ASTR 3520 Observations & Instrumentation II: Spectroscopy

1. ASTR 3520 Observations & Instrumentation II: Spectroscopy Lecture 1 Introduction

2. Overview • John Bally C323A Duane 492 5786 • john.bally@colorado.edu • bally@casa.colorado.edu • Office hours: Th after class (2:00 PM) • Wed (2:00 PM) • Adam Ginsburg C329 Duane 303 667 3805 • adam.ginsburg@colorado.edu • Office Hours: Mon, Tues 11:00 AM • or by appointment • Student & Teacher Introductions:

3. Organization • Review course structure, content, and Syllabus • Observing Projects: Stellar, nebular spectroscopy, semester projects, labs, homework. • Apache Point Observatory Field Trip: • - 5 - 6 days/ 4 - 5 nights • - Covered by Course Fees • - VLA, NSO, APO • - Last week of Oct. (depends on TAC) • Observing Proposals for Semester project due end of Sept. • 24” Observing Groups 5 groups / 3 to 4 each. • - Each group must have at last 1 experienced observer • Start spectrograph overview (once-over lightly)

4. Spectroscopy: Astronomy => Astrophysics • Light as a wave phenomenon: = c • Geometrical optics => wave optics • Diffraction •  ~  / D • Interference: • n = D sin n = 1,2,3,… • Deep insights into the nature of atoms, molecules: • Discrete wavelengths => Discrete energy levels • Electrons stable only in certain orbits. • Interference of electron waves! •  = h / p = h / mv :de Broglie waves • All matter has wave-like behavior on sufficiently • small scale!

5. Spectrograph Focal Plane collimator camera detector Dispersing element Slit Telescope Spectrograph

6. SBO Spectrograph overview • Slit & Decker: • Restrict incoming light • Spatial direction vs. Spectral direction • Collimator & Camera: • Transfer image of slit onto detector. • Grating: • Disperse light: dispersion => spectral resolution • What determines spectral resolution & coverage? • - Slit-width • - Grating properties: Ngroves , order number • - Camera / collimator magnification (focal length ratio) • - Detector pixel size and number of pixels.

7. Types of Spectroscopy • Electromagnetic Waves: Emission, absorption • Visual, near-IR., FIR, Radio, UV/X-ray, gamma-ray • - Solids, liquids, gasses, plasmas • - Emission, absorption • - Spectral line, molecular bands, continua: • - Thermal (~LTE, blackbody, grey-body): • - Non-thermal (masers, synchrotron, …) • - Electronic, vibrational, rotational transitions. • - Effects of B (Zeeman), E ( Stark), motion (Doppler), • pressure (collisions), natural life-time (line widths) • - Radiative Transfer (optical depth) • Other types (not covered in this course): • NMR • Raman • Phosprescence / Fluorecence • Astro-particle

8. Review of Some Basics • c = n x l • Angular resolution: q = 1.22 l / D radians • 206,265” in a radian • E = h n • F = L / 4 p d2 • AZ, El, RA, Dec, Ecliptic, Galactic • Siderial time, Hour Angle • G = 6.67 x 10-8 (c.g.s) • c = 3 x 1010 cm/sec, • k = 1.38 x 10-16 • h = 6.626 x 10-27 • mH ~ mproton = 1.67 x 10-24 grams • me = 0.91 x 10-27 grams • eV = 1.602 x 10-12 erg • Luminosity of Sun = 4 x 1033 erg/sec • Mass of the Sun= 2 x 1033 grams

9. The Physics of EM Radiation • Light: l, n • - l n = c = 2.998 x 1010 cm/s (in vacuum) • - E = h n Photon energy (erg) • 1 erg sec-1 = 10-7 Watt • h = 6.626 x 10-27 (c.g.s) • 1 eV = 1.602 x 10-12 erg • - p = E / c = h / l Photon momentum • - l = h / p = h / mv deBroglie wavelength • Planck Function: B(T) • Emission, absorption, continua • Discrete energy levels: Hydrogen

10. Refraction: Snell’s Law: n1 sin(d1) = n2 sin(d2) d1 n1 n1 = refractive index in region 1 n2 = refractive index in region 2 n = c / v = lvacuum / lmedium d2 n2

12. Basic Lens formulae:

13. Basic Mirror formulae:

14. L d Diffraction: Light spreads asq = l / d In the `far field’ given byL = d2 / l

15. 2 slit interference Constructive Destructive

16. 2 slit interference Anti-reflection coating

18. Multi-layer interference filter:

19. Diffraction grating:

20. Fermat’s Principle: d(optical path length) = 0 Diffraction grating: order # wavelength diffraction angle groove spacing incidence angle

