A Side of Mercury Not Seen By Mariner 10

More than 60,000 images of Mercury were taken at ~29 deg elevation during two sunrises, at 820 nm, and through a 1.35 m diameter off-axis aperture on the SOAR telescope. The sharpest resolve 0.2" (140 km) and cover 190-300 deg longitude -- a swath unseen by the Mariner 10 spacecraft -- at complementary phase angles to previous ground-based optical imagery. Our view is comparable to that of the Moon through weak binoculars. Evident are the large crater Mozart shadowed on the terminator, fresh rayed craters, and other albedo features keyed to topography and radar reflectivity, including the putative huge ``Basin S'' on the limb. Classical bright feature Liguria resolves across the northwest boundary of the Caloris basin into a bright splotch centered on a sharp, 20 km diameter radar crater, and is the brightest feature within a prominent darker ``cap'' (Hermean feature Solitudo Phoenicis) that covers the northern hemisphere between longitudes 140-250 deg. The cap may result from space weathering that darkens via a magnetically enhanced flux of the solar wind, or that reddens low latitudes via high solar insolation.Comment: 7 pages, 4 PDF figures, pdfLaTeX, typos corrected, Fig. 2 modified slightly to add crater diameters not given in published versio

An Analysis of Fundamental Waffle Mode in Early AEOS Adaptive Optics Images

Adaptive optics (AO) systems have significantly improved astronomical imaging capabilities over the last decade, and are revolutionizing the kinds of science possible with 4-5m class ground-based telescopes. A thorough understanding of AO system performance at the telescope can enable new frontiers of science as observations push AO systems to their performance limits. We look at recent advances with wave front reconstruction (WFR) on the Advanced Electro-Optical System (AEOS) 3.6 m telescope to show how progress made in improving WFR can be measured directly in improved science images. We describe how a "waffle mode" wave front error (which is not sensed by a Fried geometry Shack-Hartmann wave front sensor) affects the AO point-spread function (PSF). We model details of AEOS AO to simulate a PSF which matches the actual AO PSF in the I-band, and show that while the older observed AEOS PSF contained several times more waffle error than expected, improved WFR techniques noticeably improve AEOS AO performance. We estimate the impact of these improved WFRs on H-band imaging at AEOS, chosen based on the optimization of the Lyot Project near-infrared coronagraph at this bandpass.Comment: 15 pages, 11 figures, 1 table; to appear in PASP, August 200

Stellar Dynamics and the implications on the merger evolution in NGC6240

We report near-infrared integral field spectroscopy of the luminous merging galaxy NGC 6240. Stellar velocities show that the two K-band peaks separated by 1.6arcsec are the central parts of inclined, rotating disk galaxies with equal mass bulges. The dynamical masses of the nuclei are much larger than the stellar mass derived from the K-band light, implying that the progenitor galaxies were galaxies with massive bulges. The K-band light is dominated by red supergiants formed in the two nuclei in starbursts, triggered ~2x10^7 years ago, possibly by the most recent perigalactic approach. Strong feedback effects of a superwind and supernovae are responsible for a short duration burst (~5x10^6 years) which is already decaying. The two galaxies form a prograde-retrograde rotating system and from the stellar velocity field it seems that one of the two interacting galaxies is subject to a prograde encounter. Between the stellar nuclei is a prominent peak of molecular gas (H_2, CO). The stellar velocity dispersion peaks there indicating that the gas has formed a local, self-gravitating concentration decoupled from the stellar gravitational potential. NGC 6240 has previously been reported to fit the paradigm of an elliptical galaxy formed through the merger of two galaxies. This was based on the near-infrared light distribution which follows a r^1/4-law. Our data cast strong doubt on this conclusion: the system is by far not relaxed, rotation plays an important role, as does self-gravitating gas, and the near-infrared light is dominated by young stars.Comment: 34 pages, 11 figures, using AASTEX 5.0rc3.1, paper submitted to the Astrophysical Journal, revised versio

Two-body effects in the decay rate of atomic levels

Recoil corrections to the atomic decay rate are considered in the order of Zm/M . The expressions are treated exactly without any expansion over Z alpha. The expressions obtained are valid both for muonic atoms (for which they contribute on the level of a few percent in high Z ions) and for electronic atoms. Explicit results for Lyman-alpha transitions for low-Z of the order (Zm/M)(Z alpha)^2 are also presented.Comment: 5 pages, 1 table, email: [email protected]

Zenith-Distance Dependence of Chromatic Shear Effect: A Limiting Factor for an Extreme Adaptive Optics System

Consider a perfect AO system with a very fine wavefront sampling interval and a very small actuator interval. If this AO system senses wavefront at a wavelength, lambda_{WFS}, and does science imaging at another wavelength, lambda_{SCI}, the light paths through the turbulent atmosphere at these two wavelengths are slightly different for a finite zenith distance, z. The error in wavefront reconstruction of the science channel associated with this non-common path effect, or so-called chromatic shear, is uncorrectable and sets an upper bound of the system performance. We evaluate the wavefront variance, sigma^2(lambda_{WFS},lambda_{SCI},z) for a typical seeing condition at Mauna Kea and find that this effect is not negligible at a large z. If we require that the Strehl ratio be greater than 99 or 95%, z must be less than about 50 or 60 deg respectively, for the combination of visible wavefront sensing and infrared science imaging.Comment: To appear in 2006/12/01 issue of Ap

