2015 january/february, a possible eclipse of Alpha Comae Berenices - Help needed

[chrismlt]

Dear all,


This is my first post here. My english is not sooo good ; I hope you'll understand.


I'm Christophe, a french amateur astronomer. I discovered your forum a few months ago, and I like to read it sometimes, and to have some news from people « living with their head down » ;-) (« avec la tête en bas », as we use to say in french).


I'm in astronomy since I was a child, too many decades ago ;-)


I have been in Australia in 2002, near Broken Hill to see the TSE just above the horizon. And I came back in 2007. You're living in a very attractive country, were I would like to spend more holidays, some day, if possible !



Here you can find some images of the 2002 TSE.


https://www.flickr.com/photos/938266...n/photostream/
https://www.flickr.com/photos/938266...n/photostream/


Well.


I'm would like to ask if some of you, Dame and Gentlemen, would be nice to help to observe the possible coming eclipse of the star Alpha Comae Berenices.


You probably know this story.


Alf Com is a double star which orbital plane is almost seen from the side from Earth ; it is thought to show some eclipses once every 26 years, in fact, suspected since about the year 1850's. Last opportunity (1989), the star wasn't correctly surveyed. The next eclipse is predicted to happened sometimes between january 11 to febr 06 2015. So, this is the very hot period to survey this star, every night, right now.


The eclipse could last something like 25 to 46 hours (maybe less?), as calculated by Mr Muterspaugh (Tennessee State university), and the mag drop could be as deep as 0.5 to 0.8 mag.


As I understand that Alf Com culminates near 40° high, as seen from south of Australia and New Zealand, it should be easily visible and observable.


Visual observations are welcome : there are some comparison stars very near Alf Com : Beta Com is V4.23, 36 Com is 4.76 and 27 Com is 5.12. The main purpose here is to send an alert if an eclipse occurs.


Also, photometric observations are most wanted, of course. As Alf Com is a very bright star, defocusing is needed. A DSLR on a small tripod could do the job if the star is not saturated on the images (maybe some test needed).


We are a small group of amateur and enthousiasts from France, with observers from other european countries and from USA. Some scientists also joined us (the reference scientist is involved in this story). Our goal is to determine if an eclipse occur or not, and to caraterize it as good as possible.
Our observations will be send to AAVSO, and AFOEV (a well known association of variable star observers in France, at last).


It would be GREAT ;-) if some of you would join us to survey this star, because you're located in a very interesting longitude in Pacific/Asia area which is not very well covered now for this survey. And this is summer for you (a dream ! here, this is a cold winter with C-5 each night :-( !)



Some of our group started the survey in late december, as I did.


I use a FS102 apo, stopped down at 50 mm, and a DSLR for photometry, 100 iso, star images defocused as to form a large disk 80 pixels in diameter, exposure time is 180sec, focal lenght 640 mm. My main comp star is HD114326 (Hip Vmag 6.05), located 40' from Alf Com. The dispersion of the measures is something like 0.03 mag, which is good enough for this survey. Sometimes, when the conditions are perfect, the dispersion is no more than 0.004 mag.


There are some other stars for comps away.


The main paper to read is :
http://arxiv.org/abs/1412.1432


There is an AAVSO alert :
http://www.aavso.org/aavso-alert-notice-506


A mailing list was created for coordination of the observations and reports, were you can subscribe if you like (you are most wanted here ;- ) :
https://groups.yahoo.com/neo/groups/...m-Eclipse/info


The full story can be read here, with a large historical background (this is an automatic translation in english by Google) :
https://millimagjournal.wordpress.co...nices-english/




And the original version, in french, can be found here :
https://millimagjournal.wordpress.co...mae-berenices/




One can find charts, maps and other reference star here (sorry, in french, but maps are easy to understand, I hope;-) :
https://millimagjournal.wordpress.co...nices-updates/


Observations from december to jan 01 13 (preliminary results) can be seen here (in english) :
https://millimagjournal.wordpress.co...-observations/


There was also a paper in the january issue of S&T.


So the eclipse is yet to come. You can join, if you like. Your observations, visual and photometric, are most welcome, Dame and Gentlemen. This could be fun to help to resolve an astronomical mystery dating back from 150 years ago !



If you need some precisions, please ask.


I will come back with more results in the next coming days.


Best regards,
Christophe

[chrismlt]

Dear all,

You probably know that this campaign was cancelled soon after I send this call for observations.
Here are some news by dr Muterspaugh :

http://arxiv.org/abs/1501.05639

Christophe