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New insights into nonradiative heating in late a star chromospheres
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Walter, Frederick M. Linsky, Jeffrey L. Matthews, Lynn D. |
| Copyright Year | 1995 |
| Description | Using 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. |
| File Size | 1102732 |
| Page Count | 12 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_19960010536 |
| Archival Resource Key | ark:/13960/t7kq2xs3x |
| Language | English |
| Publisher Date | 1995-07-01 |
| Access Restriction | Open |
| Subject Keyword | Astrophysics Stellar Spectra High Temperature Plasmas Chromosphere Magnetic Variations Ultraviolet Spectra Stellar Evolution Stellar Models Photosphere Stellar Atmospheres Stellar Temperature Spectrographs A Stars Late Stars Stellar Physics Line Spectra F Stars Plasma Heating Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Article |
