The solar wind. or rather: The energy budget of the corona-solar wind system. Øystein Lie-Svendsen
|
|
- Matthew Robbins
- 6 years ago
- Views:
Transcription
1 Introduction Facts The solar wind or rather: The energy budget of the corona-solar wind system Øystein Lie-Svendsen Norwegian Defence Research Establishment and Institute of theoretical astrophysics, University of Oslo, Norway Kodai Winter School, December 2006
2 Introduction Facts Why study the solar wind? The solar wind represents loss of mass and energy (tiny!) from the Sun. The solar wind affects us ( space weather ): disturbances at high latitudes ( magnetic storms ) affecting communications, power transmission, oil installations causes the aurora may damage orbiting satellites harmful to humans in space The solar wind is an exciting physical system in its own right. We still do not understand what drives the solar wind there is work to do!
3 Introduction Facts The solar wind at solar minimum from Ulysses < 1.4 AU 5.4 AU (McComas et al., 2000)
4 Introduction Facts Comparison of minimum and maximum from Ulysses (McComas et al., 2003)
5 Introduction Facts Ulysses mass flux density at solar minimum
6 Introduction Facts Summary of observed solar wind properties Parameter Slow Fast Speed (km/s) km/s km/s Density m m 3 Flux m 2 s m 2 s 1 Helium abundance n α /n p 4% 5% T e K K T p K K Origin streamer boundary? (polar) coronal holes protons at 1 AU are supersonic, c p kt p /m p 30 km/s u wind (hence protons cannot carry information inward) while electrons remain subsonic, kte /m e 1200 km/s u wind (hence electrons may, through heat conduction, carry information inward)
7 Introduction Facts The white light corona T e 10 6 K, slightly less in open regions, slightly more in closed regions.
8 Introduction Facts The corona in the extreme ultraviolet SOHO/EIT, Fe XII 195 Å
9 Introduction Facts Polar coronal holes as seen by SOHO/UVCS Temperatures from line broadening Flow speeds from Doppler dimming (Zangrilli et al., ApJ, 574, 477, 2002) (Cranmer et al., ApJ, 511, 481, 1999)
10 Introduction Facts Escape from the gravitational potential Hence u wind v esc mv esc 2 mm S = G N R S 2GN M S v esc = 620 km/s. R s
11 Introduction Facts The fast wind from coronal holes What do these observations tell us? Protons and ions are much hotter than electrons, indicating strong (?) ion heating. Rapid acceleration of the solar wind, complete within a few solar radii.
12 Introduction Facts An enormous range of scales...
13 Introduction Facts And a transition to supersonic flow
14 Introduction Facts Questions Why is the corona hot, of order 10 6 K? Why do we even have a corona?? Is it a coincidence that the solar wind speed is of order the gravitational escape speed? Is there a relation between the coronal temperature and the wind speed? What does the fast acceleration of the wind say about driving mechanism?
15 Introduction Solar wind energy loss Heat conduction Radiation Energy balance of the corona The fact that the corona is hot either means that it is strongly heated or it cannot easily lose energy unless it becomes hot Hence we must understand not only the sources of energy but equally important the loss mechanisms.
16 Introduction Solar wind energy loss Heat conduction Radiation Sources of energy From the colder chromosphere below? Anomalous heat conduction up the temperature gradient has been proposed ( velocity filtration ), but does not seem to work. Radiative heating? Should rather equilibrate the upper atmosphere temperatures. And what can absorb photons in a fully ionized plasma? Waves from the photosphere? A likely candidate! Sound waves may not carry the required amount of energy, but Alfvén waves may work (Poynting flux dissipation). Release of magnetic energy in the corona (reconnection)? Yes, also possible through nanoflares, and lots of energy available. But no conclusive evidence. Some form of external energy source must exist we still do not know what.
17 Introduction Solar wind energy loss Heat conduction Radiation Losses of energy The possible loss mechanisms are The solar wind carries energy as it flows out. Heat conduction down towards the chromosphere. Radiation either from the corona or from layers below Sources of energy are uncertain, but losses are not uncertain!
18 Introduction Solar wind energy loss Heat conduction Radiation Calculating the energy flux As each particle flows out from the Sun it carries kinetic energy 1 2 m svs 2 gravitational and electric potential energy E pot = G N M S m s ( 1 r 1 R S ) + Q s V E (r) where M S and R S are the mass and radii of the Sun, r the heliocentric distance, Q s the particle charge and V E the electric potential (unspecified yet, but not negligible). ionization energy (13.6 ev per electron-proton pair), which we neglect. (Why?)
19 Introduction Solar wind energy loss Heat conduction Radiation The energy flux density is ( ) 1 F Es = d 3 v v r f s (r, v) 2 m sv 2 + E pot where f s is the velocity distribution function (VDF) and v r the radial component of v. Assuming a drifting Maxwellian VDF, f s = ( ms 2πkT s ) 3/2 exp ( m s(v u s ) 2 ) 2kT s we find F Es = n s u s ( 1 2 m su 2 s kt s + m s V G + Q s V E ) where V G is the gravitational potential.
20 Introduction Solar wind energy loss Heat conduction Radiation Electron-proton flow Adding possible heat conduction, the total electron/proton energy flux is ( 1 F E = n p u p 2 m pup 2 + m p V G + ev E ) 2 kt p + q p +n e u e ( ev E + 5 ) 2 kt e + q e neglecting terms m e. Neglect q p, assume charge neutrality and no current, and T e = T p = T, [ ( 1 1 F E = nu 2 m pup 2 + G N M S m p 1 ) ] + 5kT + q e R S r
21 Introduction Solar wind energy loss Heat conduction Radiation Assume all energy supplied to the wind at r = r 1. Then total energy flux is conserved through any surface beyond r 1. Since also particle flux is conserved, the conservation of F E yields 5kT 1 = 5kT m p(v 2 esc + u 2 2) + q e2 n 2 u 2 q e1 n 1 u 1 where v esc = 2G N /r 1 = 620 km/s at the surface. Neglecting also heat flux and T 2 we get T 1 = 1 ( 10 m pv esc (R S ) 2 RS u 2 ) 2 + r 1 v esc (R S ) ( 2 ( ) ) = R S u 2 2 K + r km/s
22 Introduction Solar wind energy loss Heat conduction Radiation Hence wind requires million degree corona For the fast wind (700 km/s) we then have ( ) T RS K + 1 r 1 With r 1 = 2 R S, T K A high-speed wind driven by thermal heating near the Sun requires a million-degree corona. Even a very slow wind, u 2 0, gives, for r 1 = 2 R S, T K.
23 Introduction Solar wind energy loss Heat conduction Radiation Heavy ions Neglecting the electric potential, the same argument gives the coronal ion temperature or m i T i = 1 m i ( v 2 5 k esc + u2) 2 min(t i ) = 1 m p 5 m p k v esc(r S ) 2 R S r K m i m p R S r 1 Choosing again r 1 = 2 R S, and m i /m p = 16 (oxygen) we get T 1 = K SOHO/UVCS finds that indeed T (oxygen) 10 8 K.
