High Contrast Spectral Imaging:the Case of GQ Lup B GQ Lup 0.73” Keck AO + OSIRIS • Michael McElwain (UCLA) • James Larkin (UCLA) • Stanimir Metchev (UCLA) • OSIRIS commissioning team
1–2 MJup planet? VLT AO slit spectroscopy Neuhaüser et al. (2005) 10–40 MJup brown dwarf? Keck AO + OSIRIS spectroscopy McElwain, Metchev, Larkin et al., ApJ, accepted GQ Lup B – An Exoplanet or a Brown Dwarf?
Spectral type: M9–L4 M8 V L2 2000 K, log g = 2.0 GQ Lup B 2.0 2.1 2.2 2.3 2.4 2.5 Wavelength [µm] Discovery images of GQ Lup A/B ∆K = 6 mag Na I H2O 12CO cTTS in Lupus 1; age 0.1–2 Myr (Hughes et al. 1994) (Neuhaüser et al. 2005)
y l x OSIRIS (OH-Suppressing InfraRed Imaging Spectograph) • Integral Field Spectrograph • Spectra over a contiguous rectangular field. • Spatial resolution at the Keck Diffraction Limit (<0.050”) • Spectral resolution (l/Dl) ~ 3800 • Full z, J, H, or K spectra with single exposure (16x64 lenslets) • Integrated Data Reduction Pipeline
OSIRIS - A Lenslet Based Integral Field Spectrograph (IFS) Focus Image onto a Lenslet Array 1. Image on Lenslets 2. Pupil images 4. Extracted Data Cube 3. Pupil images dispersed l y l x
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
integral field spectrograph behind Keck II AO system (PI: J. Larkin, UCLA) OSIRIS commissioning data (June 2005) L5 GQ Lup B L0, 2 Gyr 0.73” L2 J-band M9 M6 L0, 10 Myr J H Keck/OSIRIS Spectra of GQ Lup B H2O H2O FeH H2O K I GQ Lup B GQ Lup B (McElwain, Metchev et al., ApJ, in press)
AO Integral Field Spectroscopy Is More Reliable Than AO Slit Spectroscopy • AO slit spectroscopy: • slit width (40–100 mas), PSF (40–80 mas) comparable to pointing precision (~20–40 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? elevation, differential refraction H-band 53 mas-wide slit GQ Lup A/B aligned on slit
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.
commissioning OSIRIS data (Aug 2005) J- and H-band spectral type: M8 ± 2 Neuhaüser et al.: M9–L4 L5 GQ Lup B L0, 2 Gyr 0.73” L2 J-band M9 M6 L0, 10 Myr J H Keck/OSIRIS Spectra of GQ Lup B H2O H2O FeH H2O K I GQ Lup B GQ Lup B (McElwain, Metchev et al., ApJ, in press)
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
High Contrast Imaging: Speckle Suppression Typical speckle pattern for Keck II + OSIRIS Imager in the Kn3 filter At moderate Strehl ratios (< 0.95) and small separations (< 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.
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.
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 Steps in Characterizing Sub-Stellar Companions
McElwain, Metchev et al.: spectral type: M6–L0 (~2600 K) age: 1–10 Myr Neuhaüser et al. (2005): spectral type: M9–L4 (~2000 K) AO slit losses affecting K-band continuum? weakening H2 CIA absorption at 1.5–2.5 µm age: 0.1–2 Myr GQ Lup B is Hotter and Older Than Inferred by Neuhaüser et al.
Testing Evolutionary Models: “Hot-Start” Models Better at ≤3 Myr 2MASS 0535 A/B (0–3 Myr) GQ Lup B (1–10 Myr) A (0.054 MSun) B (0.034 MSun) N05 M06 3.0 (Stassun et al. 2006, Chabrier et al. 2000 models) (Neuhaüser et al. 2005, Wuchterl & Tscharnuter 2003 models)
McElwain, Metchev et al.: spectral type: M6–L0 (~2600 K) age: 1–10 Myr “hot-start” models (Burrows et al. 1997; Chabrier et al. 2000) mass: 10–40 MJup Neuhaüser et al. (2005): spectral type: M9–L4 (~2000 K) AO slit losses affecting K-band continuum? weakening H2 CIA absorption at 1.5–2.5 µm age 0.1–2 Myr “cold-start” models (Wuchterl & Tscharnuter 2003) mass: 1–2 MJup GQ Lup B is Probably a Brown Dwarf Marois et al. (accepted), 0.6–3.5 µm SED analysis: 9–20 MJup
“hot-start” models predict 3–42 MJup Burrows et al. (1997), Baraffe et al. (2002) uncertain at ≤3 Myr ages nucleated instability and collapse models predict 1–2 MJup Wuchterl et al. (2000), Wuchterl & Tscharnuter (2003) better at young ages? The Mass of GQ Lup B Which theoretical models are more accurate? Is GQ Lup B an exoplanet? (Neuhaüser et al. 2005)
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)
J H K Spectral Classification of Ultra-Cool Objects is Age-Dependent • spectral type • proxy for Teff • determined by continuum shape in brown dwarfs • but: young (<100 Myr) brown dwarfs • larger radius • lower surface gravity (g = GM/R2) • weaker K I, Na I absorption • weaker H2 CIA over 1.5–2.5 µm • spectral classification most reliable from H2O dip at 1.3 µm (Slesnick et al. 2004) H2O H2O K I H2 CIA Na I 1-50 Myr (Kirkpatrick et al. 2006)