31 research outputs found
DASCH Discovery of A Possible Nova-like Outburst in A Peculiar Symbiotic Binary
We present photometric and spectroscopic observations of a peculiar variable
(designated DASCH J075731.1+201735 or J0757) discovered from our DASCH project
using the digitized Harvard College Observatory archival photographic plates.
It brightened by about 1.5 magnitudes in B within a year starting in 1942, and
then slowly faded back to its pre-outburst brightness from 1943 to the 1950s.
The mean brightness level was stable before and after the outburst, and
ellipsoidal variations with a period of days are seen,
suggesting that the star is tidally distorted. Radial-velocity measurements
indicate that the orbit is nearly circular () with a
spectroscopic period that is the same as the photometric period. The binary
consists of a M0III star, and a
companion, very likely a white dwarf (WD). Unlike other symbiotic binaries,
there is no sign of emission lines or a stellar wind in the spectra. With an
outburst timescale of ~10 years and estimated B band peak luminosity M_B~0.7,
J0757 is different from any other known classic or symbiotic novae. The most
probable explanation of the outburst is Hydrogen shell-burning on the WD,
although an accretion-powered flare cannot be ruled out.Comment: 12 pages, 6 figures, accepted for publication in Ap
A silicate disk in the heart of the Ant
We aim at getting high spatial resolution information on the dusty core of
bipolar planetary nebulae to directly constrain the shaping process. Methods:
We present observations of the dusty core of the extreme bipolar planetary
nebula Menzel 3 (Mz 3, Hen 2-154, the Ant) taken with the mid-infrared
interferometer MIDI/VLTI and the adaptive optics NACO/VLT. The core of Mz 3 is
clearly resolved with MIDI in the interferometric mode, whereas it is
unresolved from the Ks to the N bands with single dish 8.2 m observations on a
scale ranging from 60 to 250 mas. A striking dependence of the dust core size
with the PA angle of the baselines is observed, that is highly suggestive of an
edge-on disk whose major axis is perpendicular to the axis of the bipolar
lobes. The MIDI spectrum and the visibilities of Mz 3 exhibit a clear signature
of amorphous silicate, in contrast to the signatures of crystalline silicates
detected in binary post-AGB systems, suggesting that the disk might be
relatively young. We used radiative-transfer Monte Carlo simulations of a
passive disk to constrain its geometrical and physical parameters. Its
inclination (74 degrees 3 degrees) and position angle (5 degrees 5
degrees) are in accordance with the values derived from the study of the lobes.
The inner radius is 9 1 AU and the disk is relatively flat. The dust mass
stored in the disk, estimated as 1 x 10-5Msun, represents only a small fraction
of the dust mass found in the lobes and might be a kind of relic of an
essentially polar ejection process
A measurement of the broad-band spectrum of XTE J1118+480 with BeppoSAX and its astrophysical implications
We report on results of a target of opportunity observation of the X-ray
transient XTE J1118+480 performed on 2000 April 14-15 with the Narrow Field
Instruments (0.1-200 keV) of the SAX satellite. The measured spectrum is a
power law with a photon index of ~1.7 modified by an ultrasoft X-ray excess and
a high-energy cutoff above ~100 keV. The soft excess is consistent with a
blackbody with temperature of ~40 eV and a low flux, while the cut-off power
law is well fitted by thermal Comptonization in a plasma with an electron
temperature of 100 keV and an optical depth of order of unity. Consistent with
the weakness of the blackbody, Compton reflection is weak. Though the data are
consistent with various geometries of the hot and cold phases of the accreting
gas, we conclude that a hot accretion disk is the most plausible model. The
Eddington ratio implied by recent estimates of the mass and the distance is
about 10^{-3}, which may indicate that advection is probably not the dominant
cooling mechanism. We finally suggest that the reflecting medium has a low
metallicity, consistent with location of the system in the halo.Comment: 14 pages, 8 figures, accepted for publication in The Astrophysical
Journa
An incisive look at the symbiotic star SS Leporis -- Milli-arcsecond imaging with PIONIER/VLTI
Context. Determining the mass transfer in a close binary system is of prime
importance for understanding its evolution. SS Leporis, a symbiotic star
showing the Algol paradox and presenting clear evidence of ongoing mass
