Telescopes

← Astro210

photoeletric effect

• Photoemission emisison of a electron from a material in response to a incident photon \begin{list}{-}{}
• photoemissive material (underlying material)
• work function (min energy requried to produce light)
• photoeletric effect (photoemission from atoms in certain materials)
• photoelectron (release electron)

\item particle energy of EM radiation \end{list}

Sun

Chromosphere

• Very sparse layer of gas above the photosphere
• very hot gas, emission spectra by Kirchhoff laws
• easily seen during total eclipse or with an H$\alpha$ filter

Corona

• Low density out layer of suns atmosphere. Most easily visible during total eclipse
• T = $2\times 10^6$
• Emission lines from highly ionized atoms
• x-ray emission from thermal Bremsstrahlung (not black body)
• Optical continuum is originally from photosphere
• scattered by free electrons in coronal plasma
• coronal streamers show how plasma follows magnetic field lines

Solar Wind

• Bunch of protons and other various particles ejected from the sun
• Speed of protons in the corona
• $V_{rms}={\frac{3kT}{m_p}}^{1/2}\approx 160km/s$
• Escape speed as function of distance
• ${\frac{G{M}_{\odot }}{r}}^{1/2}\approx 620km/s$
• Sun produces a solar wind with $v=400km/s$, density$p10^{-21}kg{m}^{-3}$ earth
• $\Delta M=(4\pi r^2\Delta r)\rho$
• therefore mass flux through shell
• $\frac{dM}{dt}=4\pi r^2\frac{dr}{dt}\rho$
• $\dot{M}=4\pi r^{2}v\rho$
• $\dot{M}\sim 10^{8}kg{s}^{-1};t_m\sim 10^{14}$
• Maybe try this myself with various sizes of stars?? Seems easy to verify large stars ejecting large amounts of wind

Magnetic Fields

• Lorentz force $\vec{F}=q\vec{v}\times \vec{B}$
• Charged particles follow curved helical paths
• Magnetic field energy
• $P_B={\epsilon }_B=\frac{B^2}{2{\mu }_0}$

Sunspots

• Cooler than surroundings because the magnetic field is enhanced in the spot
• Pressure due to a magnetic field
• $P_B=4\times 10^{5}N{m}^{-2}(\frac{B}{1T}{)}^2$
• pressure due to ideal gas
• $P_{gas}=nkT$

\large Pressure balance in sunspots

• gas and magnetic pressure inside sunspot must equal surrounding gas pressure
• $\frac{\rho k{T}_s}{m_p}+\frac{B^2}{2{\mu }_0}=\frac{\rho k{T}_P}{m_p}$
• $B\approx .1T$

\large Sunspot Cycle

• Star near 30$°$ N/S, migrate towards solar equator
• more numerous every 11 years