Mass Effective Temperature Research Articles

Mass–effective temperature–surface gravity relation for intermediate-mass main-sequence stars

Context. In this work a mass–effective temperature–surface gravity relation (MTGR) is developed for main-sequence stars in the range 6400 K ≤ Teff ≤ 20 000 K with log g ≳ 3.44. The MTGR allows the simple estimation of the masses of stars from their effective temperatures and surface gravities. It can be used for solar metallicity and can be rescaled for any metallicity within −1.0 ≤ [Fe/H] ≤ 0.7. The effect of α-enhanced compositions can also be considered with the help of correction terms. Aims. It is aimed to develop an MTGR that can estimate the masses of main-sequence stars from their atmospheric parameters. One advantage of an MTGR over the classical mass–luminosity relations is that its mass estimation is based on parameters that can be obtained by purely spectroscopic methods, and, therefore, the interstellar extinction or reddening do not have to be known. The use of surface gravity (g) also relates an MTGR with stellar evolution and provides a more reliable mass estimation. Methods. A synthetical MTGR is obtained from theoretical isochrones using a Levenberg-Marquardt χ2 minimization algorithm. The validity of the MTGR is then checked by testing over 278 binary components with precise absolute masses. Results. Very good agreement has been obtained between the absolute masses of 278 binary star components and their masses estimated from the MTGR. A mathematical expression is also given to calculate the propagated uncertainties of the MTGR masses. Conclusions. For the typical uncertainties in atmospheric parameters and metallicity (i.e., ±2.8% for Teff, ±0.1 dex for log g and ±0.15 dex for [Fe/H]) the typical uncertainties in the masses estimated from the MTGR mostly remain around 5–9%. The fact that this uncertainty level is only on average about three times as large as that of the absolute masses indicates that the MTGR is a very powerful tool for stellar mass estimation. A computer code, mtgr.pro, written in GDL or IDL is also provided for the relation.

Interrelated main-sequence mass–luminosity, mass–radius, and mass–effective temperature relations

Absolute parameters of 509 main-sequence stars selected from the components of detached-eclipsing spectroscopic binaries in the Solar neighbourhood are used to study mass-luminosity, mass-radius and mass-effective temperature relations (MLR, MRR and MTR). The MLR function is found better if expressed by a six-piece classical MLR ($L \propto M^{\alpha}$) rather than a fifth or a sixth degree polynomial within the mass range of $0.179\leq M/M_{\odot}\leq 31$. The break points separating the mass-ranges with classical MLR do not appear to us to be arbitrary. Instead, the data indicate abrupt changes along the mass axis in the mean energy generation per unit of stellar mass. Unlike the MLR function, the MRR and MTR functions cannot be determined over the full range of masses. A single piece MRR function is calibrated from the radii of stars with $M\leq1.5M_{\odot}$, while a second single piece MTR function is found for stars with $M>1.5M_{\odot}$. The missing part of the MRR is computed from the MLR and MTR, while the missing part of the MTR is computed from the MLR and MRR. As a result, we have interrelated MLR, MRR and MTR, which are useful in determining the typical absolute physical parameters of main-sequence stars of given masses. These functions are also useful to estimate typical absolute physical parameters from typical $T_{eff}$ values. Thus, we were able to estimate the typical absolute physical parameters of main-sequence stars observed in the Sejong Open Cluster survey, based on that survey's published values for $T_{eff}$. Since typical absolute physical parameters of main sequence stars cannot normally be determined in such photometric surveys, the interrelated functions are shown to be useful to compute such missing parameters from similar surveys.

MAIN-SEQUENCE EFFECTIVE TEMPERATURES FROM A REVISED MASS–LUMINOSITY RELATION BASED ON ACCURATE PROPERTIES

The mass-luminosity (M-L), mass-radius (M-R) and mass-effective temperature ($M-T_{eff}$) diagrams for a subset of galactic nearby main-sequence stars with masses and radii accurate to $\leq 3\%$ and luminosities accurate to $\leq 30\%$ (268 stars) has led to a putative discovery. Four distinct mass domains have been identified, which we have tentatively associated with low, intermediate, high, and very high mass main-sequence stars, but which nevertheless are clearly separated by three distinct break points at 1.05, 2.4, and 7$M_{\odot}$ within the mass range studied of $0.38-32M_{\odot}$. Further, a revised mass-luminosity relation (MLR) is found based on linear fits for each of the mass domains identified. The revised, mass-domain based MLRs, which are classical ($L \propto M^{\alpha}$), are shown to be preferable to a single linear, quadratic or cubic equation representing as an alternative MLR. Stellar radius evolution within the main-sequence for stars with $M>1M_{\odot}$ is clearly evident on the M-R diagram, but it is not the clear on the $M-T_{eff}$ diagram based on published temperatures. Effective temperatures can be calculated directly using the well-known Stephan-Boltzmann law by employing the accurately known values of M and R with the newly defined MLRs. With the calculated temperatures, stellar temperature evolution within the main-sequence for stars with $M>1M_{\odot}$ is clearly visible on the $M-T_{eff}$ diagram. Our study asserts that it is now possible to compute the effective temperature of a main-sequence star with an accuracy of $\sim 6\%$, as long as its observed radius error is adequately small (<1%) and its observed mass error is reasonably small (<6%).

