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1 2017 Div. C (High School) Astronomy Help Session Sunday, Feb. 19th, 2017 Stellar Evolution and Type 1a supernovae Scott Jackson Mt. Cuba Astronomical Observatory • SO competition on March 4th . • Resources – two computers or two 3 ring binder or one laptop plus one 3 ring binder – Programmable calculator – Connection to the internet is not allowed! – Help session before competition at Mt. Cuba Astronomical Observatory 2 3 Study aid -1 • Google each object, – Know what they look like in different parts of the spectrum. For example, the IR, optical, UV and Xray – Understand what each part of the spectrum means – Have a good qualitative feel for what the object is doing or has done within the astrophysical concepts that the student is being asked to know. 4 Study aid - 2 • Know the algebra behind the physics – Just because you think you have the right “equation” to use does not mean you know how to use it!!! – Hint for math problems: Solve equations symbolically BEFORE you put in numbers. Things tend to cancel out including parameters you do not need to have values for. – Know how to use scientific notation. 5 The test – 2 parts • Part 1 – multiple choice and a couple fill in the blanks • Part 2 – word problems for astrophysics there will be some algebra Solve the equations symbolically first then put in numbers!!!! Hint: most problems will not need a calculator if done this way Topics - 1 Stellar evolution, including - stellar classification, - spectral features and chemical composition, - H-R diagram transitions, - Accretion disks - Main sequence stars - red giants, - white dwarfs (oxygen & helium), - neutron stars, planetary nebulas Luminosity, blackbody radiation, color index, Spectral class of stars • • • • • • • • • O B A F G K M L Red Dwarfs (failed stars) T Brown Dwarfs (failed stars) 7 Categorizing stars by their spectra 1. Spectra can tell you the stars approximate temperature (blackbody radiation) 2. Absorption (dark) lines in a star’s spectra give a finger print of elements that are seen in that spectral class of stars BUT emission spectra spectra (bright lines against a dark background) are given off by nebulae – glowing gas clouds 8 Spectral class of stars He+ lines H Balmer lines (B,A & F stars) Ca+ lines (F & G stars) Fe and neural metals K & M stars) TiO2 lines 9 Spectral classification & Temperature of main sequence stars Star Spectral Class Proportion of Stars Surface Temperature (°F) Star Mass (Sun = 1.0) Star Luminosity (Sun = 1.0) Lifespan (Billions of Years) Example Star A0 1% A0 - A9 20,000 2.8 60 0.5 Vega A1 --- 18,400 2.35 22 1.0 Sirius A5 --- 15,000 2.2 20 1.0 --- F0 3% F0 - F9 13,000 1.7 6 2.0 --- F5 --- 12,000 1.25 3 4.0 Procyon A G0 9% G0 - G9 11,000 1.06 1.3 10 --- G2 --- 10,600 1.00 1.0 12 Sun Alpha Centauri A G5 --- 10,000 0.92 0.8 15 --- K0 14% K0 - K9 9,000 0.80 0.4 20 Alpha Centauri B K2 --- 8,700 0.76 0.3 24 Epsilon Eridani K5 --- 8,000 0.69 0.1 30 61 Cygni A M0 73% M0 - M9 7,000 0.48 0.02 75 --- M5 --- 5,000 0.20 0.001 200 Proxima Centauri 10 (Alpha Centauri C) 11 More on stars spectral class 12 Hertzsprung-Russell Diagram Y axis is always brightness or relative luinosity 13 X axis is always temperature, color or spectral class Each dot is a star A is the location of our sun on the main sequence B are red giant stars that are fusing helium in their core L http://outreach.atnf.csiro.au/education/senior/cosmicengine/stars_hrdiagram.html D are white dwarfs (super hot carbon stars) T C are red supergiants with Helium and Hydrogen buring in shells and carbon in its core 14 Instability gaps on an H-R diagram for the pulsating class of variable stars Period of pulses scale with absolute brightness of the star “Period-luminosity relationship” • http://outreach.atnf.csiro.au/education/senior/astrophysics/variable_pulsating.html Accretion disks • Circumstellar disks • Many accretion disks seen in binary star systems when one star hass filled its “Roche” limit and is having material “sucked” away from it to a companion start (e.g., white dwarf) Disk in Orion nebulea http://planetquest.jpl.nasa.gov/documents/RdMp272.pdf Birth of a solar mass star 17 