668 research outputs found
SDSS J141624.08+134826.7: Blue L Dwarfs and Non-Equilibrium Chemistry
We present an analysis of the recently discovered blue L dwarf SDSS
J141624.08+134826.7. We extend the spectral coverage of its published spectrum
to ~4 microns by obtaining a low-resolution L band spectrum with SpeX on the
NASA IRTF. The spectrum exhibits a tentative weak CH4 absorption feature at 3.3
microns but is otherwise featureless. We derive the atmospheric parameters of
SDSS J141624.08+134826.7 by comparing its 0.7-4.0 micron spectrum to the
atmospheric models of Marley and Saumon which include the effects of both
condensate cloud formation and non-equilibrium chemistry due to vertical mixing
and find the best fitting model has Teff=1700 K, log g=5.5 [cm s-2], fsed=4,
and Kzz=10^4 cm2 s-1. The derived effective temperature is significantly cooler
than previously estimated but we confirm the suggestion by Bowler et al. that
the peculiar spectrum of SDSS J141624.08+134826.7 is primarily a result of thin
condensate clouds. In addition, we find strong evidence of vertical mixing in
the atmosphere of SDSS J141624.08+134826.7 based on the absence of the deep 3.3
micron CH4 absorption band predicted by models computed in chemical
equilibrium. This result suggests that observations of blue L dwarfs are an
appealing way to quantitatively estimate the vigor of mixing in the atmospheres
of L dwarfs because of the dramatic impact such mixing has on the strength of
the 3.3 micron CH4 band in the emergent spectra of L dwarfs with thin
condensate clouds.Comment: Accepted for publication in the Astronomical Journa
Discovery of Four High Proper Motion L Dwarfs, Including a 10 pc L Dwarf at the L/T Transition
We discover four high proper motion L dwarfs by comparing the Wide-field
Infrared Survey Explorer (WISE) to the Two Micron All Sky Survey (2MASS). 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 (Castro & Gizis
2012) 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.Comment: 45 pages, 12 figures, accepted for publication in Ap
Two Extraordinary Substellar Binaries at the T/Y Transition and the Y-Band Fluxes of the Coolest Brown Dwarfs
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 (~0.8 arcsec, 8-15 AU), large near-IR flux
ratios (~2-3 mags), and small mass ratios (~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 ~400 K and being planetary-mass
binaries if their ages are <~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 ~1 micron 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 <~500 K.Comment: ApJ, in press (accepted Aug 1, 2012). Small cosmetic changes in
version 2 to match final publicatio
The Exemplar T8 Subdwarf Companion of Wolf 1130
We have discovered a wide separation (188.5") T8 subdwarf companion to the
sdM1.5+WD binary Wolf 1130. Companionship of WISE J200520.38+542433.9 is
verified through common proper motion over a ~3 year baseline. Wolf 1130 is
located 15.83 +/- 0.96 parsecs from the Sun, placing the brown dwarf at a
projected separation of ~3000 AU. Near-infrared colors and medium resolution
(R~2000-4000) spectroscopy establish the uniqueness of this system as a
high-gravity, low-metallicity benchmark. Although there are a number of
low-metallicity T dwarfs in the literature, WISE J200520.38+542433.9 has the
most extreme inferred metallicity to date with [Fe/H] = -0.64 +/- 0.17 based on
Wolf 1130. Model comparisons to this exemplar late-type subdwarf support it
having an old age, a low metallicity, and a small radius. However, the
spectroscopic peculiarities of WISE J200520.38+542433.9 underscore the
importance of developing the low-metallicity parameter space of the most
current atmospheric models.Comment: Accepted to ApJ on 05 September 2013; 33 pages in preprint format, 8
figures, 3 table
Spectral density analysis of time correlation functions in lattice QCD using the maximum entropy method
We study various aspects of extracting spectral information from time
correlation functions of lattice QCD by means of Bayesian inference with an
entropic prior, the maximum entropy method (MEM). Correlator functions of a
heavy-light meson-meson system serve as a repository for lattice data with
