My Life and My Journey through Solar Physics
This is the talk I gave at the workshop "Solar-Stellar Magnetism: Past, Present and Future" held in Jaipur on 18 February 2018 on the occasion of my 60th year....
Tidally driven inertial waves enhance eccentricity damping and spin evolution in planets a…
Tidal interactions influence the orbital motions of binary star systems and extrasolar planets alike. Tides also affect stellar and planetary rotation rates. We demonstrate that in addition to altering spin synchronization and pseudosynchronization,...
Quasi-periodic oscillations and the global modes of relativistic, MHD accretion discs
The high-frequency quasi-periodic oscillations (HFQPOs) that punctuate the light curves of X-ray binary systems present a window onto the intrinsic properties of stellar-mass black holes and hence a testbed for general relativity. One explanation for...
The Structure and Evolution of Young Stellar Clusters
We examine the properties of embedded clusters within 1 kiloparsec using new data from the Spitzer Space Telescope, as well as recent results from 2MASS and other ground-based near-infrared surveys. We use surveys of entire molecular clouds to unde...
Formation and Morphology of the First Galaxies in the Cosmic Morning
We investigate the formation and morphological evolution of the first galaxies in the cosmic morning ($10 \gtrsim z \gtrsim 4$) using the Horizon Run 5 (HR5) simulation. For galaxies above the stellar mass $M_{\star, {\rm min}} = 2\times 10^9\,M_{\od...
A Panchromatic Characterization of the Evening and Morning Atmosphere of WASP-107 b: Compo…
Limb-resolved transmission spectroscopy has the potential to transform our understanding of exoplanetary atmospheres. By separately measuring the transmission spectra of the evening and morning limbs, these atmospheric regions can be individually cha...
Kim 3: an Ultra-faint Star Cluster in the Constellation of Centaurus
We report the discovery of an ultra-faint star cluster in the constellation of Centaurus. This new stellar system, Kim 3, features a half light radius of $r_{h}=2.29^{+1.28}_{-0.52}$ pc and a total luminosity of $M_{V}=+0.7\pm0.3$. Approximately 26 s...
Polish Astrophysics: The First Half-Century, 1923-1973
An attempt is made to evaluate progress of the Polish astrophysical research of stars and of the inter-stellar medium (ISM) on the basis of scientific paper citations in the ADS database. Rather modest citation levels were observed in the years befor...
Nearly all Massive Quiescent Disk Galaxies have a Surprisingly Large Atomic Gas Reservoir
The massive galaxy population above the characteristic Schechter mass M*~10^10.6 Msun contributes to about half of the total stellar mass in the local Universe. These massive galaxies usually reside in hot dark matter haloes above the critical shock-...
What is the real nature of HD 108 ?
Since the beginning of the past century, the nature of HD 108 has been a subject of intense debate. One after another, astronomers explored its variability and attributed it either to binarity, or to changes in the stellar wind of a single star. In...
Limits on Mode Coherence Due to a Non-static Convection Zone
The standard theory of pulsations deals with the frequencies and growth rates of infinitesimal perturbations in a stellar model. Modes which are calculated to be linearly driven should increase their amplitudes exponentially with time; the fact that...
Dust Sensitivity of Absorption-Line Indices
We investigate the effects of dust extinction on integrated absorption-line indices that are widely used to derive constraints on the ages and metallicities of composite stellar systems. Typically, absorption-line studies have been performed on glo...
Dynamics of stars around spiral arms in an N-body/SPH simulated barred-spiral galaxy
We run N-body smoothed particle hydrodynamics (SPH) simulations of a Milky Way sized galaxy. The code takes into account hydrodynamics, self-gravity, star formation, supernova and stellar wind feedback, radiative cooling and metal enrichment. The sim...
The GALEX Arecibo SDSS Survey (GASS)
The GALEX Arecibo SDSS Survey (GASS) is a large targeted survey that started at Arecibo in March 2008. GASS is designed to measure the neutral hydrogen content of ~1000 massive galaxies (with stellar mass Mstar > 10^10 Msun) at redshift 0.025<z<0.0...
Coronal Heating as Determined by the Solar Flare Frequency Distribution Obtained by Aggreg…
Flare frequency distributions represent a key approach to addressing one of the largest problems in solar and stellar physics: determining the mechanism that counter-intuitively heats coronae to temperatures that are orders of magnitude hotter than t...
The discovery space of ELT-ANDES. Stars and stellar populations
The ArmazoNes high Dispersion Echelle Spectrograph (ANDES) is the optical and near-infrared high-resolution echelle spectrograph envisioned for the European Extremely Large Telescope (ELT). We present a selection of science cases, supported by new ca...
Stellar Populations and the Local Group Membership of the Dwarf Galaxy DDO 210
We present deep BVI CCD photometry of the stars in the dwarf galaxy DDO 210. The color-magnitude diagrams of DDO 210 show a well-defined red giant branch (RGB) and a blue plume. The tip of the RGB is found to be at I_TRGB = 20.95 +/- 0.10 mag. From...
Discovery of a Stellar Overdensity in Eridanus-Phoenix in the Dark Energy Survey
We report the discovery of an excess of main sequence turn-off stars in the direction of the constellations of Eridanus and Phoenix from the first year data of the Dark Energy Survey (DES). The Eridanus-Phoenix (EriPhe) overdensity is centered around...
Differential population studies using asteroseismology: solar-like oscillating giants in C…
Solar-like oscillating giants observed by the space-borne satellites CoRoT and Kepler can be used as key tracers of stellar populations in the Milky Way. When combined with additional photometric/spectroscopic constraints, the pulsation spectra of so...
