1,252 research outputs found
Transit spectrophotometry of the exoplanet HD189733b. I. Searching for water but finding haze with HST NICMOS
We present Hubble Space Telescope near-infrared transit photometry of the
nearby hot-Jupiter HD189733b. The observations were taken with the NICMOS
instrument during five transits, with three transits executed with a narrowband
filter at 1.87 microns and two performed with a narrowband filter at 1.66
microns. Our observing strategy using narrowband filters is insensitive to the
usual HST intra-orbit and orbit-to-orbit measurement of systematic errors,
allowing us to accurately and robustly measure the near-IR wavelength
dependance of the planetary radius. Our measurements fail to reproduce the
Swain et al. absorption signature of atmospheric water below 2 microns at a
5-sigma confidence level. We measure a planet-to-star radius contrast of
0.15498+/-0.00035 at 1.66 microns and a contrast of 0.15517+/-0.00019 at 1.87
microns. Both of our near-IR planetary radii values are in excellent agreement
with the levels expected from Rayleigh scattering by sub-micron haze particles,
observed at optical wavelengths, indicating that upper-atmospheric haze still
dominates the near-IR transmission spectra over the absorption from gaseous
molecular species at least below 2 microns.Comment: 9 pages, 7 figures. Accepted for publication in A&
Chiral Compactification on a Square
We study quantum field theory in six dimensions with two of them compactified
on a square. A simple boundary condition is the identification of two pairs of
adjacent sides of the square such that the values of a field at two identified
points differ by an arbitrary phase. This allows a chiral fermion content for
the four-dimensional theory obtained after integrating over the square. We find
that nontrivial solutions for the field equations exist only when the phase is
a multiple of \pi/2, so that this compactification turns out to be equivalent
to a T^2/Z_4 orbifold associated with toroidal boundary conditions that are
either periodic or anti-periodic. The equality of the Lagrangian densities at
the identified points in conjunction with six-dimensional Lorentz invariance
leads to an exact Z_8\times Z_2 symmetry, where the Z_2 parity ensures the
stability of the lightest Kaluza-Klein particle.Comment: 28 pages, latex. References added. Clarifying remarks included in
section 2. Minor corrections made in section
Transiting extrasolar planetary candidates in the Galactic bulge
More than 200 extrasolar planets have been discovered around relatively
nearby stars, primarily through the Doppler line shifts owing to the reflex
motions of their host stars, and more recently through transits of some planets
across the face of the host stars. The detection of planets with the shortest
known periods, 1.2 to 2.5 days, has mainly resulted from transit surveys which
have generally targeted stars more massive than 0.75 M_sun. Here we report the
results from a planetary transit search performed in a rich stellar field
towards the Galactic bulge. We discovered 16 candidates with orbital periods
between 0.4 and 4.2 days, five of which orbit stars of 0.44 to 0.75 M_sun. In
two cases, radial-velocity measurements support the planetary nature of the
companions. Five candidates have orbital periods below 1.0 day, constituting a
new class of ultra-short-period planets (USPPs), which occur only around stars
of less than 0.88 M_sun. This indicates that those orbiting very close to more
luminous stars might be evaporatively destroyed, or that jovian planets around
lower-mass stars might migrate to smaller radii.Comment: To appear in October 5, 2006 issue of Natur
The spin-orbit alignment of the transiting exoplanet WASP-3b from Rossiter-McLaughlin observations
We present an observation of the Rossiter-McLaughlin effect for the planetary
system WASP-3. Radial velocity measurements were made during transit using the
SOPHIE spectrograph at the 1.93m telescope at Haute-Provence Observatory. The
shape of the effect shows that the sky-projected angle between the stellar
rotation axis and planetary orbital axis (lambda) is small and consistent with
zero within 2 sigma; lambda = 15 +10/-9 deg. WASP-3b joins the ~two-thirds of
planets with measured spin-orbit angles that are well aligned and are thought
to have undergone a dynamically-gentle migration process such as planet-disc
interactions. We find a systematic effect which leads to an anomalously high
determination of the projected stellar rotational velocity (vsini = 19.6
+2.2/-2.1 km/s) compared to the value found from spectroscopic line broadening
(vsini = 13.4 +/- 1.5 km/s). This is thought to be caused by a discrepancy in
the assumptions made in the extraction and modelling of the data. Using a model
developed by Hirano et al. (2009) designed to address this issue, we find vsini
to be consistent with the value obtained from spectroscopic broadening
measurements (vsini = 15.7 +1.4/-1.3 km/s).Comment: 7 pages, 3 figures, published in MNRAS 405 (2010) 1867-1872. Update
includes discussion on differential rotaation and correction of typo
GTC OSIRIS transiting exoplanet atmospheric survey: detection of sodium in XO-2b from differential long-slit spectroscopy
We present two transits of the hot-Jupiter exoplanet XO-2b using the Gran
Telescopio Canarias (GTC). The time series observations were performed using
long-slit spectroscopy of XO-2 and a nearby reference star with the OSIRIS
instrument, enabling differential specrophotometric transit lightcurves capable
of measuring the exoplanet's transmission spectrum. Two optical low-resolution
grisms were used to cover the optical wavelength range from 3800 to 9300{\AA}.
