Context. EE Cep is an unusual long-period (5.6 yr) eclipsing binary discovered during the mid-twentieth century. It undergoes almost-grey eclipses that vary in terms of both depth and duration at ...different epochs. The system consists of a Be type star and a dark dusty disk around an invisible companion. EE Cep together with the widely studied ε Aur are the only two known cases of long-period eclipsing binaries with a dark, dusty disk component responsible for periodic obscurations. Aims. Two observational campaigns were carried out during the eclipses of EE Cep in 2003 and 2008/9 to verify whether the eclipsing body in the system is indeed a dark disk and to understand the observed changes in the depths and durations of the eclipses. Methods. Multicolour photometric data and spectroscopic observations performed at both low and high resolutions were collected with several dozen instruments located in Europe and North America. We numerically modelled the variations in brightness and colour during the eclipses. We tested models with different disk structure, taking into consideration the inhomogeneous surface brightness of the Be star. We considered the possibility of disk precession. Results. The complete set of observational data collected during the last three eclipses are made available to the astronomical community. The 2003 and 2008/9 eclipses of EE Cep were very shallow. The latter is the shallowest among all observed. The very high quality photometric data illustrate in detail the colour evolution during the eclipses for the first time. Two blue maxima in the colour indices were detected during these two eclipses, one before and one after the photometric minimum. The first (stronger) blue maximum is simultaneous with a “bump” that is very clear in all the UBV(RI)C light curves. A temporary increase in the I-band brightness at the orbital phase ~0.2 was observed after each of the last three eclipses. Variations in the spectral line profiles seem to be recurrent during each cycle. The Na i lines always show at least three absorption components during the eclipse minimum and strong absorption is superimposed on the Hα emission. Conclusions. These observations confirm that the eclipsing object in EE Cep system is indeed a dark, dusty disk around a low luminosity object. The primary appears to be a rapidly rotating Be star that is strongly darkened at the equator and brightened at the poles. Some of the conclusions of this work require verification in future studies: (i) a complex, possibly multi-ring structure of the disk in EE Cep; (ii) our explanation of the “bump” observed during the last two eclipses in terms of the different times of obscuration of the hot polar regions of the Be star by the disk; and (iii) our suggested period of the disk precession (~11–12 Porb) and predicted depth of about 2\hbox{$\fm$}.m for the forthcoming eclipse in 2014.
Since pulsating subdwarf B (sdBV or EC14026) stars were first discovered, observational efforts have tried to realize their potential for constraining the interior physics of extreme horizontal ...branch stars. Difficulties encountered along the way include uncertain mode identifications and a lack of stable pulsation mode properties. Here we report on Feige 48, an sdBV star for which follow-up observations have been obtained spanning more than four years. These observations show some stable pulsation modes. We resolve the temporal spectrum into five stable pulsation periods in the range 340–380 s with amplitudes less than 1 per cent, and two additional periods that appear in one data set each. The three largest amplitude periodicities are nearly equally spaced, and we explore the consequences of identifying them as a rotationally split ℓ= 1 triplet by consulting a representative stellar model. The general stability of the pulsation amplitudes and phases allows us to use the pulsation phases to constrain the time-scale of evolution for this sdBV star. Additionally, we are able to place interesting limits on any stellar or planetary companion to Feige 48.
High-resolution spectroscopic observations around the Hα line and BVRI photometry of the eclipsing short-period RS CVn star WY Cnc are presented. The solutions of our radial velocity curves and light ...curves yielded the following values for masses and radii of the components: $M_{\rm 1}=0.84$ $M_{\odot}$, $M_{\rm 2}=0.46$ $M_{\odot}$, $R_{\rm 1}=1.06$ $R_{\odot}$, $R_{\rm 2}=0.65$ $R_{\odot}$. The measured rotational broadenings of the spectral lines correspond to equatorial velocities $V_{\rm 1}=78$ km s-1 and $V_{\rm 2}=49$ km s-1. The distortions of our multicolor light curve of WY Cnc were reproduced by two cool spots on the primary star. An increase of the out-of-eclipse brightness by 0.1 mag in February 2001 was detected. Our spectra show Hα line in emission from the secondary star. The chromospheric activity appeared also in the observed emission cores of the CaII H and K lines as well as the CaI 6494 line.
