Searcharxiv⌕ Search

arXiv subjects

J. Budaj

Publications and source records attributed to J. Budaj.

33 records · Page 2Linked to original sources
arXiv2013

Follow-up photometry of TrES-3

We present new observations of the transiting system TrES-3 obtained from 2009 to 2011 at several observatories. The orbital parameters of the system were re- determined and a new linear ephemeris was calculated. The best quality light curve was used for light curve analysis, an other datasets were used to determine mid-transit times, Tc, and study transit time variation (TTV). For planet parameter determination we used two independent codes and finally, we concluded that our parameters are in agreement with previous studies. Based on our observations, we determined 14 mid-transit times. Together with published Tc we found that the timing residuals showed no significant deviation from the linear ephemeris. We concluded that a periodic TTV signal with an amplitude greater than 1 minute over a 4-year time span seems to be unlikely. Our analysis of an upper mass limit allows us to exclude an additional Earth-mass planet close to inner 3:1, 2:1, and 5:3 and outer 3:5, 1:2, and 1:3 mean-motion resonances. Using the long-term integration and applying the method of maximum eccentricity, the region from 0.015 au to 0.05 au was found unstable and the region beyond the 0.05 au was found to have a chaotic behaviour and its depletion increases with increasing values of the initial eccentricity as well as inclination.

astro-ph.SR↗
arXiv2012

Day and night side core cooling of a strongly irradiated giant planet

The internal heat loss, or cooling, of a planet determines its structure and evolution. We study the effects of irradiation, metallicity of the atmosphere, heat redistribution, stratospheres, and the depth where the heat redistribution takes place on the atmospheric structure, the core entropy, and subsequently on the cooling of the interior of the planet. We address in a consistent fashion the coupling between the day and the night sides of a planet by means of model atmosphere calculations with heat redistribution. We assume that strong convection leads to the same entropy on the day and night sides and that gravity is the same on both hemispheres. We argue that the core cooling rates from the two hemispheres of a strongly irradiated planet may not be the same and that the difference depends on several important parameters. If the day-night heat redistribution is very efficient or if it takes place at the large optical depth, then the day-side and the night-side cooling may be comparable. However, if the day-night heat transport is not efficient or if it takes place at a shallow optical depth then there can be a large difference between the day- and the night-side cooling and the night side will cool more efficiently. If stellar irradiation becomes stronger, e.g. owing to stellar evolution or migration, cooling from both the day and the night sides is reduced. Enhanced metallicity of the atmosphere would act as an added "blanket" and reduces both the day- and the night-side cooling. However, a stratosphere on the planetary day side can enhance day-side cooling since its opacity acts as a "sunshade" that screens the stellar irradiation. These effects may also influence the well-known gravity darkening and bolometric albedo effects in interacting binaries, especially for strongly irradiated cold components.

astro-ph.EP↗
arXiv2011

Abundance analysis of Am binaries and search for tidally driven abundance anomalies - III. HD116657, HD138213, HD155375, HD159560, HD196544 and HD204188

We continue here the systematic abundance analysis of a sample of Am binaries in order to search for possible abundance anomalies driven by tidal interaction in these binary systems. New CCD observations in two spectral regions (6400-6500, 6660-6760 AA) of HD116657, HD138213, HD155375, HD159560, HD196544 and HD204188 were obtained. Synthetic spectrum analysis was carried out and basic stellar properties, effective temperatures, gravities, projected rotational velocities, masses, ages and abundances of several elements were determined. We conclude that all six stars are Am stars. These stars were put into the context of other Am binaries with 10 < Porb < 200 days and their abundance anomalies discussed in the context of possible tidal effects. There is clear anti-correlation of the Am peculiarities with v sin i. However, there seems to be also a correlation with the eccentricity and may be with the orbital period. The dependence on the temperature, age, mass, and microturbulence was studied as well. The projected rotational velocities obtained by us were compared to those of Royer et al. (2002) and Abt & Morrell (1995).

astro-ph.SR↗
arXiv2011

New photometric observations of the transiting extrasolar planet TrES-3b

We present new transit observations of the transiting exoplanet TrES-3b obtained in the range 2009 -- 2011 at several observatories. The orbital parameters of the system were redetermined and the new linear ephemeris was calculated. We performed numerical simulations for studying the long-term stability of orbits.

astro-ph.EP↗
arXiv2011

Effects of dust on light-curves of εAur type stars

εAuriga is one of the most mysterious objects on the sky. Prior 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. 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 for $ε$ Aur type objects which is based on the optical properties of dust grains. The code Shellspec has been modified to calculate the light-curves and spectra of such objects. The code solves the radiative transfer along the line of sight in interacting binaries. Dust and angle dependent Mie scattering were introduced into the code for this purpose. Our model of $ε$ Aur 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 an inclined disk with a hole to explain the current eclipse of $ε$ Aur not even if there is a possible shallow mid-eclipse brightening. It was demonstrated that phase dependent light scattering and the optical properties of the dust can have an important effect on the light-curves of such stars and can even produce a mid-eclipse brightening. This is a natural consequence of the strong forward scattering. It was also demonstrated that shallow mid-eclipse brightening might result from eclipses by nearly edge-on flared (dusty or gaseous) disks.

