106 research outputs found
The performance of a composite engine consisting of a reciprocating spark-ignition engine, a blow-down turbine, and a steady-flow turbine
An Upper Limit on the Reflected Light from the Planet Orbiting the Star tau Bootis
The planet orbiting tau Boo at a separation of 0.046 AU could produce a
reflected light flux as bright as 1e-4 relative to that of the star. A spectrum
of the system will contain a reflected light component which varies in
amplitude and Doppler-shift as the planet orbits the star. Assuming the
secondary spectrum is primarily the reflected stellar spectrum, we can limit
the relative reflected light flux to be less than 5e-5. This implies an upper
limit of 0.3 for the planetary geometric albedo near 480 nm, assuming a
planetary radius of 1.2 R_Jup. This albedo is significantly less than that of
any of the giant planets of the solar system, and is not consistent with
certain published theoretical predictions.Comment: 5 pages, 1 figure, accepted by ApJ Letter
Method for Determining Pressure Drop of Air Flowing Through Constant-Area Passages for Arbitrary Heat-Input Distributions
Relative photometry of HAT-P-1b occultations
We present HST STIS observations of two occultations of the transiting
exoplanet HAT-P-1b. By measuring the planet to star flux ratio near opposition,
we constrain the geometric albedo of the planet, which is strongly linked to
its atmospheric temperature gradient. An advantage of HAT-P-1 as a target is
its binary companion ADS 16402 A, which provides an excellent photometric
reference, simplifying the usual steps in removing instrumental artifacts from
HST time-series photometry. We find that without this reference star, we would
need to detrend the lightcurve with the time of the exposures as well as the
first three powers of HST orbital phase, and this would introduce a strong bias
in the results for the albedo. However, with this reference star, we only need
to detrend the data with the time of the exposures to achieve the same
per-point scatter, therefore we can avoid most of the bias associated with
detrending. Our final result is a 2 sigma upper limit of 0.64 for the geometric
albedo of HAT-P-1b between 577 and 947 nm.Comment: 8 pages, 2 figures, 3 table
Working Papers: Astronomy and Astrophysics Panel Reports
The papers of the panels appointed by the Astronomy and Astrophysics survey Committee are compiled. These papers were advisory to the survey committee and represent the opinions of the members of each panel in the context of their individual charges. The following subject areas are covered: radio astronomy, infrared astronomy, optical/IR from ground, UV-optical from space, interferometry, high energy from space, particle astrophysics, theory and laboratory astrophysics, solar astronomy, planetary astronomy, computing and data processing, policy opportunities, benefits to the nation from astronomy and astrophysics, status of the profession, and science opportunities
HST Time-Series Photometry of the Transiting Planet of HD 209458
We have observed 4 transits of the planet of HD 209458 using the STIS
spectrograph on HST. Summing the recorded counts over wavelength between 582 nm
and 638 nm yields a photometric time series with 80 s time sampling and
relative precision of about 1.1E-4 per sample. The folded light curve can be
fit within observational errors using a model consisting of an opaque circular
planet transiting a limb-darkened stellar disk. In this way we estimate the
planetary radius R_p = 1.347 +/- 0.060 R_Jup, the orbital inclination i = 86.68
+/- 0.14 degrees, the stellar radius R_* = 1.146 +/- 0.050 R_solar, and one
parameter describing the stellar limb darkening. Our estimated radius is
smaller than those from earlier studies, but is consistent within measurement
errors, and is also consistent with theoretical estimates of the radii of
irradiated Jupiter-like planets. Satellites or rings orbiting the planet would,
if large enough, be apparent from distortions of the light curve or from
irregularities in the transit timings. We find no evidence for either
satellites or rings, with upper limits on satellite radius and mass of 1.2
Earth radii and 3 Earth masses, respectively. Opaque rings, if present, must be
smaller than 1.8 planetary radii in radial extent. The high level of
photometric precision attained in this experiment confirms the feasibility of
photometric detection of Earth-sized planets circling Sun-like stars.Comment: 28 pages, 9 figures. To be published in the Astrophysical Journa
Transit Photometry of the Core-Dominated Planet HD 149026b
We report g, V, and r photometric time series of HD 149026 spanning predicted
times of transit of the Saturn-mass planetary companion, which was recently
discovered by Sato and collaborators. We present a joint analysis of our
observations and the previously reported photometry and radial velocities of
the central star. We refine the estimate of the transit ephemeris to Tc [HJD] =
2453527.87455^{+0.00085}_{-0.00091} + N * 2.87598^{+0.00012}_{-0.00017}.
Assuming that the star has a radius of 1.45 +/- 0.10 R_Sun and a mass of 1.30
+/- 0.10 M_Sun, we estimate the planet radius to be 0.726 +/- 0.064 R_Jup,
which implies a mean density of 1.07^{+0.42}_{-0.30} g/cm^3. This density is
significantly greater than that predicted for models which include the effects
of stellar insolation and for which the planet has only a small core of solid
material. Thus we confirm that this planet likely contains a large core, and
that the ratio of core mass to total planet mass is more akin to that of Uranus
and Neptune than that of either Jupiter or Saturn.Comment: 18 pages, 4 figures, submitted to Ap
Measurement of Spin-Orbit Alignment in an Extrasolar Planetary System
We determine the stellar, planetary, and orbital properties of the transiting planetary system HD 209458 through a joint analysis of high-precision radial velocities, photometry, and timing of the secondary eclipse. Of primary interest is the strong detection of the Rossiter-McLaughlin effect, the alteration of photospheric line profiles that occurs because the planet occults part of the rotating surface of the star. We develop a new technique for modeling this effect and use it to determine the inclination of the planetary orbit relative to the apparent stellar equator (λ = -4º.4 ± 1º.4), and the line-of-sight rotation speed of the star (v sin /_★ = 4.70 ± 0.16 km s^(-1)). The uncertainty in these quantities has been reduced by an order of magnitude relative to the pioneering measurements by Queloz and collaborators. The small but nonzero misalignment is probably a relic of the planet formation epoch, because the expected timescale for tidal coplanarization is larger than the age of the star. Our determination of v sin /★ is a rare case in which rotational line broadening has been isolated from other broadening mechanisms
A Planet Orbiting the Star Rho Coronae Borealis
We report the discovery of near-sinusoidal radial velocity variations of the
G0V star rhoCrB, with period 39.6 days and amplitude 67 m/s. These variations
are consistent with the existence of an orbital companion in a circular orbit.
Adopting a mass of 1.0 M(Sun) for the primary, the companion has minimum mass
about 1.1 Jupiter masses, and orbital radius about 0.23 AU. Such an orbital
radius is too large for tidal circularization of an initially eccentric orbit
during the lifetime of the star, and hence we suggest that the low eccentricity
is primordial, as would be expected for a planet formed in a dissipative
circumstellar disk.Comment: 9 pages, LaTeX, accepted in Astrophys. J. Letter
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