transfer, in which the donor has been thought to fill its Roche lobe, is a
target particularly suited to this kind of study. Aims. Since previous
spectroscopic and interferometric observations have not been able to fully
constrain the system morphology and characteristics, we go one step further to
determine its orbital parameters, for which we need new interferometric
observations directly probing the inner parts of the system with a much higher
number of spatial frequencies. Methods. We use data obtained at eight different
epochs with the VLTI instruments AMBER and PIONIER in the H- and K-bands. We
performed aperture synthesis imaging to obtain the first model-independent view
of this system. We then modelled it as a binary (whose giant is spatially
resolved) that is surrounded by a circumbinary disc. Results. Combining these
interferometric measurements with previous radial velocities, we fully
constrain the orbit of the system. We then determine the mass of each star and
significantly revise the mass ratio. The M giant also appears to be almost
twice smaller than previously thought. Additionally, the low spectral
resolution of the data allows the flux of both stars and of the dusty disc to
be determined along the H and K bands, and thereby extracting their
temperatures. Conclusions. We find that the M giant actually does not stricto
sensus fill its Roche lobe. The mass transfer is more likely to occur through
the accretion of an important part of the giant wind. We finally rise the
possibility for an enhanced mass loss from the giant, and we show that an
accretion disc should have formed around the A star.Comment: 11 pages, 5 figures, published in A&A Appendix presenting reduced
data and extracted parameters Reduced data can be found on the CD
Development of Cheaper Embryo Vitrification Device Using the Minimum Volume Method
[EN] This study was designed to compare the efficiency of the Cryotop and Calibrated plastic inoculation loop (CPIL) devices for vitrification of rabbit embryos on in vitro development and implantation rate, offspring rate at birth and embryonic and fetal losses. CPIL is a simple tool used mainly by microbiologists to retrieve an inoculum from a culture of microorganisms. In experiment 1, embryos were vitrified using a Cryotop device and a CPIL device. There were no significant differences in hatched/hatching blastocyst stage rates after 48 h of culture among the vitrified groups (62±4.7% and 62±4.9%, respectively); however, the rates were significantly lower (P<0.05) than those of the fresh group (95±3.4%). In experiment 2, vitrified embryos were transferred using laparoscopic technique. The number of implanted embryos was estimated by laparoscopy as number of implantation sites at day 14 of gestation. At birth, total offspring were recorded. Embryonic and fetal losses were calculated as the difference between implanted embryos and embryos transferred and total born at birth and implanted embryos, respectively. The rate of implantation and development to term was similar between both vitrification devices (56±7.2% and 50±6.8% for implantation rate and 40±7.1% and 35±6.5% for offspring rate at birth); but significantly lower than in the fresh group (78±6.6% for implantation rate and 70±7.2% for offspring rate at birth, P<0.05). Likewise, embryonic losses were similar between both vitrification devices (44±7.2% and 50±6.8%), but significantly higher than in the fresh group (23±6.6%, P < 0.05). However, fetal losses were similar between groups (10±4.4%, 15±4.8% and 8±4.2%, for vitrified, Cryotop or CPIL and fresh, respectively). These results indicate that the CPIL device is as effective as the Cryotop device for vitrification of rabbit embryos, but at a cost of 0.05 per device.This research was supported by the projects Spanish Research project AGL2014-53405-C2-1-P Comision Interministerial de Ciencia y Tecnologia (FMJ, JSV) and Generalitat Valenciana research program (Prometeo II 2014/036, JSV, FMJ).Marco Jiménez, F.; Jiménez Trigos, ME.; Almela-Miralles, V.; Vicente Antón, JS. (2016). Development of Cheaper Embryo Vitrification Device Using the Minimum Volume Method. PLoS ONE. 11(2):1-9. https://doi.org/10.1371/journal.pone.0148661S1911
3D Gasdynamic Modelling of the Changes in the Flow Structure During Transition From Quiescent to Active State in Symbiotic Stars
The results of 3D modelling of the flow structure in the classical symbiotic
system Z~Andromedae are presented. Outbursts in systems of this type occur when
the accretion rate exceeds the upper limit of the steady burning range.
