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Start Over Subject population ii stars Publisher CDS
71. Radial velocity time series of HD 122563
ID:
ivo://CDS.VizieR/J/A+A/625/A33
Title:
Radial velocity time series of HD 122563
Short Name:
J/A+A/625/A33
Date:
21 Oct 2021
Publisher:
CDS
Description:
The nearby metal-poor giant HD122563 is an important astrophysical laboratory in which to test stellar atmospheric and interior physics. It is also a benchmark star for which to calibrate methods to apply to large scale surveys. Recently it has been remeasured using various methodologies given the new high precision instruments at our disposal. However, inconsistencies in the observations and models have been found. In order to better characterise this star using complementary techniques we have been measuring its radial velocities since 2016 using the Hertzsprung telescope (SONG network node) in order to detect oscillations. In this work we report the first detections of sun-like oscillations in this star, and to our knowledge, a detection in the most metal-poor giant to date. We applied the classical seismic scaling relation to derive a new surface gravity for HD122563 of logg=1.39+/-0.01dex. Reasonable constraints on the mass imposed by its PopII giant classification then yields a radius of 30.8+/-1.0R_{sun}_. By coupling this new radius with recent interferometric measurements we infer a distance to the star of 306+/-9pc. This result places it further away than was previously thought and is inconsistent with the Hipparcos parallax. Independent data from the Gaia mission corroborate the distance hypothesis (d_GDR2_=290+/-5pc), and thus the updated fundamental parameters. We confirm the validity of the classical seismic scaling relation for surface gravity in metal-poor and evolved star regimes. The remaining discrepancy of 0.04dex between logg_GDR2_ (=1.43+/-0.03) reduces to 0.02dex by applying corrections to the scaling relations based on the mean molecular weight and adiabatic exponent. The new constraints on the HR diagram (L_*v_=381+/-26L_{sun}_) significantly reduce the disagreement between the stellar parameters and evolution models, however, a discrepancy of the order of 150K still exists. Fine-tuned stellar evolution calculations show that this discrepancy can be reconciled by changing the mixing-length parameter by an amount (-0.35) that is in agreement with predictions from recent 3D simulations and empirical results. Asteroseismic measurements are continuing, and analysis of the full frequency data complemented by a distance estimate promises to bring important constraints on our understanding of this star and of the accurate calibration of the seismic scaling relations in this regime.
72. Rare earth abundances
ID:
ivo://CDS.VizieR/J/ApJS/182/80
Title:
Rare earth abundances
Short Name:
J/ApJS/182/80
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have derived new abundances of the rare earth elements Pr, Dy, Tm, Yb, and Lu for the solar photosphere and for five very metal-poor, neutron-capture r-process-rich giant stars. The photospheric values for all five elements are in good agreement with meteoritic abundances. For the low-metallicity sample, these abundances have been combined with new Ce abundances from a companion paper, and reconsideration of a few other elements in individual stars, to produce internally consistent Ba, rare earth, and Hf(56<=Z<=72) element distributions. These have been used in a critical comparison between stellar and solar r-process abundance mixes.
73. Reddenings for the MACHO bulge RR0 Lyrae stars
ID:
ivo://CDS.VizieR/J/AJ/135/631
Title:
Reddenings for the MACHO bulge RR0 Lyrae stars
Short Name:
J/AJ/135/631
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present mean reddenings toward 3525 RR0 Lyrae stars from the Galactic bulge fields of the MACHO Survey. These reddenings are determined using the color at minimum V-band light of the RR0 Lyrae stars themselves and are found to be in general agreement with extinction estimates at the same location obtained from other methods.
74. RGB stars in NGC 2808
ID:
ivo://CDS.VizieR/J/A+A/413/343
Title:
RGB stars in NGC 2808
Short Name:
J/A+A/413/343
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of the first observations, taken with FLAMES during Science Verification, of red giant branch (RGB) stars in the globular cluster NGC 2808. A total of 137 stars was observed, of which 20 at high resolution (R=47000) with UVES and the others at lower resolution (R=19000-29000) with GIRAFFE in MEDUSA mode, monitoring ~3mag down from the RGB tip. Spectra were taken of the H{alpha}, Na I D and Ca II H and K lines.
75. RPA Southern Pilot Search of 107 Stars
ID:
ivo://CDS.VizieR/J/ApJ/858/92
Title:
RPA Southern Pilot Search of 107 Stars
Short Name:
J/ApJ/858/92
Date:
21 Oct 2021
Publisher:
CDS
Description:
The recent detection of a binary neutron star merger and the clear evidence for the decay of radioactive material observed in this event have, after 60 years of effort, provided an astrophysical site for the rapid neutron- capture (r-) process which is responsible for the production of the heaviest elements in our universe. However, observations of metal-poor stars with highly-enhanced r-process elements have revealed abundance patterns suggesting that multiple sites may be involved. To address this issue and to advance our understanding of the r-process, we have initiated an extensive search for bright (V<13.5), very metal-poor ([Fe/H]<-2) stars in the Milky Way halo exhibiting strongly-enhanced r-process signatures. This paper presents the first sample collected in the southern hemisphere using the echelle spectrograph on du Pont 2.5m telescope at Las Campanas Observatory. We have observed and analyzed 107 stars with -3.13<[Fe/H]<-0.79. Of those, 12 stars are strongly enhanced in heavy r-process elements (r-II), 42 stars show moderate enhancements of heavy r-process material (r-I), and 20 stars exhibit low abundances of the heavy r-process elements and higher abundances of the light r-process elements relative to the heavy ones (limited-r). This search is more successful at finding r- process-enhanced stars compared to previous searches, primarily due to a refined target-selection procedure.
