Long-period variables in the Magellanic Clouds: Supergiants, AGB stars, supernova precursors, planetary nebula precursors, and enrichment of the interstellar medium

Journal Article · Thu Sep 01 04:00:00 EDT 1983 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/161265· OSTI ID:5542875

Wood, P; Bessell, M S; Fox, M W

Infrared JHK magnitudes and low-dispersion red spectra have been obtained for 90 long-period variables (LPVs) in the Small and Large Magellanic Clouds. The LPVs fall into two distinct groups, core helium (or carbon) burning supergiants and stars on the asymptotic giant branch (AGB). The supergiants have small pulsation amplitudes in K (<0.25 mag) whereas the AGB stars have typical amplitudes of 0.5--1.0 mag. The AGB stars extend in luminosity right up to the AGB limit (M/sub bol/roughly-equal-7.1), this being the first time that stars on the upper AGB have been identified. The existence of stars at the AGB limit provides direct evidence that the more massive AGB stars produce supernovae. Carbon star LPVs are confined to luminosities fainter than M/sub bol/approx.-6, in agreement with other studies of carbon stars in the Magellanic Clouds. Many of the oxygen-rich AGB stars show enhanced oxide bands of the s-process element Zr, indicating that dredge-up of material at helium shell flashes is occurring in these stars as well as in the carbon stars. We interpret the absence of carbon stars among the upper AGB stars as being due to CNO cycling of dredged up carbon to nitrogen during quiescent AGB evolution; thus the AGB stars are sources of primary nitrogen, as well as of carbon and s-process elements. From the theories of stellar pulsation and evolution, we deduce that stars with initial masses > or approx. =5 M/sub sun/ produce supernovae while less massive stars produce planetary nebulae with nebula masses from approx.0.1--2.1 M/sub sun/. The coreburning red supergiants appear highly overluminous for their pulsation mass, indicating that they have lost up to half their mass since the main-sequence phase.

• Research Organization: Mount Stromlo and Siding Spring Observatories, Research School of Physical Sciences, Australian National University
• OSTI ID: 5542875
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 272:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics &amp; Cosmology-- Stars &amp; Quasi-Stellar
Radio &amp; X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CARBON STARS
ERUPTIVE VARIABLE STARS
GALAXIES
GIANT STARS
INFRARED SPECTRA
INTERSTELLAR SPACE
MAGELLANIC CLOUDS
MAIN SEQUENCE STARS
NUCLEOSYNTHESIS
PHOTOMETRY
PULSATIONS
SPACE
SPECTRA
STAR EVOLUTION
STARS
SUPERGIANT STARS
SUPERNOVAE
VARIABLE STARS