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NGC 6888/WR 136
NGC 6888/WR 136
• "NGC 6888, also known as the Crescent
Nebula, is a cosmic bubble about 25 lightyears across, blown by winds from its central,
bright, massive star. This colorful portrait of
the nebula uses narrow band image data
combined in the Hubble palette. It shows
emission from sulfur, hydrogen, and oxygen
atoms in the wind-blown nebula in red, green
and blue hues. NGC 6888's central star is
classified as a Wolf-Rayet star (WR 136).
• The star is shedding its outer envelope in a
strong stellar wind, ejecting the equivalent of
the Sun's mass every 10,000 years. The
nebula's complex structures are likely the
result of this strong wind interacting with
material ejected in an earlier phase. Burning
fuel at a prodigious rate and near the end of
its stellar life this star should ultimately go out
with a bang in a spectacular supernova
explosion. Found in the nebula rich
constellation Cygnus, NGC 6888 is about
5,000 light-years away.”
NGC 6888/WR 136
Astronomy
Patty Sherman
[email protected]
Email me if you want a copy of this.
Where do I begin?
• Read the rules and then read them
again with your team.
• Have them make a list of everything
they need to know and make two copies
– One copy to check off if they know and
– One copy to write down information
First Grouping
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Hertzspring-Russell diagram
Spectra
Light curves
Motions
Cosmological distance equations and
relationships
Stellar magnitudes
Classification
Multi-wavelength images (X-ray; optical; IR; radio
Charts; graphs; animations and
Ds9 imaging
Hertzsprung-Russell Diagram
• Find an interactive video at this site:
• http://aspire.cosmicray.org/labs/star_life/support/HR_animated.s
wf ~
• Find a source of information regarding ste
• http://aspire.cosmicray.org/labs/star_life/starlife_main.html ~
Spectra
• This site has everything!!! They have a chart
with 30 different divisions that students can
look into. From absorption lines to spectral
classification and everything in between.
• http://stars.astro.illinois.edu/sow/spectra.html
#atoms ~
Light Curves
A. Is just any astronomical object observed over a month.
B. Is an eclipsing binary star
C. This curve indicates the death of a star
http://imagine.gsfc.nasa.gov/docs/science/how_l1/light_cur
ves.html ~
Motions
http://abyss.uoregon.edu/~js/ast122/lectures/lec08.html ~
Cosmological Distance
equations and relationships
•
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http://rml3.com/a20p/index.htm
http://www.astro.ucla.edu/~wright/distance.htm
Kahn
www.phy.duke.edu/courses/055/syllabus/lecture2
3.pdf Excellent powerpoint.
Cosmologic Distance ladder
Distant Standards
Cepheids
MainSequence Fitting
Parallax
Radar Ranging
More help
• This is an amazing site. Not specifically for
this topic but for a beginning spot.
• http://www.khanacademy.org/science/cosmol
ogy-and-astronomy/v/intergalactic-scale ~
• http://www.khanacademy.org/science/cosmol
ogy-and-astronomy
Stellar Magnitudes
• http://www.skyandtelescope.com/howto/basic
s/Stellar_Magnitude_System.html ~
• Gives a very good explanation of why Sirius one of the brightest objects in the night sky
has a magnitude of -1.5 and the sun has a
magnitude of -26.7. Other bright stars such
as Vega; Arcturus and Rigel are 0.
Stellar Classification
• O Type: These are relatively rare. They have a
very high surface Temperature, in the range of
30,000 K and above, and are violet-blue in color.
• B Type: This type of stars is the first of the really
populous classes. These stars are blue in color
and burn hotly, with surface temperatures lying
between 10,000 K ﾑ30,000 K.
• A Type: These stars have surface temperatures
in the range of 7,500 K ﾑ 10,000 K and are white
in color. Some of the brightest and most famous
stars in the sky belong to this classification.
• F Type: This type of star has a yellow-white
color and surface temperatures between
6,000 K ﾑ 7,500 K.
• G Type: These stars, with temperatures
ranging between 5,000 K ﾑ 6,000 K, have
spectra that betray the existence of ﾒmetalsﾓ
or ﾒheavy elementsﾓ (any element heavier
than Helium) and are yellow in color.
