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Abstract We present ∼8–40μm SOFIA-FORCAST images of seven regions of “clustered” star formation as part of the SOFIA Massive Star Formation Survey. We identify a total of 34 protostar candidates and build their spectral energy distributions (SEDs). We fit these SEDs with a grid of radiative transfer models based on the turbulent core accretion (TCA) theory to derive key protostellar properties, including initial core mass,Mc, clump environment mass surface density, Σcl, and current protostellar mass,m*. We also carry out empirical graybody (GB) estimation of Σcl, which allows a case of restricted SED fitting within the TCA model grid. We also release version 2.0 of the open-source Python packagesedcreator, which is designed to automate the aperture photometry and SED building and fitting process for sources in clustered environments, where flux contamination from close neighbors typically complicates the process. Using these updated methods, SED fitting yields values ofMc∼ 30–200M⊙, Σcl,SED∼ 0.1–3 g cm−2, andm*∼ 4–50M⊙. The GB fitting yields smaller values of Σcl,GB≲ 1 g cm−2. From these results, we do not find evidence for a critical Σclneeded to form massive (≳8M⊙) stars. However, we do find tentative evidence for a dearth of the most massive (m*≳ 30M⊙) protostars in the clustered regions, suggesting a potential impact of environment on the stellar initial mass function.
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This content will become publicly available on September 10, 2026
LZ-STAR Survey: Low-metallicity Star Formation Survey of Sh2-284. I. Ordered Massive Star Formation in the Outer Galaxy
Abstract Star formation is a fundamental, yet poorly understood, process of the Universe. It is important to study how star formation occurs in different galactic environments. Thus, here, in the first of a series of papers, we introduce the Low-metallicity Star Formation (LZ-STAR) survey of the Sh2-284 (hereafter S284) region, which, atZ ∼ 0.3–0.5Z⊙, is one of the lowest-metallicity star-forming regions of our Galaxy. LZ-STAR is a multifacility survey, including observations with JWST, the Atacama Large Millimeter/submillimeter Array (ALMA), Hubble Space Telescope, Chandra, and Gemini. As a starting point, we report JWST and ALMA observations of one of the most massive protostars in the region, S284p1. The observations of shock-excited molecular hydrogen reveal a symmetric, bipolar outflow originating from the protostar, spanning several parsecs, and fully covered by the JWST field of view and ALMA observations of CO(2–1) emission. These allow us to infer that the protostar has maintained a relatively stable orientation of disk accretion over its formation history. The JWST near-infrared continuum observations detect a centrally illuminated bipolar outflow cavity around the protostar, as well as a surrounding cluster of low-mass young stars. We develop new radiative transfer models of massive protostars designed for the low metallicity of S284. Fitting these models to the protostar’s spectral energy distribution implies a current protostellar mass of ∼10M⊙has formed from an initial ∼100M⊙core over the last ∼3 × 105yr. Overall, these results indicate that massive stars can form in an ordered manner in low-metallicity, protocluster environments.
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- PAR ID:
- 10650920
- Publisher / Repository:
- IOP
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 990
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 173
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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