3.3 Millimeter limb brightening measurements during the 30 June 1973 total solar eclipse

Solar limb brightening measurements at a wavelength of 3.3 mm were made during the 30 June 1973 total solar eclipse from a site at Lake Rudolf, Kenya. The results show that at this wavelength there is a limb brightening of about 20%, occurring within one half arc min of the limb.     

The X-ray Emission of NGC 1068

This paper summarises the X-ray properties of NGC 1068 from the observers perspective and reports new observations with the ROSAT HRI. Below ? 2 keV, the spectrum is steep and probably represents thermal emission from gas with temperature kT ? 0.1 - 0.6 keV. Above ? 2 keV, the spectrum is much flatter and may be described by a power-law with energy index α ? 0.3. Images with the ROSAT HRI reveal that about half the X-ray flux in the 0.1 - 2.4 keV band is extended on scales > 5″ (360 pc). Recent ROSAT PSPC observations of starburst galaxies show integrated soft X-ray spectra which are very similar to that of NGC 1068 below 2 keV. The spatially extended, steep, soft X-ray emission of NGC 1068 probably originates through thermal emission from a hot wind driven by the disk starburst, the Seyfert nucleus or a combination of the two. On the other hand, the hard emission above 2 keV is almost certainly dominated by the Seyfert nucleus.     

New views of Betelgeuse: multi-wavelength surface imaging and implications for models of hotspot generation

We report contemporaneous multi-wavelength interferometric imaging of the red supergiant star Betelgeuse ( α Orionis), using the Cambridge Optical Aperture Synthesis Telescope (COAST) and the William Herschel Telescope (WHT), at wavelengths of 700, 905 and 1290 nm. We find a strong variation in the apparent symmetry of the stellar brightness distribution as a function of wavelength. At 700 nm the star is highly asymmetric, and can be modelled as the superposition of three bright spots on a strongly limb-darkened disc. However, at 905 nm only a single low-contrast feature is visible and at 1290 nm the star presents a featureless symmetric disc. The change in spot contrast with wavelength is consistent with a model in which the bright spots represent unobscured areas of elevated temperature, owing perhaps to convection, on a stellar disc that itself has a different appearance, i.e. geometrical extent and limb-darkening profile, at different wavelengths. The featureless centre-to-limb brightness profile seen at 1290 nm is consistent with this model and suggests that future interferometric monitoring of the star to quantify the size changes associated with radial velocity variations should be performed at similar wavelengths in the near-infrared.     

Convergence of eclipsing binary solutions

Attention is called to the fact that convergence to negligible corrections in differential corrections solutions usually can be achieved, provided that one or both of two common causes of poor convergence are recognized and properly dealt with.     

Dust Trails of 8P/Tuttle and the Unusual Outbursts of the Ursid Shower

We calculate the position of dust trails from comet 8P/Tuttle, in an effort to explain unusual Ursid meteor shower outbursts that were seen when the comet was near aphelion. Comet 8P/Tuttle is a Halley-type comet in a 13.6-year orbit, passing just outside of Earth's orbit. We find that the meteoroids tend to be trapped in the 12:14 mean motion resonance with Jupiter, while the comet librates in a slightly shorter period orbit around the 13:15 resonance. It takes 6 centuries to decrease the perihelion of the meteoroid orbits enough to intersect Earth's orbit, during which time the meteoroids and comet separate in mean anomaly by 6 years, thus explaining the 6-year lag between the comet's return and Ursid outbursts. The resonances also prevent dispersion along the comet orbit and limit viewing to only one year in each return. We identified past dust trail encounters with dust trails from 1392 (Dec. 1945) and 1378 (Dec. 1986) and predicted another outburst on 2000 December 22 at around 7:29 and 8:35 UT, respectively, from dust trails dating to the 1405 and 1392 returns. This event was observed from California using video and photographic techniques. At the same time, five Global-MS-Net stations in Finland, Japan, and Belgium counted meteors using forward meteor scatter. The outburst peaked at 8:06±07 UT, December 22, at zenith hourly rate ∼90 per hour, and the Ursid rates were above half peak intensity during 4.2 h. We find that most Ursid orbits do scatter around the anticipated positions, confirming the link with comet 8P/Tuttle and the epoch of ejection. The 1405 and 1392 dust trails appear to have contributed similar amounts to the activity profile. Some orbits provide a hint of much older debris being present as well. This work is the strongest evidence yet for the relevance of mean motion resonances in Halley-type comet dust trail evolution.     