• K Type: These stars are occasionally referred
to as Arcturian Stars, after the brightest of
their type. Their surface temperatures are
between 3,500 K ﾑ 5,000 K, which is a
temperature low enough for simple molecules
to form and are orange in color.
• M Type: The coolest of the common star
types, these stars have very cool surface
temperatures, below 3,500 K, which allows
more complex molecules to form. These stars
are red in color.
• L Type and T Type are reserved for the
dwarves. Other types are rare but may be
included
• O B A F G K M (L T)
• www.utpa.edu/dept/physci/labs/astr1402/lab2i
.pdf
Multi-wavelength images
• Composite of
– X-ray
– Optical
– UV
– Infrared
http://chandra.harvard.edu/photo/multi.htm
l
~
Charts; graphs; and
animations
• Students need to be able to take an
unfamiliar chart or graph or animation
and interpret the information in terms of
this event.
DS9 Imaging analysis
software
• Don’t worry. You can downoad and
practice using this software
• http://chandra-ed.harvard.edu/ ~
Webinars
• http://chandra.harvard.edu/edu/olympiad.
html ~
• Donna Young - National /event
Supervisor
• 11 sessions but it was for stellar
evolution and Type I Supernovae
Second Grouping
• Stellar evolution
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Spectral features
Chemical composition
Luminosity
Blackbody radiation
Color index (B-V)
H-R diagram
transition
Stellar nurseries
Star formation
Protostars
Main Sequence stars
–Cepheid variables
–Semiregular variables
–Red supergiants
–Neutron stars
–magnetars
–Pulsars
–Wolf-Rayet stars
–Stellar mass black holes
–X-ray binary systems
–Type II supernovas
Spectral Features
• http://outreach.atnf.csiro.au/education/s
enior/astrophysics/spectra_astro_types.
html ~
• Provides links to many other useful
areas regarding spectra. Explanations
are provided if you work your way
through the information.
The 0-class spectrum has relatively weak lines but lines for ionised
He+ are present. The B, A and F stars have a similar pattern of lines
that are strongest in the A star. These are the H Balmer series for
neutral hydrogen. F and G stars have lines corresponding to ionised
Ca+. The K and M stars have many more lines visible but the Balmer
series is very weak. These lines correspond to Fe, other neutral metals
and molecules. TiO lines are visible in the spectrum of M stars.
O
B
A
F
G
K
M
Chemical Composition
• http://spiff.rit.edu/classes/phys240/lectur
es/elements/elements.html
• http://imagine.gsfc.nasa.gov/docs/ask_a
stro/answers/961112a.html
Luminosity
• http://en.wikipedia.org/wiki/Luminosity ~
• http://zebu.uoregon.edu/~soper/Light/lu
minosity.html ~
• Example from site: It is easy to measure the apparent
brightness of a star, a galaxy, a supernova, ...
• If somehow we know the luminosity of such an object, then we
can compute its distance from us.
Blackbody Radiation
• http://phet.colorado.edu/sims/blackbody
-spectrum/blackbody-spectrum_en.html
very cool interactive here. ~
• https://www.eeducation.psu.edu/astro801/content/l3_
p5.html
Color Index (B-V)
• The difference B - V between the two
magnitude estimates (photograpic and visual)
is known as the "B- V color index of the star"
(or just the "color index" for short). It gives a
numerical measurement of the color of a star.
For blue stars will be negative, while for very
red stars, it will be a positive number.
• http://domeofthesky.com/clicks/bv.html ~
• http://www.astronomynotes.com/starprop/s5.h
tm ~
H-R Diagram Transition
• http://www.spacetelescope.org/videos/h
eic1017b/ animate video - okay
• http://chandra.harvard.edu/edu/formal/v
ariable_stars/bg_info.html ~
Stellar Evolution
• http://rainman.astro.illinois.edu/ddr/stellar/index
.html
• http://www.astro.cornell.edu/academics/course
s/astro1101/java/evolve/evolve.htm
• http://casswww.ucsd.edu/archive/public/tutorial/
StevI.html ***
• http://chandra.harvard.edu/edu/formal/stellar_e
v/ ****
Stellar Nurseries
• A molecular cloud, sometimes called a stellar
nursery if star formation is occurring within, is
a type of interstellar cloud whose density and
size permits the formation of molecules, most
commonly molecular hydrogen (H2).
