• Vijayakumar H. Doddamani

Articles written in Journal of Astrophysics and Astronomy

• Solar Wind Associated with Near Equatorial Coronal Hole

Present study probes temporal changes in the area and radiative flux of near equatorial coronal hole associated with solar wind parameters such as wind speed, density, magnetic field and temperature. Using high temporal resolution data from SDO/AIA for the two wave-lengths 193 Å and 211 Å, area and radiative flux of coronal holes are extracted and are examined for the association with high speed solar wind parameters. We find a strong association between different parameters of coronal hole and solar wind. For both the wavelength bands, we also compute coronal hole radiative energy near the earth and it is found to be of similar order as that of solar wind energy. However, for the wavelength 193 Å, owing to almost similar magnitudes of energy emitted by coronal hole and energy due to solar wind, it is conjectured that solar wind might have originated around the same height where 193 Å line is formed in the corona.

• Short timescale UV variability study in NGC 4151 using IUE data

IUE has made very successful long term and intense short time-scale monitoring spectroscopic study of NGC 4151, a Seyfert 1 galaxy for over nearly 18 years from its launch in 1978 to 1996. The long-term observations have been useful in understanding the complex relation between UV continuum and emission line variability Seyfert galaxies. In this paper, we present the results of our studies on the short-timescale intense monitoring campaign of NGC 4151 undertaken during December 1–15, 1993. A most intense monitoring observation of NGC 4151 was carried out by IUE in 1993, when the source was at its historical high flux state with a shortest interval of 70 min between two successive observations.We present our results on emission line and continuum variability amplitudes characterized by $F_{\rm var}$ method.We found highest variability of nearly 8.3% at 1325 å continuum with a smallest amplitude of 4% at 2725 å. The relative variability amplitudes ($R_{\rm max}$) have been found to be 1.372, 1.319, 1.302 and 1.182 at 1325, 1475, 1655 and 2725 å continuum respectively. The continuum and emission line variability characteristics obtained in the present analysis are in very good agreement with the results obtained by Edelson et al. (1996) and Crenshaw et al. (1996) from the analysis of the same observational spectral data. The large amplitude rapid variability characteristics obtained in our study have been attributed to the continuum reprocessing of X-rays absorbed by the material in the accretion disk as proposed by Shakura and Sunyaev (1973). The continuum and emission light curves have shown four distinct high amplitude events of flux maxima during the intense monitoring campaign of 15 days, providing a good limit on the amplitude of UV variability and the BLR size in low luminosity Seyfert galaxies and are useful for constraining the continuum emission models. The decreasing $F_{\rm var}$ amplitude of UV continuum with respect to increasing wavelength obtained in the present study and consistent with similar observations by Edelson et al. (1996) and Crenshaw et al. (1996) is a significant result of the intense monitoring observations.

• UVIT observation of Milky Way satellite galaxy Reticulum II

We present the UV photometry of one of the Ultra-Faint Dwarf (UFD) Milky Way (MW) satellite galaxies, Reticulum II, using images acquired with the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat. Reticulum II is a dark matter dominated, one of the most metal-poor and old (13.5 Gyr) satellite galaxies. High resolution spectroscopy of red giant branch (RGB) stars in the galaxy showed that the stars are metal-poor and highly enhanced in rapid neutron capture process ($r$-process) elements, indicating operation of $r$-process at a very early time in the galaxy. Understanding the stellar population of the galaxy will provide insights to the sites of $r$-process production and also clues to the formation of UFDs. Here, we present UV and optical color magnitude diagrams (CMD), of Reticulum II using samples selected based on Gaia data release-II proper motions and theoretical isochrone fitting. We identified eight members including the four new members detected for the first time in this study which adds to only 24 confirmed members. These new members are bright enough for follow-up high resolution spectroscopic studies that will be very valuable to probe the early chemical history of the galaxy. We identified three blue horizontal branch (BHB) stars and a possible red horizontal branch (RHB) star in Reticulum II. RHB stars are rare among ultra faint dwarf galaxies. This might indicate the presence of more than one epoch of star formation in Reticulum II, contrary to the earlier studies.

• # 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