47 research outputs found
Subaru Coronagraphic Extreme-AO (SCExAO) wavefront control: current status and ongoing developments
Exoplanet imaging requires excellent wavefront correction and calibration. At the Subaru telescope this is achieved us- ing the 188-element facility adaptive optics system(AO188) feeding the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument; a multipurpose instrument built to deliver high contrast images of planets and disks around nearby stars. AO188 offers coarse correction while SCExAO performs fine correction and calibration of 1000 modes. The full system achieves 90%Strehl Ratio in H-band and diffraction limited images. A new Real Time Computer allowing higher performance between SCExAO and AO188 is currently implemented. Future upgrades will include a new Pyramid Wavefront Sensor and (64x64) DM to achieve extreme AO correction inside AO188. We are progressing in the development of predictive control and sensor fusion algorithms across the system to improve performance and calibration. With the new upgrades, SCExAO will be able to image giant planets in reflected light with Subaru and validate technologies necessary to image habitable Earth-like planets with the Thirty Meter Telescope (TMT)
A Visible-light Lyot Coronagraph for SCExAO/VAMPIRES
We describe the design and initial results from a visible-light Lyot
coronagraph for SCExAO/VAMPIRES. The coronagraph is comprised of four
hard-edged, partially transmissive focal plane masks with inner working angles
of 36 mas, 55 mas, 92 mas, and 129 mas, respectively. The Lyot stop is a
reflective, undersized design with a geometric throughput of 65.7%. Our
preliminary on-sky contrast is 1e-2 at 0.1" to 1e-4 at 0.75" for all mask
sizes. The coronagraph was deployed in early 2022 and is available for open
use.Comment: Proceedings of SPIE 2022 Astronomical Instrumentation and Telescopes
conference (#12184-163
High Contrast and High Angular Imaging at Subaru Telescope
Adaptive Optics projects at Subaru Telescope span a wide field of
capabilities ranging from ground-layer adaptive optics (GLAO) providing partial
correction over a 20 arcmin FOV to extreme adaptive optics (ExAO) for exoplanet
imaging. We describe in this paper current and upcoming narrow field-of-view
capabilities provided by the Subaru Extreme Adaptive Optics Adaptive Optics
(SCExAO) system and its instrument modules, as well as the upcoming
3000-actuator upgrade of the Nasmyth AO system.Comment: 11 pages, to appear in SPIE Proceedings of Astronomical Telescopes +
Instrumentation, 202
High Contrast Imaging at the Photon Noise Limit with WFS-based PSF Calibration
Speckle Noise is the dominant source of error in high contrast imaging with
adaptive optics system. We discuss the potential for wavefront sensing
telemetry to calibrate speckle noise with sufficient precision and accuracy so
that it can be removed in post-processing of science images acquired by high
contrast imaging instruments. In such a self-calibrating system, exoplanet
detection would be limited by photon noise and be significantly more robust and
efficient than in current systems. We show initial laboratory and on-sky tests,
demonstrating over short timescale that residual speckle noise is indeed
calibrated to an accuracy exceeding readout and photon noise in the high
contrast region. We discuss immplications for the design of space and ground
high-contrast imaging systems.Comment: 12 pages, 7 figures, To appear in SPIE Proceedings of Astronomical
Telescopes + Instrumentation, 2022. arXiv admin note: text overlap with
arXiv:2109.1395
Subaru Coronagraphic Extreme-AO (SCExAO) wavefront control: current status and ongoing developments
Exoplanet imaging requires excellent wavefront correction and calibration. At the Subaru telescope this is achieved us- ing the 188-element facility adaptive optics system(AO188) feeding the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument; a multipurpose instrument built to deliver high contrast images of planets and disks around nearby stars. AO188 offers coarse correction while SCExAO performs fine correction and calibration of 1000 modes. The full system achieves 90%Strehl Ratio in H-band and diffraction limited images. A new Real Time Computer allowing higher performance between SCExAO and AO188 is currently implemented. Future upgrades will include a new Pyramid Wavefront Sensor and (64x64) DM to achieve extreme AO correction inside AO188. We are progressing in the development of predictive control and sensor fusion algorithms across the system to improve performance and calibration. With the new upgrades, SCExAO will be able to image giant planets in reflected light with Subaru and validate technologies necessary to image habitable Earth-like planets with the Thirty Meter Telescope (TMT)
Retrieval study of cool, directly imaged exoplanet 51 Eri b
Retrieval methods are a powerful analysis technique for modelling
exoplanetary atmospheres by estimating the bulk physical and chemical
properties that combine in a forward model to best-fit an observed spectrum,
and they are increasingly being applied to observations of directly-imaged
exoplanets. We have adapted TauREx3, the Bayesian retrieval suite, for the
analysis of near-infrared spectrophotometry from directly-imaged gas giant
exoplanets and brown dwarfs. We demonstrate TauREx3's applicability to
sub-stellar atmospheres by presenting results for brown dwarf benchmark GJ 570D
which are consistent with previous retrieval studies, whilst also exhibiting
systematic biases associated with the presence of alkali lines. We also present
results for the cool exoplanet 51 Eri b, the first application of a free
chemistry retrieval analysis to this object, using spectroscopic observations
from GPI and SPHERE. While our retrieval analysis is able to explain
spectroscopic and photometric observations without employing cloud extinction,
we conclude this may be a result of employing a flexible temperature-pressure
profile which is able to mimic the presence of clouds. We present Bayesian
evidence for an ammonia detection with a 2.7 confidence, the first
indication of ammonia in an exoplanetary atmosphere. This is consistent with
this molecule being present in brown dwarfs of a similar spectral type. We
demonstrate the chemical similarities between 51 Eri b and GJ 570D in relation
to their retrieved molecular abundances. Finally, we show that overall
