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Spectroscopic Confirmation of a Population of Isolated, Intermediate-Mass YSOs

Kuhn, Michael A. and Saber, Ramzi and Povich, Matthew S. and de Souza, Rafael S. and Krone-Martins, Alberto and Ishida, Emille E. O. and Zucker, Catherine and Benjamin, Robert A. and Hillenbrand, Lynne A. and Castro-Ginard, Alfred and Zhou, Xingyu (2022) Spectroscopic Confirmation of a Population of Isolated, Intermediate-Mass YSOs. . (Unpublished)

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Wide-field searches for young stellar objects (YSOs) can place useful constraints on the prevalence of clustered versus distributed star formation. The Spitzer/IRAC Candidate YSO (SPICY) catalog is one of the largest compilations of such objects (~120,000 candidates in the Galactic midplane). Many SPICY candidates are spatially clustered, but, perhaps surprisingly, approximately half the candidates appear spatially distributed. To better characterize this unexpected population and confirm its nature, we obtained Palomar/DBSP spectroscopy for 26 of the optically-bright (G<15 mag) "isolated" YSO candidates. We confirm the YSO classifications of all 26 sources based on their positions on the Hertzsprung-Russell diagram, H and Ca II line-emission from over half the sample, and robust detection of infrared excesses. This implies a contamination rate of <10% for SPICY stars that meet our optical selection criteria. Spectral types range from B4 to K3, with A-type stars most common. Spectral energy distributions, diffuse interstellar bands, and Galactic extinction maps indicate moderate to high extinction. Stellar masses range from ~1 to 7 M_⊙, and the estimated accretion rates, ranging from 3 × 10⁻⁸ to 3 × 10⁻⁷ M_⊙ yr⁻¹, are typical for YSOs in this mass range. The 3D spatial distribution of these stars, based on Gaia astrometry, reveals that the "isolated" YSOs are not evenly distributed in the Solar neighborhood but are concentrated in kpc-scale dusty Galactic structures that also contain the majority of the SPICY YSO clusters. Thus, the processes that produce large Galactic star-forming structures may yield nearly as many distributed as clustered YSOs.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Kuhn, Michael A.0000-0002-0631-7514
Povich, Matthew S.0000-0001-9062-3583
de Souza, Rafael S.0000-0001-7207-4584
Krone-Martins, Alberto0000-0002-2308-6623
Ishida, Emille E. O.0000-0002-0406-076X
Zucker, Catherine0000-0002-2250-730X
Benjamin, Robert A.0000-0002-8109-2642
Castro-Ginard, Alfred0000-0002-9419-3725
Additional Information:R.S. was supported by Caltech’s Freshman Summer Research Institute (FSRI). We would like to thank Christoffer Fremling and Milan Roberson for help with DBSP software, Gregory Herczeg for assistance with observations, Rosine Lallement for access to extinction maps, and Adolfo Carvalho for valuable discussions about DIBs. This work is based, in part, on data from ESA’s Gaia mission (Gaia Collaboration et al. 2016), processed by the Data Processing and Analysis Consortium, funded by national institutions, particularly those participating in the Gaia Multilateral Agreement. This work also is based, in part, on data from the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. The Cosmostatistics Initiative (COIN, is an international network of researchers whose goal is to foster interdisciplinarity inspired by Astronomy. Facilities: Hale, Gaia, Spitzer (IRAC) Software: astropy (Astropy Collaboration et al. 2013, 2018), DBSP DRP (Roberson et al. 2021b), FITSio (Harris 2021), MASS (Venables & Ripley 2002), R (R Core Team 2021), TOPCAT & STILTS (Taylor 2005)
Group:Astronomy Department
Funding AgencyGrant Number
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Classification Code:Herbig Ae/Be stars (723) — T Tauri stars (1681) — Spectroscopy (1558) — Star formation (1569) — Stellar Associations (1582) — Young Stellar Objects (1834)
Record Number:CaltechAUTHORS:20220816-192421369
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:116314
Deposited By: George Porter
Deposited On:16 Aug 2022 22:45
Last Modified:02 Jun 2023 01:25

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