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1.
Quasisimultaneous photoelectric, polarimetric, and spectroscopic observations of the active single red dwarf LQ Hya are presented. The photometric variability of LQ Hya is fully described by a zone model. Spotted regions occupy up to 25% of the entire surface of the star with a temperature difference of 800 K between the spots and the calm photosphere. The spots are localized in the middle and low latitudes. A cyclical variation is observed in the total areas of the spotted regions and in the average latitude of the spots. The most spotted regions, local magnetic fields, and chromospherically active regions tend to concentrate in the same distinct active longitudes.  相似文献   

2.
The photoelectric observations of the neglected binary AV Hya published by Srivastava and Kandpal (1980) have been re-analyzed using Wilson-Devinney's synthetic light-curve program. The binary turns out to be a near-contact semi-detached system. The primary, more massive, more luminous and greater component, eclipsed at primary minimum, is detached from its Roche lobe (85%). The secondary fills its Roche lobe and has a temperature difference of T=,-3414 K. As with other semi-detached binaries, the secondary is more evolved than that of the primary. Thetimes of light minima of the eclipsing have been analyzed,showing that the orbital period of AV Hya undergoes acontinuous decrease with a rate of dP/dE=-8.26×10-8 day/year. The mass transfer between the twocomponents can not explain the present orbital period variationsince the secondary component is filling the Roche lobe. Theorbital period change demonstrates that the system may undergoa secular mass and angular momentum loss and the system mayevolve from the present short-period near-contact system intoan A-type contact binary.  相似文献   

3.
New differential time-series observations of KZ Hya were secured using the V filters, and 28 new times of light maximum were identified. We collected 157 times of light maximum from the literature, unpublished data and open database, and proceeded to investigate the variations of the O–C values for light maxima with the total of 185 times of light maximum. A quasi-sinusoidal character of the O–C diagram was confirmed, and this was interpreted as a light travelling time effect due to a companion moving in an eccentric (e=0.23) orbit with a period of about 24.77 years. The periods of KZ Hya were investigated and nine frequencies were determined using the Fourier decomposition method. All nine were harmonic frequencies and no other frequency was identified.  相似文献   

4.
By using data mainly from Frolovet al. (1982) for four Delta Scuti stars in eclipsing binary systems, AB Cas, Y Cam, RS Cha, and AI Hya, their physical parameters, distances, and radial pulsation modes are determined. The evolutionary track systems of Iben (1967), Paczyski (1970), and Maeder and Meynet (1988) are interpolated, in order to estimate evolutionary massesM eand agest of these variables. Their pulsation massesM Qare estimated from the fitting formulae of Faulkner (1977) and Fitch (1981). Our estimates of evolutionary massesM eand pulsation massesM Qare close to the massesM determined by Frolovet al. (1982) from the star binarity. The only exception is AB Cas, for which there is no agreement between certain star parameters.Another, independent approach is also applied to the stars RS Cha and AI Hya: by using their photometric indicesb — y andc 1 from the catalogue of López de Cocaet al. (1990) and appropriate photometric calibrations, other sets of physical parameters, distances, modes, ages, evolutionary and pulsation masses of both variables are obtained.  相似文献   

5.
In this paper, we give theBV photoelectric light curves of the Algol-type eclipsing binary EU Hydrae. We have analysed its period by means of the times of minima determined from this observation and the times of minima which other observers published. The period was found to gradually decrease with a change rate dP/dE = -3 . d 29 × 10–10. The obtained light curves have been solved using Wilson-Devinney's synthetic light-curve program. The results demonstrate that EU Hydrae is a detached system, the secondary component fills the Roche-lobe, its mass ratio is 0.205. EU Hya may evolve to be a semidetached system in which the secondary component fills the Roche-lobe.  相似文献   

6.
Photometric observations of EX Hya inB andVfilters are reported. The 67 min modulation of the light curve also is found to be in good agreement with the results of earlier studies. The (B-V) colour variation with respect to the 67 min variation is found to be opposite to those of typical colour variation during hump/superhump activity in other dwarf novae. The model of an intermediate polar is discussed.  相似文献   

7.
SW Lacertae is a short-period variable star of the W UMa-type. A total of 261 photoelectric observations for eachU, B, andV filter were obtained in 1986 while 522 photoelectric observations for eachB andV filter were obtained in 1987. All these observations were transformed to theU, B, andV colours of theUBV standard system. Nine light curves for primary and secondary eclipses were obtained, their times of minima were determined and a new linear ephemeris was obtained. The period changes of the system were also discussed.  相似文献   

