7 Arietis
A disputed eclipsing binary in Aries, faintly visible to the naked eye.
7 Arietis is a binary star system in the northern constellation of Aries, designated RR Arietis as a variable star. It is listed as an eclipsing binary with a period of 47.9 days, though its variability has been disputed and remains unconfirmed by several photometric surveys and independent observations.
Quick Facts
- Variable star designation
- RR Arietis
- Combined apparent visual magnitude
- 5.76
- Distance
- approximately 600 ly (parallax 5.39 mas)
- Orbital period (eclipsing binary)
- 47.9 days
- Primary spectral type
- K1 III (evolved giant)
Facts from the source article.
Lore & Background
7 Arietis is a binary star system with a combined apparent visual magnitude of 5.76, making it faintly visible from dark suburban skies. Based on an annual parallax shift of 5.39 milliarcseconds, it lies about 600 light-years from Earth, with a margin of error of 30 light-years, and is drifting further away at a radial velocity of +16 km/s. The system is listed as an eclipsing binary with a period of 47.9 days, during which the primary star's eclipse reduces the system's magnitude by 0.40 and the secondary's eclipse by 0.35. However, the star does not appear variable in the General Catalogue of Photometric Data, the Hipparcos data, or a study from 1979–1980. The eclipsing nature has been disputed by Italian astronomer Ennio Poretti, and observations made as part of the British Astronomical Association eclipsing binaries program by Tristram Brelstaff were also unable to confirm eclipses. The primary component is an evolved giant star with a stellar classification of K1 III, about 25 times the size of the Sun, radiating 231 times the Sun's luminosity from its photosphere at an effective temperature of 4,500 K.
Reader's Guide
7 Arietis holds significance as a variable star whose eclipsing binary status remains contested, illustrating the challenges in confirming variability for faint systems. Despite being listed as RR Arietis with a 47.9-day period and predicted magnitude drops of 0.40 and 0.35, multiple datasets—including Hipparcos and a 1979–1980 study—show no variability. The dispute, raised by Ennio Poretti and supported by Tristram Brelstaff's unsuccessful British Astronomical Association observations, means the system's classification is uncertain. Its primary component, a K1 III giant with a radius 25 times solar and luminosity 231 times solar, is well-characterized, but the binary's eclipsing behavior remains unverified. This leaves 7 Arietis as a cautionary example in variable star catalogs, where designation does not guarantee confirmed behavior. Its legacy lies in the ongoing need for careful photometric monitoring to resolve such discrepancies, and it serves as a reminder that even cataloged variable stars may require re-evaluation.
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