54 research outputs found
Optimal Occulter Design for Finding Extrasolar Planets
One proposed method for finding terrestrial planets around nearby stars is to
use two spacecraft--a telescope and a specially shaped occulter that is
specifically designed to prevent all but a tiny fraction of the starlight from
diffracting into the telescope. As the cost and observing cadence for such a
mission will be driven largely by the separation between the two spacecraft, it
is critically important to design an occulter that can meet the observing goals
while flying as close to the telescope as possible. In this paper, we explore
this tradeoff between separation and occulter diameter. More specifically, we
present a method for designing the shape of the outer edge of an occulter that
is as small as possible and gives a shadow that is deep enough and large enough
for a 4m telescope to survey the habitable zones of many stars for Earth-like
planets. In particular, we show that in order for a 4m telescope to detect in
broadband visible light a planet 0.06 arcseconds from a star shining
times brighter than the planet requires a specially-shaped occulter 50m in
diameter positioned about km in front of the telescope.Comment: 14 pages, 4 figures, 15 subfigure
Commissioning and performance results of the WFIRST/PISCES integral field spectrograph
The Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies
(PISCES) is a high contrast integral field spectrograph (IFS) whose design was
driven by WFIRST coronagraph instrument requirements. We present commissioning
and operational results using PISCES as a camera on the High Contrast Imaging
Testbed at JPL. PISCES has demonstrated ability to achieve high contrast
spectral retrieval with flight-like data reduction and analysis techniques.Comment: Author's copy - Proceedings of SPIE Volume 10400. Citation to SPIE
proceedings volume will be added when availabl
Simulating the WFIRST coronagraph Integral Field Spectrograph
A primary goal of direct imaging techniques is to spectrally characterize the
atmospheres of planets around other stars at extremely high contrast levels. To
achieve this goal, coronagraphic instruments have favored integral field
spectrographs (IFS) as the science cameras to disperse the entire search area
at once and obtain spectra at each location, since the planet position is not
known a priori. These spectrographs are useful against confusion from speckles
and background objects, and can also help in the speckle subtraction and
wavefront control stages of the coronagraphic observation. We present a
software package, the Coronagraph and Rapid Imaging Spectrograph in Python
(crispy) to simulate the IFS of the WFIRST Coronagraph Instrument (CGI). The
software propagates input science cubes using spatially and spectrally resolved
coronagraphic focal plane cubes, transforms them into IFS detector maps and
ultimately reconstructs the spatio-spectral input scene as a 3D datacube.
Simulated IFS cubes can be used to test data extraction techniques, refine
sensitivity analyses and carry out design trade studies of the flight CGI-IFS
instrument. crispy is a publicly available Python package and can be adapted to
other IFS designs.Comment: 15 page
Occulting ozone observatory science overview
We present an analysis of the Occulting Ozone Observatory (O3) - a $1 billion class mission dedicated to finding extra-solar planets down to Earth size, performing photometric characterizations of planets and disks, detecting the presence of ozone, and general astrophysics. We present trade studies for the observatory, composed of a 1 to 2 m telescope based on heritage imaging systems and a complementary sized, free-flying occulter spacecraft, to maximize the expected science yield for this mission class. Using a camera with four filters each in the 250- 550 nm and 500-1100 nm bands, this modest-size telescope can detect atmospheric ozone in Earth-like planets, methane in gas giants, determine planetary spin rotation periods, characterize the surface composition of rocky planets and determine or constrain the values of basic orbital elements. We present multiple different mission designs along with the expected number of planetary detections and photometric characterizations
Electric Field Conjugation with the Project 1640 coronagraph
The Project 1640 instrument on the 200-inch Hale telescope at Palomar
Observatory is a coronagraphic instrument with an integral field spectrograph
at the back end, designed to find young, self-luminous planets around nearby
stars. To reach the necessary contrast for this, the PALM-3000 adaptive optics
system corrects for fast atmospheric speckles, while CAL, a phase-shifting
interferometer in a Mach-Zehnder configuration, measures the quasistatic
components of the complex electric field in the pupil plane following the
coronagraphic stop. Two additional sensors measure and control low-order modes.
