BURN OUT OR FADE AWAY? ON THE X-RAY AND MAGNETIC DEATH OF INTERMEDIATE MASS STARS

Drake, Jeremy J.; Braithwaite, Jonathan; Kashyap, Vinay; Günther, H. Moritz; Wright, Nicholas J.

Abstract

The nature of the mechanisms apparently driving X-rays from intermediate mass stars lacking strong convection zones or massive winds remains poorly understood, and the possible role of hidden, lower mass close companions is still unclear. A 20 ks Chandra HRC-I observation of HR 4796A, an 8 Myr old main sequence A0 star devoid of close stellar companions, has been used to search for a signature or remnant of magnetic activity from the Herbig Ae phase. X-rays were not detected and the X-ray luminosity upper limit was LX ⩽ 1.3 × 1027 erg s−1. The result is discussed in the context of various scenarios for generating magnetic activity, including rotational shear and subsurface convection. A dynamo driven by natal differential rotation is unlikely to produce observable X rays, chiefly because of the difficulty in getting the dissipated energy up to the surface of the star. A subsurface convection layer produced by the ionization of helium could host a dynamo that should be effective throughout the main sequence but can only produce X-ray luminosities of the order 1025 erg s−1. This luminosity lies only moderately below the current detection limit for Vega. Our study supports the idea that X-ray production in Herbig Ae/Be stars is linked largely to the accretion process rather than the properties of the underlying star, and that early A stars generally decline in X-ray luminosity at least 100,000 fold in only a few million years.

Citation

Drake, J. J., Braithwaite, J., Kashyap, V., Günther, H. M., & Wright, N. J. (in press). BURN OUT OR FADE AWAY? ON THE X-RAY AND MAGNETIC DEATH OF INTERMEDIATE MASS STARS. Astrophysical Journal, 786(2), 136. https://doi.org/10.1088/0004-637x/786/2/136

• Journal Article Type: Article
• Acceptance Date: Mar 24, 2014
• Online Publication Date: Apr 24, 2014
• Deposit Date: Jun 14, 2023
• Journal: The Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 786
• Issue: 2
• Pages: 136
• DOI: https://doi.org/10.1088/0004-637x/786/2/136
• Keywords: Space and Planetary Science; Astronomy and Astrophysics