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Register a new userTOI-503: The first known brown dwarf-Am star binary from the TESS mission
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Authors
Jan v{S}ubjak
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We report the discovery of an intermediate-mass transiting brown dwarf, TOI-503b, from the TESS mission. TOI-503b is the first brown dwarf discovered by TESS and orbits a metallic-line A-type star with a period of $P=3.6772 pm 0.0001$ days. The light curve from TESS indicates that TOI-503b transits its host star in a grazing manner, which limits the precision with which we measure the brown dwarfs radius ($R_b = 1.34^{+0.26}_{-0.15} R_J$). We obtained high-resolution spectroscopic observations with the FIES, Ondv{r}ejov, PARAS, Tautenburg, and TRES spectrographs and measured the mass of TOI-503b to be $M_b = 53.7 pm 1.2 M_J$. The host star has a mass of $M_star = 1.80 pm 0.06 M_odot$, a radius of $R_star = 1.70 pm 0.05 R_odot$, an effective temperature of $T_{rm eff} = 7650 pm 160$K, and a relatively high metallicity of $0.61pm 0.07$ dex. We used stellar isochrones to derive the age of the system to be $sim$180 Myr, which places its age between that of RIK 72b (a $sim$10 Myr old brown dwarf in the Upper Scorpius stellar association) and AD 3116b (a $sim$600 Myr old brown dwarf in the Praesepe cluster). We argue that this brown dwarf formed in-situ, based on the young age of the system and the long circularization timescale for this brown dwarf around its host star. TOI-503b joins a growing number of known short-period, intermediate-mass brown dwarfs orbiting main sequence stars, and is the second such brown dwarf known to transit an A star, after HATS-70b. With the growth in the population in this regime, the driest region in the brown dwarf desert ($35-55 M_J sin{i}$) is reforesting and its mass range shrinking.
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The Transiting Exoplanet Survey Satellite (TESS) is observing bright known planet-host stars across almost the entire sky. These stars have been subject to extensive ground-based observations, providing a large number of radial velocity (RV) measurements. In this work we use the new TESS photometric observations to characterize the star $lambda^2$ Fornacis, and following this to update the parameters of the orbiting planet $lambda^2$ For b. We measure the p-mode oscillation frequencies in $lambda^2$ For, and in combination with non-seismic parameters estimate the stellar fundamental properties using stellar models. Using the revised stellar properties and a time series of archival RV data from the UCLES, HIRES and HARPS instruments spanning almost 20 years, we refit the orbit of $lambda^2$ For b and search the RV residuals for remaining variability. We find that $lambda^2$ For has a mass of $1.16pm0.03$M$_odot$ and a radius of $1.63pm0.04$R$_odot$, with an age of $6.3pm0.9$Gyr. This and the updated RV measurements suggest a mass of $lambda^2$ For b of $16.8^{+1.2}_{-1.3}$M$_oplus$, which is $sim5$M$_oplus$ less than literature estimates. We also detect a periodicity at 33 days in the RV measurements, which is likely due to the rotation of the host star. While previous literature estimates of the properties of $lambda^2$ are ambiguous, the asteroseismic measurements place the star firmly at the early stage of its subgiant evolutionary phase. Typically only short time series of photometric data are available from TESS, but by using asteroseismology it is still possible to provide tight constraints on the properties of bright stars that until now have only been observed from the ground. This prompts a reexamination of archival RV data from the past few decades to update the characteristics of the planet hosting systems observed by TESS for which asteroseismology is possible.
We present the analysis of the gravitational microlensing event OGLE-2013-BLG-0102. The light curve of the event is characterized by a strong short-term anomaly superposed on a smoothly varying lensing curve with a moderate magnification $A_{rm max}sim 1.5$. It is found that the event was produced by a binary lens with a mass ratio between the components of $q = 0.13$ and the anomaly was caused by the passage of the source trajectory over a caustic located away from the barycenter of the binary. From the analysis of the effects on the light curve due to the finite size of the source and the parallactic motion of the Earth, the physical parameters of the lens system are determined. The measured masses of the lens components are $M_{1} = 0.096 pm 0.013~M_{odot}$ and $M_{2} = 0.012 pm 0.002~M_{odot}$, which correspond to near the hydrogen-burning and deuterium-burning mass limits, respectively. The distance to the lens is $3.04 pm 0.31~{rm kpc}$ and the projected separation between the lens components is $0.80 pm 0.08~{rm AU}$.
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