ALMA observations of the transition from infall motion to Keplerian rotation around the late-phase protostar TMC-1A
- Department of Astronomy, Graduate School of Science, The University of Tokyo, 731 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
- Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, HI 96720 (United States)
- Chile Observatory, National Astronomical Obervatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan)
- Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501 (Japan)
- National Astronomical Observatory of Japan, Osawa, 2-21-1, Mitaka, Tokyo 181-8588 (Japan)
- Department of Earth and Planetary Sciences, Faculty of Sciences Kyushu University, Fukuoka 812-8581 (Japan)
- Nobeyama Radio Observatory, Nobeyama, Minamimaki, Minamisaku, Nagano 384-1305 (Japan)
- Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China)
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
We have observed the Class I protostar TMC-1A with the Atacama Millimeter/submillimeter Array (ALMA) in the emissions of {sup 12}CO and C{sup 18}O (J = 2–1) and 1.3 mm dust continuum. Continuum emission with a deconvolved size of 0.″50 × 0.″37, perpendicular to the {sup 12}CO outflow, is detected. It most likely traces a circumstellar disk around TMC-1A, as previously reported. In contrast, a more extended structure is detected in C{sup 18}O, although it is still elongated with a deconvolved size of 3.″3 × 2.″2, indicating that C{sup 18}O traces mainly a flattened envelope surrounding the disk and the central protostar. C{sup 18}O shows a clear velocity gradient perpendicular to the outflow at higher velocities, indicative of rotation, while an additional velocity gradient along the outflow is found at lower velocities. The radial profile of the rotational velocity is analyzed in detail, finding that it is given as a power law ∝r{sup −a} with an index of ∼0.5 at higher velocities. This indicates that the rotation at higher velocities can be explained as Keplerian rotation orbiting a protostar with a dynamical mass of 0.68 M{sub ⊙} (inclination corrected). The additional velocity gradient of C{sup 18}O along the outflow is considered to be mainly infall motions in the envelope. Position–velocity diagrams made from models consisting of an infalling envelope and a Keplerian disk are compared with the observations, revealing that the observed infall velocity is ∼0.3 times smaller than the free-fall velocity yielded by the dynamical mass of the protostar. Magnetic fields could be responsible for the slow infall velocity. A possible scenario of Keplerian disk formation is discussed.
- OSTI ID:
- 22882502
- Journal Information:
- Astrophysical Journal, Vol. 812, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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