- ID:
- ivo://CDS.VizieR/J/A+A/538/A36
- Title:
- Lithium abundances of bulge RGB stars
- Short Name:
- J/A+A/538/A36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A small number of K-type giants on the red giant branch (RGB) is known to be very rich in lithium (Li). This fact is not accounted for by standard stellar evolution theory. The exact phase and mechanism of Li enrichment is still a matter of debate. Our goal is to probe the abundance of Li along the RGB, from its base to the tip, to confine Li-rich phases that are supposed to occur on the RGB. For this end, we obtained medium-resolution spectra with the FLAMES spectrograph at the VLT in GIRAFFE mode for a large sample of 401 low-mass RGB stars located in the Galactic bulge. The Li abundance was measured in the stars with a detectable Li 670.8 nm line by means of spectral synthesis with COMARCS model atmospheres. A new 2MASS J-K-Teff calibration from COMARCS models is presented in the Appendix. Thirty-one stars with a detectable Li line were identified, three of which are Li-rich according to the usual criterion (log{epsilon}_Li_>1.5). The stars are distributed all along the RGB, not concentrated in any particular phase of the red giant evolution (e.g. the luminosity bump or the red clump). The three Li-rich stars are clearly brighter than the luminosity bump and red clump, and do not show any signs of enhanced mass loss. We conclude that the Li enrichment mechanism cannot be restricted to a clearly defined phase of the RGB evolution of low-mass stars (M~1M_{sun}_), contrary to earlier suggestions from disk field stars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/653/A13
- Title:
- Lithium in NGC 2243 and NGC 104
- Short Name:
- J/A+A/653/A13
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We aim to determine the initial Li content of two clusters of similar metallicity but very different age, the old open cluster NGC 2243 and the metal-rich globular cluster NGC 104. We compare the lithium abundances derived for a large sample of stars (from the turn-off to the red giant branch) in each cluster. For NGC 2243, the Li abundances are taken from the catalogues released by the Gaia-ESO Public Spectroscopic Survey, while for NGC 104 we measured the Li abundance using FLAMES/GIRAFFE spectra, which include both archival data and new observations.
- ID:
- ivo://CDS.VizieR/J/A+A/534/A95
- Title:
- LMC Cepheids radial velocities
- Short Name:
- J/A+A/534/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The extragalactic distance scale builds directly on the Cepheid Period-Luminosity (PL) relation as delineated by the sample of Cepheids in the Large Magellanic Cloud (LMC). However, the LMC is a dwarf irregular galaxy, quite different from the massive spiral galaxies used for calibrating the extragalactic distance scale. Recent investigations suggest that not only the zero-point but also the slope of the Milky Way PL relation differ significantly from that of the LMC, casting doubts on the universality of the Cepheid PL relation. We want to make a differential comparison of the PL relations in the two galaxies by delineating the PL relations using the same method, the infrared surface brightness method (IRSB), and the same precepts. The IRSB method is a Baade-Wesselink type method to determine individual distances to Cepheids. We apply a newly revised calibration of the method as described in an accompanying paper (Paper I, Cat. J/A+A/534/A94) to 36 LMC and five SMC Cepheids and delineate new PL relations in the V,I,J, & K bands as well as in the Wesenheit indices in the optical and near-IR. We present 509 new and accurate radial velocity measurements for a sample of 22 LMC Cepheids, enlarging our earlier sample of 14 stars to include 36 LMC Cepheids. The new calibration of the IRSB method is directly tied to the recent HST parallax measurements to ten Milky Way Cepheids, and we find a LMC barycenter distance modulus of 18.45+/-0.04 (random error only) from the 36 individual LMC Cepheid distances. In the J,K bands we find identical slopes for the LMC and Milky Way PL relations and only a weak metallicity effect on the zero points (consistent with a zero effect), metal poor stars being fainter. In the optical we find the Milky Way slopes are slightly shallower than the LMC slopes (but again consistent with no difference in the slopes) and small effects on the zero points. However, the important Wesenheit index in V,(V-I) shows a metallicity effect on the slope and on the zero point which is likely to be significant. We find a significant metallicity effect on the Wvi index gamma(Wvi)=-0.23+/-0.10mag/dex as well as an effect on the slope. The K-band PL relation on the other hand is found to be an excellent extragalactic standard candle being metallicity insensitive in both slope and zero-point and at the same time being reddening insensitive and showing the least internal dispersion.
- ID:
- ivo://CDS.VizieR/J/MNRAS/454/1468
- Title:
- LMC post-AGB, post-RGB star and YSOs
- Short Name:
- J/MNRAS/454/1468
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a search for optically visible post-Asymptotic Giant Branch (post- AGB) stars in the Large Magellanic Cloud (LMC). First, we selected candidates with a mid-IR excess and then obtained their optical spectra. We disentangled contaminants with unique spectra such as M-stars, C-stars, planetary nebulae, quasi-stellar objects and background galaxies. Subsequently, we performed a detailed spectroscopic analysis of the remaining candidates to estimate their stellar parameters such as effective temperature, surface gravity (logg), metallicity ([Fe/H]), reddening and their luminosities. This resulted in a sample of 35 likely post-AGB candidates with late-G to late-A spectral types, low logg, and [Fe/H]<-0.5. Furthermore, our study con- firmed the existence of the dusty post-Red Giant Branch (post-RGB) stars, discovered previously in our SMC survey, by revealing 119 such objects in the LMC. These objects have mid-IR excesses and stellar parameters (Teff, logg, [Fe/H]) similar to those of post-AGB stars except that their luminosities (<2500L_{sun}_), and hence masses and radii, are lower. These post-RGB stars are likely to be products of binary interaction on the RGB. The post-AGB and post-RGB objects show SED properties similar to the Galactic post-AGB stars, where some have a surrounding circumstellar shell, while some others have a surrounding stable disc similar to the Galactic post-AGB binaries. This study also resulted in a new sample of 162 young stellar objects, identified based on a robust logg criterion. Other interesting outcomes include objects with an UV continuum and an emission line spectrum; luminous supergiants; hot main-sequence stars; and 15 B[e] star candidates, 12 of which are newly discovered in this study.
