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Physics A-Level > Astro A2 - Stars > Flashcards

Astro A2 - Stars Flashcards

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1
Q

What is apparent magnitude scale

A

The brightness of a star as seen from earth

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2
Q

What is luminosity

A

Total power radiated by a star

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3
Q

What is intensity

A

Power per unit area at the observerq

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4
Q

What is the apparent magnitude value for the faintest stars we can see

A

6

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5
Q

How much brighter is a fourth magnitude star compared to a fifth magnitude star

A

2.51 times

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6
Q

What is our Sun’s apparent magnitude

A

-26

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7
Q

What is the astronomical unit

A

The mean distance from the Sun to the Earth

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8
Q

How to define a parsec

A

The distance from which 1AU subtends an angle of 1 arc second

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9
Q

What is the absolute magnitude

A

The apparent magnitude a star would have at a distance of 10 pc from an observer

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10
Q

What is a black body

A

A body that absorbs all the em radiation that falls on it

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11
Q

What does the graph of light intensity look for 3 stars of different temps

A

Hotter stars have a peak at a shorter wavelength. Hotter stars have a higher intensity of each wavelength of light than colder stars

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12
Q

What is the assumption for the use of the inverse-square law

A

No light is absorbed or scattered between the source and the observer. Source is treated as a point

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13
Q

What are the spectral classes in descending temperature

A

OBAFGKM

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14
Q

Describe an O-class star

A

Blue, 25000-50000K, absorption at He+, He, H

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15
Q

Describe a B-class star

A

Blue, 11000-25000K, absorption at He, H

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16
Q

Describe an A-class star

A

Blue-white, 7500-11000K, absorption at H, ionised metals

17
Q

Describe an F-class star

A

White, 6000-7500K, absorption at ionised metals

18
Q

Describe a G-class star

A

Yellow-white, 5000-6000K, absorption at ionised and neutral metals

19
Q

Describe a K-class star

A

Orange, 3500-5000K, absorption at neutral metals

20
Q

Describe an M-class star

A

Red, <3500K, absorption at neutral atoms, TiO

21
Q

What are Balmer lines

A

Spectrum produced when transitions from the energy level n=2 are made

22
Q

Where are balmer lines strongest

A

A-class star as there is a high abundance of hydrogen in n=2 state

23
Q

Where are balmer lines weak

A

O (too hot so hydrogen would be ionised), F,G,K,M (too cool to be excited)

24
Q

What are the axis on the Hertzsprung-Russell diagram

A

Spectral class on x (or temperature from 2500-50000k) and absolute magnitude on y (-10 to 15)

25
Q

Describe the evolution of the Sun

A

The Sun is currently a G-class star, a main sequence star. As hydrogen is used up, it will fuse hydrogen in the outer layers and expand, to become a giant. It will collapse, increase temp and will initiate helium fusion. Helium shell fusion will then occur and the Sun will expand again. The outer material will then be pushed away to form a planetary nebula leaving a white dwarf. After fusion is complete, it becomes a black dwarf

26
Q

What are supernovae

A

Objects which exhibit a rapid and enormous increase in absolute magnitude

27
Q

What are type 1a supernovae

A

They reach the same peak value of absolute magnitude

28
Q

What are standard candles

A

Absolute magnitude is known

29
Q

What causes a type 1a supernova

A

A white dwarf star attracts mass from its binary system and fuses again of carbon. When it reaches a critical mass, the white dwarf star explodes

30
Q

What is a neutron star

A

A core with a mass twice the mass of the Sun

31
Q

Describe the motion of neutron stars

A

Due to conservation of angular momentum as

the core collapses, they tend to be spinning very rapidly

32
Q

What are pulsars

A

Radio sources produced by strong magnetic fields and spinning of a neutron star

33
Q

What are black holes

A

More massive cores (more than about 3 solar masses) can continue to collapse
and form black holes

34
Q

What is a key feature of a black hole

A

Its escape velocity is greater than the speed of light

35
Q

What is the event horizon

A

The boundary at which the escape velocity is equal to the speed of light

36
Q

What is the Schwarzschild radius

A

Radius of the event horizon

37
Q

How is a quasar produced

A

From supermassive black holes at the centre of young active galaxies

38
Q

How can type 1a supernovae be used to measure distance

A

Type 1a supernovae has the same peak absolute magnitude (-19.3), so apparent magnitude can be measured

39
Q

What is a significant feature of quasars

A

Bright radio sources; brightest objects in the universe

Physics A-Level (19 decks)

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