22. CCD Imaging Review • Review CCD basics • - How CCDs work • - CCD properties • Dark, flat, and bias frames • Image-scales • - focal length, pixel-scale, FOV • Review photometry basics • - The magnitude system • - Calibration • - Atmospheric effects; Air mass, color terms

23. Subaru 8m (Mauna Kea): Suprime Prime Focus CCD Mosaic 8192 x 8192 pixels using SITe chips (15 mm pixels)

24. Typical Raw image With a CCD Cosmic rays Bad pixels stars

25. CCDs (Charge-Coupled Device) • Properties • - Quantum efficiency (QE): • => 90% • - Gain: • G = e- /ADU • - Dark current: • 1 e- / hr to 103e- /sec • thermal emission: => Cool to –20 to –150 C • - Read Noise: • amplifier read-out uncertainty • 3 e- to 100 e- per read • - Spatial uniformity: • Bad pixels, columns: ~ << 1% • gain & QE variations Ee = hn - E0

26. CCDs • Properties • - Cosmic Rays: • 5 to > 103 e- produced by each charged particle • usually effects 1 or few pixels. • non-gaussian charge distribution • (different from stellar image or PSF) • - Well depth: • 5 x 104 to 106 e- • - Pixel size: • 6 mm to 30 mm • - Array size: • 512 x 512 to 4096 x 4096

28. Dark current: => cooling

29. MOSAIC CCD On KPNO 0.9m Vacuum Dewar LN2 (77K) Controller Filters & slider

30. 5 10 10 0 Charge Transfer V 0 10 0 5 5

31. Charge Coupled Devices (CCDs) Output amplifier

32. Charge Coupled Devices (CCDs) Output amplifier

33. Charge Coupled Devices (CCDs) Read

34. Charge Coupled Devices (CCDs) Read

35. CCD Corrections/Calibrations • Read noise: bias frames • - 0 second exposure • Dark frames: • - Same duration as science exposure with shutter closed • Flat fields: • - Dome flats • - Twilight flats • - Super-sky flats • Standard stars • - At several air-masses • A = sec (z) = 1 / cos(z) z

36. CCD Corrections/Calibrations • Types of image combinations: • IRAF task: imarith image1 (+,-,*,/) image2 output • imcombine @list_in output • - Average: 1/N S I(n) • - Mode: Most common data value • - Median: Value in middle of range • good for rejection of outliers (e.g CRs) • Combine (median) 3,5,7,….. An odd # • - bias frames • - flat frames

37. CCD Corrections/Calibrations • Reduction: • I(raw) - median(bias) • I(reduced) = • norm [median(Flat – bias)] • Note: Bias can be a Dark if hot pixels /or dark current is large

38. Flat Field Example star cosmic ray Hot pixels star Bias or dark level Raw science frame star cosmic ray star Dark subtracted frame

39. Flat Field Example star cosmic ray star cosmic ray Flat frame

40. Flat Field Example cosmic ray Flat frame 1 Normalized, dark subtracted, median of > 3 flat frames

41. Flat Field Example cosmic ray star Science frame 1 Normalized flat frame star star Reduced science frame

42. Photometry Basics: • Vega magnitudes: • m(l) = -2.5 log [F(l) / FVega(l)] • F(l) = Counts on source • FVega(l) = Counts on Vega • A = sec (z) = 1 / cos(z) z

43. Type of Spectra • Continuum: • - Blackbody: Bn(T) • - free-free, free-bound • - Non-thermal: Synchrotron radiation • - Compton scattering • Line & Band • E dipole, B diplole, E quadrupole • fine structure, hyperfine structure • - electronic transitions • - vibrational transitions • - rotational transition

44. Types of Spectra: Hot, Opaque media Nebulae Stars

45. The Planck Function: Black-body radiation (erg s-1 cm-2 Hz-1 2 p sr-1) Wien: B(n,T) = (2 p hn3 / c2) e-hn/kT Rayleigh-Jeans: B(n,T) = 2kT/l2

46. The Planck Function: Black-body radiation Wien Rayleigh-Jeans

48. Spectrum of Hydrogen (& H-like ions) Ionization (n to infinity): E = 13.6 eV Transitions: E = hn = Eu – El Ionizationat E = 13.6 eV or less than l = 912 Angstroms a b g Balmer • = R [ 1/nl2 – 1 /nu2] R = 3.288 x 1015 Hz b a Lyman

49. Bohr model: Allowed orbits mvr = nh /2p Coulomb Force: Ze2 / r2 = mv2/r Thus,(eliminate v) r = Ze2 / mv2 = n2h2 / 4 p2 Ze2 m Energy E = - (1/2) Ze2 / r = - 2 p2 Z2e4m/ n2h2