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Register a new userMass-luminosity relation for FGK main sequence stars: metallicity and age contributions
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The stellar mass-luminosity relation (MLR) is one of the most famous empirical laws, discovered in the beginning of the 20th century. MLR is still used to estimate stellar masses for nearby stars, particularly for those that are not binary systems, hence the mass cannot be derived directly from the observations. Its well known that the MLR has a statistical dispersion which cannot be explained exclusively due to the observational errors in luminosity (or mass). It is an intrinsic dispersion caused by the differences in age and chemical composition from star to star. In this work we discuss the impact of age and metallicity on the MLR. Using the recent data on mass, luminosity, metallicity, and age for 26 FGK stars (all members of binary systems, with observational mass-errors <= 3%), including the Sun, we derive the MLR taking into account, separately, mass-luminosity, mass-luminosity-metallicity, and mass-luminosity-metallicity-age. Our results show that the inclusion of age and metallicity in the MLR, for FGK stars, improves the individual mass estimation by 5% to 15%.
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The age-metallicity relation is a fundamental tool for constraining the chemical evolution of the Galactic disc. In this work we analyse the observational properties of this relation using binary stars that have not interacted consisting of a white dwarf - from which we can derive the total age of the system - and a main sequence star - from which we can derive the metallicity as traced by the [Fe/H] abundances. Our sample consists of 46 widely separated, but unresolved spectroscopic binaries identified within the Sloan Digital Sky Survey, and 189 white dwarf plus main sequence common proper motion pairs identified within the second data release of Gaia. This is currently the largest white dwarf sample for which the metallicity of their progenitors have been determined. We find a flat age-metallicity relation displaying a scatter of [Fe/H] abundances of approximately 0.5 dex around the solar metallicity at all ages. This independently confirms the lack of correlation between age and metallicity in the solar neighbourhood that is found in previous studies focused on analysing single main sequence stars and open clusters.
In this work, a mass-effective temperature-surface gravity relation (MTGR) is developed for main sequence stars in the range of 6400 K < $T_{rm eff}$ < 20000 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 -1.00 < [Fe/H] < 0.7. The effect of alpha-enhanced compositions can also be considered with the help of correction terms. 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. A synthetical MTGR is obtained from theoretical isochrones using a Levenberg-Marquardt chi-square minimization algorithm. The validity of the MTGR is then checked by testing over 278 binary components with precise absolute masses. 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. For the typical uncertainties in atmospheric parameters and metallicity, 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/IDL is also provided for the relation.
We present a Mass-Luminosity Relation (MLR) for red dwarfs spanning a range of masses from 0.62 Msun to the end of the stellar main sequence at 0.08 Msun. The relation is based on 47 stars for which dynamical masses have been determined, primarily using astrometric data from Fine Guidance Sensors (FGS) 3 and 1r, white-light interferometers on the Hubble Space Telescope (HST), and radial velocity data from McDonald Observatory. For our HST/FGS sample of 15 binaries component mass errors range from 0.4% to 4.0% with a median error of 1.8%. With these and masses from other sources, we construct a V-band MLR for the lower main sequence with 47 stars, and a K-band MLR with 45 stars with fit residuals half of those of the V-band. We use GJ 831 AB as an analysis example, obtaining an absolute trigonometric parallax, pi_abs = 125.3 +/- 0.3 milliseconds of arc, with orbital elements yielding MA = 0.270 +/- 0.004 Msun and MB = 0.145 +/- 0.002 Msun. The mass precision rivals that derived for eclipsing binaries. A remaining major task is the interpretation of the intrinsic cosmic scatter in the observed MLR for low mass stars in terms of physical effects. In the meantime, useful mass values can be estimated from the MLR for the ubiquitous red dwarfs that account for 75% of all stars, with applications ranging from the characterization of exoplanet host stars to the contribution of red dwarfs to the mass of the Universe.
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 age-metallicity relation (AMR) is a fundamental observational constraint for understanding how the Galactic disc formed and evolved chemically in time. However, there is not yet an agreement on the observational properties of the AMR for the solar neighbourhood, primarily due to the difficulty in obtaining accurate stellar ages for individual field stars. We have started an observational campaign for providing the much needed observational input by using wide white dwarf-main sequence (WDMS) binaries. White dwarfs are natural clocks and can be used to derive accurate ages. Metallicities can be obtained from the main sequence companions. Since the progenitors of white dwarfs and the main sequence stars were born at the same time, WDMS binaries provide a unique opportunity to observationally constrain in a robust way the properties of the AMR. In this work we present the AMR derived from analysing a pilot sample of 23 WDMS binaries and provide clear observational evidence for the lack of correlation between age and metallicity at young and intermediate ages (0-7 Gyrs).
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