Gy. Szabó

Asymmetric transit curves as indication of orbital obliquity: Clues from the late-type dwarf companion in KOI-13

KOI-13.01, a planet-sized companion in an optical double star, was announced as one of the 1235 Kepler planet candidates in 2011 February. The transit curves show significant distortion that was stable over the {approx}130 days time span of the data. Here we investigate the phenomenon via detailed analyses of the two components of the double star and a re-reduction of the Kepler data with pixel-level photometry. Our results indicate that KOI-13 is a common proper motion binary, with two rapidly rotating components (vsin i {approx} 65-70 km s{sup -1}). We identify the host star of KOI-13.01 and conclude that the transit curve asymmetry is consistent with a companion orbiting a rapidly rotating, possibly elongated star on an oblique orbit. The radius of the transiter is 2.2 R{sub J} , implying an irradiated late-type dwarf, probably a hot brown dwarf rather than a planet. KOI-13 is the first example for detecting orbital obliquity for a substellar companion without measuring the Rossiter-McLaughlin effect with spectroscopy.

PIXYKLM computer package for PIXE analyses

Abstract Our previous program package PIXASE has been improved in order to have a more simple and more reliable evaluation procedure for PIXE spectra. Changes were made to the applied mathematical methods and the program has been extended to handle M lines, too. Effects of improvement are discussed together with some experimental result.

Variability in red supergiant stars: pulsations, long secondary periods and convection noise

We study the brightness variations of galactic red supergiant stars using long-term visual light curves collected by the American Association of Variable Star Observers (AAVSO) over the last century. The full sample contains 48 red semiregular or irregular variable stars, with a mean time-span of observations of 61 years. We determine periods and period variability from analyses of power density spectra and time-frequency distributions. We find two significant periods in 18 stars. Most of these periods fall into two disti nct groups, ranging from a few hundred to a few thousand days. Theoretical models imply fundamental, first and possibly second overtone mode pulsations for the shorter periods. Periods greater than 1000 days form a parallel period-luminosity relation that is similar to th e Long Secondary Periods of the Asymptotic Giant Branch stars. A number of individual power spectra shows a single mode resolved into multiple peaks under a Lorentzian envelope, which we interpret as evidence for stochastic oscillations, presumably caused by the interpl ay of convection and pulsations. We find a strong 1/f noise component in the power spectra that is remarkably similar in almost all stars of the sample. This behaviour fits the picture of irregu lar photometric variability caused by large convection cells, analogous to the granulation background seen in the Sun.

HD 181068: A Red Giant in a Triply Eclipsing Compact Hierarchical Triple System

The Kepler satellite reveals details of the oscillations patterns of an evolved star in an exotic triple-star system. Hierarchical triple systems comprise a close binary and a more distant component. They are important for testing theories of star formation and of stellar evolution in the presence of nearby companions. We obtained 218 days of Kepler photometry of HD 181068 (magnitude of 7.1), supplemented by ground-based spectroscopy and interferometry, which show it to be a hierarchical triple with two types of mutual eclipses. The primary is a red giant that is in a 45-day orbit with a pair of red dwarfs in a close 0.9-day orbit. The red giant shows evidence for tidally induced oscillations that are driven by the orbital motion of the close pair. HD 181068 is an ideal target for studies of dynamical evolution and testing tidal friction theories in hierarchical triple systems.

The properties of Jovian Trojan asteroids listed in SDSS Moving Object Catalogue 3

We analyse 1187 observations of about 860 unique candidate Jovian Trojan asteroids listed in the 3rd release of the Sloan Digital Sky Survey (SDSS) Moving Object Catalogue. The sample is complete at the faint end to r = 21.2 mag (apparent brightness) and H = 13.8 (absolute brightness, approximately corresponding to 10 km diameter). A subset of 297 detections of previously known Trojans were used to design and optimize a selection method based on observed angular velocity that resulted in the remaining objects. Using a sample of objects with known orbits, we estimate that the candidate sample contamination is about 3 per cent. The well-controlled selection effects, the sample size, depth and accurate five-band UV‐ IR photometry enabled several new findings and the placement of older results on a firmer statistical footing. We find that there are significantly more asteroids in the leading swarm (L4) than in the trailing swarm (L5): N(L4)/N(L5) = 1.6 ± 0.1, independently of limiting object’s size. The overall counts normalization suggests that there are about as many Jovians Trojans as there are main-belt asteroids down to the same size limit, in agreement with earlier estimates. We find that Trojan asteroids have a remarkably narrow colour distribution (root mean scatter of only ∼0.05 mag) that is significantly different from the colour distribution of the main-belt asteroids. The colour of Trojan asteroids is correlated with their orbital inclination, in a similar way for both swarms, but appears uncorrelated with the object’s size. We extrapolate the results presented here and estimate that the Large Synoptic Survey Telescope will determine orbits, accurate colours and measure light curves in six photometric bandpasses for about 100 000 Jovian Trojan asteroids.

Experimental and theoretical calibration of a PIXE setup for K and L X-rays

Abstract K and L line calibration has been performed for a PIXE setup by the independent use of experimental and theoretical methods. In the former case, thin film standards of known thicknesses were applied, while in the latter one cross section values were derived from different theoretical models. Programs REV5S and PIXEKL developed here were used for spectrum evaluation and concentration determination, respectively. They proved to be reliable and especially appropriate for routine serial evaluation of spectra measured on samples of nearly identical matrices. As a result of the work, an accurate calibration of the setup has been obtained and it was shown that experimental and theoretical techniques used lead to calibration curves which fit each other reasonably well.

