- ID:
- ivo://CDS.VizieR/J/ApJ/890/71
- Title:
- 5100{AA} continuum & emission lines LCs of PG2130+099
- Short Name:
- J/ApJ/890/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As one of the most interesting Seyfert 1 galaxies, PG 2130+099 has been the target of several reverberation mapping (RM) campaigns over the years. However, its measured broad H{beta} line responses have been inconsistent, with time lags of ~200days, ~25days, and ~10days being reported for different epochs while its optical luminosity changed no more than 40%. To investigate this issue, we conducted a new RM-campaign with homogenous and high cadence (about ~3days) for two years during 2017-2019 to measure the kinematics and structure of the ionized gas. We successfully detected time lags of broad H{beta}, HeII, HeI, and FeII lines with respect to the varying 5100{AA} continuum, revealing a stratified structure that is likely virialized with Keplerian kinematics in the first year of observations, but an inflow kinematics of the broad-line region from the second year. With a central black hole mass of 0.97_-0.18_^+0.15^x10^7^M_{sun}_, PG2130+099 has an accretion rate of 10^2.1+/-0.5^L_Edd_c^-2^, where L_Edd_ is the Eddington luminosity and c is speed of light, implying that it is a super-Eddington accretor and likely possesses a slim, rather than thin, accretion disk. The fast changes of the ionization structures of the three broad lines remain puzzling.
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- ID:
- ivo://CDS.VizieR/J/ApJ/850/34
- Title:
- 3000-25000{AA} spectroscopy of nearby M dwarfs
- Short Name:
- J/ApJ/850/34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent studies of the stellar population in the solar neighborhood (<20pc) suggest that there are undetected white dwarfs (WDs) in multiple systems with main-sequence companions. Detecting these hidden stars and obtaining a more complete census of nearby WDs is important for our understanding of stellar and galactic evolution, as well as the study of explosive phenomena. In an attempt to uncover these hidden WDs, we present intermediate resolution spectroscopy over the wavelength range of 3000-25000{AA} of 101 nearby M dwarfs (dMs), observed with the Very Large Telescope X-Shooter spectrograph. For each star we search for a hot component superimposed on the dM spectrum. X-Shooter has excellent blue sensitivity and thus can reveal a faint hot WD despite the brightness of its red companion. Visual examination shows no clear evidence of a WD in any of the spectra. We place upper limits on the effective temperatures of WDs that may still be hiding by fitting dM templates to the spectra and modeling the WD spectra. On average our survey is sensitive to WDs hotter than about 5300K. This suggests that the frequency of WD companions of Teff>~5300K with separation of the order of <~50 au among the local dM population is <3% at the 95% confidence level.
- ID:
- ivo://CDS.VizieR/II/336
- Title:
- AAVSO Photometric All Sky Survey (APASS) DR9
- Short Name:
- II/336
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The AAVSO Photometric All Sky Survey (APASS) project is designed to bridge the gap between the shallow Tycho2 two-bandpass photometric catalog that is complete to V=11 and the deeper, but less spatially-complete catalogs like SDSS or PanSTARRS. It can be used for calibration of a specific field; for obtaining spectral information about single sources, determining reddening in a small area of the sky; or even obtaining current-epoch astrometry for rapidly moving objects. The survey is being performed at two locations: near Weed, New Mexico in the Northern Hemisphere; and at CTIO in the Southern Hemisphere. Each site consists of dual bore-sighted 20cm telescopes on a single mount, designed to obtain two bandpasses of information simultaneously. Each telescope covers 9 square degrees of sky with 2.5arcsec pixels, with the main survey taken with B,V,g',r',i' filters and covering the magnitude range 10<V<17. A bright extension is underway, saturating at V=7 and extending the wavelength coverage from u' to Y. The current catalog is Data Release 9 and contains approximately 62 million stars. The American Association of Variable Star Observers is responsible for the overall management of the survey; a team of professional astronomers participate in the data analysis. The project was initially funded by the Robert Martin Ayers Sciences Fund, with a follow-on grant from the National Science Foundation.
