521 research outputs found
Transient jets in the symbiotic prototype Z Andromedae
We present development of the collimated bipolar jets from the symbiotic
prototype Z And that appeared and disappeared during its 2006 outburst. In 2006
July Z And reached its historical maximum at U ~ 8.0. During this period, rapid
photometric variations with Dm ~ 0.06 mag on the timescale of hours developed.
Simultaneously, high-velocity satellite components appeared on both sides of
the H-alpha and H-beta emission line profiles. They were launched
asymmetrically with the red/blue velocity ratio of 1.2 - 1.3. From about
mid-August they became symmetric. Their spectral properties indicated ejection
of bipolar jets collimated within an average opening angle of 6.1 degrees. We
estimated average outflow rate via jets to dM(jet)/dt ~
2xE10-6(R(jet)/1AU)**(1/2) M(Sun)/year, during their August - September
maximum, which corresponds to the emitting mass in jets, M(jet, emitting) ~
6xE-10(Rjet)/1AU)^{3/2} M(Sun). During their lifetime, the jets released the
total mass of M(jet, total) approx 7.4x1E-7 M(Sun). Evolution in the rapid
photometric variability and asymmetric ejection of jets around the optical
maximum can be explained by a disruption of the inner parts of the disk caused
by radiation-induced warping of the disk.Comment: 31 pages, 9 figures, 2 tables, accepted for Ap
Extremal curves in nilpotent Lie groups
We classify extremal curves in free nilpotent Lie groups. The classification
is obtained via an explicit integration of the adjoint equation in Pontryagin
Maximum Principle. It turns out that abnormal extremals are precisely the
horizontal curves contained in algebraic varieties of a specific type. We also
extend the results to the nonfree case.Comment: 30 pages, final versio
Polychromatic angle resolved IBIC analysis of silicon power diodes
This paper describes both an experimental methodology based on the Ion Beam
Induced Charge (IBIC) technique and the relevant interpretative model, which
were adopted to characterize the electronic features of power diodes. IBIC
spectra were acquired using different proton energies (from 1.2 to 2.0 MeV),
angles of incidence, and applied bias voltages. The modulation of the ion probe
range, combined with the modulation of the extensions of the depletion layer,
allowed the charge collection efficiency scale to be accurately calibrated, the
dead layer beneath the thick (6 micrometer) Al electrode and the minority
carrier lifetime to be measured. The analysis was performed by using a
simplified model extracted from the basic IBIC theory, which proved to be
suitable to interpret the behaviour of the IBIC spectra as a function of all
the experimental conditions and to characterize the devices, both for what
concerns the electrostatics and the recombination processes.Comment: 24 pagese,10 figure
The symbiotic star CH Cygni – II. The ejecta from the 1998-2000 active phase
We present Hubble Space Telescope (HST) imaging, a Very Large Array (VLA) radio map (4.74 GHz), optical high-resolution (echelle) spectroscopy and UBV photoelectric photometry of the symbiotic star CH Cyg obtained during its 1998–2000 active phase. The HST imaging, taken during eclipse, shows the central stars are embedded in a nebula extending to 620 ± 150 au for a distance of 270 ± 66 pc. The inner nebula is strongly influenced by the onset of activity and associated outflow in 1998. The surface brightness contours of the contemporaneous radio VLA observation agree well with HST images. Photometric observations of the broad 1999 U-minimum suggest that it is due to the eclipse of the active hot component by the giant on the long-period (14.5 yr) outer orbit. We also find that the onset of the 1998 and the 1992 active periods occur at the same orbital phase of the inner binary. Spectroscopic observations reveal two types of outflow from the active star: a high-velocity (>1200 km s−1) hot star wind sporadically alternating with a more massive outflow indicated by P-Cygni-like profiles. We present evidence connecting the extended nebulosity with the high-velocity shocked outflow, and hence the activity in the central binary
Multiwavelength evidence for a 15-year periodic activity in the symbiotic nova V1016 Cygni
The ~15.1 years period found in the long-term UBV photoelectric and
photographic photometry of the symbiotic nova V1016 Cyg is detected also in the
(J-K) colour index and in the UV continuum and emission line fluxes from IUE
and HUT spectra. It could be interpreted either as the effect of recurrent
enhanced mass loss episodes from the Mira type variable companion to a hot
component along its ultra-wide orbit (proposed from recent HST observations) or
the true orbital period of the inner, unresolved binary of a triple system. A
410-day delay of the maximum of UV emission lines fluxes with respect to the
maximum of continuum was found. The pulsation period of the Mira type variable
was improved to 474+/-6 days.Comment: 7 pages, 7 PostScript figures. Accepted for pubblication in A&
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