8,730 research outputs found
Line-profile tomography of exoplanet transits I: The Doppler shadow of HD 189733b
We present a direct method for isolating the component of the starlight
blocked by a planet as it transits its host star, and apply it to spectra of
the bright transiting planet HD 189733b. We model the global shape of the
stellar cross-correlation function as the convolution of a limb-darkened
rotation profile and a gaussian representing the Doppler core of the average
photospheric line profile. The light blocked by the planet during the transit
is a gaussian of the same intrinsic width, whose trajectory across the line
profile yields a precise measure of the misalignment angle and an independent
measure of v sin I. We show that even when v sin I is less than the width of
the intrinsic line profile, the travelling Doppler "shadow" cast by the planet
creates an identifiable distortion in the line profiles which is amenable to
direct modelling. Direct measurement of the trajectory of the missing starlight
yields self-consistent measures of the projected stellar rotation rate, the
intrinsic width of the mean local photospheric line profile, the projected
spin-orbit misalignment angle, and the system's centre-of-mass velocity.
Combined with the photometric rotation period, the results give a geometrical
measure of the stellar radius which agrees closely with values obtained from
high-precision transit photometry if a small amount of differential rotation is
present in the stellar photosphere.Comment: 8 pages, 5 figures, 2 tables; accepted by MNRA
Small, high-speed bearing technology for cryogenic turbo-pumps
The design of 20-mm bore ball bearings is described for cryogenic turbo-machinery applications, operating up to speeds of 120,000 rpm. A special section is included on the design of hybrid bearings. Each hybrid bearing is composed of a ball bearing in series with a conventional pressurized fluid-film journal bearing. Full details are presented on the design of a test vehicle which possesses the capability of testing the above named bearings within the given speed range under externally applied radial and axial loads
A Prograde, Low-Inclination Orbit for the Very Hot Jupiter WASP-3b
We present new spectroscopic and photometric observations of the transiting
exoplanetary system WASP-3. Spectra obtained during two separate transits
exhibit the Rossiter-McLaughlin (RM) effect and allow us to estimate the
sky-projected angle between the planetary orbital axis and the stellar rotation
axis, lambda = 3.3^{+2.5}_{-4.4} degrees. This alignment between the axes
suggests that WASP-3b has a low orbital inclination relative to the equatorial
plane of its parent star. During our first night of spectroscopic measurements,
we observed an unexpected redshift briefly exceeding the expected sum of the
orbital and RM velocities by 140 m/s. This anomaly could represent the
occultation of material erupting from the stellar photosphere, although it is
more likely to be an artifact caused by moonlight scattered into the
spectrograph.Comment: 23 pages, 4 figures, Accepted for publication in The Astrophysical
Journal, Replacement includes revised citation
The spin-orbit angle of the transiting hot jupiter CoRoT-1b
We measure the angle between the planetary orbit and the stellar rotation
axis in the transiting planetary system CoRoT-1, with new HIRES/Keck and
FORS/VLT high-accuracy photometry. The data indicate a highly tilted system,
with a projected spin-orbit angle lambda = 77 +- 11 degrees. Systematic
uncertainties in the radial velocity data could cause the actual errors to be
larger by an unknown amount, and this result needs to be confirmed with further
high-accuracy spectroscopic transit measurements.
Spin-orbit alignment has now been measured in a dozen extra-solar planetary
systems, and several show strong misalignment. The first three misaligned
planets were all much more massive than Jupiter and followed eccentric orbits.
CoRoT-1, however, is a jovian-mass close-in planet on a circular orbit. If its
strong misalignment is confirmed, it would break this pattern. The high
occurence of misaligned systems for several types of planets and orbits favours
planet-planet scattering as a mechanism to bring gas giants on very close
orbits.Comment: to appear in in MNRAS letters [5 pages
Noticing for Equity to Sustain Multilingual Literacies
This department explores how teachers can sustain students’ multilingual literacies and reimagine literacy learning across multiple contexts in conversation with researchers, practitioners, and communities
Near-infrared transit photometry of the exoplanet HD 149026b
The transiting exoplanet HD 149026b is an important case for theories of
planet formation and planetary structure, because the planet's relatively small
size has been interpreted as evidence for a highly metal-enriched composition.
