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

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop 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 M J – 15 M J 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 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 M J – 15 M J 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

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop Molecular features in NIR Dwarf spectra L dwarfs – absorption from CO and H 2 O, T dwarfs have broad absorption bands of CH 4 and H 2 O, and H 2 absorption –In near-IR photometry, M and L dwarfs become redder with decreasing T eff 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. –H 2 O 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 CH 4 absorption and H 2 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. L dwarfs – absorption from CO and H 2 O, T dwarfs have broad absorption bands of CH 4 and H 2 O, and H 2 absorption –In near-IR photometry, M and L dwarfs become redder with decreasing T eff 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. –H 2 O 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 CH 4 absorption and H 2 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.

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop M, L, T dwarf spectral features sampled by IRAC IRAC channel 1 includes much of the CH 4 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 H 2 O absorption and, for low T eff, NH 3 absorption. Channel 4 – molecular absorption due to CH 4 IRAC channel 1 includes much of the CH 4 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 H 2 O absorption and, for low T eff, NH 3 absorption. Channel 4 – molecular absorption due to CH 4

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop IRAC bandpasses and dwarf spectra

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop 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 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

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop 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 CH 4 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 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 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 CH 4 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 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

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop PAIRITEL Observation Status 68 objects in program Observations started ~Jan /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 68 objects in program Observations started ~Jan /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

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop 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 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

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop Single measurements DWARF 50 DWARF 53

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop 2MA

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop 2MA MASS

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop 2MA PAIRITEL

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop 2MASS (P=G, 2MA=R)

2006/05/16 – J. Hora 2 nd Annual PAIRITEL Workshop 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 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