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Munari U.,National institute for astrophysics | Mason E.,National institute for astrophysics | Valisa P.,ANS Collaboration
Astronomy and Astrophysics | Year: 2014

We present outburst and quiescence spectra of the classical nova KT≠Eri and discuss the appearance of a sharp HeII 4686 Å emission line, whose origin is a matter of discussion for those novae that showed a similar component. We suggest that the sharp HeII line, when it first appeared toward the end of the outburst optically thick phase, comes from the wrist of the dumbbell structure characterizing the ejecta. When the ejecta turned optically thin, the already sharp HeII line became two times narrower and originated from the exposed central binary. During the optically thin phase, the HeII line displayed a large change in radial velocity that had no counterpart in the Balmer lines (both their narrow cores and the broad pedestals). The large variability in radial velocity of the HeII line continued well into quiescence, and it remains the strongest emission line observed over the whole optical range. © 2014 ESO. Source

Raj A.,Physical Research Laboratory | Ashok N.M.,Physical Research Laboratory | Banerjee D.P.K.,Physical Research Laboratory | Munari U.,Physical Research Laboratory | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We present near-infrared (near-IR) and optical observations of the nova Scuti 2009 (V496 Sct) covering various phases - pre-maximum, early decline and nebular - during the first 10 months of its discovery followed by limited observations in the early part of 2011 April. The spectra follow the evolution of the nova when the lines had strong P Cygni profiles to a phase dominated by prominent emission lines. The notable feature of the near-IR spectra in the early decline phase is the rare presence of first overtone bands of carbon monoxide in emission. Later about 150 days after the peak brightness, the IR spectra show clear dust formation in the expanding ejecta. Dust formation in V496 Sct is consistent with the presence of lines of elements with low ionization potentials like Na and Mg in the early spectra and the detection of CO bands in emission. The light curve shows a slow rise to the maximum and a slow decline indicating a prolonged mass loss. This is corroborated by the strengthening of P Cygni profiles during the first 30 days. In the spectra taken close to the optical maximum brightness, the broad and single absorption components seen at the time of discovery are replaced by two sharper components. During the early decline phase, two sharp dips that show increasing outflow velocities are seen in the P Cygni absorption components of Fe II and HI lines. The spectra in 2010 March showed the onset of the nebular phase. Several emission lines display saddle-like profiles during the nebular phase. In the nebular stage, the observed fluxes of [O III] and Hβ lines are used to estimate the electron number densities and the mass of the ejecta. The optical spectra show that the nova is evolved in the PfeAo spectral sequence. The physical conditions in the ejecta are estimated. The absolute magnitude and the distance to the nova are estimated to be MV =-7.0 ± 0.2 and d = 2.9 ± 0.3 kpc, respectively. © 2012 The Authors Monthly Notices of the Royal Astronomical Society. Source

Munari U.,ANS Collaboration | Moretti S.,National institute for astrophysics
Baltic Astronomy | Year: 2012

The ANS Collaboration uses the UBVR cI c filters from various commercial manufacturers (Omega Optical, Custom Scientific, Schuler, Optec, Astrodon) for its ongoing photometric monitoring of symbiotic stars. We measured their transmittance profiles over the range 2000 Å to 1.1 μm for various operating conditions, and we are monitoring their evolution over time. Their field performance in terms of color equations has been evaluated by analyzing the transformations from local to standard system of the 14602 observing runs so far collected on symbiotic stars with the ANS Collaboration telescopes. Ageing effects, red leaks and transmittance vs. angle of incidence are also evaluated. Source

Munari U.,National institute for astrophysics | Dallaporta S.,ANS Collaboration
New Astronomy | Year: 2014

We obtained extensive new BVRCIC photometry of Nova KT Eri 2009 over a 539-day interval during the post-outburst quiescence, from 30 September 2011 to 22 March 2013 (days +684 to +1223 past maximum). The median magnitudes we measured are B = 15.24, V = 15.00, RC = 14.75 and IC = 14.49. A marked variability is present (total amplitude of ΔV = 1.6 mag). Accounting for a generally overlooked correction to blue photographic magnitudes calibrated against modern B-band data, we found that mean brightness and amplitude of variability of KT Eri in quiescence are the same before and after the 2009 nova outburst. The distance to KT Eri derived from standard relations involving the absolute magnitude at maximum vs rate of decline (MMRD), is ∼6.5 kpc. At such a distance, to fit the BV RCIC + JHK flux distribution of KT Eri in quiescence requires an 8200 K blackbody with a radius of 3.5 R ⊙, which is vastly larger than the radius of typical accretion disks of CVs and classical old novae (0.1 R ⊙). The distance to KT Eri could therefore be much shorter than expected from MMRD relation. We also observed a new eclipse-like minimum to occur right on time following the 752 day period suspected to modulate the quiescence of KT Eri before the outburst. The nature of this period remains unclear. The faintness of KT Eri at infrared wavelengths (K = 14.1) precludes it from being the orbital period of the accreting WD, because in such a case the Roche lobe filling companion would be a cool giant shining at K∼9 mag. © 2013 Elsevier B.V. All rights reserved. Source

Ribeiro V.A.R.M.,University of Cape Town | Munari U.,National institute for astrophysics | Valisa P.,ANS Collaboration
Astrophysical Journal | Year: 2013

The morphology of the ejected shell of the He/N Nova Monocerotis 2012 outburst was studied in detail. Synthetic line profile spectra were compared to the [O III] 4959, 5007 Å emission line profiles in order to find the best-fit morphology, an inclination angle, and a maximum expansion velocity of the ejected shell. The simplest morphology was found to be that of a bipolar structure with an inclination angle of 82°± 6° and a maximum expansion velocity of 2400 km s-1 (at day 130 after outburst). Such a high degree of shaping is unexpected for a system with a main-sequence star (as suspected from the systems colors). The degree of shaping may be disentangled with resolved optical imaging. Furthermore, these results may be confirmed with radio imaging which is expected to follow the same gross features of the outburst as the optical band and the high inclination implied here can be corroborated with a 7.1 hr period which has been suggested to arise from partial eclipses of extended emission by an accretion disk rim. © 2013. The American Astronomical Society. All rights reserved. Source

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