The Zero Point of Extinction Toward Baade's Window

We measure the zero point of the Stanek (1996) extinction map by comparing the observed (V-K) colors of 206 K giant stars with their intrinsic (V-K)_0 colors as derived from their H\beta indices. We find that the zero point of the Stanek map should be changed by \Delta A_V = -0.10 +/- 0.06 mag, obtaining as a bonus a three-fold reduction of the previous statistical error. The most direct way to test for systematic errors in this determination would be to conduct a parallel measurement based on the (V-K) colors of RR Lyraes (type ab).Comment: 10 pages, 1 figur

Anomaluos RR Lyrae (V-I)_0 colors in Baade's Window

We compare (V-I)_0-(V-K)_0 color-color and (V-I)_0-log P period-color diagrams for Baade's Window and local RRab Lyrae stars. We find that for a fixed log P the Baade's Window RR Lyrae stars are ~0.17 magnitudes redder in (V-I)_0 than the local RR Lyrae stars. We also show that there is no such effect observed in (V-K)_0. We argue that an extinction misestimate towards Baade's Window is not a plausible explanation of the discrepancy. Unlike Baade's Window RR Lyrae stars, the local ones follow a black-body color-color relation and are well approximated by theoretical models. We test two parameters, metallicity and surface gravity, and find that their effects are too small to explain the (V-I)_0 discrepancy between the two groups of stars. We do not provide any explanation for the anomalous (V-I)_0 behavior of the Baade's Window RR Lyrae stars. We note that a similar effect for clump giant stars has been recently reported by Paczynski and we caution that RR Lyrae stars and clump giants, often used as standard candles, can be subject to the same type of systematics.Comment: 10 pages, 7 figures, submitted to Ap

Clump Distance to the Magellanic Clouds and Anomalous Colors in the Galactic Bulge

I demonstrate that the two unexpected results in the local Universe: 1) anomalous intrinsic (V-I)_0 colors of the clump giants and RR Lyrae stars in the Galactic center, and 2) very short distances to the Magellanic Clouds (LMC, SMC) as inferred from clump giants, are connected with each other. The (V-I)_0 anomaly is partially resolved by using the photometry from the phase-II of the Optical Gravitational Lensing Experiment (OGLE) rather than phase-I. The need for V- or I-magnitude-based change in the bulge (V-I)_0 is one option to explain the remaining color discrepancy. Such change may originate in a coefficient of selective extinction A_V/E(V-I) smaller than typically assumed. Application of the (V-I)_0 correction (independent of its source) doubles the slope of the absolute magnitude - metallicity relation for clump giants, so that M_I(RC) = -0.23 + 0.19[Fe/H]. Consequently, the estimates of the clump distances to the LMC and SMC are affected. Udalski's (1998c) distance modulus of mu_{LMC} = 18.18 +/- 0.06 increases to mu_{LMC} = 18.27 +/- 0.07. The distance modulus to the SMC increases by 0.12 to mu_{SMC} = 18.77 +/- 0.08. I argue that a more comprehensive assessment of the metallicity effect on M_I(RC) is needed.Comment: accepted by ApJ Letters, brief review of the short distance scale dropped, discussion of the absolute magnitude - metallicity relation for clump giants shortened and made more qualitative, results basically unchange

Effect of insulin on ultrastructure and glycogenesis in primary cultures of adult rat hepatocytes

Insulin in the presence of high concentrations of glucose has a beneficial trophic effect on the development of primary cultures of hepatocytes. Compared to the situation observed in hormone-free control cultures, the flattening of the reaggregated hepatocytes is enhanced, and the reconstituted cell trabeculae are enlarged and tend to form a confluent monolayer after 3 days; the survival time is prolonged from 3 to 5 or 6 days. Ultrastructural modifications are also initiated by insulin; numerous glycogen particles appear after 24 h, in between the cisternae of the proliferated smooth endoplasmic reticulum. After 48 h, large amounts of glycogen are stored, and numerous polysomes are present. A small number of cells showed an increased synthesis of lipid droplets in the lumen of the smooth endoplasmic reticulum and form liposomes at the same time. After 72 h, cytolysomes filled with glycogen develop, simulating glycogenosis type II. Simultaneously, microtubules and microfilaments, closely related to numerous polysomes, appear in cytoplasmic extensions constituting undulating membranes. The biochemical data demonstrate that, in the absence of insulin, a high concentration of glucose stimulates glycogenesis and hinders glycogenolysis. This effect of glucose on polysaccharide synthesis is progressively lost. The addition of insulin to the culture induces after 48 and 72 h, a three- to fivefold increase of the glucose incorporation into glycogen, as compared to the controls. The presence of insulin is required to maintain the hepatocyte's capacity to store glycogen. Glycogen synthetase is converted into its active form under the influence of glucose. Insulin increases the rate of activation

