Sun-like stars are thought to accrete most of their final mass during the protostellar phase, during which the stellar embryo is surrounded by an infalling dense envelope. We present an analysis of 26 K-band spectra of Class 0 protostars, which are the youngest protostars. Of these, 18 are new observations made with the Keck MOSFIRE instrument. H i Brγ, several H2, and CO Δv = 2 features are detected and analyzed. We detect Brγ emission in 62%, CO overtone emission in 50%, and H2 emission in 90% of sources. The H i and CO emission is associated with accretion, while the H2 lines are consistent with shock excitation indicating jets/outflows. Six objects exhibit photospheric absorption features, with almost no outflow activity and no detection of the accretion-related Brγ emission line. Comparing these results with an archival sample of Class I K-band spectra, we find that the CO and Brγ emission lines are systematically more luminous in Class 0s, suggesting that the accretion is on average more vigorous in the Class 0 phase. Typically associated with the heated inner accretion disk, the much higher detection rate of CO overtone emission in Class 0s indicates also that episodes of high accretion activity are more frequent in Class 0 systems. The kinematics of the Class 0 CO overtone emission suggest either an accretion-heated inner disk or material directly infalling onto the central region. This could point toward an accretion mechanism of different nature in Class 0 systems than the typical picture of magnetospheric accretion.
New Insights on the Accretion Properties of Class 0 Protostars from 2 μm Spectroscopy
Abstract
Copyright and License
© 2024. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
The authors thank Curtis Dewitt, Marion Villenave, Kyle Kaplan, and Sylvie Cabrit for helpful discussions about the analysis of NIR lines and the statistical analysis. The authors also thank Eleonora Fiorellino for sharing the VLT KMOS of their NGC 1333 Class I data with us. We also thank Stefan Laos for providing the Keck MOSFIRE data of protostars observed in 2019. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. V.J.M.L.'s research was supported by an appointment to the NASA Postdoctoral Program at the NASA Ames Research Center, administered by Oak Ridge Associated Universities under contract with NASA. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Facilities
Keck:I (MOSFIRE) - , VLT:Antu -
Software References
Astropy (Astropy Collaboration et al. 2018), Specutils, Lifeline, matplotlib (Hunter 2007), numpy (van der Walt et al. 2011; Harris et al. 2020), panda, scipy (Virtanen et al. 2020), emcee (Foreman-Mackey et al. 2013), Spectres (Carnall 2017) python packages. PypeIt (Prochaska et al. 2020), DS9 (Joye & Mandel 2003), CDS, Vizier, Simbdad softwares
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Additional details
- ISSN
- 1538-4357
- W. M. Keck Foundation
- National Aeronautics and Space Administration
- NASA Postdoctoral Fellowship
- Caltech groups
- Astronomy Department