Sunday, 26 June 2011

Pluto + Hydra 27/06/2011


2011_06_27_14_Pluto.jpg2011_06_27_PlutoHydra/2011_06_27_14.889.jpg

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This occultation involves a bright star R 13.9. It's very important and interesting occultation as it's double with Hydra, one of the small satellites of Pluto.
The event occurs in the night of June 27 to 28, it crosses the Earth from 14:14 to 14:57 UT (for the two occultations). Shadow moves from right to left, each red dot is spaced by one minute, the nominal occultation times on the maps, are to the big red dot.



Star J2000 coordinates:
RA= 18 25 29.0100 DEC= -18 48 47.570
Day coordinates:
RA= 18 26 12.22 DEC= -18 48 18.32


Star R mag13.9
Star K mag11.9
Star + Pluto mag13.2
Magnitude drop in R0.8
Contrast52%
Max. Duration Hydra4.2s
Max. Duration Pluto130s

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 its a long duration, its advised to check the registered time right after and right before the integrations, so if there is a drift, we can correct it having the difference.

Beware of the dead times between images. If you manage an exposure time of 1 sec, but have a read time of 3 sec, then there is a 75% chance that you lose the dis(re)-appearance of the star. Then it is better to have, say, a 4 sec integration, as you have a 40% chance to miss the occultation.

-> There is many bright stars in the field, so you can select a small part of your CCD to acquire the occultation images, THIS CAN DRASTICALLY REDUCE THE DEAD TIME.

It's better if the integrations don't stop between the events, but they are about 35 minutes apart. Be careful with the disc / tape space.


Finding charts (from DSS R band):

5x5 arc min FOV
2011_06_27_PlutoHydra/field5x5min_PlutoHydra_110627.jpg

20x20 arc min FOV
2011_06_27_PlutoHydra/field20x20min_PlutoHydra_110627.jpg


30x17 arc min FOV
2011_06_27_PlutoHydra/FOV_27jun11/starry_night_27jun11_30x17_arcmin.jpg
In the image, 'Pluto' indicate the position of Pluto in the moment of the occultation.

5° x 2° FOV
2011_06_27_PlutoHydra/field5x2deg_PlutoHydra_110627.jpg

Other charts, but in pdf: 60°, 15° and 7° FOV, 5°x2°, 30x14arc min, 12x5arc min.



Marc Buie has improved the orbit determination for the satellites of Pluto using new measurements of this bodies.
Using his new ephemeris, we obtain a new position for the shadow of Hydra.
2011_06_27_PlutoHydra/2011_06_27_Hydra_australia.jpg

the same map with the informations and zoom:
Star position:
RA= 18 25 29.0100 DEC= -18 48 47.570
2011_06_27_PlutoHydra/2011_06_27_14.889.jpg


Astrometric Updates

Marcelo Assafin observed and measured the star from Pico dos Dias Observatory in the begging of June.
Bruno Sicardy derived the Pluto system ephemerids offset, using a Charon occultation observed at Chile and Brazil in 04th June 2011.

Using the star new position and the new offset, I generated the following maps.
Star position: RA= 18 25 29.0095 DEC= -18 48 47.633
2011_06_27_PlutoHydra/2011_06_27_14.326Pluto_StarLNA_ofOcc4jun.jpg

Hydra with Marc Buie ephemeris and new star position and offset.
2011_06_27_PlutoHydra/2011_06_27_14.905Hydra_StarLNA_ofOcc4jun.jpg

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Julio Camargo and Dario da Silva Neto observed and measured the star from 1.6m telescope at Pico dos Dias Observatory on 17th and 18th June.
Using the star's new position and the new offset, we obtain the following predictions. They are almost coincident with the latest, showing a stability on the star position.
Star position: RA= 18 25 29.0099 DEC= -18 48 47.626
2011_06_27_PlutoHydra/2011_06_27_14.324_Pluto.jpg

Hydra with Marc Buie ephemeris and new star position and offset.
2011_06_27_PlutoHydra/2011_06_27_14.904_Hydra.jpg

zoomed map
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Julio Camargo observed and measured the star from 60cm Zeiss telescope at Pico dos Dias Observatory on 18th and 19th June.
Using the star's new position and the new offset, we obtain the following predictions.
Star position: RA= 18 25 29.0089 DEC= -18 48 47.643
2011_06_27_PlutoHydra/2011_06_27_14.328_Pluto.jpg

Hydra with Marc Buie ephemeris and new star position and offset.
2011_06_27_PlutoHydra/2011_06_27_14.908_Hydra.jpg



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We have successfully observed the June 23th Pluto+Charon occultation.
From its reduction Bruno Sicardy derived an offset for the Pluto system, that is applied to the 27th occultation.
For the star we used the relative position derived by Julio Camargo with observations from LNA/OPD Zeiss 60cm telescope on 18th June.
2011_06_27_PlutoHydra/2011_06_27_14.302_Pluto.jpg

2011_06_27_PlutoHydra/2011_06_27_14.881_Hydra.jpg2011_06_27_PlutoHydra/2011_06_27_14.881zoomHydra.jpg
2011_06_27_PlutoHydra/2011_06_27_14.881zoomHW_Hydra.jpg
Shadow moves from right to left, so expected occultation time at Hawai is 14:48.

Maps in Longitude and Latitude by Bruno Sicardy.
2011_06_27_PlutoHydra/long_lat_Hydra_27jun11.jpg
2011_06_27_PlutoHydra/long_lat_Hydra_27jun11_Asia.jpg2011_06_27_PlutoHydra/long_lat_Hydra_27jun11_Hw_Ma.jpg