2014 Div. C (High School) Astronomy Help Session Stellar Evolution and Variable Stars Scott Jackson Mt. Cuba Astronomical Observatory • SO competition on March 1 st . • Resources – two laptop 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 on Feb 7 th before competition at Mt. Cuba Observatory • 1 2 things you need to know • Specific objects (later) • Stellar evolution, including – spectral features and chemical composition, luminosity, blackbody radiation, color index (B-V), and H-R diagram transitions, proto-stars, T Tauri variables , Cepheid variables, semiregular variables, red supergiants, Mira variables , RR Lyrae variables , neutron stars , magnetars , pulsars , x- ray binary systems , dwarf & recurrent novas, S Doradus variables, Type II and Type Ia supernovas . – Kepler’s Laws , parallax, spectroscopic parallax, and the distance modulus to calculate distances to Cepheids, RR Lyraes and Type Ia supernovas • Distance scales • Period-luminosity relationship (Cepheids & RR Lyrae) • A star’s color or spectral class or surface temperature • Scientific notation 3 Study aid -1 • Google each object, – Know what the look like in each part of the electromagnetic spectrum – 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!!! – Some 1 st year college courses in astronomy or astrophysics will have good study aids and problems to practice with. 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 6 • Mira, ---- Binary star, component A is a variable star • W49B --- Supernova remnant • Tycho’s SNR -- Supernova remnant • Vela SNR -- Supernova remnant • G1.9+0.3 -- the youngest Galactic supernova remnant • Eta Carinae -- expected to be supernova in the “near” future. • SS Cygni -- prototype periodic dwarf nova • T Tauri -- Pre-main sequence star, • GRS 1915+105 - X-ray binary star system = a regular star and a black hole • 47 Tucanae -- a globular cluster located in the constellation Tucana. • The Trapezium -- tight open cluster of stars in the heart of the Orion Nebula • T Pyxidis -- a recurrent nova and nova remnant in the constellation Pyxis • Adell 30 -- A planetary nebula • RX J0806.3+1527 -- X-ray binary star system • V1647 Ori -- a pre–main sequence star which displays an extreme change • V1 --- Var 1 in M33 -- a Luminous Blue Variable star in a nearby galaxy. • NGC1846 --- Globular Cluster in the Large Magellenic cloud • NGC3132 ---a bright planetary nebula in the constellation Vela 7 Mira or Omicron Ceti • A red giant star estimated 200–400 light years away in the constellation Cetus. Mira is a binary star, consisting of the red giant Mira A along with Mira B. Mira A is also a variable star and was one of the first non- supernova variable star discovered. Mira is one of the brightest periodic variable in the sky. It is not visible to the naked eye for part of its cycle. It is a star in the very late stages of stellar evolution, on the asymptotic giant branch, It is expelling its outer envelopes as planetary nebulae and will become a white dwarf within a few million years. Helium is fusing in its core. However, it can be thousands of times more luminous than the Sun due to its very large distended envelopes. It is pulsating due to the entire star expanding and contracting 8 W49B • Supernova remnent (SNR G043.3-00.2 or 3C 398) is a nebula resulting from a supernova. [1] If the supernova was visible from Earth it would have been seen around 1000 AD (the remnant "is about a thousand years old") which may have produced a gamma-ray burst [2] and may have produced a black hole. • W49B is barrel-shaped and located roughly 26,000 light-years from Earth. Recent findings indicate infrared "rings" (about 25 light-years in diameter) around the "barrel", and also indicate intense X-ray radiation coming from nickel and iron along its axis. The star that created this nebula is thought to have formed from a dense dust cloud before throwing off hot, gaseous rings, creating a bubble, and exploding 9 Tycho’s SNR • SN 1572 (Tycho's Supernova , Tycho's Nova ), "B Cassiopeiae" (B Cas), or 3C 10 was a supernova of Type Ia in the constellation Cassiopeia, one of about eight supernovae visible to the naked eye in historical records. It burst forth in early November 1572 and was independently discovered by many individuals. [2 The color image depicts the X-ray emission. Most of the bright regions correspond to clumps of metal enriched material ejected from the star that exploded as a supernova over 400 years ago. Most notable is the weak