@article{MTMT:34053151,
	title = {EI Eridani: A star under the influence. The effect of magnetic activity in the short and long term},
	url = {https://m2.mtmt.hu/api/publication/34053151},
	author = {Kriskovics, Levente and Kővári, Zsolt and Seli, Bálint Attila and Oláh, Katalin Ilona and Vida, Krisztián and Henry, G. W. and Granzer, T. and Görgei, A.},
	doi = {10.1051/0004-6361/202245767},
	journal-iso = {ASTRON ASTROPHYS},
	journal = {ASTRONOMY & ASTROPHYSICS},
	volume = {674},
	unique-id = {34053151},
	issn = {0004-6361},
	abstract = {Context. Homogeneous photometric time series spanning decades provide a unique opportunity to study the long-term cyclic behavior of active spotted stars such as our target EI Eridani. In addition, with ultraprecise space photometry data, it is possible to investigate the accompanying flare activity in detail. However, the rotation period of ≈2 days for EI Eri makes it impossible to achieve time-resolved surface images from a single ground-based observing site. Therefore, for this purpose, spectroscopic data from a multi-site observing campaign are needed.},
	year = {2023},
	eissn = {1432-0746},
	orcid-numbers = {Kővári, Zsolt/0000-0001-5160-307X; Seli, Bálint Attila/0000-0002-3658-2175; Görgei, A./0009-0002-1289-7946}
}

@article{MTMT:33538419,
	title = {Characteristics of flares on giant stars},
	url = {https://m2.mtmt.hu/api/publication/33538419},
	author = {Oláh, Katalin Ilona and Seli, Bálint Attila and Kővári, Zsolt and Kriskovics, Levente and Vida, Krisztián},
	doi = {10.1051/0004-6361/202243789},
	journal-iso = {ASTRON ASTROPHYS},
	journal = {ASTRONOMY & ASTROPHYSICS},
	volume = {668},
	unique-id = {33538419},
	issn = {0004-6361},
	abstract = {Context. Although late-type dwarfs and giant stars are substantially different, their flares are thought to originate in similar physical processes and differ only by a scale factor in the energy levels. We study the validity of this approach.},
	year = {2022},
	eissn = {1432-0746},
	orcid-numbers = {Seli, Bálint Attila/0000-0002-3658-2175; Kővári, Zsolt/0000-0001-5160-307X}
}

@CONFERENCE{MTMT:33087071,
	title = {Stellar FIP effect from the empirical side},
	url = {https://m2.mtmt.hu/api/publication/33087071},
	author = {Seli, Bálint Attila and Van Driel Gesztelyi, Lídia and Baker, Deborah and Laming, J. Martin and Kővári, Zsolt and Oláh, Katalin Ilona and Kriskovics, Levente and Vida, Krisztián and Balázs, Lajos},
	booktitle = {44th COSPAR Scientific Assembly. Held 16-24 July},
	unique-id = {33087071},
	abstract = {The difference between the elemental abundances of the corona and the photosphere is an apparently common feature of stellar atmospheres. The abundance difference depends on the first ionization potential of the given element, so the phenomenon is known as the FIP effect. Here we explore the variation of the strength of the FIP effect for different types of stars, through the FIP bias parameter. Using a sample of 59 main sequence and evolved stars with known coronal abundances from the literature, we look for macroscopic, measurable parameters that affect the stellar FIP bias, and also re-evaluate the simple dependence on the effective temperature.},
	year = {2022},
	orcid-numbers = {Seli, Bálint Attila/0000-0002-3658-2175; Kővári, Zsolt/0000-0001-5160-307X}
}

