5,765 research outputs found
Characterizing octagonal and rectangular fibers for MAROON-X
We report on the scrambling performance and focal-ratio-degradation (FRD) of
various octagonal and rectangular fibers considered for MAROON-X. Our
measurements demonstrate the detrimental effect of thin claddings on the FRD of
octagonal and rectangular fibers and that stress induced at the connectors can
further increase the FRD. We find that fibers with a thick, round cladding show
low FRD. We further demonstrate that the scrambling behavior of non-circular
fibers is often complex and introduce a new metric to fully capture non-linear
scrambling performance, leading to much lower scrambling gain values than are
typically reported in the literature (<1000 compared to 10,000 or more). We
find that scrambling gain measurements for small-core, non-circular fibers are
often speckle dominated if the fiber is not agitated.Comment: 10 pages, 8 figures, submitted to SPIE Advances in Optical and
Mechanical Technologies for Telescopes and Instrumentation 2016 (9912-185
Optimal non-circular fiber geometries for image scrambling in high-resolution spectrographs
Optical fibers are a key component for high-resolution spectrographs to
attain high precision in radial velocity measurements. We present a custom
fiber with a novel core geometry - a 'D'-shape. From a theoretical standpoint,
such a fiber should provide superior scrambling and modal noise mitigation,
since unlike the commonly used circular and polygonal fiber cross sections, it
shows chaotic scrambling. We report on the fabrication process of a test fiber
and compare the optical properties, scrambling performance, and modal noise
behavior of the D-fiber with those of common polygonal fibers.Comment: 7 pages, 6 figures, submitted to SPIE Astronomical Telescopes &
Instrumentation 2016 (9912-192
A Precise Water Abundance Measurement for the Hot Jupiter WASP-43b
The water abundance in a planetary atmosphere provides a key constraint on
the planet's primordial origins because water ice is expected to play an
important role in the core accretion model of planet formation. However, the
water content of the Solar System giant planets is not well known because water
is sequestered in clouds deep in their atmospheres. By contrast, short-period
exoplanets have such high temperatures that their atmospheres have water in the
gas phase, making it possible to measure the water abundance for these objects.
We present a precise determination of the water abundance in the atmosphere of
the 2 short-period exoplanet WASP-43b based on thermal
emission and transmission spectroscopy measurements obtained with the Hubble
Space Telescope. We find the water content is consistent with the value
expected in a solar composition gas at planetary temperatures (0.4-3.5x solar
at 1 confidence). The metallicity of WASP-43b's atmosphere suggested
by this result extends the trend observed in the Solar System of lower metal
enrichment for higher planet masses.Comment: Accepted to ApJL; this version contains three supplemental figures
that are not included in the published paper. See also our companion paper
"Thermal structure of an exoplanet atmosphere from phase-resolved emission
spectroscopy" by Stevenson et a
Climate of an Ultra hot Jupiter: Spectroscopic phase curve of WASP-18b with HST/WFC3
We present the analysis of a full-orbit, spectroscopic phase curve of the
ultra hot Jupiter WASP-18b, obtained with the Wide Field Camera 3 aboard the
Hubble Space Telescope. We measure the planet's normalized day-night contrast
as >0.96 in luminosity: the disk-integrated dayside emission from the planet is
at 964+-25 ppm, corresponding to 2894+-30 K, and we place an upper limit on the
nightside emission of <32ppm or 1430K at the 3-sigma level. We also find that
the peak of the phase curve exhibits a small, but significant offset in
brightness of 4.5+-0.5 degrees eastward.
We compare the extracted phase curve and phase resolved spectra to 3D Global
Circulation Models and find that broadly the data can be well reproduced by
some of these models. We find from this comparison several constraints on the
atmospheric properties of the planet. Firstly we find that we need efficient
drag to explain the very inefficient day-night re-circulation observed. We
demonstrate that this drag could be due to Lorentz-force drag by a magnetic
field as weak as 10 Gauss. Secondly, we show that a high metallicity is not
required to match the large day-night temperature contrast. In fact, the effect
of metallicity on the phase curve is different from cooler gas-giant
counterparts, due to the high-temperature chemistry in WASP-18b's atmosphere.
Additionally, we compare the current UHJ spectroscopic phase curves, WASP-18b
and WASP-103b, and show that these two planets provide a consistent picture
with remarkable similarities in their measured and inferred properties.
