Advanced Electro-Optical System Research Articles

Performance of a U-Net-based neural network for predictive adaptive optics.

We apply a U-Net-based convolutional neural network (NN) architecture to the problem of predictive adaptive optics (AO) for tracking and imaging fast-moving targets, such as satellites in low Earth orbit (LEO). We show that the fine-tuned NN is able to achieve an approximately 50% reduction in mean-squared wavefront error over non-predictive approaches while predicting up to eight frames into the future. These results were obtained when the NN, trained mostly on simulated data, tested its performance on 1 kHz Shack-Hartmann wavefront sensor data collected in open-loop at the Advanced Electro-Optical System facility at Haleakala Observatory while the telescope tracked a naturally illuminated piece of LEO space debris. We report, to our knowledge, the first successful test of a NN for the predictive AO application using on-sky data, as well as the first time such a network has been developed for the more stressing space tracking application.

Astrometric and photometric measurements of binary stars with adaptive optics: observations from 2001 to 2006

The adaptive optics system at the 3.6 m Advanced Electro-Optical System telescope was used to measure the astrometry and differential magnitude in I band of binary star systems between 2002 and 2006. We report 413 astrometric and photometric measurements of 373 stellar pairs. The astrometric measurements will be of use for future orbital determination, and the photometric measurements will be of use in estimating the spectral types of the component stars. For 21 binaries that had not been observed in decades, we are able to confirm that the systems share common proper motion. Candidate new companions were detected in 24 systems; for these we show the discovery images. Follow-up observations should be able to determine if these systems share common proper motion and are gravitationally bound objects. We computed orbits for nine binaries. Of these, the orbits of five systems are improved compared to prior orbits and four systems have their orbits computed for the first time. In addition, 315 stars were unresolved and the full-width half maxima of the images are presented.

地基望远镜塔台圆顶结构形式及设计原则

This paper reviews the functions of telescope enclosures in brief and summarizes the universal principle of observatory site selection.Then,it introduces the structure types,working characteristics and environmental conditions of typical telescope enclosures at abroad.By taking an enclosure with an aperture of 3.67 m in the advanced electro-optical system as an example,the thermal control scheme for the enclosure is analyzed,and the golden rule and methods of thermal design of modern telescope enclosures are proposed in detail.Furthermore,several kinds of key factors to be taken into account in design are pointed out.Finally,the design and analysis method for telescope piers are also discussed.

THE LYOT PROJECT DIRECT IMAGING SURVEY OF SUBSTELLAR COMPANIONS: STATISTICAL ANALYSIS AND INFORMATION FROM NONDETECTIONS

The Lyot project used an optimized Lyot coronagraph with Extreme Adaptive Optics at the 3.63m Advanced Electro-Optical System telescope (AEOS) to observe 86 stars from 2004 to 2007. In this paper we give an overview of the survey results and a statistical analysis of the observed nondetections around 58 of our targets to place constraints on the population of substellar companions to nearby stars. The observations did not detect any companion in the substellar regime. Since null results can be as important as detections, we analyzed each observation to determine the characteristics of the companions that can be ruled out. For this purpose we use a Monte Carlo approach to produce artificial companions, and determine their detectability by comparison with the sensitivity curve for each star. All the non-detection results are combined using a Bayesian approach and we provide upper limits on the population of giant exoplanets and brown dwarfs for this sample of stars. Our nondetections confirm the rarity of brown dwarfs around solar-like stars and we constrain the frequency of massive substellar companions (M>40Mjup) at orbital separation between and 10 and 50 AU to be <20%.

