Study of extremely reddened AGB stars in the Galactic bulge

Abstract

Context. Extremely reddened AGB stars lose mass at high rates of >10^-5 Msun/yr. This is the very last stage of AGB evolution, in which stars in the mass range 2.0--4.0 Msun (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. Aims. To determine the mass range of the most reddened AGB stars in the Galactic bulge. Methods. 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. Results. 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--30,000 Lsun and mass-loss rates 10^-5--3x10^-4 Msun/yr. The corresponding mass range is 1.1--6.0 Msun assuming solar metallicity. Conclusions. 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.

References in corpus (40)

• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The AKARI/IRC Mid-Infrared All-Sky Survey
• Age and Metallicity Distribution of the Galactic Bulge from Extensive Optical and Near-IR Stellar Photometry
• Scaled solar tracks and isochrones in a large region of the Z-Y plane I. From the ZAMS to the TP-AGB end for 0.15 - 2.5 Mo stars
• Evolution of asymptotic giant branch stars I. Updated synthetic TP-AGB models and their basic calibration
• VVV DR1: The First Data Release of the Milky Way Bulge and Southern Plane from the Near-Infrared ESO Public Survey VISTA Variables in the Via Lactea
• The Metal Content of Bulge Field Stars from FLAMES-GIRAFFE Spectra. I. Stellar parameters and Iron Abundances
• The metallicity distribution of bulge clump giants in Baade's Window
• Scaled solar tracks and isochrones in a large region of the Z-Y plane. II. From 2.5 to 20 solar masses
• Spitzer SAGE survey of the Large Magellanic Cloud II: Evolved Stars and Infrared Color Magnitude Diagrams
• High and Intermediate-Mass Young Stellar Objects in the Large Magellanic Cloud
• New Asymptotic Giant Branch models for a range of metallicities
• The mid- and far-infrared colours of AGB and post-AGB stars
• The Mass-Loss Return From Evolved Stars to The Large Magellanic Cloud VI: Luminosities and Mass-Loss Rates on Population Scales
• Infrared stellar populations in the central parts of the Milky Way galaxy
• Dusty winds: I. Self-similar solutions
• Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS III. The first global photometric metallicity map of the Galactic bulge
• Helium enrichment and Carbon-star Production in Metal-rich Populations
• The Mass-Loss Return From Evolved Stars to the LMC: Empirical Relations for Excess Emission at 8 and 24 μm
• The mass-loss return from evolved stars to the Large Magellanic Cloud V. The GRAMS carbon-star model grid
• Mid-Infrared Extinction and its Variation with Galactic Longitude
• Dust-enshrouded giants in clusters in the Magellanic Clouds
• Mira Variables in the OGLE Bulge fields
• H2O Maser Observations of Candidate Post-AGB Stars and Discovery of Three High-velocity Water Sources
• The UK Infrared Telescope M33 monitoring project. III. Feedback from dusty stellar winds in the central square kiloparsec
• Discovery of Extreme Carbon Stars in the Large Magellanic Cloud
• Three dimensional interstellar extinction map towards the Galactic Bulge
• Echelle long-slit optical spectroscopy of evolved stars
• SiO Maser Survey of Cold IRAS Sources
• Lifting the Dusty Veil With Near- and Mid-Infrared Photometry: III. Two-Dimensional Extinction Maps of the Galactic Midplane Using the Rayleigh-Jeans Color Excess Method
• Near-infrared observations of water-ice in OH/IR stars
• New detections of H2O masers in planetary nebulae and post-AGB stars using the Robledo-70m antenna
• Spitzer/IRS spectroscopy of high mass precursors to planetary nebulae
• ISO Mid-Infrared Spectroscopy of Galactic Bulge AGB Stars
• An infrared study of galactic OH/IR stars. I. An optical/near-IR atlas of the Arecibo sample
• The Cosmic Crystallinity Conundrum: Clues from IRAS 17495-2534
• Modelling of intermediate-age stellar populations: III Effects of dust-shells around AGB stars
• Adaptive Optics Imaging of IRAS 18276-1431: a bipolar pre-planetary nebula with circumstellar "searchlight beams" and "arcs"
• An infrared study of galactic OH/IR stars. II. The `GLMP sample' of red oxygen-rich AGB stars
• What planetary nebulae tell us about helium and the CNO elements in Galactic bulge stars

Cited by in corpus (9)

• The wind speeds, dust content, and mass-loss rates of evolved AGB and RSG stars at varying metallicity
• The VVV survey: Long-period variable stars I. Photometric catalog of ten VVV/OGLE tiles
• On the detection of CO and mass loss of Bulge OH/IR stars
• CO line observations of OH/IR stars in the inner Galactic Bulge: Characteristics of stars at the tip of the AGB
• Spectroscopic and photometric monitoring of a poorly known high-luminous OH/IR star: IRAS 18278+0931
• The Gaia Catalogue of Galactic AGB Stars
• Water vapour masers in long-period variable stars III. Mira variables U Her and RR Aql
• Water vapour masers in long-period variable stars II. The semi-regular variables R Crt and RT Vir
• A New Catalog of Asymptotic Giant Branch Stars in Our Galaxy