Sep 12, 2011 UT: Photometry of SN 2011fe in M101

Michael Richmond
Sep 12, 2011

On the night of Sep 11/12, 2011, I observed the newly discovered supernova known as PTF 11kly = SN 2011fe in the galaxy M101.

The setup was:

Meade 12-inch telescope
no focal reducer, so working at f/10
SBIG ST-8E CCD camera with BVRI filters
60-second unguided exposures

Notes from the night

The conditions were good: clear skies and cool temperatures. This was one of the best nights for observing SN 2011fe, except for ...
However, the full moon rising in the East made the sky bright.
The SN nearly saturates the detector with my standard 60-second exposure in V-band and R-band. Therefore, I de-focused slightly in V-band, and in R-band. I did re-focus for I-band, since that filter is so far from parfocal that the I-band images show little donuts otherwise.
SN 2011fe has reached its maximum light and is just starting its decline.

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 B and a radius of 4 pixels = 5.6 arcseconds in VRI, 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 clear skies permitted good measurements on this night.

Applying the color corrections determined on UT Aug 27 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 (almost exactly the same as last night)

Passband       JD-2,455,000        Mag     +/-
--------------------------------------------------
   B             816.520           9.98    0.10
   V             816.531           9.98    0.06
   R             816.539           9.95    0.07
   I             816.551          10.30    0.08
--------------------------------------------------

The uncertainties here are dominated by the systematic uncertainty in the photometric calibration.

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

You can find a complete set of the RIT Obs measurements by grabbing the file sn2011fe_mags.out. I've plotted our measurements in two graphs. First, the measurements of SN 2011fe so far:

Second, the new SN compared to another Type Ia SN, SN 1994D in NGC4526. I've shifted the SN 1994D measurements in time and in magnitude so that they sort of match the early observations of SN 2011fe.

Last modified 9/12/2011 by MWR.

Sep 12, 2011 UT: Photometry of SN 2011fe in M101

Michael Richmond Sep 12, 2011

Michael Richmond
Sep 12, 2011