Study aid -1. Google each object,

Transcription

1 2015 Div. C (High School) Astronomy Help Session Sunday, Feb 22, 2015 Stellar Evolution and star and planet formation Scott Jackson Mt. Cuba Astronomical Observatory 1 SO competition on March 7 th. 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 2 weeks (Sunday, Feb 22) before competition at Mt. Cuba Observatory

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3 3 Google each object, Study aid -1 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 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 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 Exo Planets ~25 years ago, planets and solar systems thought to be unique Now, stars not having planets may be unique What have we so far discovered? Solar systems (stars with more than one planet) Hints of atmospheres How they are discovered How astronomers estimate masses distance from the stars they are orbiting densities How and why they are formed. Solves a basic problem in astronomy conservation of angular momentum and a stars rotation rate

7 How to define planet? Mass, and the way in which it formed 1. Star: massive enough for nuclear fusion H He; M > 0.1 Msun. Light comes from heating by nuclear fusion. Formed by cloud collaspe 2. Brown dwarf: mass too small for nuclear fusion. M < 0.1 Msun (~ 80 Mjup) Light from from slow contraction, release of gravitational energy. Probably formed in a similar manner as stars. 3. Planet: Upper limit usually taken as ~ MJup. Lower mass limit not too relavent. Mars counts as a planet (0.1 Mearth), Pluto doesn t. Most of their light is reflected light from their parent star, plus a smaller amount coming from their own thermal infrared radiation. Formed from protostellar disk or disks surrounding young stars. Exoplanets classified by what they resemble most in our own solar system. Jupiters (or gas giants ); Neptunes (~ 20 Mearth); and Super-Earths (~ 5-10 Mearth). When we refer to (yet to be discovered) extrasolar planets whose masses are similar to Earth, they are called terrestrial-like or Earth-like or rocky planets

8 Current Planet Counts Total Exoplanet Discoveries 4826 Confirmed Exoplanets 1523 Exoplanet Candidates (Keplar) 3303 * Exoplanet candidates are discoveries that have yet to be confirmed as actual exoplanet discoveries. These candidates are 80-90% likely to be actual exoplanet discoveries.

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11 ~1500 confirmed discovered (and growing) Lots of hot Jupiter's-- Large planet traveling close to their star. First one discovered ~15 years ago. ~1/3 of sun like stars have earth like planets(!)

12 Solar Systems? yes! About 17% of stars with planets contain more than one planet (artist diagram of 55 Cancri next to our solar system is below)

13 Atmospheres? Yes!

14 Detection Astronomers can not easily see an exoplanet directly Does not shine Glare of the star hides stars Must use indirect methods** **Gliese 229b is one exception

15 Detection Direct imaging Observe the planet from reflected light from the star Star is generally too close and too bright Need to block out glare from star to image planet Using Hubble space telescope

16 Detection Astrometry: Stars move in straight line Wobble or drift from straight line is from the pull of a planet Astrometry precisely measures the star's position in the sky and sees the wobble Simulation at right is if the star did not move straight through sky Ability to detect depends on 1. Distance to star (closer the better) 2. Lots of time to observe (years) 3. NOT edge on 4. Massive planets away from small star

17 Microlensing The star (with the planet) goes directly in front of a very distant object. The space is curved around the star, the light from the distant object is magnified or Microlensed Creates a very symmetrical brightening of the distant object If the star has a planet, there will be strange looking spikes in the light curve Can only be observed once (No repeats!) Detection

18 Detection Doppler method: As the star is pulled by the planet, its speed varies (even though we do not see the wobble by astrometry) The change in speed is detected as a change in color the Doppler shift The spectrum of a star has well defined lines in it that move like the simulation. Remember the train whistle Ability to detect depends on: 1. No need to have the star close to us 2. Best if edge on (inclination ~0) 3. Heavy planet close to star (hot Jupiters) 4. Small star

19 Transit method: If the plane of a planet s orbit is along our line of sight, the planet will go in front of the star Its like an eclipse can measure diameter of the planet The observed brightness of the star drops by a small amount. The amount by which the star dims depends on its size and on the size of the planet. ***Combined with other techniques, astronomers can determine the mass and density of the planet Gas giant? Terrestrial planet? Best if: 1. Star is big 2. Planet is big (Hot Jupiters) 3. Planet is close to star 4. View orbit nearly edge on Detection

20 Limit of techniques Plot has Size of orbit or orbital period on horizontal axis Mass of planet on vertical axis. Snow line is where planets will condense out water or ammonia as a solid (cold!)

