- ID:
- ivo://CDS.VizieR/J/AJ/157/153
- Title:
- Atomic lines in spectra of RR Lyrae & RHB stars
- Short Name:
- J/AJ/157/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived relations between FWHMs and equivalent widths of metallic absorption lines in the spectra of RR Lyrae stars to estimate new upper limits on the axial equatorial rotational velocities of RR Lyrae and metal-poor red horizontal branch (RHB) stars. We have also derived the variations of RR Lyrae macroturbulent velocities during the pulsation cycles. In RRab cycles, the line widths are dominated by phase-dependent convolutions of axial rotation and macroturbulence, which we designate as V_macrot_. The behavior of V_macrot_ is remarkably uniform among the RRab stars, but the behavior of V_macrot_ among RRc stars varies strongly from star to star. The RRab stars exhibit an upper limit on V_macrot_ of 5+/-1 km/s with weak evidence of an anticorrelation with T_eff_. The RRc minima range from 2 to 12 km/s. The abrupt decline in large rotations with decreasing T_eff_ at the blue boundary of the instability strip and the apparently smooth continuous variation among the RRab and RHB stars suggests that HB stars gain/lose surface angular momentum on timescales that are short compared to HB lifetimes. The V_macrot_ values for our metal-poor RHB stars agree well with those derived by Fourier analysis of an independent but less metal-poor sample of Carney et al. (2008AJ....135..892C); they conform qualitatively to the expectations of Tanner et al. (2013ApJ...778..117T). A general conclusion of our investigation is that surface angular momentum as measured by V_rot_sin(i) is not a reliable indicator of total stellar angular momentum anywhere along the HB.
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- ID:
- ivo://CDS.VizieR/J/AJ/121/2159
- Title:
- Basic parameters for 372 A, F & G stars
- Short Name:
- J/AJ/121/2159
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Paper I (Cat. <J/AJ/121/2148>) of this series presented precise MK spectral types for 372 late A-, F-, and early G-type stars with the aim of understanding the nature of luminosity classification on the MK spectral classification system for this range of spectral types. In this paper, a multidimensional downhill simplex technique is introduced to determine the basic parameters of the program stars from fits of synthetic spectra and fluxes with observed spectra and fluxes from Strvmgren uvby photometry. This exercise yields useful calibrations of the MK spectral classification system but, most importantly, gives insight into the physical nature of luminosity classification on the MK spectral classification system. In particular, we find that in this range of spectral types, microturbulence appears to be at least as important as gravity in determining the MK luminosity type.
- ID:
- ivo://CDS.VizieR/J/ApJ/731/119
- Title:
- BHB candidates in Sagittarius stream
- Short Name:
- J/ApJ/731/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use a sample of blue horizontal branch (BHB) stars from the Sloan Digital Sky Survey Data Release 7 (Cat. II/294) to explore the structure of the tidal tails from the Sagittarius Dwarf Galaxy. We use a method yielding BHB star candidates with up to ~70% purity from photometry alone. The resulting sample has a distance precision of roughly 5% and can probe distances in excess of 100kpc. Using this sample, we identify a possible extension to the trailing arm at distances of 60-80kpc from the Sun with an estimated significance of at least 3.8{sigma}. Current models predict that a distant "returning" segment of the debris stream should exist, but place it substantially closer to the Sun where no debris is observed in our data. Exploiting the distance precision of our tracers, we estimate the mean line-of-sight thickness of the leading arm to be ~3kpc, and show that the two "bifurcated" branches of the debris stream differ by only 1-2kpc in distance. With a spectroscopic very pure BHB star subsample, we estimate the velocity dispersion in the leading arm, 37km/s, which is in reasonable agreement with models of Sgr disruption. We finally present a sample of high-probability Sgr BHB stars in the leading arm of Sgr, selected to have distances and velocities consistent with Sgr membership, to allow further study.
