Variability of young stars with LSST

Gregory J. HerczegKIAA

Star Formation: ISM/Molecular Clouds

Pre-main sequence stellar evolution(low-mass case)

HD141569, Clampin et al.

Classical T Tauri Stars

From Visser et al., in prep

Morphology of a classical T Tauri star

Dullemond et al., PPV

Morphology of a classical T Tauri star

• Luminosities much lower than predicted from steady infall

• Possible solution: most stellar mass accretes during rare outbursts

Luminosity Problem(Kenyon et al. 1990; Dunham, Evans, et al. 2009/2010)

Tbol

L bol

Young Star Outbursts• FUors and EXors• Very rare

- ~10 confirmed FUors• 5-8 magnitude increase

in luminosity• EXors: 1 year duration• FU Ori: 1937 outburst is

still ongoing Miller et al. 2010Palomar Transient Factory

Accretion Variability: EX Lup11

14

1893

1941

McLaughlin (1946)

2008 Outburst of EX Lup

• 5-magnitude brightness– 2 x 10-7 Msol/yr

– 100 times higher than quiescence

• Lasted about half a year– Similar strength, duration

as 1955 outburst

Aspin et al. 2010

Accretion-powered jets

• Episodic mass ejection: related to accretion events? (e.g., Reipurth et al. 1989)

Accretion Histories• Rate and strength of FUOr/EXOr outbursts– Limited to end state of accretion– Class 0/I: JCMT/SCUBA2?

• Identify physical cause of outbursts– Gravitational Instability + MRI (Zhu et al. 2010)– Multiple star/disk interactions (Reipurth et al.)– Thermal Instability (Martin et al. 2010)– Gravitational Clumping (Vorobyov & Basu 2005)

Optical accretion diagnostics

Accretion columns of AA Tau (Bouvier et al. 2007)

H-alpha line profiles

V-band periodicity

Variable accretion onto young star with disk

(Herczeg et al. in prep)

COROT observations of NGC 2264(Alencar, Bouvier, et al. 2010)

NO DISK DISK ACCRETION

Stochastic variability: changes in star-disk interaction

Longer term variability: disk instabilities

Disks Warps(e.g., Herbst et al. 2000s; Plavchan et al. 2008)

I-magnitude through 5 different seasons

Ongoing SF variability programs

• COROT observations of NGC 2264 (Alencar et al.)• YSOVar: Warm Spitzer near-IR monitoring (Stauffer et al.)• Palomar Transit Factory (Hillenbrand, Covey)• VYSSOS: daily monitoring of many SF regions (P.I. Reipurth;

not yet ongoing, uncertain future)• PAN-STARRS

Young star variability

• Accretion history (for optically visible objects)• Accretion variability: unbiased assessment, timescales• Rotational modulation (space-based monitoring best)• Disk warps: planet-induced, star/disk interactions• Light echoes: outburst bouncing off envelope, disk• Hot spots of magnetically active M-dwarfs• Eclipsing binaries as test of stellar evolution tracks

LSST, not variability (covered by VISTA?)• Low-metallicity galactic star formation (Yasui et al. 2009)• Extinction mapping• Young populations/IMF (need complementary spectra)

Formation of youngest disks(Herczeg et al. 2011)

• VLT/CRIRES M-band spectra of CO emission- R = 100,000- Usually behind AO

• Measure CO emission/profiles from disks around protostars

• Disks: either present or absent

Searching for growth of disks(Herczeg et al. 2012)

Watson et al. 2007, Nature

Spitzer/IRS spectra: hot water emission from envelope/disk accretion shock?

Herschel far-IR spectral imaging: hot water emission from the outflow, not the disk

UV Excess Measures of Accretion(Herczeg, in prep)

• Low-resolution optical spectra of 300 T Tauri stars– Palomar and Keck– 3200-9000 A, R=1000– Largest U-band spectroscopic

sample of T Tauri stars to date

• Most accurate method to measure accretion rate

- Simultaneous extinction, spectral type

• 80 more spectra from VLT/X-Shooter• 3000 A – 2.5 microns at

R=10,000

Disks, Accretion and Outflows from T Tauri stars (DAO of Tau)

(P.I. Herczeg)

• HST/FUV spectra– 1150-1800 A– R=20,000– 30 stars, 111 orbits

total)

• Hot emission from accretion shock

• Molecular emission from disks

• Wind absorption linesDiscovery of FUV CO Emission from T Tauri stars, France et al. (2011)

Variability of young stars• Accretion history for visible objects• Accretion variability: unbiased assessment, timescales• Rotational modulation (space-based monitoring best)• Disk warps: planet-induced, star/disk interactions• Light echoes: outburst bouncing off envelope structures• Hot spots of magnetically active M-dwarfs• Eclipsing binaries as test of stellar evolution tracks

LSST, not variability• Low-metallicity SF (e.g., Yasui et al.)• Extinction mapping• Young populations: need spectra (SpT, gravity, better ages)