A Planet Around Epsilon Eridani?

Epsilon Eridani is a chromospherically active star, rich in emission lines in the Ultraviolet (Prieto et al. 2000). Its spectral line shapes, magnetic field, and photospheric temperature vary with time much more than most main sequence stars (Gray and Baliunas 1995). Its abundance of heavy elements is slightly less than Solar, despite being only 1 Gyr old (Drake & Smith 1993). Moreover, the Doppler shift of Epsilon Eridani varies quickly (within a day) by ~15 m/s, constituting a "noise" in the search for a planet.

Reports of a Planet Around Epsilon Eridani by Bruce Campbell

The evidence for a planet around Epsilon Eridani was first reported by Bruce Campbell, Gordon Walker, and Stevenson Yang (Campbell et al. 1988). Their Doppler measurements suggested a companion mass of 1.2-4.7 times the mass of Jupiter (see their Table 3). Campbell's planet around Epsilon Eri remained controversial, as more velocity measurements were needed, along with a better understanding of the noise from the star.

In 1999, Andrew Cumming, G. Marcy, and P.Butler reported a clear periodicity in the Doppler measurements from Lick Observatory (Cumming et al. 1999). The probability of a false alarm was 0.002 . The period was 6.9 yr, and the implied mass resided at the low end of that which Campbell et al. had reported, and certainly in agreement.

Doppler measurements at McDonald Observatory obtained by Bill Cochran and Artie Hatzes were reported at the International Astronomical Union in August, 2000, which agree with the previous reports by Campbell et al. and Cumming et al.

Dr. Sallie Baliunas has supplied chromospheric measurements of Epsilon Eri which exhibit no apparent periodicity in the chromosphere near 6.9 yr. This has been interpreted as supporting evidence that Campbell's planet is real, rather than an artifact of the magnetically active star.

However, the Doppler behavior of magnetically active stars remains poorly explored, because so few stars are as active as Epsilon Eridani. Thus, Campbell's interpretation of a planet remains controversial.

Thus Epsilon Eridani should be compared to other K stars with planets.

George Gatewood, discoverer of the planetary system around Laland 21185, also finds a planet around Epsilon Eridani, and gives the actual mass of the planet.

Campbell, Walker, Yang 1988, Astrophys. J. 331, p902

Cumming, Marcy, Butler 1999, Astrophys.J. 526, 890

Drake and Smith 1993, Astrophys. J. 412, p797

Gray and Baliunas 1995, Astrophys, 441, p436

Hatzes et al. preprint

Prieto et al. 2000 Astrophys. J. 528, p885

G.Marcy, P.Butler, S.Vogt, D.Fischer

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