D. A. LEAHY
Articles written in Journal of Astrophysics and Astronomy
Volume 7 Issue 4 December 1986 pp 299-304
An examination of the existing period searches for 2CG195 + 4 leads to the conclusion that the 59 second periodicity is highly significant only for the 1981 March 17–18 detection of Bignami, Caraveo & Paul (1984). The statistical significance is increased substantially if the pulsation period is half the previously reported value. The period derivative is not well determined. Here we propose that 2CG 195 + 4 is a neutron star powered by accretion from a low (≲ 1
Volume 14 Issue 1 March 1993 pp 37-44
Near infrared measurements in the J, H and K bands have been carried out for a number of symbiotic stars with the 1.5 m telescope at the Rothney Astrophysical Observatory (RAO). A comparison with the earlier observations shows that the S-type symbiotic stars do not have any significant variation in the infrared flux over the past five years. However a small variation ∼ 0.3 magnitude in the infrared flux has been detected for CH Cygni. The observations of HM Sagittae show large decreases in the infrared flux compared to the previous measurements. The variability in the infrared fluxes of both these objects could be attributed to a variation in the temperature due to the cooling of the dust shell. The variability observed for V1016 Cygni is found consistent with the previous measurements.
Volume 42 All articles Published: 11 June 2021 Article ID 0044 SCIENCE RESULTS
The Large Area Proportional Counter (LAXPC) instruments onboard the AstroSat Observatory has observed the X-ray binary system Her X-1 during AstroSAT observing sessions AO2, AO3 and TO2. These include observations while Her X-1 is in different stages of its 35 day cycle: Low State, Turn-On toMain High State, peak of Main High State and early decline of Main High State. These observations also include a number of dips and one egress of neutron star eclipse. Here we present light curves and softness ratio analysis for these observations and discuss new features of the spectral changes with 35-day phase and orbital phase. We find a new phenomenon for dips during Main High State: about half of the dips show constant softness ratio as count rate decreases, which has not been seen before, and could be caused byhighly ionized matter or very dense cold matter. The other half of the dips show the normal decrease of softness ratio as count rate decreases. These are caused by cold matter absorption and were previously known.
Volume 42 All articles Published: 24 July 2021 Article ID 0084 SCIENCE RESULTS
The Andromeda galaxy (M31) has been observed with the UltraViolet Imaging Telescope (UVIT) instrument onboard the AstroSat Observatory. The M31 sky area was covered with 19 fields, in multiple UV filters per field, over the period of 2017 to 2019. The entire galaxy was observed in the FUV F148W filter, and more than half observed in the NUV filters. A new calibration and data processing isdescribed which improves the astrometry and photometry of the UVIT data. The high spatial resolution of UVIT ($\sim$1 arcsec) and new astrometry calibration ($\sim$0.2 arcsec) allow identification of UVIT sources with stars, star clusters, X-ray sources, and other source types within M31 to a much better level than previously possible. We present new results from matching UVIT sources with stars measured as part of the Panchromatic Hubble Andromeda Treasury project in M31.
Volume 44, 2023
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