- ID:
- ivo://CDS.VizieR/J/A+AS/106/373
- Title:
- AB And UBV photometry
- Short Name:
- J/A+AS/106/373
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+A/607/A131
- Title:
- Abell 520 galaxies redshifts
- Short Name:
- J/A+A/607/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mergers of galaxy clusters are the most energetic events in the universe after the Big Bang. An ever increasing fraction of local clusters exhibit signs of recent or past mergers. Our goal is to probe how these mergers affect the evolution and content of their member galaxies. We specifically aim to answer the following questions: Is the quenching of star formation in merging clusters enhanced when compared with relaxed clusters? Is the quenching accompanied by a (short lived) burst of star formation? We obtained optical spectroscopy of $>400$ galaxies in the field of the merging cluster Abell 520. We combine these observations with archival data to get a comprehensive picture of the state of star formation in the members of this merging cluster. Finally, we compare these observations with a control sample of 10 non-merging clusters at the same redshift from The Arizona Cluster Redshift Survey (ACReS). We split the member galaxies in passive, star forming or recently quenched depending on their spectra. The core of the merger shows a decreased fraction of star-forming galaxies compared to clusters in the non-merging sample. This region, dominated by passive galaxies, is extended along the axis of the merger. We find evidence of rapid quenching of the galaxies during the core passage with no signs of a star burst on the time scales of the merger. Additionally, we report the tentative discovery of an infalling group along the main filament feeding the merger, currently at ~2.5Mpc from the merger centre. This group contains a high fraction of star forming galaxies as well as ~2/3 of all the recently quenched galaxies in our survey.
- ID:
- ivo://CDS.VizieR/J/MNRAS/423/256
- Title:
- Abell 1689 imaging and spectroscopy
- Short Name:
- J/MNRAS/423/256
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present imaging and spectroscopy of Abell 1689 (z=0.183) from the Gemini multi-object spectrograph (GMOS) on the Gemini North telescope and the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). We measure integrated photometry from the GMOS g' and r' images (for 531 galaxies) and surface photometry from the HSTF625W image (for 43 galaxies) as well as velocities and velocity dispersions from the GMOS spectra (for 71 galaxies). We construct the Kormendy, Faber-Jackson and colour-magnitude relations for early-type galaxies in Abell 1689 using these data and compare them to those of the Coma cluster.
- ID:
- ivo://CDS.VizieR/J/A+A/602/A20
- Title:
- Abell 315 spectroscopic dataset
- Short Name:
- J/A+A/602/A20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Determination of cluster masses is a fundamental tool for cosmology. Comparing mass estimates obtained by different probes allows to understand possible systematic uncertainties. Aims. The cluster Abell 315 is an interesting test case, since it has been claimed to be underluminous in X-ray for its mass (determined via kinematics and weak lensing). We have undertaken new spectroscopic observations with the aim of improving the cluster mass estimate, using the distribution of galaxies in projected phase space. We identified cluster members in our new spectroscopic sample. We estimated the cluster mass from the projected phase-space distribution of cluster members using the MAMPOSSt method. In doing this estimate we took into account the presence of substructures that we were able to identify. We identify several cluster substructures. The main two have an overlapping spatial distribution, suggesting a (past or ongoing) collision along the line-of-sight. After accounting for the presence of substructures, the mass estimate of Abell 315 from 14 kinematics is reduced by a factor 4, down to M_200_=0.8_-0.4_^+0.6^10+14M_{sun}_. We also find evidence that the cluster mass concentration is unusually low, c_200_=r_200_/r_-2_<1. Using our new estimate of c200 we revise the weak lensing mass estimate down to M_200_=1.8_-0.9_^+1.7^10+14M_{sun}_. Our new mass estimates are in agreement with that derived from the cluster X-ray luminosity via a scaling relation, M_200_=0.9+/-0.2*10^14^M_{sun}_. Abell 315 no longer belongs to the class of X-ray underluminous clusters. Its mass estimate was inflated by the presence of an undetected subcluster in collision with the main cluster. Whether the presence of undetected line-of-sight structures can be a general explanation for all X-ray underluminous clusters remains to be explored using a statistically significant sample.
