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Distances from time delays Water-maser proper-motions by VLBI

Distances from time delays Water-maser proper-motions by VLBI. Appears like the Dawn Fair as the Moon Bright as the Sun Majestic as the Stars by Nari Jeong 2007. 7. 19. Distances from time delays. < Fundamental thinking > Astrophysical source’s light output changes with time

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Distances from time delays Water-maser proper-motions by VLBI

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  1. Distances from time delaysWater-maser proper-motions by VLBI Appears like the Dawn Fair as the Moon Bright as the Sun Majestic as the Stars by Nari Jeong 2007. 7. 19

  2. Distances from time delays < Fundamental thinking > Astrophysical source’s light output changes with time -> we can estimate its distance!!

  3. The ring around Supernova 1987A < Fact > IUE -> narrow emission lines from highly ionized atoms in the spectrum of the supernova. < Reason > Lines arise from radiation that has been reprocessed by material at some distance from the supernova. < How to estimate distance > Supernova : 52±3kpc

  4. Gravitational lens time delays < Fact > Large scales!! -> Gravitationally-lensed quasars. < Reason > Light passes a massive body -> path is bent by gravity. < How to estimate distance > The first term : The second term : General-relativistic time dilation <- distortion of space-time in the presence of a gravitational field

  5. < Fact > Quasar has -> two images < Reason > Different mass models would produce very different arrangements on the sky the multiple image. < Kind > • Multiple-image gravitational lens • Luminous arc • Radio ring • Microlensing

  6. < Q2237+0305, Einstein Cross >

  7. Water-maser proper-motions by VLBI Large distances!! • Bright enough to be readily detectable • Measure very small change = > H2O maser spots ( occur : active star formation ) VLBI ( very long baseline interferometry ) < Greenhill et at (1993) > H2O maser in M33 at two epochs separated by t = 479 days. Point out : large number of uncertainties

  8. < Greenhill et al (1981) > Application of such a model to a Milky Way H2O maser Source. < Miyoshi et al (1995) > VLBI observation : core of the nearby spiral galaxy NGC 4258. Distribution of H2O maser spots with a remarkably simple geometry. < Figure 7.3 > Center – rotation as r^-1/2 – Keplerian mation Middle – linearly – a single circular orbit End – similar center – disk’s inner edge => Centripetally accelerated by the central mass < Greenhill et al (1995) > Projected close to the center of the disk drift

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