C. E. Cappa

Unveiling the birth and evolution of the H II region Sh2-173

Based on a multiwavelength study, the interstellar medium around the H II region Sh2-173 has been analysed. The ionized region is clearly detected in the optical and the radio continuum images. The analysis of the H I data shows a region of low emissivity that has an excellent morphological correlation with the radio continuum emission. The H II region is partially bordered by a photodissociation region, which, in turn, is encircled by a molecular structure. The H I and CO structures related to Sh2-173 are observed in the velocity ranges from −25 to −31 km s −1 and from −27 to −39 km s −1 , respectively. Taking into account the presence of non-circular motions in the Perseus spiral arm, together with previous distance estimates for the region, we adopt a distance of 2.5 ± 0.5 kpc for Sh2-173. Seven hot stars were identified in the field of Sh2-173, being only one O-type star. The amount of energetic photons emitted by this star is enough to keep the region ionized and heat the dust. Given that an expanding H II region may trigger star formation, a search for young stellar object (YSO) candidates was made using different infrared point source catalogues. A population of 46 YSO candidates was identified, projected on to the molecular clouds. On the other hand, Sh2-173 is located in a dense edge of a large (∼5 ◦ )H I shell, GSH 117.8+1.5-35. The possibility of Sh2-173 being part of a hierarchical system of three generations is suggested. In this scenario, the large H I shell, which probably originated due to the action of Cas OB5, would have triggered the formation of Sh2-173, which, in turn, is triggering new stars in its surrounding molecular cloud. To test this hypothesis, the ages of both the H II region and the large shell were estimated and compared. We concluded that Sh2-173 is a young H II region of about 0.6–1.0 Myr old. As for the large shell, we obtained a dynamical age of 5 ± 1 Myr. These age estimates, together with the relative location of the different structures, support the hypothesis that Sh2-173 is part of a hierarchical system.

VLA and Effelsberg observations of the interstellar medium around the runaway star WR 124

Aims. We present very large array (VLA) and Effelsberg radio continuum and 21 cm H i line observations of the interstellar medium (ISM) surrounding the runaway star WR 124 and the nebula M 1-67. The H I data have been used to investigate the effects that a star with a strong stellar wind and a high peculiar velocity has on the ISM. Methods. The VLA 21 cm H I observations were combined with single-dish Effelsberg observations to produce a series of H I images sensitive to all angular scales from the VLA resolution limit (∼46 �� ) up to the primary field of individual VLA antennae (FWHM = 36 � ). MSX and IRIS images were used to analyze the infrared emission around the star. Because the star is highly supersonic with respect to its local ISM, the observed H I distribution around the star is interpreted in terms of a simple bow shock model. Results. The analysis of the H I data reveals the presence of a cavity centered on the star at an LSR velocity of ∼60 km s −1 , consistent with a distance estimate of 5 kpc for WR 124. A second H I cavity is observed located 10 � to the north of the stellar position, consistent with the direction of motion of WR 124. The VLA continuum image at 8.5 GHz shows a remarkable resemblance to the optical images. All available radio continuum data suggest a purely thermal spectrum for the nebula. The MSX and IRIS infrared data show a changing morphology with wavelength. The dust temperature deduced from the infrared luminosities is in agreement with previous observations of bow shocks.

A multifrequency study of the active star-forming complex NGC 6357 – I. Interstellar structures linked to the open cluster Pis 24

We investigate the distribution of the gas (ionized, neutral atomic and molecular), and interstellar dust in the complex star forming region NGC6357 with the goal of studying the interplay between the massive stars in the open cluster Pis24 and the surrounding interstellar matter. Our study of the distribution of the ionized gas is based on narrow-band Hα, [Sii], and [Oiii] images obtained with the Curtis-Schmidt Camera at CTIO, Chile, and on radio continuum observations at 1465 MHz taken with the VLA with a synthesized beam of 40 ′′ . The distribution of the molecular gas is analyzed using 12 CO(1-0) data obtained with the Nanten radiotelescope, Chile (angular resolution = 2. ′ 7). The interstellar dust distribution was studied using mid-infrared data from the GLIMPSE survey and far-infrared observations from IRAS. NGC6357 consists of a large ionized shell and a number of smaller optical nebulosities. The optical, radio continuum, and near- and mid-IR images delineate the distributions of the ionized gas and interstellar dust in the Hii regions and in previously unknown wind blown bubbles linked to the massive stars in Pis24 revealing surrounding photodissociation regions. The CO line observations allowed us to identify the molecular counterparts of the ionized structures in the complex and to confirm the presence of photodissociation regions. The action of the WR star HD157504 on the surrounding gas was also investigated. The molecular mass in the complex is estimated to be (4±2)×10 5 M⊙. Mean electron densities derived from the radio data suggest electron densities >200 cm −3 , indicating that NGC6357 is a complex formed in a region of high ambient density. The known massive stars in Pis24 and a number of newly inferred massive stars are mainly responsible for the excitation and photodissociation of the parental molecular cloud.

870 micron continuum observations of the bubble-shaped nebula Gum 31

Fil: Duronea, Nicolas Urbano. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico La Plata. Instituto Argentino de Radioastronomia (i); Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronomicas y Geofisicas; Argentina

The structure and kinematics of the ISM around HD 192281

Aims. This work aims at investigating the interaction of HD 192281 (O5 Vn((f))p) with its local ISM. The purpose is to analyse the effects that a massive star has on the structure and kinematics of its surrounding gas. Methods. To carry out this study, we used high-resolution radio continuum and 21-cm H i line data from the Canadian Galactic Plane Survey (CGPS). This data base was complemented with radio continuum, infrared, and molecular data retrieved from available surveys. Given that HD 192281 is very likely a runaway star, we attempt to establish whether the observed H i distribution can be interpreted in terms of a simple bow shock model. Results. Analysis of the H i data shows the presence of an H i feature likely to be associated with HD 192281. This feature remains detectable from ∼5 to –10 km s−1. At the most negative radial velocities, the shape of the H i feature is highly reminiscent of a bow shock structure seen projected onto the plane of the sky. This feature has counterparts at radio-continuum, infrared, and CO emissions. The analysis of the radio continuum data suggests a thermal spectrum for the gas related to this structure.