We present observations of 4 transits with the Near Infrared Camera and
Multi-Object Spectrometer on the Hubble Space Telescope, within a wavelength
range of 1.1--2.0 m. Analysis of the light curve gives the most precise
estimate yet of the stellar mean density, g cm. By requiring agreement between the
observed stellar properties (including ) and stellar evolutionary
models, we refine the estimate of the stellar radius: R_\sun. We also find a deeper transit than has been
measured at optical and mid-infrared wavelengths. Taken together, these
findings imply a planetary radius of , which is larger than earlier estimates. Models of the planetary interior
still require a metal-enriched composition, although the required degree of
metal enrichment is reduced. It is also possible that the deeper NICMOS transit
is caused by wavelength-dependent absorption by constituents in the planet's
atmosphere, although simple model atmospheres do not predict this effect to be
strong enough to account for the discrepancy. We use the 4 newly-measured
transit times to compute a refined transit ephemeris.Comment: 18 pages, 13 figures, accepted for publication in Ap
HATS-1b: The First Transiting Planet Discovered by the HATSouth Survey
We report the discovery of HATS-1b, a transiting extrasolar planet orbiting
the moderately bright V=12.05 G dwarf star GSC 6652-00186, and the first planet
discovered by HATSouth, a global network of autonomous wide-field telescopes.
HATS-1b has a period P~3.4465 d, mass Mp~1.86MJ, and radius Rp~1.30RJ. The host
star has a mass of 0.99Msun, and radius of 1.04Rsun. The discovery light curve
of HATS-1b has near continuous coverage over several multi-day periods,
demonstrating the power of using a global network of telescopes to discover
transiting planets.Comment: Submitted to AJ 10 pages, 5 figures, 6 table
Tidal Evolution of Close-in Planets
Recent discoveries of several transiting planets with clearly non-zero
eccentricities and some large inclinations started changing the simple picture
of close-in planets having circular and well-aligned orbits. Two major
scenarios to form such planets are planet migration in a disk, and
planet--planet interactions combined with tidal dissipation. The former
scenario can naturally produce a circular and low-obliquity orbit, while the
latter implicitly assumes an initially highly eccentric and possibly
high-obliquity orbit, which are then circularized and aligned via tidal
dissipation. We investigate the tidal evolution of transiting planets on
eccentric orbits. We show that the current and future orbital evolution of
these systems is likely dominated by tidal dissipation, and not by a more
distant companion. Although most of these close-in planets experience orbital
decay all the way to the Roche limit, there are two characteristic evolution
paths for them, depending on the relative efficiency of tidal dissipation
inside the star and the planet. We point out that the current observations may
be consistent with one of them. Our results suggest that at least some of the
close-in planets with non-zero orbital eccentricity may have been formed by
tidally circularizing an initially eccentric orbit. We also find that even when
the stellar spin-orbit misalignment is observed to be small at present, some
systems could have had a highly misaligned orbit in the past. Finally, we also
re-examine the recent claim by Levrard et. al., who found that all orbital and
spin parameters evolve on a similar timescale to orbital decay.Comment: Accepted for publication in ApJ, 22 pages, 19 figures, 2 tables,
Corrupted figures are fixe
Five New Transits of the Super-Neptune HD 149026
We present new photometry of HD 149026 spanning five transits of its
"super-Neptune" planet. In combination with previous data, we improve upon the
determination of the planet-to-star radius ratio: R_p/R_star =
0.0491^{+0.0018}_{-0.0005}. We find the planetary radius to be 0.71 +/- 0.05
R_Jup, in accordance with previous theoretical models invoking a high metal
abundance for the planet. The limiting error is the uncertainty in the stellar
radius. Although we find agreement among four different ways of estimating the
stellar radius, the uncertainty remains at 7%. We also present a refined
transit ephemeris and a constraint on the orbital eccentricity and argument of
pericenter, e cos(omega) = -0.0014 +/- 0.0012, based on the measured interval
between primary and secondary transits.Comment: To appear in ApJ [19 pages
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