IM Normae: A Second T Pyx? (Abstract)

Volume 43 number 2 (2015)

Joe Patterson

Center for Backyard Astrophysics, 25 Claremont Avenue, Apt. 7C, New York, NY 10027; jop@astro.columbia.edu

Berto Monard

CBA (Pretoria), P. O. Box 281, Calitzdorp 6661, Western Cape, South Africa

Paul Warhurst

address correspondence to J. Patterson, Center for Backyard Astrophysics, 25 Claremont Avenue, Apt. 7C, New York, NY 10027; jop@astro.columbia.edu

Gordon Myers

5 Inverness Way, Hillsborough, CA 94010; GordonMyers@hotmail.com

Abstract

(Abstract only) T Pyx is the Galaxy’s most famous recurrent nova, erupting to magnitude 6 about every 20 years. For nova hunters and variable-star observers generally, it should be quite easy to discover stars with similar properties. There are probably half a million CVs out to the distance of T Pyx, and most have an underlying structure similar to that of T Pyx: low-mass secondary, fairly massive white dwarf, short orbital period. But of these half million stars, there is no second T Pyx. The star is unique in another way: its orbital period is increasing on a timescale of 300,000 years. Like the proverbial bat out of hell. A 2002 nova eruption nominated a second star for this elite club: IM Nor, a short-orbital-period (2.5 hours) star which previously erupted in 1920. We began a program of time-series photometry to track the shallow eclipses—to test for orbital period change, the other signature of T Pyx resemblance. By 2015 we found this effect: Porb increases on a timescale of 2 million years. Thus, the two stars appear to be blowing themselves apart on a timescale of roughly a million years. This could explain why the stars are so rare: because they are rapidly self-immolating. And that could happen because the classical-nova outburst overwhelms the low-mass secondaries that live in short-period CVs—leading to unstable mass transfer which quickly evaporates the secondary. This implies that all short-Porb classical novae should be “recurrent” (erupting on a timescale of decades). Greater attention to CP Pup (1942), RW UMi (1956), GQ Mus (1983), and V Per (1887) is definitely warranted.