Examinando por Autor "Mamajek, E.E."

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    MagAO IMAGING OF LONG-PERIOD OBJECTS (MILO). II. A PUZZLING WHITE DWARF AROUND THE SUN-LIKE STAR HD 11112
    (IOP PUBLISHING, 2016-11) Rodigas, T.J.; Bergeron, P.; Simon, A.; Arriagada, P.; Faherty, J.K.; Anglada-Escudé, G.; Mamajek, E.E.; Weinberger, A.; Butler, R.P.; Males, J.R.; Morzinski, K.; Close, L.M.; Hinz, P.M.; Bailey, J.; Carter, B.; Jenkins, J.S.; Jones, H.; O'Toole, S.; Tinney, C.G.; Wittenmyer, R.; Debes, J.
    HD 11112 is an old, Sun-like star that has a long-term radial velocity (RV) trend indicative of a massive companion on a wide orbit. Here we present direct images of the source responsible for the trend using the Magellan Adaptive Optics system. We detect the object (HD 11112B) at a separation of 2 2 (100 au) at multiple wavelengths spanning 0.6-4 mu m. and show that it is most likely a gravitationally bound cool white dwarf. Modeling its spectral energy distribution suggests that its mass is 0.9-1.1M(circle dot), which corresponds to very high eccentricity, near edge-on orbits from a. Markov chain Monte Carlo analysis of the RV and imaging data together. The total age of the white dwarf is > 2 sigma, which is discrepant with that of the primary star under most assumptions. The problem can be resolved if the white dwarf progenitor was initially a double white dwarf binary that then merged into the observed high-mass white dwarf. HD 11112B is a unique and intriguing benchmark object that can be used to calibrate atmospheric and evolutionary models of cool white dwarfs and should thus continue to be monitored by RV and direct imaging over the coming years.
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    Properties of the solar neighbor WISE J072003.20-084651.2
    (EDP Sciences, 2015-02) Ivanov, V.D.; Vaisanen, P.; Kniazev, A.Y.; Beletsky, Y.; Mamajek, E.E.; Mužić, K.; Beamín, J.C.; Boffin, H.M.J.; Pourbaix, D.; Gandhi, P.; Gulbis, A.; Monaco, L.; Saviane, I.; Kurtev, R.; Mawet, D.; Borissova, J.; Minniti, D.
    Context. The severe crowding towards the Galactic plane suggests that the census of nearby stars in that direction may be incomplete. Recently, Scholz reported a new M9 object at an estimated distance d ≃ 7 pc (WISE J072003.20- 084651.2; hereafter WISE J0720) at Galactic latitude b = 2.3°. Aims. Our goals are to determine the physical characteristics of WISE J0720, its kinematic properties, and to address the question of whether it is a binary object, as was suggested in the discovery paper. Methods. Optical and infrared spectroscopy from the Southern African Large Telescope and Magellan, respectively, and spectral energy distribution fitting were used to determine the spectral type of WISE J0720. The measured radial velocity, proper motion, and parallax yielded its Galactic velocities. We also investigated if WISE J0720 may show X-ray activity based on archival data. Results. Our spectra are consistent with spectral type L0 ± 1. We find no evidence for binarity, apart from a minor 2σ level difference in the radial velocities taken at two different epochs. The spatial velocity of WISE J0720 does not connect it to any known moving group; instead, it places the object with high probability in the old thin disk or in the thick disk. The spectral energy distribution fit hints at excess in the 12 μm and 22 μm WISE bands which may be due to a redder companion, but the same excess is visible in other late-type objects, and it more likely implies a shortcoming of the models (e.g., problems with the effective wavelengths of the filters for these extremely cool objects, etc.) rather than a disk or redder companion. The optical spectrum shows some Hα emission, indicative of stellar activity. Archival X-ray observations yield no detection. Conclusions. WISE J0720 is a new member of the solar neighborhood, the third nearest L dwarf. Our data do not support the hypothesis of its binary nature. © ESO 2015.