Download Spectroscopic Calibration and Applications - Lecture Notes | AST 5765 and more Study notes Astronomy in PDF only on Docsity! UCF Physics: AST 5765/4762: (Advanced) Astronomical Data Analysis Fall 2009 Lecture Notes: 27. Spectroscopic Calibration and Applications 1 Check In: 12:30 — 12:35, 5 min • Questions? 2 Calibration Sources: 12:35 — 12:45, 10 min • Common calibration sources: Source Wavelength Resolution Doppler Slit Shifts Extra Time Object any depends on object incl. incl. no OH- sky lines near IR R>600 to resolve blends no no no Lamp: He, Ne, Ar, Xe UV–near IR all, watch blends no no yes Planetary nebulae (H, He) visible–mid IR low only (few lines) extra maybe yes Star lines UV, near IR depends on line extra? extra yes Telluric lines in starlight near IR depends on line no extra yes 3 Calibration Observations: 12:45 — 12:50, 5 min • How often? • Often enough to make sure the “solution” (fit) has not changed significantly • Depends on: – Instrument mechanics (flexure) – Instrument temperature changes – Resolution – How accurate a calibration the program requires (i.e., what’s“significant”) • 17specflex 4 Gravitational Redshift: 12:50 — 12:55, 5 min • 18specaps • Photons leaving a massive body increase their potential energy • This decreases their kinetic energy • Since E = hν, if E drops, so does ν • So, they shift to longer wavelength 1 5 Doppler Shift: 12:55 — 1:00, 5 min • If wave source moves toward observer, wave is perceived at higher frequency: z = ∆λ λ = v c (1) • At high v: v c = (z + 1)2 − 1 (z + 1)2 + 1 (2) • Wavelengths shift shorter for approaching source (blue shift) • Wavelengths shift longer for receding source (red shift) • If a 1-µm line appears at 7 µm, z = 6, v = 48 50 c • Hubble flow for distant galaxies, students from exams, etc. 6 Spectral Line Profiles: 1:00 — 1:05, 5 min • At high R, spectral lines have a shape, the line profile • Several effects combine: some intrinsic and instrumental • Instrumental: mainly the finite slit width • Intrinsic: nature has no δ functions! • Line broadening comes from: (Don’t go into detail, that’s next.) – Temperature (Doppler) broadening – Lifetime/collisional broadening – Zeeman (magnetic field) and elecric field broadening • Final profile is convolution of all independent effects 7 Electrical and Zeeman Broadening: 1:05 — 1:10, 5 min • Effects that shift or split quantum levels also shift line wavelengths • EX1: High density/pressure distorts orbital shape and energy levels • EX2: Zeeman effect: high magnetic fields (e.g., near surfaces of neutron stars or in sunspots) split and shift quantum states • Can measure amount of split, and thereby directly measure field strength in a remote object 2