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22 Measuring mass (and density) of exoplanets Need to use Doppler method and the Transit method Measure distance to star (later) and using apparent magnitude get luminosity (assumes the star is a normal star) Use luminosity to determine stars mass (m1, suns) (mass needs to be consistent with star s spectral type) Doppler or Transit method gives you periodicity of the orbit (P, measured in years) Use Kepler s law (next slide) to determine the distance between the planet and star (next slide) a in AU [assume mass of planet is much less than the mass of the star, i.e., m2 << m1] Use the Doppler method to measure velocity of star (v1) as it orbits around the center of mass. Use star s velocity (v1) to determine the mass of the planet (m2 or m planet ) using m1 * v1 = m2 * v2 where v2= 2*pi * a /P This is a plot of the log (base 10) of a stars luminosity (L) relative to the luminosity of our sun on the y axis as a function of the mass of the star on the x axis (relative to our suns mass). So a star that is 100x of our sun will have a mass that is ~3.7 times that of our sun 22

23 Kepler s laws 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 P 2 = a 3 / (m 1 + m 2 ) P = orbital period (years) a = Distance between the two bodies (expressed in astronmical units [AU] distance from earth to sun) 1 AU = sun diameters or 215 sun s radius m 1, m 2 = mass of the two bodies orbiting each other (solar masses) 23

24 Density of hot Jupiters ~ 1 gr/cc Density of terrestrial planets (like earth) ~ 5 gr/cc 24

25 Habitable zones is the distance from a star that is the right temperature to support life as we know it Depends on the size of star and stage of life. Temperature allows for liquid water (Earth s T average = about 15C) How do we estimate a planet s temperature Life??

26 Energy balance to estimate a planets temperature Stefan-Boltzmann Law (black body radiation) for the star: Energy/time/area = σ T 4 star σ = a constant (Stefan Boltzmann constant) T star = absolute surface temperature of star (Kelvin) The total surface area of a spherical star is = 4πR 2 star The total energy output by a star, Stellar Luminosity (energy emitted per second) is: L = 4πR 2 star σ T 4 star (this is the same L as you saw before) BUT the energy that is intercepted by the planet with a cross sectional area of πr 2 planet is reduced at the planet distance to the sun ( a ) since the total energy output is spread out on a sphere that is 4πa 2 in area So energy area intercepted by the planet is L/(4πa 2 ) * πr 2 planet But some of this energy is reflected by the planet s albedo, x (reflectivity) and so the intercepted energy is reduced by a factor of (1-x) The planet re-emits this energy as a black body as 4πR 2 planet σ T 4 planet SO 4πR 2 planet σ T 4 planet =(1-x)* L/(4πa 2 )*πr 2 planet 26

27 Solve for the temperature of the planet. T 4 planet =(1-x)* L/(16πa 2 * σ) Star Temperature T star [K] Radius, R star Luminosity L Planet Distance to star, a Albedo of the planet is x Temperature T planet [K] Radius, R planet Energy radiated out by the planet is 4πR 2 planet σ T 4 planet Energy radiated out by the star and absorbed by the planet is (1-x)* L/(4πa 2 )*πr 2 planet 27

28 Stars and planets appear to be black body radiators The wavelength at maximum radiation changes with temperature λ max = 550 nm 5300 K temperature for our sun. λ max x Temperature = constant = 2.9x10 6 nm- K Or = 2.9x10 7 A- K = 2.9x10 3 µm-k Nm[=] nanometers for wavelength Or A [=] Angstrom units for wavelength Or µm [=] microns units for wavelength K [=] degrees Kelvin 28

