Dave Harrington Research

The Basic Focus:

My main interests are in new instrumentation, data analysis and in applying new technology. Star formation, circumstellar material, exoplanets and stellar physics are the focus of my research. There's a lot of interesting opportunity when combining science and engineering. By using new instruments and approaches or by combining techniques (like adaptive optics, polarimetry and coronography), we can get much more powerful remote sensing tools that provide new perspectives and insights. My main projects involve the HiVIS high-resolution spectropolarimeter on the 4m AEOS telescope, the 85-element curvature AO system, Hokupa'a-85 which we are adapting to AEOS and a new charge-shuffling imaging polarimeter for the PLANETS telescope. I've also been working with several large instrument designs such as the HySPI infra-red imaging spectropolarimeter on NASA SOFIA, PreCIP the AO-corrected charge shuffling polarimeter on AEOS and assisting with instrumentation for SOLARC and ATST. I find building instruments and working with new techniques to be fascinating. The independent perspective a new instrument brings can broaden our understanding of an object or clarify a problem (or create problems).

HiVIS Spectropolarimeter:

Spectropolarimetry of stars is a rapidly growing field, but there are only a handful of instruments available. There are only a few high resolution spectropolarimeters currently working on large telescopes (>3m). HiVIS is a long-slit cross-dispersed echelle spectrograph with the polarizing optics just behind the slit. The system works at R=15,000 to 50,000 using a 4k by 4k detector. The installation, testing and calibration of the polarization optics was mostly complete by mid 2005. A number of upgrades and fixes were done leading up to the 2006-2010 observing seasons before mechanical failure of the AEOS drive motors. I've led the development of a dedicated data-reduction pipeline and to do the polarization calibration of AEOS and HiVIS. Since HiVIS uses a coude path that has many oblique reflections before the polarization analyzer, calibration has been a major development area. We have developed new calibration techniques and analysis routines. In the last few years, our group has upgraded the electronics to allow for charge-shuffling synchronous modulation with liquid crystal retarders. This greatly improves the precision of the measurements, allows for flexible tuning and optimization of the system and increases the observing efficiency of many programs. We have also adapted the instrument to create a low-resolution mode (R=1,000 to 3,000) and we have upgraded the polarimetric components to allow standard full-Stokes achromatic modes.

Stellar Spectropolarimetry:

The circumstellar environment in many stellar classes is very complex and dynamic. There is accretion, winds, disks, magnetic fields and jets. These things often occur simultaneously and all are variable in time at some level. One major problems in understanding these processes is their small spatial scale - they occur mainly within a few stellar radii of the host star. Imaging with that kind of resolution and contrast even for the closest stars is difficult and new methods must be developed. High resolution polarized spectra of a star can be used to get information about this circumstellar region. Absorption and scattering cause linear spectropolarimetric effects from circumstellar disks, stellar winds, and other regions around the star that are quite large. Models of stellar magnetic fields predict circular polarization in spectral lines, but this effect is substantially weaker for stars with substantial circumstellar material. We've been observing various stars with AEOS/HiVIS (supported by CFHT/ESPaDOnS) and have an ongoing research project to develop spectropolarimetry as a powerful measurement tool for circumstellar material.

Exoplanets & Precision Polarimetry
Planets around other stars are hard to detet because of the small angular separation between the star and the planet as well as the extreme brightness contrast. Finding and characterizing exoplanets has become a very exciting topic in the last several years with the recent discovery and detection of hundreds of these systems. In partnership with the Kiepenheuer Institute for Solar Physics, we have begun development of a new charge-shuffling imaging polarimeter that aims to combine commercial technologies, new modulation techniques and use the upcoming 2m off-axis PLANETS telescope to achieve very high performance in accomplishing precision imaging polarimetry.

CfAO Professional Development &
Akamai Workforce Initiative

There is a network of interwoven programs designed to train future teachers (grad-students and post-docs) as well as to give local Hawai'i college students the tools to get in to grad school or to get a local technology-oriented job. There are a few programs I've participated in over the last three years for education training, mentoring and workforce development. My introduction was through the Professional Development Program (PDP) and Akamai Internship Program run by the former Center for Adaptive Optics at UC. Santa Cruz. This is now run under the Institute for Science and Engineer Educators. The program provides 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. There's an intensive 1-week seminar followed by a teaching requirement. I've been an instructor in the Akamai Maui Short Course for four years. This a one week intensive course (40 contact hours) taught by 3-4 PDP participants (with help) for Hawai'i students teaching basic optics and adaptive optics. These students then do a paid summer research project either with local companies (like Trex, Textron, H-nu photonics) or research organizations (like PDC, UH, IfA). These students do extremely well, with 85% remaining on the 'science pathway' and many geting job offers from their host organizations.

