gully
commented
1 year ago Here is an overlay of Keck NIRSPEC Helium 10830 for 4 of these comparison F-stars, alongside a single visit of HAT-P-67 from HPF:
We see that the Helium absorption is less in all of the comparison sources. The sample consists of high-proper motion and apparently low metallicity stars, so it's not quite apples-to-apples, but at least the same appears to have approximately the same spectral type. The most similar pattern is from the F6 subgiant / horizontal branch star, HD 25532.
I had to run NSDRP manual and override some of its hard-code in order to reduce these apparently slightly non-standard spectra. There may be thermal background bleed in some orders stemming from the filter settings: NIRSPEC-1-open instead of NIRSPEC-. It's not clear the extent of the bleed, if any. Some expected stellar spectral lines to not line up suggesting the wavelength calibration may be poor. I had to introduce huge RV shifts to get the lines to match up near Helium 10830, but I do not think those are real, just a byproduct of a wavelength calibration offset. I am sssuming the Gaia RV's are correct, but then again a high proper motion star should probably have large RV's as well? Doesn't matter for our purposes as I am confident we have matched up the spectra to the same rest frame in the local patch surrounding 10830.
I cross-matched the Keck Observatory Archive table of NIRSPEC High-resolution J-band spectra with Gaia DR3 and Simbad to find a sample of 16 F-stars ostensibly with Helium 10830 data available:
Unfortunately none of these spectra have repeat visits (with the exception of Tau Boo, which has a single night of point-and-stare observations). The ensemble of the sources could tell us how unusual the baseline equivalent width is, and the lower vsini of the sources could give a better template for disambiguating nearby lines. It might be useful to show if the baseline Helium line is much higher or lower than all the comparison sources, for example.