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Spectroscopic observations of PSN J12355235+2755563: Another likely LBV outburst

ATel #6303; P. Sheehan, K. Follette, and D. McCarthy, University of Arizona; D. C. Leonard, San Diego State University; S. Hart, Carnegie Mellon University; J. Moustakas, Siena College; A. Beverage, C. Burns, W. Chavez, A. Fox, E. Glad, M. Gregg, Z. Griffin, J. Griggs, K. Hart, A. Holt, E. Hooper, A. Horning, L. Hou, N. Irvin, J. Keane, S. Kinman, T. Lee, C. Lewis, C. Lindsay, S. Lipstone, C. Martino, T. McMaken, B. Nelson, L. Neumann, S. Pirkl, S. Pruitt, A. Schlingman, W. Schlingman, W. M. Schlingman, E. Schwartzman, N. Stock, J. Tinker, K. Van Artsdalen, J. Vince, T. Waddell, L. Westerlund, J. Wilke, L. Wiser, 2014 Advanced Teen Astronomy Camp
on 9 Jul 2014; 18:18 UT
Credential Certification: D. C. Leonard (leonard@astro.caltech.edu)

Subjects: Optical, Star, Supernovae, Transient, Variables

Referred to by ATel #: 8755

We report on low-dispersion spectroscopy (range 370-680 nm; resolution 0.7 nm) of PSN J12355235+2755563 (CBAT TOCP), obtained with the 2.3-m Bok telescope (+ Boller & Chivens spectrograph) at Steward Observatory on June 24 UT. The spectrum exhibits strong, narrow emission lines of the H Balmer series centered on wavelengths consistent with a recession velocity of ~855 km/s. The FWHM of H-alpha is approximately 550 km/s, although the line profile is not well fit by a Gaussian since it exhibits a narrow core centered on a broader base. The higher-order Balmer lines possess blueshifted P-Cyg absorption components that indicate an expansion velocity of ~700 km/s; a similar P-Cyg profile with an emission component centered near 587.6 nm is also evident, most likely due to He I. Unresolved lines of [S II] (671.6 nm and 673.1 nm) and [O III] (495.9 nm and 500.7 nm) are also present, perhaps resulting from an underlying H II region or from fairly strong galaxy contamination in the spectrum.

The features revealed here have similarities with reported spectra of the spatially coincident PSN J12355230+2755559 that were obtained on 2012 Jan. 14 UT (cf. CBET 2976), which were deemed more compatable with a Luminous Blue Variable outburst ("SN-impostor", Van Dyk et al. 2000, PASP 112, 1532; Smith et al. 2009, ApJ, 697, L49) than with a supernova. The magnitude of this most recent outburst (mag 17.0 on 2014 June 22 UT) is also similar to the 2012 event (mag 16.7), as well as with an outburst reported on the CBAT "Transient Object Followup Reports" page for the (also) spatially coincident PSN J12355216+2755560 (mag 16.8 on 2014 Feb. 24 UT). Given these spectral and photometric similarities, this most recent event is most likely another LBV outburst from the same system.

We also suggest that this LBV may not be associated with the proposed host galaxy (NGC 4559), but rather with one of the many nearby faint satellite galaxies (see CBET 2976); given its spatial location and measured recession velocity, we propose SDSS J123551.86+275556.9 as a likely host.