A study on the mid-infrared sources that dramatically brightened

Abstract

We present results of near-infrared (NIR) photometric and spectroscopic observations of mid-infrared (MIR) sources that brightened dramatically. Using Infrared Astronomical Satellite (IRAS), AKARI, and Wide-field Infrared Survey Explorer (WISE) point source catalogs, we found that four sources (IRAS19574+4941, V2494Cyg, IRAS22343+7501, and V583Cas) significantly brightened at MIR wavelengths over a period of 20-30 yr, depending on an interval between two different observation epoch. Little is known about these sources except V2494Cyg, which is considered as an FU Orionis star. Our observation clearly resolves IRAS22343+7501 into four stars (2MASSJ22352345+7517076, 2MASSJ22352442+7517037, [RD95]C, and 2MASSJ22352497+7517113) and the first JHKs photometric data for all four sources are obtained. Two of these stars (2MASSJ22352442+7517037 and 2MASSJ22352497+7517113) are known as T Tau stars. Our spectroscopic observation reveals that IRAS19574+4941 is an M-type evolved star and V583Cas a carbon star. 2MASSJ22352345+7517076 is probably a young stellar object, judging from our observation showing that it has a featureless NIR spectrum and also showed dramatic brightening in NIR (about 4 mag in the Ks band). Likely reasons for dramatic brightening in MIR are discussed in this paper.