README.md

---
license: cc-by-4.0
pretty_name: "GALAH DR4 — Stellar Abundances for 917k Stars"
language:
  - en
description: "The fourth data release of the Galactic Archaeology with HERMES survey — radial velocities, stellar parameters, and up to 31 elemental abundances for 917,588 stars."
task_categories:
  - tabular-classification
  - tabular-regression
tags:
  - space
  - stars
  - spectroscopy
  - galah
  - abundances
  - astronomy
  - open-data
  - tabular-data
size_categories:
  - 100K<n<1M
configs:
  - config_name: default
    data_files:
      - split: train
        path: data/galah_dr4_allstar.parquet
    default: true
---

# GALAH DR4 — Stellar Abundances for 917k Stars

*Part of the [Astronomy Datasets](https://huggingface.co/collections/juliensimon/astronomy-datasets-69c24caf2f17e36128946743) collection on Hugging Face.*

The fourth data release of the GALactic Archaeology with HERMES (GALAH) survey,
providing radial velocities, stellar parameters, and up to 31 elemental abundances
for **917,588** stars observed with the HERMES spectrograph on the
Anglo-Australian Telescope.

## Dataset description

GALAH DR4 is one of the largest stellar spectroscopic surveys, designed to unravel
the formation and evolution of the Milky Way through chemical tagging. Each star has
high-resolution spectra decomposed into fundamental stellar parameters and individual
elemental abundances spanning light elements, alpha-elements, iron-peak elements,
and neutron-capture elements.

Key properties:
- **906,689** stars with radial velocity measurements
- **906,432** stars with at least one elemental abundance
- **30** elemental abundance columns ([X/Fe])
- Median **24** abundances per star
- Median SNR: **48.1** per pixel

## Schema

| Column | Type | Description |
|--------|------|-------------|
| `sobject_id` | string | GALAH observation identifier |
| `star_id` | string | GALAH unique star identifier |
| `tmass_id` | string | 2MASS identifier |
| `gaiadr3_source_id` | string | Gaia DR3 source identifier |
| `ra` | float64 | Right Ascension J2000 (degrees) |
| `dec` | float64 | Declination J2000 (degrees) |
| `teff_k` | float64 | Effective temperature (K) |
| `logg` | float64 | Surface gravity (log cm/s^2) |
| `fe_h_dex` | float64 | Iron abundance [Fe/H] (dex) |
| `vmic` | float64 | Microturbulence velocity (km/s) |
| `vsini` | float64 | Projected rotational velocity (km/s) |
| `radial_velocity_kms` | float64 | Barycentric radial velocity (km/s) |
| `radial_velocity_comp2_kms` | float64 | Binary companion RV (km/s) |
| `snr_px_ccd1`..`snr_px_ccd4` | float64 | Signal-to-noise per pixel (4 CCDs) |
| `snr_mean` | float64 | Mean SNR across all 4 CCDs |
| `flag_sp` | Int64 | Spectroscopic quality flag (0 = best) |
| `flag_red` | Int64 | Reduction pipeline quality flag |
| `li_fe`..`eu_fe` | float64 | Elemental abundances [X/Fe] (dex) — 31 elements |
| `n_abundances` | Int64 | Count of non-null abundance measurements |

### Abundance columns

Light: `li_fe`, `c_fe`, `n_fe`, `o_fe` ·
Odd-Z: `na_fe`, `al_fe`, `k_fe` ·
Alpha: `mg_fe`, `si_fe`, `ca_fe`, `ti_fe` ·
Iron-peak: `sc_fe`, `v_fe`, `cr_fe`, `mn_fe`, `co_fe`, `ni_fe`, `cu_fe`, `zn_fe` ·
s-process: `rb_fe`, `sr_fe`, `y_fe`, `zr_fe`, `mo_fe`, `ba_fe`, `la_fe`, `ce_fe`, `nd_fe` ·
r-process: `ru_fe`, `sm_fe`, `eu_fe`

## Usage

```python
from datasets import load_dataset

ds = load_dataset("juliensimon/galah-dr4-stellar-abundances", split="train")
df = ds.to_pandas()

# High-quality stars with best spectroscopic flags
best = df[df["flag_sp"] == 0]

# Metal-poor stars
metal_poor = df[df["fe_h_dex"] < -1.0]

# Stars rich in europium (r-process)
eu_rich = df[df["eu_fe"] > 0.5]

# Stars with the most measured abundances
well_measured = df.sort_values("n_abundances", ascending=False).head(1000)

# Kiel diagram (logg vs Teff)
import matplotlib.pyplot as plt
sample = df[df["flag_sp"] == 0].sample(50000)
plt.scatter(sample["teff_k"], sample["logg"], c=sample["fe_h_dex"],
            s=0.1, cmap="coolwarm", vmin=-1.5, vmax=0.5)
plt.gca().invert_xaxis()
plt.gca().invert_yaxis()
plt.xlabel("Teff (K)")
plt.ylabel("log g")
plt.colorbar(label="[Fe/H]")
```

## Data source

[GALAH Survey DR4](https://www.galah-survey.org/dr4/) (Buder et al. 2024).
Observed with the HERMES spectrograph (R ≈ 28,000) on the 3.9m Anglo-Australian
Telescope at Siding Spring Observatory.

## Update schedule

Static dataset — uploaded once from the DR4 release catalog.

## Related datasets

- [gaia-dr3-astrophysical-parameters](https://huggingface.co/datasets/juliensimon/gaia-dr3-astrophysical-parameters) — Gaia DR3 stellar parameters
- [exoplanet-catalog](https://huggingface.co/datasets/juliensimon/exoplanet-catalog) — Confirmed exoplanets
- [pulsar-catalog](https://huggingface.co/datasets/juliensimon/pulsar-catalog) — Pulsar catalog

## Pipeline

Source code: [juliensimon/space-datasets](https://github.com/juliensimon/space-datasets)

## Citation

```bibtex
@article{buder2024galah,
  author = {Buder, Sven and others},
  title = {The GALAH Survey: Data Release 4},
  year = {2024},
  journal = {arXiv preprint arXiv:2409.19858},
}
```

## License

[CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/)