1 / 11

Pulsating Variables

0. Pulsating Variables. 0. Cepheid Variables. Discovered by J. Goodricke (1784):. Prototype: d Cephei. Light curve of d Cephei. 0. Cepheid Variables: The Period-Luminosity Relation. The variability period P of a Cepheid variable is positively correlated with its luminosity:.

ifama
Download Presentation

Pulsating Variables

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 0 Pulsating Variables

  2. 0 Cepheid Variables Discovered by J. Goodricke (1784): Prototype: d Cephei Light curve of d Cephei

  3. 0 Cepheid Variables:The Period-Luminosity Relation The variability period P of a Cepheid variable is positively correlated with its luminosity: MV = -2.80 log10Pd – 1.43

  4. 0 Cepheid Variablesas Distance Indicators • Measuring a Cepheid’s period • determine its absolute magnitude • Distance indicator! Cepheids are Ib supergiants, L ~ 103 - 4 L0 => Identifiable out to several Mpc!

  5. 0 The Instability Strip Classical Cepheids W Virginis Stars: metal-deficient (Pop. II), Cepheid-like Increasing Period RR Lyrae Stars: Pop. II; horizontal-branch; nearly standard-candle luminosity! d Scuti Stars: Evolved F stars near MS

  6. Stellar Pulsations Estimate from sound travel time through the star: P ~ r-1/2 Cepheids all have approx. the same surface temperature. => Higher L => Larger R => Smaller r => Larger P

  7. 0 Radial Pulsations

  8. 0 The Valve Mechanism Nodal zone is opaque and absorbs more radiative flux than necessary to balance the weight from higher layers. => Expansion Upon expansion, nodal zone becomes more transparent, absorbs less radiative flux => weight from higher layers pushes it back inward. => Contraction. Upon compession, nodal zone becomes more opaque again, absorbs more radiative flux than needed for equilibrium => Expansion

  9. For the valve mechanism to work: k needs to increase with increasing r and T 0 Kramer’s Opacity Law aR ~ r T-7/2 log(aR [cm-1]) Gas fully ionized; opacity dominated by free-free absorption Gas gradually becoming ionized 104 105 106 107 Temperature [K] → Partial Ionization Zones!

  10. 0 Location of Partial Ionization Zones LPVs: Valve mechanism driven by H partial ionization zones ~ 104 K ~ 4x104 K Instability strip: Walve mechanism driven by He partial ionization zones

  11. Non-Radial Modes of Variability: g-modes: fnet = (dF/dV)net = g (rs – rb) bubble (‘b’) surrounding medium (‘s’)

More Related