The Era of Bright (Star) AstronomyJim Fuller

Caltech

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

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

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

TESS

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)

Gaia

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

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

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

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!

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

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

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

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

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

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

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