| Research &
last updated March 30th 2013
High resolution spectropolarimetry can applied to stellar astrophysics in multiple ways. Stellar magnetic fields, circumstellar material and atmospheric phenomena give polarimetric signals that provide unique information about the object. HiVIS is a long-slit cross-dispersed echelle spectrograph on the 3.7m AEOS telescope with new polarimetric capabilities and high sensitivity. In early 2005, polarimetric capabilities were added with a Savart plate and rotating retarders mounted just behind the entrance slit. The spectrograph delivers resolutions of 15,000 to 50,000 by selecting different slit widths. Using a 4k by 4k CCID-20 mosaic detector and two cross-dispersers, the spectrograph covers wavelengths from 550nm to 1000nm. Single exposures typicall cover >250nm with complete wavelength coverage. The installation, testing and calibration of the polarization optics was mostly complete by mid 2005 with various upgrades and improvements ongoing. In 2010 the AEOS telescope was closed for repairs. In this period, upgraded CCD drive electronics were installed to allow for charge-shuffling synchronous with modulation of liquid crystal retarders. New calibration optics and techniques improved the absolute and differential accuracy of the spectropolarimeter. The charge-shuffling allows for modulations at ~1Hz speeds greatly improving the precision of the instrument, The liquid crystals allow for flexible tuning and optimization along with increased observing efficiency of many programs. Differential measurements with a signal-to-noise ratio above 10,000 are routinely achieved. In addition, the instrument was upgraded to include a low-resolution mode (R=1,000 to 3,000).
Adaptive Optics & H85
Adaptive optics is a critical component of many instruments on large telescopes. Instrument performance is improved by using a deformable mirror to remove optical distortions caused by the atmosphere. AO can also assist other techniques such as coronography or polarimetry by stabilizing the optical beam.
Curvature AO systems use a deformable mirror that applies curvature on sub-apertures of a piezo-electric bimorph mirorr substrate. Wavefront sensing is done with a custom lenslet array, optical fibers, high-speed modulation and avalanche-photodiode based photometry.
The 85-element curvature AO system, Hokupa'a 85, was built by the UH AO group and was deployed on the 8m Gemini South telescope. H85 was also the progenitor for another 85-element curvature AO system along with the Near-Infrared Coronagraphic Imager (NICI) on Gemini South. In the last few years, H85 has been adapted for use with the 3.7m AEOS telescope. In 2008, the optical design, mounts and mechanical structures were rebuilt to optimize H85 for throughput and faint object space situational awareness applications. Last year, the system was redesigned and rebuilt with a faster optical design and smaller packaging for stability and astronomical applications.
& Precision Polarimetry
In partnership with the Kiepenheuer Institute for Solar Physics, new polarimetric imaging technologies are being developed for Maui telescopes like AEOS, PLANETS, the Harlington 85cm and others. New nematic and ferro-electirc liquid crystals, temporal modulation schemes, charge shuffling CCDs and EMCCDs are making high precision instrumentation cost-effective. Using commercial technologies, new modulation techniques and calibration algorithms, imaging polarimetric instruments for small and large telescopes are substantially easier to develop. Collaboration with industry partners, component performance testing of optics and detectors as well as high-voltage drive electonic solutions have resulted from this project.
Absolute calibration of large telescopes can be challenging with off-axis, non-symmetric and time-dependent optical designs. The AEOS telescope, the new 4m Advanced Technology Solar Telescope (ATST) on Maui and other optically complex large telescopes such as the ELT produce strong instrumental polarization. Many science use cases requre system calibrations at the 1% to 0.01% levels. By using independent calibration techniques that do not rely on faint stellar targets, calibration injection units or other data-driven techniques, effeciency and accuracy are improved. By using bright and highly polarized daytime sky as a calibration source, the AEOS + HiVIS spectropolarimeter and Keck + LRISp spectropolarimeter have been successfully calibrated as a proof-of-technique. An IDL-based simulation and calibration package has been developed for use in HiVIS observations.
