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Spectroscopic Confirmation of a Population of Isolated, Intermediate-mass Young Stellar Objects

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 (2023) Spectroscopic Confirmation of a Population of Isolated, Intermediate-mass Young Stellar Objects. Astronomical Journal, 165 (1). Art. No. 3. ISSN 0004-6256. doi:10.3847/1538-3881/ac9314.

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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 ɪɪ 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 being the 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 kiloparsec-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:Article
Related URLs:
URLURL TypeDescription
Kuhn, Michael A.0000-0002-0631-7514
Saber, Ramzi0000-0003-2015-3429
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. We would like to thank the referee for providing a thorough report and many useful suggestions. A.K.M. acknowledges the support from the Portuguese Fundação para a Ciência e a Tecnologia (FCT) through grants PTDC/FIS-AST/31546/2017, UID/FIS/00099/2019, and EXPL/FIS-AST/1368/2021. 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.
Group:Astronomy Department
Funding AgencyGrant Number
Caltech Freshman Summer Research Institute (FSRI)UNSPECIFIED
Fundação para a Ciência e a Tecnologia (FCT)PTDC/FIS-AST/31546/2017
Fundação para a Ciência e a Tecnologia (FCT)UID/FIS/ 00099/2019
Fundação para a Ciência e a Tecnologia (FCT)EXPL/FIS-AST/1368/2021
Gaia Multilateral AgreementUNSPECIFIED
Issue or Number:1
Record Number:CaltechAUTHORS:20221219-417430800.24
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:118497
Deposited By: Research Services Depository
Deposited On:20 Jan 2023 21:08
Last Modified:20 Jan 2023 21:08

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