Theodor Pribulla

Contact Binaries with Additional Components. I. The Extant Data

We have attempted to establish observational evidence for the presence of distant companions that may have acquired and/or absorbed angular momentum during the evolution of multiple systems, thus facilitating or enabling the formation of contact binaries. In this preliminary investigation we use several techniques (some of them distance-independent) and mostly disregard the detection biases of individual techniques in an attempt to establish a lower limit to the frequency of triple systems. While the whole sample of 151 contact binary stars brighter than Vmax = 10 mag gives a firm lower limit of 42% ± 5%, the corresponding number for the much better observed northern-sky subsample is 59% ± 8%. These estimates indicate that most contact binary stars exist in multiple systems.

Radial Velocity Studies of Close Binary Stars. XI.

Radial-velocity measurements and sine-curve fits to orbital radial velocity variations are presented for 10 close binary systems: DU Boo, ET Boo, TX Cnc, V1073 Cyg, HL Dra, AK Her, VW LMi, V566 Oph, TV UMi, and AG Vir. With this contribution, the David Dunlap Observatory program has reached the point of 100 published radial velocity orbits. The radial velocities have been determined using an improved fitting technique that uses rotational profiles to approximate individual peaks in broadening functions. Three systems, ET Boo, VW LMi, and TV UMi, are found to be quadruple, while AG Vir appears to be a spectroscopic triple. ET Boo, a member of a close visual binary with Pvis = 113 yr, was previously known to be a multiple system, but we show that the second component is actually a close, noneclipsing binary. The new observations have enabled us to determine the spectroscopic orbits of the companion, noneclipsing pairs in ET Boo and VW LMi. A particularly interesting case is VW LMi, for which the period of the mutual revolution of the two spectroscopic binaries is only 355 days. While most of the studied eclipsing pairs are contact binaries, ET Boo is composed of two double-lined detached binaries, and HL Dra is a single-lined detached or semidetached system. Five systems of this group have been observed spectroscopically before: TX Cnc, V1073 Cyg, AK Her (as a single-lined binary), V566 Oph, and AG Vir, but our new data are of much higher quality than in the previous studies.

The Dwarf project: Eclipsing binaries – precise clocks to discover exoplanets

We present a new observational campaign, Dwarf, aimed at detection of circumbinary extrasolar planets using the timing of the minima of low-mass eclipsing binaries. The observations will be performed within an extensive network of relatively small to medium-size telescopes with apertures of similar to 20-200 cm. The starting sample of the objects to be monitored contains (i) low-mass eclipsing binaries with M and K components, (ii) short-period binaries with a sdB or sdO component, and (iii) post-common-envelope systems containing a WD, which enable to determine minima with high precision. Since the amplitude of the timing signal increases with the orbital period of an invisible third component, the timescale of the project is long, at least 5-10 years. The paper gives simple formulas to estimate the suitability of individual eclipsing binaries for the circumbinary planet detection. Intrinsic variability of the binaries (photospheric spots, flares, pulsation etc.) limiting the accuracy of the minima timing is also discussed. The manuscript also describes the best observing strategy and methods to detect cyclic timing variability in the minima times indicating the presence of circumbinary planets. First test observations of the selected targets are presented ((c) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Recent photometry of symbiotic stars

We present new photometric observations of 15 symbiotic stars covering their last orbital cycle(s) from 2003.9 to 2007.2. We obtained our data by both classical photoelectric and CCD photometry. Main results are: EG And brightened by ∼0.3 mag in U from 2003. A ∼0.5 mag deep primary minimum developed in the U light curve (LC) at the end of 2006. ZAnd continues its recent activity that began during the 2000 autumn. A new small outburst started in summer of 2004 with a peak U magnitude of ∼ 9.2. During the spring of 2006 the star entered a massive outburst. It reached its historical maximum at U ∼ 8.0 in 2006 July. AEAra erupted in 2006 February with Δmvis ∼ 1.2 mag. BF Cyg entered a new active stage in 2006 August. A brightness maximum (U ∼ 9.4) was measured during 2006 September. CH Cyg persists in a quiescent phase. During 2006 June–December a ∼ 2 mag decline in all colours was measured. CI Cyg started a new active phase during 2006 May–June. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation

Haumea—one of the four known trans-Neptunian dwarf planets—is a very elongated and rapidly rotating body. In contrast to other dwarf planets, its size, shape, albedo and density are not well constrained. The Centaur Chariklo was the first body other than a giant planet known to have a ring system, and the Centaur Chiron was later found to possess something similar to Chariklo’s rings. Here we report observations from multiple Earth-based observatories of Haumea passing in front of a distant star (a multi-chord stellar occultation). Secondary events observed around the main body of Haumea are consistent with the presence of a ring with an opacity of 0.5, width of 70 kilometres and radius of about 2,287 kilometres. The ring is coplanar with both Haumea’s equator and the orbit of its satellite Hi’iaka. The radius of the ring places it close to the 3:1 mean-motion resonance with Haumea’s spin period—that is, Haumea rotates three times on its axis in the time that a ring particle completes one revolution. The occultation by the main body provides an instantaneous elliptical projected shape with axes of about 1,704 kilometres and 1,138 kilometres. Combined with rotational light curves, the occultation constrains the three-dimensional orientation of Haumea and its triaxial shape, which is inconsistent with a homogeneous body in hydrostatic equilibrium. Haumea’s largest axis is at least 2,322 kilometres, larger than previously thought, implying an upper limit for its density of 1,885 kilograms per cubic metre and a geometric albedo of 0.51, both smaller than previous estimates. In addition, this estimate of the density of Haumea is closer to that of Pluto than are previous estimates, in line with expectations. No global nitrogen- or methane-dominated atmosphere was detected.

