T and Y Dwarfs Arturo O Martinez Outline

T and Y Dwarfs Arturo O. Martinez

Outline • Overview/Review of Brown Dwarfs • T dwarfs Discovery Classification and Spectral Indicators � � • Y dwarfs Discovery T/Y dwarf transition � � • Peculiar T and Y dwarfs

What are Brown Dwarfs? • Mass ranges ~75 -80 (up to 90? ) MJupiter to ~13 Mjupiter � T dwarf range: 50 to 20 MJupiter Y dwarf range: 20 to 13 MJupiter � � • Temperature ranges 1800 K down to 300 K? � Image credit: NASA/JPL-Caltech

Gliese 229 B • First T dwarf identified Kirkpatrick et al. 1999

2 MASS 0559 -1404 Burgasser et al. (2003 b); Cushing, Rayner, & Vacca (2005); and Cushing et al. (2006)

2 MASS 0559 -1404 (A Closer Look) Burgasser et al. (2003 b); Cushing, Rayner, & Vacca (2005); and Cushing et al. (2006)

2 MASS 0559 -1404 (A Closer Look) Burgasser et al. (2003 b); Cushing, Rayner, & Vacca (2005); and Cushing et al. (2006)

2 MASS 0559 -1404 (A Closer Look) Burgasser et al. (2003 b); Cushing, Rayner, & Vacca (2005); and Cushing et al. (2006)

Near-Infrared Classification • First steps were… difficult Early classification in 2002 � • Based on H 2 O and CH 4 and other methods in “near-IR” • Also based on low resolution spectra (R~100 -1200)

Near-Infrared Classification Primary Standards Reasonably bright Not spectroscopically peculiar Not a variable Not a resolved multiple system Within ~25 degrees of the ecliptic � � �

Near-Infrared Classification • Telluric features are in red bands • T-dwarf spectral standards measured at a resolution of R~400 • Classification of T dwarfs are done in the IR • K I absorption Geballe et al. (2002); Burgasser et al. (2004 b); and Knapp et al. (2004)

Spectral Indices

Spectral Indices Burgasser et al. 2006

Spectral Indices • Saturation for CH 4 -K index values starting at T 7 • Final classification scheme is an average for all Exception for early T subtypes �

Teff Relations • Flattening in the L/T transition come from clouds Golimowski et al. 2004

Optical Classification

Optical Classification • Cr. H(A)/H 2 O ratio is the best classifier as spectral type discriminant • Other indices are more difficult and mostly used to differentiate in specific cases • Agree with mid-IR classification scheme within 1 sub-Sp. T… for the most part Burgasser et al. 2003, Kirkpatrick et al. (1999, 2000)

Mid-Infrared Classification • Started with the launch of Spitzer and the use of the Infrared Spectrograph • R~90 and spectral range from 5. 3 to 15. 3 microns

Mid-Infrared Classification Cushing et al. 2006

Mid-Infrared Classification • H 2 O starts to saturate and is a poor indicator of spectral type for T dwarfs • Other two show good monotonic trends Cushing et al. 2006

Metallicity, Surface Gravity, Condensate Clouds, and Temporal Variations • Pressure broadening of features P/τ ≈ g/κR � Older and more massive (increased g), and metal-poor (reduced opacity) show enhanced gas pressure � • Condensate cloud depletion as you transition into T dwarfs Currently under debate Temporal variations due rotation, log g, metallicity, and other factors? � � Create spectral variations �

Mass-Radius relation • R~M-1/8 Chabrier et al. 2009

Discovery of Y dwarfs! Cushing et al. 2011

Brown dwarfs found as of 2012 Kirkpatrick et al. 2012

T/Y dwarf transition? Kirkpatrick et al. 2012

T/Y dwarf transition? • Sudden absorption features in Y dwarfs? • No clear signature for change in Sp. T

Y dwarfs Kirkpatrick et al. 2012

Spectral Classification for Y dwarfs • Spectral indices do not work for Y dwarfs • Should do overplotting for spectral classification

Peculiar T/Y dwarfs? • Probably a binary This specific case could be a L-dwarf/T-dwarf binary � Burgasser et al. (2006 a)

In-class spectra classification

Summary • T dwarf Sp. T classification is best in near-IR • Rough Teff relation with Sp. T • Y dwarf classification Sp. T is best when overplotting