A New Strategy for Deep Wide-Field High Resolution Optical Imaging

We propose a new strategy for obtaining enhanced resolution (FWHM = 0.12 arcsec) deep optical images over a wide field of view. As is well known, this type of image quality can be obtained in principle simply by fast guiding on a small (D = 1.5m) telescope at a good site, but only for target objects which lie within a limited angular distance of a suitably bright guide star. For high altitude turbulence this 'isokinetic angle' is approximately 1 arcminute. With a 1 degree field say one would need to track and correct the motions of thousands of isokinetic patches, yet there are typically too few sufficiently bright guide stars to provide the necessary guiding information. Our proposed solution to these problems has two novel features. The first is to use orthogonal transfer charge-coupled device (OTCCD) technology to effectively implement a wide field 'rubber focal plane' detector composed of an array of cells which can be guided independently. The second is to combine measured motions of a set of guide stars made with an array of telescopes to provide the extra information needed to fully determine the deflection field. We discuss the performance, feasibility and design constraints on a system which would provide the collecting area equivalent to a single 9m telescope, a 1 degree square field and 0.12 arcsec FWHM image quality.Comment: 46 pages, 22 figures, submitted to PASP, a version with higher resolution images and other supplementary material can be found at http://www.ifa.hawaii.edu/~kaiser/wfhr

The effect of atmospheric turbulence on entangled orbital angular momentum states

We analyze the effect of atmospheric Kolmogorov turbulence on entangled orbital angular momentum states generated by parametric down-conversion. We calculate joint and signal photon detection probabilities and obtain numerically their dependence on the mode-width-to-Fried-parameter ratio. We demonstrate that entangled photons are less robust to the effects of Kolmogorov turbulence compared to single photons. In contrast, signal photons are more robust than single photons in the lowest-order mode. We also obtain numerically a scaling relation between the value of the mode-width-to-Fried-parameter ratio for which the joint detection probabilities is a maximum and the momentum mismatch between signal and idler photons after propagation through the medium.Comment: To appear in New Journal of Physic

Obliquely propagating electromagnetic waves in magnetized kappa plasmas

Velocity distribution functions (VDFs) that exhibit a power-law dependence on the high-energy tail have been the subject of intense research by the plasma physics community. Such functions, known as kappa or superthermal distributions, have been found to provide a better fitting to the VDFs measured by spacecraft in the solar wind. One of the problems that is being addressed on this new light is the temperature anisotropy of solar wind protons and electrons. In the literature, the general treatment for waves excited by (bi-)Maxwellian plasmas is well-established. However, for kappa distributions, the wave characteristics have been studied mostly for the limiting cases of purely parallel or perpendicular propagation, relative to the ambient magnetic field. Contributions to the general case of obliquely-propagating electromagnetic waves have been scarcely reported so far. The absence of a general treatment prevents a complete analysis of the wave-particle interaction in kappa plasmas, since some instabilities can operate simultaneously both in the parallel and oblique directions. In a recent work, Gaelzer and Ziebell [J. Geophys. Res. 119, 9334 (2014)] obtained expressions for the dielectric tensor and dispersion relations for the low-frequency, quasi-perpendicular dispersive Alfv\'en waves resulting from a kappa VDF. In the present work, the formalism introduced by Ref. 1 is generalized for the general case of electrostatic and/or electromagnetic waves propagating in a kappa plasma in any frequency range and for arbitrary angles. An isotropic distribution is considered, but the methods used here can be easily applied to more general anisotropic distributions, such as the bi-kappa or product-bi-kappa.Comment: Accepted for publication in Physics of Plasmas; added references for section

String Form Factors

We compute the cross section for scattering of light string probes by randomly excited closed strings. For high energy probes, the cross section factorizes and can be used to define effective form factors for the excited targets. These form factors are well defined without the need for infinite subtractions and contain information about the shape and size of typical strings. For highly excited strings the elastic form factor can be written in terms of the `plasma dispersion function', which describes charge screening in high temperature plasmas.Comment: 18 pages, 3 figures. Typos corrected, 1 footnote (in Section 4) and 1 reference adde

The optically-powerful quasar E1821+643 is associated with a 300-kpc scale FRI radio structure

We present a deep image of the optically-powerful quasar E1821+643 at 18cm made with the Very Large Array (VLA). This image reveals radio emission, over 280 kpc in extent, elongated way beyond the quasar's host galaxy. Its radio structure has decreasing surface brightness with increasing distance from the bright core, characteristic of FRI sources (Fanaroff & Riley 1974). Its radio luminosity at 5GHz falls in the classification for `radio-quiet' quasars (it is only 10^23.9 W/Hz/sr; see e.g. Kellermann et al 1994). Its radio luminosity at 151MHz (which is 10^25.3 W/Hz/sr) is at the transition luminosity observed to separate FRIs and FRIIs. Hitherto, no optically-powerful quasar had been found to have a conventional FRI radio structure. For searches at low-frequency this is unsurprising given current sensitivity and plausible radio spectral indices for radio-quiet quasars. We demonstrate the inevitability of the extent of any FRqI radio structures being seriously under-estimated by existing targetted follow-up observations of other optically-selected quasars, which are typically short exposures of z > 0.3 objects, and discuss the implications for the purported radio bimodality in quasars. The nature of the inner arcsec-scale jet in E1821+643, together with its large-scale radio structure, suggest that the jet-axis in this quasar is precessing (cf. Galactic jet sources such as SS433). A possible explanation for this is that its central engine is a binary whose black holes have yet to coalesce. The ubiquity of precession in `radio-quiet' quasars, perhaps as a means of reducing the observable radio luminosity expected in highly-accreting systems, remains to be established.Comment: Accepted by ApJ Letters; higher quality versions of figures available at http://www-astro.physics.ox.ac.uk/~km