RR Lyrae stars in M31 globular clusters: B514 (original) (raw)

The Variable Star Population of the Globular Cluster B514 in the Andromeda Galaxy

The Astrophysical Journal, 2009

A rich harvest of RR Lyrae stars has been identified for the first time in B514, a metal-poor ([Fe/H]∼-1.95 ±0.10 dex) globular cluster of the Andromeda galaxy (M31), based on Hubble Space Telescope Wide Field Planetary Camera 2 and Advanced Camera for Surveys time-series observations. We have detected and derived periods for 89 RR Lyrae stars (82 fundamental-mode −RRab− and 7 first-overtone −RRc− pulsators, respectively) among 161 candidate variables identified in the cluster. The average period of the RR Lyrae variables (P ab = 0.58 days and P c = 0.35 days, for RRab and RRc pulsators, respectively) and the position in the period-amplitude diagram both suggest that B514 is likely an Oosterhoff type I cluster.

RR Lyrae Stars in the Andromeda Halo from Deep Imaging with the Advanced Camera for Surveys

Astronomical Journal, 2004

We present a complete census of RR Lyrae stars in a halo field of the Andromeda galaxy. These deep observations, taken as part of a program to measure the star formation history in the halo, spanned a period of 41 days with sampling on a variety of time scales, enabling the identification of short and long period variables. Although the long period variables cannot be fully characterized within the time span of this program, the enormous advance in sensitivity provided by the Advanced Camera for Surveys on the Hubble Space Telescope allows accurate characterization of the RR Lyrae population in this field. We find 29 RRab stars with a mean period of 0.594 days, 25 RRc stars with a mean period of 0.316 days, and 1 RRd star with a fundamental period of 0.473 days and a first overtone period of 0.353 days. These 55 RR Lyrae stars imply a specific frequency S_RR=5.6, which is large given the high mean metallicity of the halo, but not surprising given that these stars arise from the old, metal-poor tail of the distribution. This old population in the Andromeda halo cannot be clearly placed into one of the Oosterhoff types: the ratio of RRc/RRabc stars is within the range seen in Oosterhoff II globular clusters, the mean RRab period is in the gap between Oosterhoff types, and the mean RRc period is in the range seen in Oosterhoff I globular clusters. The periods of these RR Lyraes suggest a mean metallicity of [Fe/H]=-1.6, while their brightness implies a distance modulus to Andromeda of 24.5+/-0.1, in good agreement with the Cepheid distance.

RR Lyrae Stars in the Globular Cluster NGC 6101

V-and I-band observations were taken over 9 months to study the RR Lyrae population in the metalpoor diffuse globular cluster NGC 6101. We identify one new variable, which is either a potential long-period red giant variable or eclipsing binary, and recover all previously identified RR Lyraes. One previously studied RR Lyrae is reclassified as an RRc type, while two period estimations have been significantly refined. We confirm that NGC 6101 is Oosterhoff type II with a high ratio of n(c)/n(ab þ c) ¼ 0.833 with a very long mean RRab period of 0.86 d. By using theoretical RR Lyrae period-luminosity-metallicity relations, we use our V-and I-band RR Lyrae data to gain an independent estimate of the reddening towards this cluster of E(B 2 V) ¼ 0.15 AE 0.04 and derive a distance of 12.8 AE 0.8 kpc. The majority of the work in this study was undertaken by upper secondary school students involved in the Space to Grow astronomy education project in Australia.

The RR Lyrae Variables in M54 and the Sgr Dwarf Galaxy

Symposium - International Astronomical Union, 2002

We report on new B, V and I CCD photometry of the globular cluster M54 that was aimed at the study of its variable stars. With respect to the previous most recent work on M54 we have nearly doubled the number of detected variable stars: M54 can now be classified as intermediate in the Oosterhoff groups. The metallicity can be estimated for the cluster and field red giant stellar population, and for the variables.

HST/Acs Observations of RR Lyrae Stars in Six Ultra-Deep Fields of M31

The Astronomical Journal, 2011

We present HST/ACS observations of RR Lyrae variable stars in six ultra deep fields of the Andromeda galaxy (M31), including parts of the halo, disk, and giant stellar stream. Past work on the RR Lyrae stars in M31 has focused on various aspects of the stellar populations that make up the galaxy's halo, including their distances and metallicities. This study builds upon this previous work by increasing the spatial coverage (something that has been lacking in previous studies) and by searching for these variable stars in constituents of the galaxy not yet explored. Besides the 55 RR Lyrae stars we found in our initial field located 11kpc from the galactic nucleus, we find additional RR Lyrae stars in four of the remaining five ultra deep fields as follows: 21 in the disk, 24 in the giant stellar stream, 3 in the halo field 21kpc from the galactic nucleus, and 5 in one of the halo fields at 35kpc. No RR Lyrae were found in the second halo field at 35kpc. The RR Lyrae populations of these fields appear to mostly be of Oosterhoff I type, although the 11kpc field appears to be intermediate or mixed. We will discuss the properties of these stars including period and reddening distributions. We calculate metallicities and distances for the stars in each of these fields using different methods and compare the results, to an extent that has not yet been done. We compare these methods not just on RR Lyrae stars in our M31 fields, but also on a data set of Milky Way field RR Lyrae stars.

