arXiv subjects

András Haris

Publications and source records attributed to András Haris.

3 recordsLinked to original sources

arXiv2026

Characterisation of starspot structure and differential rotation of Kepler-411

Starspots and their movements on stellar surfaces enable investigating the mechanisms of stellar magnetic activity. Information on the spot distribution and differential rotation provide important constraints for the behaviour of stellar magnetic dynamos. We analyse the Kepler photometry of Kepler-411, a known exoplanet host, to determine the distribution and properties of star spots on the stellar surface with two independent and complementary methods: modelling the photometric effect of rotation of spots on the stellar surface and mapping of spots by transiting planets. By constructing a spot model accounting for geometry, differential rotation and spot evolution, we model the spots of the stellar surface giving rise to the observed brightness variations. We also search for evidence for occultations of starspots in high-cadence photometry. Our spot models reproduce the observed photometric variations well and we are able to obtain information on the distribution and movement of spots on the stellar surface. We do not obtain evidence for differential rotation -- the rotational profile is consistent with rigid-body rotation with a period of 10.52$\pm$0.34 days. We detect three occultations of spots by planet c. The positions of these spots coincide well with the positions of larger spot structures identified by our modelling of the rotational modulation of the light curve.

astro-ph.SR↗

arXiv2025

Homogeneous search for spot transits in Kepler and TESS photometry of K $-$ M-type main-sequence stars

Late-type stars are known to host numerous exoplanets, and their photometric variability, primarily caused by rotational modulation, provides a unique opportunity to study starspots. As exoplanets transit in front of their host stars, they may occult darker, spotted regions on the stellar surfaces. The monitoring of starspots from planetary transits, known as transit mapping, offers a possibility to detect small dark regions on magnetically active, late-type stars. These spots may be so small that they would be undetectable to other methods used to reconstruct stellar magnetic activity. We describe a Bayesian analysis framework on the transit light curves of planets orbiting K- and M-type main-sequence stars in search for spot occultation event candidates. We present a systematic analysis of high-precision, high-cadence light curves from Kepler and TESS to detect and characterise starspots during exoplanetary transits. According to our tests, the set of criteria applied in the analysis is robust and not prone to false positives. Our sample comprises K- and M-dwarfs hosting transiting exoplanets observed by the Kepler or TESS space telescopes at a high cadence, totalling 99 planets meeting our selection criteria. After analysing 3273 transit light curves from 99 planets, we find 105 candidates for starspot occultation events by six planets. We report new spot occultation candidates for the K-dwarfs HD 189733 and TOI-1268. The identified dark regions have a lower limit for radii between 1.6 degrees and 29.5 degrees and contrasts up to 0.69. We estimate a spot detection frequency of 3.7% and 4.2% for K- and M-dwarfs by TESS, and 37.5% for K-dwarfs by Kepler.

astro-ph.SR↗

arXiv2022

A target list for searching for habitable exomoons

We investigate the habitability of hypothethical moons orbiting known exoplanets. This study focuses on big, rocky exomoons that are capable of maintaining a significant atmosphere. To determine their habitability, we calculate the incident stellar radiation and the tidal heating flux arising in the moons as the two main contributors to the energy budget. We use the runaway greenhouse and the maximum greenhouse flux limits as a definition of habitability. For each exoplanet we run our calculations for plausible ranges of physical and orbital parameters for the moons and the planet using a Monte Carlo approach. We calculate the moon habitability probability for each planet which is the fraction of the investigated cases that lead to habitable conditions. Based on our results, we provide a target list for observations of known exoplanets of which the top 10 planets have more than 50\% chance for hosting habitable moons on stable orbits. Two especially promising candidates are Kepler-62~f and Kepler-16~b, both of them with known masses and radii. Our target list can help to detect the first habitable exomoon.

astro-ph.EP↗