1 2016 Div. C (High School) Astronomy Help Session Sunday, Feb 21, 2016 and and formation Scott Jackson Mt. Cuba Astronomical Observatory

• SO competition on March 5th . • 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 2 weeks (Sunday, Feb 21) before competition at Mt. Cuba 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 Exo Scott Jackson About 25 ago, planets and solar systems thought to be unique – Now, 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 – – distance from the stars they are orbiting – densities How and why they are formed. What does the future hold – Far more powerful tools being developed How to define “planet”? , and the way in which it was formed 1. Star: massive enough for nuclear fusion H  He; M > 0.1 Msun. Light comes from heating by nuclear fusion. Formed by interstellar (molecular) cloud collapse 2. : 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 ~ 10 - 20 MJup. Lower mass limit not too relevant. 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. classified by what they resemble most in our own solar system. (or “gas giants”); (~ 20 Mearth); and Super- (~ 5-10 Mearth). When we refer to (yet to be discovered) extrasolar planets whose masses are similar to , they are called “terrestrial-like” or “Earth-like” or “rocky” planets How do you define “planet”? Current Planet Counts

•Total Discoveries 5429 •Confirmed Exoplanets 1624 •Exoplanet Candidates (Keplar) 4696 • 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. • The exact number is different from different sources

http://exoplanets.org/ Rate of discovery

Most found using the the Transit method (Keplar satellite)

http://exoplanetarchive.ipac.caltech.edu/exoplanetplots/exo_dischist.png Kepler candidates and confirmed planets

Jupiter

Earth http://exep.jpl.nasa.gov/presentations/blackwoodJHU/JHU_Astrobiology_Blackwood.pdf Planets found in the habitable zone (green and white areas in this plot)

Venus Earth Mars ~1500 confirmed discovered (and growing) Lots of hot 's-- Large planet traveling close to their star. First one discovered orbiting a star in 1995 ( b). ~1/3 of like stars have earth like planets(!)

http://exoplanets.org/table Solar Systems? – yes! • About 17% of stars with planets contain more than one planet (artist diagram of next to our solar system is below)

http://en.wikipedia.org/wiki/Image:Extrasolar_planet_NASA2.jpg Atmospheres? – Yes! e.g., Around WASP-43b

Water or

https://www.youtube.com/watch?v=rnLD2XAZxFk • Astronomers can not easily “see” an Detection exoplanet directly • Does not shine • Glare of the star hides stars • Must use “indirect” methods** • **HR8799, HD106906b, and HD95086 are exceptions 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 • Near-infrared Keck adaptive optics images of the HR8799 system from Marois et al. (2010). Four giant planets, 3 to 7 times the mass of Jupiter, are visible in near-infrared emission

Detection

http://www.mpia.de/homes/ppvi/chapter/fischer.pdf Detection • : • 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 http://en.wikipedia.org/wiki/Extrasolar_planet#Detection_methods Detection • 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 • Can only be observed oncehttp://planetquest.jpl.nasa.gov/documents/RdMp272.pdf (No repeats!) 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 http://exoplanets.org/doppframe.html Transit method: • If the plane of a planet’s is along our line of sight, the planet will go in front of the star Detection • 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 – ? – ? • Best if: 1. Star is big 2. Planet is big (Hot Jupiters) 3. Planet is close to star 4. View orbit nearly edge on http://www.iac.es/project/tep/tephome.html • Plot has Limit of techniques – Size of orbit on horizontal axis – Mass of planet on vertical axis Wide-Field – Yellow dots are simulations of WFIRST. Infrared Survey Telescope (microlensing)

http://wfirst.gsfc.nasa.gov/exoplanets_microlensing.html Measuring mass (and density) of exoplanets Need to use Doppler method and the Transit method

• Measure distance to star (later) and using get (assumes the star is a normal star) • Use luminosity to determine stars mass (m1, ) (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] This is a plot of the log (base 10) • Use the Doppler method to measure velocity of of a stars luminosity (L) relative to the luminosity of our sun on star (v1) as it around the center of mass. the y axis as a function of the Use star’s velocity (v1) to determine the mass of mass of the star on the x axis the planet (m2 or mplanet) using (relative to our suns mass). So m1 * v1 = m2 * v2 where v2= 2*pi * a /P a star that is 100x of our sun will have a mass that is ~3.7 times that of our sun 24 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 2 3 P = a / (m1 + m2) P = (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) 25 Density of hot Jupiters ~ 1 gr/cc

Density of terrestrial planets (like earth) ~ 5 gr/cc

26 • “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 Taverage = about 15C) • How do we estimate a planet’s temperature?

