The 100 micron surveys in the Northern and Southern Hemispheres

Partial surveys in the far infrared in the Northern and Southern Hemispheres have covered 40% of the galactic equator and assorted regions away from the galactic plane. Approximately 120 100-micron objects are known. These are distributed extensively in galactic longitude and concentrated within + or - two degrees in galactic latitude. From this information, some general conclusions can be drawn about the sensitivity and coverage required for a general sky survey in the far infrared

Rocky Planetesimals as the Origin of Metals in DZ Stars

{Abridged}. An analysis of the calcium and hydrogen abundances, Galactic positions and kinematics of 146 DZ stars from the Sloan Digital Sky Survey demonstrates that interaction with the interstellar medium cannot account for their externally polluted atmospheres. The calcium-to-hydrogen ratios for the 37 DZA stars are dominated by super-solar values, as are the lower limits for the remaining 109 DZ stars. All together their metal-contaminated convective envelopes contain 10^{20+-2} g of calcium, commensurate with the masses of calcium inferred for large asteroids. It is probable that these stars are contaminated by circumstellar matter; the rocky remains of terrestrial planetary systems. In this picture, two predictions emerge: 1) at least 3.5% of all main sequence A- and F-type stars build terrestrial planets; and 2) the DZA stars are externally polluted by both metals and hydrogen, and hence constrain the frequency and mass of water-rich, extrasolar planetesimals.Comment: Accepted to MNRA

Multi-wavelength polarimetric study towards the open cluster NGC 1893

We present multi-wavelength linear polarimetric observations for 44 stars of the NGC 1893 young open cluster region along with V-band polarimetric observations of stars of other four open clusters located between l ~160 to ~175 degree. We found evidence for the presence of two dust layers located at a distance of ~170 pc and ~360 pc. The dust layers produce a polarization Pv ~2.2%. It is evident from the clusters studied in the present work that, in the Galactic longitude range l ~160 to 175 degree and within the Galactic plane (|b| < 2 degree), the polarization angles remain almost constant, with a mean ~163 degree and a dispersion of 6 degree. The small dispersion in polarization angle could be due to the presence of uniform dust layer beyond 1 kpc. Present observations reveal that in case of NGC 1893, the foreground two dust layers, in addition to the intracluster medium, seems to be responsible for the polarization effects. It is also found that towards the direction of NGC 1893, the dust layer that exists between 2-3 kpc has a negligible contribution towards the total observed polarization. The weighted mean for percentage of polarization (Pmax) and the wavelength at maximum polarization ({\lambda}max) are found to be 2.59 \pm 0.02% and 0.55 \pm 0.01 \mum respectively. The estimated mean value of {\lambda}max indicates that the average size of the dust grains within the cluster is similar to that in the general interstellar medium. The spatial variation of the polarization is found to decrease towards the outer region of the cluster. In the present work, we support the notion, as already has been shown in previous studies, that polarimetry, in combination with (U-B)/(B-V) colour-colour diagram, is a useful tool for identifying non-members in a cluster.Comment: 36 pages, 12 figures, 10 tables, accepted for the publication in MNRA

Extended fine structure and continuum emission from S140/L1204

Grating spectra, covering the wavelength range 45 to 187μm have been taken with the ISO Long Wavelength Spectrometer (LWS) at a series of pointing positions over the S 140 region, centred on the cluster of embedded young stellar objects at the south-west corner of the L1204 molecular cloud. Extended emission from [CII]158μm and [OI]63μm is seen, peaking near the position of the embedded stars. The measurements of the fine structure lines are interpreted in terms of PDR models for the emission, as well as the underlying thermal continuum for the heated gas and dust

Determination of the primordial helium abundance from radio recombination line observations: New data. The source W51

