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5691. RR Lyrae stars in six ultra-deep fields of M31
ID:
ivo://CDS.VizieR/J/AJ/141/171
Title:
RR Lyrae stars in six ultra-deep fields of M31
Short Name:
J/AJ/141/171
Date:
21 Oct 2021
Publisher:
CDS
Description:
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.
5692. RR Lyrae stars in the Catalina Sky Survey
ID:
ivo://CDS.VizieR/J/ApJ/765/154
Title:
RR Lyrae stars in the Catalina Sky Survey
Short Name:
J/ApJ/765/154
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the analysis of 1207 RR Lyrae found in photometry taken by the Catalina Survey's Mount Lemmon telescope. By combining accurate distances for these stars with measurements for ~14000 type-ab RR Lyrae from the Catalina Schmidt telescope, we reveal an extended association that reaches Galactocentric distances beyond 100kpc and overlaps the Sagittarius stream system. This result confirms earlier evidence for the existence of an outer halo tidal stream resulting from a disrupted stellar system. By comparing the RR Lyrae source density with that expected based on halo models, we find the detection has ~8{sigma} significance. We investigate the distances, radial velocities, metallicities, and period-amplitude distribution of the RR Lyrae. We find that both radial velocities and distances are inconsistent with current models of the Sagittarius stream. We also find tentative evidence for a division in source metallicities for the most distant sources. Following prior analyses, we compare the locations and distances of the RR Lyrae with photometrically selected candidate horizontal branch stars and find supporting evidence that this structure spans at least 60{deg} of the sky. We investigate the prospects of an association between the stream and the unusual globular cluster NGC 2419.
5693. RR Lyrae survey in the Galactic Halo
ID:
ivo://CDS.VizieR/J/ApJ/678/851
Title:
RR Lyrae survey in the Galactic Halo
Short Name:
J/ApJ/678/851
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a search for RR Lyrae variable stars from archival observations of the Southern Edgeworth-Kuiper Belt Object survey. The survey covers 1675deg^2^ along the ecliptic to a mean depth of V=19.5, i.e., a heliocentric distance of ~50kpc for RR Lyrae stars. The survey reveals 2016 RR Lyrae candidates. Follow-up photometric monitoring of a subset of these candidates shows ~24% contamination by non-RR Lyrae variables. We derive a map of overdensity of RR Lyrae stars in the halo that reveals a series of structures coincident with the leading and trailing arms of debris from the Sagittarius dwarf galaxy. One of the regions of overdensity is found on the trailing arm, 200{deg} from the main body of the Sagittarius dwarf at a distance of ~45kpc. This distant detection of the stellar population of the outer trailing arm of Sagittarius offers a tight constraint on the motion of the dwarf galaxy. A distinctly separate region of overdensity is seen toward the Virgo overdensity.
5694. RR Lyrae variables in ESO294-G010 and ESO410-G005
ID:
ivo://CDS.VizieR/J/ApJ/784/76
Title:
RR Lyrae variables in ESO294-G010 and ESO410-G005
Short Name:
J/ApJ/784/76
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of our analysis of the RR Lyrae (RRL) variable stars detected in two transition-type dwarf galaxies (dTrans), ESO294-G010 and ESO410-G005 in the Sculptor group, which is known to be one of the closest neighboring galaxy groups to our Local Group. Using deep archival images from the Advanced Camera for Surveys on board the Hubble Space Telescope, we have identified a sample of RRL candidates in both dTrans galaxies (219 RRab (RR0) and 13 RRc (RR1) variables in ESO294-G010; 225 RRab and 44 RRc stars in ESO410-G005). The metallicities of the individual RRab stars are calculated via the period-amplitude-[Fe/H] relation derived by Alcock et al. This yields mean metallicities of <[Fe/H]>_ESO294_=-1.77+/-0.03 and <[Fe/H]>_ESO410_=-1.64+/-0.03. The RRL metallicity distribution functions (MDFs) are investigated further via simple chemical evolution models; these reveal the relics of the early chemical enrichment processes for these two dTrans galaxies. In the case of both galaxies, the shapes of the RRL MDFs are well described by pre-enrichment models. This suggests two possible channels for the early chemical evolution for these Sculptor group dTrans galaxies: (1) the ancient stellar populations of our target dwarf galaxies might have formed from the star forming gas which was already enriched through "prompt initial enrichment" or an "initial nucleosynthetic spike" from the very first massive stars, or (2) this pre-enrichment state might have been achieved by the end products from more evolved systems of their nearest neighbor, NGC 55. We also study the environmental effects of the formation and evolution of our target dTrans galaxies by comparing their properties with those of 79 volume limited (D_{sun}_<2Mpc) dwarf galaxy samples in terms of the luminosity-metallicity relation and the H I gas content. The presence of these RRL stars strongly supports the idea that although the Sculptor Group galaxies have a considerably different environment from the Local Group (e.g., no giant host galaxies, loosely bound and very low local density), they share a common epoch of early star formation with the dwarf satellite galaxies in the Local Group.
5695. RR Lyrae variables in 2 fields in M31 spheroid
ID:
ivo://CDS.VizieR/J/AJ/138/184
Title:
RR Lyrae variables in 2 fields in M31 spheroid
Short Name:
J/AJ/138/184
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Hubble Space Telescope observations taken with the Advanced Camera for Surveys Wide Field Channel of two fields near M32 - between 4 and 6kpc from the center of M31. The data cover a time baseline sufficient for the identification and characterization of 681 RR Lyrae variables of which 555 are ab-type and 126 are c-type.
