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Register a new userSh2-205: I. The surrounding interstellar medium
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Added by
Gisela Romero G.A.R
Publication date
2008
fields
Physics
and research's language is
English
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We present a study of the HII region Sh2-205 and its environs, based on data obtained from the CGPS, 12CO observations, and MSX data. We find that Sh2-205 can be separated in three independent optical structures: SH 149.25-0.0, SH 148.83-0.67, and LBN 148.11-0.45. The derived spectral indices show the thermal nature of SH 148.83-0.67 and LBN 148.11-0.45. The morphology of SH 148.83-0.67, both in the optical and radio data, along with the energetic requ irements indicate that this feature is an interstellar bubble powered by the UV photons of HD 24431 (O9 III). LBN 148.11-0.45 has the morphology of a classic al HII region and their ionizing sources remain uncertain. Dust and molecular gas are found related to LBN 148.11-0.45.Particularly, a photodissociation region is detected at the interface between the ionized and molecular regions. If the proposed exciting star HD 24094 were an O8--O9 type star, as suggested by its near-infrared colors, its UV photon flux would be enough to explain the ionization of the nebula. The optical, radio continuum, and 21-cm line data allow us to conclude that SH 148.83-0.67 is an interstellar bubble powered by the energetic action of HD 24431. The associated neutral atomic and ionized masses are 180 Mo and 300 Mo, respectively. The emission of SH 149.25-0.0 is too faint to derive the dust and gas parameters. An HI shell centered at (l,b) = (149.0, 1.5) was also identified. It correlates morphologically with molecular gas emission. The neutral atomic and molecular masses are 1600 Mo and 2.6 x 10^4 Mo, respectively. The open cluster NGC 1444 is the most probable responsible for shaping this HI structure.
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We present a study of active stellar forming regions in the environs of the HII region Sh2-205. The analysis is based on data obtained from point source catalogues and images extracted from 2MASS, MSX, and IRAS surveys. Complementary data are taken from CO survey. The identification of primary candidates to stellar formation activity is made following colour criteria and the correlation with molecular gas emission. A number of stellar formation tracer candidates are projected on two substructures of the HII region: SH148.83-0.67 and SH149.25-0.00. However, the lack of molecular gas related to these structures casts doubts on the nature of the sources. Additional infrared sources may be associated with the HI shell centered at (l,b) = (149degr 0arcmin, -1degr 30arcmin). The most striking active area was found in connection to the HII region LBN 148.11-0.45, where stellar formation candidates are projected onto molecular gas. The analytical model to the collect and collapse process shows that stellar formation activity could have been triggered by the expansion of this HII region.
We present 1420 MHz polarization images of a 2.5 X 2.5 degree region around the planetary nebula (PN) Sh 2-216. The images are taken from the Canadian Galactic Plane Survey (CGPS). An arc of low polarized intensity appears prominently in the north-east portion of the visible disk of Sh 2-216, coincident with the optically identified interaction region between the PN and the interstellar medium (ISM). The arc contains structural variations down to the ~1 arcminute resolution limit in both polarized intensity and polarization angle. Several polarization-angle knots appear along the arc. By comparison of the polarization angles at the centers of the knots and the mean polarization angle outside Sh 2-216, we estimate the rotation measure (RM) through the knots to be -43 +/- 10 rad/m^2. Using this estimate for the RM and an estimate of the electron density in the shell of Sh 2-216, we derive a line-of-sight magnetic field in the interaction region of 5.0 +/- 2.0 microG. We believe it more likely the observed magnetic field is interstellar than stellar, though we cannot completely dismiss the latter possibility. We interpret our observations via a simple model which describes the ISM magnetic field around Sh 2-216, and comment on the potential use of old PNe as probes of the magnetized ISM.
We use new large area far infrared maps ranging from 65 - 500 microns obtained with the AKARI and the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) missions to characterize the dust emission toward the Cassiopeia A supernova remnant (SNR). Using the AKARI high resolution data we find a new tepid dust grain population at a temperature of ~35K and with an estimated mass of 0.06 solar masses. This component is confined to the central area of the SNR and may represent newly-formed dust in the unshocked supernova ejecta. While the mass of tepid dust that we measure is insufficient by itself to account for the dust observed at high redshift, it does constitute an additional dust population to contribute to those previously reported. We fit our maps at 65, 90, 140, 250, 350, and 500 microns to obtain maps of the column density and temperature of cold dust (near 16 K) distributed throughout the region. The large column density of cold dust associated with clouds seen in molecular emission extends continuously from the surrounding interstellar medium to project on the SNR, where the foreground component of the clouds is also detectable through optical, X-ray, and molecular extinction. At the resolution available here, there is no morphological signature to isolate any cold dust associated only with the SNR from this confusing interstellar emission. Our fit also recovers the previously detected hot dust in the remnant, with characteristic temperature 100 K.
We have developed a technique to map the three-dimensional structure of the local interstellar medium using a maximum entropy reconstruction technique. A set of column densities N to stars of known distance can in principle be used to recover a three-dimensional density field n, since the two quantities are related by simple geometry through the equation N = C n, where C is a matrix characterizing the stellar spatial distribution. In practice, however, there is an infinte number of solutions to this equation. We use a maximum entropy reconstruction algorithm to find the density field containing the least information which is consistent with the observations. The solution obtained with this technique is, in some sense, the model containing the minimum structure. We apply the algorithm to several simulated data sets to demonstrate its feasibility and success at recovering ``real density contrasts. This technique can be applied to any set of column densities whose end points are specified. In a subsequent paper we shall describe the application of this method to a set of stellar color excesses to derive a map of the dust distribution, and to soft X-ray absorption columns to hot stars to derive a map of the total density of the interstellar medium.
Observations of the nebula S3 associated with the WO star in the galaxy IC 1613 and of an extended region surrounding S3 are reported. The star and bright core of the nebula were observed with a multipupil fiber spectrograph mounted on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Images in the principle spectral lines and integrated spectra of the star and three compact clumps were obtained, and the radial-velocity field constructed. An extended region of the galaxy was observed with the Very Large Array at 21 cm. A giant ring or HI shell enclosing a large fraction of the stellar population in IC 1613 was discovered. The WO star and associated bipolar nebula, which we discovered earlier, lies at the inner edge of the H ring. A local HI deficiency and two arc-like HI ridges were also detected for the first time, and probably represent the neutral component of the bipolar shell surrounding the WO star. The two arc-like ridges may also have been produced by the collective stellar wind (and supernova explosions?) in OB association No. 9 from the list of Hodge. A scenario for the formation of the extended bipolar feature is discussed, based on the new data.
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