Astronomy and Astrophysics, volume 548A, 77-77 (2012/12-1)
The complete far-infrared and submillimeter spectrum of the class 0 protostar Serpens SMM1 obtained with Herschel. Characterizing UV-irradiated shocks heating and chemistry.
GOICOECHEA J.R., CERNICHARO J., KARSKA A., HERCZEG G.J., POLEHAMPTON E.T., WAMPFLER S.F., KRISTENSEN L.E., VAN DISHOECK E.F., ETXALUZE M., BERNE O. and VISSER R.
Abstract (from CDS):
We present the first complete ∼55-671µm 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=4971K), H2O (up to 818-707 and Eu/k=1036K), OH (up to 2Π1/2 J=7/2-5/2 and Eu/k=618K), 13CO (up to Ju=16-15), HCN and HCO+ (up to Ju=12-11). Bright [OI]63, 145µm and weaker [CII]158 and [CI]370, 609µm 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 ∼10-37µm spectrum has many fewer lines, but shows clear detections of [NeII], [FeII], [SIII] and [SI] 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%), [OI] (∼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≃800K, Tkwarm≃375K and Tkcool≃150K). Gas densities n(H2)>5x106cm–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)≲0.2x10–5 and x(OH)≲10–6 with respect 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>60km/s) within an embedded atomic jet, as well as lower velocity small-scale non-dissociative shocks (vs≲20km/s) 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 [CII] and [CI] 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 [OI] 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 [OI] and OH emission.
stars: protostars - ISM: jets and outflows - infrared: ISM - shock waves
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