R. Dvorak

University of Vienna, Wien, Vienna, Austria

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Publications (190)440.68 Total impact

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    ABSTRACT: The CoRoT satellite has provided high-precision photometric light curves for more than 163,000 stars and found several hundreds of transiting systems compatible with a planetary scenario. If ground-based velocimetric observations are the best way to identify the actual planets among many possible configurations of eclipsing binary systems, recent transit surveys have shown that it is not always within reach of the radial-velocity detection limits. In this paper, we present a transiting exoplanet candidate discovered by CoRoT whose nature cannot be established from ground-based observations, and where extensive analyses are used to validate the planet scenario. They are based on observing constraints from radial-velocity spectroscopy, adaptive optics imaging and the CoRoT transit shape, as well as from priors on stellar populations, planet and multiple stellar systems frequency. We use the fully Bayesian approach developed in the PASTIS analysis software, and conclude that the planet scenario is at least 1400 times more probable than any other false positive scenario. The primary star is a metallic solar-like dwarf, with Ms = 1.099+-0.049 Msun and Rs = 1.136 (+0.038,-0.090) Rsun . The validated planet has a radius of Rp = 4.88 (+0.17,-0.39) RE and mass less than 49 ME. Its mean density is smaller than 2.56 g/cm^3 and orbital period is 9.7566+-0.0012 days. This object, called CoRoT-22 b, adds to a large number of validated Kepler planets. These planets do not have a proper measurement of the mass but allow statistical characterization of the exoplanet population.
    08/2014;
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    ABSTRACT: With the discovery of hundreds of exoplanets and a potentially huge number of Earth-like planets waiting to be discovered, the conditions for their habitability have become a focal point in exoplanetary research. The classical picture of habitable zones primarily relies on the stellar flux allowing liquid water to exist on the surface of an Earth-like planet with a suitable atmosphere. However, numerous further stellar and planetary properties constrain habitability. Apart from "geophysical" processes depending on the internal structure and composition of a planet, a complex array of astrophysical factors additionally determine habitability. Among these, variable stellar UV, EUV, and X-ray radiation, stellar and interplanetary magnetic fields, ionized winds, and energetic particles control the constitution of upper planetary atmospheres and their physical and chemical evolution. Short- and long-term stellar variability necessitates full time-dependent studies to understand planetary habitability at any point in time. Furthermore, dynamical effects in planetary systems and transport of water to Earth-like planets set fundamentally important constraints. We will review these astrophysical conditions for habitability under the crucial aspects of the long-term evolution of stellar properties, the consequent extreme conditions in the early evolutionary phase of planetary systems, and the important interplay between properties of the host star and its planets.
    07/2014;
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    ABSTRACT: We present the discovery of a candidate multiply-transiting system, the first one found in the CoRoT mission. Two transit-like features with periods of 5.11 and 11.76d are detected in the CoRoT light curve, around a main sequence K1V star of r=15.1. If the features are due to transiting planets around the same star, these would correspond to objects of 3.7$\pm$0.4 and 5.0$\pm$0.5 R_earth respectively. Several radial velocities serve to provide an upper limit of 5.7 M_earth for the 5.11~d signal, and to tentatively measure a mass of 28$^{+11}_{-11}$ M_earth for the object transiting with a 11.76~d period. These measurements imply low density objects, with a significant gaseous envelope. The detailed analysis of the photometric and spectroscopic data serve to estimate the probability that the observations are caused by transiting Neptune-sized planets as $>$26$\times$ higher than a blend scenario involving only one transiting planet, and $>$900$\times$ higher than a scenario involving two blends and no planets. The radial velocities show a long term modulation that might be attributed to a 1.5 M_jup planet orbiting at 1.8~A.U. from the host, but more data are required to determine the precise orbital parameters of this companion.
