arXiv subjects

A. Prsa

Publications and source records attributed to A. Prsa.

At least 19 recordsLinked to original sources

arXiv2020

Tango of celestial dancers: A sample of detached eclipsing binary systems containing g-mode pulsating components. A case study of KIC9850387

Eclipsing binary systems with components that pulsate in gravity modes ($g$ modes) allow for simultaneous and independent constraints of the chemical mixing profiles of stars. We aim to assemble a sample of $g$-mode pulsators in detached eclipsing binaries with the purpose of finding good candidates for future evolutionary and asteroseismic modelling. In addition, we present a case study of the eclipsing binary KIC9850387, identified as our most promising candidate. We selected all of the detached eclipsing binaries in the Kepler eclipsing binary catalogue and performed a visual inspection to determine the presence and density of $g$ modes, and the presence of $g$-mode period-spacing patterns in their frequency spectra. We then characterised our sample based on their $g$-mode pulsational parameters and binary and atmospheric parameters. A spectroscopic follow-up of KIC9850387 was then performed. We then performed spectral disentangling followed by atmospheric modelling and abundance analysis for the primary star. We utilised an iterative approach to simultaneously optimise the pulsational and eclipse models, and subsequently performed an analysis of the pressure- ($p$-) and $g$-mode pulsational frequencies. We compiled a sample of 93 Kepler eclipsing binary stars with $g$-mode pulsating components and identified clear $g$-mode period-spacing patterns in the frequency spectra of seven of these systems. We found that the $g$-mode pulsational parameters and the binary and atmospheric parameters of our sample are weakly correlated at best. We find that the eclipsing binary KIC9850387 is a double-lined spectroscopic binary in a near-circular orbit with an intermediate-mass primary, and a solar-like secondary. We find $\ell=1$ and $\ell=2$ period-spacing patterns in the frequency spectrum of KIC9850387 spanning more than ten radial orders each.

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arXiv2017

Gaia eclipsing binary and multiple systems. Two-Gaussian models applied to OGLE-III eclipsing binary light curves in the Large Magellanic Cloud

The advent of large scale multi-epoch surveys raises the need for automated light curve (LC) processing. This is particularly true for eclipsing binaries (EBs), which form one of the most populated types of variable objects. The Gaia mission, launched at the end of 2013, is expected to detect of the order of few million EBs over a 5-year mission. We present an automated procedure to characterize EBs based on the geometric morphology of their LCs with two aims: first to study an ensemble of EBs on a statistical ground without the need to model the binary system, and second to enable the automated identification of EBs that display atypical LCs. We model the folded LC geometry of EBs using up to two Gaussian functions for the eclipses and a cosine function for any ellipsoidal-like variability that may be present between the eclipses. The procedure is applied to the OGLE-III data set of EBs in the Large Magellanic Cloud (LMC) as a proof of concept. The bayesian information criterion is used to select the best model among models containing various combinations of those components, as well as to estimate the significance of the components. Based on the two-Gaussian models, EBs with atypical LC geometries are successfully identified in two diagrams, using the Abbe values of the original and residual folded LCs, and the reduced $χ^2$. Cleaning the data set from the atypical cases and further filtering out LCs that contain non-significant eclipse candidates, the ensemble of EBs can be studied on a statistical ground using the two-Gaussian model parameters. For illustration purposes, we present the distribution of projected eccentricities as a function of orbital period for the OGLE-III set of EBs in the LMC, as well as the distribution of their primary versus secondary eclipse widths.

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arXiv2017

Gaia Eclipsing Binary and Multiple Systems. A study of detectability and classification of eclipsing binaries with Gaia

In the new era of large-scale astronomical surveys, automated methods of analysis and classification of bulk data are a fundamental tool for fast and efficient production of deliverables. This becomes ever more imminent as we enter the Gaia era. We investigate the potential detectability of eclipsing binaries with Gaia using a data set of all Kepler eclipsing binaries sampled with Gaia cadence and folded with the Kepler period. The performance of fitting methods is evaluated with comparison to real Kepler data parameters and a classification scheme is proposed for the potentially detectable sources based on the geometry of the light curve fits. The polynomial chain (polyfit) and two-Gaussian models are used for light curve fitting of the data set. Classification is performed with a combination of the t-SNE (t-distrubuted Stochastic Neighbor Embedding) and DBSCAN (Density-Based Spatial Clustering of Applications with Noise) algorithms. We find that approximately 68% of Kepler Eclipsing Binary sources are potentially detectable by Gaia when folded with the Kepler period and propose a classification scheme of the detectable sources based on the morphological type indicative of the light curve, with subclasses that reflect the properties of the fitted model (presence and visibility of eclipses, their width, depth, etc.).

