A Search for Photometric Variability in the Young T3.5 Planetary-mass Companion GU Psc b

Abstract

We present a photometric J-band variability study of GU Psc b, a T3.5 co-moving planetary-mass companion (9-13 M Jup ) to a young (∼ 150 Myr) M3 member of the AB Doradus Moving Group. The large separation between GU Psc b and its host star (42 ) provides a rare opportunity to study the photometric variability of a planetary-mass companion. The study presented here is based on observations obtained from 2013 to 2014 over three nights with durations of 5-6 hr each with the WIRCam imager at Canada-France-Hawaii Telescope. Photometric variability with a peak-to-peak amplitude of 4 ± 1% at a timescale of ∼ 6 hr was marginally detected on 2014 October 11. No highsignificance variability was detected on 2013 December 22 and 2014 October 10. The amplitude and timescale of the variability seen here, as well as its evolving nature, is comparable to what was observed for a variety of field T dwarfs and suggests that mechanisms invoked to explain brown dwarf variability may be applicable to low-gravity objects such as GU Psc b. Rotation-induced photometric variability due to the formation and dissipation of atmospheric features such as clouds is a plausible hypothesis for the tentative variation detected here. Additional photometric measurements, particularly on longer timescales, will be required to confirm and characterize the variability of GU Psc b, determine its periodicity and to potentially measure its rotation period.

Cloud Atlas: Weak Color Modulations Due to Rotation in the Planetary-mass Companion GU Psc b and 11 Other Brown Dwarfs

“…Based on the integrated white light curve, the rotational modulation amplitude is at least 1.35%, or 2.7±0.8% for the peak-to-trough flux variation (i.e., the ratio of the integrated flux median at the sixth orbit to that at the third orbit). This variability level is consistent with the previously reported marginal detection of peak-to-trough variability of 4%±1% at a timescale of ∼6 hr by Naud et al (2017).…”

“…The modulations of GU Psc b described here are the first in a planetary-mass object at the end of the L/T transition (T3-T5), confirming the previous J-band marginal detection by Naud et al (2017). As the atmosphere evolves from L to T spectral type, the silicate cloud base presumably sank to deeper pressure (see the condensation curves in Helling & Casewell 2014;Robinson & Marley 2014), and hence the photosphere becomes less cloudy.…”

“…Based on the ABDMG's age of 100±30 Myr and the fitted effective temperature range, N14 estimate the mass of GU Psc b to be around 9-13 M Jup , which is close to the deuterium-burning mass limit of 12-13 M Jup (Saumon & Marley 2008)commonly adopted as the borderline between brown dwarfs and giant planets with solar metallicity. Naud et al (2017) report a tentative J-band photometric variability of GU Psc b with a peak-to-trough flux variation of 4±1% at a period of 5.9 hr based on one out of three nights of 5-6 hr observation with the WIRCam Imager at the 3.6 m Canada-France-Hawaii Telescope.…”

PSYM-WIDE: A Survey for Large-separation Planetary-mass Companions to Late Spectral Type Members of Young Moving Groups

“…As demonstrated by the in-depth photometric and spectroscopic study of GU Psc b (Naud et al 2014) and the study of its light curve evolution Naud et al (2017), wide planetary-mass companions are amenable to a level of characterization that is useful in assessing the characteristics of closer-in giant planets, which are much harder to study. Further surveys to identify wide-separation exoplanets would be valuable, especially deeper ones that are focused on the identification of lessmassive giant planets.…”

Simultaneous Multiwavelength Variability Characterization of the Free-floating Planetary-mass Object PSO J318.5−22

“…Recently, Gagné et al (2017) identified the highly variable T2.5 dwarf SIMP 0136 (Artigau et al 2009) as a likely member of the 200 Myr Carina-near moving group. Naud et al (2017) report a tentative J-band detection of variability for the wide T3.5 planetary-mass companion GU Psc b, with 4%±1% variability on a six-hour timescale detected in one monitoring epoch out of three.…”