Issue |
A&A
Volume 674, June 2023
|
|
---|---|---|
Article Number | A162 | |
Number of page(s) | 10 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361/202245241 | |
Published online | 19 June 2023 |
Discovery of an extended G giant chromosphere in the 2019 eclipse of γ Per
1
Sterrewacht Leiden,
Niels Bohrweg 2,
NL-2333CA
Leiden, Netherlands
e-mail: diamant@strw.leidenuniv.nl
2
Departamento de Astronomía, Universidad de Guanajuato,
Callejón de Jalisco s/n Col. Valenciana,
Guanajuato
36023, Mexico
3
Department of Space, Earth and Environment, Astronomy and Plasma Physics, Onsala Space Observatory, Chalmers University of Technology,
439 92
Onsala, Sweden
4
Hamburger Sternwarte, Universität Hamburg,
Gojenbergsweg 112,
21029
Hamburg, Germany
Received:
18
October
2022
Accepted:
25
March
2023
The November 2019 eclipse of γ Per was a rare opportunity to seek evidence for a chromosphere of the G8 giant, hitherto suspected but not detected. Twenty-nine years after the only other observed eclipse, we aim to find chromospheric absorption in the strong Ca II H&K lines, and to determine its column densities and scale height. Using the Telescopio Internacional de Guanajuato Robótico-Espectroscópico (TIGRE) in Guanajuato (central Mexico) before, during and after the 8 days of total eclipse, we obtained good S/N spectra of the G8 giant alone and composite spectra of the partial phases, near eclipse and far from eclipse. In the near UV of the Ca II H&K and Hϵ lines, the G giant spectrum that was adequately scaled was subtracted from the composite spectra in partial phases, near and far from eclipse, to obtain the A3 companion spectra with and without traces of chromospheric absorption. In addition, we used PHOENIX full non-local thermodynamic equilibrium model atmospheres on the blue A star spectrum, iSpec spectral analysis of the red G giant spectrum, and evolution tracks to study both components of γ Per. For the first time, we present evidence for this rare type of a not very extended G giant chromosphere, reaching out about half of an A-star radius (~1.5 Gm) with a scale height of only 0.17 Gm. By its location in the Hertzsprung-Russell diagram, the γ Per G8 giant is very close to the onset of more extended chromospheres. Furthermore, we show that this giant has a rather inactive chromosphere, and a recent 5 ksec XMM pointing reveals only a very faint, low-energy corona. While the γ Per primary has a mass of ~3.6 M⊙, and its A3 companion has one of ~2.4 M⊙, the latter is too cool (8400 ± 300 K), which is too evolved on the main sequence to be the same age as the primary. The high eccentricity of the 5329.08 days long-period orbit may therefore be reminiscent of a rare capture event. Using the eclipse method, we resolve a pivotal case of a G giant chromosphere, which seems to represent a low-gravity analogue of the inactive Sun. A systematic change of giant chromospheric extent by Hertzsprung-Russell diagram position is confirmed. Compared to the solar chromosphere, the density scale height increases with gravity by ∝ ɡ−1.5.
Key words: stars: chromospheres / binaries: eclipsing / supergiants / binaries: spectroscopic
© 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.
This article is published in open access under the Subscribe to Open model. Subscribe to A&A to support open access publication.
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.