Spectroscopic Parallax

# Spectroscopic Parallax - used for the absolute magnitude...

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Spectroscopic Parallax You can use the correlation between luminosity and temperature (spectral type) for main sequence stars to get their distances. This method is called spectroscopic parallax because a distance is found from knowledge of a star's spectral type. Distances for stars too far away to show a detectable trigonometric parallax are found this way. Here are the steps you use to find a star's distance using the spectroscopic parallax method: 1. Determine the star's spectral type from spectroscopy and measure the star's apparent brightness (flux). 2. Use a calibrated main sequence to get the star's luminosity. The Hyades cluster in the Taurus constellation is the standard calibrator. 3. Use the Inverse Square Law for Brightness to get the distance: unknown distance = calibrator distance × Sqrt [calibrator flux/unknown star's flux.] How do you do that? A G2 star appears 25 times dimmer than it would if it was at the standard distance of 10 parsecs
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Unformatted text preview: used for the absolute magnitude. The G2 star is at a distance of = 10 × Sqrt [1/(1/25)] = 10 × Sqrt [25/1] = 50 parsecs from us. Distances to red giant and supergiant stars are found in a similar way but you need to investigate their spectra more closely to see if they are the very large stars you think they are. Their position in the calibrated H-R diagram is found and their apparent brightness gives you the distance. Also, this process can be used to find the distance of an entire cluster. The entire color-magnitude diagram for the cluster is compared with a calibration cluster's color-magnitude diagram. The calibration cluster is a known distance away. Some adjustments for the cluster's age and composition differences between the stars in the cluster and the calibration cluster must be made. Such fine-tuning adjustments are called ``main-sequence fitting''....
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## This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

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