我們在年輕（約四百萬年）的疏散星團Trumpler 37中，針對一顆類似太陽的變星GM Cep進行了光學觀測。這顆恆星是一顆典型金牛座T型星，具有環星盤及活躍的吸積現象。GM Cep可能曾經歷暴發現象，因此我們懷疑它是顆EXor類型的變星。我們在2010至2011年間對GM Cep的長期觀測中，發現GM Cep在R波段經歷了約0.82等的亮度降低，為期長達38.9天，以及數個短暫的類似暴發的變亮時期，亮度變化小於1等，時間長度約10天左右。亮度變亮時恆星的顏色變藍，因此可能是由於吸積活動的增加所導致。但在亮度變暗的時期，恆星顏色也變藍；我們另外蒐集了AAVSO和文獻資料，發現這顆恆星的亮度變暗有一約311天的半週期。我們推測變暗的可能原因，是在恆星周圍有一團塵埃擋住了星光。因此我們認為GM Cep是顆UXor類型的變星，處於環星盤中微粒凝結到微行星形成的過渡階段。 We present our photometric observations of GM Cep, a solar type variable in the young (∼ 4 Myr) open cluster Trumpler 37. The star is known as a classical T Tauri star with a circumstellar disk and active accretion. GM Cep was suspected to undergo an outburst, thus a candidate for an EXor-type variable. In our monitoring campaign observations in 2010–2011, GM Cep experienced a ∼ 0.82 mag brightness decrease in the R band continuously for 39 days, and frequent, transient flare-like episodes with the amplitude < 1 mag, each lasting for about 10 days. The brightening was accompanied with a bluer color, presumably arising from increased accretion activity. Interestingly, the star also turned bluer in the fading phase. Combining the AAVSO and literature data, we found a quasi-cyclic period of ∼ 311 days for the fading event. A possible mechanism for the fading could be obscuration by a clump of dust around the star. We proposed that GM Cep therefore should be a UXor-type variable in the transition phase between grain coagulation and planetesimal formation process in the circumstellar disk.
