分类： 天文学 >> 天文学 提交时间： 2023-02-19
Carlos G. Román-Zúñiga
Marina Kounkel
Jesús Hernández
Karla Peña Ramírez
Ricardo López-Valdivia
Kevin R. Covey
Amelia M. Stutz
Alexandre Román-López
Hunter Campbell
Eliott Khilfeh
Mauricio Tapia
Guy S. Stringfellow
Juan José Downes
Keivan G. Stassun
Dante Minniti
Amelia Bayo
Jinyoung Serena Kim
Genaro Suárez
Jason Ybarra
José G. Fernández-Trincado
摘要： The Sloan Digital Sky Survey IV (SDSS-IV) APOGEE-2 primary science goal was to observe red giant stars throughout the Galaxy to study its dynamics, morphology, and chemical evolution. The APOGEE instrument, a high-resolution 300 fiber H-band (1.55-1.71 micron) spectrograph, is also ideal to study other stellar populations in the Galaxy, among which are a number of star forming regions and young open clusters. We present the results of the determination of six stellar properties ($T_{eff}$, $\log{g}$, [Fe/H], $L/L_\odot$, $M/M_\odot$, and ages) for a sample that is composed of 3360 young stars, of sub-solar to super-solar types, in sixteen Galactic star formation and young open cluster regions. Those sources were selected by using a clustering method that removes most of the field contamination. Samples were also refined by removing targets affected by various systematic effects of the parameter determination. The final samples are presented in a comprehensive catalog that includes all six estimated parameters. This overview study also includes parameter spatial distribution maps for all regions and Hertzprung-Russell ($L/L_\odot$ vs. $T_{eff}$) diagrams. This study serves as a guide for detailed studies on individual regions, and paves the way for the future studies on the global properties of stars in the pre-main sequence phase of stellar evolution using more robust samples.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Marina Kounkel
Eleonora Zari
Kevin Covey
Andrew Tkachenko
Carlos Román Zúñiga
Keivan Stassun
Amelia M. Stutz
Guy Stringfellow
Alexandre Roman-Lopes
Jesús Hernández
Karla Peña Ramírez
Amelia Bayo
Jinyoung Serena Kim
Lyra Cao
Scott J. Wolk
Juna Kollmeier
Ricardo López-Valdivia
Bárbara Rojas-Ayala
摘要： The fifth iteration of the Sloan Digital Sky Survey (SDSS-V) is set to obtain optical and near-infrared spectra of $\sim$5 million stars of all ages and masses throughout the Milky Way. As a part of these efforts, APOGEE & BOSS Young Star Survey (ABYSS) will observe $\sim10^5$ stars with ages $<$30 Myr that have been selected using a set of homogeneous selection functions that make use of different tracers of youth. The ABYSS targeting strategy we describe in this paper is aimed to provide the largest spectroscopic census of young stars to-date. It consists of 8 different types of selection criteria that take the position on the HR diagram, infrared excess, variability, as well as the position in phase space in consideration. The resulting catalog of $\sim$200,000 sources (of which a half are expected to be observed) provides representative coverage of the young Galaxy, including both nearby diffuse associations as well as more distant massive complexes, reaching towards the inner Galaxy and the Galactic center.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Justyn Campbell-White
Carlo F. Manara
Aurora Sicilia-Aguilar
Antonio Frasca
Louise D. Nielsen
P. Christian Schneider
Brunella Nisini
Amelia Bayo
Barbara Ercolano
Péter Ábrahám
Rik Claes
Min Fang
Davide Fedele
Jorge Filipe Gameiro
Manuele Gangi
Ágnes Kóspál
Karina Maucó
Monika G. Petr-Gotzens
Elisabetta Rigliaco
Connor Robinson
摘要： Absorption features in stellar atmospheres are often used to calibrate photocentric velocities for kinematic analysis of further spectral lines. The Li feature at $\sim$ 6708 {\AA} is commonly used, especially in the case of young stellar objects for which it is one of the strongest absorption lines. However, this is a complex line comprising two isotope fine-structure doublets. We empirically measure the wavelength of this Li feature in a sample of young stars from the PENELLOPE/VLT programme (using X-Shooter, UVES and ESPRESSO data) as well as HARPS data. For 51 targets, we fit 314 individual spectra using the STAR-MELT package, resulting in 241 accurately fitted Li features, given the automated goodness-of-fit threshold. We find the mean air wavelength to be 6707.856 {\AA}, with a standard error of 0.002 {\AA} (0.09 km/s) and a weighted standard deviation of 0.026 {\AA} (1.16 km/s). The observed spread in measured positions spans 0.145 {\AA}, or 6.5 km/s, which is up to a factor of six higher than typically reported velocity errors for high-resolution studies. We also find a correlation between the effective temperature of the star and the wavelength of the central absorption. We discuss how exclusively using this Li feature as a reference for photocentric velocity in young stars could potentially be introducing a systematic positive offset in wavelength to measurements of further spectral lines. If outflow tracing forbidden lines, such as [O i] 6300 {\AA}, are actually more blueshifted than previously thought, this then favours a disk wind as the origin for such emission in young stars.
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