2,054 research outputs found
The Impact of Transiting Planet Science on the Next Generation of Direct-Imaging Planet Searches
Within the next five years, a number of direct-imaging planet search
instruments, like the VLT SPHERE instrument, will be coming online. To
successfully carry out their programs, these instruments will rely heavily on
a-priori information on planet composition, atmosphere, and evolution.
Transiting planet surveys, while covering a different semi-major axis regime,
have the potential to provide critical foundations for these next-generation
surveys. For example, improved information on planetary evolutionary tracks may
significantly impact the insights that can be drawn from direct-imaging
statistical data. Other high-impact results from transiting planet science
include information on mass-to-radius relationships as well as atmospheric
absorption bands. The marriage of transiting planet and direct-imaging results
may eventually give us the first complete picture of planet migration,
multiplicity, and general evolution.Comment: 4 pages, 3 figures, IAU Transiting Planets Proceedings, in pres
Angular Differential Imaging: a Powerful High-Contrast Imaging Technique
Angular differential imaging is a high-contrast imaging technique that
reduces quasi-static speckle noise and facilitates the detection of nearby
companions. A sequence of images is acquired with an altitude/azimuth telescope
while the instrument field derotator is switched off. This keeps the instrument
and telescope optics aligned and allows the field of view to rotate with
respect to the instrument. For each image, a reference PSF is constructed from
other appropriately-selected images of the same sequence and subtracted to
remove quasi-static PSF structure. All residual images are then rotated to
align the field and are combined. Observed performances are reported for Gemini
North data. It is shown that quasi-static PSF noise can be reduced by a factor
\~5 for each image subtraction. The combination of all residuals then provides
an additional gain of the order of the square root of the total number of
acquired images. A total speckle noise attenuation of 20-50 is obtained for
one-hour long observing sequences compared to a single 30s exposure. A PSF
noise attenuation of 100 was achieved for two-hour long sequences of images of
Vega, reaching a 5-sigma contrast of 20 magnitudes for separations greater than
8". For a 30-minute long sequence, ADI achieves 30 times better signal-to-noise
than a classical observation technique. The ADI technique can be used with
currently available instruments to search for ~1MJup exoplanets with orbits of
radii between 50 and 300 AU around nearby young stars. The possibility of
combining the technique with other high-contrast imaging methods is briefly
discussed.Comment: 27 pages, 7 figures, accepted for publication in Ap
Italy: defence industries and the arms trade 1949-1989
Italy became one of the major exporters of arms by the early 1980s,
behind only the United States, the Soviet Union, and France.
Although its position was later overtaken, it remained one of Europe's
main producers and suppliers, without the presence of pronounced
military and foreign policy ambitions at the state level. The military
industries grew as a result of Italy's close association with other
Western and in particular the American defence establishment
beginning in the late 1940s. The Italians had access to some of the most
advanced military technology through co-production and licence
arrangements with its senior allies. By the 1970s, the defence area
became the fastest growing sector of the Italian economy when markets
were exploited mainly in the Third World.Although about two-thirds of the industry was state-owned,
Italian businessmen acted independently in selling arms through
Italian trade networks which thrived with very little government
direction or intervention. The absence of government assistance
actually appeared to favour the export of Italian weapons, because the
lack of interest in the sector also meant that Italy maintained perhaps
the most lenient export legislation in the West. As the industry
expanded, manufacturers availed themselves increasingly of
representatives of the foreign trade ministry, the secret services and
military attaches abroad in the promotion of Italian war equipment.
And as Italy came into the circle of the world's major economic
powers, its politicians attempted for a time to adopt the defence
industry a's a tool of international prestige. However supporters of the
industry did not resolve the contradiction between the low priority
Italy continued to give to defence and foreign policy, and the success of
the country's industrialists in supplying arms to areas of tension. As
business began to decline sharply in the late 1980s for Italy's defence
firms, industrialists turned to the possibility of reconversion programs
Gene pyramids and the balancing act of keeping pests at bay
Pyramiding R genes is a common strategy used by breeders to enhance resistance and increase durability of resistance in crops. However, the molecular mechanisms that mediate R gene interactions are not known. Kamphuis et al. (2019) analyzed Medicago truncatula plants carrying two genes that confer resistance to bluegreen aphids. They identified a potential phytohormone crosstalk triggered by the combined R gene action in response to aphid feeding that enhances resistance and minimizes R gene-associated fitness costs to the plant
Direct Imaging of Multiple Planets Orbiting the Star HR 8799
Direct imaging of exoplanetary systems is a powerful technique that can
reveal Jupiter-like planets in wide orbits, can enable detailed
characterization of planetary atmospheres, and is a key step towards imaging
Earth-like planets. Imaging detections are challenging due to the combined
effect of small angular separation and large luminosity contrast between a
planet and its host star. High-contrast observations with the Keck and Gemini
telescopes have revealed three planets orbiting the star HR 8799, with
projected separations of 24, 38, and 68 astronomical units. Multi-epoch data
show counter-clockwise orbital motion for all three imaged planets. The low
luminosity of the companions and the estimated age of the system imply
planetary masses between 5 and 13 times that of Jupiter. This system resembles
a scaled-up version of the outer portion of our Solar System.Comment: 30 pages, 5 figures, Research Article published online in Science
Express Nov 13th, 200
Astrometric Monitoring of the HR 8799 Planets: Orbit Constraints from Self-Consistent Measurements
We present new astrometric measurements from our ongoing monitoring campaign
of the HR 8799 directly imaged planetary system. These new data points were
obtained with NIRC2 on the W.M. Keck II 10 meter telescope between 2009 and
2014. In addition, we present updated astrometry from previously published
observations in 2007 and 2008. All data were reduced using the SOSIE algorithm,
which accounts for systematic biases present in previously published
observations. This allows us to construct a self-consistent data set derived
entirely from NIRC2 data alone. From this dataset, we detect acceleration for
two of the planets (HR 8799b and e) at 3. We also assess possible
orbital parameters for each of the four planets independently. We find no
statistically significant difference in the allowed inclinations of the
planets. Fitting the astrometry while forcing coplanarity also returns
consistent to within 1 of the best fit values, suggesting that if
inclination offsets of 20 are present, they are not detectable
with current data. Our orbital fits also favor low eccentricities, consistent
with predictions from dynamical modeling. We also find period distributions
consistent to within 1 with a 1:2:4:8 resonance between all planets.
This analysis demonstrates the importance of minimizing astrometric systematics
when fitting for solutions to highly undersampled orbits.Comment: 18 pages, 11 figures. Accepted for publication in A
Exoplanet Detection Techniques
We are still in the early days of exoplanet discovery. Astronomers are
beginning to model the atmospheres and interiors of exoplanets and have
developed a deeper understanding of processes of planet formation and
evolution. However, we have yet to map out the full complexity of multi-planet
architectures or to detect Earth analogues around nearby stars. Reaching these
ambitious goals will require further improvements in instrumentation and new
analysis tools. In this chapter, we provide an overview of five observational
techniques that are currently employed in the detection of exoplanets: optical
and IR Doppler measurements, transit photometry, direct imaging, microlensing,
and astrometry. We provide a basic description of how each of these techniques
works and discuss forefront developments that will result in new discoveries.
We also highlight the observational limitations and synergies of each method
and their connections to future space missions.Comment: 24 pages, 19 figures, PPVI proceedings. Appears as 2014, Protostars
and Planets VI, Henrik Beuther, Ralf S. Klessen, Cornelis P. Dullemond, and
Thomas Henning (eds.), University of Arizona Press, Tucson, 914 pp.,
p.715-73
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