The MDW Hα Sky Survey: Data Release 1

TL;DR

The MDW Hα Sky Survey DR1 delivers a high-resolution, narrow-band ($3\,\mathrm{nm}$) H$\alpha$ imaging data set over the northern sky, combining multi-epoch exposures into mean-combined stacks with star-removed variants and cross-matched point-source catalogs. The authors transition to an open-source Python-based pipeline, implement refined astrometry, robust artifact masking, and field-specific flux calibration against Pan-STARRS1 and IGAPS, achieving improved astrometric accuracy and depth (stacks reach $16.5$–$18$ AB mag, while individual exposures reach $15.4$–$16.8$ AB mag). DR1 introduces extensive data products including ~50 million stack sources and per-exposure catalogs, with color-color diagnostics and synthetic photometry anchored to MIST tracks to explore H$\alpha$ reddening and spectral-type effects. Initial science demonstrates the survey’s capability to map H$\alpha$-emitting filaments with widths around $30^{\prime\prime}$–$45^{\prime\prime}$ and to identify H$\alpha$ variability and excess sources by leveraging irregular cadence and Gaia cross-matches. The DR1 release thus establishes a scalable, community-accessible dataset that enables diffuse emission studies, stellar activity investigations, and cross-survey analyses, paving the way for DR2 with full-sky coverage and enhanced calibrations.

Abstract

The Mittelman-di Cicco-Walker (MDW) H$α$ Sky Survey is an autonomously-operated all-sky narrow-band (3nm) H$α$ imaging survey. The survey was founded by amateur astronomers and the northern sky (Decl. $\geq$ 0$^\circ$) is presented here in its second stage of refinement for academic use. Each 3.6$\times$3.6 sq. deg MDW field has 12 20-minute individual exposures with a pixel scale of 3.6", a typical PSF of 6", and a stack point source depth of 16-17 magnitudes. The northern MDW Survey Data Release 1 (DR1) includes: calibrated and raw mean and individual images, star-removed mean fields, and point source catalogs for all images matched to Data Release 1 of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1) and the INT Galactic Plane Survey (IGAPS). Our initial study of H$α$ filament widths finds a typical FWHM of 30-45" in the Lyra region. The matched catalogs (with a median match distance of ~0.5"), combined with our distinctive narrow-band photometry, are used to identify H$α$ variable and excess sources. These initial studies highlight some of the many scientific uses of the MDW H$α$ survey.

Figures (30)

• Figure 1: Footprints of the various data releases of the MDW Survey, covering the Orion region (DR0; MDW_DR0_paper), the Northern Sky (DR1; detailed here), and eventually the full sky (planned DR2). The cross indicates field 1, with center RA and Dec of $0^\circ$ (RA increases positively to the right).
• Figure 2: The throughput of the H$\alpha$ filter used in the MDW Survey, provided by the manufacturer. The band is centered around 656.3nm, with a width of 3nm. We include the velocity ranges for the filter, as well as for the NII lines that may contaminate the H$\alpha$ band.
• Figure 3: The distribution of variation in exposure observation time for the images that make up each stacked DR1 field.
• Figure 4: For each DR1 field, a 2D histogram of the observation date of its earliest exposure compared to its latest exposure.
• Figure 5: For each DR1 field, we plot the deviation in the exposures center coordinate (left) and the deviation in their horizontal and vertical spherical lengths for the same set of consecutive pixels (right). For both plots, we color the bins by the standard deviation in exposure observing times (also see Figure \ref{['fig:JD']}). Many outlier fields have either a broad or narrow range in exposure observation dates.