Life and death of stars CAPAS James Lequeux, 30 septembre 2012 Evolution of binary massive stars
Stellar evolution in the HR diagram HR diagram (Hipparcos)
Massive stars are very rare • No O-B star within 50 pc • Closest O stars (M<15 M sun ) at 500 pc (Orion) • Less than 1000 O stars known in the Galaxy HR diagram of nearby stars (Jahreiss & Gliese)
But they are very important! • Ionize interstellar matter (HII regions) • Progenitors of type II and Ib supernovae • Agitate interstellar matter through winds and explosions • Trigger star formation • Some O binaries are powerful X-ray sources
Birth of massive stars • Massive stars are born deep inside interstellar clouds; very difficult to see before parent cloud dissipate • If parent cloud has little A massive protostellar disk rotation, a protostellar seen at 10 µ m disk forms giving a single star • If parent cloud rotates fast, a massive binary forms (A. Boss)
Role of mass loss in the evolution of massive stars (Maeder and Meynet) Mass loss affects very much the evolution of massive stars
Internal structure without/with mass loss (Maeder) No mass loss Strong mass loss
Evolution of binary massive stars (de Boer and Seggewiss) Just an example. There are many other possibilities !
Range of possibilities for massive binary evolution (Podsiadlowski et al. 1992) (or black hole) • Case A: mass transfer during H-core burning of the primary • Cases B and C: after H-core burning of the primary
70% of O stars are in close binary systems • A complete spectroscopic survey of several southern associations has recently given unbiased fractions of the different cases. CE = common envelope (Sana et al. 2012)
What to do now? • About 700 O stars known in our Galaxy up to V = 11 (catalog of Cruz-Gonzalez et al., 1974). Note: this catalog does not include B0 or B0.5 stars, which are of much interest and might even be O stars due to classification uncertainties. • Multi-epoch radial velocities for less than 100 O stars • In general, no multi-epoch photometry, hence not known if system is an eclipsing binary • Hence it would be very desirable to measure radial velocities and photometry at different epochs. How difficult is this?
Example 1 O3 and O3+WO in the nearby galaxy IC 1613
Example 2 (Sana et al. 2012)
Example 3: HD 93205, O3V + O8V, 31 + 13 Msun, P = 6.08 days, V = 7.75, B-V = 0.03 (Barba et al. 2001)
Period and RV distributions Log(period) excentricity mass ratio Total velocity amplitude (km/s)
What is possible for amateurs? • Systematic measurements of radial velocity, if possible within 5 km/s or so; even 10 km/s would be enough for the most interesting objects, i.e. those with large velocity variations. This should be possible for well-equipped amateurs with a 40-50 cm telescope and a high-dispersion spectrograph… and much care for calibration, and much patience. Garmany et al. used 1.5 to 2.1 m telescopes at the coudé focus (18 A/mm) on photographic plates. CCDs are at least 10 times more sensitive. • Systematic photometric measurements, if possible within 0.01 mag. A single band is sufficient, as color is not likely to vary appreciably. • For each target, a study of the literature and of data bases is necessary before embarking in the project. • You are likely to discover many new close binaries, and quite a variety of cases. GOOD LUCK!
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