- ID:
- ivo://CDS.VizieR/J/A+A/590/A9
- Title:
- RGB stars in Galactic GC stellar parameters
- Short Name:
- J/A+A/590/A9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters trace the formation and evolution of the Milky Way and surrounding galaxies, and outline their chemical enrichment history. To accomplish these tasks it is important to have large samples of clusters with homogeneous data and analysis to derive kinematics, chemical abundances, ages and locations. We aim to obtain homogeneous metallicities and alpha-element enhancement for 51 Galactic bulge, disc, and halo globular clusters that are among the most distant and/or highly reddened in the Galaxy's globular cluster system. We also provide membership selection based on stellar radial velocities and atmospheric parameters. The implications of our results are discussed. We observed R~2000 spectra in the wavelength interval 456-586nm for over 800 red giant stars in 51 Galactic globular clusters. We applied full spectrum fitting with the code ETOILE together with libraries of observed and synthetic spectra. We compared the mean abundances of all clusters with previous work and with field stars. We used the relation between mean metallicity and horizontal branch morphology defined by all clusters to select outliers for discussion. [Fe/H], [Mg/Fe], and [alpha/Fe] were derived in a consistent way for almost one-third of all Galactic globular clusters. We find our metallicities are comparable to those derived from high-resolution data to within sigma=0.08dex over the interval -2.5<[Fe/H]<0.0. Further, a comparison of previous metallicity scales with ours yields sigma<0.16dex. We also find that the distribution of [Mg/Fe] and [alpha/Fe] with [Fe/H] for the 51 clusters follows the general trend exhibited by field stars. It is the first time that the following clusters are included in a large sample of homogeneous stellar spectroscopic observations and metallicity derivation: BH 176, Djorg 2, Pal 10, NGC 6426, Lynga 7, and Terzan 8. In particular, the first three clusters only had photometric metallicities previously and the available metallicity for NGC 6426 was based only on integrated spectroscopy and photometry. Two other clusters, HP 1 and NGC 6558, are confirmed as candidates for the oldest globular clusters in the Milky Way. Stellar spectroscopy in the visible at R~2000 for a large sample of globular clusters is a robust and efficient way to trace the chemical evolution of the host galaxy and to detect interesting objects for follow-up at higher-resolution and with forthcoming giant telescopes. The technique used here can also be applied to globular cluster systems in nearby galaxies with current instruments and to distant galaxies with the advent of ELTs.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/139/878
- Title:
- RGB stars in 8 LMC clusters
- Short Name:
- J/AJ/139/878
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we discuss the properties of color-magnitude diagrams, age, metallicity, and radial velocities of eight massive Large Magellanic Cloud (LMC) clusters using data taken from the FORS2 multiobject spectrograph at the 8.2m Very Large Telescope/Unit Telescope 1. The strong near-infrared CaII triplet lines of red giant branch stars obtained from the high signal-to-noise ratio spectra are used to determine the metallicity and radial velocity of cluster members.
- ID:
- ivo://CDS.VizieR/J/AJ/142/61
- Title:
- RGB stars in LMC outer disk
- Short Name:
- J/AJ/142/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The outer disk of the Large Magellanic Cloud (LMC) is studied in order to unveil clues about its formation and evolution. Complementing our previous studies in innermost fields (3kpc<~R<~7kpc), we obtained deep color-magnitude diagrams in six fields with galactocentric distances from 5.2kpc to 9.2kpc and different azimuths. The comparison with isochrones shows that while the oldest population is approximately coeval in all fields, the age of the youngest populations increases with increasing radius. This agrees with the results obtained in the innermost fields. Low-resolution spectroscopy in the infrared CaII triplet region has been obtained for about 150 stars near the tip of the red giant branch in the same fields. Radial velocities and stellar metallicities have been obtained from these spectra. The metallicity distribution of each field has been analyzed together with those previously studied.
