Download LESSON 8: STARS

LESSON 8: STARS
What you will need:
•
•
•
Data projector and internet access.
The Infinity Series Part 2: Deep Space - The dance of Gravity video.
A copy of the handouts for each student
Suggested Outline:
• Hand out Skyways pg 61, 62
• Hand out and work through the following Ioncmaste: 9th Grade Astronomy
Curriculum Resources webpage, Module 2 - #1 through 10. Use the applets
provided on the website throughout. This works best on a data projector. If you do
not have a data projector you may have to forgo using the applets and teach the
lesson from the handouts alone.
http://www.ioncmaste.ca/homepage/resources/web_resources/CSA_Astro9/files/h
tml/module2/module2.html#6
•
When discussing #3 “Types of Stars”
o Hand out file “#8 - Types of Variable Stars” taken from the AAVSO
website. (http://www.aavso.org/vstar/types.shtml)
o Discuss the different types of variable stars (use applet)
Intrinsic: Pulsating, Eruptive
Extrinsic: Eclipsing Binary, Rotating
o For more detailed variable star info and information on how to start
observing them the students should go to the AAVSO website.
http://www.aavso.org/
o Point out AAVSO Manual available from AAVSO website.
http://www.aavso.org/publications/manual/
•
When discussing #4 “Temperature and Colours of Stars”
o Have students do Skyways HR Diagram activity (pg 72, 73)
o Discuss stellar classifications (Oh, Be, A, Fine, Gal/ Guy, Kiss, Me)
Show file “#6 – OBAFGKM chart” or use overhead provided.
o Hand out Skyways pg 74, 75
•
When discussing #6 “The Life Cycle of a Star”
o use the “Balloon Stars” demo from Skyways pg. 63 to help illustrate a star
in equilibrium
•
Watch The Infinity Series Part 2: Deep Space - The dance of Gravity video (First
part only, about 40 min). The video discusses stellar evolution, quasars, pulsars,
galaxies and a bit of cosmology.
Between Class Assignments:
o Read Beginner’s Observing Guide chapter 7 and 16
Information about the Brightest Stars
Observing Variable Stars
o Observe from ETUC Double & Multiple Stars and Variable Stars sections.
The Brightest Stars
Star
Sun
Canopus
Procyon A
Achernar
Altair
Fomalhaut
Dened
Sirius A
Vega
Betelgeuse
Hadar
Antares
Regulus
Adhara
Bellatrix
Alnilam
Alpha Crucis B
Al Na'ir
Elnath
Alhena
The Nearest Stars
Power
log(L/Lsun)
0.00
3.15
0.88
2.84
1.00
1.11
4.76
1.34
1.72
4.16
4.00
3.96
2.20
3.96
3.60
4.38
3.22
2.34
2.54
1.90
Temperature
degrees Celsius
5,840
7,400
6,580
20,500
8,060
9,060
9,340
9,620
9,900
3,200
25,500
3,340
13,260
23,000
23,000
26,950
20,500
15,550
12,400
9,900
Star
Sun
Alpha Centauri A
Alpha Centauri B
Proxima Centauri
Barnard's Star
HD 93735
UV Ceti (B)
Sirius B
Ross 248
Ross 128
GX Andromedae
Epsilon Indi
Wolf 359
L726-8 (A)
Sirius A
Ross 154
Epsilon Eridani
L789-6
GQ Andromedae
61 Cygni A
Power
log(L/Lsun)
Temperature
degrees Celsius
0.00
0.18
-0.42
-4.29
-3.39
-2.30
-4.48
-2.58
-4.01
-3.49
-2.26
-0.90
-4.76
-4.28
1.34
-3.36
-0.56
-3.90
-3.45
-1.12
5,840
5,840
4,900
2,670
2,800
3,200
2,670
14,800
2,670
2,800
3,340
4,130
2,670
2,670
9,620
2,800
4,590
2,670
2,670
4,130
POWER / BRIGHTNESS
+6
+5
+4
+3
+2
+1
0
-1
-2
Increasing Brightness
Increasing Power Output
Icreasing Stellar Mass
-3
-4
-5
-6
123456789
123456789
0
10
TEMP
123456789
20
30
x1000 deg. C
Increasing Temperature
Red Stars
Blue Stars
Student Handouts
Module 2:
The Sun and Stars
Background Information
1. Introduction to Stars
2. Brightness of Stars
3. Types of Stars
4. Temperatures and Colours of Stars
5. Spectrum of Light
6. The Life Cycle of a Star
7. Composition of Stars
8. The Surface of the Sun
9. Studying the Sun and Stars
10. Summary
1. Introduction to Stars
Our star is a ball of gas that produces energy in its core by means of nuclear
reactions. These nuclear reactions process billions of kilograms of mass every
second, producing enormous amounts of energy in the form of heat and light.
