2,805 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
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
Co-citation Analysis: An Overview
This article gives an overview of co-citation analysis and its applications in tracking the linkages among the intellectual works and mapping the evolutionary structure of scientific disciplines. It also focuses on the features, interface, terminology used, merits and demerits of co-citation based online database applications
BVRI CCD photometric standards in the field of GRB 990123
The CCD magnitudes in Johnson and Cousins photometric passbands are
determined for 18 stars in the field of GRB 990123. These measurements can be
used in carrying out precise CCD photometry of the optical transient of GRB
990123 using differential photometric techniques during non--photometric sky
conditions. A comparison with previous photometry indicates that the present
photmetry is more precise.Comment: Tex file, 5 pages with 1 figure. Bull. Astron. Society India, Vol. 27
(accepted
A deep UVBRI CCD photometric study of open clusters Tr 1 and Be 11
We present deep CCD photometry for the young open star clusters Tr 1
and Be 11. The CCD data for Be 11 is obtained for the first time. The sample
consists of 1500 stars reaching down to 21 mag. Analysis of
the radial distribution of stellar surface density indicates that radius values
for Tr 1 and Be 11 are 2.3 and 1.5 pc respectively. The interstellar extinction
across the face of the imaged clusters region seems to be non-uniform with a
mean value of = 0.600.05 and 0.950.05 mag for Tr 1 and Be 11
respectively. A random positional variation of is present in both the
clusters. In the cluster Be 11, the reason of random positional variation may
be apparent association of the HII region (S 213). The 2MASS data in
combination with the optical data in the cluster Be 11 yields =
0.400.20 mag and = 2.200.20 mag. Colour excess diagrams
indicate a normal interstellar extinction law in the direction of cluster Be
11. The distances of Tr 1 and Be 11 are estimated as 2.60.10 and
2.20.10 Kpc respectively, while the theoretical stellar evolutionary
isochrones fitted to the bright cluster members indicate that the cluster Tr 1
and Be 11 are 4010 and 11010 Myr old. The mass functions corrected
for both field star contamination and data incompleteness are derived for both
the clusters. The slopes and for Tr 1 and Be 11
respectively are in agreement with the Salpeter's value. Observed mass
segregations in both clusters may be due to the result of dynamical evolutions
or imprint of star formation processes or both.Comment: 15 pages, 13 figures. Accepted for publication in MNRA
Star Clusters in the Magellanic Clouds-1: Parameterisation and Classification of 1072 Clusters in the LMC
We have introduced a semi-automated quantitative method to estimate the age
and reddening of 1072 star clusters in the Large Magellanic Cloud (LMC) using
the Optical Gravitational Lensing Experiment (OGLE) III survey data. This study
brings out 308 newly parameterised clusters. In a first of its kind, the LMC
clusters are classified into groups based on richness/mass as very poor, poor,
moderate and rich clusters, similar to the classification scheme of open
clusters in the Galaxy. A major cluster formation episode is found to happen at
125 +- 25 Myr in the inner LMC. The bar region of the LMC appears prominently
in the age range 60 - 250 Myr and is found to have a relatively higher
concentration of poor and moderate clusters. The eastern and the western ends
of the bar are found to form clusters initially, which later propagates to the
central part. We demonstrate that there is a significant difference in the
distribution of clusters as a function of mass, using a movie based on the
propagation (in space and time) of cluster formation in various groups. The
importance of including the low mass clusters in the cluster formation history
is demonstrated. The catalog with parameters, classification, and cleaned and
isochrone fitted CMDs of 1072 clusters, which are available as online material,
can be further used to understand the hierarchical formation of clusters in
selected regions of the LMC.Comment: 19 pages, 19figures, published in MNRAS on August 16, 2016
Supplementary material is available in the MNRAS websit
Economics of Rice Production in Pyuthan District of Nepal
A research was conducted at Pyuthan district in order to access the profitability of rice production in Pyuthan during the summer season of 2018-2019. Altogether of 70 respondents were selected randomly and surveyed with semi-structured interview schedule. The results revealed that the average land holding was 0.45 hectare, and the average rice cultivation area was 0.34 hectare. On the basis of average rice cultivation area, farmers were categorized as small (39) and large (31). The cost and return was calculated among both the category. t- test was used to compare the mean costs of inputs between small and large farmers. Cost for agronomic operations was found far higher (more than 70%) in both the category in compared to the cost of inputs. Contribution of rice grains and straw to overall return was 72.65% and 27.35% respectively. Benefit Cost ratio was found greater among large farmers. The average B:C ratio was 1.51, which was fairly higher than 1.14 in Dang district indicating the investment of rice production is expected to deliver a positive net return to the farmers of the study area. In a nutshell, rice cultivation is an important enterprise that should be encouraged, considering the fact that it is a major staple crop
Afterglow Emission from Highly Collimated Jets with Flat Electron Spectra: Application to the GRB 010222 Case?
We derive light curves of the afterglow emission from highly collimated jets
if the power-law index () of the electron energy distribution is above 1 but
below 2. We find (1) below the characteristic synchrotron frequency, the light
curve index depends generally on . (2) As long as the jet expansion is
spherical, the light curve index above the characteristic frequency increases
slowly as the spectral index of the emission increases. (3) Once the jet enters
the spreading phase, the high-frequency emission flux decays as rather than . All these results differ from those
in the case of . We compare our analytical results with the observations
on the GRB 010222 afterglow, and conclude that the jet model may be unable to
explain the observed data. Thus, a more promising explanation for this
afterglow seems to be the expansion of a relativistic fireball or a mildly
collimated jet in a dense medium.Comment: shortened version accepted for publication in ApJ Letter
GRB000301C with peculiar afterglow emission
The CCD magnitudes in Johnson V and Cousins R and I photometric passbands are
determined for GRB 000301C afterglow starting ~ 1.5 day after the gamma-ray
burst. In fact we provide the earliest optical observations for this burst.
Light curves of the afterglow emissions in U, B, V, R, I, J and K' passbands
are obtained by combining the present measurements with the published data.
Flux decay shows a very uncommon variation relative to other well observed
GRBs. Overall, there is a steepening of the optical and near-infrared flux
decay caused by a geometric and sideways expanding jet. This is superimposed by
a short term variability especially during early time (Delta t < 8 days). The
cause of variability is not well understood, though it has occurred
simultaneously with similar amplitude in all the filters. We derive the early
and late time flux decay constants using jet model. The late time flux decay is
the steepest amongst the GRB OTs observed so far with alpha ~ 3. Steepening in
the flux decay seems to have started simultaneously around Delta t ~ 7.6 day in
all passbands. The value of spectral index in the optical-near IR region is ~
-1.0. Redshift determination with z=2.0335 indicates cosmological origin of the
GRB having a luminosity distance of 16.6 Gpc. Thus it becomes the second
farthest amongst the GRBs with known distances. An indirect estimate of the
fluence > 20 keV indicates, if isotropic,> =10^53 ergs of release of energy.
The enormous amount of released energy will be reduced, if the radiation is
beamed which is the case for this event. Using a jet break time of 7.6 days, we
infer a jet opening angle of ~ 0.15 radian. This means the energy released is
reduced by a factor of ~ 90 relative to the isotropic value.Comment: LaTeX file, 11 pages including 4 figures, uses psfig.sty, Bull.
Astron. Society of India(accepted, Sept, 2000 issue
- …