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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 • • • • • • • • • • 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 • • • • 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 – – – – – – – – – – 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