6,825 research outputs found
The 8 Micron Phase Variation of the Hot Saturn HD 149026b
We monitor the star HD 149026 and its Saturn-mass planet at 8.0 micron over
slightly more than half an orbit using the Infrared Array Camera (IRAC) on the
Spitzer Space Telescope. We find an increase of 0.0227% +/- 0.0066% (3.4 sigma
significance) in the combined planet-star flux during this interval. The
minimum flux from the planet is 45% +/- 19% of the maximum planet flux,
corresponding to a difference in brightness temperature of 480 +/- 140 K
between the two hemispheres. We derive a new secondary eclipse depth of 0.0411%
+/- 0.0076% in this band, corresponding to a dayside brightness temperature of
1440 +/- 150 K. Our new secondary eclipse depth is half that of a previous
measurement (3.0 sigma difference) in this same bandpass by Harrington et al.
(2007). We re-fit the Harrington et al. (2007) data and obtain a comparably
good fit with a smaller eclipse depth that is consistent with our new value. In
contrast to earlier claims, our new eclipse depth suggests that this planet's
dayside emission spectrum is relatively cool, with an 8 micron brightness
temperature that is less than the maximum planet-wide equilibrium temperature.
We measure the interval between the transit and secondary eclipse and find that
that the secondary eclipse occurs 20.9 +7.2 / -6.5 minutes earlier (2.9 sigma)
than predicted for a circular orbit, a marginally significant result. This
corresponds to e*cos(omega) = -0.0079 +0.0027 / -0.0025 where e is the planet's
orbital eccentricity and omega is the argument of pericenter.Comment: 17 pages, 12 figure, accepted for publication in Ap
Observations of Extrasolar Planets During the non-Cryogenic Spitzer Space Telescope Mission
Precision infrared photometry from Spitzer has enabled the first direct
studies of light from extrasolar planets, via observations at secondary eclipse
in transiting systems. Current Spitzer results include the first longitudinal
temperature map of an extrasolar planet, and the first spectra of their
atmospheres. Spitzer has also measured a temperature and precise radius for the
first transiting Neptune-sized exoplanet, and is beginning to make precise
transit timing measurements to infer the existence of unseen low mass planets.
The lack of stellar limb darkening in the infrared facilitates precise radius
and transit timing measurements of transiting planets. Warm Spitzer will be
capable of a precise radius measurement for Earth-sized planets transiting
nearby M-dwarfs, thereby constraining their bulk composition. It will continue
to measure thermal emission at secondary eclipse for transiting hot Jupiters,
and be able to distinguish between planets having broad band emission versus
absorption spectra. It will also be able to measure the orbital phase variation
of thermal emission for close-in planets, even non-transiting planets, and
these measurements will be of special interest for planets in eccentric orbits.
Warm Spitzer will be a significant complement to Kepler, particularly as
regards transit timing in the Kepler field. In addition to studying close-in
planets, Warm Spitzer will have significant application in sensitive imaging
searches for young planets at relatively large angular separations from their
parent stars.Comment: 12 pages, 7 figures, to appear in "Science Opportunities for the Warm
Spitzer Mission
Studies relating to cyclotron emission from semiconductors
In this thesis studies relating to cyclotron emission in GaAs, InSb, InP and CdₓHg₁- ₓTe (C.M.T.) are described. The effect of the electric field bias on the emission intensity and linewidth in GaAs and InP is studied and a theoretical model is proposed. The study indicates the importance of nonparabolicity and polar mode scattering in determining the intensity and linewidth in these materials. Inter-excited state transitions are observed for the first time in emission- Nonparabolicity splitting is observed in InP and that in GaAs, originally observed in by Gornik (1983),is confirmed. The application of hydrostatic pressure to InSb is observed to narrow the emission line by a factor of three. In experiments on the magnetoimpurity effect in GaAs transitions between the 1S and 2P_, 2P₀, 3D-₂ and 3D-₁ impurity states are observed and central cell structure is observed for the first time. In bulk C.M.T. cyclotron resonance is studied as a function of hydrostatic pressure and reasonable agreement is achieved with accepted values for the variation of band gap with pressure. In the surface layer cyclotron resonance is observed as are Shubnikov de Haas oscillations and electric subband energies are calculated for each of these experiments. Finally the use of cyclotron emission as a spectroscopic source is demonstrated and future developments discussed
Effects of Relative Humidity and Shelf-Life on Selected Properties of Polyvinyl Acetate Adhesive Films
