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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 CatalogNames
...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)
Filter λeff(μm) Δλ(μm)U 0.36 0.07B 0.44 0.10V 0.55 0.09RCK 0.64 0.16R 0.70 0.22ICK 0.80 0.15I 0.90 0.24J 1.25 0.23H 1.65 0.29K 2.2 0.42L 3.5 0.57M 4.6 0.34N 10 6Q 19 5edge originally set by detector – now by filter
J H 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!
(99Tc has half-life of 2.1x105 yrs)
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
Brown Dwarfs
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 (discovered in 2012) – NH3 (H2O??)
L & T (brown dwarfs)
NOTE: Very Non-Planckian
HD189733b Hubble Data
Swain et al. 2008
Exoplanet “Spectra”