@article{MTMT:32732997,
	title = {Complex Modulation of Rapidly Rotating Young M Dwarfs: Adding Pieces to the Puzzle},
	url = {https://m2.mtmt.hu/api/publication/32732997},
	author = {Günther, Maximilian N. and Berardo, David A. and Ducrot, Elsa and Murray, Catriona A. and Stassun, Keivan G. and Oláh, Katalin Ilona and Bouma, L. G. and Rappaport, Saul and Winn, Joshua N. and Feinstein, Adina D. and Matthews, Elisabeth C. and Sebastian, Daniel and Rackham, Benjamin V. and Seli, Bálint Attila and Triaud, Amaury H. M. J. and Gillen, Edward and Levine, Alan M. and Demory, Brice-Olivier and Gillon, Michaël and Queloz, Didier and Ricker, George R. and Vanderspek, Roland K. and Seager, Sara and Latham, David W. and Jenkins, Jon M. and Brasseur, C. E. and Colón, Knicole D. and Daylan, Tansu and Delrez, Laetitia and Fausnaugh, Michael and Garcia, Lionel J. and Jayaraman, Rahul and Jehin, Emmanuel and Kristiansen, Martti H. and Kruijssen, J. M. Diederik and Pedersen, Peter Pihlmann and Pozuelos, Francisco J. and Rodriguez, Joseph E. and Wohler, Bill and Zhan, Zhuchang},
	doi = {10.3847/1538-3881/ac503c},
	journal-iso = {ASTRON J},
	journal = {ASTRONOMICAL JOURNAL},
	volume = {163},
	unique-id = {32732997},
	issn = {0004-6256},
	keywords = {1681; 982; 1290; 1603; 1580; 1629; 1761; 1213; 1572},
	year = {2022},
	eissn = {1538-3881},
	orcid-numbers = {Seli, Bálint Attila/0000-0002-3658-2175}
}

@article{MTMT:32726535,
	title = {Extending the FIP bias sample to magnetically active stars},
	url = {https://m2.mtmt.hu/api/publication/32726535},
	author = {Seli, Bálint Attila and Oláh, Katalin Ilona and Kriskovics, Levente and Kővári, Zsolt and Vida, Krisztián and Balázs, Lajos and Laming, J. M. and Van Driel Gesztelyi, Lídia and Baker, D.},
	doi = {10.1051/0004-6361/202141493},
	journal-iso = {ASTRON ASTROPHYS},
	journal = {ASTRONOMY & ASTROPHYSICS},
	volume = {659},
	unique-id = {32726535},
	issn = {0004-6361},
	abstract = {Context. The different elemental abundances of the photosphere and the corona are striking features of not only the Sun, but of other stars as well. This phenomenon is known as the first ionisation potential (FIP) effect, and its strength can be characterized by the FIP bias, the logarithmic abundance difference between low- and high-FIP elements in the corona, compared to the photosphere. The FIP bias was shown to depend on the surface temperature of the star. Aims: We aim to extend the Teff−FIP bias relationship to a larger stellar sample and analyse the effect of other astrophysical parameters on the relation (e.g. surface gravity, age, activity indicators). Methods: We compiled FIP bias and other parameters for 59 stars for which coronal composition is available, now including evolved stars. Using principal component analysis and linear discriminant analysis, we searched for correlations with other astrophysical parameters within the sample that may influence the stellar FIP bias. Results: Adding stars to the Teff−FIP bias diagram unveiled new features in its structure. In addition to the previously known relationship, there appears to be a second branch: a parallel sequence about 0.5 dex above it. While the Teff remains the main determinant of the FIP bias, other parameters such as stellar activity indicators also have influence. We find three clusters in the FIP bias determinant parameter space. One distinct group is formed by the evolved stars. Two groups contain main sequence stars in continuation separated roughly by the sign change of the FIP-bias value. Conclusions: The new branch of the Teff−FIP bias diagram contains stars with higher activity level, in terms of X-ray flux and rotational velocity. The Rossby number also seems to be important, indicating possible dependence on the type of dynamo operating in these stars influencing their FIP bias. The two main-sequence clusters run from the earliest spectral types of A-F with shallow convection zones through G-K-early-M stars with gradually deeper convection zones, and they end with the fully convective M dwarf stars, depicting the change of the dynamo type with the internal differences of the main sequence stars in connection with the FIP-bias values.},
	year = {2022},
	eissn = {1432-0746},
	orcid-numbers = {Seli, Bálint Attila/0000-0002-3658-2175; Kővári, Zsolt/0000-0001-5160-307X}
}

