scholarly journals Star Spots on AR Lac Type Stars

1977 ◽  
Vol 4 (2) ◽  
pp. 397-403 ◽  
Author(s):  
D. M. Popper
Keyword(s):  
Main Sequence ◽  
Light Curves ◽  
Close Binaries ◽  
Good Precision ◽  
Mass Ratio ◽  
Considerable Uncertainty ◽  
Rs Cvn Stars ◽  
Mass Ratios ◽  
Definition Of

There is no generally accepted definition of AR Lac Stars, and the term RS CVn stars is used interchangeably or to refer to a particular subgroup. For the purposes of this discussion I use the term AR Lac stars to refer to detached close binaries showing Ca II emission in at least the cooler component outside eclipse, the hotter component being a main-sequence or subgiant star of spectral type F or G. Most of the systems show irregularities in their light curves as well as period changes. In order to determine whether a system is detached, one must know both the mass ratio and the relative radii. The determination of minimum masses is a fairly straightforward spectroscopic task, and provisional values are available for 22 of the systems, two or possibly three of them being non-eclipsing. All but 3 (AD Cap, RT Lac, RV Lib) have masses of the two components within 30% of each other. Because of appreciable irregularities in the light curves, the radii are subject to considerable uncertainty even when photometry of good precision is available. Nevertheless the 9 systems with very provisional radii all appear to be detached. These all have mass ratios near unity. We may assume, as a working hypothesis, that the other systems with mass ratios near unity are also detached and hence also belong in the AR Lac group. Most of the data referred to are to be found in IBVS 1083.

scholarly journals The Occurrence of Different Wolf-Rayet Phases in Massive Close Binaries

1982 ◽  
Vol 99 ◽  
pp. 403-403
Author(s):  
C. Doom ◽  
J.P. De Grève
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Close Binary System ◽  
Close Binary ◽  
Close Binaries ◽  
Mass Ratio ◽  
The Third ◽  
Third Stage ◽  
Definition Of ◽  
Massive Close Binary

In a recent paper (Doom and De Grève, 1981) the remaining main sequence lifetime of the mass gaining component in massive close binary systems was computed. Using results of that paper and the definition of the four important events in the evolution of a massive close binary system (RLOF(M1), RLOF(M2), SN(M1), SN(M2)), four evolutionary stages in the life of the system can be defined: OB+OB, WR+OB, c+OB (or WR+WR) and c+WR. The two possibilities for the third stage depend on the initial mass ratio of the system. The final stage c+c, is not considered here.

scholarly journals Fission Candidates Among Detached Close Binaries

1984 ◽  
Vol 80 ◽  
pp. 75-83
Author(s):  
H.-A. Ott
Keyword(s):  
Main Sequence ◽  
Small Mass ◽  
Close Binaries ◽  
Mass Ratio ◽  
Model Calculations ◽  
Mass Ratios ◽  
Low Mass ◽  
Statistical Trends ◽  
Momentum Relation

AbstractA comparison between results of model calculations and observed properties of close, but detached low mass binaries with Main Sequence primaries shows statistical trends, which seem to support fission origin for some of these objects: the mass-momentum relation, the relation between mass ratio and separation and the relation between mass ratio and synchronisation speak in favour of close initial separations and small mass ratios of the components.

scholarly journals New Data on the Eclipsing Binary V1848 Ori and Improved Orbital and Light Curve Solutions

2020 ◽  
Vol 29 (1) ◽  
pp. 72-80 ◽  
Author(s):  
Fatemeh Davoudi ◽  
Atila Poro ◽  
Fahri Alicavus ◽  
Afshin Halavati ◽  
Saeed Doostmohammadi ◽  
...  
Keyword(s):  
Binary System ◽  
Light Curve ◽  
Mass Function ◽  
Light Curves ◽  
Complete Analysis ◽  
Physical Parameters ◽  
Mass Ratio ◽  
Third Body ◽  
Eclipsing Binary

