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jobovy / apogee

Tools for dealing with APOGEE data
BSD 3-Clause "New" or "Revised" License
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accessing apVisit spectra #34

Closed mrawls closed 8 years ago

mrawls commented 8 years ago

Is it possible to use this package to download and inspect apVisit spectra (individual visits) in addition to apStar spectra (all visits added together)? It's not clear from the documentation, and this would be very useful!

jobovy commented 8 years ago

No, reading apVisit files is currently not supported, but note that the apStar files do contain the individual exposures as well. The difference is that in apStar the wavelength sampling is the standard APOGEE wavelength grid (equally spaced in log10(wavelength)), while in apVisit the spectra are on the native detector wavelength grid. You can read the individual spectra in apStar by reading HDU1 and selecting the columns 2 onwards (0 and 1 are the combined spectra).

mrawls commented 8 years ago

Awesome, thanks!

mrawls commented 8 years ago

Hi again :) I recently started using this approach to access individual visit data, and realized today that there is more than just a wavelength grid difference: the apVisit files are not RV-corrected while columns 2+ from the apStar HDU1 are. This is no good for science cases like mine (measuring precise RVs). Is there any possibility of supporting non-RV-subtracted apVisit data in the future?

jobovy commented 8 years ago

Yes, that's correct: apVisit files are on a different grid (non-RV corrected) from the apStar equivalent. I don't have any immediate plans for supporting apVisit files, but I would be happy with a pull request :smile: Should be easy to do based on the apStar routines.

mrawls commented 8 years ago

That's what I was afraid you would say! OK, we'll see... :smile: