29:50 Modern Astronomy
Fall 2002
Lecture 25...November 8, 2002
Stars Like the Sun (cont.)

Announcements: Exam next, week, others Stars like the Sun, continued

(1) Classes of ``solar type stars'', ``solar analogs'', and ``solar twins'', as ideas of zeroing in on the Sun's position on the HR diagram.

Last week's thrilling episode, HR diagram of solar-type stars

(2) Blow-up of HR diagram with solar analog stars; stars with known planets named. 51 Pegasi and Reticuli

(3) How to really narrow things down to the solar twins. Make a detailed examination of spectra of stars and compare with Sun. Using spectrum as a ``fingerprint'' to match stars with the Sun.
Overall spectrum of Sun
high resolution spectrum of Sun and other G2V stars.

(4) The ``Solar Twins''; things narrowed down to 16 Cygni A & B, HR6060, and HR2290.
Transparency of Sun & closest copies.

(5) The closest match is the star HR 6060, or as it is better known, 18 Scorpii.

• reading of abstract from Astrophysical Journal article on 18 Scorpii
• Star charts showing where it is.

(6) Within the next couple of decades, we should discover fast numbers of additional solar twins. The key is a precise measurement of the distance from spacecraft parallax measurers. We have

• Hipparchos (already done): parallaxes of 118,000 stars
• FAME (US spacecraft, cancelled last year but probably will be built): 4 million stars
• GAIA (the deluxe version) proposed European spacecraft to measure parallaxes to 5 billion stars.

Within 20 years, we can anticipate knowing the existence and locations of ten thousand solar twins!

(7) Extrasolar planets: Big surprise in 1995; we had not anticipated being able to detect planets outside the solar system. First discovery was planet of 51 Pegasi. Surprise was because planets were ``hot Jupiters''.
Table of Hot Jupiters, Textbook reference in Figure 27.6.

Information on extrasolar planets
(1) Current List of Extrasolar Planets
(2) Map of the Extrasolar Planets
Artists' Conception of Extrasolar Planets (1)A vision of 55 Cancri
(2)A vision of 47 UMa
(3)HD 82943-planet swallower
(4)A vision of HD38529

(8) Ruminations on exobiology; a synthesis of astronomy, biology, geology.

(9) Knowing about stars is important in this context. They determine the nature of the alien solar systems. Will see why we can restrict attention to stars like the Sun.

(10) Old concept: the ``habitable zone'' around a star. See Figure 27.8 of book. A planet which could host life must lie in a zone around a star, an annular shell . If planet is too close, it will be too hot for liquid water. If planet is too far away, it is too cold for liquid water (it freezes).

For cool star (M star) the habitable zone is very small, and it is unlikely a planet would form there.
For O or B star, the habitable zone is very large. But what do you know about stars that indicates an O or B star would not be good for a planet with life?

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