AbstractNew observations of the eclipsing binary system V1848 Ori were carried out using the V filter resulting in a determination of new times of minima and new ephemeris were obtained. We presented the first complete analysis of the system’s orbital period behavior and analysis of O-C diagram done by the GA and MCMC approaches in OCFit code. The O-C diagram demonstrates a sinusoidal trend in the data; this trend suggests a cyclic change caused by the LITE effect with a period of 10.57 years and an amplitude of 7.182 minutes. It appears that there is a third body with mass function of f (m3) = 0.0058 M⊙ in this binary system. The light curves were analyzed using the Wilson-Devinney code to determine some geometrical and physical parameters of the system. These results show that V1848 Ori is a contact W UMa binary system with the mass ratio of q = 0.76 and a weak fillout factor of 5.8%. The O’Connell effect was not seen in the light curve and there is no need to add spot.

scholarly journals Search for dormant black holes in ellipsoidal variables III. The OGLE BULGE short-period sample

2021 ◽  
Author(s):  
Roy Gomel ◽  
Simchon Faigler ◽  
Tsevi Mazeh ◽  
Michał Pawlak
Keyword(s):  
Main Sequence ◽  
Compact Object ◽  
Close Binaries ◽  
Periodic Modulation ◽  
Mass Ratio ◽  
True Nature ◽  
The Third ◽  
Short Period ◽  
Actual Mass

Abstract This is the third of a series of papers that presents an algorithm to search for close binaries with massive, possibly compact, unseen secondaries. The detection of such a binary is based on identifying a star that displays a large ellipsoidal periodic modulation, induced by tidal interaction with its companion. In the second paper of the series we presented a simple approach to derive a robust modified minimum mass ratio (mMMR), based on the observed ellipsoidal amplitude, without knowing the primary mass and radius, assuming the primary fills its Roche lobe. The newly defined mMMR is always smaller than the actual mass ratio. Therefore, a binary with an mMMR larger than unity is a good candidate for having a massive secondary, which might be a black hole or a neutron star. This paper considers 10,956 OGLE short-period ellipsoidals observed towards the Galactic Bulge. We re-analyse their modulation and identify 136 main-sequence systems with mMMR significantly larger than unity as candidates for having compact-object secondaries, assuming their observed periodic modulations reflect indeed the ellipsoidal effect. Obviously, one needs follow-up observations to find out the true nature of these companions.

scholarly journals Empirical Determination of the Gravity-Darkening Exponent for the Secondary Components Filling the Roche Lobe in Semi-Detached Close Binary Systems

1988 ◽  
Vol 108 ◽  
pp. 217-218
Author(s):  
Masatoshi Kitamura ◽  
Yasuhisa Nakamura
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Close Binary System ◽  
Roche Lobe ◽  
Close Binary ◽  
Close Binaries ◽  
Main Sequence Stars ◽  
Local Gravity ◽  
Subsurface Layers

The ordinary semi-detached close binary system consists of a main-sequence primary and subgiant (or giant) secondary component where the latter fills the Roche lobe. From a quantitative analysis of the observed ellipticity effect, Kitamura and Nakamura (1986) have deduced empirical values of the exponent of gravity-darkening for distorted main-sequence stars in detached systems and found that the empirical values of the exponent for these stars with early-type spectra are close to the unity, indicating that the subsurface layers of early-main sequence stars in close binaries are actually in radiative equilibrium. The exponent of gravity-darkening can be defined by H ∝ gα with H as the bolonetric surface brightness and g as the local gravity on the stellar surface.

scholarly journals The Use of Praesepe for the Definition of the Lower Part of the Zero-Age Main Sequence

1978 ◽  
Vol 80 ◽  
pp. 277-280
Author(s):  
M. Golay
Keyword(s):  
Main Sequence ◽  
Absolute Magnitude ◽  
Central Star ◽  
Distance Modulus ◽  
Photometric System ◽  
Mass Ratio ◽  
Depth Effect ◽  
Fitting Procedure ◽  
Trigonometric Parallax ◽  
Definition Of