29 Another way to look at black body radiation Plot log λ (x axis) vs log of spectral intensity at that λ

30 Spectral class of stars O B A F G K M L Red Dwarfs (failed stars) T Brown Dwarfs (failed stars) 30

31 Detection Circumstellar disks Herbig Ae/Be stars, T Tauri stars Dust left over from making planets surround many stars Gives off infrared radiation (heat) Many accretion disks seen in current star birth regions Disk in Orion nebulea

32 Detecting planets by their effects on disks This is the only way to detect planets in the process of formation. nomy/education/fall08/scalo/se cure/309l_sep23_planets.pdf

33 Simulations of the birth of planets Distance from star is horizontal axis (1=earth / sun distance) Mass on vertical axis (1= earth s mass) Each dot is a simulation Evolution of 3000 protoplanetary disks shown Gas Giants Hot Jupiters Terrestial planets (earth like) Ice giants

34 Conservation of angular momentum and spin up of stars and planets As huge intersteller clouds condense, their slight amount of angular momentum must be conserved. Like a ice skater, the condensed cloud spins faster as it becomes smaller. Once the cloud becomes a star, it should spin much more rapidly than we see stars spinning (for example our sun rotates once every 24.5 days) So where did all the angular momentum go? Into the planets around the star. If all the angular momentum of the planets in our solar system goes into the sun, then the sun would rotate once in less than a second!!!! -- It would spin apart!! The lack of star rotation has been a fundamental problem in astrophysics that has been solved by discovery of planets around most stars 34

35 Conservation of angular momentum 35

36 Formation of planets

37 Hertzsprung-Russell Diagram D are white dwarfs (super hot carbon stars) L T Y axis is always brightness or relative luinosity X axis is always temperature, color or spectral class Each dot is a star 37 A is the location of our sun on the main sequence B are red giant stars that are fusing helium in their core C are red supergiants with Helium and Hydrogen buring in shells and carbon in its core

38 38 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).

39 Low mass star like our sun stops at carbon formation...

40 And fluffs off its outer layers to make a planetary nebulae and a white dwarf star....but does not necessarily makes the stuff needed for making planets

41 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 and...

42 It goes boom!!!!... A supernovae!!! (this is the Crab Nebulae) Which make lots of heavy elements needed to make terrestial (earth like) planets.

43 .. And it spreads heavy elements throughout space to be picked up by a new generation of stars,...

44 .. The shock wave either from the supernovae or from the initial star formation stage can initiate new star formation,... And planet formation

45 Herbig Ae/Be stars Defined as a group of stars by George Herbig (University of Hawaii) A star is a protostar before it is a main sequence star. They are hot because of the energy of cloud collapse (gravitational potential energy). There are three different types of protostars: T-Tauri star the lightest (becomes F, G, K, M stars) Herbig Ae/Be stars (B and A type stars) Very heavy protostars. Herbig Ae/Be stars start burning hydrogen quickly compared to T-Tauri stars. It appears as a normal star surrounded by dust. The dust hasn t had time to form planets or planetoids, fall on the star or be blown away by stellar winds yet. Herbig Ae/Be stars: A or B type stars Excess IR (infrared) radiation in their spectra (Dust re-emitting energy as heat) Hα emission (HII ionized hydrogen) In star forming regions Surrounded by what we now know are proto-planetary/accretion disks, envelopes 45

46 The spectrum of Herbig Ae/Be stars will appear as a normal young star, but a large amount of infrared (from the dust surrounding the star) is added. ontributions/monday/waters_herbigstars-2014.pdf

47 Herbig Ae/Be stars Pre-main sequence evolutionary tracks on HR diagram 2 to 8 solar masses Excess IR radiation from disk Mass of star (6.0 and 5.0 solar masses arrowed) 47 ontributions/monday/waters_herbigstars-2014.pdf Our sun