The birth of a 1 solar mass star going onto the main sequence. Before point 4, contraction of intersteller gas cloud. The cloud heats up as it contracts, causing its luminosity to increase -- we don’t see it because the protostar is hidden in dust. From point 4 to 6, -- The cloud contracts more and its luminosity drops. Point 6, hydrogen starts to fuse to helium in the stars core. The heat generated from fusion balances gravity. The star’s surface heats up slightly. This is the location of T Tauri stars Point 7. The star has reached a long lived equilibrium where the heat from fusing hydrogen to helium balances gravity. The star resides on the main sequence for most of its life (~10 billion years for a 1 solar mass star). Formation of white dwarfs Death of main sequence stars Red Giant for lower mass stars Low mass star like our sun stops at carbon formation in its core... And fluffs off its outer layers to make a planetary nebulae and a white dwarf star. Red Giant for higher mass stars But a high mass star, like those in the early universe had enough mass to fuse nuclear material all the way to iron. However, once iron accumulates in its core no net energy generation can be done by fusion of iron, gravity takes over and core collapse occurs and..... Electrons are pushed into protons making neutrons and a flood of neutrinos…. It goes boom!!!!... A supernovae!!! (this is the Crab Nebulae) … Which make lots of heavy elements needed to make terrestrial (earth like) planets. This is NOT a type 1a supernovae. It is a type II supernovae. .. And it spreads heavy elements throughout space to be picked up by a new generation of stars,..... .. The shock wave either from the supernovae or from the initial star formation stage can initiate new star formation,..... Stars and planets approximate black body radiators The wavelength at maximum radiation changes with temperature λmax = 550 nm 5300 K temperature for our sun. “G” type star (subclass “2”) or G2 λmax x Temperature = constant = 2.9x106 nm-°K Or = 2.9x107 A-°K = 2.9x103 μm-K Nm[=] nanometers for wavelength Or A [=] Angstrom units for wavelength Or μm [=] microns units for wavelength °K [=] degrees Kelvin 25 Another way to look at black body radiation Plot log λ (x axis) vs log of spectral intensity at that λ Example calculation for a star’s temperature So the shorter the wavelength the hotter or colder the star???? λmax ~ 0.9 μm What it the star’s temperature? T ~ 2.9x103 μm-K / 0.9 μm = 3200 K (M type star) λmax x Temperature = constant = 2.9x106 nm-°K Or = 2.9x107 A-°K = 2.9x103 μm-K Nm[=] nanometers for wavelength Or A [=] Angstrom units Or μm [=] microns units °K [=] degrees Kelvin If λmax ~ 10 μm What it the star’s temperature? T ~ 2.9x103 μm-K / 10 μm = 290 K (black dwarf) 27 Color Index or color – color diagrams • A way to compare the apparent magnitude of stars at different wavelengths (using photometry instead of spectrometry). • Observe at narrow bands of wavelengths ( a color) and note the difference in the intensity of these different bands. • Spectrometry (measuring the entire spectrum) is more difficult than photometry (observations at a single color). • But what is U, B and V?? https://en.wikipedia.org/wiki/Color_index 28 UBV, UBVRI and JHK systems for Color-color diagrams 29 Color Index or color – color diagrams • Where is our sun on the U-B vs B-V diagram? https://en.wikipedia.org/wiki/Color_index 30 White dwarfs (oxygen & helium) -1 • White dwarfs are the end point for moderate mass stars like our sun: Mass ~0.5 to ~4+x mass of sun (Msun) the progenitor stars are not massive enough to generate neutron stars or black holes when they die. • White dwarfs do not generate any energy – they are just cooling off and will follow a well defined “cooling” curve on the H-R diagram. • Maximum mass of a white dwarf is dictated by electron degeneracy pressure ~ 1.4 x Msun– the pressure below which the electrons are not pushed into the nucleus. This is called the Chandrasekhar limit • White dwarfs will take a long time to cool off but as they do, they will become red dwarfs and then brown dwarfs as their (black body) spectra shifts to longer wavelengths of light • . 