C. Codella

The CHESS Survey of the L1157-B1 Shock Region: CO Spectral Signatures of Jet-driven Bow Shocks

The unprecedented sensitivity of Herschel coupled with the high resolution of the HIFI spectrometer permits studies of the intensity-velocity relationship I(v) in molecular outflows, over a higher excitation range than possible up to now. Over the course of the CHESS Key Program, we have observed toward the bright bow shock region L1157-B1, the CO rotational transitions between J = 5-4 and J = 16-15 with HIFI, and the J = 1-0, 2-1, and 3-2 with the IRAM 30 m and the Caltech Submillimeter Observatory telescopes. We find that all the line profiles I_(CO)(v) are well fit by a linear combination of three exponential laws ∝ exp (– |v/v_0|) with v_0 = 12.5, 4.4, and 2.5 km s^(–1). The first component dominates the CO emission at J ≥ 13, as well as the high-excitation lines of SiO and H_(2)O. The second component dominates for 3 ≤ J up ≤ 10 and the third one for J_up ≤ 2. We show that these exponentials are the signature of quasi-isothermal shocked gas components: the impact of the jet against the L1157-B1 bow shock (T_k ≃ 210 K), the walls of the outflow cavity associated with B1 (T_k ≃ 64 K), and the older cavity L1157-B2 (T_k ≃ 23 K), respectively. Analysis of the CO line flux in the large-velocity gradient approximation further shows that the emission arises from dense gas (n(H_2) ≥ 10^(5)-10^(6) cm^(–3)) close to LTE up to J = 20. We find that the CO J = 2-1 intensity-velocity relation observed in various other molecular outflows is satisfactorily fit by similar exponential laws, which may hold an important clue to their entrainment process.

Star formation in the bright rimmed globule IC 1396N

We report mm-wave multiline and continuum observations of IC 1396N, a conspicuous bright, rimmed globule excited by the O6.5 star HD 206267 in the Cep OB2 association. Single-dish high resolution observations in CO and CS lines reveal the cometary structure of the globule with unprecedented detail. The globule head contains a dense core of 0.2 pc, whereas the tail, pointing away from the exciting star, has a total length of 0.8 pc. Two high velocity bipolar outflows have been identied in the CO maps: the rst one is located around the position of a strong IRAS source in the head of the globule, and the second one, which was previously unknown, is located in the northern region. The outflows emerge from high density clumps which exhibit strong line emission of CS, HCO + , and DCO + . Within these clumps, the sources driving the outflows have been identied thanks to mm-wave continuum observations. The globule head harbors two YSOs separated by about 10 4 AU. SiO line observations of the central outflow unveals a highly collimated structure with four clumps of sizes0: 1p c, which are located along the outflow axis and suggest episodic events in the mass loss process from the central star. Kinetic temperatures of50 100 K and hydrogen densities of fews 10 6 cm 3 have been estimated in the shocked regions traced by the strong SiO emission. The jet is also exposed to view by the means of interferometric HCO + observations that conrms that it is very narrow (0:02 pc wide). The detection of blue- and redshifted CO emission along the globule rim suggests that IC 1396N is in a transient phase, undergoing one of the expansions or compressions predicted by theoretical models describing the evolution of cometary globules. Moreover, the CO data, together with near IR observations reported elsewhere, indicate that the star forming process is occurring also in the northern part of IC 1396N, at 0.5 pc from the central CS peak. The present observations provide evidence that several star-forming sites can develop even in a moderately massive globule like IC 1396N.

The Herschel and IRAM CHESS Spectral Surveys of the Protostellar Shock L1157-B1: Fossil Deuteration

We present the first study of deuteration toward the protostellar shock L1157-B1, based on spectral surveys performed with the Herschel-HIFI and IRAM 30 m telescopes. The L1157 outflow is driven by a low-mass Class 0 protostar and is considered the prototype of the so-called chemically active outflows. The young (2000 yr), bright blueshifted bow shock, B1, is an ideal laboratory for studying the gas chemically enriched by the release of dust mantles due to the passage of a shock. A total of 12 emission lines (up to E_u = 63 K) of CH_(2)DOH, HDCO, and DCN are detected. In addition, two lines of NH_(2)D and HDO are tentatively reported. To estimate the deuteration, we also extracted from our spectral survey emission lines of non-deuterated isotopologues (^(13)CH_(3)OH, H_2 ^(13)CO, H^(13)CN, H_2 ^(13)CO, and NH_3). We infer higher deuteration fractions for CH_(3)OH (D/H = 0.2-2 × 10^(–2)) and H_(2)CO (5-8 × 10^(–3)) than for H_(2)O (0.4-2 × 10^(–3)), HCN (~10^(–3)), and ammonia (≤3 × 10^(–2)). The measurement of deuteration of water, formaldehyde, and methanol in L1157-B1 provides a fossil record of the gas before it was shocked by the jet driven by the protostar. A comparison with gas-grain models indicates that the gas passed through a low-density (≤10^3 cm^(–3)) phase, during which the bulk of water ices formed, followed by a phase of increasing density, up to 3 × 10^4 cm^(–3), during which formaldehyde and methanol ices formed.

