Radial velocity discovery of Proxima Centauri b

The sky around Alpha Centauri and Proxima Centauri

“It is true. We are convinced that there is a planet orbiting Proxima now. The evidence goes as follows: a signal was spotted back in 2013 on previous surveys (UVES and HARPS). The preliminary detection was first done by Mikko Tuomi, our in-house applied mathematician and his Bayesian codes. However, the signal was not convincing as the data were really sparse and the period was ambiguous (other possible solutions at 20 and 40 days, plus a long period signal of unknown origin). We followed up Proxima in the next years but our two observing runs were 12 days, barely sufficient to secure a signal which ended up being 11.2 days. So the Pale Red Dot was designed with the sole purpose of confirming or refuting its strict periodicity, plus carefully monitor the star for activity induced variability. We got very lucky with the weather so we obtained 54 out of 60 observations. The photometric monitoring telescopes (ASH2 and several units of Las Cumbres Observatory Global Telescope network), worked flawlessly so we could see the effect of spots, flares and rotation of the star, which also had a footprint on the spectra. However, nothing indicated that spurious variability would be happening at 11.2 days. So that’s basically it: the Pale Red Dot campaign also detects the same period, and confirms that the signal has been in phase for the 16 years of accumulated observations. This is a requirement for a proper Keplerian orbit. Features like starspots are more short lived plus affect the velocities in the time-scales of the rotation of the star, which is now confirmed at ~83 days.”

Image [section, Proxima Centauri is the orange-red star in center of this image]: ESO press release. The alpha Centauri AB pair are off to the upper left of this image and of course exceedingly bright. Here is link to the Nature paper. Text: palereddot.org. Huge and heartfelt congratulations to the Pale Red Dot Team. Also, the website contains an interview by Guillem Anglada-Escudé, who led this work, with Didier Queloz, co-discoverer of 51 Peg b back in 1995, and it is well worth reading to compare the stories of the two discoveries, as well as everything else on palereddot.org, for a sense of astronomical history.

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