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Subhajeet Karmakar

Subhajeet Karmakar
Monterey Institute for Reseach in Astronomy (MIRA) · Astronomy

Ph.D. (Physics), MSc Physics (Gold Medalist )

About

23
Publications
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52
Citations

Publications

Publications (23)
Preprint
We present a comprehensive study of three large long-duration flares detected on an active M-dwarf binary EQ Peg using the Soft X-Ray Telescope of the AstroSat observatory. The peak X-ray luminosities of the flares in the 0.3 - 7 keV band are found to be within ~5 - 10 x 10^{30} erg s^{-1}. The e-folding rise- and decay-times of the flares are deri...
Article
We present a comprehensive study of three large long-duration flares detected on an active M-dwarf binary EQ Peg using the Soft X-Ray Telescope of the AstroSat observatory. The peak X-ray luminosities of the flares in the 0.3–7 keV band are found to be within ∼5–10 × 1030 $\rm {erg}~\rm {s}^{-1}$. The e-folding rise- and decay-times of the flares a...
Article
Full-text available
We present the first detailed X-ray study and simultaneous optical observations of the active fast rotating star FR Cnc. The X-ray spectra are found to be explained by two-temperature plasma model with temperature of cool and hot components of 0.34 and 1.1 keV, respectively. The X-ray light curve in the 0.5–2.0 keV energy band is found to be rotati...
Preprint
Full-text available
We present the first detailed X-ray study and simultaneous optical observations of the active fast rotating star FR Cnc. The X-ray spectra are found to be explained by two-temperature plasma model with temperature of cool and hot components of 0.34 and 1.1 keV, respectively. The X-ray light curve in the 0.5 -- 2.0 keV energy band is found to be rot...
Article
We present the results of our new photometric observations of the chromospherically active star FR Cnc performed with a robotic telescope at the Zvenigorod Observatory of INASAN in March 2019. The observations were carried out from March 2 to 13, 2019, in the period of time that coincided most closely in time interval with the observations of this...
Preprint
We present results obtained from the studies of magnetic activities on four solar-type stars (F-type star KIC 6791060, K-type star LO Peg, and two M-type planet-hosting stars K2-33 and EPIC 211901114) by using optical observations from several ground- and space-based telescopes. In this study, we investigate magnetic activities such as spot-topogra...
Article
Full-text available
Using long-term optical, ultraviolet (UV) and X-ray data, we present a study of a classical T Tauri star CV Cha. The V -band light curve obtained from the All Sky Automated Survey (ASAS) shows short as well as long-term variability. The short-term variability could be due to rotational modulation of CV Cha. We derive the rotational period of 3.714...
Article
Full-text available
Indian Institute of Astrophysics, II Block Koramangala, Bangalore 560034, India We present results obtained from the studies of magnetic activities on four solar-type stars (F-type star KIC 6791060, K-type star LO Peg, and two M-type planet-hosting stars K2–33 and EPIC 211901114) by using optical observations from several ground- and space-based te...
Article
We discussmethods for analyzing the observational manifestations of differential rotation (DR). Based on the literary sources and our estimates (for 4 cool dwarfs), a list containing 75 stars was compiled. Using an example of analysis of the ‘ΔΩ–Teff’, ‘ΔΩ–rotation period’ and ‘ΔΩ–Rossby number’ diagrams we compared the determined parameters of DR...
Article
Full-text available
The results of an analysis of the activity of the young stars with planetary systems EPIC 211901114 and K2–33 based on observational data obtained over 70 days with the Kepler Space Telescope are presented. The rotation periods of EPIC 211901114 (8.56±0.60d) and K2–33 (6.29±0.50d) have been found. Maps of temperature inhomogeneities on the surfaces...
Preprint
Full-text available
Making use of the data obtained from Kepler satellite, we have analysed an F-type ultra-fast rotator KIC 6791060. We derive a rotational period of 0.34365$\pm$0.00004 d. Multiple periodicity with a period separation of $\sim$0.00016 d was detected, which appears to be a result of the relative velocity between the multiple spot-groups in different s...
Article
Full-text available
Using the data obtained from XMM-Newton, we show the gradual evolution of two periodicities of ~4500 s and ~2200 s in the decay phase of the flare observed in a solar analog EK Dra. The longer period evolves firstly for first 14 ks, while the shorter period evolves for next 10 ks in the decay phase. We find that these two periodicities are associat...
Article
Full-text available
Using the data obtained from Kepler satellite, we have analyzed an F-type ultra-fast rotator KIC 6791060. We derive a rotational period of 0.34365±0.00004 d. Multiple periodicity with a period separation of ~0.00016 d was detected, which appears to be a result of the relative velocity between the multiple spot-groups in different stellar latitudes...
Article
Making use of the data obtained from Kepler satellite, we have analysed an F-type ultra-fast rotator KIC 6791060. We derive a rotational period of 0.34365 ± 0.00004 d. Multiple periodicity with a period separation of ∼0.00016 d was detected, which appears to be a result of the relative velocity between the multiple spot-groups in different stellar...
Article
Full-text available
We present an in-depth study of two superflares (F1 and F2) detected on an active binary star CC Eridani by the Swift observatory. These superflares triggered the Burst Alert Telescope (BAT) in the hard X-ray band on 2008 October 16 and 2012 February 24. The rise phases of both the flares were observed only with BAT, whereas the decay phases were o...
Article
Full-text available
We performed new observations of an ultra-fast rotator of the spectral class K – the LO Peg star – in SAO RAS in 2014 and in Zvenigorod Observatory of INASAN in 2015. The light curves were used to build the maps of temperature inhomogeneities on the LO Peg surface in order to determine the longitudes corresponding to the location of active regions....
Article
Full-text available
We present analysis of a superare detected on an active binary system CC Eridani by Swift observatory. The are (F1) triggered the Burst Alert Telescope (BAT) in the hard X-ray band on 2008 October 16. The rise-phase was observed only with BAT, whereas the decay phase was observed simultaneously with X-Ray Telescope (XRT). The e-folding decay time i...
Article
Full-text available
Using the wealth of ∼24 yr multiband data, we present an in-depth study of the star-spot cycles, surface differential rotations (SDR), optical flares, evolution of star-spot distributions, and coronal activities on the surface of young, single, main-sequence, ultrafast rotator LO Peg. From the long-term V-band photometry, we derive rotational perio...
Article
We present recent polarimetric results of magnetically active late-type dwarfs. The polarization in these stars is found to be wavelength dependent, decreasing towards the longer wavelength. The average values of degree of polarization in these active dwarfs are found to be 0.16 ± 0.01, 0.080 ± 0.006, 0.056 ± 0.004 and 0.042 ± 0.003 per cent in B,...
Article
Full-text available
Using XMM-Newton observation, we investigate properties of a flare from the very active and poorly known stellar system 47 Cas. The luminosity at the peak of the flare was found to be 3.54x10^30 erg/s, which is ~2 times more than that at a quiescent state. The quiescent state corona of 47 Cas was represented by two temperature plasma: 3.7 and 11.0...
Article
Full-text available
We present an analysis of long-term X-ray and optical observations of the Wolf-Rayet binary, WR 25. Using archival data from observations with the XMM-Newton and the Swift observatories, spanning over ~10 yr, we show that WR 25 is a periodic variable in X-rays with a period of 208 ± 3 days. X-ray light curves in the 0.5-10.0 keV energy band show ph...

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