astro-legacy-archive/eht-m87-2017

EHT M87 2017 calibrated visibilities

These are the Event Horizon Telescope Collaboration's low- and high-band EHT-HOPS network-calibrated Stokes I visibility products for M87 on days 095, 096, 100, and 101 of the April 2017 campaign. They are the calibrated-data release 2019-D01-01, derived from Science Release 1 and used as the primary dataset for the First M87 EHT Results. Each source file is represented by a primary configuration named verbatim from its filename stem and queryable companion configurations for its AIPS AN and AIPS FQ extensions. The primary has one row per UVFITS random group in source order.

Target	M87, J2000, RA 187.7059307575226 deg, Dec 12.39112323919932 deg
Products	Four observing days, low and high band
Publisher averaging	“The data are time averaged to 10 seconds and frequency averaged over all 32 intermediate frequencies (IFs).”
Contents	One frequency channel, four FITS polarization slots, complex data and weights
Random groups	51,119 across eight configurations
Parquet downloads	21,270–429,656 bytes each; 24 configurations

The publisher reports 10-second time averaging and averaging over all 32 IFs. Across the 51,119 source rows, stored INTTIM is 10.0 s in 3,785 rows and shorter than 10.0 s in 47,334 rows; 10.0 s is the maximum in every configuration.

product	rows	INTTIM == 10.0	INTTIM < 10.0	minimum (s)	maximum (s)
095 lo	6,453	375	6,078	3.0203950405	10.0
095 hi	6,458	540	5,918	4.3981542587	10.0
096 lo	8,645	414	8,231	0.0642828420	10.0
096 hi	9,081	673	8,408	1.2000000477	10.0
100 lo	2,367	182	2,185	0.8000000119	10.0
100 hi	2,610	251	2,359	1.2000000477	10.0
101 lo	7,447	523	6,924	0.8000000119	10.0
101 hi	8,058	827	7,231	1.1968640089	10.0

The quoted processing statement is from the pinned 2019-D01-01 release README.

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/eht-m87-2017", "SR1_M87_2017_095_lo_hops_netcal_StokesI", split="train[:1]", columns=["BASELINE", "DATE"])
row = dataset[0]
print(row["BASELINE"], row["DATE"])

262.0 [2457848.5, 0.03200231492519379]

import json
from huggingface_hub import hf_hub_download
import pyarrow.parquet as pq
path = hf_hub_download("astro-legacy-archive/eht-m87-2017", "SR1_M87_2017_095_lo_hops_netcal_StokesI.parquet", repo_type="dataset")
print(json.loads(pq.read_metadata(path).metadata[b"visibility"])["schema"])

astro-legacy-archive/visibility

Embedded BASELINE metadata quotes Memo 117's source rule 256 * antenna_1 + antenna_2 + 0.01 * (subarray_number - 1). Embedded DATE metadata records that its two scaled occurrences sum to Julian Date. Rows use zero-based source position: Parquet row i is random group i in source order, and the source has no row-key column. DATA retains the declared DEC → RA → unnamed length-one axis → FREQ → STOKES → COMPLEX shape, and each COMPLEX triple is real part, imaginary part, and source weight; non-positive weight denotes a flagged slot.

Dataset structure

column	type	meaning
UU---SIN, VV---SIN, WW---SIN	float32	Raw source projected-baseline coordinates; resolve physical light-travel seconds as stored * pscal + pzero using the matching visibility.random_groups.parameters record
BASELINE	float32	Source AIPS baseline number
DATE	list[float32, 2]	Both source parameters named DATE, in PTYPE order
INTTIM	float32	Integration duration in seconds
TAU1, TAU2	float32	Source parameters retained under their opaque identifiers; the checked release and AIPS memo do not define them
DATA	six nested fixed-size lists, lengths 1 × 1 × 1 × 1 × 4 × 3	Source DEC → RA → unnamed length-one axis → FREQ → STOKES → COMPLEX array; real and imaginary are in source BUNIT JY, followed by the source weight

Each primary configuration links, in source HDU order, to an __AIPS AN antenna-table configuration and an __AIPS FQ frequency-table configuration. The companion configurations preserve the source column names, FITS forms, units, row order, values, and extension headers as ordinary queryable columns. Their field descriptions cite AIPS Memo 117 revised.