Achromatizing a Liquid-Crystal Spectropolarimeter: Retardance vs. Stokes-Based Calibration of HiVIS

ABSTRACTAstronomical spectropolarimeters can be subject to many sources of systematic error that limit the precision and accuracy of the instrument. We present a calibration method for observing high-resolution polarized spectra using chromatic liquid-crystal variable retarders (LCVRs). These LCVRs allow for polarimetric modulation of the incident light without any moving optics at frequencies ≥10 Hz. We demonstrate a calibration method using pure Stokes input states that enables an achromatization of the system. This Stokes-based deprojection method reproduces input polarization even though highly chromatic instrument effects exist. This process is first demonstrated in a laboratory spectropolarimeter where we characterize the LCVRs and show example deprojections. The process is then implemented on the newly upgraded HiVIS spectropolarimeter on the 3.67 m Advanced Electro-Optical System (AEOS) telescope. The HiVIS spectropolarimeter has also been expanded to include broadband full-Stokes spectropolarimetry using achromatic wave plates in addition to the tunable full-Stokes polarimetric mode using LCVRs. These two new polarimetric modes in combination with a new polarimetric calibration unit provide a much more sensitive polarimetric package with greatly reduced systematic error.

SPECKLE SUPPRESSION THROUGH DUAL IMAGING POLARIMETRY, AND A GROUND-BASED IMAGE OF THE HR 4796A CIRCUMSTELLAR DISK

We demonstrate the versatility of a dual imaging polarimeter working in tandem with a Lyot coronagraph and adaptive optics to suppress the highly static speckle noise pattern—the greatest hindrance to ground-based direct imaging of planets and disks around nearby stars. Using a double difference technique with the polarimetric data, we quantify the level of speckle suppression, and hence improved sensitivity, by placing an ensemble of artificial faint companions into real data, with given total brightness and polarization. For highly polarized sources within 0. 5, we show that we achieve 3 to 4 mag greater sensitivity through polarimetric speckle suppression than simply using a coronagraph coupled to a high-order adaptive optics system. Using such a polarimeter with a classical Lyot coronagraph at the 3.63 m Advanced Electro-Optical System telescope, we have obtained a 6.5! detection in the H band of the 76 AU diameter circumstellar debris disk around the star HR 4796A. Our data represent the first definitive ground-based near-IR polarimetric image of the HR 4796A debris disk and clearly show the two outer ansae of the disk, evident in Hubble Space Telescope NICMOS/STIS imaging. Comparing our peak linearly polarized flux with the total intensity in the lobes as observed by NICMOS, we derive a lower limit to the fractional linear polarization of >29% caused by dust grains in the disk. In addition, we fit simple morphological models of optically thin disks to our data allowing us to constrain the dust disk scale height (2.5 +5.0 # 1.3 AU) and scattering asymmetry parameter (g =$ cos %= 0.20 +.07 # .10 ). These values are consistent with several lines of evidence suggesting that the HR 4796A disk is dominated by a micron-sized dust population, and are indeed typical of disks in transition between those surrounding the Herbig Ae stars to those associated with Vega-like stars.

ADAPTIVE OPTICS PHOTOMETRY AND ASTROMETRY OF BINARY STARS. III. A FAINT COMPANION SEARCH OF O-STAR SYSTEMS

Abstract : We present the results of an adaptive optics survey for faint companions among Galactic O-type star systems (with V 8) using the Advanced Electro-Optical System (AEOS) 3.6 m telescope on Haleakala. We surveyed these O-star systems in the I -band, typically being able to detect a companion with a magnitude difference of deltam(sub I) < or ~ 6 in the projected separation range 0.5 < rho < 1.0, and deltam(sub I) < or ~ 9.5 in the range 1.0 < rho < 5.0. In the course of the survey, we discovered 40 new companions among 31 of the 116 objects examined and made astrometric and differential magnitude measurements of 24 additional known pairs, several of them being confirmation detections. We present new astrometric orbits for two binaries, BU 1032AB (WDS 05387- 0236; sigma Ori AB) and SEE 322 (WDS 17158-3344; HD 155889AB). We lack magnitude differences for other filter bands, so it is difficult to determine physical from line-of-sight companions, but we present empirical arguments for the limiting magnitude difference where field contamination is significant.

