I have several Questions regarding parameter selections in the Data Set 2 Fit Settings table
1. If the target is not a known exoplanet host star, where can you get Teff, [Fe/H] and LOG(g) surface gravity to calculate the two limb darkening coefficients in EXOFAST? Alternately, Is there a source that provides the limb darkening coefficient based on spectral class if the class is given for the star in Simbad or some other source?
2. If you don't have information to generate U1 and U2 limb darkening coefficients for the host star, what coefficients should you use.
3.Frequently, as in the case of TIC81831095.01 (TYC 4049-645-1), Simbad has both a spectral class (A3 D from "A spectrophotometric survey of stars along the Milky Way. IV" in this case) and J and K values to calculate J-K (0.206 in this case and usually from 2MASS) that are not in agreement. Which is the better parameter to use for stellar parameter at the top right of the Data Set 2 Fit Settings table? My guess is the spectral classification because there is a lot more information in a spectrum to use to identify spectral class but I have little experience in spectroscopy.
Edited PS
In this case I found Teff and Log(g) in the Tess Input Catalog and metallicity ([Fe/H] = 0.2) was available in Vizier V/136/tycdwarf -Teff and metallicities for Tycho-2 stars (Ammons+, 2006) because this candidate host is also in the Tycho2 catalog. However, many candidate hosts are not TYC stars. Most TIC stars have Teff Log(g) , J and K magnitudes listed but [Fe/H] is not one of the TIC catalog fields. Therefore that raises the question
4. If you can't find metallicity for the host star what value should one assume or is there a way to make an estimate based on information in the TIC?
Hi Brad,
Let me attempt to answer your questions:
Hope this helps,
Dennis
Thanks, Dennis.
When I checked TIC in Vizier and I didn't see a field for [Fe/H]. However, after your response I checked again. I was looking at the correct table in Vizier but I missed the field the first time through the list. Thanks for that. However, as you noted is often the case, the field was blank in TIC. That lead to a search for other possible sources by checking all surveys in Vizier dealing with abundances .v/136/tycdwarf, 'Teff and metallicities for Tycho-2 stars (Ammons+, 2006)", had a metallicity for this host since it is a Tycho2 star. That could be a helpful catalog for generating limb darkening coefficients.
Thanks for the advice re default metallicity value where none can be found. U1= 0.3 seems reasonable for V filter but from the 3 or 4 observations I have done in "I" it seems a bit high. Would something like 1.5 be a better choice for I and perhaps 2.0 for R? U2 seems close to 3.0 regardless of filter. Also, might something larger, like 3.5 or 4.0, be a better choice as a U1 default in "B?' U1 seems sensitive to filter band.
Brad
WBY,
I found a calculator, Exoplanet Characterization Toolkit (ExoCTK) that I have been using for limb darkening. It gives most of the filters that we use.
WWC