TY - JOUR
T1 - Spitzer IRAC photometry of M, L, and T dwarfs
AU - Patten, Brian M.
AU - Stauffer, John R.
AU - Burrows, Adam S.
AU - Marengo, Massimo
AU - Hora, Joseph L.
AU - Luhman, Kevin L.
AU - Sonnett, Sarah M.
AU - Henry, Todd J.
AU - Raghavan, Deepak
AU - Megeath, S. Thomas
AU - Liebert, James
AU - Fazio, Giovanni G.
PY - 2006/11/1
Y1 - 2006/11/1
N2 - We present the results of a program to acquire photometry for 86 late M, L, and T dwarfs using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We examine the behavior of these cool dwarfs in various color-color and color-magnitude diagrams composed of near-IR and IRAC data. The T dwarfs exhibit the most distinctive positions in these diagrams. In M5.8 versus [5.8]-[8.0], the IRAC data for T dwarfs are not monotonic in either magnitude or color, giving the clearest indication yet that the T dwarfs are not a one-parameter family in Teff. Because metallicity does not vary enough in the solar neighborhood to act as the second parameter, the most likely candidate then is gravity, which in turn translates to mass. Among objects with similar spectral type, the range of mass suggested by our sample is about a factor of 5 (∼70MJ to ∼15MJ), with the less massive objects making up the younger members of the sample. We also find the IRAC 4.5 μm fluxes to be lower than expected, from which we infer a stronger CO fundamental band at ∼4.67 μm. This suggests that equilibrium CH 4/CO chemistry underestimates the abundance of CO in T dwarf atmospheres, confirming earlier results based on M-band observations from the ground. In combining IRAC photometry with near-IR JHK photometry and parallax data, we find the combination of KS, IRAC 3.6 μm, and 4.5 μm bands to provide the best color-color discrimination for a wide range of M, L, and T dwarfs. Also noteworthy is the MKS versus KS-[4.5] relation, which shows a smooth progression over spectral type, and splits the M, L, and T types cleanly.
AB - We present the results of a program to acquire photometry for 86 late M, L, and T dwarfs using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We examine the behavior of these cool dwarfs in various color-color and color-magnitude diagrams composed of near-IR and IRAC data. The T dwarfs exhibit the most distinctive positions in these diagrams. In M5.8 versus [5.8]-[8.0], the IRAC data for T dwarfs are not monotonic in either magnitude or color, giving the clearest indication yet that the T dwarfs are not a one-parameter family in Teff. Because metallicity does not vary enough in the solar neighborhood to act as the second parameter, the most likely candidate then is gravity, which in turn translates to mass. Among objects with similar spectral type, the range of mass suggested by our sample is about a factor of 5 (∼70MJ to ∼15MJ), with the less massive objects making up the younger members of the sample. We also find the IRAC 4.5 μm fluxes to be lower than expected, from which we infer a stronger CO fundamental band at ∼4.67 μm. This suggests that equilibrium CH 4/CO chemistry underestimates the abundance of CO in T dwarf atmospheres, confirming earlier results based on M-band observations from the ground. In combining IRAC photometry with near-IR JHK photometry and parallax data, we find the combination of KS, IRAC 3.6 μm, and 4.5 μm bands to provide the best color-color discrimination for a wide range of M, L, and T dwarfs. Also noteworthy is the MKS versus KS-[4.5] relation, which shows a smooth progression over spectral type, and splits the M, L, and T types cleanly.
KW - Infrared: stars
KW - Stars: fundamental parameters
KW - Stars: late-type
KW - Stars: low-mass, brown dwarfs
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U2 - 10.1086/507264
DO - 10.1086/507264
M3 - Article
AN - SCOPUS:33845716749
SN - 0004-637X
VL - 651
SP - 502
EP - 516
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1 I
ER -