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.
The Planck mission may, in principle, have a large impact on stellar studies because it will cover a very important observational band. For various classes of stellar objects continuum observations at millimetric and submillimetric wavelengths would be very fruitful, because they provide essential clues to understand the physics of these stars and constitute a powerful addition to current studies, which are carried out mostly at centimetric wavelengths. However, the high level of galactic confusion together with the intrinsic low flux density make the detection of such kinds of source quite challenging. In this paper we present first results of a feasibility study aimed to investigate on the possibility to observe with Planck evolved galactic objects belonging to a evolutionary phase that strongly influences the chemical evolution of the Galaxy CMB and Physics of the Early Universe
Context. Chemically peculiar stars are upper main sequence stars that show anomalies in their optical spectra. These anomalies suggest peculiar chemical abundances of certain elements. Some chemically peculiar stars possess strong magnetic fields. Electrons originating from the ionising stellar wind travel in the magnetosphere of the star and become the source of non-thermal radio and X-ray emission. Several chemically peculiar radio stars have been detected at GHz frequencies. Aims. We used the Low-Frequency Array (LOFAR) to search for radio emission from chemically peculiar stars to constrain their emission in the frequency band 120 − 168 MHz. We aimed to use LOFAR observations to test the models for radio emission of chemically peculiar stars. Methods. We performed a targeted search of known chemically peculiar stars in the fields of the LOFAR Two Metre Survey (LoTSS) Data Release 2 in Stokes I and V. We matched positions of radio sources in the LoTSS-DR2 catalogue with positions of chemically peculiar stars. Results. We report non-thermal emission at 120 − 168 MHz from two chemically peculiar stars in Stokes I, BP Boo, and α 2 CVn. The ensuing incidence rate at these frequencies is significantly lower than for higher frequencies. This results from the turnover at low frequencies which was predicted from the theory of radio emission from chemically peculiar stars. BP Boo is detected for the first time at radio wavelengths, while α 2 CVn had already been detected at higher frequencies. The upper limit of V/I indicates a level of circular polarisation significantly below 60%. We combined data obtained at different frequencies to derive the radio spectrum of α 2 CVn. The spectrum is nearly flat beyond turnover at low frequencies. We modelled radio emission for a large magnetosphere and small local magnetic field strength. The amplitude of variation in radio emission with the rotational phase of the system decreases at low frequencies.
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