Centauri Dreams sometimes muses that we know all too little about nearby space. Ponder that it is only within the last decade that we have begun to characterize the whole category of objects known as ‘brown dwarfs,’ while our understanding of M-class dwarfs is evolving so rapidly that we’re now seeing them as potential havens for terrestrial worlds. That makes both kinds of dwarfs interesting as mission targets once we’ve created the technologies to make such journeys.
And it also means that we have to develop a better census of red and brown dwarf stars in our own neighborhood. It is within the realm of possibility, for example, that there may be a brown dwarf closer to us than the Centauri stars, and the discovery of a target, say, one light year away would give powerful impetus to interstellar propulsion studies. Even M-class stars are readily overlooked in a crowded sky, and the boundary between them and brown dwarfs can be tricky to establish.
As witness a most interesting recent find. DEN 0255-4700 is the faintest body outside our Solar System for which an intrinsic visual brightness has been measured. This tiny object is an L dwarf, a designation for low mass stars so small that they may actually be brown dwarfs. This one is almost 100 million times fainter than the Sun, and while it’s not breathtakingly close, its 16.2 light year distance makes it the 48th closest known stellar target.
We’re talking a temperature of 1700 degrees K (2600 F), and an object whose mass is probably below the 80 Jupiter mass limit thought to be required to fuse hydrogen into helium and thus ignite long-term thermonuclear reactions. The subject of an upcoming paper in the Astronomical Journal, the find is the work of Edgardo Costa and Rene Mendez (Universidad de Chile).
Costa and Mendez are working with the Cerro Tololo Inter-American Observatory Parallax Investigation (CTIOPI), which has been set up to discover overlooked stars and brown dwarfs near the Sun. The goal: to discover 300 new southern star systems within 25 parsecs. Centauri Dreams suspects CTIOPI will have much more to report in coming months as it refines our overview of Sol’s immediate neighborhood.
Hi Paul
Or should I say CD?
A nearby brown dwarf would be an incredible find. What do you think of the Binary Research Institute’s idea of a nearby BD as the Sun’s companion? There’s some evidence for a decent sized planet a bit further out than the proposed binary influencing the Oort Cloud according to some other researchers ( have you posted on their latest reports? I can’t remember.) There could also be free-floating planets – up to a trillion in the Galaxy according to some estimates I’ve read.
Even wilder would be a red dwarf the parallax surveys have missed. The southern hemisphere is under-observed so there’s still some chance for such a discovery. A true star discovery would be more of an impetus to interstellar studies than another planet or planemo.
Adam
Adam, I haven’t checked the Binary Research Institute for a while, so this is a good time to go back and have a look. The binary question, though, continues to fascinate me, and as you say, whether or not something like this could be found, we still have the possibility of a nearby brown or red dwarf that has so far gone undetected. Exciting times and this is all quite close to home!
Astrophysics, abstract
astro-ph/0608054
From: Dr Pierre Maxted [view email]
Date: Wed, 2 Aug 2006 16:21:52 GMT (314kb)
Survival of a brown dwarf after engulfment by a red giant star
Authors: P.F.L. Maxted (1), R. Napiwotzki (2), P.D. Dobbie (3), M.R. Burleigh (3) ((1)Keele University, UK, (2) University of Hertfordshire, UK, (3) University of Leicester, UK)
Comments: To appear in Nature on August 3 2006. 13 Pages, 2 figures, 2 tables
(Summary of paper) High resolution optical spectroscopy of the white dwarf WD0137-349 reveals a weak Halpha line in emission, due to a low mass companion in a close orbit. Using this emission feature, and the narrow NLTE core of the white dwarf’s Halpha absorption line, we measure the orbital period at 116 minutes, the separation at 0.65Rsun, and the mass ratio m2/m1 = K1/K2 = 0.134+/-0.006. From the mass of the white dwarf (0.39+/-0.035Msun) we derive a mass for the companion of 0.053+/-0.006Msun. This is well below the limit of about 0.075Msun commonly used to distinguish stars from brown dwarfs. The observed infrared flux distribution of WD0137-349 is also consistent with a model of an old brown dwarf spectral type mid T or slightly earlier. The system is detached, and the brown dwarf must have survived a previous phase of common envelope evolution, providing a key observational test for models of this interaction.
http://arxiv.org/abs/astro-ph/0608054