E. M. Arnal

The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections

We present the final data release of observations of ?21-cm emission from Galactic neutral hydrogen over the entire sky, merging the Leiden/Dwingeloo Survey (LDS: Hartmann & Burton 1997, Atlas of Galactic Neutral Hydrogen) of the sky north of ? = ?30? with the Instituto Argentino de Radioastronomia Survey (IAR: Arnal et al. 2000, AA and Bajaja et al. 2005, A&A, 440, 767) of the sky south of ? = ?25?. The angular resolution of the combined material is HPBW ? 0. ?6. The LSR velocity coverage spans the interval ?450 km s?1 to +400 km s?1, at a resolution of 1.3 kms?1. The data were corrected for stray radiation at the Institute for Radioastronomy of the University of Bonn, refining the original correction applied to the LDS. The rms brightness-temperature noise of the merged database is 0.07?0.09 K. Residual errors in the profile wings due to defects in the correction for stray radiation are for most of the data below a level of 20?40 mK. It would be necessary to construct a telescope with a main beam efficiency of ?MB >? 99% to achieve the same accuracy. The merged and refined material entering the LAB Survey of Galactic HI is intended to be a general resource useful to a wide range of studies of the physical and structural characteristices of the Galactic interstellar environment. The LAB Survey is the most sensitive Milky Way HI survey to date, with the most extensive coverage both spatially and kinematically.

The Interstellar Medium around Galactic WN Stars: WR 2, WR 128, and WR 151

The neutral hydrogen distribution has been studied in the direction of three Galactic Wolf-Rayet (W-R) stars, using the 100 m Effelsberg radio telescope. Neutral hydrogen voids, regions of low H I emissivity, are observed over a 10–16 km s-1 velocity range for the stars WR 2 (=HD 6327), WR 128 (=HD 187282), and WR 151 (=CX Cep). These minima are interpreted as the observable 21 cm counterpart of the interstellar bubble created by the powerful winds of W-R stars and their progenitors. The H I cavities are elongated structures having an axial ratio ranging from 1.3 (WR 151) to 2.0 (WR 128). As pointed out in previous studies, the W-R stars are always off-center with respect to either the geometric center of the H I void or the absolute minimum inside the cavity. This offset ranges from 40% to 70% of the H I holes minor axis. The major axes of these cavities are ~30 pc for both WR 2 and WR 128, and ~50 pc for WR 151. The missing H I mass amounts to 96 M⊙ (WR 128), 200 M⊙ (WR 2), and 480 M⊙ (WR 151). Some of the physical parameters of the ring nebula associated with WR 128, such as its expansion velocity, 80 ± 22 km s-1, radius, 6.3 ± 0.2 pc, and characteristic age, (7.4 ± 2.4) × 104 yr, are derived from a simple geometric model that accounts for the discrepancy between the radial velocity of the H I hole and the ring nebula related to WR 128.

GS263-02+45 : a new H I supershell with evidence of having triggered star formation?

Fil: Arnal, Edmundo Marcelo. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Instituto Argentino de Radioastronomia. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto Argentino de Radioastronomia; Argentina

A new catalog of H i supershell candidates in the outer part of the Galaxy

Aims. The main goal of this work is to a have a new neutral hydrogen (H i) supershell candidate catalog to analyze their spatial distribution in the Galaxy and to carry out a statistical study of their main properties. Methods. This catalog was carried out making use of the Leiden-Argentine-Bonn (LAB) survey. The supershell candidates were identified using a combination of two techniques: a visual inspection plus an automatic searching algorithm. Our automatic algorithm is able to detect both closed and open structures. Results. A total of 566 supershell candidates were identified. Most of them (347) are located in the second Galactic quadrant, while 219 were found in the third one. About 98% of a subset of 190 structures (used to derive the statistical properties of the supershell candidates) are elliptical with a mean weighted eccentricity of 0.8 ± 0.1, and ∼70% have their major axes parallel to the Galactic plane. The weighted mean value of the effective radius of the structures is ∼160 pc. Owing to the ability of our automatic algorithm to detect open structures, we have also identified some “galactic chimney” candidates. We find an asymmetry between the second and third Galactic quadrants in the sense that in the second one we detect structures as far as 32 kpc, while for the 3rd one the farthest structure is detected at 17 kpc. The supershell surface density in the solar neighborhood is ∼8 kpc −2 , and decreases as we move farther away form the Galactic center. We have also compared our catalog with those by other authors.

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.

The interstellar medium surrounding the Scorpius-Centaurus association revisited

Fil: Poppel, W, G. L.. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Instituto Argentino de Radioastronomia. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto Argentino de Radioastronomia; Argentina

Molecular gas associated with RCW 121 and RCW 122

The distribution of the molecular gas towards the region containing the open cluster HM 1, the Wolf-Rayet stars WR 87, WR 89, and WR 91, and the star forming regions RCW 121 and RCW 122 is analyzed with the aim of looking for a possible physical relationship among these objects. Using 12 CO observations carried out at 2.6 mm with the 4 m NANTEN radiotelescope, and adopting a distance of 5 kpc for RCW 121 and RCW 122, a giant molecular cloud (GMC) having a lineal extent of 100 20 pc is found to be associated with these galactic star-forming regions. The total mass of this GMC is of the order of 1.2 10 6 solar masses and its mean radial velocity is about 15 km s 1 .

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Intermediate angular resolution (HPBW= 8: 0 7) carbon monoxide ( 12 CO J = 1!0) line observations towards the OB association Ara OB1 are reported. The molecular line observations cover an area of 2:75 3:00, and disclose a rich and complex distribution of the molecular line emission. The molecular features likely to be associated with the OB-association Ara OB1 span the velocity range from 28 to 20 km s 1 . The most negative radial velocities are observed along NGC 6188 (Rim nebula). This nebula marks the interface between the Hii region RCW 108 and the highly absorbing molecular material located westwards of the ionised region. The dominant CO structures, labeled E and F, have a radial velocity of about 23:5 and 21: 8k m s 1 , respectively. The former harbours a bright optical knot, the infrared cluster RCW-108 and the strong IRAS source 16362 4845. IRAS point sources are also seen in projection onto 12 CO concentrations F and H. This may indicate that the star forming process is a widespread phenomenon in this molecular complex. Extended continuum emission, having a high degree of spatial correlation with both the infrared and molecular emission, is observed in the region. We believe that this emission, thermal in nature, arises from the ionised surface layers of the molecular complex. The ionising agents are the high mass stars of NGC 6193, the nucleus of Ara OB1. The total amount of molecular gas related to Ara OB1 is about1:4 10 4 M.

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Fil: Corti, Mariela Alejandra. 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