astro-ph.SR↗
arXiv2011

Young Exoplanet Transit Initiative (YETI)

We present the Young Exoplanet Transit Initiative (YETI), in which we use several 0.2 to 2.6m telescopes around the world to monitor continuously young (< 100 Myr), nearby (< 1 kpc) stellar clusters mainly to detect young transiting planets (and to study other variability phenomena on time-scales from minutes to years). The telescope network enables us to observe the targets continuously for several days in order not to miss any transit. The runs are typically one to two weeks long, about three runs per year per cluster in two or three subsequent years for about ten clusters. There are thousands of stars detectable in each field with several hundred known cluster members, e.g. in the first cluster observed, Tr-37, a typical cluster for the YETI survey, there are at least 469 known young stars detected in YETI data down to R=16.5 mag with sufficient precision of 50 milli-mag rms (5 mmag rms down to R=14.5 mag) to detect transits, so that we can expect at least about one young transiting object in this cluster. If we observe 10 similar clusters, we can expect to detect approximately 10 young transiting planets with radius determinations. The precision given above is for a typical telescope of the YETI network, namely the 60/90-cm Jena telescope (similar brightness limit, namely within +/-1 mag, for the others) so that planetary transits can be detected. For planets with mass and radius determinations, we can calculate the mean density and probe the internal structure. We aim to constrain planet formation models and their time-scales by discovering planets younger than 100 Myr and determining not only their orbital parameters, but also measuring their true masses and radii, which is possible so far only by the transit method. Here, we present an overview and first results. (Abstract shortened)

astro-ph.SR↗
arXiv2010

Transit timing variation and activity in the WASP-10 planetary system

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 $\sim$0.1 $M_{\rm{J}}$ and orbital period of $\sim$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 $\sim$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 $270 \pm 80$ Myr old. This young age can explain the large radius reported for WASP-10b.

astro-ph.EP↗
arXiv2008

Transient jets in the symbiotic prototype Z Andromedae

We present development of the collimated bipolar jets from the symbiotic prototype Z And that appeared and disappeared during its 2006 outburst. In 2006 July Z And reached its historical maximum at U ~ 8.0. During this period, rapid photometric variations with Dm ~ 0.06 mag on the timescale of hours developed. Simultaneously, high-velocity satellite components appeared on both sides of the H-alpha and H-beta emission line profiles. They were launched asymmetrically with the red/blue velocity ratio of 1.2 - 1.3. From about mid-August they became symmetric. Their spectral properties indicated ejection of bipolar jets collimated within an average opening angle of 6.1 degrees. We estimated average outflow rate via jets to dM(jet)/dt ~ 2xE10-6(R(jet)/1AU)**(1/2) M(Sun)/year, during their August - September maximum, which corresponds to the emitting mass in jets, M(jet, emitting) ~ 6xE-10(Rjet)/1AU)^{3/2} M(Sun). During their lifetime, the jets released the total mass of M(jet, total) approx 7.4x1E-7 M(Sun). Evolution in the rapid photometric variability and asymmetric ejection of jets around the optical maximum can be explained by a disruption of the inner parts of the disk caused by radiation-induced warping of the disk.

astro-ph↗
arXiv2008

Theoretical Spectra and Light Curves of Close-in Extrasolar Giant Planets and Comparison with Data

We present theoretical atmosphere, spectral, and light-curve models for extrasolar giant planets (EGPs) undergoing strong irradiation for which {\it Spitzer} planet/star contrast ratios or light curves have been published (circa June 2007). These include HD 209458b, HD 189733b, TrES-1, HD 149026b, HD 179949b, and $\upsilon$ And b. By comparing models with data, we find that a number of EGP atmospheres experience thermal inversions and have stratospheres. This is particularly true for HD 209458b, HD 149026b, and $\upsilon$ And b. This finding translates into qualitative changes in the planet/star contrast ratios at secondary eclipse and in close-in EGP orbital light curves. Moreover, the presence of atmospheric water in abundance is fully consistent with all the {\it Spitzer} data for the measured planets. For planets with stratospheres, water absorption features invert into emission features and mid-infrared fluxes can be enhanced by a factor of two. In addition, the character of near-infrared planetary spectra can be radically altered. We derive a correlation between the importance of such stratospheres and the stellar flux on the planet, suggesting that close-in EGPs bifurcate into two groups: those with and without stratospheres. From the finding that TrES-1 shows no signs of a stratosphere, while HD 209458b does, we estimate the magnitude of this stellar flux breakpoint. We find that the heat redistribution parameter, P$_n$, for the family of close-in EGPs assumes values from $\sim$0.1 to $\sim$0.4. This paper provides a broad theoretical context for the future direct characterization of EGPs in tight orbits around their illuminating stars.

