|
BY PLUTO's
23rd MAGNITUDE MOON NIX on Friday June 5 2009 around 16:35-16:45 UT - updated May 29 2009 - |
|
On June 5 2009 at 16:35-16:45 UT,
Pluto's small satellite Nix might occult
a relatively bright star 2UCAC 25152757 = 2MASS 180933.8-173812, V=12.5, R=11.8. The star will be at high elevation in
Australia and New Zealand (morning of June 6), at low elevation (21.5 deg) in
La Reunion island (evening of June 5). Probability for a positive event under
clear skies is roughly 15% at centrality. As Nix is expected to be about 100
km in diameter, star position uncertainty translates into an error band of
typically +/- 500 km on Earth. To date this is the best opportunity to
detect a Nix occultation, as potential observers will be evenly spread North
and South of the shadow's predicted trajectory. The
event is worth observing even with a small, amateur telescope using an
integration time of not more than a few seconds. Visual observations may be attempted on 30-35-cm
(12"-14") telescopes. We recommend observing between 16:20
and 16:50 UT. A regular video camera (e.g. Watec)
is sufficient for recording the event. Because this would be an
"on-off" detection, a more sensitive camera would not add crucially
to the SNR at that point. Care must be given to include nearby UCAC stars in
the field for photometrical calibration.
J2000 updated stellar coordinates : 18 09
33.8681 -17 38 12.301 Please send all observing reports
whether positive or negative (including bad weather, with
observer's latitude / longitude / altitude data, telescope, instrument,
integration time, and timing method description) to our group in Paris
Observatory at the following email addresses : thomas.widemann @ obspm.fr bruno.sicardy @ obspm.fr
Red symbols are potential observing
sites. Dots are spaced by 1-minute intervals. Dotted lines embrace the error
band of +/- 500 km mostly due to star position uncertainty. Nix's shadow is
moving from East to West (right to left) with a ground velocity of 22.6 km s-1.
Predicted time for geocentric closest approach C/A = 0.124 arcsec is 16:39 UT (larger dot near center). This
recently updated prediction is derived from a reanalysis of the star position
by the Rio group, with an updated ephemeris offset for Pluto of -0.0528 arcsec in RA and 0.1468 arcsec
in DEC. Any detection would become an ephemeris
reference point for the Pluto-Charon system for
years to come, and validate our prediction process. Size and shape of the
object might be derived at kilometer-scale accuracy and help determine the object
density, its ice/silicate ratio and constrain
the collisional history
of the Pluto system. Stellar occultation by a new satellite, or any additional
orbiting material, might also be observed in serendipity mode. Several ground-based campaigns
are organized in 2009 to observe stellar occultations by distant solar
system objects such as
large trans-Neptunian objects
(TNOs) and Pluto's small satellites Nix and Hydra, in order
to derive sizes and shapes of objects at kilometer-accuracy. References
Sicardy, B., Bellucci, A., Gendron, E., Lacombe, F., Lacour,
S., Lecacheux, J., Lellouch,
E., Renner, S., Pau, S., Roques, F., Widemann, T.,
Colas, F., et al, Nature, vol.
439, 52-54, 5 January 2006. Widemann, T., Sicardy, B., Dusser, R.,
Martinez, C., Beisker, W., Bredner,
E., Dunham, D., Maley, P., Lellouch,
E., Arlot, J.-E., Berthier, J., Colas, F., Hubbard, W.B., et al. 2009, Icarus 199, pp. 458-476 |
