• GAJENDRA PANDEY

Articles written in Journal of Astrophysics and Astronomy

• Editorial

• The horizontal branch morphology of the globular cluster NGC 1261 using AstroSat

We present the results obtained from the UV photometry of the globular cluster NGC 1261 using far-UV (FUV) and near-UV (NUV) images acquired with the Ultraviolet Imaging Telescope (UVIT) onboard the AstroSat satellite. We utilized the UVIT data combined with HST, GAIA, and ground-based optical photometric data to construct the different UV colour-magnitude diagrams (CMDs). We detected blue HB (BHB), and two extreme HB (EHB) stars in FUV, whereas full HB, i.e., red HB (RHB), BHB as well as EHB is detected in NUV CMDs. The 2 EHB stars, identified in both NUV and FUV, are confirmedmembers of the cluster. The HB stars form a tight sequence in UV-optical CMDs, which is almost aligned with Padova isochrones. This study sheds light on the significance of UV imaging to probe the HB morphology in GCs.

• Fluorine detection in hot extreme helium stars

The origin and evolution of hydrogen-deficient stars are not yet adequately understood. Their chemical peculiarities, along with hydrogen-deficiency, makes them stand out from the rest and sheds light on their possible origin. Severe fluorine enrichment (of the order of 800–8000) is one such characteristicfeature of a class of hydrogen deficient stars, mainly the RCBs (R Coronae Borealis stars) and cool EHes (Extreme Helium stars) which enforces their close connection. For hot EHes, this relationship with the cooler EHes, based on their fluorine abundance is unexplored. Here, first estimates of fluorine abundances in hot EHes are presented and discussed in the light of their cooler counterparts to try to establish an evolutionary connection. The relation between these fluorine estimates with the other elemental abundances observed in these stars plays a pivotal role to predict the formation and evolution of these exotic stars.

• Investigation of the helium enhancement in a super lithium-rich giant HD 77361

In this work, the helium-enhancement (He-enhancement) in the lithium-rich (Li-rich) K-giant HD 77361 is investigated using the strengths of the MgH band and the Mg i lines. The detailed abundance analysis and also the synthesis of the MgH band and the Mg i lines has been carried out for HD 77361. One would expect, within uncertainities, same Mg abundance from both the MgH and Mg i lines. But, we found that Mg abundance derived from MgH lines is significantly less than the abundance from Mg i lines, and this difference cannot be reconciled by changing the stellar parameters within the uncertainties, implying He enhancement in star’s photosphere. The He enhancement in the atmospheres is estimated by using models of different He/H ratios so that both the lines, MgH as well as Mg i, return the same Mg abundance for the adopted model’s He/H ratio. We found ${\rm He}={\rm H }= 0.4 \pm 0.1$ as the value for HD 77361,the normal value of He$/$H $=$ 0.1. Knowing the amount of He-enhancement in the Li-rich giants is a strong clue for understanding the scenarios responsible for the Li and He enrichment. The analysis and results are discussed.

• UOCS. V. UV study of the old open cluster NGC 188 using AstroSat

We present the UV photometry of the old open cluster NGC188 obtained using images acquired with Ultraviolet Imaging Telescope (UVIT) on board the AstroSat satellite, in two far-UV (FUV) and one near-UV (NUV) filters. UVIT data is utilised in combination with optical photometric data to construct the optical and UV colour-magnitude diagrams (CMDs). In the FUV images, we detect only hot and bright blue straggler stars (BSSs), one hot subdwarf, and one white dwarf (WD) candidate. In the NUV images, we detect members up to a faintness limit of $\sim$22 mag including 21 BSSs, 2 yellow straggler stars (YSSs), and one WD candidate. This study presents the first NUV-optical CMDs, and are overlaid with updated BaSTIIAC isochrones and WD cooling sequence, which are found to fit well to the observed CMDs. We use spectral energy distribution (SED) fitting to estimate the effective temperatures, radii, and luminosities of the UV-bright stars. We find the cluster to have an HB population with three stars ($T_{\rm eff}=4750–21000$ K). We also detect two yellow straggler stars, with one of them with UV excess connected to its binarity and X-ray emission.

• Journal of Astrophysics and Astronomy

Volume 43, 2022
All articles
Continuous Article Publishing mode

• Continuous Article Publication

Posted on January 27, 2016

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.

• Editorial Note on Continuous Article Publication

Posted on July 25, 2019