9
Figure 3. Relationships between colors and T , calculated from the grid of ATMO2020++ colors. See
eff
also Table 1. For T ≲ 350 K the F162M − F480M and F360M − F480M colors are less reliable indicators
eff
of T than M (see Figure 2 and Section 4).
eff F480M
WISE 0336A appears to be typical of the general population, based on its location in the color-
color diagrams in Figure 2, and so the system is expected to have approximately solar metallicity
and an age of a few Gyr. Calissendorff et al. (2023) estimate T = 415 ± 20 K for WISE 0336A,
eff
by comparison to Sonora and ATMO2020++ model sequences. The relationships in Table 1 imply
T = 440±24 K for the primary, assuming solar metallicity and log g = 4.5, consistent with their
eff
value.
Calissendorff et al. (2023) estimate T = 325+15 K for WISE 0336B. Figure 2 suggests that the
eff −10
secondary is cooler, and the relationship in Table 1 gives T = 295 ± 10 K, based on the F480M
eff
magnitude only, and adopting log g = 4.0 and [m/H] = 0. We find that WISE 0336B lies in the
factor of two luminosity gap between WISE 0855 and the other Y dwarfs, which have T ≳ 325 K
eff
(e.g. Leggett et al. 2021). A resolved image in the F360M filter would be valuable for further analysis
of this system.
Figure 2 suggests that WISE 0336A has log g ≈ 4.5 and [m/H] ≈ 0.0, and that WISE 0336B has a
lower gravity. A difference in gravity for the two components of ≈ 0.5 dex is consistent with a coeval
system aged a few Gyr, with component temperatures of 440 K and 300 K, and a mass ratio of ≈ 2
(Marley et al. 2021). For example, a 3 Gyr old system composed of a 15 and a 7 Jupiter mass object
would have (T , log g) values of (438, 4.6) and (295, 4.2), respectively.
eff