However, key differences in these properties, such as their brightness offsets
and radius anomalies, suggest that UHJ could be used to separate between
competing theories for the inflation of gas-giant planets.Comment: Accepted for publication in A&
Constraints on Brane Inflation and Cosmic Strings
By considering simple, but representative, models of brane inflation from a
single brane-antibrane pair in the slow roll regime, we provide constraints on
the parameters of the theory imposed by measurements of the CMB anisotropies by
WMAP including a cosmic string component. We find that inclusion of the string
component is critical in constraining parameters. In the most general model
studied, which includes an inflaton mass term, as well as the brane-antibrane
attraction, values n_s < 1.02 are compatible with the data at 95 % confidence
level. We are also able to constrain the volume of internal manifold (modulo
factors dependent on the warp factor) and the value of the inflaton field to be
less than 0.66M_P at horizon exit. We also investigate models with a mass term.
These observational considerations suggest that such models have r < 2*10^-5,
which can only be circumvented in the fast roll regime, or by increasing the
number of antibranes. Such a value of r would not be detectable in CMB
polarization experiment likely in the near future, but the B-mode signal from
the cosmic strings could be detectable. We present forecasts of what a similar
analysis using PLANCK data would yield and find that it should be possible to
rule out G\mu > 6.5*10^-8 using just the TT, TE and EE power spectra.Comment: 11 pages, 3 figures, revtex4, typos corrected, references adde
Thermal structure of an exoplanet atmosphere from phase-resolved emission spectroscopy
Exoplanets that orbit close to their host stars are much more highly
irradiated than their Solar System counterparts. Understanding the thermal
structures and appearances of these planets requires investigating how their
atmospheres respond to such extreme stellar forcing. We present spectroscopic
thermal emission measurements as a function of orbital phase ("phase-curve
observations") for the highly-irradiated exoplanet WASP-43b spanning three full
planet rotations using the Hubble Space Telescope. With these data, we
construct a map of the planet's atmospheric thermal structure, from which we
find large day-night temperature variations at all measured altitudes and a
monotonically decreasing temperature with pressure at all longitudes. We also
derive a Bond albedo of 0.18 +0.07,-0.12 and an altitude dependence in the
hot-spot offset relative to the substellar point.Comment: 28 pages, 12 figures, 1 movie, includes supplementary materials,
accepted for publication in Science. Also see two companion papers titled "A
Precise Water Abundance Measurement for the Hot Jupiter WASP-43b" by
Kreidberg et al. (2014b) and "The atmospheric circulation of the hot Jupiter
WASP-43b: Comparing three-dimensional models to spectrophotometric data" by
Kataria et al. (2014
Global Climate and Atmospheric Composition of the Ultra-Hot Jupiter WASP-103b from HST and Spitzer Phase Curve Observations
We present thermal phase curve measurements for the hot Jupiter WASP-103b
observed with Hubble/WFC3 and Spitzer/IRAC. The phase curves have large
amplitudes and negligible hotspot offsets, indicative of poor heat
redistribution to the nightside. We fit the phase variation with a range of
climate maps and find that a spherical harmonics model generally provides the
best fit. The phase-resolved spectra are consistent with blackbodies in the
WFC3 bandpass, with brightness temperatures ranging from K on the
nightside to K on the dayside. The dayside spectrum has a
significantly higher brightness temperature in the Spitzer bands, likely due to
CO emission and a thermal inversion. The inversion is not present on the
nightside. We retrieved the atmospheric composition and found the composition
is moderately metal-enriched ( solar)
and the carbon-to-oxygen ratio is below 0.9 at confidence. In
contrast to cooler hot Jupiters, we do not detect spectral features from water,
which we attribute to partial HO dissociation. We compare the phase curves
to 3D general circulation models and find magnetic drag effects are needed to
match the data. We also compare the WASP-103b spectra to brown dwarfs and young
directly imaged companions and find these objects have significantly larger
water features, indicating that surface gravity and irradiation environment
play an important role in shaping the spectra of hot Jupiters. These results
highlight the 3D structure of exoplanet atmospheres and illustrate the
importance of phase curve observations for understanding their complex
chemistry and physics.Comment: 25 pages, 17 figures, 7 tables; accepted to A
A combined transmission spectrum of the Earth-sized exoplanets TRAPPIST-1 b and c
Three Earth-sized exoplanets were recently discovered close to the habitable
zone of the nearby ultracool dwarf star TRAPPIST-1. The nature of these planets
has yet to be determined, since their masses remain unmeasured and no
