### spectral resolution

(resolution)
(measure of a spectrograph's ability to resolve features of the spectrum)

Spectral resolution is a measure of a spectrograph's ability to distinguish features in the spectrum, typically noted as Δλ, meaning the smallest division in wavelengths that the spectrograph can distinguish, i.e., a distance, e.g., in nm. The resolving power (R) is defined as:

```    λ
R = ——
Δλ
```

(These are standard definitions which do not match all common practice: an instrument's spectral resolution is often described using the ratio R rather than the distance measure.) Examples:

• STIS (HST): distinguishes 0.17 nm resolution in a 1000 nm wave (yielding 5900 as the resolving power).
• CRIRES (ESO VLT): a resolving power up to 100,000.

There is a tradeoff between spectral resolution and throughput, i.e., how much light is necessary to produce the spectrum date, which is (apparent) brightness of the source times the time necessary to produce the spectral energy distribution (SED). For example, for extremely distant galaxies that are dim to us, spectrography may be impossible, and approaching such distances, higher-resolution SEDs may be impractical or impossible.

Radial velocity (RV) measurements using spectral lines depend upon spectral resolution, but far more precise RVs are now inferred than implied by spectral resolution of the spectrograph: astrophysicists constantly develop techniques to do this, but a typical procedure is to analyze the SEDs from a number of observations and statistically work out the most likely RV-pattern to produce all of them, presuming the relatively-rough measured wavelengths of the spectral line reflect their true wavelengths according to an appropriate probability density function, e.g., the normal distribution.

(instruments,measure,EMR,specification,spectrography)
https://en.wikipedia.org/wiki/Spectral_resolution
http://slittlefair.staff.shef.ac.uk/teaching/phy217/lectures/instruments/L17/index.html

Referenced by pages:
Anglo-Australian Telescope (AAT)
ASCA
BigBOSS
Víctor M. Blanco Telescope
Chandra X-ray Observatory (CXO)
CONCERTO
continuous absorption
CRIRES
cross dispersion spectrograph
double-line spectroscopic binary (SB2)
European Extremely Large Telescope (E-ELT)
European Southern Observatory Very Large Telescope (ESO VLT)
fine structure
Fraunhofer lines
Gemini Observatory
ground state
Gran Telescopio Canarias (GTC)
H-alpha (Ha)
HARMONI
HARPS
HCI
HERMES
Hobby-Eberly Telescope (HET)
NEWS
HRS
Hubble Space Telescope (HST)
Interstellar Medium Absorption Profile Spectrograph (IMAPS)
IRAS
IRTF
Keck Planet Finder (KPF)
Large Binocular Telescope (LBT)
Las Cumbres Observatory (LCO)
Lynx
Magellan Telescopes
Mercator Telescope
Multi-object Optical and Near-IR Spectrograph (MOONS)
NIRPS
New Technology Telescope (NTT)