Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006apj...636..426p&link_type=abstract
The Astrophysical Journal, Volume 636, Issue 1, pp. 426-431.
Astronomy and Astrophysics
Astronomy
11
Stars: Activity, Stars: Coronae, Stars: Early-Type, Stars: Individual: Name: Vega, Stars: Individual: Constellation Name: Α Lyrae, X-Rays: Stars
Scientific paper
We present X-ray observations of Vega obtained with the Chandra High Resolution Camera and Advanced CCD Imaging Spectrometer. After a total of 29 ks of observation with Chandra, X-rays from Vega remain undetected. We derive upper limits to the X-ray luminosity of Vega as a function of temperature over the range of 105-107 K and find a 99.7% upper limit as low as ~2×1025 ergs s-1 at T=106.2 K. We also compare these new deeper observations with the limit derived from a reanalysis of ROSAT PSPC data. Our X-ray luminosity limit for Vega is still greater than predictions of post-Herbig Ae phase X-rays from the shear dynamo model proposed by Tout & Pringle for a Vega age of 350 Myr. If the age of Vega is closer to 100 Myr, as suggested by some indicators, our X-ray limit is then similar to Tout-Pringle model predictions. Current X-ray observations of Vega are therefore unable to discriminate between different scenarios explaining the X-ray activity of the convectively stable Herbig Ae/Be stars. Further progress is more likely to be achieved through X-ray observations of younger main-sequence early-type A stars, whose conjectured residual post-Herbig Ae phase X-ray activity would be significantly higher.
Drake Jeremy J.
Kashyap Vinay L.
Pease Deron O.
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