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Variability of young stars with LSST
Gregory J. HerczegKIAA
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Star Formation: ISM/Molecular Clouds
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Pre-main sequence stellar evolution(low-mass case)
HD141569, Clampin et al.
Classical T Tauri Stars
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From Visser et al., in prep
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Morphology of a classical T Tauri star
Dullemond et al., PPV
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Morphology of a classical T Tauri star
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• 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
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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
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Accretion Variability: EX Lup11
14
1893
1941
McLaughlin (1946)
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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
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Accretion-powered jets
• Episodic mass ejection: related to accretion events? (e.g., Reipurth et al. 1989)
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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)
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Optical accretion diagnostics
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Accretion columns of AA Tau (Bouvier et al. 2007)
H-alpha line profiles
V-band periodicity
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Variable accretion onto young star with disk
(Herczeg et al. in prep)
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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
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Disks Warps(e.g., Herbst et al. 2000s; Plavchan et al. 2008)
I-magnitude through 5 different seasons
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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
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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)
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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
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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
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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
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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)
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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)