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arXiv2017

Gaia Data Release 1: The variability processing & analysis and its application to the south ecliptic pole region

The ESA Gaia mission provides a unique time-domain survey for more than one billion sources brighter than G=20.7 mag. Gaia offers the unprecedented opportunity to study variability phenomena in the Universe thanks to multi-epoch G-magnitude photometry in addition to astrometry, blue and red spectro-photometry, and spectroscopy. Within the Gaia Consortium, Coordination Unit 7 has the responsibility to detect variable objects, classify them, derive characteristic parameters for specific variability classes, and provide global descriptions of variable phenomena. We describe the variability processing and analysis that we plan to apply to the successive data releases, and we present its application to the G-band photometry results of the first 14 months of Gaia operations that comprises 28 days of Ecliptic Pole Scanning Law and 13 months of Nominal Scanning Law. Out of the 694 million, all-sky, sources that have calibrated G-band photometry in this first stage of the mission, about 2.3 million sources that have at least 20 observations are located within 38 degrees from the South Ecliptic Pole. We detect about 14% of them as variable candidates, among which the automated classification identified 9347 Cepheid and RR Lyrae candidates. Additional visual inspections and selection criteria led to the publication of 3194 Cepheid and RR Lyrae stars, described in Clementini et al. (2016). Under the restrictive conditions for DR1, the completenesses of Cepheids and RR Lyrae stars are estimated at 67% and 58%, respectively, numbers that will significantly increase with subsequent Gaia data releases. Data processing within the Gaia Consortium is iterative, the quality of the data and the results being improved at each iteration. The results presented in this article show a glimpse of the exceptional harvest that is to be expected from the Gaia mission for variability phenomena. [abridged]

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arXiv2015

IAU 2015 Resolution B2 on Recommended Zero Points for the Absolute and Apparent Bolometric Magnitude Scales

The XXIXth IAU General Assembly in Honolulu adopted IAU 2015 Resolution B2 on recommended zero points for the absolute and apparent bolometric magnitude scales. The resolution was proposed by the IAU Inter-Division A-G Working Group on Nominal Units for Stellar and Planetary Astronomy after consulting with a broad spectrum of researchers from the astronomical community. Resolution B2 resolves the long-standing absence of an internationally-adopted zero point for the absolute and apparent bolometric magnitude scales. Resolution B2 defines the zero point of the absolute bolometric magnitude scale such that a radiation source with $M_{\rm Bol}$ = 0 has luminosity L$_{\circ}$ = 3.0128e28 W. The zero point of the apparent bolometric magnitude scale ($m_{\rm Bol}$ = 0) corresponds to irradiance $f_{\circ}$ = 2.518021002e-8 W/m$^2$. The zero points were chosen so that the nominal solar luminosity (3.828e26 W) adopted by IAU 2015 Resolution B3 corresponds approximately to $M_{\rm Bol}$(Sun) = 4.74, the value most commonly adopted in recent literature. The nominal total solar irradiance (1361 W/m$^2$) adopted in IAU 2015 Resolution B3 corresponds approximately to apparent bolometric magnitude $m_{\rm bol}$(Sun) = -26.832. Implicit in the IAU 2015 Resolution B2 definition of the apparent bolometric magnitude scale is an exact definition for the parsec (648000/$π$ au) based on the IAU 2012 Resolution B2 definition of the astronomical unit.

