1,539 research outputs found
Induction flowmeter for dielectric fluids, experimental verification final report
Experimental verification of induction flow meter for use with dielectric fluid
Low noise electromagnetic flowmeter
Parasitic hum is removed by using an isophase magnetic field created within flowmeter and an enclosure which prevents leakage of flux field. Method prevents contamination of flow conduit and eliminates zero point drift
Small molecule conjugates with dimetal species for protein inhibition
Methods for targeting a protein by providing an inhibitor covalently linked to a rhodium(II) complex, introducing the inhibitor to the target protein and allowing the inhibitor and protein to interact. The rhodium(II) complex covalently linked to the inhibitor binds the target protein both inorganically and organically and forms stabilizing secondary contacts between the rhodium(II) complex and the protein
CLOUDS search for variability in brown dwarf atmospheres
Context: L-type ultra-cool dwarfs and brown dwarfs have cloudy atmospheres
that could host weather-like phenomena. The detection of photometric or
spectral variability would provide insight into unresolved atmospheric
heterogeneities, such as holes in a global cloud deck.
Aims: It has been proposed that growth of heterogeneities in the global cloud
deck may account for the L- to T-type transition as brown dwarf photospheres
evolve from cloudy to clear conditions. Such a mechanism is compatible with
variability. We searched for variability in the spectra of five L6 to T6 brown
dwarfs in order to test this hypothesis.
Methods: We obtained spectroscopic time series using VLT/ISAAC, over
0.99-1.13um, and IRTF/SpeX for two of our targets, in J, H and K bands. We
search for statistically variable lines and correlation between those.
Results: High spectral-frequency variations are seen in some objects, but
these detections are marginal and need to be confirmed. We find no evidence for
large amplitude variations in spectral morphology and we place firm upper
limits of 2 to 3% on broad-band variability, on the time scale of a few hours.
The T2 transition brown dwarf SDSS J1254-0122 shows numerous variable features,
but a secure variability diagnosis would require further observations.
Conclusions: Assuming that any variability arises from the rotation of
patterns of large-scale clear and cloudy regions across the surface, we find
that the typical physical scale of cloud cover disruption should be smaller
than 5-8% of the disk area for four of our targets. The possible variations
seen in SDSS J1254-0122 are not strong enough to allow us to confirm the cloud
breaking hypothesis.Comment: 17 pages, 14 figures, accepted by A&
Infrared and kinematic properties of the substellar object G 196-3B
We report unusual near- and mid-infrared photometric properties of G 196-3 B,
the young substellar companion at 16 arcsec from the active M2.5-type star G
196-3 A, using data taken with the IRAC and MIPS instruments onboard Spitzer. G
196-3 B shows markedly redder colors at all wavelengths from 1.6 up to 24
micron than expected for its spectral type, which is determined at L3 from
optical and near-infrared spectra. We discuss various physical scenarios to
account for its reddish nature, and conclude that a low-gravity atmosphere with
enshrouded upper atmospheric layers and/or a warm dusty disk/envelope provides
the most likely explanations, the two of them consistent with an age in the
interval 20-300 Myr. We also present new and accurate separate proper motion
measurements for G 196-3 A and B confirming that both objects are
gravitationally linked and share the same motion within a few mas/yr. After
integration of the combined spectrophotometric spectral energy distributions,
we obtain that the difference in the bolometric magnitudes of G 196-3 A and B
is 6.15 +/- 0.10 mag. Kinematic consideration of the Galactic space motions of
the system for distances in the interval 15-30 pc suggests that the pair is a
likely member of the Local Association, and that it lay near the past positions
of young star clusters like alpha Persei less than 85 Myr ago, where the binary
might have originated. At these young ages, the mass of G 196-3 B would be in
the range 12-25 Mjup, close to the frontier between planets and brown dwarfs.Comment: Accepted for publication in ApJ
Observed Variability at 1um and 4um in the Y0 Brown Dwarf WISEP J173835.52+273258.9
We have monitored photometrically the Y0 brown dwarf WISEP
J173835.52+273258.9 (W1738) at both near- and mid-infrared wavelengths. This ~1
Gyr-old 400K dwarf is at a distance of 8pc and has a mass around 5 M_Jupiter.
