On the night of UT Apr 07, 2008, the SDSS Photometric Telescope ("PT" for short) took a series of exposures of HAT-3. We saw a full transit under good conditions, at times roughly predicted by the ephemeris.
Notes from the night
This is a chart of the field. HAT-3 is the bright star indicated by the crosshairs. The labelled stars will appear in later analysis.
The host star of HAT-3 has a magnitude V=11.59 according to HAT-P-3b: A Heavy-Element-rich Planet Transiting a K Dwarf 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. You can find the software package used to do the ensemble photometry online; it's free!
The night was very clear. The graph below shows the amount by which instrumental magnitudes from each image needed to be shifted to match the ensemble reference. On a clear night, this graph would show a straight horizontal line.
Below is a graph of the scatter in differential magnitude versus magnitude in the ensemble solution.
HAT-3 is the star near differential mag 0.7; it shows a small excess of scatter over neighboring stars of the same brightness. The "noise floor" in these measurements is about 0.003 mag -- good for the PT.
Below are the light curves for the target (green symbols) and some comparison stars in the field.
In this closeup, I have shifted the data for two comparison stars to move them closer in magnitude to the target.
My eyeball estimates for the ingress and egress are: ingress at about 563.785 and egress at about 563.865.
An ephemeris grabbed from transitsearch.org predicts for this night
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Begin Transit Window PREDICTED CENTRAL TRANSIT End Transit Window
All Times UT
HJD Year M D H M
2454563.77 2008 4 7 6 31 2454563.82 2008 4 7 7 46 2454563.88 2008 4 7 9 1
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The ephemeris ingress of UT 2008 Apr 07 06:31:00 corresponds to JD 2,454,563.772, which is a bit earlier than I estimated. The ephemeris egress of UT 2008 Apr 07 09:01:00 corresponds to JD 2,454,563.876, which agrees with my eye estimate.
Note that PT observations on Mar 12 also suggested that the ephemeris ingress time was a little bit earlier than the observed ingress.
You can grab the measurements for your own analysis. Below is a table with three flavors of time, plus the differential magnitude of the target and an estimate of the uncertainty in each measurement. I show the first few lines of the file to give you an idea of its format.
# Measurements of HAT-3 made with APO PT, Apr 7, 2008 UT. # Each exposure 45 seconds long in SDSS i-band; # 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 5.25 arcseconds. # # UT day JD-2,450,000 HJD-2,450,000 mag uncert Apr07.74310 4563.74310 4563.74636 0.727 0.003 Apr07.74458 4563.74458 4563.74784 0.725 0.003 Apr07.74962 4563.74962 4563.75288 0.724 0.003
Last modified 05/03/2008 by MWR.