31 White dwarfs (oxygen & helium) - 2 • The more massive the white dwarf – the smaller it is(!) • Many red dwarfs or brown dwarfs were not white dwarfs to start with – they may just be failed stars that did not have enough mass to initiate fusion in their cores. • Progenitor stars of lower mass will not be able to fuse helium in their shells. When they die as white dwarfs, they will appear as helium white dwarfs. • Progenitor stars of higher mass will be able to fuse helium in their shells to carbon and oxygen and these will appear as oxygen white dwarfs. 32 Neutron stars • When higher mass stars “die” gravity takes over and the core of the star collapses. Electron degeneracy pressure is overcome and electrons are pushed into the protons to form neutrons (and a flood of neutrinos – that give rise to a supernovae). • Initial angular momentum will be distributed between the supernovae remnant and the resulting neutron “star”. • The angular momentum of the neutron star can cause it to spin very quickly – creating a pulsar. • Strong magnetic fields can focus a beam of radiation like a light house • Pulsars can have an accretion disk (from the blown off remnant of the star) that generates x-rays as matter is accelerated to near the speed of light as it falls into the neutron star. 33 Planetary nebulas • Old definition: Any small, relatively round object that when first observed by early astronomers looked like a planet (but did not move like a planet in our solar system). • New definition: specifically refers to the gas and dust that is “fluffed off” a low mass dyeing star that will ultimately lead to white dwarf. • Some of the most beautiful and intricate objects in the universe. • Our sun will generate a planetary nebulae when it dies to become a white dwarf. 34 Mass of the main sequence star is reduced as it evolves and dies. Material is shed either during the formation of a planetary nebulea (white dwarf) or during a supernovae. The supernovae in this diagram are meant to be Type II and not Type Ia. 35 Type Ia supernovas, dwarf novas, AM CVn systems, Mira variable Stars, globular clusters. Topics - 2 Use Kepler’s laws of rotation and circular motion to answer questions relating to the orbital motions of binary systems; use parallax, spectroscopic parallax, the distance modulus and Hubble’s law to calculate distances to Type Ia supernovas. Type 1a supernovae A type Ia supernova occurs in binary stellar system (two stars orbiting one another) in which one of the stars is a white dwarf. The other star can be anything from a giant star to another white dwarf. Material is drawn off the other star (filling its “Roche” limit) onto the white dwarf until the white dwarf reaches the Chandrasekhar limit. Then electron degeneracy pressure is unable to prevent catastrophic collapse. If a white dwarf gradually accretes mass from a binary companion, its core will reach the ignition temperature for carbon fusion as it approaches the limit. If the white dwarf merges with another white dwarf, it will momentarily exceed the limit and begin to collapse, again raising its temperature past the nuclear fusion ignition point. Within a few seconds of initiation of nuclear fusion, a runaway reaction will occur and thus causing the supernovae Bottom line: Type 1a SN produce a consistent peak in absolute luminosity because of the uniform mass of white dwarfs that explode via the accretion mechanism. Absolute magnitude is M ~ -19.5 (negative) One explanation 38 • Bottom line: Type 1a SN produces a consistent peak in absolute luminosity because of the uniform mass of white dwarfs that explode via the accretion mechanism. Absolute magnitude is M ~ -19.5 (negative) 39 Dwarf Novae • Cataclysmic variable star • Close binary system where one companion is a white dwarf that is sucking material from its companion into an accretion disk • The material accumulating in the disk can get hot and we see it as a burst in the luminosity of the system (although it is just the disk that is shining brighter). • This matter accumulation in the disk will stop (companion star has stopped feeding the disk) and the disk cools off and drops in luminosity. • This process repeats itself from