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1.
To synthesise images of stellar photospheres with high spot filling factors, we model an extrapolated solar size distribution of spots on an immaculate SV Cam. These models of starspot coverage show that the primary star is peppered with a large number of subresolution spots. Using these model starspot distributions we generate a photometric lightcurve, which is then used as input to an maximum-entropy eclipse mapping code, that is based on chi-squared minimisation. I solve for the system parameters to show the effect of dense spot coverage on the derived system parameters, and show that surface brightness distributions reconstructed from these lightcurves have distinctive spots on the primary star at its quadrature points. It is concluded that two-spot modelling or chi-squared minimisation techniques are more susceptible to spurious structures being generated by systematic errors, arising from incorrect assumptions about photospheric surface brightness, than simple Fourier analysis of the light-curves.Marie Curie Intra-European Fellow  相似文献   

2.
In this paper we discuss a set of three consecutive VLBI observations of the binary system UX Arietis. The most interesting result is the variation with time of the source structure. The usual interpretation in terms of gyrosynchrotron emission from relativistic electrons trapped in a magnetic loop and undergoing collisional and radiative losses is not able, alone, to explain the observed variations. By using optical, radio and X-ray information we have produced a model of two giant loops anchored on a rotating star. As the star rotates, the loops change their relative position and orientation with respect to the line of sight, causing the observed variation of the source structure. The qualitative agreement found is consistent with our hypothesis and makes these observations a sort of a pilot experiment for a new way of using VLBI to observe radio-stars. In order to quantitatively test our model of evolving electrons confined in loops anchored on a rotating star, we plan in the near future a set of several phase-reference VLBI observations fully covering the 6.4 day rotational period.  相似文献   

3.
Radiation of supersoft X-ray sources (SSS) dominates both the supersof X-ray and the far-UV domain. A fraction of their radiation can be reprocessed into the thermal nebular emission, seen in the spectrum from the near-UV to longer wavelengths. In the case of symbiotic X-ray binaries (SyXBs) a strong contribution from their cool giants is indicated in the optical/near-IR. In this paper I introduce a method of multiwavelength modelling the spectral energy distribution (SED) of SSSs from the supersoft X-rays to the near-IR with the aim to determine the physical parameters of their composite spectra. The method is demonstrated on two extragalactic SSSs, the SyXB RX J0059.1-7505 (LIN 358) in the Small Magellanic Cloud (SMC), RX J0439.8-6809 in the Large Magellanic Cloud (LMC) and two Galactic SSSs, the classical nova RX J2030.5+5237 (V1974 Cyg) during its supersoft phase and the classical symbiotic star RX J1601.6+6648 (AG Dra) during its quiescent phase. The multiwavelength approach overcomes the problem of the mutual dependence between the temperature, luminosity and amount of absorption, which appears when only the X-ray data are fitted. Thus, the method provides an unambiguous solution. It was found that selection of the model (a blackbody or an atmospheric model) is not of crucial importance in fitting the global X-ray/IR SED. The multiwavelength modelling of the SED of SSSs is essential in determining their physical parameters.  相似文献   

4.
The photometric light modulation of ζ Andromedae originates from the distorted geometry of the primary, and additionally, from spots of which parameters (temperature, size, location) are variable in time. We present spot modelling results for six two-colour light curves which show that spots preferably appear on the stellar surface towards the companion star and opposite to it, where the distortion also causes dimming. Therefore, simple fitting of the measured data for the ellipticity effect does not yield correct result. Instead, ellipticity calculated from exact stellar parameters should be removed from the data to get reliable spotted light curves.  相似文献   

5.
Concatenating data from the millimetre regime to the infrared, we have performed spectral energy distribution (SED) modelling for 227 of the 405 millimetre continuum sources of Hill et al. which are thought to contain young massive stars in the earliest stages of their formation. Three main parameters are extracted from the fits: temperature, mass and luminosity. The method employed was the Bayesian inference, which allows a statistically probable range of suitable values for each parameter to be drawn for each individual protostellar candidate. This is the first application of this method to massive star formation.
The cumulative distribution plots of the SED modelled parameters in this work indicate that collectively, the sources without methanol maser and/or radio continuum associations (MM-only cores) display similar characteristics to those of high-mass star formation regions. Attributing significance to the marginal distinctions between the MM-only cores and the high-mass star formation sample, we draw hypotheses regarding the nature of the MM-only cores, including the possibility that the population itself comprises different types of source, and discuss their role in the formation scenarios of massive star formation. In addition, we discuss the usefulness and limitations of SED modelling and its application to the field. From this work, it is clear that within the valid parameter ranges, SEDs utilising current far-infrared data cannot be used to determine the evolution of massive protostars or massive young stellar objects.  相似文献   

6.
我们用美国McDonald天文台2.1米反光镜Coude Reticon观测,对31个RS CVn型双星系统的37颗子星的自转进行了测量。并结合以前测得的38颗子星的数据,对RS CVn型星是否同步作了统计分析,结果表明,绝大多数都显示出同步自转性质;但无论是短周期、正常周期还是长周期组的,都有少数与同步自转不一致的例子。这与过去认为短周期和正常周期的呈同步自转,而长周期的呈非同步自转的结论不一致。  相似文献   

