723 research outputs found
The Infrared Imaging Spectrograph (IRIS) for TMT: Volume phase holographic grating performance testing and discussion
Maximizing the grating efficiency is a key goal for the first light
instrument IRIS (Infrared Imaging Spectrograph) currently being designed to
sample the diffraction limit of the TMT (Thirty Meter Telescope). Volume Phase
Holographic (VPH) gratings have been shown to offer extremely high efficiencies
that approach 100% for high line frequencies (i.e., 600 to 6000l/mm), which has
been applicable for astronomical optical spectrographs. However, VPH gratings
have been less exploited in the near-infrared, particularly for gratings that
have lower line frequencies. Given their potential to offer high throughputs
and low scattered light, VPH gratings are being explored for IRIS as a
potential dispersing element in the spectrograph. Our team has procured
near-infrared gratings from two separate vendors. We have two gratings with the
specifications needed for IRIS current design: 1.51-1.82{\mu}m (H-band) to
produce a spectral resolution of 4000 and 1.19- 1.37 {\mu}m (J-band) to produce
a spectral resolution of 8000. The center wavelengths for each grating are
1.629{\mu}m and 1.27{\mu}m, and the groove densities are 177l/mm and 440l/mm
for H-band R=4000 and J-band R=8000, respectively. We directly measure the
efficiencies in the lab and find that the peak efficiencies of these two types
of gratings are quite good with a peak efficiency of ~88% at the Bragg angle in
both TM and TE modes at H-band, and 90.23% in TM mode, 79.91% in TE mode at
J-band for the best vendor. We determine the drop in efficiency off the Bragg
angle, with a 20-23% decrease in efficiency at H-band when 2.5 degree deviation
from the Bragg angle, and 25%-28% decrease at J-band when 5{\deg} deviation
from the Bragg angle.Comment: Proceedings of the SPIE, 9147-33
Gemini Planet Imager Observational Calibrations III: Empirical Measurement Methods and Applications of High-Resolution Microlens PSFs
The newly commissioned Gemini Planet Imager (GPI) combines extreme adaptive
optics, an advanced coronagraph, precision wavefront control and a
lenslet-based integral field spectrograph (IFS) to measure the spectra of young
extrasolar giant planets between 0.9-2.5 um. Each GPI detector image, when in
spectral model, consists of ~37,000 microspectra which are under or critically
sampled in the spatial direction. This paper demonstrates how to obtain
high-resolution microlens PSFs and discusses their use in enhancing the
wavelength calibration, flexure compensation and spectral extraction. This
method is generally applicable to any lenslet-based integral field spectrograph
including proposed future instrument concepts for space missions.Comment: 10 pages, 6 figures. Proceedings of the SPIE, 9147-282 v2: reference
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The InfraRed Imaging Spectrograph (IRIS) for TMT: Reflective ruled diffraction grating performance testing and discussion
We present the efficiency of near-infrared reflective ruled diffraction
gratings designed for the InfraRed Imaging Spectrograph (IRIS). IRIS is a first
light, integral field spectrograph and imager for the Thirty Meter Telescope
(TMT) and narrow field infrared adaptive optics system (NFIRAOS). We present
our experimental setup and analysis of the efficiency of selected reflective
diffraction gratings. These measurements are used as a comparison sample
against selected candidate Volume Phase Holographic (VPH) gratings (see Chen et
al., this conference). We investigate the efficiencies of five ruled gratings
designed for IRIS from two separate vendors. Three of the gratings accept a
bandpass of 1.19-1.37 {\mu}m (J band) with ideal spectral resolutions of R=4000
and R=8000, groove densities of 249 and 516 lines/mm, and blaze angles of 9.86
and 20.54 degrees, respectively. The other two gratings accept a bandpass of
1.51-1.82 {\mu}m (H Band) with an ideal spectral resolution of R=4000, groove
density of 141 lines/mm, and blaze angle of 9.86{\deg}. We measure the
efficiencies off blaze angle for all gratings and the efficiencies between the
polarization transverse magnetic (TM) and transverse electric (TE) states. The
peak reflective efficiencies are 98.90 +/- 3.36% (TM) and 84.99 +/- 2.74% (TM)
for the H-band R=4000 and J-band R=4000 respectively. The peak reflective
efficiency for the J-band R=8000 grating is 78.78 +/- 2.54% (TE). We find that
these ruled gratings do not exhibit a wide dependency on incident angle within
+/-3{\deg}. Our best-manufactured gratings were found to exhibit a dependency
on the polarization state of the incident beam with a ~10-20% deviation,
consistent with the theoretical efficiency predictions.Comment: Proceedings of the SPIE, 9147-34
Search for Nanosecond Near-infrared Transients around 1280 Celestial Objects
Stars and planetary system
Liger for Next Generation Keck Adaptive Optics: Opto-Mechanical Dewar for Imaging Camera and Slicer
Liger is a next generation adaptive optics (AO) fed integral field
spectrograph (IFS) and imager for the W. M. Keck Observatory. This new
instrument is being designed to take advantage of the upgraded AO system
provided by Keck All-Sky Precision Adaptive-optics (KAPA). Liger will provide
higher spectral resolving power (R4,000-10,000), wider wavelength
coverage (0.8-2.4 m), and larger fields of view than any current
IFS. We present the design and analysis for a custom-made dewar chamber for
characterizing the Liger opto-mechanical system. This dewar chamber is designed
to test and assemble the Liger imaging camera and slicer IFS components while
being adaptable for future experiments. The vacuum chamber will operate below
Torr with a cold shield that will be kept below 90 K. The dewar test
chamber will be mounted to an optical vibration isolation platform and further
isolated from the cryogenic and vacuum systems with bellows. The cold head and
vacuums will be mounted to a custom cart that will also house the electronics
and computer that interface with the experiment. This test chamber will provide
an efficient means of calibrating and characterizing the Liger instrument and
performing future experiments.Comment: 8 pages, 6 figure
Calibration Unit Design for High-Resolution Infrared Spectrograph for Exoplanet Characterization (HISPEC)
The latest generation of high-resolution spectrograph instruments on
10m-class telescopes continue to pursue challenging science cases.
