Discovery of the origin of the streamer feeding the material of the young star Per-emb-2

An illustration of gas flow from surrounding reservoir to star-forming streamer. (Credit: NAOJ)
Recent interferometer observations discovered "streamers", bringing gas from outer regions to the disk-forming regions surrounding forming stars. These streamers could change the chemical compositions of the star/planet-forming regions. It was also suggested that streamers possibly played important roles during the formation of the solar system.
　An international research group, consisting of National Astronomical Observatory of Japan (NAOJ), Max Planck Institute for Extraterrestrial Physics (MPE), and Otsuma Women’s University, have conducted mapping observations of four carbon-chain molecules (HC₃N, HC₅N, CCS, and CCH) toward the Class 0 young stellar object (YSO) Per-emb-2 in the Perseus region with the FOREST and Z45 receivers installed on the Nobeyama 45m radio telescope. The streamer of this YSO had been found by the NOEMA interferometer before, but its origin was not unrevealed. The research group aims to reveal the origin of the streamer and derive an accurate mass available for the streamer.
　The streamer comes from the north and the research group conducted mapping observations covering the northern part of the YSO Per-emb-2. A gas condensation has been discovered north with a distance of ~20,500 au from the YSO, and the streamer comes from this gas condensation. Thus, the gas condition is identified as the reservoir of the streamer. Figure 1 shows the spatial distribution of the observed carbon-chain molecules, and peaks (1) and (3) correspond to the streamer and the newly discovered reservoir, respectively. The size of the reservoir is consistent with a typical value of starless cores which will form stars. The group identified peak (2) but the relationship with the YSO is not clear, and this is left for future work.
　This research group have conducted detailed analyses of HC₃N, CCS, and HC₅N, combining data obtained by the Green Bank 100m telescope (GBT) in the USA and the IRAM 30m telescope in Spain, and derived accurate physical parameters, such as temperature and density, and molecular abundances at the streamer and reservoir. The reservoir has a temperature of 10 K and a density of 2×10⁴ cm^-3, and the streamer has a temperature and density of ~15 K and 5×10⁴ cm^-3, respectively. The physical condition of the reservoir is similar to that of starless cores, but no star will be born in the reservoir because the stellar material is flowing into the YSO Per-emb-2.
It has been shown that the reservoir and streamer are chemically young based on the comparisons between the observed CCS/HC₃N abundance ratios and the chemical simulations. The chemical age of the reservoir is similar to that of the streamer, which is additional evidence that the identified reservoir is providing gas to the streamer.
　The accurate masses of the reservoir and streamer have been derived to be ~16 M⊙ and ~13 M⊙, respectively, by comparisons between observations and chemical simulations. Thus, the total available mass of the streamer is estimated at ~29 M⊙ at most. Furthermore, the infall rate of the streamer is calculated at ~9×10^-5 M⊙/year. Based on these parameters, the lifetime of the streamer can be derived. Assuming that all of the gas in the reservoir will flow into the YSO Per-emb-2, the lifetime has been estimated~2×10⁵ years, suggesting that the mass accretion via the streamer would continue until the end of the Class I stage. This implies that the chemical environments of planet forming regions have not determined at the initial stage of the star formation processes, but have changed continuously just before stopping mass accretion of protostars.


Figure 1. Spatial distributions of carbon-chain molecules. The magenta crosses indicate the position of the YSO Per-emb-2. The white circles at the top left corner indicate the beam size of the Nobeyama 45m radio telescope. The upper panels show the results of (a) HC₃N, (b) CCS, and (c) CCH obtained by FOREST. The lower panels show the results (d) HC₃N, (e) CCS, and (f) HC₅N obtained with the Z45 receiver.


Publication information
This study was published by The Astrophysical Journal on April 17, 2024. The details are as follows:
[Journal] The Astrophysical Journal
[Issue, page] vol. 965, issue 2, article ID 162
[Title] The Reservoir of the Per-emb-2 Streamer
[Authors] Taniguchi, Kotomi; E Pineda, Jaime; Caselli, Paola; Shimoikura, Tomomi; Friesen, Rachel K.; Segura-Cox, Dominique M.; Schmiedeke, Anika
[URL] https://iopscience.iop.org/article/10.3847/1538-4357/ad2fa1

Research Group
Kotomi Taniguchi (NAOJ Fellow, Division of Science, National Astronomical Observatory of Japan)
Dr. Jaime E. Pineda (Center for Astrochemical Studies, Max Planck Institute for Extraterrestrial Physics)
Professor Paola Caselli (Center for Astrochemical Studies, Max Planck Institute for Extraterrestrial Physics)
Dr. Tomomi Shimoikura (Associate Professor, Otsuma Women’s University)
Dr. Rachel K. Friesen (Assistant Professor, University of Toronto)
Dr. Dominique M. Segura-Cox (NSF Astronomy and Astrophysics Postdoctoral Fellow, University of Texas)
Dr. Anika Schmiedeke (Green Band Observatory)