- ID:
- ivo://CDS.VizieR/J/MNRAS/468/703
- Title:
- Abell 168 ultra-diffuse galaxies distribution
- Short Name:
- J/MNRAS/468/703
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Taking advantage of the Sloan Digital Sky Survey Stripe82 data, we have explored the spatial distribution of ultra-diffuse galaxies (UDGs) within an area of 8x8Mpc^2^ centred around the galaxy cluster Abell 168 (z=0.045). This intermediate massive cluster ({sigma}=550km/s) is surrounded by a complex large-scale structure. Our work confirms the presence of UDGs in the cluster and in the large-scale structure that surrounds it, and it is the first detection of UDGs outside clusters. Approximately 50 per cent of the UDGs analysed in the selected area inhabit the cluster region (~11+/-5 per cent in the core and ~39+/-9 per cent in the outskirts), whereas the remaining UDGs are found outside the main cluster structure (~50+/-11 per cent). The colours and the spatial distribution of the UDGs within this large-scale structure are more similar to dwarf galaxies than to L* galaxies, suggesting that most UDGs could be bona fide dwarf galaxies.
- ID:
- ivo://CDS.VizieR/J/AN/326/321
- Title:
- Absolute magnitudes for late-type dwarfs
- Short Name:
- J/AN/326/321
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new formula for absolute magnitude determination for late-type dwarf stars as a function of (g-r) and (r-i) for Sloan photometry (as defined by Abazajian et al., 2003AJ....126.2081A). The absolute magnitudes estimated by this approach are brighter than those estimated by colour-magnitude diagrams, and they reduce the luminosity function rather close to the luminosity function of Hipparcos.
- ID:
- ivo://CDS.VizieR/J/AJ/124/601
- Title:
- Absolute positions and proper motions in NGC 188
- Short Name:
- J/AJ/124/601
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The field of direct imaging is experiencing a considerable growth in the number of available CCD mosaic imagers, especially on large telescopes. To fully exploit the astrometric potential of these imaging devices, we develop a technique, utilizing an astrometric standard, for precision transformation of pixel coordinates into a global coordinate system. We have constructed a new astrometric standard set of 1863 stars in the field of NGC 188 to derive the CCD chip constants for the NOAO CCD Mosaic Imager. The multiple-epoch data on the Mosaic's metrics indicate that this CCD mosaic device may have experienced a one-time nonelastic expansion. We also present a new determination of the pixel scale and the optical field angle distortion constants for the KPNO Mayall 4 m telescope prime focus field corrector. To establish a reliable history of the CCD mosaic imager metrics for current and potential future astrometric applications, we recommend obtaining astrometric calibrations for CCD mosaic imagers on a regular basis. Apart from mechanical positioning of the CCD mosaic camera on the telescope, noticeable changes in the thermal environment of CCD mosaic chips should also prompt new astrometric calibrations. It is shown that, following all precautions, the NOAO CCD Mosaic Imager can produce excellent astrometric results on the Mayall 4 m telescope.
- ID:
- ivo://CDS.VizieR/J/ApJ/691/1400
- Title:
- Absolute properties of CM Dra
- Short Name:
- J/ApJ/691/1400
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we present a complete reanalysis of the eclipsing systems, CM Dra, composed of two dM4.5 stars. New and existing light curves as well as a radial velocity curve are modeled to measure the physical properties of both components. The masses and radii determined for the components of CM Dra are M1=0.2310+/-0.0009M_{sun}_, M2=0.2141+/-0.0010M_{sun}_, R1=0.2534+/-0.0019R_{sun}_, and R2=0.2396+/-0.0015R_{sun}_. With relative uncertainties well below the 1% level, these values constitute the most accurate properties to date for fully convective stars.
- ID:
- ivo://CDS.VizieR/J/AJ/155/213
- Title:
- Absolute reflectance & new calibration site of the Moon
- Short Name:
- J/AJ/155/213
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- How bright the Moon is forms a simple but fundamental and important question. Although numerous efforts have been made to answer this question such as use of sophisticated electro-optical measurements and suggestions for calibration sites, the answer is still debated. An in situ measurement with a calibration panel on the surface of the Moon is crucial for obtaining the accurate absolute reflectance and resolving the debate. China's Chang'E-3 (CE-3) "Yutu" rover accomplished this type of measurement using the Visible-Near Infrared Spectrometer (VNIS). The measurements of the VNIS, which were at large emission and phase angles, complement existing measurements for the range of photometric geometry. The in situ reflectance shows that the CE-3 landing site is very dark with an average reflectance of 3.86% in the visible bands. The results are compared with recent mission instruments: the Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC), the Spectral Profiler (SP) on board the SELENE, the Moon Mineralogy Mapper (M^3^) on board the Chandrayaan-1, and the Chang'E-1 Interference Imaging Spectrometer (IIM). The differences in the measurements of these instruments are very large and indicate inherent differences in their absolute calibration. The M^3^ and IIM measurements are smaller than LROC WAC and SP, and the VNIS measurement falls between these two pairs. When using the Moon as a radiance source for the on-orbit calibration of spacecraft instruments, one should be cautious about the data. We propose that the CE-3 landing site, a young and homogeneous surface, should serve as the new calibration site.
