Quaoar and Weywot 17/04/2012

*See updates at the bottom of the page*

2012-04-17T02.224_Quaoar.jpg 2012-04-17_Quaoar/2012-04-17-02.472_WFIimcce_Weywot.jpg

*See updates at the bottom of the page*

Dark gray is night and light gray is astronomical twilight (Sun at less than 18° below the horizon).
Shadow moves from right to left, each red dot is separated by one minute, the nominal occultation time on the map, is for the big red dot, the closest approach
See finding charts bellow.
Doted lines are the estimated error of the star position, but the error can be bigger due to ephemeris offset!

The observations should be performed from 02:05UT to 02:25UT for Quaoar, and from 
02:23UT to 02:38UT for Weywot, whatever you are. So the best is a big sequence of observation, from 02:05UT to 02:38UT.

Weywot, the Quaoar's satellite will also occult the star, according to IMCCE's ephemeris. The occultation is predicted for 15min after Quaoar's occultation.

Star J2000 coordinates:
   RA   17 34 59.4809
DEC -15 31  32.654

Day coordinates:
 RA   17 35 43.619
DEC -15 31 59.358

Star R mag 12
Star K mag 7
Magnitude drop in R  8.0
Max. duration if 1070 km  diameter 90 sec
 Max. duration for the satellite if 80 km 7s

Observation tips:

Absolute time accuracy is essential to connect together all the observations after the fact. Check the time of your computer with many sources (phone talked hour, different internet sites, ideally with a GPS). As images should be acquired for a long time (10min at least), its advised to check the registered time right after and right before the integrations, so if there is a drift, we can correct it by having the difference.

Beware of the dead time between the images. If you manage an exposure time of 1 sec (for example), but have your camera takes 2 sec to read the image, then there is a 67% chance that you miss the dis(re)-appearance of the star. So it's better to have, for example, a 4 sec integration, so you have 67% chance to get the occultation in one of your exposures.

Finding charts:

FOV  5 x 5 arc min, from Pic du Midi T1M R filter.

 FOV 7 x 7 arc min, from Pic du Midi, R filter.
Get the 'fits' version of this image here: [ .fits ]


20 X 20 arc min from DSS

FOV in pdf with magnitudes:



field,_60,_10 and_1deg

Astrometric Updates

The initial prediction came from the ESO2.2m telescope and WFI camera:
first pred.: [2009]

With the offset derived from the occultation observed on May 04 2011, I generated the following update.
On the right have a zoomed map for Quaoar's moon (Weywot) track, the offset and star position are the same as the Quaoar's map.

2012-04-17_Quaoar/2012-04-17-02.224_WFIimcce_Quaoar.jpg 2012-04-17_Quaoar/2012-04-17-02.472_WFIimcce_WeywotZoom.jpg
updated on: [05/2011]

With observations of the star performed from OPD (Itajubá/BR) in September 2011, Julio Camargo obtained new positions of the star.
With this new position and the offset obtained from the observed occultation, I obtained this map.
updated on: [26/09/2011]

With the same telescope at OPD, Dario da Silva Neto obtained new positions last February.
updated on: [17/02/2012]

Jean Lecacheux has used the UCAC2 star position and the offset from the 2011 observed occultation to obtained the following maps.
2012-04-17_Quaoar/20120417_jpl21offRio1_JLX_Quaoar.gif 2012-04-17_Quaoar/20120417_jpl21offRio1_JLX_Weywot.gif

José Ortiz obtained on March 28th and 29 positions for the star and Quaoar using ASH2 0.4m telescope and R filter.
ATTENTION, as the dispersion between the several measurements made in those two nights is big.


updated on: [29/03/2012]

In March 30th Stefano Mottola obtained images from Calar Alto 1.2m telescope with a R filter from Quaoar and the star.
ATTENTION, we have only 3 positions from this observation, so this is a not very reliable result.
updated on: [30/03/2012]

The star was observed for several night with TRAPPIST telescope. Julio Camargo measured the images with respect to UCAC2 catalog.
The star position is very good and consistent with WFI position.
Using this position and the offset derived from the past observed stellar occultations, I obtain the following maps.
2012-04-17_Quaoar/2012-04-17-02.232_TRAPPISTimcce_Quaoar.jpg 2012-04-17_Quaoar/2012-04-17-02.481_starTRAPPIST_Weywot.jpg
updated on: [06/04/2012]

With images taken from Calar Alto 1.2m telescope on April 7th and 8th, José Ortiz obtain the following map.
updated on: [08/04/2012]

On April 9, François Colas observed the star and Quaoar from Pic du Midi. Himself, Raoul Behrend, and Julio Camargo measured the images.
I put here the different predictions from the same set of images but different reductions, so you can have a better idea of the errors on the prediction.

With François Colas reduction, Jean Lecacheux obtain this map.
updated on: [09/04/2012]

With the Julio Camargo reduction, I obtain this map.
2012-04-17_Quaoar/2012-04-17-02.237_PicAPR_imcce_Quaoar.jpg 2012-04-17_Quaoar/2012-04-17-02.486_PicAPR_imcce_Weywot.jpg
updated on: [09/04/2012]

A zoomed version of Weywot and Quaoar in the same map:

With Raoul Behrend
reduction's, I obtain this map.
2012-04-17_Quaoar/2012-04-17-02.218_PicABR_Raoul_imcce_Quaoar.jpg 2012-04-17_Quaoar/2012-04-17-02.467_PicAPR_Raoul_imcce_WeywotZoom.jpg
 updated on: [09/04/2012]

A zoomed version of Weywot and Quaoar in the same map: