Spectroscopy from Space ERIC HERBST

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

Quantized Energy Levels DE = hn True for low density gas

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

STELLAR SPECTRA COOL AND RAREFIED HOT AND DENSE

CONTINUUM/BLACK BODY

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

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)

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)

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

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 = 300 K infra-red T = 10 K radio waves

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…..

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

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

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

Soot? Coal? Graphite? Diamond?

CLASSIFICATIONS OF PROTOSTARS m m m

Protoplanetary Disk (Proplyd) Column density Cosmic rays UV X-ray midplane UV 500 AU 0.01-0.1 M0 T Tauri star – 106 yr old Keplerian rotation