High Contrast Spectral Imaging: the Case of GQ Lup

1
High Contrast Spectral Imagingthe Case of GQ Lup

• Michael McElwain (UCLA)
• James Larkin (UCLA)
• Stanimir Metchev (UCLA)
• OSIRIS commissioning team

2
GQ Lup B An Exoplanet or a Brown Dwarf?

• 1040 MJup brown dwarf?
• Keck AO OSIRIS spectroscopy
• McElwain, Metchev, Larkin et al., ApJ, accepted

• 12 MJup planet?
• VLT AO slit spectroscopy
• Neuhaüser et al. (2005)

3
Discovery images of GQ Lup A/B
?K 6 mag
Na I
H2O
12CO
cTTS in Lupus 1 age 0.12 Myr (Hughes et al.
1994)
(Neuhaüser et al. 2005)
4
OSIRIS (OH-Suppressing InfraRed Imaging
Spectograph)

• Integral Field Spectrograph
• Spectra over a contiguous rectangular field.

• Spatial resolution at the Keck Diffraction Limit
  (lt0.050)
• Spectral resolution (l/Dl) 3800
• Full z, J, H, or K spectra with single exposure
  (16x64 lenslets)
• Integrated Data Reduction Pipeline

5
OSIRIS - A Lenslet Based Integral Field
Spectrograph (IFS)
1. Image on Lenslets
Focus Image onto a Lenslet Array
2. Pupil images
4. Extracted Data Cube
3. Pupil images dispersed
l
y
l
x
6
Pre-observing planning checklist

• Natural Guide Star GQ Lup A
• R magnitude of 11.0
• Choose scale
• 0.020
• Choose integration time for desired sensitivity
• From instrument zero points
• Determine dither pattern
• Make an execution file

7
Keck/OSIRIS Spectra of GQ Lup B
H2O
H2O
FeH
H2O
K I
GQ Lup B

• integral field spectrograph behind Keck II AO
  system
• (PI J. Larkin, UCLA)
• OSIRIS commissioning data (June 2005)

GQ Lup B
(McElwain, Metchev et al., ApJ, in press)
8
AO Integral Field Spectroscopy Is More Reliable
Than AO Slit Spectroscopy
elevation, differential refraction H-band 53
mas-wide slit GQ Lup A/B aligned on slit

• AO slit spectroscopy
• slit width (40100 mas), PSF (4080 mas)
  comparable to pointing precision (2040 mas)
• differential refraction (atmosphere, AO
  transmission optics)
• especially important in high-contrast regime
• IFS AO spectroscopy
• no slit losses due to centering on slit
• no slit losses due to differential refraction
• trace PSF centroid as a function of ?
• variable extraction aperture as PSF changes?

9
IFS is Good for Target Extraction and Primary
Background Subtraction

• Correct cube for differential dispersion.
• Extract the companion spectrum.
• Fit host star PSF to estimate the background
  contribution at the location of the secondary.
• Subtract host background from the companion
  spectrum.

10
Keck/OSIRIS Spectra of GQ Lup B
H2O
H2O
H2O
FeH
K I
GQ Lup B

• commissioning OSIRIS data (Aug 2005)
• J- and H-band
• spectral type M8 2
• Neuhaüser et al. M9L4

GQ Lup B
(McElwain, Metchev et al., ApJ, in press)
11
GQ Lup A/B Astrometry Photometry

• Astrometry
• Similar to imaging
• Photometry
• Curve of growth for the telluric and GQ Lup A
  find flux ratio and magnitude for GQ Lup A
• Compare the flux ratios of the same aperture for
  GQ Lup A/B
• Determine GQ Lup B magnitude

J-band
12
High Contrast Imaging Speckle Suppression
Typical speckle pattern for Keck II OSIRIS
Imager in the Kn3 filter

• At moderate Strehl ratios (lt 0.95) and small
  separations (lt 1), speckle noise produced by
  atmospheric wavefront distortion and imperfect
  optics are the dominate noise source.
• Innovative techniques for enhancing contrast
• Simultaneous Differential Imaging
• Spectral Suppression

Keck II OSIRIS Spec in the Kbb filter
Speckles are wavelength dependent and can be
modelled for each wavelength.
13
Summary

• AO integral field spectroscopy is more reliable
  than AO slit spectroscopy
• An IFS is efficient for halo subtraction.
• Astrometry and photometry procedures are the
  similar to those for direct imaging.
• An IFS can perform speckle suppression.
• GQ Lup B is probably a brown dwarf and not an
  exoplanet.

