arXiv subjects

L. L. Kiss

Publications and source records attributed to L. L. Kiss.

At least 109 records · Page 6Linked to original sources

arXiv2011

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 valuation 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 planned ESA mission of PLATO. The method requires ~100 transit observations, therefore applicable for moons of 10-20 day period planets, assuming 3-4-5 year long observing campaigns with space observatories. The success rate for finding a 1 R_Earth moon around a 1 R_Jupiter 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 0.4 R_Earth. 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; (ii) any trend filtering must be done in such a way that the preceding and following out-of-transit phases remain unaffected.

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arXiv2011

The Kepler characterization of the variability among A- and F-type stars. I. General overview

The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. We present a first general characterization of the pulsational behaviour of A-F type stars as observed in the Kepler light curves of a sample of 750 candidate A-F type stars. We propose three main groups to describe the observed variety in pulsating A-F type stars: gamma Dor, delta Sct, and hybrid stars. We assign 63% of our sample to one of the three groups, and identify the remaining part as rotationally modulated/active stars, binaries, stars of different spectral type, or stars that show no clear periodic variability. 23% of the stars (171 stars) are hybrid stars, which is a much larger fraction than what has been observed before. We characterize for the first time a large number of A-F type stars (475 stars) in terms of number of detected frequencies, frequency range, and typical pulsation amplitudes. The majority of hybrid stars show frequencies with all kinds of periodicities within the gamma Dor and delta Sct range, also between 5 and 10 c/d, which is a challenge for the current models. We find indications for the existence of delta Sct and gamma Dor stars beyond the edges of the current observational instability strips. The hybrid stars occupy the entire region within the delta Sct and gamma Dor instability strips, and beyond. Non-variable stars seem to exist within the instability strips. The location of gamma Dor and delta Sct classes in the (Teff,logg)-diagram has been extended. We investigate two newly constructed variables 'efficiency' and 'energy' as a means to explore the relation between gamma Dor and delta Sct stars. Our results suggest a revision of the current observational instability strips, and imply an investigation of other pulsation mechanisms to supplement the kappa mechanism and convective blocking effect to drive hybrid pulsations.

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arXiv2011

Non-Blazhko RR Lyrae Stars Observed with the KEPLER Space Telescope

This paper summarizes the main results of our recent study of the non-Blazhko RR Lyrae stars observed with the Kepler space telescope. These stars offer the opportunity for studying the stability of the pulsations of RR Lyrae stars and for providing a reference against which the Blazhko RR Lyrae stars can be compared. Of particular interest is the stability of the low-dispersion (sigma < 1mmag) light curves constructed from ~18,000 long-cadence (30-min) and (for FN Lyr and AW Dra) the ~150,000 short-cadence (1-min) photometric data points. Fourier-based [Fe/H] values and other physical characteristics are also derived. When the observed periods are compared with periods computed with the Warsaw non-linear convective pulsation code better agreement is achieved assuming pulsational L and M values rather than the (higher) evolutionary L and M values.

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arXiv2011

Mass and orbit constraints of the gamma-ray binary LS 5039

We present the results of space-based photometric and ground-based spectroscopic observing campaigns on the gamma-ray binary LS 5039. The new orbital and physical parameters of the system are similar to former results, except we found a lower eccentricity. Our MOST-data show that any broad-band optical photometric variability at the orbital period is below the 2 mmag level. Light curve simulations support the lower value of eccentricity and imply that the mass of the compact object is higher than 1.8 solar masses.

