共查询到20条相似文献，搜索用时 46 毫秒
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M. V. Mekkaden S. Muneer A. V. Raveendran 《Monthly notices of the Royal Astronomical Society》2007,378(3):1079-1088
Photometric observations over three seasons show HD 288313 to be a light variable with a 2.2636-d period. The observed V amplitudes lie in the range of 0.06–0.15 mag. The star showed appreciable changes in the brightness at maximum and minimum of the light curve from season to season. The ( b − y ) colour did not show any significant variation during the photometric cycle. The light variation appears to be caused by the rotational modulation of stellar flux by cool starspots distributed asymmetrically across the stellar longitudes. The Hα line strength in HD 288313 varied drastically from completely filled-in emission to almost full absorption, that is typical of a normal star of similar spectral type. The Hα equivalent width is found to show a clear rotational modulation only occasionally. Most of the time, chromospheric active regions are distributed well across the stellar longitudes, thereby suppressing obvious rotational modulations. Broad-band linear polarization measurements show HD 288313 to be a short period, low-amplitude polarization variable. The polarization variation is, apparently, rotationally modulated. Dust grain scattering in a non-spherical circumstellar envelope of a star with inhomogeneities in the surface brightness distribution seems to be the mechanism operating in producing the observed polarization. 相似文献
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C. Trundle P.L. Dufton W.R.J. Rolleston R.S.I. Ryans D.J. Lennon N. Lehner 《Monthly notices of the Royal Astronomical Society》2001,328(1):291-300
Local thermodynamic equilibrium (LTE) absolute and differential abundances are presented for a peculiar metal-rich B-type star, HD 135485. These suggest that HD 135485 has a general enrichment of ∼0.5 dex in all the metals observed (C, N, O, Ne, Mg, Al, Si, P, S, Cl, Ar, Sc, Ti, Cr, Mn, Fe and Sr), except for nickel. The helium enhancement and hence hydrogen deficiency can account for ≤ 0.2 dex of this enhancement of metals, with the additional enhancement probably being representative of the progenitor gas. However, some of the metals appear to have greater enhancements, which may have occurred during the star's evolution. The significantly larger nitrogen abundance coupled with a modest helium enhancement observed in HD 135485 indicates that carbon–nitrogen (CN) processed material has possibly contaminated the stellar surface. Neon and carbon enhancements may indicate that helium core flashes have also occurred in HD 135485. Some of the iron-group elements (viz. Mn and Ni) appear to have similar abundance patterns to that of silicon Ap stars, but it is uncertain how these abundance patterns formed if they were not present in the progenitor gas. From a kinematical investigation it is unclear whether this star formed in a metal-rich region as implied by its chemical composition. From its position in the Hertzsprung–Russell diagram, HD 135485 would appear to be an evolved star lying close to or on the horizontal branch. 相似文献
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J. J. Lockley Janet H. Wood S. P. S. Eyres T. Naylor Sergei Shugarov 《Monthly notices of the Royal Astronomical Society》1999,310(4):963-972
We have performed high-speed UBV photometric observations on the peculiar binary V Sagittae. Using three new eclipse timings we update the orbital ephemeris and convert it to a dynamical time-scale (TDB). We also searched for quasi-periodic oscillations but did not detect them. Using the Wilson–Devinney algorithm we have modelled the light curve to find the stellar parameters of V Sge. We find that the system is a detached binary but that the primary star is very close to filling its Roche lobe, while the secondary star fills 90 per cent of its Roche lobe volume. We find temperatures of the primary and the secondary star to be T 1 =41 000 K and T 2 =22 000 K. We find i =72° and masses of 0.8 M⊙ and 3.3 M⊙ for the primary and secondary stars respectively. De-archived Hubble Space Telescope ( HST ) spectroscopy of V Sge shows evidence of mass loss via a wind or winds. In addition we report radio observations of V Sge during an optical high state at 2 cm, 3.6 cm and 6 cm wavelengths. The 3.6 cm emission is increased by a factor of more than six compared with an earlier detection in a previous optical high state. 相似文献
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Jørgen Christensen-Dalsgaard 《Astrophysics and Space Science》2003,284(1):277-294
The workshop took place at the beginning of what promises tobe a golden age of asteroseismology.Ground-based instrumentation is finally reaching a level of stabilitywhich allows detailed investigations of solar-like oscillations in atleast bright, slowly rotating main-sequence stars.Very extensive results are expected from the coming space missions,including data on a broad range of stars from the Eddington mission.The observational situation is therefore extremely promising.To make full use of these promises, major efforts are requiredtowards the efficient utilization of the data, through the developmentof techniques for the analysis and interpretation of the data.A broad range of topics related to these issues is discussed in the presentproceedings. Here I review some of the relevant problems,relate the asteroseismic investigations to broader areas of astrophysics and consider briefly the basis for our great expectations for the developmentof the field. 相似文献
