3,387 research outputs found
Ground-based near-IR observations of the secondary eclipse of CoRoT-2b
We present the results of a ground-based search for the secondary eclipse of
the 3.3 Mjup transiting planet CoRoT-2b. We performed near infrared photometry
using the LIRIS instrument on the 4.2 m William Herschel Telescope, in the H
and K_s filters. We monitored the star around two expected secondary eclipses
in two nights under very good observing conditions. For the depth of the
secondary eclipse we find in H-band a 3 sigma upper limit of 0.17%, whereas we
detected a tentative eclipse with a depth of 0.16+-0.09% in the K_s-band. These
depths can be translated into brightness temperatures of T_H<2250 K and T_{K_s}
= 1890(+260-350) K, which indicate an inefficient re-distribution of the
incident stellar flux from the planet's dayside to its nightside. Our results
are in agreement with the CoRoT optical measurement (Alonso et al. 09) and with
Spitzer 4.5 and 8 micron results (Gillon et al. 09c).Comment: Astronomical Journal, accepte
Connecting N-representability to Weyl's problem: The one particle density matrix for N = 3 and R = 6
An analytic proof is given of the necessity of the Borland-Dennis conditions
for 3-representability of a one particle density matrix with rank 6. This may
shed some light on Klyachko's recent use of Schubert calculus to find general
conditions for N-representability
The Affective Impact of Financial Skewness on Neural Activity and Choice
Few finance theories consider the influence of “skewness” (or large and asymmetric but unlikely outcomes) on financial choice. We investigated the impact of skewed gambles on subjects' neural activity, self-reported affective responses, and subsequent preferences using functional magnetic resonance imaging (FMRI). Neurally, skewed gambles elicited more anterior insula activation than symmetric gambles equated for expected value and variance, and positively skewed gambles also specifically elicited more nucleus accumbens (NAcc) activation than negatively skewed gambles. Affectively, positively skewed gambles elicited more positive arousal and negatively skewed gambles elicited more negative arousal than symmetric gambles equated for expected value and variance. Subjects also preferred positively skewed gambles more, but negatively skewed gambles less than symmetric gambles of equal expected value. Individual differences in both NAcc activity and positive arousal predicted preferences for positively skewed gambles. These findings support an anticipatory affect account in which statistical properties of gambles—including skewness—can influence neural activity, affective responses, and ultimately, choice
Temporal isolation of neural processes underlying face preference decisions
Decisions about whether we like someone are often made so rapidly from first impressions that it is difficult to examine the engagement of neural structures at specific points in time. Here, we used a temporally extended decision-making paradigm to examine brain activation with functional MRI (fMRI) at sequential stages of the decision-making process. Activity in reward-related brain structures—the nucleus accumbens (NAC) and orbitofrontal cortex (OFC)—was found to occur at temporally dissociable phases while subjects decided which of two unfamiliar faces they preferred. Increases in activation in the OFC occurred late in the trial, consistent with a role for this area in computing the decision of which face to choose. Signal increases in the NAC occurred early in the trial, consistent with a role for this area in initial preference formation. Moreover, early signal increases in the NAC also occurred while subjects performed a control task (judging face roundness) when these data were analyzed on the basis of which of those faces were subsequently chosen as preferred in a later task. The findings support a model in which rapid, automatic engagement of the NAC conveys a preference signal to the OFC, which in turn is used to guide choice
Limb darkening in spherical stellar atmospheres
(Abridged) Context. Stellar limb darkening, I({\mu} = cos{\theta}), is an
important constraint for microlensing, eclipsing binary, planetary transit, and
interferometric observations, but is generally treated as a parameterized
curve, such as a linear-plus-square-root law. Many analyses assume
limb-darkening coefficients computed from model stellar atmospheres. However,
previous studies, using I({\mu}) from plane- parallel models, have found that
fits to the flux-normalized curves pass through a fixed point, a common {\mu}
location on the stellar disk, for all values of T eff, log g and wavelength.
Aims. We study this fixed {\mu}-point to determine if it is a property of the
model stellar atmospheres or a property of the limb-darkening laws.
Furthermore, we use this limb-darkening law as a tool to probe properties of
stellar atmospheres for comparison to limb- darkening observations. Methods.
Intensities computed with plane-parallel and spherically-symmetric Atlas models
(characterized by the three fundamental parameters L\star, M\star and R\star)
are used to reexamine the existence of the fixed {\mu}-point for the
parametrized curves. Results. We find that the intensities from our spherical
models do not have a fixed point, although the curves do have a minimum spread
at a {\mu}-value similar to the parametrized curves. We also find that the
parametrized curves have two fixed points, {\mu}1 and {\mu}2, although {\mu}2
is so close to the edge of the disk that it is missed using plane-parallel
atmospheres. We also find that the spherically- symmetric models appear to
agree better with published microlensing observations relative to
plane-parallel models.Comment: 8 pages, 8 figures, figures 4 and 6 have lower resolution. A&A in
pres
Off-shell Behavior of the Mixing Amplitude
We extend a recent calculation of the momentum dependence of the
mixing amplitude to the pseudoscalar sector. The
mixing amplitude is calculated in a hadronic model where the mixing is driven
by the neutron-proton mass difference. Closed-form analytic expressions are
presented in terms of a few nucleon-meson parameters. The observed momentum
dependence of the mixing amplitude is strong enough as to question earlier
calculations of charge-symmetry-breaking observables based on the on-shell
assumption. The momentum dependence of the amplitude is,
however, practically identical to the one recently predicted for
mixing. Hence, in this model, the ratio of pseudoscalar to vector mixing
amplitudes is, to a good approximation, a constant solely determined from
nucleon-meson coupling constants. Furthermore, by selecting these parameters in
accordance with charge-symmetry-conserving data and SU(3)-flavor symmetry, we
reproduce the momentum dependence of the mixing amplitude
predicted from chiral perturbation theory. Alternatively, one can use
chiral-perturbation-theory results to set stringent limits on the value of the
coupling constant.Comment: 13 pages, Latex with Revtex, 3 postscript figures (not included)
available on request, SCRI-03089
Hubble Space Telescope Near-IR Transmission Spectroscopy of the Super-Earth HD 97658b
Recent results from the Kepler mission indicate that super-Earths (planets
with masses between 1-10 times that of the Earth) are the most common kind of
planet around nearby Sun-like stars. These planets have no direct solar system
analogue, and are currently one of the least well-understood classes of
extrasolar planets. Many super-Earths have average densities that are
consistent with a broad range of bulk compositions, including both
water-dominated worlds and rocky planets covered by a thick hydrogen and helium
atmosphere. Measurements of the transmission spectra of these planets offer the
opportunity to resolve this degeneracy by directly constraining the scale
heights and corresponding mean molecular weights of their atmospheres. We
present Hubble Space Telescope near-infrared spectroscopy of two transits of
the newly discovered transiting super-Earth HD 97658b. We use the Wide Field
Camera 3's scanning mode to measure the wavelength-dependent transit depth in
thirty individual bandpasses. Our averaged differential transmission spectrum
has a median 1 sigma uncertainty of 23 ppm in individual bins, making this the
most precise observation of an exoplanetary transmission spectrum obtained with
WFC3 to date. Our data are inconsistent with a cloud-free solar metallicity
atmosphere at the 10 sigma level. They are consistent at the 0.4 sigma level
with a flat line model, as well as effectively flat models corresponding to a
metal-rich atmosphere or a solar metallicity atmosphere with a cloud or haze
layer located at pressures of 10 mbar or higher.Comment: ApJ in press; revised version includes an updated orbital ephemeris
for the plane
- …