Two interesting occultations within 24Hrs: evenings of May 06/07

[Tim Haymes]

Long post, so here we go…happy to discuss.
1) Comet 29P/Schwassmann-Wachmann-1 predicted to occult TYC 1888-00333-1 on May 7

On May 07, 2242-2245 UT, there is a rare opportunity to obtain size constraints on the 29P comet nucleus by observing the occultation of a v11.7 star. TYC 1888-00333-1 has J2000 coordinates: 06:40:53.4 +26:51:43.5 Maximum duration of occultation: 2.0 s

29P is well known for its regular outbursts and large nucleus known to measure at least 60 km across. A campaign of stellar occultation predictions has been underway as the comet moves through Gemini. This prediction of an 11.7 magnitude star is most unusual and visible only from the UK and possibly Northern Europe. Observations are requested from anyone in or near the shadow path which covers a wide area of UK, North to South. You will need a mono CMOS imager and expose at about 5 fps for 2 minutes. More info in the links below.

Prediction: https://lesia.obspm.fr/lucky-star/occ.php?p=122512
Web page and notes: http://www.stargazer.me.uk/call4obs/29PUK20230507.htm

Send observations to Richard Miles (Director-ARPS) or Tim Haymes (Assistant Director – Occultations)

2) (121) Hermione occults 9.2mag TYC 1887-01582-1 on 2023 May 06 at 2246-2248 UT
This event is highly favourable for large parts of the UK and N Ireland and occurs 24 hrs before the 29P event above. The star should “blink out” for up to 6.1 seconds as the large 360km asteroid passes invisibly over. [ NB: The events: 29P and (121), are 2 degrees apart on the sky plain and the shadow paths are coincidentally near identical !]

Weather permitting (121) could be enjoyed by visual observers, and those with EAA equipment. Scientific measurement can be obtained with CMOS/SER or FITS file recordings when the PC clock has been synchronised to UT about an hour prior to observation. Notes as above.
Details here: https://cloud.occultwatcher.net/event/855-121-91942-649707-T01582-1/902195
And here: https://asteroidoccultations.com/2023_05/0506_121_80646.htm

Best of luck with the weather which is often spoiler ! and dont forget to send us a report 🙂
Tim Haymes (BAA-ARPS) Oxfordshire, Y98.

[Robin Leadbeater]

On an associated note, does anyone know if these kinds of events (not necessarily occulting the nucleus) can be used to probe cometary “atmospheres” (coma and tail) using multiband photometry or spectroscopy? This star would be too faint for high cadence spectroscopy but comets sometimes pass close to brighter stars

Thanks
Robin

[Tim Haymes]

Not sure Robin. Molecular absorption will be in the IR 2-20 u looking at my university notes. Interesting thought though.

Images of the target star taken last night (May 01/2), have been added to the page. http://www.stargazer.me.uk/call4obs/29PUK20230507.htm
They indicates an aperture from 8 to 10″ could image the star with exposure 100 to 200ms, even in poor transparency.

I hope some observations will be possible and we get some chords. This will be my last update to the page prior to the event.

To be clear, a “chord” across an asteroid profile is two time points: Disappearance and Reappearance of the star, as seen by the unique position of an observer.

Good luck and clear Skies !

[Nick James]

I was monitoring it in Chelmsford using an HD11 + ASI6200. Half the telescope aperture was occulted by my observatory shed and the the rest was looking through the branches of a tree. Because of this I had to use 0.25s exposure to get the star. At least the sky was clear but but no occultation detected here.

The comet is currently in a faint state. The attached is a 60s exposure taken at 2127 showing the comet and the star.

Attachments:

1. 

   29p_20230507_2127_ndj.jpg
   

[Richard Miles]

Thanks Nick for monitoring this event. The weather forecast was borderline and with such a low altitude it was likely to have been affected by clouds towards the local horizon. That’s what happened with Alex Pratt just 3 minutes before the predicted time but I must say I did not expect Alex to have a clear sky full stop. I see that Phil Denyer also recorded a negative observation from somewhere in London. His result may shift the position of the shadow track further west than yours does. The shift has a bearing on the exact prediction for the forthcoming May 21 stellar occultation involving 29P, that will be visible from across Spain but at a similarly low altitude in the sky. See:
https://astro.kretlow.de/cora/occultations/da2f2c54-7d6c-4f12-a56e-8aeeaf7efd0b/
This involves quite a bright star (~9.8R) so fast video should be possible provided the sky is clear.

[Alex Pratt]

Richard – yes, my C11 had a clear view of the 29P field until 3 minutes before the predicted time of occultation. IERS tell us that the Earth’s rotation is currently speeding up, which they measure to microseconds, but last night it seemed to ‘put on a spurt’ when the field stars faded as they slipped behind a rooftop. 🙁

Most likely I would have recorded a negative (miss) observation from my location (outside the predicted shadow zone), but very frustrating to be thwarted in that manner!

Alex.

• This reply was modified 11 months, 3 weeks ago by Alex Pratt.

[Richard Miles]

Alex – Well done for trying. At least you didn’t miss a positive from your observing site!

I have had two similar experiences; one when a few minutes before the predicted time, a cloud appeared from nowhere in a clear sky and prevented any timing. And another occasion when I had to travel 12 miles to get to my observatory so by the time I got there the sky had started to cloud over badly. I set up and managed to have enough sightings of stars to set up pointing the telescope in the right direction and, low and behold, some minutes before the due time a sucker hole appeared allowing me to achieve a timing.

Richard

[Alex Pratt]

That’s the challenge of occultation work – right place, right time, right weather.

Alex.

[Robin Leadbeater]

The 29P event was unobservable from the observatory so I set up some kit on the patio with a clear view and blue skies in the afternoon but was clouded out well before the event which was a shame as I was just inside the Eastern edge of the predicted track.

[Tim Haymes]

Thanks to all for reporting. So far no positive events but there are -ve ones (to be confirmed), and some reports to come in.
Considering the difficult conditions, many thanks for effort to observer, its much appreciated. The -ve results will help restrict the orbit better
for the next prediction.
Tim

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