24 Introduction Solar wind energy loss Heat conduction Radiation How much energy does the solar wind need? Scaling the observed solar wind energy flux density at Earth back to the Sun, we find ( ) 1 AU 2 1 F E (R S ) = (nu) E 2 m ( p v 2 esc + ue 2 ) R S With u E = 700 km/s and (nu) E = m 2 s 1, we get F E (R S ) 70 W/m 2. Hence not much compared to the radiative energy flux of (1 AU/R S ) W/m 2 50 MW/m 2...
25 Introduction Solar wind energy loss Heat conduction Radiation Estimating the wind speed Near the Sun each particle (electron-proton pair to be correct) receives energy (1 + a) 1 2 m pv 2 esc, which is converted to potential and kinetic energy at Earth (plus a small amount of thermal energy), (1 + a) 1 2 m pv 2 esc = 1 2 m p(v 2 esc + u 2 E ) where a specifies the excess energy provided. Hence u E v esc = a. Choosing the escape speed at the surface, v esc 620 km/s, we find a = 0.1 u E = av esc 200 km/s. u E = 10 km/s a
26 Introduction Solar wind energy loss Heat conduction Radiation Wind speed (contd.) We should therefore expect the speed of a stellar wind to at least be of order the gravitational escape speed in the region of the atmosphere where most of the energy needed by the wind is supplied. In this simplified picture gravity sets both coronal temperature mpv 2 esc k and the wind speed v esc
27 Introduction Solar wind energy loss Heat conduction Radiation Heat conduction In a collision-dominated fully ionized plasma (such as the low corona) the amount of heat conduction is determined by Coulomb collisions between particles. Cross section σ v v 4 collision frequency ν T 3/2 mean free path T 2 From this you can show that the heat flux in a given temperature gradient is proportional to T 5/2 T. Elaborate calculations give q e = κ e ln Λ T 5/2 T where κ e W m 1 K 7/2 (e.g., Braginskii, 1965) and ln Λ 20 in the corona.
28 Introduction Solar wind energy loss Heat conduction Radiation Heat conduction causes the transition region When the corona is heated, energy flows down towards the chromosphere in the form of heat. With no loss of energy (we discuss radiation later) 5/2 dt q e = κt dz = constant. or dt dz T 5/2. Hence the temperature gradient must steepen as the temperature is reduced towards the chromosphere.
29 Introduction Solar wind energy loss Heat conduction Radiation Energy balance between coronal heating and heat conduction Assume that an energy flux density q 0 (measured at r = R S ) is deposited at the temperature maximum in the corona at a distance r 1 from the Sun centre, and that all of this energy is conducted downwards (no solar wind loss). Also assume radially expanding flow (spherically symmetric Sun). Assuming a constant heat flux and integrating, you find T 1 [ ( 7 q 0 R S 1 R )] 2/7 S 2 κ r 1 as the maximum temperature of the corona.
30 Introduction Solar wind energy loss Heat conduction Radiation Heat conduction as a coronal thermostat Choosing r 1 = 2 R S we find q 0 = 0.1 W/m 2 T 1 = K q 0 = 10 W/m 2 T 1 = K q 0 = 100 W/m 2 T 1 = K q 0 = 50 MW/m 2 (!) T 1 = K Heat conduction works like a thermostat we get a corona of order 10 6 K with almost any heat input!
31 Introduction Solar wind energy loss Heat conduction Radiation Competition between wind and heat conduction We found that if the solar wind were the only energy loss, T 1 (solar wind) 1 G N M S m p R S 5 kr S r K for r 1 = 2 R S. At the same time heat conduction predicts T 1 (heat conduction) [ ( 7 q 0 R S 1 R )] 2/7 S 10 6 K 2 κ r 1 In an open corona, which of these two processes will dominate? Answer: We have to resort to numerical modelling, showing that the solar wind energy loss dominates (Hansteen & Leer, 1995), carrying of order 90% of the energy deposited in the corona.
32 Introduction Solar wind energy loss Heat conduction Radiation Consequences of a dominant solar wind energy loss The energy flux measured at 1 AU should be approximately equal to the actual energy flux deposited in the corona. The wind is not just the evaporating tail of the corona (as is the escape of gas from the Earth s atmosphere), but must have a large impact on the corona. Both the open corona and closed magnetic loops should have temperatures of order 10 6 K. Since T 1 (solar wind) M S /R S, stars with much lower M S /R S should have negligible heat conduction and therefore no transition region and corona.
33 Introduction Solar wind energy loss Heat conduction Radiation Radiation Radiative loss is the conversion of (electron) kinetic energy into photon energy by collisional excitation of an atom or ion. Radiative loss from a fully ionized plasma with no bound electrons is difficult. Maybe the corona doesn t radiate well? If the thermal energy of free electrons is much smaller than the lowest possible excitation energy, the radiative loss should be small too. The most important line, Lyα, caused by the n = 1 to n = 2 excitation of hydrogen, has E = 10.2 ev, corresponding to T E/k = K. But hydrogen is already fully ionized at 10 5 K... At low temperatures, kt E, only electrons in the tail of the Maxwellian can excite the atom, so the rate exp( E/kT ) is extremely sensitive to T.
34 Introduction Solar wind energy loss Heat conduction Radiation The radiative loss rate The loss from excitation of hydrogen can be written L RH = n H n e L H (T e) n 2 el H (T e ) where the last relation can be obtained by assuming balance between ionization and recombination of hydrogen. Similarly for the loss from minor ion excitation, L Ri = n i n e L i(t e ) n 2 el i (T e ). The total radiative loss rate may then to a good approximation be written (T e = T ) L R = n 2 el(t ) = P2 4k 2 T 2 L(T ) where P = 2nkT is the total electron + proton pressure and L(T ) is a function of temperature only.
35 Introduction Solar wind energy loss Heat conduction Radiation Temperature dependence of the loss rate L R (From the model of Fontenla et al., ApJ, 355, 700, 1990.)
36 Introduction Solar wind energy loss Heat conduction Radiation Consequences of the form of the loss rate L R n 2 e small radiative loss in the (outer) corona. L R has a maximum at some T R K, max(l R ) = P 2 L(T R) 4k 2 T 2 R so a heating rate larger than max(l R ) cannot be balanced by radiative loss. L R decreases with T for T > T R system is unstable beyond T R leading to runaway heating. The corona, at T 10 6 K T R, is in the unstable temperature region. Radiation does not matter for the energy balance of the corona.
37 Introduction Solar wind energy loss Heat conduction Radiation Maximum radiative cooling at T R : The chromosphere-corona dividing line If heating is such that T < T R we have a cool chromosphere. If heating is such that T > T R we form a corona. For T > T R runaway heating occurs until either heat conduction (inefficient at T 10 5 K) or the solar wind energy loss kicks in, both requiring T 10 6 K. Once a corona is formed, its very low radiative loss means that even if the heating rate is strongly reduced again, the corona will persist. If heating decreases less rapidly than n 2 e, then beyond some distance r TR the heating will be larger than the maximum radiative cooling rate P 2 L(T R )/(4k 2 T 2 R ).