MOST observations of the young open cluster NGC 2264

Context. Photometric time series obtained from space are one of the best ways to study pulsations in pre-main sequence (PMS) stars, especially as the corresponding amplitudes are at the millimagnitude level or below. We present high-precision time-series photometry of stars in the field of NGC 2264 obtained with the MOST (Microvariability & Oscillations of STars) satellite. Aims. A search for pulsating A and F type members of NGC 2264 with ultra-precise MOST photometry was conducted. Methods. 68 stars in the field of NGC 2264 were observed simultaneously with the MOST satellite, 34 of which were previously identified as potential targets to search for PMS pulsation. The routines SigSpec and Period04 were used for the frequency analysis. Results. We discovered pulsation in 4 potential A and F type PMS members of NGC 2264 with frequencies between 2.7 h and 23 min. For one of the PMS pulsators identified with MOST after the first days of observation, simultaneous ground-based Stromgren photometry was obtained with the OSN 0.9 m telescope and confirms the highest frequency identified in the MOST photometry. 26 stars with other (i.e., hotter and cooler) spectral types show clear variability: SPB and γ Doradus pulsation, red giant oscillations, eclipsing binaries and variability caused by rotational modulation.

Transient Jets in the Symbiotic Prototype Z Andromedae

We present the development of collimated bipolar jets from the symbiotic prototype Z And that appeared and disappeared during its 2006 outburst. We monitored the outburst with optical high-resolution spectroscopy and multicolor UBVR C photometry. In 2006 July, Z And reached its historical maximum at U ~ 8.0. After ~1 mag decline in mid-August, it kept its brightness at a high level of U ~ 9 up to 2007 January. During this period, rapid photometric variations with ?m ~ 0.06 mag on the timescale of hours developed. Simultaneously, high-velocity satellite components appeared on both sides of the H? and H? emission line profiles. Their presence was transient, being detected to the end of 2006. They were launched asymmetrically with a red/blue velocity ratio of 1.2-1.3. From about mid-August onward they became symmetric at ~?1200 km s?1, reducing the velocity to ~?1100 km s?1 at their disappearance. The spectral properties of these satellite emissions indicated the ejection of bipolar jets collimated within an average opening angle of 61. If the jets were expelled at the escape velocity, then the mass of the accreting white dwarf is M WD ~ 0.64 M ?. We estimated the average outflow rate via jets to M ? yr?1, during their August-September maximum, which corresponds to the emitting mass in jets, M em jet ~ 6 ? 10?10(R jet/1 AU)3/2 M ?. During their lifetime, the jets released a total mass of M total jet 7.4 ? 10?7 M ?. 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.

CONSTRAINTS ON A SECOND PLANET IN THE WASP-3 SYSTEM*

There have been previous hints that the transiting planet WASP-3b is accompanied by a second planet in a nearby orbit, based on small deviations from strict periodicity of the observed transits. Here we present 17 precise radial velocity (RV) measurements and 32 transit light curves that were acquired between 2009 and 2011. These data were used to refine the parameters of the host star and transiting planet. This has resulted in reduced uncertainties for the radii and masses of the star and planet. The RV data and the transit times show no evidence for an additional planet in the system. Therefore, we have determined the upper limit on the mass of any hypothetical second planet, as a function of its orbital period.

An active binary XY UMa revisited

New extensive multicolour photoelectric photometry, performed since 1994, is presented. 17 more- or-less complete light curves were obtained and analyzed. The Wilson-Devinney code applied to the BVRI light curves without the maculation eect together with published spectroscopic mass ratio and semi-major axis yielded new absolute parameters of the eclipsing pair: m1 =1 :10 M, m2 =0 :66 M, R1 =1 :16 R, R2 =0 :63 R, a =3 :107 R and the orbital inclination i =8 0:9. The observed orbital period changes are conclusively explained by the mutual action of the third body in the system (P3 = 30 years) and the maculation eects. Simultaneous analysis of the period changes and the visual brightness excludes the possibility of their explanation by Applegates mechanism. The dierences in the maxima heights caused by the maculation exhibit variations with the period of 70910 days. The distance to the system d =8 65 pc determined from the absolute dimensions and luminosities of the components is larger than the Hipparcos astrometric value d =6 6 6p c.

The nearby eclipsing stellar system δ Velorum - II. First reliable orbit for the eclipsing pair

Context. The nearby multiple system δ Velorum contains a widely detached eclipsing binary and a third component. Aims. We take advantage of this system offering the opportunity to determine the set of fundamental parameters (masses, luminosities, and radii) of three coeval stars with sufficient precision to test models of stellar evolution. Methods. Extensive high-resolution spectroscopy is analyzed by the broadening function technique to provide the first spectroscopic orbit of the eclipsing pair. Simultaneous analysis of the spectroscopic data and the SMEI satellite light curve is performed to provide astrophysical parameters for the components. We use a modified Roche model assuming an eccentric orbit and asynchronous rotation. Results. The observations show that components of the eclipsing pair rotate at about two-thirds of the break-up velocity, which excludes any chemical peculiarity and results in a non-uniform surface brightness. Although the inner orbit is eccentric, no apsidal motion is seen during the SMEI photometric observations. For the inner orbit, the orbital parameters are eccentricity e = 0.290, longitude of the periastron passage ω = 109 ◦ , and inclination 89.0 ◦ .