Pharmacologic modulation of experimental postischemic hepatic function

The present study, evaluated and compared the effects of SRI 63-441, a potent platelet activating factor antagonist, superoxide dismutase (SOD), an oxygen free radical scavenger, and ibuprofen, a cyclooxygenase inhibitor on hepatic function after 90 minutes of warm ischemia. After warm ischemia, livers were harvested and underwent 90 minutes of warm, oxygenated, sanguinous perfusion on an isolated liver perfusion apparatus. Pretreatment of donor animals with 20 mg/kg intravenous (I.V.) SRI 63-441 5 minutes before induction of total hepatic ischemia resulted in significantly increased bile production, a significant decrease in transaminase release, and a higher tissue adenosine triphosphate (ATP) content when compared with ischemic non-treated controls. SOD resulted in improved bile production and decreased transaminase liberation only when present in the perfusate at the time of in vitro reperfusion. Ibuprofen did not improve postischemic hepatic function in this model. Electron microscopy revealed patchy hepatocellular vacuolization with an intact sinusoidal endothelium in all ischemic livers. However, the degree of damage was less severe in the livers from those rats pretreated with 20 mg/kg SRI 63-441. This study demonstrates that SRI 63-441 pretreatment significantly reduces hepatic warm ischemic injury, and in the present model, appears superior to two other agents that have been advanced in the treatment of ischemic injury. The use of such agents singly or in combinations have important implications as regards gaining a better understanding of he basic mechanisms in organ ischemia, and moreover, for therapeutic applications in organ ischemia and preservation

Generation and reduction of the data for the Ulysses gravitational wave experiment

A procedure for the generation and reduction of the radiometric data known as REGRES is described. The software is implemented on a HP-1000F computer and was tested on REGRES data relative to the Voyager I spacecraft. The REGRES data are a current output of NASA's Orbit Determination Program. The software package was developed in view of the data analysis of the gravitational wave experiment planned for the European spacecraft Ulysses

Integral D-Finite Functions

We propose a differential analog of the notion of integral closure of algebraic function fields. We present an algorithm for computing the integral closure of the algebra defined by a linear differential operator. Our algorithm is a direct analog of van Hoeij's algorithm for computing integral bases of algebraic function fields

The X-shooter Lens Survey - II. Sample presentation and spatially resolved kinematics

We present the X-shooter Lens Survey (XLENS) data. The main goal of XLENS is to disentangle the stellar and dark matter content of massive early-type galaxies (ETGs), through combined strong gravitational lensing, dynamics and spectroscopic stellar population studies. The sample consists of 11 lens galaxies covering the redshift range from $0.1$ to $0.45$ and having stellar velocity dispersions between $250$ and $380\,\mathrm{km}\,\mathrm{s}^{-1}$. All galaxies have multi-band, high-quality HST imaging. We have obtained long-slit spectra of the lens galaxies with X-shooter on the VLT. We are able to disentangle the dark and luminous mass components by combining lensing and extended kinematics data-sets, and we are also able to precisely constrain stellar mass-to-light ratios and infer the value of the low-mass cut-off of the IMF, by adding spectroscopic stellar population information. Our goal is to correlate these IMF parameters with ETG masses and investigate the relation between baryonic and non-baryonic matter during the mass assembly and structure formation processes. In this paper we provide an overview of the survey, highlighting its scientific motivations, main goals and techniques. We present the current sample, briefly describing the data reduction and analysis process, and we present the first results on spatially resolved kinematics.Comment: Accepted for publication in MNRA

RR Lyrae Variables in Two Fields in the Spheroid of M31

We present Hubble Space Telescope observations taken with the Advanced Camera for Surveys Wide Field Channel of two fields near M32—between 4 and 6 kpc from the center of M31. The data cover a time baseline sufficient for the identification and characterization of 681 RR Lyrae variables of which 555 are ab-type and 126 are c-type. The mean magnitude of these stars is = 25.29 ± 0.05, where the uncertainty combines both the random and systematic errors. The location of the stars in the Bailey diagram and the ratio of c-type RR Lyraes to all types are both closer to RR Lyraes in Oosterhoff type I globular clusters in the Milky Way as compared with Oosterhoff II clusters. The mean periods of the ab-type and c-type RR Lyraes are = 0.557 ± 0.003 and = 0.327 ± 0.003, respectively, where the uncertainties in each case represent the standard error of the mean. When the periods and amplitudes of the ab-type RR Lyraes in our sample are interpreted in terms of metallicity, we find the metallicity distribution function to be indistinguishable from a Gaussian with a peak at = –1.50 ± 0.02, where the quoted uncertainty is the standard error of the mean. Using a relation between RR Lyrae luminosity and metallicity along with a reddening of E(B – V) = 0.08 ± 0.03, we find a distance modulus of (m – M)_0 = 24.46 ± 0.11 for M31. We examine the radial metallicity gradient in the environs of M31 using published values for the bulge and halo of M31 as well as the abundances of its dwarf spheroidal companions and globular clusters. In this context, we conclude that the RR Lyraes in our two fields are more likely to be halo objects rather than associated with the bulge or disk of M31, in spite of the fact that they are located at 4-6 kpc in projected distance from the center

Hierarchical Bayesian inference of the Initial Mass Function in Composite Stellar Populations

