Is beta Ursae Minoris a variable?

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RJN
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Is beta Ursae Minoris a variable?

Post by RJN » Sun Aug 29, 2004 3:08 pm

I decided to "try out a star" again recently to see if it was variable and to test NSL data's ability to find and track variability. I decided on beta Ursae Minoris (beta Umi) because it was near the top of the CI photometry files.

So now I think beta UMi might be quite variable -- at the level of almost 0.5 magnitudes in a single night. I used Polaris (alpha Umi) as the check star. There is a chance that I am seeing only some sort of altitude effect, but a preliminary check on that did not confirm it.

A quick literature search found almost nothing on this star. I could find two papers published in the 1800s indicating that beta UMi is variable, but nothing this century or last (1900+) so far.

Anyone want to check out beta UMi for themselves?

- RJN

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RJN
Baffled Boffin
Posts: 1670
Joined: Sat Jul 24, 2004 1:58 pm
Location: Michigan Tech

UMi maybe NOT variable

Post by RJN » Mon Aug 30, 2004 2:33 am

OK I have been studying Beta UMi a bit more and now am NOT convinced that NSL data shows it to be variable. The data shows Beta UMi dropping off toward morning on several successive CI nights. It shows the same behavior every night! Since the star can't know to do the same thing at the same time every Earth night, the variability must be caused local to Earth. Nearby Alpha UMi (Polaris) shows no such behavior, indicating that clouds and haze are not the cause.

The C5c-Bc column for ci040717 also shows a drop off. This is the column used to determine opacity. This might be expected as C5c-Bc is the average of several nights taken all at the same sidereal time (so the stars all appear in exacty the same positions).

Now the altitude of Beta UMi only changes by about 15 degrees over the data. Still, this must be enough to cause this great dimming, even though it is a red K star. Possibly this is because UMi is so near the horizon. Everything is obvious in hind sight! More later.

- RJN