days to years – not necessarily in a regular pattern. • 40 • An AM CVn star, or AM Canum Venaticorum star, is a rare type of cataclysmic variable star named after their type star, AM Canum Venaticorum. In these hot blue binary variables, a white dwarf accretes hydrogen-poor matter from a compact companion star. These binaries have extremely short orbital periods (shorter than about one hour) and have unusual spectra dominated by helium with hydrogen absent or extremely weak. They are predicted to be strong sources of gravitational radiation, strong enough to be detected with the Laser Interferometer Space Antenna. AM CVn systems consist of an accretor white dwarf star, a donor star consisting mostly of helium, and usually an accretion disk. 41 Globular Clusters • • • • • • • • • • • A gravitational bound “close” association of stars 0.4 stars per cubic parsec on average 100 to 1000 stars per cubic parsec in its core The cluster has a spherical shape. Very old objects ~10 billion years old – perhaps as old as our galaxy Very old stars Contains hundreds of thousands of stars Some may have massive black holes in their cores. These clusters form a “halo” around the center of our galaxy not necessarily found in the spiral arms Origin of globular cluster is still being debated Completely different from “open cluster” of stars 42 Mira Variable stars Instability gaps on an H-R diagram for the pulsating class of variable stars Period of pulses scale with absolute brightness of the star “Period-luminosity relationship” • http://outreach.atnf.csiro.au/education/senior/astrophysics/variable_pulsating.html 43 Mira Variables • • • • • They are red giants – very late stages of stellar evolution for low mass stars, on the asymptotic giant branch, – will expel their outer envelopes as planetary nebulae and become white dwarfs within a few million years. Massive enough that they have undergone helium fusion in their cores but are less than two solar masses, Have already lost about half their initial mass (fluffing off their planetary nebulae. Thousands of times more luminous than the Sun due to their very large distended envelopes. They are pulsating due to the entire star expanding and contracting over long time periods (~100+ days) 44 Kepler’s laws – gold standard for “weighing” stars 1. Orbits are ellipses with sun at one focus 2. Equal areas swept out in equal time 3. Harmonic law: Square of the period (P) is proportional to the cube of the semimajor axis (a). -- Gold standard for determining masses in the universe – exoplanets and binary stars. Kepler’s law P2 = a3 / (m1 + m2) P = orbital period (years) a = Distance between the two bodies (expressed in astronmical units [AU] – distance from earth to sun) 1 AU = 107.5 sun diameters or 215 sun’s radius m1, m2 = mass of the two bodies orbiting each other (solar masses) 45 Measuring Distances… First: Lets talk about time (JD or Julian Date) Then brightness of stars… 46 JD or Julian Date • The Julian Day Number (JDN) is the integer assigned to a whole solar day in the Julian day count starting from noon Universal time, with Julian day number 0 assigned to the day starting at noon on January 1, 4713 BC, proleptic Julian calendar • For example, the Julian Date for 00:30:00.0 UT January 1, 2013, is 2,456,293.520833. • Universal time is the time in Greenwich England (prime meridian) 47 Brightness of Stars • Brightness measured as luminosity or magnitude – Luminosity is the total energy output of a star • Depends on size and surface temperature • Usually measure relative to our sun, e.g., 4 times our sun. – A star’s magnitude is the logarithm of its luminosity – Apparent magnitude (m) [what we see] – is determined by four factors • Its temperature or color (wattage of a light bulb) • Its size • How far away it is • If it is obscured by dust (extinction) – Absolute magnitude (M) • Magnitude of a star when viewed from a fixed distance • Most abs magnitudes will be a negative number (bright) 48 Brightness of a star: A star’s magnitude • Magnitude is more often used to describe an objects brightness. • The higher the magnitude the dimmer the object. – The apparent magnitude of our sun is -26.7 – The