These field measurements may then be combined with a system model and data
taken separately using a white-light source internal to the AO system to
correct for both phase and amplitude aberrations. Here, we discuss and
demonstrate the procedure to maintain a half-plane dark hole in the image plane
while the spectrograph is taking data, including initial on-sky performance.Comment: 9 pages, 7 figures, in Proceedings of SPIE, 8864-19 (2013
Tropospheric methanol observations from space: retrieval evaluation and constraints on the seasonality of biogenic emissions
Methanol retrievals from nadir-viewing space-based sensors offer powerful new information for quantifying methanol emissions on a global scale. Here we apply an ensemble of aircraft observations over North America to evaluate new methanol measurements from the Tropospheric Emission Spectrometer (TES) on the Aura satellite, and combine the TES data with observations from the Infrared Atmospheric Sounding Interferometer (IASI) on the MetOp-A satellite to investigate the seasonality of methanol emissions from northern midlatitude ecosystems. Using the GEOS-Chem chemical transport model as an intercomparison platform, we find that the TES retrieval performs well when the degrees of freedom for signal (DOFS) are above 0.5, in which case the model : TES regressions are generally consistent with the model : aircraft comparisons. Including retrievals with DOFS below 0.5 degrades the comparisons, as these are excessively influenced by the a priori. The comparisons suggest DOFS > 0.5 as a minimum threshold for interpreting retrievals of trace gases with a weak tropospheric signal. We analyze one full year of satellite observations and find that GEOS-Chem, driven with MEGANv2.1 biogenic emissions, underestimates observed methanol concentrations throughout the midlatitudes in springtime, with the timing of the seasonal peak in model emissions 1-2 months too late. We attribute this discrepancy to an underestimate of emissions from new leaves in MEGAN, and apply the satellite data to better quantify the seasonal change in methanol emissions for midlatitude ecosystems. The derived parameters (relative emission factors of 11.0, 1.0, 0.05 and 8.6 for new, growing, mature, and old leaves, respectively, plus a leaf area index activity factor of 0.75 for expanding canopies with leaf area index < 2.0) provide a more realistic simulation of seasonal methanol concentrations in midlatitudes on the basis of IASI, TES, and ground-based measurements
Occulting ozone observatory science overview
We present an analysis of the Occulting Ozone Observatory (O3) - a $1 billion class mission dedicated to finding extra-solar planets down to Earth size, performing photometric characterizations of planets and disks, detecting the presence of ozone, and general astrophysics. We present trade studies for the observatory, composed of a 1 to 2 m telescope based on heritage imaging systems and a complementary sized, free-flying occulter spacecraft, to maximize the expected science yield for this mission class. Using a camera with four filters each in the 250- 550 nm and 500-1100 nm bands, this modest-size telescope can detect atmospheric ozone in Earth-like planets, methane in gas giants, determine planetary spin rotation periods, characterize the surface composition of rocky planets and determine or constrain the values of basic orbital elements. We present multiple different mission designs along with the expected number of planetary detections and photometric characterizations
End-to-end numerical modeling of the Roman Space Telescope coronagraph
The Roman Space Telescope will have the first advanced coronagraph in space,
with deformable mirrors for wavefront control, low-order wavefront sensing and
maintenance, and a photon-counting detector. It is expected to be able to
detect and characterize mature, giant exoplanets in reflected visible light.
Over the past decade the performance of the coronagraph in its flight
environment has been simulated with increasingly detailed diffraction and
structural/thermal finite element modeling. With the instrument now being
integrated in preparation for launch within the next few years, the present
state of the end-to-end modeling is described, including the measured flight
components such as deformable mirrors. The coronagraphic modes are thoroughly
described, including characteristics most readily derived from modeling. The
methods for diffraction propagation, wavefront control, and structural and
thermal finite-element modeling are detailed. The techniques and procedures
developed for the instrument will serve as a foundation for future
coronagraphic missions such as the Habitable Worlds Observatory.Comment: 113 pages, 85 figures, to be published in SPIE Journal of
Astronomical Telescopes, Instruments, and System
- …