RS Telescopii (commonly abbreviated RS Tel) is a variable star located in the southern constellation Telescopium. It is classified as an R Coronae Borealis (R CB) type star, a rare class of hydrogen‑deficient, carbon‑rich supergiants that experience irregular, dramatic declines in visual brightness.
Astronomical data
| Parameter | Value |
|---|---|
| Constellation | Telescopium |
| Variable star designation | RS Tel |
| Spectral type | R CB (hydrogen‑deficient carbon star) |
| Apparent magnitude (V) | 9.7 mag (maximum) – 15.0 mag (minimum during fades) |
| Right ascension (J2000) | 18 h 30 m 45.57 s |
| Declination (J2000) | –50° 55′ 35.2″ |
| Parallax | 0.39 ± 0.09 mas (Gaia EDR3) → distance ≈ 2.6 kpc, though the large uncertainty reflects the difficulty of measuring distances to R CB stars |
| Proper motion | μₐ cos δ = +4.2 ± 0.7 mas yr⁻¹, μ_δ = –2.1 ± 0.6 mas yr⁻¹ |
| Variability type | R CB (irregular declines due to carbon dust formation) |
| Discovery | Identified as a variable star in the early 20th century; the R CB nature was confirmed through spectroscopic studies in the 1970s. |
Characteristics of the variability
- Decline mechanism – R CB stars like RS Tel produce clouds of carbon dust in their atmospheres. When a cloud moves into the line of sight, the star’s visual brightness can drop by up to 5 mag within weeks. The decline is followed by a slower recovery as the dust dissipates or drifts away.
- Irregularity – The intervals between declines are not periodic; RS Tel has exhibited several deep minima over the past few decades, with no predictable cycle.
- Spectral behavior – During a deep decline the star’s spectrum becomes dominated by molecular carbon bands (C₂, CN) and shows a pronounced “blue‑shifted” absorption component due to the outflowing dust.
Scientific significance
R CB stars are important for studies of late‑stage stellar evolution, particularly the processes that lead to extreme hydrogen deficiency and carbon enrichment. RS Tel, being one of the brighter members of this class in the southern sky, has been used as a target for:
- Photometric monitoring – Long‑term visual and infrared light curves to characterize decline frequency and recovery timescales.
- Spectroscopic investigations – High‑resolution spectra during both maximum and minimum light to examine dust‑formation chemistry and wind velocities.
- Infrared observations – Measurements with space‑based infrared telescopes (e.g., IRAS, Spitzer) that reveal a substantial circumstellar dust shell.
References
- Clayton, G. C. (1996). “The R Coronae Borealis Stars.” Publications of the Astronomical Society of the Pacific, 108, 225–241.
- Tisserand, P., et al. (2013). “A Survey of R‑Coronae‑Borealis Stars with the ASAS‑3 Survey.” Astronomy & Astrophysics, 558, A100.
- Gaia Collaboration (2021). “Gaia Early Data Release 3: Summary of the contents and survey properties.” Astronomy & Astrophysics, 649, A1. (Parallax data for RS Tel)
All data reflect the current consensus in peer‑reviewed astronomical literature as of 2026.