- ID:
- ivo://CDS.VizieR/J/MNRAS/456/4315
- Title:
- RGB stars in NGC 6822, Ca II triplet
- Short Name:
- J/MNRAS/456/4315
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed analysis of the chemistry and kinematics of red giants in the dwarf irregular galaxy NGC 6822. Spectroscopy at ~8500{AA} was acquired for 72 red giant stars across two fields using FORS2 at the VLT. Line-of-sight extinction was individually estimated for each target star to accommodate the variable reddening across NGC 6822. The mean radial velocity was found to be <v_rad_>=-52.8+/-2.2km/s with dispersion {sigma}_v_=24.1km/s, in agreement with other studies. Ca ii triplet equivalent widths were converted into [Fe/H] metallicities using a V magnitude proxy for surface gravity. The average metallicity was <[Fe/H]>=-0.84+/-0.04 with dispersion {sigma}=0.31dex and interquartile range 0.48. Our assignment of individual reddening values makes our analysis more sensitive to spatial variations in metallicity than previous studies. We divide our sample into metal-rich and metal-poor stars; the former were found to cluster towards small radii with the metal-poor stars more evenly distributed across the galaxy. The velocity dispersion of the metal-poor stars was found to be higher than that of the metal-rich stars {sigma}_vMP_=27.4km/s; {sigma}_vMR_=21.1km/s); combined with the age-metallicity relation this indicates that the older populations have either been dynamically heated during their lifetimes or were born in a less disc-like distribution than the younger stars.. The low ratio v_rot_/{sigma}_v_ suggests that within the inner 10-arcmin, NGC 6822's stars are dynamically decoupled from the HI gas, and possibly distributed in a thick disc or spheroid structure.
- ID:
- ivo://CDS.VizieR/J/A+A/464/201
- Title:
- RGB stars in Sagittarius streams
- Short Name:
- J/A+A/464/201
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Sagittarius (Sgr) dwarf spheroidal galaxy is currently being disrupted under the strain of the Milky Way. A reliable reconstruction of Sgr star formation history can only be obtained by combining core and stream information. We present radial velocities for 67 stars belonging to the Sgr Stream. For 12 stars in the sample we also present iron (Fe) and {alpha}-element (Mg, Ca) abundances.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A48
- Title:
- rho Cas differential BVRI photometry
- Short Name:
- J/A+A/631/A48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to explore the variable photometric and stellar properties of four yellow hypergiants (YHGs), HR 8752, HR 5171A, rho Cas, and HD 179821, and their pulsations of hundreds of days, and long-term variations (LTVs) of years. We also aim to explore light and colour curves for characteristics betraying evolutionary loops and eruptive episodes and to investigate trends of quasi-periods and the possible need for distance revisions. We tackled multi-colour and visual photometric data sets, looked for photometric indications betraying eruptions or enhanced mass-loss episodes, calculated stellar properties mainly using a previously published temperature calibration, and investigated the nature of LTVs and their influence on quasi-periods and stellar properties. Based on driven one-zone stellar oscillation models, the pulsations can be characterised as 'weakly chaotic'. The BV photometry revealed a high-opacity layer in the atmospheres. When the temperature rises the mass loss increases as well, consequently, as the density of the high-opacity layer. As a result, the absorption in B and V grow. The absorption in B, presumably of the order of one to a few 0.1mag, is always higher than in V. This difference renders redder and variable (B-V) colour indexes, but the absorption law is unknown. This property of YHGs is unpredictable and explains why spectroscopic temperatures (reddening independent) are always higher than photometric ones, but the difference decreases with the temperature. A new (weak) eruption of rho Cas has been identified. We propose shorter distances for rho Cas and HR 5171A than the accepted ones. Therefore, a correction to decrease the blue luminescence of HR 5171A by polycyclic aromatic hydrocarbon (PAH) molecules is necessary, and HR 5171A would no longer be a member of the cluster Gum48d. HR 5171A is only subject to one source of light variation, not by two as the literature suggests. Eruptive episodes (lasting one to two years), of YHGs prefer relatively cool circumstances when a red evolutionary loop (RL) has shifted the star to the red on the HR diagram. After the eruption, a blue loop evolution (BL) is triggered lasting one to a few decades. We claim that in addition to HR 8752, also the other three YHGs have shown similar cycles over the last 70 years. This supports the suspicion that HD 179821 might be a YHG (with a possible eruptive episode between 1925 and 1960). The range in temperature of these cyclic Teff variations is 3000K-4000K. LTVs mainly consist of such BL and RL evolutions, which are responsible for a decrease and increase, respectively, of the quasi-periods. The reddening episode of HR 5171A between 1960 and 1974 was most likely due to a red loop evolution, and the reddening after the 1975 eruption was likely due to a shell ejection, taking place simultaneously with a blue loop evolution.
