Crash course in stellar pulsation
This presentation is the property of its rightful owner.
Sponsored Links
1 / 34

Crash Course in Stellar Pulsation PowerPoint PPT Presentation


  • 46 Views
  • Uploaded on
  • Presentation posted in: General

Crash Course in Stellar Pulsation. Ryan Maderak A540 April 27, 2005. Mechanisms. k mechanism Compression of partial ionization zones -> ionization -> small change in T k ~ r / T 3.5 , increase r -> increase k g mechanism

Download Presentation

Crash Course in Stellar Pulsation

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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Crash course in stellar pulsation

Crash Course in Stellar Pulsation

Ryan Maderak

A540

April 27, 2005


Mechanisms

Mechanisms

  • k mechanism

    • Compression of partial ionization zones -> ionization -> small change in T

    • k ~ r / T3.5, increase r -> increase k

  • g mechanism

    • Heat flow into partial ionization zone from higher temperature layers

  • So, compression -> higher k -> energy buildup -> energy release -> expansion


Mechanisms1

Mechanisms

  • e mechanism

    • Compression -> higher T -> higher energy production rate -> expansion

  • stochastic excitation

    • convective turbulence -> acoustic noise -> solar-type oscillations

  • oscillatory convection

    • convective + g-mode in rotating stars -> oscillatory modes

  • tidal interaction

    • periodic fluid motion -> non-radial modes


Hr diagram

HR Diagram

Gautschy & Saio, 1995


Main sequence

Main Sequence

  • Solar-type stars

    • solar-type oscillations expected

      • more precise photometry needed

    • ~mmag

    • greatest amp. at ~1.5 MSun


Main sequence1

Main Sequence

  • roAp = rapidly oscillating Ap stars

    • P = 5-15 min, multi-periodic, ~50 mmag

    • ~2 MSun

    • magnetically modulated rotational splitting

    • overlap with d Scuti instability strip, but excitation mechanism uncertain

      • kg in He II zone suppressed by diffusion of He

      • convection + B ? kg in Si IV zone?


Main sequence2

Main Sequence

Gautschy & Saio, 1996


Main sequence3

Main Sequence

  • d Scuti

    • P = 0.01-0.2 days, 0.003 to 0.9 mag, multi-periodic (up to 12 modes observed)

    • 1.5 – 2.5 Msun, A0 – F5 IV - V, disk population

    • non-radial p-modes, driven by kg in He II zone

    • amp. limited by coupling between p and g modes

    • “stable” stars observed within d Scuti instability strip

      • suspected to be very low amplitude variables

      • more precise photometry needed


Main sequence4

Main Sequence

  • d Scuti

http://users.skynet.be/bho/deltascutis.htm


Main sequence5

Main Sequence

  • Slowly Pulsating B Stars (SPB)

    • P = 1 – 3 days, low amp., multi-periodic

    • 2.5 – 5 Msun, B3 – B8 IV

    • kg driven g-modes

    • can be thought of as an extension of the b Cephei instability to longer periods


Main sequence6

Main Sequence

  • b Cephei

    • P = 0.1 – 0.6 days, 0.01 – 0.3 mag

      • majority multi-periodic, a few non-radial

    • 7 – 8 Msun, O8 – O6

    • p-modes, driven by kg in the “z-bump”

    • metalicity dependent pulsational stability

      • b Cep strip extends farther blue-ward for higher metalicity stars

    • b Cep-type variability appears in at least a few cases to be transient

      • Spica exhibited b Cep variability from ~1890 to 1972


Main sequence7

Main Sequence

  • bCephei

http://www.aavso.org/vstar/vsots/winter05.shtml


Main sequence8

Main Sequence

  • Be stars

    • exhibit photometric and line profile variability with periods of <1 day

    • found within the b Cep/SPB instability region -> “z-bump” driving

  • MS 60 – 120 Msun

    • models suggest e driving from CNO burning

    • e driving may be one of the factors which determines the high mass cutoff of the MS


Horizontal branch

Horizontal Branch

  • RR Lyrae

    • P = 0.3 – 1.2 days, 0.2 – 2 mag

    • < 0.75 Msun, A – F, prominent in globular clusters

    • kg driven, but convective flux is thought to be important

    • important standard candles for clusters, but the P-L relationship is metalicity dependent

      • the period decreases as cluster metalicity increases (for fixed Teff)

      • careful calibration and stellar evolution models needed


Horizontal branch1

Horizontal Branch

  • RR Lyrae

http://www.dur.ac.uk/john.lucey/astrolab/pulsating.html


Horizontal branch2

Horizontal Branch

  • RR Lyrae

    • RRab: asymmetric light curves, longer periods, higher amp.

    • RRc: nearly sinusoidal light curves, shorter periods, lower amp.