38 Introduction Solar wind energy loss Heat conduction Radiation When will stars have coronae? In order to have a wind energy loss (without heat conduction) we found that the coronal temperature had to reach the gravitational escape temperature given by 5kT esc = G NM S m p. r Equating this temperature with the maximum temperature, T R, supported by radiative loss, we have or T R = G NM S m p 5kr R r R = G NM S m p 5kT R.
39 Introduction Solar wind energy loss Heat conduction Radiation When will stars have coronae (contd.)? A corona cannot be formed beyond r = r R = G n M S m p /(5kT R ). If the heating rate is so low, or density so high, that r TR > r R, a corona is not formed the chromosphere is converted directly into a slow, cool wind. With T R = K, we find for our Sun that r R 0.7 AU! So the Sun must have a corona. However, for, say, a red giant star with M = 16 M S, R = 400 R S, we get r R 6 R, so it may not have a corona.
40 Introduction Solar wind energy loss Heat conduction Radiation Balance between heat conduction and radiation Energy supplied beyond r TR is not converted (directly) to radiation. If it is converted into heat conduction, in a steady state the radiative loss in the transition region must balance the heat flux divergence, 2 L(T (r)) AP 4kT (r) 2 = d(aq e). dr where A(r) = A 0 (r/r S ) 2 is the flow tube area. Using q e = κt 5/2 dt dr, using T instead of r as the independent variable (since the temperature is monotonically increasing), and assuming constant pressure P in the transition region, this energy balance may be rewritten d((aq e ) 2 ) dt = κ(ap)2 2k 2 T L(T ).
41 Introduction Solar wind energy loss Heat conduction Radiation Radiative energy balance (contd.) Assuming a thin transition region, so we may treat A as a constant, this equation may formally be integrated between T 1 and T 2. Expressing the result in terms of P we get 2k P = 2 (q2 2 q2 1 ) κk(t 1, T 2 ) where K(T 1, T 2 ) T 2 T 1 T L(T ) dt. Assuming that T 1 is so low that all heat has been absorbed, q 1 = 0, we get 2 P κk(t 2 ) k q 2 The transition region pressure is directly proportional to the downward heat flux q 2.
42 Introduction Solar wind energy loss Heat conduction Radiation Radiative energy balance (contd.) Pressure of the transition region, and thus the coronal density, is not an independent parameter, but is set by the energy balance! When P P bal 2 κk(t 2 ) k q 2 the transition region will move until P = P bal is restored. Hence the transition region is dynamic (and difficult to model... ). The solar wind mass flux directly affected by the energy balance of the transition region. Hence we must use so-called radiative energy balance models of the solar wind (Hammer 1982, Withbroe 1988). Even if 90% of the coronal heating goes to the wind, the remaining 10% is important since it sets the mass flux.
43 Introduction Solar wind energy loss Heat conduction Radiation Radiative energy balance (contd.) 2 P = κk(t 2 ) k q s m 1 q 2 (e.g., Rosner et al., 1978, Hansteen & Leer, 1995). With a coronal temperature of 10 6 K and a coronal hole density, inferred from observations, of n m 3, we find q 2 37 W/m 2.
44 Introduction Solar wind energy loss Heat conduction Radiation Radiative energy balance (contd.) Since we have shown that the wind needs about 70 W/m 2, this implies that more than 1/3 of the energy needs to be conducted down. Difficult to obtain in solar wind models which typically get only 10% conducted down. Hence solar wind models get a lower coronal density than observations indicate. Are the models wrong or the density observations incorrect?
45 Conservation equations Isothermal solar wind Interaction with the interstellar medium Basic conservation equation In a fluid flow with particle density n(r) and mean flow velocity u(r), assume that each particle carries an intrinsic quantity b, which can be charge (b = q), mass (b = m), number of particles (b = 1), momentum (b = mu i ) etc. Considering flow through an arbitrary, infinitesimally small volume in space, you can show that the following equation must be satisfied: (nb) + (nub) = δb t δt where the right-hand side expresses the rate of change of b per unit volume and time due to external processes.
46 Conservation equations Isothermal solar wind Interaction with the interstellar medium For b = 1 (number of particles), the right-hand side expresses the production (or loss) rate of particles due to chemical and ionization processes. In the case that the total number of particles is conserved, we thus get the continuity equation n t + (nu) = 0. In a steady state, spherically symmetric flow this simplifies further to d dr (r 2 nu) = 0 where u is the radial flow speed.
47 Conservation equations Isothermal solar wind Interaction with the interstellar medium Momentum conservation Setting b = mu x (momentum in x-direction) t (mnu x) + (mnu x u) = n(mg x + ee x ) P x + where we have included gravity, the electric force and the pressure gradient force on the right-hand side. With no production or loss of particles, and a steady state, spherically expanding flow you can simplify this to mnu du dr + nmg nee + dp dr = 0 (where gravity is assumed to point inwards).
48 Conservation equations Isothermal solar wind Interaction with the interstellar medium Setting Energy conservation b = 1 2 mu kt into the general conservation equation, we have t (1 2 mnu2 + 3 ( 1 2 kt ) + 2 mnu2 u + 3 ) 2 ktnu = +mnu g + neu E P u u P q where the work done by gravity, the electric force, the pressure has been included on the right-hand side, as well as the heat flux divergence. With the same simplifying assumptions as for the continuity and momentum equations, we end up with. 3 2 u dt dr + T d(r 2 u) r d(r 2 q) dr r 2 = 0 nk dr
49 Conservation equations Isothermal solar wind Interaction with the interstellar medium Isothermal solar wind We consider an electron-proton wind, assuming charge neutrality n e = n p = n and no current u e = u p = u. The steady state electron and proton momentum equations may then be combined, and, using the continuity equation, written as u du dr ) (1 c2 u 2 = G NM S r 2 + 4kT m p r where c 2kT /m p is the proton thermal speed. Both sides must be zero when u = c, the critical point. The critical point is located at r c = G NM S 2c 2 = With T = 10 6 K, r c 6 R S. ( vesc ) 2 RS. 2c
50 Conservation equations Isothermal solar wind Interaction with the interstellar medium Critical point density Requiring a subsonic (u c) solution near the Sun and a supersonic solution (u c) at infinity, the solution must go through the critical point. With n 0 the density at r R S, you can show that the critical point density is [ 3 n c = n 0 exp ( vesc which becomes very small when c v esc. c ) 2 ].
51 Conservation equations Isothermal solar wind Interaction with the interstellar medium The isothermal wind mass flux We now know the flow speed and density at the critical point, hence we have the solar wind mass flux without solving the equation! Scaled to Earth, we get (nu) E = where r e = 1 AU. ( RS r E ) e3/2 n o c ( vesc c ) ( 4 exp v esc 2 ) 2c 2
52 Conservation equations Isothermal solar wind Interaction with the interstellar medium The isothermal flux as a function of coronal temperature (nu) E [m -2 s -1 ] (nu) E [m -2 s -1 ] r c =R S T [K] r c =R S c/v esc The flux at Earth for n 0 = m 3. Horizontal dashed line = observed solar wind flux.
