add_airmass_fits_header.py

from astropy.io import fits
import glob
import numpy as np
from astropy import units as u
from astropy.time import Time
from astropy.coordinates import SkyCoord, EarthLocation, AltAz

data_files = glob.glob('/home/dokeeffe/Pictures/xo-2b/*.fits')

for file in data_files:
    data, header = fits.getdata(file, header=True)
    ra_dec = '{} {}'.format(header['OBJCTRA'],header['OBJCTDEC'])
    coord = SkyCoord(ra_dec, unit=(u.hourangle, u.deg))
    bobs_location = EarthLocation(lat=52.253494*u.deg, lon=-8.360614*u.deg, height=75*u.m)
    time = Time(header['DATE-OBS']) 
    altaz = coord.transform_to(AltAz(obstime=time,location=bobs_location))  
    print(altaz.secz)

    header['AIRMASS'] = float(altaz.secz)
    header['GAIN'] = 0.4
    
    fits.writeto(file, data, header, clobber=True)