Aug 04, 2013 UT: SN 2013ej in M74 on a cloudy night

Michael Richmond
Aug 5, 2013

On the night of Aug 03/04, 2013, I observed SN 2013ej in M74.

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• SBIG ST-8E CCD camera with BVRI filter
• 30-second guided exposures

Notes from the night

• A cloudy night. There were occasional breaks in the cloud cover, but it never was completely clear. I had to wait quite a while for a chance to see M74.
• At one point, a very brief and light shower sprinkled rain drops inside the dome.
• FWHM was good, around 2.3 pix (4.3 arcsec)
• I used flats from Aug 01, 2013, since the "twilight sky flats" I took tonight were filled with clouds.
• I used some clear skies early to train the RA Periodic Error Correction on the LX200 mount

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 30-second guided images -- expect in B-band: the guide star was too faint for the guider to track. I took 6 images in R, 10 images in B, 3 in V, 4 in I. Afterwards, I discarded those images which were trailed or showed a "jump" in the tracking.

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 =   12.665   +/-   0.048  (ens  0.028 zp  0.039)    2456508.75940 
V =   12.522   +/-   0.014  (ens  0.006 zp  0.012)    2456508.75270 
R =   12.368   +/-   0.030  (ens  0.024 zp  0.018)    2456508.75716 
I =   12.264   +/-   0.035  (ens  0.014 zp  0.032)    2456508.76284 

The uncertainties here are about equally due to noise in the images and transforming the instrumental magnitudes to the standard scale.

Grab the text file below for all the RIT measurements of SN 2013ej.

• sn2013ej_mags.out

It appears that the SN has reached its peak in B and V, but it still rising at longer wavelengths.

Last modified 08/05/2013 by MWR.