- ID:
- ivo://CDS.VizieR/J/A+A/579/A76
- Title:
- Galactic bulge extremely reddened AGB
- Short Name:
- J/A+A/579/A76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Extremely reddened asymptotic giant branch stars (AGB) lose mass at high rates of >10^-5^M_{sun}_/yr. This is the very last stage of AGB evolution, in which stars in the mass range ~2.0-4.0M_{sun}_ (for solar metallicity) should have been converted to C stars already. The extremely reddened AGB stars in the Galactic bulge are however predominantly O-rich, implying that they might be either low-mass stars or stars at the upper end of the AGB mass range. Our goal is to determine the mass range of the most reddened AGB stars in the Galactic bulge. Using Virtual Observatory tools, we constructed spectral energy distributions of a sample of 37 evolved stars in the Galactic bulge with extremely red IRAS colours. We fitted DUSTY models to the observational data to infer the bolometric fluxes. Applying individual corrections for interstellar extinction and adopting a common distance, we determined luminosities and mass-loss rates, and inferred the progenitor mass range from comparisons with AGB evolutionary models. The observed spectral energy distributions are consistent with a classification as reddened AGB stars, except for two stars, which are proto-planetary nebula candidates. For the AGB stars, we found luminosities in the range ~3000-30000L_{sun}_ and mass-loss rates ~10^-5^-3x10^-4^M_{sun}_/yr. The corresponding mass range is ~1.1-6.0M_{sun}_ assuming solar metallicity. Contrary to the predictions of the evolutionary models, the luminosity distribution is continuous, with many O-rich AGB stars in the mass range in which they should have been converted into C stars already. We suspect that bulge AGB stars have higher than solar metallicity and therefore may avoid the conversion to C-rich. The presence of low-mass stars in the sample shows that their termination of the AGB evolution also occurs during a final phase of very high mass-loss rate, leading to optically thick circumstellar shells.
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- ID:
- ivo://CDS.VizieR/J/A+A/614/A149
- Title:
- 417 Galactic bulge red giant O & Zn abund.
- Short Name:
- J/A+A/614/A149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Oxygen and zinc in the Galactic bulge are key elements for the understanding of the bulge chemical evolution. Oxygen-to-iron abundance ratios provide a most robust indicator of the star formation rate and chemical evolution of the bulge. Zinc is enhanced in metal-poor stars, behaving as an {alpha}-element, and its production may require nucleosynthesis in hypernovae. Most of the neutral gas at high redshift is in damped Lyman-alpha systems (DLAs), where Zn is also observed to behave as an {alpha}-element. The aim of this work is the derivation of the {alpha}-element oxygen, together with nitrogen, and the iron-peak element zinc abundances in 417 bulge giants, from moderate resolution (R~22000) FLAMES-GIRAFFE spectra. For stars in common with a set of UVES spectra with higher resolution (R~45000), the data are intercompared. The results are compared with literature data and chemodynamical models. We studied the spectra obtained for a large sample of red giant stars, chosen to be one magnitude above the horizontal branch, using FLAMES-GIRAFFE on the Very Large Telescope. We computed the O abundances using the forbidden [OI] 6300.3{AA} and Zn abundances using the ZnI 6362.34{AA} lines. Stellar parameters for these stars were established in a previous work from our group. We present oxygen abundances for 358 stars, nitrogen abundances for 403 stars and zinc abundances were derived for 333 stars. Having oxygen abundances for this large sample adds information in particular at the moderate metallicities of -1.6<[Fe/H]<-0.8. Zn behaves as an {alpha}-element, very similarly to O, Si, and Ca. It shows the same trend as a function of metallicity as the {alpha}-elements, i.e., a turnover around [Fe/H]~-0.6, and then decreasing with increasing metallicity. The results are compared with chemodynamical evolution models of O and Zn enrichment for a classical bulge. DLAs also show an enhanced zinc-to-iron ratio, suggesting they may be enriched by hypernovae.
- ID:
- ivo://CDS.VizieR/J/A+A/640/A89
- Title:
- 56 Galactic bulge red giants Co and Cu abund.
