the goal of this proposal is to elucidate the evolutinary status of j-type carbon stars by observing their extended dust shells in the far-infrared. there are non-negligible number of cool carbon stars which show low c12/c13 carbon isotopic ratios in their atmosphere (j-type carbon stars), prototype of which is y cvn. they show no s-process element enhancements, which suggests that they have not experienced the third dredge-up which is the key process to produce carbon stars on the aymptotic giant branch (agb). the lack of s-process enhancements tends to be interpreted as the sign of them being not on the agb. however, we have detected a very extended, detached dust shell around y cvn at 90 and 160 micron with isophot in our guaranteed time (gt) program, hizumiur_redstar2. our results indicate that the mass-loss rate decreased by about two orders of magnitude in the last 14,000 years. the rapid, great change of the mass-loss rate resembles to those observed toward carbon stars u hya and u ant which are known to be on the agb. such similarity suggests that y cvn is also an agb star. while the formation process of ordinary cool carbon stars on the agb is relatively well understood now, the evolutionary status of those j-type cool carbon stars is still remains to be answered. in this proposal we plan to study the dust shell of ry dra, the second brightest j-type carbon star next to y cvn, both of which have extremely low c12/c13 isotopic ratios (< 5) in the atmosphere, in order to study its mass-loss history. we will examine if ry dra also has an extended, detached dust shell similar to the one around y cvn. the results on the two stars will provide us with important information on the mass-loss history of j-type carbon stars, thus would help to understand their evolutionary status. this proposal is an extension of our gt iso observing program hizumiur_redstar2, in which we examine the structure of extended dust shells around both oxygen-rich and carbon-rich agb stars in the far-infrared using isophot.
Instrument
PHT32
Temporal Coverage
1997-05-12T01:51:34Z/1997-05-12T03:47:42Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, Izumiura et al., 1999, 'EXTENDED DUST SHELL AROUND THE J-TYPE CARBON STAR RY DRACONIS', 1.0, European Space Agency, https://doi.org/10.5270/esa-0vbhrlh