Spectropolarimetric Observations of Herbig Ae/Be Stars. I. HiVIS Spectropolarimetric Calibration and Reduction Techniques

ABSTRACTUsing the High-Resolution Visible Spectrograph (HiVIS) spectropolarimeter built for the Haleakala 3.7 m Advanced Electro-optical System (AEOS) telescope in Hawaii, we are collecting a large number of high precision spectropolarimetric observations of stars. In order to precisely measure very small polarization changes, we have performed a number of polarization calibration techniques on the AEOS telescope and HiVIS spectrograph. We have extended our dedicated IDL reduction package and have performed some hardware upgrades to the instrument. We have also used the ESPaDOnS spectropolarimeter on CFHT to verify the HiVIS results with back-to-back observations of MWC 361 and HD 163296. Comparison of this and other HiVIS data with stellar observations from the Intermediate-dispersion Spectroscopic and Imaging System (ISIS) and William-Wehlau (WW) spectropolarimeters in the literature further shows the usefulness of this instrument.

Time-Resolved I-Band Photometry of Calibration Spheres and NaK Droplets

Wehave developed a program to obtain photometry of Earth-orbiting satellites using the U.S. Air Force advanced electrooptical system 3.6m telescope’s Visible Imager instrument, which acquires time-series charge-coupled device images at typical rates of 0.1 to 2.1 Hz. Observations of 12 spherical satellites provide measurements of I-band albedos (i.e., reflectances) and evaluation of surface nonuniformities. Best-fit specular diffuse albedo models enable brightness predictions and a means to grade the quality of the spheres as photometric calibration reference objects. CalSphere-4A appears to be the highest quality calibrator of the 12, with the best-fitmodel reproducing 90% of the measurements to within 0:03 stellar magnitudes. This four-decade-old sphere reflects in a predominantly diffuse fashion and has a total albedo of 67% that is somewhat lower than expected for fresh white paint, effects likely due to space weathering. The aluminum Lincoln Calibration Sphere-1 shows predominantly specular reflection (albedos 59%) but with 0:3 magnitude deviations between data and model that recur every 30–90 s, likely due to one or more surface irregularities. Three other predominantly specular aluminum spheres display less frequent but larger amplitude deviations. Observations indicate that sodium/potassium droplets leaked from Soviet radar ocean reconnaissance satellite reactors are highly reflective specular spheres that can also serve as optical calibrators.

Enhancing the resolution of spectral images from the Advanced Electro-Optical System Spectral Imaging Sensor

This research develops a model-based spectral image reconstruction (MBSIR) algorithm to reconstruct images collected from the Advanced Electro-Optical System (AEOS) Spectral Imaging Sensor (ASIS). The development of the algorithm requires two key elements: 1. the statistics of the photon arrival and 2. estimates of the spatial and spectral transfer functions. With these two elements, the MBSIR algorithm can, through image postprocessing, dramatically increase the resolution of the images as well as give insight into the performance of the imaging sensor itself. The MBSIR algorithm is designed to simultaneously improve both the spatial and spectral resolution, and is derived for the general case of a spectrally variant imaging system. While MBSIR algorithms can be developed for any spectral imaging system, this research focuses on ASIS, a new spectral imaging sensor installed with the 3.6-m AEOS telescope at the Maui Space Surveillance Complex (MSSC). The primary purpose of ASIS is to take spatially resolved spectral images of space objects. The low-light levels and object motion inherent in imaging some objects in space, such as satellites, lead to a sensor design with less spectral resolution than required for image analysis. However, by applying MBSIR to the collected data, the sensor will be capable of achieving a higher resolution, allowing for better spectral analysis. The algorithm is shown to work with simulated ASIS data and measured data from an ASIS-like sensor.

Adaptive Optics Photometry and Astrometry of Binary Stars. II. A Multiplicity Survey of B Stars

We carried out a search for companions to B stars using the adaptive optics system of the Advanced Electro-Optical System 3.6 m telescope. We observed 70 B stars in the I band, finding 16 companions, 10 of which are newly discovered companions. For each system with a detected companion we give its measured astrometry and differential magnitude. We then put the observation in context of the system's known multiplicity and provide a somewhat crude estimate of its spectral type based on the single differential magnitude measurement. The separations range from 0.2'' to 7.31'', and the differential magnitudes range from 1.41 ? 0.01 to 10.1 ? 0.5. Finally, we present a list of the null detections and discuss the implications of null detections of selected stars.

