Photometric study of distant open clusters in the second quadrant: NGC 7245, King 9, King 13 and IC 166

We present a UBV CCD photometric study of four open clusters, NGC 7245, King 9, IC 166 and King 13, located between $l = 90^o - 135^o$. All are embedded in a rich galactic field. NGC 7245 and King 9 are close together in the sky and have similar reddenings. The distances and ages are: NGC 7245, 3.8$\pm$0.35 kpc and 400 Myr; King 9 (the most distant cluster in this quadrant) 7.9$\pm$1.1 kpc and 3.0 Gyr. King 13 is 3.1$\pm$0.3 kpc distant and 300 Myr old. King 9 and IC 166 (4.8$\pm$0.5 kpc distant & 1 Gyr old) may be metal poor clusters (Z=0.008), as estimated from isochrone fitting. The average value of the distance of young clusters from the galactic plane in the above longitude range and beyond 2 kpc ($-47\pm$16 pc, for 64 clusters), indicates that the young disk bends towards the southern latitudes

Unsteady Flow Of A Viscous Incompressible Fluid Between Parallel Plates

In the present paper an exact solution of the Navier Stokes equations has been obtained, considering the flow of a viscous incompressible fluid between two infinitely extended parallel plates when upper plate is moving with uniform velocity and the lower plate is performing linear oscillations in its own plane. The technique of Laplace transform has been employed to obtain the velocity distribution, which has been shown graphically

Night sky at the Indian Astronomical Observatory during 2000-2008

We present an analysis of the optical night sky brightness and extinction coefficient measurements in UBVRI at the Indian Astronomical Observatory (IAO), Hanle, during the period 2003-2008. They are obtained from an analysis of CCD images acquired at the 2 m Himalayan Chandra Telescope at IAO. Night sky brightness was estimated using 210 HFOSC images obtained on 47 nights and covering the declining phase of solar activity cycle-23. The zenith corrected values of the moonless night sky brightness in mag/square arcsecs are 22.14(U), 22.42(B), 21.28(V), 20.54(R) and 18.86(I) band. This shows that IAO is a dark site for optical observations. No clear dependency of sky brightness with solar activity is found. Extinction values at IAO are derived from an analysis of 1325 images over 58 nights. They are found to be 0.36 in U-band, 0.21 in B-band, 0.12 in V-band, 0.09 in R-band and 0.05 in I-band. On average, extinction during the summer months is slightly larger than that during the winter months. No clear evidence for a correlation between extinction in all bands and the average night time wind speed is found. Also presented here is the low resolution moonless optical night sky spectrum for IAO covering the wavelength range 3000-9300 \AA. Hanle region thus has the required characteristics of a good astronomical site in terms of night sky brightness and extinction, and could be a natural candidate site for any future large aperture Indian optical-infrared telescope(s).Comment: 18 pages, 7 figures, uses basi.cls, accepted for publication in Bulletin of the Astronomical Society of Indi

Absence of Conventional Spin-Glass Transition in the Ising Dipolar System LiHo_xY_{1-x}F_4

The magnetic properties of single crystals of LiHo_xY_{1-x}F_4 with x=16.5% and x=4.5% were recorded down to 35 mK using a micro-SQUID magnetometer. While this system is considered as the archetypal quantum spin glass, the detailed analysis of our magnetization data indicates the absence of a phase transition, not only in a transverse applied magnetic field, but also without field. A zero-Kelvin phase transition is also unlikely, as the magnetization seems to follow a non-critical exponential dependence on the temperature. Our analysis thus unmasks the true, short-ranged nature of the magnetic properties of the LiHo_xY_{1-x}F_4 system, validating recent theoretical investigations suggesting the lack of phase transition in this system.Comment: 5 pages, 4 figure