- Short Name:
- J/A+A/640/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Milky Way bulge is an important tracer of the early formation and chemical enrichment of the Galaxy. The abundances of different iron-peak elements in field bulge stars can give information on the nucleosynthesis processes that took place in the earliest supernovae. Cobalt (Z=27) and copper (Z=29) are particularly interesting. We aim to identify the nucleosynthesis processes responsible for the formation of the iron-peak elements Co and Cu. We derived abundances of the iron-peak elements cobalt and copper in 56 bulge giants, 13 of which were red clump stars. High-resolution spectra were obtained using FLAMES-UVES at the ESO Very Large Telescope by our group in 2000-2002, which appears to be the highest quality sample of optical high-resolution data on bulge red giants obtained in the literature to date. Over the years we have derived the abundances of C, N, O, Na, Al, Mg; the iron-group elements Mn and Zn; and neutron-capture elements. In the present work we derive abundances of the iron-peak elements cobalt and copper. We also compute chemodynamical evolution models to interpret the observed behaviour of these elements as a function of iron. The sample stars show mean values of [Co/Fe]~0.0 at all metallicities, and [Cu/Fe]~0.0 for [Fe/H]>=-0.8 and decreasing towards lower metallicities with a behaviour of a secondary element. We conclude that [Co/Fe] varies in lockstep with [Fe/H], which indicates that it should be produced in the alpha-rich freezeout mechanism in massive stars. Instead [Cu/Fe] follows the behaviour of a secondary element towards lower metallicities, indicating its production in the weak s-process nucleosynthesis in He-burning and later stages. The chemodynamical models presented here confirm the behaviour of these two elements (i.e. [Co/Fe] vs. [Fe/H] ~ constant and [Cu/Fe] decreasing with decreasing metallicities).
- ID:
- ivo://CDS.VizieR/J/A+A/493/785
- Title:
- Galactic disk stellar populations from ISOGAL
- Short Name:
- J/A+A/493/785
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify the stellar populations (mostly red giants and young stars) detected in the ISOGAL survey at 7 and 15um towards a field (LN45) in the direction l=-45, b=0.0. The sources detected in the survey of the Galactic plane by the Infrared Space Observatory were characterised based on colour-colour and colour-magnitude diagrams. We combine the ISOGAL catalogue with the data from surveys such as 2MASS and GLIMPSE. Interstellar extinction and distance were estimated using the red clump stars detected by 2MASS in combination with the isochrones for the AGB/RGB branch. Absolute magnitudes were thus derived and the stellar populations identified from their absolute magnitudes and their infrared excess. A standard approach to analysing the ISOGAL disc observations has been established. We identify several hundred RGB/AGB stars and 22 candidate young stellar objects in the direction of this field in an area of 0.16deg^2^. An overdensity of stellar sources is found at distances corresponding to the distance of the Scutum-Crux spiral arm. In addition, we determined mass-loss rates of AGB-stars using dust radiative transfer models from the literature.
- ID:
- ivo://CDS.VizieR/J/MNRAS/447/1673
- Title:
- Galactic post-AGB stars distances
- Short Name:
- J/MNRAS/447/1673
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have commenced a detailed analysis of the known sample of Galactic post-asymptotic giant branch (PAGB) objects compiled in the Torun catalogue of Szczerba et al. (2007A&A...469..799S, Cat. J/A+A/469/799), and present, for the first time, homogeneously derived distance determinations for the 209 likely and 87 possible catalogued PAGB stars from that compilation. Knowing distances are essential in determining meaningful physical characteristics for these sources and this has been difficult to determine for most objects previously. The distances were determined by modelling their spectral energy distributions (SEDs) with multiple blackbody curves, and integrating under the overall fit to determine the total distance-dependent flux. This approach was undertaken for consistency as precise spectral types, needed for more detailed fitting, were unknown in the majority of cases. The SED method works because the luminosity of these central stars is very nearly constant from the tip of the AGB phase to the beginning of the white dwarf cooling track. This then enables us to use a standard-candle luminosity to estimate the SED distances. For Galactic thin-disc PAGB objects, we use three luminosity bins based on typical observational characteristics, ranging between 3500 and 12000L_{sun}_. We further adopt a default luminosity of 4000L_{sun}_ for bulge objects and 1700L_{sun}_ for the thick-disc and halo objects. We have also applied the above technique to a further sample of 54 related nebulae not in the current edition of the Torun catalogue. In a follow-up paper, we will estimate distances to the subset of RV Tauri variables using empirical period-luminosity relations, and to the R CrB stars, allowing a population comparison of these objects with the other subclasses of PAGB stars for the first time.
