Spectroscopic follow up of the classical nova V6595 Sgr (PNV J17581670-2914490)

ATel #14533; E. Aydi, J. Strader, L. Chomiuk, K. V. Sokolovsky, A. Kawash (MSU), K-L Li (NCKU), D. A. H. Buckley (SAAO), M. Orio (INAF/UoW), K. Mukai (NASA Goddard), J. Linford (NRAO), and J. Sokoloski (Columbia Univ.)
on 8 Apr 2021; 19:39 UT
Credential Certification: Elias Aydi (eaydi@saao.ac.za)

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We report on spectroscopic follow up of the classical nova V6595 Sgr (PNV J17581670-2914490), which was discovered by Andrew Pearce on 2021-04-04.8 UT and confirmed spectroscopically by Kenta et al. (2021, ATels #14513 and #14514). On 2021-04-06.1 we obtained several low- and medium-resolution spectra of V6595 Sgr using the Goodman spectrograph (Clemens et al. 2004, SPIE, 5492, 331) on the 4.1m SOAR telescope, covering a wavelength range of 4000-7800 A. We also obtained a 600s high-resolution spectrum on 2021-04-06.9 using the High Resolution Spectrograph (HRS; Crause et al. 2014, Proc. SPIE, 91476) mounted on the 11m Southern African Large Telescope as part of the SALT Large Science Program on Transients. The observations were taken in the HR mode of HRS which covers the spectral range of 3800-8900 A at a resolution of R=67000. The data were reduced with the SALT HRS MIDAS pipeline (Kniazev et al. 2016, MNRAS 459, 3068).

The SOAR spectra show a red continuum with P Cygni profiles of H-Balmer, Fe II, and O I, with absorption troughs at around -1100 km/s relative to the rest velocities of the lines. The emission components of most of the P Cygni profiles are weak relative to the continuum, which means that the nova was at or near optical peak. The SALT spectrum, taken less than a day later, shows significant changes with broad emission lines emerging, characterized by a FWZI of more than 6000 km/s. The Previous lower velocities features are superimposed on top of the broader emissions, which is consistent with the spectral evolution described in Aydi et al. (2020, ApJ, 905,62). The emergence of broad emission component with the slow P Cygni feature on top of it indicates that by the time the SALT spectrum was taken, the nova has passed optical peak. The ASAS-SN photometry (see below) shows indeed that the nova reached optical peak on 2021-04-06.2.

The Na D interstellar absorptions show multiple components at velocities of 0, -30, -60, -115, -195 and -215 km/s, consistent with high extinction towards the line of sight. The equivalent width of the lower velocity components exceeds 1 Angstrom but these lines are saturated. We used several diffuse interstellar bands to derive an estimate of the reddening. Using these lines and the relations from Frideman et al. (2011, ApJ, 727, 33) we derive E(B-V) = 0.65 and Av = 2, assuming an extinction law Rv = 3.1. This is consistent with the reddening estimated from the Galactic reddening maps of Schlafly et al. (2011, ApJ, 737, 13) but inconsistent with the multiple Na D interstellar components and the red spectral continuum near peak.

The latest ASAS-SN sky patrol (Kochanek et al. 2017, PASP, 129, 4502) light curve: https://asas-sn.osu.edu/sky-patrol/coordinate/d34adb0a-ae8c-416e-9328-f8bb4b8c5aa0

This ATel is based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministerio da Ciencia, Tecnologia, Inovacoes e Comunicacoes do Brasil (MCTIC/LNA), the U.S. National Science Foundation's National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).