Related papers: Using Chandra/LETG spectra to probe stellar corona…
Since the end of 2018, the Transiting Exoplanet Survey Satellite (TESS) has provided stellar photometry to the astronomical community. We have used TESS data to study rotational modulation in the light curves of a sample of chemically…
Rotation is a significant characteristic of the Sun and other stars, and it plays an important role in understanding their dynamo actions and magnetic activities. In this study, the rotation of the solar chromospheric activity is…
The photospheric spot activity of some of the stars with transiting planets discovered by the CoRoT space experiment is reviewed. Their out-of-transit light modulations are fitted by a spot model previously tested with the total solar…
Recent observations of rapidly-rotating cool dwarfs have revealed H$\alpha$ line asymmetries indicative of clumps of cool, dense plasma in the stars' coronae. These clumps may be either long-lived (persisting for more than one stellar…
Slow dissipation of non-potential magnetic fields in the magnetosphere of the magnetar is assumed to accelerate particles to hundreds MeV along the magnetic field lines. We consider interaction of fast particles with the surface of the…
A fraction of the extreme horizontal branch stars of globular clusters exhibit a periodic light variability that has been attributed to rotational modulation caused by surface spots. These spots are believed to be connected to inhomogeneous…
The intense magnetic fields of neutron stars naturally lead to strong anisotropy and polarization of radiation emanating from their surfaces, both being sensitive to the hot spot position on the surface. Accordingly, pulse phase-resolved…
The variation of a stellar light curve owing to the rotational modulation by the magnetic features (starspots and faculae) on the star's surface can be used to investigate the magnetic properties of the host star. In this paper, we use the…
The simultaneous presence of a strong quasi periodic oscillation of period of about 10 seconds in the optical and X-ray lightcurves of the X-ray transient XTE J1118+480 suggests that a significant fraction of the optical flux originates…
Variations in the X-ray emission from the narrow line Seyfert 1 galaxy, Markarian 335 (Mrk 335), are studied on both long and short timescales through observations made between 2006 and 2013 with XMM-Newton, Suzaku and NuSTAR. Changes in…
On the Sun, the rotation periods of individual sunspots not only trace the latitude dependence of the surface rotation rate, but also provide clues as to the amount of subsurface fluid shear. In this paper we present the first measurements…
A long-standing question in active galactic nucleus (AGN) research is how the corona is heated up to produce X-ray radiation much stronger than that arising from the viscous heating within the corona. In this paper, we carry out detailed…
The most violent space weather events (eruptive solar flares and coronal mass ejections) are driven by the release of free magnetic energy stored in the solar corona. Energy can build up on timescales of hours to days, and then may be…
Coronal hole boundaries are the interfaces between closed and open magnetic field regions in the solar atmosphere. Many fundamental processes take place at these regions, including magnetic reconnection that is responsible for solar wind…
We examine 4-yr almost continuous Kepler photometry of 115 B stars. We find that the light curves of 39 percent of these stars are simply described by a low-frequency sinusoid and its harmonic, usually with variable amplitudes, which we…
We use high-angular-resolution images obtained with SPHERE/ZIMPOL to study the photosphere, the warm molecular layer, and the inner wind of the close-by oxygen-rich AGB star R Doradus. We present observations in filters V, cntH$\alpha$, and…
The surface magnetic and abundance inhomogeneities in chemically peculiar Ap/Bp stars are coupled and responsible for their rotationally modulated variability. Within the framework of fossil field hypothesis these inhomogeneities are…
Understanding solar coronal magnetic fields is crucial to address the long-standing mysteries of the solar corona and solar wind. Although routine photospheric magnetic fields (MFs) are available for decades, coronal MFs are rarely…
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,…
We present a new model for the coronal structure of rapidly rotating solar-type stars. The presence of prominences trapped in co-rotation 2 to 5 stellar radii above the stellar surface has been taken as evidence that the coronae of these…