99 research outputs found
High-Cadence, High-Contrast Imaging for Exoplanet Mapping: Observations of the HR 8799 Planets with VLT/SPHERE Satellite Spot-Corrected Relative Photometry
Time-resolved photometry is an important new probe of the physics of
condensate clouds in extrasolar planets and brown dwarfs. Extreme adaptive
optics systems can directly image planets, but precise brightness measurements
are challenging. We present VLT/SPHERE high-contrast, time-resolved broad
H-band near-infrared photometry for four exoplanets in the HR 8799 system,
sampling changes from night to night over five nights with relatively short
integrations. The photospheres of these four planets are often modeled by
patchy clouds and may show large-amplitude rotational brightness modulations.
Our observations provide high-quality images of the system. We present a
detailed performance analysis of different data analysis approaches to
accurately measure the relative brightnesses of the four exoplanets. We explore
the information in satellite spots and demonstrate their use as a proxy for
image quality. While the brightness variations of the satellite spots are
strongly correlated, we also identify a second-order anti-correlation pattern
between the different spots. Our study finds that PCA-based KLIP reduction with
satellite spot-modulated artificial planet-injection based photometry (SMAP)
leads to a significant (~3x) gain in photometric accuracy over standard
aperture-based photometry and reaches 0.1 mag per point accuracy for our
dataset, the signal-to-noise of which is limited by small field rotation.
Relative planet-to-planet photometry can be compared be- tween nights, enabling
observations spanning multiple nights to probe variability. Recent high-quality
relative H-band photometry of the b-c planet pair agree to about 1%.Comment: Astrophysical Journal, in pres
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
A Multi-wavelength Differential Imaging Experiment for the High Contrast Imaging Testbed
We discuss the results of a multi-wavelength differential imaging lab
experiment with the High Contrast Imaging Testbed (HCIT) at the Jet Propulsion
Laboratory. The HCIT combines a Lyot coronagraph with a Xinetics deformable
mirror in a vacuum environment to simulate a space telescope in order to test
technologies and algorithms for a future exoplanet coronagraph mission. At
present, ground based telescopes have achieved significant attenuation of
speckle noise using the technique of spectral differential imaging (SDI). We
test whether ground-based SDI can be generalized to a non-simultaneous spectral
differential imaging technique (NSDI) for a space mission. In our lab
experiment, a series of 5 filter images centered around the O2(A) absorption
feature at 0.762 um were acquired at nominal contrast values of 10^-6, 10^-7,
10^-8, and 10^-9. Outside the dark hole, single differences of images improve
contrast by a factor of ~6. Inside the dark hole, we found significant speckle
chromatism as a function of wavelength offset from the nulling wavelength,
leading to a contrast degradation by a factor of 7.2 across the entire ~80 nm
bandwidth. This effect likely stems from the chromatic behavior of the current
occulter. New, less chromatic occulters are currently in development; we expect
that these new occulters will resolve the speckle chromatism issue.Comment: 24 pages, 8 figures, 3 tables, accepted by PAS
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
- …