The Sun, despite being a typical star, appears much brighter than all other
stars simply because it is so close to us. Other stars are located so far away
that their distances from the Earth can be very difficult to grasp. A helpful
analogy for understanding this concept is to imagine the Earth as a grain of
sand with the Sun situated a metre away, leaving the nearest star some 270
kilometres away. The farthest stars visible with the naked eye would be located
almost half a million kilometres away from that small speck of sand. There are
also millions of other stars even farther away. Light from the Sun takes about
eight minutes to reach the Earth, about 4.3 years from the nearest star, and
hundreds of years from the most distant visible stars. Stars are extremely
bright and massive objects, but they are so incredibly distant that they appear
as mere points of light in our sky.
2. Brightness of Stars
While the thousands of stars in the night sky appear to be very similar, they are
more distinct from one another than their appearance would suggest. Stars
have various sizes, masses, temperatures, colours, luminosities,
compositions and lifecycles. The largest stars are several hundred times the
diameter of the Sun, and in our solar system, would easily engulf the Earth’s
orbit, while the smallest stars are smaller than the Earth itself. The most
noticeable distinction between stars, however, is the difference in their
brightness. The apparent brightness of an object in the sky is denoted by its
magnitude, a numeric scale established by Hipparchus c. 160 BC. The
brightest stars in the sky, Hipparchus stated, were of first magnitude, and the
dimmest were of sixth magnitude, making smaller numbers correspond to
brighter objects. The scale has been expanded and can now be applied to any
object in the sky. The full moon has a magnitude of -12.7, Venus at its
brightest is -4.1, the brightest star is -1.46 and the faintest objects detectable
through the largest telescopes are about +29. Magnitude values are
logarithmic, where a difference of five magnitudes is defined as a brightness
differential of 100 times. The Sun and the dimmest objects detectable through
telescopes are about 56 magnitudes apart, but this corresponds to an actual
difference in brightness of over 25 x 1021.
Load Applet
Stellar Magnitudes
3. Types of Stars
Binary Star System
courtesy Brian Martin
Most of the stars in the sky are double stars, which are pairs of stars located
in nearly the same position in the sky. The two stars that make up a double
star may not actually be close to each other in space, but simply lie in the
same line of sight from the Earth. They usually appear as a single point of light
because they are so closely aligned, so cannot be seen as individual stars
unless viewed through a telescope. Systems of double stars that are
gravitationally bound and are in orbit around each other are called binary
stars. Binary stars are often so close together they are only perceivable as two
stars by analyzing their combined light. Binary stars are very common, the Sun
being rare in that it is not part of a binary system. There are also a few
individual stars that vary in their apparent brightness as seen from Earth,
called intrinsic variable stars. The time period of the change in intensity of
variable stars can be erratic or can be very regular, ranging from days to years.
Data Sheet
Cepheid Variable
Load Applet
Variable Stars
4. Temperatures and Colours of Stars
Sunrise over the Pacific Ocean
courtesy David Vandervelde
Stars are classified by their temperature, which will affect their colour. The
stars range in colour from red through yellow and white to blue. The Sun’s
yellow surface is about 5800K (Kelvin), while some red stars are 3000K and
blue stars can have surface temperatures of over 30 000K. When we look up
at the stars, they all appear to dazzle bright white, but many stars actually do
have colour imperceptible to our eyes. The human eye is not sensitive to
colours at low light intensities like those of the stars. When we use a telescope
to look at the stars, they appear brighter and the colours become noticeable.
Spectroscopy allows for a more detailed classification system using the
chemical composition of stars. The light emitted by stars can be broken down
into the component colours at various wavelengths. The spectrum will
depend primarily on the star’s temperature, but it will also contain absorption
lines which characterize the elements present in the star. Dark bands
appearing along the spectrum will indicate the presence of specific elements,
and their abundance will affect the width of the band. A spectrum is like a
fingerprint and will reveal the chemical abundance within the star.
