Pulsating Variable Stars in the Coma Berenices dwarf spheroidal galaxy 1 (original) (raw)
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Pulsating Variable Stars in the Coma Berenices Dwarf Spheroidal Galaxy
The Astrophysical Journal, 2009
We present B, V , I time-series photometry of the Coma Berenices dwarf spheroidal galaxy, a faint Milky Way (MW) satellite, recently discovered by the Sloan Digital Sky Survey. We have obtained V , B − V and V , V − I color-magnitude diagrams that reach V ∼ 23.0−23.2 mag showing the galaxy turnoff at V ∼ 21.7 mag, and have performed the first study of the variable star population of this new MW companion. Two RR Lyrae stars (a fundamental-mode, RRab, and a first overtone, RRc, pulsator) and a short period variable with period P = 0.12468 days were identified in the galaxy. The RRab star has a rather long period of P ab = 0.66971 days and is about 0.2 mag brighter than the RRc variable and other nonvariable stars on the galaxy horizontal branch (HB). In the period-amplitude diagram, the RRab variable falls closer to the loci of Oosterhoff type-II systems and evolved fundamental-mode RR Lyrae stars in the Galactic globular cluster M3. The average apparent magnitude of the galaxy HB, V HB = 18.64 ± 0.04 mag, leads to a distance modulus for the Coma dSph μ 0 = 18.13 ± 0.08 mag, corresponding to a distance d = 42 +2 −1 kpc, by adopting a reddening E(B − V ) = 0.045 ± 0.015 mag and a metallicity [Fe/H] = −2.53 ± 0.05 dex.
DWARF SPHEROIDAL SATELLITES OF M31. I. VARIABLE STARS AND STELLAR POPULATIONS IN ANDROMEDA XIX
The Astrophysical Journal, 2013
We present B, V time-series photometry of Andromeda XIX (And XIX), the most extended (half-light radius of 6.2 ′ ) of Andromeda's dwarf spheroidal companions, that we observed with the Large Binocular Cameras at the Large Binocular Telescope. We surveyed a 23 ′ × 23 ′ area centered on And XIX and present the deepest color magnitude diagram (CMD) ever obtained for this galaxy, reaching, at V ∼ 26.3 mag, about one magnitude below the horizontal branch (HB). The CMD shows a prominent and slightly widened red giant branch, along with a predominantly red HB, which, however, extends to the blue to significantly populate the classical instability strip. We have identified 39 pulsating variable stars, of which 31 are of RR Lyrae type and 8 are Anomalous Cepheids (ACs). Twelve of the RR Lyrae variables and 3 of the ACs are located within And XIX's half light radius. The average period of the fundamental mode RR Lyrae stars ( P ab = 0.62 d, σ= 0.03 d) and the period-amplitude diagram qualify And XIX as an Oosterhoff-Intermediate system. From the average luminosity of the RR Lyrae stars ( V (RR) = 25.34 mag, σ= 0.10 mag) we determine a distance modulus of (m-M) 0 =24.52 ± 0.23 mag in a scale where the distance to the Large Magellanic Cloud (LMC) is 18.5 ± 0.1 mag. The ACs follow a well defined Period-Wesenheit (P W ) relation that appears to be in very good agreement with the P W relationship defined by the ACs in the LMC.
Short and long period variable stars in the Carina dwarf Spheroidal galaxy
International Astronomical Union Colloquium, 2004
We present first results concerning the detection of variable stars in the Carina dwarf Spheroidal fromB, Vimages collected with the 4-m CTIO telescope. We show a sample of candidate variables spanning from the tip of the Red Giant Branch down to the Main Sequence turn off. Finally, we discuss the future photometric and spectroscopic developments of this project.
The ISLAnds Project. III. Variable Stars in Six Andromeda Dwarf Spheroidal Galaxies
The Astrophysical Journal, 2017
We present a census of variable stars in six M31 dwarf spheroidal satellites observed with the Hubble Space Telescope. We detect 870 RR Lyrae (RRL) stars in the fields of AndI (296), II (251), III (111), XV (117), XVI (8), and XXVIII (87). We also detect a total of 15 Anomalous Cepheids, three eclipsing binaries, and seven field RRL stars compatible with being members of the M31 halo or the Giant Stellar Stream. We derive robust and homogeneous distances to the six galaxies using different methods based on the properties of the RRL stars. Working with the up-to-date set of Period-Wesenheit (I, B-I) relations published by Marconi et al., we obtain distance moduli of μ 0 =[24.49, 24.16, 24.36, 24.42, 23.70, 24.43] mag (respectively), with systematic uncertainties of 0.08 mag and statistical uncertainties <0.11 mag. We have considered an enlarged sample of 16 M31 satellites with published variability studies, and compared their pulsational observables (e.g., periods and amplitudes) with those of 15 Milky Way satellites for which similar data are available. The properties of the (strictly old) RRL in both satellite systems do not show any significant difference. In particular, we found a strikingly similar correlation between the mean period distribution of the fundamental RRL pulsators (RRab) and the mean metallicities of the galaxies. This indicates that the old RRL progenitors were similar at the early stage in the two environments, suggesting very similar characteristics for the earliest stages of evolution of both satellite systems.
