- ID:
- ivo://CDS.VizieR/J/AJ/155/171
- Title:
- RR Lyrae stars in and around NGC 6441
- Short Name:
- J/AJ/155/171
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Detailed elemental abundance patterns of metal-poor ([Fe/H]~-1 dex) stars in the Galactic bulge indicate that a number of them are consistent with globular cluster (GC) stars and may be former members of dissolved GCs. This would indicate that a few per cent of the Galactic bulge was built up from destruction and/or evaporation of GCs. Here, an attempt is made to identify such presumptive stripped stars originating from the massive, inner Galaxy GC NGC 6441 using its rich RR Lyrae variable star (RRL) population. We present radial velocities of 40 RRLs centered on the GC NGC 6441. All 13 of the RRLs observed within the cluster tidal radius have velocities consistent with cluster membership, with an average radial velocity of 24+/-5 km/s and a star-to-star scatter of 11 km/s. This includes two new RRLs that were previously not associated with the cluster. Eight RRLs with radial velocities consistent with cluster membership but up to three time the distance from the tidal radius are also reported. These potential extra-tidal RRLs also have exceptionally long periods, which is a curious characteristic of the NGC 6441 RRL population that hosts RRLs with periods longer than seen anywhere else in the Milky Way. As expected of stripped cluster stars, most are inline with the cluster's orbit. Therefore, either the tidal radius of NGC 6441 is underestimated and/or we are seeing dissolving cluster stars stemming from NGC 6441 that are building up the old spheroidal bulge.
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Search Results
- 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.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/861/23
- Title:
- RR Lyrae variables in the Crater II dwarf galaxy
- Short Name:
- J/ApJ/861/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of RR Lyrae variable stars in Crater II, a recently discovered large and diffuse satellite dwarf galaxy of the Milky Way (MW). Based on B, V time-series photometry obtained with the Korea Microlensing Telescope Network 1.6m telescope at Cerro Tololo Inter-American Observatory, we identified 83 ab-type and 13 c-type pulsators by fitting template light curves. The detected RR Lyrae stars are centrally concentrated, which ensures that most of them are members of Crater II. In terms of the distribution of RRab stars in the period-amplitude diagram, Crater II is clearly different from ultra-faint dwarf (UFD) galaxies, but very similar to the two classical MW dwarf spheroidal (dSph) galaxies Draco and Carina with Oosterhoff-intermediate (Oo-int) properties. Combined with the mean period of ab-type variables (<P_ab_>=0.631+/-0.004days) and the c-type fraction (~0.14) in Crater II, this suggests an Oo-int classification for Crater II and implies that its nature is more like a dSph rather than a UFD. We also estimated the mean metallicity, reddening, and distance of Crater II, from the photometric and pulsation properties of the RR Lyrae stars. The stellar population model we have constructed indicates that Crater II is dominated by an old population, but is relatively younger than the oldest globular clusters in the MW. With a lack of high-amplitude short-period RRab stars, Crater II, like most of the other less massive dSphs, is probably not a surviving counterpart of the major building blocks of the MW halo.
- ID:
- ivo://CDS.VizieR/J/A+A/625/A1
- Title:
- RR Lyrae variables NIR light-curve templates
- Short Name:
- J/A+A/625/A1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We provide homogeneous optical (UBVRI) and near-infrared (NIR, JHK) time series photometry for 254 cluster (omega Cen, M4) and field RR Lyrae (RRL) variables. We ended up with more than 551000 measurements. For 94 fundamental (RRab) and 51 first overtones (RRc) we provide a complete optical/NIR characterization (mean magnitudes, luminosity amplitudes, epoch of the anchor point). The NIR light curves of these variables were adopted to provide new light-curve templates for both RRc and RRab variables. The templates for the J and the H bands are newly introduced, together with the use of the pulsation period to discriminate among the different RRab templates. To overcome uncertainties in the fit of secondary features of the light curves we provide two independent sets of analytical functions (Fourier and periodic Gaussian series).
