The empirical mass-luminosity relation for low mass stars

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.     

The Wolf-Rayet mass-luminosity relation

We consider the mass-luminosity relation proposed for the Wolf-Rayet stars on the basis of detailed numerical models. It is found that the linear form of this relation can be explained in a straight-forward manner and is due to essentially three factors, (i) the WR stars are approximately chemically homogenous, (ii) the stars evolve under constant radiation pressure, and (iii) the stars evolve with high mass loss.     

On the mass-luminosity relation

The results of a least-squares study of the mass-luminosity relation for eclipsing and visual binary stars consisting of main sequence components are presented. Two methods are discussed. In Part A, the values of the coefficientsA andB in the relation logM=A+BM _Bol are determined. Part B presents a technique which permits the determination of α and β in the relationM=αL ^β, when only the sum of the masses, and not the individual masses of each component, is known. The results and a comparison of the two methods are discussed. It is found that the following massluminosity relation represents the observational data satisfactorily: $$log M = 0.504 - 0.103M_{BOL,} {\text{ }} - \leqslant M_{BOL} \leqslant + 10.5$$ . A discussion of the data and of the possibility that separate mass-luminosity relations may exist for visual and eclipsing binaries is given. The possiblity that more than one mass-luminosity relation is required in the range ?8≤M _Bol ≤+13 is also discussed.     

Long-period eclipsing binaries: towards the true mass-luminosity relation.I. the test sample,observations and data analysis

The mass-luminosity relation is a fundamental law of astrophysics. We have suggested that the currently used mass-luminosity relation is not correct for the M/M⊙ 2.7 range of mass since it was created utilizing double-lined eclipsing binaries, where the components are synchronized and consequently change each other's evolutionary path. To exclude this effect, we have started a project to study longperiod massive eclipsing binaries in order to construct radial velocity curves and determine masses for the components. We outline our project and present the selected test sample together with the first HRS/SALT spectral observations and the software package, FITTING BINARY STARS(FBS), that we developed for the analysis of our spectral data. As the first result, we present the radial velocity curves and best-fit orbital elements for the two components of the FP Car binary system from our test sample.     

Physical conditions of ionized gas and mass-luminosity distribution in NGC 7793

The physical state of ionized gas in NGC 7793 was studied by spectroscopical means: the electronic temperature isT _e10⁴K while the electronic density ranges fromN _e1400 cm^–3 in the nucleus toN _e1000 cm^–3 in the emission regions. There are also indications of an excess of nitrogen in the nucleus. TheM/L ratio suggests for NGC 7793, a high proportion of young objects quite uniformly distributed over its body, with a slight concentration towards the nuclear region.     

The redshift-magnitude relation for galaxies

An analysis of the redshift-magnitude data for the 98 clusters of the list of Sandage and Hardy (1973) is repeated taking into account both the effect of richness and Bautz-Morgan classification on the absolute magnitude of the brightest members. We find that while the relationship between M and B-M class—whatever it is—does not change the value ofq ₀ theM-r relation is so dependent on the model of the Universe that we cannot use all the clusters in the analysis unless we establish that relation in an independent way. The analysis of richness 1 and 2 clusters support an open model of the Universe (q ₀<0.5) while the uncertainties in the attribution of richness to the three most distant clusters do not permit to discard the steady state.     

The effect of mechanical waves on empirical solar models

Empirical solar models contain the effect of heating due to radiative energy loss from acoustic waves. We estimate here the temperature difference between the radiative equilibrium model and the empirical model. At optical depth ₅₀₀₀ = 0.1 this difference is small, but near the temperature minimum (₅₀₀₀ = 10^–4) it reaches between 53 and 83 K. The temperature difference between the equator and the poles caused by a hypothetical difference in the heating is estimated.     

The mass-radius relation in binary systems

The mass-radius relation is determined for Main-Sequence stars from observational data of well-detached binary systems. The results are compared to previous empirical relations and we discuss their application to the study of the light curves of eclipsing binaries. A comparison with theoretical Main-Sequence models has been carried out.     

The polarization-redshift relation in radio galaxies

We analyze the properties of a sample of optically polarized radio galaxies with a wide range of redshifts. The galaxies were selected both from our survey and from the literature. The aim of this work is checking whether high linear polarization is a general property of high redshift radio galaxies and how it depends on redshift. This provides a critical test on the suggestion that a considerable fraction of rest frame UV light in high redshift radio galaxies is scattered nuclear radiation. Our results show that radio galaxies withz > 0.7 are strongly polarized and that there is a strong dependence of the degree of linear polarization on the redshift. We discuss the possible origin of this correlation. Our results provide support to the validity of the Radio Quasar and Radio Galaxies unifying schemes.     

The empirical determination of damping constants in the solar photosphere

The evaluation of damping constants is discussed and the results of their empirical determination by various authors are listed in the Appendix.The results of the determination of damping constants by analysing the wings of 38 strong Fe i lines are discussed and compared with previous results obtained by the same method from 27 moderate Fe i lines.The van der Waals damping constant ₆ multiplied by an enhancement factor E = 2.5 is suggested for the interpretation of Fe i Fraunhofer lines.     

