office: 60 Garden Street
Room P-243
Mail stop 50
Cambridge, MA 02138
phones: 617-495-4984 or 496-7534
fax: 617-495-7455
page: 617-896-1241
mobile: 617-851-6924
e-mail: plsmith@cfa.harvard.edu
emergencies: 617-495-7289 (Donna Coletti),
For the 201-4/5 mission, I was the UVCS instrument scientist for the field work at GSFC and at Kennedy Space Center, leading the SAO team in the integration, alignment, co-registration, and functional tests both before and after the flights.
This WG is concerned with the in-orbit performance of UVCS: radiometric efficiency, instrument profile, scattered light, flat field, dispersion, pointing, dark counts, wavelength scale, distortion, etc. Many of these parameters are interrelated: for example, the efficiency is a function of aperture size; there is crosstalk between the grating and telescope mirror motions; and some are functions of time and/or use. The goal of the WG is to create comprehensive data analysis software and a calibration file that can be used to optimize the long term usefulness of the UVCS data.
In addition to my administrative role in the WG, I have been involved in UVCS observations designed to characterize aspects of its performance and in analysis of the resulting data. I have suggested improvements to the methods for determining the flat field; ways to evaluate the grating efficiency as a function of aperture; and new ways to look at stars, which are used as `standard candles' for radiometric calibration and for other instrument characterizations.
I also have some administrative roles in the UVCS SOHO program: I manage the Data Reduction Facility on behalf of the PI and am responsible for ensuring that the computer equipment necessary for analysis and archiving of UVCS data are available. I also created and help to maintain the UVCS Web Page and the list of UVCS publication contained there.
My experience with radiometric measurements led to an invitation from Dr. Martin Huber (Head, Space Science Department, ESTEC) to join him in writing a review article for Astronomy & Astrophysics Reviews titled Spectroradiometry in astronomy: the case of spectrometric space telescopes. Our goal is to review the current state of radiometric calibration of telescope-fed spectrometers on astronomical satellites and point out the need for improvements.
Because of the high resolution of the PF spectrometer, and the availability at the PF of a supersonic jet expansion device for cooling gases to a few 10's of Kelvin, our work is the first to permit the quantitative study of individual rotational lines and measurement of line f-valued. This is an important advance for astronomically motivated work because the molecular bands are frequently perturbed; as a consequence, the properties of individual lines, which are easily seen in astronomical spectra of cold objects where only a few rotational levels are populated, cannot be predicted from band properties.
CO is the second most abundant astrophysical molecule. We have measured photoabsorption cross sections of molecular bands and/or lines that can be used for abundance determinations and are required for models of the photochemistry of translucent clouds. Our work resolved some controversies about the magnitude of the oscillator strengths (f-values) of the bands of the strong A(n)-X(0) system. Now we are working on the first measurements of line f-values for some intersystem (spin-changing) bands. These bands are weak -- they are forbidden by L-S selection rules and owe their strength only to perturbations -- and can be useful for abundance determinations in regions where the stronger A-X bands are saturated.
We have also studied the VUV absorption spectrum of N2, the major constituent of the atmospheres of Titan, Triton, and the Earth. We have measured band oscillator strengths, absorption cross sections, and line widths. In particular, we measured line f-values for the very strong, and strongly perturbed, c4'(0)-X(0) band -- the first such measurement for individual VUV lines. The lines are important features of the airglows of N2 atmospheres and are the most likely signature of N2 in interstellar clouds.
The current focus of the work on atoms is Fe III (Fe+2). Improved data for this and many other ions are required to meet the needs of the high resolution spectra obtained by HST. In many cases, the existing atomic data are not adequate for identifying components of blended features in the spectra of stellar atmospheres.
Several years ago, the IC group was wrapping up a massive remeasurement and reanalysis of the wavelengths, energy levels, and oscillator strengths of the singly charged ions of the iron group. However, they were stymied in their attempts to move on to doubly charged ions because work with the FT spectrometer requires a stable (or pulsed but reproducible) light source containing the ions of interest. I proposed, and eventually negotiated a supplement to Parkinson's NASA grant to purchase a Penning discharge that proved to be a suitable source for the purpose. With this source, Pickering and I have improved by an order of magnitude the accuracy of wavelengths for more than 1000 strong lines of Fe III . Our plan is to carry out measurements on other doubly charged ions of the iron group shortly.
The second project at IC involves measurement of the photoabsorption cross section of SO2; Glenn Stark is collaborating in this effort as is James Rufus of Harvard. The motivation is the study of the atmospheres of Venus and Jupiter's moon Io. We're using the high resolution of the VUV FT spectrometer in order to resolve the very complex SO2 spectrum. Because of numerous strong perturbations, this spectrum has not been analyzed in detail; as a consequence, room temperature measurements cannot be used to predict the spectrum at Io temperatures, which range from 150 K to 600 K, depending upon location. Therefore, we are making the first high resolution measurements (lambda/dlambda ~ 400,000) at several temperatures, viz., 295 K and 170 K.
I took the lead role in creating the Division WWW page and in creating and maintaining the database resource. This resulted in the large Kurucz and Kelly databases of atomic lines and energy levels being available `on line' for the first time. I represented the Division on the ad hoc CfA Data Policy Committee.
In the laboratory, I advised the thesis research of Adrian Daw, brought the need for CO2 cross sections to the attention of Parkinson, who proposed for and received support for this work. I proposed that the PAPA detector would very useful in our work at the PF, and suggested that SAO IR&D funds be obtained for development of such a detector.
With Wolfgang Wiese, I proposed, organized, and edited the proceedings for a Joint Commission Meeting titled Atomic and Molecular Data for Space Astronomy: Needs, Analysis, and Availability at the 21st IAU General Assembly (GA). I was co-chair of the committee which organized a Joint Discussion titled Atomic & Molecular Data for Astrophysics: New Developments, Case Studies, Future Needs held at the recent GA in Manchester.
I suggested, and with Parkinson proposed and was co-chair of the organizing committee for, the NASA Laboratory Space Science Workshop held at Harvard in 1997. This meeting brought together over 100 NASA-funded laboratory astrophysicists and astronomers who use atomic and molecular physical and chemical parameters, as well as the properties of dust and grain surfaces. I am currently trying to persuade NASA to hold a subsequent workshop on this topic.
On a broader scale, I have been on organizing committees for several of the ICAMDATA (International Conferences on Atomic and Molecular Data and Their Applications) meetings. I am also on the International Organizing Committee for the ASOS (Atomic Spectra and Oscillator Strength) meetings. Both of these series have astrophysical needs as a major component.
Additional papers can be found through searches of the ADS Instrumentation database and the ADS Physics and Geophysics database. Beware of false `hits'.