Issue |
A&A
Volume 687, July 2024
|
|
---|---|---|
Article Number | A189 | |
Number of page(s) | 13 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361/202449476 | |
Published online | 12 July 2024 |
Stellar Population Astrophysics (SPA) with the TNG
Measurement of the He I 10 830 Å line in the open cluster Stock 2★
1
Department of Astronomy, Stockholm University, AlbaNova University centre,
Roslagstullsbacken 21,
114 21
Stockholm,
Sweden
e-mail: mingjie.jian@astro.su.se
2
Department of Astronomy, School of Science, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku,
Tokyo
113-0033,
Japan
3
Purple Mountain Observatory, Chinese Academy of Sciences,
Nanjing
210023,
PR China
e-mail: xiaoting.fu@pmo.ac.cn
4
INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna,
via P. Gobetti 93/3,
40129
Bologna,
Italy
5
Department of Physics, University of Rome Tor Vergata,
via della Ricerca Scientifica 1,
00133
Rome,
Italy
6
INAF – Osservatorio Astronomico di Padova,
Vicolo dell’ Osservatorio 5,
35122
Padova,
Italy
7
National Astronomical Observatory of Japan,
2-21-1 Osawa, Mitaka,
Tokyo
181-8588,
Japan
8
INAF – Osservatorio Astrofisico di Arcetri,
Largo E. Fermi 5,
50125
Firenze,
Italy
9
INAF – Osservatorio Astrofisico di Catania,
via S. Sofia 78,
95123
Catania,
Italy
Received:
2
February
2024
Accepted:
13
April
2024
The precise measurement of stellar abundances plays a pivotal role in providing constraints on the chemical evolution of the Galaxy. However, before spectral lines can be employed as reliable abundance indicators, particularly for challenging elements such as helium, they must undergo thorough scrutiny. Galactic open clusters, representing well-defined single stellar populations, offer an ideal setting for unfolding the information stored in the helium spectral line feature. In this study, we characterise the profile and strength of the helium transition at around 10 830 Å (He 10 830) in nine giant stars in the Galactic open cluster Stock 2. To remove the influence of weak blending lines near the helium feature, we calibrated their oscillator strengths (log 𝑔f) by employing corresponding abundances obtained from simultaneously observed optical spectra. Our observations reveal that the He 10 830 in all the targets is observed in absorption, with line strengths categorised into two groups. Three stars exhibit strong absorption, including a discernible secondary component, while the remaining stars exhibit weaker absorption. The lines are in symmetry and align with or near their rest wavelengths, suggesting a stable upper chromosphere without a significant systematic mass motion. We find a correlation between the He 10 830 strength and the Ca II log R′HK index, with a slope similar to that reported in previous studies on dwarf stars. This correlation underscores the necessity of accounting for the stellar chromosphere structure when employing He 10 830 as a probe for the stellar helium abundance. The procedure of measuring the He 10 830 we developed in this study is applicable not only to other Galactic open clusters but also to field stars, and we plan to use it to map the helium abundance across various types of stars in the future.
Key words: line: profiles / stars: atmospheres / stars: chromospheres / stars: fundamental parameters / open clusters and associations: individual: Stock 2
Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos. This study is part of the Large Programme entitled Stellar Population Astrophysics (SPA): this study of the detailed, age-resolved chemistry of the Milky Way disc (A37TAC_31, PI: L. Origlia) started in 2018 and was granted observing time with HARPS-N and GIANO-B echelle spectrographs at the TNG.
© The Authors 2024
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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