The shortest period field contact binary Rucinski, Slavek M.; Pribulla, Theodor
Monthly notices of the Royal Astronomical Society,
08/2008, Letnik:
388, Številka:
4
Journal Article
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Photometric and spectroscopic results for the contact binary GSC 01387–00475 (ASAS 083128+1953.1) are presented. The existence of this binary with the orbital period of P= 0.2178 d strengthens the ...argument that the cut-off of the period distribution for contact binaries – until now defined by CC Comae – is very sharp. The only case of a still shorter period is known in a globular cluster where more compact contact configurations are in fact expected. While the spectroscopic orbit of GSC 01387–00475 is well defined, the low orbital inclination of the binary and the presence of a spectroscopic companion contributing about 1/3 of the total light conspire to reduce the photometric variability to ≃0.09 mag. The photometric data are currently inadequate to identify the source of the small amplitude (0.02–0.03 mag) intrinsic variability of the system.
Through photometric monitoring of the extended transit window of HD 97658b with the MOST space telescope, we have found that this exoplanet transits with an ephemeris consistent with that predicted ...from radial velocity measurements. The mid-transit times are 5.6sigma earlier than those of the unverified transit-like signals reported in 2011, and we find no connection between the two sets of events. The transit depth together with our determined stellar radius (Rlow * = (ProQuest: Formulae and/or non-USASCII text omitted) Rmiddot in circle) indicates a (ProQuest: Formulae and/or non-USASCII text omitted) R+ in circle super-Earth. When combined with the radial velocity determined mass of 7.86 + or - 0.73 M sub(+ in circle), our radius measure allows us to derive a planet density of (ProQuest: Formulae and/or non-USASCII text omitted) g cm super(-3). Models suggest that a planet with our measured density has a rocky core that is enveloped in an atmosphere composed of lighter elements. The star of the HD 97658 system is the second brightest known to host a transiting super-Earth, facilitating follow-up studies of this not easily daunted, warm and likely volatile-rich exoplanet.
Observations of β Lyr in four months of 2018 by three BRIght Target Explorer (BRITE) Constellation satellites, the red-filter BRITE-Toronto and BRITE-Heweliusz, and the blue-filter BRITE-Lem, ...permitted a first, limited look into the light-curve variability in two spectral bands. The variations were found to be well correlated outside the innermost phases of the primary eclipses with the blue variations appearing to have smaller amplitudes than the red; this reduction may reflect their presumed origin in the cooler, outer parts of the accretion disk. This result must be confirmed with more extensive material as the current conclusions are based on observations spanning slightly less than three orbital cycles of the binary. The assumption of an instrumental problem and the applied corrections made to explain the unexpectedly large amplitude of the red-filter light curve observed with the BRITE-Toronto satellite in 2016 are fully confirmed by the 2018 results.
It is unclear how very close binary stars form, given that during the pre-main-sequence phase the component stars would have been inside each other. One hypothesis is that they formed farther apart ...but were brought in closer after formation by gravitational interaction with a third member of the system. If so, all close binaries should be members of triple (or higher order) systems. As a test of this prediction, we present a search for the signature of third components in archival spectra of close binaries. In our sample of 75 objects, 23 show evidence for the presence of a third component, down to a detection limit of tertiary flux contributions of about 0.8% at 5200 A (considering only contact and semidetached binaries, we find 20 out of 66). In a homogeneous subset of 59 contact binaries, we are fairly confident that the 15 tertiaries we have detected are all tertiaries present with mass ratios 0.28 M3/M12 0.75 and implied outer periods P 106 days. We find that if the frequency of tertiaries were the same as that of binary companions to solar-type stars, one would expect to detect about 12 tertiaries. In contrast, if all contact binaries were in triple systems, one would expect about 20. Thus, our results are not conclusive but are sufficiently suggestive to warrant further studies.
BRITE-Constellation is devoted to high-precision optical photometric monitoring of bright stars, distributed all over the Milky Way, in red and/or blue passbands. Photometry from space avoids the ...turbulent and absorbing terrestrial atmosphere and allows for very long and continuous observing runs with high time resolution and thus provides the data necessary for understanding various processes inside stars (e.g., asteroseismology) and in their immediate environment. While the first astronomical observations from space focused on the spectral regions not accessible from the ground it soon became obvious around 1970 that avoiding the turbulent terrestrial atmosphere significantly improved the accuracy of photometry and satellites explicitly dedicated to high-quality photometry were launched. A perfect example is BRITE-Constellation, which is the result of a very successful cooperation between Austria, Canada and Poland. Research highlights for targets distributed nearly over the entire HRD are presented, but focus primarily on massive and hot stars.
