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ATEL # 3074; A. W. Shafter (SDSU), R. Ciardullo (PSU), M. J. Darnley, M. F. Bode (Liverpool JMU, UK), K. A. Misselt (U. Arizona)
on 9 Dec 2010; 3:56 UT
Password Certification: Allen W. Shafter (firstname.lastname@example.org)
Subjects: Optical, Nova, Transients
Pietsch et al. (ATel #3013) reported the serendipitous discovery of a super-soft X-ray source (SSS) coincident with the position of the M31 globular cluster Bol 126. Shortly thereafter, Henze et al. (ATel #3019) reviewed archival observations from the Livermore Optical Transiting Imaging System (Super-LOTIS) and found that Bol 126 had brightened by about one magnitude circa 2010 Oct. 12 UT. Auxiliary observations indicated the cluster faded roughly to its quiescent brightness within ~4 days. As pointed out by Henze et al., the observed brightening of the globular cluster, followed shortly thereafter by the detection of a SSS coincident with the cluster, is consistent with the eruption of a rapidly-fading classical nova.
In an attempt to confirm that a nova had in fact erupted within Bol 126, we obtained spectroscopic observations of the cluster on 2010 Nov. 13.285 with the 9.2m Hobby-Eberly Telescope (+ Marcario Low-Resolution Spectrograph). The spectrum revealed weak and narrow Balmer and Mg b λ 516.7, 517.3, 518.3 nm absorption features characteristic of a globular cluster; but, surprisingly, no obvious Balmer emission that could be associated with a nova. Although novae typically fade slowly in H&alpha, Ciardullo et al. (1990, ApJ, 356, 472) have shown that the fastest novae can fade by as much as 3 mag in Hα over a time span of a month. Thus, we cannot exclude the possibility that the rapid optical decline of the nova reduced its spectroscopic signature below our detection threshold by the time of our observations ~1 month post eruption.
A.W.S. thanks the NSF for support through AST-0607682 and AST-1009566.