H85 & Curvature Adaptive Optics

Adaptive optics is quickly becoming a critical component of many instruments on large telescopes. By using a deformable mirror to remove the image motion and blurring caused by the atmosphere, the capability of an instrument is greatly increased. AO can also assist other techniques like coronography, polarimetry or spectroscopy. One first has to sense how the incoming light is distorted (with the wavefront sensor), then you have to correct it (with the deformable mirror). This is usually done now with a Shack-Hartmann wavefront sensor and a deformable mirror (typically with push-pull actuators). The incoming wavefront hits a lenslet array and gets broken up into an array of spots that are imaged and analyzed by software that reconstructs the wavefront shape. This wavefront shape is then sent to the deformable mirror to correct the beam.

Curvature based systems correct the beam in a moderately different way. The deformable mirror is a bi-morph and curves instead of operating by push and pull. In this system, the wavefront still hits a lenslet array, but the lenses feed avalanche photo diodes (APD's) through fibers. The lenslet is "put" upstream (extrafocal) and downstream (intrafocal) of the pupil by using an oscillating membrane mirror at an upstream focal plane allowing measurement of wavefront curvature. The lenslet array is mapped 1-to-1 with the deformable mirror simplifing the analysis. Since APD's are effectively noiseless, you can read fast and adapt your system in software for the right number actuators given the brightness your guide star.

The worlds second-largest curvature AO system, Hokupa'a 85, was built by the UH AO group and has been adapted for use with HiVIS. Hokupa'a is the progenitor for the 85-element system on the 8m Gemini South telescope (NICI).

CfAO - AO Summer School &
The IfA Maui AO Demonstrator:

AO demonstrators built people at LAO, CfAO, Iris AO, Maui Community College, and Hawaii Communitiy college are functioning AO systems built on a breadboard for use in development, design, instruction and demonstration. Various designs, capabilities and educational activities can be accomplished with a functioning AO system. After seeing an AO demonstrator work well at Maui Community College as an instructional tool in the Akamai Maui Short Course, I joined the lab instruction team for the 2008 & 2009 CfAO summer school in adaptive optics. We found that these demonstrators are a great tool for teaching geometric optics, phase conjugation and systems thinking to a wide range of learners - undergraduates, graduate students, professors entering the field and industry professionals. In the summer of 2009, I mentored an REU to build another AO demonstrator for IfA Maui in partnership with Iris AO, the UC. Santa Cruz Institute for Science and Engineer Educators and the LAO at UCSC. This system has been used for curriculum in various PDP activities, new college courses for the Engineering Technology BS program at U. Hawaii Maui College

Spectropolarimetry of Deep Impact:

We observed the Deep Impact event with the HiVIS spectropolarimeter July, 2005. This was a unique opportunity to try long-slit high-resolution spectropolarimetry on a bright comet, Tempel 1, and to be part of the huge ground-based support effort to characterize the ejected material. AEOS was one of a few to do polarimetry during the impact.

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 is quite useful, having a polarimetric accuracy well below .1% for point sources. It's simple, has a dedicated data reduction script and is open to the UH community. The design is different than most imaging polarimeters and it's designed specifically for point-sources. A savart plate provided two orthogonally polarized stellar images and two waveplates allow the measurement of the complete polarization state of the object (linear and circular). The polarimeter is mounted just upstream of the CCD. I provided some help with the concepts, the dedicated IDL reduction scripts, and initial calibration of some of the optics.

HiVIS & IR Spectropolarimeter:

HiVIS is really two spectrographs - one in the visible (450-950nm) and one in the near infra-red (1000-2500nm). The IR spectrograph is also a high-resolution (R~7000-30000) cross-dispersed echelle. It has three cross-disperser settings for J, H and K band. We've been working with the IR arm to build a spectropolarimeter.

