Search

The Milky Way is a huge system that consist of 100–400 billion stars, interstellar gas and dust, cosmic rays, electromagnetic radiation, interstellar magnetic fields, gravitational fields, dark matter. In spiral galaxies, like the Milky Way, most of the dust and gas is to be found within relatively thin gaseous disk, with a thickness of a few hundred parsecs, and within this disk nearly all of the star formation takes place. Among the least investigated directions in the Milky Way are the dark clouds in the Camelopardalis constellation. The distances of the clouds and their extinction are known with a low accuracy and only in some occasional directions. Straižys & Laugalys (2007, 2008) described a ring-like concentration of dust clouds located at the border of the Perseus, Camelopardalis, and Auriga constellations, which is perfectly seen in the Dobashi et al. (2005) atlas of dark clouds. The ring has a diameter of ∼8º and is centered on the open cluster NGC 1528. Trying to test physical reality of this dust ring, we decided to investigate distances to its clouds, extinction properties, and star formation activity. The method of investigation is based on Vilnius, 2MASS and WISE photometry of stars in 3 selected 1.5 deg2 areas centered on dust cloud TGU H994 P1, H II region Sh2-205 and star cluster King 7. CCD photometry of 4355 stars in the Vilnius seven-color photometric system was performed. Observations were made in Molėtai observatory with Maksutov telescope and with 1.8 meter VATT telescope on Mt. Graham, USA. Two-dimensional spectral types, interstellar extinction and distances for most of the observed stars were determined. The interstellar extinction run with distance and star formation activity in all investigated areas were determined. The main results of the investigation are published in three papers in ,,Baltic Astronomy“ and two papers in ,,Astronomy & Astrophysics“. The use of the Simbad (CDS), NED (NASA), SkyView (NASA), and CO Data Archive (Smithsonian AO Radio Telescope Data Center) databases is acknowledged.

The Milky Way is a huge system that consist of 100–400 billion stars, interstellar gas and dust, cosmic rays, electromagnetic radiation, interstellar magnetic fields, gravitational fields, dark matter. In spiral galaxies, like the Milky Way, most of the dust and gas is to be found within relatively thin gaseous disk, with a thickness of a few hundred parsecs, and within this disk nearly all of the star formation takes place. Among the least investigated directions in the Milky Way are the dark clouds in the Camelopardalis constellation. The distances of the clouds and their extinction are known with a low accuracy and only in some occasional directions. Straižys & Laugalys (2007, 2008) described a ring-like concentration of dust clouds located at the border of the Perseus, Camelopardalis, and Auriga constellations, which is perfectly seen in the Dobashi et al. (2005) atlas of dark clouds. The ring has a diameter of ∼8º and is centered on the open cluster NGC 1528. Trying to test physical reality of this dust ring, we decided to investigate distances to its clouds, extinction properties, and star formation activity. The method of investigation is based on Vilnius, 2MASS and WISE photometry of stars in 3 selected 1.5 deg2 areas centered on dust cloud TGU H994 P1, H II region Sh2-205 and star cluster King 7. CCD photometry of 4355 stars in the Vilnius seven-color photometric system was performed. Observations were made in Molėtai observatory with Maksutov telescope and with 1.8 meter VATT telescope on Mt. Graham, USA. Two-dimensional spectral types, interstellar extinction and distances for most of the observed stars were determined. The interstellar extinction run with distance and star formation activity in all investigated areas were determined. The main results of the investigation are published in three papers in ,,Baltic Astronomy“ and two papers in ,,Astronomy & Astrophysics“. The use of the Simbad (CDS), NED (NASA), SkyView (NASA), and CO Data Archive (Smithsonian AO Radio Telescope Data Center) databases is acknowledged.

In the inner parts of the Galaxy the Infrared Dark Clouds (IRDCs) are presently believed to be the progenitors of massive stars and star clusters. Many of them are predominantly devoid of active star formation and for now they represent the earliest observed stages of massive star formation. Their Outer Galaxy counterparts, if present, are not easily identified because of a low or absent mid-IR background. We characterize the ambient conditions in the Outer Galaxy IRDC candidate G111.80+0.58, a relatively quiescent molecular core complex in the vicinity of NGC7538. We conduct molecular line observations on a number of dense cores and analyze the data in terms of excitation temperature, column and volume density, mass and stability. The temperatures (15-20K) are higher than expected from only cosmic ray heating, but comparable to those found in massive cores. Star forming activity could be present in some cores, as indicated by the presence of warm gas and YSO candidates. The observed super-thermal line-widths are typical for star forming regions. The velocity dispersion is consistent with a turbulent energy cascade over the observed size scales. We do not find a correlation between the gas temperature and the line-width. The LTE masses we find are much larger than the thermal Jeans mass and fragmentation is expected. In that case the observed lines represent the combined emission of multiple unresolved components. We conclude that G111.80+0.58 is a molecular core complex with bulk properties very similar to IRDCs in an early, but not pristine, star forming state. The individual cores are close to virial equilibrium and some contain sufficient material to form massive stars and star clusters. The ambient conditions suggest that turbulence is involved in supporting the cores against gravitational collapse., Accepted for publication in A&A -- 19 pages, 9 figures -- high resolution available at http://www.astro.rug.nl/~frieswyk/Data/Research/OGIRDC/index.html

