Probing the mass-loss history of the unusual Mira variable R Hydrae through its infrared CO wind

Details Probing the mass-loss history of the unusual Mira variable R Hydrae through its infrared CO wind Probing the mass-loss history of the unusual Mira variable R Hydrae through its infrared CO wind

Jun 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008a%26a...484..401d&link_type=abstract

Astronomy and Astrophysics, Volume 484, Issue 2, 2008, pp.401-412

Astronomy and Astrophysics

Astrophysics

3

Line: Profiles, Radiative Transfer, Stars: Agb And Post-Agb, Stars: Circumstellar Matter, Stars: Mass-Loss, Stars: Individual: R Hya

Scientific paper

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 μm; 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 Rstar or 1.9 arcsec from the star). While the mass-loss rate before ad 1770 is estimated to be 2 × 10-7 M&sun;/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 μm 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.
Appendix A is only available in electronic form at http://www.aanda.org

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