4-8 October 2015
Hans Harnack Haus
Europe/Berlin timezone
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Contribution Contributed Talk

Hans Harnack Haus -

Compact SO Emission around Protostars: A Possible Ring due to Accretion Shocks?


  • Prof. Nagayoshi OHASHI

Primary authors



We report compact SO emission around three class 0/I protostars found as byproducts during the ALMA observations searching for Keplerian disks. The three protostars are L1527 IRS, TMC1A, and L1489 IRS in Taurus. The ALMA observations have found Keplerian disks of 50-700 AU in radius around them in C$^{18}$O ($2-1$) emission, and also have revealed that the materials surrounding the disks are accreting to them, suggesting that these disks are still under formation. In addition to C$^{18}$O ($2-1$) emission tracing the Keplerian disks and the surrounding infalling materials, compact SO(6$_5-5_4$) emission is found. The size of the SO emission is ~200-600 AU, much more compact compared to the C$^{18}$O emission. The SO emission also exhibits rotating motions with the same directions as those of the Keplerian rotation. The rotation patterns of the SO emission are, however, very different from those of the Keplerian disks, i.e., although Keplerian rotation shows clear spin-up motions, the SO emission shows rigid-body-like rotation. The most possible origin of the compact SO emission with rigid-body-like rotation is a ring rotating around the protostar. We consider that SO molecular abundance is locally enhanced in a ring region around the protostar because of higher dust temperatures (40-60 K) caused by the accretion shock. A simple 1-D shock model shows that SO sublimation is possible with relatively low pre-shock velocities (~2 km s$^{-1}$) and high pre-shock density (~10$^9$ cm$^{-3}$), and that the heated layer is rather narrow because of the short cooling timescale. In the case of L1527 IRS, LVG analysis using three different transitions of SO observed by ALMA has been performed to investigate the physical conditions of the SO emission region. The analysis suggests that the kinetic temperature of the SO gas is most likely ~ 30 K, which is not as high as the sublimation temperature of SO (40-60 K). This suggests that the SO ring has a thin postshock layer with a higher temperature at its outermost radius, while the SO recondenses onto grain surfaces at the inner edge of the ring.