The mass and radius of the M-dwarf companion in the double-lined eclipsing binary T-Cyg1-01385

We observed spectroscopically the eclipsing binary system T-Cyg1-01385 in order to determine physical properties of the components. The double-lined nature of the system is revealed for the first time and the radial velocities are obtained for both stars. We have derived masses, radii and luminosities for both components. Analyzes of the radial velocities and the KeplerCam and the TrES light curves yielded masses of M1=1.059±0.032 M⊙ and M2=0.342±0.017 M⊙ and radii of R1=1.989±0.022 R⊙ and R2=0.457±0.013 R⊙. Locations of the low-mass companion in the mass-radius and mass-effective temperature planes and comparison with the other low-mass stars show that the secondary star appears just at the transition from partially to fully convective interiors for the M dwarfs. When compared to stellar evolution models, the luminosities and effective temperatures of the components are consistent with Z=0.004 and an age of about 6Gyr. A distance to the system was calculated as d=355±7 pc using the BV and JHK magnitudes.

T-Cyg1-12664: a low-mass chromospherically active eclipsing binary in the Kepler field

The eclipsing binary T-Cyg1-12664 was observed both spectroscopically and photometrically. Radial velocities of both components and ground-based VRI light curves were obtained. The Kepler's R-data and radial velocities for the system were analysed simultaneously. Masses and radii were obtained as 0.680$\pm$0.021 M$_{\odot}$ and 0.613$\pm$0.007 R$_{\odot}$for the primary and 0.341$\pm$0.012M$_{\odot}$ and 0.897$\pm$0.012R$_{\odot}$ for the secondary star. The distance to the system was estimated as 127$\pm$14 pc. The observed wave-like distortion at out-of-eclipse is modeled with two separate spots on the more massive star, which is also confirmed by the Ca {\sc ii} K and H emission lines in its spectra. Locations of the components in the mass-radius and mass-effective temperature planes were compared with the well-determined eclipsing binaries' low-mass components as well as with the theoretical models. While the primary star's radius is consistent with the main-sequence stars, the radius of the less massive component appears to be 2.8 times larger than that of the main-sequence models. Comparison of the radii of low-mass stars with the models reveals that the observationally determined radii begin to deviate from the models with a mass of 0.27 \Msun and suddenly reaches to maximum deviation at a mass of 0.34 \Msun. Then, the deviations begin to decrease up to the solar mass. The maximum deviation seen at a mass of about 0.34 \Msun is very close to the mass of fully convective stars as suggested by theoretical studies. A third star in the direction of the eclipsing pair has been detected from our VRI images. The observed infrared excess of the binary is most probably arisen from this star which may be radiated mostly in the infrared bands.

Spectroscopic and photometric observations of the selected Algol-type binaries – II. V2080 Cygni and V2365 Ophiuchi

This paper is the second in the planned series of investigations. We present new radial velocities and photometric observations of V2080 Cyg and V2365 Oph. New UBV photometric data and radial velocities were analysed for the systems' parameters. While V2080 Cyg consists of two nearly equal F-type main-sequence stars, V2365 Oph has two different components, namely an early A-type primary and a G-type secondary star. New ephemerides are calculated for both systems. The masses of the component stars have been derived as 1.19 ± 0.02 and 1.16 ± 0.02 M⊙ for V2080 Cyg and 1.97 ± 0.02 and 1.06 ± 0.01 M⊙ for V2365 Oph. The effective temperatures and reddening of the systems have been estimated from Johnson wide-band UBV photometric calibrations. The radii have been measured by simultaneous fitting the UBV light curves using Wilson–Devinney code and are 1.60 ± 0.01 R⊙ for both components of V2080 Cyg and 2.19 ± 0.01 and 0.934 ± 0.004 R⊙ for V2365 Oph. The absolute parameters of the stars in both systems lie within the same ranges in the mass–radius, mass–effective temperature, mass–luminosity and luminosity–effective temperature planes as in detached Algol systems. A comparison between the properties of the systems of interest and the predictions of theoretical evolutionary models is undertaken in the log g–logTeff, log R– log M and radius–log age diagrams. The model predictions match the measured properties of V2080 Cyg for an age of about 5.6 Gyr and a ‘solar’ metal abundance (Z= 0.019), indicating the components near the end of their core hydrogen-burning phases. However, the position of the components of V2365 Oph on the Hertzsprung–Russell (HR) diagram is best reproduced with evolutionary models for somewhat metal-deficient (Z= 0.004) stars. We found an age of about 700 Myr, with the primary component slightly evolved off the zero-age main-sequence and the secondary one still very close to it. From the basic stellar parameters we have also redetermined the distances to V2080 Cyg and V2365 Oph as 78 ± 1 and 251 ± 8 pc, which are in agreement with, and more accurate than, Hipparcos values. The observations show that at least one of the components of V2365 Oph is an intrinsic variable with a period and peak-to-peak amplitude of 0.07 d and 0.05 mag, respectively. In accordance with its position in the HR diagram, the primary component should be considered as a δ Scuti star and it is believed to be the variable star in the system.

Studies of intermediate-mass stellar models using eclipsing binaries

Evolutionary computations for intermediate-mass stars are analyzed using observed parameters for eclipsing SB2 binaries and theoretical parameters based on evolutionary tracks. Modern observations cannot be used to distinguish between models with and without convective overshooting for stars in the vicinity of the main sequence. Statistically significant discrepancies between the observed and computed stellar parameters are associated with systematic errors in photometric effective temperatures. After taking into account systematic effects, the theoretical computations fit the observational data uniformly well throughout the entire mass interval studied. Empirical and semiempirical (i.e., reduced to the ZAMS and with solar elemental abundances) formulas for the mass-luminosity, mass-effective temperature, and mass-radius relations are proposed.