61 research outputs found
Method for reducing sidelobe impact of low order aberration in a coronagraph
The invention relates to a method for reducing a sidelobe impact of low order aberrations using a coronagraph (2) having an apodized occulting mask (10), comprising the steps of: (a) providing in the coronagraph (2) the apodized occulting disk (10) having a transmission profile which graduates from opaque to transparent along its radius and the negative of whose amplitude transmission is a Gaussian profile; (b) determining a predicted sidelobe impact of the aberrations from a particular mix of low order aberration measured in a system as described by the Zernike polynomials; (c) applying the coronagraph to a system point spread function using a given rms width for the Gaussian profile describing the apodized occulting mask (10) and determining an attenuation level of the aberration sidelobes; (d) scaling the Gaussian occulting mask (10) profile to a wider rms width if the sidelobe attenuation level is too low; and (e) repeating the steps (b) through (d) until the attenuation level is acceptable
Observing Strategies for the NICI Campaign to Directly Image Extrasolar Planets
We discuss observing strategy for the Near Infrared Coronagraphic Imager
(NICI) on the 8-m Gemini South telescope. NICI combines a number of techniques
to attenuate starlight and suppress superspeckles: 1) coronagraphic imaging, 2)
dual channel imaging for Spectral Differential Imaging (SDI) and 3) operation
in a fixed Cassegrain rotator mode for Angular Differential Imaging (ADI). NICI
will be used both in service mode and for a dedicated 50 night planet search
campaign. While all of these techniques have been used individually in large
planet-finding surveys, this is the first time ADI and SDI will be used with a
coronagraph in a large survey. Thus, novel observing strategies are necessary
to conduct a viable planet search campaign.Comment: 12 pages, 10 figures, submitted to Proceedings of the SPI
Astrometric Microlensing as a Method of Discovering and Characterizing Extra-Solar Planets
We introduce a new method of searching for and characterizing extra-solar
planets. We show that by monitoring the center-of-light motion of microlensing
alerts using the next generation of high precision astrometric instruments the
probability of detecting a planet orbiting the lens is high. We show that
adding astrometric information to the photometric microlensing lightcurve
greatly helps in determining the planetary mass and semi-major axis. We
introduce astrometric maps as a new way for calculating astrometric motion and
planet detection probabilities. Finite source effects are important for low
mass planets, but even Earth mass planets can give detectable signals.Comment: 9 pages includes 8 postscript figures, AAS Latex, submitted to Ap
The Gemini NICI Planet-Finding Campaign: The Offset Ring of HR 4796 A
We present J, H, CH_4 short (1.578 micron), CH_4 long (1.652 micron) and
K_s-band images of the dust ring around the 10 Myr old star HR 4796 A obtained
using the Near Infrared Coronagraphic Imager (NICI) on the Gemini-South 8.1
meter Telescope. Our images clearly show for the first time the position of the
star relative to its circumstellar ring thanks to NICI's translucent focal
plane occulting mask. We employ a Bayesian Markov Chain Monte Carlo method to
constrain the offset vector between the two. The resulting probability
distribution shows that the ring center is offset from the star by 16.7+/-1.3
milliarcseconds along a position angle of 26+/-3 degrees, along the PA of the
ring, 26.47+/-0.04 degrees. We find that the size of this offset is not large
enough to explain the brightness asymmetry of the ring. The ring is measured to
have mostly red reflectivity across the JHK_s filters, which seems to indicate
micron-sized grains. Just like Neptune's 3:2 and 2:1 mean-motion resonances
delineate the inner and outer edges of the classical Kuiper Belt, we find that
the radial extent of the HR 4796 A and Fomalhaut rings could correspond to the
3:2 and 2:1 mean-motion resonances of hypothetical planets at 54.7 AU and 97.7
AU in the two systems, respectively. A planet orbiting HR 4796 A at 54.7 AU
would have to be less massive than 1.6 Mjup so as not to widen the ring too
much by stirring.Comment: Accepted to A&A for publication on April 23, 2014 (15 pages, 9
figures, 4 tables
NICI: combining coronagraphy, ADI, and SDI
The Near-Infrared Coronagraphic Imager (NICI) is a high-contrast AO imager at
the Gemini South telescope. The camera includes a coronagraphic mask and dual
channel imaging for Spectral Differential Imaging (SDI). The instrument can
also be used in a fixed Cassegrain Rotator mode for Angular Differential
Imaging (ADI). While coronagraphy, SDI, and ADI have been applied before in
direct imaging searches for exoplanets. NICI represents the first time that
these 3 techniques can be combined. We present preliminary NICI commissioning
data using these techniques and show that combining SDI and ADI results in
significant gains.Comment: Proc. SPIE, Vol. 7014, 70141Z (2008
Advanced Curvature Deformable Mirrors
ABSTRACT The need for a variety of deformable mirrors (DMs) is growing steadily as more applications are brought on line, components are more widely available and adaptive control evolves into an off-the-shelf item. While the bulk of the readily available systems are of the push-pull variety, curvature mirrors have much to offer in simplicity and efficiency. We will explore paths for development of these components
Penetrating the Homunculus -- Near-Infrared Adaptive Optics Images of Eta Carinae
Near-infrared adaptive optics imaging with NICI and NaCO reveal what appears
to be a three-winged or lobed pattern, the "butterfly nebula", outlined by
bright Br and H emission and light scattered by dust. In
contrast, the [Fe II] emission does not follow the outline of the wings, but
shows an extended bipolar distribution which is tracing the Little Homunculus
ejected in Car's second or lesser eruption in the 1890's. Proper motions
measured from the combined NICI and NaCO images together with radial velocities
show that the knots and filaments that define the bright rims of the butterfly
were ejected at two different epochs corresponding approximately to the great
eruption and the second eruption. Most of the material is spatially distributed
10\arcdeg to 20\arcdeg above and below the equatorial plane apparently
behind the Little Homunculus and the larger SE lobe. The equatorial debris
either has a wide opening angle or the clumps were ejected at different
latitudes relative to the plane. The butterfly is not a coherent physical
structure or equatorial torus but spatially separate clumps and filaments
ejected at different times, and now 2000 to 4000 AU from the star.Comment: 42 pages, 12 figures, To appear in the Astronomical Journa
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