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 The light curve analysis revealed a slow rotation rate of P_rot=44.81+/-0.37 h, superseded by a very few objects only.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

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

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&

Variability of M giant stars based on Kepler photometry: general characteristics

M giants are among the longest period pulsating stars which is why their studies were traditionally restricted to analyses of low-precision visual observations, and, more recently, accurate ground-based data. Here we present an overview of M giant variability on a wide range of time-scales (hours to years), based on the analysis of 13 quarters of Kepler long-cadence observations (one point per every 29.4 min), with a total time-span of over 1000 d. About two-thirds of the sample stars have been selected from the All Sky Automated Survey (ASAS)-North survey of the Kepler field, with the rest supplemented from a randomly chosen M giant control sample. We first describe the correction of the light curves from different quarters, which was found to be essential. We use Fourier analysis to calculate multiple frequencies for all stars in the sample. Over 50 stars show a relatively strong signal with a period equal to the Kepler-year and a characteristic phase dependence across the whole field of view. We interpret this as a so far unidentified systematic effect in the Kepler data. We discuss the presence of regular patterns in the distribution of multiple periodicities and amplitudes. In the period-amplitude plane we find that it is possible to distinguish between solar-like oscillations and larger amplitude pulsations which are characteristic for Mira/semiregular stars. This may indicate the region of the transition between two types of oscillations as we move upward along the giant branch

A kozmikus por fejlődése a Tejútrendszerben és a távoli Univerzumban = Evolution of cosmic dust in the Milky Way and in the distant Universe

Kutatómunkánk során foglalkoztunk az eredeti munkatervben megjelölt mindhárom témakörrel: a por szerepe és tulajdonságai csillagközi felhőkben, csillagok körüli korongokban, valamint kozmológiai távolságú rendszerekben. Megmutattuk, hogy a sűrű csillagközi felhőkben a porszemcsék optikai tulajdonságai megváltoznak, arra utalva, hogy méretük valamilyen fizikai hatás következtében (összetapadás, jégköpeny képződés) megnő. Az extragalaktikus por tanulmányozására távoli (z <= 1) galaxisokat figyeltünk meg a Spitzer Űrtávcsővel. A legnagyobb hangsúlyt a hirtelen kifényesedést mutató eruptív fiatal csillagok körüli por- és gázkorongok tanulmányozására fektettük. A V1647 Ori kitörése során interferometrikus mérésekkel fel tudtuk bontani a csillagkörüli korong belső részét, és megmutattuk, hogy a kitörés során a belső rész geometriája megváltozik. Az EX Lupi 2008-as kitörését az Európai Déli Obszervatórium és a Spitzer Űrtávcső műszereivel követtük. A kitörés előtt felvett színkép tanúsága szerint az EX Lupit körülvevő korong felszínét kisméretű és amorf szerkezetű por borította, a kitörés csúcsát követően azonban már nagyrészt kristályos porszemcsék spektroszkópiai nyomát láthattuk. Így első ízben sikerült közvetlenül megfigyelni a porszemcsék kristályosodását egy csillagkörüli korongban, lehetséges forgatókönyvet javasolva naprendszerbeli üstökösök anyagának keletkezésére is. A felfedezést a Nature közölte 2009-ben. | We made progress in all three research areas defined in the workplan of the OTKA project: the role and properties of dust in interstellar clouds, in circumstellar disks, and in galaxies at cosmological distances. We demonstrated that the infrared emisivity of the dust particles increases in dense interstellar clouds, suggesting a particle growth via coagulation or the appearance of ice mantels. In order to study the extragalactic dust we performed far-infrared observations of SN Ia host galaxies with the Spitzer Space Telescope. Our most productive research line was, however, the investigation of gas- and dust disks around young eruptive stars. Using interferometric observations, we were able to resolve the inner disk around V1647 Ori, and concluded that the the geometrical structure of the inner part changed during the outburst. The 2008 Jan-Sep eruption of EX Lupi was followed using ESO and Spitzer instruments. Comparing pre-outburst and outburst mid-infrared spectra, we showed that while in quiescence the surface of the disk was dominated by submicron size amorphous particles, during outburst signatures of crystalline dust appeared. It was the first direct detection of on-going crystal formation in a cosmic object, offering also a scenario for the formation of the silicate crystals located in comet nuclei in the Solar System. This result was published in Nature in 2009 May

