Friday, June 10, 2022

When you know where to look

Bern University in Switzerland links to Bonavita et al., on the COPAINS survey. They looked at 25 candidates for companion bodies, southern-hemisphere. They have found ten bodies. Although some are already-reported. (It would be fourteen but four were ruled out as background.)

Five are low-mass (red) dwarfs; one is this white dwarf in GJ/Gliese 3346. The exciting stars here be HIP 21152, HIP 29724, HD 60584, and HIP 63734 since - we are now told - they have brown dwarfs. For all the press they get, we were still only up to forty as have been directly imaged around stars (as opposed to free floaters). Transits, I think, are not considered direct images, like last summer's five. Well now that's forty-four.

Slightly annoying in the team's papers is that distance from Earth is given by "pi", Gliese 3346 being "∼42 mas". That's π for πarallax; 1000/π for parsex. I also see proper-motion in these stats. I suppose this is best for astronomers, if they don't want tie their paper to some distance as might be revised later. Although Nyrath's merry band of cartographers should prefer the parsec.

The Earth-closest candidate is HIP 17439 at the highest parallax 61.84 = 16.17pa = 52.7ly. This paper didn't find anything for that one through all the dust. I suppose within 50ly if there were any brown dwarfs (or red or white!), we'd have seen 'em already.

As noted none of the new four are transits. GJ3346's companion was out at 87 AU, as befits direct-imaging. All of them are star-distant and presumed cold, except for the actual stars of course. Although - they're warm enough that we can see them. Accordingly with this star's exception, obviously old enough that its companion has died already, the other candidates are all under a billion years old. A cold brown dwarf gives no heat and, out here, they reflect no light.

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