Pipelines and Simulation Tools
Major instruments are more efficient when they are supported by well documented and thoroughly benchmarked data reduction pipelines. Performance simulation tools are also useful to predict the likely impact of various noise and error sources. Software packages have been developed for processing data from spectropolarimeters, high-speed imaging polarimeters, fiber-fed imaging spectrographs and AO-assisted imaging instruments. For a few applications, end-to-end IDL and Matlab simulations were created to identify critical performance specifications needed to overcome various sources of instrument error. In addition, Zemax scripts for estimating likely sources of polarization calibration errors, wavelength and field dependences and other image degradations have been created.
interactions in binary stars
The physical properties and evolutionary pathways of binary stars can be strongly influenced by tidal interactions. Additionally, perturbations can cause systematic uncertainties in measuring the stellar properties. A new code based on a smoothed-particle-hydrodynamic model called TIDES was created to simulate eccentric asynchronous binary stars. Recent high precision spectroscopic observations suggested that perturbations repeat over multiple orbits. Systematic errors in estimating measured spectral line properties can alter the determined stellar parameters and alter data interpretations. Most atmospheric oscillation and perturbations codes are valid only for small perturbations from circular orbits and synchronous rotation or are valid under weak forcing regimes. This code was benchmarked and tested for numerical stability using a 40+ node linux cluster called Jotun at IfA Maui. A large grid of models was run under a range of stellar input parameters to investigate the code predictions. An observing campaign is underway to test the model predictions against observations at signal-to-noise ratios above 3,000.
Reserach-informed teaching &
Having a workforce and educational pathways that provide unbiased opportunities for students from local institutions is a critical part of doing technology work in Hawai'i. Including results from modern education research in classroom teaching venues, mentorship programs and research training improves the learner experience and creates an inclusive environment for people from diverse backgrounds.
The Akamai Workforce Initiative (AWI), Professional Development Program (PDP) and Institute for Science and Engineer Educators all are programs aimed at improving diverse representation in the tech workforce, science and education. The programs provide instruction in current research-informed educational techniques, teaches how to design and implement inquiry-based curriculum and how to effectively engage a culturally diverse classroom. Intensive teacher training seminars for graduate students, summer internship programs for undergraduates and workforce development events for the Hawai'i community are all part of these programs.
As an example, the Akamai Short Course is a one week intensive 3-credit STEM course taught by teams of 3-4 PDP participants and ISEE staff designd to prepare Hawai'i students for summer internships. These paid internships are focused on technology, observatory-related engineering and science for >30 students every year. These students have done extremely well over the past 10 years of the program, with 85% remaining on the 'STEM pathway'.
The circumstellar environment around a range of stellar targets is very complex. Phenomena such as accretion, stellar winds, circumstellar disks, magnetic fields and jets can exist simultaneously. The spatial scales for these phenomena can be from stellar radii to several AU. These regions are difficult to resolve and indirect remote sensing techniques are being developed to understand this near-star region.
High resolution polarized spectra of a star at very high signal-to-noise ratios provide such a tool. Absorption and scattering cause linear spectropolarimetric effects that depend on the atomic or molecular transition properties. HiVIS and other Mauna Kea instruments have been used to develop this new remote sensing tool.
Adaptive optics demonstrators are are functioning AO systems built on a breadboard for use in development, design, instruction and demonstration. A few have been built at the Center for Adaptive Optics (CfAO), Iris AO, UH Maui College (UHMC), and Hawaii Communitiy College (HCC). Various engineering and educational activities can be accomplished with a functioning AO system. These lab systems have been used for teacing graduate students and professionals at the CfAO summer school, in UHMC, HCC and UH Hilo classes. Additionally, AWI summer internship students have been involved in system integration, techology development and software improvements. Some of these educational activities were also part of the accreditation and approval of an Engineering Technology degree at UHMC during the transition from a 2-year to a 4-year college.
of Deep Impact:
The Deep Impact event was observed with the HiVIS spectropolarimeter July, 2005. Long-slit high-resolution spectropolarimetry on a bright comet was part of the ground-based support effort to characterize the impact-ejected material.
|DBIP - UH
2.2m Imaging Polarimeter:
Joe Masiero led a group that built a dual beam imaging polarimeter for the UH 2.2m telescope. This instrument delivered a polarimetric accuracy below 0.1% for point sources. The dual-beam instrument has a dedicated data reduction script and is open to the UH community. A savart plate provides two orthogonally polarized stellar images and two waveplates allow the measurement of the complete polarization state of the target. The polarimeter is mounted just upstream of the CCD in a compact configuration.
HiVIS has a near-infrared spectrograph channel which covers wavelengths from 1000nm to 2500nm. This IR spectrograph delivers resolutions from 7,000 to 30,000 using three different cross-dispersers optimized for J, H and K bands.