1. Variability of young stars with LSST Gregory J. Herczeg KIAA

2. Star Formation: ISM/Molecular Clouds

3. Pre-main sequence stellar evolution (low-mass case) HD141569, Clampin et al. Classical T Tauri Stars

4. From Visser et al., in prep

5. Morphology of a classical T Tauri star Dullemond et al., PPV

6. Morphology of a classical T Tauri star

7. 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) T bol L bol

8. 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. 2010 Palomar Transient Factory

9. Accretion Variability: EX Lup 11 14 1893 1941 McLaughlin (1946)

10. 2008 Outburst of EX Lup 5-magnitude brightness – 2 x 10 -7 M sol /yr – 100 times higher than quiescence Lasted about half a year – Similar strength, duration as 1955 outburst Aspin et al. 2010

11. Accretion-powered jets Episodic mass ejection: related to accretion events? (e.g., Reipurth et al. 1989)

12. 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)

13. Optical accretion diagnostics

14. Accretion columns of AA Tau (Bouvier et al. 2007) H-alpha line profiles V-band periodicity

15. Variable accretion onto young star with disk (Herczeg et al. in prep)

16. 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

17. Disks Warps (e.g., Herbst et al. 2000s; Plavchan et al. 2008) I-magnitude through 5 different seasons

18. 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

19. 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)

20. 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

21. 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

22. 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

23. 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 lines Discovery of FUV CO Emission from T Tauri stars, France et al. (2011)

24. 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)