Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000a%26a...356..253j&link_type=abstract
Astronomy and Astrophysics, v.356, p.253-266 (2000)
Astronomy and Astrophysics
Astrophysics
43
Stars: Agb And Post-Agb, Stars: Atmospheres, Stars: Carbon, Molecular Processes, Stars: Variables: General, Infrared: Stars
Scientific paper
During our open and discretionary time ISO programs we have observed a number of carbon-rich and oxygen-rich AGB stars. We present here a hydrostatic analysis of 3 carbon rich stars, TX Psc, V460 Cyg, and TT Cyg, which show only modest variability. We identify absorption features of the molecules C_2, CN, CH, CO, CS, HCN, C_2H_2, and C_3 in the three stars. The relative intensities of the corresponding bands put strict limits on the possible values of T_eff, log g, and C/O. In particular the ratio of the intensity of the 3 mu m band (due to HCN and C_2H_2) and the 5 mu m band (due to CO and C_3) is a sensitive measure of the C/O ratio. We show that our model atmospheres and corresponding synthetic spectra are able to reproduce the observed spectra quite accurately from the visual region through the infrared out to approximately 10 mu m. Beyond 10 mu m the flux in the observed spectra increases compared to the computed spectra, and the photospheric 14 mu m band dominated by C_2H_2 and HCN is almost absent in the observed spectra whereas it is very strong in the synthetic ones. This discrepancy is not an artefact in the reduction or in the SWS response function, but a physical phenomenon in the stars, which does not appear in oxygen-rich giants. We exclude a so-called ``warm molecular envelope'' as an explanation of the discrepancies, and suggest that the flux excess at long wavelengths can be interpreted as clumps of ~ 500 K dense material which obscures about 10% of the photosphere. Weak spectral features seen around 13.7 mu m can be understood as even cooler gas, rich in C_2H_2, above the clumps. Other possible models to explain the long wavelength discrepancy between the computed and observed spectra need to be explored too. Based on observations with ISO, an ESA project with instruments funded by ESA member states (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA
Hron Josef
Jørgensen Uffe G.
Loidl Rudolf
No associations
LandOfFree
ISO-SWS spectra of the carbon stars TX Psc, V460 Cyg, and TT Cyg does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with ISO-SWS spectra of the carbon stars TX Psc, V460 Cyg, and TT Cyg, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and ISO-SWS spectra of the carbon stars TX Psc, V460 Cyg, and TT Cyg will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-747794