48 More mechanisms for star / planet formation Colliding galaxies The chainsaw or tadpole galaxy

49 Hot new stars forming in a galaxy HII regions Pick color in this photo.

50 FU Orionis, TW Hya 2M1207 CoRoT-2 HD b ---- Near pre-main sequence star with a disk --- the closest T Tauri star to our Solar System -- a brown dwarf in the constellation of Centaurus -- a yellow dwarf main sequence star a little cooler than the Sun -- an extrasolar planet that orbits star HD in Pegasus -- an extrasolar planet in the constellation of Vulpecula HD b Kepler-7b-- one of the first five exoplanets to be confirmed by Kepler spacecraft GJ 1214b -- is an exoplanet that orbits the star GJ 1214 Beta Pictoris --is the second brightest star in the constellation Pictor. Fomalhaut -- is the brightest star in the constellation Piscis Austrinus HR a young (~30 million-year-old) main-sequence star WISE is a binary brown-dwarf system in the southern constellation Vela Gliese 229B--a red dwarf about 19 light years away in the constellation Lepus LP A brown dwarf located in the constellation Fornax N159 --active starbirth region in the Large Magellanic Cloud (LMC) M20 ---The Trifid Nebula (catalogued as Messier 20 or M20 ) 50

51 FU Orionis a variable star in the constellation of Orion, that in 1937 rose in apparent visual magnitude from 16.5 to 9.6, and has since been around magnitude 9. For a long time it was considered unique, but in 1970 a similar star, V1057 Cygni, was discovered, and a number of additional examples have been discovered since then. These stars constitute the FU Orionis class of variable stars, GCVS type FU, often nicknamed FUors. These stars are pre main sequence stars which display an extreme change in magnitude and spectral type. FU Orionis variables (small number) are all are F or G supergiant stars with wide absorption lines, have P Cygni structure at H-α (blue-shifted spectral lines that indicate the expulsion of material), have displaced shell components, and show strong Li I λ6707. In addition, all possess strong infrared excess and are associated with arc-shaped reflection nebulae, which become visible as the star brightens. Young stars pushing dust and gas out of the way and reveling the star s light 51

52 TW Hya TW Hydrae is an orange dwarf star approximately 176 light-years away in the constellation of Hydra. The star is the closest T Tauri star to the Solar System. TW Hydrae is about 80% of the mass of the Sun, but is only about 5-10 million years old. From a wide variety of previous observations from the infrared to submillimeter, TW Hya is known to have a hot inner disk extending to radii < 4 AU, which is optically thin in the IR, and a larger cold dust disk out to about 200 AU. Recent optical interferometry finds that TW Hya also contains a hot optically thick disk on even smaller size scales of ~0.5 AU, and suggests that the optically thin disk could be due to gas clearing by a planet. TW Hya is apparently still accreting from its disk at a rate of about (4-20) x Msun/year and the most recent estimates of its spectral type, mass, are M2.5V, 0.4 Msun, 52

53 2M1207 a brown dwarf located in the constellation Centaurus; a companion object, 2M1207b, may be the first extrasolar planetary-mass companion to be directly imaged, and is the first discovered orbiting a brown dwarf. 2 2M1207 was discovered during the course of the 2MASS infrared sky survey: hence the "2M" in its name, followed by its celestial coordinates. With a fairly early (for a brown dwarf) spectral type of M8, it is very young, and probably a member of the TW Hydrae association. Its estimated mass is around 25 Jupiter masses. The companion, 2M1207b, is estimated to have a mass of 3 10 Jupiter masses. Still glowing red hot, it will shrink to a size slightly smaller than Jupiter as it cools over the next few billion years. 53

54 CoRoT-2 a yellow dwarf main sequence star a little cooler than the Sun. This star is located approximately 930 light-years away in the constellation of Aquila. The apparent magnitude of this star is 12, which means it is not visible to the naked eye but can be seen with a medium sized amateur telescope on a clear dark night. + "2MASS J , is a true physical companion of spectral type K9, making CoRoT-2 a wide binary system with at least one planet. " 54 This is a visible light image.

