Articles written in Journal of Astrophysics and Astronomy
Volume 9 Issue 2 June 1988 pp 117-124
Kinematical distances are estimated for six open star clusters. They agree fairly well with the photometric distances. The kinematical distances cannot, at present, be estimated better than the photometric distances. When more accurate proper motion measurements become available the kinematical distances will improve considerably and may then be used to calibrate the cosmic distance scale.
Volume 10 Issue 2 June 1989 pp 173-182
Mass segregation in the form of preferential concentration of more massive stars in the central regions of a number of open star clusters has been known for some time. In this paper, integrated
Volume 11 Issue 2 June 1990 pp 151-166
The open cluster NGC 2818 containing a planetary nebula has been observed in
Volume 12 Issue 2 June 1991 pp 111-117
Symbiotic stars that are strong radio sources and have cool dust emitting in the infrared are expected to have extended emission nebulae around them. In order to search for such emission nebulae, we have carried out CCD imaging of three symbiotic stars (R Aqr, RR Tel and H1-36) with narrow-band filters centred at the emission lines of [O III] λ5007, Hα λ6563, [N II] λ6584, [S II] λ6717 + 6731. RR Tel and H1-36 images do not show any extended nebulosities around them. The CCD image of the R Aqr nebulosity in the high excitation [O m] line is different from its image in Hα and the low excitation lines of [N II] and [S II] indicating ionization-stratification in the nebula. In H1-36 the optical nebulosity (if it exists) is smaller than ∽2 arcsec while the radio image size is known to be large (∽5 arcsec). This behaviour is opposite to that seen in R Aqr in which the radio emission comes from the core region of a much larger optical nebulosity. Interstellar and/or circumstellar extinctions are suggested to be responsible for this difference
Volume 18 Issue 4 December 1997 pp 295-301
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.
Volume 22 Issue 1 March 2001 pp 131-144
The design and performance of a portable three channel photometer installed at the Uttar Pradesh State Observatory (UPSO), Naini Tal is described. The photometer is modular and the whole unit can be disassembled as individual channels such that the system can also be used as a single channel or two channel photometer. The system also has provision to monitor a guide star. The instrument was put into operation since November 1999 on the 1m Sampurnanand telescope at UPSO, Naini Tal. Since then, it is used extensively for the ‘Survey of rapidly oscillating Ap (roAp) stars in the northern sky’ from UPSO. Observational results using this new photometer in its initial phase of operation are discussed. The advantage of having continuous sky measurement is demonstrated.
Volume 25 Issue 1-2 March 2004 pp 1-55
We present the results of a comparative study of the intranight optical variability (INOV) characteristics of radio-loud and radioquiet quasars, which involves a systematic intra-night optical monitoring of seven sets of high luminosity AGNs covering the redshift range
Volume 26 Issue 2-3 June 2005 pp 117-118
Volume 26 Issue 2-3 June 2005 pp 339-347
A collaborative programme searching for mmag pulsations in chemically peculiar stars in the northern hemisphere was initiated in 1997 between Nainital, India, and Cape Town, South Africa. It was therefore named as the
Volume 34 Issue 1 March 2013 pp 1-2
Volume 34 Issue 1 March 2013 pp 3-3
Volume 34 Issue 2 June 2013 pp 75-80
Volume 34 Issue 3 September 2013 pp 273-296
It is important to quantify the underestimation of rms photometric errors returned by the commonly used APPHOT algorithm in the IRAF software, in the context of differential photometry of point-like AGN, because of the crucial role it plays in evaluating their variability properties. Published values of the underestimation factor, 𝜂, using several different telescopes, lie in the range 1.3–1.75. The present study aims to revisit this question by employing an exceptionally large data set of 262 differential light curves (DLCs) derived from 262 pairs of non-varying stars monitored under our ARIES AGN monitoring program for characterizing the intra-night optical variability (INOV) of prominent AGN classes. The bulk of these data were taken with the 1-m Sampurnanad Telescope (ST). We find 𝜂 = 1.54 ± 0.05 which is close to our recently reported value of 𝜂 = 1.5. Moreover, this consistency holds at least up to a brightness mismatch of 1.5 mag between the paired stars. From this we infer that a magnitude difference of at least up to 1.5 mag between a point-like AGN and comparison star(s) monitored simultaneously is within the same CCD chip acceptable, as it should not lead to spurious claims of INOV.
