From spencer Wed Feb 9 12:32:41 1994 From spencer Wed Feb 9 12:32:41 1994 Return-Path: Date: Wed, 9 Feb 94 12:32:23 MST From: spencer (John R. Spencer) To: spencer@sunkng Subject: Io Volcano News Content-Length: 3161 X-Lines: 70 Status: RO IO VOLCANO NEWS February 9, 1994 This is an appeal for observations in support of HST, rather than a report on observations. Thanks to the success and timeliness of the HST repair mission and checkout period, we have been lucky to get HST imaging observations of Io scheduled in early March: I think they will be the first planetary images with the new improved Hubble apart from the recent SL9 observations. We will image all longitudes of Io with WFPC2 from 3500 A to 1 micron, with 22 pixels across the disk, and will image selected longitudes with the FOC at 3500 A, with (hopefully) somewhat higher resolution. The FOC longitudes are chosen to catch Voyager-era plumes near the limb, and simulations suggest we have a good chance of seeing large plumes. We also plan a 15 minute 1-micron exposure of Io in Jupiter eclipse, in the hope of seeing high-temperature volcanic thermal emission. Near-simultaneous groundbased observations, particularly of the volcanic activity, would be very valuable to help interpretation of the HST data. Priorities are: 1) Longer-wavelength (1.7 - 10 micron) photometry of the volcanic emission in Jupiter eclipse as close as possible in time to the HST eclipse observations, so we can obtain color temperatures by combining the HST 1 micron fluxes with the longer-wavelength fluxes. Any information on the spatial distribution of the emission on Io, from speckle, Jupiter occultation photometry, or whatever, would also be very valuable. 2) 5 - 20 micron observations of the passive+volcanic thermal emission at all longitudes, to correlate plume activity or albedo changes with thermal emission. Again, spatially resolved observations would be very useful. 3) 0.35 - 1 micron absolute photometry of Io, as a check on the absolute calibration of the HST images. Ideally this should be at the same wavelengths and orbital longitudes as the HST observations (wavelengths 3340, 4090, 5620, 7830, and 10200; longitudes approx 45, 135, 225, 315, 65, 160, and 210: more exact numbers available soon), and close enough in time so that the solar phase angle corrections will be small. Groundbased calibration is particularly important at 1 micron: HST isn't used much at this wavelength so photometric calibration is probably less certain here. So far I know that Bob Howell in Wyoming is planning 5 micron speckle observations of Io from Feb 23 - March 4, and Rick Pogge of Ohio State may get some 2.3 micron eclipse photometry from CTIO on Feb 25, but more observations would be very nice. Unfortunately the IRTF is out of action temporarily and the HST observations came up too quickly for me to make alternate groundbased support plans. These are the tentative dates of the HST WFPC observations. IO-LON-045 1 Mar. 03:39:52 IO-LON-135 19 Mar. 05:48:32 IO-LON-225 5 Mar. 13:47:54 IO-LON-315 5 Mar. 23:19:55 IO-ECLIPSED 6 Mar. 04:15:04 The March 6 eclipse is visible from South America including Chile, Western Europe, and West Africa including the Canaries. The FOC observations aren't scheduled yet. Contact me for more information! Best wishes, John.