313 research outputs found
LRG-BEASTS III: Ground-based transmission spectrum of the gas giant orbiting the cool dwarf WASP-80
We have performed ground-based transmission spectroscopy of the hot Jupiter
orbiting the cool dwarf WASP-80 using the ACAM instrument on the William
Herschel Telescope (WHT) as part of the LRG-BEASTS programme. This is the third
paper of a ground-based transmission spectroscopy survey of hot Jupiters using
low-resolution grism spectrographs. We observed two transits of the planet and
have constructed transmission spectra spanning a wavelength range of
4640-8840A. Our transmission spectrum is inconsistent with a previously claimed
detection of potassium in WASP-80b's atmosphere, and is instead most consistent
with a haze. We also do not see evidence for sodium absorption at a resolution
of 100A.Comment: 11 pages, 9 figures. Accepted for publication in MNRA
Structural Transition Kinetics and Activated Behavior in the Superconducting Vortex Lattice
Using small-angle neutron scattering, we investigated the behavior of a
metastable vortex lattice state in MgB2 as it is driven towards equilibrium by
an AC magnetic field. This shows an activated behavior, where the AC field
amplitude and cycle count are equivalent to, respectively, an effective
"temperature" and "time". The activation barrier increases as the metastable
state is suppressed, corresponding to an aging of the vortex lattice.
Furthermore, we find a cross-over from a partial to a complete suppression of
metastable domains depending on the AC field amplitude, which may empirically
be described by a single free parameter. This represents a novel kind of
collective vortex behavior, most likely governed by the nucleation and growth
of equilibrium vortex lattice domains.Comment: 5 pages plus 3 pages of supplemental materia
Precision study of 6p 2Pj - 8s 2S1/2 relative transition matrix elements in atomic Cs
A combined experimental and theoretical study of transition matrix elements
of the 6p 2Pj - 8s 2S1/2 transition in atomic Cs is reported. Measurements of
the polarization-dependent two-photon excitation spectrum associated with the
transition were made in an approximately 200 cm-1 range on the low frequency
side of the 6s 2S1/2 - 6p 2P3/2 resonance. The measurements depend
parametrically on the relative transition matrix elements, but also are
sensitive to far-off-resonance 6s 2S1/2 - np 2Pj - 8s 2S1/2 transitions. In the
past, this dependence has yielded a generalized sum rule, the value of which is
dependent on sums of relative two-photon transition matrix elements. In the
present case, best available determinations from other experiments are combined
with theoretical matrix elements to extract the ratio of transition matrix
elements for the 6p 2Pj - 8s 2S1/2 (j = 1/2,3/2) transition. The resulting
experimental value of 1.423(2) is in excellent agreement with the theoretical
value, calculated using a relativistic all-order method, of 1.425(2)
LRG-BEASTS: Evidence for clouds in the transmission spectrum of HATS-46 b
We have performed low-resolution ground-based spectroscopy of HATS-46 b in
transmission, using the EFOSC2 instrument on the ESO New Technology Telescope
(NTT). HATS-46 b is a highly-inflated exoplanet that is a prime target for
transmission spectroscopy, having a Jupiter-like radius (0.95 R)
but a much lower mass (0.16 M). It orbits a G-type star with a
4.7 d period, giving an equilibrium temperature of 1100 K. We observed one
transit of HATS-46 b with the NTT, with the time-series spectra covering a
wavelength range of 3900 - 9000 Angstrom at a resolution of . We
achieved a remarkably precise transmission spectrum of 1.03 photon
noise, with a median uncertainty of ppm for Angstrom wide
bins, despite the relative faintness of the host star with . The transmission spectrum does not show strong absorption features and
retrievals favour a cloudy model, ruling out a clear atmosphere with
confidence. We also place a conservative upper limit on the sodium
abundance under the alternative scenario of a clear atmosphere. This is the
eighth planet in the LRG-BEASTS survey, which uses 4m-class telescopes such as
the NTT to obtain low-resolution transmission spectra of hot Jupiters with
