21 research outputs found
Outburst evolution, historic light curve and a flash-ionized nebula around the WZ Sge-type object PNV J03093063+2638031
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 BVRI 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. It
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 inization 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 M(V)~14.2 mag. The electron density in the
nebula is estimated to be 10(+5) 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.Comment: Astronomy & Astrophysic
The nature and evolution of Nova Cygni 2006
AIMS: Nova Cyg 2006 has been intensively observed throughout its full
outburst. We investigate the energetics and evolution of the central source and
of the expanding ejecta, their chemical abundances and ionization structure,
and the formation of dust. METHOD: We recorded low, medium, and/or
high-resolution spectra (calibrated into accurate absolute fluxes) on 39
nights, along with 2353 photometric UBVRcIc measures on 313 nights, and
complemented them with IR data from the literature. RESULTS: The nova displayed
initially the normal photometric and spectroscopic evolution of a fast nova of
the FeII-type. Pre-maximum, principal, diffuse-enhanced, and Orion absorption
systems developed in a normal way. After the initial outburst, the nova
progressively slowed its fading pace until the decline reversed and a second
maximum was reached (eight months later), accompanied by large spectroscopic
changes. Following the rapid decline from second maximum, the nova finally
entered the nebular phase and formed optically thin dust. We computed the
amount of formed dust and performed a photo-ionization analysis of the
emission-line spectrum during the nebular phase, which showed a strong
enrichment of the ejecta in nitrogen and oxygen, and none in neon, in agreement
with theoretical predictions for the estimated 1.0 Msun white dwarf in Nova Cyg
2006. The similarities with the poorly investigated V1493 Nova Aql 1999a are
discussed.Comment: in press in Astronomy and Astrophysic
Projeto tecnologias sociais para a gestão da água ? TSGA: contribuição para a gestão participativa da água.
Projeto: 06.09.06.001
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Abell-35 phenomena in symbiotic stars: Discovery of 1.2 and 6.4 day periods in VV8 (V471 per)
We have collected high precision optical photometry of VV8, so far 782 individual observing runs uniformly distributed over the period 2005-2011. This dataset allows us to refine the known long periodicity of VV8 to P = 16.8 yr, with peak-to-valley amplitudes of ΔB = 0.18 and ΔV = 0.14 mag. In addition, we have discovered two new periodicities: 6.431 d (total amplitude Δ = ΔV = ΔI= 0.05 mag) and 1.185 d (ΔB = 0.022, ΔV = 0.018, ΔI = 0.014 mag). These two short periods are reminiscent of the Abell35 phenomena displayed by binary nuclei of planetary nebulae that have gone through a common envelope phase. Twice the 6.431 d period would nicely correspond to the double-peaked light-curve that the G5 III star in VV8 would display if its Roche lobe would be ellipsoidally distorted
Formation of a disk structure in the symbiotic binary AX Per during its 2007-10 precursor-type activity
AX Per is an eclipsing symbiotic binary. During active phases, deep narrow
minima are observed in its light curve, and the ionization structure in the
binary changes significantly. From 2007.5, AX Per entered a new active phase.
It was connected with a significant enhancement of the hot star wind.
Simultaneously, we identified a variable optically thick warm (Teff ~ 6000 K)
source that contributes markedly to the composite spectrum. The source was
located at the hot star's equator and has the form of a flared disk, whose
outer rim simulates the warm photosphere. The formation of the neutral
disk-like zone around the accretor during the active phase was connected with
its enhanced wind. We suggested that this connection represents a common origin
of the warm pseudophotospheres that are indicated during the active phases of
symbiotic stars.Comment: 13 pages, 9 figures, 8 tables, accepted for A&