We find that sub-mmag level slit losses between the target and reference star
prevent full optical transmission spectra from being constructed, limiting our
analysis to differential absorption depths over ~1000{\AA} regions. Wider long
slits or multi-object grism spectroscopy with wide masks will likely prove
effective in minimising the observed slit-loss trends. During both transits, we
detect significant absorption in the planetary atmosphere of XO-2b using a
50{\AA} bandpass centred on the Na I doublet, with absorption depths of
Delta(R_pl/R_star)^2=0.049+/-0.017 % using the R500R grism and 0.047+/-0.011 %
using the R500B grism (combined 5.2-sigma significance from both transits). The
sodium feature is unresolved in our low-resolution spectra, with detailed
modelling also likely ruling out significant line-wing absorption over an
~800{\AA} region surrounding the doublet. Combined with narrowband photometric
measurements, XO-2b is the first hot Jupiter with evidence for both sodium and
potassium present in the planet's atmosphere.Comment: 9 pages, 10 figures, 1 table, accepted for publication in MNRA
Gran Telescopio Canarias OSIRIS Transiting Exoplanet Atmospheric Survey: Detection of potassium in XO-2b from narrowband spectrophotometry
We present Gran Telescopio Canarias (GTC) optical transit narrow-band
photometry of the hot-Jupiter exoplanet XO-2b using the OSIRIS instrument. This
unique instrument has the capabilities to deliver high cadence narrow-band
photometric lightcurves, allowing us to probe the atmospheric composition of
hot Jupiters from the ground. The observations were taken during three transit
events which cover four wavelengths at spectral resolutions near 500, necessary
for observing atmospheric features, and have near-photon limited sub-mmag
precisions. Precision narrow-band photometry on a large aperture telescope
allows for atmospheric transmission spectral features to be observed for
exoplanets around much fainter stars than those of the well studied targets
HD209458b and HD189733b, providing access to the majority of known transiting
planets. For XO-2b, we measure planet-to-star radius contrasts of
R_pl/R_star=0.10508+/-0.00052 at 6792 Ang, 0.10640+/-0.00058 at 7582 Ang, and
0.10686+/-0.00060 at 7664.9 Ang, and 0.10362+/-0.00051 at 8839 Ang. These
measurements reveal significant spectral features at two wavelengths, with an
absorption level of 0.067+/-0.016% at 7664.9 Ang due to atmospheric potassium
in the line core (a 4.1-sigma significance level), and an absorption level of
0.058+/-0.016% at 7582 Ang, (a 3.6-sigma significance level). When comparing
our measurements to hot-Jupiter atmospheric models, we find good agreement with
models which are dominated in the optical by alkali metals. This is the first
evidence for potassium in an extrasolar planet, an element that has long been
theorized along with sodium to be a dominant source of opacity at optical
wavelengths for hot Jupiters.Comment: 11 pages, 6 figures, accepted in A&A, minor changes to wording,
primarily section 4.2, and the title has also been slightly modifie
Granular Avalanches in Fluids
Three regimes of granular avalanches in fluids are put in light depending on
the Stokes number St which prescribes the relative importance of grain inertia
and fluid viscous effects, and on the grain/fluid density ratio r. In gas (r >>
1 and St > 1, e.g., the dry case), the amplitude and time duration of
avalanches do not depend on any fluid effect. In liquids (r ~ 1), for
decreasing St, the amplitude decreases and the time duration increases,
exploring an inertial regime and a viscous regime. These regimes are described
by the analysis of the elementary motion of one grain
HST hot-Jupiter transmission spectral survey: Haze in the atmosphere of WASP-6b
We report Hubble Space Telescope (HST) optical to near-infrared transmission
spectroscopy of the hot Jupiter WASP-6b, measured with the Space Telescope
Imaging Spectrograph (STIS) and Spitzer's InfraRed Array Camera (IRAC). The
resulting spectrum covers the range m. We find evidence for
modest stellar activity of WASP-6b and take it into account in the transmission
spectrum. The overall main characteristic of the spectrum is an increasing
radius as a function of decreasing wavelength corresponding to a change of
from 0.33 to m. The spectrum suggests
an effective extinction cross-section with a power law of index consistent with
Rayleigh scattering, with temperatures of K at the planetary
terminator. We compare the transmission spectrum with hot-Jupiter atmospheric
models including condensate-free and aerosol-dominated models incorporating Mie
theory. While none of the clear-atmosphere models is found to be in good
agreement with the data, we find that the complete spectrum can be described by
models that include significant opacity from aerosols including Fe-poor
MgSiO, MgSiO, KCl and NaS dust condensates. WASP-6b is the
second planet after HD189733b which has equilibrium temperatures near
K and shows prominent atmospheric scattering in the optical.Comment: 18 pages, 15 figures, 7 table
The White Dwarf Distance to the Globular Cluster 47 Tucanae and its Age
We present a new determination of the distance (and age) of the Galactic
globular cluster 47 Tucanae (NGC 104) based on the fit of its white dwarf (WD)
cooling sequence with the empirical fiducial sequence of local WD with known
trigonometric parallax, following the method described in Renzini et al.
(1996). Both the cluster and the local WDs were imaged with HST+WFPC2 using the
same instrument setup. We obtained an apparent distance modulus of
consistent with previous ground-based determinations and
shorter than that found using HIPPARCOS subdwarfs. Coupling our distance
determination with a new measure of the apparent magnitude of the main sequence
turnoff, based on our HST data, we derive an age of Gyr.Comment: Accepted for publication on the Astrophysical Journa
- …