- ID:
- ivo://CDS.VizieR/J/AJ/161/285
- Title:
- Absorption & emission lines and RVel for vA 351
- Short Name:
- J/AJ/161/285
- Date:
- 08 Mar 2022
- Publisher:
- CDS
- Description:
- We extend results first announced by Franz et al., that identified vA351=H346 in the Hyades as a multiple star system containing a white dwarf. With Hubble Space Telescope Fine Guidance Sensor fringe tracking and scanning, and more recent speckle observations, all spanning 20.7years, we establish a parallax, relative orbit, and mass fraction for two components, with a period, P=2.70yr and total mass 2.1M{sun}. With ground-based radial velocities from the McDonald Observatory Otto Struve 2.1m Telescope Sandiford Spectrograph, and Center for Astrophysics Digital Speedometers, spanning 37 years, we find that component B consists of BC, two M-dwarf stars orbiting with a very short period (P_BC_=0.749days), having a mass ratio M_C_/M_B_=0.95. We confirm that the total mass of the system can only be reconciled with the distance and component photometry by including a fainter, higher-mass component. The quadruple system consists of three M dwarfs (A, B, C) and one white dwarf (D). We determine individual M-dwarf masses M_A_=0.53{+/-}0.10M{sun}, M_B_=0.43{+/-}0.04M{sun}, and M_C_=0.41{+/-}0.04M{sun}. The white dwarf mass, 0.54{+/-}0.04M{sun}, comes from cooling models, an assumed Hyades age of 670Myr, and consistency with all previous and derived astrometric, photometric, and radial velocity results. Velocities from H{alpha} and HeI emission lines confirm the BC period derived from absorption lines, with similar (HeI) and higher (H{alpha}) velocity amplitudes. We ascribe the larger H{alpha} amplitude to emission from a region each component shadows from the other, depending on the line of sight.
- ID:
- ivo://CDS.VizieR/J/ApJS/235/11
- Title:
- Absorption features in SDSS. I. MgII abs. doublets
- Short Name:
- J/ApJS/235/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the SDSS spectra of quasars included in the DR7Q or DR12Q catalogs, we search for MgII{lambda}{lambda}2796,2803 narrow absorption doublets in the spectra data around MgII{lambda}2798 emission lines. We obtain 17316 MgII doublets, within the redshift range of 0.3299<=z_abs_<=2.5663. We find that a velocity offset of {upsilon}_r_<6000km/s is a safe boundary to constrain the vast majority of associated Mg ii systems, although we find some doublets at {upsilon}_r_>6000km/s. If associated Mg ii absorbers are defined by {upsilon}_r_<6000km/s, ~33.3% of the absorbers are supposed to be contaminants of intervening systems. Removing the 33.3% contaminants, ~4.5% of the quasars present at least one associated MgII system with W_r_^{lambda}2796^>=0.2{AA}. The fraction of associated MgII systems with high-velocity outflows correlates with the average luminosities of their central quasars, indicating a relationship between outflows and the quasar feedback power. The {upsilon}_r_ distribution of the outflow MgII absorbers is peaked at 1023km/s, which is smaller than the corresponding value of the outflow CIV absorbers. The redshift number density evolution of absorbers (dn/dz) limited by {upsilon}_r_{>}-3000km/s differs from that of absorbers constrained by {upsilon}_r_>2000km/s. Absorbers limited by {upsilon}_r_>2000km/s and higher values exhibit profiles similar to dn/dz. In addition, the dn/dz is smaller when absorbers are constrained with larger {upsilon}_r_. The distributions of equivalent widths, and the ratio of W_r_^{lambda}2796^/W_r_^{lambda}2803^, are the same for associated and intervening systems, and independent of quasar luminosity.
