More Like this

1. The SOFIA Massive (SOMA) Star Formation Q-band follow-up: I. Carbon-chain chemistry of intermediate-mass protostars

   https://doi.org/10.1051/0004-6361/202451499  

   Taniguchi, Kotomi; Gorai, Prasanta; Tan, Jonathan C; Gómez-Garrido, Miguel; Fedriani, Rubén; Yang, Yao-Lun; Tirupati_Kumara, Sridharan; Tanaka, Kei_E I; Saito, Masao; Zhang, Yichen; et al (December 2024, Astronomy & Astrophysics)

   Context. Evidence that the chemical characteristics around low- and high-mass protostars are similar has been found: notably, a variety of carbon-chain species and complex organic molecules (COMs) form around both types. On the other hand, the chemical compositions around intermediate-mass (IM) protostars (2M_⊙<m_*< 8M_⊙) have not been studied with large samples. In particular, it is unclear the extent to which carbon-chain species form around them. Aims. We aim to obtain the chemical compositions of a sample of IM protostars, focusing particularly on carbon-chain species. We also aim to derive the rotational temperatures of HC₅N to confirm whether carbon-chain species are formed in the warm gas around these stars. Methods. We conducted Q-band (31.5–50 GHz) line survey observations toward 11 mainly IM protostars with the Yebes 40 m radio telescope. The target protostars were selected from a subsample of the source list of the SOFIA Massive Star Formation project. Assuming local thermodynamic equilibrium, we derived the column densities of the detected molecules and the rotational temperatures of HC₅N and CH₃OH. Results. Nine carbon-chain species (HC₃N, HC₅N, C₃H, C₄Hlinear-H₂CCC,cyclic-C₃H₂, CCS, C₃S, and CH₃CCH), three COMs (CH₃OH, CH₃CHO, and CH₃CN), H₂CCO, HNCO, and four simple sulfur-bearing species (¹³CS, C³⁴S, HCS⁺, and H₂CS) are detected. The rotational temperatures of HC₅N are derived to be ~20–30 K in three IM protostars (Cepheus E, HH288, and IRAS 20293+3952). The rotational temperatures of CH₃OH are derived in five IM sources and found to be similar to those of HC₅N. Conclusions. The rotational temperatures of HC₅N around the three IM protostars are very similar to those around low- and high-mass protostars. These results indicate that carbon-chain molecules are formed in lukewarm gas (~20–30 K) around IM protostars via the warm carbon-chain chemistry process. Thus, carbon-chain formation occurs ubiquitously in the warm gas around protostars across a wide range of stellar masses. Carbon-chain molecules and COMs coexist around most of the target IM protostars, which is similar to the situation for low- and high-mass protostars. In summary, the chemical characteristics around protostars are the same in the low-, intermediate- and high-mass regimes. 

   more » « less
2. Chemical Differentiation around Five Massive Protostars Revealed by ALMA: Carbon-chain Species and Oxygen/Nitrogen-bearing Complex Organic Molecules

   https://doi.org/10.3847/1538-4365/acd110  

   Taniguchi, Kotomi; Majumdar, Liton; Caselli, Paola; Takakuwa, Shigehisa; Hsieh, Tien-Hao; Saito, Masao; Li, Zhi-Yun; Dobashi, Kazuhito; Shimoikura, Tomomi; Nakamura, Fumitaka; et al (June 2023, The Astrophysical Journal Supplement Series)

   Abstract We present Atacama Large Millimeter/submillimeter Array Band 3 data toward five massive young stellar objects (MYSOs), and investigate relationships between unsaturated carbon-chain species and saturated complex organic molecules (COMs). An HC 5 N ( J = 35–34) line has been detected from three MYSOs, where nitrogen (N)-bearing COMs (CH 2 CHCN and CH 3 CH 2 CN) have been detected. The HC 5 N spatial distributions show compact features and match with a methanol (CH 3 OH) line with an upper-state energy around 300 K, which should trace hot cores. The hot regions are more extended around the MYSOs where N-bearing COMs and HC 5 N have been detected compared to two MYSOs without these molecular lines, while there are no clear differences in the bolometric luminosity and temperature. We run chemical simulations of hot-core models with a warm-up stage, and compare with the observational results. The observed abundances of HC 5 N and COMs show good agreements with the model at the hot-core stage with temperatures above 160 K. These results indicate that carbon-chain chemistry around the MYSOs cannot be reproduced by warm carbon-chain chemistry, and a new type of carbon-chain chemistry occurs in hot regions around MYSOs. 

   more » « less
3. Probing the physics of star formation (ProPStar): II. The first systematic search for streamers toward protostars

   https://doi.org/10.1051/0004-6361/202449395  

   Valdivia-Mena, María Teresa; Pineda, Jaime E; Caselli, Paola; Segura-Cox, Dominique M; Schmiedeke, Anika; Spezzano, Silvia; Offner, Stella; Ivlev, Alexei V; Kuffmeier, Michael; Cunningham, Nichol; et al (July 2024, Astronomy & Astrophysics)