    06/2014;
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    ABSTRACT: We investigate the influence of impacts of large planetesimals and small planetary embryos on the early Martian surface on the hydrodynamic escape of an early steam atmosphere that is exposed to the high soft X-ray and EUV flux of the young Sun. Impact statistics in terms of number, masses, velocities, and angles of asteroid impacts onto the early Mars are determined via n-body integrations. Based on these statistics, smoothed particle hydrodynamics (SPH) simulations result in estimates of energy transfer into the planetary surface material and according surface heating. For the estimation of the atmospheric escape rates we applied a soft X-ray and EUV absorption model and a 1-D upper atmosphere hydrodynamic model to a magma ocean-related catastrophically outgassed steam atmosphere with surface pressure values of 52 bar H2O and 11 bar CO2. The estimated impact rates and energy deposition onto an early Martian surface can account for substantial heating. The energy influx and conversion rate into internal energy is most likely sufficient to keep a shallow magma ocean liquid for an extended period of time. Higher surface temperatures keep the outgassed steam atmosphere longer in vapor form and therefore enhance its escape to space within about 0.6 Myr after its formation.
    05/2014;
  • EGU General Assembly Conference Abstracts; 05/2014
  • Rudolf Dvorak, Li-Yong Zhou, Helmut Baudisch
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    ABSTRACT: We take as dynamical model for extrasolar planetary systems a central star like our Sun and two giant planets m 1 and m 2 like Jupiter and Saturn. We change the mass ratio μ=m 2/m 1 of the two large planets for a wide range of 1/16 < μ < 16. We also change the ratio between the initial semi-major axes (ν=a 2/a 1) in the range of 1.2 < ν < 3 to model the different architecture of extrasolar planetary systems hosting two giant planets. The results for possible Trojans (Trojan planets) in the equilateral equilibrium points of the inner planet m 1 and the outer planet m 2 were derived with the aid of numerical integration. It turned out that in many configurations - depending on the mass ratios μ and the semi-major axes ratio ν - giant planets may host Trojans.
    03/2014;
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    ABSTRACT: We report the discovery of a massive and dense transiting planet CoRoT-27b on a 3.58 day orbit around a 4.2 Gyr-old G2~star. The planet candidate was identified from the CoRoT photometry, and was confirmed as a planet with ground-based spectroscopy. The confirmation of the planet candidate is based on radial velocity observations combined with imaging to rule out blends. The characterisation of the planet and its host star is carried out using a Bayesian approach where all the data (CoRoT photometry, radial velocities, and spectroscopic characterisation of the star) are used jointly. The Bayesian analysis includes a study whether the assumption of white normally distributed noise holds for the CoRoT photometry, and whether the use of a non-normal noise distribution offers advantages in parameter estimation and model selection. CoRoT-27b has a mass of $10.39 \pm 0.55$ $\mathrm{M}_{\rm Jup}$, a radius of $1.01 \pm 0.04$ $\mathrm{R}_{\rm Jup}$, a mean density of $12.6_{-1.67}^{+1.92}$ $\mathrm{g\,cm^{-3}}$, and an effective temperature of $1500 \pm 130$~K. The planet orbits around its host star, a 4.2 Gyr-old G2-star with a mass $M_{\star}=1.06$ $M_{\odot}$, and a radius $R_{\star}=1.05$ $R_{\odot}$, on a $0.048 \pm 0.007$ AU orbit every 3.58 days. The radial velocity observations allow us to exclude highly eccentric orbits, namely, $e<0.065$ with a 99% confidence. Given its high mass and density, theoretical modelling of CoRoT-27b is demanding. We identify two solutions with heavy element mass fractions of $0.11\pm0.08$ $\mathrm{M_{\oplus}}$ and $0.07\pm0.06$ $\mathrm{M_{\oplus}}$, but even solutions void of heavy elements cannot be excluded. We carry out a secondary eclipse search from the CoRoT photometry using a method based on Bayesian model selection, but conclude that the noise level is too high to detect eclipses shallower than 9% of the transit depth.
