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Cepheid Multiplicity and Masses: Fundamental Parameters Nancy Remage Evans

Delve into the intricacies of Cepheid stars' masses and multiplicity in stellar systems, focusing on binary characteristics, energy distributions, and Hubble snapshots. Learn about the challenges and breakthroughs in measuring stellar masses and their implications in stellar evolution studies.

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Cepheid Multiplicity and Masses: Fundamental Parameters Nancy Remage Evans

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  1. Ed Guinan Scott Engle Howard Bond Gail Schaefer Derck Massa Charles Proffit Alexey Rastorguev Natalia Gorynya Scott Wolk Massimo Marengo Margarita Karovska Ken Carpenter Erika Bohm-Vitense Joel Eaton Ignazio Pillitteri Leonid Berdnikov Cepheid Multiplicity and Masses: Fundamental ParametersNancy Remage Evans Poland

  2. Cepheids • Extragalactic distance scale • Stellar evolution: • ``The Cepheid Mass Problem” • Asteroseismology • Star formation: massive binaries Poland

  3. Outline • Star Formation • Binary Characteristics • Hubble, Chandra, XMM • Tr 16: X-Rays • Masses: Evolution • Velocity data Poland

  4. Cepheids • 4-7 M • Formerly B stars • Young ~50 Myr • Post-RGB, core He burning • Evolve without strong mass loss of O stars • Known distances Poland

  5. Part I: Multiplicity: Goals • Star Formation • Angular momentum • Low mass: well characterized • High mass: • rarer, broad lines, mass loss • Observations Binary, triple,…. Distribution of mass ratios Maximum separation HIGH VS LOW MASS STARS Poland

  6. High Mass Companions: IUE Survey • Particularly complete binary information: • Evolved cool stars: sharp lines • Hot companions dominate in UV • Observed the 75 brightest Cepheids with IUE • All companions through early A detected • 21% companions • Using RV: 34% Poland

  7. Energy Distributions • Hot companions • Normalized at 1600 A • Generally very low reddening • Well determined spectral types, mass Poland

  8. IUE Example • Cepheid RT Aur • Compared with main sequence stars RT Aur Poland

  9. Mass Ratios • M2/M1 • Strong preference for low mass companions • Selection: orbital periods longer than 1 year • Contrast: binaries with P<40d: equal mass preference (Tokovinin, 2000) Poland

  10. Multiplicity: Completeness • Cepheids with orbits • 18 observed with IUE => hot companions known • Multiplicity? M2unknown Poland

  11. Multiplicity: Completeness UV high res • High resolution UV spectra (HST, IUE): velocity of companion • 8 of 18 • 5 of 8 are triples Poland

  12. Multiplicity: Completeness Triples • Cepheids with orbits + companion spectrum • 8 (possibly 9) are triple: 44% (50%) Poland

  13. Hubble Snapshot Survey • HST WFC3 • V and I • Eta Aql • Hot companion known from IUE • No orbital motion Poland

  14. Eta Aql: T Mon Subtracted Poland

  15. Binary Parameters • IUE survey: identify all companions M > 2 M • 15 Cepheids • 11 have orbits, orb. motion => period • 3 resolved with WFC3 => separation • => period • (Eta Aql, V659 Cen, S Nor) • Compare distribution of separations of Cepheids (5 M) with solar mass stars (Raghavan et al., Duquennoy and Mayor) for q = M2 /M1 > 0.4 Poland

  16. Orbital Period Distributions • Cepheids vs Solar mass stars: different period distribution for comparions with mass ratio > 0.4 Cepheids Solar Mass Poland

  17. Hubble Snapshot Survey: Goal 2: Low Mass Stars • Resolved companions • HST WFC3 • l Car • ~40” x 40” • V and I • Young low mass stars produce X-rays • XMM image of l Car: no X-rays => old field stars Poland

  18. Low Mass Companions • Alpha Per Cluster: age of a typical Cepheid • Rosat observations: filled symbols are X-ray detections • Essentially all stars cooler than F5 V • Field stars would not be detected in X-rays Poland

  19. Low-Mass Companions: Chandra Observation of Polaris • Young, low mass stars prominent in X-rays • Center 3’ of ACIS-I field • Putative components marked • A = Aa + Ab • B F3 V • C, D • X-ray but no 2MASS: background AGN • Resolved companions 15 mag fainter September 2011 Poland

