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Cepheid Multiplicity and Masses: Fundamental Parameters

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### Cepheid Multiplicity and Masses: Fundamental Parameters

Nancy Remage Evans

Thanks to Henrietta Leavitt

Outline

- Multiplicity:
- Motivation
- What we know
- Implications
- Masses:
- Motivation
- What we know
- Implications

Thanks to Henrietta Leavitt

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

Multiplicity

- Star formation

Binary, triple,….

Distribution of mass ratios

Maximum separation

High vs low mass

- Basis: ground-based orbits

Thanks to Henrietta Leavitt

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

Energy Distributions

- Hot companions
- Normalized at 1600 A
- Generally very low reddening
- Well determined spectral types, mass

Thanks to Henrietta Leavitt

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

Multiplicity: Completeness

- Cepheids with orbits
- 18 observed with IUE => hot companions known
- Multiplicity?

M2unknown

Thanks to Henrietta Leavitt

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

Multiplicity:S Sge

- Orbit => mass function: M1, M2, sin i
- Mass from IUE spectrum
- Secondary double

S Sge B IUE

Thanks to Henrietta Leavitt

Multiplicity: Completeness

Triples

- Cepheids with orbits + companion spectrum
- 8 (possibly 9) are triple: 44% (50%)

Thanks to Henrietta Leavitt

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

Expectations

Duquennoy and Mayor

Solar type

- Low mass companions?
- Wide companions
- Expectations

(days)

Cepheid Orbits

Thanks to Henrietta Leavitt

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

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

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

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

Masses

- Why?
- Benchmark for evolutionary tracks
- Pulsation calculations
- Problem: mass mismatch
- Problem: blue loops

Thanks to Henrietta Leavitt

Masses: Evolutionary Tracks

- Luminosity: mass of He burning core

Core convective overshoot

Rotation

Radiative opacity

Mass loss

Thanks to Henrietta Leavitt

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

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

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

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

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

Summary: Pointers to the Future

- List of orbits: future possibilities
- Multiplicity: X-rays, (UV)
- Masses: roadmap

Thanks to Henrietta Leavitt

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