・Chemical Survey toward Young Stellar Objects in the Perseus Molecular Cloud Complex
(Motivation of PEACHES project)
Higuchi, A. E., Sakai, N., Watanabe, Y., Lopez-Sepulcre, A., Yoshida, K., Oya, Y., Imai, M., Zhang, Y., Ceccarelli, C., Lefloch, B., Codella, C., Bachiller, R., Hirota, T., Sakai, T., and Yamamoto, S., 2018, ApJS, 236, 52
The chemical diversity of gas in low-mass protostellar cores is widely recognized. In order to explore the origin of this diversity, a survey of chemical composition toward 36 Class 0/I protostars in the Perseus molecular cloud complex, which are selected in an unbiased way under certain physical conditions, has been conducted with IRAM 30 m and NRO 45 m telescope. Multiple lines of C 2H, c-C 3H 2, and CH 3OH have been observed to characterize the chemical composition averaged over a 1000 au scale around the protostar. The derived beam-averaged column densities show significant chemical diversity among the sources, where the column density ratios of C 2H/CH 3OH are spread out by two orders of magnitude. From previous studies, the hot corino sources have abundant CH 3OH but deficient C 2H, their C 2H/CH 3OH column density ratios being relatively low. In contrast, the warm-carbon-chain chemistry (WCCC) sources are found to reveal the high C 2H/CH 3OH column density ratios. We find that the majority of the sources have intermediate characters between these two distinct chemistry types. A possible trend is seen between the C 2H/CH 3OH ratio and the distance of the source from the edge of a molecular cloud. The sources located near cloud edges or in isolated clouds tend to have a high C 2H/CH 3OH ratio. On the other hand, the sources having a low C 2H/CH 3OH ratio tend to be located in the inner regions of the molecular cloud complex. This result gives an important clue toward understanding the origin of the chemical diversity of protostellar cores in terms of environmental effects.
(Motivation of PEACHES project)
Higuchi, A. E., Sakai, N., Watanabe, Y., Lopez-Sepulcre, A., Yoshida, K., Oya, Y., Imai, M., Zhang, Y., Ceccarelli, C., Lefloch, B., Codella, C., Bachiller, R., Hirota, T., Sakai, T., and Yamamoto, S., 2018, ApJS, 236, 52
The chemical diversity of gas in low-mass protostellar cores is widely recognized. In order to explore the origin of this diversity, a survey of chemical composition toward 36 Class 0/I protostars in the Perseus molecular cloud complex, which are selected in an unbiased way under certain physical conditions, has been conducted with IRAM 30 m and NRO 45 m telescope. Multiple lines of C 2H, c-C 3H 2, and CH 3OH have been observed to characterize the chemical composition averaged over a 1000 au scale around the protostar. The derived beam-averaged column densities show significant chemical diversity among the sources, where the column density ratios of C 2H/CH 3OH are spread out by two orders of magnitude. From previous studies, the hot corino sources have abundant CH 3OH but deficient C 2H, their C 2H/CH 3OH column density ratios being relatively low. In contrast, the warm-carbon-chain chemistry (WCCC) sources are found to reveal the high C 2H/CH 3OH column density ratios. We find that the majority of the sources have intermediate characters between these two distinct chemistry types. A possible trend is seen between the C 2H/CH 3OH ratio and the distance of the source from the edge of a molecular cloud. The sources located near cloud edges or in isolated clouds tend to have a high C 2H/CH 3OH ratio. On the other hand, the sources having a low C 2H/CH 3OH ratio tend to be located in the inner regions of the molecular cloud complex. This result gives an important clue toward understanding the origin of the chemical diversity of protostellar cores in terms of environmental effects.
・Rotation in the NGC 1333 IRAS 4C Outflow
Zhang, Y., Higuchi, A. E., Sakai, N., Oya, Y., Lopez-Sepulcre, A., Imai, M., Sakai, T., Watanabe, Y., Ceccarelli, C., Lefloch, B., and Yamamoto, S., 2018, ApJ, 864, 76
We report molecular line observations of the NGC 1333 IRAS 4C outflow in the Perseus Molecular Cloud with the Atacama Large Millimeter/Submillimeter Array. The CCH and CS emission reveal an outflow cavity structure with clear signatures of rotation with respect to the outflow axis. The rotation is detected from about 120 au up to about 1400 au above the envelope/disk midplane. As the distance to the central source increases, the rotation velocity of the outflow decreases while the outflow radius increases, which gives a flat specific angular momentum distribution along the outflow. The mean specific angular momentum of the outflow is about 100 {au} {km} {{{s}}} -1. On the basis of reasonable assumptions on the outward velocity of the outflow and the protostar mass, we estimate the range of outflow-launching radii to be 5-15 au. Such a launching radius rules out that this outflow is launched as an X-wind, but rather, it is more consistent to be a slow disk wind launched from relatively large radii on the disk. The radius of the centrifugal barrier is roughly estimated, and the role of the centrifugal barrier in the outflow launching is discussed.
