21 research outputs found
WISE Brown Dwarf Binaries: The Discovery of a T5+T5 and a T8.5+T9 System
The multiplicity properties of brown dwarfs are critical empirical constraints for formation theories, while multiples themselves provide unique opportunities to test evolutionary and atmospheric models and examine empirical trends. Studies using high-resolution imaging cannot only uncover faint companions, but they can also be used to determine dynamical masses through long-term monitoring of binary systems. We have begun a search for the coolest brown dwarfs using preliminary processing of data from the Wide-field Infrared Survey Explorer and have confirmed many of the candidates as late-type T dwarfs. In order to search for companions to these objects, we are conducting observations using the Laser Guide Star Adaptive Optics system on Keck II. Here we present the first results of that search, including a T5 binary with nearly equal mass components and a faint companion to a T8.5 dwarf with an estimated spectral type of T9
Wide-Field Infrared Survey Explorer Science Payload Update
The Wide Field Infrared Survey Explorer is a NASA Medium Class Explorer mission to perform a high-sensitivity, high resolution, all-sky survey in four infrared wavelength bands. The science payload is a 40 cm aperture cryogenically cooled infrared telescope with four 10242 infrared focal plane arrays covering from 2.8 to 26 μm. Mercury cadmium telluride (MCT) detectors are used for the 3.3 μm and 4.6 μm channels, and Si:As detectors are used for the 12 μm and 23 μm wavelength channels. A cryogenic scan mirror freezes the field of view on the sky over the 9.9-second frame integration time. A two-stage solid hydrogen cryostat provides cooling to temperatures less than 17 K and 8.3 K at the telescope and Si:As focal planes, respectively. The science payload collects continuous data on orbit for the seven-month baseline mission with a goal to support a year-long mission, if possible. As of the writing of this paper, the payload subassemblies are complete, and the payload has begun integration and test. This paper provides a payload overview and discusses instrument status and performance
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
The state of the focus and image quality of the Spitzer Space Telescope as measured in orbit
We describe the process by which the NASA Spitzer Space Telescope (SST) Cryogenic Telescope Assembly (CTA) was brought into focus after arrival of the spacecraft in orbit. The ground rules of the mission did not allow us to make a conventional focus sweep. A strategy was developed to determine the focus position through a program of passive imaging during the observatory cool-down time period. A number of analytical diagnostic tools were developed to facilitate evaluation of the state of the CTA focus. Initially, these tools were used to establish the in-orbit focus position. These tools were then used to evaluate the effects of an initial small exploratory move that verified the health and calibration of the secondary mirror focus mechanism. A second large move of the secondary mirror was then commanded to bring the telescope into focus. We present images that show the CTA Point Spread Function (PSF) at different channel wavelengths and demonstrate that the telescope achieved diffraction limited performance at a wavelength of 5.5 μm, somewhat better than the level-one requirement
The Discovery of Y Dwarfs Using Data from the Wide-field Infrared Survey Explorer (WISE)
We present the discovery of seven ultracool brown dwarfs identified with the
Wide-field Infrared Survey Explorer (WISE). Near-infrared spectroscopy reveals
deep absorption bands of H_2O and CH_4 that indicate all seven of the brown
dwarfs have spectral types later than UGPS J072227.51-054031.2, the latest type
T dwarf currently known. The spectrum of WISEP J182831.08+265037.8 is distinct
in that the heights of the J- and H-band peaks are approximately equal in units
of f_lambda, so we identify it as the archetypal member of the Y spectral
class. The spectra of at least two of the other brown dwarfs exhibit absorption
on the blue wing of the H-band peak that we tentatively ascribe to NH_3. These
spectral morphological changes provide a clear transition between the T dwarfs
and the Y dwarfs. In order to produce a smooth near-infrared spectral sequence
across the T/Y dwarf transition, we have reclassified UGPS J0722-0540 as the T9
spectral standard and tentatively assign WISEP J173835.52+273258.9 as the Y0
spectral standard. In total, six of the seven new brown dwarfs are classified
