150 research outputs found
Properties of the Young Milky Way Globular Cluster Whiting 1 from Near-Infrared Photometry
Whiting 1 is a member of the fast-growing group of young globular clusters in
the Milky Way halo. Preliminary estimates of its fundamental parameters have
been provided using optical photometry and low resolution spectroscopy. In an
attempt to strengthen our knowledge of Whiting 1, in this study we employ a
complementary approach. Isochrone fitting method was applied on the
Near-Infrared Color-Magnitude Diagram and yields an age t=5.70.3 Gyr,
metallicity =0.0060.001 ([Fe/H]=0.50.1) and distance modulus
=17.480.10. Our results confirm that Whiting 1 is a young and
moderately metal-rich globular cluster. It is one of the youngest from the Sgr
dSph. We fitted an Elson, Fall and Freeman (EFF) profile to the near-infrared
number counts, and measured cluster core radius
=9.13.9. Two probable eclipsing
variables in the cluster were found from multi-epoch band photometry.
Finally, an unknown galaxy cluster was identified on our vs.
color-magnitude diagram. It has a redshift z1, and it is located at about
1 from the center of Whiting 1 at , ,
contaminating the cluster photometry.Comment: Accepted for publication in MNRAS, 6 pages, 8 figure
Optical monitoring of the z=4.40 quasar Q 2203+292
We report Cousins R-band monitoring of the high-redshift (z=4.40) radio quiet
quasar Q 2203+292 from May 1999 to October 2007. The quasar shows maximum
peak-to-peak light curve amplitude of ~0.3 mag during the time of our
monitoring, and ~0.9 mag when combined with older literature data. The rms of a
fit to the light curve with a constant is 0.08 mag and 0.2 mag, respectively.
The detected changes are at ~3-sigma level. The quasar was in a stable state
during the recent years and it might have undergone a brightening event in the
past. The structure function analysis concluded that the object shows
variability properties similar to those of the lower redshift quasars. We set a
lower limit to the Q 2203+292 broad line region mass of 0.3-0.4 M_odot.
Narrow-band imaging search for redshifted Ly_alpha from other emission line
objects at the same redshift shows no emission line objects in the quasar
vicinity.Comment: 9 pages, 8 figures, accepted for publication in MNRA
The VMC Survey - VI. Quasars behind the Magellanic system
The number and spatial distribution of confirmed quasi-stellar objects (QSOs)
behind the Magellanic system is limited. This undermines their use as
astrometric reference objects for different types of studies. We have searched
for criteria to identify candidate QSOs using observations from the VISTA
survey of the Magellanic Clouds system (VMC) that provides photometry in the
YJKs bands and 12 epochs in the Ks band. The (Y-J) versus (J-Ks) diagram has
been used to distinguish QSO candidates from Milky Way stars and stars of the
Magellanic Clouds. Then, the slope of variation in the Ks band has been used to
identify a sample of high confidence candidates. These criteria were developed
based on the properties of 117 known QSOs presently observed by the VMC survey.
VMC YJKs magnitudes and Ks light-curves of known QSOs behind the Magellanic
system are presented. About 75% of them show a slope of variation in Ks>10^-4
mag/day and the shape of the light-curve is in general irregular and without
any clear periodicity. The number of QSO candidates found in tiles including
the South Ecliptic Pole and the 30 Doradus regions is 22 and 26, respectively,
with a ~20% contamination by young stellar objects, planetary nebulae, stars
and normal galaxies. By extrapolating the number of QSO candidates to the
entire VMC survey area we expect to find about 1200 QSOs behind the LMC, 400
behind the SMC, 200 behind the Bridge and 30 behind the Stream areas, but not
all will be suitable for astrometry. Further, the Ks band light-curves can help
support investigations of the mechanism responsible for the variations.Comment: 17 pages, 15 figures, replaced with accepted version by Astronomy &
Astrophysic
X-ray monitoring of classical novae in the central region of M 31. II. Autumn and winter 2007/2008 and 2008/2009
[Abridged] Classical novae (CNe) represent the major class of supersoft X-ray
sources (SSSs) in the central region of our neighbouring galaxy M 31. We
performed a dedicated monitoring of the M 31 central region with XMM-Newton and
Chandra between Nov 2007 and Feb 2008 and between Nov 2008 and Feb 2009
respectively, in order to find SSS counterparts of CNe, determine the duration
of their SSS phase and derive physical outburst parameters. We systematically
searched our data for X-ray counterparts of CNe and determined their X-ray
light curves and spectral properties. We detected in total 17 X-ray
counterparts of CNe in M 31, only four of which were known previously. These
latter sources are still active 12.5, 11.0, 7.4 and 4.8 years after the optical
outburst. From the 17 X-ray counterparts 13 were classified as SSSs. Four novae
displayed short SSS phases (< 100 d). Based on these results and previous
studies we compiled a catalogue of all novae with SSS counterparts in M 31