- ID:
- ivo://CDS.VizieR/J/ApJ/684/1143
- Title:
- BHB candidates in the Milky Way
- Short Name:
- J/ApJ/684/1143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive new constraints on the mass of the Milky Way's dark matter halo, based on 2401 rigorously selected blue horizontal-branch halo stars from SDSS DR6. This sample enables construction of the full line-of-sight velocity distribution at different galactocentric radii. To interpret these distributions, we compare them to matched mock observations drawn from two different cosmological galaxy formation simulations designed to resemble the Milky Way. This procedure results in an estimate of the Milky Way's circular velocity curve to ~60kpc, which is found to be slightly falling from the adopted value of 220km/s at the Sun's location, and implies M(<60kpc)=(4.0+/-0.7)x10^11^M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/ApJS/244/43
- Title:
- Binary stars parameters from LAMOST & Kepler obs.
- Short Name:
- J/ApJS/244/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The parameter distribution of binaries is a fundamental knowledge of the stellar systems. A statistical study on the binary stars is carried out based on the LAMOST spectral and Kepler photometric database. We presented a catalog of 1320 binary stars with plentiful parameters, including period, binary subtype, atmosphere parameters (Teff, [Fe/H], and logg), and the physical properties, such as mass, radius, and age, for the primary component stars. Based on this catalog, the unbiased distribution, rather than the observed distribution, was obtained after the correction of selection biases by the Monte Carlo method considering comprehensive affecting factors. For the first time, the orbital eccentricity distribution of the detached binaries is presented. The distribution differences between the three subtypes of binaries (detached, semidetached, and contact) are demonstrated, which can be explained by the generally accepted evolutional scenarios. Many characteristics of the binary stars, such as huge mass transfer on semidetached binaries, period cutoff on contact binaries, period-temperature relationship of contact binaries, and the evolved binaries, are reviewed by the new database. This work supports a common evolutionary scenario for all subtypes of binary stars.
- ID:
- ivo://CDS.VizieR/J/AJ/152/180
- Title:
- Bolometric fluxes of eclipsing binaries in Tycho-2
- Short Name:
- J/AJ/152/180
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present fits to the broadband photometric spectral energy distributions (SEDs) of 158 eclipsing binaries (EBs) in the Tycho-2 catalog. These EBs were selected because they have highly precise stellar radii, effective temperatures, and in many cases metallicities previously determined in the literature, and thus have bolometric luminosities that are typically good to <~10%. In most cases the available broadband photometry spans a wavelength range 0.4-10{mu}m, and in many cases spans 0.15-22{mu}m. The resulting SED fits, which have only extinction as a free parameter, provide a virtually model-independent measure of the bolometric flux at Earth. The SED fits are satisfactory for 156 of the EBs, for which we achieve typical precisions in the bolometric flux of {\simeq}3%. Combined with the accurately known bolometric luminosity, the result for each EB is a predicted parallax that is typically precise to <~5%. These predicted parallaxes-with typical uncertainties of 200{mu}as-are 4-5 times more precise than those determined by Hipparcos for 99 of the EBs in our sample, with which we find excellent agreement. There is no evidence among this sample for significant systematics in the Hipparcos parallaxes of the sort that notoriously afflicted the Pleiades measurement. The EBs are distributed over the entire sky, span more than 10mag in brightness, reach distances of more than 5kpc, and in many cases our predicted parallaxes should also be more precise than those expected from the Gaia first data release. The EBs studied here can thus serve as empirical, independent benchmarks for these upcoming fundamental parallax measurements.
- ID:
- ivo://CDS.VizieR/J/AJ/132/1630
- Title:
- CaII spectroscopy in Magellanic Cloud clusters
- Short Name:
- J/AJ/132/1630
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the FORS2 instrument on the Very Large Telescope, we have obtained near-infrared spectra for more than 200 stars in 28 populous LMC clusters. This cluster sample spans a large range of ages (~113Gyr) and metallicities (-0.3>~[Fe/H]>~-2.0) and has good areal coverage of the LMC disk. The strong absorption lines of the Ca II triplet are used to derive cluster radial velocities and abundances. We determine mean cluster velocities to typically 1.6km/s and mean metallicities to 0.04dex (random error). For eight of these clusters, we report the first spectroscopically determined metallicities based on individual cluster stars, and six of these eight have no published radial velocity measurements. Combining our data with archival Hubble Space Telescope WFPC2 photometry, we find that the newly measured cluster, NGC 1718, is one of the most metal-poor ([Fe/H]~-0.80) intermediate-age (~2Gyr) inner disk clusters in the LMC. Similar to what was found by previous authors, this cluster sample has radial velocities consistent with that of a single rotating disk system, with no indication that the newly reported clusters exhibit halo kinematics. In addition, our findings confirm previous results that show that the LMC lacks the metallicity gradient typically seen in non-barred spiral galaxies, suggesting that the bar is driving the mixing of stellar populations in the LMC.
