Download Exploring the Planet Forming Environments of Young Suns

Exploring the Planet Forming
Environments of Young Suns
Christopher M. Johns-Krull (Rice University)
IGRINS Science Workshop: August 26, 2010
Star and Planet Formation
Central Engine & Fate of Disk
Lost in an
Outflow
Edwards et al. (1994)
Shu et al. (1994)
Disk locking
Incorporated into
Planets
Accreted onto Star
Stellar Magnetic Fields
Theoretical Predictions
Konigl (1991):
       M* 

B*  3.43 
 
 
7/6
7/4
 0.35   0.5   1M 
5/6
1/2


  R*
M
 -7
 
-1  
 10 M yr   1.0R
-3
  P* 
 
 kG
  1.0d 
7/6
Cameron & Campbell (1993):
-1/3  M *
B*  1.10  
 1M



2/3
23/40



 R*
M
 -7
 
-1 
 10 M yr   1R
-3
  P* 
  
  1d 
29/24
kG
Shu et al. (1994):
  
B*  3.38  x 
 0.923 
-7/4
 M*

 1M



5/6
1/2



 R*
M
 -7
 
-1  
 10 M yr   1R
-3
  P* 
   kG
  1d 
7/6
Measuring Fields from the Zeeman Effect
Zeeman Desaturation of Optical Lines
EQ Vir
Tap 35
Bf = 1.5 kG
Bf = 1.7 kG
Model with B/Model Without B
• Basri et al. (1992): 2 TTS
LkCa 16
• Basri & Marcy (1994): Several dKe stars
• Guenther et al. (1999): 4 TTS
• Very sensitive to Teff
Bf = 0? kG
Direct Zeeman Broadening
Initial optical 2 line analyses were faulty
M Dwarf Fields in the Optical
Johns-Krull & Valenti (1996, ApJ, 459, L95)
TiO
s
Ti I
s
TiO
vsini = 4.5 km/s
McDonald Observatory 2dCoude
Fe I
Getting Rid of the TiO
Johns-Krull & Valenti (1996, ApJ, 459, L95)
McDonald Observatory 2dCoude
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
Johns-Krull et al. (1999)
Saar & Linsky (1985)
TW Hya: CTTS
Yang, Johns-Krull, & Valenti (2005)
Hubble 4: NTTS
Johns-Krull, Valenti, & Saar (2004)
Predicted vs. Observed Mean Fields
Johns-Krull (2007)
Caveats:
• Theory assumes
dipole
• We measure mean
field
• Uncertainty on xaxis difficult to
quantify
Additionally: no
correlation with
rotation rate, Rossby
number, etc.
YSOs in Other Regions
Yang & Johns-Krull (2010)
WL 17 B = 2.9 kG
Johns-Krull et al. (2009)
TWA 9A B = 3.2 kG
Yang et al. (2008)
V1348 Ori B = 3.3 kG
V1123 Ori B = 2.8 kG
Building Planets: Mechanisms
Gravitational Instabilities
Timescale?
Core Accretion
The Brown Dwarf Desert
Grether and Lineweaver (2006)
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.
Santos et al. (2004)
Fisher & Valenti (2005)
Observational Clues
HR 8799
HL Tau
Dodson-Robinson et al. (2009)
Marois et al. (2008)
X Core Accretion: Dust
Greaves et al. (2008) 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.
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)
Search for Planets Around Young Stars
Young Star Properties
• ages 1-few Myr
• rotation periods 1-15 days
• visible photospheres
• classical & weak T Tauri
Stars
Valenti et al. (1993)
Photometric Variability
Herbst et al. (2002)
McDonald Young Planet Search
Approach:
• Coude spectrograph for stability
• observe faint and bright RV
standards for uncertainties
• Th-Ar comps & cross correlation
analysis
Collaborators:
Lisa Prato (Lowell Observatory)
Naved Mahmud (Rice University)
Chris Crockett (Lowell Observatory)
Pat Hartigan (Rice University)
Dan Jaffe (University of Texas)
Marcos Huerta (AAS)
Harlan J. Smith 2.7m telescope
Testing the Approach
• RV standards show RMS
~120 m/s
• proof of concept:
exoplanet HD 68988b
(Butler+ 06)
• P=6.28d
• K=191m/s
Very Large Spots
• young, low-mass stars fully
convective
• rotating rapidly
• convection and rotation drive
strong dynamo & superspots
• observed photometrically and
spectroscopically
V410 Tau
Very Large Spots
• young, low-mass stars fully
convective
• rotating rapidly
• convection and rotation drive
strong dynamo & superspots
• observed photometrically and
spectroscopically
V410 Tau
Hatzes (1995)
Spots and Reflex Motion
Line distortions also lead to
apparent radial velocity
variations
Can We Tell the Difference?
• yes (maybe!)
• spots induce spectral line
asymmetries
• bisector span should
correlate with the radial
velocity if a spot is present
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
Some Results
• No brown dwarf
companions yet
Huerta et al. (2008)
• Some clearly
spotted stars!
Brown Dwarf: LP 944-20
Martín et al. (2006)
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)
Infrared Spectroscopy
Model composite target spectrum with combination of
stellar template (sunspot spectrum) and observed
telluric spectrum (Prato et al. 2008)
RV Precision
• Nov 2008: 61 m/s
• Feb 2009: 31 m/s
• Nov 2009: 44 m/s
• Feb 2010: 97 m/s
Overall: 69 m/s
Ruling Out Interesting Candidates
Prato et al. (2008)
V827 Tau
DN Tau
TW Hya: Planet or Spot?
-400
• 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
IR RV Variations Due to Spots
V827 Tau
Hubble 4
High Precision IR RV
Bean et al. (2010)
Thank You
Disks Are Commonly Observed
From Disks to Planets
Measuring Stellar Magnetic Fields
Field Geometry: Polarization
The Photospheric Field of BP Tau
Emission Line Polarization
He I Polarization
Like looking
only at the
sunspots
Can “Map” the Stellar Field
7 nights in November 2009
K and M Star Results
• Field strength set by pressure balance with
quiet photosphere
• Excellent Correlation with X-ray emission
• f and Bf correlated with rotation
Pevtsov et al. (2003)
Saar (1996)
Transition Disks
Marois et al. (2008)
HR 8799
Kalas et al. (2008)
NASA
Transition Disks
Najita et al. (2007)
Transition Disks
Najita et al. (2007)
Accretion onto the Star
M ~ 108 Msun yr -1 f ~ 0.01
A T Tauri star
Gullbring et al. (1998)
Valenti et al. (1993)
Garcia-Lopez et al.
(2006)
T Tauri Stars: Magnetically Controlled Accretion
• Rotation correlated with disk signatures
Edwards et al. (1994)
• Balmer line profiles
• Accretion shock models reproduce optical
veiling
Shu et al. (1994)
Disk locking
Theory gives
field at some
point in the disk
Shu et al. (1994)
X-ray Luminosity vs Magnetic Flux
Solar X-ray
Bright Points
Longcope et al.
(2001)
T Tauri Stars
Johns-Krull &
Valenti (2000)
Solar Active Regions
Fisher et al. (1998)
Quiet Sun at Solar Minimum
Pevtsov & Acton (2000)
Pevtsov et al. (2003)
F, G, and K Dwarfs
Saar (1996)
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)