Download V Example: our SUN (G2V)

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Hertzpsprung-Russell Diagrams
graphic from Astronomy Today by Eric Chaisson & Steve McMillan 2nd Ed. between pages 432 and 433
following text in part from Instructor’s Resource Manual for Seeds’s Horzions Exploring the Universe
5th ed. By Mark A. Nook
Star pressure-temperature balance
Stars produced just the right amount of energy because of the pressure-temperature
“thermostat.” If the star begins to produce more energy than it needs to support the inward
pull of gravity, the star will expand. As it expands its pressure will decrease and its
temperature will decrease. As the temperature decreases the rate at which nuclear
reactions occur also decreases so the amount of energy produced decreases. Therefore a
star may pulse between too much and too little energy generation. The relation between
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pressure, temperature, and the rate of energy generation keeps the star from producing for
‘long periods of time” either too much or not enough energy.
The Orion Star “Nursery
Eventually the Orion molecular cloud will run out of material. Giant molecular clouds contain a limited
supply of gas and dust from which to build stars so star formation can not go on forever. Additionally, as
young hot stars reach the main sequence and begin to produce large amounts of energy, they drive the
gas and dust away from them. This disperses the gas and dust of the molecular cloud. Clumps of the
cloud must remain intact if material is to contract to form new stars from that cloud
Sun Evolution
At the end of the Sun's (1 Mo or one solar mass) evolution, some of the hydrogen that the
sun started with will have been blown away by mass loss and the planetary nebula, the
rest will have been converted to helium, and most of that to carbon. A small fraction of it
will have been radiated away as electromagnetic radiation, and neutrinos during the
thermonuclear fusion of hydrogen and helium.
graphic from Astronomy Today by Eric Chaisson & Steve McMillan 2nd Ed. between pages 432 and 433
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Nova
A nova occurs when the thermonuclear fusion of hydrogen occurs on the surface of a white
dwarf. This generally occurs in a binary system containing a white dwarf and a star that is
expanding to become a giant. In a nova, neither the white dwarf nor the giant are greatly
affected by this process.
Novae occur as a star undergoing mass loss deposits fresh hydrogen on the surface of a
white dwarf. The hydrogen becomes degenerate and hot and dense enough to fuse. As
hydrogen fusion occurs in the degenerate material, the energy produced increases rapidly.
Eventually the electrons are no longer degenerate and the pressure is great enough to
blow the accreted material off the surface of the white dwarf explosively.
Supernovae
A supernova occurs when the core of the massive star collapses and a shock wave rips the
star apart, usually leaving behind a neutron star. Supernovae can also be produced when
enough material is deposited on a white dwarf so that is exceeds the Chandrasekhar limit
and collapses to a neutron star. Both types of supernova drastically alter the stars and are
the result of the collapse stellar core. In a nova no collapse occurs, just the fusion of
hydrogen on the surface of the white dwarf.
If the star undergoing mass loss and the white dwarf are a binary system, the normal star
will continually put fresh hydrogen onto the surface of the white dwarf. Each time this
material becomes hot and dense enough to fuse, a nova will occur. The continual mass
transfer form the normal star to the whited dwarf assures that the nova will repeat until
the normal star ends its mass loss.
Supernovae - Type I
Type I supernovae are the result of a white dwarf that accretes matter and increases its
mass until it exceeds the Chandrasekhar limit. When this occurs the degenerate electrons do
not supply sufficient pressure to support the mass and the star collapses violently, producing
a supernova. A white dwarf is composed of degenerate electrons and either helium or
carbon and oxygen nuclei. The only hydrogen associated with the white dwarf should be the
accreted material, and this should be a small fraction of the total mass. As the object
explodes, there are very few hydrogen nuclei around to capture electrons and produce
spectral features due to hydrogen.
Yerkes spectral line width and intensity classification
taken in part and modified from http://en.wikipedia.org/wiki/Stellar_classification
The Yerkes spectral classification, is … a two dimensional (temperature and luminosity)
classification scheme is based on spectral lines sensitive to stellar temperature and surface
gravity which is related to luminosity (whilst the Harvard classification is based on surface
temperature only). Later, in 1953, after some revisions of list of standard stars and classification
criteria, the scheme was named MK (by William Wilson Morgan and Phillip C. Keenan
initials).[26]
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Denser stars with higher surface gravity will exhibit greater pressure broadening of spectral
lines. Since the radius of a giant star is much greater than a dwarf star while their masses are
roughly comparable, the gravity and thus the gas density and pressure on the surface of a giant
star are much lower than for a dwarf. These differences, gravity, gas density, and pressure,
manifest themselves in the form of luminosity effects which affect both the width and the
intensity of spectral lines which can then be measured.