Life?? Energy balance to estimate a planets temperature Stefan-Boltzmann Law (black body radiation) for the star: 4 – Energy/time/area = s T star s = a constant (Stefan Boltzmann constant)

Tstar= absolute surface temperature of star () 2 • The total surface area of a spherical star is = 4pR star • The total energy output by a star, Stellar Luminosity (energy emitted per second) is: 2 4 – L = 4pR star s T star (this is the same L as you saw before) • BUT the energy that is intercepted by the planet with a cross sectional area 2 of pR planet is reduced at the planet distance to the sun (“a”) since the total energy output is “spread out” on a sphere that is 4pa2 in area 2 2 • So energy area intercepted by the planet is L/(4pa ) * pR 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) 2 4 • The planet re-emits this energy as a black body as 4pR planet s T planet 2 4 2 2 • SO… 4pR planet s T planet =(1-x)* L/(4pa )*pR planet

28 Solve for the temperature of the planet…. 4 2 T planet =(1-x)* L/(16pa * s) Star Planet

Temperature Tstar [K] Distance to star, a

Radius, Rstar Albedo of the planet is x

Luminosity L Temperature Tplanet [K]

Radius, Rplanet

Energy radiated out by the planet is 2 4 4pR planet s T planet

Energy radiated out by the star and absorbed by the planet is 2 2 (1-x)* L/(4pa )*pR planet

29 Stars and planets appear to be black body radiators The wavelength at maximum radiation changes with temperature

λmax = 550 nm  5300 K temperature for our sun.

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 30 Another way to look at black body radiation

Plot log λ (x axis) vs log of spectral intensity at that λ Spectral class of stars • O • B • A • F • G • K • M • L Red Dwarfs (failed stars) • T Brown Dwarfs (failed stars)

32 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??

33 https://en.wikipedia.org/wiki/Color_index UBV, UBVRI and JHK systems for Color-color diagrams

34 • Trapezium cluster in M42, the Orion Nebulae

Optical image

Infrared image showing stars that were obscured 35 Infrared Color-color diagram for the Trapezium in M42

Dotted lines indicate normal redding of stars The solid line not due to a is the main surrounding the star sequence. Stars are points. Infrared excess is indicated by the stars being to the right of the dotted lines

36 Infrared color-color diagram for classical T Tauri Stars (CTTS), Weak T Tauri Stars (WTTS) and protostellar candidates (Class I sources)

• Strong infrared excess indicates dust disks around CTTS and Class I sources. • Weak T Tauri Stars (WTTS) fall within the star redding band – no excess infrared and likely not to have dust disks around them

37 Estimating a stars temperature from the UBV color system.

• Color temperature of a star can be estimated from the B-V :

• So a B-V of 0 [~ A star] would give a temperature of 10125 K • So a B-V of 1 [late K star] would give a temperature of 4752 K

https://en.wikipedia.org/wiki/Color_index

38 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 disks seen in current star birth regions

Disk in Orion nebulea

http://planetquest.jpl.nasa.gov/documents/RdMp272.pdf Detecting planets by their effects on disks This is the only way to detect planets in the process of formation.

http://www.as.utexas.edu/astro nomy/education/fall08/scalo/se cure/309l_sep23_planets.pdf 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

http://planetquest.jpl.nasa.gov/documents/RdMp272.pdf 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 42 Conservation of angular momentum

43 Formation of planets Y axis is always 45 Hertzsprung-Russell Diagram brightness or relative luinosity 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 stars that are fusing helium in their core C are red L supergiants with T Helium and Hydrogen buring in http://outreach.atnf.csiro.au/education/senior/cosmicengine/stars_hrdiagram.html shells and carbon in D are white dwarfs (super hot carbon stars) its core 46 The birth of a 1 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 for a 1 solar mass star). Low mass star like our sun stops at carbon formation.... And fluffs off its outer layers to make a planetary nebulae and a star. ....but does not necessarily makes the stuff needed for making planets 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..... It goes boom!!!!... A supernovae!!! (this is the Crab Nebulae) … Which make lots of heavy elements needed to make terrestial (earth like) planets. .. 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 stage can initiate new star formation,..... And planet formation Herbig Ae/Be stars 53 • 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 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.

