Abstract
We have used the 2MASS all-sky survey and WISE to look for ultracool dwarfs that are part of multiple systems containing main sequence stars. We cross-matched L dwarf candidates from the surveys with Hipparcos and Gliese stars, finding two new systems. We consider the binary fraction for L dwarfs and main sequence stars, and further assess possible unresolved multiplicity within the full companion sample. This analysis shows that some of the L dwarfs in this sample might actually be unresolved binaries themselves. We have also identified a sample of common proper motion systems in which a main sequence star has a white dwarf as wide companion. These systems can help explore key issues in star evolution theory, as the initial-final mass relationship of white dwarfs, or the chromospheric activity-age relationship for stars still in the main sequence. Spectroscopy for 50 white dwarf candidates, selected from the SuperCOSMOS Science Archive, was obtained. We have also observed 6 of the main sequence star companions, and have estimated their effective temperatures, rotational and microturbulent velocities and metallicities.
Highlights
We have used the 2MASS all-sky survey and WISE to look for ultracool dwarfs that are part of multiple systems containing main sequence stars
We have identified a sample of common proper motion systems in which a main sequence star has a white dwarf as wide companion
The first binary, G255-34AB, consists of a new L2 dwarf with a K8 star as companion, at a distance of 36 pc. This L dwarf has been detected in WISE and W1 and W2 colours have been used to estimate its spectral type, later confirmed with spectroscopic observations taken with the DOLORES instrument, at the TNG telescope
Summary
The complexities of ultracool atmospheres are best confronted by observations of ultracool dwarfs (UCDs) with well known physical properties (luminosity, mass, effective temperature, surface gravity, and metallicity), so called “benchmark objects” [1]. Amongst the various types of benchmark objects, the ones that have a main sequence (MS) star as a wide companion are one of the most plentiful Assuming that both components in the system are coeval, we can infer the properties of the secondary by studying the primary and see how their spectral energy distribution depends on physical properties. 1.1 Method We have used various large infrared sky surveys (2MASS, WIDE, UKIDSS and VISTA) to look for L dwarfs. The result is the discovery of two new benchmark systems (from WISE and 2MASS), presented in Gomes et al (submitted)
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