Photometry of the galactic cluster NGC 2169

The results of photoelectricU, B, V photometry of the galactic cluster NGC 2169 are presented. The colour excessE(B-V) is 0^m.18. The distance modulus to the cluster and its age are respectively estimated at 9^m.6 and 0.9×10⁷ yr. Star No. 10 is found to be variable.     

CCD photometry inVRI bands of the galactic cluster NGC 2818

bdAbstract The open cluster NGC 2818 containing a planetary nebula has been observed inVRI bands using the CCD system at prime focus of the 2.3-metre Vainu Bappu Telescope. The study extending to starsV ∼ 21 magnitude establishes the distance modulus as(m-M) ₀ = 12.9 ±0.1 for the cluster. Based on the fitting of theoretical isochrones computed for solar metallicity, an age of 5(±1) × 10₈ years has been assigned to the cluster. Association of the planetary nebula with the cluster indicates that the progenitor mass of the planetary nebula on the main sequence is ≥2.5M_⊙ Based on observations obtained with the Vainu Bappu Telescope.     

Fundamental parameters and new variables of the galactic open cluster NGC 7128

CCD photometry in Johnson UBV and Strömgren uvby systems and medium-resolution spectroscopy of the galactic open cluster NGC 7128 are presented. Spectral types of the brightest 12 stars in the cluster field were determined based on equivalent widths of the H α and the He  i 6678-Å line. The spectroscopic observations also revealed two obvious and one probable Be-type stars showing H α emission. The analysis of the photometric diagrams gave a colour excess of E ( B − V )=1.03±0.06 mag, a distance modulus DM =13.0±0.2 mag and an age above 10 Myr. Time-resolved photometric observations obtained on one night resulted in the detection of short time-scale light variations of seven new and three already known variable stars in the cluster field.     

Two UBV sequences,north and south of the galactic cluster NGC 5823

Photoelectric UBV observations of 69 stars, distributed in two sequences north and south of the galactic star cluster NGC 5823, are reported.     

Study of the Wolf-Rayet members of the cluster NGC 6231

Two Wolf-Rayet members of the cluster NGC 6231 are studied spectrophotometrically. HD 151932, a suspected variable, shows variations in the emission line flux as well as continuum magnitude measurements. An attempt is made to understand this variation as due to the asymmetric atmospheric structure. The other, HD 152270, a (WC7 + O) binary, shows variation of emission line flux for C III and C IV lines only. This variation is studied as a possible phenomenon of atmospheric eclipses.     

Mapping the roots of the galactic outflow in NGC1569

The exact nature of the interaction between hot, fast-flowing star-cluster winds and the surrounding clumpy interstellar medium (ISM) in starburst galaxies has very few observational constraints. Besides furthering our knowledge of ISM dynamics, detailed observations of ionised gas at the very roots of large-scale outflows are required to place limits on the current generation of high-resolution galactic wind models. To this end, we conduct a detailed investigation of the ionised gas environment surrounding the young star clusters in the starburst galaxy NGC1569. Using high spatial and spectral-resolution Gemini/GMOS integral-field unit observations, we accurately characterise the line-profile shapes of the optical nebular emission lines and find a ubiquitous broad (～300 km?s^?1) component underlying a bright narrower component. By mapping the properties of the individual line components, we find correlations that suggest that the broad component results from powerful cluster wind–gas clump interactions. We propose a model to explain the properties of the line components and the general turbulent state of the ISM.     

Astrometry of the open cluster NGC 2324

New proper motion membership probabilities are given for stars in the region of the cluster NGC 2324. The space density distribution and the luminosity function are discussed. A comparison with previous investigations is presented.     

X-rays from the open cluster NGC 6633

NGC 6633 is a young, open cluster with a similar age to the Hyades and Praesepe, but probably a lower metallicity. We present the results of ROSAT High Resolution Imager observations of an optically selected catalogue of likely members of NGC 6633. 8 out of 51 NGC 6633 members have been detected, with main-sequence spectral types A to G, above a threshold X-ray luminosity of ≈6–12×10²⁸ erg s⁻¹. We find that NGC 6633 does not contain cool stars that are as X-ray luminous as the most active objects in the Hyades and that the median X-ray luminosity of F-G stars in NGC 6633 is less than that in the Hyades, but probably greater than in Praesepe. However, when X-ray activity is expressed as the X-ray to bolometric flux ratio we find that NGC 6633 and the Hyades are very similar and display similar peak levels of coronal activity. We attribute this discrepancy to a number of possible wide binary systems with higher X-ray (and bolometric) luminosities in the Hyades sample and either a low metallicity in NGC 6633, which makes its cool stars both X-ray and bolometrically less luminous at the same colour, or a distance to NGC 6633 that has been underestimated, which would decrease stellar X-ray luminosities without changing X-ray to bolometric flux ratios.     

