147 research outputs found
Astrometric Discovery of GJ 802b: In the Brown Dwarf Oasis?
The Stellar Planet Survey is an ongoing astrometric search for giant planets
and brown dwarfs around a sample of about 30 M-dwarfs. We have discovered
several low-mass companions by measuring the motion of our target stars
relative to their reference frames. The lowest mass discovery thus far is GJ
802b, a companion to the M5-dwarf GJ 802A. The orbital period is 3.14 +/- 0.03
y, the system mass is 0.214 +/- 0.045 Msolar, and the semi-major axis is 1.28
+/- 0.10 AU or 81 +/- 6 mas. Imaging observations indicate that GJ 802b is
likely to be a brown dwarf with the astrometrically determined mass 0.058 +/-
0.021 Msolar (one sigma limits). The remaining uncertainty in the orbit is the
eccentricity that is now loosely constrained. We discuss how the system age
limits the mass and the prospects to further narrow the mass range when e is
more precisely determined.Comment: 13 pages, 6 figures, accepted for publication in ApJ on May 9, 200
A New Approach to Micro-arcsecond Astrometry with SIM Allowing Early Mission Narrow Angle Measurements of Compelling Astronomical Targets
The Space Interferometry Mission (SIM) is capable of detecting and measuring the mass of terrestrial planets around stars other than our own. It can measure the mass of black holes and the visual orbits of radio and x-ray binary sources. SIM makes possible a new level of understanding of complex astrophysical processes. SIM achieves its high precision in the so-called narrow-angle regime. This is defined by a 1 degree diameter field in which the position of a target star is measured with respect to a set of reference stars. The observation is performed in two parts: first, SIM observes a grid of stars that spans the full sky. After a few years, repeated observations of the grid allow one to determine the orientation of the interferometer baseline. Second, throughout the mission, SIM periodically observes in the narrow-angle mode. Every narrow-angle observation is linked to the grid to determine the precise attitude and length of the baseline. The narrow angle process demands patience. It is not until five years after launch that SIM achieves its ultimate accuracy of 1 microarcsecond. The accuracy is degraded by a factor of approx. 2 at mid-mission. Our work proposes a technique for narrow angle astrometry that does not rely on the measurement of grid stars. This technique, called Gridless Narrow Angle Astrometry (GNAA) can obtain microarcsecond accuracy and can detect extra-solar planets and other exciting objects with a few days of observation. It can be applied as early as during the first six months of in-orbit calibration (IOC). The motivations for doing this are strong. First, and obviously, it is an insurance policy against a catastrophic mid-mission failure. Second, at the start of the mission, with several space-based interferometers in the planning or implementation phase, NASA will be eager to capture the public's imagination with interferometric science. Third, early results and a technique that can duplicate those results throughout the mission will give the analysts important experience in the proper use and calibration of SIM
Apodized vortex coronagraph designs for segmented aperture telescopes
Current state-of-the-art high contrast imaging instruments take advantage of
a number of elegant coronagraph designs to suppress starlight and image nearby
faint objects, such as exoplanets and circumstellar disks. The ideal
performance and complexity of the optical systems depends strongly on the shape
of the telescope aperture. Unfortunately, large primary mirrors tend to be
segmented and have various obstructions, which limit the performance of most
conventional coronagraph designs. We present a new family of vortex
coronagraphs with numerically-optimized gray-scale apodizers that provide the
sensitivity needed to directly image faint exoplanets with large, segmented
aperture telescopes, including the Thirty Meter Telescope (TMT) as well as
potential next-generation space telescopes.Comment: To appear in SPIE proceedings vol. 991
Segmented coronagraph design and analysis (SCDA): an initial design study of apodized vortex coronagraphs
The segmented coronagraph design and analysis (SCDA) study is a coordinated
effort, led by Stuart Shaklan (JPL) and supported by NASA's Exoplanet
Exploration Program (ExEP), to provide efficient coronagraph design concepts
for exoplanet imaging with future segmented aperture space telescopes. This
document serves as an update on the apodized vortex coronagraph designs devised
by the Caltech/JPL SCDA team. Apodized vortex coronagraphs come in two flavors,
where the apodization is achieved either by use of 1) a gray-scale
semi-transparent pupil mask or 2) a pair of deformable mirrors in series. Each
approach has attractive benefits. This document presents a comprehensive review
of the former type. Future theoretical investigations will further explore the
use of deformable mirrors for apodization.Comment: White Paper (2016-2017
Performance and sensitivity of vortex coronagraphs on segmented space telescopes
The detection of molecular species in the atmospheres of earth-like exoplanets orbiting nearby stars requires an optical system that suppresses starlight and maximizes the sensitivity to the weak planet signals at small angular separations. Achieving sufficient contrast performance on a segmented aperture space telescope is particularly challenging due to unwanted diffraction within the telescope from amplitude and phase discontinuities in the pupil. Apodized vortex coronagraphs are a promising solution that theoretically meet the performance needs for high contrast imaging with future segmented space telescopes. We investigate the sensitivity of apodized vortex coronagraphs to the expected aberrations, including segment co-phasing errors in piston and tip/tilt as well as other low-order and mid-spatial frequency aberrations. Coronagraph designs and their associated telescope requirements are identified for conceptual HabEx and LUVOIR telescope designs
High dynamic range imaging in space: overview and wavefront control
NASA is endeavoring to launch missions capable of detecting Earth-like planets around neighboring stars. In visible wavelengths, this requires better than one 10 to the minus ten suppression of scattered light as close as 50 milli-arcsec to the stellar image. This extraordinary requirement is within reach but it requires broad-band wave front control to sub-Angstrom levels. We describe several high dynamic range imaging solutions, describe the various factors that contribute to the scattered light level and introduce a novel closed-loop broad-band correction system, suitable for the Shaped Pupil Coronagraph and the Lyot Coronagraph
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