Interior Structures and Tidal Heating in the TRAPPIST-1 Planets

With seven planets, the TRAPPIST-1 system has the largest number of exoplanets discovered in a single system so far. The system is of astrobiological interest, because three of its planets orbit in the habitable zone of the ultracool M dwarf. Assuming the planets are composed of non-compressible iron, rock, and H$_2$O, we determine possible interior structures for each planet. To determine how much tidal heat may be dissipated within each planet, we construct a tidal heat generation model using a single uniform viscosity and rigidity for each planet based on the planet's composition. With the exception of TRAPPIST-1c, all seven of the planets have densities low enough to indicate the presence of significant H$_2$O in some form. Planets b and c experience enough heating from planetary tides to maintain magma oceans in their rock mantles; planet c may have eruptions of silicate magma on its surface, which may be detectable with next-generation instrumentation. Tidal heat fluxes on planets d, e, and f are lower, but are still twenty times higher than Earth's mean heat flow. Planets d and e are the most likely to be habitable. Planet d avoids the runaway greenhouse state if its albedo is $\gtrsim$ 0.3. Determining the planet's masses within $\sim0.1$ to 0.5 Earth masses would confirm or rule out the presence of H$_2$O and/or iron in each planet, and permit detailed models of heat production and transport in each planet. Understanding the geodynamics of ice-rich planets f, g, and h requires more sophisticated modeling that can self-consistently balance heat production and transport in both rock and ice layers.Comment: 34 pages, 3 tables, 4 figures. Accepted for publication in Astronomy & Astrophysics -- final version including corrections made in proof stag

Large size and slow rotation of the trans-Neptunian object (225088) 2007 OR10 discovered from Herschel and K2 observations

We present the first comprehensive thermal and rotational analysis of the second most distant trans-Neptunian object (225088) 2007 OR10. We combined optical light curves provided by the Kepler space telescope -- K2 extended mission and thermal infrared data provided by the Herschel Space Observatory. We found that (225088) 2007 OR10 is likely to be larger and darker than derived by earlier studies: we obtained a diameter of d=1535^{+75}_{-225} km which places (225088) 2007 OR10 in the biggest top three trans-Neptunian objects. The corresponding visual geometric albedo is p_V=0.089^{+0.031}_{-0.009}. The light curve analysis revealed a slow rotation rate of P_rot=44.81+/-0.37 h, superseded by a very few objects only. The most likely light-curve solution is double-peaked with a slight asymmetry, however, we cannot safely rule out the possibility of having a rotation period of P_rot=22.40+/-0.18 h which corresponds to a single-peaked solution. Due to the size and slow rotation, the shape of the object should be a MacLaurin ellipsoid, so the light variation should be caused by surface inhomogeneities. Its newly derived larger diameter also implies larger surface gravity and a more likely retention of volatiles -- CH_4, CO and N_2 -- on the surface.Comment: Accepted for publication in AJ, 8 pages in emulateapj styl

Possibility for albedo estimation of exomoons: Why should we care about M dwarfs?

Occultation light curves of exomoons may give information on their albedo and hence indicate the presence of ice cover on the surface. Icy moons might have subsurface oceans thus these may potentially be habitable. The objective of our paper is to determine whether next generation telescopes will be capable of albedo estimations for icy exomoons using their occultation light curves. The success of the measurements depends on the depth of the moon's occultation in the light curve and on the sensitivity of the used instruments. We applied simple calculations for different stellar masses in the V and J photometric bands, and compared the flux drop caused by the moon's occultation and the estimated photon noise of next generation missions with 5 $\sigma$ confidence. We found that albedo estimation by this method is not feasible for moons of solar-like stars, but small M dwarfs are better candidates for such measurements. Our calculations in the J photometric band show that E-ELT MICADO's photon noise is just about 4 ppm greater than the flux difference caused by a 2 Earth-radii icy satellite in a circular orbit at the snowline of an 0.1 stellar mass star. However, considering only photon noise underestimates the real expected noise, because other noise sources, such as CCD read-out and dark signal become significant in the near infrared measurements. Hence we conclude that occultation measurements with next generation missions are far too challenging, even in the case of large, icy moons at the snowline of small M dwarfs. We also discuss the role of the parameters that were neglected in the calculations, e.g. inclination, eccentricity, orbiting direction of the moon. We predict that the first albedo estimations of exomoons will probably be made for large icy moons around the snowline of M4 -- M9 type main sequence stars.Comment: 13 pages, 6 figures, accepted for publication in A&

Educated towards research: the first five years of the undergraduate mentoring program at Konkoly Observatory