The effects of various relative humidities and shelf-lives on the tensile and thermal properties of a commercial polyvinyl acetate copolymer emulsion (PVAC) adhesive are reported. Adhesive-free films, from both crosslinkable and uncrosslinkable resins at three different shelf-life periods, were formed in an environmental chamber (72% relative humidity). After curing, specimens were cut from the films and divided into experimental units; and each unit was conditioned at a different relative humidity (0, 40, 60, and 90%). Tensile and differential scanning calorimetry tests were conducted after the films reached equilibrium at the various relative humidities. Tensile testing results indicate that at relative humidities greater than 40% the tensile strength and modulus of elasticity of both uncrosslinked and crosslinked films decrease. Shelf-life periods of 1.5, 2.5, and 3.5 months had relatively little effect on the tensile strength and modulus of elasticity values of either crosslinked or uncrosslinked PVAC films as compared to the effects of relative humidity. Regression analysis established that the mechanical properties varied mainly as a function of relative humidity. Differential scanning calorimetry specimens were cut from the same sheets of free film as the tensile specimens. Crosslinked and uncrosslinked specimens from an initial shelf-life period of 1.5 months were tested to determine the effects of relative humidities on the calorimetric properties of the films. The results indicate that relative humidity, especially at levels greater than 40%, affects some of the calorific values obtained from the films
Comparative analysis of the Geobacillus hemicellulose utilization locus reveals a highly variable target for improved hemicellulolysis
A map of the day-night contrast of the extrasolar planet HD 189733b
"Hot Jupiter" extrasolar planets are expected to be tidally locked because
they are close (<0.05 astronomical units, where 1 AU is the average Sun-Earth
distance) to their parent stars, resulting in permanent daysides and
nightsides. By observing systems where the planet and star periodically eclipse
each other, several groups have been able to estimate the temperatures of the
daysides of these planets. A key question is whether the atmosphere is able to
transport the energy incident upon the dayside to the nightside, which will
determine the temperature at different points on the planet's surface. Here we
report observations of HD 189733, the closest of these eclipsing planetary
systems, over half an orbital period, from which we can construct a 'map' of
the distribution of temperatures. We detected the increase in brightness as the
dayside of the planet rotated into view. We estimate a minimum brightness
temperature of 973 +/- 33 K and a maximum brightness temperature of 1212 +/- 11
K at a wavelength of 8 microns, indicating that energy from the irradiated
dayside is efficiently redistributed throughout the atmosphere, in contrast to
a recent claim for another hot Jupiter. Our data indicate that the peak
hemisphere-integrated brightness occurs 166 degrees before opposition,
corresponding to a hot spot shifted east of the substellar point. The secondary
eclipse (when the planet moves behind the star) occurs 120 +/- 24 s later than
predicted, which may indicate a slightly eccentric orbit.Comment: To appear in the May 10 2007 issue of Nature, 10 pages, 2 black and
white figures, 1 colo
The climate of HD 189733b from fourteen transits and eclipses measured by Spitzer
We present observations of seven transits and seven eclipses of the
transiting planet system HD 189733 taken with Spitzer IRAC at 8 microns. We use
a new correction for the detector ramp variation with a double-exponential
function. Our main findings are: (1) an upper limit on the variability of the
day-side planet flux of 2.7% (68% confidence); (2) the most precise set of
transit times measured for a transiting planet, with an average accuracy of 3
seconds; (3) a lack of transit-timing variations, excluding the presence of
second planets in this system above 20% of the mass of Mars in low-order
mean-motion resonance at 95% confidence; (4) a confirmation of the planet's
phase variation, finding the night side is 64% as bright as the day side, as
well as an upper limit on the night-side variability of 17% (68% confidence);
(5) a better correction for stellar variability at 8 micron causing the phase
function to peak 3.5 hrs before secondary eclipse, confirming that the
advection and radiation timescales are comparable at the 8 micron photosphere;
(6) variation in the depth of transit, which possibly implies variations in the
surface brightness of the portion of the star occulted by the planet, posing a
fundamental limit on non-simultaneous multi-wavelength transit absorption
measurements of planet atmospheres; (7) a measurement of the infrared
limb-darkening of the star, in agreement with stellar atmosphere models; (8) an
offset in the times of secondary eclipse of 69 sec, which is mostly accounted
for by a 31 sec light travel time delay and 33 sec delay due to the shift of
ingress and egress by the planet hot spot; this confirms that the phase
variation is due to an offset hot spot on the planet; (9) a retraction of the
claimed eccentricity of this system due to the offset of secondary eclipse; and
(10) high precision measurements of the parameters of this system.Comment: 18 pages, 19 figures, accepted for publication in the Astrophysical
Journa
- …