September, 2011 Poland

Cepheid Multiplicity and Masses: Fundamental

ParametersNancy Remage Evans

• 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

Cepheids

• Extragalactic distance scale

• Stellar evolution:

• ``The Cepheid Mass Problem”

• Asteroseismology

• Star formation: massive binaries

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Outline

• Star Formation• Binary Characteristics

• Hubble, Chandra, XMM• Tr 16: X-Rays

• Masses: Evolution• Velocity data

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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

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Part I: Multiplicity: Goals

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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%

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Energy Distributions

• Hot companions• Normalized at 1600 A• Generally very low

reddening• Well determined

spectral types, mass

IUE Example

• Cepheid RT Aur• Compared with main

sequence stars

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RT Aur

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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)

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Multiplicity: Completeness

• Cepheids with orbits • 18 observed with IUE

=> hot companions known

• Multiplicity?

M2 unknown

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UV high res

Multiplicity: Completeness

• High resolution UV spectra (HST, IUE): velocity of companion

• 8 of 18 • 5 of 8 are triples

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Multiplicity: Completeness

• Cepheids with orbits + companion spectrum

• 8 (possibly 9) are triple: 44% (50%)

Triples

Hubble Snapshot Survey

• HST WFC3

• V and I

• Eta Aql• Hot companion

known from IUE • No orbital motion

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Eta Aql: T Mon Subtracted

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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

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Orbital Period Distributions

• Cepheids vs Solar mass stars: different period distribution for comparions with mass ratio > 0.4

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Cepheids Solar Mass

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

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September, 2011 Poland

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

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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

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HST Snapshot: Y Car

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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

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Tr 16 Late B Stars

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• 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

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• Luminosity: mass of He burning core

Core convective overshoot

Rotation

Radiative opacity

Mass loss

Part II: Masses as Evolutionary Benchmarks

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Masses

• Problem: mass mismatch between evolutionary and pulsation masses

• Problem: blue loops

Measured Masses: Orbits

• Orbits:the basis for dynamical masses

• High quality radial velocities: Moscow Univ, CORAVEL, AST

• Eg V350 Sgr

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Mass: Binary Stars

• Kepler’s Third Law

• P2(M1 + M2) = A3

• Solar system units• P: period

• M1, M2: masses

• A: semi-major axis (separation)

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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)

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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

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S Mus

• Hottest companion• GHRS high

resolution velocities• Temperature

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S Mus

• FUSE spectra• Standards reddened

to match S Mus

• H2 absorption

H2

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S Mus

• Example

S Mus, B3 V

B5 V

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W Sgr

• Spectroscopic orbit: 4.3 yr

• IUE: hot companion: A0 V

• Small orbital velocity amplitude: face-on?

• Inconsistent with reasonable Cepheid mass

• Resolved?

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W Sgr B

• STIS spectrum• Component B:

resolved, hot• Spectroscopic

binary: Cepheid Aa + Ab, cool

2800 A2625 A

Ceph +Comp Ab

Comp B

0.16”

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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

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Polaris: Orbit

• Pulsation velocity• Orbit: Kamper (1996)• Period: 30 years

• Amplitude: 3.7 km/s

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Polaris: Inclination

• Wielen, et al. 2000• Hipparcos proper motion• Nearly instantaneous in 30

year orbit• Derive inclination• 2 solutions

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Polaris: HST

• HST ACS• PSF• Comparison: white

dwarfs

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Polaris: Mass

• Dynamical mass

• Aa 4.5 + 2.2 /-1.4 M

• Ab 1.26 +/- 0.14

• Orbital motion

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Summary: Masses

• Masses: challenge to improve errors

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)

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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 progressSeptember 2011 Poland

P (yr)

1 3 10 30

q M2

0.3 1.5 100 99 99 97

0.1 0.5 98 95 89 77

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

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