58 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
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
Scaling Relation for Occulter Manufacturing Errors
For directly imaging exoplanets, NASA is considering space mission designs that use an external occulter as the principal starlight suppression system. These occulter designs range in diameter from 16 to 40 meters and separation distance from 8,000 to 60,000 kilometers for telescopes with primary diameters of 0.5 to 4 meters. Occulter shapes are solutions to an optimization problem which seeks to maximize suppression in the shadow subject to constraints such as size, separation, and wavelengths. These designs are based on scalar diffraction theory and must be verified experimentally to demonstrate predicted on-orbit performance. Due to the large sizes and separations involved the experiment must be scaled to lab size. We are currently expanding the existing experimental test-bed at Princeton to enable scaling of occulters operating at flight Fresnel sizes. Here we examine the effect on suppression performance of edge defects and their scaling to test-bed size
Astrometric Discovery of GJ 164B
We discovered a low-mass companion to the M-dwarf GJ 164 with the CCD-based
imaging system of the Stellar Planet Survey (STEPS) astrometric program. The
existence of GJ 164B was confirmed with Hubble Space Telescope NICMOS imaging
observations. A high-dispersion spectral observation in V sets a lower limit of
delta m> 2.2 mag between the two components of the system. Based upon our
parallax value of 0.082 +/- 0.008, we derive the following orbital parameters:
P = 2.04 +/- 0.03 y, a = 1.03 +/- 0.03 AU, and Mtotal = 0.265 +/- 0.020 MSun.
The component masses are MA = 0.170 +/- 0.015 MSun and MB = 0.095 +/- 0.015
MSun. Based on its mass, colors, and spectral properties, GJ 164B has spectral
type M6-8 V.Comment: pdf file 14 pages with 6 fig
Preliminary Analysis of Effect of Random Segment Errors on Coronagraph Performance
No abstract availabl
The Carnegie Astrometric Planet Search Program
We are undertaking an astrometric search for gas giant planets and brown
dwarfs orbiting nearby low mass dwarf stars with the 2.5-m du Pont telescope at
the Las Campanas Observatory in Chile. We have built two specialized
astrometric cameras, the Carnegie Astrometric Planet Search Cameras (CAPSCam-S
and CAPSCam-N), using two Teledyne Hawaii-2RG HyViSI arrays, with the cameras'
design having been optimized for high accuracy astrometry of M dwarf stars. We
describe two independent CAPSCam data reduction approaches and present a
detailed analysis of the observations to date of one of our target stars, NLTT
48256. Observations of NLTT 48256 taken since July 2007 with CAPSCam-S imply
that astrometric accuracies of around 0.3 milliarcsec per hour are achievable,
sufficient to detect a Jupiter-mass companion orbiting 1 AU from a late M dwarf
10 pc away with a signal-to-noise ratio of about 4. We plan to follow about 100
nearby (primarily within about 10 pc) low mass stars, principally late M, L,
and T dwarfs, for 10 years or more, in order to detect very low mass companions
with orbital periods long enough to permit the existence of habitable,
Earth-like planets on shorter-period orbits. These stars are generally too
faint and red to be included in ground-based Doppler planet surveys, which are
often optimized for FGK dwarfs. The smaller masses of late M dwarfs also yield
correspondingly larger astrometric signals for a given mass planet. Our search
will help to determine whether gas giant planets form primarily by core
accretion or by disk instability around late M dwarf stars.Comment: 48 pages, 9 figures. in press, Publ. Astron. Soc. Pacifi
Direct Detection of the Brown Dwarf GJ 802B with Adaptive Optics Masking Interferometry
We have used the Palomar 200" Adaptive Optics (AO) system to directly detect
the astrometric brown dwarf GJ 802B reported by Pravdo et al. 2005. This
observation is achieved with a novel combination of aperture masking
interferometry and AO. The dynamical masses are 0.1750.021 M and
0.0640.032 M for the primary and secondary respectively. The
inferred absolute H band magnitude of GJ 802B is M=12.8 resulting in a
model-dependent T of 1850 50K and mass range of
0.057--0.074 M.Comment: 4 Pages, 5 figures, emulateapj format, submitted to ApJ
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