Near-infrared observations of recurrent nova V3890 Sgr

ATel #13088; A. Evans (Keele University, UK), D. P.K. Banerjee (PRL, India), T. R. Geballe (Gemini Observatory), V. Joshi (PRL, India), C. E. Woodward, R. D. Gehrz (University of Minnesota)
on 8 Sep 2019; 21:17 UT
Credential Certification: Dipankar P.K. Banerjee (dpkb12345@gmail.com)

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We report near-infrared spectra (0.9 - 2.5 micron) of the ongoing eruption of the recurrent nova V3890 Sgr obtained on mean UT dates 2019 September 1.985 and 2019 September 2.994 respectively with the Flamingos 2 spectrograph on the 8.1m Gemini South telescope. The nova has been the subject of several investigations in the optical, infrared, UV and X-rays (ATel #13047, #13059, #13060, #13062, #13069, ATel #13050, #13072).

The lines seen in the spectra are the usual H lines of the Paschen and Brackett series; He I 1.0833, 1.7007, 2.0587, 2.1126-2.1138 micron; and OI 1.1289 (Lyman beta fluoresced) and 1.3168 micron. There are weak but unmistakable signatures in the J band of CI 1.1673, 1.1757 and 1.1827 micron, NI 1.2465-1.2473 and possibly MgI 1.1831 micron blended with CI 1.1827 micron. The carbon lines are usually seen in the Carbon-Oxygen type novae (or equivalently the Fe II class), albeit at much greater strength than seen here at this epoch. V3890 Sgr is likely an outburst on a CO core white dwarf and is thus a potential SN Type 1a progenitor candidate provided the white dwarf mass is sufficiently high. There is also a weak but unmistakable sign in the H band of the 1.6878 and 1.7414 micron lines, seen prominently in the 2006 outburst of RS Oph, which were proposed to be Lyman alpha and Lyman continuum fluoresced FeII lines (Banerjee et al. 2009, MNRAS, 99,357).

A modest narrowing of the lines is seen, indicative of the expected deceleration of the ejecta as it plows into the surrounding red giant wind and ambient medium (also see ATel #13081). For example the Pa-beta line profile is well reproduced by the sum of two gaussians viz. a broad component which forms the pedestal of the profile on which a narrow component is superposed. Gaussian decomposition of the line profile shows that between Sept 1.985 to 2.994, the FWHM of the broad component had changed from ~4950 km/s to 4700 km/s, that of the narrow component from ~1400 km/s to 1200 km/s (all FWHM undeconvolved).

It is difficult at this stage to say whether coronal lines are present but there may be some suggestion of the [SiVI] 1.9641 micron line, which is highly merged with the red wing of Br8 1.9451 micron. There is also some structure in the blue wing of HeI 2.0587 micron, which may be due to the coronal [Al IX] 2.044 micron line. These tentative identifications should become clearer as the ejecta decelerate and the lines narrow, leading to a reduction in the merging of close-by lines.

Further observations are ongoing and have been made possible by the award of Director's Discretionary Time program GS-2019B-DD-102.