V1315 Aql and IPHASX J210204.7+471015 Did Not Have Their 'Predicted' Nova Eruptions from 1889--1954

ATel #12474; Bradley E. Schaefer (Louisiana State University)
on 4 Feb 2019; 19:10 UT
Credential Certification: Bradley E. Schaefer (schaefer@lsu.edu)

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Recently, two old nova shells have been discovered around cataclysmic variables V1315 Aql (Sahman et al. 2015; 2018) and IPHASX J210204.7+471015 (Santamaria et al. 2019), with it possible to approximately determine the date of the long-ago nova eruption. Both stars are 'predicted' to have their nova events in historic times, even into the 1890s. Both nova eruptions should have peaked as naked eye stars. I have tested these claims by looking for nova eruptions on old sky photographs at the Harvard College Observatory for years after 1889.

The Harvard plate stacks have >4700 images showing each of the two targets, going back to 1890 and earlier, with a typical limiting magnitude of B=13. The two targets have average quiescent magnitudes of B=14.33 and B=15.8 respectively, so the lack of any stellar image at the target position rules out any nova eruption over many months previous to the plate. My detailed examination of the 97 all-time best observed nova light curves (Strope, Schaefer, and Henden 2010) shows that the definite classical novae (cf. Pagnotta and Schaefer 2014) all have a time interval of 200 days to >3000 days during which the light curve is more than 3.0 mags above the quiescent level. This means that one photographic plate every 200 days will certainly detect our targets in eruption. That is, the eruptions cannot escape discovery by erupting at the start of the yearly gap in coverage (centered on the time of the solar conjunction). I have examined many plates for each year from 1890 to 1954, and the result is that we can be completely confident that any eruption from 1889 to 1954 would have been discovered.

V1315 Aql is an ordinary nova-like system, except that it has a nova shell. The eruption date is estimated variously as around the year 1895, ~500-600 years ago, or up to 1200 years ago (Sahman et al. 2015; 2018), as based on the current observed expansion velocity and an assumed initial expansion velocity. With a possible eruption around the 1890s, it is worthwhile to check the Harvard plates. V1315 Aql has the earliest plate from 1890 May 20, although two isolated plates were obtained on 1886 August 9 and 1887 September 19. For example, in 1890, I examined 11 plates with median limiting magnitude of B=12.2 from May 20 to December 4. From 1890 to 1954, I have examined 1446 plates with limiting magnitudes deeper than B=13.0. No nova event was detected. Given the number and timing of plates examined, we can be certain that no eruption came anytime between 1889 and 1954. This null result is easily understood if the initial expansion velocity of the shell was somewhat slower than 2000 km/s.

IPHASX J210204.7+471015 is an ordinary nova-like system, except that it has an expanding nova shell surrounding it. The nova eruption date is estimated to be between the years 1850 and 1890, as based on its observed current expansion rate along with models for the deceleration (Santamaria et al. 2019). IPHASX J210204.7+471015 has its first plate from 1889 September 10, although one earlier plate shows B>13.0 from 1887 November 30. I have examined 1303 plates from 1889 to 1954 with a limiting magnitude of B=13.0 or deeper. No nova event was discovered, and we can be certain that none occurred anytime between 1889 and 1954. This null result is not useful, as the eruption could well have been anytime from 1850 to 1889. Nevertheless, it was a good try to seek both of these predicted very-old nova eruptions.

Pagnotta, A. and Schaefer, B. E. 2014, ApJ, 788, 164
Sahman, D. I., Dhillon, V. S., Knigge, C., and Marsh, T. R. 2015, MNRAS, 451, 2863
Sahman, D. I., Dhillon, V. S., Littlefair, S. P., and Hallinan, G. 2018, MNRAS, 477, 4483
Santamaria, E., Guerrero, M. A., Ramos-Larios, G., Sabin, L., Vazquez, R., Gomez- Munoz, M. A., and Toala, J. A. 2019, MNRAS, 483, 3773
Strope, R. J., Schaefer, B. E., and Henden, A. A. 2010, AJ, 140, 34