FreeLists / az-observing / [AZ-Observing] Re: Trapezium Eclipsing Variable Star Light Curve

[Jeff Hopkins <phxjeff@xxxxxxxxxxx>]

Tom,

While visual (eyeball) variable star observing is interesting, I 
think it is much more exciting to follow a short period variable star 
system a bit more rigorously, even if done all visually. I suggest 
comparing the variable star (component A) to other Trapezium stars, 
component C (magnitude 5.1) and D Component (magnitude 6.7). Note the 
time and relative magnitude. Write down the time and estimated 
magnitude and do this through the night. I think you will find it 
more interesting as you  can still follow the star visually, but also 
have a written record of what happened and by plotting the data you 
should be able to see the eclipse in the plot.

As I understand it, the A system eclipses every 65.43233 days  with 
the eclipse lasts around 20 hours with a minimum of close to 2.5 
hours. The system is normally at V= 6.73 and fades to V= 7.65. This 
means the ingress an egress are about 8.75 hours each.

Note: Do not use component B as a comparison star as it is an 
eclipsing binary with an even shorter period of 6.47 days.

As Brian pointed out because these stars are so close together, 
normal single channel photometry is difficult and special techniques 
are needed. CCD photometry with a small objective and long focal 
length might work well, however. Then while nowhere as precise, just 
plain eyeball photometry is even easier.

Another famous short period variable is Algol. It is easy to follow 
and presents a similar situation. I followed it photometrically over 
several nights a couple years ago. It was a lot of work (several all 
night sessions), but also very satisfying. While the system has been 
studied extensively, it was excellent practice and I was able to 
produce three nice light curves (UBV).

Good luck and I look forward to hearing how it goes.

Jeff

At 19:24 -0700 11/5/06, Tom Polakis wrote:
>Thanks for the information, Brian and Jeff.
>
>I'm still not there, though.  Since the *minimum* occurs at 
>midnight, I am more interested in knowing how the brightness varies 
>as a function of time on either side of the minimum.  That is, will 
>it be at full brightness (or close, anyway) at 8 p.m., and again at 
>4 a.m.?  If so, this event presents an uncommon opportunity to watch 
>an entire eclipse.  Thanks again to Paul Dickson for bringing it to 
>our attention.
>
>Jeff, I am interested as a casual variable star observer because I 
>have visually observed the Trapezium hundreds of times, and look 
>forward to watching one of the stars dip and rise in brightness. 
>While I have great respect for any amateur who does science with his 
>or her telescope, I enjoy the hobby on a different, more aesthetic 
>level.
>
>Tom

-- 
Jeff Hopkins
HPO SOFT
Counting Photons
http://www.hposoft.com/Astro/astro.html
Hopkins Phoenix Observatory
7812 West Clayton Drive
Phoenix, Arizona 85033-2439 U.S.A.
www.hposoft.com
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