5. Spectrum of Light
White light is composed of a mixture of colours, but appears white because our
eyes are unable to perceive the individual colours of the spectrum. It is
possible to prove this phenomenon by separating a beam of white light into its
component colours using a prism. These component colours are displayed in
the colours of the rainbow, ranging from red to violet. The difference between
the colours is in the wavelength of the light; red light has a higher wavelength
than violet, with the remaining colours lying between those two extremes.
Although the spectrum of light as seen in a rainbow is only a small portion of
the entire electromagnetic spectrum, the human eye is sensitive only to the
range of wavelengths from red to violet.
There are three types of spectra:
1. Emission Spectra - The light produced by a cool glowing gas can be
seen through a spectrometer as a series of bright coloured lines.
2. Continuous Spectra - The light produced by heating a solid, liquid or gas
to a high pressure can be seen through a spectrometer as a continuous
spectrum.
3. Absorption Spectra - The light produced by heating a solid, liquid or gas
to a high pressure that then passes through a cooler gas cloud, can be
seen through a spectrometer as a continuous spectrum with dark lines.
Load Flash Applet
Spectroscopy and Stellar Identification
6. The Life Cycle of a Star
Although it was previously thought that stars were static, never changing or
evolving, we now know that stars move through a complex life cycle – they are
created, live extremely long lives and then expire. It is, however, impossible to
witness the entire life cycle of an individual star because it is an exceptionally
lengthy process by human standards. By studying different stars in various
stages of development, astronomers have now established a detailed process
for their life cycle.
Stage 1
Stars form in cold, dark clouds of gas and dust. The cloud must
be relatively cold for stars to form because the particles must be
moving slowly enough to allow gravity to overcome internal
pressure and form clumps of matter. The interstellar cloud must
also be truly immense, covering billions of kilometres, and must
be reasonably dense with hydrogen and helium atoms for a star
to form. It is thought that a shockwave from a nearby star will
trigger a collapse of the cloud, after which the atoms slowly draw
together due to the gravitational attraction between them. As the
cloud shrinks, it breaks up into smaller fragments known as
protostars. An initial interstellar cloud can produce hundreds of
protostars. A protostar is a star in its embryonic stage, and
although it glows due to the release of gravitational energy, it is
not yet hot enough to produce nuclear reactions within its centre.
As the protostar continues to collapse due to gravity, it will attract
more atoms and continually increase in mass and density. The
increased density and gravity will cause the core temperature to
eventually rise to about ten million Kelvin, hot enough to convert
hydrogen into helium (nuclear fusion). Millions of years after the
interstellar cloud first began to collapse, a star is created.
Stage 2
The young star will gradually continue collapsing until the internal
pressure pushing out (caused by heat) equals the inward pull of
gravity. This occurs when the central core temperature has
increased to about 15 million Kelvin. The star is now in
equilibrium, and will continue to process hydrogen for most of its
life. This stable period of the star’s life will not end until the core
becomes depleted of hydrogen, which can vary between millions
and billions of years. The Sun, presently in its equilibrium phase,
is converting billions of kilograms of hydrogen into helium every
second, and will not exhaust its supply of hydrogen for about
another four billion years. The characteristics of a star are
determined by its mass, which will depend on the size of the
initial fragment of the interstellar cloud. While in its stable core
hydrogen-burning phase, higher mass stars process their fuel of
hydrogen (and produce more energy) at a much faster rate than
low mass stars. As a result, massive stars burn hotter and
brighter, have shorter lifetimes, and will typically have a larger
radius. Once the core of a star begins to exhaust its reserve of
hydrogen, the star quickly becomes unstable and will evolve from
its state of equilibrium. The core is now packed with helium, and
a thin spherical shell surrounding the core will begin to process
hydrogen. This causes the core to become increasingly dense
while the outer layers of the star will expand and cool. The gases
will glow red and the star becomes a red giant. The hydrogenburning shell will move outward from the core as it converts the
hydrogen into helium, and the core will become progressively
compact with helium. This increased pressure will raise the
temperature of the core, and will eventually become hot enough
to ignite nuclear reactions involving helium. The star now enters
another period of equilibrium, and will spend another several
million years converting helium into carbon.
Data Sheet
Red Giant
Stage 3a.
