A Study of the Time Variability and Line Profile Variations of Κ Dra

Saad, S. M.; Nouh, M. I.; Shokry, Ahmed; Zead, I.

doi:10.22201/ia.01851101p.2021.57.01.06

Cited by 4 publications

(7 citation statements)

References 18 publications

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“…For several Be stars with short-period binary companions, the variability of the V/R ratio of several Be stars was found to be synchronized with the orbital motion (Zharikov et al 2013;Saad et al 2021). For Achernar, the V/R ratio is quite stable over the two observed Be phases, with most data in the 0.75 − 1 range over the 2006, 2013-2014, and 2018 data sets.…”

Section: Discussionmentioning

confidence: 94%

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The binary system of the spinning-top Be star Achernar

Kervella

Souza

Mérand

et al. 2022

A&A

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Context. Achernar, the closest and brightest classical Be star, presents rotational flattening, gravity darkening, occasional emission lines due to a gaseous disk, and an extended polar wind. It is also a member of a close binary system with an early A-type dwarf companion. Aims. We aim to determine the orbital parameters of the Achernar system and to estimate the physical properties of the components. Methods. We monitored the relative position of Achernar B using a broad range of high angular resolution instruments of the VLT/VLTI (VISIR, NACO, SPHERE, AMBER, PIONIER, GRAVITY, and MATISSE) over a period of 13 years (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019). These astrometric observations are complemented with a series of ≈ 750 optical spectra for the period from 2003 to 2016. Results. We determine that Achernar B orbits the primary Be star on a seven-year period, eccentric orbit (e = 0.7258 ± 0.0015) which brings the two stars within 2 au at periastron. The mass of the Be star is found to be m A = 6.0 ± 0.6 M ⊙ for a secondary mass of m B = 2.0 ± 0.1 M ⊙ (the latter was estimated from modeling). We find a good agreement of the parameters of Achernar A with the evolutionary model of a critically rotating star of 6.4 M ⊙ at an age of 63 Ma. The equatorial plane of the Be star and the orbital plane of the companion exhibit a relative inclination of 30 • . We also identify a resolved comoving low-mass star, which leads us to propose that Achernar is a member of the Tucana-Horologium moving group. Conclusions. The proximity of Achernar makes this star a precious benchmark for stellar evolution models of fast rotators and intermediate mass binaries. Achernar A is presently in a short-lived phase of its evolution following the turn-off, during which its geometrical flattening ratio is the most extreme. Considering the orbital parameters, no significant interaction occurred between the two components, demonstrating that Be stars may form through a direct, single-star evolution path without mass transfer. Since component A will enter the instability strip in a few hundred thousand years, Achernar appears to be a promising progenitor of the Cepheid binary systems.

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Section: Discussionmentioning

confidence: 94%

“…These thirteen lines do not exhibit any significant emission feature over our data set. Many of them are commonly used to derive RV time series of B and Be stars that are spectroscopic binaries (Wade et al 2017;Saad et al 2021;Banyard et al 2022)…”

Section: Discussionmentioning

confidence: 99%

The binary system of the spinning-top Be star Achernar

Kervella

Souza

Mérand

et al. 2022

A&A

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Section: Appendix A: Astrometric and Photometric Datamentioning

