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NOAO Newsletter - National Solar Observatory - September 2000 - Number 63


Another Busy Summer for Students at NSO

NSO 2000 Summer Student Advisors

This summer, NSO hosted five NSF-funded Research Experiences for Undergraduates (REU) students and one graduate student, or Summer Research Assistant (SRA), at NSO-Tucson, as well as three REUs and three SRAs at NSO-Sac Peak.

Lynn Carlson (REU, Michigan State) has been modifying IDL codes, originally written by Marc Buie of Lowell Observatory, to construct computer simulations of the full disk Sun. The objective is to explain the discrepancies observed between the amplitudes of variation of the Sun and those of solar-type stars, which may be dependent upon the angle of observation. Some of these models take into account facular, sunspot, and photospheric contributions to the Sun's total irradiance, while others focus on plage and network components of the Ca II K line. Such models allow her to explore the effects of varying the angle from which the Sun is viewed. She can compare the flux from the Sun in either the full spectrum or the Ca II K line, looking at the Sun from any viewpoint, and hopefully gain some insight into the reason for the difference in amplitudes. Lynn's advisor is Richard Radick.

Jose Ceja (REU, Cal State Northridge) has been working with Harry Jones to compare magnetograms from the KPVT NASA/NSO spectromagnetograph (SPM) with observations from GONG+ and SOHO/MDI. The purpose of these comparisons is to establish the mappings between the measurement scales of each of the instruments, both as a matter of intrinsic interest and in preparation for the replacement of the SPM with the SOLIS Vector Spectromagnetograph (SPM), especially if circumstances prevent a direct comparison between the VSM and SPM. Preliminary results suggest that GONG+ data (which are not in Gauss) need to be multiplied by a factor of about one-third to agree with SPM data, while the corresponding factor for SOHO/MDI is about two-thirds. A poster paper discussing the progress of this activity will be presented at the NSO­SP summer workshop on advanced polarimetry.

Jessica Erickson (REU, Wisconsin at Platteville) is working with Jack Harvey to improve the calibration of some of NSO's synoptic data products. Jessica has derived the coefficients of linear relations from 1977 through 2000 between two different measures of the strength of the 1083-nm helium line integrated over the solar disk. One of these series of measurements, used as a fundamental reference, consists of 3-day-per-month spectra of the 1083-nm line reduced to equivalent width and corrected for blending by water vapor lines. The second series consists of images of the Sun in the 1083-nm line taken daily at the Kitt Peak Vacuum Telescope (KPVT) and reduced to an average disk value of line strength. This is the first time that the cross-calibration has been done consistently over the entire available time period. The work has shown that the KPVT measurements need to be re-calibrated. After this is done, we will compare the (KPVT) results with measurements of the total solar irradiance from 1977 to the present. There is some evidence that this important flux is behaving differently during the present solar cycle than in previous cycles. Jessica has also used the same software to study variations in the zero point of KPVT measurements of the mean magnetic flux of the Sun. Again, corrections are required. This work is important for tying the existing data archive into forthcoming SOLIS observations.

Mike Eydenberg (REU, New Mexico Institute of Mining and Technology) has been working with Michael Sigwarth and Steve Keil in developing and applying image-processing techniques for analyzing images taken at the NSO Evans Facility and the Dunn Solar Telescope. With Michael Sigwarth, he has worked on a 45-minute time series of two-dimensional spectroscopic data of a complex active region obtained with the NSO dual Fabry-Perot spectrometer and the NSO Adaptive Optics system. He has applied interpolations and auto-correlation kernal-tracking algorithms for correcting the residual image motion and image distortion. From the spectral line scans, he obtained line-of-sight velocities. Together with horizontal flows, obtained by tracing continuum features, the three-dimensional velocity map can be obtained in order to investigate the interaction of magnetic fields and convection. With Steve Keil, Mike has developed and fine-tuned image-correction algorithms for Ca K spectroheliogram data taken by the Evans facility. The images are digitally circularized, destreaked, and calibrated. The goal is to have a set of processed Ca K data spanning over two full solar cycles for use in the further implementation of algorithms for correlating active region areas with Ca K line features and solar flux, as well as for the possi-bility of using the solar variations caused by these active regions as a means for measuring solar differential rotation.

Caption: NSO-Tucson REU 2000 students. From the left: James Roberts, Jessica Erickson, Kathryn Roscoe, Rebecca Pifer, and Jose Ceja.

Robert Gutermuth (SRA, Rochester) was an NSO-REU student last summer (1999) and graduated from Alfred University in May of 2000. He has investigated vorticity signatures calculated from chromospheric surface flows as precursors to solar activity. The data used were full disk Ha images taken with the NSO Hilltop Facility's flare patrol telescope during several days in the Spring and Summer of 2000. The data were scanned from 35-mm film, and the desired region of study was projected to disk center. The surface velocities in these projected images are determined from local correlation tracking of kernels within the active region. The results are obtained by comparing time sequences of intensities, velocity magnitudes, vor-ticities, and divergences of several particularly active sub-regions, and determining how far their peak values precede each other. Robert used line-of-sight magnetograms obtained by the Kitt Peak Vacuum Telescope, as well as images from the Yokhoh SXT and SoHO EIT space-based instruments, to evaluate the correlation between the vorticity signatures detected and magnetic fields in the active regions. Robert is working under the supervision of Steve Keil and K. S. Balasubramaniam, and plans to pursue his Ph.D. at the University of Rochester in the fall.