The most apparent difference between high mass (10 to 30 solar
masses) and low mass (0.5 to 10 solar masses) stars are the
events leading up to the eventual death of the star. Low mass
stars do not have the mass required to increase the core
temperature enough to allow the carbon to fuse into heavier
elements. Once the helium is consumed, the star will die quietly
by ejecting its outer layers, creating a planetary nebula. The
central carbon core of the star is left behind and continues to
shine by stored heat. This remnant is called a white dwarf star,
and is about the size of the Earth, but is much more massive and
incredibly dense. It will cool and dim with time as its stored heat
is used up, and the star will become a cold and dark black
dwarf, ending the star’s evolution. When a white dwarf is part of
a binary system with a red giant, its gravity will suck surface
material off the red giant. Large amounts of matter falling into the
white dwarf will cause instabilities, and explosions will occur in
order to release the accumulated material. These explosions are
called novae, and the white dwarf star will brighten significantly
as seen from the Earth. A nova will last for about one week and
then slowly die off and return to its previous brightness.
Data Sheet
White Dwarf
Stage 3b.
High mass stars die much more dramatically, in violent
explosions. In contrast to a low mass star, a high mass star has
enough mass to continually increase the pressure and
temperature of its core, which causes a chain of nuclear
reactions involving heavier and heavier elements. The nuclear
reactions eventually produce iron, but iron nuclei are so compact
that they do not release energy in nuclear reactions and produce
no heat. With the end of energy production in the core, it no
longer produces enough heat to generate adequate inner
pressure to match the enormous gravitational pull. At this stage
the core is so incredibly dense that it cannot collapse any further
and the state of equilibrium comes to an end. The inner core
sucks in the surrounding layers and the star will implode and
collapse in on itself in a matter of seconds. The material of the
collapsing star rebounds off the solid core, producing a
shockwave of material that explodes into space. This explosion is
called a supernova, and will increase the luminosity of the star
by a factor of millions. A supernova is much more powerful than a
nova and will be extremely bright for a few weeks or months, until
it gradually subsides and dims. What remains after a supernova
explosion is called a supernova remnant, the star’s outer layers
that were blasted into space during the supernova. The gases
expand out from the star at incredible speeds and excite the
gaseous atoms of the interstellar medium, causing it to glow as a
nebula. Depending on the initial conditions of the star, what is left
will become either a neutron star*, a black hole, or could
simply blow itself completely apart, leaving only the remnant.
* Note that if the neutron star is rotating very rapidly and is
oriented so that the pulses of energy are aligned with the Earth it
can be called a pulsar.
Data Sheet
Pulsar
The time frame for the death of a high mass star is extremely
short. While the hydrogen-burning phase lasts for millions of
years, the final stages of a star’s life leading up to a supernova
last for progressively shorter periods, culminating in the core
collapse and explosion which last mere seconds. Because the
death of a star occurs so rapidly, we can directly witness the
process. Thus, supernovae reveal valuable information about
stars and our universe. The death of stars is an important part of
the stellar life cycle because it promotes star formation. The
explosions produce shockwaves that can trigger the collapse of
an interstellar cloud into a protostar. Stars also eject their outer
layers into space, which produces an interstellar cloud rich in
hydrogen and helium atoms. Supernovae release huge amounts
of heavy elements into the interstellar medium, which produces
perfect conditions for the birth of a star with rocky planets like our
solar system. Without the death of stars, it would be very difficult
for new stars and solar systems to form.
Data Sheets
Black Hole
Supernova Remnant
Load Flash Applet
Life of a star applet
Load Star Age Calculator
Star Age Calculator
Life Cycle of a Star
Low Mass Stars (like Sun)
1. Star forming region
2. Protostars
5. Planetary Nebula
6. White Dwarf
3. Sun-like star
4. Red Giant
3. High mass stars
4. Red Super Giant
High Mass Stars
1. Star forming region
2. Protostars
5. Supernova
explosion*
6. Supernova remnant
7a. Neutron Star
7b. Black Hole
7. Composition of Stars
In composition and size, the Sun is an average star and is in the middle of its
hydrogen-burning stage. It will continue to process hydrogen for another few
billion years before swelling into a red giant. Although the Sun is an averagesized star, it is still huge by Earthly standards, having a diameter more than
100 times that of the Earth and a volume nearly 1.3 million times as great. The
Sun is a ball of gas, and as such does not have a surface like the Earth. The
“surface” of the Sun is called the photosphere, and is where energy from the
core is emitted into space. The photosphere has a definite sharp edge as seen
from the Earth, but its granular appearance is constantly “bubbling” as heat
from the interior escapes into space. Above the photosphere lies the lower
atmosphere of the Sun, called the chromosphere, and beyond that is the
transition zone where the temperature of the atmosphere rises dramatically.
