The factors that influence protostellar multiplicity

II. Gas temperature and mass in Perseus with APEX

¹ Instituto de Astronomía, Universidad Nacional Autónoma de México, AP106, Ensenada CP 22830, B.C., Mexico
² Star and Planet Formation Laboratory, RIKEN Pioneering Research Institute, Wako, Saitama 351-0198, Japan
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 Taiwan Astronomical Research Alliance (TARA), Taiwan
⁶ Academia Sinica Institute of Astronomy and Astrophysics, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan
⁷ NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Rd, Victoria, BC V9E 2E7, Canada
⁸ Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 5C2, Canada
⁹ Department of Physics, Norwegian University of Science and Technology, 7491 Trondheim, Norway
¹⁰ Independent researcher, Sagas Väg 5, 43431 Kungsbacka, Sweden

^★ Corresponding author: nmurillo@astro.unam.mx

Received: 27 February 2025
Accepted: 15 October 2025

Abstract

Context. Protostellar multiplicity is a common outcome of the star formation process. To fully understand the formation and evolution of these systems, the physical parameters of the molecular gas together with the dust must be systematically characterized.

Aims. Using observations of molecular gas tracers, we characterize the physical properties of cloud cores in the Perseus molecular cloud (average distance of 295 pc) at envelope scales (5000-8000 AU).

Methods. We used Atacama Pathfinder EXperiment (APEX) and Nobeyama 45m Radio Observatory (NRO) observations of DCO⁺, H₂CO, and c-C₃H₂ in several transitions to derive the physical parameters of the gas toward 31 protostellar systems in Perseus. The angular resolutions ranged from 18" to 28.7", equivalent to 5000-8000 AU scales at the distance of each subregion in Perseus. The gas kinetic temperature was obtained from DCO⁺, H₂CO, and c-C₃H₂ line ratios. Column densities and gas masses were then calculated for each species and transition. Gas kinetic temperature and gas masses were compared with bolometric luminosity, envelope dust mass, and multiplicity to search for statistically significant correlations.

Results. Gas kinetic temperature derived from H₂CO, DCO⁺, and c-C₃H₂ line ratios have average values of 26 K, 14, and 16 K, respectively, with a range of 10-26 K for DCO⁺ and c-C₃H₂. The gas kinetic temperature obtained from H₂CO line ratios have a range of 13-82 K. Column densities of all three molecular species are on the order of 10¹¹ to 10¹⁴ cm⁻², resulting in gas masses of 10⁻¹¹ to 10⁻⁹ M_⊙. Statistical analysis of the physical parameters finds: i) similar envelope gas and dust masses for single and binary protostellar systems; ii) multiple protostellar systems (>2 components) tend to have slightly higher gas and dust masses than binaries and single protostars; iii) a continuous distribution of gas and dust masses is observed regardless of separation between components in protostellar systems.