Spectroscopic Data. ASTR 3010 Lecture 15 Textbook Ch.11. Spectroscopic Measurement. CCD or other digital Detector. Schematic Diagram of a Typical Spectroscopic Data. Only Readout the relevant portion of CCD array. Spectroscopic data are typically long and slender.
CCD or other digital Detector
to save the readout time and storage space…
bad pixel, bias, over-scan, trim, zero, flat-fielding
find trace extract normalize
using arc images (e.g., gas emission lines)
using stars with known smooth spectra
line width measurement, Teff, [Z/H], vsini, etc.
words in green
IRAF commands for the
finding the aperture and defining the sky regions apfind& apedit
need to trace the aperture along the dispersion axis aptrace
using arc images, you can convert pixel numbers to wavelength!
sensfunc and calibrate
continuum or splot
Telluric standard stars : stars with no (or very little) spectral line feature.
low metallicity stars, white dwarfs, fast rotating stars
splot display the extracted spectrum and do simple operations on the spectrum such as continuum normalization and equivalent width measurements.
‘h’ + ‘k’
EW fit with
A Gaussian to
area = area
EW unit is the wavelength unit of the spectrum
flat images sometime taken w/wo the dispersing element.
Which one is better? Is only one kind useful?
this spectrum is a combination of the above detector flat + spectral response of the system.
Flat-fielding is to remove the pixel-to-pixel sensitivity variation!
Other gradual, global variation can be taken out later.