The atmosphere of the Sun is extremely hot and is home to violent events
erupting from the photosphere. A prominence is an ejected pillar of glowing
gas extending thousands of kilometres from the solar surface. A prominence is
visible in photographs and lasts for days or weeks. A solar flare is a more
violent eruption from the photosphere that releases an enormous amount of
energy. While a prominence will tend to follow the magnetic field lines and
loop back down to the photosphere, a flare will shoot off into space.
Extending far into space is a star’s corona, a hot and sparse upper
atmosphere. The corona is very irregular in appearance, and it is believed that
its shape is distorted by the eruption of prominences and flares. As the corona
extends further from the Sun, it becomes the solar wind, a very thin gas of
charged particles that travels through the solar system. Although the various
levels of the Sun’s atmosphere cannot be seen except through a telescope
with a special filter, the corona is visible when the solar disk is blocked by the
Moon during an eclipse (explained in greater detail in module 3). The interior of
the Sun is composed of gases made up of about three quarters hydrogen and
one quarter helium. The density and temperature of the gas increases with
depth beneath the surface. The regions just below the photosphere are known
as the convection zone and the radiation zone; these regions allow heat
and energy to travel out from the core to the surface. The core of the Sun is
where nuclear fusion takes place, and is the energy source of the star.
Load Interactive Image
Interior of the Sun
8. The Surface of the Sun
The Sun
The surface of the Sun was originally thought to be perfect and uniform, but we
now know the photosphere is marked by numerous irregularly shaped dark
patches called sunspots. Sunspots are depressed areas on the Sun that have
a lower temperature than the surrounding surface. They are typically about the
size of the Earth, and are composed of a darker central region called the
umbra, which is surrounded by a lighter coloured ring called the penumbra.
They are temporary features and constantly alter the appearance of the
photosphere. Sunspots are closely tied to the solar magnetic field and often
occur in groups or in pairs of opposite polarity. The rotation period of the Sun
would be very difficult to determine without the aid of sunspots. Because the
Sun is not solid, it experiences differential rotation, meaning that the surface
rotates at different speeds depending on latitude, with the equatorial regions
rotating faster than the polar regions. The number of visible sunspots varies
year to year, and the frequency follows a regular 11-year cycle between times
of maximum and minimum. During times of maximum, hundreds of sunspots
are visible, whereas during a minimum, the photosphere can be devoid of any
sunspots. Complex sunspot groups cause the eruption of solar flares, which
produce a substantial release of solar particles into the solar wind. Because
charged particles from the Sun cause the aurora on Earth, the number of
sunspots directly affects these displays. During a sunspot maximum like in
2001, we tend to see amazing auroral displays, and during minimums the
aurora are essentially non-existent.
Load Flash Applet
Tracking sunspots
9. Studying the Sun and Stars
Because the Sun is so incredibly bright, we cannot safely look at it unprotected
without damaging our eyes. However, the Sun can be safely viewed with the
use of special filters or via projection. Filters can be fitted onto telescopes to
block out more than 99.99% of the incoming light, leaving images astronomers
can safely view and study. Various filters allow astronomers to observe
different areas of the Sun, including sunspots and prominences. Image
projection is a simple method that involves the projection of the Sun through a
small telescope onto a piece of paper. This method does not show any of the
solar atmospheres, but sunspots will be visible. We must never look directly at
the Sun without safety precautions, but with them in place our star is a
wonderful object to study.
Much of our knowledge of stars is obtained by studying our own star, the Sun.
Astronomers have used complex mathematical models to investigate the solar
interior, but observing the Sun in different wavelengths and with different filters
can also give them valuable information. One of the most important methods in
studying the interior of the Sun is called helioseismology, which involves
observation of the “bubbles” on the photosphere as they rise and fall. The
properties of these oscillating bubbles, combined with the mathematical
models, reveal valuable information about the Sun’s interior. Because the Sun
is an average star, we assume that the processes driving it will also be present
in other similar stars.
