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CCD Times of Minima of Selected Eclipsing Binaries
374 CCD minima observations of 187 eclipsing binaries are presented. Theobserved stars were chosen mainly from catalogue BRKA of observingprogramme of Variable Star Section of CAS.
| The new pre-cataclysmic binary PG 2200+085
Aims.We present the results of spectroscopic- and orbit-sampledphotometric observations of the faint UV-excess object PG 2200+085. Methods: .The optical CCD photometry observations of this object wereperformed by the Russian-Turkish 1.5-m telescope RTT150 at the TUBITAKNational Observatory (Turkey). The long-slit optical spectroscopyobservations with 2.6 Å resolution were carried out by 6-mtelescope BTA at the Special Astrophysical Observatory (Russia).Results: .The photometric variations over two nights are almostsinusoidal with an amplitude Δ mV = 0.04m and a periodof P = 0.3186 d. Such a light curve is typical of a detached closebinary with an illumination effect or the ellipsoidal deformation of asecondary star. The observed spectrum clearly displays a featurelessblue continuum of a hot component and a rich absorption-line andmolecular band K-star spectrum. The CaII line profiles with strongemission cores are remarkably similar to those of V471 Tau.Conclusions: .We tentatively classify PG 2200+085 as a pre-cataclysmicbinary of the V471 Tau type.
| 165. List of Timings of Minima Eclipsing Binaries by BBSAG Observers
Not Available
| The lack of close binaries among hot horizontal branch stars in NGC 6752
Aims.We present the results of a spectroscopic search for close binariesamong horizontal branch (HB) stars in NGC 6752.Methods: .We used the ESO VLT-FORS2 instrument to obtain mediumresolution (R=4100) spectra of 51 hot HB stars with 8 000 K ≤ T_eff≤ 32 000 K during four consecutive nights. Eighteen of our targetsare extreme horizontal branch (EHB) stars with {T_eff}≥ 22 000 K.Radial velocity variations were measured with cross-correlationtechniques, previously evaluated the statistical and systematic errorsassociated with them. Results: .No close binary system has beendetected among our 51 targets. The data corrected for instrumentaleffects indicate that the radial velocity variations are always below≈15 km s-1 (3σ level). From a statistical analysisof our results, we conclude that (at 95% confidence level) the fractionof binaries with a 0.5 {Mȯ} companion among EHB starsin NGC 6752 is smaller than 20%. Conclusions:.This empirical evidence sharply contrasts with what has been found forhot subdwarfs in the field, and opens new questions about the formationof EHB stars in globular clusters (and possibly in the field as well).
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| Times of Minima for Neglected Eclipsing Binaries in 2005
Times of minima obtained at Rolling Hills Observatory during 2005 for anumber of neglected eclipsing binaries are presented.
| Precise CCD Times of Minima of Selected Eclipsing Binaries
We present 135 precise CCD minima timings for 93 eclipsing binariesobtained at Ondrejov observatory during 2003-2004.
| HS 0702+6043: a star showing both short-period p-mode and long-period g-mode oscillations
Context: .The hot subdwarf B star HS 0702+6043 isknown as a large-amplitude, short-period p-mode pulsator of theEC 14026 type. Its atmospheric parameters place it atthe common boundary between the empirical instability regions of theEC 14026 variables and the typically coolerlong-period g-mode pulsators of the PG 1716 kind. Aims: .We analyse and interpret the photometric variability ofHS 0702+6043 in order to explore itsasteroseismological potential. Methods: .We report on rapid wideband CCD photometric observations to follow up on and confirm theserendipitous discovery of multiperiodic long-period luminosityvariations with typical time scales of ~1 h in HS0702+6043, in addition to the two previously known pulsationsat 363 s and 383 s. In particular, we isolate a relatively low-amplitude(~4 mmag), long-period (3538±130 s) light variation.Results: .We argue that the most likely origin for this luminosityvariation is the presence of an excited g-mode pulsation. If confirmed,HS 0702+6043 would constitute a rare addition to thevery select class of pulsating stars showing simultaneously parts oftheir pressure and gravity mode pulsation spectra. Theasteroseismological potential of such stars is immense, and HS0702+6043 thus becomes a target of choice for futureinvestigations. While our discovery appears consistent with the locationof HS 0702+6043 at the common boundary between thetwo families of pulsating sdB stars, it does challenge theory's currentdescription of stability and driving mechanisms in pulsating Bsubdwarfs. Conclusions: .
| Precatalysmic binary systems.