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arXiv2015

IAU 2015 Resolution B3 on Recommended Nominal Conversion Constants for Selected Solar and Planetary Properties

Astronomers commonly quote the properties of celestial objects in units of parameters for the Sun, Jupiter, or the Earth. The resolution presented here was proposed by the IAU Inter-Division Working Group on Nominal Units for Stellar and Planetary Astronomy and passed by the XXIXth IAU General Assembly in Honolulu. IAU 2015 Resolution B3 adopts a set of nominal solar, terrestrial, and jovian conversion constants for stellar and (exo)planetary astronomy which are defined to be exact SI values. While the nominal constants are based on current best estimates (CBEs; which have uncertainties, are not secularly constant, and are updated regularly using new observations), they should be interpreted as standard values and not as CBEs. IAU 2015 Resolution B3 adopts five solar conversion constants (nominal solar radius, nominal total solar irradiance, nominal solar luminosity, nominal solar effective temperature, and nominal solar mass parameter) and six planetary conversion constants (nominal terrestrial equatorial radius, nominal terrestrial polar radius, nominal jovian equatorial radius, nominal jovian polar radius, nominal terrestrial mass parameter, and nominal jovian mass parameter).

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arXiv2015

KIC 10080943: An eccentric binary system containing two pressure- and gravity-mode hybrid pulsators

Gamma Doradus and delta Scuti pulsators cover the transition region between low mass and massive main-sequence stars, and as such, are critical for testing stellar models. When they reside in binary systems, we can combine two independent methods to derive critical information, such as precise fundamental parameters to aid asteroseismic modelling. In the Kepler light curve of KIC10080943, clear signatures of gravity- and pressure-mode pulsations have been found. Ground-based spectroscopy revealed this target to be a double-lined binary system. We present the analysis of four years of Kepler photometry and high-resolution spectroscopy to derive observational constraints with which to evaluate theoretical predictions of the stellar structure and evolution for intermediate-mass stars. We used the method of spectral disentangling to determine atmospheric parameters for both components and derive the orbital elements. With PHOEBE, we modelled the ellipsoidal variation and reflection signal of the binary in the light curve and used classical Fourier techniques to analyse the pulsation modes. We show that the eccentric binary system KIC10080943 contains two hybrid pulsators with masses $M_1=2.0\pm0.1~M_\odot$ and $M_2=1.9\pm0.1~M_\odot$, with radii $R_1=2.9\pm0.1~R_\odot$ and $R_2=2.1\pm0.2~R_\odot$. We detect rotational splitting in the g modes and p modes for both stars and use them to determine a first rough estimate of the core-to-surface rotation rates for the two components, which will be improved by future detailed seismic modelling.

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arXiv2015

Discovery of Two New Thermally Bloated Low-Mass White Dwarfs Among the Kepler Binaries

We report the discovery of two new low-mass, thermally bloated, hot white dwarfs among the Kepler sample of eclipsing binaries. These are KIC 9164561 and KIC 10727668 with orbital periods of 1.2670 and 2.3058 days, respectively. The current primary in both systems is an A star of about 2 Msun. This brings the number of similar binaries among the Kepler sample to six, and the two new systems have the shortest orbital periods among them. The white dwarf in KIC 9164561 has the largest thermal bloating, compared to its cold degenerate radius, of about a factor of 14. We utilize RV measurements of the A star in KIC 9164561 to determine the white dwarf mass rather accurately: 0.197 +/- 0.005 Msun. The mass of the white dwarf in KIC 10727668 is based on the Doppler boosting signal in the Kepler photometry, and is less accurately determined to be 0.266 +/- 0.035 Msun. Based on the inferred radii and effective temperatures of these two white dwarfs we are able to make an independent theoretical estimate of their masses to within ~0.01 Msun based on evolutionary models of their cooling history after they lose their hydrogen-rich envelopes. We also present evidence that there is a third body in the KIC 9164561 system with an orbital period of 8-14 years.

