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.