Aug 27, 2011 UT: Photometry of SN 2011fe in M101 (and PG1633 color terms)

Michael Richmond
Aug 29, 2011

On the night of Aug 26/27, 2011, I observed the newly discovered supernova known as PTF 11kly = SN 2011fe in the galaxy M101. I also acquired images of the calibration field PG1633 in order to determine the color terms for my camera.

The setup was:

Notes from the night

This is a chart of the field of SN 2011fe, based on a stack of five R-band images. The field of view is about 10 by 8 arcminutes.

The marked objects appear in a list of comparison stars with magnitudes in BVRI, created by the AAVSO. You can find the original at the AAVSO web site; go to the Variable Star Plotter (VSP) area. I've made a simplified ASCII version of the catalog below, or you can look at the AAVSO's original version in a local copy.


#AUID   RA.   Dec.   Label   U   B   V   Rc   Ic   J   H   K   Comments
# Label            RA         Ra(deg)       Dec        Dec(deg)  ID       U    B                 V                  R                 I
000-BKD-527   14:03:49.86 [210.95775d]   54:09:05.8 [54.15161d]   117 x   -   12.268 (0.057)29  11.735 (0.040)29  11.359 (0.048)29  11.006 (0.054)29  -   -   -    
000-BKD-528   14:04:21.68 [211.09033d]   54:19:22.4 [54.32289d]   119 x   -   12.572 (0.068)29  11.948 (0.047)29  11.528 (0.056)29  11.134 (0.063)29  -   -   -    
000-BKD-529   14:02:00.79 [210.50330d]   54:23:15.8 [54.38772d]   128 x   -   13.553 (0.062)29  12.751 (0.031)29  12.253 (0.045)29  11.788 (0.056)29  -   -   -    
000-BKD-530   14:01:55.32 [210.48050d]   54:16:21   [54.27250d]   131 x   -   13.540 (0.064)29  13.094 (0.044)29  12.716 (0.051)29  12.361 (0.056)29  -   -   -    
000-BKD-531   14:02:02.00 [210.50833d]   54:20:43.9 [54.34553d]   133 x   -   14.188 (0.094)29  13.291 (0.057)29  12.772 (0.074)29  12.287 (0.088)29  -   -   -    
000-BKD-532   14:01:49.79 [210.45746d]   54:23:02.7 [54.38408d]   134 x   -   14.187 (0.047)29  13.436 (0.033)29  12.970 (0.049)29  12.534 (0.061)29  -   -   -    
000-BKD-533   14:03:13.67 [210.80696d]   54:15:43.4 [54.26205d]   138 A  -   14.699 (0.091)29  13.801 (0.046)29  13.230 (0.062)29  12.698 (0.074)29  -   -   -    
000-BKD-534   14:02:54.17 [210.72571d]   54:16:29.5 [54.27486d]   140 B   -   14.557 (0.107)29  13.991 (0.074)29  13.581 (0.078)29  13.197 (0.083)29  -   -   -    
000-BKD-535   14:02:29.54 [210.62308d]   54:16:55.2 [54.28200d]   141 C   -   14.959 (0.102)29  14.100 (0.045)29  13.598 (0.063)29  13.130 (0.077)29  -   -   -    
000-BKD-536   14:02:31.15 [210.62979d]   54:14:03.9 [54.23442d]   146 G   -   15.158 (0.078)29  14.605 (0.029)29  14.204 (0.061)29  13.828 (0.082)29  -   -   -    
000-BKD-540   14:01:50.86 [210.46191d]   54:16:08.1 [54.26892d]   149 x   -   15.373 (0.010)29  14.925 (0.000)29  14.635 (0.006)29  14.361 (0.008)29  -   -   -    
000-BKD-538   14:03:23.74 [210.84892d]   54:14:32.6 [54.24239d]   155 H   -   16.015 (0.042)29  15.475 (0.000)29  15.133 (0.046)29  14.811 (0.065)29  -   -   -    
000-BKD-539   14:03:05.64 [210.77350d]   54:17:26.2 [54.29061d]   162 x   -   16.776 (0.091)29  16.177 (0.000)29  15.640 (0.079)29  15.140 (0.112)29  -   -   -    
#Report this sequence as: 5249bgj in the chart field of your observation report. This table is for a 0.25000° fov around PTF11KLY, RA: 14:03:05.81 (210.77421) & Decl.: 54:16:25.40 (54.27372). 

I measured the instrumental magnitude of each star with aperture photometry, using a radius of 3 pixels = 4.2 arcseconds in VRI and a radius of 5 pixels = 7 arcsec in B, and sky defined by an annulus around each star. 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.

Below is a graph of the scatter in differential magnitude versus magnitude in the ensemble solution for the R-band.

The floor of this diagram is about 0.009 mag, which indicates pretty good data. The floors for each passband were

passband     magsig floor
--------------------------
  B            0.02
  V            0.009
  R            0.009
  I            0.015
--------------------------

After taking images of SN 2011fe, I moved to the field of the Landolt calibration star known as PG1633+009. You can find the photometry of these stars in Landolt, AJ 104, 340 (1992).

I took 10 60-second images of this field in VRI, and 20 in B. A few in each passband were trailed, but the untrailed images yielded a decent set of measurements of stars with a range of colors. A simple linear fit yields the following first-order color terms:

  B  =  b  +  0.238 (043) * (b - v)  +  zp1

  V  =  v  -  0.077 (010) * (v - r)  +  zp2

  R  =  r  -  0.082 (038) * (r - i)  +  zp3

  I  =  i  +  0.014 (013) * (r - i)  +  zp4

Here, the capital letters are the Johnson-Cousins magnitudes for the stars, the lower-case letters are the instrumental magnitudes, and the "zp" terms are zero-points for each passband. The first order color terms are the coefficients of the colors, with their uncertainties in parantheses. The only major one is the B-band term -- the others give corrections of just a few percent, typically.

Applying these corrections to the ensemble photometry of SN 2011fe and the comparison stars in its field, I find the magnitude of SN 2011fe on this night was:

Passband       JD-2,455,000        Mag     +/-
--------------------------------------------------
   B             800.566          13.21    0.10
   V             800.581          13.01    0.05
   R             800.600          12.90    0.07
   I             800.590          12.90    0.09
--------------------------------------------------

I have just reported these measurements to the AAVSO via their WebObs tool ....


Last modified 8/30/2011 by MWR.