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Nova Sagittarii 1943 (V1148 Sgr): A Luminous Red Nova?

Nova Sagittarii 1943 (V1148 Sgr) was an 8th-mag optical transient that was unusual in having a late-type spectrum during its outburst, in striking contrast to the normal high-excitation spectra seen in classical novae. Unfortunately, only an approximate position was given in the discovery announcement, hampering follow-up attempts to observe its remnant. We have identified the nova on two photographic plates in the Harvard archive, allowing us to determine a precise astrometric position. Apart from these two plates, obtained in 1943 and 1944, none of the photographs in the Harvard collection, from 1897 to 1950, show V1148 Sgr to limits as faint as g ~ 18.3. Modern deep images show a candidate remnant at i ~ 19.2, lying only 0".26 from the site of the nova. V1148 Sgr may have been a luminous red nova (LRN), only the sixth one known in the Milky Way. However, it lacks the near- and mid-infrared excesses, and millimeter-wave emission, seen in other LRNe, leaving its nature uncertain. We urge spectroscopy of the candidate remnant.