    Astronomy and Astrophysics 02/2014; 562. · 5.08 Impact Factor
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    ABSTRACT: Context. We investigate the effects of including material strength in multi-material planetesimal collisions. Aims. The differences between strengthless material models and including the full elasto-plastic model for solid bodies with brittle failure and fragmentation when treating collisions of asteroid-sized bodies as they occur frequently in early planetary systems are demonstrated. Methods. We study impacts of bodies of Ceres-mass with a solid rock target and an impactor with 30 wt% water content. The initial impact velocities and impact parameters are varied between the escape velocity $v_\mbox{esc}$ to about 6 $v_\mbox{esc}$ and from head-on collisions to close fly-bys, respectively. We simulate the collisions using our own SPH code using both strengthless material and the full elasto-plastic material model including brittle failure. Results. The qualitative analysis results in significant differences depending on whether material strength is included or not. This may be an effect of the relatively low-energy impacts that cannot destroy the solid material instantly. One of the most prominent differences is the higher degree of fragmentation and shattered debris clouds in the solid case. As opposed to giant impacts we also observe some water ice to get transferred from the impactor to the target.
    12/2013;
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    ABSTRACT: We announce the discovery of 7 transiting planets around a Kepler target, a current record for transiting systems. Planets b, c, e and f are reported for the first time in this work. Planets d, g and h were previously reported in the literature (Batalha et al. 2013), although here we revise their orbital parameters and confirm their planetary nature. Planets h and g are gas giants and show strong dynamical interactions. The orbit of planet g is perturbed in such way that its orbital period changes by 25.7h between two consecutive transits during the length of the observations, which is the largest such perturbation found so far. The rest of the planets also show mutual interactions: planets d, e and f are super-Earths close to a mean motion resonance chain (2:3:4), and planets b and c, with sizes below 2 Earth radii, are within 0.5% of the 4:5 mean motion resonance. This complex system presents some similarities to our Solar System, with small planets in inner orbits and gas giants in outer orbits. It is, however, more compact. The outer planet has an orbital distance around 1 AU, and the relative position of the gas giants is opposite to that of Jupiter and Saturn, which is closer to the expected result of planet formation theories. The dynamical interactions between planets are also much richer.
    The Astrophysical Journal 10/2013; 781(1). · 6.73 Impact Factor
  • Barbara Funk, Rudolf Dvorak, Richard Schwarz
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    ABSTRACT: In this investigation we treat a special configuration of two celestial bodies in 1:1 mean motion resonance namely the so-called exchange orbits. There exist—at least—theoretically—two different types: the exchange-a orbits and the exchange-e orbits. The first one is the following: two celestial bodies are in orbit around a central body with almost the same semi-major axes on circular orbits. Because of the relatively small differences in semi-major axes they meet from time to time and exchange their semi-major axes. The inner one then moves outside the other planet and vice versa. The second configuration one is the following: two planets are moving on nearly the same orbit with respect to the semi-major axes, one on a circular orbit and the other one on an eccentric one. During their dynamical evolution they change the characteristics of the orbit, the circular one becomes an elliptic one whereas the elliptic one changes its shape to a circle. This ‘game’ repeats periodically. In this new study we extend the numerical computations for both of these exchange orbits to the three dimensional case and in another extension treat also the problem when these orbits are perturbed from a fourth body. Our results in form of graphs show quite well that for a large variety of initial conditions both configurations are stable and stay in these exchange orbits.
    Celestial Mechanics and Dynamical Astronomy 09/2013; · 2.32 Impact Factor
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    Thomas I. Maindl, Rudolf Dvorak
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    ABSTRACT: We investigate the distribution of encounter velocities and impact angles describing collisions in the habitable zone of the early planetary system. Here we present a catalogue of collision characteristics for a particular mass ratio of the colliding bodies and seven different planetesimal masses ranging from a tenth of Ceres' mass to 10 times the mass of the Moon. We show that there are virtually no collisions with impact speeds lower than the surface escape velocity and a similar velocity-impact angle distribution for different planetesimal masses if velocities are normalized using the escape velocity. An additional perturbing Jupiter-like object distorts the collision velocity and impact picture in the sense that grazing impacts at higher velocities are promoted if the perturber's orbit is close to the habitable zone whereas a more distant perturber has more the effect of a mere widening of the velocity dispersion.
