HD 131399 - A young triple-star system with a planet imaged by SPHERE

A Surprising Planet with Three Suns
http://www.eso.org/public/news/eso1624/

Quote :

A team of astronomers have used the SPHERE instrument on ESO’s Very Large Telescope to image the first planet ever found in a wide orbit inside a triple-star system. The orbit of such a planet had been expected to be unstable, probably resulting in the planet being quickly ejected from the system. But somehow this one survives. This unexpected observation suggests that such systems may actually be more common than previously thought. The results will be published online in the journal Science on 7 July 2016.

Maybe this will be addressed in the paper when it comes out, but I don't see any evidence that the *true* separation between the A and BC pair are known. The projected separation is only three times the projected planetary separation, but given how much difference there is between the distances from us of the A and BC pair, the BC pair could be much further from the planet than this image suggests, and the system could be a lot more stable.

Fantastic !!

Usually ESO is pretty good at putting the research papers in their press releases, hopefully it will appear soon.

Interesting system but at the moment I'm with Sirius_Alpha on this one: projected separations can be misleading. I wonder what kind of constraints can be made for the orbital motion.

http://science.sciencemag.org/content/early/2016/07/06/science.aaf9671

Link to research article (Science Magazine)
If you pay…

Sci-Hub...

It's such a great discovery, especially in imaging field.

But... aren't we neglecting HD 40979 Ab??

Now on arXiv.

Direct Imaging Discovery of a Jovian Exoplanet Within a Triple Star System
http://arxiv.org/abs/1607.02525

The unstable fate of the planet orbiting the A-star in the HD 131399 triple stellar system
https://arxiv.org/abs/1611.00007

Well we probably don't have to worry about system stability anymore.

Evidence that the Directly-Imaged Planet HD 131399 Ab is a Background Star
https://arxiv.org/abs/1705.06851

Quote :

We present evidence that the recently discovered, directly-imaged planet HD 131399 Ab is a background star with non-zero proper motion. From new JHK1L' photometry and spectroscopy obtained with the Gemini Planet Imager, VLT/SPHERE, and Keck/NIRC2, and a reanalysis of the discovery data obtained with VLT/SPHERE, we derive colors, spectra, and astrometry for HD 131399 Ab. The broader wavelength coverage and higher data quality allow us to re-investigate its status. Its near-infrared spectral energy distribution excludes spectral types later than L0 and is consistent with a K or M dwarf, which are the most likely candidates for a background object in this direction at the apparent magnitude observed. If it were a physically associated object, the projected velocity of HD 131399 Ab would exceed escape velocity given the mass and distance to HD 131399 A. We show that HD 131399 Ab is also not following the expected track for a stationary background star at infinite distance. Solving for the proper motion and parallax required to explain the relative motion of HD 131399 Ab, we find a proper motion of 12.3 mas/yr. When compared to predicted background objects drawn from a galactic model, we find this proper motion to be high, but consistent with the top 4% fastest-moving background stars. From our analysis we conclude that HD 131399 Ab is a background K or M dwarf.

Looks like this was a fairly nasty one, and they note that Wagner et al. (2016) got really unlucky here...

Quote :

Finally, we note that HD 131399 Ab is a particularly pathological background object: W16 followed all the standard steps in their analysis, but a combination of multiple unlikely factors led to the conclusion that HD 131399 Ab was a planet. A speckle in the third SPHERE dataset, combined with the SPHERE YJH spectral coverage ending at ~1.64µm, mimicked a T-like spectrum in the H band. The apparent magnitude of the background star was consistent with a planet of the inferred spectral type and age of the system. This background object has a proper motion (in mas yr⁻¹) larger than 96% of background objects at this magnitude range in this region of the sky, and the target star’s proper motion is relatively small, only four times larger than that of the background object. This resulted in a significant deviation from the stationary background object track, and was within a factor of two of a velocity consistent with orbital motion. Further, the background object was one third of the way between HD 131399 Ab and HD 131399 BC, at the outer limit of predictions for stable orbits of planets in multiple systems. In short, this background object was almost tailor-made to pass the standard tests performed in the analysis of direct imaging data.

A couple of updates on this system. The primary star is slowly rotating and is therefore likely to evolve into an Am-star, although it has not yet developed the typical Am-star abundances: Przybilla, Aschenbrenner & Buder, arXiv:1707.07920 [astro-ph.SR]. Secondly a study of how a planet like HD 131399 Ab could form (assuming it isn't a background star): Higuchi & Ida, arXiv:1707.08127 [astro-ph.EP]).

HD 131399 A is a 10-day spectroscopic binary. The companion has a mass of at least 0.51 solar masses. Unfortunately this is unlikely to make HD 131399 A sufficiently massive that the Nielsen et al. (2017) relative motion would bring it below escape velocity. (Would require about ~3 solar masses)

Lagrange et al. (2017) "Discovery of a stellar companion to HD131399A."
https://www.aanda.org/articles/aa/pdf/forth/aa30978-17.pdf

Not sure if this would be designated D, Ac, or Aa2...