Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005jrasc..99..132a&link_type=abstract
Journal of the Royal Astronomical Society of Canada, Vol. 99, No. 4, p.132
Astronomy and Astrophysics
Astronomy
Scientific paper
When substellar-mass objects cool, they successively go through the M, L, and T spectral types; the latter being the coolest extension of the HR diagram. The L/T transition is defined as the moment when methane spectroscopic signature appears in the near-infrared. Also, the dust clouds that seclude a large fraction of metals in the dwarf atmosphere sink below the photosphere at this transition. This disappearance of clouds has a significant effect on the L/T dwarf colours and has been invoked to explain the rapid change of colour of brown dwarfs around 1200 K. The position of some brown dwarfs at the L/T boundary and early T in the near-infrared colour-magnitude diagram also suggests that their surface can be partially cloudy. Because of rotation, this patchy distribution of clouds can result in temporal variability. If very short-lived (i.e. a few hours at most) atmospheric patterns exist, variability can also arise on timescales shorter than the rotation period. Time-resolved observations of T dwarfs thus have the prospect of confirming the uneven cloud cover of L/T transition and early-T brown dwarf atmospheres and determining the lifetime of such cloud patterns. Using the CFH and OMM telescopes, we undertook nearinfrared photometric and spectroscopic observations of a sample of T dwarfs to look for such a variability. I will discuss these results and their implications for brown dwarf atmospheric models.
Artigau Étienne
Doyon Rene
Nadeau Daniel
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