Probing the mass-loss history of the unusual Mira variable R Hya through its infrared CO wind
Författare
Summary, in English
Context. The unusual Mira variable R Hya is well known for its declining period between AD 1770 and 1950, which is possibly attributed to a recent thermal pulse.
Aims. The goal of this study is to probe the circumstellar envelope (CSE) around R Hya and to check for a correlation between the derived density structure and the declining period.
Methods. We investigate the CSE around R Hya by performing an in-depth analysis of (1.) the photospheric light scattered by three vibration-rotation transitions in the fundamental band of CO at 4.6 $mu$m; and (2.) the pure rotational CO J = 1-0 through 6-5 emission lines excited in the CSE. The vibrational-rotational lines trace the inner CSE within 3.5´´, whereas the pure rotational CO lines are sensitive probes of the cooler gas further out in the CSE.
Results. The combined analysis bear evidence of a change in mass-loss rate some 220 yr ago (at ~150 $R_{star}$ or ~1.9 arcsec from the star). While the mass-loss rate before AD 1770 is estimated to be ~ $2 imes 10^$ $M_{odot}$/yr, the present day mass-loss rate is a factor of ~20 lower. The derived mass-loss history nicely agrees with the mass-loss rate estimates by Zijlstra et al. (2002) on the basis of the period decline. Moreover, the recent detection of an AGB-ISM bow shock around R Hya at 100 arcsec to the west by Wareing et al. (2006) shows that the detached shell seen in the 60 $mu$m IRAS images can be explained by a slowing-down of the stellar wind by surrounding matter and that no extra mass-loss modulation around 1-2 arcmin needs to be invoked.
Conclusions. Our results give empirical evidence to the thermal-pulse model, which is capable of explaining both the period evolution and the mass-loss history of R Hya .
Aims. The goal of this study is to probe the circumstellar envelope (CSE) around R Hya and to check for a correlation between the derived density structure and the declining period.
Methods. We investigate the CSE around R Hya by performing an in-depth analysis of (1.) the photospheric light scattered by three vibration-rotation transitions in the fundamental band of CO at 4.6 $mu$m; and (2.) the pure rotational CO J = 1-0 through 6-5 emission lines excited in the CSE. The vibrational-rotational lines trace the inner CSE within 3.5´´, whereas the pure rotational CO lines are sensitive probes of the cooler gas further out in the CSE.
Results. The combined analysis bear evidence of a change in mass-loss rate some 220 yr ago (at ~150 $R_{star}$ or ~1.9 arcsec from the star). While the mass-loss rate before AD 1770 is estimated to be ~ $2 imes 10^$ $M_{odot}$/yr, the present day mass-loss rate is a factor of ~20 lower. The derived mass-loss history nicely agrees with the mass-loss rate estimates by Zijlstra et al. (2002) on the basis of the period decline. Moreover, the recent detection of an AGB-ISM bow shock around R Hya at 100 arcsec to the west by Wareing et al. (2006) shows that the detached shell seen in the 60 $mu$m IRAS images can be explained by a slowing-down of the stellar wind by surrounding matter and that no extra mass-loss modulation around 1-2 arcmin needs to be invoked.
Conclusions. Our results give empirical evidence to the thermal-pulse model, which is capable of explaining both the period evolution and the mass-loss history of R Hya .
Avdelning/ar
Publiceringsår
2008
Språk
Engelska
Sidor
55-401
Publikation/Tidskrift/Serie
Astronomy & Astrophysics
Volym
484
Issue
2
Dokumenttyp
Artikel i tidskrift
Förlag
EDP Sciences
Ämne
- Astronomy, Astrophysics and Cosmology
Nyckelord
- stars: mass-loss
- stars: circumstellar matter
- stars: AGB and post-AGB
- line: profiles
- radiative transfer
- stars: individual: R Hya
Status
Published
ISBN/ISSN/Övrigt
- ISSN: 0004-6361