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arXiv2011

Fourier analysis of non-Blazhko ab-type RR Lyrae stars observed with the Kepler space telescope

Nineteen of the ~40 RR Lyr stars in the Kepler field have been identified as candidate non-Blazhko (or unmodulated) stars. In this paper we present the results of Fourier decomposition of the time-series photometry of these stars acquired during the first 417 days of operation (Q0-Q5) of the Kepler telescope. Fourier parameters based on ~18400 long-cadence observations per star (and ~150000 short-cadence observations for FN Lyr and for AW Dra) are derived. None of the stars shows the recently discovered `period-doubling' effect seen in Blazhko variables; however, KIC 7021124 has been found to pulsate simultaneously in the fundamental and second overtone modes with a period ratio P2/P0 ~ 0.59305 and is similar to the double-mode star V350 Lyr. Period change rates are derived from O-C diagrams spanning, in some cases, over 100 years; these are compared with high-precision periods derived from the Kepler data alone. Extant Fourier correlations by Kovacs, Jurcsik et al. (with minor transformations from the V to the Kp passband) have been used to derive underlying physical characteristics for all the stars. This procedure seems to be validated through comparisons of the Kepler variables with galactic and LMC RR Lyr stars. The most metal-poor star in the sample is NR Lyr, with [Fe/H]=-2.3 dex; and the four most metal-rich stars have [Fe/H] ranging from -0.6 to +0.1 dex. Pulsational luminosities and masses are found to be systematically smaller than L and mass values derived from stellar evolution models, and are favoured over the evolutionary values when periods are computed with the Warsaw linear hydrodynamics code. Finally, the Fourier parameters are compared with theoretical values derived using the Warsaw non-linear convective pulsation code.

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arXiv2011

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 February 2011. The transit curves show significant distortion that was stable over the ~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 (v sin i ~ 65--70 km/s). 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. After correcting the Kepler light curve to the second light of the optical companion star, we derive a radius of 2.2 R_J for the transiter, 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 from spectroscopy.

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arXiv2011

Frozen to death? -- Detection of comet Hale-Bopp at 30.7 AU

Comet Hale--Bopp (C/1995 O1) has been the single most significant comet encountered by modern astronomy, still having displayed significant activity at 25.7 AU solar distance in late 2007. It is a puzzling question when and where this activity will finally cease. Here we present new observations with the ESO 2.2m telescope at La Silla to check the activity of Hale--Bopp at 30.7 AU solar distance. On 2010-12-04, 26 CCD images were taken with 180 s exposure times for photometry and morphology. The comet was detected in R and had a total brightness of 23.3+-0.2 mag, referring to an absolute brightness of R(1,1,0)=8.3. The profile of the coma was star-like at a seeing of 1.9", without any evidence of a coma or tail extending farther than 2.5" (=55,000 km in projection) and exceeding 26.5 mag/arcs^2 surface brightness. The measured total brightness corresponds to a relative total reflecting surface, a_RC, of 485 km^2, nine times less than three years before. The calculated a_RC value would imply a nucleus with 60--65 km radius assuming 4% albedo. This size estimate is in significant contradiction with the previous results scattering around 35 km. Therefore we suggest that the comet may still be in a low-level activity, despite the lack of a prominent coma. Alternatively, if the nucleus is already dormant, the albedo should be as high as 13%, assuming a radius of 35 km. With this observation, Hale--Bopp has been the most distant comet ever observed, far beyond the orbit of Neptune.

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arXiv2011

Spectral signatures of disk eccentricity in young binary systems: I. Circumprimary case

Star formation occurs via fragmentation of molecular clouds, which means that the majority of stars born are a members of binaries. There is growing evidence that planets might form in circumprimary disks of medium-separation binaries. The tidal forces caused by the secondary generally act to distort the originally circular disk to an eccentric one. To infer the disk eccentricity from high-res NIR spectroscopy, we calculate the fundamental band emission lines of the CO molecule emerging from the atmosphere of the disk. We model circumprimary disk evolution under the gravitational perturbation of the orbiting secondary using a 2D grid-based hydrodynamical code, assuming alpha-type viscosity. The hydrodynamical results are combined with our spectral code based on the double-layer disk model to calculate the CO molecular line profiles. We find that the orbital velocity distribution of the gas parcels differs significantly from the circular Keplerian fashion, thus the line profiles are asymmetric in shape. The magnitude of asymmetry is insensitive to the binary mass ratio, the magnitude of viscosity, and the disk mass. In contrast, the disk eccentricity, thus the level of the line profile asymmetry, is influenced significantly by the binary eccentricity and the disk geometrical thickness. We demonstrate that the disk eccentricity profile in the planet-forming region can be determined by fitting the high-resolution CO line profile asymmetry using a simple 2D spectral model that accounts for the velocity distortions caused by the disk eccentricity. Thus, with our novel approach the disk eccentricity can be inferred with high-resolution near-IR spectroscopy prior to the era of high angular resolution optical or radio direct-imaging. By determining the disk eccentricity in medium-separation young binaries, we might be able to constrain the planet formation theories.