apparent magnitude of a full moon is -12.6 – The apparent magnitude of the Sirius is ~ -1 – Dimmest star you see (in Wilmington) ~+3.5 – Dimmest star you see in a dark sky location ~+5.5 • The absolute magnitude is the magnitude of the star / object if it was place a fixed distance away (10 parsecs -- later). • The absolute magnitude of our sun is ~ +4.8 49 50 Distances • Astronomical unit. Average distance between the earth and our sun. (AU = 1.496x1011 meters or 97 million miles or about 8.3 light minutes) This is a small unit of measure. – Used for interplanetary measures and for distances between stars in binary star systems (Kepler’s Laws) • Light years. The distance light travels in a year – LY = 9.46x1015 meters, 6.33x104 AU • Parsec [pc]. The distance to an object that has a parallax of 1 arc second (next slide) preferred unit by astronomers pc = 3.26 LY = 2.06x105 AU = 3.086x1016 meters • Kiloparsecs (Kpc) 1000 parsecs (103 parsecs) • Megaparsecs (Mpc) 1 million parsecs (106 parsecs) 51 52 • Geometric parallax Gold standard for distances – 1 Parsec = 3.09 × 1016 meters • parsec - (pc): distance at which an object would have a parallax of one arc second. Equals approximately 3.26 light years or about 206,265 astronomical units Star appears to move with season Don’t move 53 54 Spectroscopic Parallax 1. Measure the spectrum of a star. Lines in the spectra will indicate if it is a main sequence star . The star needs to be bright enough to provide a measurable spectrum, which is about 10 000 parsecs. 2. Using the star spectra or using the UVB index, make certain that it is on the main sequence, deduce its spectral type (O, B, A, F, G, K, M, L) 3. From the spectral type deduce its absolute magnitude [M] (H-R diagram or table) 4. Measure the apparent magnitude (m). Knowing the apparent magnitude (m) and absolute magnitude (M) of the star, one can calculate the distance modulus (m-M) and the actual distance in parsecs – next slide. Good for stars that are <~ 10,000 parsecs from us (or 32,600 light years) – most of the stars in our galaxy. 55 Distance modulus is m-M if there is no interstellar dust (or extinction) If there is interstellar dust then distance modulus is ((m-E)-M) where E is the extinction magnitude The larger the distance modulus the further away the object is. Little m is usually >+10 Capital M is usually small – many times negative, E can be as much a 1 or 2 (magnitudes of extinction due to dust in our galaxy) 56 Relationships between distance modulus, luminosity, distances in parsecs and absolute magnitude Msun = 4.8 (absolute magnitude or our sun) Astronomical unit [AU] = average earth- sun distance 1 AU = 1.496 x 108 km Diameter of our sun = 1.391 x106 km 1AU = 107.5 sun diameters What is distance modulus for our sun? 57 58 Instability gaps on an H-R diagram for the pulsating class of variable stars Period of pulses scale with absolute brightness of the star “Period-luminosity relationship” • http://outreach.atnf.csiro.au/education/senior/astrophysics/variable_pulsating.html 59 Period-Luminosity Relationship equation for type 1 Cepheid For Type I, Type II Cepheids and RR Lyrae Cepheids named after the first star discovered in the constellation Cepheus (up north) Note this is luminosity – these stars are much brighter than our sun. • M = -2.81* log(P)-1.43 P is period in days http://outreach.atnf.csiro.au/education/senior/astrophysics/variable_cepheids.html 60 Light curve for Delta Cephei • Saw tooth curve for Type 1 Cepheid variable 61 RR Lyrae and Cepheid stars as standard candles Find the period. This gives the luminosity or its absolute magnitude Measure the apparent magnitude. Determine the distance from the apparent and absolute magnitude (distance modulus) (and an estimate of the extinction [E]) The same applies to RR Lyrae variable stars. Once you know that a star is an RR Lyrae variable (eg. from the shape of its light curve), then you know its luminosity M = -2.81* log(P)-1.43 Type 1. P is period in days 62 63 Type Ia supernovae is where a white dwarf collapses because it has pulled too much material from a nearby companion star onto itself. Because the type 1a “blows up” at the same mass limit (see