14
Steps in Characterizing Sub-Stellar Companions

• Determine age and distance
• from parent stellar association (best) or primary
  star
• Determine spectral type, effective temperature
• direct near-IR spectroscopy (with AO)
• Determine mass, surface gravity
• from evolutionary models

15
GQ Lup B is Hotter and Older Than Inferred by
Neuhaüser et al.

• McElwain, Metchev et al.
• spectral type M6L0 (2600 K)
• age 110 Myr

• Neuhaüser et al. (2005)
• spectral type M9L4 (2000 K)
• AO slit losses affecting K-band continuum?
• weakening H2 CIA absorption at 1.52.5 µm
• age 0.12 Myr

16
Testing Evolutionary Models Hot-Start Models
Better at 3 Myr
2MASS 0535 A/B (03 Myr)
GQ Lup B (110 Myr)
A (0.054 MSun)
B (0.034 MSun)
N05
M06
3.0
(Neuhaüser et al. 2005, Wuchterl Tscharnuter
2003 models)
(Stassun et al. 2006, Chabrier et al. 2000 models)
17
GQ Lup B is Probably a Brown Dwarf

• McElwain, Metchev et al.
• spectral type M6L0 (2600 K)
• age 110 Myr
• hot-start models (Burrows et al. 1997 Chabrier
  et al. 2000)
• ? mass 1040 MJup

• Neuhaüser et al. (2005)
• spectral type M9L4 (2000 K)
• AO slit losses affecting K-band continuum?
• weakening H2 CIA absorption at 1.52.5 µm
• age 0.12 Myr
• cold-start models (Wuchterl Tscharnuter 2003)
• ? mass 12 MJup

Marois et al. (accepted), 0.63.5 µm SED
analysis 920 MJup
18
The Mass of GQ Lup B

• hot-start models predict 342 MJup
• Burrows et al. (1997), Baraffe et al. (2002)
• uncertain at 3 Myr ages
• nucleated instability and collapse models predict
  12 MJup
• Wuchterl et al. (2000), Wuchterl Tscharnuter
  (2003)
• better at young ages?

• Which theoretical models are more accurate?
• Is GQ Lup B an exoplanet?

(Neuhaüser et al. 2005)
19
Thanks to the OSIRIS team

• ACADEMIC
• Principal Investigator - James Larkin (UCLA)
• Project Scientist - Andreas Quirrenbach
  (University of Heidelberg)
• Co-Investigator Alfred Krabbe (Cologne)
• Research Astronomer Inseok Song, Christof
  Iserlohe (Cologne)
• Graduate Students - Matthew Barczys, David
  LaFreniere, Michael McElwain, Tommer Wizansky,
  Shelley Wright
• Close collaboration Ian McLean, Eric Becklin
• ENGINEERING
• Project Engineer - George Brims
• Mechanical Ted Aliado, John Canfield, Nick
  Magnone, Evan Kress
• Software Tom Gasaway (UCSD), Chris Johnson,
  John Milburn, Jason Weiss
• Electrical Ken Magnone, Michael Spencer, Gunnar
  Skulason,
• CARA - Paola Amico, Allan Honey, Junichi Meguro,
  Grant Tolleth, others
• ADMINISTRATIVE
• CARA Project Manager Sean Adkins, David
  Sprayberry
• Management Juleen Moon, Jim Kolonko
• Secretarial Melinda Laraneta
• (lead engineer in each area for OSIRIS in bold,
  denotes non-active team members)