AX J1749.1-2733 and AX J1749.2-2725 - the close pair of X-ray pulsars behind the Galactic Center: an optical identification

Two faint X-ray pulsars, AX J1749.2-2725 and AX J1749.1-2733, located in the direction to the Galactic Center, were studied in detail using data of INTEGRAL, XMM-Newton and Chandra observatories in X-rays, the SOFI/NTT instrument in infrared and the RTT150 telescope in optics. X-ray positions of both sources were determined with the uncertainty better than ~1 arcsec, that allowed us to identify their infrared counterparts. From the subsequent analysis of infrared and optical data we conclude that counterparts of both pulsars are likely massive stars of B0-B3 classes located behind the Galactic Center at distances of 12-20 kpc, depending on the type, probably in further parts of galactic spiral arms. In addition, we investigated the extinction law towards the galactic bulge and found that it is significantly different from standard one.Comment: 6 pages, 7 figures, will be published in MNRA

Systematics of RR Lyrae Statistical Parallax III: Apparent Magnitudes and Extinctions

We sing the praises of the central limit theorem. Having previously removed all other possible causes of significant systematic error in the statistical parallax determination of RR Lyrae absolute magnitudes, we investigate systematic errors from two final sources of input data: apparent magnitudes and extinctions. We find corrections due to each of ~0.05 mag, i.e., ~1/2 the statistical error. However, these are of opposite sign and so roughly cancel. The apparent magnitude system that we previously adopted from Layden et al. was calibrated to the photometry of Clube & Dawe. Using Hipparcos photometry we show that the Clube & Dawe system is ~0.06 mag too bright. Extinctions were previously pinned to the HI-based map of Burstein & Heiles. We argue that A_V should rather be based on new COBE/IRAS dust-emission map of Schlegel, Finkbeiner & Davis. This change increases the mean A_V by ~0.05 mag. We find M_V=0.77 +/- 0.13 at [Fe/H]=-1.60 for a pure sample of 147 halo RR Lyraes, or M_V=0.80 +/- 0.11 at [Fe/H]=-1.71 if we incorporate kinematic information from 716 non-kinematically selected non-RR Lyrae stars from Beers & Sommer-Larsen. These are 2 and 3 sigma fainter than recent determinations of M_V from main sequence fitting of clusters using Hipparcos measurements of subdwarfs by Reid and Gratton et al. Since statistical parallax is being cleared of systematic errors and since the chance of a >2 sigma statistical fluctuation is <1/20, we conclude that these brighter determinations may be in error. In the course of three papers, we have corrected 6 systematic errors whose absolute values total 0.20 mag. Had these, contrary to the expectation of the central limit theorem, all lined up one way, they could have resolved the conflict in favor of the brighter determinations. In fact, the net change was only 0.06 mag.Comment: submitted to ApJ, 21 pages, 2 tables, 4 figure

Dark Matter Density in Disk Galaxies

I show that the predicted densities of the inner dark matter halos in LCDM models of structure formation appear to be higher than estimates from real galaxies and constraints from dynamical friction on bars. This inconsistency would not be a problem for the LCDM model if physical processes that are omitted in the collisionless collapse simulations were able to reduce the dark matter density in the inner halos. I review the mechanisms proposed to achieve the needed density reduction.Comment: 12 pages, 5 figures, to appear in "The Galaxy Disk in Cosmological Context" eds Andersen, Bland-Hawthorn & Nordstro

Radial velocities and membership of stars in the old, distant open cluster Berkeley 29

Multi slit spectroscopy at the Telescopio Nazionale Galileo was employed to measure radial velocities for 20 stars in the direction of the old open cluster Berkeley 29, the farthest known in our Galaxy. Membership information was derived for stars along all the red giant branch, in particular near its tip, and on the red clump. The sample of bona-fide cluster members was used to revise the cluster distance to about 15 kpc, on the basis of an empirical comparison with the red clump in open clusters with known distances. A metallicity [Fe/H] = -0.74 +/- 0.18 was also estimated using the colours of spectroscopically confirmed red giant stars.Comment: 7 pages, 5 figures (fig. 1 at low-res, but JPEG version included too), accepted for publication in A&