On 2005, July 11 (UT), there is a predicted occultation by Charon.
This has the potential of beung the first Charon occultation
observed by multiple sites, and the first Charon occultation observed
at better than 2-second resolution.
The only previous occultation was observed from a single site
by Alister Walker
(Walker 1980 (pdf) ).
This event was reanalyzed by
Elliot and Young (1991
to place a lower limit on the radius of 601.5 km, and an upper limit on the
atmosphere of 1-57 cm-A.
Pluto has a significant lightcurve. The latest paper
with the seperate lightcurves of Pluto and Charon is from data
taken 1992 to 1993 (Buie, Tholen and Wasserman 1997, Icarus 125, 233-244).
At the time of the occultation (2005 July 11 03:36 UT), we have
r = heliocentric distance = 30.97 AU
delta = geocentric distance = 30.07 AU
Ob-lon = sub-observer longitude 98.12 deg for Pluto, 278.12 for Charon
Buie's Right-Hand-Rule longitude is approximately -Oblon).
alpha = solar phase angle = 0.87 deg.
For the star,
USNO A2-0 gives B = 15.6, R = 14.6. At c313.2's dec, these
are from the POSS-I O and E plates, not Johnson filters
(or Cousin's, for that matter).
Converting the Johnson B, V
V = r + 0.375 * (b - r) = 15.0
B - V = 0.625 * (b - r) = 0.63, B=15.6
, but errors can be as large as 0.5 mag.
USNO B1-0 gives two measurements for B, B1 = 16.61 and B2 = 16.14.
Also two for R, R1 = 14.82 and R2 = 14.70. I = 14.16.
A discussion on the color conversion
for the USNO B 2-0
Johnson B = USNO B1.0 B1 +/- 0.5 = 16.61
Johnson R = USNO B1.0 R1 +/- 0.5 = 14.81
V = 0.444R1 + 0.556B1 +/- 0.5 = 15.81
The UCAC2 magnitudes are through a filter
midway between V and R, with a UCAC2 mag of 14.99.
The 2MASS catalog actually has magnitudes that people believe,
with J=12.914 +/- 0.023, H = 12.314 +/- 0.022, and K = 12.155 +/- 0.023.
Again, there is a color transformation
Plus there are several IR system to convert into ... MKO, UKIRT, SAAO,...
It happens that the 2MASS system is within a few tenths of a mag
of the UKIRT system.
Finally, DENIS gives I = 13.9 +/- 0.04, J = 12.8 +/-0.11, K = 12.1 +/- 0.12,
with the J and K consistent with 2MASS.
B V R I J H K
Pluto 15.11 14.24 13.6?
Charon 16.96 16.25 15.7?
C313.2 16.6 15.8 14.8 13.9 12.9 12.3 12.2
Predictions can be found at Bruno Sicardy's occultation page for this event,
or at Jim Elliot's page
As usual with occultations by small, outer-solar system bodies, the
maps only show the current predicted location of the shadow. This
can change dramatically depending on refinements to the star's position.
There are three groups observing this event, led by
Jim Elliot (MIT and Williams), Bruno Sicady (Meudon, France), and
Leslie Young (SwRI and Wellesley).
The observers for the SwRI/Wellesley group are
Leslie Young (SwRI), Eliot Young (SwRI), Kevin Shoemaker (Shoemaker Labs),
Dick French (Wellesley), Brooke Gregory (NOAO), Cathy Olkin (SwRI), and Trin Ruhland (U Chicago).
Location Observers Instrument
-------- --------- ----------------------
CTIO 4-m (Blanco) Olkin/Ruhland/L Youmg Mosaic II camera
CTIO 0.9-m French/Gregory Tek #3 CCD
SOAR 4.2-m E Young/Shoemaker PHOT (our new camera)
Three finder charts generated from the Digital Sky Survey via Vizier:
2 arcmin field of view (pdf) )
17 arcmin field of view (bmp) )
60 arcmin field of view (fits) )
At the event midtime, Charon will be 225 mas East and 865 mas South of Pluto
(position angle of 165.4 degrees), according to the Plu013 ephemeris.
The PHOT group got data from all three telescopes.
Young, L. A., C. B. Olkin, E. F. Young and R. G. French
2005, Occultation by Pluto I (Charon), IAU Circular 8570.
(text file) .
The MIT/Williams group got data from several sites.
movie and description
of the event from Las Campanas Obs. in Chile.
The Meudon group got data from at least VLT.
Last updated 2005 July 20 by Leslie Young,