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arXiv2014

HD 183648: a Kepler eclipsing binary with anomalous ellipsoidal variations and a pulsating component

KIC 8560861 (HD 183648) is a marginally eccentric (e=0.05) eclipsing binary with an orbital period of P_orb=31.973d, exhibiting mmag amplitude pulsations on time scales of a few days. We present the results of the complex analysis of high and medium-resolution spectroscopic data and Kepler Q0 -- Q16 long cadence photometry. The iterative combination of spectral disentangling, atmospheric analysis, radial velocity and eclipse timing variation studies, separation of pulsational features of the light curve, and binary light curve analysis led to the accurate determination of the fundamental stellar parameters. We found that the binary is composed of two main sequence stars with an age of 0.9\+-0.2 Gyr, having masses, radii and temperatures of M_1=1.93+-0.12 M_sun, R_1=3.30+-0.07 R_sun, T_eff1=7650+-100 K for the primary, and M_2=1.06+-0.08 M_sun, R_2=1.11+-0.03 R_sun, T_eff2=6450+-100 K for the secondary. After subtracting the binary model, we found three independent frequencies, two of which are separated by twice the orbital frequency. We also found an enigmatic half orbital period sinusoidal variation that we attribute to an anomalous ellipsoidal effect. Both of these observations indicate that tidal effects are strongly influencing the luminosity variations of HD 183648. The analysis of the eclipse timing variations revealed both a parabolic trend, and apsidal motion with a period of (P_apse)_obs=10,400+-3,000 y, which is three times faster than what is theoretically expected. These findings might indicate the presence of a distant, unseen companion.

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arXiv2014

Stellar statistics along the ecliptic and the impact on the K2 mission concept

K2 is the mission concept for a repurposed Kepler mission that uses two reaction wheels to maintain the satellite attitude and provide ~85 days of coverage for ten 105-deg^2 fields along the ecliptic in the first 2.5 years of operation. We examine stellar populations based on the improved Besancon model of the Galaxy, comment on the general properties for the entire ecliptic plane, and provide stellar occurrence rates in the first 6 tentative K2 campaigns grouped by spectral type and luminosity class. For each campaign we distinguish between main sequence stars and giants and provide their density profile as a function of galactic latitude. We introduce the crowding metric that serves for optimized target selection across the campaigns. For all main sequence stars we compute the expected planetary occurrence rates for three planet sizes: 2-4 REarth, 4-8 REarth, and 8-32 REarth with orbital periods up to 50 days. In conjunction with Gaia and the upcoming TESS and Plato missions, K2 will become a gold mine for stellar and planetary astrophysics.

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arXiv2013

KIC 4544587: an Eccentric, Short Period Binary System with delta Sct Pulsations and Tidally Excited Modes

We present Kepler photometry and ground based spectroscopy of KIC 4544587, a short-period eccentric eclipsing binary system with self-excited pressure and gravity modes, tidally excited modes, tidally influenced p modes, and rapid apsidal motion of 182 y per cycle. The primary and secondary components of KIC 4544587 reside within the delta Scuti and gamma Dor instability region of the Hurtzsprung-Russell diagram, respectively. By applying the binary modelling software PHOEBE to prewhitened Kepler photometric data and radial velocity data obtained using the William Herschel Telescope and 4-m Mayall telescope at KPNO, the fundamental parameters of this important system have been determined, including the stellar masses, 1.98+/-0.07 MSun and 1.60+/-0.06 MSun, and radii, 1.76+/-0.03 RSun and 1.42+/-0.02 RSun, for the primary and secondary components, respectively. Frequency analysis of the residual data revealed 31 modes, 14 in the gravity mode region and 17 in the pressure mode region. Of the 14 gravity modes 8 are orbital harmonics: a signature of tidal resonance. While the measured amplitude of these modes may be partially attributed to residual signal from binary model subtraction, we demonstrate through consideration of the folded light curve that these frequencies do in fact correspond to tidally excited pulsations. Furthermore, we present an echelle diagram of the pressure mode frequency region (modulo the orbital frequency) and demonstrate that the tides are also influencing the p modes. A first look at asteroseismology hints that the secondary component is responsible for the p modes, which is contrary to our expectation that the hotter star should pulsate in higher radial overtone, higher frequency p modes.

