Re: Detrending Airmass
Posted by karenacollins on Aug 13, 2020; 7:22am
URL: http://astroimagej.170.s1.nabble.com/Detrending-Airmass-tp1437p1440.html
Hi Jessica,
Airmass coefficients of -0.0012 and -0.0045 seem reasonably small, but there's no real upper or lower bound on reasonable values that I could quote.
From your description, it sounds like your comp stars are fairly flat without detrending. That is helpful and possibly gives you information on the amount of airmass trend that might be contributed from those light curves. However, if they have significantly different effective temperatures (Teff) from the target star, the differential target star light curve could still have some airmass trend. I think the only way to disentangle the pulsations from airmass trend is to look up the Teff of your target star and then try to find some comparison stars in your field with similar brightness and Teff. The TIC (TESS Input Catalog) on MAST lists a reasonable Teff for almost all stars. There's an interactive mode that lets you click on stars in an image to see the Teff of stars in nearby your target, or you can click on the catalog entry and it will highlight the corresponding star.
If you are not familiar with the TESS catalog on MAST, go to:
https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html
-Then in the pull down menu at the top-left, select "MAST Catalogs", and then just below a second pull down menu will appear. Make sure it says "TESS Input v8". Then enter your target's ra and dec and a radius of a circular region to search in the "and enter target" box, like this:
-Then click search (r=5m means show the catalog for all stars within 5 arcmin of the target coordinates).
You will the see a display similar to the one below with the catalog values on the left and the image display on the right. Look for stars in your field with a similar magnitude and Teff.
I can 't support the above tool, but wanted to give you an idea about it, in case it's helpful.
Karen
URL: http://astroimagej.170.s1.nabble.com/Detrending-Airmass-tp1437p1440.html
Hi Jessica,
Airmass coefficients of -0.0012 and -0.0045 seem reasonably small, but there's no real upper or lower bound on reasonable values that I could quote.
From your description, it sounds like your comp stars are fairly flat without detrending. That is helpful and possibly gives you information on the amount of airmass trend that might be contributed from those light curves. However, if they have significantly different effective temperatures (Teff) from the target star, the differential target star light curve could still have some airmass trend. I think the only way to disentangle the pulsations from airmass trend is to look up the Teff of your target star and then try to find some comparison stars in your field with similar brightness and Teff. The TIC (TESS Input Catalog) on MAST lists a reasonable Teff for almost all stars. There's an interactive mode that lets you click on stars in an image to see the Teff of stars in nearby your target, or you can click on the catalog entry and it will highlight the corresponding star.
If you are not familiar with the TESS catalog on MAST, go to:
https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html
-Then in the pull down menu at the top-left, select "MAST Catalogs", and then just below a second pull down menu will appear. Make sure it says "TESS Input v8". Then enter your target's ra and dec and a radius of a circular region to search in the "and enter target" box, like this:
-Then click search (r=5m means show the catalog for all stars within 5 arcmin of the target coordinates).
You will the see a display similar to the one below with the catalog values on the left and the image display on the right. Look for stars in your field with a similar magnitude and Teff.
I can 't support the above tool, but wanted to give you an idea about it, in case it's helpful.
Karen
On 8/12/2020 10:56 AM, mtsacobservatory
[via AstroImageJ] wrote:
Hi Karen,
I tried detrending the target delta Scuti star with airmass using two different fit modes (the full curve transit dip that you suggested, and also the full curve flat line), but both skewed the lightcurve. I also tried running an airmass detrend on two of the comp stars. Even if that detrending doesn't automatically apply to the rel_flux_T1, it should at least give us an idea if airmass was a significant problem, right? Both comp stars look fairly flat, as they should, and the airmass coefficients I got were -0.0012 and -0.0045. Is there a reasonable range that people use to know if this value is acceptable?
Thanks again for your help,
Jessica Draper
Mt. SAC Observatory
Walnut, CA
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