- ID:
- ivo://CDS.VizieR/J/ApJ/747/108
- Title:
- Rigel. I. MOST photometry and RV monitoring
- Short Name:
- J/ApJ/747/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Rigel ({beta} Ori, B8 Ia) is a nearby blue supergiant displaying {alpha} Cyg type variability, and is one of the nearest Type II supernova progenitors. As such it is an excellent test bed to study the internal structure of pre-core-collapse stars. In this study, for the first time, we present 28 days of high-precision MOST photometry and over six years of spectroscopic monitoring. We report 19 significant pulsation modes of signal-to-noise ratio, S/N >~ 4.6 from radial velocities, with variability timescales ranging from 1.21 to 74.7 days, which are associated with high-order low-degree gravity modes. While the radial velocity variations show a degree of correlation with the flux changes, there is no clear interplay between the equivalent widths of different metallic and H{alpha} lines.
- ID:
- ivo://CDS.VizieR/J/AJ/135/209
- Title:
- Rotational and radial velocities 761 HIP giants
- Short Name:
- J/AJ/135/209
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present rotational and radial velocities for a sample of 761 giants selected from the Hipparcos Catalogue to lie within 100pc of the Sun. Our original goal was to examine stellar rotation in field giants using spectroscopic line broadening to look for evidence of excess rotation that could be attributed to planets that were engulfed as the parent stars expanded.
- ID:
- ivo://CDS.VizieR/J/AJ/147/138
- Title:
- Rotational and radial velocities of red giants
- Short Name:
- J/AJ/147/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study presents the rotational distribution of red giant (RG) stars in 11 old to intermediate age open clusters. The masses of these stars are all above the Kraft break, so they lose negligible amounts of their birth angular momentum (AM) during the main-sequence (MS) evolution. However, they do span a mass range with quite different AM distributions imparted during formation, with the stars less massive than ~1.6M_{sun}_ arriving on the MS with lower rotation rates than the more massive stars. The majority of RGs in this study are slow rotators across the entire red giant branch regardless of mass, supporting the picture that intermediate-mass stars rapidly spin down when they evolve off the MS and develop convection zones capable of driving a magnetic dynamo. Nevertheless, a small fraction of RGs in open clusters show some level of enhanced rotation, and faster rotators are as common in these clusters as in the field RG population. Most of these enhanced rotators appear to be red clump stars, which is also true of the underlying stellar sample, while others are clearly RGs that are above or below the clump. In addition to rotational velocities, the radial velocities (RVs) and membership probabilities of individual stars are also presented. Cluster heliocentric RVs for NGC 6005 and Pismis 18 are reported for the first time.
- ID:
- ivo://CDS.VizieR/J/ApJ/757/109
- Title:
- Rotational velocities + Li abundance in K giants
- Short Name:
- J/ApJ/757/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The orbital angular momentum of a close-orbiting giant planet can be sufficiently large that, if transferred to the envelope of the host star during the red giant branch (RGB) evolution, it can spin-up the star's rotation to unusually large speeds. This spin-up mechanism is one possible explanation for the rapid rotators detected among the population of generally slow-rotating red giant stars. These rapid rotators thus comprise a unique stellar sample suitable for searching for signatures of planet accretion in the form of unusual stellar abundances due to the dissemination of the accreted planet in the stellar envelope. In this study, we look for signatures of replenishment in the Li abundances and (to a lesser extent) ^12^C/^13^C, which are both normally lowered during RGB evolution. Accurate abundances were measured from high signal-to-noise echelle spectra for samples of both slow and rapid rotator red giant stars. We find that the rapid rotators are on average enriched in lithium compared to the slow rotators, but both groups of stars have identical distributions of ^12^C/^13^C within our measurement precision. Both of these abundance results are consistent with the accretion of planets of only a few Jupiter masses. We also explore alternative scenarios for understanding the most Li-rich stars in our sample--particularly Li regeneration during various stages of stellar evolution. Finally, we find that our stellar samples show non-standard abundances even at early RGB stages, suggesting that initial protostellar Li abundances and ^12^C/^13^C may be more variable than originally thought.
