TWO EXTRAORDINARY SUBSTELLAR BINARIES AT THE T/Y TRANSITION AND THE Y-BAND FLUXES OF THE COOLEST BROWN DWARFS {sup ,}
- Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Gemini Observatory, 670 North A'ohoku Place, Hilo, HI 96720 (United States)
Using Keck laser guide star adaptive optics imaging, we have found that the T9 dwarf WISE J1217+1626 and T8 dwarf WISE J1711+3500 are exceptional binaries, with unusually wide separations ( Almost-Equal-To 0.''8, 8-15 AU), large near-IR flux ratios ( Almost-Equal-To 2-3 mag), and small mass ratios ( Almost-Equal-To 0.5) compared to previously known field ultracool binaries. Keck/NIRSPEC H-band spectra give a spectral type of Y0 for WISE J1217+1626B, and photometric estimates suggest T9.5 for WISE J1711+3500B. The WISE J1217+1626AB system is very similar to the T9+Y0 binary CFBDSIR J1458+1013AB; these two systems are the coldest known substellar multiples, having secondary components of Almost-Equal-To 400 K and being planetary-mass binaries if their ages are {approx}<1 Gyr. Both WISE J1217+1626B and CFBDSIR J1458+1013B have strikingly blue Y - J colors compared to previously known T dwarfs, including their T9 primaries. Combining all available data, we find that Y - J color drops precipitously between the very latest T dwarfs and the Y dwarfs. The fact that this is seen in (coeval, mono-metallicity) binaries demonstrates that the color drop arises from a change in temperature, not surface gravity or metallicity variations among the field population. Thus, the T/Y transition established by near-IR spectra coincides with a significant change in the Almost-Equal-To 1 {mu}m fluxes of ultracool photospheres. One explanation is the depletion of potassium, whose broad absorption wings dominate the far-red optical spectra of T dwarfs. This large color change suggests that far-red data may be valuable for classifying objects of {approx}<500 K.
- OSTI ID:
- 22092066
- Journal Information:
- Astrophysical Journal, Vol. 758, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Discovery of a low-luminosity, tight substellar binary at the T/Y transition
NEAR-INFRARED PHOTOMETRY OF Y DWARFS: LOW AMMONIA ABUNDANCE AND THE ONSET OF WATER CLOUDS