Változócsillagok az instabilitási sávban és az óriás ágon = Variable stars in the instability strip and on the giant branch

Fő célunk pulzáló változócsillagok vizsgálata volt. Fotometriai és spektroszkópiai méréseket végeztünk hazai és külföldi műszerekkel, valamint felhasználtunk nemzetközi adatbázisokat. A delta Scuti és az RR Lyrae típusú csillagok esetében főleg a periódusváltozást elemeztük. A több rezgési módusban pulzáló beat-cefeidák kémiai összetételét, fémtartalmát határoztuk meg és a pulzáció és a fémtartalom közti összefüggést a pulzációs modellek tesztelésével. A félszabályos változócsillagok fénygörbéit a Fourier-analízis mellett idő-frekvencia módszerrel vizsgáltuk. Számos csillagnál kimutattuk, hogy a megfigyelt frekvenciaváltozás a pulzációs fázis sztochasztikus változásának eredménye, melyet a konvekció okoz. Több ezer vörös óriáscsillag periódus-fényesség relációjának eloszlását magyaráztuk meg, különös tekintettel az ellipszoidális változókra és a hosszú másodperiódust mutató csillagokra. Nyílt- és gömbhalmazokban sok változócsillagot fedeztünk fel. Csillagaik színképi elemzése alapján a halmazokra fémességet, kort, sebességeloszlást és dinamikai jellemzőket határoztunk meg. Kutatásaink kiterjedtek extragalaktikus szupernóvák, kettőscsillagok, kisbolygók vizsgálatára is, valamint exoholdak kimutatásának lehetőségeire. Kutatásaink széleskörű hazai és nemzetközi együttműködések keretében valósultak meg. A pályázat számával 35 folyóiratcikket és 18 konferencia anyagot publikáltunk, 150,459 impakt faktorral. Ezekre eddig 43 független hivatkozás történt. | The main aim of our research was to study pulsating variable stars. We have carried out photometric and spectroscopic measurements at Hungarian and foreign observatories. We have used international databases. In the case of delta Scuti- and RR Lyrae-stars, we have examined mainly their period variations. We have determined the iron abundances of beat-Cepheids and tested the theoretical models via the dependence of pulsation on metal abundance. The light curves of semiregular variable stars were studied with Fourier- and time-frequency methods. We have pointed out stochastic variation of the pulsational phase in many stars, which is caused by convective motions. We have investigated the explanations of the distribution of red giant stars on the period-luminosity diagram, with particular attention on ellipsoidal variables and stars with long secondary period. We have discovered many new variable stars in open- and globular clusters. From spectroscopic measurements we have determined metallicity, age, velocity distribution and dynamical properties of these clusters. We extended our research to the study of binary stars, minor planets, extragalactic supernovae and the possibilities of discovering exomoons. Our research has been carried out with broad national- and international collaborations. During the project we have published 35 papers in refereed journals and 18 conference proceedings. The impact factor is 150.459. We have received 43 independent citations

SPITZER/IRAC-MIPS Survey of NGC2451A and B: Debris Disks at 50-80 million years

We present a Spitzer IRAC and MIPS survey of NGC 2451 A and B, two open clusters in the 50-80 Myr age range. We complement these data with extensive ground-based photometry and spectroscopy to identify the cluster members in the Spitzer survey field. We find only two members with 8 micron excesses. The incidence of excesses at 24 microns is much higher, 11 of 31 solar-like stars and 1 of 7 early-type (A) stars. This work nearly completes the debris disk surveys with Spitzer of clusters in the 30-130 Myr range. This range is of inte rest because it is when large planetesimal collisions may have still been relatively common (as indicated by the one that led to the formation of the Moon during this period of the evolution of the Solar System). We review the full set of surveys and find that there are only three possible cases out of about 250 roughly solar-mass stars where very large excesses suggest that such collisions have occurred recently.Comment: Accepted for publication in ApJ. 25 pages 17 figure

Arteriolar biomechanics in a rat polycystic ovary syndrome model - effects of parallel vitamin D3 treatment.

