1 / 32

Variable Stars: Pulsation, Evolution and application to Cosmology. Shashi M. Kanbur SUNY Oswego, July 2007

Variable Stars: Pulsation, Evolution and application to Cosmology. Shashi M. Kanbur SUNY Oswego, July 2007. Contents. Lecture I: Observation Aspects/Theory Lecture II: Stellar Pulsation Lecture III: Stellar Evolution Lecture IV: Pulsation Modeling

chelsey
Download Presentation

Variable Stars: Pulsation, Evolution and application to Cosmology. Shashi M. Kanbur SUNY Oswego, July 2007

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. Variable Stars: Pulsation, Evolution and application to Cosmology.Shashi M. KanburSUNY Oswego, July 2007

  2. Contents • Lecture I: Observation Aspects/Theory • Lecture II: Stellar Pulsation • Lecture III: Stellar Evolution • Lecture IV: Pulsation Modeling • Lecture V: Applications: The distance and age scales.

  3. Lecture I: Observational Aspects • Classical Cepheids: Cepheids and RR Lyraes. • Very regular brightness fluctuations ranging from hours to days. • Pulsation is due to internal mechanism, not due to binary or occulting effects. • Comparitively rare: 1 in a million.

  4. Magnitudes and Black Bodies • Luminosity: total energy radiated into space/second: Watts, Sun’s luminosity is about 4*1026 Watts • Magnitude, M = -2.5*log L + const. • Vega defined to have zero magnitude. • Absolute and apparent magnitude • mv-MV = 5logd – 5; inverse square law, • B = L/4πd2 • Magnitudes in certain wavelength ranges, U,B,V, R,I,J, H, K etc. • Stars are good examples of black bodies, Stefan Boltzmann law: • L = 4πr2σT4 • Colors: Difference of two magnitudes: eg. B-V, V-I. • Color: independent of distance, bluer or smaller values of the color index imply hotter stars – Wien’s law.

  5. Cepheids • Young, population I,high metal content: X=0.7, Z=0.02 • Periods range from 2 days to about 100-120 days. • M: 2-10 solar masses, L: ranges from tens to thousands of solar luminosities – mass-luminosity relation (ML), Teff: 5000-6400K • Brightness fluctuations of the order of 1 magnitude, surface velocities of the order 40-60km/s. • Located in the disks of spiral galaxies.

  6. RR Lyraes • Old, population II, low metal content, X=0.7, Z = 0.001 – 0.0001. • Periods range from 0.2 -0.9 hours. • 0.5-0.9 solar masses, tens – hundreds of solar luminosities, Teff: 6000 – 7000K. • Brightness fluctuations of the order of 1 magnitude and velocity fluctuations of the order of 40-60km/s. • Located in globular clusters and in the field.

  7. Cepheids • Fundamental mode, first and second overtone oscillators – some double mode stars. • Radial Oscillators. • Many recent microlensing surveys have produced lots of new data: exciting field. • OGLE, MACHO • SDSS, LSST • Hubble Space Telescope has observed Cepheids in some 30 galaxies in our local group:HST • Amplitude of oscillations generally decreases as wavelength of observation increases.

  8. Hertzsprung Progression • Around P=7d, bumps appear on the descending branch. • At 10 days, bumps area at maximum light. • Around P=12d, bumps appear on ascending branch. • Around P=20d, bumps disappear.

  9. Fourier Decomposition • Need to quantify the structure of the light curve. • V = A0 + Σk(Aksin(kωt + φk)), • ω=2π/P, P the period in days, • The summations goes from k=1 to N, the order of the fit; typically N is about 8. • Ak,φk: Fourier amplitudes and phases • Use least squares to fit this to observed data points. • Compute Rk1=Ak/A1, φk1=φk-kφ1 and plot these against period.

  10. Fourier Decomposition and the Hertzsprung progression • Major discontinnuity in Rk1, φk1 at a period of 10 days, the center of the Hertzsprung progression. • Seen in many wavelength bands. • Seen in Galaxy, LMC and SMC at about the same period: no significant evidence of a large change in the location at 10 days as a function of metallicity. • Galaxy: metal rich (Z=0.02), LMC intermediate (Z=0.008), SMC metal poorer or at least has less metals than the LMC (Z=0.004).

  11. RR Lyraes • Again fundamental, first and second overtone pulsations: some double mode or beat stars. • Radial oscillators but ….? • Amplitude generally decreases as wavelength increases. • Some stars exhibit the “Blazhko effect”: second periodicity superimposed on the first. • Use Fourier decomposition as well to characterize light curve structure.

  12. RR Lyraes in M3 • Variables in M3

  13. The Cepheid Period-Luminosity Relation • Empirical relation initially observed by Henrietta Leavit. • MACHO PL relation in the LMC

  14. The Cepheid PL relation • MX = aX + bXlogP • How do aX bX vary from galaxy to galaxy or with metallicity? • For a given galaxy, does bX vary with period? • How do aX, bX vary with X, the waveband of observations. • Interstellar reddening: astronomical objects appear redder than they actually are:

  15. Other types of variable stars • Type II Cepheids; population II counterpart of classical Cepheids • Miras: Long period variables, periods of the order of hundreds of days. • Semi-regular variables: variable luminosity but no real regularity or repetition. • Non-Radial Oscillators: eg Sun.

  16. Lecture II: Stellar Pulsation.

More Related