Stellar photometry at the South Pole

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Figure 1. Spectra of p,-mode oscillations with 5 values of I. The ordinate is m, ranging from m = + I (retrograde sectoral harmonics) to m = 0 (zonal harmonics) to m = -I(prograde sectoral harmonics). The tilt is produced by solar rotation, which removes the degeneracy of m.

tion rate, which decreases with heliolatitude. Within the variations in the latitude dependence of the angular velocity of surface features during the solar activity cycle, the odd-indexed coefficients, which carry information about rotation, do not vary with 1. The even-indexed coefficients provide information about the latitude variation of sound speed versus depth. If the internal structure of the Sun were independent of latitude, the even coefficients should be zero. The fact that they differ significantly indicates that the structure of the convection zone is different near the equator compared with higher latitudes. These unexpected results could have profound implications for theories of the origin of the solar magnetic field and solar activity. More surprises are likely to unfold as the analysis of the data in hand continues. This work was supported in part by National Science Foundation grant DPP 81-19627.

Stellar photometry at the South Pole K.Y. CHEN, J.P. OLIVER, and F.B. WOOD Department of Astronomy University of Florida Gainesville, Florida 32611

The south pole optical telescope (SPOT) was designed, constructed, and tested in Gainesville, Florida in 1985. The design is modified somewhat from the telescope operated at the pole in 1986 REVIEW

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Figure 2. Comparison of coefficients a i determined from the spatially resolved solar oscillation measurements with the values calculated from observations of the rotation of surface features. These results provide information about the latitude and depth dependence of the rotation rate and the Sun's internal structure.

References Duvall, T.L., Jr., J.W. Harvey and M.A. Pomerantz. 1986. Latitude and depth variation of solar rotation. Nature, 321, 500-501. Harvey, J. , M. Pomerantz, and T. Duvall, Jr. 1982. Astronomy on ice. 64(6), 520-523. Pomerantz, MA., J.W. Harvey, and T. Duvall, Jr. 1982. Large-scale motions and structure of the Sun. Antarctic Journal of the U.S., 17(5),

232-233.

the winter of 1984 (Giovanne et al. 1983; Wood et al. 1984). The telescope is a twin-mirror siderostat with a 8-centimeter achromatic lens which collects and brings the light to focus at the field stop. After passing an optical filter and a Fabry lens, the light reaches a photomultiplier which measures the brightness of a selected star or sky. The function of SPOT is controlled by an AIM-65 computer. Data are recorded on floppy disk. The telescope and computer were installed in January 1986 by Oliver and McNeil! after Wood's December 1985 trip to the pole to review site preparation and station nighttime lighting plans. The telescope system is housed in a special insulated building, 12 foot x 8 foot X 8 foot, constructed by the carpenters of ITT Antarctic Services. Only the optical head of SPOT is exposed to the harsh outside environment. The telescope is in a separate 281

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room which can be heated when service is required. The computer is in a smaller room which is kept warm to protect the electronics. A picture of SPOT, before set up inside the building, is shown in the figure. During the twilight hours, the telescope system was carrying out tests while awaiting darkness. Engineering data have been sent back to Florida via the ATS-3 communications satellite with control computer at Malabar, Florida. During the austral winter 1986, SPOT is carrying out photoelectric observations of four selected stars—gamma-2 Velorium, alpha and beta Gruis, and HR3452--as well as the sky brightness at selected regions. This research project is planned for the study of light variation of gamma-2 Velorium. The South Pole as a site for stellar photometry can be evaluated also. This work was supported in part by National Science Foundation grants DPP 82-17830 and DPP 84-14128.

References

The south pole optical telescope before installation in its building. (Photo by Bill Murphy.)

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Giovanne, F., F.B. Wood, J.P. Oliver, and K.-Y. Cheri. 1983. Automatic South Pole telescope. In R.M. Genet (Ed.), Microcomputers in astronomy. Fairborn, Ohio: Fairborn Observatory. Wood, EB., K.-Y. Chen, C. Schneider, and F. Gioanne. 1984. South Pole astronomical observatory. Antarctic Journal of the U.S., 19(5), 237-238.

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