On the night of Aug 14/15, 2013, I observed UZ Boo and SN 2013ej in M74. Conditions were pretty good.
The main setup was:
Notes from the night
I took a series of images of UZ Boo, using a 90-second exposure time, since UZ Boo has been brighter recently. It was bright again tonight, around V = 14.1, so this length provided plenty of signal-to-noise.
The skies were clear tonight, as this plot of zero-point adjustment shows:
I measured UZ Boo and many other stars in the field. The bright stars "A", "B" and "D" were somewhat saturated, so I left them out of the ensemble solution. Instead of the star "A", I used the star "E" = UCAC4 561-055129 = AAVSO 000-BBV-649 to shift the instrumental magnitudes to the standard scale. Remember, the measurements are made without a filter , but I'll shift them to match the V-band scale: 000-BBV-649 has mag V = 14.267 according to the AAVSO chart 12447AMF.
Below are light curves for UZ Boo and several of the unsaturated stars in the field:
Here's a closeup of UZ Boo and another star:
Below are the first few lines of the report I've sent to the AAVSO and VSNet.
# Measurements of UZ_Boo made at RIT Obs, Aug 15, 2013 UT, # in fair conditions, # by Michael Richmond, using 12-inch Meade and SBIG ST-8E CCD. # Exposures 90 seconds long, clear filter. # Tabulated times are midexposure (FITS header time - half exposure length) # and accurate only to +/- 1 second (??). # 'mag' is a differential magnitude based on ensemble photometry # using a circular aperture of radius 7.4 arcseconds. # which has been shifted so UCAC4 561-055129 has mag=14.267 # which is its V-band magnitude according to AAVSO. # # UT_day JD HJD mag uncert Aug15.04787 2456519.54787 2456519.54610 14.007 0.012 Aug15.04918 2456519.54918 2456519.54741 14.027 0.013 Aug15.05049 2456519.55049 2456519.54872 14.015 0.012 Aug15.05178 2456519.55178 2456519.55001 14.039 0.012
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 ended up with 11 good images in B, 3 in V, 7 in R, 4 in I. --> After discarding the bad images, I was left with 7, 5, 13 and 6 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.
In the B-band, the transformation from instrumental to Johnson-Cousins magnitude had a larger uncertainty than usual (0.08 vs. 0.03 mag). I tracked the difference to measurements of the star "K" = 000-BBD-099. It appeared brighter than expected by about 0.15 mag. I saw no obvious outliers or image defects near it. Hmmm. I discarded it from the solution in the B-band only.
Results from this morning are:
filter mag mag_uncert Julian Date B = 13.239 +/- 0.032 (ens 0.011 zp 0.030) 2456519.70731 V = 12.586 +/- 0.026 (ens 0.019 zp 0.018) 2456519.70128 R = 12.310 +/- 0.028 (ens 0.010 zp 0.026) 2456519.69379 I = 12.176 +/- 0.035 (ens 0.025 zp 0.024) 2456519.71723
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.
Last modified 08/15/2013 by MWR.