astro-legacy-archive/finkbeiner-halpha

Finkbeiner Full-Sky H-alpha Composite

This dataset contains the three HEALPix NSIDE-1024 products in Douglas Finkbeiner's version 1.1 full-sky H-alpha composite: the intensity map, its estimated error map, and the source processing mask. The composite combines the Virginia Tech Spectral-Line Survey (VTSS) and Southern H-Alpha Sky Survey Atlas (SHASSA) imaging, with the Wisconsin H-Alpha Mapper (WHAM) providing the large-scale zero point.

Product	Finkbeiner full-sky H-alpha composite, version 1.1
Inputs	WHAM, VTSS, SHASSA
Pixelisation	HEALPix NSIDE 1024; 12,582,912 pixels; NESTED ordering
Coordinate frame	Galactic
Angular resolution	6 arcmin FWHM
Intensity and error unit	Rayleigh (R)
Extinction correction	None

The three configurations are the source filename stems. Each contains one scalar source column and one row per source HEALPix pixel. No pixel index, decoded mask column, reordered row, or derived value has been added.

How to use

python -m venv .venv && .venv/bin/pip install datasets huggingface_hub pyarrow

from datasets import load_dataset
dataset = load_dataset("astro-legacy-archive/finkbeiner-halpha", "Halpha_fwhm06_1024", split="train", columns=["TEMPERATURE"])
row = dataset[0]
print(row["TEMPERATURE"])

3.560737133026123

import json
from huggingface_hub import hf_hub_download
import pyarrow.parquet as pq
path = hf_hub_download("astro-legacy-archive/finkbeiner-halpha", "Halpha_fwhm06_1024.parquet", repo_type="dataset")
print(json.loads(pq.read_schema(path).metadata[b"healpix_map"])["schema"])

astro-legacy-archive/healpix-map

The three configurations separately preserve intensity, estimated error, and source mask. Their embedded documents carry the common geometry, each field unit, and each coverage record; coordinate lookup and cross-product comparison must use those recorded values.

Dataset structure

Every configuration has 12,582,912 rows, in source NESTED pixel order.

configuration	source column	Parquet type	unit	meaning
Halpha_fwhm06_1024	TEMPERATURE	float32	R	Composite H-alpha intensity
Halpha_error_fwhm06_1024	ERROR	float32	R	Estimated intensity error
Halpha_mask_fwhm06_1024	MASK	uint8	—	Source processing bitmask

The source names the H-alpha intensity field TEMPERATURE; this identifier is preserved verbatim. Source row i is HEALPix pixel i. The intensity ranges from 0.1000061 to 8409.617 R, and the estimated error ranges from 0.1754532 to 841.183 R. Both columns are entirely finite and contain no zero or negative values.

The source FITS header documents the MASK bits:

bit	source name	source meaning
0	WHAM	WHAM data used (Wisconsin)
1	VTSS	Virginia Tech Spectral line Survey
2	SHASSA	Southern Halpha Sky Survey Atlas
3	STAR	Star removed
4	SATUR	Saturated pixel nearby in continuum exposure
5	BRT_OBJ	Bright star/galaxy - measurements unreliable
6	BIG_OBJ	Near LMC, SMC, or M31; no sources removed
7	HI_VEL	High Velocity in WHAM data

These are bit meanings, not mutually exclusive classes. The stored mask is the original uint8 value; users can test a documented bit with (MASK & (1 << bit)) != 0.

Provenance

LAMBDA describes the three products as direct copies of Finkbeiner version 1.1 and supplies the product description and download table. The release notes state that the 2003-07-27 revision standardised the FITS headers without changing the data content.

source file	bytes	SHA-256
Halpha_fwhm06_1024.fits	50,342,400	8daaf304acc1c320096a0c41667bc8a5ae272b4208d64e003b7d2c1ba9512936
Halpha_error_fwhm06_1024.fits	50,342,400	b0a59e0a70033c384bb433b04f24b09c9a2c95023af6a73c2d45b7c702438f14
Halpha_mask_fwhm06_1024.fits	12,594,240	d9eae52546b61d6fbb592834869ff88adb832f84abe9bebb4b27ca6fa8f8e789

Each Parquet file contains the source bintable column in identical row order, numeric width, scalar shape, and value bits. Embedded healpix_map metadata records the original headers, source pin, coordinate and pixel rules, field description and unit, documented physics, credit, and fixed regeneration command. FITS container serialisation is outside the reconstruction promise.

