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Early Optical Spectroscopic Evolution of V745 Sco

ATel #5874; R. M. Wagner (Ohio State U.) and S. G. Starrfield (Arizona State U.)
on 10 Feb 2014; 21:47 UT
Credential Certification: R. Mark Wagner (rmw@as.arizona.edu)

Subjects: Optical, X-ray, Cataclysmic Variable, Nova

Referred to by ATel #: 5884

With the recent announcement by E. O. Waagen (CBET 3803) of the discovery by R. Stubbings, Victoria Australia, of a new outburst of the recurrent nova V745 Sco (AAVSO Alert Notice #496), we re-examined optical spectra obtained during the 1989 outburst. The most complete set of spectra covering the first month of the 1989 outburst were presented by Duerbeck (1989, ESO Messenger, 58, 34; Figure 1) and by Williams et al. (2003, Journal of Astronomical Data, 9, 3) who obtained spectra of the nova during outburst on 10 epochs extending from 1989 August 1 through 1992 April 4.

The most striking aspect of the Duerbeck montage in his Figure 1 is the presence and rapid evolution of the coronal line spectrum (Duerbeck, Schwarz, and Augusteijn IAUC 4844 ). In addition to the presence of broad (FWHM ~ 1200 km/s; FWZI ~ 9000 km/s) Balmer and He I emission lines reported previously (Wagner et al. IAUC 4822 ; Duerbeck and Schwarz IAUC 4825 ; Sekiguchi et al. 1990, MNRAS, 246, 78; Banerjee et al. ATEL #5865; Anupama et al. ATEL #5871) as well as strong He II 468.6 nm and strengthening [O III] 500.7 emission, coronal lines of [Fe XI] 789.1, [Ar XI] 694.9, [Fe X] 637.4, [Fe VII] 608.7, [Ar X] 553.6, [Fe XIV] 530.3 and perhaps [Ni XII] 423.1 nm were identified. We note that the [Ni XII] 423.1 nm line in his Figure 1 may have been incorrectly attributed to [Ni XIV].

We also obtained a spectrum on 1989 August 31.2, about 31 days after discovery, using the same telescope and instrument as described in IAUC 4822 but with broader spectral coverage (330-813 nm) and lower resolution (1 nm). By this time, the coronal line spectrum had weakened considerably. In addition to the lines noted by Duerbeck, we identify forbidden lines of [N II] 575.5 nm; [O III] 500.7, 495.9, and 436.3 nm; [Fe VII] 515.9, 567.7, 572.0, and 608.7 nm; [Ca V] 530.9 nm; [Ca VII] 561.8 nm; and [O I] 630.0, 636.3 nm. The [O I] 636.3 nm line strength was anomalously strong with respect to [O I] 630.0 nm and was likely blended with a significant contribution from [Fe X] 637.4 nm (about 1 month after maximum light) as can be seen in the Duerbeck montage as well. The observed [Fe X] to Hα intensity ratio was about 1.3% at this time.

The presence of [Fe X] in the nebular spectra of both recurrent and classical novae has long been considered a signature of the presence of a hot central source (Krautter and Williams 1989, ApJ, 341, 968; Schwarz et al. 2011, ApJS, 197, 31). With the recent detection of both strong hard X-ray emission by Mukai et al. (ATEL #5862) and the developing presence of a supersoft X-ray component (Page et al. ATEL #5870) in V745 Sco, the observation of rapid time dependent optical [Fe X] emission early in the 1989 outburst affords the opportunity to examine in detail the relationship between X-ray emission and the strength of [Fe X] in novae. We encourage both X-ray observations and optical spectroscopy (in spite of the difficult observational circumstances) during the current 2014 outburst of V745 Sco.