Automated surveys and Comets in Milky Way Starfields.

[Mick Crook]

I recently re-read Martin Mobberley’s book on Hunting and Imaging comets. Martin notes that the professional surveys often miss new comets moving through the dense starfields of the Milky Way due to the limitations of the software used (page 172), and also the polar regions above dec +80 degrees due to mount limitations. The book is a few years old now, but I was wondering if Martin’s comments are still valid today? Or are the automated surveys now able to successfully cover these areas?

Many thanks,

Mick.

[Dr Paul Leyland]

Good question.

Given that many new facilities are on alt-az mounts …

[Martin Mobberley]

I think the Dec limitation is far less relevant now but searching deep in the Milky Way is still a big problem. The original Pan-STARRS spec. took 2 to 8 images of the same field each night. The software looked for two rates of motion, 0.75″ to 1.75″/minute (slow) and 3″ to 12.5″/minute (fast). Of course, NEOs are the main target, not comets. The reason for the gap was that software searching for faster than 1.75″/minute produced loads of false suspects, but faster than 3″/minute these could be eliminated because the genuine NEOs would reveal a slight trail in 30 to 60 seconds. Some time ago Pan-STARRS stated their software had now closed the false-alarm gap, ‘away from the Galactic plane’…. So I guess that at an average rate of motion in the gap of 2.4″/minute, objects in the densest part of the Milky Way can still evade detection? There are charts of sky patrol coverage on the MPC website. Unfortunately due to the MPC computer crash of a few months ago these are not up to date, but sky coverage from earlier this year can still be checked…Unfortunately the charts are in RA and Dec only but they do show how dense the Sky Coverage is! The page is at

 https://minorplanetcenter.net/iau/SkyCoverage.html

You fill in the details and hit ‘Generate Plot’…..

Martin

[Mick Crook]

Many thanks for the detailed reply Martin. I’ve found it most useful.

Mick

[Dominic Ford]

My understanding is that the limitations in Dec have more to do with the altitude of the celestial pole, rather than the mounts the telescopes use (as Xilman says, most large telescopes are alt-az). Pan-STARRS is observing from a latitude of 20°N, so the pole is only 20° up and it’s not really worth wasting valuable observing time on it!

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