- ID:
- ivo://CDS.VizieR/J/MNRAS/399/2063
- Title:
- LMC red giants in D sequence
- Short Name:
- J/MNRAS/399/2063
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of a sample of Large Magellanic Cloud red giants exhibiting Long Secondary Periods (LSPs). We use radial velocities obtained from VLT spectral observations and MACHO and OGLE light curves to examine properties of the stars and to evaluate models for the cause of LSPs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/405/1770
- Title:
- LMC red giants in E sequence
- Short Name:
- J/MNRAS/405/1770
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have studied a sample of Large Magellanic Cloud red giant binaries that lie on sequence E in the period-luminosity plane. We show that their combined light and velocity curves unambiguously demonstrate that they are binaries showing ellipsoidal variability. By comparing the phased light and velocity curves of both sequence D and E variables, we show that the sequence D variation - the long secondary period - is not caused by ellipsoidal variability. We also demonstrate several further differences between stars on sequences D and E. These include differences in velocity amplitude, in the distribution of eccentricity and in the correlations of velocity amplitude with luminosity and period. We also show that the sequence E stars, unlike stars on sequence D, do not show any evidence of a mid-infrared excess that would indicate circumstellar dust.
- ID:
- ivo://CDS.VizieR/J/A+A/423/97
- Title:
- LMC RR Lyrae radial velocities
- Short Name:
- J/A+A/423/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the radial velocities, metallicities and the K-band magnitudes of 74 RR Lyrae stars in the inner regions of the LMC. The intermediate resolution spectra and infrared images were obtained with FORS1 at the ESO VLT and with the SOFI infrared imager at the ESO NTT.
- ID:
- ivo://CDS.VizieR/J/A+A/398/479
- Title:
- Local galaxy flows within 5 Mpc
- Short Name:
- J/A+A/398/479
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Hubble Space Telescope/WFPC2 images of sixteen dwarf galaxies as part of our snapshot survey of nearby galaxy candidates. We derive their distances from the luminosity of the tip of the red giant branch stars with a typical accuracy of ~12%.
- ID:
- ivo://CDS.VizieR/J/ApJ/711/361
- Title:
- Local Group dE galaxies. II.
- Short Name:
- J/ApJ/711/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present kinematic and metallicity profiles for the M 31 dwarf elliptical (dE) satellite galaxies NGC 147 and NGC 185. The profiles represent the most extensive spectroscopic radial coverage for any dE galaxy, extending to a projected distance of 8 half-light radii (8r_eff_~14'). We achieve this coverage via Keck/DEIMOS multislit spectroscopic observations of 520 and 442 member red giant branch stars in NGC 147 and NGC 185, respectively. In contrast to previous studies, we find that both dEs have significant internal rotation. We measure a maximum rotational velocity of 17+/-2km/s for NGC 147 and 15+/-5km/s for NGC 185. The velocity dispersions decrease gently with radius with average dispersions of 16+/-1km/s and 24+/-1km/s for NGC 147 and NGC 185, respectively. The average metallicities for NGC 147 and NGC 185 are [Fe/H]=-1.1+/-0.1 and [Fe/H]=-1.3+/-0.1, respectively; both dEs have internal metallicity dispersions of 0.5dex, but show no evidence for a radial metallicity gradient.
- ID:
- ivo://CDS.VizieR/J/AJ/158/122
- Title:
- Local structure & star formation history of the MW
- Short Name:
- J/AJ/158/122
- Date:
- 09 Mar 2022 22:00:00
- Publisher:
- CDS
- Description:
- Gaia DR2 (Cat. I/345) provides unprecedented precision in measurements of the distance and kinematics of stars in the solar neighborhood. Through applying unsupervised machine learning on DR2's 5D data set (3D position + 2D velocity), we identify a number of clusters, associations, and comoving groups within 1 kpc and |b|<30{deg} (many of which have not been previously known). We estimate their ages with the precision of ~0.15 dex. Many of these groups appear to be filamentary or string-like, oriented in parallel to the Galactic plane, and some span hundreds of parsec in length. Most of these string lack a central cluster, indicating that their filamentary structure is primordial, rather than the result of tidal stripping or dynamical processing. The youngest strings (<100 Myr) are orthogonal to the Local Arm. The older ones appear to be remnants of several other arm-like structures that cannot be presently traced by dust and gas. The velocity dispersion measured from the ensemble of groups and strings increase with age, suggesting a timescale for dynamical heating of ~300 Myr. This timescale is also consistent with the age at which the population of strings begins to decline, while the population in more compact groups continues to increase, suggesting that dynamical processes are disrupting the weakly bound string populations, leaving only individual clusters to be identified at the oldest ages. These data shed a new light on the local galactic structure and a large-scale cloud collapse.