UT Apr 10, 2024: (Brief) Photometry of MU UMa

Michael Richmond
Apr 11, 2024

On the night of Apr 09/10, 2024, under poor conditions, RIT students Rachel Kulp, Evan Olsen, and I acquired images of the variable star MU UMa. Unfortunately, clouds cut our measurements short after less than an hour.

By the way, it can be difficult to locate information about this target, as the first two letters of its designation can also be used to refer to the Greek letter μ.

• MU UMa, an RR Lyr star of mag V = 11.5 is the target of interest.
• μ UMa, V = 3 spectroscopic binary is NOT the star we want.

MU UMa

This RR Lyrae star has a period of about 6.4 hours, according to its entry in the GCVS. Its amplitude is stated to be a healthy 0.5 magnitudes.

These observations involved:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ASI 6200MM CMOS camera
• B-filter 5-sec at first, then 4-sec for the bulk of the run; V-filter 1-sec at first, then 0.7 sec for the bulk of the run
• images binned 4x4
• no guiding
• focus position on 12-inch:
  • in V: 0.504 yields FWHM 6-7 at T = 67-ish F

Notes from the night:

• scattered cloud early, a brief period of mostly clear skies, but then steadily growing cirrus forced us to stop around 10:30 PM.
• very warm and humid; as soon as we closed, raindrops started to fall
• no Moon visible
• camera at T = -5 C, due to the very warm temperatures (air inside the dome was 81/27 when we opened)

The picture below shows an image of the field of MU UMa from this evening. The field of view is about 26 arcminutes high.

I've marked the location of several comparison stars.

  star       name                  B          V         
------------------------------------------------------
    A       APASS9 5745086      10.607     -----    
    B       APASS9 5745071      10.254    10.013    
    C       APASS9 5744968      11.105    10.553    
--------------------------------------------------------------------------

 

Here's the sky background over the course of the run. Note the rise due to clouds at the end.

The FWHM rose to 5, then was steady.

The graph below shows changes in the photometric zeropoint of an ensemble solution of the instrumental magnitudes over the course of the run.