- ID:
- ivo://CDS.VizieR/J/A+A/657/A33
- Title:
- Lithium in the LRGB of 5 globular clusters
- Short Name:
- J/A+A/657/A33
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Lithium is one of the few elements produced during the Big Bang Nucleosynthesis in the early universe. Moreover, its fragility makes it useful as a proxy for stellar environmental conditions. As such, the lithium abundance in old systems is at the core of different astrophysical problems. Stars in the lower red giant branch allow studying globular clusters where main sequence stars are too faint to be observed. We use these stars to analyze the initial Li content of the clusters and compare it to cosmological predictions, to measure spreads in Li between different stellar populations, and to study signs of extra depletion in these giants.
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- ID:
- ivo://CDS.VizieR/J/ApJ/819/135
- Title:
- Lithium-rich giants in globular clusters
- Short Name:
- J/ApJ/819/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Although red giants deplete lithium on their surfaces, some giants are Li-rich. Intermediate-mass asymptotic giant branch (AGB) stars can generate Li through the Cameron-Fowler conveyor, but the existence of Li-rich, low-mass red giant branch (RGB) stars is puzzling. Globular clusters are the best sites to examine this phenomenon because it is straightforward to determine membership in the cluster and to identify the evolutionary state of each star. In 72 hours of Keck/DEIMOS exposures in 25 clusters, we found four Li-rich RGB and two Li-rich AGB stars. There were 1696 RGB and 125 AGB stars with measurements or upper limits consistent with normal abundances of Li. Hence, the frequency of Li-richness in globular clusters is (0.2+/-0.1)% for the RGB, (1.6+/-1.1)% for the AGB, and (0.3+/-0.1)% for all giants. Because the Li-rich RGB stars are on the lower RGB, Li self-generation mechanisms proposed to occur at the luminosity function bump or He core flash cannot explain these four lower RGB stars. We propose the following origin for Li enrichment: (1) All luminous giants experience a brief phase of Li enrichment at the He core flash. (2) All post-RGB stars with binary companions on the lower RGB will engage in mass transfer. This scenario predicts that 0.1% of lower RGB stars will appear Li-rich due to mass transfer from a recently Li-enhanced companion. This frequency is at the lower end of our confidence interval.
- ID:
- ivo://CDS.VizieR/J/ApJ/348/98
- Title:
- LMC AGB stars IRAS fluxes
- Short Name:
- J/ApJ/348/98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for optically obscured asymptotic giant branch (AGB) stars in the Large Magellanic Cloud (LMC), combining data obtained using the IRAS satellite with near-infrared photographic plate material of a 15deg^2^ region in the northern LMC. Of the 156 IRAS sources that are detected either in separate cross-scans or in more than one passband, 63 have [12-25] colors consistent with their being either stellar photospheres or circumstellar dust shells. Seventeen of these we identify with bright (I_c_<9) foreground stars in our own Galaxy, while a further 17 are associated with red supergiants in the LMC. Of the remaining stars, no more than five are likely to be optically visible AGB stars, while the rest have no obvious optical counterpart. This immediately rules out the presence of sufficient high-luminosity "cocoon" stars to explain the observed deficit of several hundred luminous (M_bol_<-6) AGB stars between the predictions of standard models of AGB evolution and the observed luminosity function. It remains possible that most of the unidentified sources are dusty AGB stars, evolving through a phase of enhanced mass loss toward becoming planetary nebulae. We infer bolometric magnitudes as low as M_bol_~-5 for these sources and suggest that this phase can be triggered at low luminosities, truncating AGB evolution and leading to the observed scarcity of asymptotic giant branch stars with bolometric magnitudes brighter than -6.0mag.
- ID:
- ivo://CDS.VizieR/J/MNRAS/421/2616
- Title:
- LMC eccentric ellipsoidal red giant binaries
- Short Name:
- J/MNRAS/421/2616
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Modelling ellipsoidal variables with known distances can lead to exact determination of the masses of both components, even in the absence of eclipses. We present such modelling using light and radial velocity curves of ellipsoidal red giant binaries in the Large Magellanic Cloud (LMC), where they are also known as sequence E stars. Stars were selected as likely eccentric systems on the basis of light curve shape alone. We have confirmed their eccentric nature and obtained system parameters using the Wilson-Devinney code.
