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Titolo: Envelope tomography of long-period variable stars - III. Line-doubling frequency among Mira stars
Autore: Alvarez, R; Jorissen, A; Plez, B; Gillet, D; Fokin, A; Dedecker, M;
- Indirizzi:
- Free Univ Brussels, Inst Astron & Astrophys, B-1050 Brussels, Belgium FreeUniv Brussels Brussels Belgium B-1050 hys, B-1050 Brussels, Belgium Univ Montpellier 2, GRAAL, F-34095 Montpellier 05, France Univ Montpellier2 Montpellier France 05 F-34095 Montpellier 05, France Observ Haute Provence, F-04870 St Michel, France Observ Haute Provence StMichel France F-04870 F-04870 St Michel, France Russian Acad Sci, Inst Astron, Moscow 109017, Russia Russian Acad Sci Moscow Russia 109017 Inst Astron, Moscow 109017, Russia
- Titolo Testata:
- ASTRONOMY & ASTROPHYSICS
fascicolo: 1,
volume: 379,
anno: 2001,
pagine: 305 - 322
- SICI:
- 1432-0746(200111)379:1<305:ETOLVS>2.0.ZU;2-K
- Fonte:
- ISI
- Lingua:
- ENG
- Soggetto:
- MOLECULAR STELLAR ATMOSPHERES; SHOCK-INDUCED VARIABILITY; SERIES INFRARED-SPECTROSCOPY; ALPHA-EMISSION PROFILE; GIANT BRANCH STARS; RADIATIVE SHOCKS; MASS-LOSS; CIRCUMSTELLAR ENVELOPES; WAVE INTERPRETATION; CO DELTA-NU=3;
- Keywords:
- stars : AGB and post-AGB; stars : atmospheres; stars : late-type; stars : oscillations; stars : variables : general; shock waves;
- Tipo documento:
- Article
- Natura:
- Periodico
- Settore Disciplinare:
- Physical, Chemical & Earth Sciences
- Citazioni:
- 76
- Recensione:
- Indirizzi per estratti:
- Indirizzo: Jorissen, A Free Univ Brussels, Inst Astron & Astrophys, CP 226,Blvd Triomphe, B-1050 Brussels, Belgium Free Univ Brussels CP 226,Blvd Triomphe Brussels Belgium B-1050
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- Citazione:
- R. Alvarez et al., "Envelope tomography of long-period variable stars - III. Line-doubling frequency among Mira stars", ASTRON ASTR, 379(1), 2001, pp. 305-322
Abstract
This paper presents statistics of the line-doubling phenomenon in a sampleof 81 long-period variable (LPV) stars of various periods, spectral types and brightness ranges. The set of observations consists of 315 high-resolution optical spectra collected with the spectrograph ELODIE at the Haute-Provence Observatory, during 27 observing nights at one-month intervals and spanning two years. When correlated with a mask mimicking a K0III spectrum, 54% of the sample stars clearly showed a double-peaked cross-correlation profile around maximum light, reflecting double absorption lines. Several pieces of evidence are presented that point towards the double absorption linesas being caused by the propagation of a shock wave through the photosphere. The observation of the Balmer lines appearing in emission around maximum light in these stars corroborates the presence of a shock wave. The observed velocity discontinuities, ranging between 10 and 25 km s(-1), are not correlated with the brightness ranges. A comparison with the center-of-mass (COM) velocity obtained from submm CO lines originating in the circumstellar envelope reveals that the median velocity between the red and blue peaks isblueshifted with respect to the COM velocity, as expected if the shock moves upwards. The LPVs clearly exhibiting line-doubling around maximum light with the K0III mask appear to be the most compact ones, the stellar radius being estimated from their effective temperatures (via the spectral type) and luminosities (via the period-luminosity relationship). It is not entirely clear whether or not this segregation between compact and extended LPVs is an artefact of the use of the K0III mask. Warmer masks (F0V and G2V) applied to the most extended and coolest LPVs yield asymmetric cross-correlation functions which suggest that line doubling is occurring in those stars aswell. Although a firm conclusion on this point is hampered by the large correlation noise present in the CCFs of cool LPVs obtained with warm masks, the occurrence of line doubling in those stars is confirmed by the double CO Deltav = 3 lines observed around 1.6 mum by Hinkle et al. (1984, ApJS, 56, 1). Moreover, the H delta line in emission, which is another signature ofthe presence of shocks, is observed as well in the most extended stars, although with a somewhat narrower profile. This is an indication that the shock is weaker in extended than in compact LPVs, which may also contribute tothe difficulty of detecting line doubling in cool, extended LPVs.
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Documento generato il 26/05/13 alle ore 08:35:44