2017/02/02 by A. Gonneau, A. Lançon, S. C. Trager +8 · 1 citation
Engineering · Physics and Astronomy · #Astronomical Observations and Instrumentation #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Carbon star #Extinction (optical mineralogy) #Infrared #Large Magellanic Cloud #Milky Way #Optics #Physics #Spectral line #Spectroscopy #Stars #Stellar, planetary, and galactic studies #Wavelength #astro-ph.SR
paper · pdf · doi:10.1051/0004-6361/201629750
published as A&A 601, A141 (2017) · 25 pages (11 pages main part, figures and tables in appendix)
arxiv created 2017/02/02 · openalex publication_date 2017/02/02 · arxiv updated 2017/05/24 · openalex created_date 2022/10/01 · openalex updated_date 2026/08/05
In a previous paper, we assembled a collection of medium-resolution spectra of 35 carbon stars, covering optical and near-infrared wavelengths from 400 to 2400 nm. The sample includes stars from the Milky Way and the Magellanic Clouds, with a variety of (J-Ks) colors and pulsation properties. In the present paper, we compare these observations to a new set of high-resolution synthetic spectra, based on hydrostatic model atmospheres. We find that the broad-band colors and the molecular-band strengths measured by spectrophotometric indices match those of the models when (J-Ks) is bluer than about 1.6, while the redder stars require either additional reddening or dust emission or both. Using a grid of models to fit the full observed spectra, we estimate the most likely atmospheric parameters Teff, log(g), [Fe/H] and C/O. These parameters derived independently in the optical and near-infrared are generally consistent when (J-Ks)<1.6. The temperatures found based on either wavelength range are typically within ±100K of each other, and log(g) and [Fe/H] are consistent with the values expected for this sample. The reddest stars ((J-Ks) > 1.6) are divided into two families, characterized by the presence or absence of an absorption feature at 1.53 μm, generally associated with HCN and C2H2. Stars from the first family begin to be more affected by circumstellar extinction. The parameters found using optical or near-infrared wavelengths are still compatible with each other, but the error bars become larger. In stars showing the 1.53 μm feature, which are all large-amplitude variables, the effects of pulsation are strong and the spectra are poorly matched with hydrostatic models. For these, atmospheric parameters could not be derived reliably, and dynamical models are needed for proper interpretation.