An early estimate for the size of cycle 23

Two features are found in the modern era sunspot record (cycles 10–22: ca. 1850-present) that may prove useful for gauging the size of cycle 23, the next sunspot cycle, several years ahead of its actual onset. These features include an inferred long-term increase against time of maximum amplitude (RM, the maximum value of smoothed sunspot number for a cycle) and the apparently inherent differing natures of even- and odd-numbered sunspot cycles, especially when grouped consecutively as even-odd cycle pairs. Concerning the first feature, one finds that 6 out of the last 6 sunspot cycles have had RM 110.6 (the median value for the modern era record) and that 4 out of 6 have had RM > 150. Presuming this trend to continue, one anticipates that cycle 23 will likewise have RM 110.6 and, perhaps, RM > 150. Concerning the second feature, one finds that, when one groups sunspot cycles into consecutively paired even-odd cycles, the odd-following cycle has always been the larger cycle, 6 out of 6 times. Because cycle 22 had RM = 158.5, one anticipates that cycle 23 will have RM > 158.5. Additionally, because the average difference between RM(odd) and RM(even) for consecutively paired even-odd cycles is 40.3 units (sd = 14.2), one expects cycle 23 to have RM 162.3 (RM = 198.8 ± 36.5 at the 95% level of confidence). Further, because of the rather strong linear correlation (r = 0,959, se = 13.5) found between RM(odd) and RM(even) for consecutively paired even-odd cycles, one infers that cycle 23 should have RM 176.4 (RM = 213.9 ± 37.5 at the 95% level of confidence). Since large values of RM tend to be associated with fast rising cycles of short ascent duration and high levels of 10.7-cm solar radio flux, cycle 23 is envisioned to be potentially one of the greatest cycles of the modern era, if not the greatest.     

A Comparison of Wolf's Reconstructed Record of Annual Sunspot Number with Schwabe's Observed Record of ‘Clusters of Spots’ for the Interval of 1826–1868

Samuel Heinrich Schwabe, the discoverer of the sunspot cycle, observed the Sun routinely from Dessau, Germany during the interval of 1826–1868, averaging about 290 observing days per year. His yearly counts of ‘clusters of spots’ (or, more correctly, the yearly number of newly appearing sunspot groups) provided a simple means for describing the overt features of the sunspot cycle (i.e., the timing and relative strengths of cycle minimum and maximum). In 1848, Rudolf Wolf, a Swiss astronomer, having become aware of Schwabe's discovery, introduced his now familiar ‘relative sunspot number’ and established an international cadre of observers for monitoring the future behavior of the sunspot cycle and for reconstructing its past behavior (backwards in time to 1818, based on daily sunspot number estimates). While Wolf's reconstruction is complete (without gaps) only from 1849 (hence, the beginning of the modern era), the immediately preceding interval of 1818–1848 is incomplete, being based on an average of 260 observing days per year. In this investigation, Wolf's reconstructed record of annual sunspot number is compared against Schwabe's actual observing record of yearly counts of clusters of spots. The comparison suggests that Wolf may have misplaced (by about 1–2 yr) and underestimated (by about 16 units of sunspot number) the maximum amplitude for cycle 7. If true, then, cycle 7's ascent and descent durations should measure about 5 years each instead of 7 and 3 years, respectively, the extremes of the distributions, and its maximum amplitude should measure about 86 instead of 70. This study also indicates that cycle 9's maximum amplitude is more reliably determined than cycle 8's and that both appear to be of comparable size (about 130 units of sunspot number) rather than being significantly different. Therefore, caution is urged against the indiscriminate use of the pre-modern era sunspot numbers in long-term studies of the sunspot cycle, since such use may lead to specious results.     

High resolution spectroscopy of the disk chromosphere

Two independent sets of high resolution time series spectra of the CaII H and K emission obtained at the Solar Tower and at the Big Dome of the Sacramento Peak Observatory on September 11th, 1971 are reported. The evolutionary behaviour of the emission first reported by Wilson and Evans is confirmed but the detail of the evolution is found to be more complex. In one case, a doubly peaked feature showing some K₃ emission evolves into a single K₂ (red) peak with no K₃ emission. Coincidentally, a neighbouring doubly peaked feature evolves to a very strong blue peak. In an entirely independent sequence a doubly peaked feature evolves into a single red peak. The K₂ emission then fades completely although the continuum threads are still strong. Finally a strong K₂ blue peak appears. These developments are confirmed by intensity profiles obtained from the spectra.Image motion during the sequences is measured using slit-jaw photographs and changes in the overall pattern of the spectra. It is found to be less than the size of the individual features, i.e. 1–2.While considering that the evolution can be explained by the relative motion of one feature with respect to another during the sequence, it is shown that it is possible to account for all these examples in this way only by invoking coincidence of a very high order.It is concluded that in these cases the observed evolution of the K₂ emission is due to temporal variations in the physical conditions which give rise to them.