8.
We discuss the results of simultaneous photoelectric and spectral observations of the flare star EV Lac. The observations of EV Lac were carried out at the National Astronomical Observatory of the Bulgarian Academy of Sciences in August 1986. The photoelectric observations were conducted in the U-color with 1 sec time integration on a 60cm telescope. The effective time of photoelectric observations was 13 hours. The spectral observations were carried out on a two-meter telescope. During one night 35 spectrograms of the star EV Lac were obtained, each of which lasted 2 minutes. The equivalent widths of the H emission line were measured. During the photoelectric observations 6 flares were recorded. One of the two comparison stars, C2 showed variable brightness.Translated fromAstrofizika, Vol. 37, No. 4, 1994.The authors consider it their pleasant duty to thank Professor L. V. Mirzoyan for valuable advice and the staff of the Rozhen Observatory of the Bulgarian Academy of Sciences for assistance during the observations.  相似文献   

9.
The formations of the blue straggler stars and the FK Com-type stars are unsolved problems in stellar astrophysics. One of the possibilities for their formations is from the coalescence of W UMa-type overcontact binary systems. Therefore, deep (f > 50%), low-mass ratio (q < 0.25) overcontact binary stars are a very important source to understand the phenomena of Blue Straggler/FK Com-type stars. Recently, 12 W UMa-type binary stars, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, V410 Aur, XY Boo, SX CrV, QX And, GSC 619-232, and AH Cnc, were investigated photometrically. Apart from TV Mus, XY boo, and GSC 619-232, new observations of the other 9 binaries were obtained. Complete light curves of the 10 systems, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, GSC 619-232, V410 Aur, XY Boo, and AH Cnc, were analyzed with the 2003 version of the W-D code. It is shown that all of those systems are deep (f > 50%), low-mass ratio (q < 0.25) overcontact binary stars. We found that the system GSC 619-232 has the highest degree of overcontact (f = 93.4%). The derived photometric mass ratio of V857 Her, q = 0.0653, indicates that it is the lowest-mass ratio system among W UMa-type binaries.Of the 12 sample stars, long-term period changes of 11 systems were found. About 58% (seven) of the sample binaries show cyclic period oscillation. No cyclic period changes were discovered for the other 5 systems, which may be caused by the short observational time interval or by insufficient observations. Therefore, we think that all W UMa-type binary stars may contain cyclic period variations. By considering the long-term period changes (both increase and decrease) of those binary stars, we proposed two evolutionary scenarios evolving from deep, low-mass ratio overcontact binaries into Blue Straggler/FK Com-type stars.  相似文献   

10.
The use of a coudé spectrograph for securing the high-resolution spectrograms necessary to follow the slow variations of radial velocity exhibited by visual binaries is discussed. Recent observations, using the spectrograph at the coudé focus of the Dominion Astrophysical Observatory's 48-in. reflector, are then presented for the systems ofα UMa,ɛ Hya,β LMi andγ Leo.  相似文献   

11.
A new period (P=2 . d 9042997) of the eclipsing binary system VZ Hydrae has been given, which is based on all the available times of minima. The period based on the photoelectric epochs has also been presented. The O?C diagram and detailed period study of VZ Hya have been presented for the first time, and the period changes have been estimated in different portions of the O?C diagram. Significant period changes do not appear to have occurred in VZ Hya, however, the O?C diagram suggests that the period of the system shows a slow tendency to increase. Period changes of 10?5 d (?) to 10?7 d have occurred around the years 1933, 1971, and 1975. All four period changes are noted in the time-interval 1918 to 1978. Upward treands appear stronger than the declining trends. Secondary minima show larger fluctuations than the primary minima. The fluctuations of the O?C values around the zero-line of VZ Hya demands notice for searching out the cause of period variations such as the presence of a third body.  相似文献   

12.
Photometric data on FG Hya obtained in 2002 and 2004 are presented. Three data sets show the exchange between A-type, W-type and the variable O'Connell effects. The photometric mass ratio  ( q = 0.1115 ± 0.0003)  derived from B and V light curves is almost the same as the spectroscopic mass ratio  ( q sp= 0.112 ± 0.004)  . The new photometric solutions reveal that FG Hya is a deep overcontact binary system  ( f = 85.6 ± 1.8 per cent)  with a spotted massive component. A period investigation, based on all available photoelectric or CCD times of light minimum, shows that the O–C curve of FG Hya can be explained as a combination of a secular period decrease and a cyclic variation with a period of 36.4 yr and an amplitude of 0.0289 d. By comparing the variation of the depth of the primary minimum with the change of the cyclic period, it is discovered that both of them may vary with the same cycle length of 36.4 yr and in the same phase. The variation of the light curve, the spotted primary component and the connection between the cyclic period change and the depth of the primary minimum, all may suggest that the G0-type component displays solar-type magnetic activity with a 36.4-yr cycle length. The long-time period decrease is interpreted by mass transfer from the more massive component to the less massive one or/and angular momentum loss due to mass outflow from the outer Lagrangian point.  相似文献   

