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The Luminosity Function The Luminosity Function of Ultracool Dwarfsof Ultracool Dwarfs
Kelle Cruz
UPenn American Museum of Natural History (NYC)
Cool Stars 13
July 8, 2004
Colloborators:Neill Reid (STScI)Jim Liebert (UArizona)Davy Kirkpatrick (IPAC)
Cool Stars 13 2/16Kelle Cruz
Project SummaryProject Summary
• Measure the luminosity function of low-mass stars and BDs using a large sample of nearby objects
– Sample well understood so biases and selection effects can be accounted for
– Large volume with distance limit of 20 pc
– Aimed to be complete for objects between M7 and L8
– Cover 40% of the sky
Cool Stars 13 4/16Kelle Cruz
Present-Day Mass FunctionPresent-Day Mass Function
Reid, Gizis, Hawley, 2002, AJ, 124, 2721
(M) = M--1
Salpeter
~1~0.5-1?
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2MASS Second Release2MASS Second Release
• Covers 47% of the sky in JHKS• Contains over 162 million point sources
Cool Stars 13 6/16Kelle Cruz
Selection CriteriaSelection Criteria
cool stars
ultracool dwarfs
T dwarfs
Cool Stars 13 7/16Kelle Cruz
Selection Criteria (cont.)Selection Criteria (cont.)
cool stars
ultracool dwarfs
L dwarfs
T dwarfs
giants
Cool Stars 13 8/16Kelle Cruz
The 2MU2 SampleThe 2MU2 Sample
• 1700 hits!
• Bright objects (J<9) analyzed separately
• 500 require follow-up observations
Cool Stars 13 9/16Kelle Cruz
Follow-up StatusFollow-up Status
• 98% complete. Only 15 left!
far-red
near-infrared
none
Cool Stars 13 10/16Kelle Cruz
Spectral Type DistributionSpectral Type Distribution
Optical Spectral Type
Cool Stars 13 11/16Kelle Cruz
MMJJ/ST Relation/ST Relation
Tinney, Burgasser, Kirkpatrick, 2003, AJ, 126,975
Optical Sp. Type NIR Sp. Type
Cool Stars 13 14/16Kelle Cruz
Constraining the MF with the LFConstraining the MF with the LF
Courtesy of Peter Allen
M
L
TY?
Cool Stars 13 15/16Kelle Cruz
Future WorkFuture Work
• Find more:
– Faintest 2MU2 objects with NIR and Gemini follow-up
– 2MASS All-Sky Release 2MUF, Paper X
• Study Near-infrared features (IRTF)
• Measure Multiplicity (HST and AO)
• Study Mid-Infrared Properties (Spitzer)
Cool Stars 13 16/16Kelle Cruz
• Created robust sample to measure fundamental properties of M7–L8 dwarfs
• Completing the census of the Solar Neighborhood
• First measurement of LF of objects that span the stellar/brown dwarf boundary
• Need more T dwarf data to put strong constraints on the mass function
• Papers:
– Cruz et al. 2003 (Paper V)
– Cruz et al. in prep (Paper IX)
SummarySummary