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On the Age, Spectral Type, Orbit, and Comparison to Evolutionary Models of AB Dor C

Published online by Cambridge University Press:  02 May 2006

L. M. Close
Affiliation:
Steward Observatory, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721 USA, email: lclose@as.arizona.edu
E. L. Nielsen
Affiliation:
Steward Observatory, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721 USA, email: lclose@as.arizona.edu
J. C. Guirado
Affiliation:
Departament d'Astronomia i Astrofisica, Universitat de Valencia, E-46100 Burjassot, Valencia, Spain
B. A. Biller
Affiliation:
Steward Observatory, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721 USA, email: lclose@as.arizona.edu
R. Lenzen
Affiliation:
Max-Plank-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
W. Brandner
Affiliation:
Max-Plank-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
M. Hartung
Affiliation:
European Southern Observatory, Alonso de Cordova 3107, Santiago 19, Chile
C. Lidman
Affiliation:
European Southern Observatory, Alonso de Cordova 3107, Santiago 19, Chile
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Abstract

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We expand upon the results of Close et al. 2005 regarding the young, low-mass object AB Dor C and its role as a calibration point for theoretical tracks. We argue for a new 70$\pm$30 Myr age estimate and present two additional detections of C with the Simultaneous Differential Imaging (SDI) camera. Our improved analysis (Nielsen et al. 2005) confirms our spectral type of M8 ($\pm$1) and mass of 0.090 $\pm$0.003 M$_{\hbox{\it \scriptsize sun}}$ for AB Dor C. However, Luhman & Potter (2006) argue for a hotter spectral type (M6$\pm$1). Here we adopt the consistent spectral range of M7$\pm$1 in this paper as a final spectral type. Plotting AB Dor C (and all other young (${<}0.12$ Myr), low-mass ($0.3-0.05 M_{\hbox{\it \scriptsize sun}}$) objects with accurate dynamical masses) on the HR diagram suggests a trend where current evolutionary models tend to over-predict the temperature (or under-predict the mass) for young low-mass stars and high-mass brown dwarfs. With our uncertainties, there is a $\sim$90% chance that the mass of AB Dor C is underestimated by the DUSTY tracks in the HR diagram.

Type
Contributed Papers
Copyright
© 2006 International Astronomical Union