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Spectroscopic confirmation of HBC 722 as a new FU Orionis star in NGC 7000

ATel #2808; U. Munari, (INAF Padova-Asiago, Italy), A. Milani, P. Valisa (ANS Collaboration, Italy), E. Semkov (Institute of Astronomy, Sofia, Bulgaria)
on 23 Aug 2010; 17:46 UT
Credential Certification: Ulisse Munari (ulisse.munari@oapd.inaf.it)

Subjects: Optical, Variables

Referred to by ATel #: 2819, 2854, 3040, 3296

The photometric discovery of an outburst from HBC 722, a faint emission line object in the region of NGC 7000/IC 5070, has been recently reported in ATel #2801, where a nature similar to FU Orionis pre-Main sequence objects has been proposed.

We have obtained a low resolution spectrum of HBC 722 on Aug. 21.9 UT with the 0.6m telescope of the Schiaparelli Observatory in Varese, equipped with a multi-mode grating spectrograph. The spectrum extends from 3900 to 7800 Ang, with a dispersion of 2.12 Ang/pix, and has been accurately calibrated into absolute fluxes. Integration on the spectrum through the respective band-passes provide the following magnitudes: B=15.55 V=14.04 Rc=13.03.

Our spectrum support the interpretation of HBC 722 as a new FU Orionis star. The only emission line clearly visible is Halpha, which integrated flux is 4.7e-14 erg cm-2 sec-1. Strong absorptions are visible in Hbeta, NaI D1-D2, MgI triplet 5174 Ang, BaII 5854 and 6497 Ang. A weaker absorption due to LiI 6707 is also present. The overall appearance of the absorption spectrum is reminiscent of the FU Orionis objects BBW 76 (Reipurth et al. 2002, AJ 124, 2194) and V733 Cep (Reipurth et al. 2007, AJ 133, 1000), and of the recently erupted object V582 Aur (Munari et al. 2009, CBET #1898). CaII 3934 Ang could also be in emission, our spectrum being however quite noisy blue-ward of 4400 Ang. At the resolution of our spectrum, the emission profile of Halpha is double peaked. It is nicely fitted by the combination of an emission component at a heliocentric radial velocity of -55 km/s and FWHM=450 km/s, and an absorption component at a heliocentric radial velocity of -95 km/s and FWHM=150 km/s. The mean heliocentric radial velocity of the other absorption lines is -110 km/s.