Tidal interactions between binary stars drives lithium production in low-mass red giants
Theoretical models of stellar evolution predict that most of the lithium inside a star is destroyed as the star becomes a red giant. However, observations reveal that about 1% of red giants are peculiarly rich in lithium, often exceeding the amount i...
CGCG 480-022: A distant lonesome merger?
We present a complete analysis, which includes morphology, kinematics, stellar populations and N-body simulations of CGCG 480-022, the most distant (cz=14317 km/s) isolated galaxy studied so far in such detail. The results all support the hypothesi...
Non-gray rotating stellar models and the evolutionary history of the Orion Nebular Cluster
Rotational evolution in the pre-main sequence (PMS) is described with new sets of PMS evolutionary tracks including rotation, non-gray boundary conditions (BCs) and either low (LCE) or high convection efficiency (HCE). Using observational data and...
Abundances of disk and bulge giants from high-resolution optical spectra -- IV. Zr, La, Ce…
Stellar mass and metallicity are factors that affect the neutron-capture process. Due to this, the enrichment of the ISM and the abundance of neutron-capture elements vary with time, making them suitable probes for the Galactic chemical evolution. In...
Population III Star Formation and IMF
We review recent 3D cosmological hydrodynamic simulations of primordial star formation from cosmological initial conditions (Pop III.1) and from initial conditions that have been altered by radiative feedback from stellar sources (Pop III.2). We co...
Using Neural Network Models to Estimate Stellar Ages from Lithium Equivalent Widths: An EA…
We present an Artificial Neural Network (ANN) model of photospheric lithium depletion in cool stars (3000 < Teff / K < 6500), producing estimates and probability distributions of age from Li I 6708A equivalent width (LiEW) and effective temperature d...
On the self-consistent time-dependent linearized response of stellar discs to external per…
We study the explicitly time-dependent response of a razor-thin axisymmetric disc to externally imposed perturbations by recasting the linearized Collisionless Boltzmann equation as an integral equation and applying Kalnajs' matrix method. As an appl...
The First Photometric and Orbital Period Investigation of an Extremely Low Mass Ratio Cont…
Photometric observations for the totally eclipsing binary system TYC 4002-2628-1, were obtained between November 2020 and November 2021. To determine the stellar atmospheric parameters, a spectral image was taken with the 2.16 m telescope at National...
Observing solar-like oscillations
We review techniques for measuring stellar oscillations in solar-type stars. Despite great efforts, no unambiguous detections have been made. A new method, based on monitoring the equivalent widths of strong lines, shows promise but is yet to be co...
Multiwavelength and astrometric study of the DBS-89-90-91 embedded clusters region
Aims. Our main targets were to improve the understanding of the main properties of G316.8-0.1 (IRAS 14416-5937) radio source where the DBS 89-90-91 embedded clusters are located, to identify the stellar population present in this region, and to study...
Metallicity Estimates for Old Star Clusters in M33
Using the theoretical stellar population synthesis models of BC96, Kong et al. (2003) showed that some BATC colors and color indices could be used to disentangle the age and metallicity effect. They found that there is a very good relation between...
Nuclear electron capture rate in stellar interiors and the case of 7Be
Nuclear electron capture rate from continuum in an astrophysical plasma environment (like solar core) is calculated using a modified Debye-Huckel screening potential and the related non-Gaussian q-distribution of electron momenta. For q=1 the well-...
A brown dwarf desert for intermediate mass stars in Sco OB2?
We present JHK observations of 22 intermediate-mass stars in Sco OB2, obtained with VLT/NACO. The survey was performed to determine the status of (sub)stellar candidate companions of A and late-B members. The distinction between companions and back...
Fundamental Parameters of Massive Stars
We discuss the determination of fundamental parameters of `normal' hot, massive OB-type stars, namely temperatures, luminosities, masses, gravities and surface abundances. We also present methods used to derive properties of stellar winds -- mass-l...
Zeta Pup: the merger of at least two massive stars
We first discuss the stellar and wind parameters of zeta Pup resulting from detailed UV diagnostics. These parameters together with the runaway nature of the star can most easily be explained by dynamical binary-binary or binary-single star interacti...
The Impact of Massive Stars on the Formation of Young Stellar Clusters
Massive OB stars play an important role in the evolution of molecular clouds and star forming regions. The OB stars both photo--ionize molecular gas as well as sweep up and compress interstellar gas through winds, ionization fronts, and supernovae....
The Galactic Chemical Evolution of phosphorus observed with IGRINS
Phosphorus (P) is considered to be one of the key elements for life, making it an important element to look for in the abundance analysis of spectra of stellar systems. Yet, there exists only a handful of spectroscopic studies to estimate the P abund...
TDCOSMO 2025: Cosmological constraints from strong lensing time delays
We present cosmological constraints from 8 strongly lensed quasars (hereafter, the TDCOSMO-2025 sample). Building on previous work, our analysis incorporated new deflector stellar velocity dispersions measured from spectra obtained with the James Web...
Arp 58 and Arp 68: two M 51- type systems
We study two M 51-type systems Arp 68 and Arp 58, which strongly differ by their stellar masses, gas content and environment. Long-slit spectral observations obtained at the 6-m telescope BTA were used to trace the distributions of a line-of-sight (L...
Comparing Approximate Bayesian Computation with the Poisson-Likelihood Method for Exoplane…
We present Kepler exoplanet occurrence rates inferred with approximate Bayesian computation (ABC). By using the same planet catalogue, stellar sample, and characterization of completeness and reliability as Bryson et al. (2020), we are able to provid...
Optimal neutron-star mass ranges to constrain the equation of state of nuclear matter with…
Exploiting a very large library of physically plausible equations of state (EOSs) containing more than $10^{7}$ members and yielding more than $10^{9}$ stellar models, we conduct a survey of the impact that a neutron-star radius measurement via elect...