Origin of the hot gas in low-mass protostars

Abstract

Aims. "Water In Star-forming regions with Herschel" (WISH) is a Herschel key programme aimed at understanding the physical and chemical structure of young stellar objects (YSOs) with a focus on water and related species. [O i] emission is seen in low-velocity gas, assumed to be related to the envelope, and is also seen shifted up to 170 km s −1 in both the red-and blue-shifted jets. Envelope models are constructed based on previous observational constraints. They indicate that passive heating of a spherical envelope by the protostellar luminosity cannot explain the high-excitation molecular gas detected with PACS, including CO lines with upper levels at >2500 K above the ground state. Instead, warm CO and H 2 O emission is probably produced in the walls of an outflow-carved cavity in the envelope, which are heated by UV photons and non-dissociative C-type shocks. The bright OH and [O i] emission is attributed to J-type shocks in dense gas close to the protostar. In the scenario described here, the combined cooling by far-IR lines within the central spatial pixel is estimated to be 2 × 10 −2 L , with 60-80% attributed to J-and C-type shocks produced by interactions between the jet and the envelope.

Chemical and kinematic structure of extremely high-velocity molecular jets in the Serpens Main star-forming region

“…A.1a). This particular position has also been associated with a series of blueshifted water maser emissions (van Kempen et al 2009) and a bright spot of ion emission in the near-IR (Dionatos et al 2014). In Fig.…”

“…Since only a single transition of each molecule was observed, it is not possible to derive an excitation temperature from these data. The CO excitation temperature is set to 75 K, based on statistics of excitation temperatures for low-mass protostars (Yıldız et al 2015;van Kempen et al 2009) which show that the bulk of the low-J CO emission can be fitted with this value. Assessment of the excitation temperatures for other molecules is not straightforward.…”

Water in star‐forming regions with Herschel

“…The next step consists of detailed 2D modeling for each protostar. Such a model has already been developed and tested for the low-mass protostar HH46 (van Kempen et al 2010;Visser et al, in prep.). The model consists of three separate physical components: the molecular envelope heated by the accretion luminosity of the protostar, UVheating of the outflow cavity walls and shocks along the cavity walls (see Fig.…”

THE WARM CO GAS ALONG THE UV-HEATED OUTFLOW CAVITY WALLS: A POSSIBLE INTERPRETATION FOR THE HERSCHEL /PACS CO SPECTRA OF EMBEDDED YSOs

“…van Kempen et al (2010a) and Visser et al (2012) explored the origin of the mid-J CO emission as arising from the UVheated gas along the outflow cavity walls (the photondominated region, PDR) and small-scale C-type shocks inside the walls. Furthermore, Visser et al (2012) suggested that the PDR contributes more to the FIR CO emission as the protostar evolves.…”

“…Furthermore, it may not be negligible because FUV observations toward classical T Tauri stars find that these stars emit UV photons at a few percent of the accretion luminosity (e.g., Herczeg et al 2002;Yang et al 2012). These UV photons can affect the physical and chemical properties of exposed gas within the outflow cavity and along the walls (van Kempen et al 2010a;Visser et al 2012;Lee et al 2014b, hereafter Paper I). In this regard, Yıldız et al (2012) used spectrally resolved observations of 13 CO J = 6-5, finding that the narrow emission lines (D < -v 2 km s 1 ) toward NGC 1333-IRAS 4A are consistent with emission from UV-heated outflow cavity walls, which encapsulate the broad outflow lines (D > -v 10 km s 1 ).…”