ANS Collaboration

Asiago, Italy

ANS Collaboration

Asiago, Italy
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Munari U.,National institute for astrophysics | Henden A.,AAVSO | Valisa P.,ANS Collaboration | Dallaporta S.,ANS Collaboration | Righetti G.L.,ANS Collaboration
Publications of the Astronomical Society of the Pacific | Year: 2010

Absolute spectrophotometry, high-resolution echelle spectroscopy, and BVRCIc photometry were obtained to monitor and study the outburst evolution of Nova Aql 2009. When discovered, it was setting near evening twilight, and this prevented the observations from extending past the optically thick phase. The evolution has been particularly smooth, with the V-band maximum being reached on 2009 December 17.2 at 9.90 mag. The B-band maximum preceded the I C-band maximum by 1 day, consistent with an initial fireball expansion. The reddening is high, EB-V = 1:35, and the distance is d = 5:0 kpc, for a height above the Galactic plane of z = 180 pc. The decline times of tV2 = 7:0 and tV 3 = 16:0 days qualify Nova Aql 2009 as a very fast nova. The minimum outburst amplitude (set by the magnitude limit of preoutburst SDSS-II survey images) has been ΔRC ≥ 12:5 mag. The spectral evolution has been typical of a Fe II-type nova, with an ejecta expansion velocity of ∼915 km s-1. The combination of a very fast decline with a slow ejection velocity sets Nova Aql 2009 apart from the bulk of other novae. The evolution in absolute intensity of the various emission lines was derived, and the time of their maximum flux determined. The Fe II emission reached its maximum value before tV2, Ha around tV2, and O I 8446 (excited by Bowen fluorescence from Lyβ) halfway between t V2 and tV3. The oxygen mass in the ejecta is calculated to be 2 × 10-5 M⊙ from analysis of [O I] lines. © 2010. The Astronomical Society of the Pacific. All rights reserved.

Munari U.,National institute for astrophysics | Henden A.,AAVSO | Banerjee D.P.K.,Physical Research Laboratory | Ashok N.M.,Physical Research Laboratory | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The outburst of Nova Sgr 2011 N.2 (=V5588 Sgr) was followed with optical and near-IR photometric and spectroscopic observations for 3.5 yr, beginning shortly before the maximum. V5588 Sgr is located close to Galactic Centre, suffering from E(B - V) = 1.56 (±0.1) extinction. The primary maximum was reached at V = 12.37 on UT 2011 April 2.5 (±0.2), and the underlying smooth decline was moderately fast with tV 2 = 38 and tV 3 = 77 d. On top of an otherwise normal decline, six self-similar, fast evolving and bright secondary maxima (SdM) appeared in succession. Only very few other novae have presented so clear SdM. Both the primary maximum and all SdM occurred at later times with increasing wavelengths, by amounts in agreement with expectations from fireball expansions. The radiative energy released during SdM declined following an exponential pattern, while the breadth of individual SdM and the time interval between them widened. Emission lines remained sharp (FWHM ~ 1000 km s-1) throughout the whole nova evolution, with the exception of a broad pedestal with a trapezoidal shape (Δvel = 3600 km s-1 at the top and 4500 km s-1 at the bottom) which was only seen during the advanced decline from SdM maxima and was absent in between SdM. V5588 Sgr at maximum light displayed a typical Fe II-class spectrum which did not evolve into a nebular stage. About 10 d into the decline from primary maximum, a typical high-ionization He/Nclass spectrum appeared and remained visible simultaneously with the Fe II-class spectrum, qualifying V5588 Sgr as a rare hybrid nova. While the Fe II-class spectrum faded into oblivion, the He/N-class spectrum developed strong [Fe X] coronal lines. © 2014 The Authors.

Munari U.,National institute for astrophysics | Joshi V.,Physical Research Laboratory | Ashok N.M.,Physical Research Laboratory | Banerjee D.P.K.,Physical Research Laboratory | And 5 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2011

The nova outburst experienced in 2010 by the symbiotic binary Mira V407 Cyg has been extensively studied at optical and infrared wavelengths with both photometric and spectro-scopic observations. This outburst, reminiscent of similar events displayed by RS Oph, can be described as a very fast He/N nova erupting while being deeply embedded in the dense wind of its cool giant companion. The hard radiation from the initial thermonuclear flash ionizes and excites the wind of the Mira over great distances (recombination is observed on a time scale of 4 d). The nova ejecta is found to progressively decelerate with time as it expands into the Mira wind. This is deduced from linewidths which change from a FWHM of 2760 km s-1 on day +2.3 to 200 km s-1 on day +196. The wind of the Mira is massive and extended enough for an outer neutral and unperturbed region to survive at all outburst phases. © 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS.

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.

Munari U.,National institute for astrophysics | Henden A.,AAVSO | Belligoli R.,ANS Collaboration | Castellani F.,ANS Collaboration | And 3 more authors.
New Astronomy | Year: 2013

Accurate and densely populated BVRCIC lightcurves of supernovae SN 2011fe in M101, SN 2012aw in M95 and SN 2012cg in NGC 4424 are presented and discussed. The SN 2011fe lightcurves span a total range of 342 days, from 17 days pre- to 325 days post-maximum. The observations of both SN 2012aw and SN 2012cg were stopped by solar conjunction, when the objects were still bright. The lightcurve for SN 2012aw covers 92 days, that of SN 2012cg spans 44 days. Time and brightness of maxima are measured, and from the lightcurve shapes and decline rates the absolute magnitudes are obtained, and the derived distances are compared to that of the parent galaxies. The color evolution and the bolometric lightcurves are evaluated in comparison with those of other well observed supernovae, showing no significant deviations. © 2012 Elsevier B.V. All rights reserved.