The time sequence of 105 spectra covering one full orbital period of AA Dor has been analysed. Direct determination of V sin i for the sdOB component from 97 spectra outside of the eclipse for the ...lines Mg ii 4481 Å and Si iv 4089 Å clearly indicated a substantially smaller value than estimated before. Detailed modelling of line-profile variations for eight spectra during the eclipse for the Mg ii 4481 Å line, combined with the out-of-eclipse fits, gave V sin i= 31.8 ± 1.8 km s−1. The previous determinations of V sin i, based on the He ii 4686 Å line, appear to be invalid because of the large natural broadening of the line. With the assumption of the solid-body, synchronous rotation of the sdOB primary, the measured values of the semi-amplitude K1 and V sin i lead to the mass ratio q= 0.213 ± 0.013 which in turn gives K2 and thus the masses and radii of both components. The sdOB component appears to be less massive than assumed before, M1= 0.25 ± 0.05 M⊙, but the secondary has its mass–radius parameters close to theoretically predicted for a brown dwarf, M2= 0.054 ± 0.010 M⊙ and R2= 0.089 ± 0.005 R⊙. Our results do not agree with the recent determination of Vŭcković et al. based on a K2 estimate from line-profile asymmetries.
We have used the MOST (Microvariability and Oscillations of STars) microsatellite to obtain four weeks of contiguous high-precision broad-band visual photometry of the O7.5III(n)((f)) star ξ Persei ...in 2011 November. This star is well known from previous work to show prominent DACs (discrete absorption components) on time-scales of about 2 d from UV spectroscopy and non-radial pulsation with one (l = 3) p-mode oscillation with a period of 3.5 h from optical spectroscopy. Our MOST-orbit (101.4 min) binned photometry fails to reveal any periodic light variations above the 0.1 mmag 3σ noise level for periods of a few hours, while several prominent Fourier peaks emerge at the 1 mmag level in the two-day period range. These longer period variations are unlikely due to pulsations, including gravity modes. From our simulations based upon a simple spot model, we deduce that we are seeing the photometric modulation of several corotating bright spots on the stellar surface. In our model, the starting times (random) and lifetimes (up to several rotations) vary from one spot to another yet all spots rotate at the same period of 4.18 d, the best-estimated rotation period of the star. This is the first convincing reported case of corotating bright spots on an O star, with important implications for drivers of the DACs (resulting from corotating interaction regions) with possible bright-spot generation via a breakout at the surface of a global magnetic field generated by a subsurface convection zone.
Results of the time variability monitoring of the two classical T Tauri stars, RU Lup and IM Lup, are presented. Three photometric data sets were utilized: (1) simultaneous (same field) MOST ...satellite observations over four weeks in each of the years 2012 and 2013, (2) multicolour observations at the South African Astronomical Observatory in April-May of 2013, (3) archival V-filter All Sky Automated Survey (ASAS) data for nine seasons, 2001-2009. They were augmented by an analysis of high-resolution, public-domain VLT-UT2 Ultraviolet Visual Echelle Spectrograph spectra from the years 2000 to 2012. From the MOST observations, we infer that irregular light variations of RU Lup are caused by stochastic variability of hotspots induced by unstable accretion. In contrast, the MOST light curves of IM Lup are fairly regular and modulated with a period of about 7.19-7.58 d, which is in accord with ASAS observations showing a well-defined 7.247 plus or minus 0.026 d periodicity. We propose that this is the rotational period of IM Lup and is due to the changing visibility of two antipodal hotspots created near the stellar magnetic poles during the stable process of accretion. Re-analysis of RU Lup high-resolution spectra with the broadening function approach reveals signs of a large polar coldspot, which is fairly stable over 13 years. As the star rotates, the spot-induced depression of intensity in the broadening function profiles changes cyclically with period 3.710 58 d, which was previously found by the spectral cross-correlation method.
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