Considerations for use

• The product is a reprocessed composite, not a homogeneous observation from one instrument. Inspect MASK when survey origin or processing flags matter.
• The map has 6 arcmin FWHM resolution and must not be interpreted at finer angular scales.
• No extinction correction has been applied. Dust extinction can suppress the observed H-alpha intensity, especially near the Galactic plane.
• The estimated error is a per-pixel uncertainty. Finkbeiner (2003, §3.5) says that it excludes covariance introduced by the processing steps, making covariance-dependent statistical studies such as χ² analyses suspect. It also does not describe artifacts from saturation bleed trails, very bright stars, and similar processing failures; use the bitmask for these.
• Finkbeiner's Table 2 directs users to apply both BRT_OBJ and BIG_OBJ for any full-sky statistical study. Regions carrying HI_VEL may have WHAM zero-point errors greater than both 10% and 0.2 R.
• Genuine ISM structure was sometimes removed near bright stars. For analysis of a particular region, Finkbeiner directs users to the original full-resolution VTSS or SHASSA survey data.
• The source primary header declares SAMPLED=F.

Unconverted companion products

LAMBDA also serves sibling map/error/mask trios in two projections that this dataset does not convert:

projection	map	error	mask
Cartesian 8640 × 4320	Halpha_map.fits	Halpha_error.fits	Halpha_mask.fits
HEALPix NSIDE 512	lambda_halpha_fwhm06_0512.fits	lambda_halpha_error_fwhm06_0512.fits	lambda_halpha_mask_fwhm06_0512.fits

The Cartesian products are the native projection described by Finkbeiner; the NSIDE-512 products are explicitly undersampled at 6.9-arcmin pixels. They remain separate source products rather than being folded into these NSIDE-1024 configurations.

Licensing and credit

HEASARC states verbatim:

HEASARC materials are all available freely for your use.

This is a free-use statement rather than a named formal licence.

No named or formal licence is published for this product. HEASARC states that its materials are freely available for use; this is the free-use basis rather than a licence identifier. Credit Finkbeiner's composite and the WHAM, VTSS, and SHASSA source surveys. LAMBDA requests:

We acknowledge the use of the Legacy Archive for Microwave Background Data Analysis (LAMBDA), part of the High Energy Astrophysics Science Archive Center (HEASARC). HEASARC/LAMBDA is a service of the Astrophysics Science Division at the NASA Goddard Space Flight Center.

Citations

@article{Finkbeiner2003,
  author  = {Finkbeiner, Douglas P.},
  title   = {A Full-Sky H-alpha Template for Microwave Foreground Prediction},
  journal = {The Astrophysical Journal Supplement Series},
  volume  = {146},
  pages   = {407--415},
  year    = {2003},
  doi     = {10.1086/374411},
  eprint  = {astro-ph/0301558}
}

@article{Haffner2003,
  author  = {Haffner, L. M. and Reynolds, R. J. and Tufte, S. L. and
             Madsen, G. J. and Jaehnig, K. P. and Percival, J. W.},
  title   = {The Wisconsin H-alpha Mapper Northern Sky Survey},
  journal = {The Astrophysical Journal Supplement Series},
  volume  = {149},
  pages   = {405--422},
  year    = {2003},
  doi     = {10.1086/378850},
  eprint  = {astro-ph/0309117}
}

@article{Dennison1998,
  author  = {Dennison, Brian and Simonetti, John H. and Topasna, Gregory A.},
  title   = {An Imaging Survey of Northern Galactic H-alpha Emission with
             Arcminute Resolution},
  journal = {Publications of the Astronomical Society of Australia},
  volume  = {15},
  pages   = {147--148},
  year    = {1998},
  doi     = {10.1071/AS98147}
}

@article{Gaustad2001,
  author  = {Gaustad, John E. and McCullough, Peter R. and Rosing, Wayne and
             Van Buren, Dave},
  title   = {A Robotic Wide-Angle H-alpha Survey of the Southern Sky},
  journal = {Publications of the Astronomical Society of the Pacific},
  volume  = {113},
  pages   = {1326--1348},
  year    = {2001},
  doi     = {10.1086/323969},
  eprint  = {astro-ph/0108518}
}

Errata and requests

To report an erratum, propose a correction, or ask a question about this dataset, open a Discussion or Pull Request in its Community tab; posting requires a free Hugging Face account. Dataset requests and archive-wide questions may be posted in the README space's Community tab or the Community tab of any dataset. Confirmed corrections are made in the source conversion tools and published by rebuilding the dataset.