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Filling the Brown Dwarf Census of the Solar Neighbourhood

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Filling the Brown Dwarf Census of the Solar Neighbourhood 201: Milky Way and the Local Volume Filling the brown dwarf census of the Solar neighbourhood Ralf-Dieter Scholz, Gabriel Bihain, Jesper Storm, Olivier Schnurr Summary Many brown dwarf (BD) neighbours have recently been discovered thanks to new surveys in the mid- and near-infrared (MIR,NIR) but the number of red dwarfs is also still growing (Fig.1). The number of BDs is now about six times lower than that of stars in the same volume (Kirkpatrick et al. 2012, see also Fig.2). Our aim is to detect and classify new nearby BDs, contributing to the eventual completeness of their census in the immediate solar neighbourhood. We combine multi-epoch data from optical, NIR, and MIR surveys (Fig.3) to detect BD neighbours of the Sun by their high proper motion (HPM), concentrating on relatively bright MIR (w2 < 13.5) BD candidates from the Wide-Field Infrared Survey Explorer (WISE). With low-resolution NIR spectroscopy (Fig.4) we classify the new BDs and estimate their distances and velocities. Fig.2: Update for the immediate solar neighbourhood with results from WISE. Among the BDs, there are some still lacking accurate trigonometric parallaxes, for which spectroscopic distances are used. Among the marked AIP discoveries, there are two M dwarfs, LHS 2090 (Scholz et al. 2001) and L 449-1 (Scholz et al. 2005), that were already listed in old HPM catalogues, and five T dwarfs, ε Indi Ba,Bb (Scholz et al. 2003, McCaughrean et al. 2004), WISE J0254+0223 and WISE J1741+2553 (Scholz et al. 2011), and WISE J0521+1025 (Bihain et al. 2013), discovered by their HPM. Fig.1: Progress of the last 12 years, as reported by RECONS (only systems with trigonometric parallax errors <10mas are considered), where the results obtained from WISE are not yet included. Within 10pc, there are 357 known objects in 259 systems as of 2012-01-01. Fig.3: Multi-epoch, optical (DSS), NIR (2MASS) and MIR (WISE) finding charts of the T7.5 dwarf WISE J0521+1025 (Bihain et al. 2013). The red open circle marks the position at the WISE epoch (centre of each image), Fig.4: LBT/LUCI spectra of the new T7.5 dwarf (black) discovered by Bihain et al the red arrow points to the (2013) and of a young T8 dwarf (blue, from Scholz et al. 2011) overplotted with bright WISE source and the lower resolution spectrum (red) of a T8 standard (from Burgasser et al. 2004). the correct (blue) 2MASS The insert shows the region of the K I doublet at 1.243/1.252μm. Except for the H counterpart. This nearby band, there is a good agreement of the spectra of WISE J0521+1025 and Ross (d≈5pc) HPM object was 458C (discovered by Goldman et al. 2010 and Scholz 2010 and described as low previously overlooked, surface gravity and super-solar metallicity T8 dwarf by Burgasser et al. 2010). We probably because of the have classified WISE J0521+1025 as T7.5 though, in good agreement with overlapping background spectral indices measured in the HK band, as defined in Burgasser et al. (2006). object seen in DSS 2MASS. Science Advisory Board visit at AIP, 2013.
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