Pre-main Sequence Brackett Emitters in the APOGEE DR17 Catalog: Line Strengths and Physical Properties of Accretion Columns

Abstract

Very young (t $\lesssim$ 10 Myrs) stars possess strong magnetic fields that channel ionized gas from the interiors of their circumstellar discs 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$\sim$5000 K for $n_e\sim 10^{12}$ cm${}^{-3}$, to T$\sim$12500 K at $n_e\sim 10^{11}$ cm${}^{-3}$). These physical parameters are in good agreement with predictions from modelling 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 DR17 dataset.

19 pages, 9 figures, accepted to AJ

References in corpus (16)

• The 2.5 m Telescope of the Sloan Digital Sky Survey
• APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE) Spectrographs
• Target Selection for the SDSS-IV APOGEE-2 Survey
• Accretion Outbursts in Self-gravitating Protoplanetary Disks
• IN-SYNC II: Virial Stars from Sub-Virial Cores -- The Velocity Dispersion of Embedded Pre-Main-Sequence Stars in NGC 1333
• Final Targeting Strategy for the SDSS-IV APOGEE-2S Survey
• Final Targeting Strategy for the SDSS-IV APOGEE-2N Survey
• IN-SYNC I: Homogeneous Stellar Parameters from High Resolution APOGEE Spectra for Thousands of Pre-main Sequence Star
• Probing stellar accretion with mid-infrared hydrogen lines
• High-resolution, H band Spectroscopy of Be Stars with SDSS-III/APOGEE: I. New Be Stars, Line Identifications, and Line Profiles
• The Evolution Of The Inner Regions of Protoplanetary Disks
• X-Shooter spectroscopy of young stellar objects - VI - HI line decrements
• Line and continuum radiative transfer modelling of AA Tau
• Hydrogen Emission from Accretion and Outflow in T Tauri Stars
• The G 305 Star-forming Region: II. Irregular variable stars

Cited by in corpus (1)

• ABYSS I: Targeting strategy for APOGEE & BOSS young star survey in SDSS-V