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

Increasing T Catalog Names

...also collisions with electrons...

Balmer Series & Balmer Jump IR UV Visual!

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

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

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

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

Near-IR Detail

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

Log L T Luminosity Classes V = Main Sequence

Spectral Resolution

Measuring Stars at Different λs – “ Alphabet Soup Photometry ” - UBVRIJHKLMNQ “ Standard ” Johnson System (and newer Bessell Cousins-Kron filters) Filterλ eff (μm)Δλ(μm) U B V R CK R I CK I J H K L M N106 Q195 edge originally set by detector – now by filter

JH K L M

Photometry of 4 dusty stars

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

The relative brightness of a star at 2 different λs:

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.

Beyond OBAFGKM S Stars - dominated by ZrO C/O~1, sometimes Tc present! ( 99 Tc has half-life of 2.1x10 5 yrs)

Carbon Stars C/O >1 R - C/O > 1bands of C 2, C 3, CH, CN, etc. N - C/O > 1 and s-process elements like Ba & Sr CH - Old stars with stronger CH

Brown Dwarfs

Brown Dwarf Spectral Classes M - Above 2000 K, TiO and VO dominate T= K, TiO condenses into solids CaTiO 3 in M, Ti 3 O 5 & Ti 2 O 3 in cooler objects L (“new”!) - TiO and VO gone T (“new”!) - CH 4 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 (discovered in 2012) – NH 3 (H 2 O??)

L & T (brown dwarfs)

NOTE: Very Non-Planckian

HD189733b Hubble Data Swain et al Exoplanet “Spectra”