RR Lyrae Variables in the Globular Clusters of M31: A First Detection of Likely Candidates (original) (raw)

RR Lyrae stars in M31 globular clusters: B514

2008

We present preliminary results of a variable star search in the metal-poor globular cluster B514 of the Andromeda galaxy (M31), based on Hubble Space Telescope Wide Field Planetary Camera 2 and Advanced Camera for Surveys observations. A large number of RR Lyrae stars have been identified for the first time in a globular cluster of M31. The average period of

RR LYRAE VARIABLES IN M32 AND THE DISK OF M31

The Astrophysical Journal, 2010

We observed two fields near M32 with the Advanced Camera for Surveys/High Resolution Channel (ACS/HRC) on board the Hubble Space Telescope (HST). The main field, F1, is 1. ′ 8 from the center of M32; the second field, F2, constrains the M31 background, and is 5. ′ 4 distant. Each field was observed for 16-orbits in each of the F435W (narrow B) and F555W (narrow V ) filters. The duration of the observations allowed RR Lyrae stars and other short-period variables to be detected. A population of RR Lyrae stars determined to belong to M32 would prove the existence of an ancient population in that galaxy, a subject of some debate.

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.

A Multicolor and Fourier Study of RR Lyrae Variables in the Globular Cluster NGC 5272 (M3)

The Astronomical Journal, 2005

We have performed a detailed study of the pulsational and evolutionary characteristics of 133 RR Lyrae stars in the globular cluster NGC5272 (M3) using highly accurate BVI data taken on 5 separate epochs. M3 seems to contain no less than ∼32% of Blazhko stars, and the occurrence and characteristics of the Blazhko effect have been analyzed in detail. We have identified a good number (∼ 14%) of overluminous RR Lyrae stars that are likely in a more advanced evolutionary stage off the Zero Age Horizontal Branch (ZAHB). Physical parameters (i.e. temperature, luminosity, mass) have been derived from (B-V) colors and accurate color-temperature calibration, and compared with Horizontal Branch evolutionary models and with the requirements of stellar pulsation theory. Additional analysis by means of Fourier decomposition of the V light curves confirms, as expected, that no metallicity spread is present in M3. Evolution off the ZAHB does not affect [Fe/H] determinations, whereas Blazhko stars at low amplitude phase do affect [Fe/H] distributions as they appear more metal-rich. Absolute magnitudes derived from Fourier coefficients might provide useful average estimates for groups of stars, if applicable, but do not give reliable individual values. Intrinsic colors derived from Fourier 167, 168, 170, 188 and 209. Finally, Car98 provided also I photometry with the warning that it may be affected by a zero-point error in the absolute calibration. We treat this problem in some detail in Sect. 4.1, but we anticipate here that indeed Car98 I data are most likely too faint by ∼ 0.083 mag. The same type of comparison with Kal98 data, using intensity integrated < V > magnitudes for both data sets (note however that the published Kal98 < V > are magnitude integrated), shows that the CC01 V magnitudes are brighter than Kal98 V photometry in the SOUTH and NORTH fields by 0.028 and 0.018 mags, respectively. Car98 and Kal98 data have been corrected by the above offsets, when they have been used along with CC01 data (e.g. for Blazhko stars). On the other hand, a comparison of CC01 photometry with 15 randomly selected secondary standard stars from Sandage (1970) shows that CC01 V magnitudes are fainter by 0.009 ± 0.024 mag, and the B magnitudes are brighter by 0.004 ± 0.014 mag, as already noted by CC01. Only the stars with well defined light curves in both B and V bands have been taken into account for the present study. This led us to consider a total of 133 stars out of the 201 RR Lyraes observed by CC01, in particular 23 RRc out of 43, 67 RRab out of 111, and 43 Blazhko stars out of 47. The stars we have not considered in the present study all have very noisy light curves, which may be due to photometric errors (contamination from companions) or to intrinsic phenomena such as double-mode pulsation or unidentified Blazhko modulation. They may be very interesting objects in themselves, and surely deserve further and more careful investigation (cf. Clementini et al. 2004). However, for the purpose of the present analysis, we shall use only those stars that show the "cleanest" light curves so as to keep the noise at the minimum level, taking advantage of the fact that M3 is probably the only cluster where one can afford to be very selective, due to the richness of its variable star population. 2.2. The Blazhko variables The Blazhko effect, first noticed and studied by Blazhko (1907), is a modulation of the basic pulsation variability that produces variations of the light curve shape showing as larger photometric scatter and significant changes in the light curve amplitude. The timescale of this modulation is typically tens of days but can be as large as a few hundred days. Several mechanisms have been proposed to explain the origin of this phenomenon, which however is still an open question. We refer the reader to Smith (1995) for a recent and comprehensive discussion on this topic. According to CC01 data no less than ∼32% of the total RR Lyrae variable star population in M3 is affected by Blazhko variability. This fraction might easily be larger if some of the stars with noisy light curves, that we have not considered in the present analysis, turn out to be Blazhko variables in future studies. The frequency of this phenomenon we find in M3 is consistent with previous results in other stellar systems (cf. Smith 1995) and has been recently confirmed in another cluster, NGC3201, where Piersimoni et al. (2002) have identified about 30% such stars. However,