The AIPS AN companion contains antenna identity, station coordinates, orbital parameters, antenna number, mount type, axis offset, feed polarization and position-angle records, feed-calibration arrays, and the non-standard served SEFD field. The AIPS FQ companion contains the frequency-setup identifier, IF offset, channel separation, spectral-window width, and sideband code. Memo 117 defines SIDEBAND=-1 as lower sideband and SIDEBAND=+1 as upper sideband. It does not define the extra SEFD column in these files.

The source PTYPE order is UU---SIN, VV---SIN, WW---SIN, BASELINE, DATE, DATE, INTTIM, TAU1, TAU2. The two identically named source parameters are stored unchanged, in PTYPE order, in one length-2 DATE list. Their sum is the visibility Julian Date.

For these files, antenna numbers are floor(BASELINE / 256) and BASELINE modulo 256. The 21 baselines use antennas 1–7. The preserved AIPS AN table has eight records; NOSTA 8, SR, participates in no baseline. The source-provided lo- and hi-band centre frequencies are respectively 227070703125 Hz and 229070703125 Hz. The source GROUPS axes are COMPLEX, STOKES, FREQ, an unnamed length-one axis, RA, and DEC. Arrow nesting reads all six in reverse, outermost-first order. A one-based axis element j has value CRVAL + (j - CRPIX) * CDELT. For STOKES this gives the four FITS codes -1, -2, -3, and -4. FREQ additionally uses the AIPS FQ IF offset preserved in the linked AIPS FQ companion configuration. The AIPS FQ header's NO_IF=1 independently records one spectral window; it does not supply a CTYPE name for the unnamed GROUPS axis.

config suffix	random groups	timestamps	baselines	flagged slots	Parquet bytes
095_lo_hops_netcal_StokesI	6,453	701	21	3,530	328,664
095_hi_hops_netcal_StokesI	6,458	701	21	3,540	322,296
096_lo_hops_netcal_StokesI	8,645	900	21	4,262	420,347
096_hi_hops_netcal_StokesI	9,081	900	21	4,428	429,656
100_lo_hops_netcal_StokesI	2,367	186	21	1,106	166,323
100_hi_hops_netcal_StokesI	2,610	186	21	1,200	172,817
101_lo_hops_netcal_StokesI	7,447	781	21	3,142	367,022
101_hi_hops_netcal_StokesI	8,058	801	21	3,414	383,958

For every source file, its AIPS AN companion is 45,910 bytes and its AIPS FQ companion is 21,270 bytes.

Across the eight AIPS AN tables, all 64 rows have SEFD=0.0, ORBPARM=0.0, MNTSTA=0, POLTYA=R, POLTYB=L, POLAA=0.0, and POLAB=90.0. All eight AIPS FQ rows have SIDEBAND=1. These are measured source values. Memo 117 defines mount code 0 as alt-azimuth, R and L as the feed polarization codes, POLAA and POLAB in degrees, and sideband code +1 as upper sideband. ORBPARM is the source orbital-parameter field. The checked memo and release sources supply no definition or zero-value interpretation for SEFD.

The source represents an estimated Stokes I product in all four polarization slots. RR and LL both carry an estimated Stokes I value; RL and LR and their errors were deliberately set to zero by the publisher. The slots are not four independent polarization measurements. RR and LL measurement errors are each sqrt(2) times the statistical error for Stokes I. A non-positive source weight marks a flagged value. Infinite weights are source values, not nulls.

Memo 117 defines the weight component in Jy−2. In the publisher's pinned day-095 low-band text product, all 6,453 reported Isigma values satisfy Isigma = 1 / sqrt(2 * RR_weight) when compared with the positive source weights. The maximum absolute difference is 1.1186823023479064e-08 Jy and the maximum relative difference is 2.4738604812023641e-06. No derived uncertainty is stored in this dataset.

