Calcium chloride in cool stars

The SC and CS stars are thermal-pulsing AGB stars with C/O ratio close to unity. Within this small group, the Mira variable BH Cru recently evolved from spectral type SC (showing ZrO bands) to CS (showing weak C2). Wavelet analysis shows that the spectral evolution was accompanied by a dramatic period increase, from 420 to 540 days, indicating an expanding radius. The pulsation amplitude also increased. Old photographic plates are used to establish that the period before 1940 was around 490 days. Chemical models indicate that the spectral changes were caused by a decrease in stellar temperature, related to the increasing radius. There is no evidence for a change in C/O ratio. The evolution in BH Cru is unlikely to be related to an on-going thermal pulse. Periods of the other SC and CS stars, including nine new periods, are determined. A second SC star, LX Cyg, also shows evidence for a large increase in period, and one further star shows a period inconsistent with a previous determination. Mira periods may be intrinsically unstable for C/O ~ 1; possibly because of a feedback between the molecular opacities, pulsation amplitude, and period. LRS spectra of 6 SC stars suggest a feature at wavelength > 15 micron, which resembles one recently attributed to the iron-sulfide troilite. Chemical models predict a large abundance of FeS in SC stars, in agreement with the proposed association.Comment: 14 pages, 20 figures. MNRAS, 2004, accepted for publication. Janet Mattei, one of the authors, died on 22 March, 2004. This paper is dedicated to her memor

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“…Both these stars are long‐period Miras. Clegg & Wyckoff (1977) show that CaCl is favoured by high‐density environments.…”

Section: Equilibrium Chemistry: Zro and C2mentioning

confidence: 89%

Period and chemical evolution of SC stars

Zijlstra

Bedding

Markwick

et al. 2004

Monthly Notices of the Royal Astronomical Society

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“…In particular a laboratory search for the rotational spectra of many astrophysically interesting halides has now become feasible. 16 The bulk of their spectra are found in the millimeter and submillimeter wave region.…”

Section: Discussionmentioning

confidence: 99%

Millimeter wave spectrum of barium sulfide in a low-pressure flame. Current millimeter wave measurements of high-temperature species

Helms¹,

Winnewisser²,

Winnewisser³

1980

J. Phys. Chem.

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“…Pressures in the condensation region are estimated to be I to I03 dyne/cm2 (23), so that condensation v.UI uuc 'Ne/ X 'Ne Fig. 3.…”

mentioning

confidence: 99%

Noble Gases in the Murchison Meteorite: Possible Relics of s -Process Nucleosynthesis

Srinivasan

Anders

1978

Science

147

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The Murchison carbonaceous chondrite contains a new type of xenon component, enriched by up to 50 percent in five of the nine stable xenon isotopes, mass numbers 128 to 132. This component, comprising 5 x 10(-5) of the total xenon in the meteorite, is released at 1200 degrees to 1600 degrees C from a severely etched mineral fraction, and probably resides in some refractory mineral. Krypton shows a similar but smaller enrichment in the isotopes 80 and 82. Neon and helium released in the same interval also are quite anomalous, being highly enriched in the isotopes 22 and 3. These patterns are strongly suggestive of three nuclear processes believed to take place in red giants: the s process (neutron capture on a slow time scale), helium burning, and hydrogen shell burning. If this interpretation is correct, then primitive meteorites contain yet another kind of alien, presolar material: dust grains ejected from red giants.

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Calcium chloride in cool stars

Cited by 11 publications

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Period and chemical evolution of SC stars

Period and chemical evolution of SC stars

Millimeter wave spectrum of barium sulfide in a low-pressure flame. Current millimeter wave measurements of high-temperature species

Noble Gases in the Murchison Meteorite: Possible Relics of s -Process Nucleosynthesis

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