Sep 03, 2013 UT: SN 2013ej in M74, and a look at ASASSN-13ck

Michael Richmond
Sep 03, 2013

On the night of Sep 02/03, 2013, I observed SN 2013ej in M74, as well as checking UZ Boo and the new cataclysmic variable ASASSN-13ck. Conditions were good at first, but clouds approached just as the SN was rising in the east. I managed to get a few images.

The main setup was:

Notes from the night


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, but the B-band is so insensitive that, as usual, the guider couldn't hold the guide star reliably. After discarding the bad images, I was left with 8, 4, 4, and 5 images in B, V, R, and I, respectively. . On this night, I did not have time to focus in the I-band (as clouds were coming), so the I-band images are slightly out of focus.

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 =   14.346   +/-   0.140  (ens  0.129 zp  0.054)    2456538.62743 
V =   13.142   +/-   0.034  (ens  0.027 zp  0.020)    2456538.62004 
R =   12.677   +/-   0.021  (ens  0.010 zp  0.018)    2456538.61737 
I =   12.403   +/-   0.062  (ens  0.059 zp  0.019)    2456538.62575 


The uncertainties here are dominated by extracting the instrumental magnitudes.

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.


ASASSN-13ck

The All-Sky Automated Survey for Supernovae at Ohio State has found a number of interesting variable stars in addition to supernovae. You can read all about their "transients" at http://www.astronomy.ohio-state.edu/~assassin/transients.html . One of those is called "ASASSN-13ck", and is an interesting cataclysmic variable star.


RA = 00:11:33.71   Dec = +04:51:23  

Here's a chart of the region from the DSS:

I took a short series of 30-second V-band images of the field last night while waiting for SN 2013ej to rise above the trees. This star is pretty close to SN 2013ej in the sky. One of our images is shown below: the field of view is about 15-by-10 arcminutes.

The stars marked "B", "C", and "D" have magnitudes provided by the AAVSO, in their sequence 12635FGO:


#
# Report this sequence as: 12635FGO in the chart field of your observation report.
# 
# AUID             RA.           Dec.    my        B                  V                  B-V             Rc                 Ic    
000-BLD-228    0:12:23.76     4:37:23.8     117  12.407 (0.081)   11.745 (0.056)   0.662 (0.098)   11.555 (0.419)   11.373 (0.590)29 
000-BLD-229    0:11:35.97     5:01:27.5     122  12.839 (0.062)   12.183 (0.034)   0.656 (0.071)   11.998 (0.438)   11.820 (0.619)29
000-BLD-230    0:11:52.92     4:41:53.2     125  13.265 (0.090)   12.543 (0.049)   0.722 (0.102)   12.368 (0.432)   12.200 (0.609)29  
000-BLD-231    0:12:16.60     5:01:36       127  13.304 (0.072)   12.696 (0.049)   0.608 (0.087)   12.490 (0.480)   12.293 (0.676)29 
000-BLD-232    0:11:57.29     4:44:45.3     131  13.860 (0.081)   13.065 (0.056)   0.795 (0.098)   12.826 (0.446)   12.598 (0.628)29 
000-BLD-233    0:11:47.66     4:46:26.2  B  136  14.235 (0.093)   13.603 (0.053)   0.632 (0.107)   13.411 (0.444)   13.226 (0.626)29 
000-BLD-234    0:11:51.00     4:59:53.2     138  14.476 (0.086)   13.843 (0.052)   0.633 (0.100)   13.723 (0.461)   13.604 (0.650)29
000-BLD-235    0:11:24.39     4:55:00.5  D  141  15.140 (0.072)   14.146 (0.033)   0.994 (0.079)   13.613 (0.113)   13.116 (0.156)29 
000-BLD-236    0:11:40.47     4:52:53.9  C  144  15.127 (0.082)   14.357 (0.048)   0.770 (0.095)   14.148 (0.469)   13.948 (0.662)29 
000-BLD-237    0:11:35.79     4:57:58.4     147  15.780 (0.085)   14.693 (0.046)   1.087 (0.097)   14.304 (0.495)   13.939 (0.699)29 
000-BLD-238    0:11:52.60     4:53:01.2     155  16.521 (0.112)   15.497 (0.045)   1.024 (0.121)   15.215 (0.379)   14.948 (0.534)29 

The few measurements I was able to make on this night show clearly that I'll need much longer exposures in V-band to get good signal-to-noise ratio on this star.


Last modified 09/03/2013 by MWR.