	The Basic Focus: My main interests are in new instrumentation, data analysis and in applying new technology. Star formation, circumstellar material, exoplanets and stellar physics are the focus of my research. There's a lot of interesting opportunity when combining science and engineering. By using new instruments and approaches or by combining techniques (like adaptive optics, polarimetry and coronography), we can get much more powerful remote sensing tools that provide new perspectives and insights. My main projects involve the HiVIS high-resolution spectropolarimeter on the 4m AEOS telescope, the 85-element curvature AO system, Hokupa'a-85 which we are adapting to AEOS and a new charge-shuffling imaging polarimeter for the PLANETS telescope. I've also been working with several large instrument designs such as the HySPI infra-red imaging spectropolarimeter on NASA SOFIA, PreCIP the AO-corrected charge shuffling polarimeter on AEOS and assisting with instrumentation for SOLARC and ATST. I find building instruments and working with new techniques to be fascinating. The independent perspective a new instrument brings can broaden our understanding of an object or clarify a problem (or create problems).
	HiVIS Spectropolarimeter: Spectropolarimetry of stars is a rapidly growing field, but there are only a handful of instruments available. There are only a few high resolution spectropolarimeters currently working on large telescopes (>3m). HiVIS is a long-slit cross-dispersed echelle spectrograph with the polarizing optics just behind the slit. The system works at R=15,000 to 50,000 using a 4k by 4k detector. The installation, testing and calibration of the polarization optics was mostly complete by mid 2005. A number of upgrades and fixes were done leading up to the 2006-2010 observing seasons before mechanical failure of the AEOS drive motors. I've led the development of a dedicated data-reduction pipeline and to do the polarization calibration of AEOS and HiVIS. Since HiVIS uses a coude path that has many oblique reflections before the polarization analyzer, calibration has been a major development area. We have developed new calibration techniques and analysis routines. In the last few years, our group has upgraded the electronics to allow for charge-shuffling synchronous modulation with liquid crystal retarders. This greatly improves the precision of the measurements, allows for flexible tuning and optimization of the system and increases the observing efficiency of many programs. We have also adapted the instrument to create a low-resolution mode (R=1,000 to 3,000) and we have upgraded the polarimetric components to allow standard full-Stokes achromatic modes.
	Stellar Spectropolarimetry: The circumstellar environment in many stellar classes is very complex and dynamic. There is accretion, winds, disks, magnetic fields and jets. These things often occur simultaneously and all are variable in time at some level. One major problems in understanding these processes is their small spatial scale - they occur mainly within a few stellar radii of the host star. Imaging with that kind of resolution and contrast even for the closest stars is difficult and new methods must be developed. High resolution polarized spectra of a star can be used to get information about this circumstellar region. Absorption and scattering cause linear spectropolarimetric effects from circumstellar disks, stellar winds, and other regions around the star that are quite large. Models of stellar magnetic fields predict circular polarization in spectral lines, but this effect is substantially weaker for stars with substantial circumstellar material. We've been observing various stars with AEOS/HiVIS (supported by CFHT/ESPaDOnS) and have an ongoing research project to develop spectropolarimetry as a powerful measurement tool for circumstellar material.
	Exoplanets & Precision Polarimetry Planets around other stars are hard to detet because of the small angular separation between the star and the planet as well as the extreme brightness contrast. Finding and characterizing exoplanets has become a very exciting topic in the last several years with the recent discovery and detection of hundreds of these systems. In partnership with the Kiepenheuer Institute for Solar Physics, we have begun development of a new charge-shuffling imaging polarimeter that aims to combine commercial technologies, new modulation techniques and use the upcoming 2m off-axis PLANETS telescope to achieve very high performance in accomplishing precision imaging polarimetry.