Observations of H and He radio recombination lines in the source W51 have been performed with the RT-22 radio telescope (Pushchino) in two transitions: 56α (8 mm) and 65α (13 mm). We have estimated the spectral line parameters and determined the relative abundance of ionized helium, y + = (9.3 ± 0.35)%. We have carried out a model study of the correction (R) for the ionization structure of HII regions (when passing from the observed y + = N(He+)/N(H+) to the actual y = N(He)/N(H)) as a function of the spectral type of the ionizing star. Hence it follows that it is desirable to choose the sources excited by hot stars of spectral types no later than O6 V to estimate the helium abundance. In this case, the correction is expected to be small and essentially constant, R in the range 1.0-1.05. We have analyzed the correction for the ionization structure of W51, obtained an actual abundance of helium in the range y = (8.9-9.7)%, and determined its primordial abundance Y p (produced during primordial nucleosynthesis in the Universe) in this source. We have made a new estimate of the primordial helium abundance from six Galactic HII regions, where we observed H and He radio recombination lines at different times. The weighted mean Y p = 25.64(±0.70)% has been obtained. On the one hand, this value of Y p does not yet disagree strongly with the conclusions of the standard cosmologicalmodel, but, on the other hand, it admits the existence of at least one unknown light particle in the period of primordial nucleosynthesis outside the scope of the standard cosmological model. One should continue to refine Y p for more reliable conclusions to be reached. © 2013 Pleiades Publishing, Inc

Broad-band Optical Polarimetric Studies toward the Galactic young star cluster Be 59

We present multiwavelength optical linear polarimetric observations of 69 stars toward the young open cluster Be 59. The observations reveal the presence of three dust layers located at the distances of \sim300, \sim500 and \sim700 pc. The dust layers produce a total polarization Pv \sim 5.5 per cent. The mean values of polarization and polarization angles due to the dust layers are found to increase systematically with distance. We show that polarimetry in combination with the (U - B) - (B - V) colour-colour diagram yields a better identification of cluster members. The polarization measurements suggest that the polarization due the intra-cluster medium is \sim 2.2 per cent. An anomalous reddening law exists for the cluster region, indicating a relatively larger grain size than that in the diffuse ISM. The spatial variation of the polarization and E(B - V) is found to increase with radial distance from the cluster center, whereas the {\theta}v and {\lambda}max are found to decrease with increasing radial distance from the cluster center. About 40 per cent of cluster members show the signatures of either intrinsic polarization or rotation in their polarization angles. There is an indication that the star light of the cluster members might have been depolarized because of non-uniform alignment of dust grains in the foreground dust layers and in the intra-cluster medium.Comment: 22 pages, 14 figures and 7 tables, Accepted in MNRA

Modeling far-infrared line emission from the HII region S125

We present ISO-LWS spectral line observations of the [OI] 63 and 146 μm lines, the [CII] 158 μm line, and the [NII] 122 μm line at 17 positions in the HII region S125. We model this emission by a two-dimensional geometrical blister model, utilizing the parameters derived from our previous modeling of the HII, HI and FIR dust emission in this source, thereby deriving an interpretation of the region that takes account of the thermal continuum radiation and the line emission self- consistently. We show very good agreement with the observed line emission in the central region, but in order to fit the spatial profile, it is necessary to allow for a systematic increase in the gas temperature along the PDR boundary with decreasing distance from the ionizing star. This would not be predicted by PDR models, hence we suggest that the size distribution of small grains responsible for the photoelectric heating may be changing along the boundary, depending on the distance from the star. The model shows that the HII region, the PDR region, as well as H2 molecular region all make contributions to the emission observed in these fine structure lines and that accurate modeling of the PDR region needs to include the radiation coupling between the ionized region and the neutral molecular cloud. Comparison with values derived from one-dimensional, constant density slab models shows the present blister modeling giving higher G0 values for the radiation field at the PDR boundary.


Modeling far-infrared emission from the HII region S125

In the calculation of the RI model continuum emission spectra shown in Fig. 10 on page 1048, the dust density in the neutral region was inadvertently reduced by the same “density reduction factor” as the dust density in the HII region. The model spectra shown should therefore be multiplied by the factor of 1.8. However, this does not change our conclusions that the model in general provides too low emission and peaks at too short wavelengths. The only exception is that the model now gives excess emission at the central position N, similar to the result of the blister model shown in Fig. 12. No other calculations or conclusions were affected by this error