https://www.eso.org/sci/meetings/2014/Haebe2014/C ontributions/Monday/Waters_herbigstars-2014.pdf Herbig Ae/Be stars 55 • Pre-main sequence evolutionary tracks on HR diagram • 2 to 8 solar masses Mass of star (6.0 and 5.0 solar • Excess IR radiation from disk masses arrowed)

Our sun https://www.eso.org/sci/meetings/2014/Haebe2014/C ontributions/Monday/Waters_herbigstars-2014.pdf 56 Infrared color-color diagram for Herbig Ae/Be stars

• Strong infrared excess indicates dust disks • The open triangles and diamonds are models of the Herbig Ae/Be stars More mechanisms for star / planet formation

• Colliding • The “chainsaw” or “tadpole” Hot new stars forming in a

galaxy HII regions Pick color in this photo. 59

• T Tauri --- first of a class of stars recognized to be pre-main sequence • HL Tauri ---a very young T Tauri type of star • AB Aurigae--A star with a dust disk possibly a condensing planet or brown dwarf • HAT-P-11b -- An exoplanet orbiting HAT-P-11 with water vapor detected • 51 Pegasi -- Main sequence star with a orbiting it • WASP-43b-- Very hot Jupiter, Atmosphere mapped using Hubble • WASP-18b-- Hot Jupiter, orbit decaying and destroying the planet in a 106 yrs • HD 106906b-- Planet at an extreme distance from its star. • WISE 0855-0714-- One of the closest known failed stars (a brown dwarf) • 2MASSJ22282889-431026-- Failed star with wind driven planet size clouds First time clouds observed on a planet • M42 --Orion’s Nebulae Hot bed of new star birth • Barnard 68-- A dark cloud (Bok globules) that can be birth place for stars • 55 Cancri-- A with one component having a solar system • Kepler-186--M1 dwarf star with a solar system. One planet may be in the habital zone • HD 95086--Pre-main sequence star with debris fields separated by a planet • GD 165 --Two dwarf stars, one white, one brown (or a failed star) L4 spectral type • HR 8799-- star with 4 known planets detected by direct imaging. 60 • T Tauri was the first of a class of pre-main-sequenceT Tauri 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 (M☉), These stars are pre–main sequence stars which display an extreme change in magnitude and spectral type. They are stars in the process of being “born”

They are found near molecular clouds and are known by their variability in optical wavelengths and show emission lines indicating the presence of a – a layer in the star above the . 61 HL Tauri • Is a very young T Tauri type of star. It is in the of Taurus (the bull – as is T Tauri). Less than 100,000 years old. It has a that shows bands that may indicate the presence of planets in the process of forming.

Taurus . HL Tauri is shrouded near the region indicated by the arrows.

submillimeter image of HL Tauri AB Aurigae 62 • AB Aurigae is a star in the constellation that is about 455 lights years away. It is better known for hosting a dust disk that may harbor a condensing planet or brown dwarf. The star could host a possible substellar companion in wide orbit. • The star is about 45 times the brightness of our sun and about 2.5 times the mass of our sun. There is great uncertainty in these values since the star is shrouded in some dust. • We see a face on view of the disk surrounding AB Auriga. • It was taken in infrared light that can see the debris disk surrounding the star. • The disk is about 210 AU in diameter • The green band is a gap in the disc at about 100 AU that would indicate a yet to be found planet or brown dwarf. HAT-P-11b or Kepler-3b • An exoplanet orbiting HAT-P-11. The planet was discovered using the transit method • It is 120 light years away in the constellation of Cygnus. • The orbital period is five days. • Water vapor was detected on the planet presumably as a result of an atmosphere that contained significant amounts of water.

