Astro 3310 Fall 2015
LAB #7 (version 1.2):
-----Please copy this document to the REPORT sub-directory from the
expanded LAB7_Data_Package_FA15.tar.gz. Then, edit it to write your
answers in all the "______" areas. When finished, create a tar.gz
archive of the REPORT directory and all of its contents, then scp
the file to datafarm.astro.cornell.edu and place it in:
/data/Courses/A3310/FA15/”your netid”/LAB7/
Remember that you will only get credit for the files that you put in
the REPORT sub-directory and copy to datafarm. Please make sure
that you keep a Matlab workbook with all of the commands you used to
answer the questions in the lab. Feel free to comment and organize
your workbook so that it will be easy for us to follow your
algorithms when we execute the code. If you generate any functions
for the lab, ensure that they are also in the REPORT sub-directory
and properly called from the workbook file. For you convenience,
there is a template for the workbook file already in the REPORT subdirectory.
YOUR NAME: _______________________________
Your NetID: __________
The purpose of this lab is to familiarize you with exoplanet
transits, and the data from the NASA Kepler mission.
Part 1:
Go to planethunters.org and sign up. Start looking for transits!
If you find one, insert a figure of your lightcurve here, or insert
a figure of the most interesting lightcurve you find.
We will do this part in class so you can discuss the lightcurves you
see and their features.
Part 2:
Familiarize yourself with the NASA Exoplanet Archive at
http://exoplanetarchive.ipac.caltech.edu/index.html
Use the Kepler Object of Interest Table to choose a target to
analyze. Objects with deep, short period transits, and confirmed
planets (especially with small Kepler-numbers) will generally be
easier to analyze than unconfirmed candidates. However, the
unconfirmed candidates are where you might make a discovery!
Take note of the “Effective Temperature” of the star – you will need
it in part 4.
Part 3:
Download the lightcurve data, and using the known periods, generate
a phase-folded lightcurve. Phase is the time in fractions of a
transit period relative to each transit, so you can generate the
phase of a vector time relative to time0, folded on period like
this:
t = (time – time0);
phase = t./period – round(t./period);
Then plot phase vs flux.
You may use only a single quarter of data, or several. If you
use several quarters of data, the result will be better, but you
will need to address the offsets between quarters. In general the
later quarters (after quarter 5) have better behaved data
characteristics. In some cases it will also improve the lightcurve
by addressing drifts and stellar variability by subtracting a moving
average (averaged over a period longer than the transit), or
otherwise filtering the time series.
Answer:
Insert a figure of your phase-folded lightcurve.
Part 4:
Use the transit depth and impact parameter from the exoplanet
archive, and limb darkening parameters from the theoretical values
from the Sing “Stellar Limb-Darkening Coefficients for CoRot &
Kepler” paper to plot a model for the lightcurve of your transit
with the Mandel and Agol lightcurve routine matransit in the
SUBROUTINES directory.
Answer:
Insert a figure of the model lightcurve.
Part 5:
To measure the parameters of the light curve, it is necessary to fit
a model of the light curve to the data. This is conceptually the
same as fitting a linear relation to data such as you performed in
lab 1, but requires a “non-linear” fitting routine, which is passed
a function that describes the model to be fit. Use the matlab nonlinear least squares fitting routine lsqcurvefit or lsqnonlin along
with the Mandel and Agol lightcurve routine matransit in the
SUBROUTINES directory to fit for the planet parameters. Use nlparci
to determine the confidence intervals (uncertainties) for these
parameters
Answer:
Insert a figure of your lightcurve with fitted result.
How do your fitted limb darkening parameters compare to those from
the paper?
Background:
http://planethunters.org
Exoplanet Archive
http://exoplanetarchive.ipac.caltech.edu/index.html
Winn, Transits and Occultations
http://arxiv.org/abs/1001.2010
Mandel and Agol Light Curve Tools
http://www.astro.washington.edu/users/agol/transit.html
Sing Stellar Limb-Darkening Coefficients for CoRot & Kepler
Kepler Data Processing Handbook (extensive)
https://archive.stsci.edu/kepler/documents.html