Life and death of stars CAPAS James Lequeux, 30 septembre 2012 - - PowerPoint PPT Presentation

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 Msun) 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

rotation, a protostellar disk forms giving a single star

• If parent cloud rotates

fast, a massive binary forms

A massive protostellar disk seen at 10 µm

(A. Boss)

Role of mass loss in the evolution of massive stars

Mass loss affects very much the evolution of massive stars

(Maeder and Meynet)

Internal structure without/with mass loss

No mass loss Strong mass loss

(Maeder)

Evolution of binary massive stars

Just an example. There are many other possibilities !

(de Boer and Seggewiss)

Range of possibilities for massive binary evolution

• Case A: mass transfer during H-core burning of the primary
• Cases B and C: after H-core burning of the primary

(Podsiadlowski et al. 1992)

(or black hole)

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

• r 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
• f cases. GOOD LUCK!