Non Inverted Isothermal Equation of state for NaCl-CsCl type Crystals

The Pressure-Volume-temperature(P-V-T) relation using non inverted equation of state (EOS) viz. Murnaghan EOS, Usual-Tait EOS, Vinet EOS, Born-Mayer EOS, Birch EOS, Kumar EOS, Shanker EOS, Brennan Stacey EOS, Poirier- Tarantola EOS, Universal EOS and Freund & Ingalls EOS for NaCl-CsCl type crystals has been studied. It is found that except Murnaghan EOS, Brennan-Stacey EOS and Poirier Tarantola EOS all other EOS gives close agreement with each other even at high compression ranges. Also another remarkable characteristic observed when the value of compression decreases from 0.5 the variation in value of pressure as calculated by different EOS increases

X-ray emission from O-type stars : DH Cep and HD 97434

We present X-ray emission characteristics of the massive O-type stars DH Cep and HD 97434 using archival XMM-Newton observations. There is no convincing evidence for short term variability in the X-ray intensity during the observations. However, the analysis of their spectra reveals X-ray structure being consistent with two-temperature plasma model. The hydrogen column densities derived from X-ray spectra of DH Cep and HD 97434 are in agreement with the reddening measurements for their corresponding host clusters NGC 7380 and Trumpler 18, indicating that the absorption by stellar wind is negligible. The X-ray emission from these hot stars is interpreted in terms of the standard instability-driven wind shock model.Comment: 13 pages ; 2 figures; 2 tables (Accepted for publication in New Astronomy

Broad Band Optical Polarimetric Study of IC 1805

We present the BVR broad band polarimetric observations of 51 stars belonging to the young open cluster IC 1805. Along with the photometric data from the literature we have modeled and subtracted the foreground dust contribution from the maximum polarization (P_{max}) and colour excess (E_{B-V}). The mean value of the P_max for intracluster medium and the foreground are found to be 5.008 +/-0.005 % and 4.865 +/-0.022 % respectively. Moreover, the mean value of the wavelength of maximum polarization (lambda_{max}) for intracluster medium is 0.541 +/- 0.003 micro m, which is quite similar as the general interstellar medium (ISM). The resulting intracluster dust component is found to have negligible polarization efficiency as compared to interstellar dust. Some of the observed stars in IC 1805 have shown the indication of intrinsic polarization in their measurements.Comment: 8 pages, 7 figures, Accepted for publication in MNRA

New optical telescope projects at Devasthal Observatory

Devasthal, located in the Kumaun region of Himalayas is emerging as one of the best optical astronomy site in the continent. The minimum recorded ground level atmospheric seeing at the site is 0.6 arcsec with median value at 1.1 arcsec. Currently, a 1.3-m fast (f/4) wide field-of-view (66 arcmin) optical telescope is operating at the site. In near future, a 4-m liquid mirror telescope in collaboration with Belgium and Canada, and a 3.6-m optical telescope in collaboration with Belgium are expected to be installed in 2013. The telescopes will be operated by Aryabhatta Research Institute of Observational Sciences. The first instruments on the 3.6-m telescope will be in-house designed and assembled faint object spectrograph and camera. The second generation instruments will be including a large field-of-view optical imager, high resolution optical spectrograph, integral field unit and an optical near-infrared spectrograph. The 1.3-m telescope is primarily used for wide field photometry imaging while the liquid mirror telescope will see a time bound operation to image half a degree wide strip in the galactic plane. There will be an aluminizing plant at the site to coat mirrors of sizes up to 3.7 m. The Devasthal Observatory and its geographical importance in between major astronomical observatories makes it important for time critical observations requiring continuous monitoring of variable and transient objects from ground based observatories. The site characteristics, its expansions plans and first results from the existing telescope are presented.Comment: Invited paper, 12 pages, SPIE Conference, July 201

New initiatives in optical astronomy at ARIES

The Institute is establishing a 3.6-m new technology modern optical telescope at Devasthal. This telescope will have instruments providing high resolution spectral and seeing-limited imaging capabilities at visible and near-infrared bands. In addition to optical studies of a wide variety of astronomical topics, it will be used for follow-up studies of sources identified in the radio region by GMRT and UV/X-ray by ASTROSAT. A few other facilities with very specific goals are also being established. These are 1.3-m optical telescope to monitor optically variable sources, a 0.5-m wide field (25 square degrees) Baker-Nunn Schmidt telescope to produce a digital map of the Northern sky at optical bands, and a 4-m liquid mirror telescope for deep sky survey of transient sources. These optical facilities with specialized back-end instruments are expected to become operational within the next few years. All the telescopes, except the 0.5-m Schmidt, will be located at Devasthal, Nainital in the central Himalayas

Multiwavelength study of a young open cluster NGC 7419

Using new UBVRI H αCCD photometric observations and the archival infrared and X-ray data, we have carried out a multiwavelength study of a Perseus arm young open star cluster NGC 7419. An age of 22.5 ± 3.0 Myr and a distance of 3230+330-430 pc are derived for the cluster. Our photometric data indicate a higher value of colour excess ratio E(U-B)/E(B-V) than the normal one. There is an evidence for mass segregation in this dynamically relaxed cluster and in the range 1.4-8.6 M⊚, the mass function slope is in agreement with the Salpeter value. Excess emissions in near-infrared and H α support the existence of a young (≤ 2 Myr) stellar population of Herbig Ae/Be stars (≥3.0 M⊚) indicating a second episode of star formation in the cluster region. Using XMM-Newton observations, we found several X-ray sources in the cluster region but none of the Herbig Ae/Be stars is detected in X-rays. We compare the distribution of upper limits for Herbig Ae/Be stars with the X-ray distribution functions of the T Tauri and the Herbig Ae/Be stars from previous studies, and found that the X-ray emission level of these Herbig Ae/Be stars is not more than LX~ 5.2 × 1030 ergs-1, which is not significantly higher than for the T Tauri stars. Therefore, X-ray emission from Herbig Ae/Be stars could be the result of either unresolved companion stars or a process similar to T Tauri stars. We report an extended X-ray emission from the cluster region NGC 7419, with a total X-ray luminosity estimate of ~1.8 × 1031 erg s-1 arcmin-2. If the extended emission is due to unresolved emission from the point sources then we estimate ~288 T Tauri stars in the cluster region each having X-ray luminosity ~1.0 × 1030 ergs-1. Investigation of dust attenuation and 12CO emission map of a square degree region around the cluster indicates the presence of a foreground dust cloud which is most likely associated with the local arm star-forming region (Sh2-154). This cloud harbours uniformly distributed pre-main-sequence stars (0.1-2.0 M⊚ ), with no obvious trend of their distribution with either (H-K) excess or AV. This suggests that the star formation in this cloud depend mostly upon the primordial fragmentation