• http://en.wikipedia.org/wiki/Molecular_cloud
Protostars
• Equilibrium for a protostar occurs when gas pressure
equals gravity. Gravity remains constant, so what
changes the gas pressure in a protostar? Gas pressure
depends upon two things to maintain it: a very hot
temperature (keep those atoms colliding!) and density
(lots of atoms in a small space).
•
There are two options for a protostar at this point:
• Option 1: If a critical temperature in the core of a
protostar is not reached, it ends up a brown dwarf. This
mass never makes “star status.”
• Option 2: If a critical temperature in the core of a
protostar is reached, then nuclear fusion begins. We
identify the birth of a star as the moment that it begins
fusing hydrogen in the core into helium.
Main Sequence Stars
• Stars live out the majority of their lives in a phase
termed as the Main Sequence. Once achieving
nuclear fusion, stars radiate (shine) energy into
space. The star slowly contracts over billions of years
to compensate for the heat and light energy lost. As
this slow contraction continues, the star’s
temperature, density, and pressure at the core
continue to increase. The temperature at the center
of the star slowly rises over time because the star
radiates away energy, but it is also slowly contracting.
This battle between gravity pulling in and gas
pressure pushing out will go on over the entire life
span of the star.
Cepheid Variables
• Certain stars that have used up their main supply of
hydrogen fuel are unstable and pulsate.
• RR Lyrae variables have periods of about a day.
Their brightness doubles from dimest to brightest.
• Typical light curve for a Cepheid variable star.
• Cepheid variables have longer periods, from one day
up to about 50 days. Their brightness also doubles
from dimmest to brightest.
• From the shape of the ``light curve'' of a Cepheid
variable star, one can tell that it is a Cepheid variable.
The period is simple to measure, as is the apparent
brightness at maximum brightness.
Semiregular variables
• are giants or supergiants of intermediate and
late spectral type showing considerable
periodicity in their light changes,
accompanied or sometimes interrupted by
various irregularities. Periods lie in the range
from 20 to more than 2000 days, while the
shapes of the light curves may be rather
different and variable with each cycle. The
amplitudes may be from several hundredths
to several magnitudes (usually 1-2
magnitudes in the V filter).
•
* SRA: Spectral-type (M, C, S or Me, Ce, Se) giants displaying persistent
periodicity and usually small amplitude, less than 2.5 magnitudes in V. Z
Aquarii is an example of this class. Amplitudes and light-curve shapes
generally vary and periods are in the range of 35–1200 days..
• * SRB: Spectral-type (M, C, S or Me, Ce, Se) giants with poorly defined
periodicity (mean cycles in the range of 20 to 2300 days) or with
alternating intervals of periodic and slow irregular changes. Some may
occasionally cease varying at all for a time. RR Coronae Borealis and AF
Cygni are examples of this behavior. Every star of this type may usually be
assigned a certain mean period. In a number of cases, the simultaneous
presence of two or more periods of light variation is observed.
• * SRC: Spectral-type (M, C, S or Me, Ce, Se) supergiants with amplitudes
of about 1 mag and periods of light variation from 30 days to several
thousand days. Mu Cephei and Betelgeuse are bright examples of this
class.
• * SRD: Giants and supergiants of F, G, or K spectral types, sometimes
with emission lines in their spectra. Amplitudes of light variation are in the
range from 0.1 to 4 mag, and the range of periods is from 30 to 1100 days.
SX Herculis and SV Ursae Majoris are examples of this class. The
globular cluster M13 contains a dozen red variable stars from 11.95 to
12.25 visual magnitude, and with period of 43 days (V24) to 97 days
(V43).
Red Supergiants
• After a helium-burning red giant runs out of helium fuel in its
core, the star's core starts to collapse and heat up. This
causes the outer layers of the star to expand and cool,
similar to the process that occurred after the star ran out of
hydrogen fuel and left the main sequence. As the star
swells larger and larger, it eventually becomes a red
supergiant.
• Extremely massive supergiants can generate high enough
pressure and temperature to fuse elements even heavier
than carbon and oxygen. Near the end of the red
supergiant phase, a high mass star will develop several
"onion layers" of heavier and heavier elements.
