Serendipty and Cataclysmic Variables

Cataclysmic variable star research has benefited from the, often accidental, discovery of CVs during the course of astronomers doing other research. This has led to a lot of license plate type names like RSXJ01234.45+2345.6, HS 1234+5678 and PG 1234+67. These are prefix based names that indicate the space satellite or ground survey that discovered the star. RSX means it was a ROSAT satellite x-ray source, HS stands for the Hamburg Quasar Survey, and PG means it was discovered by the Palomar Green Survey (also looking for quasars). For more information on this plethora of naming conventions see my article "What's In A Name?"

Serendipity comes into play because all of these previously mentioned examples are stars discovered by surveys looking for other types of objects. ROSAT was looking for x-ray sources on the sky and the Palomar and Hamburg surveys were looking for blue objects in their search for quasars. The most common way CVs are discovered from these population of objects is by going into outburst and revealing themselves as much brighter in new images compared to older images. Until recently, it would be safe to say half of all CVs were discovered by their telltale outbursts or optical variability when active or bright.

Today a paper was published on ArXiv describing a new CV, RAT J1943+1859, discovered while astronomers were looking for variable stars in the field of the globular cluster M71. RAT stands for RApid Temporal Survey, an experiment utilizing the Isaac Newton Telescope. Even though the astronomers were actually looking for variable stars this time, what they didn't expect to find were stars exhibiting quasi-periodic oscillations (QPOs), a little understood phenomena of cataclysmic variables, while the CVs are in quiescence (faint).

That is exactly what happened in this case. Astronomers found a periodic oscillation of about 0.3 magnitudes with a period of approximately 20 minutes. Observations taken later with another telescope revealed the object to be four magnitudes brighter than the first set of observations. They caught it in outburst! Further observations and spectroscopy suggest an orbital period of about 90 minutes, which means it is very likely to be a UGSU type dwarf nova at a distance of about 1.5 kiloparsecs. If this distance is accurate, RAT J1943+1859 is one of the most luminous sources observed by ROSAT.

So far, observations have measured the system at minimum around 20th magnitude, and in outburst approximately 16.5V. If it is a UGSU it will have superoutbursts somewhat brighter than this that will last longer, perhaps a couple weeks. This puts it right around the faint limit for 30cm amateur telescopes to study in outburst to determine its type, orbital period and superhump period if it goes into a superoutburst.

Even more exciting than the fact this might be another interesting system for amateurs to monitor, is the fact that RATS has several million light curves in their data that can now be searched for this same kind of behavior. These astronomers may have discovered a new way to discover CVs! This also has implications as more surveys like LSST and PanSTARRS are readying to come online in the near future. Scientists will be developing ways to sort out specific kinds of stars from the terabytes of data these surveys will create every night.

In that new era, amateurs will be needed more than ever to sift through the strange and unique discoveries these surveys stumble on while monitoring the cosmos every night in unprecendented detail.

RATS, QPOs, serendipity and discovery. It's a new age already.