Aug 10, 2013 UT: UZ Boo and SN 2013ej, through clouds

Michael Richmond
Aug 12, 2013

On the night of Aug 09/10, 2013, I observed UZ Boo and SN 2013ej in M74. The sky was covered with broken clouds, unfortunately, so I managed only a few measurements, and they aren't very good.

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• SBIG ST-8E CCD camera with no filter (UZ Boo) and BVRI filters (SN 2013ej)
• 30-second guided and unguided exposures

Notes from the night

• The sky was clear after sunset briefly, but then clouds came and went continually.
• FWHM varied from good (2.8 pix in B) to bad (3.5 pix in B).

UZ Boo -- just a single measurement

I took a long series of images of UZ Boo, but the poor conditions made it difficult to get good measurements from them. Look at the image-to-image zero-point offsets:

Moreover, UZ Boo was very faint tonight, as it had faded considerably since its initial outburst. Take a look at the picture below, which is a composite of 5 30-second images.

I measured both UZ Boo and the star labelled "A", UCAC4 561-055134, which has mag V = 11.094 according to the AAVSO chart 12447AMF. Remember that my images were taken without a filter. If we simply add the difference in instrumental mag to the V-band mag of star "A", we get

    JD  2456514.572     V = 16.7 +/- 0.1

SN 2013ej in M74

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

After discarding the bad images, I was left with 17, 4, 5 and 6 images in B, V, R, and I, repsectively.

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 morning are:

filter  mag         mag_uncert                          Julian Date

B =   12.964   +/-   0.056  (ens  0.018 zp  0.053)    2456514.70262 
V =   12.527   +/-   0.075  (ens  0.022 zp  0.072)    2456514.69471 
R =   12.297   +/-   0.051  (ens  0.022 zp  0.046)    2456514.68018 
I =   12.239   +/-   0.034  (ens  0.018 zp  0.029)    2456514.68665 

The uncertainties here are dominated by 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 08/12/2013 by MWR.