The publisher says independent flux calibration used estimated station sensitivities during the campaign. Paper III describes validation and estimated systematic errors, with additional details in Wielgus et al. (2019). The pinned 2019-D01-02 imaging release also cautions that these single-precision Stokes-I products differ slightly from the dual-polarization data used in Paper IV.

The same pinned repository provides sibling derived csv/ and txt/ forms, their conversion scripts, the top-level run.sh, and three convenience tarballs for UVFITS, CSV and text.

Provenance

The eight UVFITS files total 4,495,680 bytes and are pinned to release commit 27ae76aacb9067a83388395c3826012b97aac371.

source file	bytes	SHA-256
SR1_M87_2017_095_lo_hops_netcal_StokesI.uvfits	567,360	97492ee1146b05e12b1783e6c9a8253a0f50d789835286ffcc3ed5d248d51a8e
SR1_M87_2017_095_hi_hops_netcal_StokesI.uvfits	567,360	a11a874bdbf205089192b5270abc5894ad85e4ab54f0f677e3280c5639ea3e0d
SR1_M87_2017_096_lo_hops_netcal_StokesI.uvfits	751,680	f3394b2c272ba92980c21e3522987344f9175a78c333648a36458c917216c365
SR1_M87_2017_096_hi_hops_netcal_StokesI.uvfits	786,240	5bc42247ccd01b58460d95e8c17f91e337c79ffe99a0718aacf0a91c77ad24ec
SR1_M87_2017_100_lo_hops_netcal_StokesI.uvfits	224,640	ee90ca5aec0bd8ed27f5ea13c941ae3f24c188d5c8a9aa87ab4b5606f57334be
SR1_M87_2017_100_hi_hops_netcal_StokesI.uvfits	244,800	76104537313cd6879c497901f313bad667f4608c48df961e67ac5615d84b2c00
SR1_M87_2017_101_lo_hops_netcal_StokesI.uvfits	650,880	697af2bb3bbf732115108ffefacd3e59e307f38fe685c3c4579146b0bd661298
SR1_M87_2017_101_hi_hops_netcal_StokesI.uvfits	702,720	618c3019f60e88268980267a9db68f638b379a85842d83c06003d28550d191f5

Rebuild from the repository root at conversion commit 9ed9f9568026b7901f1a89102a6cfa08f3444e08:

python tools/make_eht_m87_visibility.py --out /var/tmp/will/eht-m87-2017/build --source /var/tmp/will/eht-m87-2017/source --provenance-commit 9ed9f9568026b7901f1a89102a6cfa08f3444e08

Each file carries a versioned visibility metadata document containing field and axis definitions, the ordered random-group parameter definitions, complete FITS headers, the ordered companion-configuration manifest, source provenance, credit, and regeneration command. PyArrow schema inspection exposes field descriptions and their structured definition, unit and decode records; load_dataset retains types but strips field metadata. The loaded primary table contains the raw, unscaled random parameters, both source DATE occurrences in one length-2 field, and DATA with every declared source axis at its declared length. Reconstruction joins the complete three-configuration set and restores the source parameter definitions and array shape, every random parameter occurrence, the full group array, and each auxiliary bintable with identical dtype, shape, order, headers, and values. FITS container serialisation and padding are outside that comparison.

Licensing and credit

The pinned release states:

The data files in this data set are licensed under the ODC-PDDL license https://www.opendatacommons.org/licenses/pddl/1.0/index.html.

The release publishes this credit line and no separately worded requested acknowledgement:

Authors: The Event Horizon Telescope Collaboration et al.

Citations

The release names First M87 EHT Results III: Data Processing and Calibration as its primary reference. It also cites the complete First M87 EHT Results series: I, II, IV, V, and VI.

The release also cites the reduction and calibration papers Blackburn et al. (2019), arXiv:1903.08832 and Janssen et al. (2019), arXiv:1902.01749. The same pinned release reference list includes Issaoun et al. (2017), EHT Memo 2017-CE-02, Janssen et al. (2019), EHT Memo 2019-CE-01, and Wielgus et al. (2019), EHT Memo 2019-CE-02.

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.