154 research outputs found
Modeling giant extrasolar ring systems in eclipse and the case of J1407b: sculpting by exomoons?
The light curve of 1SWASP J140747.93-394542.6, a 16 Myr old star in the
Sco-Cen OB association, underwent a complex series of deep eclipses that lasted
56 days, centered on April 2007. This light curve is interpreted as the transit
of a giant ring system that is filling up a fraction of the Hill sphere of an
unseen secondary companion, J1407b. We fit the light curve with a model of an
azimuthally symmetric ring system, including spatial scales down to the
temporal limit set by the star's diameter and relative velocity. The best ring
model has 37 rings and extends out to a radius of 0.6 AU (90 million km), and
the rings have an estimated total mass on the order of . The ring
system has one clearly defined gap at 0.4 AU (61 million km), which we
hypothesize is being cleared out by a exosatellite orbiting
around J1407b. This eclipse and model implies that we are seeing a
circumplanetary disk undergoing a dynamic transition to an
exosatellite-sculpted ring structure and is one of the first seen outside our
Solar system.Comment: 13 pages, 6 figures, 3 tables. Accepted for publication in ApJ. Data
and computer code for model at: http://github.com/mkenworthy/exoring
Infrared Variability of the Gliese 569B System
Gliese 569B is a multiple brown dwarf system whose exact nature has been the
subject of several investigations over the past few years. Interpretation has
partially relied on infra-red photometry and spectroscopy of the resolved
components of the system. We present seeing limited Ks photometry over four
nights, searching for variability in this young low mass substellar system. Our
photometry is consistent with other reported photometry, and we report the
tentative detection of several periodic signals consistent with rotational
modulation due to spots on their surfaces. The five significant periods range
from 2.90 hours to 12.8 hours with peak to peak variabilities from 28 mmag to
62 mmag in the Ks band.
If both components are rotating with the shortest periods, then their
rotation axes are not parallel with each other, and the rotation axis of the Bb
component is not perpendicular to the Ba-Bb orbital plane. If Bb has one of the
longer rotational periods, then the Bb rotation axis is consistent with being
parallel to the orbital axis of the Ba-Bb system.Comment: 22 pages, 7 figures, accepted for publication in the Astrophysical
Journa
SPIRAL Phase A: A Prototype Integral Field Spectrograph for the AAT
We present details of a prototype fiber feed for use on the Anglo-Australian
Telescope (AAT) that uses a dedicated fiber-fed medium/high resolution (R >
10000) visible-band spectrograph to give integral field spectroscopy (IFS) of
an extended object. A focal reducer couples light from the telescope to the
close-packed lenslet array and fiber feed, allowing the spectrograph be used on
other telescopes with the change of a single lens. By considering the
properties of the fibers in the design of the spectrograph, an efficient design
can be realised, and we present the first scientific results of a prototype
spectrograph using a fiber feed with 37 spatial elements, namely the detection
of Lithium confirming a brown dwarf candidate and IFS of the supernova remnant
SN1987A.Comment: 41 pages, 15 figures, 3 tables; accepted by PAS
Minimizing Strong Telluric Absorption in Near Infra-red Stellar Spectra
We have obtained high resolution spectra (R = 25000) of an A star over
varying airmass to determine the effectiveness of telluric removal in the limit
of high signal to noise. The near infra-red line HeI at 2.058 microns, which is
a sensitive indicator of physical conditions in massive stars, supergiants, HII
regions and YSOs, resides among pressure broadened telluric absorption from
carbon dioxide and water vapor that varies both in time and with observed
airmass.
Our study shows that in the limit of bright stars at high resolution,
accuracies of 5% are typical for high airmass observations (greater than 1.9),
improving to a photon-limited accuracy of 2% at smaller airmasses (less than
1.15). We find that by using the continuum between telluric absorption lines of
a ro-vibrational fan a photon-limited 1% accuracy is achievable.Comment: 14 pages, 7 figures. Accepted for publication in PAS
Polarization dOTF: on-sky focal plane wavefront sensing
The differential Optical Transfer Function (dOTF) is a focal plane wavefront
sensing method that uses a diversity in the pupil plane to generate two
different focal plane images. The difference of their Fourier transforms
recovers the complex amplitude of the pupil down to the spatial scale of the
diversity. We produce two simultaneous PSF images with diversity using a
polarizing filter at the edge of the telescope pupil, and a polarization camera
to simultaneously record the two images. Here we present the first on-sky
demonstration of polarization dOTF at the 1.0m South African Astronomical
Observatory telescope in Sutherland, and our attempt to validate it with
simultaneous Shack-Hartmann wavefront sensor images.Comment: 11 pages, 9 figures, Proc. SPIE Vol. 991
Pupil Plane Phase Apodization
Phase apodization coronagraphs are implemented in a pupil plane to create a
dark hole in the science camera focal plane. They are successfully created as
"Apodizing Phase Plates" (APPs) using classical optical manufacturing, and as
"vector-APPs" using liquid-crystal patterning with essentially achromatic
performance. This type of coronagraph currently delivers excellent broadband
contrast (10) at small angular separations (few ) at
ground-based telescopes, owing to their insensitivity to tip/tilt errors.Comment: Invited chapter, to be published in the "Handbook of Astronomical
Instrumentation", Vol. 3, eds. A. Moore and D. Burrows, WSPC (2018). 9 pages,
1 figur
First On-Sky High Contrast Imaging with an Apodizing Phase Plate
We present the first astronomical observations obtained with an Apodizing
Phase Plate (APP). The plate is designed to suppress the stellar diffraction
pattern by 5 magnitudes from 2-9 lambda/D over a 180 degree region. Stellar
images were obtained in the M' band (4.85 microns) at the MMTO 6.5m telescope,
with adaptive wavefront correction made with a deformable secondary mirror
designed for low thermal background observations. The measured PSF shows a halo
intensity of 0.1% of the stellar peak at 2 lambda/D (0.36 arcsec), tapering off
as r^{-5/3} out to radius 9 lambda/D. Such a profile is consistent with
residual errors predicted for servo lag in the AO system.
We project a 5 sigma contrast limit, set by residual atmospheric
fluctuations, of 10.2 magnitudes at 0.36 arcsec separation for a one hour
exposure. This can be realised if static and quasi-static aberrations are
removed by differential imaging, and is close to the sensitivity level set by
thermal background photon noise for target stars with M'>3. The advantage of
using the phase plate is the removal of speckle noise caused by the residuals
in the diffraction pattern that remain after PSF subtraction. The APP gives
higher sensitivity over the range 2-5 lambda/D compared to direct imaging
techniques.Comment: 22 pages, 5 figures, 1 table, ApJ accepte
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