Very active chromosphere stars and the age, chromosphere activity relation

Journal Article · Wed Nov 01 00:00:00 EST 1989 · Astronomical Journal; (USA)

DOI:https://doi.org/10.1086/115263· OSTI ID:7242542

Eggen, O J ^[1]

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1. Observatorio Interamericano de Cerro Tololo, La Serena (Chile)

The wide range of objects in stellar superclusters and groups near the sun is used in an attempt to define normal stellar chromospheric behavior, with which 'very active chromosphere' (VAC) stars can be isolated. Two chromosphere signatures, soft X-ray flux, and Mg II h and k line flux, are discussed. The X-ray flux is of limited use in this regard because of a wide range of variation with time, although the maximum values are well defined for stars of a given age. The VAC stars, which have an excessive X-ray flux, also have an excessive bolometric flux. The ratio of the Mg II h and k (and Ca II H and K) line emission and the total bolometric emission, R(hk) decreases with bolometric luminosity. The rate of decrease in log R(hk), 0.175 (35.00 - log L sub BOL), is not very dependent on stellar age, but the zero point at log L sub BOL = 35.00 decades varies from log R(hk) = -4.45 decades for main-sequence stars in the Pleiades supercluster (200-300 million yr) to - 4.91 decades for those in the HR 1614 group (8 billion yr). The age dependence of R(hk) is clearly demonstrated not only by the supercluster and group stars but by the 'Mount Wilson sample' of objects that have been observed in Ca II H and K for over 15 years (e.g., Noyes et al., 1984). Several determinations (e.g., Soderblom and Clements, 1987) have established a linear relation between R(hk) and R(HK). Some 50 stars in the Mount Wilson sample have well-established luminosities and space motions (e.g., Eggen, 1989) that allow the separation of young and old disk stars in velocity space (Eggen, 1989). The young disk stars all have values of R(hk) that identify them as having ages less than the youngest Hyades supercluster members (about 600 million yr). 46 refs.

• OSTI ID: 7242542
• Journal Information: Astronomical Journal; (USA), Vol. 98; ISSN 0004-6256
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
STELLAR CHROMOSPHERES
STELLAR ACTIVITY
AGE ESTIMATION
BOLOMETERS
COSMIC X-RAY SOURCES
EMISSION SPECTRA
LUMINOSITY
MAIN SEQUENCE STARS
SOFT X RADIATION
STAR CLUSTERS
ATMOSPHERES
COSMIC RAY SOURCES
ELECTROMAGNETIC RADIATION
IONIZING RADIATIONS
MEASURING INSTRUMENTS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
SPECTRA
STARS
STELLAR ATMOSPHERES
X RADIATION
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
Radio & X-Ray Sources