Sep 06, 2013 UT: SN 2013ej in M74

Michael Richmond
Sep 06, 2013

On the night of Sep 05/06, 2013, I observed SN 2013ej in M74. Conditions were fair, with clouds arriving only for an hour or so. However, I did struggle with equipment for quite a while...

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• SBIG ST-8E CCD camera with BVRI filters
• 30-second BVRI exposures of SN 2013ej

Notes from the night

• Decent weather, with clouds coming after midnight for about one hour.
• FWHM was fair: 2.8 - 3.2 pixels
• I did succeed in guiding in B-band for SN 2013ej, using 10-sec exposures.
• Early in the evening, I tried to improve the telescope's polar alignment and really screwed up, setting it about 10 degrees off. Whoops. It took me several tries and several hours to put the telescope back into at least mediocre alignment. It was good enough to track, once I had found M74, but I think I'll have to do it again before I observe next time; the pointing may be inaccurate now.

SN 2013ej in M74

SN 2013ej is a Type II supernova in the relatively nearby galaxy M74. It was discovered by the KAIT group about one 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 30-second guided images in VRI, and on this night managed to guide (poorly) in B-band, too. After discarding the bad images, I was left with 10, 7, 9, and 7 images in B, V, R, and I, respectively.

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 to convert the ensemble instrumental magnitudes to the standard Johnson-Cousins BVRI scale.

Results from this evening are:

filter  mag         mag_uncert                          Julian Date

B =   14.442   +/-   0.052  (ens  0.040 zp  0.033)    2456541.76062 
V =   13.228   +/-   0.024  (ens  0.023 zp  0.007)    2456541.75294 
R =   12.734   +/-   0.020  (ens  0.013 zp  0.016)    2456541.74640 
I =   12.491   +/-   0.045  (ens  0.021 zp  0.040)    2456541.77009 

The uncertainties here are roughly equally distributed between extracting the instrumental magnitudes and transforming the instrumental magnitudes to the standard scale.

Grab the text file below for all the RIT measurements of SN 2013ej. All these values have been recomputed with the new color terms of UT 2013 Aug 05.

• sn2013ej_mags.out

Last modified 09/06/2013 by MWR.