Jan Budaj
Slovak Academy of Sciences
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The Astronomical Journal | 2011
Jan Budaj
Extrasolar planets are a natural extension of the interacting binaries towards the companions with very small masses and similar tools might be used to study them. Unfortunately, the generally accepted treatment of the reflection effect in interacting binaries is not very suitable to study cold objects irradiated by hot objects or extrasolar planets. Our simple model of the reflection effect takes into account the reflection (scattering), heating and heat redistribution over the surface of the irradiated object. The shape of the objects is described by the Roche potential and limb and gravity darkening can be taken into account. The orbital revolution and rotation of the planet with proper Doppler shifts for the scattered and thermal radiation are also accounted for. Subsequently, light-curves and/or spectra of exoplanets were modeled and the effects of the heat redistribution, limb darkening/brightening, (non-)grey albedo, and non-spherical shape were studied. Recent observations of HD189733b, WASP12b, and Wasp-19b were reproduced reasonably well. HD189733b has low Bond albedo and intense heat redistribution. Wasp-19b has low Bond albedo and low heat redistribution. We also calculate the exact Roche shapes and temperature distribution over the surface of all 78 transiting extrasolar planets known so far. It is found that the departures from the sphere vary considerably within the sample. Departures of about 1% are common. In some cases: WASP-12b, WASP-19b, WASP-33b departures can reach about 14, 12, and 8%, respectively. The mean temperatures of these planets also vary considerably from 300 K to 2600 K. The extreme cases are WASP-33b, WASP-12b, and WASP-18b with mean temperatures of about 2600, 2430, and 2330 K, respectively.There are many similarities between interacting binary stars and stars with a close-in giant extrasolar planet. The reflection effect is a well-known example. Although the generally accepted treatment of this effect in interacting binaries is successful in fitting light curves of eclipsing binaries, it is not very suitable for studying cold objects irradiated by hot objects or extrasolar planets. The aim of this paper is to develop a model of the reflection effect which could be easily incorporated into the present codes for modeling of interacting binaries so that these can be used to study the aforementioned objects. Our model of the reflection effect takes into account the reflection (scattering), heating, and heat redistribution over the surface of the irradiated object. The shape of the object is described by the non-spherical Roche potential expected for close objects. Limb and gravity darkening are included in the calculations of the light output from the system. The model also accounts for the orbital revolution and rotation of the exoplanet with appropriate Doppler shifts for the scattered and thermal radiation. Subsequently, light curves and/or spectra of several exoplanets have been modeled and the effects of the heat redistribution, limb darkening/brightening, (non-)gray albedo, and non-spherical shape have been studied. Recent observations of planet-to-star flux ratio of HD189733b, WASP12b, and WASP-19b at various phases were reproduced with very good accuracy. It was found that HD189733b has a low Bond albedo and intense heat redistribution, while WASP-19b has a low Bond albedo and low heat redistribution. The exact Roche geometries and temperature distributions over the surface of all 78 transiting extrasolar planets have been determined. Departures from the spherical shape may vary considerably but departures of about 1% in the radius are common within the sample. In some cases, these departures can reach 8%, 12%, or 14%, for WASP-33b, WASP-19b, and WASP-12b, respectively. The mean temperatures of these planets also vary considerably from 300 K to 2600 K. The extreme cases are WASP-18b, WASP-12b, and WASP-33b, with mean temperatures of 2330 K, 2430 K, and 2600 K, respectively.
