Delta Cassiopeiae (δ Cassiopeiae) is a multiple star system located in the northern constellation Cassiopeia. The primary component, often identified simply as δ Cas, bears the traditional name Ruchbah (also rendered Ruchba, Rucbah, or Rujbah).
Designation and Nomenclature
- Bayer designation: δ Cassiopeiae
- Flamsteed designation: 34 Cassiopeiae
- Traditional name: Ruchbah (Arabic رُخبة Rukhbah, meaning “the knee”) – the star marks the knee of the mythological queen Cassiopeia in classical asterisms.
- Other catalog identifiers: HD 104841, HIP 58899, HR 4595, SAO 23607, BD +60°0410.
Position and Visibility
- Right ascension (J2000): 00 h 57 m 23.5 s
- Declination (J2000): + 60° 15′ 55″
- Apparent magnitude (V): 2.68, making it readily visible to the naked eye under most night‑sky conditions.
- Distance: Parallax measurements from the Hipparcos and Gaia missions give a parallax of ≈ 9.0 mas, corresponding to a distance of roughly 350 light‑years (≈ 108 parsecs).
Physical Characteristics (Primary component, δ Cas A)
- Spectral type: B0.5 IV (blue‑white subgiant)
- Effective temperature: ≈ 25 000 K
- Luminosity: ≈ 10 000 L☉ (solar luminosities)
- Radius: ≈ 5 R☉ (solar radii)
- Mass: ≈ 7–8 M☉ (solar masses)
- Absolute magnitude (V): ≈ –2.1
These parameters indicate that δ Cassiopeiae A is a massive, evolved B‑type star that has exhausted hydrogen in its core and is progressing toward the giant phase.
System Architecture
Δ Cassiopeiae is a wide visual binary consisting of:
| Component | Approx. visual magnitude | Angular separation from primary | Remarks |
|---|---|---|---|
| δ Cas A (Ruchbah) | 2.68 | — | B0.5 IV subgiant; dominates the system’s light. |
| δ Cas B | ~9.7 | ~73 arcseconds (≈ 0.02 pc) | A faint, likely main‑sequence star (spectral type estimated near G or K). |
The large separation implies a very long orbital period (tens of thousands of years) and a weak gravitational binding. No closer spectroscopic companions have been confirmed with certainty; reports of additional components remain unverified.
Observational Notes
- Color: Appears blue‑white due to its high surface temperature.
- Variability: No significant photometric variability has been established; the star is classified as non‑variable in major variability catalogs.
- Proper motion: Small, reflecting its distance and location near the celestial pole.
Cultural and Historical Context
The name Ruchbah entered Western star catalogs through the work of Arabic‑speaking astronomers of the Middle Ages and was later Latinized. In Chinese astronomy the star is part of the asterism “The Crown” (皇冠, Huáng Guān). In Western mythology, the star’s position near the knee of the figure of Cassiopeia aligns with its Arabic meaning.
References
- Hipparcos and Tycho Catalogues (ESA, 1997) – astrometric data.
- Gaia Early Data Release 3 – refined parallax and proper motion.
- Bright Star Catalogue (Hoffleit & Jaschek, 1991) – spectral classification and photometric data.
- IAU Working Group on Star Names (WGSN) – official adoption of the name “Ruchbah”.
All data reflect the consensus of peer‑reviewed astronomical literature as of 2024.