Wednesday, June 13, 2012

Stellar Occultation of P20120614 by Pluto

Stefan Réner, Ahmed Daassou and Zouhair Benkhaldoun took this image of Pluto and the target star, using the T60cm from Atlas Golf Marrakesh on the night 12 to 13 June. Credit

Although the suddenness of such an event is rather peculiar (as such an event should have been in ephemerides without such short notice), Pluto perhaps will occult the a star, P20120614 of the 13.7 magnitude during the night of June 13-14. In an alert entitled "Possible Pluto occultation Wednesday night (2012/06/14 03:28 UT) from US East coast" issued by Leslie Young, we find that Pluto's occultation hopefully will conclude to be helpful for more insight to Pluto, as it is a world of which we do not have much information from. The occultation is planned to last around sixty-eight seconds starting on June 14 at 3:22 UT (June 13 11:22 pm EDT) at a low altitude in the sky for the eastern United States and Canada. The RA (Right Ascension) of the star is 18h 35m 48.69s while declination is at –19° 17' '43.6".

From the alert, we learn that stellar occultations prove to help us learn more about Pluto, but particularly its atmosphere. "Pluto's thin, nitrogen atmosphere is in vapor-pressure equilibrium with the surface ice, and changes seasonally", so observable occultations will help astronomers learn more about the atmosphere. When Pluto passes in front of a star, we get a good view of the atmosphere by the light from the star behind the planet and meanwhile, at ~10 km resolution, temperature and pressure is measured accordingly. More information can be obtained here.

Visibility Map: Across the globe pictured above, the three solid lines correspond to the northern limit, centerline, and southern limit of Pluto's shadow. The northern and southern limits correspond to a radius of 1400 km. The upper and lower dashed lines indicate 3-sigma errors. The shaded area represents where the sun is more than 12 degrees below the horizon.

Table 1: Prediction Details
Pluto Geocentric Mid-time (yyyy month dd hh:mm:ss)
2012 June 14 03:26:12± 00:00:42 UT
Pluto Minimum Geocentric Separation
0.275± 0.025 arcsec
Position Angle (Pluto relative to the star; measured north through east)
–6.40 degrees
Geocentric Velocity
22.89 km/sec
Occultation Star R magnitude

Table 2: Reference Star Position
Reference star position:
(at epoch of event)
RA (h:m:s; J2000)
Dec (d:m:s; J2000)
P20120614 Catalog
18 35 48.6931
–19 17 43.617

P20120614 Measured
18 35 48.6883 ± 0.002
–19 17 43.639 ± 0.009
From 5 SMARTS Telescope frames.
Table 3: Projected KBO Offsets from Reference Ephemeris at the Time of the Event
RA (arcsec)
Dec (arcsec)

–0.1392± 0.041
+0.225± 0.023

Above Tables and Visibility Map Thanks to P20120614 Occultation June 14, 2012. Below map credit same site the image of Pluto and Star (beneath the title) was accessed.

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

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