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1.
G.Handler A. A.Pamyatnykh W.Zima D. J.Sullivan N.Audard A.Nitta 《Monthly notices of the Royal Astronomical Society》1998,295(2):377-385
We present 132 h of new time-series photometric observations of the δ Scuti star CD−24 7599 acquired during 86 nights from 1993 to 1996 to study its frequency and amplitude variations. By using all published observations we demonstrate that the three dominating pulsation modes of the star can change their photometric amplitudes within one month at certain times, while the amplitudes can remain constant within the measurement errors at other times. CD−24 7599 also exhibits frequency variations, which do not show any correspondence between the different modes. The typical time-scale for the amplitude variations is found to be several hundred days, which is of the same order of magnitude as the inverse linear growth rates of a selected model. We find no evidence for periodic amplitude modulation of two of the investigated modes ( f 2 and f 3 ), but f 1 may exhibit periodic modulation. The latter result could be spurious and requires confirmation. The observed frequency variations may either be continuous or reflect sudden frequency jumps. No evidence for cyclical period changes is obtained. We exclude precession of the pulsation axis and oblique pulsation for the amplitude variations. Beating of closely spaced frequencies cannot explain the amplitude modulations of two of the modes, while it is possible for the third. Evolutionary effects, binarity, magnetic field changes or avoided crossings cannot be made responsible for the observed period changes. Only resonance between different modes may be able to explain the observations. However, at this stage a quantitative comparison is not possible. More observations, especially data leading to a definite mode identification and further measurements of the temporal behaviour of the amplitudes and frequencies of CD−24 7599, are required. 相似文献
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In this paper the researchers collected 28 times of maximum light including 4 times of those observed at the Xinglong station,
the National Astronomical Observation of China between May 27, 2004 and June 1, 2004 and 1 time of maximum light from a 60
cm telescope on May 4, 1984. It found that the O-C point distribution was more completely compared than in any papers published
before. The period is decreasing at the rate of about (1.4±0.1)×10−8 per year, which should not be caused by stellar evolution. It might be only part of a binary orbital light-time variation
or other unknown reason. The time scale is longer than Pocs and Szeidl’s suggestion; the star needs more observations before
we can be certain of the exact light-time variation. 相似文献
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Jian-Ning Fu Chao Zhang Kanokwan Marak Chayan Boonyarak Pongsak Khokhuntod Shi-Yang Jiang 《中国天文和天体物理学报》2008,8(2):237-244
New time-series photometric observations of BL Cam in the V band and white light were made during 2005 to 2007 at the Xinglong Station of China. The frequency analysis confirms two closely separated frequencies, 25.181 d-1 and 25.571 d-1, but the frequency of 31-32 d-1 reported in the literature was not detected in the new data. New times of maximum light were determined from both our light curves and those available on Internet, allowing a more comprehensive study of the O - C diagram, together with the times of maximum light in the literature. A new interpretation, including the period increasing before 1988 and decreasing since 1992 of BL Cam and the light-time effect in a binary system, looks plausible. 相似文献
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Y. Frémat P. Lampens H. Hensberge 《Monthly notices of the Royal Astronomical Society》2005,356(2):545-556
DG Leo is a spectroscopic triple system composed of three stars of late-A spectral type, one of which was suggested to be a δ Scuti star. Seven nights of observations at high spectral and high time-resolution at the Observatoire de Haute-Provence with the ELODIE spectrograph were used to obtain the component spectra by applying a Fourier transform spectral disentangling technique. Comparing these with synthetic spectra, the stellar fundamental parameters (effective temperature, surface gravity, projected rotation velocity and chemical composition) are derived. The inner binary consists of two Am components, at least one of which is not yet rotating synchronously at the orbital period though the orbit is a circular one. The distant third component is confirmed to be a δ Scuti star with normal chemical composition. 相似文献
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《New Astronomy》2015
CCD photometry observation of a newly discovered, high amplitude Delta Scuti star GSC 1566-2802, with a visible filter, is presented. The observations were carried out at Alborz Observatory located in Mahdasht, Karaj, Iran.The main goal of this project was to update our knowledge of the periodic variations of the target star. This paper covers three analyses, first calculating a new ephemeris and plotting a new light curve based on 19 times of maxima; then a Fourier analysis of the observed data points which results in determining probable oscillation modes, as well as computing its physical parameters which guide us to its harmonics and pulsation modes. 相似文献
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A collaborative programme searching for mmag pulsations in chemically peculiar stars in the northern hemisphere was initiated
in 1997 between Nainital, India, and Cape Town, South Africa. It was therefore named as theNainital-Cape Survey programme. The detection limits imposed by the observing conditions (including atmospheric noise and telescope size) at both
Manora Peak and Devasthal sites are described. The scintillation noise on the best photometric nights is≈ 0.1 to 0.2 mmag for these sites. Both places allow one to detect few mmag variation in bright stars(B ≤ 12 mag), and are therefore particularly well-suited for carrying out the proposed survey work. The main characteristics of
the three-channel photometer developed at ARIES for carrying out the observations are also presented. This excellent instrument
has been used extensively since 1999 at the f/13 Cassegrain focus of ARIES’ 104 cm telescope. In particular, it allowed the
survey to result in the discovery of δ Scuti like pulsations in four Am stars, in one rapidly oscillating Ap star, and in
a number of probable variables so far. The future prospects are then presented, which regard the acquisition of a high speed
time series CCD photometer, a project to build a 3-metre class telescope at Devasthal, and collaborative observations with
Indian and foreign astronomical sites. 相似文献
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H. Bruntt D. Stello J. C. Suárez T. Arentoft T. R. Bedding M. Y. Bouzid Z. Csubry T. H. Dall Z. E. Dind S. Frandsen R. L. Gilliland A. P. Jacob H. R. Jensen Y. B. Kang S.-L. Kim L. L. Kiss H. Kjeldsen J.-R. Koo J.-A. Lee C.-U. Lee J. Nuspl C. Sterken R. Szabó 《Monthly notices of the Royal Astronomical Society》2007,378(4):1371-1384