The jet and the disk of the HH 212 low-mass protostar imaged by ALMA: SO and SO₂emission

Abstract

Context. The investigation of the disk formation and jet launching mechanism in protostars is crucial to understanding the earliest stages of star and planet formation. Aims. We aim to constrain the physical and dynamical properties of the molecular jet and disk of the HH 212 protostellar system at unprecedented angular scales, exploiting the capabilities of the Atacama Large Millimeter Array (ALMA). Methods. The ALMA observations of HH 212 in emission lines from sulfur-bearing molecules, SO 9 8 −8 7 , SO 10 11 −10 10 , SO 2 8 2,6 −7 1,7 , are compared with simultaneous CO 3−2, SiO 8−7 data. The molecules column density and abundance are estimated using simple radiative transfer models. Results. SO 9 8 −8 7 and SO 2 8 2,6 −7 1,7 show broad velocity profiles. At systemic velocity, they probe the circumstellar gas and the cavity walls. Going from low to high blue-and red-shifted velocities the emission traces the wide-angle outflow and the fast (∼100−200 km s −1 ), collimated (∼90 AU) molecular jet revealing the inner knots with timescales ≤50 yr. The jet transports a massloss rate ≥0.2−2×10 −6 M yr −1 , implying high ejection efficiency (≥0.03−0.3). The SO and SO 2 abundances in the jet are ∼10 −7 −10 −6 . SO 10 11 −10 10 emission is compact and shows small-scale velocity gradients, indicating that it originates partly from the rotating disk previously seen in HCO + and C 17 O, and partly from the base of the jet. The disk mass is ≥0.002−0.013 M and the SO abundance in the disk is ∼10 −8 −10 −7 . Conclusions. SO and SO 2 are effective tracers of the molecular jet in the inner few hundreds AU from the protostar. Their abundances indicate that 1−40% of sulfur is in SO and SO 2 due to shocks in the jet/outflow and/or to ambipolar diffusion at the wind base. The SO abundance in the disk is 3−4 orders of magnitude larger than in evolved protoplanetary disks. This may be due to an SO enhancement in the accretion shock at the envelope-disk interface or in spiral shocks if the disk is partly gravitationally unstable.

Interaction between a pulsating jet and a surrounding disk wind

“…outflows (Lavalley-Fouquet et al 2000;Podio et al 2015). As shown by our simulations, this shape modeling (in the narrow jet limit) allows one to estimate the sideways ejection velocity from the IWS and the length scale of the bowshock.…”

The ALMA Protostellar Interferometric Line Survey (PILS)

“…The recent images from the Atacama Large Millimeter/submillimeter Array (ALMA) of a potentially planet-forming disk around a young star with an age of only 0.5-1 Myr, HL Tau, (ALMA Partnership et al 2015) has highlighted the importance of the physics and chemistry of the early protostellar stages: how do stars evolve during their earliest evolutionary stages and in particular, to what degree does the chemistry reflect this early evolution relative to, e.g., the conditions in the environment from which the stars are forming? Already during its first years ALMA has demonstrated enormous potential for addressing these issues with its high angular resolution and sensitivity making it possible to zoom in on solar system scales of young stars and map the chemical complexity in their environments (e.g., Pineda et al 2012;Jørgensen et al 2012Jørgensen et al , 2013Persson et al 2013;Codella et al 2014;Sakai et al 2014;Friesen et al 2014;Lindberg et al 2014;Oya et al 2014;Murillo et al 2015;Podio et al 2015;Belloche et al 2016;Müller et al 2016).…”

Comprehensive Study of Thermal Desorption of Grain-surface Species by Accretion Shocks around Protostars

“…Keplerian disks have been observed around protostars in the early evolutionary stages, such as Class I (Hogerheijde 2001;Brinch et al 2007;Lommen et al 2008;Jørgensen et al 2009;Lee 2010;Yen et al 2013Yen et al , 2014Harsono et al 2014), Class 0/I (Tobin et al 2012;Hara et al 2013)and Class 0 (Choi et al 2010;Codella et al 2014;Lee et al 2014;Ohashi et al 2014;Tobin et al 2015) protostars,butthe formation process is not yet well understood. Recent Atacama Large Millimeter Array (ALMA) observations have suggested that some molecular species are enhanced at the boundary between the infalling envelope and the forming Keplerian disk, suggesting thermal desorption from the grain surfaces (Sakai et al 2014a(Sakai et al , 2014bPodio et al 2015;Oya et al 2016). Thermal desorption of the grain-surface species is one of the astrophysical processes that affects the chemical evolution of a nebula.…”