UVIS auroral update- June Wayne Pryor -Contributed to Kurth et al., Saturn chapter on “auroral processes” -Mitchell et al paper compared UVIS auroras to INCA ring current data -Gustin et al., 2009 FUSE/UVIS auroral spectroscopy -Contributed to Clarke et al., 2009 HST paper -Distributed “UVIS Auroral Book” among Cassini teams

UVIS auroral “book” PDF file Over 540 FUV images are presented (with or without “red end” Rayleigh scattered light) Geometry overlays added, assuming 1100 km auroral emissions Latest version includes auroral footprint “box” at sub- Enceladus longitude near 60 N and 60 S (Crary- recommended latitudes) Some calculations were done: used interception of oblate spheroid with offset dipole, got a slight offset northward from Crary #’s To do: get some one on MAG to predict Enceladus footprint point from their favorite models

An Enceladus footprint search was requested John Clarke’s team (Wannawichian et al. 2008) published that the upper limit on the Enceladus footprint was < few kR BUT at the last MAPS meeting in San Antonio, Rhymer presented evidence for episodic field aligned “beams” near Enceladus Several people then asked UVIS to check on this (Crary, Alexander, Gombosi…..) The next couple of slides will cover the Saturn search Josh helped in modifying geometry tools to obtain Enceladus sub- longitude Amanda and Candy will look for Enceladus aurora in UVIS eclipse data Joe Ajello has provided electron impact on water spectra for comparisons

1 st image found with spot… lower panel adds geometry overlay, terminator (white) and Enceladus foot box

Following image shows weaker spot……

Best Evidence For Enceladus Foot Emission:

Search Summary 5 images show an obvious spot in the box Statistically very significant; same spots show in EUV. An early image pair (16 min. apart) from shows a night-side spot in the box (but not clean: along-slit scattering was significant); looks better with full spectrum. An image pair (84 min. apart) from from close range (6-7 R s altitude) shows a good dayside spot near 65 N that moves with Enceladus, looks better with red end out. – Enceladus orbital period of 1.37 days-> 11 degrees/hr – Saturn rotation period of hrs-> 34 degrees/hr Spot is usually absent or below our detection threshhold

To Do… Estimate mean energy per electron from absorptions in spectra Plot box-contents for all images vs bkg. Refine Rayleighs (result depends on assumed emission area, which may be small with converging field lines….) Watts of excess emission should be a clean result Watts of input energy can be estimated from previous work by Dols and others…. Present this at MOP at end of July Quick Paper in coming weeks