1,143 research outputs found
Properties, evolution and morpho-kinematical modelling of the very fast nova V2672 Oph (Nova Oph 2009), a clone of U Sco
V2672 Oph reached maximum brightness V=11.35 on 2009 August 16.5. With
observed t2(V)=2.3 and t3(V)=4.2 days decline times, it is one of the fastest
known novae, being rivalled only by V1500 Cyg (1975) and V838 Her (1991) among
classical novae, and U Sco among the recurrent ones. The line of sight to the
nova passes within a few degrees of the Galactic centre. The reddening of V2672
Oph is E(B-V)=1.6 +/-0.1, and its distance ~19 kpc places it on the other side
of the Galactic centre at a galacto-centric distance larger than the solar one.
The lack of an infrared counterpart for the progenitor excludes the donor star
from being a cool giant like in RS Oph or T CrB. With close similarity to U
Sco, V2672 Oph displayed a photometric plateau phase, a He/N spectrum
classification, extreme expansion velocities and triple peaked emission line
profiles during advanced decline. The full width at zero intensity of Halpha
was 12,000 km/s at maximum, and declined linearly in time with a slope very
similar to that observed in U Sco. We infer a WD mass close to the
Chandrasekhar limit and a possible final fate as a SNIa. Morpho-kinematical
modelling of the evolution of the Halpha profile suggests that the overall
structure of the ejecta is that of a prolate system with polar blobs and an
equatorial ring. The density in the prolate system appeared to decline faster
than that in the other components. V2672 Oph is seen pole-on, with an
inclination of 0+/-6 deg and an expansion velocity of the polar blobs of 4800
+900/-800 km/s. On the basis of its remarkable similarity to U Sco, we suspect
this nova may be a recurrent. Given the southern declination, the faintness at
maximum, the extremely rapid decline and its close proximity to the Ecliptic,
it is quite possible that previous outbursts of V2672 Oph have been missed.Comment: in press in MNRA
Observations of GRB 060526 Optical Afterglow with Russian-Turkish 1.5-m Telescope
We present the results of the photometric multicolor observations of GRB
060526 optical afterglow obtained with Russian-Turkish 1.5-m Telescope (RTT150,
Mt. Bakirlitepe, Turkey). The detailed measurements of afterglow light curve,
starting from about 5 hours after the GRB and during 5 consecutive nights were
done. In addition, upper limits on the fast variability of the afterglow during
the first night of observations were obtained and the history of afterglow
color variations was measured in detail. In the time interval from 6 to 16
hours after the burst, there is a gradual flux decay, which can be described
approximately as a power law with an index of -1.14+-0.02. After that the
variability on the time scale \delta t < t is observed and the afterglow
started to decay faster. The color of the afterglow, V-R=~0.5, is approximately
the same during all our observations. The variability is detected on time
scales up to \delta t/t =~ 0.0055 at \Delta F_\nu/F_\nu =~ 0.3, which violates
some constraints on the variability of the observed emission from
ultrarelativistic jet obtained by Ioka et al. (2005). We suggest to explain
this variability by the fact that the motion of the emitting shell is no longer
ultrarelativistic at this time.Comment: 6 pages, 7 figures, Astronomy Letters, 2007, 33, 797, The on-line
data tables and the original text in Russian can be found at
http://hea.iki.rssi.ru/grb/060526/indexeng.htm
Echo-Mapping of Swift J1753.5-0127
We present two epochs of coordinated X-ray-optical timing observations of the
black hole candidate Swift J1753.5-0127 during its 2005 outburst. The first
epoch in July occurred at outburst peak. Two consecutive nights of observations
using the McDonald Observatory Argos camera with the Rossi X-ray Timing
Explorer show a consistent correlation with an immediate response and an
extended tail lasting ~5s. The properties of the variability and the
correlation are consistent with thermal reprocessing in an accretion disk. The
shortness of the lag suggests a short orbital period consistent with that
recently claimed. The second epoch in August used the VLT FORS2 HIT mode again
in conjunction with RXTE. Again a repeatable correlation is seen between two
independent subsets of the data. In this case, though, the cross-correlation
function has an unusual structure comprising a dip followed by a double-peak.
