399 research outputs found
The Collapse of the Wien Tail in the Coldest Brown Dwarf? Hubble Space Telescope Near-Infrared Photometry of WISE J085510.83-071442.5
We present Hubble Space Telescope (HST) near-infrared photometry of the
coldest known brown dwarf, WISE J085510.83071442.5 (WISE 08550714). WISE
08550714 was observed with the Wide Field Camera 3 (WFC3) aboard HST using
the F105W, F125W, and F160W filters, which approximate the , , and
near-infrared bands. WISE 08550714 is undetected at F105W with a
corresponding 2 magnitude limit of 26.9. We marginally detect
WISE 08550714 in the F125W images (S/N 4), with a measured magnitude
of 26.41 0.27, more than a magnitude fainter than the band magnitude
reported by Faherty and coworkers. WISE J08550714 is clearly detected in the
F160W band, with a magnitude of 23.90 0.02, the first secure detection of
WISE 08550714 in the near-infrared. Based on these data, we find that WISE
08550714 has extremely red F105WF125W and F125WF160W colors relative
to other known Y dwarfs. We find that when compared to the models of Saumon et
al. and Morley et al., the F105WF125W and F125WF160W colors of WISE
08550714 cannot be accounted for simultaneously. These colors likely
indicate that we are seeing the collapse of flux on the Wien tail for this
extremely cold object.Comment: Accepted for publication in ApJ Letter
The Schizophrenic Spectrum of LSR 1610-0040: a Peculiar M Dwarf/Subdwarf
We present a moderate resolution (R=2000), 0.8-4.1 micron spectrum of LSR
1610-0040, a high proper motion star classified as an early-type L subdwarf by
Lepine and collaborators based on its red-optical spectrum. The near-infrared
spectrum of LSR 1610-0040 does not fit into the (tentative) M/L subdwarf
sequence but rather exhibits a mix of characteristics found in the spectra of
both M dwarfs and M subdwarfs. In particular, the near-infrared spectrum
exhibits a Na I doublet and CO overtone bandheads in the K band, and Al I and K
I lines and an FeH bandhead in the H band, all of which have strengths more
typical of field M dwarfs. Furthermore the spectrum of Gl 406 (M6 V) provides a
reasonably good match to the 0.6-4.1 micron spectral energy distribution of LSR
1610. Nevertheless the near-infrared spectrum of LSR 1610 also exhibits
features common to the spectra of M subdwarfs including a strong Ti I multiplet
centered at ~0.97 microns, a weak VO band at ~1.06 microns, and possible
collision-induced H_2 absorption in the H and K bands. We discuss a number of
possible explanations for the appearance of the red-optical and near-infrared
spectrum of LSR 1610-0040. Although we are unable to definitively classify LSR
1610-0040, the preponderance of evidence suggests that it is a mildly
metal-poor M dwarf. Finally, we tentatively identify a new band of TiO at ~0.93
microns in the spectra of M dwarfs.Comment: Accepted for publication in the Astronomical Journa
Three New Cool Brown Dwarfs Discovered with the Wide-field Infrared Survey Explorer (WISE) and an Improved Spectrum of the Y0 Dwarf WISE J041022.71+150248.4
As part of a larger search of Wide-field Infrared Survey Explorer (WISE) data
for cool brown dwarfs with effective temperatures less than 1000 K, we present
the discovery of three new cool brown dwarfs with spectral types later than T7.
