"Inverted light curve"

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"Inverted light curve"

David
Hello,

First, AstroImageJ has been a great help in my work, thank you.

Second, I was making a light curve of an exoplanet transit and the
transit feature showed up inverted. I know that can happen if one subtracts the target
from calibrator instead of the other way around, so is it possible
for someone to accidently do this with AstroImageJ ?

I take it that the units of "rel_flux_T1" is in magnitudes, it could be useful
if instead one used percentage flux change instead.

Thank you
David
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Re: "Inverted light curve"

karenacollins
Administrator
Hi David,
   
Under the Multi-plot Main->Y-axis menu, you have two options to display the y-axis orientation ("Invert Y-axis" and "Negate relative magnitude calculations"). Set these to display in the orientation that you prefer.

The "rel_flux_T1" columns contains the raw values after dividing the target star integrated counts by the total of the comp star integrated counts. This is neither normalized nor in magnitude. However, you can display the data in relative magnitude by selecting "Out Mag" on the desired plot row in the Multi-plot Y-data panel.

On the other hand, if you want to display the data normalized to a region of the data, in the Multi-plot Y-data panel select a "Norm/Mag Ref" mode, such as to normalize using the out-of-transit portion of a light curve (i.e. the baseline), and then using the Multi-plot Main "Fit and Normalize Region Selection" controls for "Left" and "Right" to define T1 (start of ingress) and T4 (end of egress points). Then the baseline data will be normalized to an average value of 1.0. The error data will be normalized by the same multiplier. This is essentially the percent relative flux change that you are asking for (divided by 100).

To save any normalized data or plotted in magnitude, click to "New Col" button on the left hand side of the corresponding plot row (in the Multi-plot Y-data panel). This will allow you to add the newly formatted data to new columns in the table to use in other programs or to submit to collaborators.

To find information on all of the data columns, go to Multi-plot Main->Help->Data naming convention...".

If you haven't discovered section 10 in the latest version of the user guide (10. Step-by-Step Guide to Differential Photometry in AIJ), I would encourage you to work through that section. For reference, the guide is here:
http://www.astro.louisville.edu/software/astroimagej/guide/AstroImageJ_User_Guide_2.1.4.pdf

Karen



On 8/8/2014 3:19 AM, David [via AstroImageJ] wrote:
Hello,

First, AstroImageJ has been a great help in my work, thank you.

Second, I was making a light curve of an exoplanet transit and the
transit feature showed up inverted. I know that can happen if one subtracts the target
from calibrator instead of the other way around, so is it possible
for someone to accidently do this with AstroImageJ ?

I take it that the units of "rel_flux_T1" is in magnitudes, it could be useful
if instead one used percentage flux change instead.

Thank you
David


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Re: "Inverted light curve"

Francois
Hello,
Is it possible to get the data (images) that are used in the chapter 10 of the latest version of the user guide (10. Step-by-Step Guide to Differential Photometry in AIJ)
Thanks in advance
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Re: "Inverted light curve"

karenacollins
Administrator
I'm in the process of getting the example WASP-12b calibrated images
posted to a website where they can be downloaded. The zip file is 4.5
GB, so the download could be time consuming depending on your internet
connection. I'll post back with the download link when I have it.
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Re: "Inverted light curve"

karenacollins
Administrator
Find the WASP-12b example image at the link below. Just download the file and unzip to the individual images.

http://www.astro.louisville.edu/software/astroimagej/examples/

The file name is:

WASP-12b_example_images.zip

Let me know that you were able to download the files properly since this is the first time the download facility is being used.

Karen
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