References

• Colas F., Arlot J.-E., 1991, A&A 252, 402 NASA ADS
• Harper D., Taylor D.B., 1993, A&A 268, 326 NASA ADS
• Harper D., Murray C.D., Beurle K., et al., 1997, A&AS 121, 65 NASA ADS
• Harper D. (to be submitted to A&A)