Agemegos mentioned on his Roadbed thread
that there's a new Extended HIP database available.
I'm still going over the new data - annoyingly the 7.7ly link I had found using a brown dwarf (see here
) between the RECONS data and the Arcturus/Eta Bootis 'clump' has disappeared when I used the XHIP data instead of New Reduction. Humph.
Let's take a look at HIP 72944 (a.k.a CE Bootis, a binary M V system) - this is the system that the brown dwarf linked to in NRH but not in XHIP that I mentioned above. The parallax for it in each version of Hipparcos is:
HIP1: 101.91 ± 1.67 mas
NRH: 103.59 ± 1.72 mas
XHIP: 101.91 ± 1.72 mas
(HIP1 = original Hipparcos, NRH = New Reduction Hipparcos (2007), XHIP = Extended HIP (2012))
I'm honestly not sure which is better for parallaxes out of the original HIP (HIP1) or New Reduction HIP (NRH). XHIP "elected" to use HIP1 parallaxes over NRH parallaxes for the multiple systems if the parallax error in NRH is higher than the parallax error in HIP1, but from the sound of it they're just assuming
that the HIP1 parallax in these cases is more accurate. In this case (at least) they seem to have just used the HIP1 parallax and tacked on the NRH error bar.
The other complication is that it turns out that the BD that is connecting to CE Bootis actually had its parallax determined "spectrophotometrically", which isn't as accurate as trigonometric parallax (it's not even parallax at all - it's "find it's magnitude, figure out what its spectral type is and what luminosity it should have, and then figure out the distance from that). So it could
actually be close enough to CE Bootis to link to it (whether I use CE Bootis' flexible error bars or not). Or it might not be, for all I know. Sigh.
EDIT: On further examination, the BD in question has a "spectrophotometric parallax" of 127 mas ± 27
mas. Which is a ridonkulous error bar that essentially means "I can put the damn thing anywhere I like in that area", so... ノಠ益ಠ)ノ彡┻━┻
I think there comes a point where one has to draw a line, or one will get tied up in all these niggly little details. Short of turning every system into a line (denoting where the system could be due to its error bars) rather than a point, I think "accurate enough" will suffice. For my own purposes, I think I may just stick with the New Reduction data as it is - if I need data on the stars, I can look them up individually.
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