Detection of a dense clump in a filament interacting with W51e2

In the framework of the Herschel/PRISMAS Guaranteed Time Key Program, the line of sight to the distant ultracompact HII region W51e2 has been observed using several selected molecular species. Most of the detected absorption features are not associated with the background high-mass star-forming region and probe the diffuse matter along the line of sight. We present here the detection of an additional narrow absorption feature at ~70 km/s in the observed spectra of HDO, NH3 and C3. The 70 km/s feature is not uniquely identifiable with the dynamic components (the main cloud and the large-scale foreground filament) so-far identified toward this region. The narrow absorption feature is similar to the one found toward low-mass protostars, which is characteristic of the presence of a cold external envelope. The far-infrared spectroscopic data were combined with existing ground-based observations of 12CO, 13CO, CCH, CN, and C3H2 to characterize the 70 km/s component. Using a non-LTE analysis of multiple transitions of NH3 and CN, we estimated the density (n(H2) (1-5)x10^5 cm^-3) and temperature (10-30 K) for this narrow feature. We used a gas-grain warm-up based chemical model with physical parameters derived from the NH3 data to explain the observed abundances of the different chemical species. We propose that the 70 km/s narrow feature arises in a dense and cold clump that probably is undergoing collapse to form a low-mass protostar, formed on the trailing side of the high-velocity filament, which is thought to be interacting with the W51 main cloud. While the fortuitous coincidence of the dense clump along the line of sight with the continuum-bright W51e2 compact HII region has contributed to its non-detection in the continuum images, this same attribute makes it an appropriate source for absorption studies and in particular for ice studies of star-forming regions.

The chemistry of C3 & Carbon Chain Molecules in DR21(OH)

(Abridged) We have observed velocity resolved spectra of four ro-vibrational far-infrared transitions of C3 between the vibrational ground state and the low-energy nu2 bending mode at frequencies between 1654--1897 GHz using HIFI on board Herschel, in DR21(OH), a high mass star forming region. Several transitions of CCH and c-C3H2 have also been observed with HIFI and the IRAM 30m telescope. A gas and grain warm-up model was used to identify the primary C3 forming reactions in DR21(OH). We have detected C3 in absorption in four far-infrared transitions, P(4), P(10), Q(2) and Q(4). The continuum sources MM1 and MM2 in DR21(OH) though spatially unresolved, are sufficiently separated in velocity to be identified in the C3 spectra. All C3 transitions are detected from the embedded source MM2 and the surrounding envelope, whereas only Q(4) & P(4) are detected toward the hot core MM1. The abundance of C3 in the envelope and MM2 is sim6x10^{-10} and sim3x10^{-9} respectively. For CCH and c-C3H2 we only detect emission from the envelope and MM1. The observed CCH, C3, and c-C3H2 abundances are most consistent with a chemical model with n(H2)sim5x10^{6} cm^-3 post-warm-up dust temperature, T_max =30 K and a time of sim0.7-3 Myr. Post warm-up gas phase chemistry of CH4 released from the grain at tsim 0.2 Myr and lasting for 1 Myr can explain the observed C3 abundance in the envelope of DR21(OH) and no mechanism involving photodestruction of PAH molecules is required. The chemistry in the envelope is similar to the warm carbon chain chemistry (WCCC) found in lukewarm corinos. The observed lower C3 abundance in MM1 as compared to MM2 and the envelope could be indicative of destruction of C3 in the more evolved MM1. The timescale for the chemistry derived for the envelope is consistent with the dynamical timescale of 2 Myr derived for DR21(OH) in other studies.

