UT Oct 10, 2020: Photometry of KK Cnc

Michael Richmond
Oct 10, 2020

On the night of Oct 09/10, 2020, under fair conditions, I acquired images of the star KK Cnc . A message from Taichi Kato, sent to VSNet on Oct 6, 2020, requested observations of dwarf nova; the last time it was observed in outburst was 2007.

Re: KK Cnc outburst!!

   ASAS-SN data.  The object started rising on Oct. 3.

https://asas-sn.osu.edu/light_curves/715b58ff-70a3-441b-8132-7a39641c60e7

   The last superoutburst was in 2007.

My measurements suggest that the star may be varying in a gentle sinusoidal pattern with a small amplitude (just 0.02-0.04 mag?), but the duration is too short to be sure.

KK Cnc

You can find some basic information on this star at the SIMBAD page.

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ATIK 11000 CCD camera
• no filter, 20-second exposures
• images binned 2x2
• no guiding
• focus position unknown (see below), FWHM = 4.0 pixels.
• camera ran at T = -20 C

Notes from the night:

• very warm for the season: 64/18 at open 3:30 AM, 61/16 at close 7:14 AM
• bright third-quarter Moon low in East, not far from target --- ugh
• thin cirrus at start of run, clear for most of the run, maybe cirrus returned at the end
• temperature was very warm, for this time of year.
• the focuser software did not correctly connect with the mechanism, so I was unable to read the position of the unit; however, I was able to move the motor by pressing the white buttons on the control box by hand. I pressed the "In" button in six brief bursts to change focus from "V" to "clear".
• at very end of night, I tried to re-set the park position of the telescope. Normally, when one moves to the new position and tells the hand-paddle to use this as new park position, there is a brief "beep" and the word "Set" appears on the controller. But this time, the controller displayed "synchronize", and when I pressed "Enter", the mount started to move towards the polar position! Morever, it wouldn't step when I pressed "Mode". Yikes!

  The mount moved until the CCD camera pressed into the fork, the sort of ground to a halt. I cut the power. After a brief wait, I re-booted, and moved the telescope away from the fork. I then pointed manually to the Moon and Procyon to re-synchronize the telescope. When I tried to re-set the Park Position again, all went well. I hope this is the end of this issue.

The object is at

  RA = 08:07:14.25     Dec = +11:38:12.5    (J2000)

A chart of the field is shown below. The size of the chart is about 16 x 16 arcminutes.

I've marked the location of several comparison stars.

  star       ID                  B          V         
-------------------------------------------------------------------------

   A     APASS 53280329        11.356     10.028                        

   C     APASS 53295398        12.827     13.350      (mags from AAVSO)

--------------------------------------------------------------------------

 

I used star "C" to shift the instrumental magnitudes to the V-band scale, following the values given for this star in the AAVSO chart X25677BDK.

• AAVSO table of photometry for KK Cnc
• AAVSO chart X25677BDK for KK Cnc

I took a photo of the finder TV's screen when pointing to KK Cnc; this could be a useful reference for the future:

I ran the camera at the normal temperature of -20 C. Nothing out of the ordinary.

I took a series of 248 exposures of the field, using no filter and an exposure time of 20 seconds.

The sky value shows that the sky was mostly clear, and that it grew bright at dawn.

The number of objects detected. The large scatter is probably due to trailing in some images.

I used an aperture with radius 5.0 pixels tonight.

Using aperture photometry with a radius of 5 pixels (binned 2x2, each pixel is 1.25 arcsec, so a radius of 6.25 arcsec), I measured the instrumental magnitudes of a number of reference stars and the target. Following the procedures outlined by Kent Honeycutt's article on inhomogeneous ensemble photometry, I used all stars available in each image to define a reference frame, and measured each star against this frame.

Sigma-vs-mag plots show that the floor was about 0.005 mag overall. KK Cnc is the star barely peeking up out of the stellar locus at instrumental mag 3.5.

Here are light curves of the variable and the field stars.

I used the AAVSO value for the V-band magnitude of star "B" = APASS 53295398 to shift the ensemble UNFILTERED magnitudes to the standard V-band scale.

Here's a closeup on the variable. It shows a hint of variation with a small amplitude and timescale of at least two hours.

You can download my measurements below. A copy of the header of the file is shown to explain the format.

# Measurements of KKCnc made at RIT Obs, UT 2020 Oct 10, 
#    in fair conditions, 
#    by Michael Richmond, 
#    using Meade 12-inch LX200 and ATIK 11000. 
# Exposures 20 seconds long, clear filter. 
# Tabulated times are midexposure (FITS header time - half exposure length) 
#    and accurate only to +/- 1 second (??). 
# 'mag' is a differential magnitude based on ensemble photometry 
#    using a circular aperture of radius 5 pix = 6.2 arcseconds.  
#    which has been shifted so 000-BKD-933 has mag=12.827 
#    which is its V-band magnitude according to AAVSO chart X25677BDJ.  
# 
# UT_day             JD            HJD        mag    uncert
Oct10.35737     2459132.85737  2459132.85597  13.190  0.020 
Oct10.35839     2459132.85839  2459132.85699  13.148  0.019 

• Download ASCII text file with photometry of KK Cnc from 2020 Oct 10 UT

Last modified 10/10/2020 by MWR.