Using low-resolution, near-infrared spectra obtained with the NASA Infrared
Telescope Facility and the Hubble Space Telescope we derive spectral types of
T9.5 for WISE J094305.98+360723.5, T8 for WISE J200050.19+362950.1, and Y0: for
WISE J220905.73+271143.9. The identification of WISE J220905.73+271143.9 as a Y
dwarf brings the total number of spectroscopically confirmed Y dwarfs to
seventeen. In addition, we present an improved spectrum (i.e. higher
signal-to-noise ratio) of the Y0 dwarf WISE J041022.71+150248.4 that confirms
the Cushing et al. classification of Y0. Spectrophotometric distance estimates
place all three new brown dwarfs at distances less than 12 pc, with WISE
J200050.19+362950.1 lying at a distance of only 3.9-8.0 pc. Finally, we note
that brown dwarfs like WISE J200050.19+362950.1 that lie in or near the
Galactic plane offer an exciting opportunity to measure their mass via
astrometric microlensing.Comment: Accepted for publication in the Astronomical Journa
FeH Absorption in the Near-Infrared Spectra of Late M and L Dwarfs
We present medium-resolution z-, J-, and H-band spectra of four late-type
dwarfs with spectral types ranging from M8 to L7.5. In an attempt to determine
the origin of numerous weak absorption features throughout their near-infrared
spectra, and motivated by the recent tentative identification of the E 4\Pi- A
^4\Pi system of FeH near 1.6 microns in umbral and cool star spectra, we have
compared the dwarf spectra to a laboratory FeH emission spectrum. We have
identified nearly 100 FeH absorption features in the z-, J-, and H-band spectra
of the dwarfs. In particular, we have identified 34 features which dominate the
appearance of the H-band spectra of the dwarfs and which appear in the
laboratory FeH spectrum. Finally, all of the features are either weaker or
absent in the spectrum of the L7.5 dwarf which is consistent with the weakening
of the known FeH bandheads in the spectra of the latest L dwarfs.Comment: accepted by Ap
A Method of Correcting Near-Infrared Spectra for Telluric Absorption
We present a method for correcting near-infrared medium-resolution spectra
for telluric absorption. The method makes use of a spectrum of an A0V star,
observed near in time and close in airmass to the target object, and a
high-resolution model of Vega, to construct a telluric correction spectrum that
is free of stellar absorption features. The technique was designed specifically
to perform telluric corrections on spectra obtained with SpeX, a 0.8-5.5
micron, medium-resolution cross-dispersed spectrograph at the NASA Infrared
Telescope Facility, and uses the fact that for medium resolutions there exist
spectral regions uncontaminated by atmospheric absorption lines. However, it is
also applicable (in a somewhat modified form) to spectra obtained with other
near-infrared spectrographs. An IDL-based code that carries out the procedures
is available for downloading via the World Wide Web from the IRTF website.Comment: 39 pages, 10 figures, To appear in the Feb 2003 issue of PASP; IDL
source code, as well as full resolution versions of the figures, are
available at http://irtfweb.ifa.hawaii.edu/Facility/spex
WISE J163940.83-684738.6: A Y Dwarf identified by Methane Imaging
We have used methane imaging techniques to identify the near-infrared
counterpart of the bright WISE source WISEJ163940.83-684738.6. The large proper
motion of this source (around 3.0arcsec/yr) has moved it, since its original
WISE identification, very close to a much brighter background star -- it
currently lies within 1.5" of the J=14.90+-0.04 star 2MASS16394085-6847446.
Observations in good seeing conditions using methane sensitive filters in the
near-infrared J-band with the FourStar instrument on the Magellan 6.5m Baade
telescope, however, have enabled us to detect a near-infrared counterpart. We
have defined a photometric system for use with the FourStar J2 and J3 filters,
and this photometry indicates strong methane absorption, which unequivocally
identifies it as the source of the WISE flux. Using these imaging observations
we were then able to steer this object down the slit of the FIRE spectrograph
on a night of 0.6" seeing, and so obtain near-infrared spectroscopy confirming
a Y0-Y0.5 spectral type. This is in line with the object's
near-infrared-to-WISE J3--W2 colour. Preliminary astrometry using both WISE and
FourStar data indicates a distance of 5.0+-0.5pc and a substantial tangential
velocity of 73+-8km/s. WISEJ163940.83-684738.6 is the brightest confirmed Y
dwarf in the WISE W2 passband and its distance measurement places it amongst
the lowest luminosity sources detected to date.Comment: Accepted for publication in The Astrophysical Journal, 20 September
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