53 Conservation equations Isothermal solar wind Interaction with the interstellar medium A physically sensible solution requires r c > R S, or v esc > 2c or T < m p 8k v 2 esc K.
54 Conservation equations Isothermal solar wind Interaction with the interstellar medium Comparison with adiabatic wind The isothermal wind produces a reasonable mass flux with c 0.2v esc, or T K. Our energy flux argument, which neglected heat conduction entirely, predicted a coronal temperature necessary for a wind, (with v esc at r = R S ). T 1 m p 10 k v esc K Thus the isothermal case, with infinitely efficient heat conduction, produces a wind at a lower temperature. But even the isothermal wind requires c/v esc not much less than unity to have a realistic mass flux. Even in this extreme case a million-degree corona is required, or both mass and energy fluxes become extremely small.
55 Conservation equations Isothermal solar wind Interaction with the interstellar medium The isothermal result The mass flux problem nu n 0 c ( vesc c ) ( 4 exp v esc 2 ) 2c 2 indicates that the mass flux is extremely sensitive to the coronal temperature when c v esc. Why is the (fast) solar wind mass flux then so constant? Answer: The mass flux is limited by the energy supply to the corona: F E nu 1 2 m p(vesc 2 + ue 2 ) F E 1 2 m pvesc 2 As long as the total coronal heating rate remains constant, and most of the energy is lost in the solar wind, the mass flux cannot change by a large amount.
56 Conservation equations Isothermal solar wind Interaction with the interstellar medium Interaction of the wind with the interstellar medium As the wind expands, its density decreases as r 2. At some distance the dynamic pressure of the wind becomes smaller than the pressure of the interstellar medium, and a termination shock will form. Here the supersonic, tenuous solar wind is abruptly slowed down, converted into the slower flow of the interstellar gas. This point marks the end of the solar system.
57 Conservation equations Isothermal solar wind Interaction with the interstellar medium Fluid shock relations Flux conservation We assume the shock is at rest, so time derivatives may be neglected. The continuity equation d dr (r 2 nu) = 0 must be satisfied everywhere. Denoting upstream (solar wind side) quantities by subscript 1 and downstream values by subscript 2, the continuity equation may be integrated across the shock to read r 2 1 n 1 u 1 = r 2 2 n 2 u 2 or, if the shock is so thin that r 1 r 2, n 1 u 1 = n 2 u 2.
58 Conservation equations Isothermal solar wind Interaction with the interstellar medium The momentum equation Shock relations (contd.) Pressure balance m p nu du dr + d (nkt ) = 0. dr With the aid of the continuity equation this may be written d m p dr (nu2 ) + 2 r m pnu 2 + d (nkt ) = 0. dr Integrating across the shock, assuming a very thin shock and that all variables (but not their derivatives) remain finite within the shock, we obtain m p n 1 u n 1 kt 1 = m p n 2 u n 2 kt 2 expressing pressure balance at the shock.
59 Conservation equations Isothermal solar wind Interaction with the interstellar medium Shock relations (contd.) Energy conservation From the steady state energy conservation equation in spherical geometry [ ( 1 d 1 r 2 r 2 nu dr 2 m pu )] 2 kt = 1 d(r 2 q) r 2 dr (neglecting gravity) we obtain the energy conservation requirement across the shock ( 1 n 1 u 1 2 m pu ) ( 1 2 kt 1 + q 1 = n 2 u 2 2 m pu ) 2 kt 2 + q 2. If heat conduction can be neglected outside the shock (it may not be negligible inside) we get the final result: 1 2 m pu kt 1 = 1 2 m pu kt 2.
60 Conservation equations Isothermal solar wind Interaction with the interstellar medium Summary of shock relations n 1 u 1 = n 2 u 2 m p n 1 u1 2 + n 1 kt 1 = m p n 2 u2 2 + n 2 kt m pu kt 1 = 1 2 m pu kt 2 Since we have 3 equations and 6 unknowns, three of these need to be specified in order to have a unique solution, for instance the solar wind speed u 1 and the interstellar gas density n 2 and pressure n 2 kt 2. In the pressure balance, the magnetic as well as cosmic ray pressure of the interstellar gas may have to be included.
61 Conservation equations Isothermal solar wind Interaction with the interstellar medium Location of the termination shock From the pressure balance condition, neglecting the thermal solar wind pressure, the heliospheric distance r T to the termination shock is m p (nu) E u E r T = 1 AU m p n 2 u2 2 + n 2kT 2 Choosing n 2 = 10 5 m 3, T 2 = 7000 K, and u 2 = 25 km/s on the upwind side of the Sun (Axford & Suess) we find m p n 2 u Pa n 2 kt Pa m p (nu) E u E Pa
62 Conservation equations Isothermal solar wind Interaction with the interstellar medium Location of termination shock (contd.) On the upwind side the dynamic pressure dominates over the thermal pressure of the interstellar gas At 1 AU the solar wind dynamic ( ram ) pressure is 10 4 times larger than the interstellar gas pressure, so the termination shock must be far from us! With these parameters we find r T 140 AU.
hermally driven winds Viggo H. Hansteen Insititute of Theoretical Astrophysics, University of Oslo
hermally driven winds Viggo H. Hansteen Insititute of Theoretical Astrophysics, University of Oslo Introduction last decade has seen a large change in our understand e solar wind, due both theoretical,
More informationTurbulent Origins of the Sun s Hot Corona and the Solar Wind
Turbulent Origins of the Sun s Hot Corona and the Solar Wind Steven R. Cranmer Harvard-Smithsonian Center for Astrophysics Turbulent Origins of the Sun s Hot Corona and the Solar Wind Outline: 1. Solar
More informationStellar Winds. Star. v w
Stellar Winds Star v w Stellar Winds Geoffrey V. Bicknell 1 Characteristics of stellar winds Solar wind Velocity at earth s orbit: Density: Temperature: Speed of sound: v 400 km/s n 10 7 m 3 c s T 10 5
More informationVII. Hydrodynamic theory of stellar winds
VII. Hydrodynamic theory of stellar winds observations winds exist everywhere in the HRD hydrodynamic theory needed to describe stellar atmospheres with winds Unified Model Atmospheres: - based on the
More informationPlasmas as fluids. S.M.Lea. January 2007
Plasmas as fluids S.M.Lea January 2007 So far we have considered a plasma as a set of non intereacting particles, each following its own path in the electric and magnetic fields. Now we want to consider
More informationProblem set: solar irradiance and solar wind
Problem set: solar irradiance and solar wind Karel Schrijver July 3, 203 Stratification of a static atmosphere within a force-free magnetic field Problem: Write down the general MHD force-balance equation
More informationAtmospheric escape. Volatile species on the terrestrial planets
Atmospheric escape MAVEN s Ultraviolet Views of Hydrogen s Escape from Mars Atomic hydrogen scattering sunlight in the upper atmosphere of Mars, as seen by the Imaging Ultraviolet Spectrograph on NASA's
More informationExploring the Solar Wind with Ultraviolet Light
Timbuktu Academy Seminar, Southern University and A&M College, November 19, 2003 Exploring the Solar Wind with Ultraviolet Light Steven R. Cranmer Harvard-Smithsonian Center for Astrophysics, Cambridge,
More informationSurvey of the Solar System. The Sun Giant Planets Terrestrial Planets Minor Planets Satellite/Ring Systems
Survey of the Solar System The Sun Giant Planets Terrestrial Planets Minor Planets Satellite/Ring Systems The Sun Mass, M ~ 2 x 10 30 kg Radius, R ~ 7 x 10 8 m Surface Temperature ~ 5800 K Density ~ 1.4
More informationChapter 9 The Sun. Nuclear fusion: Combining of light nuclei into heavier ones Example: In the Sun is conversion of H into He
Our sole source of light and heat in the solar system A common star: a glowing ball of plasma held together by its own gravity and powered by nuclear fusion at its center. Nuclear fusion: Combining of
More information2. Basic Assumptions for Stellar Atmospheres
2. Basic Assumptions for Stellar Atmospheres 1. geometry, stationarity 2. conservation of momentum, mass 3. conservation of energy 4. Local Thermodynamic Equilibrium 1 1. Geometry Stars as gaseous spheres!