- ID:
- ivo://CDS.VizieR/J/ApJ/847/127
- Title:
- Abundance analyses of V652 Her and HD 144941
- Short Name:
- J/ApJ/847/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Optical high-resolution spectra of V652 Her and HD 144941, the two extreme helium stars with exceptionally low C/He ratios, have been subjected to a non-LTE abundance analysis using the tools TLUSTY and SYNSPEC. Defining atmospheric parameters were obtained from a grid of non-LTE atmospheres and a variety of spectroscopic indicators including HeI and HeII line profiles, and the ionization equilibrium of ion pairs such as CII/CIII and NII/NIII. The various indicators provide a consistent set of atmospheric parameters: Teff=25000+/-300K, logg=3.10+/-0.12(cgs), and {xi}=13+/-2km/s are provided for V652 Her, and Teff=22000+/-600K, logg=3.45+/-0.15(cgs), and {xi}=10km/s are provided for HD 144941. In contrast to the non-LTE analyses, the LTE analyses-LTE atmospheres and an LTE line analysis-with the available indicators do not provide a consistent set of atmospheric parameters. The principal non-LTE effect on the elemental abundances is on the neon abundance. It is generally considered that these extreme helium stars with their very low C/He ratio result from the merger of two helium white dwarfs. Indeed, the derived composition of V652 Her is in excellent agreement with predictions by Zhang & Jeffery (2012MNRAS.419..452Z), who model the slow merger of helium white dwarfs; a slow merger results in the merged star having the composition of the accreted white dwarf. In the case of HD 144941, which appears to have evolved from metal-poor stars, a slow merger is incompatible with the observed composition but variations of the merger rate may account for the observed composition. More detailed theoretical studies of the merger of a pair of helium white dwarfs are to be encouraged.
- ID:
- ivo://CDS.VizieR/J/ApJ/865/129
- Title:
- Abundance analysis of HD 222925
- Short Name:
- J/ApJ/865/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed abundance analysis of the bright (V=9.02), metal-poor ([Fe/H]=-1.47+/-0.08) field red horizontal-branch star HD222925, which was observed as part of an ongoing survey by the R-Process Alliance. We calculate stellar parameters and derive abundances for 46 elements based on 901 lines examined in a high-resolution optical spectrum obtained using the Magellan Inamori Kyocera Echelle spectrograph. We detect 28 elements with 38<=Z<=90; their abundance pattern is a close match to the solar r-process component. The distinguishing characteristic of HD222925 is an extreme enhancement of r-process elements ([Eu/Fe]=+1.33+/-0.08, [Ba/Eu]=-0.78+/-0.10) in a moderately metal-poor star, so the abundance of r-process elements is the highest ([Eu/H]=-0.14+/-0.09) in any known r-process-enhanced star. The abundance ratios among lighter (Z<=30) elements are typical for metal-poor stars, indicating that production of these elements was dominated by normal Type II supernovae, with no discernible contributions from Type Ia supernovae or asymptotic giant branch stars. The chemical and kinematic properties of HD 222925 suggest it formed in a low-mass dwarf galaxy, which was enriched by a high-yield r-process event before being disrupted by interaction with the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJ/838/90
- Title:
- Abundance analysis of 9 very metal-poor stars
- Short Name:
- J/ApJ/838/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a differential line-by-line chemical abundance analysis, ultimately relative to the Sun, of nine very metal-poor main-sequence (MS) halo stars, near [Fe/H]=-2dex. Our abundances range from -2.66<=[Fe/H]<=-1.40dex with conservative uncertainties of 0.07dex. We find an average [{alpha}/Fe]=0.34+/-0.09dex, typical of the Milky Way. While our spectroscopic atmosphere parameters provide good agreement with Hubble Space Telescope parallaxes, there is significant disagreement with temperature and gravity parameters indicated by observed colors and theoretical isochrones. Although a systematic underestimate of the stellar temperature by a few hundred degrees could explain this difference, it is not supported by current effective temperature studies and would create large uncertainties in the abundance determinations. Both 1D and <3D> hydrodynamical models combined with separate 1D non-LTE effects do not yet account for the atmospheres of real metal-poor MS stars, but a fully 3D non-LTE treatment may be able to explain the ionization imbalance found in this work.
