Chromospheric Mg I emission lines of pre-main-sequence stars

被引:1
|
作者
Yamashita, Mai [1 ]
Itoh, Yoichi [2 ]
Takagi, Yuhei [3 ]
机构
[1] Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, 3-1-1 Yoshinodai,Chuo Ku, Sagamihara, Kanagawa 2525210, Japan
[2] Univ Hyogo, Ctr Astron, Nishi Harima Astron Observ, 407-2 Nishigaichi, Sayo, Hyogo 6795313, Japan
[3] Natl Astron Observ Japan, Subaru Telescope, 650 North Aohoku Pl, Hilo, HI 96720 USA
基金
日本学术振兴会;
关键词
accretion; accretion disks; techniques: spectroscopic; stars: chromospheres; stars: low-mass; stars: pre-main sequence; stars: rotation; METAL-POOR STARS; MILKY-WAY DISC; CHEMICAL ABUNDANCES; SOLAR VICINITY; ELEMENTAL ABUNDANCE; TIME EVOLUTION; GALACTIC DISK; FAINT STARS; BIRTH RADII; THICK DISK;
D O I
10.1051/0004-6361/202452025
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
ontext. To reveal details of the internal structure, the relationship between chromospheric activity and the Rossby number has been extensively examined for main-sequence stars. For active pre-main-sequence (PMS) stars, it is suggested that the level of activity be assessed using optically thin emission lines, such as Mg I. Aims. We aim to detect Mg I chromospheric emission lines from PMS stars and to determine whether the chromosphere is activated by the dynamo process or by mass accretion from protoplanetary disks. Methods. We analyzed high-resolution optical spectra of 64 PMS stars obtained with the Very Large Telescope (VLT)/X-shooter and UVES and examined the infrared Ca II (8542 angstrom) and Mg I (8807 angstrom) emission lines. To detect the weak chromospheric emission lines, we determined the atmospheric parameters (T-eff and log ) and the degree of veiling of the PMS stars by comparing the observed spectra with photospheric model spectra. Results. After subtracting the photospheric model spectrum from the PMS spectrum, we detected Ca II and Mg I as emission lines. The strengths of the Mg I emission lines in PMS stars with no veiling are comparable to those in zero-age main-sequence (ZAMS) stars if both types of stars have similar Rossby numbers. The Mg I emission lines in these PMS stars are thought to be formed by a dynamo process similar to that in ZAMS stars. In contrast, the Mg I emission lines in PMS stars with veiling are stronger than those in ZAMS stars. These objects are believed to have protoplanetary disks, where mass accretion generates shocks near the photosphere, heating the chromosphere. Conclusions. The chromosphere of PMS stars is activated not only by the dynamo process but also by mass accretion.
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页数:17
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