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

The Age of Globular Clusters

I review here recent developments which have affected our understanding of both the absolute age of globular clusters and the uncertainties in this age estimate, and comment on the implications for cosmological models. This present estimate is in agreement with the range long advocated by David Schramm. The major uncertainty in determining ages of globular clusers based upon the absolute magnitude of the main sequence turn-off remains the uncertainty in the distance to these clusters. Estimates of these distances have recently been upwardly revised due to Hipparcos parallax measurements, if one calibrates luminosities of main sequence stars. However, it is important to realize that at the present time, different distance measures are in disagreement. A recent estimate is that the oldest clusters are $11.5 \pm 1.3$ Gyr, implying a one-sided 95% confidence level lower limit of 9.5 Gyr, if statistical parallax distance measures are not incorporated. Incorporating more recent measures, including Hipparcos based statistical parallax measures, raises the mean predicted age to $12.8 \pm 1$ Gyr, with a 95 % confidence range of 10-17 Gyr. I conclude by discussing possible improvements which may allow a more precise age distribution in the near future.Comment: latex (using elsart macro for Physics Reports), 16 pages including 4 figures. To appear in Physics Reports, David Schramm Memorial Volum

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

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

The Large-Scale Extinction Map of the Galactic Bulge from the MACHO Project Photometry

We present a (V-R)-based reddening map of about 43 square degrees of the Galactic bulge/bar. The map is constructed using template image photometry from the MACHO microlensing survey, contains 9717 resolution elements, and is based on (V-R)-color averages of the entire color-magnitude diagrams (CMDs) in 4 by 4 arc-minute tiles. The conversion from the observed color to the reddening follows from an assumption that CMDs of all bulge fields would look similar in the absence of extinction. Consequently, the difference in observed color between various fields originates from varying contribution of the disk extinction summed along different lines of sight. We check that our (V-R) colors correlate very well with infrared and optical reddening maps. We show that a dusty disk obeying a cosec|b| extinction law, E(V-R) = 0.0274 cosec|b|, provides a good approximation to the extinction toward the MACHO bulge/bar fields. The large-scale (V-R)-color and visual extinction map presented here is publicly available in the electronic edition of the Journal and on the World Wide Web.Comment: 24 pages, 3 tables, 7 figures (6 in color), version accepted to AJ, added comparisons with Schlegel et al. (1998) and Dutra et al. (2003) reddening map

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&

Detailed abundances for M giants in two inner bulge fields from Infrared Spectroscopy

We report abundance analysis for 30 M giant stars in two inner Galactic bulge fields at (l,b)=(0,-1.75) deg and at (l,b)=(1,-2.65) deg, based on R=25,000 infrared spectroscopy from 1.5-1.8um using NIRSPEC at the Keck II telescope. We find iron abundances of =-0.16 +/- 0.03 dex with a 1-sigma dispersion of 0.12 +/- 0.02 and =-0.21 +/- 0.02 dex, with a 1-sigma dispersion of 0.09+/- 0.016 for the (l,b)=(0,-1.75) and (l,b)=(1,-2.65) deg fields, respectively. In agreement with all prior studies, we find enhanced [alpha/Fe] of +0.3 dex. We confirm the lack of any major vertical abundance or composition gradient in the innermost ~600 pc between Baade's window and 150 pc from the Galactic plane. We also confirm that the known enhancement of alpha elements observed between 500 and 1000 pc from the nucleus is also present over the volume of the inner bulge and may therefore be presumed to be a general characteristic of bulge/bar stars within 1 kpc of the Galactic Center.Comment: Accepted for publication in the Astrophysical Journal. 27 pages manuscript format, 6 figure

The Absolute Magnitude of RRc Variables From Statistical Parallax

We present the first definitive measurement of the absolute magnitude of RR Lyrae c-type variable stars (RRc) determined purely from statistical parallax. We use a sample of 247 RRc selected from the All Sky Automated Survey (ASAS) for which high-quality light curves, photometry and proper motions are available. We obtain high-resolution echelle spectra for these objects to determine radial velocities and abundances as part of the Carnegie RR Lyrae Survey (CARRS). We find that M_(V,RRc) = 0.52 +/- 0.11 at a mean metallicity of [Fe/H] = -1.59. This is to be compared with previous estimates for RRab stars (M_(V,RRab) = 0.75 +/- 0.13 and the only direct measurement of an RRc absolute magnitude (RZ Cephei, M_(V, RRc) = 0.27 +/- 0.17). We find the bulk velocity of the halo to be (W_pi, W_theta, W_z) = (10.9,34.9,7.2) km/s in the radial, rotational and vertical directions with dispersions (sigma_(W_pi), sigma_(W_theta), sigma_(W_z)) = (154.7, 103.6, 93.8) km/s. For the disk, we find (W_pi, W_theta, W_z) = (8.5, 213.2, -22.1) km/s with dispersions (sigma_(W_pi), sigma_(W_theta), sigma_(W_z)) = (63.5, 49.6, 51.3) km/s. Finally, we suggest that UCAC2 proper motion errors may be overestimated by about 25%Comment: Submitted to ApJ. 11 pages including 6 figure

The distance to the Galactic Centre based on Population-II Cepheids and RR Lyrae stars

Context: The distance to the Galactic Centre (GC) is of importance for the distance scale in the Universe. The value derived by Eisenhauer et al. (2005) of 7.62 +- 0.32 kpc based on the orbit of one star around the central black hole is shorter than most other distance estimates based on a variety of different methods. Aim: To establish an independent distance to the GC with high accuracy. To this end Population-II Cepheids are used that have been discovered in the OGLE-II and III surveys. Method: Thirty-nine Pop-II Cepheids have been monitored on 4 nights spanning 14 days. Light curves have been fitted using the known periods from the OGLE data to determine the mean K-band magnitude. It so happens that 37 RR Lyrae stars are in the field-of-views and mean K-band magnitudes are derived for this sample as well. Results: The period-luminosity relation of Pop-II Cepheids in the K-band is determined, and the derived slope of -2.24 +- 0.14 is consistent with the value derived by Matsunaga et al. (2006). Fixing the slope to their more accurate value results in a zero point, and implies a distance modulus to the GC of 14.51 +- 0.12, with an additional systematic uncertainty of 0.07 mag. Similarly, from the RR Lyrae K-band PL-relation we derive a value of 14.48 +- 0.17 (random) +- 0.07 (syst.). The two independent determinations are averaged to find 14.50 +- 0.10 (random) +- 0.07 (syst.), or 7.94 +- 0.37 +- 0.26 kpc.Comment: A&A accepte

The Proper Motion of NGC 6522 in Baade's Window

We have detected seven stars with a common proper motion which are located within 2.5 arcminutes of the globular cluster NGC 6522 in the Baade's Window field of the Galactic bulge. We argue that these stars are members of the cluster, and derive a weighted mean proper motion and heliocentric radial velocity of mu_l = 1.4 +/- 0.2 mas/yr, mu_b = -6.2 +/- 0.2 mas/yr, v = -28.5 +/- 6.5 km/s. We rederive the distance to NGC 6522 (0.91 +/- 0.04 R_0, where R_0 is the Galactocentric distance) and metallicity ([Fe/H] = -1.28 +/- 0.12), making use of recent revisions in the foreground extinction toward the cluster (A_V = 1.42 +/- 0.05). We find the spatial velocity of the cluster and conclude that the cluster stays close to the Galactic center, and may have experienced significant bulge/disk shocking during its lifetime.Comment: submitted to AJ, 21 pages, 5 figure