Cepheid Multiplicity and Masses: Fundamental Parameters

1. Cepheid Multiplicity and Masses: Fundamental Parameters Nancy Remage Evans Thanks to Henrietta Leavitt

2. Outline • Multiplicity: • Motivation • What we know • Implications • Masses: • Motivation • What we know • Implications Thanks to Henrietta Leavitt

3. Cepheids • 4-7 M • Formerly B stars • Young ~50 Myr • Post-RGB, core He burning • Evolve without strong mass loss of O stars Thanks to Henrietta Leavitt

4. Multiplicity • Star formation Binary, triple,…. Distribution of mass ratios Maximum separation High vs low mass • Basis: ground-based orbits Thanks to Henrietta Leavitt

5. 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% Thanks to Henrietta Leavitt

6. Energy Distributions • Hot companions • Normalized at 1600 A • Generally very low reddening • Well determined spectral types, mass Thanks to Henrietta Leavitt

7. 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) Thanks to Henrietta Leavitt

8. Multiplicity: Completeness • Cepheids with orbits • 18 observed with IUE => hot companions known • Multiplicity? M2unknown Thanks to Henrietta Leavitt

9. Multiplicity: Completeness UV high res • High resolution UV spectra (HST, IUE): velocity of companion • 8 of 18 • 5 of 8 are triples Thanks to Henrietta Leavitt

10. Multiplicity:S Sge • Orbit => mass function: M1, M2, sin i • Mass from IUE spectrum • Secondary double S Sge B IUE Thanks to Henrietta Leavitt

11. Multiplicity: Completeness Triples • Cepheids with orbits + companion spectrum • 8 (possibly 9) are triple: 44% (50%) Thanks to Henrietta Leavitt

12. Low Mass Companions? • Cepheid companions young • 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 Thanks to Henrietta Leavitt

13. Expectations Duquennoy and Mayor Solar type • Low mass companions? • Wide companions • Expectations (days) Cepheid Orbits Thanks to Henrietta Leavitt

14. Chandra Observation of Polaris • Center 3’ of ACIS-I field • Putative components marked • A = Aa + Ab • B F3 V • C, D • X-ray but no 2MASS: background AGN Thanks to Henrietta Leavitt

15. System Summary • A = Aa +Ab • B (no low mass companion) • 2 possible distant stars (0.16 and 0.29 pc) • Searched: Magnitude difference of 15 mag Mass ratio range of 10 Separation of 0.1 pc Thanks to Henrietta Leavitt

16. Polaris A • Originally: no full amplitude Cepheid had been detected in X-rays • Probability favored Ab dwarf companion • BAAS 2009: Engle, Guinan, Evans, and DePasquale X-rays with XMM from 2 other Cepheids • X-rays not so good for unresolved low mass companions • Cepheid + K companion • Very interesting for atmospheric heating Thanks to Henrietta Leavitt

17. Multiplicity: Results • High binary fraction • High triple fraction • Many small M2/M1for P > 1 yr • Needed: low mass companions? • Needed: Cepheid X-rays? Thanks to Henrietta Leavitt

18. Masses • Why? • Benchmark for evolutionary tracks • Pulsation calculations • Problem: mass mismatch • Problem: blue loops Thanks to Henrietta Leavitt

19. Masses: Evolutionary Tracks • Luminosity: mass of He burning core Core convective overshoot Rotation Radiative opacity Mass loss Thanks to Henrietta Leavitt

20. Masses • How? • Ground-based spectroscopic orbit • 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) Thanks to Henrietta Leavitt

21. Masses • Evolutionary framework • Padua, Geneva tracks: decreasing overshoot from left to right • S Mus,V350 Sgr:HST velocities • W Sgr, FF Aql: Benedict orbits No overshoot Thanks to Henrietta Leavitt

22. S Mus • Hottest companion • GHRS high resolution velocities • Temperature Thanks to Henrietta Leavitt

23. S Mus H2 • FUSE spectra • Standards reddened to match S Mus • H2 absorption Thanks to Henrietta Leavitt

24. S Mus • Example S Mus, B3 V B5 V Thanks to Henrietta Leavitt

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

26. 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 Thanks to Henrietta Leavitt

27. 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 Thanks to Henrietta Leavitt

28. Eta Aql • B9.8 V companion • Orbit? • Eaton: 1 year Thanks to Henrietta Leavitt

29. Summary: Pointers to the Future • List of orbits: future possibilities • Multiplicity: X-rays, (UV) • Masses: roadmap Thanks to Henrietta Leavitt