7.
We discuss the European effort in the study of millimeter-wave circumstellar masers with very long baseline interferometry. We show some results of the first observations, and discuss present and future work.  相似文献   

8.
For this paper, we collected all infrared carbon stars (IRCSs) known so far from the literature and identified the 2MASS counterparts of all IRCSs. Using 2MASS, IRAS and ISO SWS data, we investigate the infrared properties of IRCSs. We find that the infrared colors and temperatures of IRCSs—not only in the IRAS region but also in the near infrared—are between those for visual carbon stars and extreme carbon stars. The results in this paper strongly support the suggestion that the sequence of visual carbon stars → infrared carbon stars → extreme carbon stars is the evolutionary sequence in the AGB phase for carbon-rich stars. In addition, using the ISO SWS data, we find that an evolutionary sequence also exists within the IRCS stage.  相似文献   

9.
The study of detached eclipsing binaries in open clusters can provide stringent tests of theoretical stellar evolutionary models, which must simultaneously fit the masses, radii, and luminosities of the eclipsing stars and the radiative properties of every other star in the cluster. We review recent progress in such studies and discuss two unusually interesting objects currently under analysis. GV Carinae is an A0 m + A8 m binary in the Southern open cluster NGC 3532; its eclipse depths have changed by 0.1 mag between 1990 and 2001, suggesting that its orbit is being perturbed by a relatively close third body. DW Carinae is a high-mass unevolved B1 V + B1 V binary in the very young open cluster Collinder 228, and displays double-peaked emission in the centre of the Hα line which is characteristic of Be stars. We conclude by pointing out that the great promise of eclipsing binaries in open clusters can only be satisfied when both the binaries and their parent clusters are well-observed, a situation which is less common than we would like.  相似文献   

10.
Recent theoretical calculations of stellar evolutionary tracks for rotating high-mass stars suggests that the chemical composition of the surface layers changes even whilst the star is evolving on the Main Sequence. The abundance analysis of binary components with precisely known fundamental stellar quantities allows a powerful comparison with theory. The observed spectra of close binary stars can be separated into the individual spectra of the component stars using the method of spectral disentangling on a time-series of spectra taken over the orbital cycle. Recently, Pavlovski and Hensberge (2005, A&A, 439, 309) have shown that, even with moderately high line-broadening, metal abundances can be derived from disentangled spectra with a precision of 0.1 dex. In a continuation of this project we have undertaken a detailed abundance analysis of the components of another two high-mass binaries, V453 Cyg, and V380 Cyg. Both binaries are well-studied systems with modern solutions. The components are close to the TAMS and therefore very suitable for an observational test of early mixing in high-mass stars.  相似文献   

11.
With the aim of investigating the possible particular behavior of carbon in a sample of chemically peculiar stars of the main sequence without turning to modeling, we performed spectroscopic observations of three important and usually prominent single ionized carbon lines: 4267.261, 6578.052 and 6582.882 Å. In addition, we observed a large number of standard stars in order to define a kind of normality strip, useful for comparing the observed trend for the peculiar stars. We paid particular attention to the problem of the determination of fundamental atmospheric parameters, especially for the chemically peculiar stars for which the abundance anomalies change the flux distribution in such a way that the classical photometric methods to infer effective temperatures and gravities parameter cannot be applied. Regarding CP stars, we found a normal carbon abundance in Hg–Mn, Si (with some exceptions) and He strong stars. He weak stars are normal too, but with a large spread out of the data around the mean value. A more complicated behavior has been noted in the group of SrCrEu stars: four out of seven show a strong overabundance, being the others normal.  相似文献   

12.
New data acquired on the active, cool binary CC Eri ranged across the spectrum from Chandra X-ray to broadband photometry and microwave observations using the VLA and ATCA. Also, high-dispersion spectropolarimetry using the AAT enabled Zeeman-Doppler imaging to be performed. Our interpretations infer strong localised concentrations of the stellar magnetic field, manifested by surface activity and related large coronal plasma structures. Comprehensive matching of the modelling parameters awaits more detailed investigation.This brief interim review includes consideration of the ATCA data. Microwave radio emission is usually low level (‘quiescent’), but occasionally flares of several mJy peak intensity are observed. We associate the emission, generally, with wave-like mechanisms, expanding through the outer atmosphere. Related characteristics of this emission are discussed.  相似文献   

13.
Measuring eigenfrequencies and identifying eigenmodes provide the observational basis for a significant improvement in our understanding of stellar evolution and structure.Development throughout the last few years show that we may be at the dawn of a `Golden Age'for Asteroseismology. For this to become a reality we only need two things:Better data and better models. In this paper I describe some aspectsof how one detects stellar oscillations.  相似文献   