Spectroscopic observations around the Hα line and BVR photometry of the eclipsing short-period RS CVn-star CG Cyg are presented. The solutions of the radial velocity curves and the light curves ...yielded the following masses and radii of the star components: $M_{\rm 1}=0.97~ M_{\odot}$, $M_{\rm 2}=0.80~M_{\odot}$, $R_{\rm 1}=1.00 ~R_{\odot}$, $R_{\rm 2}=0.83 ~R_{\odot}$. The measured rotational broadenings of the observed lines correspond to equatorial velocities $V_{\rm 1}=80$ km s-1 and $V_{\rm 2}=66$ km s-1. The distortions of our multicolor light curve were reproduced by two cool spots on the primary star. The strong absorption feature between the spectral lines of the two stars was explained by extended structure around the mass center of the system. The Hα emission line of the secondary star in the August spectra was attributed to a prolonged flare of this star.
This paper analyses the Whole Earth Telescope observations of HL Tau 76, the first discovered pulsating DA white dwarf. The star was observed during two Whole Earth Telescope campaigns. It was a ...second priority target during the XCOV13 campaign in 1996 and the first priority one during the XCOV18 campaign in 1999. The 1999 campaign reached 66.5% duty cycle. With a total duration of 18 days, the frequency resolution achieved is 0.68 μHz. With such a frequency resolution, we were able to find as many as 78 significant frequencies in the power spectrum, of which 34 are independent frequencies after removal of all linear combinations. In taking into account other frequencies present during the 1996 WET campaign and those present in earlier data, which do not show up in the 1999 data set, we find a total of 43 independent frequencies. This makes HL Tau 76 the richest ZZ Ceti star in terms of number of observed pulsation modes. We use those pulsation frequencies to determine as much as possible of the internal structure of HL Tau 76. The pulsations in HL Tau 76 cover a wide range of periods between 380 s and 1390 s. We propose an identification for 39 of those 43 frequencies in terms of $\ell=1$ and $\ell=2$ non-radial g-modes split by rotation. We derive an average rotation period of 2.2 days. The period distribution of HL Tau 76 is best reproduced if the star has a moderately “thick” hydrogen mass fraction log $q_{\rm H} \geq -7.0$. The results presented in this paper constitute a starting point for a detailed comparison of the observed periods with the periods calculated for models as representative as possible of HL Tau 76.
Context. The so-called Barbarian asteroids share peculiar, but common polarimetric properties, probably related to both their shape and composition. They are named after (234) Barbara, the first on ...which such properties were identified. As has been suggested, large scale topographic features could play a role in the polarimetric response, if the shapes of Barbarians are particularly irregular and present a variety of scattering/incidence angles. This idea is supported by the shape of (234) Barbara, that appears to be deeply excavated by wide concave areas revealed by photometry and stellar occultations. Aims. With these motivations, we started an observation campaign to characterise the shape and rotation properties of Small Main-Belt Asteroid Spectroscopic Survey (SMASS) type L and Ld asteroids. As many of them show long rotation periods, we activated a worldwide network of observers to obtain a dense temporal coverage. Methods. We used light-curve inversion technique in order to determine the sidereal rotation periods of 15 asteroids and the convergence to a stable shape and pole coordinates for 8 of them. By using available data from occultations, we are able to scale some shapes to an absolute size. We also study the rotation periods of our sample looking for confirmation of the suspected abundance of asteroids with long rotation periods. Results. Our results show that the shape models of our sample do not seem to have peculiar properties with respect to asteroids with similar size, while an excess of slow rotators is most probably confirmed.
Eccentricity of Selected Eclipsing Systems Ogłoza, W.; Kreiner, J. M.; Stachowski, G. ...
Proceedings of the International Astronomical Union,
07/2011, Letnik:
7, Številka:
S282
Journal Article
Recenzirano
This paper presents the results of verification of known stars showing evidence of orbital eccentricity and apsidal motion.
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