Stars/X-ray classification/Quiz

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This is a Chandra X-ray Observatory image of LP 944-20 before flare and during flare. Credit: CXO/NASA.

X-ray classification of stars is a lecture in the X-ray astronomy of stars. It is part of the X-ray astronomy/Course.

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1 True or False, To emit X-rays a source must have some small amount of plasma near or above 106 K.


2 The Sun as a star has what geographical property?

it's a primordial population III star
it passes once a year across the Lockman Hole
silicates have been discovered in its interior structure
optical reflectance studies have found evidence of magnesium
it has a surface temperature of ~700 K
it has a longitude and latitude grid system for locating surface features

3 Yes or No, Only a plasma may be luminous.


4 Which of the following is not a phenomenon usually associated with sunspots?

solar photosphere
a hole in the granulated photosphere
production of 7Be
solar cycle
flip-flop cycle

5 True or False, Any object forming on a dynamical timescale, by gravitational instability, may be a star.


6 Which of the following is not a phenomenon associated with a flip-flop cycle?

active regions
hemisphere shifts
binary RS CVn stars
single stars
cyclical period
meridian passage

7 True or False, All gaseous bodies may be a star.


8 Complete the text:



originate in magnetically

around visible


9 True or False, An O class star is not hot enough on the surface of its photosphere to emit X-rays.


10 The population of coronal loops can be directly linked with the?

11 True or False, A spicule is a dynamic jet of about 500 km diameter in the chromosphere of a star.


12 Which of the following are associated with the stellar active region control group?

solar cycle
closed magnetic structures
solar wind
long-lived loop arcades
helmet streamers
the Sun

13 True or False, Coronal loops project into the coronal cloud, through the transition region and the chromosphere.


14 Active regions are the result of enhanced what?

15 True or False, Stars of spectral classes F and G, such as our sun, have color temperatures that make them look "greenish".


16 Phenomena associated with nanoflares?

1017 Joules
very high X-ray emission from happening every 20 s
mass eruptions
active regions

17 True or False, The photosphere of a star may be the result of omnidirectional incoming electrons.


18 About one third of ejecta observed by satellites at Earth is composed of what?

19 True or False, The Ca XV emission line is a yellow coronal line at 569.4 nm.


20 Which stars of the alpha Centauri system are known to have stellar active regions?

Proxima Centauri
Alpha Centauri B
Barnard's star
Alpha Centauri A
Rigel Kent
Alpha Centauri C
Alpha Centauri D

21 True or False, "75% of the naked sunspots represented the return of large dominant f spots which had been part of large active regions during previous rotations."


22 The type star that goes through fairly extreme changes of brightness: for instance, in 1952, its brightness increased by 75 times in only 20 seconds, is what star?

23 True or False, T Tauri stars are likely to have large areas of starspot coverage.



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  1. Stars that are in different classes based on their photosphere temperatures may be in the same class based on their X-ray spectra.

See also

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{{Radiation astronomy resources}}