UT Jul 24, 2019: Photometry of TCP J21040470+4631129

Michael Richmond
Jul 24, 2019

On the night of Jul 23/24, 2019, I acquired a set of observations of the newly discovered WV Sge cataclysmic variable star TCP J21040470+4631129 (see also Astronomer's Telegram 12947 ).

Tonight, the variable star showed strong superhumps for the first time. Hooray!

TCP J21040470+4631129 (or TCP for short)

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ATIK 11000 CCD camera
• V filter, 20-second exposures (longer exposure for better S/N)
• night was slightly cooler, so used T = -20 C for CCD
• images binned 2x2
• focus with V best at 0.308 inches, yielding FWHM = 3.5 pix
• guiding, with 5-second exposures and aggressiveness set to (0.1, 0.0) in (x, y)

Notes from the night:

• worked until 3 AM, so got about 4 hours of data
• Moon rose late in the run
• Not so hot: T = 80/26 at start, cooling to 60/16 at end
• the white finder telescope seemed to have slid slighly downward in its retaining rings, so I loosened them, slid it up, and re-tightened. Will have to re-align it with main telescope.
• The photometry improves if I use only stars in a central box (600 x 600 pixels instead of the 1200 x 1400 I had been using); I suspect off-axis PSF variations are responsible

The object is located at

  RA = 21:04:04.7    Dec = +46:31:12.9 

A chart of the field is shown below. The size of the chart is about 21 by 15 arcminutes.

I've marked the location of several comparison stars, which also appear in light curves below.

  star        UCAC4              B          V
----------------------------------------------------
   A       683-095755          10.832       10.528
   B       683-095722          11.142       10.948
   C       683-095772          12.342       10.960
   D       683-095866          12.814       12.414
   E       683-095811          14.017       12.691

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

 

When the telescope is pointed at the field, the finder scope's image on the television screen looks like this (North up, East left):

The dark current looked like this:

The sky value shows only a small bump due to very light clouds.

Here's a record of the telescope's drift. I made no adjustments to the mount during the night.

The number of objects detected.

I used an aperture with radius 4.0 pixels. I made no changes to focus.

Using aperture photometry with a radius of 4 pixels (binned 2x2, each pixel is 1.34 arcsec, so a radius of 5.4 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 0.007 mag overall, the best so far on this target. I marked the brightest two stars in the ensemble as "variable," due to saturation.

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

I used the UCAC value for the V-band magnitude of star "A" = UCAC4 683-095755 to shift the ensemble magnitudes to the standard V-band scale.

Here's a closeup of the variable and stars of similar magnitude. The target reminds me of Nessie.

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

# Measurements of TCPJ21040470+4631129 made at RIT Obs, UT 2019 Jul 24, 
#    in good conditions, 
#    by Michael Richmond,  
#    using Meade 12-inch LX200 and ATIK 11000. 
# Exposures 20 seconds long, V 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 4 pix = 5.3 arcseconds.  
#    which has been shifted so UCAC4 683-095755 has mag=10.528 
#    which is its V-band magnitude according to UCAC4.  
# 
# UT_day             JD            HJD        mag    uncert
Jul24.11463     2458688.61463  2458688.61687  10.909  0.007 
Jul24.11502     2458688.61502  2458688.61726  10.911  0.007 
Jul24.11541     2458688.61541  2458688.61765  10.913  0.007 

• Download ASCII text file with photometry of TCPJ21040470+4631129 from Jul 24 UT

Last modified 7/24/2019 by MWR.