observational constraint is available for the planetary population surrounding
ultracool dwarfs, of which the TRAPPIST-1 planets are the first transiting
example. Theoretical predictions span the entire atmospheric range from
depleted to extended hydrogen-dominated atmospheres. Here, we report a
space-based measurement of the combined transmission spectrum of the two inner
planets made possible by a favorable alignment resulting in their simultaneous
transits on 04 May 2016. The lack of features in the combined spectrum rules
out cloud-free hydrogen-dominated atmospheres for each planet at 10-
levels; TRAPPIST-1 b and c are hence unlikely to harbor an extended gas
envelope as they lie in a region of parameter space where high-altitude
cloud/haze formation is not expected to be significant for hydrogen-dominated
atmospheres. Many denser atmospheres remain consistent with the featureless
transmission spectrum---from a cloud-free water vapour atmosphere to a
Venus-like atmosphere.Comment: Early release to inform further the upcoming review of HST's Cycle 24
proposal
Transiting Exoplanet Studies and Community Targets for JWST's Early Release Science Program
The James Webb Space Telescope will revolutionize transiting exoplanet
atmospheric science due to its capability for continuous, long-duration
observations and its larger collecting area, spectral coverage, and spectral
resolution compared to existing space-based facilities. However, it is unclear
precisely how well JWST will perform and which of its myriad instruments and
observing modes will be best suited for transiting exoplanet studies. In this
article, we describe a prefatory JWST Early Release Science (ERS) program that
focuses on testing specific observing modes to quickly give the community the
data and experience it needs to plan more efficient and successful future
transiting exoplanet characterization programs. We propose a multi-pronged
approach wherein one aspect of the program focuses on observing transits of a
single target with all of the recommended observing modes to identify and
understand potential systematics, compare transmission spectra at overlapping
and neighboring wavelength regions, confirm throughputs, and determine overall
performances. In our search for transiting exoplanets that are well suited to
achieving these goals, we identify 12 objects (dubbed "community targets") that
meet our defined criteria. Currently, the most favorable target is WASP-62b
because of its large predicted signal size, relatively bright host star, and
location in JWST's continuous viewing zone. Since most of the community targets
do not have well-characterized atmospheres, we recommend initiating preparatory
observing programs to determine the presence of obscuring clouds/hazes within
their atmospheres. Measurable spectroscopic features are needed to establish
the optimal resolution and wavelength regions for exoplanet characterization.
Other initiatives from our proposed ERS program include testing the instrument
brightness limits and performing phase-curve observations.(Abridged)Comment: This is a white paper that originated from an open discussion at the
Enabling Transiting Exoplanet Science with JWST workshop held November 16 -
18, 2015 at STScI (http://www.stsci.edu/jwst/science/exoplanets). Accepted
for publication in PAS
Spitzer phase curve observations and circulation models of the inflated ultra-hot Jupiter WASP-76b
The large radii of many hot Jupiters can only be matched by models that have
hot interior adiabats, and recent theoretical work has shown that the interior
evolution of hot Jupiters has a significant impact on their atmospheric
structure. Due to its inflated radius, low gravity, and ultra-hot equilibrium
temperature, WASP-76b is an ideal case study for the impact of internal
evolution on observable properties. Hot interiors should most strongly affect
the non-irradiated side of the planet, and thus full phase curve observations
are critical to ascertain the effect of the interior on the atmospheres of hot
Jupiters. In this work, we present the first Spitzer phase curve observations
of WASP-76b. We find that WASP-76b has an ultra-hot day side and relatively
cold nightside with brightness temperatures of / at 3.6~\micron and / at 4.5~\micron, respectively. These results provide evidence
for a dayside thermal inversion. Both channels exhibit small phase offsets of
at 3.6~\micron and at
. We compare our observations to a suite of general
circulation models that consider two end-members of interior temperature along
with a broad range of frictional drag strengths. Strong frictional drag is
necessary to match the small phase offsets and cold nightside temperatures
observed. From our suite of cloud-free GCMs, we find that only cases with a
cold interior can reproduce the cold nightsides and large phase curve amplitude
at 4.5~\micron, hinting that the hot interior adiabat of WASP-76b does not
significantly impact its atmospheric dynamics or that clouds blanket its
nightside.Comment: 24 pages, 10 Figures, 5 Tables. Accepted to AJ. Co-First Author
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