More informationStellar Winds: Mechanisms and Dynamics
Astrofysikalisk dynamik, VT 010 Stellar Winds: Mechanisms and Dynamics Lecture Notes Susanne Höfner Department of Physics and Astronomy Uppsala University 1 Most stars have a stellar wind, i.e. and outflow
More informationConvection When the radial flux of energy is carried by radiation, we derived an expression for the temperature gradient: dt dr = - 3
Convection When the radial flux of energy is carried by radiation, we derived an expression for the temperature gradient: dt dr = - 3 4ac kr L T 3 4pr 2 Large luminosity and / or a large opacity k implies
More informationInfluence of Mass Flows on the Energy Balance and Structure of the Solar Transition Region
**TITLE** ASP Conference Series, Vol. **VOLUME***, **YEAR OF PUBLICATION** **NAMES OF EDITORS** Influence of Mass Flows on the Energy Balance and Structure of the Solar Transition Region E. H. Avrett and
More informationOpen magnetic structures - Coronal holes and fast solar wind
Open magnetic structures - Coronal holes and fast solar wind The solar corona over the solar cycle Coronal and interplanetary temperatures Coronal holes and fast solar wind Origin of solar wind in magnetic
More informationWeek 8: Stellar winds So far, we have been discussing stars as though they have constant masses throughout their lifetimes. On the other hand, toward
Week 8: Stellar winds So far, we have been discussing stars as though they have constant masses throughout their lifetimes. On the other hand, toward the end of the discussion of what happens for post-main
More informationThermal Equilibrium in Nebulae 1. For an ionized nebula under steady conditions, heating and cooling processes that in
Thermal Equilibrium in Nebulae 1 For an ionized nebula under steady conditions, heating and cooling processes that in isolation would change the thermal energy content of the gas are in balance, such that
More informationThe Sun. Chapter 12. Properties of the Sun. Properties of the Sun. The Structure of the Sun. Properties of the Sun.
Chapter 12 The Sun, Our Star 1 With a radius 100 and a mass of 300,000 that of Earth, the Sun must expend a large amount of energy to withstand its own gravitational desire to collapse To understand this
More informationThe Sun. The Sun is a star: a shining ball of gas powered by nuclear fusion. Mass of Sun = 2 x g = 330,000 M Earth = 1 M Sun
The Sun The Sun is a star: a shining ball of gas powered by nuclear fusion. Mass of Sun = 2 x 10 33 g = 330,000 M Earth = 1 M Sun Radius of Sun = 7 x 10 5 km = 109 R Earth = 1 R Sun Luminosity of Sun =
More informationCollisions and transport phenomena
Collisions and transport phenomena Collisions in partly and fully ionized plasmas Typical collision parameters Conductivity and transport coefficients Conductivity tensor Formation of the ionosphere and
More information2. Basic assumptions for stellar atmospheres
. Basic assumptions for stellar atmospheres 1. geometry, stationarity. conservation of momentum, mass 3. conservation of energy 4. Local Thermodynamic Equilibrium 1 1. Geometry Stars as gaseous spheres
More information2. Basic assumptions for stellar atmospheres
. Basic assumptions for stellar atmospheres 1. geometry, stationarity. conservation of momentum, mass 3. conservation of energy 4. Local Thermodynamic Equilibrium 1 1. Geometry Stars as gaseous spheres
More informationOur sole source of light and heat in the solar system. A very common star: a glowing g ball of gas held together by its own gravity and powered
The Sun Visible Image of the Sun Our sole source of light and heat in the solar system A very common star: a glowing g ball of gas held together by its own gravity and powered by nuclear fusion at its
More informationThe Sun Our Star. Properties Interior Atmosphere Photosphere Chromosphere Corona Magnetism Sunspots Solar Cycles Active Sun
The Sun Our Star Properties Interior Atmosphere Photosphere Chromosphere Corona Magnetism Sunspots Solar Cycles Active Sun General Properties Not a large star, but larger than most Spectral type G2 It
More informationESS 200C. Lectures 6 and 7 The Solar Wind
ESS 200C Lectures 6 and 7 The Solar Wind The Earth s atmosphere is stationary. The Sun s atmosphere is not stable but is blown out into space as the solar wind filling the solar system and then some. The
More informationOverview spherical accretion
Spherical accretion - AGN generates energy by accretion, i.e., capture of ambient matter in gravitational potential of black hole -Potential energy can be released as radiation, and (some of) this can
More informationLecture 5 The Formation and Evolution of CIRS
Lecture 5 The Formation and Evolution of CIRS Fast and Slow Solar Wind Fast solar wind (>600 km/s) is known to come from large coronal holes which have open magnetic field structure. The origin of slow
More information1 A= one Angstrom = 1 10 cm
Our Star : The Sun )Chapter 10) The sun is hot fireball of gas. We observe its outer surface called the photosphere: We determine the temperature of the photosphere by measuring its spectrum: The peak
More informationCoronal Heating versus Solar Wind Acceleration
SOHO 15: Coronal Heating, 6 9 September 2004, University of St. Andrews, Scotland Coronal Heating versus Solar Wind Acceleration Steven R. Cranmer Harvard-Smithsonian Center for Astrophysics, Cambridge,
More informationAy 1 Lecture 8. Stellar Structure and the Sun
Ay 1 Lecture 8 Stellar Structure and the Sun 8.1 Stellar Structure Basics How Stars Work Hydrostatic Equilibrium: gas and radiation pressure balance the gravity Thermal Equilibrium: Energy generated =
More informationThe Sun ASTR /17/2014
The Sun ASTR 101 11/17/2014 1 Radius: 700,000 km (110 R ) Mass: 2.0 10 30 kg (330,000 M ) Density: 1400 kg/m 3 Rotation: Differential, about 25 days at equator, 30 days at poles. Surface temperature: 5800
More informationAy Fall 2004 Lecture 6 (given by Tony Travouillon)
Ay 122 - Fall 2004 Lecture 6 (given by Tony Travouillon) Stellar atmospheres, classification of stellar spectra (Many slides c/o Phil Armitage) Formation of spectral lines: 1.excitation Two key questions:
More informationRadiation Zone. AST 100 General Astronomy: Stars & Galaxies. 5. What s inside the Sun? From the Center Outwards. Meanderings of outbound photons
AST 100 General Astronomy: Stars & Galaxies 5. What s inside the Sun? From the Center Outwards Core: Hydrogen ANNOUNCEMENTS Midterm I on Tue, Sept. 29 it will cover class material up to today (included)
More informationAnnouncements. - Homework #5 due today - Review on Monday 3:30 4:15pm in RH103 - Test #2 next Tuesday, Oct 11
Announcements - Homework #5 due today - Review on Monday 3:30 4:15pm in RH103 - Test #2 next Tuesday, Oct 11 Review for Test #2 Oct 11 Topics: The Solar System and its Formation The Earth and our Moon
More informationFundamental Stellar Parameters. Radiative Transfer. Stellar Atmospheres
Fundamental Stellar Parameters Radiative Transfer Stellar Atmospheres Equations of Stellar Structure Basic Principles Equations of Hydrostatic Equilibrium and Mass Conservation Central Pressure, Virial
More information! The Sun as a star! Structure of the Sun! The Solar Cycle! Solar Activity! Solar Wind! Observing the Sun. The Sun & Solar Activity
! The Sun as a star! Structure of the Sun! The Solar Cycle! Solar Activity! Solar Wind! Observing the Sun The Sun & Solar Activity The Sun in Perspective Planck s Law for Black Body Radiation ν = c / λ
More informationThe Sun: A Star of Our Own ASTR 2110 Sarazin
The Sun: A Star of Our Own ASTR 2110 Sarazin Sarazin Travel Wednesday, September 19 afternoon Friday, September 21 Will miss class Friday, September 21 TA Molly Finn will be guest lecturer Cancel Office
More informationO 5+ at a heliocentric distance of about 2.5 R.
