466 research outputs found
UBVRI CCD photometry of the OB associations Bochum 1 and Bochum 6
We report the first deep CCD photometry of 2460 stars in the field of
two poorly studied OB associations Bochum 1 and Bochum 6. We selected 15 and 14
probable members in Bochum 1 and Bochum 6 respectively using photometric
criteria and proper motion data of Tycho 2. Our analysis indicates variable
reddening having mean value of 0.470.10 and 0.710.13 mag
for Bochum 1 and Bochum 6 respectively. Using the zero-age main-sequence
fitting method, we derive a distance of 2.80.4 and 2.50.4 Kpc for
Bochum 1 and Bochum 6 respectively. We obtain an age of 105 Myrs for both
the associations from isochrone fitting. In both associations high and low mass
stars have probably formed together. Within the observational uncertainties,
mass spectrum of the both associations appears to be similar to the Salpeter's
one.Comment: 14 pages, 7 figures, 6 tables. Accepted for Bull. Astr. Soc. Indi
The ages of the galactic globular clusters
The Galactic globular clusters are believed to be among the most ancient objects for which reliable ages can be determined. As the Universe can not be younger than the oldest object it contains, the oldest Galactic globular clusters provide one of the few most important constraints that one can have on cosmological models. Latest estimates indicate that the absolute age of the oldest globular clusters is 14 ± 3 Gyr. The calibration of absolute ages is still subject to observational and theoretical uncertainties at the ≈ 20% level, and represents a major limitation on our ability to test cosmological models. However, relative ages are starting to be much better known due to the super colour-magnitude diagrams that have been obtained through the use of CCD detectors on large telescopes and the Hubble Space Telescope. The available data are consistent with the majority of Galactic globular clusters being virtually coeval but with a minority having significantly lower ages. The existence of "prehistoric" clusters with ages of around 50 Gyr, as hypothesised in the quasi-steady state cosmology, should be readily recognised
Indo-Belgian co-operation in Astrophysics: From inception to future prospects
In this manuscript, an overview of the accomplishments of the Indo-Belgian
co-operation is presented in the current era of multi-wavelength global
astronomy. About two decades ago, in the field of astronomy and astrophysics,
academicians from India and Belgium embarked on formal interaction and
collaboration. The Belgo-Indian Network for Astronomy & astrophysics (BINA),
initiated in 2014, has been very productive and its activities have set a
landmark for Indo-Belgian co-operation. Under this program, three international
workshops were conducted. Several exchange work visits were also made among the
astronomers of the two 13countries. Since the necessary foundation work has
already been done, continuation of the BINA activities in future is strongly
recommended.Comment: accepted for publication, 13 pages, 5 figures, based on invited talk
given during 3rd BINA worksho
Non-uniform extinction in young open star clusters
The extinction law and the variation of colour excess with position,
luminosity as well as spectral class in young open star clusters NGC 663,
NGC869, NGC 884, NGC 1502, NGC 1893, NGC 2244, NGC 2264, NGC 6611, Tr 14, Tr
15,Tr 16, Coll 228, Tr 37 and Be 86 have been studied. The difference in the
minimum and maximum values of E(B-V) of cluster members has been considered as
a measure of the presence of non-uniform gas and dust inside the clusters. Its
value ranges from 0.22 to 1.03 mag in clusters under study, which indicates
that non-uniform extinction is present in all the clusters. It has been noticed
for the first time in NGC 1502 and Tr 37. It is also found that the
differential colour excess in open clusters, which may be due to the presence
of gas and dust, decreases systematically with the age of clusters indicating
that matter is used either in star formation or blown away by hot stars or
both. There is no uniformity in the variation of E(B-V) with either position or
spectral class or luminosity.Comment: 11 pages, 8 figures, 4 tables; accepted for publication in MNRAS,
typos adde
Aryabhatta Research Institute of Observational Sciences: reincarnation of a 50 year old State Observatory of Nainital
The fifty year old State Observatory, well known as U.P. State Observatory till the formation of Uttaranchal in November 2000, was reincarnated on March 22, 2004 as Aryabhatta Research Institute of Observational Sciences with acronym ARIES, an autonomous institute, under the Department of Science & Technology, Government of India. The growth of academic and technical activities and new mandate of the Institute are briefly described. In early 60's, the Institute was one of the 12 centres established by the Smithsonian Astrophysical Observatory, USA, all over the globe but the only centre in India for imaging artificial earth satellites. Commensurating with its observing capabilities, the Institute started a number of front-line research programmes during the last decade, e.g., optical follow up observations of GRB afterglows, radio and space borne astronomical resources, intra-night optical variability in active galactic nuclei as well as gravitational microlensing and milli-magnitude variations in the rapidly oscillating peculiar A type stars. As a part of atmospheric studies, characterisation of aerosol at an altitude of about 2 km is going on since 2002. ARIES has plans for establishing modern observing facilities equipped with latest backend instruments in the area of both astrophysics and atmospheric science. Formation of ARIES, therefore augurs well for the overall development of astrophysics and atmospheric science in India
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