HIPPARCOS Results for Solar Analogs
Giusa Cayrel de Strobel (Observatoire de Paris/Meudon) & Eileen D. Friel (NSF/Boston Univ.)

7. Final Comments

During this talk we have seen that the combination of detailed spectroscopic analyses, internal structure calculations, and precise distance determinations yields an evolutionary mass, a chemical composition, and state of evolution, hence age, of the observed sample of 52 photometric solar analogs of unprecedented accuracy. About our choice of the best solar analog, here in this workshop, we have to confess that the name of the best candidate has changed regularly in the 5 papers we have written on the subject in the last 16 years. Please note, though, that the principles for recognizing solar analogs have not changed in our group.

In 1981 no spectroscopic solar analog was chosen, because of poor spectroscopic results. In 1989 our choice went to Hardorp's spectrophotoelectric analog, HD 44594. In 1993 Friel et al. chose two stars ex equo as best solar analogs: the two components of the binary 16 Cyg. In the 1996 paper the planet star 51 Peg was elected best solar analog of the year. Today, I hope that you all will agree with me that 18 Sco is currently the best match to the Sun.

We shall finish in posing this interesting question: To know if there is a serious hope to find some other solar twins in the near future as good as 18 Sco? The answer is certainly "yes" if we agree to pay the price: i.e. to look for stars fainter than magnitude 8.0. However, the statistics are not very encouraging, because of the triple constraint on mass or effective temperature, on metallicity, and on age. If we are not wrong their number would not exceed 5 in a sample of 100,000 stars.

Acknowledgments

First of all our grateful thoughts go to the memory of Johannes Hardorp who was first in stimulating this research. And then our thanks go to Lodewijk Woltjer who has invited Giusa Cayrel to write a review on ``Stars resembling the Sun" prior to the arrival of the Hipparcos results, to Conard Dahn who in the early stage of this project has sent us some precious USNO CCD parallaxes of stars belonging to our priority list of solar analog candidates, to Catherine Turon and to the members of the former Hipparcos Consortia, to Monique Spite for her help in solving problems in spectroscopic detailed analyses, to Yveline Lebreton who allowed us, in supplying an up-to-date grid of internal structure models, to determine the evolutionary status of our sample of solar analogs, and last but not least, to Jeff Hall who invited us to this Workshop. Special thanks go to Nora Knowles and Claire Bentolila who, since 1978, actively took part in this research, and to Danielle Morin for her prompt reply to all our questions concerning the utilized Hipparcos data.

References

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