5696. RR Lyrae variables in M33
ID:
ivo://CDS.VizieR/J/AJ/132/1361
Title:
RR Lyrae variables in M33
Short Name:
J/AJ/132/1361
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present observations of RR Lyrae variables in the Local Group late-type spiral galaxy M33. Using the Advanced Camera for Surveys on the Hubble Space Telescope, we have identified 64 ab-type RR Lyrae stars in M33. We have estimated reddenings for these stars based on their minimum light V-I colors and metallicities based on their periods. From the distributions of these properties, we conclude that the RR Lyrae stars belong to two populations: one associated with the halo of M33 and the other associated with its disk. Given that RR Lyrae stars are produced by populations older than 10Gyr, this suggests that not only does the field halo of M33 contain an old component, but so does its disk. This is one of the best pieces of evidence for the existence of a halo field component in M33. Using a relation between RR Lyrae absolute magnitude and metallicity (M_V_(RR)=0.23[Fe/H]+0.93), we estimate a mean distance modulus of (m-M)0=24.67+/-0.08 for M33. This places M33 approximately 70kpc beyond M31 in line-of-sight distance.
5697. RR Lyrae variables in M33
ID:
ivo://CDS.VizieR/J/MNRAS/468/870
Title:
RR Lyrae variables in M33
Short Name:
J/MNRAS/468/870
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a re-analysis of M33 RR Lyrae variables in four different fields: two inner disc fields and two outer disc fields. These are located at 8.5, 8.7, 36 and 46 arcmin from the centre of M33, respectively. We identify 48 new RR Lyrae variable stars and refine the light-curve properties of 51 previously identified variables. From the light curves, we calculate reddenings and metallicities for each star. Using data in this paper and previously published material, we are able to construct a radial density profile for the RR Lyrae stars in M33. This profile, when plotted in log space, has a slope of ~-2.0+/-0.15 which agrees with the radial distribution of halo stars in the Milky Way and M31. This suggests that the majority of M33 RR Lyrae variables observed so far belong to the halo. We also examine the RR Lyrae specific frequency and absolute magnitude relation in M33 and find good agreement with previous studies.
5698. RR Lyrae Variables in M15
ID:
ivo://CDS.VizieR/J/AJ/110/704
Title:
RR Lyrae Variables in M15
Short Name:
J/AJ/110/704
Date:
21 Oct 2021
Publisher:
CDS
Description:
New CCD photometry is presented for RR Lyrae variable stars in the globular cluster M15. This photometry, mainly in V and R, with some additional B and I, is used to construct lightcurves of 44 RR Lyraes and one Cepheid in M15. One new low-amplitude RR Lyrae star was discovered. The observable parameters of the light curves are used, in conjunction with theoretical photometric indices, to obtain effective temperatures and bolometric magnitudes in the RR Lyrae stars. We confirm that the regions occupied by RRab and RRcd variables in M15 have little or no overlap in effective temperature. Photometry for variable and nonvariable horizontal branch stars in M15 is used to establish the high and low temperature boundaries of the instability strip. There is evidence that the blue edge of the M15 RR Lyrae instability strip becomes cooler at higher luminosities. Employing Cox's value of the mass of RRd stars, 0.75 Msun, and the pulsation equation, the absolute magnitude of the RR Lyrae stars in M15 is estimated to be <M_V_> = +0.36+/-0.12 mag. However, this result depends upon the adopted mass, bolometric correction, and color-temperature relation, which remain significantly uncertain. The implications of the absolute magnitude determination for the ages of the globular clusters are discussed.
5699. RR Lyrae variables in M32 and M31
ID:
ivo://CDS.VizieR/J/ApJ/708/817
Title:
RR Lyrae variables in M32 and M31
Short Name:
J/ApJ/708/817
Date:
21 Oct 2021
Publisher:
CDS
Description:
We observed two fields near M32 with the Advanced Camera for Surveys/High Resolution Channel (ACS/HRC) on board the Hubble Space Telescope. 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 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. We detected 17 RR Lyrae variables in F1 and 14 in F2. A 1{sigma} upper limit of 6 RR Lyrae variables belonging to M32 is inferred from these two fields alone. Use of our two ACS/WFC parallel fields provides better constraints on the M31 background, however, and implies that 7^+4^_-3_ (68% confidence interval) RR Lyrae variables in F1 belong to M32. We have therefore found evidence for an ancient population in M32. It seems to be nearly indistinguishable from the ancient population of M31. The RR Lyrae stars in the F1 and F2 fields have indistinguishable mean V-band magnitudes, mean periods, distributions in the Bailey diagram, and ratios of RRc to RRtotal types. However, the color distributions in the two fields are different, with a population of red RRab variables in F1 not seen in F2. We suggest that these might be identified with the detected M32 RR Lyrae population, but the small number of stars rules out a definitive claim.
5700. RR Lyrae variables in M33. II.
ID:
ivo://CDS.VizieR/J/ApJ/724/799
Title:
RR Lyrae variables in M33. II.
Short Name:
J/ApJ/724/799
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of an extensive survey of RR Lyrae (RRL) stars in three fields along the major axis of the Triangulum Galaxy (M33). From images taken with the Advanced Camera for Surveys (ACS) Wide Field Channel on board the Hubble Space Telescope through two passbands (F606W and F814W), we have identified and characterized a total of 119 RRL variables (96 RRab (RR0) and 23 RRc (RR1)) in M33. Using the properties of 83 RRL stars (65 RRab and 18 RRc) in the innermost ACS field (hereafter DISK2), we find mean periods of <P_ab_>=0.553+/-0.008(error1)+/-0.05(error2) and <P_c_>=0.325+/-0.008(error1)+/-0.05(error2), where the "error1" value represents the standard error of the mean and the "error2" value is based on the error of an individual RRL period calculated from our synthetic light curve simulations. The VI minimum-light colors of the RRab stars are used to calculate a mean line-of-sight reddening toward the DISK2 field of <E(V-I)>=0.175.