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Rotating Gas Motion around Protostars

Image Credit: Yen, Takakuwa and Ohashi

Morphology (contour) and kinematics (color scale) of envelopes around a sample of Class 0 and I protostars seen in the C18O (2-1) emission observed with the SMA. The color scale shows gas motions moving away from us (redshifted) and toward us (blueshifted). Dashed lines denote the rotational axes of these envelopes, and black crosses represent the positions of the protostars.

Stars form in interstellar clouds of molecular gas and dust, “molecular clouds”. Solar-type stars being formed, often called “protostars”, grow through "accretion" from the surrounding molecular gas and dust in molecular clouds, "envelopes". Because of the surrounding dusty envelopes protostars are invisible at optical wavelength. On the other hand, at far-infrared, submillimeter, and millimeter wavelengths we can study structures and kinematics of envelopes and how stars are formed from envelopes. Through observations of molecular lines at millimeter and submillimeter wavelengths we can measure gas motions in envelopes, such as rotations and infall. Our SMA observations in the C18O (2-1) line toward a sample of Class 0 and I protostars have revealed systematic gas motions in the envelopes surrounding those protostars, which can be interpreted as envelope rotations. Furthermore, we found that the envelopes around the more evolved protostars (Class I: TMC-1A & L1489 IRS) tend to exhibit faster rotations than those around the less evolved protostars (Class 0: B335, IRAS 4B, L1527 IRS & L1448-mm). These results suggest that the rotational motion in the envelopes around the protostars likely increases with time evolution (Yen, Takakuwa & Ohashi, 2010, ApJ, 710, 1786, 2011, ApJ, 742, 57)