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arXiv2011

Cepheid investigations using the Kepler space telescope

We report results of initial work done on selected candidate Cepheids to be observed with the Kepler space telescope. Prior to the launch 40 candidates were selected from previous surveys and databases. The analysis of the first 322 days of Kepler photometry, and recent ground-based follow-up multicolour photometry and spectroscopy allowed us to confirm that one of these stars, V1154 Cyg (KIC 7548061), is indeed a 4.9-d Cepheid. Using the phase lag method we show that this star pulsates in the fundamental mode. New radial velocity data are consistent with previous measurements, suggesting that a long-period binary component is unlikely. No evidence is seen in the ultra-precise, nearly uninterrupted Kepler photometry for nonradial or stochastically excited modes at the micromagnitude level. The other candidates are not Cepheids but an interesting mix of possible spotted stars, eclipsing systems and flare stars.

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arXiv2010

Dust formation in the ejecta of the Type II-P supernova 2004dj

Core-collapse supernovae (CC SNe), especially Type II-Plateau ones, are thought to be important contributors to cosmic dust production. SN 2004dj, one of the closest and brightest SN since 1987A, offered a good opportunity to examine dust formation processes. To find signs of newly formed dust, we analyze all available mid-infrared (MIR) archival data from the Spitzer Space Telescope. We re-reduce and analyze data from IRAC, MIPS and IRS instruments obtained between +98 and +1381 days after explosion, generating light curves and spectra for each epoch. Observed spectral energy distributions are fitted with both analytic and numerical models, using the radiative-transfer code MOCASSIN for the latter ones. We also use imaging polarimetric data obtained at +425 days by the Hubble Space Telescope. We present convincing evidence of dust formation in the ejecta of SN 2004dj from MIR light curves and spectra. Significant MIR excess flux is detected in all bands between 3.6 and 24 um. In the optical, a ~0.8% polarization is also detected at a 2-sigma level, which exceeds the interstellar polarization in that direction. Our analysis shows that the freshly-formed dust around SN 2004dj can be modeled assuming a nearly spherical shell containing amorphous carbon grains, cooling from ~700 K to ~400 K between +267 and +1246 days. Persistent excess flux has been found above 10 um, which is explained by a cold (~115 K) dust component. If this cold dust is of circumstellar origin, it is likely to be condensed in a cool, dense shell between the forward and reverse shocks. Pre-existing circumstellar dust is less likely, but cannot be ruled out. An upper limit of ~8x10^{-4} M_sun was derived for the dust mass, which is similar to previously published values for other dust-producing SNe.

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arXiv2010

A short-period censor of sub-Jupiter mass exoplanets with low density

Despite the existence of many short-period hot Jupiters, there is not one hot Neptune with an orbital period less than 2.5 days. Here we discuss a cluster analysis of the currently known 106 transiting exoplanets to investigate a possible explanation for this observation. We find two distinct clusters in the mass-density space, one with hot Jupiters with a wide range of orbital periods (0.8--114 days) and a narrow range of planet radii (1.2 +- 0.2 R_J); and another one with a mixture of super-Earths, hot Neptunes and hot Jupiters, exhibiting a surprisingly narrow period distribution (3.7 +- 0.8 days). These two clusters follow different distributions in the period-radius parameter plane. The branch of sub-Jupiter mass exoplanets is censored by the orbital period at large-radii: no planets with mass between 0.02--0.8 M_J or with radius between 0.25--1.0 R_J are known with P_orb<2.5 days. This clustering is not predicted by current theories of planet formation and evolution that we also review briefly.