55 HD b HD b (sometimes though unofficially named Osiris) is an extrasolar planet that orbits the star HD in the constellation Pegasus, some 150 light-years from Earth's solar system. The radius of the planet's orbit is 7 million kilometres, about astronomical units, or one eighth the radius of Mercury's orbit. This small radius results in a year that is 3.5 Earth days long and an estimated surface temperature of about 1,000 C (about 1,800 F). Its mass is 220 times that of Earth (0.69 Jupiter masses) and its volume is some 2.5 times greater than that of Jupiter. The high mass and great volume of HD b indicate that it is a gas giant.

56 HD189733b an extrasolar planet approximately 63 light-years away from the Solar System in the constellation of Vulpecula, the Fox. The planet was discovered orbiting the star HD A on October 5, 2005, when astronomers in France observed the planet transiting across the face of the star. With a mass 13% higher than that of Jupiter, HD b orbits its host star once every 2.2 days at an orbital speed of kilometres per second (341,000 mph), making it a hot Jupiter with poor prospects for life as we know it. Being the closest transiting hot Jupiter to Earth, HD b is a subject for extensive atmospheric examination. HD b was the first extrasolar planet for which a thermal map was constructed, to be detected through polarimetry, to have its overall colour determined (deep blue), to have a transit detected in x-ray spectrum and to have carbon dioxide in its atmosphere. In July, 2014, NASA announced finding very dry atmospheres on three exoplanets (HD b, HD b, WASP-12b) orbiting Sun-like stars. 56

57 Kepler-7b one of the first five exoplanets to be confirmed by NASA's Kepler spacecraft, and was confirmed in the first 33.5 days of Kepler's science operations. It orbits a star slightly hotter and significantly larger than the Sun that is expected to soon reach the end of the main sequence. Kepler-7b is a hot Jupiter that is about half the mass of Jupiter, but is nearly 1.5 times its size; at the time of its discovery, Kepler-7b was the second most diffuse planet known, surpassed only by WASP-17b. It orbits its host star every five days at a distance of approximately 0.06 AU (9,000,000 km; 5,600,000 mi). It is the first extrasolar planet to have a crude map of cloud coverage. 57

58 GJ 1214b is an exoplanet that orbits the star GJ The parent star is 42 light-years from the Sun, in the constellation Ophiuchus. The planet was discovered in December It is a super- Earth because it is larger than Earth but has a mass and radius significantly less than those of the gas giants in the Solar System. After COROT-7b, it was the second such planet to be known and is the first of a new class of planets with small size and relatively low density. GJ 1214 b is also significant because its parent star is relatively near the Sun and because it transits (crosses in front of) that parent star, which allows the planet's atmosphere to be studied using spectroscopic technologies. 58 In December 2013, NASA reported that clouds may have been detected in the atmosphere of GJ 1214 b T

59 Beta Pictoris is the second brightest star in the constellation Pictor. It is located 63.4 light years from our solar system, and is 1.75 times as massive and 8.7 times as luminous as the Sun. The Beta Pictoris system is very young, only 8 20 million years old, although it is already in the main sequence stage of its evolution. Beta Pictoris is the title member of the Beta Pictoris moving group, an association of young stars which share the same motion through space and have the same age. Beta Pictoris shows an excess of infrared emission compared to normal stars of its type, which is caused by large quantities of dust and gas (including carbon monoxide) near the star. Detailed observations reveal a large disk of dust and gas orbiting the star, which was the first debris disk to be imaged around another star. In addition to the presence of several planetesimal belts and cometary activity, there are indications that planets have formed within this disk and that the processes of planet formation may still be ongoing. Material from the Beta Pictoris debris disk is thought to be the dominant source of interstellar meteoroids in our solar system. 59 Is this a Herbig Ae/Be object? maybe but probably not too light

60 is the brightest star in the constellation Piscis Austrinus and one of the brightest stars in the sky. It is a class A star on the main sequence approximately 25 lightyears (7.7 pc) from Earth as measured by the Hipparcos astrometry satellite. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. It is classified as a Vega-like star that emits excess infrared radiation, indicating it is surrounded by a circumstellar disk. Fomalhaut, K-type star TW Piscis Austrini and M-type star LP constitute a trinary system. Fomalhaut holds a special significance in extrasolar planet research, as it is the center of the first stellar system with an extrasolar planet candidate (Fomalhaut b) imaged at visible wavelengths. The image was published in Science in November Fomalhaut is the third brightest star known to have a planetary system (as viewed from Earth), after Pollux and the Sun. 60 Fomalhaut