- ID:
- ivo://CDS.VizieR/J/AJ/149/154
- Title:
- CaII spectroscopy of SMC red giants. III.
- Short Name:
- J/AJ/149/154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtained spectra of red giants in 15 Small Magellanic Cloud (SMC) clusters in the region of the CaII lines with FORS2 on the Very Large Telescope. We determined the mean metallicity and radial velocity with mean errors of 0.05dex and 2.6km/s, respectively, from a mean of 6.5 members per cluster. One cluster (B113) was too young for a reliable metallicity determination and was excluded from the sample. We combined the sample studied here with 15 clusters previously studied by us using the same technique, and with 7 clusters whose metallicities determined by other authors are on a scale similar to ours. This compilation of 36 clusters is the largest SMC cluster sample currently available with accurate and homogeneously determined metallicities. We found a high probability that the metallicity distribution is bimodal, with potential peaks at -1.1 and -0.8dex. Our data show no strong evidence of a metallicity gradient in the SMC clusters, somewhat at odds with recent evidence from CaII triplet spectra of a large sample of field stars. This may be revealing possible differences in the chemical history of clusters and field stars. Our clusters show a significant dispersion of metallicities, whatever age is considered, which could be reflecting the lack of a unique age-metallicity relation in this galaxy. None of the chemical evolution models currently available in the literature satisfactorily represents the global chemical enrichment processes of SMC clusters.
- ID:
- ivo://CDS.VizieR/J/AJ/152/58
- Title:
- CaII spectroscopy of SMC red giants. IV.
- Short Name:
- J/AJ/152/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper represents a major step forward in the systematic and homogeneous study of Small Magellanic Cloud (SMC) star clusters and field stars carried out by applying the calcium triplet technique. We present in this work the radial velocity and metallicity of approximately 400 red giant stars in 15 SMC fields, with typical errors of about 7km/s and 0.16dex, respectively. We added to this information our previously determined metallicity values for 29 clusters and approximately 350 field stars using the identical techniques. Using this enlarged sample, we analyze the metallicity distribution and gradient in this galaxy. We also compare the chemical properties of the clusters and of their surrounding fields. We find a number of surprising results. While the clusters, taken as a whole, show no strong evidence for a metallicity gradient (MG), the field stars exhibit a clear negative gradient in the inner region of the SMC, consistent with the recent results of Dobbie et al. For distances to the center of the galaxy less than 4{deg}, field stars show a considerably smaller metallicity dispersion than that of the clusters. However, in the external SMC regions, clusters and field stars exhibit similar metallicity dispersions. Moreover, in the inner region of the SMC, clusters appear to be concentrated in two groups: one more metal-poor and another more metal-rich than field stars. Individually considered, neither cluster group presents an MG. Most surprisingly, the MG for both stellar populations (clusters and field stars) appears to reverse sign in the outer regions of the SMC. The difference between the cluster metallicity and the mean metallicity of the surrounding field stars turns out to be a strong function of the cluster metallicity. These results could be indicating different chemical evolution histories for these two SMC stellar populations. They could also indicate variations in the chemical behavior of the SMC in its internal and external regions.
- ID:
- ivo://CDS.VizieR/J/MNRAS/411/1013
- Title:
- CaII triplet in Sextans dSph galaxy
- Short Name:
- J/MNRAS/411/1013
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use Very Large Telescope (VLT)/Fibre Large Array Multi Element Spectrograph (FLAMES) intermediate-resolution (R~6500) spectra of individual red giant branch stars in the near-infrared Ca ii triplet (CaT) region to investigate the wide-area metallicity properties and internal kinematics of the Sextans dwarf spheroidal galaxy (dSph). Our final sample consists of 174 probable members of Sextans with accurate line-of-sight velocities (+/-2km/s) and CaT [Fe/H] measurements (+/-0.2dex).
