Astrophysics - Test 1

Other name for variable stars

Other name for cepheids

Variable stars characteristic

Brightness varies with time

Who and why used cepheids ?

Shapely to determine the distance of various globular clusters

Cepheids function

Distance indicators

How many techniques to find double stars

Three techniques

Optical binaries

DS

Seen as two (naked eye or telescope)

Spectroscopic binaries

DS

Spectroscopy : wDetected because of the Doppler effect : Motion of the stars causes a blueshift, a redshift, a blueshift, …

Eclipsing binaries

DS

Photometry : Detected by the variation of the brightness (mv). One star eclipse the other.

Eclipsing binaries graph

Classification basis of stars

Surface temperature (K)

Main spectral types

O, B, A, F, G, K, M

*Oh ! Be a fine guy, kiss me !

Hot satrs color

Blue

Cold stars color

Red

Luminosity classes

I : Supergiant

(II : Bright giant)

III : Giant

(IV : Sub-giant)

V : Dwarf or Main-sequence

Absorption line

When light is absorbed by elements, leaving a dark mark in spectral data

Most luminous stars class

I : Supergiant

White dwarfs characteristics

Small luminosity, small radius, very high temperature.

What star class shows a correlation between L and T ?

Only main-sequence shows correlation between those two characteristics

For main sequence, what is the correlation between L & T

The more luminous a star is, the hotter it is

Key factor in main sequence stars

Mass

Axis of HR diagram

Luminosity and Temperature axis

HR diagram type of graph

Log-log graph

3 main luminosity classes

I : Supergiant, III : Giant, V : Main sequence

Life cycle of stars

1. Born

2. V : main sequence

3. III : Giant 

4. Drop in luminosity 

5. I : Supergiant

6. POWW !!

7. White dwarf

Types of deep-sky objects ?

(10)

Open star clusters, Globular star clusters, Planetary nebulas, Supernova remnants, Bright nebulas, Dark nebulas, Spiral “nebulas”, Elliptical galaxies, Irregular galaxies, Quasars

Population classification

I : Normal (like the Sun)

II : Ionized once (different from the Sun)

III : Ionized twice (completely different from the Sun)

Open star clusters example

The Pleiades 

Open star clusters characteristics

• Contains 100 - 10 000 stars

• Relatively weak concentration of stars

• May contain some interstellar gas

• Tend to be young objects with newly formed stars (of population I)

• Tend to break up into individual stars 

• Distributed in the disk of spiral galaxies 

Globular clusters example

M13

Globular star clusters characteristics

• 10 000 - 1 million stars (very luminous)

• Strong concentration of stars

• Do NOT contain interstellar gas

• Tend to be old objects with old stars (of population II)

• Do not break up, remain stable (because of the many stars)

• Distributed in the halo of galaxies

Planetary nebula example

M57 : Ring nebula

Planetary nebula

• Explosion of a star

• Gas expelled by a star that becomes a white dwarf

• Expand with time

• Gas ionized (switch in energy level which causes light) by the hot central star

• Get dispersed astronomically rapidly : in ~10 000 years

Supernova remnants example

M1 : Crab nebula

Supernova remnants characteristics

• Gas expelled by a star that collapses into a neutron or into a black hole

• Type I : white drawf that collapses