61 It is a young (~30 million-year-old) mainsequence star located 129 light years (39 parsecs) away from Earth in the constellation of Pegasus, with roughly 1.5 times the Sun's mass and 4.9 times its luminosity. It is part of a system that also contains a debris disk and at least four massive planets. Those planets, along with Fomalhaut b, were the first extrasolar planets whose orbital motion was confirmed via direct imaging. The designation HR 8799 is the star's identifier in the Bright Star Catalogue. The star is a Gamma Doradus variable: its luminosity changes because of non-radial pulsations of its surface. The star is also classified as a Lambda Boötis star, which means its surface layers are depleted in iron peak elements. This may be due to the accretion of metal-poor circumstellar gas. It is the only known star which is simultaneously a Gamma Doradus variable, a Lambda Boötis type, and a Vega-like star (a star with excess infrared emission caused by a circumstellar disk). HR 8799 Is this a Herbig Ae/Be object? Probably not too light 61

62 WISE Luhman 16 (WISE , WISE J ) is a binary brown-dwarf system in the southern constellation Vela at a distance of approximately 6.6 light-years (2.0 pc) from the Sun. They are the closest known brown dwarfs, and the closest system found since the measurement of the proper motion of Barnard's Star in The primary is of spectral type L8±1 and the secondary of type T1±2 (and is hence near the L T transition). Luhman 16 A and B orbit each other at a distance of about 3 AU[2] with an orbital period of approximately 25 years. 62

63 Gliese 229B 63 Gliese 229 (also written as Gl 229 or GJ 229) is a red dwarf star with a brown dwarf companion about 19 light years away in the constellation Lepus. The red dwarf has 58% of the mass of the Sun, 69% of the Sun's radius, and a very low projected rotation velocity of 1 km/s at the stellar equator. A substellar companion was discovered in 1994 and confirmed in 1995 as Gliese 229B, one of the first two instances of clear evidence for a brown dwarf, along with Teide 1. Although too small to sustain hydrogenburning nuclear fusion as in a main sequence star, with a mass of 20 to 50 times that of Jupiter (0.02 to 0.05 solar masses), it is still too massive to be a planet. As a brown dwarf, its core temperature is high enough to initiate the fusion of deuterium with a proton to form helium-3, but it is thought that it used up all its deuterium fuel long ago. This object now has a surface temperature of 950 K..

64 LP LP is a dim brown dwarf of spectral class M9, located about 21 light-years distant from the Solar System in the constellation of Fornax. With a visual apparent magnitude of 18, it has one of the dimmest visual magnitudes listed on the RECONS page. Chandra has detected the first flare from a brown dwarf, or failed star. For most of the observation there were no X-rays from the brown dwarf (left panel), then the brown dwarf turned on with a bright X-ray flare (right panel). The energy emitted in the flare was comparable to a small solar flare and is thought to be produced by a twisted magnetic field. 64 LP is one of the best studied brown dwarfs because it is only 16 light years from Earth. It is about 500 million years old and has a mass that is about 60 times that of Jupiter, or 6 percent of the Sun's mass. The brown dwarf's diameter is about one-tenth that of the Sun and it has a rotation period of less than five hours. X-ray light curve Illustration

65 N159 Hubble Space Telescope view of a turbulent cauldron of starbirth, called N159, taking place 170,000 light-years away in our satellite galaxy, the Large Magellanic Cloud (LMC). Torrential stellar winds from hot newborn massive stars within the nebula sculpt ridges, arcs, and filaments in the vast cloud, which is over 150 light-years across. Visible in the above picture are bright newborn stars, dark filaments of dust, and redglowing hydrogen gas. The aptly named Papillon Nebula (French for butterfly), is the unusual central compact cloud, highlighted in the inset. Reasons for the bipolar shape of the Papillon Nebula are currently unknown, but might indicate the presence of unseen high-mass stars and a thick gaseous disk. Will likely be Herbig stars in the near future. 65