@article{MTMT:32106991,
	title = {A confined dynamo: Magnetic activity of the K-dwarf component in the pre-cataclysmic binary system V471 Tauri},
	url = {https://m2.mtmt.hu/api/publication/32106991},
	author = {Kővári, Zsolt and Kriskovics, Levente and Oláh, Katalin Ilona and Odert, P. and Leitzinger, M. and Seli, Bálint Attila and Vida, Krisztián and Borkovits, Tamás and Carroll, T.},
	doi = {10.1051/0004-6361/202140707},
	journal-iso = {ASTRON ASTROPHYS},
	journal = {ASTRONOMY & ASTROPHYSICS},
	volume = {650},
	unique-id = {32106991},
	issn = {0004-6361},
	abstract = {Context. Late-type stars in close binary systems can exhibit strong magnetic activity owing to rapid rotation supported by tidal locking. On the other hand, tidal coupling may suppress the differential rotation which is a key ingredient of the magnetic dynamo. Aims: We studied the red dwarf component in the eclipsing binary system V471 Tau in order to unravel the relations between the different activity layers, from the stellar surface through the chromosphere up to the corona. Our aim is to study how the magnetic dynamo in the late-type component is affected by the close white dwarf companion. Methods: We used space photometry, high-resolution spectroscopy, and X-ray observations from different space instruments to explore the main characteristics of magnetic activity. We applied a light curve synthesis program to extract the eclipsing binary model and to analyze the residual light variations. Photometric periods were obtained using a Fourier-based period search code. We searched for flares by applying an automated flare detection code. Spectral synthesis was used to derive or specify some of the astrophysical parameters. Doppler imaging was used to reconstruct surface temperature maps, which were cross-correlated to derive surface differential rotation. We applied different conversion techniques to make it possible to compare the X-ray emissions obtained from different space instruments. Results: From the K2 photometry we found that 5-10 per cent of the apparent surface of the red dwarf is covered by cool starspots. From seasonal photometric period changes we estimated a weak differential rotation. From the flare activity we derived a cumulative flare frequency diagram which suggests that frequent flaring could have a significant role in heating the corona. Using high-resolution spectroscopy we reconstructed four Doppler images for different epochs which reveal an active longitude, that is, a permanent dominant spot facing the white dwarf. From short term changes in the consecutive Doppler images we derived a weak solar-type surface differential rotation with αDR = 0.0026 shear coefficient, similar to that provided by photometry. The long-term evolution of X-ray luminosity reveals a possible activity cycle length of ≈12.7 yr, traces of which were also discovered in the Hα spectra. Conclusions: We conclude that the magnetic activity of the red dwarf component in V471 Tau is strongly influenced by the close white dwarf companion. We confirm the presence of a permanent dominant spot (active longitude) on the red dwarf facing the white dwarf. The weak differential rotation of the red dwarf is very likely the result of tidal confinement by the companion. We find that the periodic appearance of the inter-binary Hα emission from the vicinity of the inner Lagrangian point is correlated with the activity cycle.},
	keywords = {Astrophysics - Solar and Stellar Astrophysics; starspots; binaries: eclipsing; Stars: late-type; Stars: activity; stars: flare; stars: individual: V471 Tau},
	year = {2021},
	eissn = {1432-0746},
	orcid-numbers = {Kővári, Zsolt/0000-0001-5160-307X; Seli, Bálint Attila/0000-0002-3658-2175; Borkovits, Tamás/0000-0002-8806-496X}
}

@article{MTMT:32100131,
	title = {Activity of TRAPPIST-1 analog stars observed with TESS},
	url = {https://m2.mtmt.hu/api/publication/32100131},
	author = {Seli, Bálint Attila and Vida, Krisztián and Moór, Attila and Pál, András and Oláh, Katalin Ilona},
	doi = {10.1051/0004-6361/202040098},
	journal-iso = {ASTRON ASTROPHYS},
	journal = {ASTRONOMY & ASTROPHYSICS},
	volume = {650},
	unique-id = {32100131},
	issn = {0004-6361},
	abstract = {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 and photometric signatures related to starspots, continuous monitoring is necessary, which can be achieved with spaceborne observatories such as the Transiting Exoplanet Survey Satellite (TESS). We present an analysis of TRAPPIST-1 analog ultracool dwarfs with TESS full-frame image photometry from the first two years of the primary mission. A volume-limited sample up to 50 pc is constructed consisting of 339 stars closer than 0.(m)5 to TRAPPIST-1 on the Gaia color-magnitude diagram. We analyzed the 30 min cadence TESS light curves of 248 stars, searching for flares and rotational modulation caused by starspots. The composite flare frequency distribution of the 94 identified flares shows a power-law index that is similar to TRAPPIST-1 and contains flares up to E-TESS=3x10(33) erg. Rotational periods shorter than 5(d) were determined for 42 stars, sampling the regime of fast rotators. The ages of 88 stars from the sample were estimated using kinematic information. A weak correlation between rotational period and age is observed, which is consistent with magnetic braking.},
	keywords = {stars: statistics; starspots; Stars: late-type; Stars: activity; stars: low-mass; stars: flare},
	year = {2021},
	eissn = {1432-0746},
	orcid-numbers = {Seli, Bálint Attila/0000-0002-3658-2175}
}