Therefore, in order to realize the transition from a quiescent to an active
state it is necessary to find a mechanism able to sufficiently increase the
accretion rate on a time scale typical to the duration of outburst development.
Our calculations have confirmed the transition mechanism from quiescence to
outburst in classic symbiotic systems suggested earlier on the basis of 2D
calculations (Bisikalo et al, 2002). The analysis of our results have shown
that for wind velocity of 20 km/s an accretion disc forms in the system. The
accretion rate for the solution with the disc is ~22.5-25% of the mass loss
rate of the donor, that is, ~4.5-5*10^(-8)Msun/yr for Z And. This value is in
agreement with the steady burning range for white dwarf masses typically
accepted for this system. When the wind velocity increases from 20 to 30 km/s
the accretion disc is destroyed and the matter of the disc falls onto the
accretor's surface. This process is followed by an approximately twofold
accretion rate jump. The resulting accretion rate growth is sufficient for
passing the upper limit of the steady burning range, thereby bringing the
system into an active state. The time during which the accretion rate is above
the steady burning value is in a very good agreement with observations.
The analysis of the results presented here allows us to conclude that small
variations in the donor's wind velocity can lead to the transition from the
disc accretion to the wind accretion and, as a consequence, to the transition
from quiescent to active state in classic symbiotic stars.Comment: 21 pages, 7 figure
Proper-motion age dating of the progeny of Nova Scorpii AD 1437.
'Cataclysmic variables' are binary star systems in which one star of the pair is a white dwarf, and which often generate bright and energetic stellar outbursts. Classical novae are one type of outburst: when the white dwarf accretes enough matter from its companion, the resulting hydrogen-rich atmospheric envelope can host a runaway thermonuclear reaction that generates a rapid brightening. Achieving peak luminosities of up to one million times that of the Sun, all classical novae are recurrent, on timescales of months to millennia. During the century before and after an eruption, the 'novalike' binary systems that give rise to classical novae exhibit high rates of mass transfer to their white dwarfs. Another type of outburst is the dwarf nova: these occur in binaries that have stellar masses and periods indistinguishable from those of novalikes but much lower mass-transfer rates, when accretion-disk instabilities drop matter onto the white dwarfs. The co-existence at the same orbital period of novalike binaries and dwarf novae-which are identical but for their widely varying accretion rates-has been a longstanding puzzle. Here we report the recovery of the binary star underlying the classical nova eruption of 11 March AD 1437 (refs 12, 13), and independently confirm its age by proper-motion dating. We show that, almost 500 years after a classical-nova event, the system exhibited dwarf-nova eruptions. The three other oldest recovered classical novae display nova shells, but lack firm post-eruption ages, and are also dwarf novae at present. We conclude that many old novae become dwarf novae for part of the millennia between successive nova eruptions
Diagnosis and management of Cornelia de Lange syndrome:first international consensus statement
Cornelia de Lange syndrome (CdLS) is an archetypical genetic syndrome that is characterized by intellectual disability, well-defined facial features, upper limb anomalies and atypical growth, among numerous other signs and symptoms. It is caused by variants in any one of seven genes, all of which have a structural or regulatory function in the cohesin complex. Although recent advances in next-generation sequencing have improved molecular diagnostics, marked heterogeneity exists in clinical and molecular diagnostic approaches and care practices worldwide. Here, we outline a series of recommendations that document the consensus of a group of international experts on clinical diagnostic criteria, both for classic CdLS and non-classic CdLS phenotypes, molecular investigations, long-term management and care planning