The LBT Yp Project: MODS Optical Spectra of Metal-Poor Nebulae

1d wavelength- and flux-calibrated optical spectra from 3300-10,000A of 58 low-metallicity galaxies from the Large Binocular Telescope (LBT) Multi-Object Double Spectrographs (MODS1 and MODS2).  These data were used by the LBT Yp Project, and described in Paper II (Rogers et al., 2026, ApJ, 1008, 238 (doi.org/10.3847/1538-4357/ae87a0).

The LBT Yp Project papers were released as an ApJ Focus Issue.

These are FITS bintable format files of the 1d spectra (wavelength, flux, and errors).  All spectra are on a linear wavelength scale with 0.5A/pixel.

• Wavelengths are observed wavelength in Angstroms
• Fluxes are relative flux in F_lambda units.  0.0 means "no data"
• Flux errors in relative F_lambda units.  0.0 means "no data"

Most of the spectra were acquired with both MODS1 and MODS2, but some were taken with MODS1 or MODS2 alone when the other spectrograph was unavailable (e.g., offline for maintenance).  See Rogers et al. 2026 for the full details of the spectral reduction and analysis. 

Primary HDU

The primary header data units (HDUs) of the FITS files have additional metadata describing the individual observations:

OBJECT - galaxy name (e.g., Markarian 71)

OBJRA,OBJDEC - object J2000 celestial coordinates

EQUINOX, RADECSYS - celestial coordinate equinox and system

DATE-OBS - observing date and time in UTC at start of the observation sequence

MJDOBS - modified UTC Julian Date at start of the observation sequence

EXPTIME - unit exposure time in seconds of each individual spectrum

POSANGLE - celestial position angle of the slit in degrees east of north

EXPTOTAL - total accumulated exposure time in seconds summed over all combined dither positions.  If both MODS were used, this is the total exposure time for both (e.g., 7200 sec = 2x3600s on MODS1 and MODS2)

PROJECT, PI_NAMES - Project name and PIs

PIPELINE - spectral data reduction pipeline software and version used

PUBTITLE - title of the associated journal paper

AUTHOR - lead author of the associated journal paper

PUBDOI - publication DOI for the associated ApJ paper

REPODOI - this data repository's DOI (Zenodo)

DATE - UTC data/time this FITS file was created

CREATOR - software used to create this FITS file

TELESCOP - Telescope for the observations

OBSERVAT - Observatory site where the telescope is located

INSTRUME - Instrument(s) used for the observations.  Value is MODS1+2 if data are co-added from both MODS, otherwise MODS1 or MODS2 if only one MODS was available for use

SLITMASK - MODS segmented long-slit mask identifier, LS = long-slit mask, followed by format code NxLxW; N = number of slits, L = slit length in arcseconds, W = slit width in arcseconds

SLITWID - mask slit width in arcseconds

RGRATING/BGRATING - MODS red/blue channel grating used

RGRORDER/BGRORDER - MODS red/blue channel grating order (integer)

RCENLAM/BCENLAM - nominal central wavelength for the red/blue grating in Angstroms

LAMPIX - the linear dispersion in angstroms/pixel of the 1d spectrum