Substellar companion(s?) to Gliese 758

Discovery of the Coldest Imaged Companion of a Sun-Like Star
http://arxiv.org/abs/0911.1127

Abstract wrote:

We present the discovery of a brown dwarf or possible planet at a projected separation of 1.9" = 29 AU around the star GJ 758, placing it between the separations at which substellar companions are expected to form by core accretion (~5 AU) or direct gravitational collapse (typically >100 AU). The object was detected by direct imaging of its thermal glow with Subaru/HiCIAO. At 10-40 times the mass of Jupiter and a temperature of 550-640 K, GJ 758 B constitutes one of the few known T-type companions, and the coldest ever to be imaged in thermal light around a Sun-like star. Its orbit is likely eccentric and of a size comparable to Pluto's orbit, possibly as a result of gravitational scattering or outward migration. A candidate second companion is detected at 1.2" at one epoch.

This is first discovery program SEEDS (Subaru Strategic Exploration of Exoplanets and Disks with HiCIAO/AO188)?

So at that kind of temperature you wouldn't see a glow in the visible light... this kind of discovery is probing the "class III atmospheres" regime for giant planets, it'll be interesting to see how the classification holds up, especially with regards to the T/Y transition.

Quote :

Furthermore, the higher quality of the second observation revealed another faint signal of 5.6 sigma at an even smaller separation, whose nature remains unknown until its physical existence and proper motions can be proven with a follow-up detection at a later epoch. Both runs had excellent weather conditions (0.500 natural seeing in H band).

If the second object is confirmed, that this will look like massive planetary system, not brown dwarves.

Oh definitely. It's one of no doubt countless examples of why there may be no non-arbitrary dividing line between planets and brown dwarfs.

Lazarus wrote:

So at that kind of temperature you wouldn't see a glow in the visible light... this kind of discovery is probing the "class III atmospheres" regime for giant planets, it'll be interesting to see how the classification holds up, especially with regards to the T/Y transition.

The paper wrote that there should be significant methane absorption, given current models. I agree, it would be great to follow up on. That and HR 8799's planets.

And for curiosity, at what temperature would you begin to see an infrared glow?

Edit: The EPE has listed Gliese 758 b as an unconfirmed exoplanet.

High-Contrast 3.8 Micron Imaging Of The Brown Dwarf/Planet-Mass Companion to GJ 758
http://arxiv.org/abs/1008.1983

Abstract wrote:

We present L' band (3.8 $\mu m$) MMT/Clio high-contrast imaging data for the nearby star GJ 758, which was recently reported by Thalmann et al. (2009) to have one -- possibly two-- faint comoving companions (GJ 758B and ``C", respectively). GJ 758B is detected in two distinct datasets. Additionally, we report a \textit{possible} detection of the object identified by Thalmann et al as ``GJ 758C" in our more sensitive dataset, though it is likely a residual speckle. However, if it is the same object as that reported by Thalmann et al. it cannot be a companion in a bound orbit. GJ 758B has a H-L' color redder than nearly all known L--T8 dwarfs. Based on comparisons with the COND evolutionary models, GJ 758B has T$_{e}$ $\sim$ 560 K$^{^{+150 K}_{-90K}}$ and a mass ranging from $\sim$ 10--20 M$_{J}$ if it is $\sim$ 1 Gyr old to $\sim$ 25--40 M$_{J}$ if it is 8.7 Gyr old. GJ 758B is likely in a highly eccentric orbit, e $\sim$ 0.73$^{^{+0.12}_{-0.21}}$, with a semimajor axis of $\sim$ 44 AU$^{^{+32 AU}_{-14 AU}}$. Though GJ 758B is sometimes discussed within the context of exoplanet direct imaging, its mass is likely greater than the deuterium-burning limit and its formation may resemble that of binary stars rather than that of jovian-mass planets.

So we deal with a brown dwarf, rather a planet. Nice to see it independently confirmed.

Near-Infrared Multi-Band Photometry of the Substellar Companion GJ 758 B
http://arxiv.org/abs/1011.5505

Quote :

GJ 758 B is a cold (~600K) companion to a Sun-like star at 29 AU projected separation, which was recently detected with high-contrast imaging. Here we present photometry of the companion in seven photometric bands from Subaru/HiCIAO, Gemini/NIRI and Keck/NIRC2, providing a rich sampling of the spectral energy distribution in the 1-5 micron wavelength range. A clear detection at 1.58 micron combined with an upper limit at 1.69 micron shows methane absorption in the atmosphere of the companion. The mass of the companion remains uncertain, but an updated age estimate indicates that the most likely mass range is ~30-40 Mjup. In addition, we present an updated astrometric analysis that imposes tighter constraints on GJ 758 B's orbit and identifies the proposed second candidate companion, "GJ 758 C", as a background star.

Fairly substantial downward revision of the orbital eccentricity there. Wonder if there are any planets around either of GJ 758 A or B.

Planetary domain uppermost limit seems getting higher and higher: GJ 758 B is currently classed as planet ("b") at EPE:  

http://exoplanet.eu/catalog/gj_758_b/