1,524 research outputs found
Confidence Level and Sensitivity Limits in High Contrast Imaging
In long adaptive optics corrected exposures, exoplanet detections are
currently limited by speckle noise originating from the telescope and
instrument optics, and it is expected that such noise will also limit future
high-contrast imaging instruments for both ground and space-based telescopes.
Previous theoretical analysis have shown that the time intensity variations of
a single speckle follows a modified Rician. It is first demonstrated here that
for a circular pupil this temporal intensity distribution also represents the
speckle spatial intensity distribution at a fix separation from the point
spread function center; this fact is demonstrated using numerical simulations
for coronagraphic and non-coronagraphic data. The real statistical distribution
of the noise needs to be taken into account explicitly when selecting a
detection threshold appropriate for some desired confidence level. In this
paper, a technique is described to obtain the pixel intensity distribution of
an image and its corresponding confidence level as a function of the detection
threshold. Using numerical simulations, it is shown that in the presence of
speckles noise, a detection threshold up to three times higher is required to
obtain a confidence level equivalent to that at 5sigma for Gaussian noise. The
technique is then tested using TRIDENT CFHT and angular differential imaging
NIRI Gemini adaptive optics data. It is found that the angular differential
imaging technique produces quasi-Gaussian residuals, a remarkable result
compared to classical adaptive optic imaging. A power-law is finally derived to
predict the 1-3*10^-7 confidence level detection threshold when averaging a
partially correlated non-Gaussian noise.Comment: 29 pages, 13 figures, accepted to Ap
WFIRST Coronagraph Technology Requirements: Status Update and Systems Engineering Approach
The coronagraphic instrument (CGI) on the Wide-Field Infrared Survey
Telescope (WFIRST) will demonstrate technologies and methods for high-contrast
direct imaging and spectroscopy of exoplanet systems in reflected light,
including polarimetry of circumstellar disks. The WFIRST management and CGI
engineering and science investigation teams have developed requirements for the
instrument, motivated by the objectives and technology development needs of
potential future flagship exoplanet characterization missions such as the NASA
Habitable Exoplanet Imaging Mission (HabEx) and the Large UV/Optical/IR
Surveyor (LUVOIR). The requirements have been refined to support
recommendations from the WFIRST Independent External Technical/Management/Cost
Review (WIETR) that the WFIRST CGI be classified as a technology demonstration
instrument instead of a science instrument. This paper provides a description
of how the CGI requirements flow from the top of the overall WFIRST mission
structure through the Level 2 requirements, where the focus here is on
capturing the detailed context and rationales for the CGI Level 2 requirements.
The WFIRST requirements flow starts with the top Program Level Requirements
Appendix (PLRA), which contains both high-level mission objectives as well as
the CGI-specific baseline technical and data requirements (BTR and BDR,
respectively)... We also present the process and collaborative tools used in
the L2 requirements development and management, including the collection and
organization of science inputs, an open-source approach to managing the
requirements database, and automating documentation. The tools created for the
CGI L2 requirements have the potential to improve the design and planning of
other projects, streamlining requirement management and maintenance. [Abstract
Abbreviated]Comment: 16 pages, 4 figure
Speckle Control with a remapped-pupil PIAA-coronagraph
The PIAA is a now well demonstrated high contrast technique that uses an
intermediate remapping of the pupil for high contrast coronagraphy
(apodization), before restoring it to recover classical imaging capabilities.
This paper presents the first demonstration of complete speckle control loop
with one such PIAA coronagraph. We show the presence of a complete set of
remapping optics (the so-called PIAA and matching inverse PIAA) is transparent
to the wavefront control algorithm. Simple focal plane based wavefront control
algorithms can thus be employed, without the need to model remapping effects.
Using the Subaru Coronagraphic Extreme AO (SCExAO) instrument built for the
Subaru Telescope, we show that a complete PIAA-coronagraph is compatible with a
simple implementation of a speckle nulling technique, and demonstrate the
benefit of the PIAA for high contrast imaging at small angular separation.Comment: 6 figures, submitted to PAS
GQ Lup B Visible & Near-Infrared Photometric Analysis
We have re-analyzed archival HST and Subaru data of the recently discovered
planetary mass companion (PMC) GQ Lup B. With these we produce the first R and
I band photometry of the companion and fit a radius and effective temperature
using detailed model atmospheres. We find an effective temperature of 2335 +/-
100K, and a radius of 0.38 +/- 0.05 Rsol and luminosity of log(L/Lsol) = -2.42
+/- 0.07 (at 140pc). Since we fit wavelengths that span most of the emitted
radiation from GQ Lup this luminosity estimate is robust, with uncertainty
dominated by the distance uncertainty (+/- 50 pc). The radius obtained for
140pc (0.38Rsol) is significantly larger than the one originally derived and
larger than model predictions. The mass of the object is much more
model-dependent than the radiative properties, but for the GAIA dusty models we
find a mass between 10-20 MJup, in the range of the brown dwarf and PMC
deuterium burning boundary. Assuming a distance of 140pc, observations fit to
1sigma the Baraffe evolution model for a ~15 MJup brown dwarf. Additionally,
the F606W photometric band is significantly overluminous compared to model
predictions and other brown dwarfs. Such overluminosity could be explained by a
bright Halpha emission from chromospheric activity, interaction with another
undetected companion, or accretion. Assuming that GQ Lup B has a bright Halpha
emission line, its Halpha emission strength is 10^(-1.71 +/- 0.10) Lbol,
significantly larger than field late-type dwarfs. GQ Lup B might be strongly
accreting and still be in its formation phase.Comment: 14 pages, 3 figures, ApJL final accepted versio
The VAST Survey - IV. A wide brown dwarf companion to the A3V star Delphini
We report the discovery of a wide co-moving substellar companion to the
nearby ( pc) A3V star Delphini based on imaging and
follow-up spectroscopic observations obtained during the course of our
Volume-limited A-Star (VAST) multiplicity survey. Del was observed over
a five-year baseline with adaptive optics, revealing the presence of a
previously-unresolved companion with a proper motion consistent with that of
the A-type primary. The age of the Del system was estimated as
Myr based on the position of the primary on the colour-magnitude
and temperature-luminosity diagrams. Using intermediate-resolution
near-infrared spectroscopy, the spectrum of Del B is shown to be
consistent with a mid-L dwarf (L), at a temperature of K.
Combining the measured near-infrared magnitude of Del B with the
estimated temperature leads to a model-dependent mass estimate of
M, corresponding to a mass ratio of . At a
projected separation of au, Del B is among the most
widely-separated and extreme-mass ratio substellar companions to a
main-sequence star resolved to-date, providing a rare empirical constraint of
the formation of low-mass ratio companions at extremely wide separations.Comment: 12 pages, 11 figures, accepted for publication in the Monthly Notices
of the Royal Astronomical Society, 2014 September 25. Revised to incorporate
typographical errors noted during the proofing proces
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