20
Spectral Classification of Ultra-Cool Objects is
Age-Dependent
H2O
H2O
K I

• spectral type
• proxy for Teff
• determined by continuum shape in brown dwarfs
• but young (lt100 Myr) brown dwarfs
• larger radius
• lower surface gravity
• (g GM/R2)
• weaker K I, Na I absorption
• weaker H2 CIA over 1.52.5 µm
• spectral classification most reliable from H2O
  dip at 1.3 µm (Slesnick et al. 2004)

H2 CIA
Na I
1-50 Myr
(Kirkpatrick et al. 2006)
21
Independent Confirmation of the Mass of GQ Lup B
Is Necessary

• AO slit spectroscopy near bright objects is
  challenging
• spectroscopic classification is gravity (i.e.,
  age) dependent
• theoretical models for sub-stellar objects are
  unreliable at lt3 Myr

22
GQ Lup B is Hotter Than Inferred by Neuhaüser et
al.

• McElwain, Metchev et al.
• spectral type M6L0 (2600 K)

• Neuhaüser et al. (2005)
• spectral type M9L4 (2000 K)
• AO slit losses affecting K-band continuum?
• weakening H2 CIA absorption at 1.52.5 µm
  (Borysow et al. 1997, Kirkpatrick et al. 2006)

23
An Updated Age for Lupus 1 110 Myr
0.1 Myr
1 Myr
0.12 Myr
10 Myr
100 Myr
(Hughes et al. 1994, DAntona Mazzitelli 1994
tracks)
24
GQ Lup A Sub-Stellar Companion and a Disk

• projected binary separation 110 AU
• disk mass 0.01 M
• GQ Lup B may be accreting
• J KS 1.8 0.1 mag
• 1.0 mag for late-M dwarfs
• KS L 1.4 0.3 mag
• 0.8 mag for late-M dwarfs
• relevant for theories of brown-dwarf formation
• similar objects
• 2MASS 12073932 B (Chauvin et al. 2004)
• IRAS 04382540 B (Apai et al. 2005)

25
Summary

• Teff at L/T transition is a function of age at
  gt0.1 Gyr
• or sub-stellar radius is independent of age at
  gt0.1 Gyr
• no observational data at lt0.1 Gyr planetary
  realm
• Characterization of young brown dwarfs is
  challenging
• Teff and g have degenerate spectroscopic
  signatures (H2 CIA)
• mass estimates are strongly model dependent
• GQ Lup B 1040 MJup brown dwarf rather than 12
  MJup planet
• Very low mass ratio (M2/M1 0.03) resolved young
  systems
• 5 known HD 203030 B, GQ Lup B, HR 7329 B, AB Pic
  B, HN Peg B
• important for inferring the photospheric
  properties of extrasolar giant planets to be
  imaged in the future

26
AO Imaging Contrast is Limited by Variable
Speckle Noise
Keck AO speckles at 2 µm

• speckles limit the detectability of exo-planets

(Kalas et al. 2002)
27
Pushing the Contrast Limit Speckle Suppression

• speckles are images of the primary
• same spectrum
• sub-stellar companion is much cooler
• optimal weighting
• adjust to any companion spectral type
• caveats
• need Nyquist sampling of PSF
• need broad spectral range

optimal weighting
(McElwain et al., in prep.)
28
Closing the Gap to R.V. Exo-Planets

• companions discovered in direct imaging, 515
  MJup
• a 1550 AU
• limited by contrast of conventional AO
• r.v. planets, 0.215 MJup
• a 6 AU
• limited by survey length
• intermediate regime
• 650 AU
• to be probed by speckle suppression techniques

29
OSIRIS An Integral Field Spectrograph for Keck AO

• 1.02.4 µm
• R 3700
• spectroscopy over a 2-D field of view
• 3-D data cube
• FOV
• from 0.32"?1.20" (20 mas/lenslet)
• to 4.8"?6.4" (100 mas/lenslet)
• Keck diffraction limit 50 mas at 2.2 µm
• commissioned 2005

(Larkin et al. 2006)
30
AO Slit Spectroscopy is Challenging
Gemini AO K-band
HD 130948 B/C L2 2
(Potter et al. 2002)
31
AO Slit Spectroscopy is Challenging
HD 130948 C L2 2 ? L4 1
(Goto et al. 2003)