Candidate diffuse-ISM WEAVE pointings from IGAPS Hα and r images

In Greimel et al (submitted) we present a method (HaGrid) for interrogating Hα and r image data in order to extract from them candidate ionized ISM pointings for use in the WEAVE spectroscopic survey (Jin et al, in prep). The list generated via HaGrid can be downloaded from here.

The list is supplied in fits format and is a table of 187,541 rows and 45 columns. A feature of the supplied data is that an estimate of the surface brightness in erg cm-2 s-1 arcsec-2, based on the image photometric zero points. For details of the table columns, refer to the table below.

Column name Description
id Unique name for selected position of form "run number"-"CCD"-nnn, where nnn is a serial integer starting from 0, rising to a maximum of 200 (per CCD).
ra ICRS right ascension (decimal degrees, Gaia DR2 reference frame)
dec ICRS declination (decimal degrees, Gaia DR2 reference frame)
l Galactic longitude (degrees)
b Galactic latitude (degrees)
Ha_xpeak x pixel on frame at Hα narrowband peak
Ha_ypeak y pixel on frame at Hα narrowband peak
Ha_peak_count Hα narrowband count at peak
Ha_peak_variance Variance on Hα peak count
Ha_sky_used Adopted sky count for Hα narrowband frame. Either the median estimated for the frame or the mean of this direct estimate and an estimate predicted from matched r frame (see Greimel et al for details).
Ha_sky_median The median sky count for Hα frame
Ha_sky_variance The sky variance for Hα frame
Ha_CASU_sky Pipeline sky estimate for Hα frame
Ha_CASU_skynoise Pipeline sky noise estimate for Hα frame
Ha_photzp Photometric zero point for Hα frame (mag.)
Ha_net_count Peak Hα count for position less the sky count
Ha_mag Hα narrowband magnitude per arcsec-2 at position
Ha_S Hα narrowband surface brightness at position (erg cm-2 s-1 arcsec-2)
r_count Counts in the companion r band frame at the same sky position as Hα peak
r_variance Variance on the r count
r_sky_median Median sky count for the companion r frame
r_sky_variance Sky variance for companion r frame
r_CASU_sky Pipeline sky estimate for companion r frame
r_CASU_skynoise Pipeline sky noise estimate for companion r frame
r_photzp Photometric zero point for companion r frame (mag.)
r_factor Mostly 4, sometimes 12. This is the ratio between the Hα and companion r frame exposure times.
r_net_count Count in the r frame less sky, at the position of the Hα peak.
r_mag Companion r frame magnitude per arcsec-2, at the position of the Hα peak
Hα_sky_prediction Sky count prediction, based on companion r frame sky, of Hα narrowband sky (important in highly nebulous regions)
Hα_star_prediction Count prediction, based on companion r frame net count at position, of Hα narrowband peak for the case of a continuum source (i.e. a star)
sp_masked_fraction Fraction of 25x25 superpixel that was masked (less than 0.5 always)
sigma Error on the distance between the Hα net count, as a function of the corresponding r net count, and the nebular trend line. (See figure 10 in Greimel et al, submitted.)
nsigma The distance between the Hα net count and the nebular trend line in units of sigma.
star_sigma Error on the distance between the Hα net count, as a function of the corresponding r net count, and the stellar trend line. (See figure 10 in Greimel et al, submitted.)
star_nsigma The distance between the Hα net count and the stellar trend line in units of star_sigma.
fieldid Field identifier, of form nnnn or nnnno where nnnn is a 4-digit integer and o, when appended, indicates a field offset pointing.
run Run number, always starts with "r"
CCD CCD number (1, 2, 3 or 4)
utstart UT at beginning of Hα narrowband eposure
moon_phase Moon phase at time of Hα exposure expressed as a fraction (0.0 is new moon)
moon_separation Angular distance to moon from telescope pointing (degrees)
moon_altitude Height of moon above horizon at time of Hα exposure (degrees)
uni_cal True if frames passed through IGAPS uniform calibration; false if pipeline calibrated only
qcgrade Quality grade assigned to r, i, Hα exposure set in building the IGAPS catalogue (A++ best, D worst). See Monguio et al 2020 for details.
qcproblems Note on nature of quality control problems picked up