2007/01/17 by M. Busso, R. Guandalini, Roald Guandalini +3 · 26 citations
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Asymptotic giant branch #Carbon star #Circumstellar dust #Galaxy #Infrared #Infrared excess #Luminosity #Photometry (optics) #Physics #Sky #Stars #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/512612
published in The Astronomical Journal 133(5), 2310-2319 (Institute of Physics) · Accepted for publication in the Astronomical Journal - 35 pages (in preprint), 9 figures, 5 tables
arxiv created 2007/01/17 · openalex publication_date 2007/04/04 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present ground-based mid-IR imaging for 27 M-, S-, and C-type asymptotic giant branch (AGB) stars. The data are compared with those of the database available thanks to the IRAS , Infrared Space Observatory , Midcourse Space Experiment , and Two Micron All Sky Survey catalogs. Our goal is to establish relations between the IR colors, the effective temperature T eff , the luminosity L , and the mass-loss rate , for improving the effectiveness of AGB modeling. Bolometric (absolute) magnitudes are obtained through distance compilations and by applying previously derived bolometric corrections; the variability is also studied, using data accumulated since the IRAS epoch. The main results are as follows: (1) Values of L and for C stars fit relations previously established by us, with Mira variables being on average more evolved and mass-losing than semiregular variables. (2) Moderate IR excesses (as compared to evolutionary tracks) are found for S and M stars in our sample: they are confirmed to originate from the dusty circumstellar environment. (3) A larger reddening characterizes C-rich Mira variables and post-AGB stars. In this case, part of the excess is due to AGB models overestimating T eff for C stars, as a consequence of the lack of suitable molecular opacities. This has a large effect on the colors of C-rich sources, and sometimes disentangling the photospheric and circumstellar contributions is difficult; better model atmospheres should be used in stellar evolutionary codes for C stars. (4) The presence of a long-term variability at mid-IR wavelengths seems to be limited to sources with maximum emission in the 8-20 μm region, usually Mira variables (one-third of our sample). Most of the semiregular and post-AGB stars studied here have remained remarkably constant in the mid-IR over the last 20 years.