We observed W1738 using two near-infrared filters at lambda~1um, Y and J, on
Gemini observatory, and two mid-infrared filters at lambda~4um, [3.6] and
[4.5], on the Spitzer observatory. Twenty-four hours were spent on the source
by Spitzer on each of June 30 and October 30 2013 UT. Between these
observations, around 5 hours were spent on the source by Gemini on each of July
17 and August 23 2013 UT. The mid-infrared light curves show significant
evolution between the two observations separated by four months. We find that a
double sinusoid can be fit to the [4.5] data, where one sinusoid has a period
of 6.0 +/- 0.1 hours and the other a period of 3.0 +/- 0.1 hours. The
near-infrared observations suggest variability with a ~3.0 hour period,
although only at a <~2 sigma confidence level. We interpret our results as
showing that the Y dwarf has a 6.0 +/- 0.1 hour rotation period, with one or
more large-scale surface features being the source of variability. The
peak-to-peak amplitude of the light curve at [4.5] is 3%. The amplitude of the
near-infrared variability, if real, may be as high as 5 to 30%. Intriguingly,
this size of variability and the wavelength dependence can be reproduced by
atmospheric models that include patchy KCl and Na_2S clouds and associated
small changes in surface temperature. The small number of large features, and
the timescale for evolution of the features, is very similar to what is seen in
the atmospheres of the solar system gas giants.Comment: Accepted by ApJ July 26 2016. Twenty-six pages include 8 Figures and
5 Table
The discovery of a T6.5 subdwarf
We report the discovery of ULAS J131610.28+075553.0, an sdT6.5 dwarf in the UKIDSS Large Area Survey 2 epoch proper motion catalogue. This object displays significant spectral peculiarity, with the largest yet seen deviations from T6 and T7 templates in the Y and K bands for this subtype. Its large, similar to 1 arcsec yr(-1), proper motion suggests a large tangential velocity of V-tan approximate to 240-340 km s(-1), if we assume its M-J lies within the typical range for T6.5 dwarfs. This makes it a candidate for membership of the Galactic halo population. However, other metal-poor T dwarfs exhibit significant under luminosity both in specific bands and bolometrically. As a result, it is likely that its velocity is somewhat smaller, and we conclude it is a likely thick disc or halo member. This object represents the only T dwarf earlier than T8 to be classified as a subdwarf, and is a significant addition to the currently small number of known unambiguously substellar subdwarfs.Peer reviewe
Cannibalism as a life boat mechanism
Under certain conditions a cannibalistic population can survive when food for the adults is too scarce to support a non-cannibalistic population. Cannibalism can have this lifeboat effect if (i) the juveniles feed on a resource inaccessible to the adults; and (ii) the adults are cannibalistic and thus incorporate indirectly the inaccessible resource. Using a simple model we conclude that the mechanism works when, at low population densities, the average yield, in terms of new offspring, due to the energy provided by one cannibalized juvenile is larger than one
An L Band Spectrum of the Coldest Brown Dwarf
The coldest brown dwarf, WISE 0855, is the closest known planetary-mass,
free-floating object and has a temperature nearly as cold as the solar system
gas giants. Like Jupiter, it is predicted to have an atmosphere rich in
methane, water, and ammonia, with clouds of volatile ices. WISE 0855 is faint
at near-infrared wavelengths and emits almost all its energy in the
mid-infrared. Skemer et al. 2016 presented a spectrum of WISE 0855 from 4.5-5.1
micron (M band), revealing water vapor features. Here, we present a spectrum of
WISE 0855 in L band, from 3.4-4.14 micron. We present a set of atmosphere
models that include a range of compositions (metallicities and C/O ratios) and
water ice clouds. Methane absorption is clearly present in the spectrum. The
mid-infrared color can be better matched with a methane abundance that is
depleted relative to solar abundance. We find that there is evidence for water
ice clouds in the M band spectrum, and we find a lack of phosphine spectral
features in both the L and M band spectra. We suggest that a deep continuum
opacity source may be obscuring the near-infrared flux, possibly a deep
phosphorous-bearing cloud, ammonium dihyrogen phosphate. Observations of WISE
0855 provide critical constraints for cold planetary atmospheres, bridging the
temperature range between the long-studied solar system planets and accessible
exoplanets. JWST will soon revolutionize our understanding of cold brown dwarfs
with high-precision spectroscopy across the infrared, allowing us to study
their compositions and cloud properties, and to infer their atmospheric
dynamics and formation processes.Comment: 19 pages, 21 figures. Accepted for publication in Ap
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