Near-IR spectroscopy is presented for Nova Scorpii 2014. It is shown that the outburst occurred in a symbiotic binary system - an extremely rare configuration for a classical nova outburst to occur in but appropriate for the eruption of a recurrent n
ova of the T CrB class. We estimate the spectral class of secondary as M5III $pm$ (two sub-classes). The maximum magnitude versus rate of decline (MMRD) relations give an unacceptably large value of 37.5 kpc for the distance. The spectra are typical of the He/N class of novae with strong HeI and H lines. The profiles are broad and flat topped with full width at zero intensities (FWZIs) approaching 9000-10000 km s$^{-1}$ and also have a sharp narrow component superposed which is attributable to emission from the giants wind. Hot shocked gas, accompanied by X-rays and $gamma$ rays, is expected to form when the high velocity ejecta from the nova plows into the surrounding giant wind. Although X-ray emission was observed no $gamma$-ray emission was reported. It is also puzzling that no signature of a decelerating shock is seen in the near-infrared (NIR), seen in similar systems like RS Oph, V745 Sco and V407 Cyg, as rapid narrowing of the line profiles. The small outburst amplitude and the giant secondary strongly suggest that Nova Sco 2014 could be a recurrent nova.
We present near-infrared (1-2.5 micron) JHK photo-spectroscopic results of the unusually slow nova V5558 Sgr (2007). V5558 Sgr showed a slow climb to maximum that lasted for about 60 days and then underwent at least five strong secondary outbursts. W
e have analyzed the optical light curve to derive large t2 and t3 values of 281 +/- 3 and 473 +/- 3 days respectively. An alternate approach is adopted to derive a distance estimate of 1.55 +/- 0.25 kpc as conventional MMRD relation may not be applicable for a slow nova. In the pre-maxima stage the spectra showed narrow (FWHM ~ 400 - 550 km/s and strong emission lines of Paschen and Brackett series with prominent P-Cygni components. In the later phase the spectra show significant changes with the development of strong and broad ~ 1000 km/s emission lines of HI, HeI, OI, and NI and some uncommon Fe II emission lines. No evidence of dust formation is seen. V5558 Sgr has been shown to be a rare hybrid nova showing a transition from He/N to Fe II type from optical spectra. However the near-infrared data do not show such a transition and we discuss this anomalous behavior. A recombination analysis of the Brackett lines allows us to constrain the electron density and emission measure during the early optically thick phase and to estimate the mass of the ejecta to be (6.0 +/- 1.5) x 10^(-4) Msun, assuming a filling factor of unity, from later observations.
The recurrent nova (RN) V745 Scorpii underwent its third known outburst on 2014 February 6. Infrared monitoring of the eruption on an almost daily basis, starting from 1.3d after discovery, shows the emergence of a powerful blast wave generated by th
e high velocity nova ejecta exceeding 4000 kms$^{-1}$ plowing into its surrounding environment. The temperature of the shocked gas is raised to a high value exceeding 10$^{8}$K immediately after outburst commencement. The energetics of the outburst clearly surpass those of similar symbiotic systems like RS Oph and V407 Cyg which have giant secondaries. The shock does not show a free-expansion stage but rather shows a decelerative Sedov-Taylor phase from the beginning. Such strong shockfronts are known to be sites for $gamma$ ray generation. V745 Sco is the latest nova, apart from five other known novae, to show $gamma$ ray emission. It may be an important testbed to resolve the crucial question whether all novae are generically $gamma$ ray emitters by virtue of having a circumbinary reservoir of material that is shocked by the ejecta rather than $gamma$ ray generation being restricted to only symbiotic systems with a shocked red giant (RG) wind. The lack of a free-expansion stage favors V745 Sco to have a density enhancement around the white dwarf (WD), above that contributed by a RG wind. Our analysis also suggests that the WD in V745 Sco is very massive and a potential progenitor for a future SN Ia explosion.
We review the near-infrared properties of classical novae in the J, H and K bands at wavelengths between 1.08 to 2.4 micron. A classification system exists for the early post-outburst optical spectra of novae on the basis of the strength of group of
non-hydrogen emission lines. A similar scheme for the near-infrared regime, which is not available at present, is presented here. In the optical system there are two principal classes, namely, Fe II and He/N for novae with either prominent Fe II lines or prominent He/N lines. There is also a small subset of the hybrid Fe IIb type. From spectroscopic observations we show the differences and similarities between these classes of novae in the near-infrared. The spectral lines common to the two principal classes arise from H, He, N and O. However, the near-IR features that separate these two classes are the numerous, and often strong, Carbon lines which are seen only in the spectra of the Fe II class of novae. The dust formation process in novae is discussed based on broad-band observations. The first-overtone carbon monoxide (CO) detections in novae are analyzed to understand the formation and evolution of this molecule in the nova ejecta and to discuss the observed 12C/13C ratio.
We describe a search for the A-X infrared bands of AlO with a view to better understand the characteristics of this radical. These bands are infrequently encountered in astronomical sources but surprisingly were very prominent in the spectra of two w
ell-known, nova-like variables (V838 Mon and V4332 Sgr) thereby motivating us to explore the physical conditions necessary for their excitation. In this study, we present the detection of A-X bands in the spectra of 13 out of 17 stars, selected on the basis of their J-K colors as potential candidates for detection of these bands. The majority of the AlO detections are in AGB stars viz. 9 OH/IR stars, 2 Mira variables and 2 bright infrared sources. Our study shows that the A-X bands are fairly prevalent in sources with low temperature and O-rich environments. Interesting variation in strength of the AlO bands in one of the sources (IRAS 18530+0817) is reported and the cause for this is examined. Possible applications of the present study are discussed in terms of the role of AlO in alumina dust formation, the scope for estimating the radioactive $^{26}$Al content in AGB stars from the A-X bands, and providing possible targets for further mm/radio studies of AlO which has recently been discovered at millimeter wavelengths.
The detection of rotational transitions of the AlO radical at millimeter wavelengths from an astronomical source has recently been reported. In view of this, rotational transitions in the ground X^2 Sigma^+ state of AlO have been reinvestigated. Comp
arisons between Fourier transform and microwave data indicate a discrepancy regarding the derived value of gamma_D in the v = 0 level of the ground state. This discrepancy is discussed in the light of comparisons between experimental data and synthesized rotational spectra in the v = 0, 1 and 2 levels of X^2 Sigma^+. A list of calculated rotational lines in v = 0, 1 and 2 of the ground state up to N = 11 is presented which should aid astronomers in analysis and interpretation of observed AlO data and also facilitate future searches for this radical.
