Chariklo  23/07/2017

*Prediction based on pre-Gaia DR2 position*

2017-07-23_Chariklo/2017-07-23-05h58m48s_Chariklo_GDR2_NIMAv13.jpg





Observation tips:

- Shadow moves from **East to West**;

- The nominal occultation time on the map, corresponds to the big red dot, the closest approach
.
- Each red dot is separated by one minute;
- Dark gray is night and light gray is astronomical twilight (Sun at less than 18 deg below the horizon);

- From South America, observations are requested from 05:48 to 05:58 UT.    


  Main goal is to derive Chariklo's size and shape!
Star J2000 coordinates:
   RA  18 48 09.2214
DEC  -31 26 32.460
Day coordinates of Chariklo:
RA  18 49 17.924
DEC  -31 25 10.65


Star V mag 14.4
Star G mag 13.9
Star K mag 11.6
Magnitude drop in R  4.7*
Maximum duration
Main body (Chariklo)
12 sec
Maximum duration
Main ring
0.33 sec
Ring-body-ring
Maximum duration
38 sec
*Att: there is a nearby star with almost the same magnitude of the target star.
If they are merged, the magnitude drop in R will be of only ~0.25.

Important note
:

*Absolute time accuracy is essential**

to connect all the observations
together after the fact. Check the time of your computer with many sources (phone talked hour, different internet sites, ideally with a GPS). 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 from DSS:
5 x 5 arcmin FOV (North is up, East is left)
2017-07-23_Chariklo/Chariklo20170723_5x5.png

 
15
x 15 arcmin FOV (North is up, East is left)
2017-07-23_Chariklo/Chariklo20170723_15x15.png

 
30
x 30 arcmin FOV
(North is up, East is left)
2017-07-23_Chariklo/Chariklo20170723_30x30.png



Prediction

Prediction is based on preliminary GAIA DR2 (i) star position with an accuracy of ~0.3 miliarcsec, considering proper motion and Chariklo's NIMAv11 (ii) ephemeris with an accuracy of ~5 mas. This corresponds to an error of around 80 km on the shadow path, about a third of Chariklo diameter.
../2017-07-23_Chariklo/2017-07-23-05h58m52s_Chariklo_GDR2pmGDR2_NIMAv11.jpg


Prediction is based on preliminary GAIA DR2 (i) star position with an accuracy of ~0.3 miliarcsec, considering proper motion and the latest Chariklo NIMAv13 (iii) ephemeris with an accuracy of ~2 mas, that takes into account the position derived from the detected occultation of June 22nd.
This corresponds to an error of around 20 km on the shadow path, and 1.5 sec in time.

2017-07-23_Chariklo/2017-07-23-05h58m48s_Chariklo_GDR2_NIMAv13.jpg

Download the KMZ file
(updated on July 13)


(i) https://www.cosmos.esa.int/web/gaia/news_20170523
(ii) http://lesia.obspm.fr/lucky-star/predictions/2017/Chariklo/html/2017-07-23-05h58m52s_Chariklo_GDR2_NIMAv11.html
(iii) http://lesia.obspm.fr/lucky-star/predictions/2017/Chariklo/html/2017-07-23-05h58m48s_Chariklo_GDR2_NIMAv13.html


Please, see the observation tips at the top!