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Asteroseismology and the Time Domain Revolution in
Astronomy
Marc Pinsonneault
Ohio State UniversityCollaborators:The APOKASC teamMelissa NessMarie Martig
The Need for Precision Stellar Astrophysics
Stars are important across a wide range of astrophysics
Origins Questions– Planet Formation– Structure Formation
Complex Observational Patterns: Things Move!Þ Precise Data NeededÞ Need Better Stellar Physics
Kepler mission:160,000 stars
monitored
Waves are Generated by Turbulence in Stars
Two Major Impacts of AsteroseismologyWe can measure fundamental properties (mass, radius, age, rotation) in bulk stellar populations
Extremely precise surface gravities are a natural product
We have entirely new categories of stellar observables– Surface CZ depth– He ionization– Core rotation– Core mass and density
Spectroscopy + Asteroseismology 2Gether 4Ever
Solar-like Oscillations in Kepler16 Cyg AMetcalfe et al. 2012
Pure p-mode pattern
nmaxRotational Splittings
The observed oscillation
pattern is a strong
function of log g
From Chaplin & Miglio 2013
Giants and Kepler
Giants are high-amplitude pulsators– Periods of days to months
Long period is a huge advantageÞ Accessible with 30 minute cadenceÞ 16,000 stars monitored, essentially all detected
(Mosser et al. 2009; Hekker et al. 2010)
Observed frequency pattern is complex!
Giant and Dwarf Frequency Patterns Compared
CM13
The Complex Giant Pattern is Explained by Mixed Modes
Mixed modes propagate as p-modes in the convective envelope and g-modes in the deep core; especially strong impact on l=1
l=0 modes are pure p-modes
Seen in red giants (Bedding et al. 2010) because the p and g mode frequencies become commensurate
Comparing the two yields distinct diagnostics of core and envelope properties
Distinct Patterns in Different Evolutionary States
Dwarf Subgiant
RGB RCCM13
Scaling Relations for Bulk Populations
Two most basic observables: – Frequency of maximum
power– Mean frequency spacing
Hekker et al. 2010data for Kepler giants
Radius and Mass Scaling in ClustersDiscrepancy for clump giant radii relative to RGB radii (~0.05) tied to structural properties
Small but real mass difference 0.06-0.08 Msun, RGB vs. that expected from EB constraints on the MS (Brogaard et al. 2012)
Miglio et al. (2012)
Epstein et al. (2014)
Trouble In Halo-Land
Halo Star Masses From SR Are WellAbove Expected Values….
Beyond Scaling Relations:Towards Reliable Masses
Boutique Modeling:Reasonable Mass!
Parallax+ Dn:Reasonable Mass!
Gaia will have a huge impact
Calibrate…Correct…OR
Two Paths ForwardBoutique Modeling
Use the full information in the frequency spectrum
Use absolute frequencies for evolutionary state
Replace nu(max) with g-mode spacings
Add in proper modeling of mean density
Parallax Über Alles
P + Fluxes+ Teff = R
Add in proper modeling of mean density
Profit!
APOGEE at a GlanceThe Apache Point Observatory Galactic Evolution ExperimentOperates in the near-infrared (H band): 1.51-1.68 mmTargeted ~105 RG stars sampling the bulge, disk(s), and halo(es)DR10 (Ahn et al. 2014): [M/H], [a/Fe] DR11-12 (Alam et al. 2015) 15 Element Mix (C, N, O, Na, Mg, Al, Si, S, K, Ca, Ti, V, Mn, Fe, Ni)
More numbers!• S/N = 100+/pixel• R ~ 22,500• ~230 science fibers, 7 deg2
FOV• RV precision: ~ 100 m/s• Abundance precision: <0.1
dexS. R. Majewski
APOKASC SummarizedORIGINAL KEPLER FIELD
Dwarfs: Kepler Field Control– ~2,000 (AU 2015)– ~7,000 (SU 2016)
Giants: Population Asteroseismology– DR10: 1,916 (Pinsonneault et al. 2014)– DR11+12: ~8,000 (AU 2015)– DR13: ~16,000 (SU 2016)
Targeting Criterion:H<11 (1 hour exposure)Teff < 5500 K
Automated Pipeline Analysis
Boutique analysis of 100,000 targets…NO.
Automated fitting algorithm (FERRE) for the entire H band spectrum
Ex post facto calibration of results against independent measurements– Star cluster members– Asteroseismic log g
Calibrating the Pipeline: Temperatures
Meszaros et al. (2013)Star Cluster Data
Holtzman et al. (2015)Low Reddening Photometric Temperatures
Calibrating the Pipeline:Surface Gravity
Meszaros et al. (2013):Cluster Star + asteroseismic log g
Holtzman et al. (2015)Pure asteroseismic log g
Calibrating the Pipeline:Metallicities
Meszaros et al. (2013)
Holtzman et al. (2015)
New: 15 Element Mixture
Individual Elements fit with a limited line list calibrated vs. cluster stars
APOGEE: 100,000 Red Giant Spectra
The APOKASC ApproachAPOGEE sample: 1916 stars that pass quality control checks
Extract mean asteroseismic properties (Dn, nmax)
Scaling relations + grid-based modeling
Pinsonneault et al. 2014
Results: Snapping Into Focus
Photometry Spectroscopy Asteroseismology +SpectroscopyPinsonneault et al. 2014
Mass Trends, Fixed [Fe/H]
Metallicity Trends, Fixed Mass
A Test of Atmospheres
The difference between asteroseismic and spectroscopic log g is different for RC, RGB
Is this an atmospheres or asteroseismic systematic?
One Size Does Not Fit All
Macroturbulence is very different in the clump and RGB
Þ Different line broadening
Þ Impacts gravities
Massarotti et al. 2008
Testing the Assumptions of Chemical Tagging
Martig et al. 2015 4% of high [a/Fe] stars are young (or mergers)
…Invisible to Traditional Surveys
On the Way:Much larger a-rich, metal-poor samples
New in 2015: Richer Phase Space Coverage
Much Larger Sample Size
The Future of Large Spectroscopic Surveys?
Ness et al. 2015a
“Cannon”
Compare Spectra toEmpirical Calibrators,Not Directly to Models
From Spectra to Mass and Age
Surface C/N, C12/C13 are strongly related to mass through 1st dredge-up
=> Spectroscopic Mass labelling of red giants!
Martig et al. 2015b
An Age Map of the Red Clump…
Asteroseismic Masses Inferred From Spectra (Ness et al. 2015b)
…Across the Galaxy
Ness et al. 2015b
Kepler Rebooted: K2
The New Kepler Mission: Step and Stare in the Ecliptic PlaneStrong overlap with APOGEE fields; opportunity for samplinga wide range of stellar populations-TESS; PLATO;…..
Future: SDSS-4 + K2
SDSS-4: Two spectrographs (north and south)
K2 – numerous APOGEE targets already in fields, used for targeting.
10,000+ fibers reserved for K2 targets
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