L1157-mm powers a molecular outflow that is well-known for its shock-induced chemical activity in several hot-spots. We have studied the molecular emission toward L1157-mm searching for a jet component responsible for these spots. We used the IRAM 30
m telescope to observe the vicinity of L1157-mm in several lines of SiO. The SiO(5-4) and SiO(6-5) spectra toward L1157-mm present blue and red detached components about 45 km/s away from the ambient cloud. These extremely high-velocity (EHV) components are similar to those found in the L1448 and IRAS 04166+2706 outflows, and probably arise from a molecular jet driven by L1157-mm. Observations of off-center positions indicate that the jet is unresolved in SiO(5-4) (<11). The EHV jet seen in SiO probably excites L1157-B1 and the other chemically active spots of the L1157 outflow.
We present a multiline CS survey towards the brightest bow-shock B1 in the prototypical chemically active protostellar outflow L1157. We made use of (sub-)mm data obtained in the framework of the Chemical HErschel Surveys of Star forming regions (CHE
SS) and Astrochemical Surveys at IRAM (ASAI) key science programs. We detected $^{12}$C$^{32}$S, $^{12}$C$^{34}$S, $^{13}$C$^{32}$S, and $^{12}$C$^{33}$S emissions, for a total of 18 transitions, with $E_{rm u}$ up to $sim$ 180 K. The unprecedented sensitivity of the survey allows us to carefully analyse the line profiles, revealing high-velocity emission, up to 20 km s$^{-1}$ with respect to the systemic. The profiles can be well fitted by a combination of two exponential laws that are remarkably similar to what previously found using CO. These components have been related to the cavity walls produced by the $sim$ 2000 yr B1 shock and the older ($sim$ 4000 yr) B2 shock, respectively. The combination of low- and high-excitation CS emission was used to properly sample the different physical components expected in a shocked region. Our CS observations show that this molecule is highlighting the dense, $n_{rm H_2}$ = 1--5 $times$ 10$^{5}$ cm$^{-3}$, cavity walls produced by the episodic outflow in L1157. In addition, the highest excitation (E$_u$ $geq$ 130 K) CS lines provide us with the signature of denser (1--5 $times$ 10$^{6}$ cm$^{-3}$) gas, associated with a molecular reformation zone of a dissociative J-type shock, which is expected to arise where the precessing jet impacting the molecular cavities. The CS fractional abundance increases up to $sim$ 10$^{-7}$ in all the kinematical components. This value is consistent with what previously found for prototypical protostars and it is in agreement with the prediction of the abundances obtained via the chemical code Astrochem.
Interstellar molecules with a peptide link -NH-C(=O)-, like formamide (NH$_2$CHO), acetamide (NH$_2$COCH$_3$) and isocyanic acid (HNCO) are particularly interesting for their potential role in pre-biotic chemistry. We have studied their emission in t
he protostellar shock regions L1157-B1 and L1157-B2, with the IRAM 30m telescope, as part of the ASAI Large Program. Analysis of the line profiles shows that the emission arises from the outflow cavities associated with B1 and B2. Molecular abundance of $approx~(0.4-1.1)times 10^{-8}$ and $(3.3-8.8)times 10^{-8}$ are derived for formamide and isocyanic acid, respectively, from a simple rotational diagram analysis. Conversely, NH$_2$COCH$_3$ was not detected down to a relative abundance of a few $leq 10^{-10}$. B1 and B2 appear to be among the richest Galactic sources of HNCO and NH$_2$CHO molecules. A tight linear correlation between their abundances is observed, suggesting that the two species are chemically related. Comparison with astrochemical models favours molecule formation on ice grain mantles, with NH$_2$CHO generated from hydrogenation of HNCO.
Molecular outflows powered by young protostars strongly affect the kinematics and chemistry of the natal molecular cloud through strong shocks resulting in substantial modifications of the abundance of several species. As part of the Chemical Hersche
l Surveys of Star forming regions guaranteed time key program, we aim at investigating the physical and chemical conditions of H20 in the brightest shock region B1 of the L1157 molecular outflow. We observed several ortho- and para-H2O transitions using HIFI and PACS instruments on board Herschel, providing a detailed picture of the kinematics and spatial distribution of the gas. We performed a LVG analysis to derive the physical conditions of H2O shocked material, and ultimately obtain its abundance. We detected 13 H2O lines probing a wide range of excitation conditions. PACS maps reveal that H2O traces weak and extended emission associated with the outflow identified also with HIFI in the o-H2O line at 556.9 GHz, and a compact (~10) bright, higher-excitation region. The LVG analysis of H2O lines in the bow-shock show the presence of two gas components with different excitation conditions: a warm (Tkin~200-300 K) and dense (n(H2)~(1-3)x10^6 cm-3) component with an assumed extent of 10 and a compact (~2-5) and hot, tenuous (Tkin~900-1400 K, n(H2)~10^3-10^4 cm-3) gas component, which is needed to account for the line fluxes of high Eu transitions. The fractional abundance of the warm and hot H2O gas components is estimated to be (0.7-2)x10^{-6} and (1-3)x10^{-4}, respectively. Finally, we identified an additional component in absorption in the HIFI spectra of H2O lines connecting with the ground state level, probably arising from the photodesorption of icy mantles of a water-enriched layer at the edges of the cloud.
