311 research outputs found
Mid-Infrared Spectroscopy of Uranus from the Spitzer Infrared Spectrometer: 2. Determination of the Mean Composition of the Upper Troposphere and Stratosphere
Mid-infrared spectral observations Uranus acquired with the Infrared
Spectrometer (IRS) on the Spitzer Space Telescope are used to determine the
abundances of C2H2, C2H6, CH3C2H, C4H2, CO2, and tentatively CH3 on Uranus at
the time of the 2007 equinox. For vertically uniform eddy diffusion
coefficients in the range 2200-2600 cm2 s-1, photochemical models that
reproduce the observed methane emission also predict C2H6 profiles that compare
well with emission in the 11.6-12.5 micron wavelength region, where the nu9
band of C2H6 is prominent. Our nominal model with a uniform eddy diffusion
coefficient Kzz = 2430 cm2 sec-1 and a CH4 tropopause mole fraction of 1.6x10-5
provides a good fit to other hydrocarbon emission features, such as those of
C2H2 and C4H2, but the model profile for CH3C2H must be scaled by a factor of
0.43, suggesting that improvements are needed in the chemical reaction
mechanism for C3Hx species. The nominal model is consistent with a CH3D/CH4
ratio of 3.0+-0.2x10-4. From the best-fit scaling of these photochemical-model
profiles, we derive column abundances above the 10-mbar level of 4.5+01.1/-0.8
x 10+19 molecule-cm-2 for CH4, 6.2 +- 1.0 x 10+16 molecule-cm-2 for C2H2 (with
a value 24% higher from a different longitudinal sampling), 3.1 +- 0.3 x 10+16
molecule-cm-2 for C2H6, 8.6 +- 2.6 x 10+13 molecule-cm-2 for CH3C2H, 1.8 +- 0.3
x 10+13 molecule-cm-2 for C4H2, and 1.7 +- 0.4 x 10+13 molecule-cm-2 for CO2 on
Uranus. Our results have implications with respect to the influx rate of
exogenic oxygen species and the production rate of stratospheric hazes on
Uranus, as well as the C4H2 vapor pressure over C4H2 ice at low temperatures
Spitzer-MIPS Observations of the eta Cha Young Association
We have mapped the eta Chamaeleontis young stellar association in the
far-infrared with the Multiband Imaging Photometer for Spitzer (MIPS) on the
Spitzer Space Telescope. All sixteen members within the map region were
detected at 24 um, along with five members at 70 um and two at 160 um. Ten
stars show far-infrared excess emission indicating the presence of
circumstellar disks; six of these have central clearings as evidenced by the
onset of excess emission at >5 um. No new infrared excess sources are
identified among the 113 2MASS field stars with 24 um photometry but not seen
as X-ray sources, indicating that membership lists derived from X-ray surveys
are reasonably complete. Circumstellar disks in the eta Cha association span
the range from 1e-1 to 1e-4 in their fractional infrared luminosity, with a
median Ldust /Lstar of 0.04. The presence of optically thick, optically thin,
and intermediate optical depth disks within the same stellar group, in
combination with the large fraction of disks with inner holes, indicates that
the Cha association represents a crucial stage in circumstellar disk evolution.Comment: To appear in The Astrophysical Journa
Spitzer Infrared Spectrograph Observations of M, L, and T Dwarfs
We present the first mid-infrared spectra of brown dwarfs, together with
observations of a low-mass star. Our targets are the M3.5 dwarf GJ 1001A, the
L8 dwarf DENIS-P J0255-4700, and the T1/T6 binary system epsilon Indi Ba/Bb. As
expected, the mid-infrared spectral morphology of these objects changes rapidly
with spectral class due to the changes in atmospheric chemistry resulting from
their differing effective temperatures and atmospheric structures. By taking
advantage of the unprecedented sensitivity of the Infrared Spectrograph on the
Spitzer Space Telescope we have detected the 7.8 micron methane and 10 micron
ammonia bands for the first time in brown dwarf spectra.Comment: 4 pages, 2 figure
Moderate Resolution Spitzer Infrared Spectrograph (IRS) Observations of M, L, and T Dwarfs
We present 10 - 19 um moderate resolution spectra of ten M dwarfs, one L
dwarf, and two T dwarf systems obtained with the Infrared Spectrograph (IRS)
onboard the Spitzer Space Telescope. The IRS allows us to examine molecular
spectroscopic features/lines at moderate spectral resolution in a heretofore
untapped wavelength regime. These R~600 spectra allow for a more detailed
examination of clouds, non-equilibrium chemistry, as well as the molecular
