Paul Broberg Ast 4001 Dec. 10, 2007
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1 Paul Broberg Ast 4001 Dec. 10, 2007
2 What are W-R stars? How do we characterize them? What is the life of these stars like? Early stages Evolution Death What can we learn from them? Spectra Dust
3 1867: Charles Wolf and Georges Rayet at Paris Observatory 1892: First spectra recorded by Campbell Early 1900 s: Found to be present in many planetary nebulae.
4 Massive stars typically 20 to 80 M Extremely hot! ~50,000 K Lifetimes ~ 0.5 million years Identified by intense, broad emission lines from stellar winds Absence of Hydrogen ( < 15 % H)
5 Believed to originate from type O or B stars First to leave the main sequence Evolution greatly dependent on mass of O-type star and composition as W-R star
6 3 basic types of W-R Stars WN (Nitrogen rich) (~ 1% N) Strong He and N emission lines WC (Carbon rich) (~ 10-60% C) Strong C, O and He emission lines Little or no N present ( > 0.05%) WO (Oxygen rich) Strong O lines
7 Type O star W-R star LBV star Super Nova
8 Originate from type O or B stars with masses typically from 20 to 80 M Found close to galactic plane Follow massive star evolution Hydrogen burning Shell burning (H and He; heavy element core) End up in CNO cycle in core Evolve into Super Giants or Luminous Blue Variable (LBV) stars
9 Huge luminosities are generated (~3x10 5 times larger than the sun) Wind velocities ~ 2,500 km/s Blow off outer layers (including most/ all of its hydrogen). Lose approximately 10-5 M each year
10 Nuclear core is revealed Leftover hydrogen is burned into He Helium is still abundant Fusion reactions continue CNO cycle Higher effective temperatures Mixing (rotational and convective) creates diverse surface environment Hard to resolve beyond winds
11
12 Type O star W-R star LBV star Super Nova
13 Have only been around 5x10 5 years Have lost >40 % of initial mass Very dense core composed of heavy elements
14 Tend to end in some sort of Super Nova WC stars will go as type Ic SNs WN stars will go as type Ib SNs or type IIs
15 No observed absorption lines in W-R stars Stellar wind is massive and hot Absence of Hydrogen Stars classified by chemical abundance
16 Spectral evolution from O type to W-R O7 Main Sequence O8 Super Giant WN7 Wolf-Rayet WC8 Wolf-Rayet
17 Crowther, pp 181
18 Circum stellar gases can form dust (larger molecules) Generally formed by cooler stars (RSGs) Also formed in collisions of stellar winds shocks Optically thick to long wavelengths Difficult to see inside of the stellar winds Difficult to determine properties of star
19 Can learn about dust formation and radiation production Formation of dust is present in large mass stars, binaries, and supernovae Can determine properties of stellar interior from observations in this range.
20 Excess temperatures could explained by free-free emission in the circumstellar clouds T g = grain temp T * = star temp T s = shell temp F * = radiation flux from star F s = radiation flux from shell Grain Temperature: T g = T * (F * /4F s ) 1/3 Radius of star R s = R * (T * F s /T s F * ) 1/2
21 W-R stars are vey hot, massive stars characterized by strong stellar winds, lack of H, and intense, broad emission lines. Accepted to be part of normal evolution of very massive stars Spectra and dust formations of these stars can tells us about the star s properties
22 Abbot D. C., Conti P. S. (1987) Wolf-Rayet Stars. Annual Reviews of Astronomy and Astrophysics. Vol 25: Beals, C. S. (1929). On the nature of Wolf-Rayet emission. Monthly Notices of the Royal Astronomical Society 90: Retrieved on Clowes, C. (2006) Wolf-Rayet Stars. 9/o7/ /16/ Crowther, P. A. (2007) Physical Properties of Wolf-Rayet Stars. Annual Reviews of Astronomy and Astrophysics. Vol 45: de Loor C., J.P. De Greve and D. Vanberen (1978). Evolution of O stars and the origin of Wolf-Rayet Stars. Hackwell J.A., Gehrz R. D, Smith J.R. (1976). Infrared Light Variations of Wolf-- Rayet Stars. Astrophysical Jounal. 120: Wolf-Rayet Stars Institut d'astrophysique et de Géophysique de l'université de Liège. vela.astro.ulg.ac.be/themes/stellar/massive/wr_e.html
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