Last night, Ice-In-Space member AstroJunk observed a 12.2 second occultation of the trans-Neptunian object 2002 VE95 from south Queensland. It's the first time VE95 has been seen in occultation, and the occultation has already garnered interest from the science community.
While VE95 has an apparent magnitude of +20, and thus is pretty well invisible to all but Large Scopes, the occultation was of a mag. +14.5 star which is much more do-able with telescopes that amateurs can acquire.
VE95 is about 29 AU from earth at present, close to perihelion; at aphelion it is around 40AU distant.
Previously VE95 had a diameter determined from photometry of about 248km +/- 13km; the occultation means it is likely to be at least 30km larger than this.
Thanks for the plug Tony, it's not often we get to bag an event with such a scientific payload! I'm looking forward to seeing a paper based on it. Shame we didn't get a second chord, but it's only a matter of time before the Aussie observers get another chance.
I've you-tubed the video here: https://youtu.be/ISNsb6H-sa8 Amazing how such an insignificant 'blip' can tell us so much about our outer solar system
Excellent work Jonathan and thanks for the heads up Tony.
What was the optical system (aperture and fl) that you used to acquire the video sequence, which was so much more positive and unambiguous than I had expected?
Congratulations indeed Jonathan. Your dedication and hard work paying off.
Peter
Dedication maybe
Quote:
Originally Posted by Robh
I'm surprised that a body of that size has not had a previous occultation result.
It's incredible how rare these events are, and even more so how localised the shadow path. This year, only two events involving TNO's have been detected by the combined professional and amateur communities, and both of those events have been me! I'm the only person on Earth this year to measure a TNO. And from my back yard, I find that amazing.
Quote:
Originally Posted by Dennis
What was the optical system (aperture and fl) that you used to acquire the video sequence, which was so much more positive and unambiguous than I had expected?
14" Meade LX200 @ f2 using Hyperstar. Under sampling is the key to occultation observing - the images are not so pretty, but the S/N ratio is fantastic
Fantastic results! Didn't even know that you could Hyperstar a Meade. I am sure someone will go and write a paper on it at some point, not my field of research though :/
Fantastic results! Didn't even know that you could Hyperstar a Meade. I am sure someone will go and write a paper on it at some point, not my field of research though :/
The older 14"ers had a Hyperstar, otherwise its purely a Celestron thing.
A paper is likely to follow - It turns out that my observation means that the TNO is somewhat larger than expected which means that it is either irregular or less dense than usual. Both outcomes are getting the professional community animated!
Normally it requires at least two observations of an object during a single event to provide a significant scientific payload. We just got lucky that I may have been very close to the Centre line so that despite not being able to construct a shape from two or more chords, there is enough data to be interesting!
Jonathan - I have little experience of this type of event - or interpreting such data, but from your photometry graph, there appears to be a non-abrupt 'ramp' from >12:30:15 UT to 12:30:20, which is not seen at the commencement of the occultation (12:30:05).
Could this be indicative of VE95 being non-spherical (or perhaps a contact binary)?
(Please excuse my ignorance if I'm talking dribble!)
Thanks. In this case, I would take it as a relic of the integtation method of the camera rather than an actual event. If the actual occultation happens mid integration the step is like that on the left, if it is closer to the integtation boundary then the step is like that on the Right.
Ive attached a couple of main-belt events I captured in 2013 with brighter target stars, one was a double star discovery, the second I think may have been a contact binary in a N-S attitude, but not really distinguisgable from possible Fresnel effects. That one was never followed up.
That's the fun of Occultation timing, you never know what you are going to find!
The theory goes that if the star is also a disk and not a point (they are usually a I milli-arc second dot) then there may be Fresnel effects, but that is very uncommon and certainly not in the case of the observation I made.
Each data point represents (usually) 40 milliseconds, so in a normal instantaneous event then there will be a straight line drop with possibly a data point in-between if the actual event was mid exposure. In my speculative contact binary example, there are too many data points during disappearance and reappearance.
I've just found this diagram I did which suggests also an oblique event. If the latter were true, then the asteroid would most likely be a variable, but I can't recall that being the case.
I'm now puzzled by your 'double star' event: why would the data be symmetrical?
If the 1st 'dip' is occultation of one of the binary star pair, and the 2nd dip is indicative of the same for the other star, how can the process subsequently be exactly reversed?
Surely there should be an initial 'dip' (1st) , a final 'dip' (2nd) then restoration to normal with no intervening steps?
The nearest I've seen is (I think) the demonstration that Uranus (or Neptune?) has a ring system - the rings were seen to partially occult a star, then complete occultation by the planetary disc, emergence followed by partial occultation by the rings on the other side of the planet, then back to normal.
Which is just what your 'binary star occultation' data look like to my (perhaps distorted?!) thinking!
Could your 2013 binary star data also be interpreted as the occulting body having a ring system & hence the detected luminance symmetry?
I take it all back - I can see how relative geometry can account for such observations - a the components of a binary star can appear to us in any orientation & the occultation can similarly take place in any given plane.
Follow up observations can be critical - as you gave already worked out, there are many different ways to interpret the data and a single event is often only indicative of what is going on. As more observers record an occultation, the value of an event goes up enormously. Unfortunately, we are pretty thin on the ground in Australia.
and thanks for the heads up Tony.
