1. Spectroscopy from Space
ERIC HERBST

2. How do we learn about the composition of other objects in the universe?
SPECTROSCOPY

9. Quantized Energy Levels
DE = hn
True for low density gas

10. TYPES OF SPECTRA Hot/high pressure/solid “continuum” Hot/low pressure
Cool/low pressure
Needs continuum

11. STELLAR SPECTRA
COOL AND RAREFIED
HOT AND DENSE

12. CONTINUUM/BLACK BODY

13. Fraunhofer Lines C =H; D = Na; E = Fe; K,H = Ca; A = O2 B
Bunsen and Kirchhoff did original analyses

14. WHAT WE LEARN ABOUT STARS
Atmosphere mainly atoms (some neutral and some ionic)
How much of each element there is:
H > He >> C, N, O  10-4H
Stellar spectral classes:
O B A F G K M (Sun G2)

15. Molecules versus Atoms
Transitions between electron energy levels (ultraviolet)
Transitions between rotational levels (radio)
Transitions between vibrational levels (infrared)
Transitions between electron energy levels (vis/UV)

16. The most common use is to make what is known as a potential energy surface (PES).
If we solve the SE for fixed nuclear distances we get the energy of the molecule at various points as is shown to the right for H2

17. Molecules in Space Prefer cool to toasty places
Interstellar clouds cold (10 K)
How look for molecules there?
Cool regions emit at long wavelengths: T = 6000 K visible
T = K infra-red
T = K radio waves

18. MOLECULAR ROTATION E = B J(J+1) “radio” emissions J+1 l = 1 mm J
DE = hn
E = B J(J+1)
n = 2B(J+1) = 2B, 4B, 6B…..

21. Orion KL Spectrum at the C18O line frequency
J = 2 -> 1
Taken at 218 GHz using a 1 GHz wide spectrometer

22. Atmospheric junk
Learn: molecular concentrations, temperature, overall density, turbulent and thermal motions, rotation

24. MOLECULAR VIBRATIONS
INFRARED RADIATION
E = hn (n+ ½)

25. Soot?
Coal?
Graphite?
Diamond?

26. CLASSIFICATIONS OF PROTOSTARSm m m

27. Protoplanetary Disk (Proplyd)
Column density
Cosmic rays UV
X-ray
midplane UV
500 AU M0
T Tauri star – 106 yr old
Keplerian rotation