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arXiv2010

Structure and evolution of debris disks around F-type stars: I. Observations, database and basic evolutionary aspects

Although photometric and spectroscopic surveys with the Spitzer Space Telescope increased remarkably the number of well studied debris disks around A-type and Sun-like stars, detailed analyzes of debris disks around F-type stars remained less frequent. Using the MIPS camera and the IRS spectrograph we searched for debris dust around 82 F-type stars with Spitzer. We found 27 stars that harbor debris disks, nine of which are new discoveries. The dust distribution around two of our stars, HD 50571 and HD 170773, was found to be marginally extended on the 70um MIPS images. Combining the MIPS and IRS measurements with additional infrared and submillimeter data, we achieved excellent spectral coverage for most of our debris systems. We have modeled the excess emission of 22 debris disks using a single temperature dust ring model and of 5 debris systems with two-temperature models. The latter systems may contain two dust rings around the star. In accordance with the expected trends, the fractional luminosity of the disks declines with time, exhibiting a decay rate consistent with the range of model predictions. We found the distribution of radial dust distances as a function of age to be consistent with the predictions of both the self stirred and the planetary stirred disk evolution models. A more comprehensive investigation of the evolution of debris disks around F-type stars, partly based on the presented data set, will be the subject of an upcoming paper.

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arXiv2010

Practical suggestions on detecting exomoons in exoplanet transit light curves

The number of known transiting exoplanets is rapidly increasing, which has recently inspired significant interest as to whether they can host a detectable moon. Although there has been no such example where the presence of a satellite was proven, several methods have already been investigated for such a detection in the future. All these methods utilize post-processing of the measured light curves, and the presence of the moon is decided by the distribution of a timing parameter. Here we propose a method for the detection of the moon directly in the raw transit light curves. When the moon is in transit, it puts its own fingerprint on the intensity variation. In realistic cases, this distortion is too little to be detected in the individual light curves, and must be amplified. Averaging the folded light curve of several transits helps decrease the scatter, but it is not the best approach because it also reduces the signal. The relative position of the moon varies from transit to transit, the moon's wing will appear in different positions on different sides of the planet's transit. Here we show that a careful analysis of the scatter curve of the folded light curves enhances the chance of detecting the exomoons directly.

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arXiv2010

Kepler photometry of the prototypical Blazhko star RR Lyr: An old friend seen in a new light

We present our analysis of the long cadence Kepler data for the well-studied Blazhko star RR Lyr, gathered during the first two quarters of the satellite's observations and covering a total of 127d. Besides being of great importance for our understanding of RR Lyrae stars in general, these RR Lyr data can be regarded as a case study for observations of bright stars with Kepler. Kepler can perform high-precision photometry on targets like RR Lyr, as the saturated flux is conserved to a very high degree. The Kepler data on RR Lyr are revolutionary in several respects. Even with long-cadence sampling (one measurement per 29.4 min), the unprecedented precision (< mmag) of the Kepler photometry allows the study of the star's extreme light curve variations in detail. The multiplet structures at the main frequency and its harmonics, typical for Blazhko stars, are clearly detected up to the quintuplets. For the first time, photometric data of RR Lyr reveal the presence of half-integer frequencies, linked to a period doubling effect. This phenomenon may be connected to the still unexplained Blazhko modulation. Moreover, with three observed Blazhko cycles at our disposal, we observe that there is no exact repetition in the light curve changes from one modulation cycle to the next for RR Lyr. This may be due to additional periodicities in the star, or to transient or quasi-periodic changes.

