Browsing by Author "Kounkel, M"
ABYSS. I. Targeting Strategy for the APOGEE and BOSS Young Star Survey in SDSS-V
(ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 2023-05-01) Kounkel, M; Zari, E; Covey, K; Tkachenko, A; [et al.]
The fifth iteration of the Sloan Digital Sky Survey is set to obtain optical and near-infrared spectra of similar to 5 million stars of all ages and masses throughout the Milky Way. As a part of these efforts, APOGEE and BOSS Young Star Survey (ABYSS) will observe similar to 10(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 eight different types of selection criteria that take the position on the H-R diagram, infrared excess, variability, as well as the position in phase space in consideration. The resulting catalog of similar to 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 toward the inner Galaxy and the Galactic center.
Pre-main-sequence Brackett Emitters in the APOGEE DR17 Catalog: Line Strengths and Physical Properties of Accretion Columns
(ASTROPHYSICAL JOURNAL, 2023-02-01) Campbell, H; Khilfeh, E; Covey, KR; Kounkel, M; [et al.]
Very young (t less than or similar to 10 Myr) stars possess strong magnetic fields that channel ionized gas from the interiors of their circumstellar disks to the surface of the star. Upon impacting the stellar surface, the shocked gas recombines and emits hydrogen spectral lines. To characterize the density and temperature of the gas within these accretion streams, we measure equivalent widths of Brackett (Br) 11-20 emission lines detected in 1101 APOGEE spectra of 326 likely pre-main-sequence accretors. For sources with multiple observations, we measure median epoch-to-epoch line strength variations of 10% in Br11 and 20% in Br20. We also fit the measured line ratios to predictions of radiative transfer models by Kwan & Fischer. We find characteristic best-fit electron densities of n ( e ) = 10(11)-10(12) cm(-3), and excitation temperatures that are inversely correlated with electron density (from T similar to 5000 K for n ( e ) similar to 10(12) cm(-3) to T similar to 12,500 K at n ( e ) similar to 10(11) cm(-3)). These physical parameters are in good agreement with predictions from modeling of accretion streams that account for the hydrodynamics and radiative transfer within the accretion stream. We also present a supplementary catalog of line measurements from 9733 spectra of 4255 Brackett emission-line sources in the APOGEE Data Release 17 data set.
Stellar Properties for a Comprehensive Collection of Star-forming Regions in the SDSS APOGEE-2 Survey
(ASTRONOMICAL JOURNAL, 2023-01-01) Román-Zúñiga, CG; Kounkel, M; Hernández, J; Ramírez, KP; [et al.]
The Sloan Digital Sky Survey 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 300fiber H-band (1.55-1.71 mu m) 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 (Teff, log g, [Fe/H], L/L-circle dot, M/M-circle dot, and age) for a sample that is composed of 3360 young stars, of subsolar to supersolar types, in 16 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 Hertzsprung-Russell (log L/L-circle dot 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.