    Proceedings of the International Astronomical Union 07/2013;
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    ABSTRACT: We give a brief introduction to smoothed particle hydrodynamics methods for continuum mechanics. Specifically, we present our 3D SPH code to simulate and analyze collisions of asteroids consisting of two types of material: basaltic rock and ice. We consider effects like brittle failure, fragmentation, and merging in different impact scenarios. After validating our code against previously published results we present first collision results based on measured values for the Weibull flaw distribution parameters of basalt.
    Astronomische Nachrichten 06/2013; · 1.40 Impact Factor
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    ABSTRACT: The study of meteorite craters on Earth provides information about the dynamic evolution of bodies within the Solar System. Bosumtwi crater is a well studied, 10.5 km in diameter, ca. 1.07 Ma old impact structure located in Ghana. The impactor was �1 km in diameter, an ordinary chondrite and struck the Earth with an angle between 30� and 45� from the horizontal. We have used a two phase backward integration to constrain the most probable parent region of the impactor. We find that the most likely source region is a high inclination object from the Middle Main Belt.
    Astronomische Nachrichten 04/2013; 334(9):936. · 1.40 Impact Factor
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    S. Rothwangl, S. Eggl, R. Dvorak
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    ABSTRACT: Investigations were carried out on the stability of the two gas giant system HD 60532 itself including additional, smaller bodies. The methods used were numerical simulations with the Lie Series integration method, and secular perturbation theory. The aims were to find stable regions for potential Earth-like planets within the system, and confirming the stability of the detected planets. As results, the given configuration can be considered stable for a period of at least 65 million years. The two planets create a large unstable section between 0.25 and 3.6 AU, where no additional body is able to remain stable. Variations in the mutual inclination between test bodies and the rest of the system of up to 20{\deg} have little effects on the size of the zone of instability.
    04/2013;
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    ABSTRACT: Hungaria asteroids, whose orbits occupy the region in element space between $1.78< a< 2.03$ AU, $e<0.19$, $12^\circ<i<31^\circ$, are a possible source of Near-Earth Asteroids (NEAs). Named after (434) Hungaria these asteroids are relatively small, since the largest member of the group has a diameter of just about 11 km. They are mainly perturbed by Jupiter and Mars, possibly becoming Mars-crossers and, later, they may even cross the orbits of Earth and Venus. In this paper we analyze the close encounters and possible impacts of escaped Hungarias with the terrestrial planets. Out of about 8000 known Hungarias we selected 200 objects which are on the edge of the group. We integrated their orbits over 100 million years in a simplified model of the planetary system (Mars to Saturn) subject only to gravitational forces. We picked out a sample of 11 objects (each with 50 clones) with large variations in semi-major axis and restarted the numerical integration in a gravitational model including the planets from Venus to Saturn. Due to close encounters, some of them achieve high inclinations and eccentricities which, in turn, lead to relatively high velocity impacts on Venus, Earth, and Mars. We statistically analyze all close encounters and impacts with the terrestrial planets and determine the encounter and impact velocities of these fictitious Hungarias.
    Planetary and Space Science 03/2013; 84(August 2013):5-13. · 2.11 Impact Factor
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    ABSTRACT: The Hungaria asteroid family, which consists of more than 8000 members with semi-major axes between 1.78 and 2.03 AU, is regarded as one source for Near-Earth Asteroids. Named after (434) Hungaria these asteroids are relatively small (mean diameter $\sim 1$ km) and have inclinations of the order of $20^\circ$. They are mainly perturbed by Jupiter and Mars, and are ejected because of mean motion and secular resonances with these planets and then become Mars-crossers; later they may even cross the orbits of Earth and Venus. We are interested to analyse the close encounters and possible impacts with these planets. For 200 selected objects which are on the edge of the group we integrated their orbits over 100 million years in a simplified model of the planetary system (Mars to Saturn) subject to only gravitational forces. We picked out a sample of 11 objects (each with 50 clones) with large variations in semi-major axis and restarted the numerical integration in the model Venus to Saturn. Due to close encounters in connection with mean motion and secular resonances some of them achieve high inclinations and eccentricities which then leads to relatively high velocity impacts on Venus, Earth, and Mars. We report all close encounters and impacts with the terrestrial planets and statistically determine collision velocities of these fictitious Hungarias. With this data we compute the effect of the possible impacts with the terrestrial planets and estimate the diameter of the crater depending on the impact energy released, the impact velocity and the impact angle.
