373 research outputs found
Warm Ice Giant GJ 3470b. I. A Flat Transmission Spectrum Indicates a Hazy, Low-methane, and/or Metal-rich Atmosphere
We report our spectroscopic investigation of the transiting ice giant GJ
3470b's atmospheric transmission, and the first results of extrasolar planet
observations from the new Keck/MOSFIRE spectrograph. We measure a planet/star
radius ratio of Rp/Rs = 0.0789 +/- 0.0020 in a bandpass from 2.09-2.36 micron
and in six narrower bands across this wavelength range. When combined with
existing broadband photometry, these measurements rule out cloud-free
atmospheres in chemical equilibrium assuming either solar abundances (5.4 sigma
confidence) or a moderate level of metal enrichment (50x solar abundances, 3.8
sigma), confirming previous results that such models are not representative for
cool, low-mass, externally irradiated extrasolar planets. Current measurements
are consistent with a flat transmission spectrum, which suggests that the
atmosphere is explained by high-altitude clouds and haze, disequilibrium
chemistry, unexpected abundance patterns, or the atmosphere is extremely
metal-rich (>200x solar). Because GJ 3470b's low bulk density sets an upper
limit on the planet's atmospheric enrichment of <300x solar, the atmospheric
mean molecular weight must be <9. Thus, if the atmosphere is cloud-free its
spectral features should be detectable with future observations. Transit
observations at shorter wavelengths will provide the best opportunity to
discriminate between plausible scenarios. We obtained optical spectroscopy with
the GMOS spectrograph, but these observations exhibit large systematic
uncertainties owing to thin, persistent cirrus conditions. Finally, we also
provide the first detailed look at the steps necessary for well-calibrated
MOSFIRE observations, and provide advice for future observations with this
instrument.Comment: Accepted to A&A. Light curves will be available at CDS (or download
arXiv tarball
Re-evaluating Hot Jupiter WASP-12b: An Update
The hot Jupiter WASP-12b is one of the largest, hottest, and best-studied
extrasolar planets. We revisit our recent analysis of WASP-12b's emission
spectrum in light of near-infrared spectroscopic measurements which have been
claimed to support either a hydride-dominated or carbon-rich atmospheric
composition. We show that this new spectrum is still consistent with a
featureless blackbody, indicating a nearly isothermal photosphere on the
planet's day side. Thus the ensemble of occultation measurements for WASP-12b
is still insufficient to constrain the planet's atmospheric composition.Comment: 4 pages, 2 figures. Submitted as Proceedings to the ROPACS meeting
"Hot Planets and Cool Stars" (Nov. 2012, Garching),
http://www.mpe.mpg.de/events/ropacs-2012/Home.htm
Using supervised learning algorithms as a follow-up method in the search of gravitational waves from core-collapse supernovae
We present a follow-up method based on supervised machine learning (ML) to improve the performance in the search of gravitational wave (GW) bursts from core-collapse supernovae (CCSNe) using the coherent WaveBurst (cWB) pipeline. The ML model discriminates noise from signal events by using a set of reconstruction parameters provided by cWB as features. Detected noise events are discarded yielding a reduction in the false alarm rate (FAR) and the false alarm probability thus enhancing the statistical significance. We tested the proposed method using strain data from the first half of the third observing run of advanced LIGO, and CCSNe GW signals extracted from 3D simulations. The ML model is tuned using a dataset of noise and signal events, and then used to identify and discard noise events in the cWB analyses. Noise and signal reduction levels were examined in single (L1 and H1) and two detector network (L1H1). The FAR was reduced by a factor of ∼10 to ∼100 resulting in an enhancement in the statistical significance of ∼1σ to ∼2σ, while not impacting the detection efficiencies
Using Supervised Learning Algorithms as a Follow-Up Method in the Search of Gravitational Waves from Core-Collapse Supernovae
We present a follow-up method based on supervised machine learning (ML) to improve the performance in the search of gravitational wave (GW) bursts from core-collapse supernovae (CCSNe) using the coherent WaveBurst (cWB) pipeline. The ML model discriminates noise from signal events by using a set of reconstruction parameters provided by cWB as features. Detected noise events are discarded yielding a reduction in the false alarm rate (FAR) and the false alarm probability thus enhancing the statistical significance. We tested the proposed method using strain data from the first half of the third observing run of advanced LIGO, and CCSNe GW signals extracted from 3D simulations. The ML model is tuned using a dataset of noise and signal events, and then used to identify and discard noise events in the cWB analyses. Noise and signal reduction levels were examined in single (L1 and H1) and two detector networks (L1H1). The FAR was reduced by a factor of ∼10 to ∼100 resulting in an enhancement in the statistical significance of ∼1σ to ∼2σ, while not impacting the detection efficiencies
Hyb:A bioinformatics pipeline for the analysis of CLASH (crosslinking, ligation and sequencing of hybrids) data
Peer reviewedPublisher PD
Third-person knowledge ascriptions: a crucial experiment for contextualism
