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3 - Stellar Spectra

3 - Stellar Spectra. Why a slit?. No slit. Slit. Sky Backgrounds and Telescope Nods. star slit. Visual & Photographic & 2D Electronic Detectors. 1D or “Compressed” 2D Electronic Detectors. Catalog Names. Increasing T. ...also collisions with electrons. Balmer Series & Balmer Jump. IR.

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3 - Stellar Spectra

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  1. 3 - Stellar Spectra

  2. Why a slit? No slit Slit

  3. Sky Backgrounds and Telescope Nods star slit

  4. Visual & Photographic & 2D Electronic Detectors 1D or “Compressed” 2D Electronic Detectors

  5. Catalog Names Increasing T

  6. ...also collisions with electrons...

  7. Balmer Series & Balmer Jump IR Visual! UV

  8. BLUE part of the visual spectrum.... Old Photographic NEGATIVES that Defined Spectral Classification

  9. Pressure Broadening & Pressure Ionization (Energy Level Perturbation & Changing Recombination Rate)

  10. Modern Digital Spectra (from Silva & Cornell 1992, ApJS, 81, 865)

  11. Near-IR Spectra (Rayner et al. 2009, PASP, 185, 289)

  12. Near-IR Detail

  13. Originally, classification was based on spectra at visible wavelengths, since that’s all that was available at the time!

  14. Luminosity Classes Log L V = Main Sequence T

  15. Spectral Resolution

  16. Measuring Stars at Different λs – “Alphabet Soup Photometry” - UBVRIJHKLMNQ "alphabet soup"? “Standard” Johnson System (the most common one in use today) Filter λeff(μm) Δλ(μm) U 0.36 0.07 B 0.44 0.10 V 0.55 0.09 R 0.70 0.22 I 0.90 0.24 J 1.25 0.23 H 1.65 0.29 K 2.2 0.42 L 3.5 0.57 M 4.6 0.34 N 10 6 Q 19 5

  17. K J H L M

  18. Photometry of 4 dusty stars

  19. Photometry & Stellar Magnitudes where const(λ) is set by the photometric system Relative brightnesses of 2 stars at a given λ:

  20. The relative brightness of a star at 2 different λs:

  21. For a collection of stars at the same distance from us, and T versus L diagram translates into a Color-Magnitude diagram. The magnitude can be either M or m without destroying this correspondence.

  22. Beyond OBAFGKM S Stars - dominated by ZrO C/O~1, sometimes Tc present! (99Tc has half-life of 2.1x105 yrs)

  23. Carbon Stars C/O >1 R - C/O > 1 bands of C2, C3, CH, CN, etc. N - C/O > 1 and s-process elements like Ba & Sr CH - Old stars with stronger CH

  24. Brown Dwarfs

  25. Brown Dwarf Spectral Classes M - Above 2000 K, TiO and VO dominate T=2000-2200 K, TiO condenses into solids CaTiO3 in M, Ti3O5 & Ti2O3 in cooler objects L (new!) - TiO and VO gone T (new!) - CH4 appears in “H” and “K” photometric bands (actually in “L” at M5, in “K” at L8, and in “H” at T0 - “The Goldilocks Problem”) Y (just discovered!) – NH3 (H2O??)

  26. L & T (brown dwarfs)

  27. NOTE: Very Non-Planckian

  28. Exoplanet “Spectra” HD189733b Hubble Data Swain et al. 2008

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