astro-ph↗
arXiv2007

Am stars in binary systems

It is argued that apart from the well known dependence of the Am phenomenon on the mass, age (effective temperature, gravity) and rotation there is also a complex dependence on the orbital parameters in binary systems. This is why the generally accepted scenario in which the Am star rotation plays a unique role needs to be revisited, the strong correlations between the rotation, orbital period and eccentricity need to be properly addressed and tidal effects taken into account. Recent observations of Am stars in binary systems are reviewed.

astro-ph↗
arXiv2007

Possible Solutions to the Radius Anomalies of Transiting Giant Planets

We calculate the theoretical evolution of the radii of all fourteen of the known transiting extrasolar giant planets (EGPs) for a variety of assumptions concerning atmospheric opacity, dense inner core masses, and possible internal power sources. We incorporate the effects of stellar irradiation and customize such effects for each EGP and star. Looking collectively at the family as a whole, we find that there are in fact two radius anomalies to be explained. Not only are the radii of a subset of the known transiting EGPs larger than expected from previous theory, but many of the other objects are smaller than the default theory would allow. We suggest that the larger EGPs can be explained by invoking enhanced atmospheric opacities that naturally retain internal heat. This explanation might obviate the necessity for an extra internal power source. We explain the smaller radii by the presence in perhaps all the known transiting EGPs of dense cores, such as have been inferred for Saturn and Jupiter. Importantly, we derive a rough correlation between the masses of our "best-fit" cores and the stellar metallicity that seems to buttress the core-accretion model of their formation. Though many caveats and uncertainties remain, the resulting comprehensive theory that incorporates enhanced-opacity atmospheres and dense cores is in reasonable accord with all the current structural data for the known transiting giant planets.

astro-ph↗
arXiv2002

Radiative accelerations on Ne in the atmospheres of late B stars

Radiative accelerations on Ne are calculated for the atmospheres of main sequence stars with 11000 < Teff < 15000 K, corresponding to the range of the HgMn stars. The calculations take into account neon fine structure as well as shadowing of neon lines using the entire Kurucz line list, bound-bound, bound-free, and free-free opacity of H, He, and C as well as some NLTE effects. NLTE effects modify the radiative acceleration by a factor of order 100 in the outer atmosphere. The dependence of the radiative acelerations on the Ne abundance, Teff, and gravity is studied. Radiative accelerations are well below gravity in the entire range of Teff and it is predicted that in stable atmospheres Ne should sink and be observed as underabundant. This agrees with recent observations of low Ne abundances in HgMn stars.

astro-ph↗
arXiv2000

Neon abundances in normal late-B and mercury-manganese stars

We make new Non-LTE calculations to deduce abundances of neon from visible-region echelle spectra of selected Ne I lines in 7 normal stars and 20 HgMn stars. We find that the best strong blend-free Ne line which can be used at the lower end of the Teff range is 6402 A, although several other potentially useful Ne I lines are found in the red region of the spectra of these stars. The mean neon abundance in the normal stars (log A =8.10) is in excellent agreement with the standard abundance of neon (8.08). However, in HgMn stars, neon is almost universally underabundant, ranging from marginal deficits of 0.1-0.3 dex to underabundances of an order of magnitude or more. In many cases, the lines are so weak that only upper limits can be established. The most extreme example found is upsilon Her with an underabundance of at least 1.5 dex. These underabundances are qualitatively expected from radiative acceleration calculations, which show that Ne has a very small radiative acceleration in the photosphere and is expected to undergo gravitational settling if mixing processes are sufficiently weak, and there is no strong stellar wind. According to the theoretical predictions of Landstreet et al. (1998), the low Ne abundances place an important constraint on the intensity of such stellar winds, which must be less than $10^-14 M_sun per yr if they are non-turbulent.

astro-ph↗
arXiv1998

The effects of binarity in driving CP phenomena

A lot of evidence has recently accumulated that physical characteristics of CP stars (delta m_1, Ca/Fe ratio, Li abundance, distribution of orbital periods, vsini, Delta (V1-G), magnetic field) depend on orbital period or eccentricity. Consequently, the "tidal mixing + stabilization" hypothesis has been formulated to account for such features and the "binarity x magnetism" hypothesis of Abt & Snowden (1973) was reanalyzed. We conclude that all mentioned characteristics and properties of CP stars, including even CP star magnetism, may be affected or governed by binarity.

astro-ph↗