EFFECT OF THE LINE-OF-SIGHT INTEGRATION ON THE PROFILES OF CORONAL LINES N.-E. Raouafi and S. K. Solanki Max-Planck-Institut für Aeronomie, 37191 Katlenburg-Lindau, Germany E-mail: Raouafi@linmpi.mpg.de;
More informationThe Sun. October 21, ) H-R diagram 2) Solar Structure 3) Nuclear Fusion 4) Solar Neutrinos 5) Solar Wind/Sunspots
The Sun October 21, 2002 1) H-R diagram 2) Solar Structure 3) Nuclear Fusion 4) Solar Neutrinos 5) Solar Wind/Sunspots Review Blackbody radiation Measuring stars distance luminosity brightness and distance
More information2. Basic assumptions for stellar atmospheres
. Basic assumptions for stellar atmospheres 1. geometry, stationarity. conservation of momentum, mass 3. conservation of energy 4. Local Thermodynamic Equilibrium 1 1. Geometry Stars as gaseous spheres
More informationA100 Exploring the Universe: How Stars Work. Martin D. Weinberg UMass Astronomy
A100 Exploring the Universe: How Stars Work Martin D. Weinberg UMass Astronomy weinberg@astro.umass.edu October 11, 2012 Read: Chaps 14, 15 10/11/12 slide 1 Exam scores posted in Mastering Exam keys posted
More information6. Stellar spectra. excitation and ionization, Saha s equation stellar spectral classification Balmer jump, H -
6. Stellar spectra excitation and ionization, Saha s equation stellar spectral classification Balmer jump, H - 1 Occupation numbers: LTE case Absorption coefficient: = n i calculation of occupation numbers
More information6. Interstellar Medium. Emission nebulae are diffuse patches of emission surrounding hot O and
6-1 6. Interstellar Medium 6.1 Nebulae Emission nebulae are diffuse patches of emission surrounding hot O and early B-type stars. Gas is ionized and heated by radiation from the parent stars. In size,
More informationThe Sun sends the Earth:
The Sun sends the Earth: Solar Radiation - peak wavelength.visible light - Travels at the speed of light..takes 8 minutes to reach Earth Solar Wind, Solar flares, and Coronal Mass Ejections of Plasma (ionized
More information6. Stellar spectra. excitation and ionization, Saha s equation stellar spectral classification Balmer jump, H -
6. Stellar spectra excitation and ionization, Saha s equation stellar spectral classification Balmer jump, H - 1 Occupation numbers: LTE case Absorption coefficient: = n i calculation of occupation numbers
More informationHII regions. Massive (hot) stars produce large numbers of ionizing photons (energy above 13.6 ev) which ionize hydrogen in the vicinity.
HII regions Massive (hot) stars produce large numbers of ionizing photons (energy above 13.6 ev) which ionize hydrogen in the vicinity. Detailed nebular structure depends on density distribution of surrounding
More informationChapter 14 Lecture. Chapter 14: Our Star Pearson Education, Inc.
Chapter 14 Lecture Chapter 14: Our Star 14.1 A Closer Look at the Sun Our goals for learning: Why does the Sun shine? What is the Sun's structure? Why does the Sun shine? Is it on FIRE? Is it on FIRE?
More informationThe Interior Structure of the Sun
The Interior Structure of the Sun Data for one of many model calculations of the Sun center Temperature 1.57 10 7 K Pressure 2.34 10 16 N m -2 Density 1.53 10 5 kg m -3 Hydrogen 0.3397 Helium 0.6405 The
More informationA new mechanism to account for acceleration of the solar wind
A new mechanism to account for acceleration of the solar wind Henry D. May Email: hankmay@earthlink.net Abstract An enormous amount of effort has been expended over the past sixty years in attempts to
More informationA Closer Look at the Sun
Our Star A Closer Look at the Sun Our goals for learning Why was the Sun s energy source a major mystery? Why does the Sun shine? What is the Sun s structure? Why was the Sun s energy source a major mystery?