earlier discussion) (Chandrasekhar limit ~1.4x mass of our sun) they have about the same absolute magnitude at its peak brightness Standard candle 64 Using Type Ia supernovae as a standard candle • Because a type Ia “explodes” at the Chandrasekhar limit, all type Ia SN are about the same brightness – Type 1a have an absolute magnitude of about M~ -19.5 (that is a negative sign) • Observed in distant galaxies. • Observe a supernovae as it occurs, • Construct its light curve • From the light curve determine if it is a type 1a and estimate is maximum apparent magnitude (m) • Distance modulus is then (m+19.5) for Type Ia supernovae (m is apparent magnitude) 65 66 Red shifting a star’s spectrum Wavelength of light (nanometers, nm) 1 nm = 1x10-9 meters Increasing red shift 67 Hubble’s law (measurement to very distant galaxies) Fundamental parameter measure of the expansion of our universe Hubble’s Law: d = Vr or for small distances d = z * c (z < 0.5) Ho Ho d = distance in megaparsecs (millions of parsecs) Vr is recessional velocity (km/sec) Measure using red shift of the light spectrum of a galaxy Ho is Hubble’s constant, ~75 km/sec / megaparsecs z is the red shift = wavelength of the observed light wavelength of the emitted light -1 C is the speed of light (3x 105 km/sec) Problem: if wavelength of the observed light is 440 nm and the wavelength of the emitted light is 400 nm What is Z? What is recessional velocity? What is the distance using Hubble’s law? In mpc? In light years? 68 Answer to problem z = 440 -1 = 1.1 -1 = 0.1 400 Vr = 0.1 x 3x 105 (km/sec) = 3x 104 (km/sec) What is the distance using Hubble’s law? D = 3x 104 km/sec / (75 km/sec/mpc [kilometers/second/megaparces]) = 3/7.5 x 103 megaparces (mpc) = 0.4 x 103 mpc = 400 mpc = 3.26 light year / pc x 106 pc/mpc x 400 mpc = 1304 x 106 light years or = 1.3 x 109 ly 69 • If the apparent magnitude of a star is +7 and it has a parallex of 0.01 arc seconds, what is its luminosity relative to our sun? • What is the mass of the star in number of suns? 70 More info… An star’s is named using its constellation and letter of multiple letter designation. So… RY Sagittarii is in the constellation Sagittarius (summer sky) and counting up using the alphabet (a, b, c, d, e… z, AA, AB,…. ) it is star RY in this constellation. A class of stars (like the Cepheid variables or RR Lyrae variables) are named after the first star discovered in that class of stars. So the first Cepheid variable was discovered in the constellation of Cepheus. The RR Lyrae variables are named after the RR Lyrae (in the constellation of Lyra [string instrument]). The T Tauri stars were named after T Tauri (a star in Taurus). 71 72 73 J075141/J174140, - Binary white dwarfs that will evolve to AM CVn type objects NGC 2392 – Eskimo nebulae – planetary nebulae in Gemini, m=10.1 SNR 0509-67.5 – type 1a SNR in the Large Magellanic Cloud in Dorado constellation Omicron Ceti Mira variable: the first in a class of very long period variable stars SN 2011fe a type 1a supernovae in M101 (pinwheel galaxy) in Ursa Major SNR G1.9+0.3, the most recent supernovae in the Milky Way galaxy. NGC 2440, – planetary nebulae in Puppis, ~ 4000 ly from earth Henize 2-248, - planetary nebulae in Aquila with binary double white dwarf system. Henize 3-1357 (Stingray Nebula), youngest planetary nebulae known. Tycho’s SNR, (B Cas) Type 1a supernovae observed by Tycho Brahe in 1572 SS Cygni, Cataclysmic variable or “dwarf novae” -- a close binary star system M15, a globular cluster in Pegasus ~12 billion years old HM Cancri two dense white dwarf stars orbiting each other, generating x-rays Sirius A & B, brightest star in the sky is a binary star system. The B component is a white dwarf NGC 1846 A globular cluster of stars (like M15) in the Large Magellanic Cloud that appears to contain a green planetary nebulae(!) J075141 & J174140, -Two binary white dwarf systems - known by their shortened names of J0751 and J1741 – that are predicted to evolve into AM CVn type of objects - Observed in X-rays by NASA's Chandra X-ray Telescope and ESA's XMM-Newton telescope. Neither Chandra nor XMM-Newton detected any X-rays from these systems. - Predicted to give off gravitational waves causing the orbits to decay and eventually pulling material from the less massive white dwarf to the more massive (and smaller) white dwarf. - Once mass accumulates, thermonuclear explosion will occur causing a type 1a supernova or a type .1a outburst - .1a is more likely given the low combined mass of these systems. 