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Early Optical Spectra of U Sco in Outburst

ATel #15422; C. E. Woodward (Minnesota), I. Perron (Minnesota), R. M. Wagner (Ohio State U.), S. Starrfield (Arizona State U.), J. Rupert (MDM Observatory)
on 8 Jun 2022; 10:49 UT
Credential Certification: R. Mark Wagner (rmw@as.arizona.edu)

Subjects: Optical, Cataclysmic Variable, Nova

Referred to by ATel #: 15423, 15436, 15502, 15508, 15513

We obtained optical spectra of U Sco on 2022 June 7.24 and June 8.23 using the 2.4 m Hiltner telescope (+OSMOS) of the MDM Observatory on Kitt Peak and with the 6.5 m MMT (+Blue Channel Spectrograph) on Mount Hopkins. The MDM spectra cover the range 398-687 nm at a resolution of 0.30 nm while the MMT spectra cover the range 393-706 nm at a resolution of 0.38 nm. While the spectral coverage and resolution of the two spectra are similar, the MMT spectra were obtained as part of a larger time series looking for rapid spectral variations in the line profiles covering about 40 and 45 min respectively on the two nights. These will be described later.

The MDM spectrum on June 7.24 exhibits emission lines of the Balmer series of Hydrogen, He I, N II, and N III with P Cygni-like line profiles superposed on a blue continuum and is similar to the spectrum reported earlier by Siviero and Munari (ATel #15417). For Hα the emission line can be deconvolved into two Gaussian components one of which is near line center with a FWHM of about 2732 km/s and the other is centered at +2700 km/s with a FWHM of 2074 km/s. The Hα absorption component is centered at a velocity of -2870 km/s with respect to line center and has a FWHM of about 1988 km/s.

The MDM spectrum obtained on June 8.23 and thus about 24 hours after our first spectrum looks completely different than our spectrum obtained the previous night. The spectrum exhibits extremely strong emission lines of the Balmer lines, He I, N II, and N III, and perhaps the presence of Fe II emission lines in multiplets 42, 49, and 74 as well. The P Cygni-like line profiles are only obvious in the higher order Balmer lines in our spectra. The Balmer line profiles of Hα and Hβ emission are extremely broad and rectangular with a castellated peak consisting of 3 main components as also reported by Taguchi, Yamanaka, and Isogal (ATel #15420). The FWHM of Hα and Hβ emission are about 7300 and 7100 km/s respectively while the FWZI of Hα emission is about 9900 km/s.

Our MDM spectrum obtained on June 8.23 is astonishingly similar to the early spectrum of U Sco obtained on day 0.831 after optical maximum during the 2010 outburst and shown in Figure 2 of Amupama et al. (2013, A&A, 559, A121). Amupama et al. remark that the spectra and their evolution during the 2010 outburst appeared to be similar to previous outbursts of U Sco in 1999 and perhaps 1979 and 1987 as well. Continued optical spectroscopy of U Sco during the present outburst are encouraged.