Kapteyn's Star - Ancient two-planet system with one planet in the HZ

Two planets orbit nearby ancient star
http://phys.org/news/2014-06-astronomers-ancient-worlds-galaxy-door.html

Surprised it was made public this soon.

Two planets around Kapteyn's star : a cold and a temperate super-Earth orbiting the nearest halo red-dwarf
http://arxiv.org/abs/1406.0818

Quote :

Exoplanets of a few Earth masses can be now detected around nearby low-mass stars using Doppler spectroscopy. In this paper, we investigate the radial velocity variations of Kapteyn's star, which is both a sub-dwarf M-star and the nearest halo object to the Sun. The observations comprise archival and new HARPS, HIRES and PFS Doppler measurements. Two Doppler signals are detected at periods of 48 and 120 days using likelihood periodograms and a Bayesian analysis of the data. Using the same techniques, the activity indicies and archival ASAS-3 photometry show evidence for low-level activity periodicities of the order of several hundred days. However, there are no significant correlations with the radial velocity variations on the same time-scales. The inclusion of planetary Keplerian signals in the model results in levels of correlated and excess white noise that are remarkably low compared to younger G, K and M dwarfs. We conclude that Kapteyn's star is most probably orbited by two super-Earth mass planets, one of which is orbiting in its circumstellar habitable zone, becoming the oldest potentially habitable planet known to date. The presence and long-term survival of a planetary system seems a remarkable feat given the peculiar origin and kinematic history of Kapteyn's star. The detection of super-Earth mass planets around halo stars provides important insights into planet-formation processes in the early days of the Milky Way.

We have a Kepler-186f at only 13 light years !! Great !

Kepler-186f is probably not a mini-Neptune/gas dwarf, as the minimum-mass of Kapteyn's Star b would seem to imply.

I… yeah. Wow. I'm… impressed. Not sure how else to put it.

Nice to see they have more reasonable parameter errors this time. Was getting concerned.

I suppose we get to look at an inaccurate depiction of the system tomorrow?

Complete with green continents!


How's this?
http://phl.upr.edu/press-releases/kapteyn
-M-

Old, metal-poor, extragalactic origin... nice to have something fill the gap since HIP 13044b got disproven.

Now there are Barnars and Luyten's star left to have exoplanets detected (or confirmed).   

Any probability for transit for planet b?

Sirius_Alpha wrote:

Kepler-186f is probably not a mini-Neptune/gas dwarf, as the minimum-mass of Kapteyn's Star b would seem to imply.

After the Kepler-10c a giant super-earth also found around an old star like this article say,I wouldn't be surprise that  Kapteyn b & c can be a super-earth instead of a gas dwarf,without the size we can't know for sure.  

Kepler-10c boosts case for life on other worlds

http://www.smh.com.au/technology/sci-tech/astronomy/kepler10c-boosts-case-for-life-on-other-worlds-20140603-zrwdx.html

I don't know how appropriate it is to cherry-pick planets for which to set expectations. While I definitely admit Kapteyn's Star b could be rocky, it is still true that the overwhelming majority of planets with masses similar to the minimum mass of Kapteyn's Star b are low-density planets.

The optimistic scenario is that the planet is not habitable and never was.

If the universe was building habitable planets at 11 Ga, it makes it more likely that the reason for the Great Silence is likely to be something that is located in our future, e.g. that technological civilisations have short lifetimes and don't last long enough to engage in interstellar travel.

Lazarus wrote:

The optimistic scenario is that the planet is not habitable and never was.

If the universe was building habitable planets at 11 Ga, it makes it more likely that the reason for the Great Silence is likely to be something that is located in our future, e.g. that technological civilisations have short lifetimes and don't last long enough to engage in interstellar travel.

This can be consider only one of many hypotheses for why of the Great Silence (Fermi Paradox),could be civilizations that are so old that we could not ever detect them because they are too sophisticate to we understand them,we just don't know...

I noticed that they used the visible earth cloud map to use as the dark spots on the planet in the press release.

