The Prototypical Young L/T-Transition Dwarf HD 203030B Likely Has Planetary Mass

Abstract

Upon its discovery in 2006, the young L7.5 companion to the solar analog HD 203030 was found to be unusual in being ≈200 K cooler than older late-L dwarfs. HD 203030B offered the first clear indication that the effective temperature at the L-to-T spectral type transition depends on surface gravity: now a well-known characteristic of low-gravity ultra-cool dwarfs. An initial age analysis of the G8V primary star indicated that the system was 130-400 Myr old, and so the companion between 12-31 M Jup . Using moderate resolution near-infrared spectra of HD 203030B, we now find features of very low gravity comparable to those of 10-150 Myr-old L7-L8 dwarfs. We also obtained more accurate near infrared and Spitzer/IRAC photometry, and find a (J − K) MKO color of 2.56 ± 0.13 mag-comparable to those observed in other young planetary-mass objects-and a luminosity of log(L bol /L ) = −4.75 ± 0.04 dex. We further reassess the evidence for the young age of the host star, HD 203030, with a more comprehensive analysis of the photometry and updated stellar activity measurements and age calibrations. Summarizing the age diagnostics for both components of the binary, we adopt an age of 100 Myr for HD 203030B and an age range of 30-150 Myr. Using cloudy evolutionary models, the new companion age range and luminosity result in a mass of 11 M Jup with a range of 8-15 M Jup , and an effective temperature of 1040 ± 50 K.

The Hawaii Infrared Parallax Program. III. 2MASS J0249–0557 c: A Wide Planetary-mass Companion to a Low-mass Binary in the β Pic Moving Group* †

“…2MASSJ0249 −0557c (11.6 +1.3 −1.0 M Jup ) has an unusual combination of high mass ratio (∼0.1) and wide separation (1950±200 au), strikingly different from the other planetary-mass companions in the βPic moving group (βPicb and 51Erib), which are among the smallest-separation, lowest-mass-ratio companions known. For this plot, we used the compilation of system properties from Bowler (2016) and added HIP65426b (Chauvin et al 2017), 2MASSJ2236 +4751b (Bowler et al 2017), 2MASSJ1119−1137AB (Best et al 2017), and HD203030B (Metchev & Hillenbrand 2006;Miles-Páez et al 2017). When a companion orbits a binary, we use the total mass of the binary to compute the mass ratio.…”

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

“…Surface gravity may be part of the puzzle too. Small samples of L/T transition brown dwarfs suggest that the L/T transition occurs at lower effective temperatures for low-gravity objects (Metchev & Hillenbrand 2006;Dupuy et al 2009;Marley et al 2012;Bowler et al 2013;Liu et al 2016;Miles-Páez et al 2017). The magnitude of J-band brightening could also be larger for low-gravity objects if we include directly imaged planets (see Figure 16 in Dupuy & Liu 2012).…”

Let the Great World Spin: Revealing the Stormy, Turbulent Nature of Young Giant Exoplanet Analogs with the Spitzer Space Telescope

“…Faherty et al (2013) noted its extremely red near-infrared colors and underluminosity compared to field brown dwarfs. These peculiarities were first noted by Metchev & Hillenbrand (2006) for the young companion HD203030 B (Miles-Páez et al 2017), and are shared by directly-imaged exoplanets such as 2M1207 b and HR8799 bcd. Our kinematic analysis, which makes use of Gaia proper motions and parallax confirms that it is a member of AB Doradus using BANYAN Σ.…”