Kai Langhans (SRA, Kiepenheuer Institute) is work-ing on his Ph.D. thesis on the thermal structure of G-Band bright points and their formation. He is working with Thomas Rimmele on data obtained during the campaign at the German VTT in Tenerife, where the NSO low-order AO system was installed. At the Dunn Solar Telescope in August, Langhans and Rimmele carried out simultaneous observations at 430.5 nm with the horizontal spectrograph and a fast camera to acquire time series of G-Band spectra with high resolution both in space and time. The goal was to obtain information on possible reasons for the brightness of the G-Band bright points (increased dissociation of CH?) and the altitude of formation of the CH lines.

Erica Raffauf (REU, Indiana) has been working with Steve Keil on the comparison of disk-integrated Calcium II K-line spectra and K-line spectro-heliograms. The project goals are to understand how chromospheric features contribute to the K-line spectrum, attempt to use the line as a ground-based proxy for solar UV and EUV emissions, determine the disk-integrated flux's sensitivity to surface differential rotation, and use the disk-integrated flux to monitor the Sun as a star for comparison with similar stellar measurements. Changes in K-line parameters are indicative of chromospheric heating as well as solar activity levels. The data, covering 2.5 solar cycles, was obtained at NSO-SP--the disk-integrated data with the Littrow Spectrograph located in the Evans Solar Facility (ESF) and the disk-resolved spectroheliograms with the ECF spectroheliograph. Erica has developed algorithms to standardize digitized spectroheliograms, identify active regions, and compare image parameters with spectral line parameters. Erica is a physics major with minors in astronomy, mathematics, and Spanish. She has also had research experience in high-energy physics and photometry of open clusters.

Caption: NSO-Sac Peak REU 2000 students. From the left: Erica Raffauf, Eric Tatulli, Kai Langhans, Lynn Carlson, Robert Gutermuth, Axel Settele, and Michael Eydenberg.

James Roberts (REU, Virginia Tech) has been working with Mark Giampapa on the reduction and analysis of nightly photometry of the solar-age and solar-metallicity open cluster, M67. A small (0.5-m), automated telescope operated by Eric Craine of the Global Network of Automated Telescopes (GNAT) was utilized to monitor with CCD photometry the solar-type stars in M67. The objective of this program was to characterize the intranight and internight precisions that could be attained with the GNAT telescope and CCD. James reduced and analyzed approximately 25 nights of unfiltered, CCD photometry of a portion of the M67 cluster that includes many solar-type stars. This project is a prelude to a long-term program to detect and characterize short-term and long-term, low-amplitude variability in the solar counterparts in M67. He made a valuable contribution toward this goal by developing a systematic approach to the reduction of the numerous CCD images that are obtained for this kind of long-term program.

Kathryn Roscoe (REU, Cal State Chico) has been working with Rachel Howe on short-term temporal variations in the frequencies of solar modes measured by GONG. The aim of the project is to determine whether the solar cycle-related changes seen in data averaged over the usual 2- or 3-month periods can be followed on shorter time scales. Kathryn has analyzed six months of GONG data in 1-month and half-month chunks, covering two 3-month periods at different activity levels.

Markus Roth (SRA, Albert-Ludwigs University, Freiburg) is working on his Ph.D. thesis at the Kiepenheuer Institute for Solar Physics. He has been working with Rudolf Komm and Rachel Howe, studying the influence of velocity fields, located in the solar convection zone, on the frequency of p-modes. The goal is to determine whether it is possible to detect large-scale organized structures in the solar convection zone, so-called giant cells, by measuring mode frequencies. The existence of these giant cells is postulated, but they have not been unambiguously observed. Markus, building on his thesis work, developed a computer program to calculate the frequency shifts caused by a velocity field of a given geometry and strength, in addition to the shifts caused by the solar rotation. He calculated these shifts for complete mode sets, as observed by GONG, which allows him to compare the numerical results with observations. In addition, Markus determined p-mode parameters from a 108-day MDI data set to compare them with the corresponding GONG data set.

Axel Settele (SRA, Astrophysical Institute Potsdam) has concentrated on the oscillation of the magnetic field in sunspots and the transmission of waves through sunspots. Working with Michael Sigwarth, Axel obtained data at the Dunn Solar Telescope in June 2000 with the Advanced Stokes Polarimeter (ASP). He calibrated the data and analyzed a time series of one hour of a 6.3-arcsec segment of Active Region 9036. Each scan took about one minute and recorded the Stokes spectra in Fe 6301.5, Fe 6302.5, the line profiles of Fe 5691, and the Ca K line center. He calculated power spectra and phase shifts between the photospheric and chromospheric lines to compare these with his theoretical work, and looked for oscillations in the magnetic field.


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