Kapteyn b : another fake ?

http://arxiv.org/abs/1505.02778

Stellar activity mimics a habitable-zone planet around Kapteyn's star

Kapteyn's star is an old M subdwarf believed to be a member of the Galactic halo population of stars. A recent study has claimed the existence of two super earth planets around the star based on radial velocity (RV) observations. The innermost of these candidate planets--Kapteyn b (P = 48 days)--resides within the circumstellar habitable zone. Given recent progress in understanding the impact of stellar activity in detecting planetary signals, we have analyzed the observed HARPS data for signatures of stellar activity. We find that while Kapteyn's star is photometrically very stable, a suite of spectral activity indices reveals a large-amplitude rotation signal, and we determine the stellar rotation period to be 143 days. The spectral activity tracers are strongly correlated with the purported RV signal of "planet b," and the 48-day period is an integer fraction (1/3) of the stellar rotation period. We conclude that Kapteyn b is not a planet in the Habitable Zone, but an artifact of stellar activity.

Ouch. Looks more and more like this kind of analysis should be done before making announcements about planets. (Interesting that these activity artifacts seem to occur mainly at periods that would correspond to planets near the HZ, I guess this is an unfortunate consequence of typical M-dwarf rotation periods?)

I consider this a good news,more space for truly earth mass/size exoplanet in the habitable zone of this star that soon can be detected with the next generation of instruments and telescopes like the E-ELT or the EXPRESSO high precision radial velocity of VLT among other numerous other instruments that been in development or in test phase.

Lazarus wrote:

Old, metal-poor, extragalactic origin... nice to have something fill the gap since HIP 13044b got disproven.

Or maybe not extragalactic after all?

Navarette et al. (2015) "The Kapteyn moving group is not tidal debris from ω Centauri"
http://arxiv.org/abs/1506.02041

Fight !!

http://arxiv.org/abs/1506.09072

No evidence for activity correlations in the radial velocities of Kapteyn's star

Stellar activity may induce Doppler variability at the level of a few m/s which can then be confused by the Doppler signal of an exoplanet orbiting the star. To first order, linear correlations between radial velocity measurements and activity indices have been proposed to account for any such correlation. The likely presence of two super-Earths orbiting Kapteyn's star was reported in Anglada et al. (2014, MNRAS 443L, 89A), but this claim was recently challenged by Robertson et al. (2015, ApJ 805L, 22R) arguing evidence of a rotation period (143 days) at three times the orbital period of one of the proposed planets (Kapteyn's b, P=48.6 days), and the existence of strong linear correlations between its Doppler signal and activity data. By re-analyzing the data using global optimization methods and model comparison, we show that such claim is incorrect given that; 1) the choice of a rotation period at 143 days is unjustified, and 2) the presence of linear correlations is not supported by the data. We conclude that the radial velocity signals of Kapteyn's star remain more simply explained by the presence of two super-Earth candidates orbiting it. We also advocate for the use of global optimization procedures and objective arguments, instead of claims lacking of a minimal statistical support.

That seems rather caustic

The next round in the debate:

A Gaussian Process Regression Reveals No Evidence for Planets Orbiting Kapteyn's Star
https://arxiv.org/abs/2103.02709

Quote :

Radial-velocity (RV) planet searches are often polluted by signals caused by gas motion at the star's surface. Stellar activity can mimic or mask changes in the RVs caused by orbiting planets, resulting in false positives or missed detections. Here we use Gaussian process (GP) regression to disentangle the contradictory reports of planets vs. rotation artifacts in Kapteyn's star (Anglada-Escude et al. 2014, Robertson et al. 2015, Anglada-Escude et al. 2016). To model rotation, we use joint quasi-periodic kernels for the RV and H-alpha signals, requiring that their periods and correlation timescales be the same. We find that the rotation period of Kapteyn's star is 125 days, while the characteristic active-region lifetime is 694 days. Adding a planet to the RV model produces a best-fit orbital period of 100~years, or 10 times the observing time baseline, indicating that the observed RVs are best explained by star rotation only. We also find no significant periodic signals in residual RV data sets constructed by subtracting off realizations of the best-fit rotation model and conclude that both previously reported "planets" are artifacts of the star's rotation and activity. Our results highlight the pitfalls of using sinusoids to model quasi-periodic rotation signals.