Volume 548, December 2012
|Number of page(s)||17|
|Section||Interstellar and circumstellar matter|
|Published online||26 November 2012|
The complete far-infrared and submillimeter spectrum of the Class 0 protostar Serpens SMM1 obtained with Herschel
Characterizing UV-irradiated shocks heating and chemistry⋆,⋆⋆
Centro de Astrobiología (CSIC/INTA), Ctra. de Torrejón a Ajalvir, km 4,
Torrejón de Ardoz, Madrid
2 Max-Planck-Institut für extraterrestrische Physik (MPE), Postfach 1312, 85741 Garching, Germany
3 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
4 Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, HaiDian Qu, 100871 Beijing, PR China
5 RAL Space, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK
6 Institute for Space Imaging Science, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta T1J 1B1, Canada
7 Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade5-7, 1350 København K, Denmark
8 Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
9 CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
10 Department of Astronomy, University of Michigan, 500 Church St., Ann Arbor, MI 48109, USA
Accepted: 17 September 2012
We present the first complete ~55−671 μm spectral scan of a low-mass Class 0 protostar (Serpens SMM1) taken with the PACS and SPIRE spectrometers onboard Herschel. More than 145 lines have been detected, most of them rotationally excited lines of 12CO (full ladder from Ju = 4−3 to 42−41 and Eu/k = 4971 K), H2O (up to 818−707 and Eu/k = 1036 K), OH (up to 2Π1/2 J = 7/2−5/2 and Eu/k = 618 K), 13CO (up to Ju = 16−15), HCN and HCO+ (up to Ju = 12−11). Bright [O i]63, 145 μm and weaker [C ii]158 and [C i]370, 609 μm lines are also detected, but excited lines from chemically related species (NH3, CH+, CO+, OH+ or H2O+) are not. Mid-infrared spectra retrieved from the Spitzer archive are also first discussed here. The ~10−37 μm spectrum has many fewer lines, but shows clear detections of [Ne ii], [Fe ii], [Si ii] and [S i] fine structure lines, as well as weaker H2 S(1) and S(2) pure rotational lines. The observed line luminosity is dominated by CO (~54%), H2O (~22%), [O i] (~12%) and OH (~9%) emission. A multi-component radiative transfer model allowed us to approximately quantify the contribution of the three different temperature components suggested by the 12CO rotational ladder (Tkhot ≈ 800 K, Tkwarm ≈ 375 K and Tkcool ≈ 150 K). Gas densities n(H2) ≳ 5 × 106 cm-3 are needed to reproduce the observed far-IR lines arising from shocks in the inner protostellar envelope (warm and hot components) for which we derive upper limit abundances of x(CO) ≲ 10-4, x(H2O) ≲ 0.2 × 10-5 and x(OH) ≲ 10-6 withrespect to H2. The lower energy submm 12CO and H2O lines show more extended emission that we associate with the cool entrained outflow gas. Fast dissociative J-shocks (vs > 60 km s-1) within an embedded atomic jet, as well as lower velocity small-scale non-dissociative shocks (vs ≲ 20 km s-1) are needed to explain both the atomic fine structure lines and the hot CO and H2O lines respectively. Observations also show the signature of UV radiation (weak [C ii] and [C i] lines and high HCO+/HCN abundance ratios) and thus, most observed species likely arise in UV-irradiated shocks. Dissociative J-shocks produced by a jet impacting the ambient material are the most probable origin of [O i] and OH emission and of a significant fraction of the warm CO emission. In addition, H2O photodissociation in UV-irradiated non-dissociative shocks along the outflow cavity walls can also contribute to the [O i] and OH emission.
Key words: stars: protostars / ISM: jets and outflows / infrared: ISM / shock waves
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2012
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