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G. A. J. Hussain C. Allende Prieto S. H. Saar M. Still 《Monthly notices of the Royal Astronomical Society》2006,367(4):1699-1708
We present surface spot maps of the K2V primary star in the pre-cataclysmic variable binary system, V471 Tau. The spot maps show the presence of large high-latitude spots located at the sub-white dwarf longitude region. By tracking the relative movement of spot groups over the course of four nights (eight rotation cycles), we measure the surface differential rotation rate of the system. Our results reveal that the star is rotating rigidly with a surface shear rate, dΩ= 1.6 ± 6 mrad d−1 . The single active star AB Dor has a similar spectral type, rotation period and activity level as the K star in V471 Tau, but displays much stronger surface shear (46 < dΩ < 58 mrad d−1 ) . Our results suggest that tidal locking may inhibit differential rotation; this reduced shear, however, does not affect the overall magnetic activity levels in active K dwarfs. 相似文献
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B. Montesinos John H. Thomas P. Ventura I. Mazzitelli 《Monthly notices of the Royal Astronomical Society》2001,326(3):877-884
The correlation between stellar activity, as measured by the indicator Δ R HK , and the Rossby number Ro in late-type stars is revisited in light of recent developments in solar dynamo theory. Different stellar interior models, based on both mixing-length theory and the full spectrum of turbulence, are used in order to see to what extent the correlation of activity with Rossby number is model dependent, or otherwise can be considered universal. Although we find some modest model dependence, we find that the correlation of activity with Rossby number is significantly better than with rotation period alone for all the models we consider. Dynamo theory suggests that activity should scale with the dynamo number. A current model of the solar dynamo, the so-called interface dynamo, proposes that the amplification of the toroidal magnetic field by differential rotation (the ω -effect) and the production of the poloidal magnetic field from toroidal by helical turbulence (the α -effect) take place in different, adjacent layers near the base of the convection zone. A new scale analysis based on the interface dynamo shows that the appropriate dynamo number does not depend on the Rossby number alone, but also depends on an additional dimensionless factor related to the differential rotation. This leads to a new interpretation of the correlation between activity and Rossby number, which in turn leads to some conclusions about the magnitude of differential rotation in the dynamo layers of late-type main-sequence stars. 相似文献
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In this panel discussion contributions were made by K. Strom, L. Nordh and H. Zinnecker on the contributions of surveys to the study of star formation regions, by B. Burton on a survey of galactic H I and by E. Dwek on the detection of galactic supernovae by infrared surveys. The contributions of K. Strom, L. Nordh and E. Dwek are summarized here. 相似文献
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M. Desmet M. Briquet † A. Thoul ‡ W. Zima P. De Cat G. Handler I. Ilyin E. Kambe J. Krzesinski H. Lehmann S. Masuda P. Mathias D. E. Mkrtichian J. Telting K. Uytterhoeven S. L. S. Yang C. Aerts 《Monthly notices of the Royal Astronomical Society》2009,396(3):1460-1472
We present the results of a spectroscopic multisite campaign for the β Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high-resolution high S/N spectra gathered with eight different telescopes in a time span of 11 months. In addition, we make use of numerous archival spectroscopic measurements. We confirm 10 independent frequencies recently discovered from photometry, as well as harmonics and combination frequencies. In particular, the slowly pulsating B-stars (SPB)-like g -mode with frequency 0.3428 d−1 reported before is detected in our spectroscopy. We identify the four main modes as (ℓ1 , m 1 ) = (1, 1), (ℓ2 , m 2 ) = (0, 0), (ℓ3 , m 3 ) = (1, 0) and (ℓ4 , m 4 ) = (2, 1) for f 1 = 5.178 964 d−1 , f 2 = 5.334 224 d−1 , f 3 = 5.066 316 d−1 and f 4 = 5.490 133 d−1 , respectively. Our seismic modelling shows that f 2 is likely the radial first overtone and that the core overshooting parameter αov is lower than 0.4 local pressure scale heights. 相似文献
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发展了一种简单的双温模型用于研究黑子对活动星的视星等、颜色和视Li丰度的影响.在适当的黑子覆盖因子下,恒星黑子能产生可观的活动星的视星等(V星等约±0.2星等)、颜色(B-V颜色约-0.1星等)和Li I λ6708 (?)谱线等值宽度(约-0.2-0.3 dex)的变化.与非活动的正常恒星相比,表面被黑子覆盖的活动星有更蓝的B-V颜色,它们的Li I λ6708 (?)谱线的等值宽度也变窄.根据观测到的活动星黑子引起的光变变幅,估计视圆面黑子覆盖率的变化范围△Fs从百分之几到约0.2.视圆面黑子覆盖率不太可能超过0.3. 相似文献
