The experimental research presented in this article explores the wire electrical discharge machining of Monel 400 alloy. An L-18 orthogonal array has been used for experimentation by considering machine controllable factors (i.e. wire tension, pulse-on time, pulse frequency, peak current and servo voltage) and machine uncontrollable factors (namely flushing nozzle height, workpiece thickness and corner angle) as process parameters. Using Taguchi methodology, the influence of the process parameters on the responses, such as material removal rate, surface roughness and corner error, were studied. The impact of pulse parameters modification in corner accuracy improvement has been analyzed. Finally, using Taguchi’s additive model predictions and Pareto optimality approach, a sample technology table for a specific machining condition has been reported for ready use.

Optical spectra of the 2006 outburst of RS Ophiuchi beginning one day after discovery to over a year after the outburst are presented here. The spectral evolution is found to be similar to that in previous outbursts. The early phase spectra are dominated by hydrogen and helium (I & II) lines. Coronal and nebular lines appear in the later phases. Emission line widths are found to narrow with time, which is interpreted as a shock expanding into the red giant wind. Using the photoionisation code CLOUDY, spectra at nine epochs spanning 14 months after the outburst peak, thus covering a broad range of ionisation and excitation levels in the ejecta, are modelled. The best-fit model parameters indicate the presence of a hot white dwarf source with a roughly constant luminosity of 1.26 × 10 37 erg s −1 . During first three months, the abundances (by number) of He, N, O, Ne, Ar, Fe, Ca, S and Ni are found above solar abundances; abundances of these elements decreased in the later phase. Also presented are spectra obtained during quiescence. Photoionisation model of the quiescence spectrum indicates the presence of a low luminosity accretion disk. The helium abundance is found to be subsolar at quiescence.

The optical spectroscopic observations of ASASSN-18fv observed from 2018 March 24 to 2019 January 26 are presented. The optical spectra are obtained from Mirranook, Vainu Bappu, and South African Astronomical observatories. The spectra are dominated by the hydrogen Balmer, Fe ii, and O i lines with P-Cygni profiles in the early phase, typical of an Fe ii class nova. The spectra show He i lines along with H i and O i emission lines in the decline phase placing the nova in the hybrid class of novae. The spectra show rapid development in high-ionization lines in this phase. Analysis of the light curve indicates t2 and t3 values of about 50 and 70 d, respectively, placing the nova in the category of moderately fast nova. The ejectum geometry, inclination, and position angle are estimated using morpho-kinematic analysis. The geometry of the ejecta is found to be an asymmetric bipolar structure with an inclination angle of about 53○. The ejected mass using photoionization analysis is found to be 6.07 × 10−4 M⊙.

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An abundance analysis has been conducted for a sample of nine post‐asymptotic giant branch (AGB) candidate stars; eight of them have not been explored before. We find four very promising objects like HD 105262, HD 53300 and CpD‐62° 5428 among them. We find strong evidence of dust–gas separation through selective depletion of refractive elements in HD 105262. The same effect is also observed in HD 53300, CpD‐62° 5428 and HD 114855 although abundance peculiarities are relatively smaller for the last two stars. We find strong enrichment of nitrogen for HD 725, HD 842, HD 1457, HD 9233 and HD 61227 but no further evidence to support their post‐AGB nature. We have compared the observed [N/C] ratios of these stars with the predictions of evolutionary models which include the rotation‐induced mixing.