Variable Stars in the Newly Discovered Milky Way Dwarf Spheroidal Satellite Canes Venatici I
The Astrophysical Journal, 2008
We have identified 23 RR Lyrae stars and three possible anomalous Cepheids (ACs) among 84 candidate variables in the recently discovered Canes Venatici I (CVn I) dwarf spheroidal galaxy. The mean period of 18 RRab type stars, days, and the location of these stars in the period-amplitude diagram suggest AP S p 0.60 ע 0.01 ab that CVn I is likely an Oosterhoff-intermediate system. The average apparent magnitude of the RR Lyrae stars, mag, gives a distance of 210 kpc, for an adopted reddening mag. We
2010
We present the results of a new search for variable stars in the Local Group (LG) isolated dwarf galaxy IC 1613, based on 24 orbits of F475W and F814W photometry from the Advanced Camera for Surveys onboard the Hubble Space Telescope. We detected 259 candidate variables in this field, of which only 13 (all of them bright Cepheids) were previously known. Out of the confirmed variables, we found 90 RR Lyrae stars, 49 classical Cepheids (including 36 new discoveries), and 38 eclipsing binary stars for which we could determine a period. The RR Lyrae include 61 fundamental (RRab) and 24 first-overtone (RRc) pulsators, and 5 pulsating in both modes simultaneously (RRd). As for the majority of LG dwarfs, the mean periods of the RRab and RRc (0.611 and 0.334 day, respectively) as well as the fraction of overtone pulsators (f c =0.28) place this galaxy in the intermediate regime between the Oosterhoff types. From their position on the period-luminosity diagram and light-curve morphology, we can unambiguously classify 25 and 14 Cepheids as fundamental and firstovertone mode pulsators, respectively. Another two are clearly second-overtone Cepheids, the first ones to be discovered beyond the Magellanic Clouds. Among the remaining candidate variables, five were classified as δ-Scuti and five as long-period variables. Most of the others are located on the main-sequence, the majority of them likely eclipsing binary systems, although some present variations similar to pulsating stars. We estimate the distance to IC 1613 using various methods based on the photometric and pulsational properties of the Cepheids and RR Lyrae stars. The values we find are in very good agreement with each other and with previous estimates based on independent methods. When corrected to a common reddening of E(B−V)=0.025 and true LMC distance modulus of (m−M) LMC,0 =18.515±0.085, we find that all the distance determinations from the literature converge to a common value of (m−M) 0 =24.400±0.014 (statistical), or 760 kpc. The parallel WFPC2 field, which lies within three core radii, was also searched for variable stars. We discovered nine RR Lyrae stars (4 RRab, 4 RRc and 1 RRd) and two Cepheids, even though the lower signal-to-noise ratio of the observations did not allow us to measure their periods as accurately as for the variables in the ACS field-of-view. We provide their coordinates and approximate properties for completeness.
The Astrophysical Journal, 2009
We present the first study of the variable star populations in the isolated dwarf spheroidal galaxies (dSph) Cetus and Tucana. Based on Hubble Space Telescope images obtained with the Advanced Camera for Surveys in the F475W and F814W bands, we identified 180 and 371 variables in Cetus and Tucana, respectively. The vast majority are RR Lyrae stars. In Cetus we also found three anomalous Cepheids, four candidate binaries and one candidate long-period variable (LPV), while six anomalous Cepheids and seven LPV candidates were found in Tucana. Of the RR Lyrae stars, 147 were identified as fundamental mode (RRab) and only eight as first-overtone mode (RRc) in Cetus, with mean periods of 0.614 and 0.363 day, respectively. In Tucana we found 216 RRab and 82 RRc giving mean periods of 0.604 and 0.353 day. These values place both galaxies in the so-called Oosterhoff Gap, as is generally the case for dSph. We calculated the distance modulus to both galaxies using different approaches based on the properties of RRab and RRc, namely the luminosity-metallicity and period-luminosity-metallicity relations, and found values in excellent agreement with previous estimates using independent methods: (m−M) 0,Cet =24.46±0.12 and (m−M) 0,T uc =24.74±0.12, corresponding to 780±40 kpc and 890±50 kpc. We also found numerous RR Lyrae variables pulsating in both modes simultaneously (RRd): 17 in Cetus and 60 in Tucana. Tucana is, after Fornax, the second dSph in which such a large fraction of RRd (∼17%) has been observed. We provide the photometry and pulsation parameters for all the variables, and compare the latter with values from the literature for well-studied dSph of the Local Group and Galactic globular clusters.