Optical Photometry of the GRB 010222 Afterglow

The optical afterglow of GRB 010222 was observed using the recently installed 2-m telescope at the Indian Astronomical Observatory, Hanle, and the telescopes at the Vainu Bappu Observatory, Kavalur, beginning ~ 0.6 day after the detection of the event. The results based on these photometric observations combined with others reported in the literature are presented in this paper. The R band light curve shows an initial decline of intensities proportional to t^{-0.542} which steepens, after 10.3 hours, to t^{-1.263}. Following the model of collimated outflow, the early break in the light curve implies a very narrow beam angle (~ 2-3 deg). The two decay rates are consistent with the standard jet model in a uniform density ambient medium, but require a hard spectrum of electron power density with p ~ 1.5. The R band light between 14 and 17 hours since outburst departs from the power law fit by 0.1 mag and shows some evidence for fluctuations over timescales of an hour in the observer's frame. Such deviations are expected due to density inhomogeneities if the ambient medium is similar to the local interstellar medium. GRB 010222 is thus an example of a highly collimated outflow with a hard spectrum of electron energy distribution in normal interstellar environment.Comment: 15 pages, Latex, including 2 postscript figures, to appear in the Bull. astro. Soc. India, September 2001 issu

The COMPLETE Nature of the Warm Dust Ring in Perseus

The Perseus molecular cloud complex is a ~30pc long chain of molecular clouds most well-known for the two star-forming clusters NGC1333 and IC348 and the well-studied outflow source in B5. However, when studied at mid- to far-infrared wavelengths the region is dominated by a ~10pc diameter shell of warm dust, likely generated by an HII region caused by the early B-star HD278942. Using a revised calibration technique the COMPLETE team has produced high-sensitivity temperature and column-density maps of the Perseus region from IRAS Sky Survey Atlas (ISSA) 60 and 100um data. In this paper, we combine the ISSA based dust-emission maps with other observations collected as part of the COMPLETE Survey, along with archival H-alpha and MSX observations. Molecular line observations from FCRAO and extinction maps constructed by applying the NICER method to the 2MASS catalog provide independent estimates of the ``true'' column-density of the shell. H-alpha emission in the region of the shell confirms that it is most likely an HII region located behind the cloud complex, and 8um data from MSX indicates that the shell may be interacting with the cloud. Finally, the two polarisation components previously seen towards background stars in the region can be explained by the association of the stronger component with the shell. If confirmed, this would be the first observation of a parsec-scale swept-up magnetic field.Comment: Accepted by ApJ. Figures have been compressed - full resolution version available at http://cfa-www.harvard.edu/COMPLETE/results.htm

Loss of correlation between HIV viral load and CD4+ T-cell counts in HIV/HTLV-1 co-infection in treatment naive Mozambican patients

Seven hundred and four HIV-1/2-positive, antiretroviral therapy (ART) naïve patients were screened for HTLV-1 infection. Antibodies to HTLV-1 were found in 32/704 (4.5%) of the patients. Each co-infected individual was matched with two HIV mono-infected patients according to World Health Organization clinical stage, age +/-5 years and gender. Key clinical and laboratory characteristics were compared between the two groups. Mono-infected and co-infected patients displayed similar clinical characteristics. However, co-infected patients had higher absolute CD4+ T-cell counts (P = 0.001), higher percentage CD4+ T-cell counts (P < 0.001) and higher CD4/CD8 ratios (P < 0.001). Although HIV plasma RNA viral loads were inversely correlated with CD4+ T-cell-counts in mono-infected patients (P < 0.0001), a correlation was not found in co-infected individuals (P = 0.11). Patients with untreated HIV and HTLV-1 co-infection show a dissociation between immunological and HIV virological markers. Current recommendations for initiating ART and chemoprophylaxis against opportunistic infections in resource-poor settings rely on more readily available CD4+ T-cell counts without viral load parameters. These guidelines are not appropriate for co-infected individuals in whom high CD4+ T-cell counts persist despite high HIV viral load states. Thus, for co-infected patients, even in resource-poor settings, HIV viral loads are likely to contribute information crucial for the appropriate timing of ART introduction