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arXiv2013

Kepler-62: A five-planet system with planets of 1.4 and 1.6 Earth radii in the Habitable Zone

We present the detection of five planets -- Kepler-62b, c, d, e, and f -- of size 1.31, 0.54, 1.95, 1.61 and 1.41 Earth radii, orbiting a K2V star at periods of 5.7, 12.4, 18.2, 122.4 and 267.3 days, respectively. The outermost planets (Kepler-62e & -62f) are super-Earth-size (1.25 < planet radius/earth radius < 2.0) planets in the habitable zone (HZ) of their host star, receiving 1.2 +- 0.2 and 0.41 +- 0.05 times the solar flux at Earth's orbit. Theoretical models of Kepler-62e and -62f for a stellar age of ~7 Gyr suggest that both planets could be solid: either with a rocky composition or composed of mostly solid water in their bulk.

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arXiv2011

The architecture of the hierarchical triple star KOI 928 from eclipse timing variations seen in Kepler photometry

We present a hierarchical triple star system (KIC 9140402) where a low mass eclipsing binary orbits a more massive third star. The orbital period of the binary (4.98829 Days) is determined by the eclipse times seen in photometry from NASA's Kepler spacecraft. The periodically changing tidal field, due to the eccentric orbit of the binary about the tertiary, causes a change in the orbital period of the binary. The resulting eclipse timing variations provide insight into the dynamics and architecture of this system and allow the inference of the total mass of the binary ($0.424 \pm 0.017 \text{M}_\odot$) and the orbital parameters of the binary about the central star.

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arXiv2011

Kepler photometry of KIC 10661783: a binary star with total eclipses and delta Scuti pulsations

We present Kepler satellite photometry of KIC 10661783, a short-period binary star system which shows total eclipses and multi-periodic delta Scuti pulsations. A frequency analysis of the eclipse-subtracted light curve reveals at least 68 frequencies of which 55 or more can be attributed to pulsation modes. The main limitation on this analysis is the frequency resolution within the 27-day short-cadence light curve. Most of the variability signal lies in the frequency range 18 to 31 c/d, with amplitudes between 0.1 and 4 mmag. One harmonic term (2.f) and a few combination frequencies (f_i+f_j) have been detected. From a plot of the residuals versus orbital phase we assign the pulsations to the primary star in the system. The pulsations were removed from the short-cadence data and the light curve was modelled using the Wilson-Devinney code. We are unable to get a perfect fit due to the residual effects of pulsations and also to the treatment of reflection and reprocessing in the light curve model. A model where the secondary star fills its Roche lobe is favoured, which means that KIC 10661783 can be classified as an oEA system. Further photometric and spectroscopic observations will allow the masses and radii of the two stars to be measured to high precision and hundreds of delta Scuti pulsation frequencies to be resolved. This could lead to unique constraints on theoretical models of delta Scuti stars, if the evolutionary history of KIC 10661783 can be accounted for.

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arXiv2010

Pre-Spectroscopic False Positive Elimination of Kepler Planet Candidates

Ten days of commissioning data (Quarter 0) and thirty-three days of science data (Quarter 1) yield instrumental flux timeseries of ~150,000 stars that were combed for transit events, termed Threshold Crossing Events (TCE), each having a total detection statistic above 7.1-sigma. TCE light curves are modeled as star+planet systems. Those returning a companion radius smaller than 2R_J are assigned a KOI (Kepler Object of Interest) number. The raw flux, pixel flux, and flux-weighted centroids of every KOI are scrutinized to assess the likelihood of being an astrophysical false-positive versus the likelihood of a being a planetary companion. This vetting using Kepler data is referred to as data validation. Herein, we describe the data validation metrics and graphics used to identify viable planet candidates amongst the KOIs. Light curve modeling tests for a) the difference in depth of the odd- versus even-numbered transits, b) evidence of ellipsoidal variations, and c) evidence of a secondary eclipse event at phase=0.5. Flux-weighted centroids are used to test for signals correlated with transit events with a magnitude and direction indicative of a background eclipsing binary. Centroid timeseries are complimented by analysis of images taken in-transit versus out-of-transit, the difference often revealing the pixel contributing the most to the flux change during transit. Examples are shown to illustrate each test. Candidates passing data validation are submitted to ground-based observers for further false-positive elimination or confirmation/characterization.

