177 research outputs found
Imaging faint brown dwarf companions close to bright stars with a small, well-corrected telescope aperture
We have used our 1.6 m diameter off-axis well-corrected sub-aperture (WCS) on
the Palomar Hale telescope in concert with a small inner-working-angle (IWA)
phase-mask coronagraph to image the immediate environs of a small number of
nearby stars. Test cases included three stars (HD 130948, HD 49197 and HR7672)
with known brown dwarf companions at small separations, all of which were
detected. We also present the initial detection of a new object close to the
nearby young G0V star HD171488. Follow up observations are needed to determine
if this object is a bona fide companion, but its flux is consistent with the
flux of a young brown dwarf or low mass M star at the same distance as the
primary. Interestingly, at small angles our WCS coronagraph demonstrates a
limiting detectable contrast comparable to that of extant Lyot coronagraphs on
much larger telescopes corrected with current-generation AO systems. This
suggests that small apertures corrected to extreme adaptive optics (ExAO)
levels can be used to carry out initial surveys for close brown dwarf and
stellar companions, leaving followup observations for larger telescopes.Comment: accepted for publication in the Astrophysical Journa
Improving Interferometric Null Depth Measurements using Statistical Distributions: Theory and First Results with the Palomar Fiber Nuller
A new "self-calibrated" statistical analysis method has been developed for
the reduction of nulling interferometry data. The idea is to use the
statistical distributions of the fluctuating null depth and beam intensities to
retrieve the astrophysical null depth (or equivalently the object's visibility)
in the presence of fast atmospheric fluctuations. The approach yields an
accuracy much better (about an order of magnitude) than is presently possible
with standard data reduction methods, because the astrophysical null depth
accuracy is no longer limited by the magnitude of the instrumental phase and
intensity errors but by uncertainties on their probability distributions. This
approach was tested on the sky with the two-aperture fiber nulling instrument
mounted on the Palomar Hale telescope. Using our new data analysis approach
alone-and no observations of calibrators-we find that error bars on the
astrophysical null depth as low as a few 10-4 can be obtained in the
near-infrared, which means that null depths lower than 10-3 can be reliably
measured. This statistical analysis is not specific to our instrument and may
be applicable to other interferometers
Mid-infrared laser light nulling experiment using single-mode conductive waveguides
Aims: In the context of space interferometry missions devoted to the search
of exo-Earths, this paper investigates the capabilities of new single mode
conductive waveguides at providing modal filtering in an infrared and
monochromatic nulling experiment; Methods: A Michelson laser interferometer
with a co-axial beam combination scheme at 10.6 microns is used. After
introducing a Pi phase shift using a translating mirror, dynamic and static
measurements of the nulling ratio are performed in the two cases where modal
filtering is implemented and suppressed. No additional active control of the
wavefront errors is involved. Results: We achieve on average a statistical
nulling ratio of 2.5e-4 with a 1-sigma upper limit of 6e-4, while a best null
of 5.6e-5 is obtained in static mode. At the moment, the impact of external
vibrations limits our ability to maintain the null to 10 to 20 seconds.;
Conclusions: A positive effect of SM conductive waveguide on modal filtering
has been observed in this study. Further improvement of the null should be
possible with proper mechanical isolation of the setup.Comment: Accepted in A&A, 7 pages, 5 figure
Extreme adaptive optics imaging with a clear and well-corrected off-axis telescope sub-aperture
Rather than using an adaptive optics (AO) system to correct a telescope s
entire pupil, it can instead be used to more finely correct a smaller
sub-aperture. Indeed, existing AO systems can be used to correct a sub-aperture
1/3 to 1/2 the size of a 5-10 m telescope to extreme adaptive optics (ExAO)
levels. We discuss the potential performance of a clear off-axis well-corrected
sub-aperture (WCS), and describe our initial imaging results with a 1.5 m
diameter WCS on the Palomar Observatory s Hale telescope. These include
measured Strehl ratios of 0.92-0.94 in the infrared (2.17 microns), and 0.12 in
the B band, the latter allowing a binary of separation 0.34 arc sec to be
easily resolved in the blue. Such performance levels enable a variety of novel
observational modes, such as infrared ExAO, visible-wavelength AO, and
high-contrast coronagraphy. One specific application suggested by the high
Strehl ratio stability obtained (1%) is the measurement of planetary transits
and eclipses. Also described is a simple dark-hole experiment carried out on a
binary star, in which a comatic phase term was applied directly to the
deformable mirror, in order to shift the diffraction rings to one side of the
point spread function.Comment: accepted by Ap
Are dust shell models well-suited to explain interferometric data of late-type stars in the near-infrared?