BV photometry of RR Lyrae variables in the globular cluster M92

Publications of the Astronomical Society of the Pacific, 1992

We present B V CCD photometry for seven RR Lyrae variables in the globular cluster M92 (NGC 6341). New ephemerides are computed, and V, B, and B-V light curves are given. A color-magnitude diagram based on two V and two B short exposures is given, reaching from above the horizontal branch to below the main sequence turn-off. A comparison with results from other workers shows we agree with the photometry of Cathey, and Stetson and Harris. We study also the timing of the secondary bumps in the light curves of five of the RRab variables, finding it to be consistent with prediction from the echo model. Expansion radii derived from radial velocities are not consistent with the photospheric infall model of the secondary bump.

RR Lyrae variables in the globular cluster M�5

Astronomy and Astrophysics Supplement Series, 2000

We present V -band CCD photometry of 65 RR Lyr variables from the globular cluster M5. We have estimated the basic physical parameters for 16 RRc stars and 26 RRab stars using a Fourier decomposition of the light curves of the variables. The mean values of mass, luminosity, effective temperature and relative helium abundance for the RRc stars are measured to be M = 0.54 M ⊙ , log(L/L ⊙ ) = 1.69, T ef f = 7353 K and Y = 0.28, respectively. For the RRab variables the derived mean values of absolute magnitude, metallicity and effective temperature are: M V = 0.81, [Fe/H] = −1.23 and T ef f = 6465 K. We find that the V amplitude of an RRab star for a given period is a function of metal abundance rather than Oosterhoff type.

Near-Infrared Observations of RR Lyrae Variables in Galactic Globular Clusters. I. The Case of M92

The Astronomical Journal, 2005

We present near-infrared J,H, and K-band time series observations of the Galactic Globular Cluster (GGC) M92. On the basis of these data, we derived well-sampled light curves for eleven out of the seventeen cluster RR Lyrae variables, and in turn, accurate mean near-infrared (NIR) magnitudes. The comparison between predicted and empirical slopes of NIR Period-Luminosity (PL) relations indicates a very good agreement. Cluster distance determinations based on independent theoretical NIR P L relations present uncertainties smaller than 5% and agree quite well with recent distance estimates based on different distance indicators. We also obtained accurate and deep NIR color-magnitude diagrams (CMDs) ranging from the tip of the Red Giant Branch (RGB) down to the Main Sequence Turn-Off. We detected the RGB bump and the NIR luminosities of this evolutionary feature are, within theoretical and empirical uncertainties, in good agreement with each other.

RR Lyrae in LMC Globular Clusters

AIP Conference Proceedings, 2009

We are using a hierarchical Bayes model to analyze the distances, luminosities, and kinematics of RR Lyrae stars. Our model relates these characteristics to the raw data of proper motions, radial velocities, apparent luminosities and metallicities of each star. A combination of Gibbs and Metropolis-Hastings sampling, using latent variables for the actual velocity and luminosity of each star, is used to draw a sample from the full posterior distribution of these variables, with consideration to identifiability and the properness of the hierarchical model, and draw inferences on the quantities of interest in the usual way. We have applied our model to the large HIPPARCOS database, and we have attempted to include metallicity and period in our model, which has not been done previously.

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.