Monthly Notices of the Royal Astronomical Society | 2011
G. Maciejewski; D. Dimitrov; R. Neuhäuser; N. Tetzlaff; A. Niedzielski; St. Raetz; W. P. Chen; Frederick M. Walter; C. Marka; S. Baar; T.Krejčová; Jan Budaj; V. Krushevska; Kengo Tachihara; H. Takahashi; M. Mugrauer
Transit timing analysis may be an effective method of discovering additional bodies in extrasolar systems which harbour transiting exoplanets. The deviations from the Keplerian motion, caused by mutual gravitational interactions between planets, are expected to generate transit timing variations of transiting exoplanets. In 2009 we collected 9 light curves of 8 transits of the exoplanet WASP-10b. Combining these data with published ones, we found that transit timing cannot be explained by a constant period but by a periodic variation. Simplified three-body models which reproduce the observed variations of timing residuals were identified by numerical simulations. We found that the configuration with an additional planet of mass of ∼0.1 MJ and orbital period of ∼5.23 d, located close to the outer 5:3 mean motion resonance, is the most likely scenario. If the second planet is a transiter, the estimated flux drop will be ∼0.3 per cent and can be observable with a ground-based telescope. Moreover, we present evidence that the spots on the stellar surface and rotation of the star affect the radial velocity curve giving rise to spurious eccentricity of the orbit of the first planet. We argue that the orbit of WASP-10b is essentially circular. Using the gyrochronology method, the host star was found to be 270± 80 Myr old. This young age can explain the large radius reported for WASP-10b.
Astronomy and Astrophysics | 2012
Tereza Krejčová; Jan Budaj
The planet-star interaction is manifested in many ways. It has been found that a close-in exoplanet causes small but measurable variability in the cores of a few lines in the spectra of several stars, which corresponds to the orbital period of the exoplanet. Stars with and without exoplanets may have different properties. The main goal of our study is to search for the influence that exoplanets might have on atmospheres of their host stars. Unlike the previous studies, we do not study changes in the spectrum of a host star or differences between stars with and without exoplanets. We aim to study a large number of stars with exoplanets and the current level of their chromospheric activity and to look for a possible correlation with the exoplanetary properties. To analyse the chromospheric activity of stars, we exploited our own and publicly available archival spectra, measured the equivalent widths of the cores of Ca II H and K lines, and used them to trace their activity. Subsequently, we searched for their dependence on the orbital parameters and the mass of the exoplanet. We found statistically significant evidence that the equivalent width of the Ca II K line emission and log RHK activity parameter of the host star varies with the semi-major axis and mass of the exoplanet. Stars with Teff less than 5500 K having exoplanets with semi-major axis a less than 0.15 AU (Porb less than 20 days) have a broad range of Ca II K emissions and much stronger emission in general than stars at similar temperatures but with higher values of semi-major axes. The Ca II K emission of cold stars (Teff less than 5500 K) with close-in exoplanets (a less than 0.15 AU) is also more pronounced for more massive exoplanets. The overall level of the chromospheric activity of stars may be affected by their close-in exoplanets, and stars with massive close-in exoplanets may be more active.
Astronomy and Astrophysics | 2011
Jan Budaj
Context. � Auriga is one of the most mysterious objects in the sky. Previous modeling of its light-curve assumed a dark, inclined, non-transparent or semi-transparent dusty disk with a central hole. The hole was necessary to explain the light-curve with a sharp mid-eclipse brightening. Aims. The aim of the present paper is to study the effects of dust on the light-curves of eclipsing binary stars and to develop an alternative physical model forAur-type objects that is based on the optical properties of dust grains. Methods. The code Shellspec was modified to calculate the light-curves and spectra of these objects. The code solves the radiative transfer along the line of sight in interacting binaries. Dust and angle-dependent Mie scattering were included in the code for this purpose. Results. Our model ofAur consists of two geometrically thick flared disks: an internal optically thick disk and an external optically thin disk, which absorbs and scatters radiation. Disks are in the orbital plane and are almost edge-on. We argue that there is no need for a highly inclined disk with a hole to explain the current eclipse ofAur even if there is a possible shallow mid-eclipse brightening. We demonstrate that phase-dependent light scattering and the optical properties of the dust can have a significant effect on the light-curves of these stars and can even produce a mid-eclipse brightening. This is a natural consequence of the strong forward scattering. We also demonstrate that shallow mid-eclipse brightening might result from eclipses by nearly edge-on flared (dusty or gaseous) disks.
