Dave McDonald discovers new variable star!

Woah, slow down guys! I can't keep pace with mails to SDAS members about the latest discoveries or honours in the Irish astronomy community :laugh: :laugh: :laugh:

Seriously, my heartiest congratulations Dave on this latest find. The work you and all the other active observers put in is surely instilling the joy of astronomical discovery in many, many others.

One amazing variable star find I recall from a good few years ago is that by Peter Collins in the US. He was looking at a photo of the Dumbbell Nebula on the cover of an issue of Astronomy magazine and noticed a star out of place. It turned out to be a new variable!

Talk soon,

John

Dear Dave,

My heartfelt congrats as well.

I am going by memory but were the asteroid discoveries by yourself and that guy Grennan also not in the month of October (2008 or 2009)?

Anyway, this is great news and especially involving personal friends (yeah, Grennan too).

When you have a few minutes to kill (there is an oxymoron), can you provide us some details as to the process involved in getting suitable data for AAVSO? I had a similar indication a few weeks ago but I did not follow it up (just too lazy).

Congrats once again!

Anthony.

well done dave, you are setting the standards for the other "real" observatory in kildare .

Folks - I'm a tad busy at the mo but I'll fire up an in depth post a little later tonight and I'll give ye all the scoop image too - not published anywhere else. But don't get too excited...

Firstly - thanks to you all for the usual kind words. Sorry John - we'll try slow down for you... The anecdote is classic!

Anthony - yes, October is a productive month indeed - October 2008 were the two asteroid discoveries, followed by two more in March 2009. October 2010 is the Supernova and the Eclipsing Binary. So, March 2011 will be interesting... Especially for the other "real" Kildare observatory...

Trevor - that's great that you've refound the passion - long may it continue. And yes Peter, time to change the name - visions of the movie Spartacus come to mind...

So, a bit more background information for those with an interest.

I've been working up to photometry for the last few years and just a few weeks ago got my first asteroid lightcurve. That went so well that I'm currently tracking another asteroid with an unknown lightcurve. It must be a million-to-one shot that I chose the right asteroid, at the right time, and in the right part of its orbit, with a clear night, and at the weekend, and only my second serious asteroid lightcurve... But, I did.

So the process for the asteroid lightcurve is take as many images as possible for as long as possible. The images are then analysed - I chose five stars to use as comparisons for the asteroid. So, if we assume the asteroid is a potato (not literally of course) and tumbling around, its reflected light will alter. But the comparison stars shouldn't. We can therefore do some processing, add in some maths and work out *how* the asteroid lightcurve changes and graph it. It can then be published and the data is useful.

One of the first steps in the processing cycle is to look at the curve of the comparison stars - all five of them. You're looking for a nice straight line - ie a steady magnitude. Of course, I was surprised to see a very small "dip" in one of the stars. My very first reaction was actually - "oh that's a pain, I have to go find another steady comparison". My second reaction was "oh, that's a funny dip" and I put it to one side.

I processed the images with my asteroid (5714 Kransisky) and got a partial curve - but realised I needed at least a couple more nights to complete the curve. So then I went back and I made the "oh, that's funny" star the subject for investigation. After processing, it was clear that this was a *big* dip - about 0.4 mag in the space of about 90 minutes or so.

Then I decided to mail Brian D Warner - the Author of Canopus, the photometry software I use - and he mailed back telling me to check it out with AAVSO. He also asked Arne Henden (Director of AAVSO) for an opinion and he also agreed it was worth following up. Now, I have a confession - in the tiredness of the night or due to my lack of knowledge of variables, or whatever, I accidentally flipped the curve upside down to make it look like the star had risen in magnitude. But Brian and Arne were very forgiving of my faux pas...

Anyhow, checking AAVSO, there was no variable star noted at the position I had. Sure, there was a star alright, but it was just not noted as a variable. Then followed a really tricky process for me because I was now firmly out of my comfort zone. I had to complete an AAVSO report for the very fisrt time - I couldn't have done it without the patience and assistance of Sebastian Otero - an AAVSO moderator. And then sure enough, word came back in the wee small hours of today, Tuesday 19th October that it was a new variable star.

Initial indications show that it is possibly an eclipsing binary. To confirm this, we need to try and find the second dip - there is usually a second dip for binaries, but not always. So the work continues and watch this space.


As with any aspect of this hobby, I have discovered over the years the following:

1. There are so many people out there willing to give freely of their valuable time to help out
2. You cannot do this stuff on your own

For all the work I have done and for the achievements I've been lucky to attain, there are many many other people who have freely and gladly given of their time - you know who you are. Thank you all. This is your discovery too.

For those that have an interest, I have always and will always give my time back to anyone who wants it. Quid pro quo.

Now for the scoop that you all deserve.

The image is its first publication anywhere. The lightcurve show you the extent (and steepness) of the dip. I've also included links to higher quality versions too.

You'll see the images are copyrighted - don't worry - they are free for all usage. If they are used in publications though, I'd appreciate you dropping me a line just to let me know. See www.astroshack.net for my email address or drop me a pm from this site.

Thanks again and enjoy.
Dave





Links to higher quality files
Chart: www.astroshack.net/images/000-BJX-116-chart.jpg
Image: www.astroshack.net/images/000-BJX-116-img.jpg

Heartiest congrats Dave on the 'accidental' find! I'm sure Holly knew it all along! :laugh:

stepryan wrote:

well done dave, you are setting the standards for the other "real" observatory in kildare .

As if there was any doubt!

Paul.