PAIRITEL Photometry of Dwarfs from the IRAC GTO sample

1. PAIRITEL Photometry of Dwarfs from the IRAC GTO sample Joseph L. Hora Brian Patten, Massimo Marengo Harvard-Smithsonian Center for Astrophysics 2nd Annual PAIRITEL Workshop

2. IRAC M/L/T Dwarf Program • IRAC bands at 3.6, 4.5, 5.8, and 8 μm • IRAC sensitivity, molecular features and continuum sampled • Sample: 87 late M, L, T dwarfs, masses ~70 MJ – 15 MJ • Chosen based on known sources in 2002 • Trigonometric parallax • Well-determined spectral types • Located in uncrowded fields, not known binaries (although some are now known or suspected) • Sources of near-IR photometry are 2MASS, DENIS, SDSS • Possible problems in converting from other photometric systems to 2MASS • Near-IR photometry on this reference sample necessary to identify and classify additional M, L, T candidates 2nd Annual PAIRITEL Workshop

3. Molecular features in NIR Dwarf spectra • L dwarfs – absorption from CO and H2O, T dwarfs have broad absorption bands of CH4 and H2O, and H2 absorption • In near-IR photometry, M and L dwarfs become redder with decreasing Teff in J −H and H−K. • The L to T dwarf transition occurs as the silicate and iron condensates (clouds) become buried at increasing depth in late-L dwarfs. • H2O absorption begins to dominate the near-IR spectrum, leading to a bluing of the near-IR colors through the early-T types. • The colors then become even bluer from early-T to late-T with the onset and growth of CH4 absorption and H2 in K. • The overall result is that the J−H and H−K colors for T dwarfs become bluer with increasing spectral subtype, becoming degenerate with the colors of higher mass K and M dwarfs. 2nd Annual PAIRITEL Workshop

4. M, L, T dwarf spectral features sampled by IRAC • IRAC channel 1 includes much of the CH4 fundamental absorption band (~3.3 μm). • Channel 2 includes the continuum peak present for all stars cooler than 3000 K, making this the most sensitive IRAC channel for the study of sub-stellar objects. • Channel 2 also contains the broad but shallow CO fundamental absorption band (~4.7 μm), whose presence in the T dwarfs provides evidence for non-equilibrium chemistry models • Channel 3 includes H2O absorption and, for low Teff , NH3 absorption. • Channel 4 – molecular absorption due to CH4 2nd Annual PAIRITEL Workshop

5. IRAC bandpasses and dwarf spectra 2nd Annual PAIRITEL Workshop

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7. Color vs Spectral Type • IRAC-IRAC colors are slowly changing until L-T boundary • Near-IR to IRAC colors show trends throughout the range of types • Combination of all data allow better determination of object class 2nd Annual PAIRITEL Workshop

8. Goals of PAIRITEL Measurements • Improved photometry • Some targets close to sensitivity limits of original 2MASS, or SDSS or DENIS surveys • Some photometry affected by nearby sources in field, due to high proper motion the stars are now better separated • Variability monitoring • Variations for example due to uneven coverage of the surface in CH4 or other types of weather which could cause changes in flux • Rotation periods 1-10 hr have been detected in dwarfs • Presence of variations in T dwarfs not well established • 2–17% variations observed by Artigau et al. 2003 in J &H • Others report monitoring with no variations detected • PAIRITEL observations to sample at various frequencies of 1/night+ over months+ timescales • IRAC continuous monitoring for hours of dwarfs saw no variability • Cycle 3 GTO program to sample hours, weeks, months timescales 2nd Annual PAIRITEL Workshop

9. PAIRITEL Observation Status • 68 objects in program • Observations started ~Jan 23 2006 • 24/35 done for objects where only 1 observation requested • 24/33 of monitoring stars have at least one measurement • Median number is 17 samples, most have goal of 50 samples 2nd Annual PAIRITEL Workshop

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11. Quick look at DWARF program data • A couple stars with M<15 have been observed ~20 x • Use pipeline mosaics • Poor weather data tossed out • All sources >10σ in each band found • Aperture photometry performed (iraf/phot task) on sources • Bandmerge performed to generate J/H/K catalog • Catalog then matched to 2MASS data • Zero point adjustment determined to minimize median difference between 2MASS and PAIRITEL photometry for all matched sources <15mag • To obtain higher S/N, mosaics averaged and photometry performed as above on these frames 2nd Annual PAIRITEL Workshop

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14. Single measurements • DWARF 50 • DWARF 53 2nd Annual PAIRITEL Workshop

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17. 2MA1237+6527 2nd Annual PAIRITEL Workshop

18. 2MA1237+6527 2MASS 2nd Annual PAIRITEL Workshop

19. 2MA1237+6527 PAIRITEL 2nd Annual PAIRITEL Workshop

20. 2MASS 15394189-05204026 (P=G, 2MA=R) 2nd Annual PAIRITEL Workshop

21. Next steps - • Refine photometry extraction – • Find optimal photometry parameters – radius, background estimation, zero point adjustments • Confirm error estimate • Automate process • Perform photometry on remainder of sample • Perform frequency analysis • Identify candidates that have variations or differences from 2MASS photometry • Continue monitoring candidates • Write up results 2nd Annual PAIRITEL Workshop