A Closer Look at the Alpha Persei Coronal Conundrum
- 27 February 2017
- journal article
- research article
- Published by American Astronomical Society in The Astrophysical Journal
- Vol. 837 (1), 14
- https://doi.org/10.3847/1538-4357/837/1/14
Abstract
A ROSAT survey of the Alpha Per open cluster in 1993 detected its brightest star, the mid-F supergiant α Persei: the X-ray luminosity and spectral hardness were similar to coronally active late-type dwarf members. Later, in 2010, a Hubble Cosmic Origins Spectrograph SNAPshot of α Per found the far-ultraviolet (FUV) coronal-proxy Si iv unexpectedly weak. This, and a suspicious offset of the ROSAT source, suggested that a late-type companion might be responsible for the X-rays. Recently, a multifaceted program tested that premise. Ground-based optical coronography and near-UV imaging with Hubble Space Telescope (HST) Wide-Field Camera 3 searched for any close-in faint candidate coronal objects, but without success. Then, a Chandra pointing found the X-ray source single and coincident with the bright star. Significantly, the Si iv emissions of α Per, in a deeper FUV spectrum collected by the HST Cosmic Origin Spectrograph as part of the joint program, are aligned well with chromospheric atomic oxygen (which must be intrinsic to the luminous star), within the context of cooler late-F and early-G supergiants, including Cepheid variables. This pointed to the X-rays as the fundamental anomaly. The overluminous X-rays still support the case for a hyperactive dwarf secondary, albeit now spatially unresolved. However, an alternative is that α Per represents a novel class of coronal source. Resolving the first possibility now has become more difficult, because the easy solution—a well-separated companion—has been eliminated. Testing the other possibility will require a broader high-energy census of the early-F supergiants.This publication has 50 references indexed in Scilit:
- Supersaturation and activity-rotation relation in PMS stars: the young cluster h PerseiAstronomy & Astrophysics, 2016
- THE FLARE-ONA OF EK DRACONISThe Astronomical Journal, 2015
- THE FAR-ULTRAVIOLET UPS AND DOWNS OF ALPHA CENTAURIThe Astronomical Journal, 2015
- THE CURIOUS CASE OF THE ALPHA PERSEI CORONA: A DWARF IN SUPERGIANT'S CLOTHING?The Astrophysical Journal, 2011
- Chandra Observations of Coronal Emission from the Early G Supergiants α and β AquariiThe Astrophysical Journal, 2005
- X‐Rays from Hybrid StarsThe Astrophysical Journal, 2005
- Positional Uncertainties and Detection Limits ofROSATX‐Ray SourcesThe Astrophysical Journal, 2004
- Buried Alive in the Coronal GraveyardThe Astrophysical Journal, 2003
- Space Telescope Imaging Spectrograph Survey of Far‐Ultraviolet Coronal Forbidden Lines in Late‐Type StarsThe Astrophysical Journal, 2003
- Sleuthing the Dynamo. II.Hubble Space TelescopeGoddard High Resolution Spectrograph Observations of Solar‐Type Dwarfs in Young Galactic ClustersThe Astrophysical Journal, 1999