Chapter 10

Question 1

How many stars are in binary or multiple systems?

Answer 1

Over 50%

Question 2

What happens if the stellar masses in the binary are widely separated?

Answer 2

Each star evolves as a single star

Question 3

What happens if the stellar masses in the binary are close?

Answer 3

Evolution can be drastically different from that of a single star

Question 4

What happens during the evolution of the stars?

Answer 4

One star must expand during evolution to approx the separation of the stars

Question 5

What is the inner Lagrangian point L1?

Answer 5

It is where forces from stars balance

Question 6

What is the Roche lobe of a star?

Answer 6

The region where material is bound to that star

Question 7

What happens if one star expands to fill its Roche Lobe?

Answer 7

It can transfer matter to its companion through the L1 point

Question 8

How many types of binaries are there?

Answer 8

3:
Detached binary
Semi-Detached binary
Closed Binary

Question 9

What happens during mass transfer in interacting binaries?

Answer 9

The Classical Novae

Question 10

When does the Classical Novae occur?

Answer 10

When white dwarf star accretes hydrogen rich material to its companion
This material on the WD surface becomes extremely dense and hot and even degenerate

Question 11

When does a thermonuclear runaway occur?

Answer 11

T is high enough for H fusion to begin.
This heats the material but as it is degenerate, it doesn’t expand
T increases and more fusion reactions and Thermonuclear runaway occurs

Question 12

What happens on surface of WD after runaway reaction?

Answer 12

Outburst of material
Accreted material is ejected from star
System brightens by order of millions
Both stars unaffected by explosion

Question 13

How does mass transfer occur in binary systems?

Answer 13

Via an accretion disk as angular momentum is conserved and this needs to be removed before material can fall on star

Question 14

What can mass transfer drastically alter?

Answer 14

Mass
Luminosity
Evolution
Abundances

of stars in binary systems

Question 15

What do binary properties help to determine?

Answer 15

The stellar parameters with great precision

Question 16

What is the Algol paradox?

Answer 16

When the lower mass companion has evolved off the Main Sequence already while the massive object is still on it

(paradox because massive stars live much shorter than lower mass stars)

Question 17

What is the solution to the Algol paradox?

Answer 17

Mass is transferred between the stars
e.g the present-day low mass star started as the more massive component and became a Red Giant. It then lost mass to the lower mass companion

Question 18

What are blue stragglers?

Answer 18

MS stars which appear on the blue of the observed “turn off point” on HR diagram

Question 19

What remains in the same position during the evolution of binary systems?

Answer 19

Centre of mass

Question 20

What can degenerate stars do in interacting binaries?

Answer 20

They can accrete mass from their companion

Question 21

What can the limited masses of binary systems lead to?

Answer 21

A Supernova of Type Ia and a conversion of:
WD to NS
NS to BH

Question 22

What happens when the most massive star loses mass?

Answer 22

The orbit shrinks

Question 23

What happens when the least massive star loses mass?

Answer 23

The orbit expands

Question 24

When do binary companions affect each other’s evolution?

Answer 24

If they are close enough to each other