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- Decin, L., et al.
(författare)
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Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles. I. Theoretical model - Mass-loss history unravelled in VY CMa
- 2006
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 456:2, s. 549-563
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Tidskriftsartikel (refereegranskat)abstract
- Context: Mass loss plays a dominant role in the evolution of low mass stars while they are on the Asymptotic Giant Branch (AGB). The gas and dust ejected during this phase are a major source in the mass budget of the interstellar medium. Recent studies have pointed towards the importance of variations in the mass-loss history of such objects.Aims: By modelling the full line profile of low excitation CO lines emitted in the circumstellar envelope, we can study the mass-loss history of AGB stars.Methods: We have developed a non-LTE radiative transfer code, which calculates the velocity structure and gas kinetic temperature of the envelope in a self-consistent way. The resulting structure of the envelope provides the input for the molecular line radiative calculations which are evaluated in the comoving frame. The code allows for the implementation of modulations in the mass-loss rate. This code has been benchmarked against other radiative transfer codes and is shown to perform well and efficiently.Results: We illustrate the effects of varying mass-loss rates in case of a superwind phase. The model is applied to the well-studied case of VY CMa. We show that both the observed integrated line strengths as the spectral structure present in the observed line profiles, unambiguously demonstrate that this source underwent a phase of high mass loss (~3.2 × 10-4 Mȯ yr-1) some 1000 yr ago. This phase took place for some 100 yr, and was preceded by a low mass-loss phase (~1 × 10-6 Mȯ yr-1) taking some 800 yr. The current mass-loss rate is estimated to be in the order of 8 × 10-5 Mȯ yr-1.Conclusions: In this paper, we demonstrate that both the relative strength of the CO rotational line profiles and the (non)-occurrence of spectral structure in the profile offer strong diagnostics to pinpoint the mass-loss history.
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| 2. |
- Decin, L., et al.
(författare)
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Probing the Mass-Loss History of VY CMa
- 2008
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Ingår i: Mass Loss from Stars and the Evolution of Stellar Clusters, Proceedings of conference in Lunteren May-June 2006, The Netherlands, eds. A. de Koter, L.J. Smith, L.B.F.M. Waters, ASP Conference Series, San Francisco. ; 388, s. 159-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Mass loss plays a dominant role in the evolution of low mass stars while they are on the Asymptotic Giant Branch (AGB). Recent studies have hinted towards the importance of time variability of the mass-loss rates of such objects. Likewise, more massive stars (MZAMS ⪆ 8 Msun) may pass through a red supergiant phase and lose mass in a similar manner. By modelling the full line profiles of low excitation CO transitions emitted in the circumstellar envelope (CSE), we have studied the mass-loss history of the well-studied supergiant VY CMa. We show that this source underwent a phase of high mass loss (˜ 2.8 × 10-4 Msun/yr) some 1000 yr ago, lasting some 100 yr, followed by a low mass-loss phase (˜ 1 × 10-6 Msun/yr) taking some 800 yr. The current mass-loss rate is estimated to be in the order of 1 × 10-4 Msun/yr.
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| 3. |
- Decin, L., et al.
(författare)
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Probing the mass-loss history of the unusual Mira variable R Hydrae through its infrared CO wind
- 2008
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 484:2, s. 401-U55
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Tidskriftsartikel (refereegranskat)abstract
- 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 similar to 150 R-* or similar to 1.9 arcsec from the star). While the mass-loss rate before ad 1770 is estimated to be similar to 2 x 10(-7) M-circle dot/yr, the present day mass-loss rate is a factor of similar to 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.
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