Not Available
| Helium, Carbon and Silicon Abundances in the HW VIR Eclipsing Binary Subdwarf-B Primary
Light curve solutions show HW Vir and PG 1336-018 to be remarkablysimilar eclipsing binaries. The subdwarf-B (sdB) primary of PG 1336-018is a pulsator but pulsation is not detected in the sdB primary of HWVir. Ultraviolet spectra were used to obtain carbon and siliconabundances in the sdB primary of HW Vir; in due course these should becompared with those in the sdB primary of PG 1336-018 to see ifpulsation in the latter could be explained by the κ -mechanism,arising from higher metal abundances and microscopic diffusion.
| Minima Kurt Locher 2004-2005
Minima observed 2004..2005 by Kurt Locher visually, not accepted by IBVSas part of BBSAG Bulletin.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| 164. List of Timings of Minima Eclipsing Binaries by BBSAG Observers
Not Available
| CCD Times of Minima of Several Eclipsing Binaries
54 CCD minima timings of 28 eclipsing binaries made mainly by the authorare presented.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Six detached white-dwarf close binaries
We determine the orbits of four double-degenerate systems (DDs),composed of two white dwarfs and two white-dwarf-M-dwarf binaries. Thefour DDs, WD1022+050, WD1428+373, WD1824+040 and WD2032+188, showorbital periods of 1.157155(5), 1.15674(2), 6.26602(6) and 5.0846(3) d,respectively. These periods combined with estimates for the masses ofthe brighter component, based on their effective temperatures, allow usto constrain the masses of the unseen companions. We estimate that theupper limit for the contribution of the unseen companions to the totalluminosity in the four DDs ranges between 10 and 20 per cent. In thecase of the two white-dwarf-M-dwarf binaries, WD1042-690 and WD2009+622,we calculate the orbital parameters by fitting simultaneously theabsorption line from the white dwarf and the emission core from the Mdwarf. Their orbital periods are 0.337083(1) and 0.741226(2) d,respectively. We find signatures of irradiation on the inner face of thecompanion to WD2009+622. We calculate the masses of both components fromthe gravitational redshift and the mass-radius relationship for whitedwarfs and find masses of 0.75-0.78 and 0.61-0.64Msolar forWD1042-690 and WD2009+622, respectively. This indicates that the starsprobably reached the asymptotic giant branch in their evolution beforeentering a common envelope phase. These two white-dwarf-M-dwarf binarieswill become cataclysmic variables, although not within a Hubble time,with orbital periods below the period gap.
| Times of Minima for Neglected Eclipsing Binaries in 2004
Times of minima obtained during 2004 for a number of neglected eclipsingbinaries are presented.
| Reconstructing the evolution of white dwarf binaries: further evidence for an alternative algorithm for the outcome of the common-envelope phase in close binaries
We determine the possible masses and radii of the progenitors of whitedwarfs in binaries from fits to detailed stellar evolution models anduse these to reconstruct the mass-transfer phase in which the whitedwarf was formed. We confirm the earlier finding that in the first phaseof mass transfer in the binary evolution leading to a close pair ofwhite dwarfs, the standard common-envelope formalism (theα-formalism) equating the energy balance in the system (implicitlyassuming angular momentum conservation) does not work. An algorithmequating the angular momentum balance (implicitly assuming energyconservation) can explain the observations. This conclusion is now basedon 10 observed systems rather than three. With the latter algorithm (theγ-algorithm) the separation does not change much for approximatelyequal-mass binaries. Assuming constant efficiency in the standardα-formalism and a constant value of γ, we investigate theeffect of both methods on the change in separation in general andconclude that when there is observational evidence for strong shrinkageof the orbit, the γ-algorithm also leads to this. We then extendour analysis to all close binaries with at least one white dwarfcomponent and reconstruct the mass-transfer phases that lead to thesebinaries. In this way we find all possible values of the efficiency ofthe standard α-formalism and of γ that can explain theobserved binaries for different progenitor and companion masses. We findthat all observations can be explained with a single value of γ,making the γ-algorithm a useful tool to predict the outcome ofcommon-envelope evolution. We discuss the consequences of our findingsfor different binary populations in the Galaxy, including massivebinaries, for which the reconstruction method cannot be used.
| BAV-Beobachter-Treffen 2005 in Hartha.
Not Available
| Two new EC14026 stars: PG 0048+091 and PG 0154+182
We present new time-resolved photometry for two sdB stars, PG 0048+091and PG 0154+182, which clearly shows them to be rapidly pulsating stars of the ``EC14026'' class. In PG 0048+091 we detect, with some confidence,seven frequencies between 5252 and 9368 μHz corresponding to periodsbetween 190 and 107 s. In PG 0154+182, for which our data aremuch sparser, we identify only a single frequency near 6090 μHz (164s). New spectroscopy, combined with archival (2MASS) infraredphotometry, indicates that PG 0048+091 has a companion of spectraltype near G0V-G2V, whilst PG 0154+182 has a companion of laterspectral type, probably in the range G5V-K5V.