RR Lyrae Variables in the Globular Clusters of M31: A First Detection of Likely Candidates

The Astrophysical Journal, 2001

The purpose of this paper is to show that RR Lyrae variables exist and can be detected in M31 globular clusters. We report on the first tentative identification of RR Lyrae candidates in four globular clusters of the Andromeda galaxy, i.e. G11, G33, G64 and G322. Based on HST-WFPC2 archive observations in the F555W and F814W filters spanning a total interval of about 5 consecutive hours we find evidence for 2, 4, 11 and 8 RR Lyrae variables of both ab and c Bailey types in G11, G33, G64 and G322, respectively. Several more candidates can be found by relaxing slightly the selection criteria. These numbers are quite consistent with the horizontal branch morphology exhibited by the four clusters, starting from the very blue HB in G11, and progressively moving to redder HBs in G64, G33 and G322.

The Globular Cluster NGC 5286. II. Variable Stars

Astronomical Journal, 2010

We present the results of a search for variable stars in the globular cluster (GC) NGC 5286, which has recently been suggested to be associated with the Canis Major dwarf spheroidal galaxy. Fifty-seven variable stars were detected, only 19 of which had previously been known. Among our detections one finds 52 RR Lyrae (22 RRc and 30 RRab), 4 long-period variables, and 1 type II Cepheid of the BL Herculis type. Periods are derived for all of the RR Lyrae as well as the Cepheid, and BV light curves are provided for all the variables. The mean period of the RRab variables is P ab = 0.656 days, and the number fraction of RRc stars is N c /N RR = 0.42, both consistent with an Oosterhoff II (OoII) type-thus making NGC 5286 one of the most metal-rich ([Fe/H] = −1.67) OoII globulars known to date. The minimum period of the RRabs, namely P ab,min = 0.513 d, while still consistent with an OoII classification, falls toward the short end of the observed P ab,min distribution for OoII GCs. As was recently found in the case of the prototypical OoII GC M15 (NGC 7078), the distribution of stars in the Bailey diagram does not strictly conform to the previously reported locus for OoII stars. We provide Fourier decomposition parameters for all of the RR Lyrae stars detected in our survey, and discuss the physical parameters derived therefrom. The values derived for the RRcs are not consistent with those typically found for OoII clusters, which may be due to the cluster's relatively high metallicity-the latter being confirmed by our Fourier analysis of the ab-type RR Lyrae light curves. Using the recent recalibration of the RR Lyrae luminosity scale by Catelan & Cortés, we derive for the cluster a revised distance modulus of (m − M) V = 16.04 mag.

RR Lyrae variables in the globular cluster M3 (NGC 5272) — I. BVI CCD photometry

1998

New BVI CCD photometry is presented for 60 RR Lyrae variables in the globular cluster M3. Light curves have been constructed and ephemerides have been (re)-derived for all of them. Four stars (i.e. V29, V136, V155 and V209), although recognized as variables, had no previous period determinations. Also, the period derived for V129 is significantly different from the one published by Sawyer-Hogg (1973). Light curve parameters, i.e. mean magnitudes, amplitudes and rise-times, have been derived. The discussion of these results in the framework of the stellar evolution and pulsation theories will be presented in a forthcoming paper.

RR Lyrae the Stellar Beacons of the Galactic Structure

arXiv: Solar and Stellar Astrophysics, 2011

We present some recent findings concerning the use of RR Lyrae as distance indicators and stellar tracers. We outline pros and cons of field and cluster RR Lyrae stars and discuss recent theoretical findings concerning the use of the Bailey (amplitude vs pulsation period) diagram to constrain the possible occurrence of Helium enhanced RR Lyrae stars. Nonlinear, convective RR Lyrae models indicate that the pulsation properties of RR Lyrae stars are minimally affected by the helium content. The main difference between canonical and He enhanced models is due to the increase in luminosity predicted by evolutionary models. Moreover, we focus our attention on the near-infrared Period-Luminosity (PL) relation of RR Lyrae and summarize observational evidence concerning the slope of the K-band PL relation in a few globulars (M92, Reticulum, M5, Omega Cen) covering a range in metallicity of ~1 dex. Current findings suggest that the slope has a mild dependence on the metal content when moving ...