@CONFERENCE{MTMT:32079892,
	title = {KIC 2852961 – a superflaring red monster in the Kepler field},
	url = {https://m2.mtmt.hu/api/publication/32079892},
	author = {Kővári, Zsolt and Oláh, Katalin Ilona and Günther, M. N. and Vida, Krisztián and Kriskovics, Levente and Seli, Bálint Attila},
	booktitle = {The 20.5th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun (CS20.5)},
	doi = {10.5281/zenodo.4555348},
	unique-id = {32079892},
	abstract = {Superflares on giant stars have up to 100,000 times more energy than the high energy solar flares. However, it is disputed, whether scaling up a solar-type dynamo could explain such a magnitude difference. We investigate the flaring activity of KIC 2852961, a late-type spotted giant. We seek for flares in the Kepler Q0-Q17 datasets by an automated technique together with visual inspection. Flare occurence rate and flare energies are analyzed and compared to flare statistics of different targets with similar flare activity at different energy levels. We find that the flare energy distribution of KIC 2852961 does not seem to be consistent with that of superflares on solar-type stars. Also, we believe that in case of KIC 2852961 spot activity should have an important role in producing such superflares.},
	keywords = {Astrophysics - Solar and Stellar Astrophysics; LATE-TYPE STARS; MAGNETIC ACTIVITY; FLARES; stars: individual: KIC 2852961; superflares},
	year = {2021},
	orcid-numbers = {Kővári, Zsolt/0000-0001-5160-307X; Seli, Bálint Attila/0000-0002-3658-2175}
}

@CONFERENCE{MTMT:32079884,
	title = {Activity of TRAPPIST-1 analogue stars observed with TESS},
	url = {https://m2.mtmt.hu/api/publication/32079884},
	author = {Seli, Bálint Attila and Vida, Krisztián and Moór, Attila and Pál, András and Oláh, Katalin Ilona},
	booktitle = {The 20.5th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun (CS20.5)},
	doi = {10.5281/zenodo.4566167},
	unique-id = {32079884},
	abstract = {We present an analysis of TRAPPIST-1 like ultracool dwarfs with TESS full-frame image photometry from the first two years of the primary mission. We constructed a volume-limited sample up to 50 pc, consisting of stars in the vicinity of TRAPPIST-1 on the Gaia color-magnitude diagram. We searched for flares and rotational modulation on the light curves of 248 stars. We determined rotational periods for 42 stars, and estimated the ages of 88 stars using kinematic information. A weak correlation between rotational period and age is observed. The composite flare frequency distribution shows a power-law index similar to TRAPPIST-1, and it is extended to higher energies. The results imply that while superflares can be expected every few decades, the flare rate of such stars is insufficient to fully destroy the possible ozone layer of orbiting planets.},
	keywords = {Very low mass stars},
	year = {2021},
	orcid-numbers = {Seli, Bálint Attila/0000-0002-3658-2175}
}

@article{MTMT:31922644,
	title = {Toward the true number of flaring giant stars in the Kepler field: Are their flaring specialities associated with their being giant stars?},
	url = {https://m2.mtmt.hu/api/publication/31922644},
	author = {Oláh, Katalin Ilona and Kővári, Zsolt and Günther, M. N. and Vida, Krisztián and Gaulme, P. and Seli, Bálint Attila and Pál, András},
	doi = {10.1051/0004-6361/202039674},
	journal-iso = {ASTRON ASTROPHYS},
	journal = {ASTRONOMY & ASTROPHYSICS},
	volume = {647},
	unique-id = {31922644},
	issn = {0004-6361},
	year = {2021},
	eissn = {1432-0746},
	orcid-numbers = {Oláh, Katalin Ilona/0000-0001-5160-307X; Kővári, Zsolt/0000-0001-5160-307X; Seli, Bálint Attila/0000-0002-3658-2175}
}