In an attempt to determine the Hyades distance (Golay, 1973), it was assumed that stars of the same “photometric 0m.01 box” (see Golay, 1977a) have the same visual absolute magnitude. The large amount of photometric data in the UBV B1B2V1G photometric system allows a discussion on this hypothesis (Golay, 1977b). We have 60 “photometric 0m.01 boxes”, each containing a central star of known trigonometric parallax and at least one Praesepe star. We select the 16 boxes (Table I) containing single stars or binaries with an estimated mass ratio, a relative probable error < 30% for the parallaxes and a standard deviation for colors <0m.007. The UBV B1B2V1G colors, the indices (B-V), (B2-V1) and the magnitude mVare taken from theSecond Catalogue(Rufener, 1976) and the internal catalogue of the Geneva Observatory. The color index (B-V) is taken from Johnson (1952, 1957), Johnson and Knuckles (1955), the trigonometric parallax from Jenkins (1952, 1963) and Gliese (1969) and the spectral type for Hyades stars from Morgan and Hiltner (1965). The listings of all 0m.01 photometric star boxes in the UBV B1B2V1G system are given by Golay (1977c). The parallax obtained for Praesepe is π(0″.001) = 6.175 ± p.e. 0.1, i.e. a distance modulus (m-M) = 6m.05 and a distance of 162 parsecs. Golay (1977c) published the differences of the distance moduli for pairs of clusters having stars in the same box. The distances of these clusters is given in Table III, assuming a distance of 162 pc for Praesepe. The accuracy of this method is independent of both the distance magnitude and the chemical composition of the stars of a cluster since the stars have to be in the same box as a star with a known trigonometric parallax. The main sequence of Praesepe and a sample of Hyades stars, in the same photometric box with a Praesepe star is given in Table II. The depth effect in Praesepe being very small, the main sequence is very thin and the main sequence fitting procedure is better starting from Praesepe than from the Hyades.

scholarly journals Asteroseismic potential of CHEOPS

2018 ◽  
Vol 620 ◽  
pp. A203 ◽  
Author(s):  
A. Moya ◽  
S. Barceló Forteza ◽  
A. Bonfanti ◽  
S. J. A. J. Salmon ◽  
V. Van Grootel ◽  
...  
Keyword(s):  
Time Series ◽  
Main Sequence ◽  
Uncertainty Reduction ◽  
Light Curves ◽  
Accuracy And Precision ◽  
Mass Uncertainty ◽  
The Impact ◽  
Host Stars

Context. Asteroseismology has been impressively boosted during the last decade mainly thanks to space missions such as Kepler/K2 and CoRoT. This has a large impact, in particular, in exoplanetary sciences since the accurate characterization of the exoplanets is convoluted in most cases with the characterization of their hosting star. In the decade before the expected launch of the ESA mission PLATO 2.0, only two important missions will provide short-cadence high-precision photometric time-series: NASA–TESS and ESA–CHEOPS missions, both having high capabilities for exoplanetary sciences. Aims. In this work we want to explore the asteroseismic potential of CHEOPS time-series. Methods. Following the works estimating the asteroseismic potential of Kepler and TESS, we have analysed the probability of detecting solar-like pulsations using CHEOPS light-curves. Since CHEOPS will collect runs with observational times from hours up to a few days, we have analysed the accuracy and precision we can obtain for the estimation of νmax. This is the only asteroseismic observable we can recover using CHEOPS observations. Finally, we have analysed the impact of knowing νmax in the characterization of exoplanet host stars. Results. Using CHEOPS light-curves with the expected observational times we can determine νmax for massive G and F-type stars from late main sequence (MS) on, and for F, G, and K-type stars from post-main sequence on with an uncertainty lower than a 5%. For magnitudes V <  12 and observational times from eight hours up to two days, the HR zone of potential detectability changes. The determination of νmax leads to an internal age uncertainty reduction in the characterization of exoplanet host stars from 52% to 38%; mass uncertainty reduction from 2.1% to 1.8%; radius uncertainty reduction from 1.8% to 1.6%; density uncertainty reduction from 5.6% to 4.7%, in our best scenarios.

scholarly journals Mass-Ratio Determination in Contact Binaries

1974 ◽  
Vol 59 ◽  
pp. 199-199
Author(s):  
J. B. Hutchings
Keyword(s):  
Spectroscopic Data ◽  
Theoretical Work ◽  
Light Curves ◽  
Line Profiles ◽  
Mass Ratio ◽  
Recent Theoretical Work ◽  
Mass Ratios ◽  
Contact Binaries ◽  
Ratio Determination ◽  
The Masses

