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Register a new userThe Short Period End of the Distribution of Contact Binary Stars
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Contact binary systems (also known as W UMa systems) consist of a pair of hydrogen-burning dwarf stars orbiting each other so closely that they share a common envelope. Although they are relatively common, there is as yet no established consensus on the principle evolutionary questions surrounding them: how do they form, how do they evolve over time, what do they become? One observational clue to their evolutionary history has been the abrupt termination of the orbital period distribution around 5.2 hours. We have undertaken an observational study of this by 1) discovery of fast W UMa systems in our Calvin-Rehoboth Observatory data archive, 2) follow-up with the Calvin-Rehoboth Observatory of candidate fast systems from the Catalina Sky Survey, and 3) follow-up of other reports of potentially fast systems in other recently published surveys. We find the follow-up to have been particularly important as many surveys taken for other purposes lead to ambiguous or incorrect claims for periods less than five hours. Our results to date may be characterized as showing two distinct components: the steeply decaying tail associated with the previously known cutoff along with a low-amplitude, but apparently uniform distribution that extends down to 3.6 hours. The confirmation at greater sensitivity of the abruptness of the cutoff seems to imply that the dominant mechanism for system formation (or the mechanism that determines system lifetime) does have a strong period dependence. At the same time, there appears to be a second mechanism at work as well which leads to the formation of the ultrafast component of the histogram.
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A present prevailing open problem planetary nebulae research, and photoionized gaseous nebulae research at large, is the systematic discrepancies in ionic abundances derived from recombination and collisionally excited lines in many H II regions and planetary nebulae. Peimbert (1967) proposed that these discrepancies were due to temperature fluctuations in the plasma, but the amplitude of such fluctuations remain unexplained by standard phtoionization modeling. In this letter we show that large amplitude temperature oscillations are expected to form in gaseous nebulae photoionized by short-period binary stars. Such stars yield periodically varying ionizing radiation fields, which induce periodic oscilla- tions in the heating-minus-cooling function across the nebula. For flux oscillation periods of a few days any temperature perturbations in the gas with frequencies similar to those of the ionizing source will undergo resonant amplification. In this case, the rate of growth of the perturbations increases with the amplitude of the variations of the ionizing flux and with decreasing nebular equilibrium temperature. We also present a line ratios diagnostic plot that combines [O III] collisional lines and O II recombination lines for diagnosing equilibrium and fluctuation am- plitude temperatures in gaseous nebulae. When applying this diagnostic to the planetary nebula M 1-42 we find an equilibrium temperature of ~6000 K and a resonant temperature fluctuation amplitude (Trtf ) of ~4000 K. This equilibrium temperature is significantly lower than the temperature estimated when temperature perturbations are ignored.
The two objects 1SWASP J150822.80-054236.9 and 1SWASP J160156.04+202821.6 were initially detected from their SuperWASP archived light curves as candidate eclipsing binaries with periods close to the short-period cut-off of the orbital period distribution of main sequence binaries, at ~0.2 d. Here, using INT spectroscopic data, we confirm them as double-lined spectroscopic and eclipsing binaries, in contact configuration. Following modelling of their visual light curves and radial velocity curves, we determine their component and system parameters to precisions between ~2 and 11%. The former system contains 1.07 and 0.55 M_sun components, with radii of 0.90 and 0.68 R_sun respectively; its primary exhibits pulsations with period 1/6 the orbital period of the system. The latter contains 0.86 and 0.57 M_sun components, with radii of 0.75 and 0.63R_sun respectively.
SuperWASP light curves for 53 W UMa-type eclipsing binary (EB) candidates, identified in previous work as being close to the contact binary short-period limit, were studied for evidence of period change. The orbital periods of most of the stars were confirmed, and period decrease, significant at more than 5 sigma, was observed in three objects: 1SWASP J174310.98+432709.6 (-0.055 pm0.003 s/yr), 1SWASP J133105.91+121538.0 (-0.075 pm0.013 s/yr) and 1SWASP J234401.81-212229.1 (-0.313 pm0.019 s/yr). The magnitudes of the observed period changes cannot be explained by magnetic braking or gravitational radiation effects, and are most likely primarily due to unstable mass transfer from primary to secondary components, possibly accompanied by unstable mass and angular momentum loss from the systems. If these period decreases persist, the systems could merge on a relatively short timescale.
We present our new photometry of DV Psc obtained in 2010 and 2011, and new spectroscopic observation on Feb. 14, 2012. During our observations, three flare-like events might be detected firstly in one period on DV Psc. The flare rate of DV Psc is about 0.017 flares per hour. Using Wilson-Devinney program, we derived the preliminary starspot parameters. Moreover, the magnetic cycle is 9.26(+/-0.78) year analyzed by variabilities of Max.I - Max.II.
In this study we determined precise orbital and physical parameters of the very short period low-mass contact binary system CC Com. The parameters are obtained by analysis of the new CCD data with the archival spectroscopic data. The physical parameters of the components derived as $M_textrm{c}$ = 0.717(14) $M_{odot}$, $M_textrm{h}$ = 0.378(8) $M_{odot}$, $R_textrm{c}$ = 0.708(12) $R_{odot}$, $R_textrm{h}$ = 0.530(10) $R_{odot}$, $L_textrm{c}$ = 0.138(12) $L_{odot}$, $L_textrm{h}$ = 0.085(7) $L_{odot}$, and the distance of the system is estimated as 64(4) pc. The times of minima obtained in this study and with those published before enable us to calculate the mass transfer rate between the components which is $1.6times10^{-8}$ M$_{odot}$yr$^{-1}$. Finally, we discuss the possible evolutionary scenario of CC Com.
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