In 2017 the Konkoly Observatory in Budapest published its first call for application inviting university students to carry out financially supported supervised research work and observing duties. The initiative quickly became popular and, so far, the program has supported 37 students. Five years later, is now time to summarize the experience gathered from both the institute and the participants. Notable results include numerous OTDK (student project) prizes awarded, first papers published, and acceptances into MSc and PhD programs both domestically and abroad, thus laying the foundations for the careers of several students. Among the feedback we have received from the students is the need for a more complex mentoring program, over and above of the funded research opportunities. A survey we conducted among the students indicates that communal and educational events are in the greatest demand, probably also induced by the lockdown restrictions experienced in the last few years. Through such events the students would not only build their community and start professional collaborations, but also learn more about various aspects of academia. In light of these results, we review possible avenues to improve the program.Comment: Originally published in the journal Magyar Tudom\'any in Hungarian: this is a slightly edited translatio

Developing an integrated land use planning system on reclaimed wetlands of the Hungarian Plain using economic valuation of ecosystem services

The establishment of a sustainable land use system is crucial in Hungary (SE Europe) where 30% of croplands lie on former floodplains, and 40–45% of arable lands are drought-prone. We calculated and compared the monetary value of the main wetland ecosystem services, the profitability of land use and the additional costs of grain producer system on land at risk from groundwater inundation on the Hungarian Plain. We show that orchards and forestry generate a much higher profitability in former wetlands than cropland farming. Using the replacement cost method, we prove that the reservoir capacity of restored wetlands with an ecologically optimal 0.5 m water depth could replace 2150 €ha−1 flood protection investment cost. The calculated costs of protecting land under the two highest groundwater risk categories between 1999–2005 was 37.2 €ha−1 y−1 and 14.9 €ha−1 y−1, respectively. Although the flood protection benefits of former wetlands may provide an appropriate value base for restoration per se, combined with the potential advantages of land use change from cropland to forest in former wetlands and the carbon sequestration benefit provide ‘win-win’ solutions for land users and institutional actors interested in flood prevention, environmental protection and climate mitigation

Physical Properties of Galactic RV Tauri Stars from Gaia DR2 Data

We present the first period–luminosity and period–radius relation of Galactic RV Tauri variable stars. We have surveyed the literature for all variable stars belonging to this class and compiled the full set of their photometric and spectroscopic measurements. We crossmatched the final list of stars with the Gaia Data Release 2 database and took the parallaxes, G-band magnitudes, and effective temperatures to calculate the distances, luminosities, and radii using a probabilistic approach. As it turned out, the sample was very contaminated, and thus we restricted our study to those objects for which the RV Tau nature was securely confirmed. We found that several stars are located outside the red edge of the classical instability strip, which implies a wider pulsational region for RV Tau stars. The period–luminosity relation of galactic RV Tauri stars is steeper than that of the shorter-period Type II Cepheids, in agreement with previous results obtained for the Magellanic Clouds and globular clusters. The median masses of RVa and RVb stars were calculated to be 0.45–0.52 M ⊙ and 0.83 M ⊙, respectively

Periodicities of the RV Tauri-type pulsating star DF Cygni: A combination of Kepler data with ground-based observations

Context. The RV Tauri stars constitute a small group of classical pulsating stars with some dozen known members in the Milky Way. The light variation is caused predominantly by pulsations, but these alone do not explain the full complexity of light curves. High-quality photometry of RV Tau-type stars is very rare. DF Cygni is the only member of this class of stars in the original Kepler field, hence allowing the most accurate photometric investigation of any RV Tauri star to date. Aims: The main goal is to analyse the periodicities of the RV Tauri-type star DF Cygni by combining four years of high-quality Kepler photometry with almost half a century of visual data collected by the American Association of Variable Star Observers (AAVSO). Methods: Kepler quarters of data were stitched together to minimize the systematic effects of space data. The mean levels have been matched with AAVSO visual data. Both datasets were submitted to Fourier and wavelet analyses, while the stability of the main pulsations was studied with the O-C method and analysis of time-dependent amplitudes. Results: DF Cygni shows very rich behaviour on all timescales. The slow variation has a period of 779.606 d and it has been remarkably coherent during the whole time span of the combined data. On top of the long-term cycles, the pulsations appear with a period of 24.925 d, or the double period of 49.85 d if we take the RV Tau-type alternation of the cycles into account. Both types of light variation significantly fluctuate in time, with a constantly changing interplay of amplitude and phase modulations. Long-period change (i.e. the RVb signature) somewhat resembles the long secondary period (LSP) phenomenon of pulsating red giants, whereas short-period pulsations are very similar to those of the Cepheid variables. Comparing the pulsation patterns with the latest models of Type-II Cepheids, we found evidence of strong non-linear effects that are directly observable in the Kepler light curve