AAVSO: American Association of Variable Star Observers

No Longer Eclipsing—The Strange Case of RS Crateris

Volume 51 number 2 (2023)

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Stephen P. Cook
910 Oak Terrace Drive, Prescott, AZ 86301; scook@projectworldview.org


For decades mistakenly classified as a solar (spectral class G0) Algol-type eclipsing binary with 0.7-magnitude amplitude, RS Crt is now listed as constant at V magnitude 10.62 in the AAVSO’s International Variable Star Index (VSX). The author’s 2020 differential photometry supports this reclassification, showing RS Crt to be constant (with 0.042 V mag. scatter). Investigating when its light variation ceased, the author analyzes data (including his own) from several observers obtained between 1972 and 1995 and concludes none show periodic variation. Citing the poor quality of the 1930–1944 data upon which its previous classification was based, one could argue RS Crt never was an eclipsing binary. Finding eight new minima (from 1929 to 1948) in the digitized Harvard Plate Collection/DASCH—and deriving a period of 0.8272 day that fits the early data better than the older period of 0.8168 day—the author seemingly refutes that contention. Four additional minima (from 1964 to 1971) gleaned from the APPLAUSE archive strengthen his contentions including that the period drastically shortened before eclipses ceased. Confirming it quit eclipsing—and admitting it to a tiny, select group of objects—would require spectroscopic confirmation of its binary nature. If such much-needed future observation fails to show that, speculations—of its compact binary past with spiral death march ending with coalescence into a single object, or of a history marked by a collision with a high-speed interloper—might be strengthened. Despite its recent constant classification, TESS data show RS Crt varies with amplitude <0.01 magnitude in a roughly four-day periodic fashion. Study of the beats, overtones, and damping in this light curve might lead to portraying its past in terms of pulsations, not eclipses.