13.
The newB andV photoelectric observations of DO Cas, obtained during 1979 and 1980, are presented, analysed, and discussed. The observations were made at the National Observatory of Athens, Greece, and their analysis was based on the frequency domain, techniques. New geometric, photometric, and absolute elements for the system are given.  相似文献   

14.
The discovery of solar-like oscillations in the giant star ξ Hya (G7 III) was reported by Frandsen et al. (2002). Their frequency analysis was very limited due to alias problems in the data set (caused by single-site observations). The extent to which the aliasing affected their analysis was unclear due to the unknown damping time of the stellar oscillation modes. In this paper we describe a simulator created to generate time series of stochastically excited oscillations, which takes as input an arbitrary window function and includes both white and non-white noise. We also outline a new method to compare a large number of simulated time series with an observed time series to determine the damping time, amplitude, and limited information on the degree of the stochastically excited modes. For ξ Hya we find the most likely amplitude to be ∼ 2 m s−1, in good agreement with theory (Houdek and Gough, 2002), and the most likely damping time to be ∼ 2 days, which is much shorter than the theoretical value of 15–20 days calculated by Houdek and Gough (2002).  相似文献   

15.
Far-infrared mapping observations of a Mira-type AGB star R Hya were carried out with the imaging photo-polarimeter ISOPHOT. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

16.
Published discussions of photometric observations of VZ Hya and CM Lac disagree as to whether the deeper eclipses are transits or occultations. The evolutionary histories of these systems are critically dependent on a resolution of the disagreement. The luminosity ratio of the components of VZ Hya, inferred from spectrograms, shows unequivocally that the deeper eclipse is a transit. The case of CM Lac is less definitive. While the photometric observations favor primary minimum as a transit, the ratio of the radii is close to unity, and neither the spectrograms nor the photometry leads to an unequivocal result. Some confusion in notation appearing in a discussion of the components of EI Cep is noted. In each of the three cases the observational evidence favors a straightforward evolutionary interpretation in which the more massive star is the larger.  相似文献   

17.
Further study of the observedU, B, V light curves of VZ Hya reveals that the primary eclipse is an occultation.  相似文献   

18.
Using Wood's (1972) model we have re-analyzed the photoelectric light curve of the eclipsing binary AI Cru, published and unsatisfactorily discussed by Ollongren (1956), in order to obtain reliable photometric elements. Our photometric solution differs considerably from Ollongren's (1956). For our photometric mass ratio,q=0.8, both components, though detached from their Roche lobes, are fairly close to a contact configuration.AI Cru, composed of a brighter and larger B5 primary and a fainter and smaller (around B9.5) secondary, is probably not a normal Main Sequence system, since the ratios of the secondary's mass and radius over the primary's turn out to be larger than expected for main sequence stars of the same spectral types.  相似文献   

19.
This Letter contains some comments on the communication by Diethelm and Locher (1988) concerning the period variations in the eclipsing binary systems EE Aqr, BZ Eri, IZ Per, and VZ Hya. Significance of the BBSAG visual observations has been discussed.  相似文献   

20.
As part of a long‐term project to determine abundances and astrophysical properties of evolved red stars in open clusters, we present high‐precision DDO photoelectric observations for a sample of 33 red giant candidates projected in the fields of nine Galactic open clusters. These data are supplemented with UBV photoelectric photometry of 24 of these stars as well as with CORAVEL radial‐velocity observations for 13 red giant candidates in four of the clusters. We also present Washington photoelectric photometry of a small sample of red giant candidates of the open cluster Ruprecht 97. The likelihood of cluster membership for each star photometrically observed and for 23 additional red giant candidates with UBV and DDO data available in the literature, is evaluated by using two independent photometric criteria. Nearly 82% of the analysed stars are found to have a high probability of being cluster giants. Photometric membership probabilities show very good agreement with those obtained from CORAVEL radial velocities. While E (B –V) colour excesses were determined from combined B – V and DDO colours, calibrations of the DDO system were used to derive MK spectral types, effective temperatures and metallicities. The derived DDO metallicities range between values typical of moderately metal‐poor clusters ([Fe/H] = –0.19) to moderately metal‐rich ([Fe/H] = 0.25) ones. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

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