Christopher M. Johns-Krull (Rice University)
description
Transcript of Christopher M. Johns-Krull (Rice University)
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Christopher M. Johns-Krull (Rice University)
IGRINS Science Workshop: August 26, 2010
Exploring the Planet Forming Environments of Young Suns
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Star and Planet Formation
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Central Engine & Fate of Disk
Incorporated into Planets
Accreted onto Star
Lost in an Outflow
Shu et al. (1994)
Edwards et al. (1994)
Disk locking
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Stellar Magnetic Fields
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kG1.0d
P
1.0R
R
yrM10
M
1M
M
0.50.35 3.43B
7/6
*
-3
*
1/2
1-
7-
5/6
*
7/47/6
*
kG1d
P
1R
R
yrM10
M
1M
M 1.10B
29/24
*
-3
*
23/40
1-
7-
2/3
*1/3-*
kG1d
P
1R
R
yrM10
M
1M
M
0.923 3.38B
7/6
*
-3
*
1/2
1-
7-
5/6
*
-7/4
x*
Theoretical Predictions
Konigl (1991):
Cameron & Campbell (1993):
Shu et al. (1994):
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Measuring Fields from the Zeeman Effect
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Zeeman Desaturation of Optical Lines
• Basri et al. (1992): 2 TTS
• Basri & Marcy (1994): Several dKe stars
• Guenther et al. (1999): 4 TTS
• Very sensitive to Teff
Model with B/Model Without B
Bf = 1.5 kGBf = 1.7 kG
Tap 35
EQ Vir
Bf = 0? kG
LkCa 16
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Direct Zeeman BroadeningInitial optical 2 line analyses were faulty
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M Dwarf Fields in the Optical
Johns-Krull & Valenti (1996, ApJ, 459, L95)
McD
on
ald
Ob
serv
ato
ry 2
dC
ou
de
Fe I
Ti I
TiOTiO
vsini = 4.5 km/s
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Getting Rid of the TiOM
cDon
ald
Ob
serv
ato
ry 2
dC
ou
de
Johns-Krull & Valenti (1996, ApJ, 459, L95)
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Going to the Infrared
• Kitt Peak 4m + FTS & NASA IRTF (3m) + CSHELL spectrometer
• R ~ 35,000-44,000 spectra
• Excess Broadening Seen in the Ti I line
Saar & Linsky (1985)
Johns-Krull et al. (1999)
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TW Hya: CTTSYang, Johns-Krull, & Valenti (2005)
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Hubble 4: NTTSJohns-Krull, Valenti, & Saar (2004)
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Predicted vs. Observed Mean Fields
Caveats:• Theory assumes dipole• We measure mean field• Uncertainty on x-axis difficult to quantify
Additionally: no correlation with rotation rate, Rossby number, etc.
Johns-Krull (2007)
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YSOs in Other RegionsYang & Johns-Krull (2010)
Yang et al. (2008)
V1348 Ori B = 3.3 kG
V1123 Ori B = 2.8 kG
TWA 9A B = 3.2 kG
WL 17 B = 2.9 kG
Johns-Krull et al. (2009)
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Building Planets: Mechanisms
Timescale?
Core Accretion
Gravitational Instabilities
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The Brown Dwarf DesertGrether and Lineweaver (2006)
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Observational Clues
Core Accretion: Dust collides and sticks together, building up larger bodies. May take about 10 Myr to build Jupiter.
X GI: Gravitational instability leads to rapid planet formation.
Fisher & Valenti (2005)Santos et al. (2004)
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Observational Clues
X Core Accretion: Dust collides and sticks together, building up larger bodies. May take about 10 Myr to build Jupiter.
X GI: Gravitational instability leads to rapid planet formation.