10. Summary
Billions of stars populate our universe. The nuclear reactions within their core
release incredible amounts of energy, and they would appear much brighter if
it were not for their considerable distances. While looking up at the night sky,
the only perceivable difference between stars is their apparent magnitude, but
stars each have their own characteristics. Although difficult to detect, stars
shine different colours depending on their temperature. Spectroscopy is an
accurate method of determining a star's colour, and will reveal the relative
abundance of elements within its atmosphere. Many stars vary their brightness
on their own, either due to their association in a double star system or due to
unique processes within the star. Stars evolve through a life cycle that begins
with their creation in an interstellar cloud. The cloud slowly collapses due to
gravity, a protostar is formed and soon the internal temperature rises high
enough to ignite nuclear fusion. A star processes hydrogen for the majority of
its life before dying quietly as a planetary nebula or violently as a supernova.
The Sun is in the middle of its hydrogen-burning stage, and will live another
few billion years before dying.
The solar atmosphere is composed of three main layers: the chromosphere,
the transition zone and the corona. Prominences and flares erupt into the
atmosphere, releasing energy and particles into the corona and eventually
extending into the solar wind. The Sun’s energy is generated within its core,
and the internal regions transport this energy to the surface. The surface of the
Sun is called the photosphere and is yellow and granular in appearance.
Randomly covering the photosphere are dark patches cooler than the rest of
the surface. These sunspots are temporary, and their numbers follow an 11year cycle between times of maximum and minimum. They often occur in
complex groups and are associated with the aurora on the Earth because they
are the origin of solar flares. The Sun is an important object to study, but
because it is so luminous it is extremely dangerous to look at the Sun without
proper protection. The use of a special filter or the method of projection allows
the Sun to be studied safely to better understand the processes within the
stars. The Sun and the stars are incredible objects, and without them, life on
Earth would not exist.
Back | Ahead
AAVSO: Types of Variable Stars
Page 1 of 7
AAVSO HOME > variable stars > types
Types of Variable Stars
Variable Stars
Variable Star of the
Season
Powerpoint Intro
Stars Easy-To-Observe
Historical Light Curves
Naming
Harvard Designation
Types
Further Reading
Research: AAVSO in Print
Observing Manual
Main sections of web
The AAVSO
Variable Stars
Observing
Access Data
Publications
Online Store
Education: HOA
Pick a star
Variable Stars are stars that vary in their light output.
The origins of these light variations define the
classification system of variable stars.
There are two kinds of variable stars; intrinsic in which
variation is due to physical changes in the star or stellar
system and extrinsic in which variability is due to the
eclipse of one star by another or the effects of stellar
rotation.
Impression of a Cataclysmic Var
Acretion Disk
There are four main classes of variable stars. Within
Image by Mark A. Garlick (http://sp
the intrinsic group of variables there are two classes:
pulsatingand eruptive. Within the extrinsicgroup there are two classes: eclipsing
rotating stars. Below is a more thorough investigation of these four classes of varia
Pulsating Variables
Click on image
to show video.
Pulsating Variables are stars that show periodic expansion and con
their surface layers. Pulsations may be radial or non-radial. A radia
pulsating star remains spherical in shape, while a star experiencing
radial pulsations may deviate from a sphere periodically. The follow
of pulsating variables may be distinguished by the pulsation period
and evolutionary status of the star, and the characteristics of their p
Create a light curve
Recent Observations
Find charts
Cepheids (Period: 1-70 days; Amplitude of variation: .1 to 2.0 mag.)
These massive stars have high luminosity and are of F spectral class at maximum,
at minimum. The later the spectral class of a Cepheid, the longer is its period. Ceph
a strict period-luminosity relationship. An example of a Cepheid variable light curve
below.
http://www.aavso.org/vstar/types.shtml
4/2/2005
AAVSO: Types of Variable Stars
Page 2 of 7
RR Lyrae stars (Period: .2 to 1.0 days; Amplitude of variation: .3 to 2 mag.)
These are short-period, pulsating, white giant stars, usually of spectral class A. The
and less massive than Cepheids.
RV Tauri stars (Period: 30-100 days; Amplitude of variation: up to 3.0 mag)
These are yellow supergiants having a characteristic light variation with alternating
shallow minima. Their periods are defined as the interval between two deep minima
these stars show long-term cyclic variations from hundreds to thousands of days. G
the spectral class ranges from G to K.
Long Period Variables (LPVs)
(Period: 80-1000 days; Amplitude of variation: 2.5 to 5.0 mag.)
These are giant red variables that show characteristic emission lines. The spectral
range through M, C, and S. Also known as “Miras” after the prototype star.
