93 research outputs found
Early evolution of the extraordinary Nova Del 2013 (V339 Del)
We determine the temporal evolution of the luminosity L(WD), radius R(WD) and
effective temperature Teff of the white dwarf (WD) pseudophotosphere of V339
Del from its discovery to around day 40. Another main objective was studying
the ionization structure of the ejecta. These aims were achieved by modelling
the optical/near-IR spectral energy distribution (SED) using low-resolution
spectroscopy (3500 - 9200 A), UBVRcIc and JHKLM photometry. During the fireball
stage (Aug. 14.8 - 19.9, 2013), Teff was in the range of 6000 - 12000 K, R(WD)
was expanding non-uniformly in time from around 66 to around 300 (d/3 kpc)
R(Sun), and L(WD) was super-Eddington, but not constant. After the fireball
stage, a large emission measure of 1.0-2.0E+62 (d/3 kpc)**2 cm**(-3)
constrained the lower limit of L(WD) to be well above the super-Eddington
value. The evolution of the H-alpha line and mainly the transient emergence of
the Raman-scattered O VI 1032 A line suggested a biconical ionization structure
of the ejecta with a disk-like H I region persisting around the WD until its
total ionization, around day 40. It is evident that the nova was not evolving
according to the current theoretical prediction. The unusual non-spherically
symmetric ejecta of nova V339 Del and its extreme physical conditions and
evolution during and after the fireball stage represent interesting new
challenges for the theoretical modelling of the nova phenomenon.Comment: 14 pages, 9 figures, 3 tables, accepted for Astronomy and
Astrophysic
The hydrogen and helium lines of the symbiotic binary Z And during its brightening at the end of 2002
High resolution observations in the region of the lines Halpha, He II 4686
and Hgamma of the spectrum of the symbiotic binary Z And were performed during
its small-amplitude brightening at the end of 2002. The profiles of the
hydrogen lines were double-peaked. These profiles give a reason to suppose that
the lines can be emitted mainly by an optically thin accretion disc. The Halpha
line is strongly contaminated by the emission of the envelope, therefore for
consideration of accretion disc properties we use the Hgamma line. The Halpha
line had broad wings which are supposed to be determined mostly from radiation
damping but high velocity stellar wind from the compact object in the system
can also contribute to their appearance. The Hgamma line had a broad emission
component which is assumed to be emitted mainly from the inner part of the
accretion disc. The line He II 4686 had a broad emission component too, but it
is supposed to appear in a region of a high velocity stellar wind. The outer
radius of the accretion disc can be calculated from the shift between the
peaks. Assuming, that the orbit inclination can ranges from 47 to
76, we estimate the outer radius as 20 - 50 R_sun. The behaviour of the
observed lines can be considered in the framework of the model proposed for
interpretation of the line spectrum during the major 2000 - 2002 brightening of
this binary.Comment: 19 pages, 5 figures. Accepted for publication in Astronomy Report
Formation of a disk-structure and jets in the symbiotic prototype Z And during its 2006-2010 active phase
We present an analysis of spectrophotometric observations of the latest cycle
of activity of the symbiotic binary Z And from 2006 to 2010. We estimate the
temperature of the hot component of Z And to be \approx 150000 - 170000 K at
minimum brightness, decreasing to \approx 90000 K at the brightness maximum.
Our estimate of the electron density in the gaseous nebula is
N_{e}=10^{10}-10^{12} cm^{-3} in the region of formation of lines of neutral
helium and 10^6-10^7 cm^{-3} in the region of formation of the [OIII] and
[NeIII] nebular lines. A trend for the gas density derived from helium lines to
increase and the gas density derived from [OIII] and [NeIII] lines to
simultaneously decrease with increasing brightness of the system was observed.
Our estimates show that the ratios of the theoretical and observed fluxes in
the [OIII] and [NeIII] lines agree best when the O/Ne ratio is similar to its
value for planetary nebulae. The model spectral energy distribution showed
that, in addition to a cool component and gaseous nebula, a relatively cool
pseudophotosphere (5250-11 500 K) is present in the system. The simultaneous
presence of a relatively cool pseudophotosphere and high-ionization spectral
lines is probably related to a disk-like structure of the pseudophotosphere.