• Eventually stars this massive die explosive deaths and
become type II supernovae.
Neutron Stars
• Neutron stars are compact objects that are created in
the cores of massive stars during supernova
explosions. The core of the star collapses, and
crushes together every proton with a corresponding
electron turning each electron-proton pair into a
neutron. The neutrons, however, can often stop the
collapse and remain as a neutron star.
• Neutron stars are fascinating objects because they
are the most dense objects known. They are only
about 10 miles in diameter, yet they are more
massive than the Sun. One sugar cube of neutron
star material weighs about 100 million tons, which is
about as much as a mountain.
Magnetars
• http://chandra.harvard.edu/xray_source
s/neutron_stars.html ~
• This is a very new discovery and
information is not consistent. Use
Chandra for your final information since
the event comes from their astronomer.
Magnetars are very
small (12 km across)
but have a mass
greater than our sun.
They are another
kind of neutron star
but have a stronger
magnetic field and
rotates more slowly.
Pulsars
• A pulsar is a highly magnetized, rotating
neutron star that emits a beam of
electromagnetic radiation. This radiation can
only be observed when the beam of emission
is pointing towards the Earth, much the way a
lighthouse can only be seen when the light is
pointed in the direction of an observer, and is
responsible for the pulsed appearance of
emission. Neutron stars are very dense, and
have short, regular rotational periods.!
Discovered in 1967
by Jocelyn Bell Burnell
•
Crab Pusar off
Crab Pusar on
“Little green men; white dwarves or pulsars.”
Wolf-Rayet Stars
• Wolf-Rayets stars are divided into 3
classes based on their spectra, the WN
stars (nitrogen dominant, some carbon),
WC stars (carbon dominant, no
nitrogen), and the rare WO stars with
C/O < 1
• They are losing mass rapidly by means of a
very strong stellar wind, with speeds up to
2000 km/s. While our own Sun loses
approximately 10−14 solar masses every year,
Wolf–Rayet stars typically lose 10−5 solar
masses a year.[1]
• Wolf–Rayet stars are extremely hot, with
surface temperatures in the range of 30,000
K to around 200,000K.[2]
• They are also highly
luminous. (not necessarily
bright.)
WR 124 in our galaxy
Stellar Mass Black Holes
• When a star runs out of nuclear fuel, it
will collapse. If the core, or central
region, of the star has a mass that is
greater than three Suns, no known
nuclear forces can prevent the core
from forming a deep gravitational warp
in space called a black hole.
• Anything that passes beyond the event
horizon is doomed to be crushed as it
descends ever deeper into the
gravitational well of the black hole. No
visible light, nor X-rays, nor any other
form of electromagnetic radiation, nor
any particle, no matter how energetic,
can escape. The radius of the event
horizon (proportional to the mass) is
very small, only 30 kilometers for a
non-spinning black hole with the mass
of 10 Suns.
Illustration of Blackhole
X-ray Binary Systems
• A binary system is a system of two
objects in space (usually stars, but also
planets, galaxies, or asteroids) which
are so close that their gravitational
interaction causes them to orbit about a
common center of mass.
• http://wonka.physics.ncsu.edu/~blondin/
AAS/ (amazing powerpoint)
Type II Supernovas
• These supernovae occur at the end of a
massive star's lifetime, when its nuclear
fuel is exhausted and it is no longer
supported by the release of nuclear
energy. If the star's iron core is massive
enough, it will collapse and become a
supernova.
Taken in 1987
Taken before 1987
Kepler’s laws
• 1st law (law of elliptic orbits): Each star
or planet moves in an elliptical orbit with
the center of mass at one focus.
• Ellipses that are highly flattened are
called highly eccentric. Ellipses that are
close to a circle have low eccentricity.
Kepler’s First law
Kepler’s Second law
• 2nd law (law of equal areas): a line between
one star and the other (called the radius
vector) sweeps out equal areas in equal
times
• This law means that objects travel fastest at
the low point of their orbits, and travel slowest
at the high point of their orbits.
Kepler’s Second law
Kepler’s Third law
• * 3rd law (law of harmonics): The square of a
star or planet's orbital period is proportional to
its mean distance from the center of mass
cubed
• It is this last law that allows us to determine
the mass of the binary star system (note only
the sum of the two masses).
