We report on a timing analysis of archival observations of the anomalous X-ray pulsar 1RXS J170849.0À400910 made with the RXTE Proportional Counter Array. We detect a new large glitch (D= ' 3 Â 10 À6 ) that occurred between 2001 March 27 and May 6, with an associated large increase in the spin-down rate (D _ = _ ' 0:3). The short time (1.5 yr) elapsed from the previously detected glitch and the large amplitude of the new spin-up place this source among the most frequent glitchers, with large average glitch amplitudes, similar to those of the Vela pulsar. The source shows different recoveries after the glitches: in the first one it is well described by a long-term linear trend similar to those seen in Vela-like glitches; in the second case the recovery is considerably faster and is better described by an exponential plus a fractional change in the long-term spin-down rate of the order of 1%. No recovery of the latter is detected, but additional observations are necessary to confirm this result. We find minor but significant changes in the average pulse profile after both glitches. No bursts were detected in any light curve, but our search was limited in sensitivity with respect to short (t < 60 ms) bursts. Observed glitch properties are compared to those of radio pulsar glitches; current models are discussed in light of our results. It appears that glitches may represent yet another peculiarity of anomalous X-ray pulsars. Starquake-based models appear to be preferred on qualitative grounds. Alternative models can be applied to individual glitches but fail in explaining both. Thus the two events may as well arise from two different mechanisms.

Neptune has a collection of incomplete narrow rings, known as ring arcs, which should in isolation be destroyed by differential motion in a matter of months. Yet since ®rst discovered 1 by stellar occultations in 1984, they appear to have persisted 2±6 , perhaps through a gravitational resonance effect involving the satellite Galatea 6±8 . Here we report ground-based observations of the ring arcs, obtained using an adaptive optics system. Our data, and those obtained using the Hubble Space Telescope (reported in a companion paper 9 ), indicate that the ring arcs are near, but not within the resonance with Galatea, in contrast to what is predicted by some models.Our data set consists of nine 600-s exposures taken at the Canada±France±Hawaii telescope in Hawaii between 11:44 and 13:15 UT on 6 July 1998, using a 1.72-mm ®lter. After standard¯at-®elding and background subtraction, each image was deconvolved with an estimated point-spread function, clearly revealing some of the small inner satellites, namely Proteus, Larissa and Galatea, and more marginally, Despina. Neptune's centre was determined to within half a pixel (,0.017 arcsec) using both the motion of the satellites and the planet cloud cover. To enhance the signal-to-noise ratio, each pixel in individual images was rotated into Neptune's equatorial plane according to the orbital motion at the corresponding point, so as to show the neptunian system at a prescribed time, namely 12:29:39 UT (Earth time). A median ®lter was then applied when co-adding the nine images, while bright pixels near the planet were masked out. On this ®nal image, Proteus, Larissa, Galatea and the arcs are detected, while Despina is lost in the glare of the planet (Fig. 1).Small differences were found between the observed orbital phases of the satellites and those predicted from Voyager observations 10,11 . Proteus, Larissa and Galatea are respectively 0:0 6 0:3, 1:65 6 1:0 and 4:75 6 1:7 degrees ahead of their expected longitude. However, the accumulated nominal errors since the Voyager observations in August 1989 are respectively 2.9, 5.2 and 8.1 degrees for the three satellites. Thus, none of these discrepancies in longitude are signi®cant.The arcs appear in Fig. 1 as a region of enhanced intensity alongÐbut slightly outsideÐGalatea's orbit, near its maximum western elongation (right side of Neptune). Such a structure is clearly absent on the east side (left of Neptune). The arcs are embedded in a tenous ring, Adams, which is about ten times fainter than the arcs 4 , and is thus undetectable in our images. To eliminate the background illumination, the intensity distribution on the east side was locally ®tted by polynomials and then symmetrically subtracted from the west side. The arc intensity was then integrated over a width of 6 pixels (,0.2 arcsec) and plotted as a function of longitude (solid line in Fig. 2). This intensity is expressed in terms of an`equivalent width', E arc ; that is, the width of a perfect Lambert diffuser that would re¯ect sunlight at the distance of Neptune...

Abstract-Using an H-plot analysis, we identify 234 currently known near-Earth objects that are accessible for rendezvous with a "best case" delta-V of less than 7 km/s. We provide a preliminary compositional interpretation and assessment of these potential targets by summarizing the taxonomic properties for 44 objects. Results for one-half (22) of this sample are based on new spectroscopic measurements presented here. Our approach provides an easy-to-update method for giving guidelines to both observers and mission analysts for focusing on objects for which actual mission opportunities are most likely to be found. Observing prospects are presented for categorizing the taxonomic properties of the most accessible targets that are not yet measured.

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