Bibcode
Bouy, H.; Martín, E. L.; Brandner, W.; Forveille, T.; Delfosse, X.; Huélamo, N.; Basri, G.; Girard, J.; Zapatero Osorio, M.-R.; Stumpf, M.; Ghez, A.; Valdivielso, L.; Marchis, F.; Burgasser, A. J.; Cruz, K.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 481, Issue 3, 2008, pp.757-767
Fecha de publicación:
4
2008
Revista
Número de citas
19
Número de citas referidas
18
Descripción
Context: Astrometric observations of resolved binaries provide estimates
of orbital periods and will eventually lead to measurement of dynamical
masses. Only a few very low mass star and brown dwarf masses have been
measured to date, and the mass-luminosity relation still needs to be
calibrated. Aims: We have monitored 14 very low mass multiple
systems for several years to confirm their multiplicity and, for those
with a short period, derive accurate orbital parameters and dynamical
mass estimates. Methods: We have used high spatial resolution
images obtained at the Paranal, Lick and HST observatories to obtain
astrometric and photometric measurements of the multiple systems at
several epochs. The targets have periods ranging from 5 to 200 years,
and spectral types in the range M7.5-T5.5. Results: All of our
14 multiple systems are confirmed as common proper motion pairs. One
system (2MASSW J0920122+351742) is not resolved in our new images,
probably because the discovery images were taken near maximum
elongation. Six systems have periods short enough to allow dynamical
mass measurements within the next 15 to 20 years. We estimate that only
8% of the ultracool dwarfs in the solar neighborhood are binaries with
separations large enough to be resolved, and yet periods short enough to
derive astrometric orbital fits over a reasonable time frame with
current instrumentation. A survey that doubles the number of ultracool
dwarfs observed with high angular resolution is called for to discover
enough binaries for a first attempt to derive the mass-luminosity
relationship for very low-mass stars and brown dwarfs.