__________________________________________________________________________ T H E O L E R O E M E R M E S S E N G E R _______________________________________________ JJJJ C G JJJJJJ I E JJJJ __________________________________________________________________________ Newsletter of the International Jupiter Watch Satellite Discipline E-mail issue 16 April 18, 1995 Editor and Discipline Leader: John Spencer Voice: (520) 774-3358 Lowell Observatory Fax: (520) 774-6296 1400 W. Mars Hill Rd. (Note the new telephone area code) Flagstaff, AZ 86001 Internet: spencer@lowell.edu ___________________________________________________________________________ CONTENTS 1) Io Activity Update 2) "New" Voyager-era plumes on Io 3) Postdoc opportunity 4) IUE proposals due May 22, 1995 5) Possible Saturnian Satellites ___________________________________________________________________________ 1) IO ACTIVITY UPDATE Bob Howell (rhowell@uwyo.edu) reports on his March observations... We got very little data during our March runs. It is our snowiest month. I took data during the eclipse and occultation on March 7. The occultation data is worthless because of clouds. I may have a little data from the eclipse, but it is badly affected by the clouds so I haven't made reducing it a priority. The longitude should be such that we don't see your outburst. We also got some speckle photometry at 4.8 um the next night (the 8th UT) from about 14UT -> 15UT which is at about 200 degrees longitude. Once again, that's the wrong longitude for your outburst. Murray Silverstone (murray@eggneb.astro.ucla.edu) reports K' (2.1 micron) photometry of Io in eclipse in March using the 24" telescope on the UCLA campus, from the monitoring program that he is doing with Eric Becklin. The numbers show quantitatively the previously-reported dramatic brightening which began between 3/16 and 3/22: I have our final nubers for the two IO eclipses. The error is roughly approximated, particularly for the 7th. March 7 1995 K' = 11.66 error = 0.25 mag March 30 1995 K' = 8.96 error = 0.15 mag If all goes well, I should be observing the April 15 eclipse. I'll try for occultation observations too. Regarding future plans, Murray reports: So far we are planning on observing every eclipse we can from UCLA. It looks like we should be able to observe the April 15, April 22, May 1, and May 8 (all the dates I have looked at so far) eclipses. Our window for the April 22 eclipse will end when the Sun comes up, so we wouldn't be able to observe the occultation during that eclipse. Disk-resolved images of Io taken at the IRTF by Glenn Orton with NSFCAM at 3.8 microns at 15 UT on 95/04/05, with a central longitude near 140, do not show any sign of the March 2nd outburst, which at longitude c. 95 would have been on the disk at that time. As reported previously, the late-March brightening of Io had faded considerably when Io was seen in eclipse at 2.3 microns on 1995/04/08 by Spencer at the Lowell 72", but Io was still brighter than it had been on 3/16, before the brightening. On 4/08 the brightest 2.3 micron hot spot on Io, which was probably the remnant of the late-March brightening, was occulted by Jupiter at 10:19:00, just before the predicted occultation of the center of Io and thus was near longitude 0, implying that the late-March brightening was *not* at Loki. The 4/08 eclipse and occultation were also observed by Bob Howell (rhowell@uwyo.edu) at the Wyoming Infrared Observatory. He reports... We also mangaged to get some data on the April 8 eclipse and occultation. The conditions were about as non-photometric as they can be and still make it worthwhile to take any data. All of the following fluxes are uncertain by 50%, and perhaps even worse. However, it is clear that the 3.4 um emission was relatively weak. I also think we saw the in-eclipse occultation disappearance, and we get a result different than that which you reported. Because all of our results are in our narrow 3.4 um filter, perhaps we are seeing different spots. First, we observed the tail end of the eclipse disappearance, in eclipse, the in-eclipse occultation, and the in-sunlight reappearance. The last part of the reappearance was trashed by clouds. Using Phi Oph as our local standard, and assuming that it has magnitude 2.26, we get an Io in-eclipse magnitude of 9.03. That corresponds to only about a 1% flux from the spot compared to the disk. The 10:18:05 time of Bob Howell's 4/08 3.4 um Jupiter occultation "event" corresponds to a hotspot in the leading hemisphere, but this event was not seen in Spencer's simultaneous 2.3 micron occultation lightcurve (taken in near-photometric conditions), and Spencer's 10:19:00 event was not seen in Howell's lightcurve. Possibly the data can be reconciled with extreme temperature contrasts for the hot spots, or the Howell observations may just be strongly affected by clouds. The 4/15 eclipse and occultation were observed by Bob Howell at Wyoming and John Spencer and Christophe Dumas at the IRTF: Io was faint in eclipse, indicating that the 3/23 - 4/08 hot spot had mostly subsided. Spencer and Dumas observed the occultation at 2.3 microns, Howell observed it at 3.4 microns. 