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The pre-Nova Lightcurve of KT Eri (Nova Eridani 2009)

ATel #2331; A. J. Drake, S. G. Djorgovski, M. J. Graham, A. A. Mahabal, R. Williams (Caltech); Wils, P. (Vereniging Voor Sterrenkunde), Greaves, J. (Northants., UK); M. Catelan (PUC); J. Prieto (OCIW); E. C. Beshore, S. M. Larson, A. Boattini, A. Gibbs, A. Grauer, R. Hill, R. Kowalski (LPL/UA); E. Christensen (Gemini Observatory).
on 4 Dec 2009; 22:03 UT
Credential Certification: Andrew J. Drake (ajd@cacr.caltech.edu)

Subjects: Optical, Nova, Transient

Here we report on historical observations of the pre-Nova source of KT Eri (Nova Eridani 2009).

Following the detection of the possible Nova at mag 8.1 by Yamaoka et al. (2009, CBET#2050), we carried out a search of Catalina Sky Survey 0.7m data covering the location of this event. Photometry of the source was found with dates between 2005-01-17 and 2009-11-18 UT. The Nova was clearly seen in outburst in images taken on Nov. 18 UT, but was not detected in our CRTS transient search because of very high level saturation. The CSS observations also show that the Nova outburst occurred after 2009 Nov. 10.41 UT. The light curve of this object clearly exhibits variations of approximately 1.8 magnitudes as shown here. A search for a periodicity within the photometry yields a possible period to be ~210 days. However, this detection does not appear to have high significance.

Following the Nova outburst, Ragan et al. (2009, ATEL#2327) obtain photometric and spectroscopic observations of the Nova. They further note that "A distance of 6.5 kpc means that the 15 mag star observed at approximately the same coordinates before the outburst is too bright to be a progenitor of Nova Eri 2009."
Although the CSS data is of insufficient resolution to determine whether the observed Nova is indeed blended with the 15th magnitude star, the high level of observed variability suggests that the a much fainter progenitor would have to exhibit a very high level of variability to cause such variations, unless the 15th mag star itself was an unusual type of highly variable star. These two possibilities are unlikely. Furthermore, the degree of variation observed for the 15th mag object is similar to that observed for Nova CSS081007:030559+054715 (discovered by CRTS and characterized by Pejcha et al (2008, ATel#1825) and Prieto et al. (2008 ATel#1835)). For this event, the observed variability in the pre-Nova lightcurve was slightly larger at ~2.5 magnitudes (Drake et al. 2009, Atel#1940), as seen here. Also, like KT Eri this event was observed at high Galactic latitude (-43.7deg). Therefore, we conclude that the 15th magnitude star is most likely associated with the observed Nova.