p240_1_slit.jpeg shows Pluto, Charon, the star P240.1,
and two orientations of the slit.  Axes are marked in arcsec.
North is up, East is to the left.

This used star position from Ron Stone, the FASTT transit telescope,
June16-July 11.
Ra =  17 17 31.7801 Dec = -14 22 19.967 (J2000)
error: 22 mas

Star is not double, according to preliminary measurements 
by Bill Merline at Keck and VLT.

Pluto and Charon positions are from Horizons web page.
Estimated errors are about 60 mas, based on previous
occultation predictions.

(1) The star should miss both objects - no occultation

Charon C/A 8:59 xi = -0.11  eta = 0.25  miss = 0.27 arcsec
Pluto C/A  9:03 xi = -0.43  eta = 1.03  miss = 1.11 arcsed

(2) The slit should be rotated -22 deg
For East-West, we get contanination from the star for hours before C/A.
This is conveniently near the Pluto-Charon line.

(3) We should not take spectra of Pluto from 8:30 to 9:30 to
avoid contamination by the star

(4) I'd like to focus, then image the star from ~8:50 to 9:10 to measure the
miss distance of the appulse