UT Apr 17, 2024: Photometry of asteroid (3) Juno

Michael Richmond
Apr 17, 2024

On the night of Apr 16/17, 2024, under fair conditions, RIT students Alex Speyer, Ben Hyman and I acquired images of the asteroid (3) Juno. They are part of the PHYS 373 "Observational Astronomy" class, and their project is to measure the rotation period of this asteroid. We acquired images covering a portion of the light curve on Mar 24/25, and the goal tonight was to fill in the gap in the light curve.

Clouds moved in near the end of our run, but we did take lots of good images earlier. Did we fill in the gap? Only time will tell ...

Asteroid (3) Juno

This asteroid has been studied for over 200 years. Its rotation period is thought to be about 7.2 hours, but we decided to measure it ourselves.

These observations involved:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ASI 6200MM CMOS camera
• B filter, 30 second exposures, and V filter, 30 second exposures
• images binned 4x4
• no guiding
• focus position on 12-inch:
  • in V: 0.507 yields FWHM 5 at T = 50/10

Notes from the night:

• Clear when we started at 10:50 PM, though the air felt somewhat humid. Clouds arrived around midnight, and forced us to close around 2:15 AM
• waxing gibbous Moon high south
• camera at T = -20 C
• temperature dropped from 50/10 at start of night to 42/5 when we quit at 2:17 AM
• slight scent of skunks around 10:30 PM!

The picture below shows an image of the field of Juno from this evening. The field of view is about 22 arcminutes across.

I've marked the location of several comparison stars from APASS9.

  star       RA       Dec          B          V         
------------------------------------------------------
    A    158.2520   +09.9507       11.074   10.858  
    B    158.0103   +09.9039       12.378   11.900  
------------------------------------------------------

 

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

The FWHM:

The graph below shows changes in the photometric zeropoint of an ensemble solution of the instrumental magnitudes over the course of the run. Note the evidence for clouds near the end.