G24.78+0.08: A cluster of high-mass (proto)stars

We present the results of high angular resolution observations at millimeter wavelengths of the high-mass star forming region G24.78+0.08, where a cluster of four young stellar objects is detected. We discuss evidence for these to be high-mass (proto)stars in dierent evolutionary phases. One of the sources is detected only in the continuum at 2 and 2.6 mm and we suggest it may represent a good candidate of a high-mass protostar.

SiO collimated outflows driven by high-mass YSOs in G24.78+0.08

We imaged the molecular outflows towards the cluster of high-mass young stellar objects G24.78+0.08 at high-angular resolution using SiO emission, which is considered the classical tracer of protostellar jets. We performed SiO observations with the VLA interferometer in the J = 1-0 v=0 transition and with the SMA array in the 5-4 transition. A complementary IRAM 30-m single-dish survey in the (2-1), (3-2), (5-4), and (6-5) SiO lines was also carried out. Two collimated SiO high-velocity outflows driven by the A2 and C millimeter continuum massive cores have been imaged. On the other hand, we detected no SiO outflow driven by the young stellar objects in more evolved evolutionary phases that are associated with ultracompact (B) or hypercompact (A1) HII regions. The LVG analysis reveals high-density gas (10^3-10^4 cm-3), with well constrained SiO column densities (0.5-1 10^15 cm-2). The driving source of the A2 outflow is associated with typical hot core tracers such as methyl formate, vinyl cyanide, cyanoacetilene, and acetone. The driving source of the main SiO outflow in G24 has an estimated luminosity of a few 10^4 Lsun (typical of a late O-type star) and is embedded in the 1.3 mm continuum core A2, which in turn is located at the centre of a hot core that rotates on a plane perpendicular to the outflow main axis. The present SiO images support a scenario similar to the low-mass case for massive star formation, where jets that are clearly traced by SiO emission, create outflows of swept-up ambient gas usually traced by CO.

High SiO abundance in the HH212 protostellar jet

Context. Previous SiO maps of the innermost regions of HH212 set strong constraints on the structure and origin of this jet. They rule out a fast wide-angle wind, and tentatively favor a magneto-centrifugal disk wind launched out to 0.6 AU. Aims. We aim to assess the SiO content at the base of the HH212 jet to set an independent constraint on the location of the jet launch zone with respect to the dust sublimation radius. Methods. We present the first sub-arcsecond (0. �� 44 × 0. �� 96) CO map of the HH212 jet base, obtained with the IRAM Plateau de Bure Interferometer. Combining this with previous SiO(5–4) data, we infer the CO(2–1) opacity and mass-flux in the high-velocity jet and arrive at a much tighter lower limit to the SiO abundance than possible from the (optically thick) SiO emission alone. Results. Gas-phase SiO at high velocity contains at least 10% of the elemental silicon if the jet is dusty, and at least 40% if the jet is dust-free, if CO and SiO have similar excitation temperatures. Such a high SiO content is challenging for current chemical models of both dust-free winds and dusty interstellar shocks. Conclusions. Updated chemical models (equatorial dust-free winds, highly magnetized dusty shocks) and observations of higher J CO lines are required to elucidate the dust content and launch radius of the HH212 high-velocity jet.

Formation of ethylene glycol and other complex organic molecules in star-forming regions

