Searching for Substellar Objects Michael McElwain Advisor: Dr. James Larkin Science in collaboration with Dr. Adam Burgasser

Overview Introduction to Brown Dwarfs Lick Wide-Field T Dwarf Search 2 field T dwarf discoveries First substellar subdwarf discovered Digital Filtering to Search for Substellar Companions in the Halo of Nearby Stars Advantage of using OSIRIS data cubes Quicklook v2.0

Brown Dwarf Formation & Evolution Brown dwarfs have masses below the hydrogen burning minimum mass (HBMM) log(age) Gyrs T eff K log(L) L s Burrows et al. 1997

Searches for Brown Dwarfs Companions to nearby stars Direct Imaging Infrared speckle imaging Coronographic imaging Radial velocities Adaptive Optics Imaging Young clusters Field Searches *2MASS

T dwarfs Spectral features dominated by CH 4, H 2 O, CIA H 2, and K I absorption features. T < ~1350 K M J ~ T dwarf Near Infrared Spectra

Why Search for Additional Field T Dwarfs? Only 39 T dwarfs known Improved search parameters Larger samples needed to lower uncertainties in substellar properties substellar statistics in the Solar Neighborhood substellar mass function Discover unique objects Discover cooler substellar objects Characterize substellar properties

Sample Coverage & Selection Techniques Sample Selection d > -20 ° 15 ° < |b| < 88 ° J < 16 J-H < 0.3 H-K s < 0 No optical counterpart within 5” of the 2MASS coordinates on the USNO-A2.0 catalog 2MASS database is flagged to ignore detections of known minor planets L M T

Selection Techniques 267,646 candidates pass the initial selection criterion. Visual examination of DSS images for faint optical counterparts to candidates Roughly 99.5% of candidates are removed in the visual examination

Reimaging Campaign Gemini Infrared Camera (Lick Observatory) Uncataloged minor planets remain Reimage field at J & K to confirm the presence of a candidate Roughly 25% of the remaining candidates are removed in this manner Palomar 60” CCD Camera Identify faint background stars r-J < 6 that can pass initial criteria Roughly 80% of the remaining candidates are removed in this manner

Spectroscopy Gemini Infrared Camera Simultaneous observations at J/K or H/K Low resolution ( /   500) CH 4 + H 2 O absorption detection a decisive test for identifying T dwarfs Comparison spectra were taken for known M, L, and T dwarfs

J Comparison Spectra T dwarfs are recognized by the strong CH 4 absorption and increased H 2 O absorption. M3V M8V L1V sdL M6V T2V T5.5V

Results 13 spectra of candidates 2MASS (mid T) J-K=-0.5 2MASS (T 5.5V) J=13.9, third brightest T dwarf known D ~ 8pc 2MASS SdL First Substellar Subdwarf Strong CIA H 2 absorption in K band 2MASS SdL 2MASS (mid T) 2MASS (T 5.5V)

Substellar Companions Multiple systems occur in roughly 60% of solar- type systems (Duquennoy & Mayor 1991) Rate of multiplicity decreases for lower mass stars “Brown Dwarf Desert” to solar type stars reported by radial velocity measurements a < 4AU (Marcy & Benitez 1989) ~35% of field M dwarfs, a ~ 3-30AU (Fischer & Marcy 1992, Henry & McCarthy 1993, Reid & Gizis 1997) ~20% of field L dwarfs, a < 15 AU (Koerner et al. 1999, Reid et al. 2001, Leggett et al. 2001, Close et al. 2002) ~20% of field T dwarfs, a < 3AU (Burgasser et al. 2003)

Using OSIRIS to Search for Substellar Companions High angular resolution Keck telescope Keck AO system Moderate Spectral Resolution Obtain simultaneous spatial and spectral information If unresolved, use spectral information to search for companions

Digital Filtering of OSIRIS Data Cubes Many reasons to apply digital filters to OSIRIS data cubes Suppress OH contamination Make a K´ or K s image from the broadband K Simulate JHK filter transmissions from other instruments or telescopes Search for substellar companions in the halos of nearby stars

Weighted Digital Filter for Substellar Companions When looking for a companion in the halo of the host star, the spectra will constructively interfere within a particular spatial element in the OSIRIS data cube.  L1V G8V (L1V/ G8V)-1

Quicklook v2.0 Comprehensive 3 dimensional image analysis tool written in IDL conforming to Keck coding standards Object Oriented Program, capable of managing multiple windows Typical image manipulation functions as well as more specific image analysis tools

Quicklook v2.0 Plots Ability to take cuts of the data cube in multiple orientations. Easily customized plot parameters Can set QL2 to remember plot parameters.