Period and light‐curve fluctuations of the Kepler Cepheid V1154 Cygni

We present a detailed period analysis of the bright Cepheid-type variable star V1154 Cygni (V1154 Cyg; V = 9.1 mag, P ≈ 4.9 d) based on almost 600 d of continuous observations by the Kepler space telescope. The data reveal significant cycle-to-cycle fluctuations in the pulsation period, indicating that classical Cepheids may not be as accurate astrophysical clocks as commonly believed: regardless of the specific points used to determine the O − C values, the cycle lengths show a scatter of 0.015–0.02 d over 120 cycles covered by the observations. A very slight correlation between the individual Fourier parameters and the O − C values was found, suggesting that the O − C variations might be due to the instability of the light-curve shape. Random-fluctuation tests revealed a linear trend up to a cycle difference 15, but for long term, the period remains around the mean value. We compare the measurements with simulated light curves that were constructed to mimic V1154 Cyg as a perfect pulsator modulated only by the light travel time effect caused by low-mass companions. We show that the observed period jitter in V1154 Cyg represents a serious limitation in the search for binary companions. While the Kepler data are accurate enough to allow the detection of planetary bodies in close orbits around a Cepheid, the astrophysical noise can easily hide the signal of the light-time effect.

The young, massive, star cluster Sandage-96 after the explosion of supernova 2004dj in NGC 2403

The bright Type II-plateau supernova (SN) 2004dj occurred within the young, massive stellar cluster Sandage-96 in a spiral arm of NGC 2403. New multiwavelength observations obtained with several ground-based and space-based telescopes were combined to study the radiation from Sandage-96 after SN 2004dj faded away. Sandage-96 started to dominate the flux in the optical bands starting from 2006 September (~800 days after explosion). The optical fluxes are equal to the pre-explosion ones within the observational uncertainties. An optical Keck spectrum obtained ~900 days after explosion shows the dominant blue continuum from the cluster stars shortward of 6000? ? as well as strong SN nebular emission lines redward. The integrated spectral energy distribution (SED) of the cluster has been extended into the ultraviolet region by archival XMM-Newton and new Swift observations, and compared with theoretical models. The outer parts of the cluster have been resolved by the Hubble Space Telescope, allowing the construction of a color-magnitude diagram (CMD). The fitting of the cluster SED with theoretical isochrones results in cluster ages distributed between 10 and 40 Myr, depending on the assumed metallicity and the theoretical model family. The isochrone fitting of the CMDs indicates that the resolved part of the cluster consists of stars having a bimodal age distribution: a younger population at ~10-16 Myr and an older one at ~32-100? Myr. The older population has an age distribution similar to that of the other nearby field stars. This may be explained with the hypothesis that the outskirts of Sandage-96 are contaminated by stars captured from the field during cluster formation. The young age of Sandage-96 and the comparison of its pre and postexplosion SEDs suggest 12 M prog 20 M ? as the most probable mass range for the progenitor of SN 2004dj. This is consistent with, but perhaps slightly higher than, most of the other Type II-plateau SN progenitor masses determined so far.

Spin–orbit resonance, transit duration variation and possible secular perturbations in KOI‐13

KOI-13 is the first known transiting system exhibiting light-curve distortions due to gravity darkening of the rapidly rotating host star. In this Letter, we analyse publicly available Kepler Q2–Q3 short-cadence observations, revealing a continuous light variation with a period of Prot = 25.43 ± 0.05 h and a half-amplitude of 21 ppm, which is linked to stellar rotation. This period is in exact 5:3 resonance with the orbit of KOI-13.01, which is the first detection of a spin–orbit resonance in a host of a substellar companion. The stellar rotation leads to stellar oblateness, which is expected to cause secular variations in the orbital elements. We indeed detect the gradual increment of the transit duration with a rate of (1.14±0.30)×10 −6 d cycle −1 . The confidence of this trend is 3.85σ , and the two-sided false alarm probability is 0.012 per cent. We suggest that the reason for this variation is the expected change of the impact parameter, with a rate of db/dt =− 0.016 ± 0.004 yr −1 . Assuming b ≈ 0.25, KOI-13.01 may become a non-transiting object in 75–100 years. The observed rate is compatible with the expected secular perturbations due to the stellar oblateness yielded by the fast rotation.

Signals of exomoons in averaged light curves of exoplanets

The increasing number of transiting exoplanets sparked a significant interest in discovering their moons. Most of the methods in the literature utilize timing analysis of the raw light curves. Here we propose a new approach for the direct detection of a moon in the transit light curves via the so-called scatter peak. The essence of the method is the evaluation of the local scatter in the folded light curves of many transits. We test the ability of this method with different simulations: Kepler ‘short cadence’, Kepler ‘long cadence’, ground-based millimagnitude photometry with 3-min cadence and the expected data quality of the ESA planned planetary transits and oscillations of stars (PLATO) mission. The method requires ≈100 transit observations, therefore, applicable for moons of 10–20 d period planets, assuming 3–5 year long observing campaigns with space observatories. The success rate for finding a 1REarth moon around an 1RJupiter exoplanet turned out to be quite promising even for the simulated ground-based observations, while the detection limit of the expected PLATO data is around 0.4REarth. We give practical suggestions for observations and data reduction to improve the chance of such a detection: (i) transit observations must include out-of-transit phases before and after a transit, spanning at least the same duration as the transit itself, and (ii) any trend filtering must be done in such a way that the preceding and following out-of-transit phases remain unaffected.