A recurring spike in the light curve (below) has been interpreted as a star spot. 51 Pegasi 64 • A sun like star in that is 51 light years away. It was one of the first main- sequence star to have a planet orbiting it. • The star is about 6 to 8 billion years old. • It is slightly bigger (25%) than our sun and slightly more massive (11%) than our sun. • In 1995 a planet was discovered using the method. • The planet 51 Pegasi b is considered a hot Jupiter. At the time is was discovered, it was thought that hot Jupiters could not exist. • It has a mass of about 0.5 Mjup and is 0.05 AU from the star • The planet has an orbital period of 4.2 days(!) • It has an estimated surface temperature of 1280 K. • This discovery of a hot Jupiter caused more astronomers to look for similar planets. WASP-43b 65 • Is a transiting planet around the star WASP-43. It is 260 light years away in the constellation of Sextons. • It is a hot Jupiter with a mass about 2 Mjup, an orbital period of 0.81 days, at a distance from the star of 0.0142 AU (!) and an estimated day side temperature of 1725 K and a night temperature of less that 700 K. • It has one of the shortest orbital periods ever measured. • It has an atmosphere mapped by the Hubble (below) Its orbit is decaying so that it will eventually be “consumed” by the star.

http://hubblesite.org/newscenter/archive/releases/201 4/28/image/a/format/web/ WASP-18b 66 • is an exoplanet that orbits the star WASP-18. • It is considered a hot Jupiter with a mass of about 10 Jupiter masses and about 1.1 times the diameter of Jupiter. • The star is about 325 light years away. • The planet is only 1.9 million miles from the star and is expected to merge with the host star in less than a million years.

Artist created T HD 106906 b 67 • Is a exoplanet that was discovered by direct imaging. It is a planet of star HD 106906. • It is 300 light years away in the constellation of . • It is estimated to be about 11 times the mass of Jupiter. • It is much further (at 650 AU) away from its star – much more than thought possible for the normal mechanism for planet formation. • It is the only planet known to be orbiting HD 106906. • HD 106906 is a pre- main sequence star that is about 1.5 times the mass of our sun and 6 times its luminosity. • There is a debris disk that is much smaller than the orbit of the planet. 68 WISE 0855-0714 • A brown dwarf (failed star) that is 2.3 away in the constellation of Hydra. • Discovered using the wide field infrared Survey Explorer satellite. • Has a very high (3rd highest) of 8130 milliarcseconds / (mas) • It is one of the closest brown dwarfs known • It has a surface temperature of ~225 to 260 Kelvin and is one of the coldest brown dwarf discovered. 2MASSJ22282889-431026 69 • A brown dwarf observed by both the Spitzer and Hubble space telescopes. • These combined observations indicate wind driven planet size clouds on this “failed star”. The star rotates every 1.4 hours. • Its temperature is about 600 to 700 Centigrade (900 to 1000 Kelvin) • One of the first time that surface feature (clouds) were “observed” on a object outside our solar system.

Artist imagination M42 70 • The great nebulae in Orion. • Large molecular and dust cloud in the constellation of Orion located about 1500 light years away. It is about 20 light years in size. • Contains a very young called the Trapezium • The region is a hot bed of new star formation (next slide). • Multiple protodisks have been observed indicating new stars with likely planets being formed. (next slide) •. 71 Barnard 68 72 • A dark cloud that obscures the light of stars behind it. Small molecular clouds like this are also called Bok globules. The temperature inside these clouds is only on the order of ten Kelvin. The outer regions can reach temperatures on the order of thousand Kelvin due to illumination by other stars. The main constituent of these clouds is molecular hydrogen, but also a vast range of other molecules are able to form, e.g. CO, NH3, CS, and HCN.

On the left, a composite of images in the optical filters B (blue), V (green), and I (red) is shown, while on the right a false-colour composite of images in the filters B (blue), I (green), and Ks (red) is displayed (Image credit: ESO) https://www.physnet.uni- hamburg.de/services/biblio/dissertation/dissfbPhysik/___Volltexte/Natascha___Rudolf/Natascha___Rudolf.p df 55 Cancri 73 • Is a binary star that is 40 light years away in the constellation of (the crab). One star is a G-type star [G8V] (known as 55 Cancri A and ) while the other is a star (55 Cancri B) . The two stars are gravitationally bound since they have the same proper motion. • There does not appear to be a debris disk around either of the stars. 55 Cancri A is 7 to 10 billion years with the uncertainty due to its high metallic content.

