S. Cichowolski

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.

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.

An

We investigate the ISM in the vicinity of the O-type stars BDxa0+24°3866 (O8.5II(f)), BDxa0+24°3881 (O6.5III(f)) andxa0BDxa0+24° 3952 (O8) based on radio continuum andxa0Hixa0line data obtained with the Synthesis Telescope of the Dominion Radio Astrophysical Observatory (DRAO) with synthesized beams of 1

\ion{H}{i}

farcm

interstellar bubble linked to the O-type stars BD +24°3866 and BD +25°3952

5 and 7´u2000at 1420 andxa0408xa0MHz, respectively. High angular resolution IRAS data ( HIRES ) are also analyzed. BDxa0+24°3866 is found to be located close to the inner border of a slowly expanding shell. The evolved Hiiu2000region Sh2-88, which is excited by BDxa0+25°3952, appears to be interacting with neutral material in the approaching part of this shell. The whole structure is at a distance ofxa02.4xa0kpc and is about 23

The radio and infrared counterparts of the ring nebula around HD 211564

times

Triggered star formation in a molecular shell created by a SNR

15xa0pc in radius. The total swept up mass is 1300xa0

GS100-02-41: a new large H i shell in the outer part of the Galaxy

M_odot

A multi-wavelength analysis of the diffuse H ii region G25.8700+0.1350

. The stellar winds of BDxa0+24°3866 and BDxa0+25°3952, are mainly responsible for shaping the Hiu2000structure. An Hiu2000expanding shell was also found to be related to the Hiixa0region G61.7+0.9. At a kinematic distance ofxa02.4xa0kpc, this feature is 10xa0pc in radius and has neutral and ionized masses of 200 andxa0135xa0