Blue and yellow long-period variables in the direction of the Small Magellanic Cloud

Abstract

<b>Aims.</b> We investigate the nature of a sample of 17 long-term periodic variables in the direction of the Small Magellanic Cloud. <b>Methods.</b> Based on new spectroscopic data, we determined spectral types, radial velocities, absolute magnitudes, and colors for these stars. We present a refined discussion of their OGLE light curves along with an analysis of their 2MASS photometry. <b>Results.</b> Most stars turned out to be B-A giants members of the Small Magellanic Cloud. We find a new interacting eclipsing binary with a period of 184 days and two new early-type ellipsoidal variables. One of our objects is the ROSAT source RX J0058.2-7231. We analyzed 11-years of data for this Be X-ray binary finding that their photometric period varies by ∼4% quasiperiodically, on a time scale of ∼1200 days. We find evidence of multiple photometric periods in 2 Ae-type and 1 late-Be type stars. The case of OGLE00445466-7328029 is especially interesting, as this late-type Be star shows a beating phenomenon primarily caused by two closely-spaced frequencies, 0.05733 c/d (17.44 d) and 0.06347 c/d (15.76 d). Four other emission-line objects show stable long-term periodicities and probably correspond to Be-star binaries. Transient photometric periods are only found in 4 non-emission early-type stars.