Chandra X-ray study confirms that the magnetic standard Ap star KQ Vel hosts a neutron star companion
Abstract
Context. KQ Vel is a peculiar A0p star with a strong surface magnetic field of about 7.5 kG. It has a slow rotational period of nearly 8 years. Bailey et al. (A&A, 575, A115) detected a binary companion of uncertain nature and suggested that it might be a neutron star or a black hole.
Aims: We analyze X-ray data obtained by the Chandra telescope to ascertain information about the stellar magnetic field and/or interaction between the star and its companion.
Methods: We confirm previous X-ray detections of KQ Vel with a relatively high X-ray luminosity of 2 × 1030 erg s-1. The X-ray spectra suggest the presence of hot gas at > 20 MK and, possibly, of a nonthermal component. The X-ray light curves are variable, but data with better quality are needed to determine a periodicity, if any.
Results: We interpret the X-ray spectra as a combination of two components: the nonthermal emission arising from the aurora on the A0p star, and the hot thermal plasma filling the extended shell that surrounds the "propelling" neutron star.
Conclusions: We explore various alternatives, but a hybrid model involving the stellar magnetosphere along with a hot shell around the propelling neutron star seems most plausible. We speculate that KQ Vel was originally a triple system and that the Ap star is a merger product. We conclude that KQ Vel is an intermediate-mass binary consisting of a strongly magnetic main-sequence star and a neutron star.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 2020
- DOI:
- 10.1051/0004-6361/202038214
- arXiv:
- arXiv:2007.11591
- Bibcode:
- 2020A&A...641L...8O
- Keywords:
-
- binaries: spectroscopic;
- stars: chemically peculiar;
- stars: individual: KQ Vel;
- X-rays: binaries;
- X-rays: individuals: KQ Vel;
- magnetic fields;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- accepted to A&