Chapter 10 Flashcards
How many stars are in binary or multiple systems?
Over 50%
What happens if the stellar masses in the binary are widely separated?
Each star evolves as a single star
What happens if the stellar masses in the binary are close?
Evolution can be drastically different from that of a single star
What happens during the evolution of the stars?
One star must expand during evolution to approx the separation of the stars
What is the inner Lagrangian point L1?
It is where forces from stars balance
What is the Roche lobe of a star?
The region where material is bound to that star
What happens if one star expands to fill its Roche Lobe?
It can transfer matter to its companion through the L1 point
How many types of binaries are there?
3:
Detached binary
Semi-Detached binary
Closed Binary
What happens during mass transfer in interacting binaries?
The Classical Novae
When does the Classical Novae occur?
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
When does a thermonuclear runaway occur?
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
What happens on surface of WD after runaway reaction?
Outburst of material
Accreted material is ejected from star
System brightens by order of millions
Both stars unaffected by explosion
How does mass transfer occur in binary systems?
Via an accretion disk as angular momentum is conserved and this needs to be removed before material can fall on star
What can mass transfer drastically alter?
Mass
Luminosity
Evolution
Abundances
of stars in binary systems
What do binary properties help to determine?
The stellar parameters with great precision
What is the Algol paradox?
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)
What is the solution to the Algol paradox?
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
What are blue stragglers?
MS stars which appear on the blue of the observed “turn off point” on HR diagram
What remains in the same position during the evolution of binary systems?
Centre of mass
What can degenerate stars do in interacting binaries?
They can accrete mass from their companion
What can the limited masses of binary systems lead to?
A Supernova of Type Ia and a conversion of:
WD to NS
NS to BH
What happens when the most massive star loses mass?
The orbit shrinks
What happens when the least massive star loses mass?
The orbit expands
When do binary companions affect each other’s evolution?
If they are close enough to each other
