TZ Arietis
A flare star with confirmed and disputed planetary candidates.
TZ Arietis, also cataloged as Gliese 83.1, GJ 9066, or L 1159-16, is a red dwarf located in the northern constellation Aries. Though it sits relatively nearby at a distance of 4.47 parsecs, its typical apparent visual magnitude of 12.3 makes it invisible to the unaided eye. The star is classified as a flare star, capable of sudden, short-lived brightness increases.
Variability was first reported for TZ Arietis by William E. Kunkel in 1968. As a flare star, it exhibits brief surges in luminosity caused by surface eruptions; in the ultraviolet range, these flares can exceed one magnitude. The star also displays long-term brightness variations, likely linked to starspots and rotation, which may qualify it as a BY Draconis variable. The variable-star designation TZ Arietis was assigned in 1970.
Three candidate planets were proposed in a June 2019 preprint, with orbital periods of 2, 240, and 770 days. A subsequent August 2020 paper confirmed the 240-day and 770-day objects, naming them "b" and "c," respectively. In March 2022, astronomers at the Calar Alto Observatory, working with the CARMENES survey, independently confirmed the 770-day planet—which they designated "b"—but found no evidence for the 240-day candidate. They also determined that the 2-day signal was a spurious chromatic effect tied to the star’s rotation. The NASA Exoplanet Archive continues to list the confirmed 770-day planet as "c."
- Designations
- TZ Arietis, Gliese 83.1, GJ 9066, L 1159-16
- Constellation
- Aries
- Apparent magnitude
- 12.3
- Distance
- 4.47 pc
- Spectral type
- red dwarf
- Rotation period
- 2.0 days
- Variable star designation year
- 1970
Lore & Background
William E. Kunkel announced that TZ Arietis is a variable star in 1968. It is a flare star, showing brief increases in brightness due to eruptions from its surface. In the ultraviolet, flares of over a magnitude have been observed. In addition it shows long-term variations in brightness which may be due to starspots and rotation, possibly classifying it as a BY Draconis variable. It was given the variable star designation TZ Arietis in 1970.
In a preprint submitted to arXiv in June 2019, three candidate planets were reported in orbit around this star with orbital periods of 2, 240, and 770 days. A paper published in August 2020 reported a confirmation of the 240-day and 770-day planets, designating them 'b' and 'c', respectively.
In March 2022, astronomers using the Calar Alto Observatory in Spain, as part of the CARMENES survey project, reported an independent confirmation of the 770-day planet, which they designated 'b'. However, they found no evidence for the 240-day planet, and confidently defined the 2-day candidate as nothing more than a spurious chromatic effect of the star, linked to its rotation. The NASA Exoplanet Archive still refers to the confirmed, 770-day planet as 'c'.
Reader's Guide
TZ Arietis is notable as a nearby red dwarf that exhibits both flare activity and long-term brightness variations consistent with BY Draconis-type variability. Its flaring behavior, with ultraviolet flares exceeding a magnitude, makes it a target for studying stellar activity in low-mass stars. The star gained further attention due to the announcement of three candidate planets in 2019, though subsequent observations have led to a disputed planetary system. The 770-day planet was independently confirmed by the CARMENES survey in 2022, but the 240-day planet was not detected, and the 2-day candidate was dismissed as a rotation-related artifact. The naming of the confirmed planet remains inconsistent, with the CARMENES team calling it 'b' while the NASA Exoplanet Archive retains the designation 'c'. This star illustrates the challenges of confirming exoplanets around active, flaring red dwarfs, where stellar variability can mimic or obscure planetary signals.
Did You Know?
- TZ Arietis has a normal apparent visual magnitude of 12.3, making it invisible to the naked eye.
- It is located at a distance of 4.47 pc from Earth.
- The star's rotation period is 2.0 days.
- The 2-day planet candidate was later determined to be a spurious chromatic effect linked to the star's rotation.
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