Bibcode
Pérez Garrido, A.; Lodieu, N.; Béjar, V. J. S.; Ruiz, M. T.; Gauza, B.; Rebolo, R.; Zapatero Osorio, M. R.
Bibliographical reference
Astronomy and Astrophysics, Volume 567, id.A6, 8 pp.
Advertised on:
7
2014
Journal
Citations
9
Refereed citations
9
Description
Aims: The aim of the project is to find the stars closest to the
Sun and to contribute to the completion of the stellar and substellar
census of the solar neighbourhood. Methods: We identified a new
late-M dwarf within 5 pc, looking for high proper motion sources in the
2MASS-WISE cross-match. We collected astrometric and photometric data
available from public large-scale surveys. We complemented this
information with low-resolution (R ~ 500) optical (600-1000 nm) and
near-infrared (900-2500 nm) spectroscopy with instrumentation on the
European Southern Observatory New Technology Telescope to confirm the
nature of our candidate. We also present a high-quality
medium-resolution VLT/X-shooter spectrum covering the 400 to 2500 nm
wavelength range. Results: We classify this new neighbour as an
M7.0 ± 0.5 dwarf using spectral templates from the Sloan Digital
Sky Survey and spectral indices. Lithium absorption at 670.8 nm is not
detected in the X-shooter spectrum, indicating that the M7 dwarf is
older than 600 Myr and more massive than 0.06 M⊙. We also
derive a trigonometric distance of 4.4+0.5-0.4 pc,
in agreement with the spectroscopic distance estimate, making 2MASS
J154043.42-510135.7 (2M1540) the nearest M7 dwarf to the Sun. This
trigonometric distance is somewhat closer than the ~6 pc distance
reported by the ALLWISE team, who independently identified this object
recently. This discovery represents an increase by 25% in the number of
M7-M8 dwarfs already known at distances closer than 8 pc from our Sun.
We derive a density of ρ = 1.9 ± 0.9 × 10-3
pc-3 for M7 dwarfs in the 8 pc volume, a value similar to
those quoted in the literature. Conclusions: This new ultracool
dwarf is among the 50 closest systems to the Sun, demonstrating that our
current knowledge of the stellar census within the 5 pc sample remains
incomplete. 2M1540 represents a unique opportunity to search for
extrasolar planets around ultracool dwarfs due to its proximity and
brightness.
Based on observations collected at the European Organisation for
Astronomical Research in the Southern Hemisphere, Chile.
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