The Leo IV Dwarf Spheroidal Galaxy: Color-Magnitude Diagram and Pulsating Stars
The Astrophysical Journal, 2009
We present the first V, B − V color−magnitude diagram of the Leo IV dwarf spheroidal galaxy, a faint Milky Way satellite recently discovered by the Sloan Digital Sky Survey. We have obtained B, V time-series photometry reaching about half a magnitude below the Leo IV turnoff, which we detect at V = 24.7 mag, and have performed the first study of the variable star population. We have identified three RR Lyrae stars (all fundamental−mode pulsators, RRab) and one SX Phoenicis variable in the galaxy. In the period−amplitude diagram the Leo IV 1 Based on data collected at the 2.5 m Isaac Newton Telescope, La Palma, Canary Island, Spain, at the 4.2 m William Herschel Telescope, Roche de los Muchachos, Canary Islands, Spain, and at the 4.1 m Southern -2 -RR Lyrae stars are located close to the loci of Oosterhoff type I systems and the evolved fundamental-mode RR Lyrae stars in the Galactic globular cluster M3. However, their mean pulsation period, P ab =0.655 days, would suggest an Oosterhoff type II classification for this galaxy. The RR Lyrae stars trace very well the galaxy's horizontal branch, setting its average magnitude at V RR = 21.48 ± 0.03 mag (standard deviation of the mean). This leads to a distance modulus of µ 0 = 20.94 ± 0.07 mag, corresponding to a distance of 154 ± 5 kpc, by adopting for the Leo IV dSph a reddening E(B − V ) = 0.04 ± 0.01 mag and a metallicity of [Fe/H] = −2.31 ± 0.10.
RR Lyrae Variable Stars in the Dwarf Spheroidal Galaxy Leo I
The Astrophysical Journal, 2001
We report the discovery of a significant population of RR Lyrae variables in the dwarf spheroidal galaxy Leo I. Based on 40 V and 22 B images of the galaxy taken using the ESO Wide Field Imager we have identified so far 74 candidate RR Lyrae's in two CCD's hosting the main body of the galaxy. Full coverage of the light variations and pulsation periods have been obtained for 54 of them, 47 of which are Bailey ab-type RR Lyrae's (RRab's) and 7 are c-type (RRc's). The period distribution of the presently confirmed sample of RRab's peaks at P=0. d 60, with a minimum period of 0. d 54. The pulsational properties indicate for Leo I an intermediate Oosterhoff type, similar to other dwarf galaxies in the Local Group and the LMC. However, the rather long minimum period of the ab-type variables, and the significant number of RRab's with long period and large amplitude, suggest that the bulk of the old population in Leo I is more like the Oosterhoff type II globular clusters. The most straightforward interpretation is that a range in metallicity is present among the RR Lyrae's of Leo I, with a significant population of very metal-poor stars. Alternatively, these OoII variables could be more evolved. The average apparent magnitude of the RR Lyrae's across the full cycle is V (RR) = 22.60 ± 0.12 mag, yielding a distance modulus (m − M) V,0 = 22.04 ± 0.14 mag for Leo I on the "long" distance scale.
Monthly Notices of the Royal Astronomical Society, 2012
We investigate the variable star content of the isolated, Local Group, dwarf spheroidal galaxy (dSph) Cetus. Multi-epoch, wide-field images collected with the VLT/VIMOS camera allowed us to detect 638 variable stars (630 RR Lyrae stars and 8 Anomalous Cepheids), 475 of which are new detections. We present a full catalogue of periods, amplitudes, and mean magnitudes. Motivated by the recent discovery that the pulsational properties of the RR Lyrae stars in the Tucana dSph revealed the presence of a metallicity gradient within the oldest (10 Gyr old) stellar populations, we investigated the possibility of an analogous effect in Cetus. We found that, despite the obvious radial gradient in the Horizontal Branch (HB) and Red Giant Branch (RGB) morphologies, both becoming bluer on average for increasing distance from the center of Cetus, the properties of the RR Lyrae stars are homogeneous within the investigated area (out to r∼15 ′), with no significant evidence of a radial gradient. We discuss this in connection with the star formation history (SFH) previously derived for the two galaxies. The observed differences between these two systems show that even systems this small show a variety of early evolutionary histories. These differences could be due to different merger or accretion histories.