Jun 02, 2016 UT: Photometry of SN 2016coj in NGC 4125

Michael Richmond
Jun 21, 2016

On the night of Jun 01/02, 2016, I observed SN 2016coj in NGC4125.

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• SBIG ST-9E CCD camera with BVRI filter, 1.38 arcsec/pixel
• 30-second unguided exposures

Notes from the night

• mostly clear early, but thick cirrus arrived during my observations of SN 2016coj
• no Moon
• FWHM average, around 3.0 pixels (4.1 arcsec)
• twilight sky flats
• this was the last night that I acquired images of M66, home of SN 2016cok

SN 2016coj is a Type Ia supernova in the relatively nearby galaxy NGC4125. It was discovered by the KAIT group some time before maximum light:

• Astronomer's Telegram number 9095 announces the discovery

NGC 4125 RA = 12:08:05.7 Dec = +65:10:30 (J2000)

There are, alas, no really good sources of photometry for the stars marked above. I have created an interim set of magnitudes using the UCAC4 and converting the SDSS r and i magnitudes into Johnson-Cousins R and I via the conversion formulae of Jester et al. (2005). I hope to replace these interim values with better ones at some point.

letter   B     sigB    V     sigV    R     sigR    I    sigI
-------------------------------------------------------------------------
A      10.981 0.004   9.888 0.006   9.247 0.032   8.651 0.036   
B      15.202 0.004  14.130 0.005  13.621 0.032  13.146 0.035  

C      13.320 0.004  12.671 0.006  12.302 0.032  11.955 0.036 
D      15.939 0.003  15.038 0.007  14.370 0.031  13.749 0.034 

F      13.066 0.004  11.663 0.006  10.947 0.032  10.282 0.035  
G      15.047 0.006  14.365 0.006  13.977 0.032  13.613 0.035 
-------------------------------------------------------------------------

I took fewer than the usual 10 images per filter tonight, as I was racing against the clouds. The total number of good images was 7, 10, 5, 11, in B, V, R, I, respectively.

I used the rotsub technique to remove the galaxy's light, as best I could. It's not perfect.

Using aperture photometry with a radius of 3 pixels (radius of 4.1 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. I used the interim reference magnitudes above plus color terms which I am currently revising -- so please treat these results as preliminary to convert the ensemble instrumental magnitudes to the standard Johnson-Cousins BVRI scale.

Results from this evening are worse than usual, due to the clouds this evening.

filter        mag         mag_uncert                          Julian Date

   SN  B =   13.742   +/-   0.121  (ens  0.036 zp  0.116)    2457541.60920 
   SN  V =   13.538   +/-   0.161  (ens  0.028 zp  0.159)    2457541.61072 
   SN  R =   13.237   +/-   0.162  (ens  0.018 zp  0.161)    2457541.61012 
   SN  I =   13.260   +/-   0.210  (ens  0.048 zp  0.204)    2457541.61270 

Last modified 06/21/2016 by MWR.