We suggest that this may be equivalent to the dip plus single peak structure
seen by Kanbach et al. (2001) in XTE J1118+480 and attributed there to
synchrotron emission; a similar structure was seen during later activity of
Swift J1753.5-0127 by Durant et al. (2008).Comment: 7 pages, accepted for publication in Monthly Notices of the Royal
Astronomical Societ
CCD-based observations of PG 0856+121 and a theoretical analysis of its oscillation modes
BVRI CCD-based and near-IR (J) imaging, together with unfiltered photometry
of the hot subdwarf B star PG 0856+121 are reported. Two close, faint, red,
point-like sources are resolved. They account for the previously reported IR
excess observed in this hot subdwarf. In addition, the new unfiltered
differential photometry of PG 0856+121 confirms its previously reported
pulsational nature. A comparison with the oscillation modes of stellar models
suggests the possible presence of g modes.Comment: Accepted for publication in A&A. Seven pages, four figures include
A photometric and astrometric investigation of the brown dwarfs in Blanco 1
We present the results of a photometric and astrometric study of the low mass
stellar and substellar population of the young open cluster Blanco 1. We have
exploited J band data, obtained recently with the Wide Field Camera (WFCAM) on
the United Kingdom InfraRed Telescope (UKIRT), and 10 year old I and z band
optical imaging from CFH12k and Canada France Hawaii Telescope (CFHT), to
identify 44 candidate low mass stellar and substellar members, in an area of 2
sq. degrees, on the basis of their colours and proper motions. This sample
includes five sources which are newly discovered. We also confirm the lowest
mass candidate member of Blanco 1 unearthed so far (29MJup). We determine the
cluster mass function to have a slope of alpha=+0.93, assuming it to have a
power law form. This is high, but nearly consistent with previous studies of
the cluster (to within the errors), and also that of its much better studied
northern hemisphere analogue, the Pleiades.Comment: 8 Pages, 5 Figures, 2 Tables and 1 Appendix. Accepted for publication
in MNRA
Analysis of the Reaction Rate Coefficients for Slow Bimolecular Chemical Reactions
Simple bimolecular reactions are analyzed
within the framework of the Boltzmann equation in the initial stage of a
chemical reaction with the system far from chemical equilibrium. The
Chapman-Enskog methodology is applied to determine the coefficients of the
expansion of the distribution functions in terms of Sonine polynomials for
peculiar molecular velocities. The results are applied to the reaction
, and the influence of the non-Maxwellian
distribution and of the activation-energy dependent reactive cross sections
upon the forward and reverse reaction rate coefficients are discussed.Comment: 11 pages, 5 figures, to appear in vol.42 of the Brazilian Journal of
Physic
New apparatus for DTA at 2000 bar: thermodynamic studies on Au, Ag, Al and HTSC oxides
A new DTA (Differential Thermal Analysis) device was designed and installed
in a Hot Isostatic Pressure (HIP) furnace in order to perform high-pressure
thermodynamic investigations up to 2 kbar and 1200C. Thermal analysis can be
carried out in inert or oxidising atmosphere up to p(O2) = 400 bar. The
calibration of the DTA apparatus under pressure was successfully performed
using the melting temperature (Tm) of pure metals (Au, Ag and Al) as standard
calibration references. The thermal properties of these metals have been
studied under pressure. The values of DV (volume variation between liquid and
solid at Tm), ROsm (density of the solid at Tm) and ALPHAm (linear thermal
expansion coefficient at Tm) have been extracted. A very good agreement was
found with the existing literature and new data were added. This HP-DTA
apparatus is very useful for studying the thermodynamics of those systems where
one or more volatile elements are present, such as high TC superconducting
oxides. DTA measurements have been performed on Bi,Pb(2223) tapes up to 2 kbar
under reduced oxygen partial pressure (p(O2) = 0.07 bar). The reaction leading
to the formation of the 2223 phase was found to occur at higher temperatures
when applying pressure: the reaction DTA peak shifted by 49C at 2 kbar compared
to the reaction at 1 bar. This temperature shift is due to the higher stability