We report on the study of interstellar extinction across the Tarantula nebula (30 Doradus), in the Large Magellanic Cloud, using observations from the Hubble Tarantula Treasury Project in the 0.3 - 1.6 micron range. The considerable and patchy extinction inside the nebula causes about 3500 red clump stars to be scattered along the reddening vector in the colour-magnitude diagrams, thereby allowing an accurate determination of the reddening slope in all bands. The measured slope of the reddening vector is remarkably steeper in all bands than in the the Galactic diffuse interstellar medium. At optical wavelengths, the larger ratio of total-to-selective extinction, namely Rv = 4.5 +/- 0.2, implies the presence of a grey component in the extinction law, due to a larger fraction of large grains. The extra large grains are most likely ices from supernova ejecta and will significantly alter the extinction properties of the region until they sublimate in 50 - 100 Myr. We discuss the implications of this extinction law for the Tarantula nebula and in general for regions of massive star formation in galaxies. Our results suggest that fluxes of strongly star forming regions are likely to be underestimated by a factor of about 2 in the optical., Comment: 15 pages, 10 figures, accepted for publication in MNRAS; Updated references, corrected typos in Table 3

We present a multiwavelength study of the infrared dark cloud MSXDC G034.43 + 00.24. Dust emission, traced by millimeter/submmillimeter images obtained with the IRAM, JCMT, and CSO telescopes, reveals three compact cores within this infrared dark cloud with masses of 170 - 800 M-circle dot and sizes

We present a multiwavelength study of the infrared dark cloud MSXDC G034.43 + 00.24. Dust emission, traced by millimeter/submmillimeter images obtained with the IRAM, JCMT, and CSO telescopes, reveals three compact cores within this infrared dark cloud with masses of 170 - 800 M-circle dot and sizes

This paper presents the near-IR imaging observations of CB 107, a small dark globule projected against a rich stellar background. By means of accurate photometry, the near-IR two-color diagram J - H versus H - K was obtained for the stellar background. This information was used to estimate the color excesses of the detected stars so that, given the reddening curve, it was possible to derive the extinction map of the cloud. The structural properties of the dark globule were investigated by plotting the extinction dispersion σ, obtained in a given spatial box, as a function of the mean extinction AV. This relationship has shown quite a definite linear behavior, with the slope increasing with the box size. The results of the present analysis, compared with those obtained by other authors on larger dark clouds, suggest that for a given spatial scale the slope of the σ versus AV relation is greater in CB 107 than in larger clouds. The so-called Δ-variance method was also used to investigate the structure of the dark globule by evaluating the drift behavior of its extinction map. In this way, we have found that the power spectrum of the extinction map is characterized by a power law with exponent β ~ 2.7. This value is lower than expected, for the same range of spatial scales, on the basis of previous work on large molecular clouds.

Three medium-band photometric systems proposed for the Gaia space mission are intercompared in determining color excesses for stars of spectral classes from O to M at V = 18 mag. A possibility of obtaining a three-dimensional map of the interstellar extinction is discussed.

We present observations of the 4.8 and 8.6 GHz continuum emission towards 11 southern H II regions made with the Australian Telescope Compact Array. The observed objects were selected from the Infrared Space Observatory (ISO) spectral catalogue of compact H II regions (Peeters et al. 2002b). The morphologies observed for practically all the sources are consistent with them being ionized by a cluster of stars, rather than by a single star. The linear diameters of the regions range from 0.03 pc to 3 pc, the electron densities from 300 to 2.5x10(4) cm(-3), and the Lyman continuum photon flux from 10(47) to 10(50) s(-1). We confirm the existence of a relation between the density and size of H II regions which can be fit by a power law shallower than that predicted by the classic Stromgren theory. The radio observations provide, in addition, information about the distribution of the ionized gas within the ISO apertures. As a result of the combined radio and infrared study, estimates of the extinction in the infrared and the metal content of the nebular gas were calculated. In this analysis, we also included several (ultra) compact H II regions previously observed by the Very Large Array. Values for extinction in the K-band between similar to0 and 6 mag are found. The elemental abundances of nitrogen, neon, argon and sulphur were found to decrease with Galactocentric distance. Finally, the degree of ionization of the nebulae is confirmed to be correlated with the metal content.

We present the first detection of unidentified infrared (UIR) emission features at similar to6.4 and 7.9 mum in the spectrum of the dusty WC8 Wolf-Rayet star WR 48a. Based on the H-deficient nature of WC stars, we attribute the emission features to large carbonaceous molecules or amorphous carbon dust grains in the circumstellar environment of WR 48a. The 6.4 mum feature resembles the emission feature seen toward H-deficient planetary nebulae (PNe), while the 7.9 mum profile resembles that of some PNe with H-deficient WC10 central stars. These similarities point toward a similar origin of the dust in these H-deficient environments and highlights the apparent sensitivity of the UIR bands to physical conditions. In the case of WR 48a and the [WC10] PNe, shock processing may play a major role in dust formation.

We present the first detection of unidentified infrared (UIR) emission features at similar to6.4 and 7.9 mum in the spectrum of the dusty WC8 Wolf-Rayet star WR 48a. Based on the H-deficient nature of WC stars, we attribute the emission features to large carbonaceous molecules or amorphous carbon dust grains in the circumstellar environment of WR 48a. The 6.4 mum feature resembles the emission feature seen toward H-deficient planetary nebulae (PNe), while the 7.9 mum profile resembles that of some PNe with H-deficient WC10 central stars. These similarities point toward a similar origin of the dust in these H-deficient environments and highlights the apparent sensitivity of the UIR bands to physical conditions. In the case of WR 48a and the [WC10] PNe, shock processing may play a major role in dust formation.