The AB Doradus System Revisited: The Dynamical Mass of AB Dor A

DOI: 10.1007/978-3-642-11250-8_13

ABSTRACT We report new radio interferometric observations of the quadruple pre-main-sequence (PMS) system ABD oradus. From these observations,
combined with existing VLT near-infrared relative astrometry, we have refined the estimates of the dynamical masses of the
system. In particular, we find component masses of 0.86 ± 0.09M⊙ and 0.090 ± 0.003M⊙ for ABD or A and ABD or C, respectively. These dynamical masses, coupled with temperatures and luminosities, allow for comparison
with theoretical stellar models. The case of ABDorC, in terms of calibration of evolutionary models of low-mass young stars
has been widely reported in previous studies. In this contribution, we compare the measured properties of ABDorA with several
solar-composition models for PMS stars. The models used in this comparison predict the dynamical mass to within the quoted

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    ABSTRACT: We present an astrometric analysis of the binary systems AB Dor A /AB Dor C and AB Dor Ba /AB Dor Bb. These two systems of well-known late-type stars are gravitationally associated and they constitute the quadruple AB Doradus system. From the astrometric data available at different wavelengths, we report: (i) a determination of the orbit of AB Dor C, the very low mass companion to AB Dor A, which confirms the mass estimate of 0.090 $M_\odot$ reported in previous works; (ii) a measurement of the parallax of AB Dor Ba, which unambiguously confirms the long-suspected physical association between this star and AB Dor A; and (iii) evidence of orbital motion of AB Dor Ba  around AB Dor A, which places an upper bound of 0.4 $M_\odot$ on the mass of the pair AB Dor Ba /AB Dor Bb  (50% probability). Further astrometric monitoring of the system at all possible wavelengths would determine with extraordinary precision the dynamical mass of its four components.
    Astronomy and Astrophysics 02/2006; 446(2). DOI:10.1051/0004-6361:20053757 · 4.48 Impact Factor
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    ABSTRACT: We present evolutionary calculations for very-low-mass stars and brown dwarfs based on synthetic spectra and non-grey atmosphere models which include dust formation and opacity, i.e. objects with $\te\simle 2800$ K. The interior of the most massive brown dwarfs is shown to develop a conductive core after $\sim 2$ Gyr which slows down their cooling. Comparison is made in optical and infrared color-magnitude diagrams with recent late-M and L-dwarf observations. The saturation in optical colors and the very red near-infrared colors of these objects are well explained by the onset of dust formation in the atmosphere. Comparison of the faintest presently observed L-dwarfs with these dusty evolutionary models suggests that dynamical processes such as turbulent diffusion and gravitational settling are taking place near the photosphere. As the effective temperature decreases below $\te\approx 1300-1400$ K, the colors of these objects move to very blue near-infrared colors, a consequence of the ongoing methane absorption in the infrared. We suggest the possibility ofa brown dwarf dearth in $J,H,K$ color-magnitude diagrams around this temperature.
    The Astrophysical Journal 06/2000; DOI:10.1086/309513 · 6.28 Impact Factor
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    ABSTRACT: We present new photometric and spectroscopic measurements for the unique, young, low-mass evolutionary track calibrator AB Dor C. While the new Ks photometry is similar to that previously published in Close et al. (2005) the spectral type is found to be earlier. Based on new H & K IFS spectra of AB Dor C (Thatte et al. 2007; paper 1) we adopt a spectral type of M5.5+/-1.0 for AB Dor C. This is considerably earlier than the M8+/-1 estimated in Close et al. (2005) and Nielsen et al. (2005) yet is consistent with the M6+/-1 independently derived by Luhman & Potter (2005). However, the spectrum presented in paper 1 and analyzed here is a significant improvement over any previous spectrum of AB Dor C. We also present new astrometry for the system which further supports a 0.090+/-0.005 Msun mass for the system. Once armed with an accurate spectrum and Ks flux we find L=0.0021+/-0.0005 Lsun and Teff=2925{+170}{-145}K for AB Dor C. These values are consistent with a ~75 Myr 0.090+/-0.005 Msun object like AB Dor C according to the DUSTY evolutionary tracks (Chabrier et al. 2000). Hence masses can be estimated from the HR diagram with the DUSTY tracks for young low-mass objects like AB Dor C. However, we cautiously note that underestimates of the mass from the tracks can occur if one lacks a proper (continuum preserved) spectra or is relying on NIR fluxes alone.
    The Astrophysical Journal 03/2007; 665(1). DOI:10.1086/518207 · 6.28 Impact Factor