2,723 research outputs found
Detection of Radio Emission from the Hyperactive L Dwarf 2MASS J13153094-2649513AB
We report the detection of radio emission from the unusually active L5e + T7
binary 2MASS J13153094-2649513AB made with the Australian Telescope Compact
Array. Observations at 5.5 GHz reveal an unresolved source with a continuum
flux of 370+/-50 microJy, corresponding to a radio luminosity of L_rad = nuL_nu
= (9+/-3)x10^23 erg/s and log10(L_rad/L_bol) = -5.44+/-0.22. No detection is
made at 9.0 GHz to a 5 sigma limit of 290 microJy, consistent with a power law
spectrum S_nu ~ nu^-a with a > 0.5. The emission is quiescent, with no evidence
of variability or bursts over 3 hr of observation, and no measurable
polarization (V/I < 34%). 2MASS J1315-2649AB is one of the most radio-luminous
ultracool dwarfs detected in quiescent emission to date, comparable in strength
to other cool sources detected in outburst. Its detection indicates no decline
in radio flux through the mid-L dwarfs. It is unique among L dwarfs in having
strong and persistent Halpha and radio emission, indicating the coexistence of
a cool, neutral photosphere (low electron density) and a highly active
chromosphere (high electron density and active heating). These traits, coupled
with the system's mature age and substellar secondary, makes 2MASS J1315-2649AB
an important test for proposed radio emission mechanisms in ultracool dwarfs.Comment: 5 pages, 4 figures, accepted for publication in ApJ Letter
The Chemical Composition of an Extrasolar Minor Planet
We report the relative abundances of 17 elements in the atmosphere of the
white dwarf star GD 362, material that, very probably, was contained previously
in a large asteroid or asteroids with composition similar to the Earth/Moon
system. The asteroid may have once been part of a larger parent body not unlike
one of the terrestrial planets of our solar system.Comment: ApJ, in pres
Shocks and a Giant Planet in the Disk Orbiting BP Piscium?
Spitzer IRS spectroscopy supports the interpretation that BP Piscium, a gas
and dust enshrouded star residing at high Galactic latitude, is a first-ascent
giant rather than a classical T Tauri star. Our analysis suggests that BP
Piscium's spectral energy distribution can be modeled as a disk with a gap that
is opened by a giant planet. Modeling the rich mid-infrared emission line
spectrum indicates that the solid-state emitting grains orbiting BP Piscium are
primarily composed of ~75 K crystalline, magnesium-rich olivine; ~75 K
crystalline, magnesium-rich pyroxene; ~200 K amorphous, magnesium-rich
pyroxene; and ~200 K annealed silica ('cristobalite'). These dust grains are
all sub-micron sized. The giant planet and gap model also naturally explains
the location and mineralogy of the small dust grains in the disk. Disk shocks
that result from disk-planet interaction generate the highly crystalline dust
which is subsequently blown out of the disk mid-plane and into the disk
atmosphere.Comment: 25 pages, 4 figures, 1 table. Accepted to Ap
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