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New insights into nonradiative heating in late A star chromospheresUsing new and archival spectra from the Goddard High Resolution Spectrograph, we have searched for evidence of chromospheric and transition region emission in six stars of mid to late A spectral type. Two of the stars, alpha Aq1 (A7 IV-V) and alpha Cep (A7 IV-V), show emission in the C II 1335 A doublet, confirming the presence of hot plasma with temperatures comparable to that of the solar transition region. Using radiative equilibrium photospheric models, we estimate the net surface fluxes in the CII emission line to be 9.4 x 10(exp 4) ergs/sq cm/s for alpha Aq1 and 6.5 x 10(exp 4)ergs/sq cm/s for alpha Cep. These are comparable to fluxes observed in stars as hot as approximately 8000 K (B-V = 0.22). We find no evidence for the blueshifted emission reported by Simon et al. (1994). We estimate the basal flux level to be about 30% of that seen in early F stars, and that the bulk of the emission is not basal in origin. We conclude that the basal flux level drops rapidly for B-V approximately less than 0.3, but that magnetic activity may persist to B-v as small as 0.22.
Document ID
19960010536
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Walter, Frederick M. (State Univ. of New York Stony Brook, NY, United States)
Matthews, Lynn D. (State Univ. of New York Stony Brook, NY, United States)
Linsky, Jeffrey L. (Joint Inst. for Lab. Astrophysics Boulder, CO., United States)
Date Acquired
September 6, 2013
Publication Date
July 1, 1995
Subject Category
Astrophysics
Report/Patent Number
NASA-CR-200001
NIPS-96-07106
NAS 1.26:200001
Accession Number
96N17702
Funding Number(s)
CONTRACT_GRANT: NAG5-1962
Distribution Limits
Public
Copyright
Public Use Permitted.

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