Discovery of a Wide Planetary-Mass Companion to the Young M3 Star Gu PSC

Abstract

We present the discovery of a co-moving planetary-mass companion ∼ 42 ′′ (∼ 2000 AU) from a young M3 star, GU Psc, likely member of the young AB Doradus Moving Group (ABDMG). The companion was first identified via its distinctively red i-z color (> 3.5) through a survey made with Gemini-S/GMOS. Follow-up Canada-France-Hawaii Telescope/WIRCam near-infrared (NIR) imaging, Gemini-N/GNIRS NIR spectroscopy and Wide-field Infrared Survey Explorer photometry indicate a spectral type of T3.5 ± 1 and reveal signs of low gravity which we attribute to youth. Keck/Adaptive Optics NIR observations did not resolve the companion as a binary. A comparison with atmosphere models indicates T eff = 1000-1100 K and log g = 4.5-5.0. Based on evolution models, this temperature corresponds to a mass of 9-13 M Jup for the age of ABDMG (70-130 Myr). The relatively well-constrained age of this companion and its very large angular separation to its host star will allow its thorough characterization and will make it a valuable comparison for planetary-mass companions that will be uncovered by forthcoming planet-finder instruments such as Gemini Planet Imager and SPHERE.

2MASS 0213+3648 C: A wide T3 benchmark companion to an an active, old M dwarf binary

“…GU Psc b is unique amongst our comparison objects in that it shows a distinct slope in the Y and J bands compared to the other objects. We do not see sufficient evidence to suggest that 2MASS J0213+3648 C is spectrally peculiar and note that it does not have the enhanced K-band emission that Naud et al (2014) attributed to reduced collision-induced absorption resulting from the lower surface gravity (i.e. younger age) of GU Psc b.…”

“…It is well fitted by the spectral standards with only a possibly weaker 1.25-µm potassium doublet hinting at reduced gravity. By contrast, the younger (∼100 Myr), lower mass T3.5 GU Psc b (Naud et al 2014) diverges significantly from the spectral standards in the Y, J and K bands. Naud et al (2014) suggest that this may be due to a differing amount of collision-induced absorption from molecular hydrogen or possibly due to an unresolved, cooler companion.…”

“…Fig. 9 also shows a comparison with the young (∼100 Myr) T3 GU Psc b (Naud et al 2014), the young (∼300 Myr) T2.5 HN Peg B (Luhman et al 2007), the original T3 standard (2MASS J120956.13−100400.8, Burgasser et al 2006), and the alternative T3 standard (SDSS J120602.51+281328.7) suggested by Liu et al (2010) after 2MASS J120956.13−100400.8 was found to be a binary. We note that 2MASS J0213+3648 C has a narrower J band peak and deeper J-band water absorption than SDSS J120602.51+281328.7 but matches both HN Peg B and 2MASS J120956.13−100400.8 well in this regime, the H and K bands the spectrum are a better fit to SDSS J120602.51+281328.7.…”

“…Our spectrum of 2MASS J02132062+3648506C, we classify this object as a T3 ± 0.5. Shown for comparison are the spectra for the young (∼100 Myr) T3.5 GU Psc b (Naud et al 2014), the young (∼300 Myr) T2.5 HN Peg B (Luhman et al 2007), the alternative T3 dwarf standard SDSSJ120602.51+281328.7 (Chiu et al 2006) [as suggested by Liu et al (2010)], the previous T3 standard 2MASS J120956.13−100400.8 (Burgasser et al 2004(Burgasser et al , 2006; now known to be a binary) and the blue T dwarf (Burningham et al 2010;Marocco et al 2015). All spectra are smoothed to similar resolutions and normalized to the J-band peak.…”

What Do Young Brown Dwarfs Tell Us About Exoplanets?

“…Summary of T eff as a function of spectral type for ultracool dwarfs. Field (old) objects (grey) and young companions (blue) are from the calculations and compilation by Bowler et al(2013), with additions from Naud et al(2014) and Gauza et al(2015). Young field objects (orange) are primarily from Liu et al(in prep), with additional objects from , Gizis et al(2015), and Gagne et al(2015).…”