High resolution spectroscopy of the young eruptive star V2492 Cyg currently peaking at record brightness

ATel #10183; U. Munari (INAF Padova), G. Traven (Univ. Ljubljana), S. Dallaporta (ANS Collaboration), D. Lorenzetti, T. Giannini, S. Antoniucci (INAF Roma)
on 18 Mar 2017; 18:45 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

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Recently, Ibryamov and Semkov (ATel #10170) have reported on a new record brightness attended by the young eruptive star V2492 Cyg along the complex outburst it started in 2010 (Itagaki CBET #2426, Munari et al. CBET #2428). They monitored the star to rise from V=14.63 on Nov 5, 2016 to V=13.52 on Mar 5, 2017.

We have obtained BVRI photometry of V2492 Cyg with ANS Collaboration telescope 31 on Mar 17.141 UT and found B=15.681 (+/-0.019), V=13.930 (+/-0.009), Rc=12.884 (+/-0.005), and Ic=11.840 (+/-0.004). While our colors are only mildly redder than those measured by Ibryamov and Semkov at peak brightness, the fainter magnitude we obtain signals the object is now past the recent maximum.

Simultaneous with the photometry, on March 17.135 UT we exposed also a deep and high-resolution spectrum of V2492 Cyg with the Echelle spectrograph mounted on the Asiago 1.82m telescope (range 3600-7300 Ang, resolving power 18,000). The spectrum is characterized by a great deal of emission lines from low ionization metals, with the FWHM ranging from 45 to 85 km/s depending on ion and multiplet. Deep P-Cyg profiles characterize the Balmer lines, with the absorption component being distinctively boxy in shape due to the essentially null transmission at the center. The flat bottom runs from -90 to -220 km/sec for Halpha, and from -55 to -200 for NaI doublet (seen split from the corresponding interstellar components). FeII multiplets 42 and 49 and MgI multiplet 2 are seen in absorptions at -120 km/s heliocentric RV, with a nearly Gaussian profile of FWHM=150 km/s. The emission profile of Balmer lines has at least two components: one weak and very broad (FWZI of 1300 km/s) on top of which sits the main one, with +80 km/s heliocentric RV and FWHM=255 km/s. While the emission line spectrum bears resemblace to that for 2010 Sept 5 presented by Colin (2011, AJ 141, 196), the absorptions are now far stronger. An emission line is seen at 6707.7 Ang, its identification with null-velocity LiI as proposed by Hillenbrand et al. (2013 AJ 145, 59) needs however careful scrutiny given the great number of other similarly weak emission lines present all around. Various diffuse interstellar bands are present (in particular DIBs 5778, 5780, 5797 and 6614 Ang).