Spectroscopy of U Sco in outburst

ATel #15417; A. Siviero (Univ. Padova), U. Munari (INAF Padova)
on 7 Jun 2022; 07:49 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

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A new outburst of the recurrent nova U Sco has been announced by Masayuki Moriyama via VSNET Alert N.26798, reporting the nova at unfiltered 11.4 mag on 2022 June 6.720 UT, with a negative detection at >17.3mag just 3.7 hours earlier. On June 6.773 the nova has been estimated at V=9.2 by Hiroyuki Maehara (vsnet alert 26802), and on June 6.886 measured at V=8.71 by Tonny Vanmunster (vsnet alert N.26803). As for previous eruptions, also the present one has been characterized by a very rapid rise in brightness, a jump by >8.6mag in less than 8 hours.

We have recorded a low resolution spectrum (range 4250-6600 Ang at 1.13 Ang/pix dispersion) of U Sco on June 6.976 UT with the Asiago 1.22m + B&C telescope, fluxed against nearby spectrophotometric standards.

The spectrum presents a marked blue slope corresponding to a Stromgren color index b-y=0.2 mag, and it clearly belongs to the He/N class. At the early outburst stage of our spectrum, P-Cyg emission components are still rather weak and unstructured, and essentially confined to Balmer (FWHM~1700 km/s) and HeI lines (FWHM~1250 km/s), for which the corresponding absorption component locates around -2350 km/s. The spectrum is adorned by very deep and broad absorption lines, the strongest belonging to NII 5680, 5005, 4651, 4794, and NIII 4600, with a FWHM~2000 km/s and a rather symmetric shape.