicities in the mid-rapidity region. The response of water Cherenkov detectors and comparisons to other interaction models are shown.
We perform a kinematic analysis of the Hipparcos and TRC proper motions of stars by using a linear Ogorodnikov-Milne model. All of the distant (r more than 0.2 kpc) stars of the Hipparcos catalog have been found to rotate around the Galactic y axis with an angular velocity of -0.36 +- 0.09 mas/year. One of the causes of this rotation may be an uncertainty in the lunisolar precession constant adopted when constructing the ICRS. In this case? the correction to the IAU (1976) lunisolar precession constant in longitude is shown to be -3.26 +- 0.10 mas/yr. Based on the TRC catalog, we have determined the main Oort constants: A = 14.9 +- 1.0 and B = -10.8 +- 0.3 km/s/kpc. The component of the model that describes the rotation of all TRC stars around the Galactic y axis is nonzero for all magnitudes, My= -0.86 +- 0.11 mas/yr.
We present a pilot study of atmospheres of accreting magnetic white dwarfs irradiated by intense fluxes at ultraviolet to infrared wavelengths. The model uses a standard LTE stellar atmosphere code which is expanded by introducing an angle-dependent external radiation source. The present results are obtained for an external source with the spectral shape of a 10000K blackbody and a freely adjustable spectral flux. The model provides an explanation for the observed largely filled-up Lyman lines in the prototype polar AM Herculis during its high states. It also confirms the hypotheses (i) that irradiation by cyclotron radiation and other radiation sources is the principle cause for the large heated polar caps surrounding the accretion spots on white dwarfs in polars and (ii) that much of the reprocessed light appears in the far ultraviolet and not in the soft X-ray regime as suggested in the original simple theories. We also briefly discuss the role played by hard X-rays in heating the polar cap.
We analyzed the space velocities of Gould Belt stars younger than 125 Myr
located at heliocentric distances <650 pc. We determined the rotation and
expansion parameters of the Gould Belt by assuming the existence of a single
kinematic center whose direction was found to be the following:
$l_\circ=128^\circ$ and $R_\circ=150$ pc. The linear velocities reach their
maximum at a distance of $\approx300$ pc from the center and are -6 km s$^{-1}$
for the rotation (whose direction coincides with the Galactic rotation) and +4
km s$^{-1}$ for the expansion. The stellar rotation model used here is shown to
give a more faithful description of the observed velocity field than the linear
model based on the Oort constants $A_G$ and $B_G$. We present evidence that the
young clusters $\beta$ Pic, Tuc/HorA, and TWA belong to the Gould Belt
structure.
Based on the most complete list of the results of an individual comparison of the proper motions for stars of various programs common to the Hipparcos catalog, each of which is an independent realization of the inertial reference frame with regard to stellar proper motions, we redetermined the vector $\omega$ of residual rotation of the ICRS system relative to the extragalactic reference frame. The equatorial components of this vector were found to be the following: $\omega_x = +0.04+-0.15$ mas yr$^{-1}$, $\omega_y = +0.18+-0.12$ mas yr$^{-1}$, and $\omega_z = -0.35+-0.09$ mas yr$^{-1}$.
We summarize the main features of several dark matter candidates in extra-dimensional theories. In particular, we review Kaluza-Klein (KK) gravitons in universal extra dimensions and branons in brane-world models. KK gravitons are superWIMP (superweakly-interacting massive particle) dark matter, and branons are WIMP (weakly-interacting massive particle) dark matter. Both dark matter candidates are naturally produced in the correct amount to form much or all of dark matter.
We consider the problem of mapping with ultra-high angular resolution using a space-ground radio interferometer with a space antenna in a high orbit,whose apogee height exceeds the radius of the Earth by a factor of ten. In this case, a multielement interferometer essentially degenerates into a two-element interferometer. The degeneracy of the close-phase relations prevents the use of standard methods for hybrid mapping and self-calibration for the correct reconstruction of images. We propose a new phaseless mapping method based on methods for the reconstruction of images in the complete absence of phase information, using only the amplitudes of the spatial-coherence function of the source. In connection with this problem, we propose a new method for the reliable solution of the phase problem, based on optimizing information-carrying nonlinear functionals, in particular, the Shannon entropy. Results of simulations of mapping radio sources with various structures with ultra-high angular resolution in the framework of the RADIOASTRON mission are presented.
Previously, large discrepancies have been found between theory and observation for Fe XV emission line ratios in solar flare spectra covering the 224-327 A wavelength range, obtained by the Naval Research Laboratory's S082A instrument on board Skylab. These discrepancies have been attributed to either errors in the adopted atomic data or the presence of additional atomic processes not included in the modelling, such as fluorescence. However our analysis of these plus other S082A flare observations (the latter containing Fe XV transitions between 321-482 A), performed using the most recent Fe XV atomic physics calculations in conjunction with a CHIANTI synthetic flare spectrum, indicate that blending of the lines is primarily responsible for the discrepancies. As a result, most Fe XV lines cannot be employed as electron density diagnostics for solar flares, at least at the spectral resolution of S082A and similar instruments (i.e. ~ 0.1 A). An exception is the intensity ratio I(321.8 A)/I(327.0 A), which appears to provide good estimates of the electron density at this spectral resolution.
The spectroscopic properties of a selected optical photospheric spectra of
core collapse supernovae (CCSNe) are investigated.Special attention is devoted
to traces of hydrogen at early phases.
