Re: Modeled transit depth value doesn't correspond to what is plotted
Posted by karenacollins on Mar 05, 2021; 9:17am
URL: http://astroimagej.170.s1.nabble.com/Modeled-transit-depth-value-doesn-t-correspond-to-what-is-plotted-tp1517p1518.html
Hi Mathilde,
AIJ current reports only (Rp/R*)^2 and does not report depth (i.e. the flux minimum at mid-transit). Of course the (Rp/R*)^2 and depths are not the same for grazing (V-shaped) transits since the full disk of the planet is not obscuring the star.
We plan to add reporting of depth at mid-transit to AIJ, but for now the best approach is to use the left and right markers to delineate the apparent t1 and t4 times, and use the OOT normalization mode (
), combined
with a baseline shift that places the baseline of the model fit on a
horizontal tick mark line (try -0.04 for this light curve), and then
estimate the depth by eye from the plot. You've already estimated
about 40 ppt, which is probably close, but maybe a little high.
The bottom line is that I think you are doing everything as best as can be done with the fit. It is just a current limitation of AIJ that it only reports (Rp/R*)^2 and does not report depth (i.e. the flux minimum at mid-transit).
Karen
URL: http://astroimagej.170.s1.nabble.com/Modeled-transit-depth-value-doesn-t-correspond-to-what-is-plotted-tp1517p1518.html
Hi Mathilde,
AIJ current reports only (Rp/R*)^2 and does not report depth (i.e. the flux minimum at mid-transit). Of course the (Rp/R*)^2 and depths are not the same for grazing (V-shaped) transits since the full disk of the planet is not obscuring the star.
We plan to add reporting of depth at mid-transit to AIJ, but for now the best approach is to use the left and right markers to delineate the apparent t1 and t4 times, and use the OOT normalization mode (
), combined
with a baseline shift that places the baseline of the model fit on a
horizontal tick mark line (try -0.04 for this light curve), and then
estimate the depth by eye from the plot. You've already estimated
about 40 ppt, which is probably close, but maybe a little high.The bottom line is that I think you are doing everything as best as can be done with the fit. It is just a current limitation of AIJ that it only reports (Rp/R*)^2 and does not report depth (i.e. the flux minimum at mid-transit).
Karen
On 3/5/2021 3:52 AM, mathtimm [via
AstroImageJ] wrote:
Hi Karen,
I'm having issues with the modeling of a V shaped transit. The depth value given by the model doesn't correspond to what is plotted. As you can see on the image, the depth is about 0.040 but the value given by the model is 0.1487. This high value varies whenever I unlock the prior value but it is always something unrealistic. I've tried playing with the prior values but it seems the plotted model does not vary in depth anymore above a value of 0.039 eventhough the value is locked. The BIC also decreases slowly when the prior value is going up.
Do you have an idea on how to resolve this issue ?
Thanks a lot in advance for your help !
All the best,
Mathilde
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