• Two stars in a binary system are bound by gravity and revolve around
a common center of mass. Kepler's 3rd law of planetary motion can
be used to determine the sum of the mass of the binary stars if the
distance between each other and their orbital period is known.
• Kepler's 3rd law states that the square of a planet's or star's orbital
period is proportional to its mean distance from each other such that
• r 3 = k P2
• where P is the orbital period in years and r is the distance between
each other in Astronomical Units (the distance from the Earth to the
Sun). The constant, k, is derived from Newton's law of gravity to be
the sum of the masses of the stars, M1 + M2, in units of solar masses.
So the full equation becomes:
• M1 + M2 = r3/P2
Parallax
• Kahn Academy
Spectroscopic Parallax
• http://outreach.atnf.csiro.au/education/s
enior/astrophysics/photometry_specpar
allax.html
Distance Modulus
• Apparent magnitude (m)
– Hipparchus 1 to 6
– Lower numbers brighter
• Absolute magnitude (M)
– Corrected to standard distance of 10pc
– Can be determined from spectra
• Distance modulus (m- M)
• M - M = 5log(distance in parsecs/10)
Third Grouping
• Alphabet soup
• NGC - new general catalogue
• SN - supernova
• PSR - pulsar
Cas A
An x-ray
image of a
star that
exploded
about 300
years ago.
From
Chandra
site.
IGR J17091
The strong gravity of the black hole, on the left, is pulling
gas away from a companion star on the right. This gas
forms a disk of hot gas around the black hole, and the
wind is driven off this disk. (artist’s depiction)
PSR J0108-1431
The Chandra source in the center of the image is the ancient pulsar PSR
J0108-1431 (J0108 for short), located only 770 light years from us. The
elongated object immediately to its upper right is a background galaxy that is
unrelated to the pulsar. Since J0108 is located a long way from the plane of our
galaxy, many distant galaxies are visible in the larger-scale optical image.
Cygnus x-1
On the left, an optical image from the Digitized Sky Survey shows Cygnus X-1, outlined in a
red box. Cygnus X-1 is located near large active regions of star formation in the Milky Way, as
seen in this image that spans some 700 light years across. An artist's illustration on the right
depicts what astronomers think is happening within the Cygnus X-1 system. Cygnus X-1 is a
so-called stellar-mass black hole, a class of black holes that comes from the collapse of a
massive star. The black hole pulls material from a massive, blue companion star toward it.
This material forms a disk (shown in red and orange) that rotates around the black hole before
falling into it or being redirected away from the black hole in the form of powerful jets.
SXP 1062
In this composite image, X-rays
from Chandra and XMM-Newton
have been colored blue and
optical data from Chile are
colored red and green. The
pulsar is the bright white source
located on the right-hand side of
the image in the middle of the
diffuse blue emission inside a red
shell. The diffuse X-rays and
optical shell are both evidence
for a supernova remnant
surrounding the pulsar. The
optical data also displays
spectacular formations of gas
and dust in a star-forming region
on the left side of the image.
M1
Pictured above is a composite image of the center of the
Crab Nebula where red represents radio emission, green
represents visible emission, and blue represents X-ray
emission.
V838 Mon
(Monoceros)
2002 this was the brightest star in the Milky Way - briefly
Delta Cep
Binary System
Alpha Orionis
Betelgeuse
“Armpit of
the Central one”
SN 2010J1
Supernova
shock wave
NGC 3582
Minor nebula in
the Sagittarius
arm of the Milky
Way galaxy. It
is part of starforming region
RCW 57 in
Carina.
lHa115-N19
At a distance of only
200,000 light years, the
Small Magellanic Cloud
(SMC) is one of the Milky
Way's closest galactic
neighbors. It offers
astronomers a chance to
study phenomena across
the stellar life cycle. In
various regions of the SMC,
massive stars and
supernovas are creating
expanding envelopes of
dust and gas. Evidence for
these structures is found in
optical (red) and radio
(green) data in this
composite image.
Antares/Rho
Ophiuchi Cloud Complex
White area and blue bow area represent
emission nebula and red is reflection nebula
IC 1396 Star Cluster
The Elephant’s
Trunk Nebula is
a concentration
of interstellar
gas and dust in
the constellation
Cepheus