Quiz Question: Binary Stars

Transcription

1 Quiz Question: Binary Stars In which type of binary star system is the plane of the orbit in our line of sight? A)Visual binary B)Eclipsing binary C)Spectroscopic binary

2 Quiz Question: Binary Stars In which type of binary star system is the plane of the orbit in our line of sight? A)Visual binary we can see each star distinctly B)Eclipsing binary plane of orbit in our line of sight C)Spectroscopic binary Doppler shift evident in the spectral lines

3 Questions Stellar Evolution What determines the mainsequence lifetime of a star? What are star clusters and how do we determine their ages? How will the Sun evolve?

4 The Hertzprung-Russell Diagram Types of Stars Main sequence Giants Supergiants White dwarfs Stellar radii Fig

5 Stellar lifetimes are determined by stellar masses: Stellar Lifetimes Fig Empirically luminosity is proportional to mass cubed: L M 3 Lifetime = (Amount of fuel)/(rate of burning) Algebraically τ = M/L = M/M 3 τ = M -2

6 Concept Question: Stellar Lifetimes Lifetime = Mass -2 τ = M -2 The main sequence lifetime of the Sun is going to be (10 billion) years (yikes, we re half way there!). What is the main sequence lifetime of a 10 solar mass star? A)10 8 years B)10 10 years C)10 12 years

7 Concept Question: Stellar Lifetimes Lifetime Mass -2 τ M -2 The main sequence lifetime of the Sun is going to be (10 billion) years (yikes, we re half way there!). What is the main sequence lifetime of a 10 solar mass star ( star x )? A)10 8 years B)10 10 years C)10 12 years τ M -2 τ(sun) M -2 (sun) τ(x) M -2 (x) τ(x)/τ(sun) = M -2 (x)/m -2 (sun) τ(x)/τ(sun) = [M(sun)/M(x)] 2 τ(x)/τ(sun) = [1/10] 2 = 0.01 τ(x) = 0.01τ(sun) = 10 8 years

8 Star Clusters There are two types of star clusters: open clusters, which are small (<1000 stars), young, and unbound, and globular clusters, which are large (up to 10 6 stars), old, and bound. The Pleiades (10 8 years old) Fig M80 (>1.2x10 10 years old) Fig

9 Star Cluster Ages We measure the ages of clusters from their main sequence turnoff points. Fig

10 Turning Off the MS: The Sun Over time, the H in the core of the Sun is converted into He. The core becomes denser, enhancing gravity and hence the pressure & temperature. Eventually, all the H in the core is used up (converting ~30% of it s mass to He). The Sun will then turn off the main sequence and become a subgiant. Fig. 17.9

11 Concept Question As the Sun ages on the main sequence, which will it become? A)Less luminous B)It will stay the same luminosity C)More luminous

12 Concept Question As the Sun ages on the main sequence, which will it become? A)Less luminous B)It will stay the same luminosity C)More luminous density, pressure, and temperature in the core increase, increasing the rate of fusion

13 Turning Off the MS: The Sun The Sun will expand The photosphere will be cooler The Sun will be on it s way to becoming a red giant Fig

14 The Post Main-Sequence Evolution of the Sun Main Sequence H He in core Duration years Luminosity doubles over lifetime

15 The Post Main-Sequence Evolution of the Sun Main Sequence H He in core Duration years Luminosity doubles over lifetime Red Giant He core contracts rapid H fusion in shell Star expands to 100 R solar (Mercury s orbit!) He core degenerate Duration 10 8 years

16 The Post Main-Sequence Evolution of the Sun Main Sequence H He in core Duration years Luminosity doubles over lifetime Red Giant He core contracts rapid H fusion in shell Star expands to 100 R solar (Mercury s orbit!) He core degenerate Duration 10 8 years He Core Burning He flash when core reaches 10 8 K 3 x 4 He 12 C + energy; strong wind Duration 5x10 7 years

17 The Post Main-Sequence Evolution of the Sun Double Shell Burning Red Giant C core, He burning inner shell, H burning outer shell Degenerate core very dense: 1 cm 3 has 1000 kg mass! Small amount of oxygen created

18 The Post Main-Sequence Evolution of the Sun Double Shell Burning Red Giant C core, He burning inner shell, H burning outer shell Degenerate core very dense: 1 cm 3 has 1000 kg mass! Small amount of oxygen created Unstable Fusion in Shells Envelope blown off creating a planetary nebula, leaving a white dwarf behind

19 The Post Main-Sequence Evolution of the Sun on the H-R Diagram Fig

20 Planetary Nebulae Fig a

21 Evolution of The Sun s Luminosity Fig A

22 Evolution of the Sun s Radius Fig B