The High Chromospheres of the Late A Stars

Details The High Chromospheres of the Late A Stars The High Chromospheres of the Late A Stars

1997-01-20

arxiv.org/abs/astro-ph/9701132v1

Astronomy and Astrophysics

Astrophysics

LaTex, 12 pages, 3 Postscript figures, uses aaspp4, accepted by ApJ

Scientific paper

10.1086/304251

We report the detection of N V 1239 A transition region emission in HST/GHRS spectra of the A7 V stars, Alpha Aql and Alpha Cep. Our observations provide the first direct evidence of 1-3 x 10^5 K material in the atmospheres of normal A-type stars. For both stars, and for the mid-A--type star Tau3 Eri, we also report the detection of chromospheric emission in the Si III 1206 A line. At a B-V color of 0.16 and an effective temperature of 8200 K, Tau3 Eri becomes the hottest main sequence star known to have a chromosphere and thus an outer convection zone. We see no firm evidence that the Si III line surface fluxes of the A stars are any lower than those of moderately active, solar-type, G and K stars. This contrasts sharply with their coronal X-ray emission, which is >100 times weaker than that of the later-type stars. Given the strength of the N V emission observed here, it now appears unlikely that the X-ray faintness of the A stars is due to their forming very cool, <= 1 MK coronae. An alternative explanation in terms of mass loss in coronal winds remains a possibility, though we conclude from moderate resolution spectra of the Si III lines that such winds, if they exist, do not penetrate into the chromospheric Si III--forming layers of the star, since the profiles of these lines are *not* blueshifted, and may well be redshifted with respect to the star.

Affiliated with

Also associated with

No associations

Rating

The High Chromospheres of the Late A Stars does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with The High Chromospheres of the Late A Stars, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The High Chromospheres of the Late A Stars will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-423807