Chandra Observation of Polaris: Census of Low-mass Companions
Abstract
We have observed Cepheid Polaris (α UMi A: F7 Ib [Aa] + F6 V [Ab]) with Chandra ACIS-I for 10 ks. An X-ray source was found at the location of Polaris with log LX = 28.89 erg s-1 (0.3-8 keV) and kT = 0.6 keV. A spectrum this soft could come from either the supergiant or the dwarf, as shown by comparable coronal stars. Two resolved low-mass visual companions, "C" and "D," are not physical members of the system based on the lack of X-rays (indicating an age older than the Cepheid) and inconsistent proper motions. Polaris B is not an X-ray source, consistent with its early F spectral type, and probably does not have a lower mass companion itself. A possible more distant member is identified, and an additional less plausible one. This provides a complete census of companions out to 0.1 pc covering a mass ratio range of an order of magnitude and a ΔV of nearly 15 mag.
Based on observations made with the NASA Chandra Satellite.- Publication:
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The Astronomical Journal
- Pub Date:
- May 2010
- DOI:
- 10.1088/0004-6256/139/5/1968
- Bibcode:
- 2010AJ....139.1968E
- Keywords:
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- binaries: general;
- stars: variables: Cepheids;
- X-rays: stars