The Ages of Optically Bright Subclusters in the Serpens Star-forming Region

Creators: Zhou, Xingyu; Herczeg, Gregory J.; Liu, Yao; Fang, Min; Kuhn, Michael

Abstract

The Serpens Molecular Cloud is one of the most active star-forming regions within 500 pc, with over 1000 young stellar objects (YSOs) at different evolutionary stages. The ages of the member stars inform us about the star formation history of the cloud. In this paper, we develop a spectral energy distribution (SED) fitting method for nearby evolved (diskless) young stars from members of the Pleiades to estimate their ages, with a temperature scale adopted from APOGEE spectra. When compared with literature temperatures of selected YSOs in Orion, the SED fits to cool (<5000 K) stars have temperatures that differ by an average of ≲50 K and have a scatter of ∼210 K for both disk-hosting and diskless stars. We then apply this method to YSOs in the Serpens Molecular Cloud to estimate ages of optical members previously identified from Gaia DR2 astrometry data. The optical members in Serpens are concentrated in different subgroups with ages from ∼4 to ∼22 Myr; the youngest clusters, W40 and Serpens South, are dusty regions that lack enough optical members to be included in this analysis. These ages establish that the Serpens Molecular Cloud has been forming stars for much longer than has been inferred from infrared surveys.

Additional Information

© 2022. 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. Received 2021 August 12; revised 2022 May 5; accepted 2022 May 9; published 2022 July 5. We thank the anonymous referee for the helpful comments and suggestions that helped to significantly improve the analysis and the clarity of the paper. We thank Marina Kounkel for discussion of APOGEE temperature and ages of Serpens and Kevin Covey for discussion of temperature scales. We thank Jennifer Hatchell, Carlo Manara, Doug Johnstone, Michael Dunham, Anupam Bhardwaj, Jessy Jose, and Zhen Yuan for their effort in our initial paper that developed the sample used here. X.Y.Z. and G.J.H. are supported by general grants 12173003 and 11773002 awarded by the Natural Science Foundation of China. Y.L. acknowledges financial support by the Natural Science Foundation of China (grant No. 11973090) and by the Natural Science Foundation of Jiangsu Province of China (grant No. BK20181513). This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. We acknowledge with thanks the variable star observations from the AAVSO International Database contributed by observers worldwide and used in this research. This research has made use of NASA's Astrophysics Data System. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. This research has made use of the Spanish Virtual Observatory (http://svo.cab.inta-csic.es) supported by the Spanish MICINN/FEDER through grant AyA2017-84089. This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013).

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