QSO identification with BATC multiband data

We present intermediate-band spectral energy distributions (SED) of QSO candidates in 1 square degree field around Leo Triplet. Leo Triplet consists of three galaxies, NGC3623, 3627, and 3628, which appear to interact with each other. BATC survey data of 15 intermediate-band filters offer excellent opportunity to study low spectral resolution SED for thousands of point sources in the field simultaneously. In order to derive SED of high signal to noise ratio, we have combined hundreds of images for each passband and made photometric measurements for every point sources in the combined images. Two dozens of new QSO candidates are identified based on the shape of derived SED curves. We also investigated SEDs of known QSO candidates in the field, but their SED differs greatly from model predictions made for cataloged redshift. While we plan to carry out spectroscopic observations for further confirmation, this indicates that QSO identification based on objective prism and X-ray methods should be taken more cautiously.