In the past few years there has been a turn towards evaluating the empirical foundation of epistemic contextualism using formal (rather than armchair) experimental methods. By-and-large, the results of these experiments have not supported the original motivation for epistemic contextualism. That is partly because experiments have only uncovered effects of changing context on knowledge ascriptions in limited experimental circumstances (when contrast is present, for example), and partly because existing experiments have not been designed to distinguish between contextualism and one of its main competing theories, subject-sensitive invariantism. In this paper, we discuss how a particular, “third-person”, experimental design is needed to provide evidence that would support contextualism over subject-sensitive invariantism. In spite of the theoretical significance of third-person knowledge ascriptions for debates surrounding contextualism, no formal experiments evaluating such ascriptions that assess contextualist claims have previously been conducted. In this paper, we conduct an experiment specifically designed to examine that central gap in contextualism’s empirical foundation. The results of our experiment provide crucial support for epistemic contextualism over subject-sensitive invariantism
High Resolution, Differential, Near-infrared Transmission Spectroscopy of GJ 1214b
The nearby star GJ 1214 hosts a planet intermediate in radius and mass
between Earth and Neptune, resulting in some uncertainty as to its nature. We
have observed this planet, GJ 1214b, during transit with the high-resolution,
near-infrared NIRSPEC spectrograph on the Keck II telescope, in order to
characterize the planet's atmosphere. By cross-correlating the spectral changes
through transit with a suite of theoretical atmosphere models, we search for
variations associated with absorption in the planet atmosphere. Our
observations are sufficient to rule out tested model atmospheres with
wavelength-dependent transit depth variations >5e-4 over the wavelength range
2.1 - 2.4 micron. Our sensitivity is limited by variable slit loss and telluric
transmission effects.
We find no positive signatures but successfully rule out a number of
plausible atmospheric models, including the default assumption of a gaseous,
H-dominated atmosphere in chemical equilibrium. Such an atmosphere can be made
consistent if the absorption due to methane is reduced. Clouds can also render
such an atmosphere consistent with our observations, but only if they lie
higher in the atmosphere than indicated by recent optical and infrared
measurements.
When taken in concert with constraints from other groups, our results support
a consensus model in which the atmosphere of GJ 1214b contains significant H
and He, but where methane is depleted. If this depletion is the result of
photochemical processes, it may also produce a haze that suppresses spectral
features in the optical.Comment: 32 pages, 15 figures, preprint, accepted to ApJ, responded to
referee's comments. Comments welcom
Ground-based, Near-infrared Exospectroscopy. II. Tentative Detection of Emission From the Extremely Hot Jupiter WASP-12b
We report the tentative detection of the near-infrared emission of the Hot
Jupiter WASP-12b with the low-resolution prism on IRTF/SpeX. We find a K-H
contrast color of 0.137% +/- 0.054%, corresponding to a blackbody of
temperature 2400 (+1500/-500) K and consistent with previous, photometric
observations. We also revisit WASP-12b's energy budget on the basis of
secondary eclipse observations: the dayside luminosity is a relatively poorly
constrained (2.0-4.3) x 10^30 erg/s, but this still allows us to predict a
day/night effective temperature contrast of 200-1,000 K (assuming A_B=0). Thus
we conclude that WASP-12b probably does not have both a low albedo and low
recirculation efficiency. Our results show the promise and pitfalls of using
single-slit spectrographs for characterization of extrasolar planet
atmospheres, and we suggest future observing techniques and instruments which
could lead to further progress. Limiting systematic effects include the use of
a too-narrow slit on one night -- which observers could avoid in the future --
and chromatic slit losses (resulting from the variable size of the seeing disk)
and variations in telluric transparency -- which observers cannot control.
Single-slit observations of the type we present remain the best option for
obtaining lambda > 1.7 micron spectra of transiting exoplanets in the brightest
systems. Further and more precise spectroscopy is needed to better understand
the atmospheric chemistry, structure, and energetics of this, and other,
intensely irradiated planet.Comment: ApJ accepted. 16 pages, 15 figure
Detecting and reconstructing gravitational waves from the next galactic core-collapse supernova in the advanced detector era
We performed a detailed analysis of the detectability of a wide range of gravitational waves derived from core-collapse supernova simulations using gravitational-wave detector noise scaled to the sensitivity of the upcoming fourth and fifth observing runs of the Advanced LIGO, Advanced Virgo, and KAGRA. We use the coherent WaveBurst algorithm, which was used in the previous observing runs to search for gravitational waves from core-collapse supernovae. As coherent WaveBurst makes minimal assumptions on the morphology of a gravitational-wave signal, it can play an important role in the first detection of gravitational waves from an event in the Milky Way. We predict that signals from neutrino-driven explosions could be detected up to an average distance of 10 kpc, and distances of over 100 kpc can be reached for explosions of rapidly-rotating progenitor stars. An estimated minimum signal-to-noise ratio of 10–25 is needed for the signals to be detected. We quantify the accuracy of the waveforms reconstructed with coherent WaveBurst and we determine that the most challenging signals to reconstruct are those produced in long-duration neutrino-driven explosions, and models that form black holes a few seconds after the core bounce
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