  20. HST Snapshot: Y Car Poland

  21. Low Mass Companions of B Stars B stars: comparable mass to Cepheids • Late B stars: no X-rays • X-rays taken to be from low mass companions • Identified late B stars in Tr 16 using photometry and proper motions • Chandra ACIS image: B stars: blue: detected; purple: not detected Poland

  22. Tr 16 Late B Stars • X-rays: dot => low mass companion ( 1.4 to 0.5 M) • 39% of late B stars • Complementary estimate of more massive companions from IUE: 34% • Preliminary: q < 0.1 lacking Poland

  23. Part II: Masses as Evolutionary Benchmarks • Luminosity: mass of He burning core Core convective overshoot Rotation Radiative opacity Mass loss Poland

  24. Masses • Problem: mass mismatch between evolutionary and pulsation masses • Problem: blue loops Poland

  25. Measured Masses: Orbits • Orbits:the basis for dynamical masses • High quality radial velocities: Moscow Univ, CORAVEL, AST • Eg V350 Sgr Poland

  26. Mass: Binary Stars • Kepler’s Third Law • P2(M1 + M2) = A3 • Solar system units • P: period • M1, M2: masses • A: semi-major axis (separation) Poland

  27. Masses of Galactic Cepheids • How? • Ground-based spectroscopic orbit • Inclination • Double-lined spectroscopic binaries:high resolution UV spectroscopy: orbital velocity amplitude ratio + mass of secondary • Astrometric orbit of Cepheid (Benedict, et al.) + mass of secondary • Astrometric orbit of both (Polaris) Poland

  28. Masses of Galactic Cepheids • Padua, Geneva tracks: decreasing overshoot from left to right • S Mus,V350 Sgr: HST velocities • W Sgr, FF Aql: Benedict orbits • Polaris: HST No overshoot Poland

  29. S Mus • Hottest companion • GHRS high resolution velocities • Temperature Poland

  30. S Mus H2 • FUSE spectra • Standards reddened to match S Mus • H2 absorption Poland

  31. S Mus • Example S Mus, B3 V B5 V Poland

  32. W Sgr • Spectroscopic orbit: 4.3 yr • IUE: hot companion: A0 V • Small orbital velocity amplitude: face-on? • Inconsistent with reasonable Cepheid mass • Resolved? Poland

  33. W Sgr B 2625 A • STIS spectrum • Component B: resolved, hot • Spectroscopic binary: Cepheid Aa + Ab, cool 2800 A Ceph +Comp Ab 0.16” Comp B Poland

  34. W Sgr • Solid: extracted Cepheid Aa+ Ab spectrum • Dashed: Alp Aqr: slightly cooler than Cepheid • Ab not detected • MAb < 1.4 M • Mcep< 5.4 M Poland

  35. Polaris: Orbit • Pulsation velocity • Orbit: Kamper (1996) • Period: 30 years • Amplitude: 3.7 km/s Poland

  36. Polaris: Inclination • Wielen, et al. 2000 • Hipparcos proper motion • Nearly instantaneous in 30 year orbit • Derive inclination • 2 solutions Poland

  37. Polaris: HST • HST ACS • PSF • Comparison: white dwarfs Poland

  38. Polaris: Mass • Dynamical mass • Aa 4.5 + 2.2/-1.4 M • Ab 1.26 +/- 0.14 • Orbital motion Poland

  39. Summary: Masses • Masses: challenge to improve errors Poland

  40. Binary Properties • (Return to Part I) • Accurate velocities • For some stars span of 30 years • Identify velocity shift of 2 km/s between years (corrected for pulsation) Poland

  41. Detection Probability (%) • For an orbit with 5 Msun primary • Ignore eccentricity • For M2, P compute • orbital velocity • Detect 2 km/s velocity shift • Compute inclination (detection probability) • Work in progress Poland

  42. Summary: Multiplicity • New Multiwavelength Approaches/Results: • 44% (maybe 50%) of binaries are triples • Favor small mass ratios for P > 1 year • HST high resolution images • Period distribution: differences • between high and low mass stars • Resolved low mass companions: X-rays • Late B stars: 39% low mass companions • Velocities: orbits and limits Poland

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