The structure of hot gas in Cepheus B

By observing radiation-affected gas in the Cepheus B molecular cloud we probe whether the sequential star formation in this source is triggered by the radiation from newly formed stars. We used the dual band receiver GREAT onboard SOFIA to map [C II] and CO 13--12 and 11--10 in Cep B and compared the spatial distribution and the spectral profiles with complementary ground-based data of low-$J$ transitions of CO isotopes, atomic carbon, and the radio continuum. The interaction of the radiation from the neighboring OB association creates a large photon-dominated region (PDR) at the surface of the molecular cloud traced through the photoevaporation of C^+. Bright internal PDRs of hot gas are created around the embedded young stars, where we detect evidence of the compression of material and local velocity changes; however, on the global scale we find no indications that the dense molecular material is dynamically affected.

The Herschel M33 extended survey (HerM33es): PACS spectroscopy of the star forming region BCLMP 302

Context: The emission line of [CII] at 158 micron is one of the strongest cooling lines of the interstellar medium (ISM) in galaxies. Aims: Disentangling the relative contributions of the different ISM phases to [CII] emission, is a major topic of the HerM33es program, a Herschel key project to study the ISM in the nearby spiral galaxy M33. Methods: Using PACS, we have mapped the emission of [CII] 158 micron, [OI] 63 micron, and other FIR lines in a 2x2 region of the northern spiral arm of M33, centered on the HII region BCLMP302. At the peak of H-alpha emission, we have observed in addition a velocity resolved [CII] spectrum using HIFI. We use scatterplots to compare these data with PACS 160 micron continuum maps, and with maps of CO and HI data, at a common resolution of 12 arcsec or 50 pc. Maps of H-alpha and 24 micron emission observed with Spitzer are used to estimate the SFR. We have created maps of the [CII] and [OI] 63 micron emission and detected [NII] 122 micron and NIII 57 micron at individual positions. Results: The [CII] line observed with HIFI is significantly broader than that of CO, and slightly blue-shifted. In addition, there is little spatial correlation between [CII] observed with PACS and CO over the mapped region. There is even less spatial correlation between [CII] and the atomic gas traced by HI. Detailed comparison of the observed intensities towards the HII region with models of photo ionization and photon dominated regions, confirms that a significant fraction, 20--30%, of the observed [CII] emission stems from the ionized gas and not from the molecular cloud. The gas heating efficiency, using the ratio between [CII] and the TIR as a proxy, varies between 0.07 and 1.5%, with the largest variations found outside the HII region.

Optical/IR counterpart to the resolved X-ray jet source CXO J172337.5-373442 and its distance

We present results of observations in the optical to mid-infrared wavelengths of the X-ray source CXO J172337.5-373442, which was serendipitously discovered in the Chandra images and was found to have a fully resolved X-ray jet. The observations include a combination of photometry and spectroscopy in the optical using ground-based telescopes and mid-infrared photometry using Spitzer. We detect the optical/IR counterpart of CXO J172337.5-373442 and identify it to be a G9-V star located at a distance of 334+-60~pc. Comparable values of the hydrogen column densities determined independently from the optical/IR observations and X-ray observations indicate that the optical source is associated with the X-ray source. Since the X-ray luminosity can not be explained in terms of emission from a single G9-V star, it is likely that CXO J172337.5-373442 is an accreting compact object in a binary system. Thus, CXO J172337.5-373442 is the nearest known resolved X-ray jet from a binary system, which is not a symbiotic star. Based on the existing X-ray data, the nature of the compact object can not be confirmed. However the low luminosity of the X-ray point source, 7.1x10^{30} Lsun combined with estimates of the age of the jet and a lack of detection of bright outburst, suggests that the X-ray jet was launched during extreme quiescence of the object. The measured low X-ray luminosity of the jet suggests the likelihood of such jets being more ubiquitous than our current understanding.

