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Cepheid Multiplicity and Masses: Fundamental Parameters. Nancy Remage Evans. Outline. Multiplicity: Motivation What we know Implications Masses: Motivation What we know Implications. Cepheids. 4-7 M  Formerly B stars Young ~50 Myr Post-RGB, core He burning

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cepheid multiplicity and masses fundamental parameters

Cepheid Multiplicity and Masses: Fundamental Parameters

Nancy Remage Evans

Thanks to Henrietta Leavitt

outline
Outline
  • Multiplicity:
    • Motivation
    • What we know
    • Implications
  • Masses:
    • Motivation
    • What we know
    • Implications

Thanks to Henrietta Leavitt

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

Thanks to Henrietta Leavitt

mass ratios
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
Multiplicity: Completeness
  • Cepheids with orbits
  • 18 observed with IUE => hot companions known
  • Multiplicity?

M2unknown

Thanks to Henrietta Leavitt

multiplicity completeness1
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
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 completeness2
Multiplicity: Completeness

Triples

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

Thanks to Henrietta Leavitt

low mass companions
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
Expectations

Duquennoy and Mayor

Solar type

  • Low mass companions?
  • Wide companions
  • Expectations

(days)

Cepheid Orbits

Thanks to Henrietta Leavitt

chandra observation of polaris
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
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
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
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
Masses
  • Why?
  • Benchmark for evolutionary tracks
  • Pulsation calculations
  • Problem: mass mismatch
  • Problem: blue loops

Thanks to Henrietta Leavitt

masses evolutionary tracks
Masses: Evolutionary Tracks
  • Luminosity: mass of He burning core

Core convective overshoot

Rotation

Radiative opacity

Mass loss

Thanks to Henrietta Leavitt

masses1
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

masses2
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

s mus
S Mus
  • Hottest companion
  • GHRS high resolution velocities
  • Temperature

Thanks to Henrietta Leavitt

s mus1
S Mus

H2

  • FUSE spectra
  • Standards reddened to match S Mus
  • H2 absorption

Thanks to Henrietta Leavitt

s mus2
S Mus
  • Example

S Mus, B3 V

B5 V

Thanks to Henrietta Leavitt

w sgr
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
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 sgr1
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

eta aql
Eta Aql
  • B9.8 V companion
  • Orbit?
  • Eaton: 1 year

Thanks to Henrietta Leavitt

summary pointers to the future
Summary: Pointers to the Future
  • List of orbits: future possibilities
  • Multiplicity: X-rays, (UV)
  • Masses: roadmap

Thanks to Henrietta Leavitt

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