| Beyond the iron group: Heavy metals in hot subdwarfs
We report the discovery of strong photospheric resonance lines of GaIII, Ge IV, Sn IV and Pb IV in the UV spectra of more than two dozen sdBand sdOB stars at temperatures ranging from 22 000 K to 40 000 K. Linesof other heavy elements are also detected, however in these cases moreatomic data are needed. Based on these discoveries, we present ahypothesis to explain the apparent lack of silicon in sdB stars hotterthan 32 000 K. The existence of triply ionised Ge, Sn, and Pbsuggests that rather than silicon sinking deep into the photosphere, itis removed from the star in a fractionated stellar wind. This hypothesisprovides a challenge to diffusion models of sdB stars.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS 5-26555. These observations areassociated with program #8635 and #5319.
| 163. List of Minima Timings of Eclipsing Binaries by BBSAG Observers
Not Available
| CaII Line Formation in the Spectra of Irradiated Atmospheres
We have studied the effect of external radiation on the formation of LTEand non-LTECaII lines in the spectra of A-M-star atmospheres. Threefrequency distributions were chosen for the external radiation: X-rayradiation specified by the power law at 1 16.5 keV and UV radiationspecified by blackbody distributions with the temperatures T rad=50000and 15000 K. We analyze the influence of variations in the irradiatingflux and its angle of incidence on the profiles and equivalent widths ofthe λλ3933, 3968 Å resonance doublet and theλλ8498, 8542, 8662 Å infrared triplet. For any typeof external radiation, allowing for deviations from LTE decreases thereflection effects for the CaII lines. We conclude that the CaIIprofiles do not display emission components in the spectra of opticallythick stellar atmospheres irradiated by X-rays. Therefore, CaII emissionlines observed in the radiation of cataclysmic variables must be formedin an optically thin plasma. CaII emission lines are likely to form inthe spectra of stars with UV irradiation if CaII is the dominantionization state in atmospheric layers close to the depths at which thecontinuum is formed. As a result, the spectra of symbiotic variableswith hot primaries can contain CaII lines originating on the surfaces ofthe M-giants and supergiant secondaries due to reflection effects. Theselines can be used to analyze the reflection effects and the temperaturestructure in the atmospheres of the secondaries only if non-LTE effectsare included. In the spectra of close binaries with cool white dwarfs,CaII emission lines originate in the irradiated atmospheres of thesecondaries under conditions close to thermalization. These lines can beused to study the reflection effects and calcium abundances even in anLTE approximation. We calculated the profiles and equivalent widths ofCaII lines in the spectra of the four precataclysmic variables BE UMa,EG UMa, MS Peg, and HR Cam. The observed and theoretical reflectioneffects in the λλ3933, 8542 Å emission lines for thespecified parameters of the systems and a solar calcium abundance in theatmospheres of the red dwarfs are in good agreement.
| HS 2333+3927: A new sdB+dM binary with a large reflection effect
We have discovered periodic light variations (P = 0.1718023 d) in thesdB star HS 2333+3927 in the BVR bands withamplitudes of 0.21, 0.28 and 0.33 mag, respectively. Sinusoidal radialvelocity variations at the same period were detected with asemi-amplitude of K1 = 89.6 km s-1, indicatingthat it is binary system and that the light variations are caused by thereflection effect with no eclipses. A mass function of f(m)= 0.0128Mȯ has been determined. The analysis of the light curvedid not yield a unique solution, mainly because the albedo of thesecondary is poorly constrained. Two solutions of equal quality with ahigh (A2= 1.0) and a low (A2= 0.39) albedo wereconsidered further. Variability of the Balmer line profiles, mostnotably for Hα, was discovered, probably also caused by thereflection effect. A spectroscopic analysis results in Teff =36 500 K, log g = 5.70, and log (nHe/nH) = -2.15.These characteristics are typical for sdB stars. Mass-radius relationsare derived from the results of the analysis of light andradial-velocity curves. Comparison with the observed mass-radiusrelation of the sdB star and with that of lower main sequence stars forthe companion allows us to discard the high albedo solution, because theresulting mass of the primary and the radius of the secondary would beunreasonably low. From a discussion of evolutionary models we constrainthe plausible mass of the sdB to the range between 0.29Mȯ and 0.47 Mȯ. Accordingly, the mass ofthe secondary is between 0.24 Mȯ and 0.32Mȯ, indicating a spectral type of M3 to M4. HS 2333+3927is only the sixth sdB+dM system discovered so far. An improvedmeasurement of the gravity and the projected rotational velocity of thesdB star is required to further constrain the masses and to identify theevolutionary state of the sdB star uniquely.Based on observations obtained at the German-Spanish Astronomical Center(DSAZ) at Calar Alto, the Nordic Optical Telescope (NOT) and the JacobusKapteyn Telescope (JKT) on La Palma, the Hoher List Observatory inGermany and the 80 cm telescope of the Instituto de Astrofisica deCanarias (IAC80) on Tenerife.
