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Main Sequence Fitting of Globular Clusters
- what kind of distances can you get between globular clusters
- how do you get absolute distances
- how accurate are the distances
- - relative
- - absolute = must measure the absolute distance to one cluster, using cepheids, parallax measurements, or RR Lyraes
- - accuracy 2-5%
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Main Sequence Fitting
- starts with the same temperature will have the same ____________
- groups of stars at different distances are ___________ on the HR diagram
- - luminosity
- - "shifted" downwards
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Supernovae Type 1A
- what is it?
- how do you use it
- - brightest type of standard candle (white dwarfs accumulating mass and becoming neutron stars)
- - watch its light curve and measure its peak flux
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Methods of Distance Measurement (6 types)
- - parallax (direct, geometric)
- - stellar classification (standard candles, large systematic uncertainties
- - Cepheid Variables (standard candles, open clusters, other galaxies)
- - RR Lyrae variables (standard candles, open clusters, nearby galaxies)
- - main sequence fitting (standard candles, globular clusters)
- - supernovae (standard candles; type 1A)
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Tully Fisher Relation
- Tully Fisher Relation
- - In disk galaxies, LGalaxy is correlated with the rotational velocity (Vrot) of gas in the disk (21 cm line is broadened in the spectrum).
- - Why is the line broadened? More massive galaxies -> higher luminosity and stronger gravity, which increases Vrot in the disk. This Doppler shifts the emission line across a wider wavelength range --> broader line!
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Faber-Jackson Relation
- -Similar to the Tully-Fisher Relation: but for elliptical Galaxies
- - LGalaxy is correlated with the velocity dispersion of stars.
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Whats the relationship of uncertainty to the number of times you perform an experiment
fractional uncertainty decreases as you increase the number of trials
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Other Distance Indicators - the cores of distant elliptical galaxies vs nearby galaxies
- (stars are closer or farther apart in each)
- which shows larger fluctuations in the flux/pixel?
- - more distant - stars look more bunched together
- - when there are fewer stars per pixel (nearby galaxies), adding one or two more stars produces a bigger total flux jump in that pixel
- - nearby galaxies
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Usefulness of distance measurements starting with closest objects to farther away
- radar randing (10-4 ly - solar system)
- parallax - nearby stars (102 ly main sequence fitting - milky way 105 ly
- cepheids - nearby galaxies (107 ly)
- type 1a supernovae, tully fisher relation, distant standards - nearby clusters (1010 ly)
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