confidence: 99%

The binary system of the spinning-top Be star Achernar

Kervella,

Borgniet,

de Souza

et al. 2022

Preprint

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Context. Achernar, the closest and brightest classical Be star, presents rotational flattening, gravity darkening, occasional emission lines due to a gaseous disk, and an extended polar wind. It is also a member of a close binary system with an early A-type dwarf companion. Aims. We aim to determine the orbital parameters of the Achernar system and to estimate the physical properties of the components. Methods. We monitored the relative position of Achernar B using a broad range of high angular resolution instruments of the VLT/VLTI (VISIR, NACO, SPHERE, AMBER, PIONIER, GRAVITY, and MATISSE) over a period of 13 years (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019). These astrometric observations are complemented with a series of ≈ 750 optical spectra for the period from 2003 to 2016. Results. We determine that Achernar B orbits the primary Be star on a seven-year period, eccentric orbit (e = 0.7258 ± 0.0015) which brings the two stars within 2 au at periastron. The mass of the Be star is found to be m A = 6.0 ± 0.6 M for a secondary mass of m B = 2.0 ± 0.1 M (the latter was estimated from modeling). We find a good agreement of the parameters of Achernar A with the evolutionary model of a critically rotating star of 6.4 M at an age of 63 Ma. The equatorial plane of the Be star and the orbital plane of the companion exhibit a relative inclination of 30 • . We also identify a resolved comoving low-mass star, which leads us to propose that Achernar is a member of the Tucana-Horologium moving group. Conclusions. The proximity of Achernar makes this star a precious benchmark for stellar evolution models of fast rotators and intermediate mass binaries. Achernar A is presently in a short-lived phase of its evolution following the turn-off, during which its geometrical flattening ratio is the most extreme. Considering the orbital parameters, no significant interaction occurred between the two components, demonstrating that Be stars may form through a direct, single-star evolution path without mass transfer. Since component A will enter the instability strip in a few hundred thousand years, Achernar appears to be a promising progenitor of the Cepheid binary systems.

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“…The spectral type is B5 IIIe according to Slettebak (1982), B6 IIIpe according to the Bright Star Catalogue (Hoffleit & Jaschek 1991;Hoffleit & Warren 1995), and B6 from the temperature derived by Saad et al (2004). Several SB1 orbital solutions have been published in the last few decades, for instance, by Juza et al (1991) and the latest one by Saad et al (2021), all resulting in a circular orbit with an orbital period of 61.55 days. Spectral lines of the secondary were not identified in optical spectra, nor was a signature of a hot sdO companion found in the FUV from International Ultraviolet Explorer (IUE) spectra (Wang et al 2017).…”

Section: Introductionmentioning

confidence: 99%

“…Object κ Dra is also known for the rapid variability of its photospheric absorption line profiles, which include traveling subfeatures in the observed line profiles, whose origin is uncertain (Hill et al 1991;Saad et al 2021). Not connected to binarity, nonradial pulsations (NRPs) are found in virtually all well-observed Be stars (Rivinius et al 2003;Labadie-Bartz et al 2022) and made spectroscopically visible by the perturbation of the velocity field across the rotationally broadened line profiles.…”

Section: Introductionmentioning

confidence: 99%

Dynamical Masses of the Primary Be Star and Secondary sdB Star in the Single-lined Binary κ Dra (B6 IIIe)

Klement

Baade

Rivinius

et al. 2022

ApJ

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Because many classical Be stars may owe their nature to mass and angular-momentum transfer in a close binary, the present masses, temperatures, and radii of their components are of high interest for comparison to stellar evolution models. Object κ Dra is a 61.5 day single-lined binary with a B6 IIIe primary. With the CHARA Array instruments MIRC/MIRC-X and MYSTIC, we detected the secondary at (approximately photospheric) flux ratios of 1.49% ± 0.10% and 1.63% ± 0.09% in the H and K band, respectively. From a large and diverse optical spectroscopic database, only the radial velocity curve of the Be star could be extracted. However, employing the parallaxes from Hipparcos and Gaia, which agree within their nominal 1σ errors, we could derive the total mass and found component masses of 3.65 ± 0.48 and 0.426 ± 0.043 M ⊙ for the Be star and the companion, respectively. Previous cross-correlation of the observed FUV spectrum with O-type subdwarf (sdO) spectral model templates had not detected a companion belonging to the hot sdO population known from ∼20 earlier-type Be stars. Guided by our full 3D orbital solution, we found a strong cross-correlation signal for a stripped subdwarf B-type companion (FUV flux ratio of 2.3% ± 0.5%), enabling the first firm characterization of such a star and making κ Dra the first mid- to late-type Be star with a directly observed subdwarf companion.

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A Study of the Time Variability and Line Profile Variations of Κ Dra

Cited by 4 publications

References 18 publications

The binary system of the spinning-top Be star Achernar

The binary system of the spinning-top Be star Achernar

The binary system of the spinning-top Be star Achernar

Dynamical Masses of the Primary Be Star and Secondary sdB Star in the Single-lined Binary κ Dra (B6 IIIe)

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