    10/2012;
  • åp. 05/2012; 541:A149.
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    Rudolf Dvorak, Christoph Lhotka, Liyong Zhou
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    ABSTRACT: Recently the first Earth Trojan has been observed (Mainzer et al., ApJ 731) and found to be on an interesting orbit close to the Lagrange point L4 (Connors et al., Nature 475). In the present study we therefore perform a detailed investigation on the stability of its orbit and moreover extend the study to give an idea of the probability to find additional Earth-Trojans. Our results are derived using different approaches: a) we derive an analytical mapping in the spatial elliptic restricted three-body problem to find the phase space structure of the dynamical problem. We explore the stability of the asteroid in the context of the phase space geometry, including the indirect influence of the additional planets of our Solar system. b) We use precise numerical methods to integrate the orbit forward and backward in time in different dynamical models. Based on a set of 400 clone orbits we derive the probability of capture and escape of the Earth Trojan asteroids 2010 TK7. c) To this end we perform an extensive numerical investigation of the stability region of the Earth's Lagrangian points. We present a detailed parameter study in the regime of possible stable tadpole and horseshoe orbits of additional Earth-Trojans, i.e. with respect to the semi-major axes and inclinations of thousands of fictitious Trojans. All three approaches underline that the Earth Trojan asteroid 2010 TK7 finds himself in an unstable region on the edge of a stable zone; additional Earth-Trojan asteroids may be found in this regime of stability.
    Astronomy and Astrophysics 02/2012; · 5.08 Impact Factor
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    ABSTRACT: We report the discovery by the CoRoT space mission of a new giant planet, CoRoT-20b. The planet has a mass of 4.24 ± 0.23 MJup and a radius of 0.84 ± 0.04 RJup. With a mean density of 8.87 ± 1.10 g cm-3, it is among the most compact planets known so far. Evolutionary models for the planet suggest a mass of heavy elements of the order of 800 M⊕ if embedded in a central core, requiring a revision either of the planet formation models or both planet evolution and structure models. We note however that smaller amounts of heavy elements are expected by more realistic models in which they are mixed throughout the envelope. The planet orbits a G-type star with an orbital period of 9.24 days and an eccentricity of 0.56.The star's projected rotational velocity is vsini = 4.5 ± 1.0 km s-1, corresponding to a spin period of 11.5 ± 3.1 days if its axis of rotation is perpendicular to the orbital plane. In the framework of Darwinian theories and neglecting stellar magnetic breaking, we calculate the tidal evolution of the system and show that CoRoT-20b is presently one of the very few Darwin-stable planets that is evolving toward a triple synchronous state with equality of the orbital, planetary and stellar spin periods. The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany, and Spain.
    Astronomy and Astrophysics 01/2012; 538:145. · 5.08 Impact Factor
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    Astronomy and Astrophysics. 01/2012; 237(2012-2):511-529.

Publication Stats

1k Citations
440.68 Total Impact Points

Institutions

  • 1984–2014
    • University of Vienna
      • Department of Astrophysics
      Wien, Vienna, Austria
  • 2012
    • Nanjing University
      • Department of Astronomy
      Nan-ching, Jiangsu Sheng, China
  • 2010–2011
    • Instituto de Astrofísica de Canarias
      San Cristóbal de La Laguna, Canary Islands, Spain
  • 1999
    • University of Florida
      • Department of Astronomy
      Gainesville, FL, United States
  • 1996
    • Athens State University
      Athens, Alabama, United States
  • 1993
    • Observatoire de la Côte d'Azur
      Grasse, Provence-Alpes-Côte d'Azur, France