Planet Found Around Star with Least Metal Yet

The HARPS search for southern extrasolar planets: XXXVI. New multi-planet systems in the HARPS volume limited sample: a super-Earth and a Neptune in the habitable zone
http://arxiv.org/abs/1301.2741

Quote :

The vast diversity of planetary systems detected to date is defying our capability of understanding their formation and evolution. Well-defined volume-limited surveys are the best tool at our disposal to tackle the problem, via the acquisition of robust statistics of the orbital elements. We are using the HARPS spectrograph to conduct our survey of ~850 nearby solar-type stars, and in the course of the past nine years we have monitored the radial velocity of HD103774, HD109271, and BD-061339. In this work we present the detection of five planets orbiting these stars, with m*sin(i) between 0.6 and 7 Neptune masses, four of which are in two multiple systems, comprising one super-Earth and one planet within the habitable zone of a late-type dwarf. Although for strategic reasons we chose efficiency over precision in this survey, we have the capability to detect planets down to the Neptune and super-Earth mass range, as well as multiple systems, provided that enough data points are made available.

Nice bit of ambiguity in the title... did you initially read it as

(a super-Earth and a Neptune) in the habitable zone

or

(a super-Earth) and (a Neptune in the habitable zone)

To me it sounds as if both were in the HZ.

-M-

Indeed. I misread it and gave the thread a much more interesting title before changing it shortly thereafter.

They are listed at EPE, though the planet count keeps on missing many confirmed planets.

Nothing interesting as we have plenty of such planets

Haha how far exoplanet discovery has come that this kind of thing is now "nothing interesting"...

Well soon super earth in hz will be nothing interesting

Independent confirmation of BD-whatnot (Gliese 221)'s planets with Magellan/PFS:

Two planetary companions around the K7 dwarf GJ 221 : a hot super-Earth and a candidate in the sub-Saturn desert range

This doesn't reference the ESO paper, despite apparently being submitted just last Thursday. the HARPS archive and HARPS-TERRA make a… load-bearing appearance, with the PFS dataset being rather small.

Furthermore GJ 221b = BD-06°1339c and vice-versa

A third planet at GJ 221 / BD-06°1339.
http://arxiv.org/abs/1401.4000

Updates for some HARPS multiplanet systems

The HARPS search for southern extra-solar planets. XXXVII. Bayesian re-analysis of three systems. New super-Earths, unconfirmed signals, and magnetic cycles

Quote :

We present the analysis of the entire HARPS observations of three stars that host planetary systems: HD1461, HD40307, and HD204313. The data set spans eight years and contains more than 200 nightly averaged velocity measurements for each star. This means that it is sensitive to both long-period and low-mass planets and also to the effects induced by stellar activity cycles. We modelled the data using Keplerian functions that correspond to planetary candidates and included the short- and long-term effects of magnetic activity. A Bayesian approach was taken both for the data modelling, which allowed us to include information from activity proxies such as log(R′HK) in the velocity modelling, and for the model selection, which permitted determining the number of significant signals in the system. The Bayesian model comparison overcomes the limitations inherent to the traditional periodogram analysis. We report an additional super-Earth planet in the HD1461 system. Four out of the six planets previously reported for HD40307 are confirmed and characterised. We discuss the remaining two proposed signals. In particular, we show that when the systematic uncertainty associated with the techniques for estimating model probabilities are taken into account, the current data are not conclusive concerning the existence of the habitable-zone candidate HD40307 g. We also fully characterise the Neptune-mass planet that orbits HD204313 in 34.9 days.

So the "new" super-Earth around HD 1461 is in fact the c planet in the unpublished paper of Mayor et al. (2011). Also good to get some details on HD 40307 after the presentation indicating the non-confirmation of planet g.

http://arxiv.org/abs/1511.03941

The HARPS search for southern extra-solar planets.
XXXIX. HD175607 b, the most metal-poor G dwarf with an orbiting sub-Neptune

Context. The presence of a small-mass planet (Mp<0.1\,MJup) seems, to date, not to depend on metallicity, however, theoretical simulations have shown that stars with subsolar metallicities may be favoured for harbouring smaller planets. A large, dedicated survey of metal-poor stars with the HARPS spectrograph has thus been carried out to search for Neptunes and super-Earths. Aims. In this paper, we present the analysis of \object{HD175607}, an old G6 star with metallicity [Fe/H] = -0.62. We gathered 119 radial velocity measurements in 110 nights over a time span of more than nine years. Methods. The radial velocities were analysed using Lomb-Scargle periodograms, a genetic algorithm, a Markov chain Monte Carlo analysis, and a Gaussian processes analysis. The spectra were also used to derive stellar properties. Several activity indicators were analysed to study the effect of stellar activity on the radial velocities. Results. We find evidence for the presence of a small Neptune-mass planet (Mpsini=8.98±1.10\,M⊕) orbiting this star with an orbital period P=29.01±0.02\, days in a slightly eccentric orbit (e=0.11±0.08). The period of this Neptune is close to the estimated rotational period of the star. However, from a detailed analysis of the radial velocities together with the stellar activity, we conclude that the best explanation of the signal is indeed the presence of a planetary companion rather than stellar related. An additional longer period signal (P∼1400\,d) is present in the data, for which more measurements are needed to constrain its nature and its properties. Conclusions. HD\,175607 is the most metal-poor FGK dwarf with a detected low-mass planet amongst the currently known planet hosts. This discovery may thus have important consequences for planet formation and evolution theories

Is it a population II star?

I would say yes. The thin disk metallicity distribution rarely seems to produce stars below Fe/H ~< -0.3 - -0.4, and I can't think of any thin disk stars with Fe/H values as low as ~-0.6. I also get values of the stellar space velocities [U, V, W] of [-103.0, 16.1, -90.3] km/s via the formulations outlined in Johnson & Soderblom (1987) and the values of the LSR from Schönrich et al. (2010), though I'm not certain I did it right. If they are, then the star is definitely population II, though I don't know enough to say if it's thick disk or halo.

There's also the isochronal age given in the paper (10.32 ± 1.58 Gyr) which is thick disk, though isochronal ages should be taken with a grain of salt for very old stars, and the errors may be mildly underestimated.


Also… the only thing that joins these papers together is that they use HARPS. They're not even part of the same internal surveys. I would say give them their own threads, but a HARPS megathread would be nice…

Quote :

In this case, the star HD175607 appears to have a planet orbiting it at a distance that's about a third of Mercury's to the sun. It completes a "year" of orbit in 29 days and weighs between 7.88 and 10.08 times as much as Earth, putting it at about two-thirds the mass of Neptune — which has a mass that's about 17 times that of Earth's.

Maybe I've been out of practice for a bit long, but the bolded part confused me; I forgot how the two are different...

They finally listed it!

http://exoplanet.eu/catalog/hd_175607_b/