| |
 |
| Paper: |
Analysis of CH4 Q-branch Absorption in Brown Bwarf Spectra Observed by AKARI |
| Volume: |
448, 16th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun |
| Page: |
945 |
| Authors: |
Sorahana, S.; Yamamura, I. |
| Abstract: |
We present the result of our analysis about the appearance of 3.3 μm CH4 band in the spectra of brown dwarfs with the Japanese infrared astronomical satellite, AKARI.
The CH4 bands at 1.6 and 2.2 μm have been regarded as a key indicative features for classification of T-type brown dwarfs,
while the 3.3μm CH4 band has been detected in the dwarfs as early as L5.
This implies that the presence of CH4 does not simply rely on the effective temperature,
and that we need more investigation to understand how the 3.3 μm CH4 absorption band appears in the infrared spectra of brown dwarfs.
We are constructing a comprehensive sample of brown dwarfs in the 2.5–5.0 μm with AKARI.
We obtained good quality spectra for 13 objects that enable us
to have a better understanding of the atmospheric structure and onset of the CH4 band.
We confirm that the 3.3 μm CH4 fundamental band starts appearing at L5.
The band is seen in two of four L5-dwarfs in our sample.
We derive the physical parameters of the photosphere of the objects
by applying the Unified Cloudy Model.
We find that the sources with/without 3.3 μm CH4 band have systematically different parameters, i.e. different photospheric structures.
We find that the abundance of CH4 depend on the critical temperature (Tcr) and the surface gravity (log g) rather than the effective temperature (Teff).
We suspect that the two groups are different in mass and age. |
|
|
|
|
|
