Ramkrishna Das

Near-infrared studies of V1280 Sco (Nova Scorpii 2007)

We present spectroscopic and photometric results of Nova V1280 Sco which was discovered in outburst in early 2007 February. The large number of spectra obtained of the object leads to one of the most extensive, near-infrared spectral studies of a classical nova. The spectra evolve from a P-Cygni phase to an emission-line phase and at a later stage is dominated by emission from the dust that formed in this nova. A detailed model is computed to identify and study characteristics of the spectral lines. Inferences from the model address the vexing question of which novae have the ability to form dust. It is demonstrated, and strikingly corroborated with observations, that the presence of lines in the early spectra of low-ionization species like Na and Mg indicative of low temperature conditions - appear to be reliable indicators that dust will form in the ejecta. It is theoretically expected that mass loss during a nova outburst is a sustained process. Spectroscopic evidence for such a sustained mass loss, obtained by tracing the evolution of a P-Cygni feature in the Brackett γ line, is presented here allowing a lower limit of 25-27 days to be set for the mass-loss duration. Photometric data recording the nova’s extended 12 day climb to peak brightness after discovery is used to establish an early fireball expansion and also show that the ejection began well before maximum brightness. The JHK light curves indicate the nova had a fairly strong second outburst � 100 days after the first.

A Near-Infrared Shock Wave in the 2006 Outburst of Recurrent Nova RS Ophiuchi

Near-infrared spectra are presented for the recent 2006 outburst of the recurrent nova RS Ophiuchi.We report the rare detection of an infrared shock wave as the nova ejecta plows into the preexisting wind of the secondary in the RS Oph system consisting of a white dwarf (WD) primary and a red giant secondary. The evolution of the shock is traced through a free expansion stage to a decelerative phase. The behavior of the shock velocity with time is found to be broadly consistent with current shock models. The present observations also imply that the WD in the RS Oph system has a high mass indicating that it could be a potential Type Ia supernova (SN Ia) candidate. We also discuss the results from a recent study showing that the near-IR continuum from the recent RS Oph eruption does not originate in an expanding fireball. However, the present work shows that the IR line emission does have an origin in an expanding shock wave.

Near-infrared H- and K-band studies of the 2006 outburst of the recurrent nova RS Ophiuchi

We present near-infrared photo-spectroscopy in the H and K bands of the 2006 outburst of the recurrent nova RS Ophiuchi (RS Oph). The observations cover the period between 1 to 94 days after the eruption. The near infrared light curve is presented. An extensive set of spectra are presented, lines identified and the general characteristics of the spectra discussed. Analysis of the HI line profiles show the presence of broad wings on both flanks of a strong central component indicating the presence of a bipolar velocity flow in the ejecta. Such a flow is kinematically consistent with the bipolar structure that the object displays in high-resolution spatial images. We discuss the behaviour and origin of the Fe II lines at 1.6872 and 1.7414 � m that are prominently seen throughout the span of the observations. It is examined and shown that Lyman α and Lyman continuum fluorescence are viable mechanisms to excite these lines. We draw upon the result, that collisional excitation can also contribute in exciting and significantly enhancing the strength of these Fe II lines, to propose that these lines originate from a site of high particle density. Such a likely site could be the high-density, low temperature contact surface that should exist in the shockfront in between the shocked ejecta and red giant wind. Recombination analysis of the HI lines indicate deviations from Case B conditions during most of the span of our observations indicating optical depth effects. It appears likely that the breakout of the shockfront had not yet occured till the end of our observations. An analysis is made of the temporal evolution of the [Si VI] 1.9641 � m coronal line and another coronal line at 2.0894 � m which is attributed to [Mn XIV]. Assuming collisional effects to dominate in the hot coronal gas, estimates are made of the ion temperature in the gas.

Detection and evolution of the CO (Δv= 2) emission in Nova V2615 Ophiuchi (2007)

We present near-infrared (1-2.5 μm) spectroscopic and photometric results of Nova V2615 Ophiuchi which was discovered in outburst in 2007 March. Our observations span a period of ~80 d starting from 2007 March 28 when the nova was at its maximum light. The evolution of the spectra is shown from the initial P Cygni phase to an emission-line phase and finally to a dust formation stage. The characteristics of the JHK spectra are very similar to those observed in a nova outburst occurring on a carbon-oxygen white dwarf. We analyse an observed line at 2.088 μm and suggest that it could be due to Fe II excited by Lyman α fluorescence. The highlight of the observations is the detection of the first overtone bands of carbon monoxide (CO) in the 2.29-2.40 μm region. The CO bands are modelled to estimate the temperature and mass of the emitting CO gas and also to place limits on the 12 C/ 13 C ratio. The CO bands are recorded over several epochs, thereby allowing a rare opportunity to study the evolution from a phase of constant strength through a stage when the CO is destroyed fairly rapidly. We compare the observed time-scales involved in the evolution of the CO emission and find a good agreement with model predictions that investigate the chemistry in a nova outflow during the early stages.

Near‐infrared observations of nova V574 Puppis (2004)

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 4 months, starting from 2004 November 25 (4 d after the nova outburst) to 2005 March 20. The near-infrared JHK light curve is presented - it shows no evidence of the fact that dust formation has 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, O I, C I and He I. We also detect the fairly uncommon Fe II line at 1.6872 μm in the early part of our observations. The strengths of the He I lines at 1.0830 and 2.0585 μm 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 does not show any significant change during the course of our observations. The slope of the continuum spectrum was found to have a λ -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 H I 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 M ☉ .

Near-infrared studies of the 2010 outburst of the recurrent nova U Scorpii

We present near-infrared (near-IR) observations of the 2010 outburst of U Sco.JHK photometry is presented on 10 consecutive days starting from 0.59 d after outburst. Such photometry can gainfully be integrated into a larger data base of other multiwavelength data which aim to comprehensively study the evolution of U Sco. Early near-IR spectra, starting from 0.56 d 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 ∼10 000 km s −1 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 M � for the ejected mass.

The young cluster NGC 2282: a multiwavelength perspective

We present the analysis of the stellar content of NGC~2282, a young cluster in the Monoceros constellation, using deep optical

Near-infrared studies of V5558 Sgr: an unusually slow nova with multiple outbursts

BVI

Optical spectroscopy of the recurrent nova RS Ophiuchi – from the outburst of 2006 to quiescence

and IPHAS photometry along with infrared (IR) data from UKIDSS and

Phase-dependent Photometric and Spectroscopic Characterization of the MASTER-Net Optical Transient J212444.87+321738.3: An Oxygen-rich Mira

Spitzer