diverse statistical quality. Attention is given to spectral mass density
functions, inferred from the data, and their dependence on the parameters of
the MEM. We propose to employ simulated annealing, or cooling, to solve the
Bayesian inference problem, and discuss practical issues of the approach.Comment: 11 pages, 30 figure files (eps), some references added and updated,
requires REVTeX 4.0 and prerequisites (AMS-LaTeX 2.0, graphicx, dcolumn, bm)
see http://publish.aps.org/revtex4
Discovery of a Bright Field Methane (T-type) Brown Dwarf by 2MASS
We report the discovery of a bright (J = 13.830.03) methane brown dwarf,
or T dwarf, by the Two Micron All Sky Survey. This object, 2MASSI
J0559191-140448, is the first brown dwarf identified by the newly commissioned
CorMASS instrument mounted on the Palomar 60-inch Telescope. Near-infrared
spectra from 0.9 - 2.35 \micron show characteristic CH bands at 1.1, 1.3,
1.6, and 2.2 \micron, which are significantly shallower than those seen in
other T dwarfs discovered to date. Coupled with the detection of an FeH band at
0.9896 \micron and two sets of K I doublets at J-band, we propose that 2MASS
J0559-14 is a warm T dwarf, close to the transition between L and T spectral
classes. The brightness of this object makes it a good candidate for detailed
investigation over a broad wavelength regime and at higher resolution.Comment: 21 pages, 3 figures, 2 tables, accepted to AJ for publication August
200
Observed Variability at 1um and 4um in the Y0 Brown Dwarf WISEP J173835.52+273258.9
We have monitored photometrically the Y0 brown dwarf WISEP
J173835.52+273258.9 (W1738) at both near- and mid-infrared wavelengths. This ~1
Gyr-old 400K dwarf is at a distance of 8pc and has a mass around 5 M_Jupiter.
We observed W1738 using two near-infrared filters at lambda~1um, Y and J, on
Gemini observatory, and two mid-infrared filters at lambda~4um, [3.6] and
[4.5], on the Spitzer observatory. Twenty-four hours were spent on the source
by Spitzer on each of June 30 and October 30 2013 UT. Between these
observations, around 5 hours were spent on the source by Gemini on each of July
17 and August 23 2013 UT. The mid-infrared light curves show significant
evolution between the two observations separated by four months. We find that a
double sinusoid can be fit to the [4.5] data, where one sinusoid has a period
of 6.0 +/- 0.1 hours and the other a period of 3.0 +/- 0.1 hours. The
near-infrared observations suggest variability with a ~3.0 hour period,
although only at a <~2 sigma confidence level. We interpret our results as
showing that the Y dwarf has a 6.0 +/- 0.1 hour rotation period, with one or
more large-scale surface features being the source of variability. The
peak-to-peak amplitude of the light curve at [4.5] is 3%. The amplitude of the
near-infrared variability, if real, may be as high as 5 to 30%. Intriguingly,
this size of variability and the wavelength dependence can be reproduced by
atmospheric models that include patchy KCl and Na_2S clouds and associated
small changes in surface temperature. The small number of large features, and
the timescale for evolution of the features, is very similar to what is seen in
the atmospheres of the solar system gas giants.Comment: Accepted by ApJ July 26 2016. Twenty-six pages include 8 Figures and
5 Table
A T8.5 Brown Dwarf Member of the Xi Ursae Majoris System
The Wide-field Infrared Survey Explorer has revealed a T8.5 brown dwarf (WISE
J111838.70+312537.9) that exhibits common proper motion with a
solar-neighborhood (8 pc) quadruple star system - Xi Ursae Majoris. The angular
separation is 8.5 arc-min, and the projected physical separation is about 4000
AU. The sub-solar metallicity and low chromospheric activity of Xi UMa A argue
that the system has an age of at least 2 Gyr. The infrared luminosity and color
of the brown dwarf suggests the mass of this companion ranges between 14 and 38
Jupiter masses for system ages of 2 and 8 Gyr respectively.Comment: AJ in press, 12 pages LaTeX with 6 figures. More astrometric data and
a laser guide star adaptive optics image adde
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