retrieval conclusions for 51 Eri b can vary when employing different spectral
data and modelling components, such as temperature-pressure and cloud
structures
Exploring the Ability of HST WFC3 G141 to Uncover Trends in Populations of Exoplanet Atmospheres Through a Homogeneous Transmission Survey of 70 Gaseous Planets
We present the analysis of the atmospheres of 70 gaseous extrasolar planets
via transit spectroscopy with Hubble's Wide Field Camera 3 (WFC3). For over
half of these, we statistically detect spectral modulation which our retrievals
attribute to molecular species. Among these, we use Bayesian Hierarchical
Modelling to search for chemical trends with bulk parameters. We use the
extracted water abundance to infer the atmospheric metallicity and compare it
to the planet's mass. We also run chemical equilibrium retrievals, fitting for
the atmospheric metallicity directly. However, although previous studies have
found evidence of a mass-metallicity trend, we find no such relation within our
data. For the hotter planets within our sample, we find evidence for thermal
dissociation of dihydrogen and water via the H opacity. We suggest that the
general lack of trends seen across this population study could be due to i) the
insufficient spectral coverage offered by HST WFC3 G141, ii) the lack of a
simple trend across the whole population, iii) the essentially random nature of
the target selection for this study or iv) a combination of all the above. We
set out how we can learn from this vast dataset going forward in an attempt to
ensure comparative planetology can be undertaken in the future with facilities
such as JWST, Twinkle and Ariel. We conclude that a wider simultaneous spectral
coverage is required as well as a more structured approach to target selection.Comment: Accepted for publication in ApJ
Exploring the Ability of Hubble Space Telescope WFC3 G141 to Uncover Trends in Populations of Exoplanet Atmospheres through a Homogeneous Transmission Survey of 70 Gaseous Planets
We present analysis of the atmospheres of 70 gaseous extrasolar planets via transit spectroscopy with Hubble’s Wide Field Camera 3 (WFC3). For over half of these, we statistically detect spectral modulation that our retrievals attribute to molecular species. Among these, we use Bayesian hierarchical modeling to search for chemical trends with bulk parameters. We use the extracted water abundance to infer the atmospheric metallicity and compare it to the planet’s mass. We also run chemical equilibrium retrievals, fitting for the atmospheric metallicity directly. However, although previous studies have found evidence of a mass–metallicity trend, we find no such relation within our data. For the hotter planets within our sample, we find evidence for thermal dissociation of dihydrogen and water via the H− opacity. We suggest that the general lack of trends seen across this population study could be due to (i) the insufficient spectral coverage offered by the Hubble Space Telescope’s WFC3 G141 band, (ii) the lack of a simple trend across the whole population, (iii) the essentially random nature of the target selection for this study, or (iv) a combination of all the above. We set out how we can learn from this vast data set going forward in an attempt to ensure comparative planetology can be undertaken in the future with facilities such as the JWST, Twinkle, and Ariel. We conclude that a wider simultaneous spectral coverage is required as well as a more structured approach to target selection
Focal plane wavefront sensing on SUBARU/SCExAO
Focal plane wavefront sensing is an elegant solution for wavefront sensing since near-focal images of any source taken by a detector show distortions in the presence of aberrations. Non-Common Path Aberrations and the Low Wind Effect both have the ability to limit the achievable contrast of the finest coronagraphs coupled with the best extreme adaptive optics systems. To correct for these aberrations, the Subaru Coronagraphic Extreme Adaptive Optics instrument hosts many focal plane wavefront sensors using detectors as close to the science detector as possible. We present seven of them and compare their implementation and efficiency on SCExAO. This work will be critical for wavefront sensing on next generation of extremely large telescopes that might present similar limitations
The beta Pictoris system: Setting constraints on the planet and the disk structures at mid-IR wavelengths with NEAR
[abridged] We analyzed mid-infrared high-contrast coronagraphic images of the
beta Pictoris system, taking advantage of the NEAR experiment using the
VLT/VISIR instrument. The goal of our analysis is to investigate both the
detection of the planet beta Pictoris b and of the disk features at mid-IR
wavelengths. In addition, by combining several epochs of observation, we expect
to constrain the position of the known clumps and improve our knowledge on the
dynamics of the disk. To evaluate the planet b flux contribution, we extracted
the photometry and compared it to the flux published in the literature. In
addition, we used previous data from T-ReCS and VISIR, to study the evolution
of the position of the southwest clump that was initially observed in the
planetary disk back in 2003. While we did not detect the planet b, we were able
to put constraints on the presence of circumplanetary material, ruling out the
equivalent of a Saturn-like planetary ring around the planet. The disk presents
several noticeable structures, including the known southwest clump. Using a
16-year baseline, sampled with five epochs of observations, we were able to
examine the evolution of the clump: the clump orbits in a Keplerian motion with
an sma of 56.1+-0.4 au. In addition to the known clump, the images clearly show
the presence of a second clump on the northeast side of the disk and fainter
and closer structures that are yet to be confirmed. We found correlations
between the CO clumps detected with ALMA and the mid-IR images. If the
circumplanetary material were located at the Roche radius, the maximum amount
of dust determined from the flux upper limit around beta Pictoris b would
correspond to the mass of an asteroid of 5 km in diameter. Finally, the
Keplerian motion of the southwestern clump is possibly indicative of a
yet-to-be-detected planet or signals the presence of a vortex.Comment: Accepted in Astronomy and Astrophysic