of the Pb-rich precursor phases under pressure, as the high isostatic pressure
prevents Pb from evaporating.Comment: 6 figures, 3 tables, Thermodynamics, Thermal property, Bi-2223,
fundamental valu
Photometric AGN reverberation mapping - an efficient tool for BLR sizes, black hole masses and host-subtracted AGN luminosities
Photometric reverberation mapping employs a wide bandpass to measure the AGN
continuum variations and a suitable band, usually a narrow band (NB), to trace
the echo of an emission line in the broad line region (BLR). The narrow band
catches both the emission line and the underlying continuum, and one needs to
extract the pure emission line light curve. We performed a test on two local
AGNs, PG0003+199 (=Mrk335) and Ark120, observing well-sampled broad- (B, V) and
narrow-band light curves with the robotic 15cm telescope VYSOS-6 on Cerro
Armazones, Chile. In PG0003+199, H_alpha dominates the flux in the NB by 85%,
allowing us to measure the time lag of H_alpha against B without the need to
correct for the continuum contribution. In Ark120, H_beta contributes only 50%
to the flux in the NB. The cross correlation of the B and NB light curves shows
two distinct peaks of similar strength, one at lag zero from the autocorrelated
continuum and one from the emission line at tau_cent = 47.5 +/- 3.4 days. We
constructed a synthetic H_beta light curve, by subtracting a scaled V light
curve, which traces the continuum, from the NB light curve. The cross
correlation of this synthetic H_beta light curve with the B light curve shows
only one major peak at tau_cent = 48.0 +/- 3.3 days, while the peak from the
autocorrelated continuum at lag zero is absent. We conclude that, as long as
the emission line contributes at least 50% to the bandpass, the pure emission
line light curve can be reconstructed from photometric monitoring data so that
the time lag can be measured. For both objects the lags we find are consistent
with spectroscopic reverberation results. While the dense sampling (median 2
days) enables us to determine tau_cent with small (10%) formal errors, we
caution that gaps in the light curves may lead to much larger systematic
uncertainties. (Abstract shortened, see the manuscript.)Comment: 12 pages, 15 figures, accepted for publication in Astronomy and
Astrophysic
High contrast optical imaging of companions: the case of the brown dwarf binary HD-130948BC
High contrast imaging at optical wavelengths is limited by the modest
correction of conventional near-IR optimized AO systems.We take advantage of
new fast and low-readout-noise detectors to explore the potential of fast
imaging coupled to post-processing techniques to detect faint companions to
stars at small separations. We have focused on I-band direct imaging of the
previously detected brown dwarf binary HD130948BC,attempting to spatially
resolve the L2+L2 benchmark system. We used the Lucky-Imaging instrument
FastCam at the 2.5-m Nordic Telescope to obtain quasi diffraction-limited
images of HD130948 with ~0.1" resolution.In order to improve the detectability
of the faint binary in the vicinity of a bright (I=5.19 \pm 0.03) solar-type
star,we implemented a post-processing technique based on wavelet transform
filtering of the image which allows us to strongly enhance the presence of
point-like sources in regions where the primary halo dominates. We detect for
the first time the BD binary HD130948BC in the optical band I with a SNR~9 at
2.561"\pm 0.007" (46.5 AU) from HD130948A and confirm in two independent
dataset that the object is real,as opposed to time-varying residual speckles.We
do not resolve the binary, which can be explained by astrometric results
posterior to our observations that predict a separation below the NOT
resolution.We reach at this distance a contrast of dI = 11.30 \pm 0.11, and
estimate a combined magnitude for this binary to I = 16.49 \pm 0.11 and a I-J
colour 3.29 \pm 0.13. At 1", we reach a detectability 10.5 mag fainter than the
primary after image post-processing. We obtain on-sky validation of a technique
based on speckle imaging and wavelet-transform processing,which improves the
high contrast capabilities of speckle imaging.The I-J colour measured for the
BD companion is slightly bluer, but still consistent with what typically found
for L2 dwarfs(~3.4-3.6).Comment: accepted in A\&
- …