# 研究成果・発表論文

## Light absorption efficiencies of photosynthetic pigments: the dependence on spectral types of central stars

### Komatsu, Yu,   Umemura, Masayuki,   Shoji, Mitsuo,   Kayanuma, Megumi,   Yabana, Kazuhiro,   & Shiraishi, Kenji

##### 要旨
For detecting life from reflection spectra on extrasolar planets, trace of photosynthesis is one of the indicators. However, it is not yet clear what kind of radiation environments is acceptable for photosynthesis. Light absorption in photosystems on the Earth occurs using limited photosynthetic pigments such as chlorophylls (Chls) and bacteriochlorophylls (BChls). Efficiencies of light absorption for the pigments were evaluated by calculating the specific molecular absorption spectra at the high accuracy-quantum mechanical level. We used realistic stellar radiation spectra such as F, G, K and M-type stars to investigate the efficiencies. We found that the efficiencies are increased with the temperature of stars, from M to F star. Photosynthetic pigments have two types of absorption bands, the Q $_ y$ and Soret. In higher temperature stars like F star, contributions from the Soret region of the pigments are dominant for the efficiency. On the other hand, in lower temperature stars like M stars, the Q $_ y$ band is crucial. Therefore, differences on the absorption intensity and the wavelength between the Q $_ y$ and Soret band are the most important to characterize the photosynthetic pigments. Among photosynthetic pigments, Chls tend to be efficient in higher temperature stars, while BChls are efficient for M stars. Blueward of the 4000 ̊A break, the efficiencies of BChls are smaller than Chls in the higher temperature stars.