Faint stars with strong emission in and around the Orion nebula.

In a previous investigation of the spectra of variable stars in the Orion nebula made by Greenstein and Struve,1 it has been said that the "lack of emission distinguishes the Orion variables clearly from the T Tauri variables discussed by A. H. Joy."2 The observed lack of emission previously found in the Orion variables has been interpreted as probably due either to the fact that these stars are not deeply immersed in dark material or because the presence of the very hot, bright stars of the Trapezium may change the character of nebulous material. In an investigation carried on with the ~6-inch prism of the Tonanzintla Schmidt camera many stars with Hot in emission fainter than the ioth magnitude and as faint as the 17th magnitude were registered. In an area of about 2.5 square degrees centered on the Trapezium the spectra of 113 stars were recorded with more or less strong emission in Hot. The variables recognized as such in Kukarkin and Parenago's Catalogue, that appear on the Tonanzintla plates with Hot in emission are the following Orion variables: AA, AB, AG, AM, AR, AU, AV, AX, BC, BF, BO, BS, BV, BW, BX, BZ, CD, CE, CF, CH, RZ, ST, SU, SY, T, TV, TW, VW, VX, VZ, WW, WZ, XX, XY, XZ, YY and YZ. It seems that the emission characteristics in many of these stars are not permanent and that the intensity of the emission in some cases varies and may even disappear. An interesting case of variation of emission lines of these stars is that observed in the variable T Orionis. This variable appears to have on the Tonanzintla plates Hot in emission in the red part of the spectrum and He I X447i and X4i44 in the photographic region. The absorption spectrum corresponds to an A~-type star. This variable is undoubtedly a very peculiar one. In the present investigation an area of approximately 25 squ~re degrees centered near the Trapezium has been photographed. In this area 143 stars with more or less strong emission in Hot have been found; of these stars 113 are situated in an area of 2.5 square degrees centered on the Trapezium. Therefore it seems obvious that there is a concentration of emission line stars in the region of the Orion nebula. I.Pub. A. S. P. ~8, 366, 1946. 2.Ap. J. 102, i68, 1945. Observatorio A strofisico lYacional, Tonansintla, Mexico.