Starship Asterisk*

Here is an example of finding stellar variability with NSL data. First, I went to http://alcyone.de/ and looked for variable stars. I decided that I wanted something that could show variability in one night, was bright, and was visible in recent days to the Cerro Pachon (CP) CONCAM which has been returning great data.

Recent experience shows that CONCAMs can usually find variablility at the level of 0.1 magnitudes or higher without sophisticated analysis.

So I looked at Alcyone's variable star page here: http://alcyone.de/SIT/variables.html and tried to find a bright, fast, big-change variable. I noticed on that page that the Delta Scuti variable section here: http://alcyone.de/SIT/delsct/delsct.htm lists some variables that change in just a few hours. Several of these appear visible to CONCAMs but I chose Rho Pup, a variable with a listed variability of 0.2 magnitudes over 0.14 days.

Then I went to into the CP archive here: http://nightskylive.net/cp/archive.html
and clicked on a night new new moon here: http://nightskylive.net/cp/cp050210.html and then clicked on (any) one of the photometry files when the sky was clear like this one:
http://nightskylive.net/cp/cp050210/cp0 ... 2501p.html
and then clicked on the hotlinked HD link for both Rho Pup and Tau Pup. Tau Pup would be a constant check star. I wanted the same constellation so that they would be near each other in the sky.

I then copied the photometry file for Rho Pup here: http://nightskylive.net/cp/cp050210/HD67523.html
to Excel and right next to it the photometry file for Tau Pup here: http://nightskylive.net/cp/cp050210/HD50310.html . I passed up on some brighter stars in the Pup constellation because they sometimes saturated the detector coming near 64,000 counts.

Next I took the ratio of each stars (C5-B) counts to its own listed (C5c-Bc) counts. The then took another ratio of the result for the two stars. This method uses canonical C5c-Bc parameter computed by Lior's WOLF program as a same-sidereal-time standard. You still need a check star (at least one!) because the whole sky could be somewhat cloudy at any time.

The resulting Excel spreadsheet is here: http://nightskylive.net/temp/RhoPup.xls .

The resulting plot of the brightness ratio is here:


Note that the ratio is nearly equivalent to magnitude change. It appears to me that variability is evident at the 0.1 magnitude level (i.e. ratio 1.1) at the 0.14 day period.

This was for one night! Possibly this star could be checked for other nights. Possibly just finding the modern values of the amplitude and period independently from NSL data could be worth a short paper.

- RJN

following are the plots for the Tau & Eta Puppis which are constant stars according to alcyone.de

This plot shows Delta Mag Vs Truncated Julian Day (TJD). The magnitude change is within 0.1 m


This is same as the above plot except that here Eta Pup is the reference star instead of canonical frame. Notice the Delta Mag increase.


This plot shows the Delta Mag of Tau & Eta Pup Vs altitude seperation between them. So if we are taking reference as another star in the same constellation, we should be careful in choosing the reference star so that it is not farther than just few degrees.


So the conclusion is , taking canonical frame as the reference is better than taking other reference star. Now this holds true for constant star. I donot know if this would work also for variable star.