A5103045631- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Solar and Space Plasma Dynamics
- Astronomical Observations and Instrumentation
- Gamma-ray bursts and supernovae
- History and Developments in Astronomy
- Geophysics and Gravity Measurements
- Adaptive optics and wavefront sensing
- Historical Astronomy and Related Studies
- Geomagnetism and Paleomagnetism Studies
- Astrophysics and Cosmic Phenomena
- Atomic and Molecular Physics
- Superconducting Materials and Applications
- Infrared Target Detection Methodologies
- Spacecraft Dynamics and Control
- Cold Atom Physics and Bose-Einstein Condensates
- Computational Physics and Python Applications
- Astrophysical Phenomena and Observations
- Spacecraft and Cryogenic Technologies
- CCD and CMOS Imaging Sensors
- Advanced Frequency and Time Standards
- Advanced Measurement and Metrology Techniques
- Historical Geography and Cartography
Research Centre for Astronomy and Earth Sciences
2015-2024
Konkoly Observatory
2015-2024
Hungarian Academy of Sciences
2009-2020
Leibniz Institute for Astrophysics Potsdam
2008-2009
Royal Astronomical Society
1991
Astronomical Observatory
1991
Weatherford College
1991
Abstract We perform a study of stellar flares for the 24,809 stars observed with 2 minute cadence during first two months TESS mission. Flares may erode exoplanets’ atmospheres and impact their habitability, but might also trigger genesis life around small stars. provides new sample bright dwarf in our galactic neighborhood, collecting data thousands M dwarfs that host habitable exoplanets. Here, we use an automated search accompanied by visual inspection. Then, public allesfitter code...
Over the duration of Kepler mission, KIC8462852 was observed to undergo irregularly shaped, aperiodic dips in flux up $\sim 20$\%. The dipping activity can last for between 5 and 80 days. We characterize object with high-resolution spectroscopy, spectral energy distribution fitting, radial velocity measurements, imaging, Fourier analyses light curve. determine that is a typical main-sequence F3 V star exhibits no significant IR excess, has very close interacting companions. In this paper, we...
We study the time variations of cycles 20 active stars based on decades-long photometric or spectroscopic observations. A method time-frequency analysis, as discussed in a companion paper, is applied to data. Fifteen definitely show multiple cycles; records rest are too short verify timescale for second cycle. The typically systematic changes. For three stars, we found two each them that not harmonics, and which vary parallel, indicating common physical mechanism arising from dynamo...
The ultrafast-rotating (Prot ≈ 0.44 d) fully convective single M4 dwarf V374 Peg is a well-known laboratory for studying intense stellar activity in stable magnetic topology. As an observable proxy the field, we study stability of light curve, hence spot configuration. We also measure occurrence rate flares and coronal mass ejections (CMEs). have analysed spectroscopic observations, BV(RI)C photometry covering 5 yrs, additional RC that expands temporal base over 16 yr. curve suggests almost...
We analyze short cadence K2 light curve of the TRAPPIST-1 system. Fourier analysis data suggests $P_\mathrm{rot}=3.295\pm0.003$ days. The shows several flares, which we analyzed 42 events, these have integrated flare energies $1.26\times10^{30}-1.24\times10^{33}$ ergs. Approximately 12% flares were complex, multi-peaked eruptions. flaring and possible rotational modulation no obvious correlation. activity probably continuously alters atmospheres orbiting exoplanets, making less favorable for...
We analyze the light curve of M5.5 dwarf Proxima Centauri obtained by TESS in Sectors 11 and 12. In $\approx 50$ day-long we identified analyzed 72 flare events. The rate was 1.49 events per day, total, 7.2% data classified as flaring. estimated energies were order $10^{30}-10^{32}$ ergs passband ($\approx4.8\times$ higher bolometric energies, but same magnitude). Most eruptions appeared groups. Two showed quasi-periodic oscillations during their decay phase with a time scale few hours, that...
The ultrafast-rotating ($P_\mathrm{rot}\approx0.44 d$) fully convective single M4 dwarf V374 Peg is a well-known laboratory for studying intense stellar activity in stable magnetic topology. As an observable proxy the field, we study stability of light curve, and thus spot configuration. We also measure occurrence rate flares coronal mass ejections (CMEs). analyse spectroscopic observations, $BV(RI)_C$ photometry covering 5 years, additional $R_C$ that expands temporal base over 16 years....
We study the different patterns of interannual magnetic variability in stars on or near lower main sequence, approximately solar-type (G-K dwarf) time series 36 years from Mount Wilson Observatory Ca\,{\sc ii}\,H\&K survey. Our aim is to search for correlations between cycles, activity measures and ages. Time-frequency analysis has been used discern reveal morphology stellar including multiple changing datasets. Both results short-term Fourier transform its refinement using Choi-Williams...
Stellar flares are abundant in space photometric light curves. As they now available large enough numbers, the statistical study of their overall temporal morphology is timely. We use curves from Transiting Exoplanet Survey Satellite (TESS) to shapes stellar beyond a simple parameterization by duration and amplitude, we reveal possible connections astrophysical parameters. retrained used long-short term memory neural network find 2-min cadence TESS first five years mission (sectors 1--69)....