66 M20 The Trifid Nebula (catalogued as Messier 20 or M20 and as NGC 6514) is an H II region located in Sagittarius. It was discovered by Charles Messier on June 5, Its name means 'divided into three lobes'. The object is an unusual combination of an open cluster of stars; an emission nebula (the lower, red portion), a reflection nebula (the upper, blue portion) and a dark nebula (the apparent 'gaps' within the emission nebula that cause the trifurcated appearance; these are also designated Barnard 85). Viewed through a small telescope, the Trifid Nebula is a bright and peculiar object, and is thus a perennial favorite of amateur astronomers. 66

67 Planet formation FU Orionis Variables Herbig Ae/Be stars Brown Dwarfs Protoplanetary disks Debris disks H I/II regions Molecular clouds Exoplanets including Gas giants Terrestrial planets Super Earths Mini-Nepturnes Hot Jupiters Topics Stellar evolution Spectral feataures Black body radiation H-R diagram transitions Protostars Kepler s laws Parallex Distance Modulus Spectroscopic Parallex Radial velocity and transit timing Methods to determine planets properties Calculate surface temperature to determine hatability 67

68 68 Measuring Distances First brightness of stars

69 Brightness of Stars 69 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 Absolute magnitude (M) Magnitude of a star when viewed from a fixed distance Most abs magnitudes will be a negative number (bright)

70 70 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 The apparent magnitude of a full moon is 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

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72 72 Distances Astronomical unit. Average distance between the earth and our sun. (AU = 1.496x10 11 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 = 9.46x10 15 meters, 6.33x10 4 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 = 2.06x10 5 AU = 3.086x10 16 meters Kiloparsecs (Kpc) 1000 parsecs (10 3 parsecs) Megaparsecs (Mpc) 1 million parsecs (10 6 parsecs)

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74 Geometric parallax Gold standard for distances 1 Parsec = 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 74

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76 Spectroscopic Parallax 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 parsecs. 2. Using the star spectra, 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 below) 4. Measure the apparent magnitude (m). Knowing the apparent magnitude (m) and absolute magnitude (M) of the star, one can calculate the distance (d, 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.

77 Relationship between absolute and apparent magnitude and distance Distance modulus is m-m 77 The larger the distance modulus the further away the object is. Little m is usually >+10 Capital M is usually small some times negative,

78 78 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 = x 10 8 km Diameter of our sun = x10 6 km 1AU = sun diameters What is distance modulus for our sun?

79 Categorizing stars by their spectra 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 nebulae glowing gas clouds

80 Full spectrum from gamma rays to very long radio waves 80 Black body radiation is applicable across the whole spectrum An object emitting radio waves is very cold An object emitting xrays is very hot.

81 More on stars spectral class 81

82 Spectral class of stars He+ lines 82 H Balmer lines (B,A & F stars) Ca+ lines (F & G stars) Fe and neural metals K & M stars) TiO2 lines

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84 Hydrogen is the most common material in the Universe. There are three states of hydrogen, HI/ HII emissions / HI - unionized form of atomic hydrogen HII - ionized form of hydrogen regions H2 - molecular hydrogen HI is typically detected at the 21-cm wavelength using radio telescopes. This is used to map the shape of our galaxy. HII is typically seen as Hα lines (656.3 nm) regions exist mostly in the disk of a spiral galaxy. There must be a source to provide the ionizing heat required to strip the electron, HII regions are common near very hot stars ~10,000K. O, B and white dwarfs are hot enought These are called emission nebula. These are areas of starbirth and are strong in UV radiation. Newly formed stars within the spiral of galaxy are literally blown away from its association with other stars formed in the same "nursery." A great example of this is the Orion Nebula. Old galaxies - like elliptical type galaxies - will have little HII regions as star birth and supernova would have either used up or cleared away these areas. 84

85 Hot new stars forming in a galaxy HII regions In the spiral arms of a galaxy Pink color in this photo.

86 More info 86 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).