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A.F. Kholtygin S.N. Fabrika G.A. Chountonov T.E. Burlakova G.G. Valyavin Dong-il Kang 《Astronomische Nachrichten》2007,328(10):1170-1172
The variability of line profiles in spectra of bright OB stars has been studied.We obtain more than 1000 high quality spectra of δ Ori A, λ Ori A, α Cam, 19 Cep, ι Her, ρ Leo and other target stars. We revealed the line profile microvariability of small amplitude (0.5–3% in the adjacent continuum units) for all observed stars. For most stars only cyclic components of the line profile variability (LPV) at the time scales from hours to days were detected. These components seem to be connected with both the non-radial pulsations (NRP) and rotation line profile modulation. In the spectra of δ Ori A and λ Ori A we found the evidences of the stochastic LPV in spectra, probably connected with the small clumps in the stellar wind. On the basis of recent observations we discuss the origin of the magnetic field of early-type stars. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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C. Brocksopp R. P. Fender V. Larionov V. M. Lyuty A. E. Tarasov G. G. Pooley W. S. Paciesas P. Roche 《Monthly notices of the Royal Astronomical Society》1999,309(4):1063-1073
We present the results of a 2.5-yr multiwavelength monitoring programme of Cygnus X-1, making use of hard and soft X-ray data, optical spectroscopy, UBVJHK photometry and radio data. In particular, we confirm that the 5.6-d orbital period is apparent in all wavebands, and note the existence of a wavelength dependence to the modulation, in the sense that higher energies reach minimum first. We also find a strong modulation at a period of 142±7 d, which we suggest is caused by precession and/or radiative warping of the accretion disc. Strong modulation of the hard and soft X-ray flux at this long period may not be compatible with simple models of an optically thin accretion flow and corona in the low state. We present the basic components required for more detailed future modelling of the system – including a partially optically thick jet, quasi-continuous in the low state, the base of which acts as the Comptonizing corona. In addition, we find that there are a number of flares that appear to be correlated in at least two wavebands and generally in more. We choose two of these flares to study in further detail, and find that the hard and soft X-rays are well correlated in the first, and that the soft X-rays and radio are correlated in the second. In general, the optical and infrared show similar behaviour to each other, but are not correlated with the X-rays or radio. 相似文献
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Bhaskar Datta Arun V. Thampan Paul J. Wiita 《Journal of Astrophysics and Astronomy》1995,16(3-4):357-374
For accretion on to neutron stars possessing weak surface magnetic fields and substantial rotation rates (corresponding to
the secular instability limit), we calculate the disk and surface layer luminosities general relativistically using the Hartle
& Thorne formalism, and illustrate these quantities for a set of representative neutron star equations of state. We also discuss
the related problem of the angular momentum evolution of such neutron stars and give a quantitative estimate for this accretion
driven change in angular momentum. Rotation always increases the disk luminosity and reduces the rate of angular momentum
evolution. These effects have relevance for observations of low-mass X-ray binaries. 相似文献
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G. J. Harris J. Tennyson B. M. Kaminsky Ya. V. Pavlenko H. R. A. Jones 《Monthly notices of the Royal Astronomical Society》2006,367(1):400-406
We build an accurate data base of 5200 HCN and HNC rotation–vibration energy levels, determined from existing laboratory data. 20 000 energy levels in the Harris et al. linelist are assigned approximate quantum numbers. These assignments, lab-determined energy levels and Harris et al. energy levels are incorporated in to a new energy level list. A new linelist is presented, in which frequencies are computed using the lab-determined energy levels where available, and the ab initio energy levels otherwise.
The new linelist is then used to compute new model atmospheres and synthetic spectra for the carbon star WZ Cas. This results in better fit to the spectrum of WZ Cas in which the absorption feature at 3.56 μm is reproduced to a higher degree of accuracy than has previously been possible. We improve the reproduction of HCN absorption features by reducing the abundance of Si to [Si/H]=−0.5 dex, however, the strengths of the Δ v = 2 CS band heads are overpredicted. 相似文献
The new linelist is then used to compute new model atmospheres and synthetic spectra for the carbon star WZ Cas. This results in better fit to the spectrum of WZ Cas in which the absorption feature at 3.56 μm is reproduced to a higher degree of accuracy than has previously been possible. We improve the reproduction of HCN absorption features by reducing the abundance of Si to [Si/H]=−0.5 dex, however, the strengths of the Δ v = 2 CS band heads are overpredicted. 相似文献