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AL Com

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Xilman's picture
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Last seen: 2 hours 6 min ago
Joined: 24/03/2018 - 15:17
AL Com

This is a bit of silliness.  AL Com is one of the VSS program stars which spends much of its time down at 19th magnitude or so but I keep an eye on it for any outbursts.  My kit would need several hours exposure through a V filter to get anything measurable when the star is at minimum but on this occasion (20190303/4) I kept taking images until something appeared.  Still not measurable but visible, sort of.  The only reason for doing so is that M88 is in the same FOV and it was an opportunity to take a pretty picture.  The images show AL Com (circled pixels) with  maximally stretched contrast, and the spiral arms of M88 in a quick&dirty co-added image.  Doubtless a far prettier image of the galaxy can be obtained from the data.  I may even post it one day. Total exposure time was 5675 seconds.

AL Com would have been very obvious in an unfiltered image.

garypoyner's picture
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Joined: 04/03/2014 - 15:40
AL Com & M88

I've picked it up a few times at minimum with the old BRT and new COAST telescopes, unfiltered and 60-80 seconds exposure varying between 18.5-19.5.  It has quite a range at quiescence ~18.5-21.00.  Seen a few outbursts visually too.  More exciting than ogling the galaxy ;-)

Gary

Xilman's picture
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Joined: 24/03/2018 - 15:17
Re: AL Com & M88

I'm not sure about the apertures of those scopes.  Could you enlighten me please?

Experience from my Sycorax adventure last year suggests that 21.0 or brighter should be possible with my 40cm unfiltered iand with decent seeing. When the seeing is >10 arcsec, which it has been quite often recently, dilution by sky background can be substantial.

Despite my "silliness" quip, is there any value from taking unfiltered measurements?  If so I may repeat the experiment as I've essentially no interest in taking images of no scientific importance.  If there were a SN in M88 to be discovered on the other hand ...

garypoyner's picture
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AL Com

The scopes are C14's.

The value of unfiltered measurements is immense.  See the number of papers in the BAAJ or other (professional) journals which contain unfiltered data from amateurs to see just how important they are.

Simple patrolling for outbursts for example - deeper images unfiltered or less exposure time.  Time series observations during outburst are just as valuable unfiltered - it's the period and amplitude which are important here, not necessarily the intrinsic brightness.  And of course, an unfiltered observation is better than no observation at all!

Gary

Martin Mobberley's picture
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Last seen: 1 month 6 days ago
Joined: 05/03/2014 - 09:02
AL Com

I last imaged the field, after a false alarm, back in 2015, with the 24-inch itel T24 in California. 3 mins unfiltered.

http://martinmobberley.co.uk/images/AL_Com_20151114_1301_mpm.jpg

Martin