UBVRI CCD photometry of the OB associations Bochum 1 and Bochum 6

We report the first deep $UBVRI$ 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 $E(B-V)=$ 0.47$\pm$0.10 and 0.71$\pm$0.13 mag for Bochum 1 and Bochum 6 respectively. Using the zero-age main-sequence fitting method, we derive a distance of 2.8$\pm$0.4 and 2.5$\pm$0.4 Kpc for Bochum 1 and Bochum 6 respectively. We obtain an age of 10$\pm$5 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

BVRI CCD photometric standards in the field of GRB 990123

The CCD magnitudes in Johnson $BV$ and Cousins $RI$ 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

Physical Parameters for the Afterglows of GRB 980703, 990123, 990510, and 991216 Determined from Modeling of Multi-Frequency Data

We model the radio, optical, and X-ray emission for the afterglows of GRB 980703, 990123, 990510, and 991216, within the framework of relativistic jets, to determine their physical parameters. The models that yield acceptable fits to the data have jet energies mostly between 10^{50} to 10^{51} erg and initial opening angles between 1 deg and 4 deg. The external medium density is uncertain by at least one order of magnitude in each case, being around 10^{-3}/cm^3 for GRB 980703 and 990123, ~0.1/cm^3 for GRB 990510, and ~3/cm^3 for GRB 991216. If the jets are uniform (i.e. there are no angular gradients of the energy per solid angle) then the 20 keV -- 1 MeV radiative efficiency during the GRB phase must have been at least 2-3% for GRB 990510, 20% for GRB 990123, and 30% for GRB 991216.Comment: accepted for publication by the ApJ, vol. 554. 11 pages, color figures. Last figures replaced with probability distributions of model parameter

A deep UVBRI CCD photometric study of open clusters Tr 1 and Be 11

We present deep $UBVRI$ 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 $\sim$ 1500 stars reaching down to $V$ $\sim$ 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 $E(B-V)$ = 0.60$\pm$0.05 and 0.95$\pm$0.05 mag for Tr 1 and Be 11 respectively. A random positional variation of $E(B-V)$ 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 $JHK$ data in combination with the optical data in the cluster Be 11 yields $E(J-K)$ = 0.40$\pm$0.20 mag and $E(V-K)$ = 2.20$\pm$0.20 mag. Colour excess diagrams indicate a normal interstellar extinction law in the direction of cluster Be 11. The distances of Tr 1 and Be 11 are estimated as 2.6$\pm$0.10 and 2.2$\pm$0.10 Kpc respectively, while the theoretical stellar evolutionary isochrones fitted to the bright cluster members indicate that the cluster Tr 1 and Be 11 are 40$\pm$10 and 110$\pm$10 Myr old. The mass functions corrected for both field star contamination and data incompleteness are derived for both the clusters. The slopes $1.50\pm0.40$ and $1.22\pm0.24$ 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

CCD photometric and mass function study of 9 young Large Magellanic Cloud star clusters

We present CCD photometric and mass function study of 9 young Large Magellanic Cloud star clusters namely NGC 1767, NGC 1994, NGC 2002, NGC 2003, NGC 2006, SL 538, NGC 2011, NGC 2098 and NGC 2136. The BVRI data reaching down to V ~ 21 mag, are collected from 3.5-meter NTT/EFOSC2 in sub-arcsec seeing conditions. For NGC 1767, NGC 1994, NGC 2002, NGC 2003, NGC 2011 and NGC 2136, broad band photometric CCD data are presented for the first time. Seven of the 9 clusters have ages between 16 to 25 Myr while remaining two clusters have ages $32\pm4$ Myr (NGC 2098) and $90\pm10$ Myr (NGC 2136). For 7 younger clusters, the age estimates based on a recent model and the integrated spectra are found to be systematically lower ($\sim$ 10 Myr) from the present estimate. In the mass range of $\sim 2 - 12$ $M_{\odot}$, the MF slopes for 8 out of nine clusters were found to be similar with the value of $\gamma$ ranging from $-1.90\pm0.16$ to $-2.28\pm0.21$. For NGC 1767 it is flatter with $\gamma = -1.23\pm0.27$. Mass segregation effects are observed for NGC 2002, NGC 2006, NGC 2136 and NGC 2098. This is consistent with the findings of Kontizas et al. for NGC 2098. Presence of mass segregation in these clusters could be an imprint of star formation process as their ages are significantly smaller than their dynamical evolution time. Mean MF slope of $\gamma = -2.22\pm0.16$ derived for a sample of 25 young ($\le 100$ Myr) dynamically unevolved LMC stellar systems provide support for the universality of IMF in the intermediate mass range $\sim 2-12 M_{\odot}$.Comment: To appear in MNRA

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 ($p$) 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 $p$. (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 $\propto t^{-(p+6)/4}$ rather than $\propto t^{-p}$. All these results differ from those in the case of $p>2$. 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

Emission from Bow Shocks of Beamed Gamma-Ray Bursts

Beamed gamma-ray burst (GRB) sources produce a bow shock in their gaseous environment. The emitted flux from this bow shock may dominate over the direct emission from the jet for lines of sight which are outside the angular radius of the jet emission, theta. The event rate for these lines of sight is increased by a factor of 260*(theta/5_degrees)^{-2}. For typical GRB parameters, we find that the bow shock emission from a jet with half-angle of about 5 degrees is visible out to tens of Mpc in the radio and hundreds of Mpc in the X-rays. If GRBs are linked to supernovae, studies of peculiar supernovae in the local universe should reveal this non-thermal bow shock emission for weeks to months following the explosion.Comment: ApJ, submitted, 15 pages, 3 figure