| High-speed photometry of the pre-cataclysmic binary HW Virginis and its orbital period change
The broad band B and V light curves of the pre-cataclysmic eclipsingbinary HW Vir were obtained. All the available eclipse timings,including the new ones, spanning 19 years were analyzed under thethird-body hypothesis. The residuals between the observed and calculatedtimes of mid-eclipse show a long-term sinusoidal variation. The analysisyields the parameters of the third-body orbit, as well as limiting massfor the tertiary object. The result of this analysis gives a light-timesemi-amplitude of 112 s, an orbital period of 18.8 yr and aneccentricity of 0.12. The mass of the third star is below thetheoretical threshold of 0.07 Mȯ for a hydrogen burningstar. Its minimum mass is about 0.022 Mȯ and for a widerange of inclinations of third-body orbit, i.e. i ≥19o,the mass is smaller than 0.07 Mȯ. Therefore, we suggestthat the third star may be a brown dwarf candidate. Combining thesemi-amplitudes of the radial velocities and the photometric light curvesolution has allowed us to model the short-period detached binary HWVir. The luminosity and radius of the dM companion are slightly largerthan that given by low-mass models.
| Photoelectric Minima of Selected Eclipsing Binaries
Not Available
| A Whole Earth Telescope campaign on the pulsating subdwarf B binary system PG 1336-018 (NY Vir)
We present results from a multisite (`Whole Earth Telescope')photometric campaign on PG 1336-018, the close eclipsing binary systemcontaining a pulsating subdwarf B (sdB) star. The main part of thecampaign (1999 April) resulted in ~172 h of observations, representing acoverage of about 47 per cent, and additional data were obtained outsidethe core campaign. Periodogram analysis shows that the light variationsare dominated by three frequencies near 5757, 5585 and 5369 μHz(~174, 179 and 186 s, respectively), although many frequencies arepresent, particularly in the range 5000-6000 μHz (~200-170 s). Weidentify, with some confidence, 28 frequencies down to a semi-amplitudeof 0.0005 in fractional intensity (equivalent to about 0.5 mmag). It isclear that the pulsation frequencies of PG 1336-018 have changedsubstantially since the 1996 discovery observations were made, and thatamplitude changes occur, at least in the dominant three frequencies, onrelatively short time-scales (of the order of a day). On the assumptionthat the pulsating star is phase-locked in the binary system, we havesearched for rotational splitting of frequencies near the orbital andhalf of the orbital period, but the results are confused by aliasing atthose frequencies (due to the data gaps caused by the eclipses). Apreliminary model qualitatively matches the distribution of frequenciesin PG 1336-018, with some good individual correspondences, but cannot beconsidered adequate because geometric cancellation should hide some ofthe modes which are apparently detected. Analysis of the pulsationsduring eclipse recovers three of the strongest modes, but the limitedeclipse data - which can, at best, be only about 9 per cent of the total- do not allow mode identification at this stage. Simulations indicatethat an overall coverage of about 80 per cent would be required for thisto be viable. An attempt was made to determine phase shifts in thepulsation frequencies as a way of directly measuring the size of thebinary orbit, but the uncertainties in the method are comparable to thelight travel time across the orbit (probably less than a second).
| New VIC photometry of the sdOB binary AA Dor and an improved photometric model
New VIC CCD photometry, obtained with integration times of 20s, of the sdOB+degenerate-dwarf eclipsing binary system AA Dor hasprovided new complete light curves with an rms scatter about a meancurve of +/-0.004 mag. These data are analysed with an improved LIGHT2light-curve synthesis code to yield more accurate determinations of theradii of both stars, the orbital inclination, and the flux ratio betweenthe two components. These radii are only a little different from thevalues derived 25 years ago from less complete data, but theuncertainties on these values are improved by a factor of 2. Theapparent discrepancy remains between the surface gravity of the sdOBprimary star obtained from the light-curve solution with the publishedspectroscopic orbit and that obtained from non-local thermodynamicequilibrium analysis of high-resolution spectra of the sdOB star.The substantial reflection effect in the system is adequatelyrepresented by the LIGHT2 code with a bolometric albedo of unity inlight curves extending from 0.35 to 2.2 μm. However, there aredifferences at individual wavelengths in the derived albedo, which mayindicate a redistribution of flux from shorter wavelengths into the Vand IC passbands.
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 48 minima times of 10 eclipsing binaries.
| 162-nd List of Minima Timings of Eclipsing Binaries by BBSAG Observers
Not Available
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