astro-legacy-archive/msam-released-products

MSAM released flight products

This dataset contains the complete numeric contents of the three MSAM1 flight archives served by LAMBDA: the June 1992, June 1994, and June 1995 observation tables, sampled beam maps, and released 1994/1995 covariance matrices. The 38 configuration identifiers preserve the flight directory and source filename stem.

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/msam-released-products", "jun95__data_2_cmbr", split="train[:2]", columns=["Column 1", "Column 2"])
for row in dataset:
    print(row["Column 1"], row["Column 2"])

0.0 31.9017
0.0 30.7165

import json
from huggingface_hub import hf_hub_download
import pyarrow.parquet as pq
path = hf_hub_download("astro-legacy-archive/msam-released-products", "jun95__var_2_cmbr.parquet", repo_type="dataset")
print(json.loads(pq.read_schema(path).metadata[b"dense_matrix"])["array"]["shape"])

[275, 275]

Dataset structure

The archive contains 26 source-verbatim statistical products and 12 dense matrices. Observation tables have six unnamed source columns, retained as Column 1 through Column 6: Zero (ah, history), observed data, X coordinate, statistical weight of data, Y coordinate, and twist or roll angle. X, Y, and roll are in degrees. The released CMBR value unit is uK for 1992 and uK degree² for 1994 and 1995. The dust value unit is 10^6 optical depth at 1 icm for 1992 and 10^6 optical depth degree² at 22.5 cm^-1 for 1994 and 1995. The source README states no unit for Zero or statistical weight.

Sampled beam maps have three unnamed source columns, retained as Column 1, Column 2, and Column 3: X coordinate in degrees, Y coordinate in degrees, and beam amplitude with no published unit. Grid dimensions remain in the source header; no image grid is derived.

Each covariance member retains its flattened source values as one square dense matrix whose column and array name is the source filename stem. Its field unit is the square of the corresponding observation unit. The exact shape, first_numeric_line, axis names, source structure, source URL, member byte size, member SHA-256, and description are in the JSON document at Parquet schema metadata key dense_matrix. For every observation and beam-map configuration, the corresponding details and every field's description, unit, role, and source position are in statistical_product; read json.loads(pq.read_schema(path).metadata[b"statistical_product"])["fields"]. This is the canonical machine-readable route for all 38 configurations.

Provenance

LAMBDA publishes the MSAM product table. The pinned source archives are:

archive	bytes	SHA-256
msam_jun92.tar	634,880	2b52a651faabdd0fdb2d6fd73fe763a02c153770fcef895e8726f1b6a666e953
msam_jun94.tar	1,556,480	eab3d02b3ccfa1bad83f8d59e0465b9b856abbdc0a45551e2a86fa99ac790101
msam_jun95.tar	3,102,720	1053a0b90ef25ecfb076e16accc6e33ef5374ff1de855984040cc31c7af3fbf9

The embedded flight documentation is also pinned: jun92/README.tex, 2,494 bytes, SHA-256 b272eccbe039b6b253634c65a3de3a64aafddc47faa36455e6fef0c35db69eda; jun94/README.tex, 4,325 bytes, SHA-256 c427a1bceb4be346087f77a9c42e92766b6967b185766b9a941e56d606937e42; and jun95/README.tex, 3,637 bytes, SHA-256 11ee9cf7e5a205687eede78190818d8f0f813981d434978565134264820a7799. Each configuration's metadata additionally pins its exact archive member.

Considerations for use

The 1994 README states that its reduced datasets were reconstructed after a disk crash and that its beam maps copy the 1992 beam maps. The 1994 and 1995 covariances have their overall-offset mode zeroed; consumers must handle that mode as documented by the release. The statistical-weight column should be ignored where the release recommends using the covariance instead.

The observed-data value is the integral of the antenna pattern times the sky signal. Its normalization therefore depends on the antenna-pattern normalization and must be interpreted with the matching beam map. For the 1992 release, the README gives beam solid angles of 0.18 deg² for CMBR and 0.19 deg² for dust when the beam-map amplitudes are normalized as supplied.

For the 1994 and 1995 covariance matrices, the release identifies the zero-eigenvalue vector as v_o=(1,...,1). It directs consumers to use SVD and invert only the subspace orthogonal to v_o. If another covariance matrix is added, the release says to zero this mode in the result with the projection operator P=1-v_o v_o^T.

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 formal licence is published.

No product-specific requested credit line is published.

Citations

The governing flight papers are Cheng et al., “A Measurement of the Medium-Scale Anisotropy in the Cosmic Microwave Background Radiation,” ApJ 422, L37 (1994); Cheng et al., “MSAM1-94: Repeated Measurement of Medium-Scale Anisotropy in the Cosmic Microwave Background Radiation,” ApJ 456, L71 (1996), together with Inman et al., “A CMBR Measurement Reproduced: A Statistical Comparison of MSAM1-94 to MSAM1-92” (1997); and Cheng et al., “Detection of Cosmic Microwave Background Anisotropy by the Third Flight of MSAM,” ApJ 488, L59 (1997).