- ID:
- ivo://CDS.VizieR/J/A+A/574/A116
- Title:
- G and K giant stars stellar parameters
- Short Name:
- J/A+A/574/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained precise radial velocities for a sample of 373 G and K type giants at Lick Observatory regularly over more than 12 years. Planets have been identified around 15 of these giant stars, and an additional 20 giant stars host planet candidates. We are interested in the occurrence rate of substellar companions around giant stars as a function of stellar mass and metallicity. We probe the stellar mass range from approximately 1 to beyond 3M_{sun}_, which is not being explored by main-sequence samples. We fit the giant planet occurrence rate as a function of stellar mass and metallicity with a Gaussian and an exponential distribution, respectively.
- ID:
- ivo://CDS.VizieR/J/ApJ/769/20
- Title:
- 22GHz H_2_O maser survey toward IR sources
- Short Name:
- J/ApJ/769/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a 22GHz H_2_O maser survey toward a new sample of asymptotic giant branch (AGB) and post-AGB star candidates. Most of the objects are selected for the first time based on the AKARI data, which have high flux sensitivity in the mid-infrared ranges. We aim at finding H_2_O maser sources in the transient phase between the AGB and post-AGB stages of evolution, where the envelopes start to develop large deviations from spherical symmetry. The observations were carried out with the Effelsberg 100m radio telescope. Among 204 observed objects, 63 detections (36 new) were obtained. We found four objects that may be "water fountain" sources (IRAS 15193+3132, IRAS 18056-1514, OH 16.3-3.0, and IRAS 18455+0448). They possess an H_2_O maser velocity coverage much smaller than those in other known water fountains. However, the coverage is still larger than that of the 1612MHz OH maser. It implies that there is an outflow with a higher velocity than the envelope expansion velocity (typically <=25km/s), meeting the criterion of the water fountain class. We suggest that these candidates are possibly oxygen-rich late AGB or early post-AGB stars in a stage of evolution immediately after the spherically symmetric AGB mass loss has ceased.
- ID:
- ivo://CDS.VizieR/J/AJ/89/636
- Title:
- Giant M stars in Baade's Window
- Short Name:
- J/AJ/89/636
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Near-infrared small-dispersion spectra obtained with a grism at the prime focus of CTIO's 4-m telescope have been used to survey and classify late-type red giants found in a circular area with a diameter of 24.4 arcmin which is contained within Baade's Window. The survey is complete to a distance that extends past the galactic nuclear bulge. The presented stars therefore constitute a unique complete sample of the red giant population of the nuclear bulge. A total of 306 red giants, including all giants of type M6 or later, are presented with a list of their coordinates, spectral classes, and apparent I magnitudes. A finding chart is also given. No C or S stars were found even though they should have been detected if they exist. Evidence is presented of uneven foreground interstellar obscuration in Baade's Window.
- ID:
- ivo://CDS.VizieR/J/A+AS/127/251
- Title:
- Giants and supergiants ROSAT data
- Short Name:
- J/A+AS/127/251
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present X-ray data for all late-type (A,F,G,K,M) giants and supergiants (luminosity classes I to III-IV) listed in the Bright Star Catalogue that have been detected in the ROSAT all-sky survey. The selection of the sample stars, the data analysis, the criteria for an accepted match between star and X-ray source, and the determination of X-ray fluxes are described.
- ID:
- ivo://CDS.VizieR/J/A+A/603/L7
- Title:
- 6 giants atomic data and equivalent widths
- Short Name:
- J/A+A/603/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observed six He-clump stars of the intermediate-age stellar cluster Gaia1 with the MIKE/MAGELLAN spectrograph. A possible extra-galactic origin of this cluster, recently discovered thanks to the first data release of the ESA Gaia mission, has been suggested, based on its orbital parameters. Abundances for Fe, {alpha}, proton- and neutron-capture elements have been obtained. We find no evidence of intrinsic abundance spreads. The iron abundance is solar ([FeI/H]=+0.00+/-0.01; {sigma}=0.03dex). All the other abundance ratios are generally solar-scaled, similar to the Galactic thin disk and open cluster stars of similar metallicity. The chemical composition of Gaia1 does not support an extra-galactic origin for this stellar cluster, which can be considered as a standard Galactic open cluster.
