Download Cepheid Multiplicity and Masses - The Project ASK `Sounding Stars

Cepheid Multiplicity and
Masses: Fundamental
Parameters
Nancy Remage Evans
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September, 2011
Ed Guinan
Scott Engle
Howard Bond
Gail Schaefer
Derck Massa
Charles Proffit
Alexey Rastorguev
Natalia Gorynya
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Poland
Scott Wolk
Massimo Marengo
Margarita Karovska
Ken Carpenter
Erika Bohm-Vitense
Joel Eaton
Ignazio Pillitteri
Leonid Berdnikov
Cepheids
• Extragalactic distance scale
• Stellar evolution:
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``The Cepheid Mass Problem”
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Asteroseismology
• Star formation: massive binaries
September 2011
Poland
Outline
• Star Formation
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Binary Characteristics
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Hubble, Chandra, XMM
Tr 16: X-Rays
• Masses: Evolution
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Velocity data
September, 2011
Poland
Cepheids
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4-7 M
Formerly B stars
Young ~50 Myr
Post-RGB, core He burning
Evolve without strong mass loss of O
stars
• Known distances
September, 2011
Poland
Part I: Multiplicity: Goals
• Star Formation
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Angular momentum
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Low mass: well characterized
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High mass:
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rarer, broad lines, mass loss
• Observations
Binary, triple,….
Distribution of mass ratios
Maximum separation
HIGH VS LOW MASS STARS
September 2011
Poland
High Mass Companions: IUE
Survey
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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%
September, 2011
Poland
Energy Distributions
• Hot companions
• Normalized at 1600 A
• Generally very low
reddening
• Well determined
spectral types, mass
September, 2011
Poland
IUE Example
• Cepheid RT Aur
• Compared with main
sequence stars
September, 2011
RT Aur
Poland
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)
September, 2011
Poland
Multiplicity: Completeness
• Cepheids with orbits
• 18 observed with IUE
=> hot companions
known
• Multiplicity?
M2 unknown
September, 2011
Poland
Multiplicity: Completeness
UV high res
• High resolution UV
spectra (HST, IUE):
velocity of
companion
• 8 of 18
• 5 of 8 are triples
September, 2011
Poland
Multiplicity: Completeness
Triples
• Cepheids with orbits +
companion spectrum
• 8 (possibly 9) are
triple: 44% (50%)
September, 2011
Poland
Hubble Snapshot Survey
• HST WFC3
• V and I
• Eta Aql
• Hot companion
known from IUE
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No orbital motion
September, 2011
Poland
Eta Aql: T Mon Subtracted
September, 2011
Poland
Binary Parameters
• IUE survey: identify all companions M > 2 M
• 15 Cepheids
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11 have orbits, orb. motion => period
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3 resolved with WFC3 => separation
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=> period
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(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
September, 2011
Poland
Orbital Period Distributions
• Cepheids vs Solar
mass stars: different
period distribution
for comparions with
mass ratio > 0.4
September, 2011
Poland
Cepheids
Solar Mass
Hubble Snapshot Survey:
Goal 2: Low Mass Stars
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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
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
September, 2011
Poland
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
HST Snapshot: Y Car
September, 2011
Poland
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
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Chandra ACIS image: B
stars: blue: detected; purple:
not detected
September, 2011
Poland
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
September, 2011
Poland
Part II: Masses as
Evolutionary Benchmarks
• Luminosity: mass of
He burning core
Core convective
overshoot
Rotation
Radiative
opacity
Mass loss
September, 2011
Poland
Masses
• Problem: mass mismatch between
evolutionary and pulsation masses
• Problem: blue loops
September, 2011
Poland
Measured Masses: Orbits
• Orbits:the basis for
dynamical masses
• High quality radial
velocities: Moscow
Univ, CORAVEL, AST
• Eg V350 Sgr
September, 2011
Poland
Mass: Binary Stars
• Kepler’s Third Law
• P2(M1 + M2) = A3
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Solar system units
P: period
M1, M2: masses
A: semi-major axis (separation)
September, 2011
Poland
Masses of Galactic Cepheids
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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)
September, 2011
Poland
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
September, 2011
Poland
No overshoot
S Mus
• Hottest companion
• GHRS high
resolution velocities
• Temperature
September, 2011
Poland
S Mus
H2
• FUSE spectra
• Standards reddened
to match S Mus
• H2 absorption
September, 2011
Poland
S Mus
• Example
S Mus, B3 V
B5 V
September, 2011
Poland
W Sgr
• Spectroscopic orbit: 4.3 yr
• IUE: hot companion: A0 V
• Small orbital velocity amplitude: faceon?
• Inconsistent with reasonable Cepheid
mass
• Resolved?
September, 2011
Poland
W Sgr B
2625 A
• STIS spectrum
• Component B:
resolved, hot
• Spectroscopic
binary: Cepheid Aa
+ Ab, cool
2800 A
0.16”
Ceph +Comp Ab
Comp B
September, 2011
Poland
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
September, 2011
Poland
Polaris: Orbit
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Pulsation velocity
Orbit: Kamper (1996)
Period: 30 years
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Amplitude:
3.7 km/s
September, 2011
Poland
Polaris: Inclination
• Wielen, et al. 2000
• Hipparcos proper motion
• Nearly instantaneous in 30
year orbit
• Derive inclination
• 2 solutions
September, 2011
Poland
Polaris: HST
• HST ACS
• PSF
• Comparison: white
dwarfs
September, 2011
Poland
Polaris: Mass
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Dynamical mass
Aa 4.5 + 2.2 /-1.4 M
Ab 1.26 +/- 0.14
Orbital motion
September, 2011
Poland
Summary: Masses
• Masses: challenge to improve errors
September, 2011
Poland
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)
September 2011
Poland
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
September 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:
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44% (maybe 50%) of binaries are triples
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Favor small mass ratios for P > 1 year
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HST high resolution images
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Period distribution: differences
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between high and low mass stars
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Resolved low mass companions: X-rays
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Late B stars: 39% low mass companions
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Velocities: orbits and limits
September 2011
Poland