Volume 34 Issue 4 December 2013 pp 393-429
We present a detailed investigation of X-ray source contents of eight young open clusters with ages between 4 to 46 Myr using archival X-ray data from XMM-NEWTON. The probable cluster memberships of the X-ray sources have been established on the basis of multi-wavelength archival data, and samples of 152 pre-main sequence (PMS) low mass (< 2𝑀⊙), 36 intermediate mass (2-10𝑀⊙) and 16 massive (> 10𝑀⊙) stars have been generated. X-ray spectral analyses of high mass stars reveal the presence of high temperature plasma with temperature < 2 keV, and mean 𝐿𝑋/𝐿bol of 10-6.9. In the case of PMS low mass stars, the plasma temperatures have been found to be in the range of 0.2 keV to 3 keV with a median value of ∼ 1.3 keV, with no significant difference in plasma temperatures during their evolution from 4 to 46 Myr. The X-ray luminosity distributions of the PMS low mass stars have been found to be similar in the young star clusters under study. This may suggest a nearly uniform X-ray activity in the PMS low mass stars of ages ∼ 4–14 Myr. These observed values of 𝐿𝑋/𝐿bol are found to have a mean value of 10-3.6 ± 0.4, which is below the X-ray saturation level. The 𝐿𝑋/𝐿bol values for the PMS low mass stars are well correlated with their bolometric luminosities, that implies its dependence on the internal structure of the low mass stars. The difference between the X-ray luminosity distributions of the intermediate mass stars and the PMS low mass stars has not been found to be statistically significant. Their 𝐿𝑋/𝐿bol values, however have been found to be significantly different from each other with a confidence level greater than 99.999% and the strength of X-ray activity in the intermediate mass stars is found to be lower compared to the low mass stars. However, the possibility of X-ray emission from the intermediate mass stars due to a low mass star in close proximity of the intermediate mass star can not be ruled out.
Volume 35 Issue 1 March 2014 pp 39-54 General Editorial on Publication Ethics
We present, for the first time, an analysis of seven intense X-ray flares observed from six stars (LAV 796, LAV 1174, SHM2002 3734, 2MASS 02191082+5707324, V553 Car, V557 Car). These stars are located in the region of young open star clusters NGC 869 and IC 2602. These flares detected in the XMM-Newton data show a rapid rise (10–40 min) and a slow decay (20–90 min). The X-ray luminosities during the flares in the energy band 0.3–7.5 keV are in the range of 1029.9 to 1031.7 erg s-1. The strongest flare was observed with the ratio ∼ 13 for count rates at peak of the flare to the quiescent intensity. The maximum temperature during the flares has been found to be ∼ 100 MK. The semi-loop lengths for the flaring loops are estimated to be of the order of 1010 cm. The physical parameters of the flaring structure, the peak density, pressure and minimum magnetic field required to confine the plasma have been derived and found to be consistent with flares from pre-main sequence stars in the Orion and the Taurus-Auriga-Perseus region.
Volume 38 Issue 1 March 2017 Article ID 0000 Editorial
Volume 38 Issue 4 December 2017 Article ID 0060 Editorial
Volume 39 Issue 6 December 2018 Article ID 0071
Volume 41 All articles Published: 25 September 2020 Article ID 0022
Quasars are ideal targets to use for astrometric calibration of large scale astronomical surveys as they have negligible proper motion and parallax. The forthcoming 4-m International Liquid Mirror Telescope (ILMT) will survey the sky that covers a width of about 27$'$. To carry out astrometric calibration of theILMT observations, we aimed to compile a list of quasars with accurate equatorial coordinates and falling in the ILMT stripe. Towards this, we cross-correlated all the quasars that are known till the present date with the sources in the
Volume 41 All articles Published: 11 December 2020 Article ID 0033 Review
The 3.6-meter Indo–Belgian Devasthal optical telescope (DOT) has been used for optical and nearinfrared (NIR) observations of celestial objects. The telescope has detected stars of $B=24.5 \pm 0.2$, $R = 24.6 \pm 0.12$ and $g= 25.2 \pm 0.2$ mag in exposure times of 1200, 4320 and 3600 s respectively. In one hour of exposure time, a distant galaxy of $24.3 \pm 0.2$ mag and point sources of $\sim$25 mag have been detected in the SDSS $i$ band. The NIR observations show that stars up to $J = 20\pm 0.1$, $H = 18.8 \pm 0.1$ and $K = 18.2 \pm 0.1$ mag can be detected in effective exposure times of 500, 550 and 1000 s respectively. The $nbL$ band sources brighter than $\sim$9.2 mag and strong ($\geq$0.4 Jy) $PAH$ emitting sources like Sh 2-61 can also be observed with the 3.6-meter DOT. A binary star with angular separation of 0:$''$4 has been resolved by the telescope. Sky images with sub-arcsec angular resolutions are observed with the telescope at wavelengths ranging from optical to NIR for a good fraction of observing time. The on-site performance of the telescope is found to be at par with the performance of other, similar telescopes located elsewhere in the world. Owing to the advantage of its geographicallocation, the 3.6-meter DOT can provide optical and NIR observations for a number of frontline galactic and extra-galactic astrophysical research problems, including optical follow-up of GMRT and AstroSat sources and optical transient objects.
Volume 42 All articles Published: 30 July 2021 Article ID 0089 SCIENCE RESULTS
King 2, one of the oldest clusters in the Milky Way, with an age of $\sim$6 Gyr and distance of $\sim$5700 pc, has been observed with UVIT payload on the AstroSat. With membership information derived from
Volume 42, 2021
Continuous Article Publishing mode
Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.
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