To clarify the effects of dihydrotestosterone (DHT)-induced polycystic ovary syndrome (PCOS) on arteriolar biomechanics in a rat model and the possible modulatory role of vitamin D3. METHODS AND RESULTS: The PCOS model was induced in female Wistar rats by ten-weeks DHT treatment. Arteriolar biomechanics was tested in arterioles by pressure arteriography in control as well as DHT- and DHT with vitamin D3-treated animals in contracted and passive conditions. Increased wall stress and distensibility as well as increased vascular lumen were detected after DHT treatment. Concomitant vitamin D3 treatment lowered the mechanical load of the arterioles and restored the vascular diameter. CONCLUSION: The hyperandrogenic state resulted in more rigid, less flexible arteriolar walls with increased vascular lumen compared with controls. DHT treatment caused eutrophic remodelling of gracilis arteriole. These prehypertensive alterations caused by chronic DHT treatment were mostly reversed by concomitant vitamin D3 administration

Period and chemical evolution of SC stars

The SC and CS stars are thermal-pulsing AGB stars with C/O ratio close to unity. Within this small group, the Mira variable BH Cru recently evolved from spectral type SC (showing ZrO bands) to CS (showing weak C2). Wavelet analysis shows that the spectral evolution was accompanied by a dramatic period increase, from 420 to 540 days, indicating an expanding radius. The pulsation amplitude also increased. Old photographic plates are used to establish that the period before 1940 was around 490 days. Chemical models indicate that the spectral changes were caused by a decrease in stellar temperature, related to the increasing radius. There is no evidence for a change in C/O ratio. The evolution in BH Cru is unlikely to be related to an on-going thermal pulse. Periods of the other SC and CS stars, including nine new periods, are determined. A second SC star, LX Cyg, also shows evidence for a large increase in period, and one further star shows a period inconsistent with a previous determination. Mira periods may be intrinsically unstable for C/O ~ 1; possibly because of a feedback between the molecular opacities, pulsation amplitude, and period. LRS spectra of 6 SC stars suggest a feature at wavelength > 15 micron, which resembles one recently attributed to the iron-sulfide troilite. Chemical models predict a large abundance of FeS in SC stars, in agreement with the proposed association.Comment: 14 pages, 20 figures. MNRAS, 2004, accepted for publication. Janet Mattei, one of the authors, died on 22 March, 2004. This paper is dedicated to her memor

Testing Newtonian Gravity with AAOmega: Mass-To-Light Profiles and Metallicity Calibrations From 47 Tuc and M55

Globular clusters are an important test bed for Newtonian gravity in the weak-acceleration regime, which is vital to our understanding of the nature of the gravitational interaction. Recent claims have been made that the velocity dispersion profiles of globular clusters flatten out at large radii, despite an apparent paucity of dark matter in such objects, indicating the need for a modification of gravitational theories. We continue our investigation of this claim, with the largest spectral samples ever obtained of 47 Tucanae and M55. Furthermore, this large sample allows for an accurate metallicity calibration based on the equivalent widths of the calcium triplet lines and K band magnitude of the Tip of the Red Giant Branch. Assuming an isothermal distribution, the rotations of each cluster are also measured with both clusters exhibiting clear rotation signatures. The global velocity dispersions of NGC 121 and Kron 3, two globular clusters in the Small Magellanic Cloud, are also calculated. By applying a simple dynamical model to the velocity dispersion profiles of 47 Tuc and M55, we calculate their mass-to-light profiles, total masses and central velocity dispersions. We find no statistically significant flattening of the velocity dispersion at large radii for M55, and a marked increase in the profile of 47 Tuc for radii greater than approximately half the tidal radius. We interpret this increase as an evaporation signature, indicating that 47 Tuc is undergoing, or has undergone, core-collapse, but find no requirement for dark matter or a modification of gravitational theories in either cluster.Comment: 11 pages, 12 figures, 4 tables. Accepted by MNRA