Applying Digital Filters with QL2 QL v2 is supplied with a tool to apply digital filters. 2 column data containing wavelength and multiplication factor are read. Data is sampled onto the OSIRIS wavelength grid and displayed in a plot window. Can apply and remove filters from the image in the image window gui.

Simulation of the Keck AO Point Spread Function Wavelength coverage µm and a sampling rate of µm. r o of 0.3 at 0.5 µm Strehl ratio of 0.6 Plate scale of 0.02 "/pix 2 second integration time Bruce MacIntosh, LLNL Problem!

Digital Filter Applied to the Host and Target Simulated with the Simulated PSF Simulated PSF produces an inaccurate representation of the halo for a 15 minute exposure Resolved components increased contrast by a factor of 10. Before filterAfter filter

Conclusions Lick Wide Field T Dwarf Search identified two T dwarfs, one substellar subdwarf OSIRIS is an ideal instrument to search for substellar companions Simultaneous spatial and spectral information Advantage of using OSIRIS data cubes Quicklook v2.0 is a comprehensive 3 dimensional analysis software

T dwarfs 39 Known T dwarfs 2MASS (19) Sloan (11) Deep Fields (3) Stellar/Substellar Companions (6)

2 Micron All Sky Survey (2MASS) Made possible by the introduction of large-scale, sensitive infrared arrays 1.3 m telescopes on Mt. Hopkins, AZ and CTIO, Chile. 256  256 HgCdTe array with ~8.5’ FOV Simultaneous observations in J, H, K s MagnitudeLimits BandWavelength (µm)Point Sources (SNR=10) Extended Sources J H KsKs

Spectral Reduction Spectra were reduced using the REDSPEC software Developed at UCLA by Prato, Kim, & McLean for NIRSPEC data Reduction procedure Spatial rectification Spectra rectification Subtract dithered frames to remove background emission Divide by flat-dark frame Divide target spectra by a calibrator spectra to correct for telluric absorption Paschen and Brackett hydrogen lines are removed from the calibrator spectra by linear interpolation. Multiply by a blackbody consistent to the calibrator spectra

H Comparison Spectra Continuum spectrum in M dwarfs, late types exhibiting H 2 O absorption L dwarfs marked by increased H 2 O absorption. Again, T dwarfs are recognized by their strong CH 4 absorption and increased H 2 O absorption.

K Comparison Spectra Continuum spectrum in M dwarfs, exhibiting some CO absorption. L dwarfs have increased CO absorption T dwarfs are marked by their suppressed flux due to CIA H 2. CH 4 absorption is present in this band too.

Next Infrared Sky Survey? HgCdTe and Si:As 1024  1024 arrays to survey at 3.5, 4.6, 12 and 23 microns 2.2” pixel scale Sensitive to brown dwarfs, even cooled to temperatures less than 200 K! Principal Investigator, Dr. Edward L. Wright

OSIRIS Overview OH-Suppressing Infra-Red Imaging Spectrograph z, J, H, K bands Spectral resolution of  64 broad band (1700 spectral channels) or 64  64 narrow band mode (400 spectral channels) 0.02”, 0.035”, 0.5”, and 0.10” pixel scales FOV from 1.32  1.28” to 6.4  6.4” Combined with Keck AO, OSIRIS will be the most sensitive spectrograph to date

Construction of the Weighted Digital Filter Linearly interpolate the normalized flux of the target and host onto the OSIRIS wavelength grid. Calculate the weight to assign for each channel, t i / h i. Construct a zero mean filter by subtracting 1.