3.8 micron disk-resolved images in sunlight at the IRTF, at central longitudes of c. 340 and 12, showed no bright hot spots. Murray Silverstone at UCLA also observed the eclipse (but not the occultation) and also noted that Io appearad to have returned to the low brightness levels that it had before the late-March eruption. ___________________________________________________________________________ 2) "NEW" VOYAGER-ERA PLUMES ON IO Alfred McEwen (amcewen@masursky.wr.usgs.gov) reports: Dear Iophiles, I just discovered 1 or 2 "new" plumes on Io from Voyager 2 images!! They can be seen just beyond the terminator and above the projected limb in 4 frames (FDS 20641.52, 20641.55, 20641.58, and 20642.01): Latitude Longitude minimum height estim. height -------------------------------------------------------- +50 250 30 km 55 km +58 250 15 km 40 km (positions +/- 10 degrees longitude; +/- 2 degrees latitude). I can't really prove they aren't mountains rather than plumes, but they would then be enormous mountains. Voyager 1 images do not reveal mountains in this region, but it is poorly imaged (near bright limb at about 4 km/pixel.) The highest known mountains on Io are about 10 km high. The plume colors are similar to Io's surface, consistent with either mountains or optically thick ejecta like the inner portion of Loki. They look like plumes morphologically, but are not well resolved. The height estimates depend on the location of the source vent (or mountain). The brightenings begin between the terminator and limb, so the estimated heights above (and longitudes) are based on assuming that they are exactly halfway between the limb and terminator. These are the highest latitudes at which we've seen plumes. These are relatively small plumes, and add to the case that there are in fact many more small plumes on Io. Alfred ___________________________________________________________________________ 3) POSTDOC OPPORTUNITY We haven't done job ads in this newsletter before, but it seems appropriate, so here's an advertisement that I submitted to the May 1995 AAS Job Register. Please spread it around... Postdoctoral Researcher LOWELL OBSERVATORY 1400 West Mars Hill Road Flagstaff, AZ 86001 Tel: (520) 774-3358 Fax: (520) 774-6296 E-mail: spencer@lowell.edu Attention: John Spencer Lowell Observatory invites applicants for a postdoctoral research position in planetary astronomy. The successful applicant would be expected to spend 70% of his or her time obtaining and analysing infrared images and Jupiter occultation lightcurves of the volcanic hot spots on Jupiter's moon Io, at Lowell Observatory and at Mauna Kea, Hawaii. Analysis will have the goal of determining the locations, temperatures, and variability of the hot spots over a period of several years that will include the duration of the Galileo spacecraft tour of the Jovian system. Io's small angular diameter (one arcsecond) demands innovative image analysis techniques to extract the maximum information from the observations. The position is offered initially for two years, with a possibility for a third year if funds allow. Applicants should have a PhD in astronomy or a related subject, and experience with astronomical observations and image analysis, preferably including model fitting techniques. To apply, send a resume, the names and addresses of three references, and a statement of research interests to the above address. Applications received by 1 July 1995 will receive full consideration. Starting date for this position should be no later than October 1st, 1995. EOE. ___________________________________________________________________________ 4) IUE PROPOSALS DUE MAY 22, 1995 NASA, ESA and PPARC are pleased to announce the 19th observing episode of the International Ultraviolet Explorer (IUE). The 19th episode will place emphasis on key science programs; we estimate that approximately half of the available time will be awarded to key projects for the full year of observations. The episode will start on or around 1 October 1995 and end 30 September 1996 for the NASA science program. Potential proposers should be aware of important changes in the manner and mode of observatory operations after 1 October 1995. Printed copies of the IUE proposal package will be available within a few days. An electronic copy of the full Announcement of Opportunity (AO) is available through anonymous ftp at iuesn1.gsfc.nasa.gov (IP address 128.183.57.16) in the directory pub/proposal. It is also available on the World Wide Web from the IUE Project page (URL=http://iuesn1.gsfc.nasa.gov/iue/iue_homepage.html). Follow the link label "IUE 19th Episode Proposal Instructions" (URL=ftp://iuesn1.gsfc.nasa.gov/pub/proposal). The due date for proposals is close of business on 22 May 1995. For more information please contact Dr. Donald West, IUE Operations Scientist at (301) 286-6901, or Dr. Andrew Michalitsianos (301) 286-6177, or by e-mail michalits@torte.gsfc.nasa.gov _____________________________________________________________________________ 5) POSSIBLE SATURNIAN SATELLITES The following report appeared in IAU Circular 6162, dated April 14 1995: POSSIBLE SATELLITES OF SATURN M. K. Gordon, C. D. Murray and K. Beurle, Queen Mary and West- field College, University of London, report on the possible existence of additional satellites of Saturn in the Voyager 2 data. They also quote S. P. Synnott as noting that the seven satellite candidates discussed by him on IAUC 3651, 3656, and 3660 should be reduced to three (S/1981 S 7, 10, and 11), together with a very faint fourth one, designated S/1981 S 14, observed on 1981 Aug. 23.9955 UT around 2.0 x 10^5 km from Saturn. Summarized below are the 1981 Aug. UT dates of the new images (not the 'earth received' times), approximate planet-centered distances (in units of 10^5 km) and longitudes (in deg), assuming circular orbits in the equatorial plane (in J2000.0 coordinates fixed on 1981 Aug. 21.2), and estimated apparent visual geocentric opposition magnitudes: S/1981 S 15, 21.2439, 1.74, 222, 18; S/1981 S 16, 21.2789, 2.20, 290, 18; S/1981 S 17, 22.1928, 2.31, 282, 18; S/1981 S 18, 23.9050, 1.85, 206, 24; S/1981 S 19, 23.9866, 1.86, 109, 22. Pointing-error corrections in the Voyager database for S/1981 S 18 and 19 could not be corrected; consequently, the error bars for these two features are on the order of two to three thousand km. The orbital radii above are particularly sensitive to the assumption that the possible satellites are on orbits in the equatorial plane. Orbits with moderate inclinations (1-1.5 deg) could produce changes of several thousands of kilometers in the radial positions. Based on dynamical considerations, S/1981 S 16 and 18 may be separate observations of a single small satellite coorbital with Mimas (Saturn I) with an orbital inclination comparable to that of Mimas. _____________________________________________________________________________