14.
The multiplicity of early-type stars is still not well established. The derived binary fraction is different for individual star forming regions, suggesting a connection with the age and the environment conditions. The few studies that have investigated this connection do not provide conclusive results. To fill in this gap, we started the first detailed adaptive-optic-assisted imaging survey of early-type field stars to derive their multiplicity in a homogeneous way. The sample has been extracted from the Hipparcos Catalog and consists of 341 BA-type stars within ∼300 pc from the Sun. We report the current status of the survey and describe a Monte-Carlo simulation that estimates the completeness of our companion detection.  相似文献   

15.
In this article, a period analysis of the late-type eclipsing binary VV UMa is presented. This work is based on the periodic variation of eclipse timings of the VV UMa binary. We determined the orbital properties and mass of a third orbiting body in the system by analyzing the light-travel time effect. The O−C diagram constructed for all available minima times of VV UMa exhibits a cyclic character superimposed on a linear variation. This variation includes three maxima and two minima within approximately 28,240 orbital periods of the system, which can be explained as the light-travel time effect (LITE) because of an unseen third body in a triple system that causes variations of the eclipse arrival times. New parameter values of the light-time travel effect because of the third body were computed with a period of 23.22 ± 0.17 years in the system. The cyclic-variation analysis produces a value of 0.0139 day as the semi-amplitude of the light-travel time effect and 0.35 as the orbital eccentricity of the third body. The mass of the third body that orbits the eclipsing binary stars is 0.787 ± 0.02 M⊙, and the semi-major axis of its orbit is 10.75 AU.  相似文献   

16.
The aim of this work is to compare a neutron star with an accreted crust and one with a non-accreted crust, and estimate which one is potentially a better source of gravitational waves (i.e. can sustain a larger “mountain”). To do this we present a new formalism, and find that a non-accreted crust can sustain a slightly larger “mountain”. We also discuss the importance of relativistic effects.   相似文献   

17.
In this paper we discuss the prospects for asteroseismology with spatial resolution and motivate studies of the most chemically peculiar roAp star HD 101065. We present the first results from a high-precision radial velocity (RV) study of HD 101065 based on data spanning four nights that were acquired using the HARPS echelle-spectrometer at the ESO 3.6 m telescope. The analysis of individual nights showed the amplitude and phase modulation of the dominant mode. The analysis of the whole data set showed the presence of multi-periodic oscillations with two groups of equally-spaced modes. We find Δυ = 65.2μHz and δυ = 7.3μHz for the large and the small spacing, respectively. HD 101065 is the only roAp star to show the existence of two groups ofl = 0, 2 andl = 1, 3 excited modes.  相似文献   

18.
We present first observations of Mira stars obtained at the Very Large Telescope Interferometer (VLTI) at 2 microns, equipped with the VINCI instrument, using different baselines with both the test siderostats and the 8.2 m unit telescopes. These observations, collected in the course of the VLTI commissining program, have targeted so far about sixty cool giant stars. In this talk, we list and describe the measurements obtained for 14 Mira stars, many of them representing first-time determinations of the visibility. In particular, we devote special attention to a study of Mira itself, for which very accurate determinations of the visibility at several baseline lenghts and orientations could be obtained. We find that a two-component model is more consistent with the data than a single stellar disc. Further observations are needed for a better understanding of this source. The VLTI will constitute an ideal instrument for such studies in the future. In particular it will permit detailed investigations of southern AGB stars, such as accurate measurements of surface structureparameters (diameters, diameter variations, asymmetries, center-to-limbvariations, special features like hot spots) and of circumstellar envelopes. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
White dwarfs are the evolutionary endpoint of the low-and-medium mass stars. In the studies of white dwarfs, the mass of white dwarf is an important physical parameter. In this paper, we give an analysis about the velocity distribution of DA white dwarfs in the Sloan Digital Sky Survey (SDSS), and hope to find the relation between mass and velocity distribution of white dwarfs. We get the radial velocity and tangential velocity of every DA white dwarf according to their proper motion and spectral shift. Through analyzing the velocity distribution of DA white dwarfs, we find that the small-mass white dwarfs, which are produced from the single-star evolution channel, have a relatively large velocity dispersion.  相似文献   

20.
This work is devoted to improving empirical mass-luminosity relations (MLR) and mass-metallicity-luminosity relation (MMLR) for low mass stars. For these stars, observational data in the mass-luminosity plane or the mass-metallicity-luminosity space subject to non-negligible errors in all coordinates with different dimensions. Thus a reasonable weight assigning scheme is needed for obtaining more reliable results. Such a scheme is developed, with which each data point can have its own due contribution. Previous studies have shown that there exists a plateau feature in the MLR. Taking into account the constraints from the observational luminosity function, we find by fitting the observational data using our weight assigning scheme that the plateau spans from 0.28M⊙ to 0.50M⊙. Three-piecewise continuous improved MLRs in K, J, H and V bands, respectively, are obtained. The visual MMLR is also improved based on our K band MLR and the available observational metallicity data.  相似文献   

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