    • RRd: bi-periodic

    • RRab’s exhibit a periodic change in light curve shape and amp. -> “Blazhko” effect

      • coupling between B and rotation?


Horizontal branch3

Horizontal Branch

  • P-L Relation

http://zebu.uoregon.edu/~soper/MilkyWay/cepheid.html


Horizontal branch4

Horizontal Branch

  • “Classical” Cepheids

    • P = 1 – 135 days, ~0.01 – 2 mag

    • > 4 – 5 MSun, F at maximum light, G - K at minimum light

    • stars above 4 – 5 MSun pass through the instability strip during each of one or more blue loops

      • for ~4 MSun -> bi-periodic cepheid


Horizontal branch5

Horizontal Branch

  • Classical Cepheid

http://www.astronomynotes.com/ismnotes/s5.htm


Horizontal branch6

Horizontal Branch

  • “Classical” Cepheids

    • masses from evolution versus pulsation theories did not agree historically, but improved opacities solved the problem

    • but pulsational models using the improved values give periods that are metalicity dependent

      • careful abundance measurements are needed to use the P-L relationship accurately


Crash course in stellar pulsation

AGB

  • W Virginis (Population II Cepheids)

    • P = 0.8 – 35 days, 0.3 – 1.2 mag

    • M ~ 0.5 MSun

    • cross instability strip in late HB or early AGB evolution

    • fundamental or 1st harmonic, driven by He II and H/He I zones

    • instability strip is wider for metal poor stars


Crash course in stellar pulsation

AGB

  • W Virginis

http://www.astronomynotes.com/ismnotes/s5.htm


Crash course in stellar pulsation

AGB

  • RV Tau

    • P = 30 – 150 days, 1.5 – 2 mag

    • M = 0.5 – 0.7 MSun, F – G at maximum light, K – M at minimum light

    • driven by H and He I zones

    • characteristic “double peak” pattern

      • resonances between fundamental and 1st harmonic

      • chaotic motion of multiple atmospheric layers

      • low-dimensional chaotic attractors


Crash course in stellar pulsation

AGB

  • RV Tauri


Crash course in stellar pulsation

AGB

  • RV Tau

    • various irregularities

      • change in depth of primary and secondary minima

      • changes in period

    • relatively few known ~130 (GCVS)

    • duration of phase only ~500yr

    • believed to be post-AGB/proto-planetary

      • have experienced significant mass loss

    • RVb: long term (600 – 1500 day) variation in mean brightness

      • eclipsing binary? episodic mass loss? dust shell eclipse?


Crash course in stellar pulsation

AGB

  • Mira

    • P = 80 – 1000 days, 2.5 – 11 mag

    • low-mass, Me – Se

    • First variable discovered: 1595

    • fundamental, driven by H and He I zones

    • coupling between pulsation and convection


Crash course in stellar pulsation

AGB

  • Mira


Crash course in stellar pulsation

AGB

  • Semi-Regular

    • P = 20 – 2000+, ~0.01 – 2 mag, multi-periodic

    • occupy same part of HR diagram as Mira’s – physically similar

      • distinguished by amplitude

      • difference due to mass, composition, age

    • SRb: power spectra exhibit broadened mode-envelopes

      • stochastic excitation?


Crash course in stellar pulsation

AGB

  • Semi-Regular


Planetary nebula

Planetary Nebula

  • PG1159 (variable planetary nebula nuclei = PNNV)

    • P = 7 – 30 min

    • g-modes, driven by C and/or O K-shell ionization

    • Teff = 70000 – 170000, strong C, He, and O features


Cooling track

Cooling Track

  • DB-type variable WD (DBV)

    • P = 140 – 1000 seconds, non-radial

    • M ~ 0.6 MSun, Teff = 21500 – 24000

    • g-modes, driven by He II zone

    • complicated power spectra

      • need high time resolution and long data sets to resolve peaks -> WET


Cooling track1

Cooling Track

  • ZZ Ceti (DA-type variable WD)

    • Similar to DBV

    • g-modes may be driven by ionization of a surface H layer

    • lower Teff -> blue edge of instability ~13000K

    • H rich, with almost no He or metals


Future work

Future Work

  • Larger samples of Cepheids and RR Lyrae’s ---> more accurate determination of metalicity dependence of P-L

  • Continued high time resolution, long duration astroseismology -> better understanding of interior structure and excitation mechanisms

  • Better theory of convection -> better understanding of coupling between convection and pulsation


References

References

  • Carrol, B.W., & Ostlie, D.A. 1996, “An Introduction to Modern Astrophysics,” Addison-Wesley, Reading, MA.

  • Gautschy, A., & Saio, H. 1995, ARA&A, 34, 551.

  • Gautschy, A., & Saio, H. 1996, ARA&A, 33, 75.

  • “GCVS Variability Types.” http://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt


  • Login