Issue |
A&A
Volume 670, February 2023
|
|
---|---|---|
Article Number | A72 | |
Number of page(s) | 6 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/202245568 | |
Published online | 07 February 2023 |
HD 213258: A new rapidly oscillating, super slowly rotating, strongly magnetic Ap star in a spectroscopic binary
1
European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
e-mail: gmathys@eso.org
2
Département de Physique et d’Astronomie, Université de Moncton, Moncton, E1A 3E9 NB, Canada
3
Institut de Physique, Laboratoire d’Astrophysique, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
Received:
28
November
2022
Accepted:
21
December
2022
We report on HD 213258, an Ap star that we recently identified as presenting a unique combination of rare, remarkable properties. Our study of this star is based on ESPaDOnS Stokes I and V data obtained at seven epochs spanning a time interval slightly shorter than 2 yr, on TESS data, and on radial velocity measurements from the CORAVEL data base. We confirm that HD 213258, which was originally suspected to be an F str λ 4077 star, is definitely an Ap star. We found that, in its spectrum, the Fe IIλ 6149.2 Å line is resolved into its two magnetically split components. The mean magnetic field modulus of HD 213258, ⟨B⟩∼3.8 kG, which we determined from this splitting, does not show significant variations over ∼2 yr. Comparing our mean longitudinal field determinations with a couple of measurements from the literature, we show that the stellar rotation period is likely of the order of 50 yr, with a reversal of the field polarity. Moreover, HD 213258 is a rapidly oscillating Ap (roAp) star, in which high overtone pulsations with a period of 7.58 min are detected. Finally, we confirm that HD 213258 has a mean radial velocity exceeding (in absolute value) that of at least 99% of Ap stars. The radial velocity shows low amplitude variations, which suggests that the star is a single-line spectroscopic binary. It is also a known astrometric binary. While its orbital elements remain to be determined, its orbital period is likely one of the shortest known for a binary roAp star. Its secondary is close to the borderline between stellar and substellar objects. There is a significant probability that it is a brown dwarf. The pair represents a combination that has never been observed before. Most of the above-mentioned properties taken in isolation are only observed in a small fraction of the whole population of Ap stars. Thus, the probability that a single star possesses all of them is extremely low. This makes HD 213258 an exceptionally interesting object that deserves to be studied in detail in the future.
Key words: stars: individual: HD 213258 / stars: chemically peculiar / stars: magnetic field / stars: rotation / stars: oscillations
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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