• 5 planets have ben discover to orbit 55 Cancri A. Kepler-186 74 • A main sequence M1 type dwarf star. It is about 490 light years away in the constellation of Cygnus. • It has 5 known planets discovered by the Kepler spacecraft. • The furthest out (Kepler-186f) is slightly larger than the earth but its orbit size is the same size of Mercury. But it is believed to be in the habital zone of the star that is smaller (and cooler) than our sun. 75 HD 95086 • Is a pre-main sequence star. It has a mass of about 1.6 solar masses and is approximately 90 parsecs away in the constellation of Carina. • It has at least one planet that is ~ 56-61 AU away and it has a debris disk. • The planet, denoted as HD 95086b was detected at infrared wavelengths by direct imaging. • One debris disk is next to the star, a cooler debris disk was discovered past the orbit of the planet. Both were detected at submillimeter wavelengths • A system of two “stars” – a 76 white dwarf and a brown dwarf GD 165 – in the constellation of Bootes. It is located about 103 light years away. • GD stands for “Giclas Dwarf” (Giclas was an American astronomer who worked at the Lowell Observatory). • The brown dwarf (designated as GD 165B) is relatively cool – 1800 to 1900 K and is not big enough to have started nuclear fusion. As a result it is not a star. • GD 165B is one of the first brown dwarfs discovered and was assigned a new spectral type of L with a subclass of 4 (or L4 for short). • It has an estimated mass of 0.08 to 0.11 solar masses 77 HR 8799

• A young main-sequence start in the constellation of Pegasus. It is about 130 light years away and about 1.5 times the mass of the sun. It has a debris disk with at least 4 planets embedded in it.

Near infrared image Infared image from Keck Telescope Near-infrared Keck adaptive optics images of the HR8799 system from Marois et al. (2010). Four giant planets, 3 to 7 times the mass of Jupiter, are visible in near-infrared emission

http://www.mpia.de/homes/ppvi/chapter/fischer.pdf Topics 79 • Planet formation • Stellar evolution • FU Orionis Variables • Spectral feataures • Herbig Ae/Be stars • Black body radiation • Brown Dwarfs • H-R diagram transitions • Protoplanetary disks • Protostars • Debris disks • Kepler’s laws • H I/II regions • Parallex • Molecular clouds • Distance Modulus • Exoplanets including • Spectroscopic Parallex – Gas giants • Radial velocity and transit timing – Terrestrial planets Methods to determine planets – Super Earths properties – Mini-Nepturnes • Calculate surface temperature to – Hot Jupiters determine hatability 80

Measuring Distances…

First brightness of stars… 81 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 – (M) • Magnitude of a star when viewed from a fixed distance • Most abs magnitudes will be a negative number (bright) 82 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 83 84

Distances • . 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 • [pc]. The distance to an object that has a 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) 85 • Geometric parallax  Gold standard for distances 86 – 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 87 88 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 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. 89 Relationship between absolute and apparent magnitude and distance  Distance modulus is m-M

The larger the distance modulus the further away the object is. Little m is usually >+10 Capital M is usually small – some times negative, Relationships between distance90 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? 91 Categorizing stars by their spectra

1. Spectra can tell you 2. Absorption (dark) the stars approximate lines in a star’s spectra temperature give a finger print of (blackbody radiation) 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 92 Full spectrum from gamma rays to very long radio waves

• Black body radiation is applicable across the whole spectrum • An object emitting radio waves is very cold • An object emitting xrays is very hot. More on stars spectral class 93 Spectral class of stars 94 He+ lines

H Balmer lines (B,A & F stars)

Ca+ lines (F & G stars)

Fe and neural metals K & M stars)

TiO2 lines 95 96 Hydrogen is the most common material in the Universe. There are three states of hydrogen, HI - unionized form of atomic hydrogen HI/ HII emissions / HII - ionized form of hydrogen H2 - molecular hydrogen regions 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 . 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. Hot new stars forming in a

galaxy HII regions In the spiral arms of a galaxy

Pink color in this photo. 98 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).