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We present optical ($B$, $V$, $R_{rm c}$, $I_{rm c}$ and $y$) and near infrared ($J$, $H$ and $K_{rm s}$) photometric and spectroscopic observations of a classical nova V1280 Scorpii for five years from 2007 to 2011. Our photometric observations show a declining event in optical bands shortly after the maximum light which continues $sim$ 250 days. The event is most probably caused by a dust formation. The event is accompanied by a short ($sim$ 30 days) re-brightening episode ($sim$ 2.5 mag in $V$), which suggests a re-ignition of the surface nuclear burning. After 2008, the $y$ band observations show a very long plateau at around $y$ = 10.5 for more than 1000 days until April 2011 ($sim$ 1500 days after the maximum light). The nova had taken a very long time ($sim$ 50 months) before entering the nebular phase (clear detection of both [ion{O}{iii}] 4959 and 5007) and is still continuing to generate the wind caused by H-burning. The finding suggests that V1280 Sco is going through the historically slowest evolution. The interval from the maximum light (2007 February 16) to the beginning of the nebular phase is longer than any previously known slow novae: V723 Cas (18 months), RR Pic (10 months), or HR Del (8 months). It suggests that the mass of a white dwarf in the V1280 Sco system might be 0.6 $M_mathrm{sun}$ or smaller. The distance, based on our measurements of the expansion velocity combined with the directly measured size of the dust shell, is estimated to be 1.1 $pm$ 0.5 kpc.
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We present multi-color light curves and optical spectra of V1280 Scorpii obtained from 2007 to 2012. It is shown that V1280 Sco is the extremely slow nova and the mass of white dwarf appears to be $sim$ 0.6 M$odot$ or lower. Blue-shifted multiple absorption lines of Na {sc i} D, Ca {sc ii} HK, and He {sc i*} are detected on high-resolution spectra. We also discuss that an approach using metastable He absorption lines is useful to investigate structures of nova shells.
We present multi-epoch near-infrared photo-spectroscopic observations of Nova Cephei 2014 and Nova Scorpii 2015, discovered in outburst on 2014 March 8.79 UT and 2015 February 11.84 UT respectively. Nova Cep 2014 shows the conventional NIR characteristics of a Fe II class nova characterized by strong CI, HI and O I lines, whereas Nova Sco 2015 is shown to belong to the He/N class with strong He I, HI and OI emission lines. The highlight of the results consists in demonstrating that Nova Sco 2015 is a symbiotic system containing a giant secondary. Leaving aside the T CrB class of recurrent novae, all of which have giant donors, Nova Sco 2015 is shown to be only the third classical nova to be found with a giant secondary. The evidence for the symbiotic nature is three-fold; first is the presence of a strong decelerative shock accompanying the passage of the novas ejecta through the giants wind, second is the H$alpha$ excess seen from the system and third is the spectral energy distribution of the secondary in quiescence typical of a cool late type giant. The evolution of the strength and shape of the emission line profiles shows that the ejecta velocity follows a power law decay with time ($t^{-1.13 pm 0.17}$). A Case B recombination analysis of the H I Brackett lines shows that these lines are affected by optical depth effects for both the novae. Using this analysis we make estimates for both the novae of the emission measure $n_e^2L$, the electron density $n_e$ and the mass of the ejecta.
We present near-IR observations of the 2010 outburst of U Sco. JHK photometry is presented on ten consecutive days starting from 0.59 days after outburst. Such photometry can gainfully be integrated into a larger database of other multi-wavelength data which aim to comprehensively study the evolution of U Sco. Early near-IR spectra, starting from 0.56 days after outburst, are presented and their general characteristics discussed. Early in the eruption, we see very broad wings in several spectral lines, with tails extending up to ~10000km/s along the line of sight; it is unexpected to have a nova with ejection velocities equal to those usually thought to be exclusive to supernovae. From recombination analysis, we estimate an upper limit of 10^-4.64[+0.92.-0.74]Msun for the ejected mass.
We present the results of our photometric and spectroscopic observations of Nova Sco 2007 N.1 (V1280 Sco). The photometric data was represented by a single data point in the light curve since the observation was carried out only for one night. The spectra cover two different phases of the objects evolution during the outburst, i.e. pre-maximum and post-maximum. Measurements of the P-Cygni profile on Na I D line (5889 AA) was derived as the velocity of shell expansion, yielding $1567.43 pm 174.14$ km s$^{-1}$. We conclude that V1280 Sco is a fast Fe II-type nova.
We present results obtained from extensive near-infrared spectroscopic and photometric observations of nova V574 Pup during its 2004 outburst. The observations were obtained over four months, starting from 2004 November 25 (four days after the nova outburst) to 2005 March 20. The near-IR JHK light curve is presented - no evidence is seen from it for dust formation to have occurred during our observations. In the early decline phase, the JHK spectra of the nova are dominated by emission lines of hydrogen Brackett and Paschen series, OI, CI and HeI. We also detect the fairly uncommon Fe II line at 1.6872 micron in the early part of our observations. The strengths of the HeI lines at 1.0830 micron and 2.0585 micron are found to become very strong towards the end of the observations indicating a progression towards higher excitation conditions in the nova ejecta. The width of the emission lines do not show any significant change during the course of our observations. The slope of the continuum spectrum was found to have a lambda^{-2.75} dependence in the early stages which gradually becomes flatter with time and changes to a free-free spectral dependence towards the later stages. Recombination analysis of the HI lines shows deviations from Case B conditions during the initial stages. However, towards the end of our observations, the line strengths are well simulated with case B model values with electron density n_e = 10^{9-10} cm^{-3} and a temperature equal to 10^4 K. Based on our distance estimate to the nova of 5.5 kpc and the observed free-free continuum emission in the later part of the observations, we estimate the ionized mass of the ejecta to be between 10^{-5} and 10^{-6} solar-mass.
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