The initial mass function (IMF) is a key ingredient in many studies of galaxy formation and evolution. Although the IMF is often assumed to be universal, there is continuing evidence that it is not universal. Spectroscopic studies that derive the IMF of the unresolved stellar populations of a galaxy often assume that this spectrum can be described by a single stellar population (SSP). To alleviate these limitations, in this paper we have developed a unique hierarchical Bayesian framework for modelling composite stellar populations (CSPs). Within this framework we use a parameterized IMF prior to regulate a direct inference of the IMF. We use this new framework to determine the number of SSPs that is required to fit a set of realistic CSP mock spectra. The CSP mock spectra that we use are based on semi-analytic models and have an IMF that varies as a function of stellar velocity dispersion of the galaxy. Our results suggest that using a single SSP biases the determination of the IMF slope to a higher value than the true slope, although the trend with stellar velocity dispersion is overall recovered. If we include more SSPs in the fit, the Bayesian evidence increases significantly and the inferred IMF slopes of our mock spectra converge, within the errors, to their true values. Most of the bias is already removed by using two SSPs instead of one. We show that we can reconstruct the variable IMF of our mock spectra for signal-to-noise ratios exceeding $\sim$75.Comment: Accepted for publication in MNRAS, 16 pages, 8 figure

The Star Formation History of M32

We use deep HST ACS/HRC observations of a field within M32 (F1) and an M31 background field (F2) to determine the star formation history (SFH) of M32 from its resolved stellar population. We find that 2-5Gyr old stars contribute \som40%+/- 17% of M32's mass, while 55%+/-21% of M32's mass comes from stars older than 5 Gyr. The mass-weighted mean age and metallicity of M32 at F1 are =6.8+/-1.5 Gyr and =-0.01+/-0.08 dex. The SFH additionally indicates the presence of young (<2 Gyr old), metal-poor ([M/H]\sim-0.7) stars, suggesting that blue straggler stars contribute ~2% of the mass at F1; the remaining \sim3% of the mass is in young metal-rich stars. Line-strength indices computed from the SFH imply a light-weighted mean age and metallicity of 4.9 Gyr and [M/H] = -0.12 dex, and single-stellar-population-equivalent parameters of 2.9+/-0.2 Gyr and [M/H]=0.02+/-0.01 dex at F1 (~2.7 re). This contradicts spectroscopic studies that show a steep age gradient from M32's center to 1re. The inferred SFH of the M31 background field F2 reveals that the majority of its stars are old, with \sim95% of its mass already acquired 5-14 Gyr ago. It is composed of two dominant populations; \sim30%+/-7.5% of its mass is in a 5-8 Gyr old population, and \sim65%+/-9% of the mass is in a 8-14 Gyr old population. The mass-weighted mean age and metallicity of F2 are =9.2+/-1.2 Gyr and =-0.10+/-0.10 dex, respectively. Our results suggest that the inner disk and spheroid populations of M31 are indistinguishable from those of the outer disk and spheroid. Assuming the mean age of M31's disk at F2 (\sim1 disk scale length) to be 5-9 Gyr, our results agree with an inside-out disk formation scenario for M31's disk.Comment: Accepted to ApJ. 24 pages, 18 figures. A high-resolution version can be downloaded from http://www.astro.rug.nl/~monachesi/monachesi-sfh.pd

Synchronous Evolution of Galaxies in Groups: NGC 524 Group

By means of panoramic spectroscopy at the SAO RAS BTA telescope, we investigated the properties of stellar populations in the central regions of five early-type galaxies -- the NGC 524 group members. The evolution of the central regions of galaxies looks synchronized: the average age of stars in the bulges of all the five galaxies lies in the range of 3--6 Gyr. Four of the five galaxies revealed synchronized bursts of star formation in the nuclei 1--2 Gyr ago. The only galaxy, in which the ages of stellar population in the nucleus and in the bulge coincide (i.e. the nuclear burst of star formation did not take place) is NGC 502, the farthest from the center of the group of all the galaxies studied.Comment: Slightly edited version of the paper to appear in the Astrophysical Bulletin, 67(3); 24 pages including 8 figure

Evidence for Blue Straggler Stars Rejuvenating the Integrated Spectra of Globular Clusters

Integrated spectroscopy is the method of choice for deriving the ages of unresolved stellar systems. However, hot stellar evolutionary stages, such as hot horizontal branch stars and blue straggler stars (BSSs), can affect the integrated ages measured using Balmer lines. Such hot, "non-canonical" stars may lead to overestimations of the temperature of the main sequence turn-off, and therefore underestimations of the integrated age of a stellar population. Using an optimized Hbeta index in conjunction with HST/WFPC2 color-magnitude diagrams (CMDs), we show that Galactic globular clusters exhibit a large scatter in their apparent "spectroscopic" ages, which does not correspond to that in their CMD-derived ages. We find for the first time that the specific frequency of BSSs, defined within the same aperture as the integrated spectra, shows a clear correspondence with Hbeta in the sense that, at fixed metallicity, higher BSS ratios lead to younger "apparent" spectroscopic ages. Thus, the specific frequency of BSSs in globular clusters sets a fundamental limit on the accuracy for which spectroscopic ages can be determined for globular clusters, and maybe for other stellar systems like galaxies. The observational implications of this result are discussed.Comment: 5 pages, 2 figures, 1 table. Accepted for publication in ApJ