At the observational frontier of local solar space: RECONS and the ten parsec census

RECONS-grabImage credit: A. Riedel and the RECONS group, P.I. Todd J. Henry taken from a new visualization by the RECONS consortium (www.recons.org) which can be seen on youtube. This is my final post (for now) on the subject of the completeness of our knowledge of stellar and planetary systems near the Sun. Stars here are plotted coloured broadly by spectral type and sized approximately by luminosity class (dwarfs or giants). The horizontal blue circle is the galactic plane crossed by the equatorial plane (grey circle) plotted at 2, 5, 10 and 25 parsecs distance. RECONS is preparing a 10 parsec census for publication and leads the field in both observation and visualization. The latest data were presented last year by Henry to the 227th meeting of the American Astronomical Society, and I reproduce the abstract in part below. In the meantime, Bihain & Scholz (2016) have investigated the projected distribution of brown dwarfs around the Sun and listed 26 brown dwarfs within 6.5 parsecs distance (as compared to 136 stars) in their Table 1 (also below):

The sample of stars, brown dwarfs, and exoplanets known within 10 parsecs of our Solar System as of January 1, 2015 is presented. All systems have trigonometric parallaxes of 100 mas or more with errors of 10 mas or less. Included in the sample are 12 systems in the southern sky added to the sample via new parallaxes from the RECONS (REsearch Consortium On Nearby Stars, www.recons.org) effort at the CTIO/SMARTS 0.9m.The census consists of 366 stars (including the Sun and white dwarfs), 37 brown dwarfs, and 34 planets (eight in our Solar System and 26 exoplanets). Red dwarfs clearly dominate the sample, accounting for 75% of all stars known within 10 pc, while brown dwarfs are currently outnumbered 10 to 1 by stars. The completeness of the sample is assessed, indicating that additional discoveries of red, brown, and white dwarfs within 10 pc, both as primaries and secondaries, are likely, although we estimate that roughly 90% of the stellar systems have been identified. The evolution of the 10 pc sample over the past 70 years is outlined to illustrate the growth of the sample. The luminosity and mass functions are described. In contrast to many studies, once all known close multiples are resolved into individual components, the true stellar mass function rises to the end of the main sequence. With far fewer brown dwarfs than stars, different formation scenarios for objects that fuse hydrogen and those that do not are likely. Of 270 stellar primaries, 28% have companion stars, only 2% have brown dwarf companions, and 6% have detected planets. The planetary rate so far is low but climbing, while searches for brown dwarf companions to stars within 10 pc have been quite rigorous, so the brown dwarf companion rate is unlikely to rise noticeably. Overall, the solar neighborhood is dominated by small stars that are potentially orbited by many small, as yet unseen, planets.

bihain-grabBrown dwarfs near the Sun. Red dwarfs like Barnard’s star are missing. The coldest known brown dwarf WISE J0855-0714 (~250K) is third on the list following Luhman 16AB, given its WISE designation in the table. WISE J0720-0846B is the mid-T companion to Scholz’s star, a 6 pc distant M9 dwarf.

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