Methane Imaging of Brown Dwarfs and Planetary Mass

Methane Imaging of Brown Dwarfs and Planetary Mass Objects in Rho Ophiuchi Karl Haisch Jr. (Utah Valley University) Artist’s rendition of a brown dwarf: R. Hurt (NASA)

Collaborators Mary Barsony Chris Tinney Tom Greene Chris Mc. Carthy San Francisco State University of New South Wales NASA Ames Research Center San Francisco State University

Outline I. What are T dwarfs? II. Past methane imaging of L/T dwarfs III. Why methane imaging of young clusters? - Rho Ophiuchi IV. IMF V. Summary & Future work

Brown Dwarf Properties L dwarfs (stars+brown dwarfs) metallic hydrides, H 2 O red in visible and in near-IR Teff < 2300 K T dwarfs (brown dwarfs) CH 4, H 2 O red in visible, vast color range in near-IR Teff < 1500 K Classification in near-IR Burgasser et al. 2002

Most L’s and T’s Discovered with Methane Imaging Found in Large-Area Sky Surveys >500 ~100 Dwarf. Archives. org

Why Young (1 - 10 Myr) Clusters? Stars roughly coeval with known ages, as opposed to field T dwarfs with unknown ages. Brown dwarfs much more luminous at this stage of their evolution than those in the field, or in older clusters. Relatively small physical sizes, so significant fractions of the cluster can be surveyed in reasonable amounts of observing time.

Why methane imaging? Methane signatures so unique (only T dwarfs and giant planets) that greatly reduce need for spectroscopic confirmation. Imaging in two methane filters nearly simultaneously (differential photometry). Doesn’t suffer from background contamination (i. e. there is no such thing as a “methane giant”)

Facilities Mainzer et al. (2003) have used CH 4 imaging in IC 348. We are using AAT and Anglo-Australian Telescope, Siding Springs, Australia Palomar to search for T dwarfs in young, nearby star-forming regions. Palomar Observatory, California

The Rho Ophiuchi Star-Forming Cloud (distance = 120 pc) 2 MASS Image of r Oph Robert Hurt, SSC

Area Covered in Methane Imaging Survey (945 sq. arcmin) 22 11 12 9 2 3 8 1 7 6 13 32 14 33 4 15 34 5 16 19 2 MASS Image of r Oph Robert Hurt, SSC

Near-IR Observations Instrument: IRIS 2 Telescope: Anglo-Australian 4 -meter telescope Filters: J (1. 25 m), Ks (2. 2 m), CH 4 s (1. 59 m), CH 4 l (1. 67 m) Plate Scale: 0. 45 arcsec/pixel Completeness limits: m. K = 18. 5, m. H = 19. 5, m. J = 20. 0

Methane Filter Bandpasses Tinney et al. (2005)

Mass sensitivity Burrows et al. (2001)

J, K, Methane Color-Color Diagram Tinney et al. (2005)

A T 4 dwarf in Rho Ophiuchi A T 4 dwarf based on methane color (CH 4 s - CH 4 l). A total of 27 T dwarf candidates found out of 5434 stars surveyed. CH 4 s CH 4 l E N CH 4 s - CH 4 l = -0. 37 Follow-up spectroscopy of T dwarf candidates for the purpose of examining their spectra and refining atmospheric models will be pursued. Haisch et al. (in prep)

Exti nctio n Infrared Color-Color Diagram

Infrared Color-Color Diagram Haisch et al. (in prep)

Minimum Mass for Star-Formation? Idea of minimum mass first arose from Jeans mass arguments (Low & Lynden-Bell 1976). Jeans mass 10 MJ; Deuterium burning 13 MJ - In agreement understand very low mass star formation Not so fast! Recent evidence has clouded the issue. . . - simulations including B field 1 MJ brown dwarfs (Boss 2001) - brown dwarf companions with masses < 10 MJ (Chauvin et al. 2005) - cluster mass functions don’t terminate at 10 MJ (e. g. , Bouvier, Luhman) - new formation mechanisms for brown dwarfs (e. g. , Reipurth & Clarke)

Brown Dwarf Mass Functions Pleiades IMF well studied ( = 0. 6; Moraux et al. 2003) Field stars have = 1. 0. Look at IMF in T dwarf mass range in young clusters to critically probe shape of IMF at masses where brown dwarfs and exoplanets overlap, and address issues related to mass segregation of clusters. Reid et al. (1999); Allen et al. (2005)

Summary & Future Work • Methane imaging is a powerful and efficient method of finding T dwarf candidates. • Identified 27 T dwarf candidates out of 5434 stars surveyed. • Complete CH 4 survey of remaining star-forming regions. • Follow-up spectroscopy of T dwarf candidates to examine their spectra and refine atmospheric models. • IMF in T dwarf mass range.