Marois et al. (2008)
HR 8799
HL Tau
Greaves et al. (2008)
Dodson-R
obinson et al. (2009)
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Origin of the Desert
• Some feature (disk mass, disk lifetime, etc.) of the planet formation process prevents brown dwarfs forming
• Brown dwarfs do form, but then migrate in (Armitage & Bonnell 2002)
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Search for Planets Around Young Stars
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Young Star Properties
• ages 1-few Myr• rotation periods 1-15 days• visible photospheres• classical & weak T Tauri
Stars
Herbst et al. (2002)
Photometric VariabilityValenti et al. (1993)
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• Coude spectrograph for stability• observe faint and bright RV standards for uncertainties • Th-Ar comps & cross correlation analysis
Approach: Harlan J. Smith 2.7m telescope
McDonald Young Planet Search
Lisa Prato (Lowell Observatory)Naved Mahmud (Rice University)Chris Crockett (Lowell Observatory)Pat Hartigan (Rice University)Dan Jaffe (University of Texas)Marcos Huerta (AAS)
Collaborators:
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Testing the Approach
• RV standards show RMS ~120 m/s• proof of concept: exoplanet HD 68988b (Butler+ 06)• P=6.28d• K=191m/s
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Very Large Spots
• young, low-mass stars fully convective• rotating rapidly• convection and rotation drive strong dynamo & superspots• observed photometrically and spectroscopically
V410 Tau
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Very Large Spots
• young, low-mass stars fully convective• rotating rapidly• convection and rotation drive strong dynamo & superspots• observed photometrically and spectroscopically
Hatzes (1995)
V410 Tau
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Line distortions also lead to apparent radial velocity variations
Spots and Reflex Motion
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Can We Tell the Difference?
• bisector span should correlate with the radial velocity if a spot is present
• yes (maybe!)• spots induce spectral line asymmetries
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Young RV Planets to Date
• Setiawan et al. (2007) identified long period (852d) planet around 100 Myr old star HD 70573• In 2008 team claimed detection of a 10MJ, 10 Myr old planet @ TW Hya
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Some Results
• No brown dwarf companions yet
• Some clearly spotted stars!
Huerta et al. (2008)
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Brown Dwarf: LP 944-20
Martín et al. (2006)
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Infrared Spectroscopy
• CSHELL spectrograph, cassegrain mounted on telescope• flexure? No I2 cell• need Earth’s telluric lines for calibration (e.g., Blake et al. 2007, 2008)
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Infrared Spectroscopy
Model composite target spectrum with combination of stellar template (sunspot spectrum) and observed telluric spectrum (Prato et al. 2008)
• Nov 2008: 61 m/s• Feb 2009: 31 m/s• Nov 2009: 44 m/s• Feb 2010: 97 m/s
Overall: 69 m/s
RV Precision
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Ruling Out Interesting Candidates
V827 Tau DN Tau
Prato et al. (2008)
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TW Hya: Planet or Spot?
• Setiawan et al. (2008): no line bisector radial velocity correlation?• Huelamo et al. (2008): find correlation between line bisector and radial velocity
Radial Velocity (m/s)-400 +400
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IR RV Variations Due to Spots
V827 Tau Hubble 4
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High Precision IR RV
Bean et al. (2010)
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Thank You
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Disks Are Commonly Observed
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From Disks to Planets
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Measuring Stellar Magnetic Fields
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Field Geometry: Polarization
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The Photospheric Field of BP Tau
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Emission Line Polarization
He I Polarization
Like looking only at the sunspots
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Can “Map” the Stellar Field
7 nights in November 2009
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K and M Star Results
Pevtsov et al. (2003)
Saar (1996)• Field strength set by pressure balance with quiet photosphere
• Excellent Correlation with X-ray emission
• f and Bf correlated with rotation
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Transition DisksMarois et al. (2008)
Kalas et al. (2008)
HR 8799
NASA
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Transition Disks
Najita et al. (2007)
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Transition Disks
Najita et al. (2007)
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Accretion onto the Star
A T Tauri starf ~ 0.01-1
sun8 yr M10~ M
Valenti et al. (1993)
Garcia-Lopez et al. (2006)
Gullbring et al. (1998)
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T Tauri Stars: Magnetically Controlled Accretion
Shu et al. (1994)
• Rotation correlated with disk signatures• Balmer line profiles• Accretion shock models reproduce optical veiling
Edwards et al. (1994)
Disk lockingTheory gives field at some point in the disk
Shu et al. (1994)
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X-ray Luminosity vs Magnetic Flux
F, G, and K DwarfsSaar (1996)
Solar Active RegionsFisher et al. (1998)
Solar X-rayBright PointsLongcope et al.(2001)
Quiet Sun at Solar MinimumPevtsov & Acton (2000)
T Tauri StarsJohns-Krull &Valenti (2000)
Pevtso
v e
t al. (2
003
)
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Collaborators Jeff Valenti (STScI) Hao Yang (JILA) Wei Chen (Rice) Lisa Prato (Lowell Observatory) Naved Mahmud (Rice University) Chris Crockett (Lowell Observatory) Pat Hartigan (Rice University) Dan Jaffe (University of Texas) Marcos Huerta (AIP/AVS)