juliensimon/hot-subdwarf-stars

Hot Subdwarf Star Catalog

Credit: NASA/ESA/Hubble

Part of a dataset collection on Hugging Face.

Dataset description

The Catalogue of Hot Subdwarf Stars (Kilkenny, Heber & Drilling 1988), retrieved from VizieR III/137. The compendium remains the historical reference for the population of spectroscopically identified subdwarf B (sdB) and subdwarf O (sdO) stars — evolved low-mass stars that occupy the extreme horizontal branch of the Hertzsprung-Russell diagram.

Hot subdwarfs are believed to be the bare helium-burning cores of red giants that lost almost all of their hydrogen envelopes near the tip of the giant branch. The dominant formation channel is binary interaction (Roche-lobe overflow or common-envelope ejection), making sdB stars a key laboratory for testing binary stellar evolution theory and the origin of single hot subdwarfs via mergers. They are also major contributors to the ultraviolet excess (UV upturn) observed in elliptical galaxies. Each entry in this catalog records the J2000 sky position, primary designation, V-band photometry, color indices, spectral classification, and the atmospheric parameters effective temperature and surface gravity (log g) when available.

This dataset complements juliensimon/gaia-dr3-white-dwarfs (the post-AGB end-state into which some hot subdwarfs evolve), juliensimon/cataclysmic-variable-catalog and juliensimon/xray-binary-catalog (compact binary systems formed by similar evolutionary pathways), and juliensimon/brown-dwarf-catalog and juliensimon/cns5-nearby-stars for broader stellar-population context.

This dataset is suitable for tabular classification tasks.

Schema

Column	Type	Description	Sample	Null %
catalog_number	int64	Sequence number in the Kilkenny-Heber-Drilling catalog; entries 1-N are listed in spectral-type order	2	0.0%
ra	float64	Right ascension (degrees, J2000, 0-360)	44.64495833333333	0.0%
dec	float64	Declination (degrees, J2000, -90 to +90)	3.181222222222222	0.0%
name	str	Primary star designation (e.g. 'PB 6958', 'PG 0044+097', 'EC 11481-2303'); compiled from the discovery survey	PB 6958	0.0%
v_magnitude_reference	str	Bibliographic reference code for the V-band photometry	75	63.7%
v_magnitude	float64	Apparent V-band magnitude (Johnson V); brighter sources have smaller values	15.08	63.6%
color_index_1	float64	Color index 1 (U-B or B-V depending on photometric system; Johnson UBV by default)	-0.15	64.2%
color_index_2	float64	Color index 2 (typically B-V or Stromgren b-y)	-1.14	64.2%
color_index_3	float64	Color index 3 (third photometric color, system-dependent)	-0.08	87.6%
spectral_type	str	Spectral classification (e.g. 'sdB', 'sdO', 'sdB+F'); 'sd' denotes subdwarf; the secondary letter (B or O) marks the underlying spectral class; '+X' suffix indicates a composite spectrum with cool companion of type X	sdB	15.2%
spectral_type_reference	str	Bibliographic reference code for the spectral classification	75	15.4%
effective_temperature_k	float64	Effective temperature (Kelvin); sdB stars cluster around 25,000-35,000 K, sdO stars at 40,000-80,000 K	4.74	90.0%
log_g	float64	Logarithm (base 10) of surface gravity in cgs units (cm/s^2); hot subdwarfs occupy log_g = 5-6, intermediate between main-sequence (4-5) and white dwarfs (7-9)	4.0	92.9%
log_g_reference	str	Bibliographic reference code for the log_g determination	76	90.0%

Quick stats

• 1,714 spectroscopically identified hot subdwarf stars
• 770 sdB-type + 470 sdO-type entries
• 22 composite-spectrum binaries (e.g. sdB+F, sdO+K)
• Effective temperatures span 3 to 5 K
• Surface gravities (log g) cluster between 3.30 and 7.00 cgs

Usage

from datasets import load_dataset

ds = load_dataset("juliensimon/hot-subdwarf-stars", split="train")
df = ds.to_pandas()

from datasets import load_dataset
import matplotlib.pyplot as plt

df = load_dataset("juliensimon/hot-subdwarf-stars", split="train").to_pandas()

# Kiel diagram (Teff vs log g) — the standard plane for hot subdwarf analysis
mask = df["effective_temperature_k"].notna() & df["log_g"].notna()
fig, ax = plt.subplots(figsize=(8, 6))
ax.scatter(df.loc[mask, "effective_temperature_k"], df.loc[mask, "log_g"],
           c=df.loc[mask, "v_magnitude"], s=30, cmap="viridis_r")
ax.invert_xaxis()  # hot on the left
ax.invert_yaxis()  # large gravity on the bottom
ax.set_xscale("log")
ax.set_xlabel("Effective temperature (K)")
ax.set_ylabel("log g (cgs)")
ax.set_title("Kiel diagram of hot subdwarfs — sdB cluster vs sdO tail")
plt.tight_layout()
plt.show()

# Spectral-type breakdown
print(df["spectral_type"].value_counts().head(20))

Data source

https://cdsarc.cds.unistra.fr/viz-bin/cat/III/137

Related datasets

• juliensimon/gaia-dr3-white-dwarfs

• juliensimon/cataclysmic-variable-catalog

• juliensimon/xray-binary-catalog

• juliensimon/brown-dwarf-catalog

• juliensimon/cns5-nearby-stars

• juliensimon/carbon-stars

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About the author

Created by Julien Simon — AI Operating Partner at Fortino Capital. Part of the Space Datasets collection.

Citation

@dataset{hot_subdwarf_stars,
  title = {Hot Subdwarf Star Catalog},
  author = {juliensimon},
  year = {2026},
  url = {https://huggingface.co/datasets/juliensimon/hot-subdwarf-stars},
  publisher = {Hugging Face}
}

License

CC-BY-4.0