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arXiv2010

HAT-P-13: a multi-site campaign to detect the transit of the second planet in the system

A possible transit of HAT-P-13c has been predicted to occur on 2010 April 28. Here we report on the results of a multi-site campaign that has been organised to detect the event. CCD photometric observations have been carried out at five observatories in five countries. We reached 30% time coverage in a 5 days interval centered on the suspected transit of HAT-P-13c. Two transits of HAT-P-13b were also observed. No transit of HAT-P-13c has been detected while the campaign was on. By a numerical experiment with 10^5 model systems we conclude that HAT-P-13c is not a transiting exoplanet with a significance level from 65% to 72%, depending on the planet parameters and the prior assumptions. We present two times of transit of HAT-P-13b ocurring at BJD 2455141.5522 +- 0.0010 and BJD 2455249.4508 +- 0.0020. The TTV of HAT-P-13b is consistent with zero within 0.001 days. The refined orbital period of HAT-P-13b is 2.916293 +- 0.000010 days.

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arXiv2010

A search for new members of the beta Pic, Tuc-Hor and epsilon Cha moving groups in the RAVE database

We report on the discovery of new members of nearby young moving groups, exploiting the full power of combining the RAVE survey with several stellar age diagnostic methods and follow-up high-resolution optical spectroscopy. The results include the identification of one new and five likely members of the beta Pictoris moving group, ranging from spectral types F9 to M4 with the majority being M dwarfs, one K7 likely member of the epsilon Cha group and two stars in the Tuc-Hor association. Based on the positive identifications we foreshadow a great potential of the RAVE database in progressing toward a full census of young moving groups in the solar neighbourhood.

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arXiv2010

Period-luminosity relations of pulsating M giants in the solar neighbourhood and the Magellanic Clouds

We analyse the results of a 5.5-yr photometric campaign that monitored 247 southern, semi-regular variables with relatively precise Hipparcos parallaxes to demonstrate an unambiguous detection of Red Giant Branch (RGB) pulsations in the solar neighbourhood. We show that Sequence A' contains a mixture of AGB and RGB stars, as indicated by a temperature related shift at the TRGB. Large Magellanic Cloud (LMC) and Galactic sequences are compared in several ways to show that the P-L sequence zero-points have a negligible metallicity dependence. We describe a new method to determine absolute magnitudes from pulsation periods and calibrate the LMC distance modulus using Hipparcos parallaxes to find μ(LMC) = 18.54 +- 0.03 mag. Several sources of systematic error are discussed to explain discrepancies between the MACHO and OGLE sequences in the LMC. We derive a relative distance modulus of the Small Magellanic Cloud (SMC) relative to the LMC of Δμ= 0.41 +- 0.02 mag. A comparison of other pulsation properties, including period-amplitude and luminosity-amplitude relations, confirms that RGB pulsation properties are consistent and universal, indicating that the RGB sequences are suitable as high-precision distance indicators. The M giants with the shortest periods bridge the gap between G and K giant solar-like oscillations and M-giant pulsation, revealing a smooth continuity as we ascend the giant branch.

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arXiv2010

Methods for exomoon characterisation: combining transit photometry and the Rossiter-McLaughlin effect

It has been suggested that moons around transiting exoplanets may cause observable signal in transit photometry or in the Rossiter-McLaughlin (RM) effect. In this paper a detailed analysis of parameter reconstruction from the RM effect is presented for various planet-moon configurations, described with 20 parameters. We also demonstrate the benefits of combining photometry with the RM effect. We simulated 2.7x10^9 configurations of a generic transiting system to map the confidence region of the parameters of the moon, find the correlated parameters and determine the validity of reconstructions. The main conclusion is that the strictest constraints from the RM effect are expected for the radius of the moon. In some cases there is also meaningful information on its orbital period. When the transit time of the moon is exactly known, for example, from transit photometry, the angle parameters of the moon's orbit will also be constrained from the RM effect. From transit light curves the mass can be determined, and combining this result with the radius from the RM effect, the experimental determination of the density of the moon is also possible.

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