The New HiVIS Spectropolarimeter and Spectropolarimetric Calibration of the AEOS Telescope

ABSTRACTWe have designed, built, and calibrated a new spectropolarimeter for the HiVIS spectrograph (R ∼ 12,000–49,000) on the Advanced Electro‐Optical System (AEOS) telescope. We have also conducted a polarization calibration of the telescope and instrument. In this paper, we introduce the design and use of the spectropolarimeter, in addition to a new data‐reduction package we have developed, and then discuss the polarization calibration of the spectropolarimeter and the AEOS telescope. We used observations of unpolarized standard stars at many pointings to measure the telescope‐induced polarization and compare it with a Zemax model. The telescope induces polarization of 1%–6%, with a strong variation with wavelength and pointing, consistent with the expected altitude and azimuth variation. We then used scattered sunlight as a linearly polarized source to measure the telescope's spectropolarimetric response to linearly polarized light. Finally, we made an all‐sky map of the telescope’s polarization response to calibrate future spectropolarimetry.

Adaptive Optics Photometry and Astrometry of Binary Stars

We present astrometric and photometric measurements of 39 binary stars made with the adaptive optics system on the 3.6 m Advanced Electro-Optical System (AEOS) telescope, taken from 2002 November to 2003 March. The binaries have separations ranging from 008 to 511 and differential magnitudes ranging from 0.096 to 7.9. Also, we include a list of observations of 23 known binaries that we were unable to resolve. In the process of these measurements, we discovered three new companions to two previously known binary stars. We also discuss the effects of scintillation and anisoplanatism on measurements of binary star photometry in adaptive optics images. Suggestions on how to minimize these effects are then given.

The Lyot Project: Understanding the AEOS Adaptive Optics PSF

Adaptive optics (AO) systems have significantly improved astronomical imaging capabilities over the last decade, and are revolutionizing the kinds of science possible with 45 m class ground-based telescopes. A thorough understanding of AO system performance at the telescope can enable new frontiers of science as observations push AO systems to their performance limits. We look at the understanding we have gained from recent Lyot Project images at the Advanced Electro-Optical System (AEOS) 3.6 m telescope to show how progress made in improving WFR can be measured directly in improved science images. We describe how wave front errors affect the AO point-spread function (PSF), and model details of AEOS AO to simulate a PSF which matches the actual AO PSF in the astronomical H-band. Finally, we estimate the impact of improvements to wave front reconstruction techniques on diffractionlimited coronagraphy with the Lyot Project near-infrared coronagraph.

Scintillation and pupil illumination in AO coronagraphy

The Lyot Project near-infrared JHK coronagraph achieved first light on the Advanced Electro-Optical System (AEOS) in March 2004. Optical pupil plane imaging at video rates from this coronagraph provides data on atmospheric scintillation and quasi-static pupil intensity variations. We examine the effect of these variations on coronagraphic performance. Early simulations suggested Strehl ratio reductions of the order of 2–3% due to residual uncorrected phase aberrations in H-band. We find that static or quasi-static pupil illumination non-uniformity in I-band reduces Strehl by 2% in I-band. Some of the static intensity variations in the pupil are due to pinned deformable mirror (DM) actuators. We simulate the effects a pinned actuator has on the coronagraph. The resultant speckles in simulated coronagraphic images show similarities to some Lyot Project PSFs. This highlights the importance of knowledge of the pupil in next-generation extreme AO coronagraphs in order to realize the predicted photometric dynamic range of their images.