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arXiv2009

HD 174884: a strongly eccentric, short-period early-type binary system discovered by CoRoT

Accurate photometric CoRoT space observations of a secondary seismological target, HD 174884, led to the discovery that this star is an astrophysically important double-lined eclipsing spectroscopic binary in an eccentric orbit (e of about 0.3), unusual for its short (3.65705d) orbital period. The high eccentricity, coupled with the orientation of the binary orbit in space, explains the very unusual observed light curve with strongly unequal primary and secondary eclipses having the depth ratio of 1-to-100 in the CoRoT 'seismo' passband. Without the high accuracy of the CoRoT photometry, the secondary eclipse, 1.5 mmag deep, would have gone unnoticed. A spectroscopic follow-up program provided 45 high dispersion spectra. The analysis of the CoRoT light curve was performed with an adapted version of PHOEBE that supports CoRoT passbands. The final solution was obtained by simultaneous fitting of the light and the radial velocity curves. Individual star spectra were derived by spectrum disentangling. The uncertainties of the fit were derived by bootstrap resampling and the solution uniqueness was tested by heuristic scanning. The results provide a consistent picture of the system composed of two late B stars. The Fourier analysis of the light curve fit residuals yields two components, with orbital frequency multiples and an amplitude of about 0.1 mmag, which are tentatively interpreted as tidally induced pulsations. An extensive comparison with theoretical models is carried out by means of the Levenberg-Marquardt minimization technique and the discrepancy between models and the derived parameters is discussed. The best fitting models yield a young system age of 125 million years which is consistent with the eccentric orbit and synchronous component rotation at periastron.

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arXiv2009

CoRoT photometry and high-resolution spectroscopy of the interacting eclipsing binary AU Mon

Analyses of very accurate CoRoT space photometry, past Johnson V photoelectric photometry and high-resolution échelle spectra led to the determination of improved and consistent fundamental stellar properties of both components of AU Mon. We derived new, accurate ephemerides for both the orbital motion (with a period of 11.113d) and the long-term, overall brightness variation (with a period of 416.9d) of this strongly interacting Be + G semi-detached binary. It is shown that this long-term variation must be due to attenuation of the total light by some variable circumbinary material. We derived the binary mass ratio $M_{\rm G}/M_{\rm B}$ = 0.17\p0.03 based on the assumption that the G-type secondary fills its Roche lobe and rotates synchronously. Using this value of the mass ratio as well as the radial velocities of the G-star, we obtained a consistent light curve model and improved estimates of the stellar masses, radii, luminosities and effective temperatures. We demonstrate that the observed lines of the B-type primary may not be of photospheric origin. We also discover rapid and periodic light changes visible in the high-quality residual CoRoT light curves. AU Mon is put into perspective by a comparison with known binaries exhibiting long-term cyclic light changes.

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arXiv2009

Near-Infrared Light Curves of the Brown Dwarf Eclipsing Binary 2MASS J05352184-0546085: Can Spots Explain the Temperature Reversal?

We present the JHKs light curves for the double-lined eclipsing binary 2MASS J05352184-0546085, in which both components are brown dwarfs. We analyze these light curves with the published Ic-band light curve and radial velocities to provide refined measurements of the system's physical parameters. The component masses and radii are here determined with an accuracy of ~6.5% and ~1.5%, respectively. We confirm the previous surprising finding that the primary brown dwarf has a cooler effective temperature than its companion. Next, we perform a detailed study of the variations in the out-of-eclipse phases of the light curves to ascertain the properties of any inhomogeneities on the surfaces of the brown dwarfs. Our analysis reveals two low-amplitude periodic signals, one attributable to the rotation of the primary (with a period of 3.293+/-0.001 d) and the other to that of the secondary (14.05+/-0.05 d). Finally, we explore the effects on the derived physical parameters of the system when spots are included in the modeling. The observed low-amplitude rotational modulations are well fit by cool spots covering a small fraction of their surfaces. To mimic the observed ~200 K suppression of the primary's temperature, our model requires that the primary possess a very large spot coverage fraction of ~65%. Altogether, a spot configuration in which the primary is heavily spotted while the secondary is lightly spotted can explain the apparent temperature reversal and can bring the temperatures of the brown dwarfs into agreement with the predictions of theoretical models.

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