Context. The detection of complex organic molecules related with prebiotic chemistry in star-forming regions allows us to investigate how the basic building blocks of life are formed. Aims. Ethylene glycol (CH 2 OH) 2 is the simplest sugar alcohol and the reduced alcohol of the simplest sugar glycoladehyde (CH 2 OHCHO). We study the molecular abundance and spatial distribution of (CH 2 OH) 2 , CH 2 OHCHO and other chemically related complex organic species (CH 3 OCHO, CH 3 OCH 3 , and C 2 H 5 OH) towards the chemically rich massive star-forming region G31.41+0.31. Methods. We analyzed multiple single-dish (Green Bank Telescope and IRAM 30 m) and interferometric (Submillimeter Array) spectra towards G31.41+0.31, covering a range of frequencies from 45 to 258 GHz. We fitted the observed spectra with a local thermodynamic equilibrium (LTE) synthetic spectra, and obtained excitation temperatures and column densities. We compared our findings in G31.41+0.31 with the results found in other environments, including low- and high-mass star-forming regions, quiescent clouds and comets. Results. We report for the first time the presence of the aGg’ conformer of (CH 2 OH) 2 towards G31.41+0.31, detecting more than 30 unblended lines. We also detected multiple transitions of other complex organic molecules such as CH 2 OHCHO, CH 3 OCHO, CH 3 OCH 3 , and C 2 H 5 OH. The high angular resolution images show that the (CH 2 OH) 2 emission is very compact, peaking towards the maximum of the 1.3 mm continuum. These observations suggest that low abundance complex organic molecules, like (CH 2 OH) 2 or CH 2 OHCHO, are good probes of the gas located closer to the forming stars. Our analysis confirms that (CH 2 OH) 2 is more abundant than CH 2 OHCHO in G31.41+0.31, as previously observed in other interstellar regions. Comparing different star-forming regions we find evidence of an increase of the (CH 2 OH) 2 /CH 2 OHCHO abundance ratio with the luminosity of the source. The CH 3 OCH 3 /CH 3 OCHO and (CH 2 OH) 2 /C 2 H 5 OH ratios are nearly constant with luminosity. We also find that the abundance ratios of pairs of isomers (CH 2 OHCHO/CH 3 OCHO and C 2 H 5 OH/CH 3 OCH 3 ) decrease with the luminosity of the sources. Conclusions. The most likely explanation for the behavior of the (CH 2 OH) 2 /CH 2 OHCHO ratio is that these molecules are formed by different chemical formation routes not directly linked, although different formation and destruction efficiencies in the gas phase cannot be ruled out. The most likely formation route of (CH 2 OH) 2 is by combination of two CH 2 OH radicals on dust grains. We also favor that CH 2 OHCHO is formed via the solid-phase dimerization of the formyl radical HCO. The interpretation of the observations also suggests a chemical link between CH 3 OCHO and CH 3 OCH 3 , and between (CH 2 OH) 2 and C 2 H 5 OH. The behavior of the abundance ratio C 2 H 5 OH/CH 3 OCH 3 with luminosity may be explained by the different warm-up timescales in hot cores and hot corinos.

Water and acetaldehyde in HH212: The first hot corino in Orion

Aims. Using the unprecedented combination of high resolution and sensitivity offered by ALMA, we aim to investigate whether and how hot corinos, circumstellar disks, and ejected gas are related in young solar-mass protostars. Methods. We observed CH3CHO and deuterated water (HDO) high-excitation (Eu up to 335 K) lines towards the Sun-like protostar HH212−MM1. Results. For the first time, we have obtained images of CH3CHO and HDO emission in the inner � 100 AU of HH212. The multifrequency line analysis allows us to contrain the density (≥10 7 cm −3 ), temperature (� 100 K), and CH3CHO abundance (� 0.2−2 × 10 −9 ) of the emitting region. The HDO profile is asymmetric at low velocities (≤ 2k ms −1 from Vsys). If the HDO line is optically thick, this points to an extremely small (∼20−40 AU) and dense (≥10 9 cm −3 ) emitting region. Conclusions. We report thefirst detection of a hot corino in Orion. The HDO asymmetric profile indicates a contribution of outflowing gas from the compact central region, possibly associated with a dense disk wind.

ERRATUM: “THE HERSCHEL AND IRAM CHESS SPECTRAL SURVEYS OF THE PROTOSTELLAR SHOCK L1157-B1: FOSSIL DEUTERATION” (2012, ApJ, 757, L9)

C. Codella1,2, C. Ceccarelli2, B. Lefloch2,3, F. Fontani1, G. Busquet4, P. Caselli5, C. Kahane2, D. Lis6, V. Taquet2, M. Vasta1, S. Viti7, and L. Wiesenfeld2 1 INAF, Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze, Italy; codella@rcetri.astro.it 2 UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041, France 3 Centro de Astrobiologia, CSIC-INTA, Carretera de Ajalvir, Km 4, Torrejon de Ardoz, E-28850, Madrid, Spain 4 INAF-Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere 100, I-00133 Roma, Italy 5 School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK 6 California Institute of Technology, Cahill Center for Astronomy and Astrophysics 301-17, Pasadena, CA 91125, USA 7 Department of Physics and Astronomy, University College London, London, UK Received 2012 October 9; published 2012 October 26

Close encounters of the protostellar kind in IC 1396N

We have mapped in the 2.7 mm continuum and 12 CO with the PdBI the IR-dark “tail” that crosses the IC 1396N globule from south to north, and is the most extincted part of this cloud. These observations have allowed us to distinguish all possible associations of molecular hydrogen emission features by revealing two well-collimated low-mass protostellar outflows at the northern part of the globule. The outflows are located almost in the plane of the sky and are colliding with each other towards the position of a strong 2.12 μ mH 2 line emission feature.