The factors that influence protostellar multiplicity

I. Gas temperature, density, and mass in Perseus with Nobeyama

¹ Star and Planet Formation Laboratory, RIKEN Cluster for Pioneering Research, Wako, Saitama 351-0198 Japan
² Instituto de Astronomía, Universidad Nacional Autónoma de México, AP106, Ensenada CP 22830, B. C., Mexico
³ Fox2Space - FTSCO, The Fault Tolerant Satellite Computer Organization, Weigunystrasse 4, 4040 Linz, Austria
⁴ Institute of Astronomy, Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
⁵ Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
⁶ NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Rd, Victoria, BC, V9E 2E7, Canada
⁷ Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8P 5C2, Canada
⁸ Institutt for Fysikk, Norwegian University of Science and Technology, Høgskloreringen 5, Trondheim, 7491, Norway
⁹ Université Paris Cité CNRS, CNES, Astroparticule et Cosmologie, 75013 Paris, France
¹⁰ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
¹¹ National Radio Astronomy Observatory, Charlottesville, VA 22903, USA
¹² Independent researcher, Sagas Väg 5, 43431 Kungsbacka, Sweden

Received: 28 September 2023
Accepted: 18 July 2024

Abstract

Context. Protostellar multiplicity is common at all stages and mass ranges. However, the factors that determine the multiplicity of protostellar systems have not been systematically characterized through their molecular gas.

Aims. We characterize the physical properties of the Perseus molecular cloud at ≥5000 AU scales by mapping the diagnostic molecular lines.

Methods. We used Nobeyama 45m Radio Observatory (NRO) on-the-fly maps of HCN, HNC, HCO⁺, and N₂H⁺ (J=1–0) toward five subregions in Perseus, complemented with single-pointing Atacama Pathfinder Experiment (APEX) observations of HNC (J = 4–3), to derive the physical parameters of the dense gas. The spatial resolutions of both observations were ~18″, which is equivalent to ~5000 AU scales at the distance of Perseus. The kinetic gas temperature was derived from the I(HCN)/I(HNC) J ratio, and the H₂ density was obtained from the HNC J=4–3/J=1–0 ratio. These parameters were used to obtain the N₂H⁺ (cold) and HCO⁺ (warm) gas masses. The inferred and derived parameters were then compared to source the parameters, including protostellar multiplicity, bolometric luminosity, and dust envelope mass.

Results. The inferred mean kinetic gas temperature (I(HCN)/I(HNC) J=1–0 ratio; ranging between 15 and 26 K), and H₂ volumetric density (HNC J=4–3/J=1–0; 10⁵−10⁶ cm⁻³) are not correlated with multiplicity in Perseus. The derived gas and dust masses, 1.3 to 16 × 10⁻⁹ M_⊙ for the cold-gas mass (N₂H⁺), 0.1 to 25 M_⊙ for the envelope dust masses (850 μm), and 0.8 to 10 × 10⁻¹⁰ M_⊙ for the warm-gas mass (HCO⁺), are correlated to multiplicity and to the number of protostellar components. The warm-gas masses are lower by a factor of 16 than the cold-gas masses.

Conclusions. The gas and dust mass is correlated to multiplicity at ~5000 AU scales in Perseus. Higher-order multiples tend to have higher gas and dust masses in general, while close binaries (separations ≤7″) and single protostars have similar gas and dust mass distributions. On the other hand, the H₂ density and kinetic gas temperature are not correlated with multiplicity.