DISCOVERY OF FOUR HIGH PROPER MOTION L DWARFS, INCLUDING A 10 pc L DWARF AT THE L/T TRANSITION^,

Abstract

We discover four high proper motion L dwarfs by comparing the Wide-field Infrared Survey Explorer (WISE) to the Two Micron All Sky Survey. WISE J140533.32+835030.5 is an L dwarf at the L/T transition with a proper motion of 0.85 ± 0. 02 yr −1 , previously overlooked due to its proximity to a bright star (V ≈ 12 mag). From optical spectroscopy we find a spectral type of L8, and from moderate-resolution J band spectroscopy we find a near-infrared spectral type of L9. We find WISE J140533.32+835030.5 to have a distance of 9.7 ± 1.7 pc, bringing the number of L dwarfs at the L/T transition within 10 pc from six to seven. WISE J040137.21+284951.7, WISE J040418.01+412735.6, and WISE J062442.37+662625.6 are all early L dwarfs within 25 pc, and were classified using optical and low-resolution near-infrared spectra. WISE J040418.01+412735.6 is an L2 pec (red) dwarf, a member of the class of unusually red L dwarfs. We use follow-up optical and low-resolution near-infrared spectroscopy to classify a previously discovered fifth object WISEP J060738.65+242953.4 as an (L8 Opt/L9 NIR), confirming it as an L dwarf at the L/T transition within 10 pc. WISEP J060738.65+242953.4 shows tentative CH 4 in the H band, possibly the result of unresolved binarity with an early T dwarf, a scenario not supported by binary spectral template fitting. If WISEP J060738.65+242953.4 is a single object, it represents the earliest onset of CH 4 in the H band of an L/T transition dwarf in the SpeX Library. As very late L dwarfs within 10 pc, WISE J140533.32+835030.5 and WISEP J060738.65+242953.4 will play a vital role in resolving outstanding issues at the L/T transition.

WISEA J064750.85-154616.4: a new nearby L/T transition dwarf

“…The spectrum of WISEA J1405+8350 fits best with the L8 standard (slightly closer to L8 than L9 in H band and well-fitted by L8 in K band), whereas Castro et al (2013) classified it as L8 in the optical, but L9 in the NIR. From three spectral indices, which we were able to measure for WISEA J1405+8350 (H 2 O-H = 0.709, CH 4 -H = 1.051, CH 4 -K = 0.874), the first leads to L6.2, the second cannot be applied, and the third corresponds to a spectral type of L8.1 according to Burgasser (2007).…”

“…The two other objects are WISEA J140533.13+835030.7 (hereafter WISEA J1405+8350), which has been meanwhile discovered and described as an L9 dwarf (NIR) at a distance of 9.7 ± 1.7 pc by Castro et al (2013), and WISEA J042144.33+192943.8 (hereafter WISEA J0421+1929). For these relatively red (J−K s > 1.5) targets with K s < 14, we used the NIR spectrograph LUCI 1 (Mandel et al 2008;Seifert et al 2010; ).…”

Wisep J060738.65+242953.4: A Nearby Pole-on L8 Brown Dwarf With Radio Emission

“…Each pixel is 4 by 4 arcseconds. Folding the observed W0607+24 optical spectrum from Castro et al (2013) through the Kepler spectral response curve (Koch et al 2010) and scaling from the observed Kepler count rate (550 DN s −1 ) for the L1 dwarf WISEP J190648.47+401106.8 , we expect a K2 count rate of ∼ 100 DN s −1 . As shown in Figure 4, it is the red tail of the Kepler filter that allows a detection; we calculate that the effective wavelength of the Kepler filter is 832 nm for W0607+24.…”

“…One such target is the nearby brown dwarf WISEP J060738.65+242953.4 (Castro & Gizis 2012, hereafter W0607+24). Classified as L8 in the optical and L9 in the near-infrared, with a preliminary trigonometric parallax placing it at a distance of 7.19 +0.11 −0.10 pc (Castro et al 2013), W0607+24 is the nearest known late-L dwarf northern hemisphere, and the third-nearest on the whole sky. W0607+24 is therefore a prime target in understanding the physics of the L/T transition, across which mineral condensate clouds are believed to sink below the photosphere (see Tremblin et al 2016 for an alternate, cloudless model).…”

“…The predicted counts as a function of wavelength for W0607+24 (solid curve). The optical spectrum ofCastro et al (2013) has been folded through the Kepler filter curve (dotted). The effective wavelength of 8320Å for this target is shown as a dashed line.…”