76. RR Lyrae Metallicities
ID:
ivo://CDS.VizieR/III/176
Title:
RR Lyrae Metallicities
Short Name:
III/176
Date:
21 Oct 2021
Publisher:
CDS
Description:
This catalog presents metal abundance, distance and radial velocity data on a sample of 302 ab-type RR Lyrae variables within about 2.5 kpc of the Sun. The metal abundance information was obtained from low-medium resolution spectra, using the pseudo-equivalent widths of the Ca II K line and the the H-delta, H-gamma and H-beta lines. The technique employed was similar to Preston's (1959ApJ...130..507P) {Delta}-S method, though significant differences exist; see the source reference for details. The data were calibrated to the Zinn & West (1984ApJS...55...45Z) globular cluster abundance scale. The photometry employed in the distance determinations was primarily taken from the General Catalog of Variable Stars (1985, hereafter GCVS4). Exceptions are noted in column 29; the letters match the footnotes in Table 10 of Layden (1994AJ....108.1016L). The minimum and maximum light photometry, and rise-time were combined following Barnes & Hawley (1986ApJ...307L...9B) to give an estimate of the intensity- averaged magnitude, i.e. the magnitude the star would have if it were not variable. When the GCVS4 quoted magnitudes in passbands other than V, the GCVS4 magnitudes were transformed to the V passband using the relations established in Layden (1994AJ....108.1016L). The interstellar absorption estimates are from Burstein & Heiles (1982AJ.....87.1165B), modified by a simple dust-distribution model. The distances were computed assuming the Mv(RR)-[Fe/H] relation of Carney, Storm & Jones (1992ApJ...386..663C). Radial velocities were measured from the spectra via cross-correlation with secondary velocity standards. The velocities from the individual spectra were fit with a standard radial velocity curve in the (phase, velocity) plane, to give an estimate of the systemic (center of mass) velocity of each star. The error in this value was estimated from the scatter about the best-fit velocity curve, and the quality of the spectra employed. Other methods were used to combine the individual velocities when the situation demanded (cm = 2,3 in column 70; see Layden (1994AJ....108.1016L) for details). The observed velocities were combined with values from the literature to produce a final, best estimate of the systemic radial velocity of each star, and its error.
77. 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.
78. SAGA extremely metal-poor stars
ID:
ivo://CDS.VizieR/J/MNRAS/412/843
Title:
SAGA extremely metal-poor stars
Short Name:
J/MNRAS/412/843
Date:
21 Oct 2021
Publisher:
CDS
Description:
We discuss the characteristics of known extremely metal-poor (EMP) stars in the Galaxy using the Stellar Abundances for Galactic Archaeology (SAGA) data base. We find the transition of the initial mass function to be at [Fe/H]~-2 from the viewpoint of the distribution of carbon abundance and the frequency of carbon-enhanced stars. Analyses of carbon-enhanced stars in our sample suggest that nucleosynthesis in asymptotic giant branch (AGB) stars can contribute to carbon enrichment in a different way depending on whether the metallicity is above or below [Fe/H]~-2.5, which is consistent with the current models of stellar evolution at low metallicity.
79. Sgr dSph nucleus stars chemical abundances
ID:
ivo://CDS.VizieR/J/A+A/605/A46
Title:
Sgr dSph nucleus stars chemical abundances
Short Name:
J/A+A/605/A46
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Iron, Magnesium, Calcium, and Titanium abundances for 235 stars in the central region of the Sagittarius dwarf spheroidal galaxy (within 9.0'~=70pc from the center) from medium-resolution Keck/DEIMOS spectra. All the considered stars belong to the massive globular cluster M 54 or to the central nucleus of the galaxy (Sgr,N). In particular we provide abundances for 109 stars with [Fe/H]>=-1.0, more than doubling the available sample of spectroscopic metallicity and {alpha}-elements abundance estimates for Sgr dSph stars in this metallicity regime. We find for the first time a metallicity gradient in the Sgr,N population, whose peak iron abundance goes from [Fe/H]=-0.38 for R<=2.5' to [Fe/H]=-0.57 for 5.0<R<=9.0 arcmin. On the other hand the trends of [Mg/Fe], [Ca/Fe], and [Ti/Fe] with [Fe/H] are the same over the entire region explored by our study. We reproduce the observed chemical patterns of the Sagittarius dwarf spheroidal as a whole with a chemical evolution model implying a high mass progenitor (M_DM_=6x10^10^M_{sun}_) and a significant event of mass-stripping occurred a few Gyr ago, presumably starting at the first peri-Galactic passage after infall.
80. Short-period variables near Galactic Centre
ID:
ivo://CDS.VizieR/J/MNRAS/429/385
Title:
Short-period variables near Galactic Centre
Short Name:
J/MNRAS/429/385
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the result of our near-infrared survey of short-period variable stars (P<60d) in a field of view of 20'x30' towards the Galactic Centre (GC). Forty-five variables are discovered and we classify the variables based on their light-curve shapes and other evidence. In addition to 3 classical Cepheids reported previously, we find 16 type II Cepheids, 24 eclipsing binaries, 1 pulsating star with P=0.265d (RR Lyr or {delta} Sct) and 1 Cepheid-like variable whose nature is uncertain. Eclipsing binaries are separated into the foreground objects and those significantly obscured by interstellar extinction. One of the reddened binaries contains an O-type supergiant and its light curve indicates an eccentric orbit. We discuss the nature and distribution of type II Cepheids as well as the distance to the GC based on these Cepheids and other distance indicators. The estimates of R_0_(GC) we obtained based on photometric data agree with previous results obtained with kinematics of objects around the GC. Furthermore, our result gives support to the reddening law obtained by Nishiyama and collaborators, A_Ks_/E(H-Ks)=1.44, because a different reddening law would result in a rather different distance estimate.

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