Jul 30, 2013 UT: Photometry of SN 2013ej in M74

Michael Richmond
Aug 1, 2013

On the night of July 29/30, 2013, I observed SN 2013ej in M74.

The main setup was:

Notes from the night

SN 2013ej is a Type II supernova in the relatively nearby galaxy M74. It was discovered by the KAIT group some time (a week?) before maximum light. Here's a chart showing the galaxy, the SN, and some reference stars:

The reference stars marked above have magnitudes in AAVSO chart 12459CA, as follows:

 letter      B     sigB       V     sigV      R      sigR     I    sigI
  B        13.012  0.019   12.510  0.019    12.154  0.019   11.834  0.019
  F        13.848  0.026   13.065  0.022    12.622  0.025   12.152  0.027   
  H        14.338  0.029   13.692  0.024    13.329  0.029   12.964  0.030
  I        14.832  0.027   13.912  0.023    13.416  0.026   12.939  0.030
  K        15.192  0.034   14.613  0.027    14.275  0.034   13.915  0.036

I took some 60-second images, but the guiding wasn't very good, so I switched to 30-second images. I took 5-15 in each filter, and discarded those with trailing.

Using aperture photometry with a radius of 4 pixels (radius of 7.4 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. I used the AAVSO magnitudes, 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 morning are:


filter  mag         mag_uncert                          Julian Date

B =   12.711   +/-   0.035  (ens  0.010 zp  0.033)    2456503.81423
V =   12.647   +/-   0.012  (ens  0.004 zp  0.011)    2456503.80427
R =   12.564   +/-   0.021  (ens  0.007 zp  0.020)    2456503.78972
I =   12.524   +/-   0.024  (ens  0.006 zp  0.023)    2456503.79351

The uncertainties here are dominated by transforming the instrumental magnitudes to the standard scale.


Last modified 08/01/2013 by MWR.