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.

The environment of the Wolf-Rayet (WR) star WR 130 has been studied using the 21 cm H I line and radio continuum data at 408 and 1420 MHz obtained with the Dominion Radio Astrophysical Observatory (DRAO) Synthesis Telescope. In addition, the H110a recombination line and 21 cm H I line were observed using the Very Large Array in the DnC and D conÐgurations. The Sharpless H II region, Sh 98 (size D15@), and two OB stars are observed near the Wolf-Rayet star position. An extended ring-shaped structure (G68.1]1.1) of size D20@ is observed in the radio continuum and infrared data. Of four compact radio sources seen superposed on the ring, one is an H II region of size D3@ (G68.14]0.92), while the others are probably extragalactic. The spectral index of G68.1]1.1 is a \ 0.0^0.1. (S l P la) The thermal nature of G68.1]1.1 is conÐrmed by an analysis of the correlation between the brightness temperature at 21 cm and the brightness at 60 km, as observed with IRAS. The DRAO H I data show an H I bubble in the velocity range [12 to 1 km s~1. The most striking characteristic of the H I cavity is the excellent correlation with the radio continuum ring. The WR star is not at the center of the ring, but in the dense border to the east. This eccentric position can be explained by a combination of a high spatial velocity for the star and projection e †ects. The possible contribution of the OB stars present in the area is also considered. From our H110a observations, together with other recombination lines observed in the area, we deduce a distance of 12 kpc for the compact H II region G68.14]0.92 and 5 kpc for G68.1]1.1. We conclude that G68.1]1.1 is the radio counterpart of the optical H II region Sh 98, while G68.14]0.92 is a chance superposition of a much more distant source. The ionized mass of the ring is estimated at D3000 and the rms electron density at D3 cm~3, assuming a homogene-M _ ous distribution. A missing H I mass of 500 is obtained for the cavity and an excess H I mass of M _ 1500 for the shell.

We observed the supernova remnant (SNR) Puppis A in the 21 cm line with the Australia Telescope Compact Array with the aim of determining the systemic velocity and, hence, the corresponding kinematic distance. For the compact, background sources in the field, we obtain absorption spectra by applying two methods: (a) subtracting profiles on-and off-source towards continuum emission, and (b) filtering short spacial frequencies in the Fourier plane to remove large scale emission. One of the brightest features to the East of the shell of Puppis A was found to be a background source, probably extragalactic. Removing the contribution from this and the previously known unrelated sources, the systemic velocity of Puppis A turns out to be limited between 8 and 12 km s −1 , which places this source at a distance of 1.3 ± 0.3 kpc. From the combined images that include both single dish and interferometric data, we analyze the distribution of the interstellar hydrogen. We suggest that an ellipsoidal ring at v ∼ +8 km s −1 could be the relic of a bubble blown by the progenitor of Puppis A, provided the distance is 1.2 kpc. The main consequences of the new systemic velocity and distance as compared with previous publications (v = +16 km s −1 and d = 2.2 kpc) are the absence of a dense interacting cloud to the East to explain the morphology, and the decrease of the shell size and the neutron star velocity, which are now in better agreement with statistical values.

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