74 NGC 2392 also known as NGC2392 or Eskimo nebulae or Clownface nebulae or Caldwell 39. It is a bipolar (two lobes) with a double shell, planetary nebulae. 2,870 light years away in the constellation of Gemini with an apparent magnitude of 10.1 Represents the death of a near solar mass star. 75 SNR 0509-67.5 – type 1a supernovae remnant in the LMC in the constellation of Dorado (southern hemisphere). 160,000 light years away Light echo off of interstellar dust allowed astronomers to confirm that it was a type 1a SN 76 Omicron Ceti a giant red star in the constellation of Cetus. Binary system with a long term variable red giant (Mira A) as the primary and white dwarf as the secondary. Mira A is on the asymptotic giant branch (AGB) of the H-R diagram -- thermally pulsating Mira A (red giant) UV light showing tail optical 77 78 SN 2011fe a type 1a supernovae in M101 (pinwheel galaxy) in the constellation of Ursa Major (big dipper). Relatively close type 1a SN allowing astronomers to better calibrate the use of type 1a SN as “standard candles” to measure distances in the universe. 79 What is the distance modulus to SN 2011fe (use visual magnitude) 80 SNR G1.9+0.3, the most recent supernovae to have occurred in the Milky Way galaxy. In the constellation of Sagittarius. Type 1a SN that would have been visible in 1868 had it not been obscured by dust in the plane of our galaxy. NGC 2440 – planetary nebulae in Puppis, ~ 4000 ly from earth Central star (HD62166) is one of the hottest known (200,000K) m=17.5 Luminosity = 1100 suns Nebulae glows as a result of intense UV radiation from the dying star. 81 Henize 2-248 - planetary nebulae in Aquila with binary double white dwarf system. The pair are expected to merge and explode in a Type Ia supernova. The inspiralling of the stars is caused by the emission of gravitational waves, resulting in the loss of orbital energy. The explosion is due to the combined mass of the merged star exceeding the Chandrasekhar limit of 1.4 solar masses. This is the first candidate for binary double white dwarf star merger. 82 Henize 3-1357 (Stingray Nebula), youngest planetary nebulae known. 83 Tycho’s SNR, (B Cas) Type 1a supernovae observed by Tycho Brahe in 1572 in Cassiopeia 84 SS Cygni Variable star in Cygnus, one of the most observed variable stars in the sky. Cataclysmic variable or “dwarf novae” consisting of a close binary star system. One is a red dwarf (of failed sun, ~0.4 Msun) the other is a compact white dwarf (~0.6 Msun) separated by ~100,000 miles (very small distance). Period of orbit ~6.5 hours. The system is about 372 ly away. Changes in the rate of flow of material into the disk can cause it to suddenly burn much hotter and brighter. Not only does the disk radiate more light, but it can heat the surface of the companion star, causing it to glow more brightly, too. Flow of material to white dwarf 85 M15, Messier 15, a globular cluster in Pegasus ~12 billion years old, the first planetary nebulae in a globular cluster, Pease 1, is in M15. 35,000 ly away. ~100,000 gravitational bound stars Possible black hole in its core. Contains a Double neutron star system 86 HM Cancri, two dense white dwarf stars orbiting each other, generating x-rays. Also known as RX J0806.3+1527. Period is 321.5 seconds. 50,000 miles apart (very close), The white dwarfs will eventually merge as a result of the loss of orbital energy by the generation gravity waves. Mass of each white dwarf is estimated to be ~0.5 suns. Artist’s depiction 87 Sirius A & B - brightest star in the sky is a binary star system. The B component is a white dwarf. 8.6 ly away, m= -1.46 88 NGC 1846. A globular cluster of stars (like M15) in the Large Magellanic Cloud that appears to contain a green planetary nebulae(!) Unusual since globular clusters are VERY old and planetary nebulae are relatively young. 89