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Astrometry and photometry of PHA (162082) 1998 HL1


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About this observation
Alex Pratt
Time of observation
04/11/2019 - 00:00
PHA (162082) 1998 HL1
Observing location
C11 f/10 with f/3.3 focal reducer
Watec 910 video camera
IOTA-VTI GPS time inserter
OccuRec (recorder)
Tangra (analysis)
Various short exposure settings <=1.28s
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Better skies in the second half of October allowed me to obtain 25 GPS-timestamped video recordings on 7 nights of the flyby of this PHA (Potentially Hazardous Asteroid). Astrometry and photometry were reported to the MPC.

NEODyS automatically scans any observations of NEOs reported in the MPC Circulars, it analyses the data and makes it available on its website. The results include each observation's residuals measured in RA, Dec and magnitude, using OrbFit software. This allowed me to compare motion-fitted GPS-timestamped video astrometry and traditional CCD astrometry.

The attached diagram shows the residuals in RA, Dec and magnitude for the second half of October. I was surprised to see such a large amount of scatter from some of the CCD stations, particularly for the magnitude estimates, where CCDs should be more accurate than video. (NEODyS derive residuals from G, R and V magnitude estimates, so this could explain some of the variability).

Overall, the raw data showed small O-Cs for the measures of RA, and larger O-Cs in Dec. NEODyS give a multi-year RMS residual of 0.498".


djswan2002's picture

Your data is impressive. How much video data apart from yours in out there? A bigger comparison data set (CCD vs video) might be interesting.

A R Pratt's picture

Hi David,

There's a small number of observers using video astrometry and submitting reports to the MPC, although I didn't see any monitoring this flyby. When an object has an apparent sky motion >2"/min Tangra performs motion-fitting and the times of its 'mini-normal' measurements are given to 6 decimal places, e.g.

G2082         n2019 10 26.97675902 04 42.50 +17 20 08.0          12.4 R

The 'n' in column 15 indicates astrometry derived from video mini-normal measurments. I didn't see any other observations in this format during late October.

My user guide can be found here. I need to update it to include the current workflow using OccuRec, but most of the text is still valid.

djswan2002's picture

I wonder how many people have a true video camera with time inserter hooked up to a Hyperstar configuration....

A R Pratt's picture

Hi David,

I guess there won't be too many Hyperstar systems used for astrometry. They give a nice wide field and in dark skies can reach good limiting mags, but I wonder if the image scale isn't helpful for astrometry. My C11 working at f/3.3 and Watec 910 video camera gives an image scale of ~1.8 arcsec / pixel. Does the Hyperstar give a flat field across the sensor?

Clear skies,


djswan2002's picture

These are good points. With a small chip you get a very flat, very well illuminated, field about 1deg across. That's what I tend to use most of the time as it suits me. Obviously with the larger sensors, field illumination away from the centre becomes an increasing problem. I'm not sure about field curvature in the outer reaches. David

A R Pratt's picture

My setup gives a field of 0.5 degrees across the sensor's diagonal, so as long as that's well collimated and in good focus I can obtain good astrometry from this central zone.



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