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Stellar Activity at the End of the Main Sequence: GHRS Observations of the M8 Ve Star VB 10We present Goddard High Resolution Spectrograph observations of the M8 Ve star VB 10 (equal to G1 752B), located very near the end of the stellar main sequence, and its dM3.5 binary companion G1 752A. These coeval stars provide a test bed for studying whether the outer atmospheres of stars respond to changes in internal structure as stars become fully convective near mass 0.3 solar mass (about spectral type M5), where the nature of the stellar magnetic dynamo presumably changes, and near the transition from red to brown dwarfs near mass 0.08 solar mass (about spectral type M9), when hydrogen burning ceases at the end of the main sequence. We obtain upper limits for the quiescent emission of VB 10 but observe a transition region spectrum during a large flare, which indicates that some type of magnetic dynamo must be present. Two indirect lines of evidence-scaling from the observed X-ray emission and scaling from a time-resolved flare on AD Leo suggest that the fraction of the stellar bolometric luminosity that heats the transition region of VB 10 outside of obvious flares is comparable to, or larger than, that for G1 752A. This suggests an increase in the magnetic heating rates, as measured by L(sub line)/L(sub bol) ratios, across the radiative/convective core boundary and as stars approach the red/brown dwarf boundary. These results provide new constraints for dynamo models and models of coronal and transition-region heating in late-type stars.
Document ID
19970022983
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.1086/176614
Authors
Linsky, Jeffrey L. (National Inst. of Standards and Technology Boulder, CO United States)
Wood, Brian E. (Joint Inst. for Lab. Astrophysics Boulder, CO United States)
Brown, Alexander (Joint Inst. for Lab. Astrophysics Boulder, CO United States)
Giampapa, Mark S. (National Optical Astronomy Observatories Tucson, AZ United States)
Ambruster, Carol (Villanova Univ. PA United States)
Date Acquired
September 6, 2013
Publication Date
December 20, 1995
Publication Information
Publication: The Astrophysical Journal
Publisher: The American Astronomical Society
Volume: 455
Subject Category
Astrophysics
Report/Patent Number
NAS 1.26:204893
NASA-CR-204893
Report Number: NAS 1.26:204893
Report Number: NASA-CR-204893
Accession Number
97N23394
Funding Number(s)
CONTRACT_GRANT: NAS5-26555
CONTRACT_GRANT: NASA Order S-56500-D
Distribution Limits
Public
Copyright
Public Use Permitted.

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