The GJ 504 system revisited: Combining interferometric, radial velocity, and high contrast imaging data

Bonnefoy, M.; Perraut, K.; Lagrange, A.-M.; Delorme, P.; Vigan, A.; Line, M.; Rodet, L.; Ginski, C.; Mourard, D.; Marleau, Gabriel-Dominique; Samland, M.; Tremblin, P.; Ligi, R.; Cantalloube, F.; Mollière, P.; Charnay, B.; Kuzuhara, M.; Janson, M.; Morley, C.; Homeier, D.; ... (2018). The GJ 504 system revisited: Combining interferometric, radial velocity, and high contrast imaging data. Astronomy and astrophysics, 618, A63. EDP Sciences 10.1051/0004-6361/201832942

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The G-type star GJ504A is known to host a 3 to 35 MJup companion whose temperature, mass, and projected separation all contribute to make it a test case for the planet formation theories and for atmospheric models of giant planets and light brown dwarfs. We collected data from the CHARA interferometer, SOPHIE spectrograph, and VLT/SPHERE high contrast imager to revisit the properties of the system. We measure a radius of 1.35+/- 0.04Rsun for GJ504A which yields isochronal ages of 21+/-2Myr or 4.0+/-1.8Gyr for the system and line-of-sight stellar rotation axis inclination of 162.4+3.8−4.3 degrees or 18.6+4.3−3.8 degrees. We re-detect the companion in the Y2, Y3, J3, H2, and K1 dual band SPHERE images. The complete 1-4 μm SED shape of GJ504b is best reproduced by T8-T9.5 objects with intermediate ages (≤1.5Gyr), and/or unusual dusty atmospheres and/or super-solar metallicities. All six atmospheric models used yield Teff=550±50K for GJ504b and point toward a low surface gravity (3.5-4.0 dex). The accuracy on the metallicity value is limited by model-to-model systematics. It is not degenerate with the C/O ratio. We derive logL/L⊙=−6.15±0.15 dex for the companion compatible with masses of M=1.3+0.6−0.3MJup and M=23+10−9MJup for the young and old age ranges, respectively. The semi-major axis (sma) is above 27.8 au and the eccentricity lower than 0.55. The posterior on GJ~504b's orbital inclination suggests a misalignment with GJ~504A rotation axis. We combine the radial velocity and multi-epoch imaging data to exclude additional objects (90\% prob.) more massive than 2.5 and 30 MJup with sma in the range 0.01-80 au for the young and old system ages, respectively. The companion is in the envelope of the population of planets synthetized with our core-accretion model.

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