A 4 MJ planet imaged at GJ 504

Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-like Star GJ 504
http://arxiv.org/abs/1307.2886

Quote :

Several exoplanets have recently been imaged at wide separations of >10 AU from their parent stars. These span a limited range of ages (<50 Myr) and atmospheric properties, with temperatures of 800--1800 K and very red colors (J - H > 0.5 mag), implying thick cloud covers. Furthermore, substantial model uncertainties exist at these young ages due to the unknown initial conditions at formation, which can lead to an order of magnitude of uncertainty in the modeled planet mass. Here, we report the direct imaging discovery of a Jovian exoplanet around the Sun-like star GJ 504, detected as part of the SEEDS survey. The system is older than all other known directly-imaged planets; as a result, its estimated mass remains in the planetary regime independent of uncertainties related to choices of initial conditions in the exoplanet modeling. Using the most common exoplanet cooling model, and given the system age of 160 [+350, -60] Myr, GJ 504 b has an estimated mass of 4 [+4.5, -1.0] Jupiter masses, among the lowest of directly imaged planets. Its projected separation of 43.5 AU exceeds the typical outer boundary of ~30 AU predicted for the core accretion mechanism. GJ 504 b is also significantly cooler (510 [+30, -20] K) and has a bluer color (J-H = -0.23 mag) than previously imaged exoplanets, suggesting a largely cloud-free atmosphere accessible to spectroscopic characterization. Thus, it has the potential of providing novel insights into the origins of giant planets, as well as their atmospheric properties.

a.k.a. 59 Virginis.

Maybe also take a look at the thread title... GJ 504 not 507.

Lazarus wrote:

Maybe also take a look at the thread title... GJ 504 not 507.

Oops! Thanks.

http://spaceref.com/exoplanets/astronomers-image-lowest-mass-exoplanet-around-a-sun-like-star.html

What a lovely pink colour

Direct Imaging Detection of Methane in the Atmosphere of GJ 504 b
http://arxiv.org/abs/1310.4183

Quote :

Most exoplanets detected by direct imaging so far have been characterized by relatively hot (> ~1000 K) and cloudy atmospheres. A surprising feature in some of their atmospheres has been a distinct lack of methane, possibly implying non-equilibrium chemistry. Recently, we reported the discovery of a planetary companion to the Sun-like star GJ 504 using Subaru/HiCIAO within the SEEDS survey. The planet is substantially colder (<600 K) than previously imaged planets, and has indications of fewer clouds, which implies that it represents a new class of planetary atmospheres with expected similarities to late T-type brown dwarfs in the same temperature range. If so, one might also expect the presence of significant methane absorption, which is characteristic of such objects. Here, we report the detection of deep methane absorption in the atmosphere of GJ 504 b, using the Spectral Differential Imaging mode of HiCIAO to distinguish the absorption feature around 1.6 um. We also report updated JHK photometry based on new Ks-band data and a re-analysis of the existing data. The results support the notion that GJ 504 b has atmospheric properties distinct from other imaged exoplanets, and will become a useful reference object for future planets in the same temperature range.

Fuhrmann & Chini (2015) "On the Age of Gliese 504"

Apparently it is an old star, so the companion is a brown dwarf. They invoke recent accretion of a substellar object to explain the star's rotation.

Unfortunately the article is paywalled so can't see the details, only the abstract.

Using (spooky) black magic, I can see through the paywall. The authors make a rather convincing case for an old age for the star; though the invocation of mass accretion is harder to swallow, they calculate the minimum mass required to spin up the star is only ~3 Mjup, and make qualitative arguments in favour of this being possibly due to the wide companion.

There's some more work that could be done (particularly the dynamics that lead to accretion), but the case is pretty strong.

I guess, if true, then this would lead to the previous observations of T-dwarf-like atmospheric characteristics being due to the companion actually being a T-dwarf.

Skemer et al. "The LEECH Exoplanet Imaging Survey: Characterization of the Coldest Directly Imaged Exoplanet, GJ 504 b, and Evidence for Super-Stellar Metallicity"
http://arxiv.org/abs/1511.09183

Considers both young and old possible ages for the GJ 504 system. The estimate for the gravity suggests a low-mass object, and the authors suggest that the super-stellar metallicity of GJ 504 b indicates that it likely formed as a planet rather than as a binary companion.