- ID:
- ivo://CDS.VizieR/J/ApJ/900/118
- Title:
- RSGs in the LMC & sp. follow-up for LMC & SMC
- Short Name:
- J/ApJ/900/118
- Date:
- 20 Jan 2022 11:32:23
- Publisher:
- CDS
- Description:
- The binary fraction of unevolved massive stars is thought to be 70%-100% but there are few observational constraints on the binary fraction of the evolved version of a subset of these stars, the red supergiants (RSGs). Here we identify a complete sample of RSGs in the Large Magellanic Cloud (LMC) using new spectroscopic observations and archival UV, IR, and broadband optical photometry. We find 4090 RSGs with logL/L_{sun}_>3.5, with 1820 of them having logL/L_{sun}_>4, which we believe is our completeness limit. We additionally spectroscopically confirmed 38 new RSG + B-star binaries in the LMC, bringing the total known up to 55. We then estimated the binary fraction using a k-nearest neighbors algorithm that classifies stars as single or binary based on photometry with a spectroscopic sample as a training set. We take into account observational biases such as line-of-sight stars and binaries in eclipse while also calculating model- dependent corrections for RSGs with companions that our observations were not designed to detect. Based on our data, we find an initial result of 13.5_-6.67_^+7.56^% for RSGs with O- or B-type companions. Using the Binary Population and Spectral Synthesis models to correct for unobserved systems, this corresponds to a total RSG binary fraction of 19.5_-6.7_^+7.6^% . This number is in broad agreement with what we would expect given an initial OB binary distribution of 70%, a predicted merger fraction of 20%-30%, and a binary interaction fraction of 40%-50%.
- ID:
- ivo://CDS.VizieR/J/MNRAS/446/4008
- Title:
- RT Aur and SZ tau UBV light curves
- Short Name:
- J/MNRAS/446/4008
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The quantity and quality of satellite photometric data strings is revealing details in Cepheid variation at very low levels. Specifically, we observed a Cepheid pulsating in the fundamental mode and one pulsating in the first overtone with the Canadian MOST (Microvariability and Oscillations of Stars) satellite. The 3.7-d period fundamental mode pulsator (RT Aur) has a light curve that repeats precisely, and can be modelled by a Fourier series very accurately. The overtone pulsator (SZ Tau, 3.1d period) on the other hand shows light-curve variation from cycle to cycle which we characterize by the variations in the Fourier parameters. We present arguments that we are seeing instability in the pulsation cycle of the overtone pulsator, and that this is also a characteristic of the O-C curves of overtone pulsators. On the other hand, deviations from cycle to cycle as a function of pulsation phase follow a similar pattern in both stars, increasing after minimum radius. In summary, pulsation in the overtone pulsator is less stable than that of the fundamental mode pulsator at both long and short time-scales.
- ID:
- ivo://CDS.VizieR/J/PASP/125/17
- Title:
- RU Eri UBV differential light curves
- Short Name:
- J/PASP/125/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- RU Eri is a near-contact eclipsing binary (V~9.24mag) with a 0.632-day orbital period. The Wilson-Devinney program is used to simultaneously solve new UBV light curves obtained between 1973 and 1981 at the Fernbank Science Center Observatory, together with existing single-lined radial velocity measurements. Light and velocity solution parameters, orbital elements, and absolute dimensions are presented. A period of 0.632198836+/-0.000000046d is found.
- ID:
- ivo://CDS.VizieR/J/AJ/156/98
- Title:
- Runaway stars in the 30 Doradus region of the LMC
- Short Name:
- J/AJ/156/98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of relative proper motions for 368787 stars in the 30 Doradus region of the Large Magellanic Cloud (LMC), based on a dedicated two-epoch survey with the Hubble Space Telescope and supplemented with proper motions from our pilot archival study. We demonstrate that a relatively short epoch difference of three years is sufficient to reach a level of precision of ~0.1 mas/yr or better. A number of stars with relative proper motions exceeding a 3{sigma} error threshold represent a mixture of Milky Way denizens and 18 potential LMC runaway stars. Based upon 183 VFTS OB stars with the best proper motions, we conclude that none of them moves faster than ~0.3 mas/yr in each coordinate-equivalent to ~70 km/s. Among the remaining 351 VFTS stars with less accurate proper motions, only one candidate OB runaway can be identified. We rule out any OB star in our sample moving at a tangential velocity exceeding ~120 km/s. The most significant result of this study is finding 10 stars over a wide range of masses that appear to have been ejected from the massive star cluster R136 in the tangential plane to angular distances from 35" out to 407", equivalent to 8-98 pc. The tangential velocities of these runaways appear to be correlated with apparent magnitude, indicating a possible dependence on the stellar mass. Lastly, a comparison to proper motions from Gaia DR 2 shows that for several relatively bright stars the DR 2 has an unexpected scatter that cannot be accounted for by the formal errors.