In the wake of recent theoretical work on contact systems (e.g. Whelan, 1972; Biermann and Thomas, 1972; Lucy, 1968), it is of importance to determine fundamental data from observations. This has been done recently by several groups in analysing light curves (Mochnacki and Doughty, 1972; Hutchings and Hill, 1973; Wilson and Devinney, 1973), and it is found that shapes, temperature differences and distributions, and mass-ratios, can be determined in many cases. However, where spectroscopic data are also available, the mass-ratios are not always in agreement. Using the photometric models, it is possible (Hutchings, 1973) to calculate the distortion of line profiles resulting (primarily) from the non-uniform brightness over the component stars in these systems. This distortion leads to the characteristically observed ‘square’ velocity curves for the systems (e.g. Binnendijk, 1967). Correction for the effect in most cases (a) resolves the mass-ratio discrepancy and (b) leads to better estimates for the masses. The faintness of most contact systems makes detailed spectroscopy difficult, but there appears to be a need for further work in the directions outlined here to improve the fundamental data available on them. These results should also be borne in mind in inspecting previous work on contact binaries.

scholarly journals Binary frequency among the O-type stars

1979 ◽  
Vol 83 ◽  
pp. 261-264
Author(s):  
Catharine D. Garmany
Keyword(s):  
Orbital Period ◽  
Selection Effect ◽  
Close Binaries ◽  
General Question ◽  
Mass Ratio ◽  
Double Line ◽  
Mass Ratios ◽  
Low Amplitude ◽  
Different Sources ◽  
Amplitude Versus

A great deal of work has been done on the theory of mass loss and evolution in close binaries, and numerous individual systems have been discussed in this connection, but the general question of the binary frequency of O-stars, and in particular, the initial binary mass ratio frequency or distribution of secondary masses, has not been completely answered. In general, we know that about half of all O-type stars are binaries; the most recent determination by Conti, Leep and Lorre (1977) found 58% of their sample to be certain or probable binaries. However, many of these stars were judged to be variable on the basis of only a few spectra from different sources, and therefore require further study. Another point to be examined concerns the binaries with available orbits: two thirds of these are double line systems. Figure 1 shows a plot of the semi-amplitude versus orbital period for all known systems, along with some theoretical curves for different mass ratios. Not only is the lack of single line systems obvious, but low amplitude systems are almost completely missing. This would appear to be only an observational selection effect, although it is to be noted that low amplitude double line Wolf-Rayet systems have been detected. If the effect is real, it implies that O-type binaries with mass ratios (m1/m2) greater than about three do not exist.

scholarly journals Further investigations with a Wilson Chamber. III.—The accuracy of the angle determination

1932 ◽  
Vol 136 (829) ◽  
pp. 338-348 ◽  
Keyword(s):  
Energy Levels ◽  
Probable Error ◽  
Average Error ◽  
Mass Ratio ◽  
Angle Measurements ◽  
Mass Ratios ◽  
Calculated Mass ◽  
The Difference ◽  
Error Of Measurement

I.—The question of the precision of the determination of the angles of forked tracks is of considerable importance, in particular owing to the possibility of determining nuclear energy levels from Wilson photographs. In an earlier paper some experiments were described in which an artificial track consisting of a bent glass fibre was photographed in different positions. The average error of determination of the angle was found to be 10 minutes of arc. This error was attributed to the lack of perfect adjustment of the camera. That the error of measuring actual tracks could be nearly as small as this was shown by measurements of three collisions in which the difference between the calculated and expected mass ratios was consistent with a probable error of about 10 minutes of arc for the angle measurements. Only such forks were used for these calculations of the mass ratio, for which the three arms appeared unusually straight and for which the test for coplanarity was accurately satisfied. Subsequently two collisions with hydrogen nuclei were described in which the error of the angles was held to be as low as 6 minutes of arc. It was pointed out at the time that many tracks did not, in fact, satisfy these conditions, but sufficient data were not then available for a statistical analysis of the distribution of calculated mass ratios, from which a reliable estimation of the probable error of measurement of an average fork could be made. Since then a great many more photographs have been taken with a larger chamber and an improved camera and such a statistical test is now possible. To test the camera itself five photographs were taken of two black lines ruled on a card. The angles calculated from the photographs were:—

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