^{totally not late}

A critical reassessment of the fundamental properties of GJ 504: Chemical composition and age

Quote :

The recent development of brand new observational techniques and theoretical models have greatly advanced the exoplanet research field. Despite significant achievements, which have allowed the detection of thousands extrasolar systems, a comprehensive understanding of planetary formation and evolution mechanisms is still desired. One relevant limitation is given by the accuracy in the measurements of planet-host star ages. The star GJ 504 has been found to host a substellar companion whose nature is strongly debated. There has been a recent difference of opinion in the literature owing to the uncertainty on the age of the system: a young age of ∼ 160 Myr would imply a giant planet as a companion, but a recent revision pointing to a solar age (∼ 4 Gyr) instead suggests a brown dwarf. With the aim of shedding light on this debated topic, we have carried out a high-resolution spectroscopic study of GJ 504 to derive stellar parameters, metallicity, and abundances of both light and heavy elements, providing a full chemical characterisation. The main objective is to infer clues on the evolutionary stage (hence the age) of this system. We performed a strictly differential (line-by-line) analysis of GJ 504 with respect to two reference stars, that is the planet-host dwarf ι Hor and the subgiant HIP 84827. The former is crucial in this context because its stellar parameters (hence the evolutionary stage) is well constrained from asteroseismic observations. Regardless of the zero point offsets, our differential approach allows us to put tight constraints on the age of GJ 504 with respect to ι Hor, thereby minimising the internal uncertainties. We found that the surface gravity of GJ 504 is 0.2 ± 0.07 dex lower than that of the main-sequence star ι Hor, suggesting a past turn-off evolution for our target. The isochrone comparison provides us with an age range between 1.8 and 3.5 Gyr, with a most probable age of ≈ 2.5 Gyr. Thus, our findings support an old age for the system; further evidence comes from the barium abundance, which is compatible with a solar pattern and not enhanced as observed in young stars. We envisaged a possible engulfment  scenario to reconcile all the age indicators (spectroscopy, isochrones, rotation, and activity); this engulfment could have occurred very recently and could be responsible for the enhanced levels of rotation and chromospheric activity, as previously suggested. We tested this hypothesis, exploiting a tidal evolution code and finding  that the engulfment of a hot Jupiter, with mass not larger than ≈ 3 M_j and initially located at ≈ 0.03 AU, seems to be a very likely scenario.

While not yet a subgiant the star is clearly leaving the main sequence, and hence an old age appears to be difficult to dispute. The modelling of the merger scenario leaves some details desired (the natural loss of stellar angular momentum is not considered, despite its relevance to the simulation), but the occurrence of the event appears to be fairly well-attested.

From the conclusion:

Quote :

Our tests indicate that a very plausible system architecture would result in an initial configuration of a planetary companion (with mass not larger than ∼ 3 M_J) located at 0.03 AU. This is probably because Kozai cycles (due to the presence of the external substellar companion) have caused an inward migration. From such a small distance, the low-mass body has been affected by the stellar tides and slowly started to spiral down on the central star. If this were the case, we would expect to reveal planetary remnants such as rocky cores of the now defunct hot Jupiter in the proximity of star GJ 504. Current measurements prevent us from investigating this issue, but we plan to have purposely designed observations to detect such a small signal in radial velocity variations.

Perhaps we may be seeing a Cthonian planet sometime in the future.

While looking through literature for something else some months ago, I came across this paper by Fuhrmann. While unfortunately paywalled, the parts relevant to 59 Virginis were essentially an identification of its old age by isochrone, comments on its fast rotation, and then a merger hypothesis to explain the fast rotation. This is more or less the same as contents of the 2015 paper (which is noted in the latters abstract), so the old age theory significantly antedates the detection of the companion.

They don't give the inferred mass of GJ 504 B from their age range, but I'd guess it puts it somewhere around 15–20 Jupiter masses, based on figure 2 of the Fuhrmann & Chini (2015) paper.