rim of emission seen clearly around the entire remnant, which is believed to be the blast wave propagating through the surrounding circumstellar (or interstellar) medium 10 VELA SNR • The Vela supernova remnant is a supernova remnant in the southern constellation Vela. Its source supernova exploded approximately 11,000-12,300 years ago (and was about 800 light years away). The association of the Vela supernova remnant with the Vela pulsar, made by astronomers at the University of Sydney in 1968, was direct observational proof that supernovae form neutron stars. The Vela supernova remnant includes NGC 2736. It also overlaps the Puppis Supernova Remnant, which is four times more distant. Both the Puppis and Vela remnants are among the largest and brightest features in the X-ray sky. This is a visible light image. 11 G1.9+0.3 the youngest Galactic supernova remnant (SNR), The expansion is shown in the lower image. NASA's Chandra X-ray Observatory image obtained in early 2007 is shown in orange and the radio image from NRAO's Very Large Array (VLA) from 1985 is in blue. The difference in size between the two images shows the expansion, allowing the X ray time since the original supernova explosion (about 140 years) to be estimated. This makes the original explosion the most recent supernova in the Galaxy, as measured in Earth's time-frame (referring to when events are observable at Earth). Equivalently, this is the youngest known supernova remnant in the Galaxy (140 years old), X ray (2007) and radio image (1985 – light blue) Eta Carinae • The system contains at least two stars, of which the primary is a luminous blue variable (LBV) that initially had around 150 solar masses, of which it has lost at least 30. A hot supergiant of approximately 30 solar masses is in orbit around the primary, although an enormous thick red nebula surrounding Eta Carinae makes it impossible to see this companion optically. The Eta Carinae system is enclosed in the Homunculus Nebula, itself part of the much larger Carina Nebula, and currently has a combined luminosity of over five million times the Sun's. Because of its mass and the stage of its life, it is expected to explode in a supernova or hypernova in the astronomically near future. 13 SS Cygni SS Cygni is a variable star in the northern constellation Cygnus (the Swan). It is perhaps the prototype dwarf nova, meaning that it undergoes frequent and regular brightness outbursts - every 7 or 8 weeks . SS Cyg, like all other cataclysmic variables, consists of a close binary system. One of the components is a red dwarf-type star, cooler than our Sun, while the other is a white dwarf. Studies suggest that the stars in the SS Cyg system are separated (from surface to surface) by "only" 100,000 miles or less. In fact, the stars are so close that they complete their orbital revolution in slightly over 6 1/2 hours Artists conception 14 T Tauri • T Tauri stars (TTS) are a class of variable stars named after their prototype – T Tauri. They are found near molecular clouds and identified by their optical variability and strong chromospheric lines. T Tauri stars are pre-main sequence stars in the process of contracting to the main sequence along the Hayashi track, a luminosity-temperature relationship obeyed by infant stars of less than 3 solar masses in the pre-main-sequence phase of stellar evolution. It ends when a star of 0.5 solar masses develops a radiative zone, or when a larger star commences nuclear fusion on the main sequence T Tauri stars are the youngest visible F, G, K, M spectral type stars (<2 Solar mass). Their surface temperatures are similar to those of main sequence stars of the same mass, but they are significantly more luminous because their radii are larger. Their central temperatures are too low for hydrogen fusion. Instead, they are Artists conception powered by gravitational energy released as the stars contract, while moving towards the main sequence, which they reach after about 100 million years. They typically rotate with a period between one and twelve days, compared to a month for the Sun, and are very active and variable 15 T Tauri 16 GRS 1915+105 • GRS 1915+105 or V1487 Aquilae is an X-ray binary star system which features a regular star and a black hole. It was discovered on August 15, 1992 by the WATCH all-sky monitor aboard Granat [1] "GRS" stands for "GRANAT source", "1915" is the right ascension (19 hours and 15 minutes) and "105" is declination in units of 0.1 degree (i.e.