Generating Light Curves - APT and Excel

Install APT

Heres some info that a previous group put together for installing and using APT Aperture photometry using APT.

APT Settings

For our practice light curves, we wanted to compare the various aperture settings as discribed in Don's IRAC notes File:IRAC notes.pdf The aperture and background settings we used were

aperture/background

3-3-7
3-12-20
5-5-10
5-12-20
10-12-20

We also chose to have APT subtract the background using setting B subtracting the mean background

Excel to Generate Light Curve and Standard Deviation

APT Photometry data are saved in a table named APT.tbl in the programs root directory. To open this file in Excel, open Excel, navigate to the APT directory, allow all files to show be shown and open APT.tbl. Excel will allow you to separate the data into cells automatically. If all data ends up in one column, choose that column and then find the "text to columns" option to separate.

You can use this spreadsheet to check to see that you

• gathered data from all three stars for each image
• did not duplicate any data
• did not skip any images
• subtracted the background using method B

As of now, we need to get the Julian Date by hand from the individual fits headers for each image set and insert it in to Excel.

Data can be graphed, Julian Day vs. Luminosity using Excel

Mean value and standard deviation can be found for each individual star by sorting by image name and then using the formulas function in Excel.

Test Light Curve Images

Mysterious IRAC images, along with a chart indicating 3 stars for which you should perform photometry. Construct light curves by plotting your photometry as a function of time (found in the image headers)

[1] Click here or paste this into browser ftp://anon-ftp.ipac.caltech.edu/outgoing/hoard/nitarp/test_lightcurve_data.tar.gz

Sample IRAC images from each channel for HAT-P-1b, TrES-2, and TrES-4 [2] Click here or paste this into browser ftp://anon-ftp.ipac.caltech.edu/outgoing/hoard/nitarp/sample_images.tar.gz

Reading FITS names

A note on IRAC image file names: Here's a sample image name...

SPITZER_I1_24745472_0002_0000_4_bcd.fits

This follows a general file naming convention, as follows:

"SPITZER" = in case you forgot which satellite you were using

"I1" = Instrument (I for IRAC) and channel number. In this case, channel 1 = 3.6 microns. Other channel possibilities include 2 = 4.5 microns, 3 = 5.8 microns, 4 = 8 microns. Note that, as described in the IRAC Data Handbook and the document on performing IRAC photometry that I circulated amongst you a while ago, these channel wavelengths are not the "true" (or isophotal) values that should be used during data analysis. The isophotal values are channel 1 = 3.544 microns, 2 = 4.479, 3 = 5.710, 4 = 7.844.

"24745472" = Unique AOR identifier for this observation (not for this IMAGE, but for all images comprising a single Spitzer visit to the target).

"0002" = Image sequence number in this observation; in this case, the second image of the sequence.

"0000" = Some observing modes obtain more than one exposure per "image". In such cases, this sequence number would increment upwards.

"4" = number of times this image has been reprocessed through successive (improved) versions of the data processing and calibration pipeline. All of the data I have sent to you (indeed, all of the IRAC data now available in the Spitzer archive) have been processed with the latest and greatest version of the pipeline, S18.7.0.

"bcd" = Basic Calibrated Data. The standard result from raw Spitzer data that have been run through the processing and calibration pipeline. This is the data product that we work with.

".fits" = It's a standard FITS image, can be loaded into DS9. The BCD images are flux calibrated in units of surface brightness per pixel, MJy/sr (mega-Jansky per steradian). The also include world coordinate solutions in their image headers, so can be displayed in the usual format (N up, E to the left) and have, for example, 2MASS catalogs overlaid on them, etc.

-Don --- Dr. Donald W. Hoard, Ph.D. Research Scientist, California Institute of Technology Science Applications Administrator, Infrared Processing and Analysis Center Science User Support Team, Spitzer Science Center

The Truth

Look here for what the light curves really should look like per Don