Occultation of trans-neptunian asteroid Huya

[jimao22]

Last night (Sunday to Monday), a rare event happens. A dim star (mag 10) was occultated by the trans-neptunian asteroid - Huya. The strip where this event was visible passed near by my observatory. So 2:53 local time I was outside to take pictures of this event. It was a very nice night, with clear sky and good temerature for this time of the year. My data obtained by me is already to the profesional astronomers in La Palma, where they will obtain new information about this remote celestial body. I was not alone in this enterprise - another 10 astronomers around the country being involved in the project. I used my data to make a short film of the event with the most important part - occultation itself.

 

The strip where this event was visible:

[orion25]

That is fantastic! Thanks for sharing this rare event; the video was fascinating. You were very fortunate to be in the zone

Reggie

[Wiu-Wiu]

so this object isn't even visible? I am very surprised by that! What magnitude does it usually have? Very interesting, thanks for sharing! 

[Nigel G]

Wow, great capture.

[geoflewis]

Superb video

[tooth_dr]

Class!

[Victor Boesen]

WOW!!! Very impressive capture!!!

[Craney]

Interesting to see how close to the UK that occultation line passes.....  if extrapolated backwards / forwards in time.   Looks North Sea'ish or Scotland.

[Paul M]

A very impressive capture and I'm sure very rewarding work!

Thanks.

[Phil Fargaze]

6 hours ago, Wiu-Wiu said:

so this object isn't even visible? I am very surprised by that! What magnitude does it usually have? Very interesting, thanks for sharing! 

The magnitude of the asteroid was around 19.6.

[jimao22]

Thank you all !

Is just about now I am back on my computer. Some brief information about the set-up, the exposures and the target.

So I took the shots from my backyard observatory, MPC code L15 (Saint George).  I have a topic with the building process of my observatory here on this forum - is called "A Romanian observatory". The camera was the ATIK 460 EX mono, the telescope - MN190 and the mount - an EQ6 belt drive (a DIY old project). Because we need to obtain valuable data by having a very accurate light curve, the exposures should be as short as possible. This contradicts the need of good signal to noise ratio (about 10 minimum). On the other side, a CCD camera have a long delay of downloading all data, is the sensor is big. So I had to make exposures at binning 3x3 and to reduce the field at minimum, all for a fast download and high SNR. At bin3, my camera have around 916 x 730 pixels. I made a subframe of 200x200 pixels which is roughly 11'x11', enough to have 2 other stars near by our Star as references when photometry  will be applied.  With these settings I could made exposures of 3 sec with a delay for download of 0.74 sec (a ratio of 80% / 20% - which apparently is the best approach).

The target - Huya - is a trans-neptunian (also called a plutino object). It was discovered in 2000 by an astronomer from Venezuela - Ignacio Ferin - and it have around 450 km diameter. Hubble found  that Huya have a satellite with a diameter of 200 km, so is a binary system.  

The extended map of the occultation strip is bellow.

 

[Phil Fargaze]

Great team work by yourself and the other 10 astronomers. I have attached a map which shows the sites of other potential stations that were announced to get an observation, maybe you are aware of it.  You can see that there is a high concentration to the west of the prediction with a lower probability of success, but the exact path can always shift so it does show how valuable the fact that you and your observing colleagues managed to obtain some data (plus had clear skies). 

I obtained the information on the map from the freeware programme Occult Watcher which I use myself to organise my occultation observing. Link here

[jimao22]

Is interesting that as we know till now, only 14 astronomers had took pictures to this occultation and 11 of them are from Romania. The one who did organize the whole event was Marcel Popescu, a Romanian astronomer from La Palma, so perhaps this is the reason why so many Romanians...

Thanks for sharing the program. I will give him a try asap.

[SIDO]

Well done...Indeed.

[jimao22]

I made some (poor) photometric analysis in MaximDL with my data. What I know is the shape of the light curve is correct. I don't know (yet) how to adjust the parameters inside the program to have right magnitude of the stars. I used 1 reference star and 1 check star.

I made 2 graphs - first made from all my data (around 790 exposures) , to see if any other object intersect the path of star light and the second graph made from only 70 exposures centered around the occultation itself, to have a clearer idea about the shape of the curve.

Is not to much, but it is fun - I can tell you.    

[Chrystian]

Hi all

I'm one of other astronomers involved with analysis of data.

In total we have 17 sites with positive chords for this event (lots of data to analyse).

Congratulations!

[jimao22]

We have an update from the astronomer Pablo Santos Sanz from IAA Granada, the coordinator of this project. He sent us some preliminary data and a map with the observers of this event. Is truly a rare event, as he said in the mail received.

" I have generated a preliminary elliptical fit to the shape of Huya that I am attaching (North is up, East to the left). In my attached fit I have removed the scale in kilometers and the observers legend. 
Data are still under analysis and we cannot provide numbers in order to "protect" the future scientific publication currently in preparation. 

The additional information you could need: the occultation was observed from 50 sites (involving more than 50 people, including professional -from professional observatories- and amateur astronomers). From this 50 sites 21 recorded a positive occultation.
Occultations by TNOs are really rare, and involving an occulted star so bright (about 10 mag) are even more rare. Usually we catch occultations by TNOs in the range 16-18 mag for the occulted stars, for this events we can predict now about 5-10 per month, but we catch positive around only 1 per month (in the best cases). This is the first stellar occultation by Huya, and a record in terms of the number of positive detections! The first stellar occultation by a TNO was detected in 2009 (2002TX300) and up to date we have detected 70 stellar occultations by TNOs/Centaurs (43 by 24 TNOs, and 27 by 5 Centaurs), and we have participated in more than 90% of them! The work to predict one of this occultations is really hard, and can last for years in some cases, due to the high uncertainties in the orbits of the TNOs and the small angular size of these bodies in the plane of the sky (GAIA DR2 is helping a lot, with a very accurate position of the stars). "

The graphs down bellow is the photometry analysis for the Romanian astronomers involved in this (only two are a professional but one o them made the acquisitions from his private backyard observatory). I can tell you only that I'm number 7 in that list.