1. Karl Haisch Jr. (Utah Valley University)
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)

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

3. 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

4. Brown Dwarf Properties
L dwarfs (stars+brown dwarfs)
metallic hydrides, H2, H2O
red in visible and in near-IR
Teff < 2300 K
T dwarfs (brown dwarfs)
CH4, H2, H2O
red in visible, vast color
range in near-IR
Teff < 1500 K
Classification in near-IR
point out large color values (normalized to BB) -> red objects; MS stars
T dwarfs hard to find (methane, H2 CIA)
Burgasser et al. 2002

5. Most L’s and T’s Discovered with Methane Imaging Found in Large-Area Sky Surveys
>500
~100
Large population -> address some fundamental questions
DwarfArchives.org

6. 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.
Foreground field T dwarfs MUCH older and less luminous than targets….can be detected out to distances of only ~50pc.

7. 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”)
Also, since reddening and methane absorption act in opposite directions, extinction can’t create a false T detection.
T dwarfs discovered here will be youngest, lowest gravity T dwarfs ever directly observed (OR coolest free-floating planets ever discovered).

8. Facilities Mainzer et al. (2003) have used CH4 imaging in IC 348.
We are using AAT and Palomar to search for T dwarfs in young, nearby star-forming regions.
Anglo-Australian Telescope, Siding Springs, Australia
Palomar Observatory, California

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

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

11. Near-IR Observations Instrument: IRIS2
Telescope: Anglo-Australian 4-meter telescope
Filters: J (1.25 m), Ks (2.2 m), CH4s (1.59 m), CH4l (1.67 m)
Plate Scale: 0.45 arcsec/pixel
Completeness limits: mK = 18.5, mH = 19.5, mJ = 20.0

12. Methane Filter Bandpasses
Tinney et al. (2005)

13. Mass sensitivity Burrows et al. (2001)
This graph is for 300 pc. We’ll do even better at closer distances.
Burrows et al. (2001)

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

15. A T4 dwarf in Rho Ophiuchi
A T4 dwarf based on methane color (CH4s - CH4l). A total
of 27 T dwarf candidates found out of 5434 stars surveyed.
CH4s
CH4l E N
CH4s - CH4l = -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)

16. Infrared Color-Color Diagram
Extinction
Excess
Disks

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

18. 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
Not so fast! Recent evidence has clouded the issue...
- In agreement  understand very low mass star formation
- simulations including B field  1MJ 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)

19. 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.
Hyades IMF even flatter mass function suggesting that as clusters age, dynamical evolution causes the lowest mass members to dissipate into the field.
Reid et al. (1999); Allen et al. (2005)

20. 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 CH4 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.