We reconstruct a time series of 28 surface temperature maps (Doppler-images) the spotted single K2-dwarf LQ Hya from 35 consecutive stellar rotations in Nov.–Dec. 1996. Two more are obtained data late April and early May 2000. All show spot activity preferably at low latitudes between -20° +50°, with concentration band centered around +30°, only occasional evidence for higher-latitude extension. No trace polar is found any above epochs. Most this morphology can be reproduced by our flux-tube...
New sets of young M dwarfs with complex, sharp-peaked, and strictly periodic photometric modulations have recently been discovered Kepler/K2 (scallop shells) TESS (complex rotators). All are part star-forming associations, distinct from other variable stars, likely belong to a unified class. Suggested hypotheses include star spots, accreting dust disks, co-rotating clouds material, magnetically constrained spots misaligned pulsations. Here, we provide comprehensive overview add new...
Flares, sometimes accompanied by coronal mass ejections (CMEs), are the result of sudden changes in magnetic field stars with high energy release through reconnection, which can be observed across a wide range electromagnetic spectrum from radio waves to optical X-rays. In our observational review, we attempt collect some fundamental new results, largely linked Big Data era that has arrived due expansion space photometric observations over last two decades. We list different types showing...
Context. Surface differential rotation and other global surface flows on magnetically active stars are among the observable manifestations of stellar dynamo working underneath. Therefore, such observations important for theory useful constraints solar studies as well. Aims. The K1-giant component long-period RS CVn-type binary system sigma Gem its flow pattern is revisited. Methods. We refine law from recovering spot migration pattern. apply a detailed cross-correlation technique to unique...
This article reviews the current knowledge and status of investigations on variable magnetic activity cool stars. We discuss Sun in context solar‐type stars, highlighting peculiarities common features terms its variability over different time scales. examine how both theory observations are providing new clues about main physical processes that generate fields interior as well those lead to evolving stellar surface magnetism varying chromospheric coronal phenomena. then proceed relations...
We have searched the Kepler light curves of ~3900 M-star targets for evidence periodicities that indicate, by means effects starspots, rapid stellar rotation. Several analysis techniques, including Fourier transforms, inspection folded curves, 'sonograms', and phase tracking individual modulation cycles, were applied in order to distinguish due rotation from those pulsations, eclipsing binaries, or transiting planets. find 178 with periods, P_rot, < 2 days, 110 P_rot 1 day. Some 30 systems...
From our sample of spotted late-type stars showing surface differential rotation we find that the relationship between period and shear coefficient $\alpha=\Delta\Omega/\Omega_{\rm eq}$ is significantly different for single compared to members in close binaries. Single follow a general trend $\alpha$ increases with period. However, binary systems shows much weaker dependence on rotation, if any, suggesting such tidal forces operate as controlling mechanism rotation.
Abstract We have discovered a young M star of mass 0.16 M⊙ and radius 0.63 R⊙, likely in the Upper Sco Association, that exhibits only single 80 per cent deep occultation 1-d duration. The has frequent flares low-amplitude rotational modulation, but is otherwise quiet over 160 d cumulative observation during K2 campaigns C2 C15. discuss how such eclipse not possible by one crossing another any binary or higher order stellar system which no transfer occurred. two explanations we are left with...
As more exoplanets are being discovered around ultracool dwarfs, understanding their magnetic activity -- and the implications for habitability is of prime importance. To find stellar flares photometric signatures related to starspots, continuous monitoring necessary, which can be achieved with spaceborn observatories like Transiting Exoplanet Survey Satellite (TESS). We present an analysis TRAPPIST-1 dwarfs TESS full-frame image photometry from first two years primary mission. A...
We investigate the fast-rotating (), active dwarf binary V405 And (M0V+M5V) using photometric and optical spectroscopic data. The light variation is caused by combined effect of spottedness binarity with a small eclipse. estimate system parameters from available radial velocity curves. Three flare events occurred during observations: two were found in data one was observed photometrically colours. An interesting eruptive phenomenon emerged measurements that can be interpreted as series...
Abstract We have searched for short periodicities in the light curves of stars with T eff cooler than 4000 K made from 2-minute cadence data obtained Transiting Exoplanet Survey Satellite sectors 1 and 2. Herein we report discovery 10 rapidly rotating M dwarfs highly structured rotational modulation patterns among 371 found to rotation periods less day. Starspot models cannot explain periodic variations that typically exhibit between 40 Fourier harmonics. A similar set objects was previously...
The most powerful superflares reaching 10$^{39}$erg bolometric energy are from giant stars. mechanism behind flaring is supposed to be the magnetic reconnection, which closely related activity including starspots. However, it poorly understood, how underlying dynamo works and flare stellar properties eventually control action. We analyse of KIC 2852961, a late-type star, in order understand statistics that other stars with flares what role observed generating is. search for full Kepler...
Abstract We present and apply a new computer program named SpotModeL to analyze single multiple bandpass photometric data of spotted stars. It is based on the standard analytical formulae from Budding Dorren. The determines position, size, temperature up three spots by minimizing fit residuals with help Marquardt‐Levenberg non‐linear least‐squares algorithm. also expand this procedure full time‐series analysis differential data, just as real observations would deliver. If multi‐bandpass are...
The active K1 giant σ Gem and its differential surface rotation is revisited. We refine our previous inconclusive result by recovering the spot migration pattern of this long-period RS CVn-type binary through application technique “average cross-correlation contiguous Doppler images” to a set six images from 3.6 consecutive cycles. find an anti-solar law with shear -0.022±0.006. also evidence poleward trend spots average velocity ≈300 m s-1.