The spectral and reddening properties of 211 highly reddened proper‐motion members with V < 15 mag in six young galactic star clusters are investigated using low‐resolution spectroscopic, broad‐band UBVRIJHK and mid‐infrared (IR) data. We report emission features in Ca ii HK and H i lines for a sample of 29 stars including 11 stars reported for the first time and also provide either a new or more reliable spectral class for a sample of 24 stars. Ca ii triplet width measurements are used to indicate the presence of an accretion disc for a dozen stars and to indicate luminosity for a couple of stars. On the basis of spectral features, near‐IR excesses, dereddened colour–colour diagrams and mid‐IR spectral indices we identify a group of 28 pre‐main‐sequence cluster members including five highly probable Herbig Ae/Be and six classical T Tauri stars. A total of 25 non‐emission main‐sequence (MS) stars, amounting to ∼10 per cent early‐type MS members, appears to show Vega‐like characteristics or are precursors to such a phenomenon. The various membership indicators suggest that ∼16 per cent of the proper‐motion members are non‐members. A significant fraction (>70 per cent) of programme stars in NGC 1976, NGC 2244, NGC 6530 and NGC 6611 show anomalous reddening with RV= 4.78 ± 0.10, 3.54 ± 0.04, 3.87 ± 0.05 and 3.56 ± 0.02, respectively, indicating the presence of grain size dust larger than that typical of the diffuse medium. A small number of stars in NGC 1976, NGC 2244 and NGC 6611 also show normal behaviour while the cluster NGC 6823 appears to have normal reddening. Three highly luminous late‐type giants, one in NGC 2244 and two in NGC 6530, appear to be members and are in post‐hydrogen‐core‐burning stages, suggesting a prolonged duration (∼25 Myr) of star formation.

Abstract. Based on an extensive site survey conducted during [1980][1981][1982][1983][1984][1985][1986][1987][1988][1989][1990] in the Shivalik Hills of the Central Himalayan range, a promising site Devasthal has been identified. The longitude and latitude of Devasthal Peak are 79• 41 E and 29• 23 N. It is situated at an altitude of 2540 m and about 50 km by road from Nainital towards East. The surroundings of Devasthal are thinly populated and it is logistically well suited for establishing modern optical observational facilities. The prevailing wind direction at Devasthal is NW. For a large fraction of the night time, variation in the ambient temperature was less than a degree and wind speed was less than 10 m/s. During spectroscopic nights (> 200 in a year) relative humidity is less than 80% for about 70% of the time. During 1997 and 1998 seeing measurements using differential image motion techniques have been carried out close to ground at two locations namely Site 1 and Site 2 in Devasthal. Our observations for Site 1 carried over 88 nights yield a median seeing value of 1. 4. For Devasthal Site 2 observations carried over 37 nights yield a median seeing value of 1. 1. Devasthal Site 2 has therefore been selected for locating a modern 3 m optical telescope.

We present a study of the properties of star-forming regions within a sample of 7 Wolf-Rayet (WR) galaxies. We analyze their morphologies, colours, star-formation rate (SFR), metallicities, and stellar populations combining broad-band and narrowband photometry with low-resolution optical spectroscopy. The U BV RI observations were made through the 2m HCT (Himalayan Chandra Telescope) and 1m ARIES telescope. The spectroscopic data were obtained using the Hanle Faint Object Spectrograph Camera (HFOSC) mounted on the 2m HCT. The observed galaxies are NGC 1140, IRAS 07164+5301, NGC 3738, UM 311, NGC 6764, NGC 4861 and NGC 3003. The optical spectra have been used to search for the faint WR features, to confirm that the ionization of the gas is consequence of the massive stars, and to quantify the oxygen abundance of each galaxy using several and independent empirical calibrations. We detected the broad features originated by WR stars in NGC 1140 and NGC 4861 and used them to derive their population of massive stars. For these two galaxies we also derive the oxygen abundance using a direct estimation of the electron temperature of the ionized gas. The N/O ratio in NGC 4861 is ∼0.25-0.35 dex higher than expected, which may be a consequence of the chemical pollution by N-rich material released by WR stars. Using our Hα images we have identified tens of regions within these galaxies, for which we derived the SFR. Our Hα-based SFR usually agrees with the SFR computed using the far-infrared and the radio-continuum flux. For all regions we found that the most recent star-formation event is 3 -6 Myr old. We used the optical broad-band colours in combination with Starburst99 models to estimate the internal reddening and the age of the dominant underlying stellar population within all these regions. Knots in NGC 3738, NGC 6764 and NGC 3003 generally show the presence of an important old (400 -1000 Myr) stellar population. However, the optical colours are not able to detect stars older than 20 -50 Myr in the knots of the other four galaxies. This fact suggests both the intensity of the starbursts and that the star-formation activity has been ongoing for at least some few tens of million years in these objects.

No abstract

No abstract