Semiregular (Period: 30-1000 days; Amplitude of variation: 1.0 to 2.0 mag.)
These are giants and supergiants showing appreciable periodicity accompanied by
irregular light variation.
http://www.aavso.org/vstar/types.shtml
4/2/2005
AAVSO: Types of Variable Stars
Page 3 of 7
Cataclysmic Variables
Click on image
to show video.
Cataclysmic variables (also known as Eruptive variables), as the n
implies, are stars that have occasional violent outbursts caused by
thermonuclear processes either in their surface layers or deep with
interiors.
Supernovae (Period: none; Amplitude of variation: 20+)
These massive stars show sudden, dramatic, and final magnitude increases as a re
catastrophic stellar explosion.
Photograph of Before and After SN1987A
Resized from the original photograph copyright of the Anglo-Australian Observatory
(http://www.aao.gov.au/images.html).
Novae (Period: 1-300+days; Amplitude of variation: 7-16 mag.)
These close binary systems consist of a main sequence, Sun-like star and a white
They increase in brightness by 7 to 16 magnitudes in a matter of one to several hun
After the outburst, the star fades slowly to the initial brightness over several years o
Near maximum brightness, the spectrum is generally similar to that of an A or F gia
http://www.aavso.org/vstar/types.shtml
4/2/2005
AAVSO: Types of Variable Stars
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Recurrent Novae (Period: 1-200+days; Amplitude of variation: 7-16 mag.)
These objects are similar to novae, but have two or more slightly smaller-amplitude
during their recorded history.
Dwarf Novae These are close binary systems made up of a Sun-like star, a white d
an accretion disk surrounding the white dwarf. There are three sub-classes of dwar
U Geminorum (Period: 30-500 days: Amplitude range variation: 2-6 mag.)
After intervals of quiescence at minimum light, they suddenly brighten. The duration
outburst is generally from 5 to 20 days.
Z Camelopardalis
These systems show cyclic variations, interrupted by intervals of constant brightnes
“standstills”. These standstills last the equivalent of several cycles, with the star “stu
brightness approximately one-third of the way from maximum to minimum.
http://www.aavso.org/vstar/types.shtml
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AAVSO: Types of Variable Stars
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SU Ursae Majoris
These systems have two distinct kinds of outbursts: one is faint, frequent, and shor
duration of 1 to 2 days; the other (“superoutburst”) is bright, less frequent, and long
duration of 10 to 20 days. During superoutbursts, small periodic modulations (“supe
appear.
Symbiotic stars (Period: semi-periodic; Amplitude of variation: up to 3 mag.)
These close binary systems consist of a red giant and a hot blue star, both embedd
nebulosity. They show nova-like outbursts, up to three magnitudes in amplitude.
R Coronae Borealis (Period: irregular; Amplitude of variation: up to 9 mag.)
These are rare, luminous, hydrogen-poor, carbon-rich, variables that spend most o
at maximum light, occasionally fading as much as nine magnitudes at irregular inte
then slowly recover to their maximum brightness after a few months to a year. Mem
this group have F to K and R spectral types.
Eclipsing Binary Stars
These are binary systems of stars with an orbital plane lying near the line-of-sight o
observer. The components periodically eclipse one another, causing a decrease in
apparent brightness of the system as seen by the observer. The period of the eclips
coincides with the orbital period of the system, can range from minutes to years.
http://www.aavso.org/vstar/types.shtml
4/2/2005
AAVSO: Types of Variable Stars
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Rotating Stars
Rotating stars show small changes in light that may be due to dark
spots, or patches on their stellar surfaces (“starspots”). Rotating sta
often binary systems.
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Other Types of Variable Stars
The following types of stars are not recommended for observation by inexperienced
due to either their irregularity, or the small amplitude of variation that they exhibit.
Flare stars
Also known as UV Ceti stars, these are intrinsically faint, cool, red, main-sequence
undergo intense outbursts from localized areas of the surface. The result is an incre
brightness of two or more magnitudes in several seconds, followed by a decrease t
normal minimum in about 10 to 20 minutes.
Irregular variables
These stars, which include the majority of red giants, are pulsating variables. As the
implies, these stars show luminosity changes with either no periodicity or with a ver
periodicity.
The GCVS (General Catalogue of Variable Stars) classification of variable stars pro
thorough description of the different types of variable stars.
z
Outline of Variable Star Types
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