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Register a new userThe mass and radius of the M-dwarf companion in the double-lined eclipsing binary T-Cyg1-01385
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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. Analyses of the radial velocities and the KeplerCam and the T$r$ES light curves yielded masses of M$_1$=1.059$pm$0.032 Msun ~and M$_2$=0.342$pm$0.017 {Msun} and radii of R$_1$=1.989$pm$0.022 {Rsun} and R$_2$=0.457$pm$0.013 {Rsun}. Locations of the low-mass companion in the mass-radius and mass-effective temperature planes and comparison with the other low-mass stars show that the secondary star appears just at the transition from partially to fully convective interiors for the M dwarfs. When compared to stellar evolution models, the luminosities and effective temperatures of the components are consistent with Z=0.004 and an age of about 6 Gyr. A distance to the system was calculated as d=355$pm$7 pc using the BV and JHK magnitudes.
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We derive masses and radii for both components in the single-lined eclipsing binary HAT-TR-205-013, which consists of a F7V primary and a late M-dwarf secondary. The systems period is short, $P=2.230736 pm 0.000010$ days, with an orbit indistinguisha
ble from circular, $e=0.012 pm 0.021$. We demonstrate generally that the surface gravity of the secondary star in a single-lined binary undergoing total eclipses can be derived from characteristics of the light curve and spectroscopic orbit. This constrains the secondary to a unique line in the mass-radius diagram with $M/R^2$ = constant. For HAT-TR-205-013, we assume the orbit has been tidally circularized, and that the primarys rotation has been synchronized and aligned with the orbital axis. Our observed line broadening, $V_{rm rot} sin i_{rm rot} = 28.9 pm 1.0$ kms, gives a primary radius of $R_{rm A} = 1.28 pm 0.04$ rsun. Our light curve analysis leads to the radius of the secondary, $R_{rm B} = 0.167 pm 0.006$ rsun, and the semimajor axis of the orbit, $a = 7.54 pm 0.30 rsun = 0.0351 pm 0.0014$ AU. Our single-lined spectroscopic orbit and the semimajor axis then yield the individual masses, $M_{rm B} = 0.124 pm 0.010$ msun and $M_{rm A} = 1.04 pm 0.13$ msun. Our result for HAT-TR-205-013 B lies above the theoretical mass-radius models from the Lyon group, consistent with results from double-lined eclipsing binaries. The method we describe offers the opportunity to study the very low end of the stellar mass-radius relation.
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 Keplers 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 stars 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.
We present spectroscopy and photometry of GD 448, a detached white dwarf - M dwarf binary with a period of 2.47h. We find that the NaI 8200A feature is composed of narrow emission lines due to irradiation of the M dwarf by the white dwarf within broad absorption lines that are essentially unaffected by heating. Combined with an improved spectroscopic orbit and gravitational red shift measurement from spectra of the H-alpha line, we are able to derive masses for the white dwarf and M dwarf directly (0.41 +/- 0.01 solar masses and 0.096 +/- 0.004 solar masses, respectively). We use a simple model of the CaII emission lines to establish the radius of the M dwarf assuming the emission from its surface to be proportional to the incident flux per unit area from the white dwarf. The radius derived is 0.125 +/- 0.020 solar radii. The M dwarf appears to be a normal main-sequence star in terms of its mass and radius and is less than half the size of its Roche lobe. The thermal timescale of the M dwarf is much longer than the cooling age of the white dwarf so we conclude that the M dwarf was unaffected by the common-envelope phase. The anomalous width of the H-alpha emission from the M dwarf remains to be explained, but the strengh of the line may be due to X-ray heating of the M dwarf due to accretion onto the white dwarf from the M dwarf wind.
In this paper we present the discovery of a highly unequal-mass eclipsing M-dwarf binary, providing a unique constraint on binary star formation theory and on evolutionary models for low-mass binary stars. The binary is discovered using high- precision infrared light curves from the WFCAM Transit Survey (WTS) and has an orbital period of 2.44 d. We find stellar masses of M1 = 0.53 (0.02) Msun and M2 = 0.143 (0.006) Msun (mass ratio 0.27), and radii of R1 = 0.51 (0.01) Rsun and R2 = 0.174 (0.006) Rsun. This puts the companion in a very sparsely sampled and important late M-dwarf mass-regime. Since both stars share the same age and metallicity and straddle the theoretical boundary between fully and partially convective stellar interiors, a comparison can be made to model predictions over a large range of M-dwarf masses using the same model isochrone. Both stars appear to have a slightly inflated radius compared to 1 Gyr model predictions for their masses, but future work is needed to properly account for the effects of star spots on the light curve solution. A significant, subsynchronous, ~2.56 d signal with ~2% peak-to-peak amplitude is detected in the WFCAM light curve, which we attribute to rotational modulation of cool star spots. We propose that the subsynchronous rotation is either due to a stable star-spot complex at high latitude on the (magnetically active) primary (i.e. differential rotation), or to additional magnetic braking, or to interaction of the binary with a third body or circumbinary disk during its pre-main-sequence phase.
We report the discovery of KELT J041621-620046, a moderately bright (J$sim$10.2) M dwarf eclipsing binary system at a distance of 39$pm$3 pc. KELT J041621-620046 was first identified as an eclipsing binary using observations from the Kilodegree Extremely Little Telescope (KELT) survey. The system has a short orbital period of $sim$1.11 days and consists of components with M$_1$ = $0.447^{-0.047}_{+0.052},M_odot$ and M$_2$ = $0.399^{-0.042}_{+0.046},M_odot$ in nearly circular orbits. The radii of the two stars are R$_1$ = $0.540^{-0.032}_{+0.034},R_odot$ and R$_2$ = $0.453pm0.017,R_odot$. Full system and orbital properties were determined (to $sim$10% error) by conducting an EBOP global modeling of the high precision photometric and spectroscopic observations obtained by the KELT Follow-up Network. Each star is larger by 17-28% and cooler by 4-10% than predicted by standard (non-magnetic) stellar models. Strong H$alpha$ emission indicates chromospheric activity in both stars. The observed radii and temperature discrepancies for both components are more consistent with those predicted by empirical relations that account for convective suppression due to magnetic activity.
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