Zhang, Y., Higuchi, A. E., Sakai, N., Oya, Y., Lopez-Sepulcre, A., Imai, M., Sakai, T., Watanabe, Y., Ceccarelli, C., Lefloch, B., and Yamamoto, S., 2018, ApJ, 864, 76
We report molecular line observations of the NGC 1333 IRAS 4C outflow in the Perseus Molecular Cloud with the Atacama Large Millimeter/Submillimeter Array. The CCH and CS emission reveal an outflow cavity structure with clear signatures of rotation with respect to the outflow axis. The rotation is detected from about 120 au up to about 1400 au above the envelope/disk midplane. As the distance to the central source increases, the rotation velocity of the outflow decreases while the outflow radius increases, which gives a flat specific angular momentum distribution along the outflow. The mean specific angular momentum of the outflow is about 100 {au} {km} {{{s}}} -1. On the basis of reasonable assumptions on the outward velocity of the outflow and the protostar mass, we estimate the range of outflow-launching radii to be 5-15 au. Such a launching radius rules out that this outflow is launched as an X-wind, but rather, it is more consistent to be a slow disk wind launched from relatively large radii on the disk. The radius of the centrifugal barrier is roughly estimated, and the role of the centrifugal barrier in the outflow launching is discussed.
・The Perseus ALMA Chemistry Survey (PEACHES). I. The Complex Organic Molecules in Perseus Embedded Protostars (Summary of the paper on PEACHES)
Yao-Lun Yang, Nami Sakai, Yichen Zhang, Nadia M. Murillo, Ziwei Zhang, Aya, E. Higuchi, Shaoshan Zeng, Ana Lopez-Sepulcre, Satoshi Yamamoto, Bertrand Lefloch, Mathilde Bouvier, Cecillia Ceccarelli, Tomoya Hirota, Muneaki Imai, Yoko Oya, Takeshi Sakai, and Yoshimasa Watanabe, 2021, ApJ, in press
To date, about two dozen low-mass embedded protostars exhibit rich spectra with COM lines. These protostars seem to possess different enrichment in COMs. However, the statistics of COM abundance in low-mass protostars are limited by the scarcity of observations. This study introduces the Perseus
ALMA Chemistry Survey (PEACHES), which aims at unbiasedly characterizing the chemistry of COMs toward the embedded (Class 0/I) protostars in the Perseus molecular cloud. Among the 50 embedded protostars surveyed, 58% of them have emission from COMs. A 56%, 32%, and 40% of protostars have CH 3OH, CH 3OCHO, and N-bearing COMs, respectively. The detectability of COMs depends on neither the averaged continuum brightness temperature, a proxy of the H 2 column density, nor the bolometric luminosity and the bolometric temperature. For the protostars with detected COMs, CH 3OH has a tight correlation with CH 3CN, spanning more than two orders of magnitude in column densities normalized by the continuum brightness temperature, suggesting a chemical relation between CH 3OH and CH 3CN and large chemical diversity among the PEACHES samples at the same time. A similar trend with more scatter is also found between all identified COMs, hinting at common chemistry for the sources with COMs. The correlation between COMs is insensitive to the protostellar properties, such as the bolometric luminosity and the bolometric temperature. The abundance of larger COMs (CH 3OCHO and CH 3OCH 3) relative to that of smaller COMs (CH 3OH and CH 3CN) increases with the inferred gas column density, hinting at an e_cient production of complex species in denser envelopes.
Yao-Lun Yang, Nami Sakai, Yichen Zhang, Nadia M. Murillo, Ziwei Zhang, Aya, E. Higuchi, Shaoshan Zeng, Ana Lopez-Sepulcre, Satoshi Yamamoto, Bertrand Lefloch, Mathilde Bouvier, Cecillia Ceccarelli, Tomoya Hirota, Muneaki Imai, Yoko Oya, Takeshi Sakai, and Yoshimasa Watanabe, 2021, ApJ, in press
To date, about two dozen low-mass embedded protostars exhibit rich spectra with COM lines. These protostars seem to possess different enrichment in COMs. However, the statistics of COM abundance in low-mass protostars are limited by the scarcity of observations. This study introduces the Perseus
ALMA Chemistry Survey (PEACHES), which aims at unbiasedly characterizing the chemistry of COMs toward the embedded (Class 0/I) protostars in the Perseus molecular cloud. Among the 50 embedded protostars surveyed, 58% of them have emission from COMs. A 56%, 32%, and 40% of protostars have CH 3OH, CH 3OCHO, and N-bearing COMs, respectively. The detectability of COMs depends on neither the averaged continuum brightness temperature, a proxy of the H 2 column density, nor the bolometric luminosity and the bolometric temperature. For the protostars with detected COMs, CH 3OH has a tight correlation with CH 3CN, spanning more than two orders of magnitude in column densities normalized by the continuum brightness temperature, suggesting a chemical relation between CH 3OH and CH 3CN and large chemical diversity among the PEACHES samples at the same time. A similar trend with more scatter is also found between all identified COMs, hinting at common chemistry for the sources with COMs. The correlation between COMs is insensitive to the protostellar properties, such as the bolometric luminosity and the bolometric temperature. The abundance of larger COMs (CH 3OCHO and CH 3OCH 3) relative to that of smaller COMs (CH 3OH and CH 3CN) increases with the inferred gas column density, hinting at an e_cient production of complex species in denser envelopes.