PT observation of transit of HAT-3 on UT 2008 May 06 = MJD 54592

Michael Richmond
Douglas Tucker
June 20, 2008

On the night of UT May 06, 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 0.002 mag -- some of the best I've seen 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: a sharp ingress at about 592.78, and a much more gradual egress at about 592.88.

Justin's notes indicate that the ephemeris prediction is for ingress at 592.781 -- which agrees with my eyeball estimate -- and egress at 592.867 -- close to my estimate, which was hard to make due to the shallow appearance of the egress.

Note that PT observations on Mar 12 suggested that the ephemeris ingress time was a little bit earlier than the observed ingress. In this case, I see no significant difference.

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, May 6, 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
May06.74142      4592.74142   4592.74374   0.720  0.003 
May06.74293      4592.74293   4592.74525   0.722  0.003 
May06.74442      4592.74442   4592.74674   0.724  0.003 

Last modified 06/20/2008 by MWR.