A number of different luminosity classes are distinguished: our Sun is G2V
Graph from http://upload.wikimedia.org/wikipedia/commons/thumb/7/7a/HR-diag-w-text.svg/525px-HR-diag-wtext.svg.png


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0 hypergiants
I supergiants
o Ia-0 (hypergiants or extremely luminous supergiants (later addition)), Example:
Eta Carinae (spectrum-peculiar)
o Ia (luminous supergiants), Example: Deneb (spectrum is A2Ia)
o Iab (intermediate luminous supergiants) Example: Betelgeuse (spectrum is
M2Iab)
o Ib (less luminous supergiants)
II bright giants
o IIa, Example: β Scuti (HD 173764) (spectrum is G4 IIa)
o IIab Example: HR 8752 (spectrum is G0Iab:)
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o
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IIb, Example: HR 6902 (spectrum is G9 IIb)
III normal giants
o IIIa, Example: ρ Persei (spectrum is M4 IIIa)
o IIIab Example: δ Reticuli (spectrum is M2 IIIab)
o IIIb, Example: Pollux (spectrum is K2 IIIb)
IV subgiants
o IVa, Example: ε Reticuli (spectrum is K1-2 IVa-III)
o IVab
o IVb, Example: HR 672 A (spectrum is G0.5 IVb)
V main-sequence stars (dwarfs)
o
o
o
o
o
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
V Example: our SUN (G2V)
Va, Example: AD Leonis (spectrum M4Vae)
Vab[27]
Vb, Example: 85 Pegasi A (spectrum G5 Vb)
"Vz", Example: LH10 : 3102 (spectrum O7 Vz), located in the Large Magellanic
Cloud.[28]
VI subdwarfs. Subdwarfs are generally represented with a prescript of sd or esd (extreme
subdwarf) in front of the spectra.
o sd, Example: SSSPM J1930-4311 (spectrum sdM7)
o esd, Example: APMPM J0559-2903 (spectrum esdM7)
VII (uncommon) white dwarfs. White dwarfs are represented with a prescript wD or
WD.
Marginal cases are allowed; for instance a star classified as Ia-0 would be a very luminous
supergiant, verging on hypergiant. Examples are below. The spectral type of the star is not a
factor.
Marginal Symbols Example
Explanation
G2 I-II A star is between supergiant and bright giant.
O9.5 Ia+ A star is a hypergiant star.
+
F2 IV/V A star is either a subgiant or a dwarf star.
/
https://sjhsrc.wikispaces.com/file/view/spectral_class.JPG/32181525/spectral_class.JPG
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Modified in part from http://astronomyonline.org/Stars/HighMassEvolution.asp
A white dwarf is the degenerate carbon core of a low mass star (like our Sun).
A neutron star is the degenerate iron core of a high mass star.
A pulsar is spinning neutron star.
A black hole is the remnant of the collapse of neutron star from a more massive star.
Black hole
If the high mass star is around 25 Solar masses, the stellar remnant can compress much further
than a neutron star resulting in a black hole.
It's important to realize that a black hole is not a hole in space, it's just an object with extremely
high surface gravity - but since we have yet to "see" one (and we probably never will), we can
only infer their existence by its effect on surrounding matter. Thus its name because we can’t
see it (we can see but by its emission X-rays as it absorbs matter) and it takes in matter like a
hole.
Classifications of Supernova
Type:
Characteristics:
Mechanism:
1a
No H lines, strong Si II lines
Thermonuclear runaway on white dwarf surface
1b
No H lines, prominent He I
lines
Core collapse of massive star stripped of hydrogen
envelope
1c
No H, Si II or He I lines
Core collapse of massive star stripped of helium (and
hydrogen) envelope
II-P
H lines - flat light curve
Core collapse of massive star
II-L
H lines - no flat light curve
Core collapse of massive star
Common to all dying stars
The fusing of hydrogen to helium is being performed in both low and high mass stars.
High mass stars primarily burn hydrogen through the CNO cycle (Carbon, Nitrogen, Oxygen).
Carbon acts as the catalyst in the fusion of hydrogen and nitrogen and oxygen absorb the
protons to create helium.
The main reason for this is increased temperature and pressure at the core of a high mass star. .
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The hydrogen burning shell and helium ash core also exist in the high mass star.
One major difference between a high mass star and a low mass star is the helium flash - there is
no flash of helium fusion in a high mass star.
Iron (Fe) can NOT fuse, so a type II supernova in > 4
Because a high mass star (> 4 Solar Masses) has considerably more gravity than low mass star,
several shell burning stages can occur: But there is a limit. Iron cannot fuse, and when it tries
the end result is a highly compacted core and intense temperature. The core density is 4 x 1017
kg/m3. This is very degenerate and cannot be compressed further. The intense heat generated
by this compression (core bounce) blows the star apart in a type II supernova.
THE END