(2060)Chiron Lucky-Star campaign: 2019-Sep-08

Updated: 2019 Aug 03

Introduction

Prof. Bruno Sicardy et.al. (ERC Lucky Star project, l'Observatoire de Paris) and IOTA-ES (pro-am collaboration) request amateur observers in the UK to monitor this prediction involving the total occultation of 16.3 magnitude star in Pisces: UCAC4 474+000226 at altitude/azimuth of 35/141 on September 8th centered at 2304 30s +/- 13 sec UT. The Moon is setting.

Suggested recording time is 2302 to 2307 UT. The maximum event (D-R) duration is 10 sec. A 40 to 70 cm appeture has been suggested and 1 sec cadence (or shorter)


http://lesia.obspm.fr/lucky-star/occ.php?p=3885

Chiron is one of the Centaurs, otherwise classified as 95P/Chiron, the most distant minor planet at the time of discovery in 1977 and believed to be a comet with an Aphelion of 18.9 AU, and orbital period of 50 years.

The next star occultation is over the British Isles on 2019 Sept 08 at 2304 UT, when the shadow is predicted to cross Northern England and Scotland. The uncertainty indicates that observers anywhere in the UK should attempt to observe. It will be a challenging observation so planning and test runs are suggested. It should be interesting! The probability of recording an occultation (due to prediction errors) is 39%. Please report all recordings.

Predicted shadow and centre line. Some observatories are marked.

 

Key: Invited observatories ( List under development )

Planned observations ( test runs and other factors allowing...)

Sherwood Observatory, (Mansfield and Sutton AS)
West Park Observatory, (Leeds),
The Amateur Astronomy Centre, ( AAC,Todmorden)
University of St Andrews
University of Central Lancashire (uclan)
S Kidd (Stevenage)
Isle of Man AS

Observing Aims

The lucky-star project need many more chords to improve the shape profile of this minor planet. A time accuracy (exposure) of 0.5 to 1 sec should provide new data. Of more interest is the search and detection of rings or possible satellites. This will require a time resolution (exposure) of the order of 100ms. Ring detection may require a 50 to 80cm class instruments and dark skies.

What the amateur can contribute with 30 to 40cm, are the chord information (duration of occultation) from widely spaced positions across the path. Video cameras such as the integrating WAT-910HX would be ideal, but any mono camera could be used. Larger CCD/CMOS cameras should be operated in binning mode (e.g. 2x2 or 3x3) to obtain a plate scale near 1 arcsec/pixel (typical). Some experimentation prior to the event will be needed. Please check the PC clock time is correct to within 50ms of UT prior to recording, and afterwards.

Suggested systems:

30-40cm SCT, F 3.3 reducer,

50 to 70cm Newonian. RC etc.

Large Dob and CCD Drift Scan (untested by the writer)


Observing / recording protocol

Obtain some test sequences on the star field days/week before under good conditions to check detection, and become familiar with the setup.
We assume the observatory will have some light pollution, and SQM 20 may be typical (20 mag/arcsc2).

Check the PC clock is synchronize to UT via NTP, or some other means. Make a note of any offset before and after observation.

Focus the camera
Goto the star.
Use binning and/or sub-frame to optimise detection and cadence.
Check there is at least one other brighter star in the field of view to monitor seeing condiions.

Prepare to record from 2302 to 2307 UT at 1 frame per second, or adjust for best detection.


Optimisation

1) Use a focal length that matches the detector pixel size. We should aim for a star image that fills one pixel. Due to changes in seeing stability the star image can fluctuate between 1 and 3 arcseconds in size. The image should be oversampled a little bit, but not a lot. Using my 30cm F/4, the plate scale with a video camera of 8.5x8.5um pixels is 1.5 arc sec. (good)

A 40cm SCT with F3.3 reducer and same video camera gives 1.3 arcsec/pixel

A 40cm F/8 RC and ATIK 314L+ produces 0.4 arcsec/pixel. This is a bit too small, and CCD 2x2 binning would improve sensitivity and lower the image size Kb and improve cadence.

https://www.atik-cameras.com/news/binnning-the-differences-between-cmos-and-ccd/

2) Focus. A basic requirement and so important. Get good focus at the centre of the field using software or a mask, or use the diffraction spikes of a bright star.

3) Reduce light pollution. Not easy. Local lighting can be nuisance, even inside the observatory.

4) Unsure of this, but a mono USB2/3 planetary camera has greater bit depth (10 - 12 bit) compared to analogue video (8 bit). This should give better definition when looking with faint objects like this.

 

FINDER CHARTS:

Coordinates for UCAC4 474-000226
00h 10m 13", +04d 37' 05" (J2000)

Star magnitude 16.1 to 16.5 depending on spectral type.

7 degree field:

1 degree field

 

0.3 degree field:

 

ALADIN Field. A cross marks the star.


General tips for observers / recorders:

1. Planning:
1) Let the writer know if you plan to observe and your location (even if you don't observe in the end). occultations AT stargazer DOT me DOT uk
2) Please do observe even if you are outside the dotted line limits. These observations may be negative or short duration.
3 ) Allow enough time to find the correct star. The asteroid will be much fainter.
4 ) If you use a mobile telescope, make notes on its location so that we can get its coordinates from Google Earth.

2. Planetary Cameras:
1) Where possible use a focal reducer to get F3.3 to F5 or thereabouts.
2) Download and install Dimension 4 software and use it to update the computer clock to +/- 0.05 sec. ( for NTP)
3) Use the camera software control to add the computer UT time stamp to the frames. This can be done with SharpCap and FireCapture (or other products).
4) Often there is a log file function. Use this to add extra info.
5 ) Select an integration time that records the target star. Use trial and error to get best result beforehand. If unsure make a recording anyway.

3 Reporting:
1) The observer should play back the file and note the approximate times of any events. A software analysis will be needed to extract the exact times.
2) There is a free software tool (TANGRA) if the observer does the analysis, otherwise send the file to the writer for analysis (drop box, wetransfer etc).
3) Negative result (no occultation) are as important as the positives. Please report negatives or "unsure".
4) There is standard report to fill out. Contact me if you have a successful recording.

Good luck...

Tim Haymes

Tim Haymes: occultations AT stargazer DOT me DOT uk

Assistant Director, BAA Asteroids and Remote Planets Section, Occultations.
Member of IOTA/ES

[ PS: If you see any typos, drop me an email thanks :-) ]

 

More information:

About occultations and this page:
This is a personal web page to support occultation observers. There is a Yahoo! group: UKoccultations which observers are welcome to join.
An observation sent to the writer is checked and forwarded to the BAA which will perform a preliminary analysis prior to submission to IOTA-ES
and for PRO-AM collaborations, to the designated data collector.

Acknowledgements:
ERC Lucky-Star
SkyMap pro 11 was used to present the path on the sky and the star fields.