RR Lyrae stars in M31 globular clusters: B514 (original) (raw)
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 ...
Characteristics of bright ab-type RR Lyrae stars from the ASAS and WASP surveys
Monthly Notices of the Royal Astronomical Society, 2014
In this article, we present results based on high-density, high-precision Wide-Angle Search for Planets (WASP) light curves supplemented with lower-precision photometry from the All-Sky Automated Survey (ASAS) for 268 RR Lyrae stars (176 regular, 92 Blazhko). Light curves were Fourier-decomposed and coefficients from WASP were transformed to the ASAS standard using 24 common stars. Coefficients were then compared with similar data from Galactic globular clusters, the Galactic bulge and the Large and Small Magellanic Clouds (LMC and SMC). Using Fourier coefficients, we also calculated physical parameters via standard equations from the literature. We confirmed the results of previous authors, including lower amplitudes and longer rise times for Blazhko stars. It was found that in the R 31 versus R 21 plot the location of a star depends mainly on its metallicity and that Blazhko stars prefer a different location from modulation-free stars. Field and globular cluster RR Lyrae variables have a different φ 21 and φ 31 from stars in the LMC, SMC and Galactic bulge. Although there are some weak indications that Blazhko stars could tend towards a slightly lower metallicity and shorter periods, no convincing proof was found. The most interesting highlight is the identification of a very recently proposed new group of metal-rich RR Lyrae type stars. These low-luminosity, metal-strong variables, comprising both Blazhko and regular stars, have shorter periods and about 180 K higher temperature at constant (B − V) 0 than the rest of the stars in the sample.
Astronomical Journal, 1999
We present the results of a photometric study of RR Lyrae variables in the Ðeld of the globular cluster M55. We have discovered nine new RR Lyrae stars, increasing the number of known RR Lyrae variables in this cluster to 15 stars. Five of the newly discovered variables are Bailey type RRc, and two are type RRab. Two background RRab stars are probable members of the Sagittarius dwarf galaxy. Fourier decomposition of the light curves was used to derive basic properties of the present sample of RR Lyrae variables. From an analysis of the RRc variables we obtain a mean mass of M \ 0.53^0.03
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.
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,
The Astronomical Journal, 2003
We present the results of a Hubble Space Telescope snapshot program to survey the inner region of the metal-rich globular cluster NGC 6441 for its variable stars. A total of 57 variable stars were found, including 38 RR Lyrae stars, six Population II Cepheids, and 12 long-period variables. Twenty-four of the RR Lyrae stars and all of the Population II Cepheids were previously undiscovered in ground-based surveys. Of the RR Lyrae stars observed in this survey, 26 are pulsating in the fundamental mode with a mean period of 0.753 days and 12 are first-overtone-mode pulsators with a mean period of 0.365 days. These values match up very well with those found in ground-based surveys. Combining all the available data for NGC 6441, we find mean periods of 0.759 and 0.375 days for the RRab and RRc stars, respectively. We also find that the RR Lyrae stars in this survey are located in the same regions of a period-amplitude diagram as those found in ground-based surveys. The overall ratio of RRc to total RR Lyrae stars is 0.33. Although NGC 6441 is a metal-rich globular cluster and would, on that ground, be expected either to have few RR Lyrae stars or to be an Oosterhoff type I system, its RR Lyrae stars more closely resemble those in Oosterhoff type II globular clusters. However, even compared with typical Oosterhoff type II systems, the mean period of its RRab stars is unusually long. We also derived I-band period-luminosity relations for the RR Lyrae stars. Of the six Population II Cepheids, five are of W Virginis type and one is a BL Herculis variable star. This makes NGC 6441, along with NGC 6388, the most metal-rich globular cluster known to contain these types of variable stars. Another variable, V118, may also be a Population II Cepheid, given its long period and its separation in magnitude from the RR Lyrae stars. We examine the period-luminosity relation for these Population II Cepheids and compare it with those in other globular clusters and in the Large Magellanic Cloud. We argue that there does not appear to be a change in the period-luminosity relation slope between the BL Herculis and W Virginis stars, but that a change of slope does occur when the RV Tauri stars are added to the period-luminosity relation.