From spencer Mon Aug 21 09:32:14 1995
From spencer Mon Aug 21 09:32:14 1995
To: oleroemer
Subject: Io Volcano news
X-Sun-Charset: US-ASCII
Content-Length: 2111
X-Lines: 44
Status: RO

Two more reports on the current enhanced volcanic activity
on Io.  The August 19th eclipse of Io by Jupiter was observed
by at least three groups (Lowell, JPL/IRTF, Wyoming),and all
of us noted Io's unusual brightness.

First from Jay Goguen (jdg@kookaburra.jpl.nasa.gov).  (Note that
the current eruption was first seen on 7/20 by Murray Silverstone at
UCLA, not by myself):

  J. Goguen and D. Blaney observed Io in eclipse on 8/19/95 UT with
  a bolometer at the IRTF.  Preliminary analysis gives the
  following magnitudes:

  M (4.8 um) = 5.17
  8.7 um     = 2.08

  Both the M and 8.7 um fluxes are approximately twice those 
  we observed for Io in eclipse on 7/2 and 7/18 suggesting that
  the ~month old eruption first reported by Spencer on 7/20 has
  now emplaced sufficient flows to increase the mid-IR flux.  
  The post-eclipse reappearance fluxes, however, are within the 
  range observed for this orbital longitude during the past decade 
  (Veeder et al. JGR Planets 99, 17095-17162, 1994).

And also from Bob Howell (rhowell@uwyo.edu) (Bob also observed
the Jupiter occultation reappearance):

  I've finished the preliminary reduction for the Aug. 19 eclipse
  photometry at L' and 3.4 microns.  It does show a factor of several
  increase compared to the (very low) level of activity seen in Spring
  1995.  It may also show about a 20% increase since the eclipse on
  August 4.  I'm still reducing that early August data.  The weather
  here is bad so I won't get to observe the event this afternoon (Aug
  20 UT).  My next scheduled time is Sept. 3 UT, but I'll see if others
  can make some additional observations.

  For the Aug. 19 event, if I use the local (and IRTF) standard Phi Oph
  and assume it is 2.20 at both L' and in the 3.4 micron filter, then
  in eclipse Io is magnitude 6.84 at L' and 7.32 at 3.4um.  These
  numbers should be good to about 5%.  (I'm still working on the
  standards, and this is a slightly different value for Phi Oph than I
  used in my messages this spring.)  In any case, at 3.4 um Io is about
  1.6 magnitudes brighter than we saw in the spring.