969 research outputs found
A new 1.6-micron map of Titanâs surface
We present a new map of Titan's surface obtained in the spectral 'window' at âŒ1.6 ÎŒm between strong methane absorption. This pre-Cassini view of Titan's surface was created from images obtained using adaptive optics on the W.M. Keck II telescope and is the highest resolution map yet made of Titan's surface. Numerous surface features down to the limits of the spatial resolution (âŒ200â300 km) are apparent. No features are easily identifiable in terms of their geologic origin, although several are likely craters
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Contrasting fast precipitation responses to tropospheric and stratospheric ozone forcing
The precipitation response to radiative forcing (RF) can be decomposed into a fast precipitation response (FPR), which depends on the atmospheric component of RF, and a slow response, which depends on surface temperature change. We present the first detailed climate model study of the FPR due to tropospheric and stratospheric ozone changes. The FPR depends strongly on the altitude of ozone change. Increases below about 3 km cause a positive FPR; increases above cause a negative FPR. The FPR due to stratospheric ozone change is, per unit RF, about 3 times larger than that due to tropospheric ozone. As historical ozone trends in the troposphere and stratosphere are opposite in sign, so too are the FPRs. Simple climate model calculations of the time-dependent total (fast and slow) precipitation change, indicate that ozone's contribution to precipitation change in 2011, compared to 1765, could exceed 50% of that due to CO2 change
Orbital characterization of the \beta Pictoris b giant planet
In June 2010, we confirmed the existence of a giant planet in the disk of the
young star Beta Pictoris, located between 8 AU and 15 AU from the star. This
young planet offers the rare opportunity to monitor a large fraction of the
orbit using the imaging technique over a reasonably short timescale. Using the
NAOS-CONICA adaptive-optics instrument (NACO) at the Very Large Telescope
(VLT), we obtained repeated follow-up images of the Bpic system in the Ks and
L' filters at four new epochs in 2010 and 2011. Complementing these data with
previous measurements, we conduct a homogeneous analysis, which covers more
than eight yrs, to accurately monitor the Bpic b position relative to the star.
On the basis of the evolution of the planet's relative position with time, we
derive the best-fit orbital solutions for our measurements. More reliable
results are found with a Markov-chain Monte Carlo approach. The solutions favor
a low-eccentricity orbit e < 0.17, with semi-major axis in the range 8--9 AU
corresponding to orbital periods of 17--21 yrs. Our solutions favor a highly
inclined solution with a peak around i=88.5+-1.7 deg, and a longitude of
ascending node tightly constrained at Omega = -147.5+-1.5 deg. These results
indicate that the orbital plane of the planet is likely to be above the
midplane of the main disk, and compatible with the warp component of the disk
being tilted between 3.5 deg and 4.0 deg. This suggests that the planet plays a
key role in the origin of the inner warped-disk morphology of the Bpic disk.
Finally, these orbital parameters are consistent with the hypothesis that the
planet is responsible for the transit-like event observed in November 1981, and
also linked to the cometary activity observed in the Bpic system.Comment: 10 pages, 12 figures, accepted to A&
Directly Imaging Rocky Planets from the Ground
Over the past three decades instruments on the ground and in space have
discovered thousands of planets outside the solar system. These observations
have given rise to an astonishingly detailed picture of the demographics of
short-period planets, but are incomplete at longer periods where both the
sensitivity of transit surveys and radial velocity signals plummet. Even more
glaring is that the spectra of planets discovered with these indirect methods
are either inaccessible (radial velocity detections) or only available for a
small subclass of transiting planets with thick, clear atmospheres. Direct
detection can be used to discover and characterize the atmospheres of planets
at intermediate and wide separations, including non-transiting exoplanets.
Today, a small number of exoplanets have been directly imaged, but they
represent only a rare class of young, self-luminous super-Jovian-mass objects
orbiting tens to hundreds of AU from their host stars. Atmospheric
characterization of planets in the <5 AU regime, where radial velocity (RV)
surveys have revealed an abundance of other worlds, is technically feasible
with 30-m class apertures in combination with an advanced AO system,
coronagraph, and suite of spectrometers and imagers. There is a vast range of
unexplored science accessible through astrometry, photometry, and spectroscopy
of rocky planets, ice giants, and gas giants. In this whitepaper we will focus
on one of the most ambitious science goals --- detecting for the first time
habitable-zone rocky (<1.6 R_Earth) exoplanets in reflected light around nearby
M-dwarfsComment: 8 pages, 1 figure, Astro2020 Science White Pape
The Peculiar Debris Disk of HD 111520 as Resolved by the Gemini Planet Imager
Using the Gemini Planet Imager (GPI), we have resolved the circumstellar
debris disk around HD 111520 at a projected range of ~30-100 AU in both total
and polarized -band intensity. The disk is seen edge-on at a position angle
of ~165 along the spine of emission. A slight inclination or
asymmetric warping are covariant and alters the interpretation of the observed
disk emission. We employ 3 point spread function (PSF) subtraction methods to
reduce the stellar glare and instrumental artifacts to confirm that there is a
roughly 2:1 brightness asymmetry between the NW and SE extension. This specific
feature makes HD 111520 the most extreme examples of asymmetric debris disks
observed in scattered light among similar highly inclined systems, such as HD
15115 and HD 106906. We further identify a tentative localized brightness
enhancement and scale height enhancement associated with the disk at ~40 AU
away from the star on the SE extension. We also find that the fractional
polarization rises from 10 to 40% from 0.5" to 0.8" from the star. The
combination of large brightness asymmetry and symmetric polarization fraction
leads us to believe that an azimuthal dust density variation is causing the
observed asymmetry.Comment: 9 pages, 8 Figures, 1 table, Accepted to Ap
Legal determinants of external finance revisited : the inverse relationship between investor protection and societal well-being
This paper investigates relationships between corporate governance traditions and quality of life as measured by a number of widely reported indicators. It provides an empirical analysis of indicators of societal health in developed economies using a classification based on legal traditions. Arguably the most widely cited work in the corporate governance literature has been the collection of papers by La Porta et al. which has shown, inter alia, statistically significant relationships between legal traditions and various proxies for investor protection. We show statistically significant relationships between legal traditions and various proxies for societal health. Our comparative evidence suggests that the interests of investors may not be congruent with the interests of wider society, and that the criteria for judging the effectiveness of approaches to corporate governance should not be restricted to financial metrics
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