Observing the martian surface albedo pattern: Comparing the AEOS and TES data sets

High spatial resolution images of Mars were acquired with the Advanced Electro-Optical System (AEOS) 3.63-meter telescope at the Maui Space Surveillance System (MSSS) during both the 2001 and 2003 Mars apparitions. Comparisons are made of the surface albedo patterns obtained from these AEOS images to the surface albedo maps constructed from the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) data taken during the same time periods. These comparisons demonstrate that the images provide albedo information in a limited area surrounding the sub-Earth point that is consistent with the TES-derived albedo field. Additionally, it is shown that by employing adaptive optics (AO), the typical ground-based observing season of Mars can be extended. This is the only known published AO data set of Mars with temporal coverage over an entire apparition. Changes in the surface albedo affect the local ground temperature, which impacts the depth of the planetary boundary layer (PBL) above the surface. Since it is the state of the PBL that controls surface/atmospheric interaction, albedo variations have the power to alter the amount of dust that is lifted. A one-dimensional radiative/convective version of the NASA Ames Mars General Circulation Model is used to demonstrate that the measured albedo variations can alter the daytime ground temperatures by as much as 5 K, which in turn alters the structure of the planetary boundary layer (PBL). Therefore, albedo changes are thermodynamically important, and the ability to characterize them, should orbital observations become unavailable, is a valuable capability.

An Analysis of Fundamental Waffle Mode in Early AEOS Adaptive Optics Images11Based on observations made at the Maui Space Surveillance System, operated by Detachment 15 of the US Air Force Research Laboratory’s Directed Energy Directorate.

ABSTRACTAdaptive optics (AO) systems have significantly improved astronomical imaging capabilities over the last decade and are revolutionizing the kinds of science possible with 4–5 m class ground‐based telescopes. A thorough understanding of AO system performance at the telescope can enable new frontiers of science as observations push AO systems to their performance limits. We look at recent advances with wave‐front reconstruction (WFR) on the Advanced Electro‐Optical System (AEOS) 3.6 m telescope to show how progress made in improving WFR can be measured directly in improved science images. We describe how a “waffle mode” wave‐front error (which is not sensed by a Fried geometry Shack‐Hartmann wave‐front sensor) affects the AO point‐spread function. We model details of AEOS AO to simulate a PSF that matches the actual AO PSF in the I band and show that while the older observed AEOS PSF contained several times more waffle error than expected, improved WFR techniques noticeably improve AEOS AO performance. We estimate the impact of these improved WFRs on H‐band imaging at AEOS, chosen based on the optimization of the Lyot Project near‐infrared coronagraph at this bandpass.

Prolonging the Lifetime of Mirror Coatings with a Mirror Purge System11Based on observations made at the Maui Space Surveillance System, operated by Detachment 15 of the US Air Force Research Laboratory’s Directed Energy Directorate.

ABSTRACTMost ground‐based telescope mirror coatings are exposed to hostile environments, as the humidity, dust, and reactive gases in the air corrode and tarnish the coating. As the coating degrades the scatter increases. Eventually, every mirror needs to be recoated. This is a costly, time‐consuming process that requires telescope down time and involves risks to both people and to equipment. The AEOS (Advanced Electro‐Optical System) telescope has a mirror purge system that fills the mirror cell with dry air while the telescope is stowed. We present results conclusively demonstrating that this system extends the lifetime of the AEOS primary mirror coating, reducing the need for burdensome recoating.

ι Cassiopeiae: Orbit, Masses, and Photometry from Adaptive Optics Imaging in theIandHBands

The multiple-star system ι Cas was observed as a calibration for our adaptive optics observations in 2001 July with the Advanced Electro-Optical System (AEOS) 3.63 m telescope in Maui, Hawaii, and the first ever image of the faint astrometric component Aa (along with A and B) was obtained at the H-band wavelength. Another image was obtained in 2002 February with the same telescope, but that time in the I band. This wider image includes the C component and is the first to show four components. By combining our images with seven recent speckle interferometry measurements, a 47 yr period relative orbit is derived for the A-Aa components. Comparing the motion of B with respect to the A-Aa system, previous A-B orbits are rejected in favor of simple rectilinear motion of B across the field. Nevertheless, the history of the relative vector separation between B and A reveals the suborbital motion of A around its center of gravity with Aa, leading to a true orbit for A. The masses of A and Aa are thus determined to be 1.99 ± 0.28 and 0.69 ± 0.12 M☉, respectively. Combining our differential photometry in the I and H bands with B and V information from the Tycho-2 catalog, we derive spectral types for all four from their colors: component A is spectral type A3 with peculiar red colors, Aa is G6, B is F5, and C is K3.