Excitation and Abundance of C3 in star forming cores:Herschel/HIFI observations of the sight-lines to W31C and W49N

We present spectrally resolved observations of triatomic carbon (C3) in several ro-vibrational transitions between the vibrational ground state and the low-energy nu2 bending mode at frequencies between 1654-1897 GHz along the sight-lines to the submillimeter continuum sources W31C and W49N, using Herschels HIFI instrument. We detect C3 in absorption arising from the warm envelope surrounding the hot core, as indicated by the velocity peak position and shape of the line profile. The sensitivity does not allow to detect C3 absorption due to diffuse foreground clouds. From the column densities of the rotational levels in the vibrational ground state probed by the absorption we derive a rotation temperature (T_rot) of ~50--70 K, which is a good measure of the kinetic temperature of the absorbing gas, as radiative transitions within the vibrational ground state are forbidden. It is also in good agreement with the dust temperatures for W31C and W49N. Applying the partition function correction based on the derived T_rot, we get column densities N(C3) ~7-9x10^{14} cm^{-2} and abundance x(C3)~10^{-8} with respect to H2. For W31C, using a radiative transfer model including far-infrared pumping by the dust continuum and a temperature gradient within the source along the line of sight we find that a model with x(C3)=10^{-8}, T_kin=30-50 K, N(C3)=1.5 10^{15} cm^{-2} fits the observations reasonably well and provides parameters in very good agreement with the simple excitation analysis.

Young Stars and Protostellar Cores near NGC 2023

We investigate the young (proto)stellar population in NGC 2023 and the L 1630 molecular cloud bordering the HII region IC 434, using Spitzer IRAC and MIPS archive data, JCMT SCUBA imaging and spectroscopy as well as targeted BIMA observations of one of the Class 0 protostars, NGC 2023 MM1. We have performed photometry of all IRAC and MIPS images, and used color-color diagrams to identify and classify all young stars seen within a 22x26 field along the boundary between IC 434 and L 1630. For some stars, which have sufficient optical, IR, and/or sub-millimeter data we have also used the online SED fitting tool for a large 2D archive of axisymmetric radiative transfer models to perform more detailed modeling of the observed SEDs. We identify 5 sub-millimeter cores in our 850 and 450 micron SCUBA images, two of which have embedded class 0 or I protostars. Observations with BIMA are used to refine the position and characteristics of the Class 0 source NGC 2023 MM 1. These observations show that it is embedded in a very cold cloud core, which is strongly enhanced in NH2D. We find that HD 37903 is the most massive member of a cluster with 20 -- 30 PMS stars. We also find smaller groups of PMS stars formed from the Horsehead nebula and another elephant trunk structure to the north of the Horsehead. We refine the spectral classification of HD 37903 to B2 Ve. Our study shows that the expansion of the IC 434 HII region has triggered star formation in some of the dense elephant trunk structures and compressed gas inside the L 1630 molecular cloud. This pre-shock region is seen as a sub-millimeter ridge in which stars have already formed. The cluster associated with NGC 2023 is very young, and has a large fraction of Class I sources.

SCUBA Mapping of Outer Galaxy Protostellar Candidates

We aim to study dust properties of massive star forming regions in the outer Galaxy, in a direction opposite to the Galactic center. We present observations of six outer Galaxy point sources IRAS 01045+6505, 01420+6401, 05271+3059, 05345+3556, 20222+3541 and 20406+4555, taken with the Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT) at 450 and 850 micron. Single temperature greybody models are fitted to the Spectral Energy Distribution of the detected sub-mm cores to derive dust temperature, dust emissivity index and optical depth at 250 micron. The observed radial intensity profiles of the sub-mm cores were fitted with power laws to derive the indices describing the density distribution. At a resolution of 15 all six IRAS point sources show multiple emission peaks. Only four out of fourteen detected sub-mm cores show associated mid-infrared emission. For the sub-mm cores we derive dust temperatures of 32+-5 K and dust emissivity indices between 0.9 and 2.5. The density profiles of the sub-mm cores can be fitted by a single power law distribution with indices -1.5+-0.3, with most cores showing an index of -1.5. This is consistent with most observations of massive star forming regions and supports predictions of models of star formation which consider non-thermal support against gravitational collapse.