Recently available near-infrared interferometric data on late-type stars show
a strong increase of diameter for asymptotic giant branch (AGB) stars between
the K (2.0 - 2.4 \mu m) and L (3.4 - 4.1 \mu m) bands. Aiming at an explanation
of these findings, we chose the objects \alpha Orionis (Betelgeuse), SW
Virginis, and R Leonis, which are of different spectral types and stages of
evolution, and which are surrounded by circumstellar envelopes with different
optical thicknesses. For these stars, we compared observations with spherically
symmetric dust shell models. Photometric and 11 \mu m interferometric data were
also taken into account to further constrain the models. -- [...] -- We
conclude that AGB models comprising a photosphere and dust shell, although
consistent with SED data and also interferometric data in K and at 11 \mu m,
cannot explain the visibility data in L; an additional source of model opacity,
possibly related to a gas component, is needed in L to be consistent with the
visibility data.Comment: 12 pages, 4 figures, to be published in A&A; Latex aa class, uses
packages graphicx, hyperref, natbib, and txfonts; keywords: Techniques:
interferometric -- Radiative transfer -- Circumstellar matter -- Infrared:
stars -- Stars: late-type -- Stars: individual: \alpha Orionis, SW Virginis,
R Leoni
Simultaneous Water Vapor and Dry Air Optical Path Length Measurements and Compensation with the Large Binocular Telescope Interferometer
The Large Binocular Telescope Interferometer uses a near-infrared camera to
measure the optical path length variations between the two AO-corrected
apertures and provide high-angular resolution observations for all its science
channels (1.5-13 m). There is however a wavelength dependent component to
the atmospheric turbulence, which can introduce optical path length errors when
observing at a wavelength different from that of the fringe sensing camera.
Water vapor in particular is highly dispersive and its effect must be taken
into account for high-precision infrared interferometric observations as
described previously for VLTI/MIDI or the Keck Interferometer Nuller. In this
paper, we describe the new sensing approach that has been developed at the LBT
to measure and monitor the optical path length fluctuations due to dry air and
water vapor separately. After reviewing the current performance of the system
for dry air seeing compensation, we present simultaneous H-, K-, and N-band
observations that illustrate the feasibility of our feedforward approach to
stabilize the path length fluctuations seen by the LBTI nuller.Comment: SPIE conference proceeding
Co-phasing the Large Binocular Telescope: status and performance of LBTI/PHASECam
The Large Binocular Telescope Interferometer is a NASA-funded nulling and
imaging instrument designed to coherently combine the two 8.4-m primary mirrors
of the LBT for high-sensitivity, high-contrast, and high-resolution infrared
imaging (1.5-13 um). PHASECam is LBTI's near-infrared camera used to measure
tip-tilt and phase variations between the two AO-corrected apertures and
provide high-angular resolution observations. We report on the status of the
system and describe its on-sky performance measured during the first semester
of 2014. With a spatial resolution equivalent to that of a 22.8-meter telescope
and the light-gathering power of single 11.8-meter mirror, the co-phased LBT
can be considered to be a forerunner of the next-generation extremely large
telescopes (ELT).Comment: 8 pages, 5 figures, SPIE Conference proceeding
L'-band AGPM vector vortex coronagraph's first light on LBTI/LMIRCam
We present the first observations obtained with the L'-band AGPM vortex
coronagraph recently installed on LBTI/LMIRCam. The AGPM (Annular Groove Phase
Mask) is a vector vortex coronagraph made from diamond subwavelength gratings.
It is designed to improve the sensitivity and dynamic range of high-resolution
imaging at very small inner working angles, down to 0.09 arcseconds in the case
of LBTI/LMIRCam in the L' band. During the first hours on sky, we observed the
young A5V star HR\,8799 with the goal to demonstrate the AGPM performance and
assess its relevance for the ongoing LBTI planet survey (LEECH). Preliminary
analyses of the data reveal the four known planets clearly at high SNR and
provide unprecedented sensitivity limits in the inner planetary system (down to
the diffraction limit of 0.09 arcseconds).Comment: 9 pages, 4 figures, SPIE proceeding
Modal Filtering for Nulling Interferometry-First Single-Mode Conductive Waveguides in the Mid-Infrared
This paper presents the work achieved for the manufacturing and
characterization of first single-mode waveguides to be used as modal filters
for nulling interferometry in the mid-infrared range [4-20 um]. As very high
dynamic range is mandatory for detection of Earth-like planets, modal filtering
is one of the most stringent instrumental aspects. The hollow metallic
waveguides (HMW) presented here are manufactured using micro-machining
techniques. Single-mode behavior has been investigated in laboratory through a
technique of polarization analysis while transmission features have been
measured using flux relative comparison. The single-mode behavior have been
assessed at lambda=10.6 um for rectangular waveguides with dimensions a=10 um
and b<5.3 um with an accuracy of ~2.5 %. The tests have shown that a
single-polarization state can be maintained in the waveguide. A comparison with
results on multi-mode HMW is proposed. Excess losses of 2.4 dB (~ 58 %
transmission) have been measured for a single-mode waveguide. In particular,
the importance of coupling conditions into the waveguide is emphasized here.
The goal of manufacturing and characterizing the first single-mode HMW for the
mid-infrared has been achieved. This opens the road to the use of integrated
optics for interferometry in the mentioned spectral range.Comment: 10 pages, 6 figures, accepted in A&
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