- 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/AJ/137/4810
- Title:
- LMC-SAGE AGB star candidates
- Short Name:
- J/AJ/137/4810
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present empirical relations describing excess emission from evolved stars in the Large Magellanic Cloud (LMC) using data from the Spitzer Space Telescope Surveying the Agents of a Galaxy's Evolution (SAGE) survey which includes the Infrared Array Camera (IRAC) 3.6, 4.5, 5.8, and 8.0um and Multiband Imaging Photometer (MIPS) 24, 70, and 160um bands. We combine the SAGE data with the Two Micron All Sky Survey (2MASS; J, H, and Ks) and the optical Magellanic Cloud Photometric Survey (MCPS; U, B, V, and I) point source catalogs in order to create complete spectral energy distributions (SEDs) of the asymptotic giant branch (AGB) star candidates in the LMC. AGB star outflows are among the main producers of dust in a galaxy, and this mass loss results in an excess in the fluxes observed in the 8 and 24um bands. The aim of this work is to investigate the mass loss return by AGB stars to the interstellar medium of the LMC by studying the dependence of the infrared excess flux on the total luminosity.
- ID:
- ivo://CDS.VizieR/J/ApJ/811/145
- Title:
- LMC & SMC evolved stars detected with Herschel
- Short Name:
- J/ApJ/811/145
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using observations from the Herschel Inventory of The Agents of Galaxy Evolution (HERITAGE) survey of the Magellanic Clouds (MC), we have found 35 evolved stars and stellar end products that are bright in the far-infrared. These 28 (LMC) and 7 (SMC) sources were selected from the 529 evolved star candidates in the HERITAGE far-infrared point source catalogs. Our source identification method is based on spectral confirmation, spectral energy distribution characteristics, careful examination of the multiwavelength images and includes constraints on the luminosity, resulting in a thoroughly vetted list of evolved stars. These sources span a wide range in luminosity and hence initial mass. We found 13 low- to intermediate-mass evolved stars, including asymptotic giant branch (AGB) stars, post-AGB stars, planetary nebulae, and a symbiotic star. We also identify 10 high mass stars, including 4 of the 15 known B[e] stars in the MC, 3 extreme red supergiants that are highly enshrouded by dust, a Luminous Blue Variable, a Wolf-Rayet star, and two supernova remnants. Further, we report the detection of 9 probable evolved objects which were previously undescribed in the literature. These sources are likely to be among the dustiest evolved objects in the MC. The Herschel emission may either be due to dust produced by the evolved star or it may arise from swept-up interstellar medium material.
- 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/149/184
- Title:
- Long-term photometry for 4 O-rich PPne
- Short Name:
- J/AJ/149/184
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new light curves covering 14-19years of observations of four bright proto-planetary nebulae (PPNs), all oxygen-rich and of F spectral type. They each display cyclical light curves with significant variations in amplitude. All four were previously known to vary in light. Our data were combined with published data and searched for periodicity. The results are as follows: IRAS 19475+3119 (HD331319; 41.0days), 17436+5003 (HD161796; 45.2days), 19386+0155 (101.8days), and 18095+2704 (113.3days). The two longer periods are in agreement with previous studies while the two shorter periods each reveal for the first time a dominant period over these long observing intervals. Multiple periods were also found for each object. The secondary periods were all close to the dominant periods, with P_2_/P_1_ ranging from 0.86 to 1.06. The variations in color reveal maximum variations in T_eff_of 400-770K. These variations are due to pulsations in these post-asymptotic giant branch objects. Maximum seasonal light variations are all less than 0.23mag (V), consistent for their temperatures and periods with the results of Hrivnak et al. for 12 C-rich PPNs. For all of these PPNs, there is an inverse relationship between period and temperature; however, there is a suggestion that the period-temperature relationship may be somewhat steeper for the O-rich than for the C-rich PPNs.