features of H2O, NH3, and other trace molecular species that are the hallmarks
of these objects. A cloud-free model best fits our mid-infrared spectrum of the
T1 dwarf epsilon Indi Ba, and we find that the NH3 feature in epsilon Indi Bb
is best explained by a non-equilibrium abundance due to vertical transport in
its atmosphere. We examined a set of objects (mostly M dwarfs) in multiple
systems to look for evidence of emission features, which might indicate an
atmospheric temperature inversion, as well as trace molecular species; however,
we found no evidence of either.Comment: 19 pages, 7 figures, accepted ApJ 1/12/0
Discovery of a Companion at the L/T Transition with the Wide-field Infrared Survey Explorer
We report the discovery of a substellar companion to the nearby solar-type
star HD 46588 (F7V, 17.9 pc, ~3 Gyr). HD 46588 B was found through a survey for
common proper motion companions to nearby stars using data from the Wide-field
Infrared Survey Explorer and the Two-Micron All-Sky Survey. It has an angular
separation of 79.2" from its primary, which corresponds to a projected physical
separation of 1420 AU. We have measured a spectral type of L9 for this object
based on near-infrared spectroscopy performed with TripleSpec at Palomar
Observatory. We estimate a mass of 0.064+0.008/-0.019 Msun from a comparison of
its luminosity to the values predicted by theoretical evolutionary models for
the age of the primary. Because of its companionship to a well-studied star, HD
46588 B is one of the few known brown dwarfs at the L/T transition for which
both age and distance estimates are available. Thus, it offers new constraints
on the properties of brown dwarfs during this brief evolutionary phase. The
discovery of HD 46588 B also illustrates the value of the Wide-field Infrared
Survey Explorer for identifying brown dwarfs in the solar neighborhood via
their proper motions.Comment: Astrophysical Journal, in pres
The CatWISE Preliminary Catalog: Motions from WISE and NEOWISE Data
CatWISE is a program to catalog sources selected from combined WISE and NEOWISE all-sky survey data at 3.4 and 4.6 μm (W1 and W2). The CatWISE Preliminary Catalog consists of 900,849,014 sources measured in data collected from 2010 to 2016. This data set represents four times as many exposures and spans over 10 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 eight epochs over the 6.5 yr span of the data. From comparison to Spitzer, signal-to-noise ratio = 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 Gaia, 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⁻¹ and 30 mas yr⁻¹ 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
The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
The all sky surveys done by the Palomar Observatory Schmidt, the European
Southern Observatory Schmidt, and the United Kingdom Schmidt, the InfraRed
Astronomical Satellite and the 2 Micron All Sky Survey have proven to be
extremely useful tools for astronomy with value that lasts for decades. The
Wide-field Infrared Survey Explorer is mapping the whole sky following its
launch on 14 December 2009. WISE began surveying the sky on 14 Jan 2010 and
completed its first full coverage of the sky on July 17. The survey will
continue to cover the sky a second time until the cryogen is exhausted
(anticipated in November 2010). WISE is achieving 5 sigma point source
sensitivities better than 0.08, 0.11, 1 and 6 mJy in unconfused regions on the
ecliptic in bands centered at wavelengths of 3.4, 4.6, 12 and 22 microns.
Sensitivity improves toward the ecliptic poles due to denser coverage and lower
zodiacal background. The angular resolution is 6.1, 6.4, 6.5 and 12.0
arc-seconds at 3.4, 4.6, 12 and 22 microns, and the astrometric precision for
high SNR sources is better than 0.15 arc-seconds.Comment: 22 pages with 19 included figures. Updated to better match the
accepted version in the A
The discovery of an M4+T8.5 binary system
The original article can be found at: http://www3.interscience.wiley.com Copyright Blackwell Publishing / Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.14620.xWe report the discovery of a T8.5 dwarf, which is a companion to the M4 dwarf Wolf 940. [Please see original online abstract for complete version with correct notation]Peer reviewe
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