Previous far-infrared observations at low-angular resolution have reported the presence of water associated with low-velocity outflow shocks and protostellar envelopes. The outflow driven by the intermediate-mass class 0 protostar Cep E is among the
most luminous outflows detected so far. Using the IRAM 30m telescope, we searched for and detected the para-water line emission at 183 GHz in the Cep E star-forming core. The emission arises from high-velocity gas close to the protostar, which is unresolved in the main beam of the telescope. Complementary observations at 2 resolution with the Plateau de Bure interferometer helped establish the origin of the emission detected and the physical conditions in the emitting gas. The water line profile and its spatial distribution are very similar to those of SiO. We find that the water emission arises from warm ($sim 200K$), dense ($(1-2)times 10^6cmmt$) gas, and its abundance is enhanced by one to two orders of magnitude with respect to the protostellar envelope. We detect water emission in strong shocks from the high-velocity jet at 1000 AU from the protostar. Despite the large beam size of the telescope, such emission should be detectable with Herschel.
The outflow driven by the low-mass class 0 protostar L1157 is the prototype of the so-called chemically active outflows. The bright bowshock B1 in the southern outflow lobe is a privileged testbed of magneto-hydrodynamical (MHD) shock models, for whi
ch dynamical and chemical processes are strongly interdependent. We present the first results of the unbiased spectral survey of the L1157-B1 bowshock, obtained in the framework of the key program Chemical Herschel Surveys of Star Forming Regions (CHESS). The main aim is to trace the warm and chemically enriched gas and to infer the excitation conditions in the shock region. The CO 5-4 and H2O lines have been detected at high-spectral resolution in the unbiased spectral survey of the HIFI-Band 1b spectral window (555-636 GHz), presented by Codella et al. in this volume. Complementary ground-based observations in the submm window help establish the origin of the emission detected in the main-beam of HIFI, and the physical conditions in the shock.}{Both lines exhibit broad wings, which extend to velocities much higher than reported up to now. We find that the molecular emission arises from two regions with distinct physical conditions: an extended, warm (100K), dense (3e5 cm-3) component at low-velocity, which dominates the water line flux in Band~1; a secondary component in a small region of B1 (a few arcsec) associated with high-velocity, hot (> 400 K) gas of moderate density ((1.0-3.0)e4 cm-3), which appears to dominate the flux of the water line at 179mu observed with PACS. The water abundance is enhanced by two orders of magnitude between the low- and the high-velocity component, from 8e-7 up to 8e-5. The properties of the high-velocity component agree well with the predictions of steady-state C-shock models.
We have obtained maps of the 1.25mm thermal dust emission and the molecular gas emission over a region of 20 by 10 arcmin around the Trifid Nebula (M20), with the IRAM 30m and the CSO telescopes as well as in the mid-infrared wavelength with ISO and
SPITZER. Our survey is sensitive to features down to N(H2) sim 10^{22} cm-2 in column density. The cloud material is distributed in fragmented dense gas filaments (n(H2) sim 1000 cm-3) with sizes ranging from 1 to 10 pc. A massive filament, WF, with properties typical of Infra Red Dark Clouds, connects M20 to the W28 supernova remnant. These filaments pre-exist the formation of the Trifid and were originally self-gravitating. The fragments produced are very massive (100 Msun or more) and are the progenitors of the cometary globules observed at the border of the HII region. We could identify 33 cores, 16 of which are currently forming stars. They are usually gravitationally unbound and have low masses of a few Msun. The densest starless cores (several 10^5 cm-3) may be the site for the next generation of stars. The physical gas and dust properties of the cometary globules have been studied in detail and have been found very similar. They all are forming stars. Several intermediate-mass protostars have been detected in the cometary globules and in the deeply embedded cores. Evidence of clustering has been found in the shocked massive cores TC3-TC4-TC5. M20 is a good example of massive-star forming region in a turbulent, filamentary molecular cloud. Photoionization appears to play a minor role in the formation of the cores. The observed fragmentation is well explained by MHD-driven instabilities and is usually not related to M20. We propose that the nearby supernova remnant W28 could have triggered the formation of protostellar clusters in nearby dense cores of the Trifid.