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.

Munari U.,National institute for astrophysics | Dallaporta S.,ANS Collaboration | Castellani F.,ANS Collaboration | Valisa P.,ANS Collaboration | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present and discuss accurate and densely mapped BVRCIC light curves of the neon Nova Mon 2012, supplemented by the evolution in Stromgren b and y bands and in the integrated flux of relevant emission lines. Our monitoring started with the optical discovery of the nova (50 days past the first detection in gamma-rays by Fermi-LAT) and extend to day +270, well past the end of the super-soft phase in X-rays. The nova was discovered during the nebular decline, well past t3 and the transition to optically thin ejecta. It displayed very smoothly evolving light curves. A bifurcation between y and V light curves took place at the start of the super-soft X-ray source (SSS) phase, and a knee developed towards the end of the SSS phase. The apparent magnitude of the nova at the unobserved optical maximum is constrained to+3 ≤ V ≤ 4.5. The appearance, grow in amplitude and then demise of a 0.29585 (±0.00002) days orbital modulation of the optical brightness was followed along the nova evolution. The observed modulation, identical in phase and period with the analogue seen in the X-ray and satellite ultraviolet, has a near-sinusoidal shape and a weak secondary minimum at phase 0.5. We favour an interpretation in terms of super-imposed ellipsoidal distortion of the Roche lobe filling companion and irradiation of its side facing the WD. Similar light curves are typical of symbiotic stars where a Roche lobe filling giant is irradiated by a very hot WD. Given the high orbital inclination, mutual occultation between the donor star and the accretion disc could contribute to the observed modulation. The optical+infrared spectral energy distribution of Nova Mon 2012 during the quiescence preceding outburst is nicely fitted by an early K-type main-sequence star (~K3V) at 1.5 kpc distance, reddened by E(B - V) = 0.38, with a WD companion and an accretion disc contributing to the observed blue excess and moderate Ha emission. A typical early K-type main-sequence star with a mass of ~0.75M⊙ and a radius of ~0.8 R⊙ would fill its Roche lobe for a P = 0.29585 d orbital period and a more massive WD companion (as implied by the large Ne overabundance of the ejecta). © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Munari U.,National institute for astrophysics | Jurdana-Sepic R.,University of Rijeka | Ochner P.,National institute for astrophysics | Cherini G.,ANS Collaboration
Astronomy and Astrophysics | Year: 2015

We have monitored the 2014 superoutburst of the WZ Sge-type transient PNV J03093063+2638031 for more than four months, from V = 11.0 maximum brightness down to V = 18.4 mag, close to quiescence value, by obtaining BVRCIC photometry and low resolution fluxed spectroscopy. The evolution was normal and no late-time "echo" outbursts were observed. The absolute integrated flux of emission lines kept declining along the superoutburst, and their increasing contrast with the underlying continuum was simply the result of the faster decline of the continuum compared to the emission lines. Inspection of historical Harvard plates covering the 1899-1981 period did not reveal previous outbursts, neither "normal" nor "super". We discovered an extended emission nebula (radius ~1 arcmin) around PNV J03093063+2638031, that became visible for a few months as the result of photo-ionization from the superoutburst of the central star. The nebula is not present on Palomar I and II sky survey images and it quickly disappeared when the outburst was over. From the rate at wich the ionization front swept through the nebula, we derive a distance of ~120 pc to the system. The nebula is density bounded with an outer radius of 0.03 pc, and the absolute magnitude of the central star in quiescence is MV ~ 14.2 mag. The electron density in the nebula is estimated to be 105 cm-3 from the observed recombination time scale. Given the considerable substructures seen across the nebula, a low filling factor is inferred. Similar nebulae have not been reported for other WZ Sge objects and the challenges posed to models are considered. © ESO, 2015.

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.

Munari U.,National institute for astrophysics | Siviero A.,National institute for astrophysics | Dallaporta S.,ANS Collaboration | Cherini G.,ANS Collaboration | And 2 more authors.
New Astronomy | Year: 2011

The photometric and spectroscopic evolution of the He/N and very fast Nova Cyg 2008 N.2 (V2491 Cyg) is studied in detail. A primary maximum was reached at V = 7.45 ± 0.05 on April 11.37 (±0.1) 2008 UT, followed by a smooth decline characterized by t2 V=4.8 days, and then a second maximum was attained at V = 9.49 ± 0.03, 14.5 days after the primary one. This is the only third nova to have displayed a secondary maximum, after V2362 Cyg and V1493 Aql. The development and energetics of the secondary maximum is studied in detail. The smooth decline that followed was accurately monitored until day +144 when the nova was 8.6 mag fainter than maximum brightness, well into its nebular phase, with its line and continuum emissivity declining as t-3. The reddening affecting the nova was E B-V = 0.23 ± 0.01, and the distance of 14 kpc places the nova at a height above the galactic plane of 1.1 kpc, larger than typical for He/N novae. The expansion velocity of the bulk of ejecta was 2000 km/s, with complex emission profiles and weak P-Cyg absorptions during the optically thick phase, and saddle-like profiles during the nebular phase. Photo-ionization analysis of the emission line spectrum indicates that the mass ejected by the outburst was 5.3 × 10-6 M⊙ and the mass fractions to be X = 0.573, Y = 0.287, Z = 0.140, with those of individual elements being N = 0.074, O = 0.049, Ne = 0.015. The metallicity of the accreted material was [Fe/H] = -0.25, in line with ambient value at the nova galacto-centric distance. Additional spectroscopic and photometric observations at days +477 and +831 show the nova returned to the brightness level of the progenitor and to have resumed the accretion onto the white dwarf. © 2010 Elsevier B.V. All rights reserved.

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