Activity in the quiet Sun

Macrospicules have been observed in H and He i D₃, on the disk and above the limb. In 1975, a rate of 1400 (A day)^–1 is inferred, and the ratio of equatorial to polar rates 2. D₃ intensities are a few × 10^–3 of the disk center, and do not decrease in coronal holes. The ratio of H to D₃ intensities is 10. The integral number of macrospicules with D₃ intensity I ₀ is proportional to I ₀ ^–1.     

Torsional waves on the Sun and the activity cycle

Some properties of the recently-discovered torsional oscillations of the Sun are presented. The detailed relation of this velocity feature to magnetic activity gives evidence that these motions represent a fundamental oscillation within the Sun that is responsible for the solar activity cycle and that they are not a natural consequence of an - dynamo. A new torsional oscillation with wave number 1 hemisphere^–1 is demonstrated to exist on the Sun.     

Are the high-latitude torsional oscillations of the sun real?

A numerical test is made to determine if the high-latitude torsional wave is generated from the low-latitude torsional pattern as a result of our reduction procedures. The results indicate that the high-latitude motions are not an artifact of the analysis, but are true solar features. We demonstrate also that the one-wave-per-hemisphere torsional oscillation does not result from the reduction procedure. These results place the observations in conflict with the predictions of - () models of the solar cycle.Now at Institute for Astronomy, University of Hawaii, Honolulu, Hawaii 96822, U.S.A.     

The Mees CCD imaging spectrograph

The Mees CCD (MCCD) instrument is an imaging spectroscopy device which uses the 25 cm coronagraph telescope and the 3.0 m Coudé spectrograph at Mees Solar Observatory (MSO) on Haleakala, Maui. The instrument works with resolving power up to R 200 000 with significant throughput from 3934 Å (Caii K) to 10 000 Å. A fast guiding active mirror stabilizes the image during observations. A rapidly writing magnetic tape storage system allows observations to be recorded at 256 kbytes s^–1. Currently, the MCCD is used for imaging spectroscopy of solar flares at 6563 Å (H), and velocity measurements of umbral oscillations; future plans include emission line studies of active region coronae, and photospheric studies of solar oscillations.     

Hα observations of the August 12, 1975 type III-RS bursts

We present H filtergram observations of a number of the Type III-RS (reverse slope) bursts that occurred on August 12, 1975. Solar radio emission was peculiar on that date in that a large number, and proportion, of the usually rare reverse slope bursts were observed (Tarnstrom and Zehntner, 1975). We show that the radio bursts coincide in time with a homologous set of H flares located at the limbward edge of spot group Mt. Wilson 19598. We propose a model in which the reverse slope bursts are the downward branches of U bursts, whose upward branches are hidden behind the coronal density enhancement over the spot group.     

Moving Dipolar Features in an Emerging Flux Region

Solar Physics - On 25 January, 2000, we observed active region NOAA&;nbsp;8844 with the Flare Genesis Experiment (FGE), a balloon-borne observatory with an 80-cm solar telescope. FGE was...     

The orientation of the solar rotation axis from Doppler velocity observations

Mt. Wilson observations of solar velocity fields have been examined for evidence that the rotation axis of the nonmagnetic gas at the solar surface is oriented differently than the axis found by Carrington (1863) from sunspot observations. No difference is found with an accuracy of 0°.15 in the angle of inclination of the axis to the ecliptic.     

The magnetic flux in the quiet sun network

The Ca ii K line emission from the quiet Sun network does not vary with the 11-year cycle (White and Livinston, 1981). We confirm this result from direct magnetic measurements. This effect is not simply explained by present empirical models of the evolution of surface magnetic fields.Now at Institute for Astronomy, University of Hawaii, Honolulu, Hawaii 96822, U.S.A.     

A measurement of the helium D3 profile with a birefringent filter

The D₃ line profile in plages on the disk is measured using a birefringent filter. The best fit Gaussian has a 1/e width of 0.4 Å, with negligible instrumental contribution. The D₃ opacity is produced in regions with thermal linewidth -0.1 Å; the much larger observed width indicates large non-thermal motions in the chromosphere.     

Photon Spectroscopy with Imaging X-Ray Instruments

Individual X-ray photons in the keV energy range produce hundreds of photoelectrons in a single pixel of a CCD array detector. The number of photoelectrons produced is a linear function of the photon energy, allowing the measurement of spectral information with an imaging detector system. Most solar X-ray telescopes, such as Yohkoh/SXT and Hinode/XRT, use CCD detectors in an integrating mode and are designed to make temperature estimates from multiband filter photometry. We show how such instruments can be used in a new way to perform a limited type of this photon spectroscopy. By measuring the variance in intensity of a series of repeated images through a single filter of an X-ray source, the mean energy per detected photon can be determined. This energy is related to the underlying coronal spectrum, and hence it can be used to deduce the mean plasma temperature. We apply this technique to data from the Yohkoh Soft X-Ray Telescope and compare the temperatures obtained with this technique with the temperatures derived using the standard filter ratio method for a postflare loop system. Given the large dynamic range of the soft X-ray flux observed from the Sun, we describe the requirements for a future instrument that would be better suited to performing photon spectroscopy. B.J. Labonte deceased 24 October 2005.