A new era of observational capability at Ritter Observatory spectropolarimetry from exoplanets to circumstellar disks and beyond The University of Toledo The University of Toledo Digital Repository Th[.]
The University of Toledo The University of Toledo Digital Repository Theses and Dissertations 2013 A new era of observational capability at Ritter Observatory : spectropolarimetry from exoplanets to circumstellar disks and beyond James W Davidson The University of Toledo Follow this and additional works at: http://utdr.utoledo.edu/theses-dissertations Recommended Citation Davidson, James W., "A new era of observational capability at Ritter Observatory : spectropolarimetry from exoplanets to circumstellar disks and beyond" (2013) Theses and Dissertations Paper 59 This Dissertation is brought to you for free and open access by The University of Toledo Digital Repository It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of The University of Toledo Digital Repository For more information, please see the repository's About page A Dissertation entitled A New Era of Observational Capability at Ritter Observatory: Spectropolarimetry from Exoplanets to Circumstellar Disks and Beyond by James W Davidson Jr Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Physics & Astronomy Dr Karen S Bjorkman, Committee Chair Dr Robert W Collins, Committee Member Dr S Thomas Megeath, Committee Member Dr J.D Smith, Committee Member Dr John P Wisniewski, Committee Member Dr Patricia R Komuniecki, Dean College of Graduate Studies The University of Toledo May 2013 Copyright 2013, James W Davidson Jr This document is copyrighted material Under copyright law, no parts of this document may be reproduced without the expressed permission of the author An Abstract of A New Era of Observational Capability at Ritter Observatory: Spectropolarimetry from Exoplanets to Circumstellar Disks and Beyond by James W Davidson Jr Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Physics & Astronomy The University of Toledo May 2013 We undertook efforts to restore and relocate the University of Wisconsin’s HalfwavePolarimeter (HPOL) spectropolarimeter to the University of Toledo’s Ritter Observatory This process required fairly extensive work to the optical-mechanical alignment of the Ritter Observatory 1-meter telescope Ultimately the restoration and relocation efforts were successful, with first light at Ritter Observatory on March 11th, 2012 Extensive observations of unpolarized standard stars were carried out in the first six months of observing time at Ritter Observatory The results of this effort has shown the polarimetric stability in the observations is at the same level or better compared to almost 10 years of observations at Pine Bluff Observatory, after the upgrade to the detector Aside from continued spectropolarimetric monitoring programs which were initially focused on a selection of Be and Wolf-Rayet stars, we sought to investigate potential polarimetric variability in exoplanet systems In particular we focused on the system HD189733, as there was previous observational work in the literature claiming both a detection and non-detection at different optical wavelengths The goal was to investigate this system with HPOL to provide simultaneous observations across the entire optical wavelength range to investigate the possibility of a wavelength dependent variable polarization with orbital phase While the variability claimed in iii the literature is below the noise limits of our observations, an interesting and yet unexplained increase in the polarization level occurred in one of our observations This higher than expected signal had vanished by the next observation, which was several nights later due to weather, and did not reappear in any of the observations thereafter, implying such a higher than expected signal must be short lived, lasting less than a couple orbital periods This increase is around an order of magnitude larger than the claimed detection in the literature from light scattering off the exoplanets atmosphere, and would seem to be caused by some other physical mechanism in the system Continued observations of HD189733 with HPOL in the next observing season starting in July 2013 will help to identify if the increased polarization level is repeatable iv To my family Acknowledgments I would like to thank my advisor, Karen Bjorkman, for all her assistance and support during this work; Jon Bjorkman for many great discussions and for all his guidance in collimating the Ritter Observatory 1-meter telescope; and my committee members for all their help, particularly John Wisniewski I would like to thank those involved in the HPOL efforts: From Denver University, Jennifer Hoffman and Jamie Lomax; From the University of Wisconsin at Madison, HPOL creator Ken Nordsieck, Brian Babler for help with the calibration, Marilyn Meade for help with data reduction, Rick Williams for technical help with HPOL, and Richard Bonomo for help restoring the HPOL control computer; And from the University of Toledo, Rick Irving for computer assistance, Ashok Bhandary for helping testing HPOL in the lab, Mike Brown for help getting HPOL operating on the Ritter 1-meter telescope, Adolf Witt for all his help in regards to Ritter Observatory, and Scott Lee for generously loaning the optical equipment used to collimate the telescope I would like to thank my office mates for the better part of six years, Charles Poteet and Blagoy Rangelov, for many great conversations I would also like to thank my family and friends for all their support over the years, in particular my soon to be wife, Kăara Lindelof, who moved to Toledo with me and has been a tremendous source of support Thank you, and I love you all This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France This work has been partially funded by a Small Research Grant from the AAS, and by the Scott E Smith Fund for Research at Ritter Observatory vi Contents Abstract iii Acknowledgments vi