Astronomische Nachrichten | 2013
R. Errmann; R. Neuhäuser; Laurence A. Marschall; Guillermo Torres; M. Mugrauer; W. P. Chen; S.C.-L. Hu; C. Briceño; R. Chini; Ł. Bukowiecki; D. Dimitrov; Diana P. Kjurkchieva; Eric L. N. Jensen; David H. Cohen; Z.-Y. Wu; Theodor Pribulla; M. Vaňko; V. Krushevska; Jan Budaj; Yumiko Oasa; A. K. Pandey; Matilde Fernández; A. Kellerer; C. Marka
With an apparent cluster diameter of 1.5° and an age of 4 Myr, Trumpler 37 is an ideal target for photometric monitoring of young stars as well as for the search of planetary transits, eclipsing binaries and other sources of variability. The YETI consortium has monitored Trumpler 37 throughout 2010 and 2011 to obtain a comprehensive view of variable phenomena in this region. In this first paper we present the cluster properties and membership determination as derived from an extensive investigation of the literature. We also compared the coordinate list to some YETI images. For 1872 stars we found literature data. Among them 774 have high probability of being member and 125 a medium probability. Based on infrared data we re-calculate a cluster extinction of 0.9–1.2 mag. We can confirm the age and distance to be 3–5 Myr and870 pc. Stellar masses are determined from theoretical models and the mass function is fitted with a power-law index of α = 1.90 (0.1–0.4 M⊙) and α = 1.12 (1–10 M⊙). (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Monthly Notices of the Royal Astronomical Society | 2017
M. Vanko; Guillermo Torres; L. Hambálek; Theodor Pribulla; Lars A. Buchhave; Jan Budaj; P. Dubovský; Z. Garai; C. Ginski; K. Grankin; R. Komzík; V. Krushevska; E. Kundra; C. Marka; M. Mugrauer; R. Neuhäuser; J. Ohlert; Š. Parimucha; V. Perdelwitz; S. Raetz; Sergei Yu. Shugarov
We report new multi-colour photometry and high-resolution spectroscopic observations of the long-period variable V501 Aur, previously considered to be a weak-lined T-Tauri star belonging to the Taurus-Auriga star-forming region. The spectroscopic observations reveal that V501 Aur is a single-lined spectroscopic binary system with a 68.8-day orbital period, a slightly eccentric orbit (e ~ 0.03), and a systemic velocity discrepant from the mean of Taurus-Auriga. The photometry shows quasi-periodic variations on a different, ~55-day timescale that we attribute to rotational modulation by spots. No eclipses are seen. The visible object is a rapidly rotating (vsini ~ 25 km/s) early K star, which along with the rotation period implies it must be large (R > 26.3 Rsun), as suggested also by spectroscopic estimates indicating a low surface gravity. The parallax from the Gaia mission and other independent estimates imply a distance much greater than the Taurus-Auriga region, consistent with the giant interpretation. Taken together, this evidence together with a re-evaluation of the LiI~
arXiv: Earth and Planetary Astrophysics | 2011
Tereza Krejčová; Jan Budaj; J. Koza
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Proceedings of the International Astronomical Union | 2011
I. Stateva; Ilian Kh. Iliev; Jan Budaj
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Proceedings of the International Astronomical Union | 2011
Jan Budaj; Adam S. Burrows; Ivan Hubeny
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Astronomy and Astrophysics | 2012
Jan Budaj; Ivan Hubeny; Adam Burrows
lines shows that V501 Aur is not a T-Tauri star, but is instead a field binary with a giant primary far behind the Taurus-Auriga star-forming region. The large mass function from the spectroscopic orbit and a comparison with stellar evolution models suggest the secondary may be an early-type main-sequence star.