The generated spectra are found to match the observed ones reasonably well,
including a list of only 23 candidate ions. Guided by SN Ib 1990I, the observed
trough near 6300\AA is attributed to H$\alpha$ in almost all Type Ib events,
although in some objects it becomes too weak to be discernible, especially at
later phases. Alternative line identifications are discussed. Differences in
the way hydrogen manifests its presence within CCSNe are highlighted. In Type
Ib SNe, the H$\alpha$ contrast velocity (i.e. line velocity minus the
photospheric velocity) seems to increase with time at early epochs, reaching
values as high as 8000 km s$^{-1}$ around 15-20 days after maximum and then
remains almost constant. The derived photospheric velocities, indicate a lower
velocity for Type II SNe 1987A and 1999em as compared to SN Ic 1994I and SN IIb
1993J, while Type Ib events display a somewhat larger variation. The scatter,
around day 20, is measured to be $\sim$5000 km s$^{-1}$. Following two simple
approaches, rough estimates of ejecta and hydrogen masses are given. A mass of
hydrogen of approximately 0.02 $M_\odot$ is obtained for SN 1990I, while SNe
1983N and 2000H ejected $\sim$0.008 $M_\odot$ and $\sim$0.08 $M_\odot$ of
hydrogen, respectively. SN 1993J has a higher hydrogen mass, $\sim 0.7$
$M_\odot$ with a large uncertainty. A low mass and thin hydrogen layer with
very high ejection velocities above the helium shell, is thus the most likely
scenario for Type Ib SNe. Some interesting and curious issues relating to
oxygen lines suggest future investigations.
Some rapidly variable extra-galactic radio sources show very high brightness temperatures T_B>10^{12}K and high degrees of circular polarisation (1%). Standard synchrotron models that assume a power-law electron distribution cannot produce such high temperatures and have much lower degrees of intrinsic circular polarisation. We examine the synchrotron and inverse Compton radiation from a monoenergetic electron distribution using standard synchrotron theory. Constraints on the source parameters are found by formulating the results as functions of the source size, Doppler boosting factor, optical depth to synchrotron self-absorption, maximum frequency of synchrotron emission, and the strength of the inverse Compton radiation. The model gives brightness temperatures T_B=10^{13}K to 10^{14}K for moderate (<10) Doppler boosting factors and intrinsic degrees of circular polarisation at the percent level. It predicts a spectrum I_\nu\propto\nu^{1/3} between the radio and the infra-red as well as emission in the MeV to GeV range. We find the conditions under which electrons do not cool within the source, enabling the GHz emission to emerge without absorption and the potentially catastrophic energy losses by inverse Compton scattering to be avoided. We suggest that sources such as PKS 1519 -273, PKS 0405 -385 and J 1819 +3845 can be understood within this scenario without invoking high Doppler boosting factors, coherent emission mechanisms, or the dominance of proton synchrotron radiation.
In this paper we present and discuss the effects of scattered light echoes (LE) on the luminosity and spectral appearance of Type Ia Supernovae (SNe). After introducing the basic concepts of LE spectral synthesis, by means of LE models and real observations we investigate the deviations from pure SN spectra, light and colour curves, the signatures that witness the presence of a LE and the possible inferences on the extinction law. The effects on the photometric parameters and spectral features are also discussed. In particular, for the case of circumstellar dust, LEs are found to introduce an apparent relation between the post-maximum decline rate and the absolute luminosity which is most likely going to affect the well known Pskowski-Phillips relation.
We present the results of a systematic analysis of gamma-ray burst afterglow spectral energy distributions (SEDs) in the optical/near-infrared bands. Our input list includes the entire world sample of afterglows observed in the pre-Swift era by the end of 2004 that have sufficient publicly available data. We apply various dust extinction models to fit the observed SEDs (Milky Way, Large Magellanic Cloud and Small Magellanic Cloud) and derive the corresponding intrinsic extinction in the GRB host galaxies and the intrinsic spectral slopes of the afterglows. We then use these results to explore the parameter space of the power-law index of the electron distribution function and to derive the absolute magnitudes of the unextinguished afterglows.
Understanding the physical nature of the dark energy which appears to drive the accelerated expansion of the unvierse is one of the key problems in physics and cosmology today. This important problem is best studied using a variety of mutually complementary approaches. Daly and Djorgovski (2003, 2004) proposed a model independent approach to determine a number of important physical parameters of the dark energy as functions of redshift directly from the data. Here, we expand this method to include the determinations of its potential and kinetic energy as functions of redshift. We show that the dark energy potential and kinetic energy may be written as combinations of the first and second derivatives of the coordinate distance with respect to redshift. We expand the data set to include new supernova measurements, and now use a total of 248 coordinate distances that span the redshift range from zero to 1.79. First and second derivatives of the coordinate distance are obtained as functions of redshift, and these are combined to determine the potential and kinetic energy of the dark energy as functions of redshift. An update on the redshift behavior of the dimensionless expansion rate E(z), the acceleration rate q(z), and the dark energy pressure p(z), energy density f(z), and equation of state w(z) is also presented. We find that the standard Omega = 0.3 and Lambda = 0.7 model is in an excellent agreement with the data. We also show tentative evidence that the Cardassian and Chaplygin gas models in a spatially flat universe do not fit the data as well.