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Unformatted text preview: AST 4723 Spectroscopy Lab Due Thursday, November 11, 5pm Background: Spectroscopy is a fundamental tool in all subfields of astronomy. One of the most basic applications of spectroscopy is to determine the radial velocity of an object information that can be used to detect exosolar planets (via variations in the Doppler shift of the host star), determine proper motions of stars in our galaxy, or determine the redshifts of external galaxies. Redshift, which refers to the recessional velocity (v) of a galaxy relative to the speed of light, is defined as z = v/c = / where v is the recessional velocity and c is the speed of light, or equivalently observed = (1+z) rest where observed and rest respective refer to the observed wavelength and the wavelength that light from the galaxy would have if the recessional velocity were zero. In addition, spectra also provide information about the physical properties of an object. For a star one can determine the temperature and chemical composition; for a galaxy one can determine quantities such as the chemical composition and the mean age of a stellar population (e.g. whether the galaxy has ongoing star formation, or if not how long it has been since star formation ceased). For a galaxy, one of the most basic things that can be extracted from the spectrum is whether the galaxy is star-forming, or quiescent (passive, with no ongoing star formation). In class we saw spectra for different types of galaxies. Objective: In this lab you will be analyzing spectra for four galaxies. The goals of the lab will be to do the following: i. Extract one-dimensional spectra from the 2D spectra you are given ii. Determine redshifts for the galaxies iii. Determine whether each galaxy is star-forming or passive iv. Identify the spectral features present in the spectra and measure the linewidths and equivalent widths of these features Table of Important Wavelengths (): 3727 [O II] (doublet) 3934 Ca H 3968 Ca K 4305 G band 4340 H 4861 H 4959,5007 [O III] 5175 Mg I 6562 H 6583 [NII] Software Notes:...
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- Fall '10