Digging in the coronal graveyard - A Rosat observation of the red giant Arcturus

Journal Article · Thu Aug 01 04:00:00 EDT 1991 · Astrophysical Journal; (United States)

DOI:https://doi.org/10.1086/186099· OSTI ID:5184767

Ayres, T R; Fleming, T A; Schmitt, J H.M.M. ^[1]

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1. Colorado, University, Boulder (United States) Max-Planck-Institut fuer Extraterrestrische Physik, Garching (Federal Republic of Germany)

A deep exposure of the bright star Arcturus (Alpha Bootis: K1 III) with the Roentgensatellit (Rosat) failed to detect soft X-ray emission from the archetype 'noncoronal' red giant. The 3-sigma upper limit in the energy band 0.1-2.4 keV corresponds to an X-ray luminosity of less than 3 x 10 to the 25th erg/s, equivalent to a coronal surface flux density of less than 0.0001 solar. The nondetection safely eliminates coronal irradiation as a possible mechanism to produce the highly variable He I 10830 feature and emphasizes the sharp decline in solarlike coronal activity that accompanies the evolution of low-mass single stars away from the main sequence. While the most conspicuous object in the Rosat field of view was not visible in X-rays, at least one fainter star is among the about 60 sources recorded: the Sigma Sct variable CN Boo, an A8 giant in the UMa Stream. 28 refs.

• OSTI ID: 5184767
• Journal Information: Astrophysical Journal; (United States), Journal Name: Astrophysical Journal; (United States) Vol. 376; ISSN ASJOA; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
DETECTION
DIAGRAMS
ELECTROMAGNETIC RADIATION
GIANT STARS
HERTZSPRUNG-RUSSELL DIAGRAM
IONIZING RADIATIONS
LIMITING VALUES
LUMINOSITY
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
RED GIANT STARS
SOFT X RADIATION
STARS
STELLAR ATMOSPHERES
STELLAR CORONAE
X RADIATION