Consequently, ever more precise calibration methods are necessary to enable
trail-blazing science methodology. We present the High-resolution Infrared
SPectrograph for Exoplanet Characterization (HISPEC) Calibration Unit (CAL),
designed to facilitate challenging science cases such as Doppler imaging of
exoplanet atmospheres, precision radial velocity, and high-contrast
high-resolution spectroscopy of nearby exoplanets. CAL builds upon the heritage
from the pathfinder instrument Keck Planet Imager and Characterizer (KPIC) and
utilizes four near-infrared (NIR) light sources encoded with wavelength
information that are coupled into single-mode fibers. They can be used
synchronously during science observations or asynchronously during daytime
calibrations. A hollow cathode lamp (HCL) and a series of gas absorption cells
provide absolute calibration from 0.98 {\mu}m to 2.5 {\mu}m. A laser frequency
comb (LFC) provides stable, time-independent wavelength information during
observation and CAL implements a lower finesse astro-etalon as a backup for the
LFC. Design lessons from instrumentation like HISPEC will serve to inform the
requirements for similar instruments for the ELTs in the future.Comment: 16 pages, 14 figure
Constraints on the architecture of the HD 95086 planetary system with the Gemini Planet Imager
We present astrometric monitoring of the young exoplanet HD 95086 b obtained
with the Gemini Planet Imager between 2013 and 2016. A small but significant
position angle change is detected at constant separation; the orbital motion is
confirmed with literature measurements. Efficient Monte Carlo techniques place
preliminary constraints on the orbital parameters of HD 95086 b. With 68%
confidence, a semimajor axis of 61.7^{+20.7}_{-8.4} au and an inclination of
153.0^{+9.7}_{-13.5} deg are favored, with eccentricity less than 0.21. Under
the assumption of a co-planar planet-disk system, the periastron of HD 95086 b
is beyond 51 au with 68% confidence. Therefore HD 95086 b cannot carve the
entire gap inferred from the measured infrared excess in the SED of HD 95086.
We use our sensitivity to additional planets to discuss specific scenarios
presented in the literature to explain the geometry of the debris belts. We
suggest that either two planets on moderately eccentric orbits or three to four
planets with inhomogeneous masses and orbital properties are possible. The
sensitivity to additional planetary companions within the observations
presented in this study can be used to help further constrain future dynamical
simulations of the planet-disk system.Comment: Accepted for publication in ApJ
Dynamical Mass Measurement of the Young Spectroscopic Binary V343 Normae AaAb Resolved With the Gemini Planet Imager
We present new spatially resolved astrometry and photometry from the Gemini
Planet Imager of the inner binary of the young multiple star system V343
Normae, which is a member of the beta Pictoris moving group. V343 Normae
comprises a K0 and mid-M star in a ~4.5 year orbit (AaAb) and a wide 10" M5
companion (B). By combining these data with archival astrometry and radial
velocities we fit the orbit and measure individual masses for both components
of M_Aa = 1.10 +/- 0.10 M_sun and M_Ab = 0.290 +/- 0.018 M_sun. Comparing to
theoretical isochrones, we find good agreement for the measured masses and JHK
band magnitudes of the two components consistent with the age of the beta Pic
moving group. We derive a model-dependent age for the beta Pic moving group of
26 +/- 3 Myr by combining our results for V343 Normae with literature
measurements for GJ 3305, which is another group member with resolved binary
components and dynamical masses.Comment: 12 pages, 7 figures. Accepted to A
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