as Y dwarfs: four are classified as Y0, one is classified as Y0 (pec?), and
WISEP J1828+2650 is classified as >Y0. We have also compared the spectra to the
model atmospheres of Marley and Saumon and infer that the brown dwarfs have
effective temperatures ranging from 300 K to 500 K, making them the coldest
spectroscopically confirmed brown dwarfs known to date.Comment: Submitted June 11 and accepted August 2 for publication in the
Astrophysical Journa
The CatWISE Preliminary Catalog: Motions from and Data
CatWISE is a program to catalog sources selected from combined
and all-sky survey data at 3.4 and 4.6 m (W1 and W2). The
CatWISE Preliminary Catalog consists of 900,849,014 sources measured in data
collected from 2010 to 2016. This dataset represents four times as many
exposures and spans over ten times as large a time baseline as that used for
the AllWISE Catalog. CatWISE adapts AllWISE software to measure the sources in
coadded images created from six-month subsets of these data, each representing
one coverage of the inertial sky, or epoch. The catalog includes the measured
motion of sources in 8 epochs over the 6.5 year span of the data. From
comparison to , the SNR=5 limits in magnitudes in the Vega
system are W1=17.67 and W2=16.47, compared to W1=16.96 and W2=16.02 for
AllWISE. From comparison to , CatWISE positions have typical
accuracies of 50 mas for stars at W1=10 mag and 275 mas for stars at W1=15.5
mag. Proper motions have typical accuracies of 10 mas yr and 30 mas
yr for stars with these brightnesses, an order of magnitude better than
from AllWISE. The catalog is available in the WISE/NEOWISE Enhanced and
Contributed Products area of the NASA/IPAC Infrared Science Archive.Comment: 53 pages, 20 figures, 5 tables. Accepted by ApJ
The CatWISE2020 Catalog
The CatWISE2020 Catalog consists of 1,890,715,640 sources over the entire sky
selected from WISE and NEOWISE survey data at 3.4 and 4.6 m (W1 and W2)
collected from 2010 Jan. 7 to 2018 Dec. 13. This dataset adds two years to that
used for the CatWISE Preliminary Catalog (Eisenhardt et al., 2020), bringing
the total to six times as many exposures spanning over sixteen times as large a
time baseline as the AllWISE catalog. The other major change from the CatWISE
Preliminary Catalog is that the detection list for the CatWISE2020 Catalog was
generated using (Schlafly et al. 2019), while the CatWISE
Preliminary Catalog used the detection software used for AllWISE. These two
factors result in roughly twice as many sources in the CatWISE2020 Catalog. The
scatter with respect to photometry at faint magnitudes in the
COSMOS field, which is out of the Galactic plane and at low ecliptic latitude
(corresponding to lower WISE coverage depth) is similar to that for the CatWISE
Preliminary Catalog. The 90% completeness depth for the CatWISE2020 Catalog is
at W1=17.7 mag and W2=17.5 mag, 1.7 mag deeper than in the CatWISE Preliminary
Catalog. From comparison to , CatWISE2020 motions are accurate at
the 20 mas yr level for W115 mag sources, and at the mas
yr level for W117 mag sources. This level of precision represents
a 12 improvement over AllWISE. The CatWISE catalogs are available in
the WISE/NEOWISE Enhanced and Contributed Products area of the NASA/IPAC
Infrared Science Archive.Comment: 27 pages, 24 figure, 2 tables. Accepted for publication in ApJS.
arXiv admin note: text overlap with arXiv:1908.0890
The state of the focus and image quality of the Spitzer Space Telescope as measured in orbit
We describe the process by which the NASA Spitzer Space Telescope (SST) Cryogenic Telescope Assembly (CTA) was brought into focus after arrival of the spacecraft in orbit. The ground rules of the mission did not allow us to make a conventional focus sweep. A strategy was developed to determine the focus position through a program of passive imaging during the observatory cool-down time period. A number of analytical diagnostic tools were developed to facilitate evaluation of the state of the CTA focus. Initially, these tools were used to establish the in-orbit focus position. These tools were then used to evaluate the effects of an initial small exploratory move that verified the health and calibration of the secondary mirror focus mechanism. A second large move of the secondary mirror was then commanded to bring the telescope into focus. We present images that show the CTA Point Spread Function (PSF) at different channel wavelengths and demonstrate that the telescope achieved diffraction limited performance at a wavelength of 5.5 μm, somewhat better than the level-one requirement