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7.3 Relative Distance Estimators

7.3 Relative Distance Estimators. 김대원. Absolute distance estimator. Direct method to determine distance to particular objects. Simple and powerful. However most astronomical phenomena is not that simple, no such simple modeling is possible anymore when we want to estimate their distances.

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7.3 Relative Distance Estimators

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  1. 7.3 Relative Distance Estimators 김대원

  2. Absolute distance estimator • Direct method to determine distance to particular objects. • Simple and powerful. • However most astronomical phenomena is not that simple, no such simple modeling is possible anymore when we want to estimate their distances. Empirical relationship after calibration can be used as distance estimator.

  3. Typical features of relative distance estimators • Distance-independent properties which vary with distance. • Properties which is empirically based. • To calibrate relative distance, we MUST obtain, at least, one absolute distance to the objects.

  4. Advantages of R.D. • Not subject to the systematic uncertainties that arises if our assumptions are incorrect. • Can be estimated using common sources  we can measure the distances to many more sources!

  5. 7.3.1 Luminosities ofvariable stars • Cepehid variable M_v ~ -3, RR Lyrae M_v ~ 0.6 • Excellent standard candles. • Can be observed to reasonably large distances because they are bright. • Can be calibrated quite straightforwardly because large number of them are found near the Sun. • Under optimal conditions, the distances error is ~ 10%.

  6. 7.3.2 Luminosity functions • Globular clusters • By Shapley, 1953. • Average luminosities of GC in the Milky Way, the LMC and M31 are similar. • For the MW, Mv_GC = -7.4 +- 0.1 • One caveat : different natures between spiral and elliptical galaxies.

  7. http://www.noao.edu/jacoby/pnlf/pnlf.html If we adopt a distance to M31 of 740 +- 40 kpc, we obtain an absolute magnitude for the cut_off = -4.6 +-0.1 • Planetary nebulae • Narrow bandpass filters centered on the 500.7nm, oxygen line, show planetary luminosity function with cut-off apparent magnitude, m^cut_PN.

  8. 7.3.3 Novae and supernovae • Novae : properties • Explosive ignition of accreted material on the surface of WD. • M_v ~ -7 at maximum brightness. • Rather independent on the metallicity if their host systems.

  9. Novae : distance indicator for MW. • Expansion parallax • cannot be used for extra-galactic novae due to their small angular diameters.

  10. Novae : distance indicator in extra-galactic scale. • M_v : from -4.8 to -8.9  Only the intrinsic are not standard candles. • However, their decline rates of luminosities depend on their absolute brightness. (faint novae decays more slowly) ; where t_2 is the time that the nova took to decline in brightness by two magnitudes from this maximum. See Figure 7.5.

  11. Novae : etc. • Distance uncertainty is ~ 25% • Some novae are fainter or brighter than predicted by previous equations. • LF of novae at maximum brightness shows double-peaked function, which could be used as standard candle.

  12. Type Ia supernovae : properties • All Ia follow remarkably similar evolution.  luminosities of Ia might also all be very similar.  ideal standard candles. • M_v = -19.52 +- 0.07, M_b = -19.48 +- 0.97, when adopting Cepheid distance scale. • Theoretically, M_b = -19.4 +- 0.3, consistent with the empirical calibrations.

  13. Type Ia supernovae : etc. • Maza et al (1994) • Studied two Ia SN. They should differ by only 0.1 mag. But they differ 0.8+-0.2 in the B band and 0.4+-0.2 in the I band. • Phillips (1995) suggested that their colors vary with luminosity declines. • Hoflich & Khokhlov (1996) simulated Ia supernovae and found that the peak luminosities and light curve shape could be vary from system to system.

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