Steven Tomczyk

A compact dopplergraph/magnetograph suitable for space-based measurements of solar oscillations and magnetic fields

Abstract A compact Dopplergraph/magnetograph placed in a continuous solar-viewing orbit will allow us to make major advancements in our understanding of solar internal structure and dynamics. An international program is currently being conducted at JPL and Mt. Wilson to develop such an instrument. By combining a unique magneto-optical resonance filter with CID and CCD cameras we have been able to obtain full- and partial-disk Dopplergrams and magnetograms. Time series of the velocity images are converted into k-ω power spectra which show clear- the solar nonradial p-mode oscillations. Magnetograms suitable for studying the long-term evolution of solar active regions have also been obtained with this instrument. A flight instrument based on this concept is being studied for possible inclusion in the SOHO mission.

Measurements of Solar Internal Rotation Obtained with the Mt. Wilson 60-Foot Solar Tower

We have obtained estimates of the solar internal rotational velocity from measurements of the frequency splittings of p-mode oscillations. Specifically, we have analyzed a 10-day time series of full-disk Dopplergrams obtained during July and August 1984 at the 60- Foot Tower Telescope of the Mt. Wilson Observatory. The Dopplergrams were obtained with a Na magneto-optical filter and a 244 x 248-pixel CID camera. From the time series we computed power spectra for all of the prograde and retrograde sectoral p-modes from l = 0 to 200 and for all of the tessaral harmonics up to l = 89. We then applied a cross- correlation analysis to the resulting sectoral power spectra to obtain estimates of the frequency splittings. From l = 4 to l = 30 we obtained a mean value of the frequency spitting of roughly 450 nHz (sidereal) in close agreement with most previously published results, while from l = 40 to l = 140 we obtained a mean value of about 470 nHz. We believe that the latter value is slightly higher than the surface rotational splitting of 461 nHz because of possible confusion due to the temporal sidelobes introduced by the day/night observing cycle. Confirmation of this possibility will have to await our computation of tesseral power spectra for degrees greater than our current limit of 89. Finally, for degrees between 140 and 200, the frequency splittings are indistinguishable from the surface rotation rate.

Full-Disk Solar Dopplergrams Observed with a One-Megapixel CCD Camera and a Sodium Magneto-Optical Filter

We present here the first two full-disk solar Dopplergrams obtained with the new 1024 × 1024-pixel CCD camera which has recently been installed at the 60-Foot Tower Telescope of the Mt. Wilson Observatory. These Dopplergrams have a spatial resolution of 2.2 arcseconds and were obtained in a total of one minute of time. The Dopplergrams were obtained with a magneto-optical filter which was designed to obtain images in the two Na D lines. The filter and the camera were operated together as part of the development of a Solar Oscillations Imager (SOI) esperiment which is currently being designed at JPL for the joint NASA/ESA Solar and Heliospheric Observatory (SOHO) mission. We also include here two difference images obtained by subtracting two pairs of the Dopplergrams from the initial time series.

Estimates of the Solar Internal Angular Velocity Obtained with the MT. Wilson 60-Foot Solar Tower

We have obtained estimates of the solar internal angular velocity from measurements of the freguency splittings of p-mode oscillations. Specifically, we have analyzed a 16-day time series of full-disk Dopplergrams obtained during July and August 1984 at the 60-Foot Tower Telescope of the Mt. Wilson Observatory. From this time series we computed power spectra for all of the zonal, tesseral, and sectoral p-modes from l = 0 to 89 and for all the sectoral p-modes from l = 90 to 200. We next calculated a mean power spectrum for each degree up to 89 and then computed the frequency differences of all of the different non-zonal modes from these mean power spectra. The resulting freguency-difference curves for l = 1 to 89 were then expanded as a series of Legendre polynomials. For the odd-order terms in these expressions our results agreed reasonably well with the earlier results of Duvall, Harvey, and Pomerantz1. Next we combined the odd-order expansion coefficients into estimates of the solar internal equatorial rotational freguency splitting. We checked these estimates by similarly combining the published coefficients of Duvall, Harvey, and Pomerantz. We also compared our estimates with the earlier results of Hill and his colleagues at SCLERA. Our comparisons showed reasonably close agreement with the Duvall, Harvey, and Pomerantz results but sharp disagreement with SCLERA results.

Applications of the magneto-optical filter to stellar pulsation measurements

A proposed method of employing the Cacciani magneto-optical filter (MOF) for stellar seismology studies is described which is different from that employed by Fossat and his colleagues in Nice. The method relies on the fact that the separation of the filter bandpasses in the MOF can be changed by varying the level of input power to the filter cells. With the use of a simple servo system the bandpass of a MOF can be tuned to compensate for the changes in the radial velocity of a star introduced by the orbital motion of the earth. Such a tuned filter can then be used to record intensity fluctuations through the MOF bandpass over an extended period of time for each given star. Also, the use of a two cell version of the MOF makes it possible to alternately “chop” between the bandpass located in the stellar line wing and a second bandpass located in the stellar continuum. Rapid interchange between the two channels makes it possible for atmospheric-introduced noise to be removed from the time series.

The analysis of solar models–neutrinos and oscillations

Tests of solar neutrino flux and solar oscillation frequencies were used to assess standard stellar structure theory. Standard and non-standard solar models are enumerated and discussed. The field of solar seismology, wherein the solar interior is studied from the measurement of solar oscillations, is introduced.

Full-Disk Solar Dopplergrams Observed with a 1024 X 1024-Pixel CCD Camera

We present here the first full-disk solar Dopplergram obtained with the new 1024 x 1024-pixel CCD camera which has recently been installed at the 60-Foot Tower Telescope of the Mt. Wilson Observatory. This Dopplergram has a spatial resolution of 2.2 arcseconds and was obtained in less than one minute of time. The Dopplergram was obtained with a magneto-optical filter which was designed to obtain images in the two Na D lines. The filter and the camera were operated together as part of the development of a Solar Oscillations Imager (SOI) esperiment which is currently being designed at JPL for the joint NASA/ESA Solar and Heliospheric Observatory (SOHO) mission.

The 1984 Solar Oscillation Program of the Mt. Wilson 60-Foot Tower

We describe here the instrumentation, data, and preliminary results from the summer, 1984, solar oscillation observing program which was carried out using the 60-foot tower telescope of the Mt. Wilson Observatory. This program was carried out with a dedicated solar oscillation observing system and obtained full-disk Dopplergrams every 40 seconds for up to 11 hours per day. Between June and September, 1984, observations were obtained with a Na magneto-optical filter on 90 different days. The data analysis has progressed to the point that spherical harmonic filter functions have been employed to generate a few one-dimensional power spectra from a single day’s observations.