The pseudophotosphere formed very rapidly, over several weeks, during a period
of increasing brightness of Z And. We infer that in 2009, as in 2006, the
activity of the system was accompanied by a collimated bipolar ejection of
matter. In contrast to the situation in 2006, the jets were detected even
before the system reached its maximum brightness. Moreover, components with
velocities close to 1200 km/s disappeared at the maximum, while those with
velocities close to 1800 km/s appeared.Comment: 18 pages, 19 figures, Accepted for publication in Astronomy Report
The symbiotic star CH Cygni. III. A precessing radio jet
VLA, MERLIN and Hubble Space Telescope imaging observations of the extended
regions of the symbiotic system CH Cygni are analysed. These extensions are
evidence of a strong collimation mechanism, probably an accretion disk
surrounding the hot component of the system. Over 16 years (between 1985 and
2001) the general trend is that these jets are seen to precess. Fitting a
simple ballistic model of matter ejection to the geometry of the extended
regions suggests a period of 6520 +/- 150 days, with a precession cone opening
angle of 35 +/- 1 degrees. This period is of the same order as that proposed
for the orbital period of the outer giant in the system, suggesting a possible
link between the two. Anomalous knots in the emission, not explained by the
simple model, are believed to be the result of older, slower moving ejecta, or
possibly jet material that has become disrupted through sideways interaction
with the surrounding medium.Comment: 9 pages, 4 figure
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
The symbiotic star CH Cygni â 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 1998â2000 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 sâ1) 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
Signaling via PI3K/FOXO1A pathway modulates formation and survival of human embryonic stem cell-derived endothelial cells
Vascular derivatives of human embryonic stem cells (hESC) are being developed as sources of tissue-specific cells for organ regeneration. However, identity of developmental pathways that modulate the specification of endothelial cells is not known yet. We studied phosphatidylinositol 3-kinase (PI3K)-Forkhead box O transcription factor 1A (FOXO1A) pathways during differentiation of hESC toward endothelial lineage and on proliferation, maturation, and cell death of hESC-derived endothelial cells (hESC-EC). During differentiation of hESC, expression of FOXO1A transcription factor was linked to the expression of a cluster of angiogenesis- and vascular remodeling-related genes. PI3K inhibitor LY294002 activated FOXO1A and induced formation of CD31(+) hESC-EC. In contrast, differentiating hESC with silenced FOXO1A by small interfering RNA (siRNA) showed lower mRNA levels of CD31 and angiopoietin2. LY294002 decreased proliferative activity of purified hESC-EC, while FOXO1A siRNA increased their proliferation. LY294002 inhibits migration and tube formation of hESC-EC; in contrast, FOXO1A siRNA increased in vitro tube formation activity of hESC-EC. After in vivo conditioning of cells in athymic nude rats, cells retain their low FOXO1A expression levels. PI3K/FOXO1A pathway is important for function and survival of hESC-EC and in the regulation of endothelial cell fate. Understanding these properties of hESC-EC may help in future applications for treatment of injured organs
The large-scale ionised outflow of CH Cygni
HST and ground-based [OII} and [NII] images obtained from 1996 to 1999 reveal
the existence of a ionised optical nebula around the symbiotic binary CH Cyg
extending out to 5000 A.U. from the central stars. The observed velocity range
of the nebula, derived from long-slit echelle spectra, is of 130 km/s. In spite
of its complex appearence, the velocity data show that the basic morphology of
the inner regions of the optical nebula is that of a bipolar (or conical)
outflow extending nearly along the plane of the sky out to some 2000 A.U. from
the centre. Even if the extension of this bipolar outflow and its position
angle are consistent with those of the radio jet produced in 1984 (extrapolated
to the time of our optical imagery), no obvious counterpart is visible of the
original, dense radio bullets ejected by the system. We speculate that the
optical bipolar outflow might be the remannt of the interaction of the bullets
with a relatively dense circumstellar medium.Comment: 8 text pages + 3 figures (jpeg). ApJ in press. For a full PostScript
version with figures inline see
ftp://ftp.ll.iac.es/pub/research/preprints/PP252001.ps.g
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