RR Telescopii is a symbiotic nova in the southern constellation Telescopium. It was recorded on photographic survey plates as a faint variable star between photographic magnitude (mpg) 9 to 16.6 from 1889 to 1944. In late 1944 the star began to brighten, increasing by about 7 magnitudes, from mpg ≈ 14 to brighter than 8. Brightening continued with a diminished rate of increase after early 1945, but the overall outburst was not noted until the star was seen at about 6.0, the threshold of naked eye brightness, in July 1948. At that time it was given the designation Nova Telescopii 1948. Since mid-1949 it has declined in brightness slowly, albeit accompanied by some remarkable changes in its spectrum, and as of August 2013 it had faded to visual magnitude around 12.
Pre-eruption and outburst RR Telescopii was periodically observed in a survey program by the southern station of Harvard College Observatory starting in 1889, as well as other southern observatories begun at later dates. Williamina Fleming in 1908 reported variations in brightness between about magnitude 9 and 11.5, and suggested it might be the same type of star as SS Cygni. In later plates it showed modest irregular variability between mpg 12.5 and 14, up to about 1930. At that time it began slow periodic variations in brightness between magnitudes 12 and 16; the period of these variations was 387 days, and the star could be characterized as a peculiar semi-regular variable. No spectra seem to have been taken of the star prior to outburst, since it was too faint to be included in the Henry Draper Catalog and was undistinguished until outburst. In 1944 the periodic variations broke off, and RR Tel brightened by more than 7 magnitudes over the course of about four years. Starting about mpg 14 in late 1944, survey plates recorded it brighter than magnitude 8 early in 1945, and the star was observed at mpg 7.4 in September–October 1946, 7.0 in March 1948, and 6.0 in July 1948. In 1948 it was noticed, and received the designation Nova Tel 1948. In July 1949 the star began fading slowly. The information about RR Tel's pre-outburst behavior as seen in the Harvard survey plates was published by Margaret Mayall in February 1949, and the already long duration of the outburst, years as opposed to days or weeks, made it clear that RR Tel had to be very different from the novae which had been previously observed; it was called a slow nova in acknowledgement of that not understood difference. The first spectroscopic observations were made in June 1949 before it began fading, when the spectrum showed a pure absorption spectrum resembling that of an F-type supergiant. The next spectra were taken in September–October of that year, by which time the character of the spectrum had changed to a continuum with many emission lines but no discernible absorption lines.
Decline In visible light, RR Tel has faded steadily (albeit not with a constant rate) since 1949. It was about visual magnitude 10.0 in 1977 and is about magnitude 11.8 in mid-2013. Its visible spectrum has kept the same general character, though it has evolved to include emission lines of progressively higher excitation, including both permitted lines and forbidden lines of many elements. Absorption features due to TiO (the hallmark of M stars) were seen in the spectrum of RR Tel beginning in the 1960s. As other wavelengths became observable with instruments resulting from advancing technology, these tools were turned upon RR Tel. Infrared photometry found an excess of radiation from 1 to 20 μm, indicating the presence of circumstellar dust with a temperature of a few hundred kelvin. Observing at shorter wavelengths has been very productive. RR Tel was observed in the ultraviolet with IUE, the ultraviolet spectrometer aboard Voyager 1, and Hubble Space Telescope, and in X-rays with Einstein Observatory, EXOSAT, and ROSAT. Observing in the ultraviolet in particular allows direct detection of the white dwarf component of the system, which was impossible before the advent of the space observatories.
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