Bibcode
Marocco, F.; Day-Jones, A. C.; Lucas, P. W.; Jones, H. R. A.; Smart, R. L.; Zhang, Z. H.; Gomes, J. I.; Burningham, B.; Pinfield, D. J.; Raddi, R.; Smith, L.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 439, Issue 1, p.372-386
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3
2014
Citations
58
Refereed citations
53
Description
We report the discovery of a peculiar L dwarf from the United Kingdom
Infrared Deep Sky Survey Large Area Survey, ULAS J222711-004547. The
very red infrared photometry (MKO J - K = 2.79 ± 0.06, WISE W1-W2
= 0.65 ± 0.05) of ULAS J222711-004547 makes it one of the reddest
brown dwarfs discovered so far. We obtained a moderate resolution
spectrum of this target using the XSHOOTER spectrograph on the Very
Large Telescope, and we classify it as L7pec, confirming its very red
nature. Comparison to theoretical models suggests that the object could
be a low-gravity L dwarf with a solar or higher than solar metallicity.
Nonetheless, the match of such fits to the spectral energy distribution
is rather poor, and this and other less red peculiar L dwarfs pose new
challenges for the modelling of ultracool atmospheres, especially to the
understanding of the effects of condensates and their sensitivity to
gravity and metallicity. We determined the proper motion of ULAS
J222711-004547 using the data available in the literature, and we find
that its kinematics do not suggest membership of any of the known young
associations. We show that applying a simple de-reddening curve to its
spectrum allows it to resemble the spectra of the L7 spectroscopic
standards without any spectral features that distinguish it as a
low-metallicity or low-gravity dwarf. Given the negligible interstellar
reddening of the field containing our target, we conclude that the
reddening of the spectrum is mostly due to an excess of dust in the
photosphere of the target. De-reddening the spectrum using extinction
curves for different dust species gives surprisingly good results and
suggests a characteristic grain size of ˜0.5 μm. We show that
by increasing the optical depth, the same extinction curves allow the
spectrum of ULAS J222711-004547 to resemble the spectra of unusually
blue L dwarfs and even slightly metal-poor L dwarfs. Grains of similar
size also yield very good fits when de-reddening other unusually red L
dwarfs in the L5-L7.5 range. These results suggest that the diversity in
near-infrared colours and spectra seen in late L dwarfs could be due to
differences in the optical thickness of the dust cloud deck.
Related projects
Very Low Mass Stars, Brown Dwarfs and Planets
Our goal is to study the processes that lead to the formation of low mass stars, brown dwarfs and planets and to characterize the physical properties of these objects in various evolutionary stages. Low mass stars and brown dwarfs are likely the most numerous type of objects in our Galaxy but due to their low intrinsic luminosity they are not so
Rafael
Rebolo López