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تسجيل مستخدم جديدThe complete far-infrared and submillimeter spectrum of the Class 0 protostar Serpens SMM1 obtained with Herschel. Characterizing UV-irradiated shocks heating and chemistry
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We present the first complete 55-671 um spectral scan of a low-mass Class 0 protostar (Serpens SMM1) taken with the PACS and SPIRE spectrometers on board Herschel. More than 145 lines have been detected, most of them rotationally excited lines of 12CO (full ladder from J=4-3 to 42-41), H2O, OH, 13CO, HCN and HCO+ . Bright [OI]63,145um and weaker [CII]158 and [CI]370,609um lines are also detected. Mid-IR spectra retrieved from the Spitzer archive are also first discussed here, they show 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 non-LTE radiative transfer model allowed us to quantify the contribution of the 3 different temperature components suggested by the 12CO rotational ladder (Tk(hot)~800 K, Tk(warm)~375 K and Tk(cool)~150 K). Gas densities n(H2)~5x10^6 cm^-3 are needed to reproduce the observed far-IR lines arising from shocks in the inner protostellar envelope for which we derive upper limit abundances of x(CO)~10^-4, x(H2O)~0.2x10^-5 and x(OH)~10^-6. 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 (v_s > 60 km s^-1) as well as lower velocity non-dissociative shocks (v_s < 20 km s^-1) are needed to explain both the atomic lines and the hot CO and H2O lines respectively. Observations also show the signature of UV radiation and thus, most observed species likely arise in UV-irradiated shocks. Dissociative J-shocks produced by an atomic jet 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 can also contribute to the [OI] and OH emission.
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presence in this early stage is the norm. Likewise, while complex organics have been detected toward some Class~0 objects, their distribution is unknown as they could reside in the hottest parts of the envelope, in the emerging disk itself or in other components of the protostellar system, such as shocked regions related to outflows. Aims: In this work, we aim to address two related issues regarding protostars: when rotationally supported disks form around deeply embedded protostars and where complex organic molecules reside in such objects. Methods: We observed the deeply embedded protostar, L483, using Atacama Large Millimeter/submillimeter Array (ALMA) Band~7 data from Cycles~1 and 3 with a high angular resolution down to $sim$~0.1$^{primeprime}$ (20~au) scales. Results: We find that the kinematics of CS~$J=7$--$6$ and H$^{13}$CN~$J=4$--$3$ are best fitted by the velocity profile from infall under conservation of angular momentum and not by a Keplerian profile. The spatial extents of the observed complex organics are consistent with an estimated ice sublimation radius of the envelope at $sim$~50~au, suggesting that the complex organics exist in the hot corino of L483. Conclusions: We find that L483 does not harbor a Keplerian disk down to at least $15$~au in radius. Instead, the innermost regions of L483 are undergoing a rotating collapse. This result highlights that some Class~0 objects contain only very small disks, or none at all, with the complex organic chemistry taking place on scales inside the hot corino of the envelope, in a region larger than the emerging disk.
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