Research Note

Far-infrared CO and H₂O emission in intermediate-mass protostars^⋆

¹ Astronomical Observatory, Adam Mickiewicz University, Słoneczna 36, 60-268 Poznań, Poland
e-mail: agata.karska@gmail.com
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³ Kavli Institut for Astronomy and Astrophysics, Yi He Yuan Lu 5, HaiDian Qu, Peking University, 100871 Beijing, PR China
⁴ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁵ Observatorio Astronómico Nacional (OAN, IGN), Apdo 112, 28803 Alcalá de Henares, Spain

Received: 4 March 2015
Accepted: 13 April 2015

Abstract

Context. Intermediate-mass young stellar objects (YSOs) provide a link to understanding how feedback from shocks and UV radiation scales from low- to high-mass star forming regions.

Aims. Our aim is to analyze excitation of CO and H₂O in deeply embedded intermediate-mass YSOs and compare it with similar studies on low-mass and high-mass YSOs.

Methods. Herschel/PACS spectral maps are analyzed for six YSOs with bolometric luminosities of L_bol ~ 10²−10³L_⊙. The maps cover spatial scales of ~10⁴ AU in several CO and H₂O lines located in the ~55–210 μm range.

Results. Rotational diagrams of CO show two temperature components at T_rot ~ 320 K and T_rot ~ 700–800 K, comparable to low- and high-mass protostars probed at similar spatial scales. The diagrams for H₂O show a single component at T_rot ~ 130 K, as seen in low-mass protostars, and about 100 K lower than in high-mass protostars. Since the uncertainties in T_rot are on the same order as the difference between the intermediate and high-mass protostars, we cannot conclude whether the change in rotational temperature occurs at a specific luminosity or whether the change is more gradual from low- to high-mass YSOs.

Conclusions. Molecular excitation in intermediate-mass protostars is comparable to the central 10³ AU of low-mass protostars and consistent within the uncertainties with the high-mass protostars probed at 3 × 10³ AU scales, suggesting similar shock conditions in all those sources.