Star forming regions linked to RCW78 and the discovery of a new IR bubble

Aims. With the aim of investigating the presence of molecular and dust clumps linked to two star forming regions identified in the expanding molecular envelope of the stellar wind bubble RCW 78, we analyzed the distribution of the molecular gas and cold dust. Methods. To accomplish this study we performed dust continuum observations at 870 μ ma nd 13 CO(2–1) line observations with the Atacama Pathfinder EXperiment (APEX) telescope, using the Large Apex BOlometer CAmera (LABOCA) and SHeFI-1 instruments, respectively, and analyzed Herschel images at 70, 160, 250, 350, and 500 μm. Results. These observations allowed us to identify cold dust clumps linked to region B (that we have named the southern clump) and region C (clumps 1 and 2), and an elongated filament. Molecular gas was clearly detected linked to the southern clump and the filament. The velocity of the molecular gas is compatible with the location of the dense gas in the expanding envelope of RCW 78. We estimate dust temperatures and total masses for the dust condensations from the emissions at different wavelengths in the far-IR and from the molecular line using local thermodynamic equilibrium and the virial theorem. Masses obtained through different methods agree within a factor of 2–6. Color–color diagrams and spectral energy distribution analysis of young stellar objects (YSOs) confirmed the presence of intermediate and low-mass YSOs in the dust regions, indicating that moderate star formation is present. In particular, a cluster of IR sources was identified inside the southern clump. The IRAC image at 8 μm revealed the existence of an infrared dust bubble of 16 �� in radius probably linked to the O-type star HD 117797 located at 4 kpc. The distribution of the near- and mid-IR emission indicate that warm dust is associated with the bubble.

Molecules, dust, and protostars in NGC 3503

Aims. We are presenting here a follow-up study of the molecular gas and dust in the environs of the star forming region NGC 3503. This study aims at dealing with the interaction of the Hii region NGC 3503 with its parental molecular cloud, and also with the star formation in the region, that was possibly triggered by the expansion of the ionization front against the parental cloud . Methods. To analyze the molecular gas we use CO(J=2→1), 13 CO(J=2→1), C 18 O(J=2→1), and HCN(J=3→2) line data obtained with the on-the-fly technique from the APEX telescope. To stu dy the distribution of the dust, we make use of unpublished images at 870 µm from the ATLASGAL survey and IRAC-GLIMPSE archival images . We use public 2MASS and WISE data to search for infrared candidate YSOs in the region. Results. The new APEX observations allowed the substructure of the molecular gas in the velocity range from∼−28 to−23 km s −1 to be imaged in detail. The morphology of the molecular gas close to the nebula, the location of the PDR, and the shape of radio continuum emission suggest that the ionized gas is expanding against its parental cloud, and confirm the “champagne flow” sce nario. We have identified several molecular clumps and determined som e of their physical and dynamical properties such as density, excitation temperature, mass, and line width. Clumps adjacent to the ionization front are expected to be affected by the Hii region, unlike those that are distant to it. We have compared the physical properties of the two kind of clumps to investigate how the molecular gas has been affected by the Hii region. Clumps adjacent to the ionization fronts of NGC 3503 and/or the bright rimmed cloud SFO 62 have been heated and compressed by the ionized gas, but their line width is not different to those that are too distant to the ionization fronts. We identified several candidate YSOs in the region. Their spa tial distribution suggests that stellar formation might ha ve been boosted by the expansion of the nebula. We discard the “collect and collapse” scenario and propose alternative mechanisms such as radiatively driven implosion on pre-existing molecular clumps or small-scale Jeans gravitational instabilities.

Molecular gas toward G18.8+1.8

Fil: Vasquez, Javier. Provincia de Buenos Aires. Gobernacion. Comision de Invest.cientificas. Instituto Argentino de Radioastronomia. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - la Plata. Instituto Argentino de Radioastronomia; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronomicas y Geofisicas; Argentina

Molecular gas and star formation towards the IR dust bubble S24 and its environs

Fil: Cappa, Cristina Elisabeth. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico la Plata. Instituto Argentino de Radioastronomia (i); Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronomicas y Geofisicas; Argentina

Molecular gas associated with IRAS 10361-5830

Aims. We analyze the distribution of the molecular gas and dust in the molecular clump linked to IRAS 10361-5830, located in the environs of the bubble-shaped Hii region Gum 31 in the Carina region, with the aim of determining the main parameters of the associated material and of investigating the evolutionary state of the young stellar objects identified there. Methods. Using the APEX telescope, we mapped the molecular emission in the J = 3−2 transition of three CO isotopologues, 12 CO, 13 CO and C 18 O, over a 1. 5 × 1. � 5 region around the IRAS position. We also observed the high-density tracers CS and HCO + toward the source. The cold- dust distribution was analyzed using submillimeter continuum data at 870 μm obtained with the APEX telescope. Complementary IR and radio data at different wavelengths were used to complete the study of the interstellar medium. Results. The molecular gas distribution reveals a cavity and a shell-like structure of ∼0.32 pc in radius centered at the position of the IRAS source, with some young stellar objects projected onto the cavity. The total molecular mass in the shell and the mean H2volume