Contents vii List of Tables xi List of Figures xii List of Abbreviations xvi Introduction 1.1 Background on Polarization 1.2 Solar System Polarization 1.3 Polarization of Unresolved stars 1.4 Polarization of Circumstellar Material 11 1.5 Polarization of Exoplanet Systems 11 1.5.1 Scattered Light from an Exoplanet Atmosphere 12 1.5.2 Using Exoplanets to Probe Limb Polarization of Host Stars 13 1.5.3 Starspots as a Source of Variable Polarization 16 The HPOL Spectropolarimeter 18 2.1 History of the Instrument 18 2.2 Description of the Instrument 19 vii 2.3 2.2.1 Arc and Flat Lamp Assembly 19 2.2.2 Polarizing Prism 22 2.2.3 Slit & Decker Assembly 23 2.2.4 Filters 24 2.2.5 Halfwave Plate 24 2.2.6 Cylindrical Lens 25 2.2.7 Wollaston Prism 26 2.2.8 Gratings 29 2.2.9 Camera 30 2.2.10 Detector 30 The End of the PBO Era 31 Restoration & Relocation 3.1 33 Restoring HPOL to Operation 33 3.1.1 Control System Software Restoration 33 3.1.2 Slit Camera Replacements 34 3.2 Relocation to Ritter Observatory 34 3.3 New Layout of Equipment 35 Ritter Observatory 4.1 37 Telescope Collimation 38 Optical Aberrations 38 4.1.1.1 Spherical 38 4.1.1.2 Coma 39 4.1.1.3 Astigmatism 40 4.1.2 Two Mirror Mis-alignments 43 4.1.3 Collimating the Ritter Observatory 1-meter Telescope 45 4.1.4 Development of a New Collimation Procedure 45 4.1.1 viii Optical Table Assembly 46 4.1.4.2 Defining the Telescope Optical Axis 47 4.1.4.3 Setting the Rotation of the Secondary Mirror Ring 60 4.1.4.4 Aligning the Secondary Mirror Housing Assembly and Spider with the Telescope Optical Axis 62 4.1.4.5 Adjusting the Tilt of the Secondary Mirrors 65 4.1.4.6 Adjusting the Tilt of the Primary Mirror 67 4.1.4.7 Final Adjustments On-Sky 68 4.1.5 Installing Monofilament Crosshairs 72 4.1.6 Identification and Solution to a Flexure Issue in Secondary Mirror Assembly 73 Extender for HPOL 74 Summary of Telescope Collimation 75 4.1.7 4.2 4.1.4.1 Polarization Calibration 77 5.1 Observing Unpolarized Stars 79 5.2 Constructing a Calibration File 80 5.3 The Final Calibration File 97 5.4 Comparison With 10 Years of Previous PBO Calibration Work 103 Polarimetric Observations of the Exoplanet System HD189733 107 6.1 Observations 108 6.2 Data Reduction 109 6.3 Results 111 6.4 Higher Than Expected Signal 113 6.5 Conclusions 129 Future Work 130 ix Figure 7-1 φ-Per results from PBO Observation from February 16, 2004 Standard tri-plot for HPOL data with Fλ at the top, %POL in the middle and position angle on the bottom The %POL and P.A have been binned to a constant error of 0.03% 134 Figure 7-2 φ-Per results from Ritter Observation from August 29, 2012 Standard tri-plot for HPOL data with Fλ at the top, %POL in the middle and position angle on the bottom The %POL and P.A have been binned to a constant error of 0.03% 135 Figure 7-3 ψ-Per results from PBO Observation from February 18, 2004 Standard tri-plot for HPOL data with Fλ at the top, %POL in the middle and position angle on the bottom The %POL and P.A have been binned to a constant error of 0.03% 136 Figure 7-4 ψ-Per results from Ritter Observation from November 29, 2012 Standard tri-plot for HPOL data with Fλ at the top, %POL in the middle and position angle on the bottom The %POL and P.A have been binned to a constant error of 0.02% 137 Figure 7-5 π-Aqr results from PBO Observation from October 10, 2004 Standard tri-plot for HPOL data with Fλ at the top, %POL in the middle and position angle on the bottom The %POL and P.A have been binned to a constant error of 0.025% Figure 7-5 is the last observation of the Be star π-Aqr taken from PBO, while Figure 7-6 is the first observation from Ritter An increase in the polarization can be seen between PBO, Figure 7-5, and Ritter, Figure 7-6 There is also a change in the position angle associated with the increased polarization, from ∼140° in the PBO results to ∼150° in the Ritter results The polarization Balmer Jump and Paschen Jump have reappeared, signifying a strengthening of the disk Figure 7-7 is the last observation of the Be star ζ-Tau taken from PBO, while Figure 7-8 is the first observation from Ritter As seen for the other stars, there is a significant improvement in the Ritter results compared to PBO This time the level 138 Figure 7-6 π-Aqr results from Ritter Observation from August 31, 2012 Standard tri-plot for HPOL data with Fλ at the top, %POL in the middle and position angle on the bottom The %POL and P.A have been binned to a constant error of 0.02% 139 Figure 7-7 ζ-Tau results from PBO Observation from October 3, 2004 Standard tri-plot for HPOL data with Fλ at the top, %POL in the middle and position angle on the bottom The %POL and P.A have been binned to a constant error of 0.08% of polarization decreased, however it appears the amount of H-α emission has also decreased The results from Ritter again show some outstanding data Not only is H-α seen to be de-polarized, it is easy to pick out additional lines in the Balmer series: H-β, H-γ, H-δ and H-ǫ 7.5 Conclusions The HPOL spectropolarimeter is collecting data and producing great results Several future improvements to the polarization calibration file, such as the removal of β-Cas as an unpol for HPOL and the truncation of the calibration around 3200˚ A 140 Figure 7-8 ζ-Tau results from Ritter Observation from November 29, 2012 Standard tri-plot for HPOL data with Fλ at the top, %POL in the middle and position angle on the bottom The %POL and P.A have been binned to a constant error of 0.02% 141 will finalize the data reduction process Once these final adjustments are complete, observations taken with HPOL at Ritter Observatory will be prepared for publication The restoration of faint-mode observation with HPOL should greatly benefit the study of the exoplanet system HD189733 by increasing the signal-to-noise and number of observations This mode will also open up additional observational capability for other scientific projects with HPOL Monitoring 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