Infrared observations of nova V5588 Sagittarii

ATel #3345; D. P.K. Banerjee and N. M. Ashok, Physical Research Laboratory, India
on 13 May 2011; 06:38 UT
Credential Certification: N.M. Ashok (ashok@prl.res.in)

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We report near-IR 1.08 to 2.3 micron spectroscopy of the nova V5588 Sgr using the NICMOS3 imager/spectrograph and the 1.2m Mount Abu telescope of the Physical Research Laboratory. The spectra were taken on 26 April and 4 May 2011, after the large second rebrightening of the nova reported on 25.11 April (Munari et al., CBET 2707) when it reached V = 11.7, a brightness level comparable to that of the primary maximum of V = 11.2 reached on 7 April 2011. The spectra of 26 April are qualitatively similar to those of 28 April reported in CBET 2720 by Rudy & Russell with the H I lines displaying two distinct emission components: the narrow component with a full-width-at-half-maximum of 1000-1100 km/s and a broad, relatively flat-topped component with a full-width-at-zero-intensity of 4500-5000 km/s. The He I line profiles as pointed out, unlike those of H I, display only the broad component. However, by 4 May 2011, the broad component of the H lines has almost entirely disappeared leaving only a strikingly strong narrow component (for e.g the peak-to-continuum ratio in the Paschen beta line is about 40 vis-a-vis a value of about 10 for the 26 April observations). The structure of the HeI 2.0585 micron line has also changed appreciably with the flat-topped structure being replaced by a more gaussian like profile. There is also an interesting weak line seen at 2.0894 microns, which has earlier been tentatively identified as a coronal line due to [MnXIV] in the few instances where it has been seen in novae spectra (in nova V1974 Cyg - Wagner and Depoy, 1996, ApJ, 467, 860; in RS Oph - Banerjee et al. 2009, MNRAS, 399, 357). In case this is indeed coronal emission, it is being seen earlier than generally expected in the course of a nova's development (the discovery date is 27.8 March, Arai et al. IAUC 9203 ). However, the possibility exists that coronal emission could be due to shock-heating triggered by the collision of high-velocity matter (associated with the broad component of the profiles) ejected around the secondary maximum catching up and colliding with matter lost earlier.