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The Era of Bright (Star) AstronomyJim Fuller
Caltech
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The stellar renaissance• High-cadence photometry • High-accuracy astrometry• Wide-field spectroscopy
• Unprecedented data for Nx106 stars• Perfect data for “very bright” (V < 13) stars• Excellent data for “bright” (V < 20) stars
• Stars are bedrock of exoplanet, galactic structure, stellar explosion studies
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Great convergence of the 2020s
The missions:
• High-cadence photometry • TESS, CHEOPS, PLATO • ZTF, Blackgem, ATLAS, LCOGT, ASAS, Evryscope, PanSTARRS• LSST
• High-accuracy astrometry• Gaia
• Wide-field spectroscopy• SDSS-V, DESI, APOGEE, LAMOST
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Photometry• TESS
• All sky, high-precision (<mmag), short baseline (<year), shallow (g<12)
• Ground-based (ZTF, Blackgem, LSST, etc.)• Most sky, low-precision, longer baseline, deep
• Enormous number of stellar variables• Eclipsing binaries• RR Lyrae, Cepheids• Galactic pulsating red giants• Extragalactic pulsating RSGs, LBVs, etc.• Tabby’s stars, R Cor Bors, and other bizarre objects
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TESS
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Gaia Astrometry
• Parallax for over 109 stars• Distance• Luminosity• Radius
• Proper motions• Binaries, multiples, and planets
• Radial Velocities for millions of bright stars (G < 12)
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Gaia
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Spectroscopy• Wide-field, multiplexed, multi-epoch spectroscopy
• SDSS-V• R~20,000 NIR spectra
• H<12: 20 abundances, 30 m/s RVs• R~2,000 optical spectra
• G< 18.5, 5-10 abundances• 2.5M observations per year
• DESI• ~107 stellar spectra• visible/NIR, R~5000
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The maturation of asteroseismology
• Precise characterization of tens of thousands of stars
• Radius (3-5%)• Mass (5-10%)• Age (15-30%)
• Asteroseismic gold standard• Used to calibrate spectral techniques
(e.g., the Cannon) • Used to check Gaia data
Yu et al. 2018
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Revolutions in Stellar Astrophysics• Novel developments in understanding of stars
• Hydrogen vs. helium burning• Convective overshoot• Internal rotation rates• Internal magnetic fields
Stello et al. 2016Mosser et al. 2012
Non-magnetic
Core
MagneticCoreSlowly Rotating
Cores
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Numerical Astrophysics
• Stellar evolution codes (MESA)• Open-source, well-documented, widely used, customizable
• “Standardized” stellar evolution• “Validated” with code comparison (Dartmouth, Geneva, etc)• Ongoing “Verification” with observational data
• Even observers can use it!
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Example #1: Tabby’s Stars, from prototype to population
• 1 in 105 Kepler stars equates to ~105 Tabby’s stars in Milky Way
• Many can be found with ZTF, LSST, etc.
• ~104 will have Gaia distances
• ~102 will have SDSS-V spectra
Boyajian et al. 2015
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Example #2: Single-lined Eclipsing Binaries• Millions from photometric surveys
• Measure orbital period, eclipse duration, eclipse depth
• Gaia measures distance, R1
• Calculate a, Mtot, vorb = GMtot/a
• Measure RV from Gaia/AS4
• Calculate M1/M2, M1 and M2
• Eclipse depths yield R2
parvi2005
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Example #3: Galactic Archaeology
• SDSS spectra used to measure stellar masses via machine learning
• Calibrated/combined with asteroseismology
• Gaia will provide distances, proper motions
• Accurate census of galactic population (mass, age, composition, etc.)
Ness et al. 2016
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The path forward• Stars will be next decade’s fashion
• Public opinion can sway quickly (e.g., exoplanet revolution)• Will influence ways we use big glass• Unknown unknowns
• Big data analysis • Could be bottleneck
• Spectral follow-up is key• Rate-limiting step is RVs, high-res spectra• Support SDSS-V!
• Community action plan
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Single-lined Eclipsing Binaries
• Historically hard to characterize accurately• Oodles of SEBs from ZTF galactic plane survey• Eclipse duration is tec ~ 2Porb(R1/a)• Gaia measures distance, luminosity, SED• Calculate R1, a, M1+M2
• Measure radial velocities from Gaia/AS4• Calculate M1/M2, and hence, M1 and M2
• Eclipse depth yields R2
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Compact Object-Stellar Binaries
• Gaia data reveals motion of star around barycenter• Also tells us orbital period, inclination, distance, radius of star
• Radial velocities can be measured with Gaia/AS4• There is remaining degeneracy between total mass and mass ratio
• In some cases, especially for subgiant/red giant primaries, can use TESS photometry for asteroseismology to measure stellar mass
• Yields accurate measurement of mass of compact object
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Short period white dwarf binaries
• Find eclipsing binaries, ellipsoidal modulation binaries in ZTF data
• Some may also be found from AS4 radial velocities
• Gaia distances allows to distinguish between short period binaries with ellipsoidal modulation and stellar pulsators
• Can be followed up with Chimera and Keck for white dwarf masses, radii, orbital separation, orbital decay timescale