Hubble STIS Observations of Comet Hale-Bopp
(27 August 1997)

STIS is an acronym for the Space Telescope Imaging Spectrograph (STIS), a "second generation" HST instrument installed during the most recent servicing mission in February 1997. STIS has both imaging and spectroscopic modes and operates from about 120 nm to 1000 nm. Unlike the case for its two predecessor spectrographs on HST, STIS spectra contain both spatial and spectral information, which is very important in studying spatially-extended objects like comets. 

STIS first observed Hale-Bopp on 27 August 1997, which is when the comet emerged from the HST solar exclusion zone. (HST could not observe Hale-Bopp earlier in 1997 because the angle between the sun and the comet was smaller than 50 degrees and pointing HST that close to the sun could damage the telescope and/or its instruments.) The next HST Hale-Bopp observations are scheduled to occur during early November. Information on those observations will also be posted at: http://www.pha.jhu.edu/~weaver/ (you'll find there further information on the August 1997 observation, as well) .

You can access two times larger versions of all the figures appearing below by clicking on them. 

Credits: Harold Weaver (Johns Hopkins University) and NASA 
 
figure 1
 Figure 1: The above image is a composite of two STIS CCD exposures taken at 04:05 UT (2 sec integration) and 04:06 UT (20 sec integration) on 27 Aug 1997. The heliocentric and geocentric distances of the comet were 2.476 AU and 2.989 AU, respectively. The direction to the sun projected onto this image is at 53.6 deg clockwise from the +x-axis (where the +x-axis points to the right and the +y-axis points straight up), but the solar phase angle (the sun-comet-earth angle) is 18 degrees, which means that the direction to the sun is only 18 degrees from being perpendicular to the plane of this image. A "long-pass" filter was used that transmits all light longward of approximately 5500 angstroms (10 angstroms = 1 nanometer) and rejects light shortward of that wavelength. The image is 28 arcsec on a side, which subtends 60,680 km at the distance of the comet. Individual STIS CCD pixels are 0.0508 arcsec across, which projects to 110 km at the comet. 
 
figure 2
 Figure 2: The image in Figure 1 has been divided by a circularly symmetric image that gives the best match to the azimuthally-averaged surface brightness profile of the comet. This "ratio" image thus shows the deviations of Hale-Bopp's dust production from spherically symmetric, steady-state outflow. We see from the above image that Hale-Bopp is still clearly showing the strong jet activity that started becoming prominent towards late summer in 1996. 
 
figure 3
 Figure 3: This figure is similar to Fig. 2, except that the azimuthally-averaged image has been subtracted from the data. This technique enhances the region near the nucleus, but otherwise shows the same features as the ratio image given above. 
 
figure 4
 Figure 4: a STIS spectral image taken using the CCD and the G230MB grating and shows the detection of many lines in the OH(0,0) band centered near 3090 angstroms.