- ID:
- ivo://CDS.VizieR/J/AJ/144/95
- Title:
- Abundance in stars of the outer galactic disk. IV.
- Short Name:
- J/AJ/144/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radial velocities and chemical abundances for nine stars in the old, distant open clusters Be18, Be21, Be22, Be32, and PWM4. For Be18 and PWM4, these are the first chemical abundance measurements. Combining our data with literature results produces a compilation of some 68 chemical abundance measurements in 49 unique clusters. For this combined sample, we study the chemical abundances of open clusters as a function of distance, age, and metallicity. We confirm that the metallicity gradient in the outer disk is flatter than the gradient in the vicinity of the solar neighborhood. We also confirm that the open clusters in the outer disk are metal-poor with enhancements in the ratios [{alpha}/Fe] and perhaps [Eu/Fe]. All elements show negligible or small trends between [X/Fe] and distance (<0.02dex/kpc), but for some elements, there is a hint that the local (R_GC_<13kpc) and distant (R_GC_>13kpc) samples may have different trends with distance. There is no evidence for significant abundance trends versus age (<0.04dex/Gyr). We measure the linear relation between [X/Fe] and metallicity, [Fe/H], and find that the scatter about the mean trend is comparable to the measurement uncertainties. Comparison with solar neighborhood field giants shows that the open clusters share similar abundance ratios [X/Fe] at a given metallicity. While the flattening of the metallicity gradient and enhanced [{alpha}/Fe] ratios in the outer disk suggest a chemical enrichment history different from that of the solar neighborhood, we echo the sentiments expressed by Friel et al. that definitive conclusions await homogeneous analyses of larger samples of stars in larger numbers of clusters. Arguably, our understanding of the evolution of the outer disk from open clusters is currently limited by systematic abundance differences between various studies.
- ID:
- ivo://CDS.VizieR/J/ApJ/705/328
- Title:
- Abundance measurements in Sculptor dSph
- Short Name:
- J/ApJ/705/328
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present measurements of Fe, Mg, Si, Ca, and Ti abundances for 388 radial velocity member stars in the Sculptor dwarf spheroidal galaxy (dSph), a satellite of the Milky Way (MW). This is the largest sample of individual {alpha} element (Mg, Si, Ca, and Ti) abundance measurements in any single dSph. The measurements are made from Keck/Deep Imaging Multi-Object Spectrometer medium-resolution spectra (6400-9000{AA}, R~6500). Based on comparisons to published high-resolution (R>~20000) spectroscopic measurements, our measurements have uncertainties of {alpha}[Fe/H]=0.14 and {alpha}[{alpha}/Fe]=0.13. We have discovered one star with [Fe/H]=-3.80+/-0.28, which is the most metal-poor star known anywhere except the MW halo, but high-resolution spectroscopy is needed to measure this star's detailed abundances.
- ID:
- ivo://CDS.VizieR/J/ApJ/754/91
- Title:
- Abundances and velocities of NGC 6397 stars
- Short Name:
- J/ApJ/754/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used three sets of high-resolution spectra acquired with the multifiber facility FLAMES at the Very Large Telescope of the European Southern Observatory to investigate the chemical and kinematical properties of a sample of 42 horizontal branch (HB) stars, 18 blue straggler stars (BSSs), and 86 main-sequence (MS) turnoff (TO) and sub-giant branch stars in the nearby globular cluster NGC 6397. We measured rotational velocities and Fe, O, and Mg abundances. All of the unevolved stars in our sample have low rotational velocites (vsin i<10km/s), while the HB stars and BSSs show a broad distribution, with values ranging from 0 to ~70km/s. For HB stars with T<10500K there is a clear temperature-oxygen anticorrelation that can be understood if the star position along the HB is mainly determined by the He content. The hottest BSSs and HB stars (with temperatures T>8200K and T>10500K, respectively) also show significant deviations in their iron abundance with respect to the cluster metallicity (as traced by the unevolved stars, [Fe/H]=-2.12). While similar chemical patterns have already been observed in other hot HB stars, this is the first evidence ever collected for BSSs. We interpret these abundance anomalies as due to the metal radiative levitation, occurring in stars with shallow or no convective envelopes.