The High-Energy Environs of the Anomalous Coronal Source Alpha Persei
Abstract
This is a joint Chandra/HST program to investigate the F-type supergiant Alpha Persei, brightest star in the young (50 Myr) open cluster that bears its name. The central question is whether the bright ROSAT X-ray source identified as Alpha Per truly is associated with the supergiant (which would make it quite an anomalous object in its class), or instead is due to a low-mass coronally active cluster member in the immediate vicinity of Alpha Per, but which has escaped detection owing to the glare of the very bright star nearby. In fact, the ROSAT LX is similar to that of active G dwarfs in the young cluster, and the X-ray source appears to be shifted slightly from the optical position of the bright star. Furthermore, a brief COS SNAPshot FUV spectrum of Alpha Per appeared to lack significant high-energy features (e.g., Si IV 140 nm) expected from a powerful X-ray source, although the bright FUV photospheric continuum of the warm supergiant was a major source of interference. The observational objectives of the HST part of the program are: (1) image the field with WFC3 to pin down positions of any faint, low-mass stars in the immediate vicinity of the supergiant (chromospherically active dwarfs have a large contrast advantage, for example, at Mg II 280 nm); and (2) take a deeper COS FUV spectrum than was possible in the Cycle 17 SNAPshot program, including the important Lyman Alpha region, which was forbidden in the SNAP program owing to safety issues. We now know that the Lyman Alpha observation would be safe, and access to the G130M side-B spectrum would capture key hot lines like N V 124 nm, where the FUV continuum is weaker, to help characterize the activity levels of the iconic supergiant.
- Publication:
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HST Proposal
- Pub Date:
- October 2015
- Bibcode:
- 2015hst..prop14349A