Membership in the open cluster NGC 2301

Astrometric cluster membership probabilities have been derived from proper motion of the open cluster NGC 2301. A comparison with previous investigations is presented.     

Photometry of open cluster NGC 1931

PhotoelectricUBV magnitudes and colours have been determined for stars in the field of NGC 1931. The reddening across the cluster varies from 0 _. ^m 33 to 1 _. ^m 20. A distance of 2.16 kiloparsecs has been estimated for the cluster. It is concluded that the age of the cluster lies between the ages of NGC 6231 and NGC 2362 groups.     

A study of the open cluster NGC 2374

The results of modified objective grating observations and photoelectric as well as photographic photometry of the open cluster NGC 2374 are presented. The cluster contains at least twenty stars as definite members down tom _v ≈ 15mag. There is a uniform extinction ofE(B - V) = 0.175 mag and the distance is 1.2 ± 0.1 kpc. The most likely age of this cluster is 7.5 ×10⁷ years.     

The young open cluster NGC 2129

The first charge-coupled device   UBV ( RI )_C  photometric study in the area of the doubtful open cluster NGC 2129 is presented. Photometry of a field offset 15 arcmin northwards is also provided, to probe the Galactic disc population towards the cluster. Using star counts, proper motions from the UCAC2 catalogue, colour–magnitude and colour–colour diagrams, we demonstrate that NGC 2129 is a young open cluster. The cluster radius is 2.5 arcmin, and across this region we find evidence of significant differential reddening, although the reddening law seems to be normal towards its direction. Updated estimates of the cluster fundamental parameters are provided. The mean reddening is found to be   E ( B − V ) = 0.80 ± 0.08  and the distance modulus is  ( m − M )₀= 11.70 ± 0.30  . Hence, NGC 2129 is located at 2.2 ± 0.2 kpc from the Sun inside the Local spiral arm. The age derived from 37 photometrically selected members is estimated to be approximately 10 Myr. These stars are used to provide new estimates of the cluster absolute proper-motion components.     

Variable stars in the open cluster NGC 2141

We report the results of a search for variable stars in the open cluster NGC 2141. Ten variable stars are detected, among which nine are new variable stars and they are classified as three short-period W UMa-type eclipsing binaries, two EAtype eclipsing binaries, one EB-type eclipsing binary, one very short-period RS CVntype eclipsing binary, one d-type RR Lyrae variable star, and one unknown type of variable star. The membership and physical properties are discussed, based on their light curves, positions in the color magnitude diagrams, spatial locations and periods.A known EB-type eclipsing binary is also identified as a blue straggler candidate in the cluster. Furthermore, we find that all eclipsing contact binaries have prominent asymmetric eclipses and display the O'Connell effect, which increases with a decrease in orbital periods. This suggests that the O'Connell effect is probably related to the evolution of the orbital period in short period eclipsing binary systems.     

Variable stars in the globular cluster NGC 6362

We report the results of a CCD search for short-period variables in the field of a southern globular cluster NGC 6362. We identified 19 new candidate variables, five of which are cluster RR Lyraes, four are probable SX Phe-type stars and eight are eclipsing binaries. Of the discovered binaries, three are EA-type systems, two of which are located on the cluster CMD in the turn-off region and the third 1 mag above the turn-off point, in the yellow straggler region. Five other systems are of W UMa type, three of which are foreground objects and two are likely cluster members. The remaining two candidates exhibit a modulation of the brightness level with an amplitude of 0.1–0.2 mag; further observations are needed to reveal the nature of their variability. Phased VI light curves for 20 variables (18 RR Lyrae stars and two blue stragglers) located in the central region of the cluster are presented.     

Mass distribution in the open cluster NGC 1664

We start with the hypotheses that the cluster space is limited by an ellipsoid with a semiprincipal axis directed to the observer and that the star density inside of concentric ellipsodal layers remains constant, although varying from layer to layer. It results that the mean star mass at the periphery of the cluster is 0.59 Sun masses smaller than that at the center.