7 research outputs found
Model Bond albedos of extrasolar giant planets
The atmospheres of extrasolar giant planets are modeled with various
effective temperatures and gravities, with and without clouds. Bond albedos are
computed by calculating the ratio of the flux reflected by a planet (integrated
over wavelength) to the total stellar flux incident on the planet. This
quantity is useful for estimating the effective temperature and evolution of a
planet. We find it is sensitive to the stellar type of the primary. For a 5
M_Jup planet the Bond albedo varies from 0.4 to 0.3 to 0.06 as the primary star
varies from A5V to G2V to M2V in spectral type. It is relatively insensitive to
the effective temperature and gravity for cloud--free planets. Water clouds
increase the reflectivity of the planet in the red, which increases the Bond
albedo. The Bond albedo increases by an order of magnitude for a 13 M_Jup
planet with an M2V primary when water clouds are present. Silicate clouds, on
the other hand, can either increase or decrease the Bond albedo, depending on
whether there are many small grains (the former) or few large grains (the
latter).Comment: 6 pages, 9 figures, uses egs.cls and epsfig.sty, submitted to Physics
and Chemistry of the Earth (proceedings of the April 1998 EGS meeting in
Nice, France
The Brown Dwarf Kinematics Project (BDKP): V. Radial and rotational velocities of T Dwarfs from Keck/NIRSPEC high-resolution spectroscopy
Stars and planetary system
Interactions between brown-dwarf binaries and Sun-like stars
Several mechanisms have been proposed for the formation of brown dwarfs, but
there is as yet no consensus as to which -- if any -- are operative in nature.
Any theory of brown dwarf formation must explain the observed statistics of
brown dwarfs. These statistics are limited by selection effects, but they are
becoming increasingly discriminating. In particular, it appears (a) that brown
dwarfs that are secondaries to Sun-like stars tend to be on wide orbits, a\ga
100\,{\rm AU} (the Brown Dwarf Desert), and (b) that these brown dwarfs have a
significantly higher chance of being in a close (a\la 10\,{\rm AU}) binary
system with another brown dwarf than do brown dwarfs in the field. This then
raises the issue of whether these brown dwarfs have formed {\it in situ}, i.e.
by fragmentation of a circumstellar disc; or have formed elsewhere and
subsequently been captured. We present numerical simulations of the purely
gravitational interaction between a close brown-dwarf binary and a Sun-like
star. These simulations demonstrate that such interactions have a negligible
chance () of leading to the close brown-dwarf binary being captured by
the Sun-like star. Making the interactions dissipative by invoking the
hydrodynamic effects of attendant discs might alter this conclusion. However,
in order to explain the above statistics, this dissipation would have to favour
the capture of brown-dwarf binaries over single brown-dwarfs, and we present
arguments why this is unlikely. The simplest inference is that most brown-dwarf
binaries -- and therefore possibly also most single brown dwarfs -- form by
fragmentation of circumstellar discs around Sun-like protostars, with some of
them subsequently being ejected into the field.Comment: 10 pages, 8 figures, Accepted for publication in Astrophysics and
Space Scienc
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An Improved Near-infrared Spectrum of the Archetype y Dwarf WISEP J182831.08+265037.8
We present a Hubble Space Telescope/Wide-Field Camera 3 near-infrared spectrum of the archetype Y dwarf WISEP 182831.08+265037.8. The spectrum covers the 0.9-1.7 μm wavelength range at a resolving power of λ/Δλ ≈ 180 and is a significant improvement over the previously published spectrum because it covers a broader wavelength range and is uncontaminated by light from a background star. The spectrum is unique for a cool brown dwarf in that the flux peaks in the Y, J, and H bands are of near equal intensity in units of f λ . We fail to detect any absorption bands of NH3 in the spectrum, in contrast to the predictions of chemical equilibrium models, but tentatively identify CH4 as the carrier of an unknown absorption feature centered at 1.015 μm. Using previously published ground- and spaced-based photometry, and using a Rayleigh-Jeans tail to account for flux emerging longward of 4.5 μm, we compute a bolometric luminosity of, which is significantly lower than previously published results. Finally, we compare the spectrum and photometry to two sets of atmospheric models and find that the best overall match to the observed properties of WISE 1828+2650 is a ∼1 Gyr old binary composed of two T eff ∼ 325 K, ∼5 M Jup brown dwarfs with subsolar [C/O] ratios. © 2021. The American Astronomical Society. All rights reserved..Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
The first AllWISE proper motion discovery : WISEA J070720.50+170532.7
While quality checking a new motion-aware co-addition of all 12.5 months of Wide-field Infrared Survey Explorer (WISE) data, we found that the source WISE J070720.48+170533.0 moved 0.''9 in six months. Backtracking this motion allowed us to identify this source as 2MASS J07071961+1705464, with several entries in the USNO B catalog. An astrometric fit to these archival data gives a proper motion of μ = 1793 ± 2 mas yr–1 and a parallax of piv = 35 ± 42 mas. Photometry from WISE, 2MASS, and the POSS can be fit reasonably well by a blackbody with T = 3658 K and an angular radius of 4.36 × 10–11 radians. No clear evidence of H2 collision-induced absorption is seen in the near-infrared. An optical spectrum shows broad deep CaH bands at 638 and 690 nm, broad deep Na D at 598.2 nm, and weak or absent TiO, indicating that this source is an ultra-subdwarf M star with a radial velocity v rad ≈ –21 ± 18 km s–1 relative to the Sun. Given its apparent magnitude, the distance is about 39 ± 9 pc and the tangential velocity is probably ≈330 km s–1, but a more precise parallax is needed to be certain
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The CatWISE2020 Catalog
The CatWISE2020 Catalog consists of 1,890,715,640 sources over the entire sky selected from Wide-field Infrared Survey Explorer (WISE) and NEOWISE survey data at 3.4 and 4.6 μm (W1 and W2) collected from 2010 January 7 to 2018 December 13. This data set adds two years to that used for the CatWISE Preliminary Catalog, bringing the total to six times as many exposures spanning over 16 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 crowdsource from Schlafly et al., 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 Spitzer 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. In comparison to Gaia, CatWISE2020 motions are accurate at the 20 mas yr-1 level for W1∼15 mag sources and at the ∼100 mas yr-1 level for W1∼17 mag sources. This level of accuracy 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. © 2021. The American Astronomical Society. All rights reserved..Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]