   Context. The detections of narrow channels of accretion toward protostellar disks, known as streamers, have increased in number in the last few years. However, it is unclear whether streamers are a common feature around protostars that were previously missed, or if they are a rare phenomenon. Aims. Our goals are to obtain the incidence of streamers toward a region of clustered star formation and to trace the origins of their gas to determine whether they originate within the filamentary structure of molecular clouds or from beyond. Methods. We used combined observations of the nearby NGC 1333 star-forming region, carried out with the NOEMA interferometer and the IRAM 30m single dish. Our observations cover the area between the systems IRAS 4 and SVS 13. We traced the chemically fresh gas within NGC 1333 with HC₃N molecular gas emission and the structure of the fibers in this region with N₂H⁺emission. We fit multiple velocity components in both maps and used clustering algorithms to recover velocity-coherent structures. Results. We find streamer candidates toward 7 out of 16 young stellar objects within our field of view. This represents an incidence of approximately 40% of young stellar objects with streamer candidates in a clustered star-forming region. The incidence increases to about 60% when we only considered embedded protostars. All streamers are found in HC₃N emission. Conclusions. Given the different velocities between HC₃N and N₂H⁺emission, and because by construction, N₂H⁺traces the fiber structure, we suggest that the gas that forms the streamers comes from outside the fibers. This implies that streamers can connect cloud material that falls onto the filaments with protostellar disk scales. 

   more » « less
4. An Improved Upper Limit of Cyanodiacetylene (HC5N) in the Atmosphere of Titan

   https://doi.org/10.3847/1538-3881/ae0621  

   Iino, Takahiro; Taniguchi, Kotomi; Sagawa, Hideo; Cordiner, Martin A; Tan, Shuya; Takahashi, Shigeru; Kubota, Hikaru (November 2025, The Astronomical Journal)

   Abstract In the complex Titan atmospheric chemistry, photochemical reactions involving cyanodiacetylene (HC₅N) may be important as reaction pathways that could lead to the production of amines and aromatic molecules. We carried out a new comprehensive search of HC₅N in Titan’s atmosphere using Band 6 (215–275 GHz or 1.1–1.4 mm in wavelength) spectroscopic archival data from the Atacama Large Millimeter/submillimeter Array. To search for a faint spectral line feature of HC₅N, we used a spectral stacking method that integrates different transition data. Integrating six independent observation data sets with a total integration time of ∼15,000 s, we found no statistically significant detection of an HC₅N spectral feature. Using the Planetary Spectrum Generator for radiative transfer modeling and employing the previously predicted vertical distribution proposed by V. Vuitton et al., E. Lellouch et al., J. C. Loison et al., and V. A. Krasnopolsky, we derived the upper limit column density of HC₅N, corresponding to 3σnoise level, to be 0.3–10 × 10¹³molecules cm^–2above ∼60 km altitude (depending on the assumed vertical profile). The corresponding upper limit of [HC₅N]/[HC₃N] ratio value derived from three of four models seem to be lower than that measured in high-mass protostellar objects, possibly due to the lower abundance of C₄H₂. 

   more » « less
5. The Reservoir of the Per-emb-2 Streamer

   https://doi.org/10.3847/1538-4357/ad2fa1  

   Taniguchi, Kotomi; Pineda, Jaime E; Caselli, Paola; Shimoikura, Tomomi; Friesen, Rachel K; Segura-Cox, Dominique M; Schmiedeke, Anika (April 2024, The Astrophysical Journal)

   Abstract Streamers bring gas from outer regions to protostellar systems and could change the chemical composition around protostars and protoplanetary disks. We have carried out mapping observations of carbon-chain species (HC₃N, HC₅N, CCH, and CCS) in the 3 mm and 7 mm bands toward the streamer flowing to the Class 0 young stellar object (YSO) Per-emb-2 with the Nobeyama 45 m radio telescope. A region with a diameter of ∼0.04 pc is located to the north at a distance of ∼20,500 au from the YSO. The streamer connects to this northern region, which is its origin. The reservoir has high density and low temperature ( $n_{{\mathrm{H}}_2}\approx 1.9\times {10}^4$ cm⁻³,T_kin= 10 K), which are similar to those of early-stage starless cores. By comparison of the observed abundance ratios of CCS/HC₃N to the chemical simulations, the reservoir and streamer are found to be chemically young. The total mass available for the streamer is derived to be 24–34M_⊙. It has been estimated that, if all of the gas in the reservoir were to accrete onto the Per-emb-2 protostellar system, the lifetime of the streamer would be (1.1–3.2) × 10⁵yr, suggesting that the mass accretion via the streamer would continue until the end of the Class I stage. 

   more » « less