The empirical determination of damping constants in the solar photosphere

We determine empirical damping constants for 73 selected Fe i lines following the method of Gurtovenko and Kondrashova (1980), employing high-quality observations and the accurate list of Fe i oscillator strengths by Gurtovenko and Kostik (1980).The results show: (i) No increase of the enhancement factor to van der Waals broadening with excitation potential, as predicted by Edmunds (1975), and with the frequency of the transition (Figure 1); (ii) a substantial part of the commonly-used enhancement factor for weaker lines is not due to collisional damping (Figure 2), but to a misrepresentation of the inhomogeneous structure of the deep photosphere. This false damping effect is not seen in the stronger lines which yield an average damping constant : 1.3₆ 1.5 ₆.     

The angular momentum-vs-mass relation for spectroscopic binaries

The spectroscopic binaries, considered as a single data point, fall roughly on the universal power-law of index 1.8 for angular momentum vs total mass, as defined by planets, spiral galaxies, and numerous other objects. But the individual systems in theSeventh Catalogue of the Orbital Elements of Spectroscopic Binary Systems define a curve of rather shallower slope, 1.63±0.07, over more than two orders of magnitude in mass and four in angular momentum. Various subsets (long and short periods; single and double line systems; known and unknown orbital orientations) all yield slopes from 1.48 to 1.77. These values, as well as the slightly larger one found for eclipsing systems by Sisteró and Marton, are very much what one would expect, given the form of Kepler's Third Law and the Stellar mass-radius relation.If only these well-known pieces of physics are at work, then the still-wider visual binaries should yield a slope near 5/3. Catalogues currently in press will permit easy testing of this prediction. It seems unlikely that deep clues to the origin of either binary systems or angular momentum are to be found from considerations of this nature.     

The color-redshift relation for giant elliptical galaxies

The colors of giant elliptical (gE) galaxies in clusters out to redshiftz=0.2, observed by Oke and Sandage (1968), are studied for systematic color-redshift effects. To reveal any intrinsic changes, theK term is subtracted from each color, after correction for galactic reddening and the resulting (B-V) _c -K _B-V versus z relation analysed. If the Oke and SandageK terms (relevant to nuclear colors) are used, the best fitting linear relation shows negligible change withz. But if the Whitford (1970)K terms (relevant to integrated colors) are used, there is a trend to bluer colors, by 0.07 mag.atz=0.2 if higher weight is given the better observed clusters. An upper limit, of ±0.08 mag. atz=0.2, is set to possible systematic aperture effects, by the total change between nuclear and integrated B-V and U-B of nearbygE galaxies.The color-redshift trends, interpreted as evolutionary changes, are related to evolution in the magnitude-redshift relation by means of models of stellar evolution in agE galaxy. If one uses the linear fit to the color-redshift relation obtained with WhitfordK terms and neglect of any aperture effects (which is the appropriate case if Oke and Sandage used large enough apertures), and if one adopts plausible limits to the ratio between color and magnitude evolution, the effect of evolution in the magnitude-redshift relation results in a negative value ofq ₀. There are still substantial observational and theoretical uncertainties affecting this conclusion.     

The relation between far-UV and visible extinctions

For directions of sufficient reddening (E(B−V)>∼0.25), there is a simple relation between the slope of the extinction curve in the far-UV and E(B−V). Regardless of direction, the far-UV extinction curve is proportional to 1/λⁿ e^{−2E(B−V)/λ} (λ in μm, n=4), in accordance with the idea that reddened stars spectra are contaminated by scattered light (Zagury, 2001b).This relation is not compatible with the standard theory of extinction which states that far-UV and visible extinctions are due to different classes of particle. In that model the two (far-UV and visible) extinctions vary thus independently according to the proportion of each type of particle.In preceding papers I have shown that the standard theory cannot explain UV observations of nebulae, and is contradicted by the UV spectra of stars with very low reddening: for how long shall the standard theory be considered as the interpretation of the extinction curve?     

The relation between hot and cool loops

In order to study the origin of the hot (3 MK) corona above active regions, we compare Yohkoh/SXT X-ray images, which represent a broad temperature range above 2.5 MK, with TRACE EUV coronal images whose primary sensitivities are in the 1–2 MK range. Nearly simultaneous X-ray and EUV snapshots show that there are loops that appear similar in these images of different temperature sensitivities, but they are not exactly cospatial with each other. A significant difference is noted in the active region core, where bright loops are seen in X-ray images but not in EUV images, reflecting their high (5 MK) temperatures. In SXT time-sequence images, these loops are found to undergo repetitive minor brightenings, suggestive of their flare-like origin. This is consistent with the absence of the EUV counterparts of the X-ray loops in TRACE time-sequence images at earlier and later times. We need to revisit the validity of the assumption that coronal loops are steady.     

The X-ray intensity-hardness ratio relation in LMXRB

It is sometimes suggested that the change from the horizontal to the normal branch in the X-ray intensity-hardness ratio diagram of low mass X-ray binaries, is due to a change from a thin to a thick disk. It is shown here that wind from the hot thick disk depletes the amount of matter reaching the neutron star, thus causing the observed reduction of X-ray intensity as hardness ratio decreases in the normal branch.