More information2/6/18. Topics for Today and Thur. ASTR 1040: Stars & Galaxies. EUV and Visible Images
2/6/18 ASTR 1040: Stars & Galaxies Topics for Today and Thur Consider Sun s energy source (fusion H--He) Solar granulation Prof. Juri Toomre TAs: Peri Johnson, Ryan Horton Lecture 7 Tues 6 Feb 2018 What
More informationStudy of Electron Energy and Angular Distributions and Calculations of X-ray, EUV Line Flux and Rise Times
J. Astrophys. Astr. (1987) 8, 263 270 Study of Electron Energy and Angular Distributions and Calculations of X-ray, EUV Line Flux and Rise Times Ranjna Bakaya, Sunil Peshin, R. R. Rausaria & P. N. Khosa
More informationThe Sun. Nearest Star Contains most of the mass of the solar system Source of heat and illumination
The Sun Nearest Star Contains most of the mass of the solar system Source of heat and illumination Outline Properties Structure Solar Cycle Energetics Equation of Stellar Structure TBC Properties of Sun
More informationProtostars 1. Early growth and collapse. First core and main accretion phase
Protostars 1. First core and main accretion phase Stahler & Palla: Chapter 11.1 & 8.4.1 & Appendices F & G Early growth and collapse In a magnetized cloud undergoing contraction, the density gradually
More informationLesson 3 THE SOLAR SYSTEM
Lesson 3 THE SOLAR SYSTEM THE NATURE OF THE SUN At the center of our solar system is the Sun which is a typical medium sized star. Composed mainly of Hydrogen (73% by mass), 23% helium and the rest is
More informationWhat do we see on the face of the Sun? Lecture 3: The solar atmosphere
What do we see on the face of the Sun? Lecture 3: The solar atmosphere The Sun s atmosphere Solar atmosphere is generally subdivided into multiple layers. From bottom to top: photosphere, chromosphere,
More informationEnergy transport: convection
Outline Introduction: Modern astronomy and the power of quantitative spectroscopy Basic assumptions for classic stellar atmospheres: geometry, hydrostatic equilibrium, conservation of momentum-mass-energy,
More informationRadiative & Magnetohydrodynamic Shocks
Chapter 4 Radiative & Magnetohydrodynamic Shocks I have been dealing, so far, with non-radiative shocks. Since, as we have seen, a shock raises the density and temperature of the gas, it is quite likely,
More informationIonosphères planétaires (introduction)
Ionosphères planétaires (introduction) email: arnaud.zaslavsky@obspm.fr Structure de l atmosphère terrestre Temperature gradients determined by IR radiation from Earth (low altitude Troposhere) And from
More informationHigh-Energy Astrophysics Lecture 6: Black holes in galaxies and the fundamentals of accretion. Overview
High-Energy Astrophysics Lecture 6: Black holes in galaxies and the fundamentals of accretion Robert Laing Overview Evidence for black holes in galaxies and techniques for estimating their mass Simple
More informationPROBLEM 1 (15 points) In a Cartesian coordinate system, assume the magnetic flux density
PROBLEM 1 (15 points) In a Cartesian coordinate system, assume the magnetic flux density varies as ( ) where is a constant, is the unit vector in x direction. a) Sketch the magnetic flux density and the
More informationChapter 14 Our Star Pearson Education, Inc.
Chapter 14 Our Star Basic Types of Energy Kinetic (motion) Radiative (light) Potential (stored) Energy can change type, but cannot be created or destroyed. Thermal Energy: the collective kinetic energy
More informationIntroduction to Plasma Physics
Introduction to Plasma Physics Hartmut Zohm Max-Planck-Institut für Plasmaphysik 85748 Garching DPG Advanced Physics School The Physics of ITER Bad Honnef, 22.09.2014 A simplistic view on a Fusion Power
More informationThe Sun. How are these quantities measured? Properties of the Sun. Chapter 14
The Sun Chapter 14 The Role of the Sun in the Solar System > 99.9% of the mass Its mass is responsible for the orderly orbits of the planets Its heat is responsible for warming the planets It is the source
More informationChapter 8 The Sun Our Star
Note that the following lectures include animations and PowerPoint effects such as fly ins and transitions that require you to be in PowerPoint's Slide Show mode (presentation mode). Chapter 8 The Sun
More informationThe Solar Resource: The Active Sun as a Source of Energy. Carol Paty School of Earth and Atmospheric Sciences January 14, 2010
The Solar Resource: The Active Sun as a Source of Energy Carol Paty School of Earth and Atmospheric Sciences January 14, 2010 The Sun: A Source of Energy Solar Structure Solar Wind Solar Cycle Solar Activity
More informationB.V. Gudiksen. 1. Introduction. Mem. S.A.It. Vol. 75, 282 c SAIt 2007 Memorie della
Mem. S.A.It. Vol. 75, 282 c SAIt 2007 Memorie della À Ø Ò Ø ËÓÐ Ö ÓÖÓÒ B.V. Gudiksen Institute of Theoretical Astrophysics, University of Oslo, Norway e-mail:boris@astro.uio.no Abstract. The heating mechanism
More information6. Stellar spectra. excitation and ionization, Saha s equation stellar spectral classification Balmer jump, H -
6. Stellar spectra excitation and ionization, Saha s equation stellar spectral classification Balmer jump, H - 1 Occupation numbers: LTE case Absorption coefficient: κ ν = n i σ ν$ à calculation of occupation
More informationThe Project. National Schools Observatory
Sunspots The Project This project is devised to give students a good understanding of the structure and magnetic field of the Sun and how this effects solar activity. Students will work with sunspot data
More informationChapter 14 Lecture. The Cosmic Perspective Seventh Edition. Our Star Pearson Education, Inc.
Chapter 14 Lecture The Cosmic Perspective Seventh Edition Our Star 14.1 A Closer Look at the Sun Our goals for learning: Why does the Sun shine? What is the Sun's structure? Why does the Sun shine? Is
More informationExplain how the sun converts matter into energy in its core. Describe the three layers of the sun s atmosphere.
Chapter 29 and 30 Explain how the sun converts matter into energy in its core. Describe the three layers of the sun s atmosphere. Explain how sunspots are related to powerful magnetic fields on the sun.
More informationLecture 14 Cosmic Rays
Lecture 14 Cosmic Rays 1. Introduction and history 2. Locally observed properties 3. Interactions 4. Demodulation and ionization rate 5. Midplane interstellar pressure General Reference MS Longair, High
More information9-1 The Sun s energy is generated by thermonuclear reactions in its core The Sun s luminosity is the amount of energy emitted each second and is
1 9-1 The Sun s energy is generated by thermonuclear reactions in its core The Sun s luminosity is the amount of energy emitted each second and is produced by the proton-proton chain in which four hydrogen
More informationMesoscale Variations in the Heliospheric Magnetic Field and their Consequences in the Outer Heliosphere
Mesoscale Variations in the Heliospheric Magnetic Field and their Consequences in the Outer Heliosphere L. A. Fisk Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor,
More informationGuidepost. Chapter 08 The Sun 10/12/2015. General Properties. The Photosphere. Granulation. Energy Transport in the Photosphere.
Guidepost The Sun is the source of light an warmth in our solar system, so it is a natural object to human curiosity. It is also the star most easily visible from Earth, and therefore the most studied.
More informationAstr 1050 Mon. March 30, 2015 This week s Topics
Astr 1050 Mon. March 30, 2015 This week s Topics Chapter 14: The Sun, Our Star Structure of the Sun Physical Properties & Stability Photosphere Opacity Spectral Line Formation Temperature Profile The Chromosphere
More informationSW103: Lecture 2. Magnetohydrodynamics and MHD models
SW103: Lecture 2 Magnetohydrodynamics and MHD models Scale sizes in the Solar Terrestrial System: or why we use MagnetoHydroDynamics Sun-Earth distance = 1 Astronomical Unit (AU) 200 R Sun 20,000 R E 1
More informationA100 Exploring the Universe: How Stars Work. Martin D. Weinberg UMass Astronomy
A100 Exploring the Universe: How Stars Work Martin D. Weinberg UMass Astronomy astron100-mdw@courses.umass.edu October 07, 2014 Read: Chaps 14, 15 10/07/12 slide 1 Exam scores posted in Mastering Questions
More informationThe Sun is the nearest star to Earth, and provides the energy that makes life possible.
