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Neptune Image 2017/10/05(UT)

Luigi Morrone
L.Morrone

Luigi Morrone
I show you my experience and acquisition of the occultation of the star UCAC4 410-143659 (Mag. V + 12.6) by Triton.
As follows some considerations.
In the night between Thursday 5 and Friday, October 6, 
the star UCAC4 410-143659 (a relatively bright star located in the Aquarium Constellation, with a V magnitude of about +12.6) has been ocuted by Neptune's main satellite: Triton.
With its approximately 2700 kilometers in diameter, in terms of size Triton is a little smaller than the Moon, and is almost identical to Pluto. 
As the latter has a low nitrogen atmosphere. 
In occultation, the interest of astronomers is precisely at the opportunity to observe the atmosphere of Triton and its transformations, which have been studied in recent decades.
The first direct observation of Triton's atmosphere was made in 1989 by the Nasa Voyager 2 probe. 
It was discovered on that occasion that it was extremely tiny and stretched for about 800 kilometers above the surface of the satellite, 
with a temperature around the 38 degrees Kelvin (-235 ‹ C). 
Eight years later, in 1987, an obstruction allowed astronomers to carry out some measurements with the Hubble telescope and unexpectedly found that 
Triton's atmosphere temperature had increased by 5 percent: a value that indicated a considerable heating, not whether due to seasonal cycles or a change in the volume of the atmosphere itself.
Shooting took place at Agerola: 40 ‹ 38'N - 14 ‹ 33'E.
Setup used:
Celestron C11 XLT - ASI178M Camera with No Filter- A lens hood to Limit Moon Reflection - NEQ6 Frame - Sampling 0.17 "/ pixel
The light curve was obtained using Tangra freeware software.
The recovery of the occlusion has not bee difficult, as the magnitude variation in V was +1.1, but at the same time not easy. 
About 11" from Triton obviously was the planet Neptune, which shone with a magnitude of +7.8 in V. Also at just 33 ‹ there was the full moon!
The maximum duration of occlusion has been approximately of 161 seconds.
Given that the height of the Tritonian troposphere is about 8 km, very short set times of 0.1 € 1 s needed to sample the vertical structure of this part of the atmosphere appropriately. 
For the setting parameters of the shooting, a few hours before the event, I made various attempts in terms of gain and framerates. In the end I chose an exposure time of about 800ms. 
I started taking about 15 minutes before occultation and I continued for another 15 minutes to make sure I got the event. Some clouds wanted to ruin the party but in the end we brought home the result.
Below are the curves of light in which the photometric drop is evident. The star is hidden at 23:46:00 UT, the time of the star's appearance is at 23:48:30 UT.
It is to be said that stellar occultations are very powerful tools. To realize that, at the time of occultation, Tritons was¬ be about 29 UAs from Earth (about 4.338 billion km), 
and to study its 8 km high troposphere, it means having a resolution of only 0.0004 " you could have been using a telescope of 315 m in diameter!

[Luigi Morrone : City Agerola Italy]

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2017/10/10
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