	CfAO Professional Development & Akamai Workforce Initiative There is a network of interwoven programs designed to train future teachers (grad-students and post-docs) as well as to give local Hawai'i college students the tools to get in to grad school or to get a local technology-oriented job. There are a few programs I've participated in over the last three years for education training, mentoring and workforce development. My introduction was through the Professional Development Program (PDP) and Akamai Internship Program run by the former Center for Adaptive Optics at UC. Santa Cruz. This is now run under the Institute for Science and Engineer Educators. The program provides 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. There's an intensive 1-week seminar followed by a teaching requirement. I've been an instructor in the Akamai Maui Short Course for four years. This a one week intensive course (40 contact hours) taught by 3-4 PDP participants (with help) for Hawai'i students teaching basic optics and adaptive optics. These students then do a paid summer research project either with local companies (like Trex, Textron, H-nu photonics) or research organizations (like PDC, UH, IfA). These students do extremely well, with 85% remaining on the 'science pathway' and many geting job offers from their host organizations.
	H85 & Curvature Adaptive Optics Adaptive optics is quickly becoming a critical component of many instruments on large telescopes. By using a deformable mirror to remove the image motion and blurring caused by the atmosphere, the capability of an instrument is greatly increased. AO can also assist other techniques like coronography, polarimetry or spectroscopy. One first has to sense how the incoming light is distorted (with the wavefront sensor), then you have to correct it (with the deformable mirror). This is usually done now with a Shack-Hartmann wavefront sensor and a deformable mirror (typically with push-pull actuators). The incoming wavefront hits a lenslet array and gets broken up into an array of spots that are imaged and analyzed by software that reconstructs the wavefront shape. This wavefront shape is then sent to the deformable mirror to correct the beam. Curvature based systems correct the beam in a moderately different way. The deformable mirror is a bi-morph and curves instead of operating by push and pull. In this system, the wavefront still hits a lenslet array, but the lenses feed avalanche photo diodes (APD's) through fibers. The lenslet is "put" upstream (extrafocal) and downstream (intrafocal) of the pupil by using an oscillating membrane mirror at an upstream focal plane allowing measurement of wavefront curvature. The lenslet array is mapped 1-to-1 with the deformable mirror simplifing the analysis. Since APD's are effectively noiseless, you can read fast and adapt your system in software for the right number actuators given the brightness your guide star. The worlds second-largest curvature AO system, Hokupa'a 85, was built by the UH AO group and has been adapted for use with HiVIS. Hokupa'a is the progenitor for the 85-element system on the 8m Gemini South telescope (NICI).
	CfAO - AO Summer School & The IfA Maui AO Demonstrator: AO demonstrators built people at LAO, CfAO, Iris AO, Maui Community College, and Hawaii Communitiy college are functioning AO systems built on a breadboard for use in development, design, instruction and demonstration. Various designs, capabilities and educational activities can be accomplished with a functioning AO system. After seeing an AO demonstrator work well at Maui Community College as an instructional tool in the Akamai Maui Short Course, I joined the lab instruction team for the 2008 & 2009 CfAO summer school in adaptive optics. We found that these demonstrators are a great tool for teaching geometric optics, phase conjugation and systems thinking to a wide range of learners - undergraduates, graduate students, professors entering the field and industry professionals. In the summer of 2009, I mentored an REU to build another AO demonstrator for IfA Maui in partnership with Iris AO, the UC. Santa Cruz Institute for Science and Engineer Educators and the LAO at UCSC. This system has been used for curriculum in various PDP activities, new college courses for the Engineering Technology BS program at U. Hawaii Maui College
	Spectropolarimetry of Deep Impact: We observed the Deep Impact event with the HiVIS spectropolarimeter July, 2005. This was a unique opportunity to try long-slit high-resolution spectropolarimetry on a bright comet, Tempel 1, and to be part of the huge ground-based support effort to characterize the ejected material. AEOS was one of a few to do polarimetry during the impact.
	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 is quite useful, having a polarimetric accuracy well below .1% for point sources. It's simple, has a dedicated data reduction script and is open to the UH community. The design is different than most imaging polarimeters and it's designed specifically for point-sources. A savart plate provided two orthogonally polarized stellar images and two waveplates allow the measurement of the complete polarization state of the object (linear and circular). The polarimeter is mounted just upstream of the CCD. I provided some help with the concepts, the dedicated IDL reduction scripts, and initial calibration of some of the optics.
	HiVIS & IR Spectropolarimeter: HiVIS is really two spectrographs - one in the visible (450-950nm) and one in the near infra-red (1000-2500nm). The IR spectrograph is also a high-resolution (R~7000-30000) cross-dispersed echelle. It has three cross-disperser settings for J, H and K band. We've been working with the IR arm to build a spectropolarimeter.