ESO’s Paranal Observatory – VLT TelescopesCourse AnnouncementsAssignmentsHydrogen Energy DiagramSpectrum of HydrogenAtoms heavier than HydrogenAtoms heavier than HydrogenSpectrum of an Emission NebulaMolecular LinesMolecular LinesMolecular LinesSpectral Line AnalysisSpectral ThermometerRadial VelocityLine BroadeningThermal Broadening - TemperatureCollisional/Pressure BroadeningRotational BroadeningMagnetic Field BroadeningChapter 5Class QuestionClass Question - AnswerWhat is a telescopeRefracting and Reflecting TelescopesRefractionRefraction to focus lightRefraction to focus lightReflection to focus lightESO’s Paranal Observatory – VLT TelescopesCredit: ESO/B. TafreshiCourse Announcements•Welcome to the 2nd day of Fall!–Autumnal Equinox was yesterday•Exam 1 will take place Wednesday, 28 Sept.–Will cover Chapters 1 – 4–Study Materials Now Available•“Must Knows”; Chapter Slides; and MA Study Guide–Study sessions next Monday and Tuesday evenings (combined with A151)•A151 Primary - Monday Night at 5:30 – 6:30 PM •A152 Primary – Tuesday Night at 5:30 – 6:30 PM–Both in Room 304AssignmentsReading Assignments•No new readingParallel Lectures•No new parallel lecturesMastering Astronomy•Chapter 4 Homework[Due Monday, 26 Sept. at 11:59 PM EDT]Hydrogen Energy DiagramSpectral SeriesLyman SeriesUV PhotonsTransitions starting or ending at theGround State (n = 1)Balmer SeriesVisible Light PhotonsTransitions starting or ending at the 1st Excited State (n = 2)n = 1n = 2Wavelengths in ÅngstromsSpectrum of HydrogenThe Balmer Series – Visible Light Emission/AbsorptionHydrogen Alpha - HαHydrogen Beta - Hβ Hγ HδA spectrum of an element gives us a view of the energy structure of that element’s electron energy levelsAtoms heavier than HydrogenNew Energy Structure•More protons and electrons means different electrical structure of atom–Different electron orbital energy levels•More electrons means more transitions means more spectral linesMore protons => more electrons => more complicated energy structure => more complicated spectral linesHeliumCarbon2 Protons2 Electrons6 Protons6 ElectronsAtoms heavier than HydrogenIonization Comlications•Multiple stages of ionization (loss of electrons)•Each ionization changes the energy structure–Hence, each ion has it’s own set of spectral lines–Ionized spectral lines (e.g., doubly-ionized Oxygen lines or ionized He lines)-and-Neutral spectral lines (the ones we have already discussed)More protons => more electrons => more complicated energy structure => more complicated spectral linesHeliumCarbon2 Protons2 Electrons6 Protons6 Electrons1543…Spectrum of an Emission NebulaOmega Nebula (M17); nebula means gas cloudThink of the white squiggly line as the number of photons measured of each wavelength of light. More intensity means more photons of that color. Hence the red glow.The Emission Spectrum tells us about the composition of the nebulaMolecular LinesA more complex scenario•A molecule is tightly bound group of atoms held together by interactions between their orbiting electrons (chemical bonds)•More ways to absorb or release energy–Still quantized!Molecular LinesSpectral Line Formation•Still have electronic transitions–UV, Visible, and Near Infrared lines•Molecular Vibrations (bending and stretching of the chemical bonds)–Infrared Lines•Molecular Rotations–Microwave and Radio LinesMolecular LinesAtomic Hydrogen versus Molecular Hydrogen (H2)Molecular Hydrogen, or Diatomic Hydogen (H2)Atomic Hydrogen (H)Spectral Line AnalysisWhat information is contained in spectral lines?•Chemical Composition•Temperature•Rotation State•Radial Velocity•Density and Pressure•Magnetic Field StrengthSpectral ThermometerThe presence, absence, and strength (how bright) of a spectral lines are all indicative of temperatureWhere are the electrons? How excited or ionized.Radial VelocityApplying the Doppler Effect – Part I: Motion toward or away from the observer“It’s coming right for us!”“Run Away! Run Away!”redshiftedblueshiftedBlueshift Case with Hβchange in wavelength recession velocitytrue wavelength wave speed=Line BroadeningSpectral lines are not infinitesimally thin, they are spread out over a small range of wavelengths.Spectral lines are broadened due to:1) Thermal motions of particles2) Rotation of a macroscopic object3) Collisions between atoms4) Magnetic Fields – Zeeman EffectThermal Broadening - Temperature•Random motion (speed and direction) means atoms have some component moving toward or away an incoming photon (or vice versa)•The Doppler Shift applied to that photon (or atom) spreads out the precise energy required for absorption or emission •This broadens the the spectral line•Most of the atoms statistically have small thermal velocities, so Doppler shifted only small amount. [Gives shape of line]Applying the Doppler Effect – Part II: Random motions of particles also affect by Doppler EffectCollisional/Pressure Broadening•The energy associated with the collision between two particles needs to be accounted for•Number of collisions depends on the density and of the gas–Hence widths of spectral lines can give us density of the gas.Particles bump into each other with some energy, which will slightly offset the specific acceptable photon energyRotational BroadeningApplying the Doppler Effect – Part III: A rotating body has components moving toward us or away from usMagnetic Field BroadeningThe Zeeman EffectA fundamental property of electron orbitals is a magnetic component (the details… see Quantum Mechanics). The end result is when exposed to a magnetic field, the electron orbital energies split (due to the intrinsic magnetic moment), and hence the transition energies (wavelengths of photons absorbed or emitted) changes. How far the energy levels “split” depends on the strength of the magnetic field. This will broaden the spectral linestl;drMagnetic fields split spectral lines. Why? Quantum Mechanics is weirdHow split gives mag. fieldCHAPTER 5TelescopesClass QuestionWhat is the primary purpose of telescopes with respect to viewing astronomical objects? What do we want to do to the objects we observe?Apache Point Observatory. Sunspot, New MexicoTop: Sloan TelescopeMiddle: 1 m robotic telescopeBottom: 3.5 m Apache Point telescopeClass Question - AnswerIt’s not magnification (making things bigger) we are after, but rather, it’s
View Full Document
Unlocking...