precisions of around one atmospheric scale height.Comment: 10 pages, 7 figures, 4 tables, accepted for publication in MNRA
Crustal structure across the Grand Banks–Newfoundland Basin Continental Margin – II. Results from a seismic reflection profile
Author Posting. © Blackwell, 2006. This is the author's version of the work. It is posted here by permission of Blackwell for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 167 (2006): 157-170, doi:10.1111/j.1365-246X.2006.02989.x.New multi-channel seismic (MCS) reflection data were collected over a 565km
transect covering the non-volcanic rifted margin of the central eastern Grand Banks and the Newfoundland Basin in the northwestern Atlantic. Three major crustal zones are interpreted from west to east over the seaward 350-km of the profile: (1) continental crust; (2) transitional basement; (3) oceanic crust. Continental crust thins over a wide zone (~160 km) by forming a large rift basin (Carson Basin) and seaward fault block, together with a series of smaller fault blocks eastward beneath the Salar and Newfoundland basins. Analysis of selected previous reflection profiles (Lithoprobe 85-4, 85-2 and Conrad NB-1) indicates that prominent landward-dipping reflections observed under the continental slope are a regional phenomenon. They define the landward edge of a deep serpentinized mantle layer, which underlies both extended continental crust and transitional basement. The 80-km-wide transitional basement is defined landward by a basement high that may consist of serpentinized peridotite and seaward by a pair of basement highs of unknown crustal origin.
Flat and unreflective transitional basement most likely is exhumed, serpentinized mantle,
although our results do not exclude the possibility of anomalously thinned oceanic crust. A Moho reflection below interpreted oceanic crust is first observed landward of magnetic
anomaly M4, 230 km from the shelf break. Extrapolation of ages from chron M0 to the edge of interpreted oceanic crust suggests that the onset of seafloor spreading was ~138Ma (Valanginian) in the south (southern Newfoundland Basin) to ~125Ma (Barremian-Aptian boundary) in the north (Flemish Cap), comparable to those proposed for the conjugate margins.This work was funded by NSF grants OCE-9819053 and OCE-0326714 to
Woods Hole Oceanographic Institution, NSERC (Canada) and the Danish Research Council.
B. Tucholke also acknowledges support from the Henry Bryant Bigelow Chair in
Oceanography at Woods Hole Oceanographic Institution
Hot Stars With Kepler Planets Have High Obliquities
It has been known for a decade that hot stars with hot Jupiters tend to have
high obliquities. Less is known about the degree of spin-orbit alignment for
hot stars with other kinds of planets. Here, we re-assess the obliquities of
hot Kepler stars with transiting planets smaller than Neptune, based on
spectroscopic measurements of their projected rotation velocities (vsini). The
basis of the method is that a lower obliquity -- all other things being equal
-- causes sini to be closer to unity and increases the value of vsini. We
sought evidence for this effect using a sample of 150 Kepler stars with
effective temperatures between 5950 and 6550K and a control sample of 101 stars
with matching spectroscopic properties and random orientations. The planet
hosts have systematically higher values of vsini than the control stars, but
not by enough to be compatible with perfect spin-orbit alignment. The mean
value of sini is 0.856 +/- 0.036, which is 4-sigma away from unity (perfect
alignment), and 2-sigma away from pi/4 (random orientations). There is also
evidence that the hottest stars have a broader obliquity distribution: when
modeled separately, the stars cooler than 6250K have = 0.928 +/- 0.042,
while the hotter stars are consistent with random orientations. This is similar
to the pattern previously noted for stars with hot Jupiters. Based on these
results, obliquity excitation for early-G and late-F stars appears to be a
general outcome of star and planet formation, rather than being exclusively
linked to hot Jupiter formation.Comment: AJ, in press [15 pages
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