Last update: 2009 Mar 02

Stellar occultations: Nix, Aug 25, 2007


Nix Alert Email from Thomas Widemann

From: Thomas Widemann 
To: Leslie Young ,
        Eliot Young , Amanda Gulbis,
        "James E. Elliot" ,
        "Jay M. Pasachoff" ,
        Mike Person , "Marc W. Buie" ,
        Cathy Olkin ,
        David Tholen ,
        Richard French ,
        Wolf Juergen , Ted Dunham ,
        Michael Brown 
Cc: Bruno Sicardy 
Subject: Nix alert, March 4
Date: Sat, 28 Feb 2009 01:13:28 +0100

Nix alert, March 4

On March 4,13:56:01 UT, Nix might occult a V =
12.6, I = 11.5 star, an event visible in Hawaii.
Time is for geocentric closest approach (C/A),
note that the actual event would occur 5 minutes
earlier in Hawaii. The maximum duration is about
5 s (relative velocity 15.69 km s-1). The star
J2000.0 coordinates are 18 12 09.86  -17 42 03.3.

We have used Dave Tholen's update position of Nix
1.5849 arcsec west and 0.8499 arcsec north of
Pluto at time of the event, i.e. +9 mas (east)
and -6 mas (south) to JPL Horizons ephemeris. We
have also improved Pluto's offset wrt DE413,
using a linear fit to astrometric reconstruction
of occultations from 2005 to 2008 :

Delta alpha = - 87 mas
Delta delta = + 146 mas

Our resulting prediction attached is close to the
previous one due to compensation in Pluto's and
Nix' offset corrections. It is however about 25
seconds EARLIER than previously posted, the event
central time is now 13:50:37 UT (in Hawaii).
Estimated error bar is ± 30 sec in time and ± 500
km N-S. A probability of about 10 percent for a
positive event can be assessed. This is the best
probability we can obtain considering our
cumulated error bars on star position and Pluto's
offset,  and Dave's Nix Plutocentric ephemeris.

With this in mind, we would again stress this is
an unusually "bright" event combined with a  rare
geometry across the state of Hawaii. Even visual
observations using a 12" telescope and a timing
device would be useful. Beyond large facilities
on Mauna Kea and Haleakala who would be willing
to consider observing the event, additional
observers you may contact should spread over the
islands to as many different locations as




Telescope                      Approx. Location  Cameras              Contact
Windward community college 16" Kaneohe, Oahu     visual               Dave Tholen (observer)
PanSTARRS                      Haleakala, Maui                        Dave Tholen
AEOS 3.67-m                    Haleakala, Maui                        Dave Tholen
Faulkes                        Haleakala, Maui                        Jay Pasachoff
IRTF 3.0-m                     Mauna Kea, Hawaii POETS                Amanda Gulbis
CFHT                           Mana Kea, Hawaii  MegaCam Guide Camera Bruno Sicardy


Star Positions

Using the star positions measured by the Brazil group as the reference position, we find

Source          RA            Dec              dra     ddec errx erry
-------------- -------------- -------------   ----- ------- ---- ----
Brazil          18:12:09.8612 -17:42:03.225   
UCAC2_2006      18:12:09.8653 -17:42:03.229   59        -4  42   42
RA and Dec are epoch of date (where proper motion is known), equinox J2000.
dra and ddec are the offsets from the reference position in mas.
errx and erry are the quoted errors in position (and therefore in dra, ddec) in mas.

Brazil - Brazilian astrometric group that Bruno Sicardy and co. are working with.

UCAC2-2006: the position remeasured with the UCAC2 telescope in 2006, provided by Norbert Zacharias. This catalog is available here .

Finder Charts

10 arcmin FOV 5 arcmin FOV 2 arcmin FOV