1 Chapter 8: The Sun The Sun is the nearest star to Earth, and provides the energy that makes life possible. PRIMARY SOURCE OF INFORMATION about the nature of the Universe NEVER look at the Sun directly!!
More informationZach Meeks. Office: Ford ES&T Phone: (918) Please let me know if you have any questions!
Zach Meeks Office: Ford ES&T 2114 Email: zachary.meeks@gatech.edu Phone: (918) 515-0052 Please let me know if you have any questions! The scope of space physics Solar-Terrestrial Relations Solar-Terrestrial
More informationTWO-DIMENSIONAL MAGNETOHYDRODYNAMIC MODELS OF THE SOLAR CORONA: MASS LOSS FROM THE STREAMER BELT Eirik Endeve 1 and Egil Leer 1
The Astrophysical Journal, 589:1040 1053, 2003 June 1 # 2003. The American Astronomical Society. All rights reserved. Printed in U.S.A. TWO-IMENSIONAL MAGNETOHYROYNAMIC MOELS OF THE SOLAR CORONA: MASS
More informationPhysics Homework Set 2 Sp 2015
1) A large gas cloud in the interstellar medium that contains several type O and B stars would appear to us as 1) A) a reflection nebula. B) a dark patch against a bright background. C) a dark nebula.
More informationSOLAR WIND ION AND ELECTRON DISTRIBUTION FUNCTIONS AND THE TRANSITION FROM FLUID TO KINETIC BEHAVIOR
SOLAR WIND ION AND ELECTRON DISTRIBUTION FUNCTIONS AND THE TRANSITION FROM FLUID TO KINETIC BEHAVIOR JUSTIN C. KASPER HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS GYPW01, Isaac Newton Institute, July 2010
More informationReading Clicker Q 2/7/17. Topics for Today and Thur. ASTR 1040: Stars & Galaxies
ASTR 1040: Stars & Galaxies Solar granulation Prof. Juri Toomre TAs: Piyush Agrawal, Connor Bice Lecture 7 Tues 7 Feb 2017 zeus.colorado.edu/astr1040-toomre Topics for Today and Thur Consider Sun s energy
More informationDavid versus Goliath 1
David versus Goliath 1 or A Comparison of the Magnetospheres between Jupiter and Earth 1 David and Goliath is a story from the Bible that is about a normal man (David) who meets a giant (Goliath) Tomas
More informationSome Good News. Announcements. Lecture 10 The Sun. How does the Sun shine? The Sun s Energy Source
Announcements Homework due today. Put your homework in the box NOW. Please STAPLE them if you have not done yet. Quiz#3 on Tuesday (Oct 5) Announcement at the end of this lecture. If you could not pick
More informationIdeal Magnetohydrodynamics (MHD)
Ideal Magnetohydrodynamics (MHD) Nick Murphy Harvard-Smithsonian Center for Astrophysics Astronomy 253: Plasma Astrophysics February 1, 2016 These lecture notes are largely based on Lectures in Magnetohydrodynamics
More information2. Stellar atmospheres: Structure
2. Stellar atmospheres: Structure 2.1. Assumptions Plane-parallel geometry Hydrostatic equilibrium, i.e. o no large-scale accelerations comparable to surface gravity o no dynamically significant mass loss
More informationModel Atmospheres. Model Atmosphere Assumptions
Model Atmospheres Problem: Construct a numerical model of the atmosphere to estimate (a) Variation of physical variables (T, P) with depth (b) Emergent spectrum in continuum and lines Compare calculated
More information1 Energy dissipation in astrophysical plasmas
1 1 Energy dissipation in astrophysical plasmas The following presentation should give a summary of possible mechanisms, that can give rise to temperatures in astrophysical plasmas. It will be classified
More informationCoronal Heating Problem
PHY 690C Project Report Coronal Heating Problem by Mani Chandra, Arnab Dhabal and Raziman T V (Y6233) (Y7081) (Y7355) Mentor: Dr. M.K. Verma 1 Contents 1 Introduction 3 2 The Coronal Heating Problem 4
More informationThe Black Hole in the Galactic Center. Eliot Quataert (UC Berkeley)
The Black Hole in the Galactic Center Eliot Quataert (UC Berkeley) Why focus on the Galactic Center? The Best Evidence for a BH: M 3.6 10 6 M (M = mass of sun) It s s close! only ~ 10 55 Planck Lengths
More informationMechanisms for particle heating in flares
Mechanisms for particle heating in flares J. F. Drake University of Maryland J. T. Dahlin University of Maryland M. Swisdak University of Maryland C. Haggerty University of Delaware M. A. Shay University
More informationStars. The size of the Sun
Stars Huge spheres of gas floating in space Composed primarily of H, He. Produce their own energy. Our Galaxy: 10 11 (100 billion) stars. The Sun: a typical star Stars range from ~ 0.1 to ~ 20 M M = solar
More informationAstronomy Chapter 12 Review
Astronomy Chapter 12 Review Approximately how massive is the Sun as compared to the Earth? A. 100 times B. 300 times C. 3000 times D. 300,000 times E. One million times Approximately how massive is the
More informationStellar Interior: Physical Processes
Physics Focus on Astrophysics Focus on Astrophysics Stellar Interior: Physical Processes D. Fluri, 29.01.2014 Content 1. Mechanical equilibrium: pressure gravity 2. Fusion: Main sequence stars: hydrogen
More information10/17/ A Closer Look at the Sun. Chapter 11: Our Star. Why does the Sun shine? Lecture Outline
Lecture Outline 11.1 A Closer Look at the Sun Chapter 11: Our Star Our goals for learning: Why does the Sun shine? What is the Sun's structure? Why does the Sun shine? Is it on FIRE? Is it on FIRE? Chemical
More informationA Framework for Atmospheric Escape from Low-Mass Planets. Ruth Murray-Clay Harvard-Smithsonian Center for Astrophysics
A Framework for Atmospheric Escape from Low-Mass Planets Ruth Murray-Clay Harvard-Smithsonian Center for Astrophysics 1 hot Jupiter Mercury 0.39 AU Earth 1 AU ~0.05 AU ~ 10 R * Star Sun: LUV ~ 10-6 Lbol
More informationWeight of upper layers compresses lower layers
Weight of upper layers compresses lower layers Gravitational equilibrium: Energy provided by fusion maintains the pressure Gravitational contraction: Provided energy that heated core as Sun was forming
More informationHigh-Energy Neutrinos Produced by Interactions of Relativistic Protons in Shocked Pulsar Winds
High-Energy Neutrinos Produced by Interactions of Relativistic Protons in Shocked Pulsar Winds S. Nagataki Yukawa Institute for Theoretical Physics, Kyoto University, Oiwake-cho Kitashirakawa Sakyo-ku,
More information