known so far. We used this catalogue to derive correlations between the
following X-ray and optical nova parameters: turn-on time, turn-off time,
effective temperature (X-ray), t2 decay time and expansion velocity of the
ejected envelope (optical). Furthermore, we found a first hint for the
existence of a difference between SSS parameters of novae associated with the
stellar populations of the M 31 bulge and disk. Additionally, we conducted a
Monte Carlo Markov Chain simulation on the intrinsic fraction of novae with SSS
phase. This simulation showed that the relatively high fraction of novae
without detected SSS emission might be explained by the inevitably incomplete
coverage with X-ray observations in combination with a large fraction of novae
with short SSS states, as expected from the WD mass distribution. In order to
verify our results with an increased sample further monitoring observations are
needed.Comment: 31 pages, 23 figures, 10 tables; submitted to A&
Dissecting the long-term emission behaviour of the BL Lac object Mrk 421
We report on long-term multiwavelengthmonitoring of blazar Mrk 421 by the GLAST-AGILE
Support Program of the Whole Earth Blazar Telescope (GASP-WEBT) collaboration and
Steward Observatory, and by the Swift and Fermi satellites. We study the source behaviour in
the period 2007–2015, characterized by several extreme flares. The ratio between the optical,
X-ray and γ -ray fluxes is very variable. The γ -ray flux variations show a fair correlation with
the optical ones starting from 2012.We analyse spectropolarimetric data and find wavelengthdependence
of the polarization degree (P), which is compatible with the presence of the
host galaxy, and no wavelength dependence of the electric vector polarization angle (EVPA).
Optical polarimetry shows a lack of simple correlation between P and flux and wide rotations of
the EVPA.We build broad-band spectral energy distributions with simultaneous near-infrared
and optical data from the GASP-WEBT and ultraviolet and X-ray data from the Swift satellite.
They show strong variability in both flux and X-ray spectral shape and suggest a shift of
the synchrotron peak up to a factor of ∼50 in frequency. The interpretation of the flux and
spectral variability is compatible with jet models including at least two emitting regions that
can change their orientation with respect to the line of sight.http://10.0.4.69/mnras/stx2185Accepted manuscrip
WEBT multiwavelength monitoring and XMM-Newton observations of BL Lacertae in 2007-2008. Unveiling different emission components
In 2007-2008 we carried out a new multiwavelength campaign of the Whole Earth
Blazar Telescope (WEBT) on BL Lacertae, involving three pointings by the
XMM-Newton satellite, to study its emission properties. The source was
monitored in the optical-to-radio bands by 37 telescopes. The brightness level
was relatively low. Some episodes of very fast variability were detected in the
optical bands. The X-ray spectra are well fitted by a power law with photon
index of about 2 and photoelectric absorption exceeding the Galactic value.
However, when taking into account the presence of a molecular cloud on the line
of sight, the data are best fitted by a double power law, implying a concave
X-ray spectrum. The spectral energy distributions (SEDs) built with
simultaneous radio-to-X-ray data at the epochs of the XMM-Newton observations
suggest that the peak of the synchrotron emission lies in the near-IR band, and
show a prominent UV excess, besides a slight soft-X-ray excess. A comparison
with the SEDs corresponding to previous observations with X-ray satellites
shows that the X-ray spectrum is extremely variable. We ascribe the UV excess
to thermal emission from the accretion disc, and the other broad-band spectral
features to the presence of two synchrotron components, with their related SSC
emission. We fit the thermal emission with a black body law and the non-thermal
components by means of a helical jet model. The fit indicates a disc
temperature greater than 20000 K and a luminosity greater than 6 x 10^44 erg/s.Comment: 11 pages, 7 figures, accepted for publication in A&
A new activity phase of the blazar 3C 454.3. Multifrequency observations by the WEBT and XMM-Newton in 2007-2008
We present and analyse the WEBT multifrequency observations of 3C 454.3 in
the 2007-2008 observing season, including XMM-Newton observations and near-IR
spectroscopic monitoring, and compare the recent emission behaviour with the
past one. In the optical band we observed a multi-peak outburst in July-August
2007, and other faster events in November 2007 - February 2008. During these
outburst phases, several episodes of intranight variability were detected. A mm
outburst was observed starting from mid 2007, whose rising phase was
contemporaneous to the optical brightening. A slower flux increase also
affected the higher radio frequencies, the flux enhancement disappearing below
8 GHz. The analysis of the optical-radio correlation and time delays, as well
as the behaviour of the mm light curve, confirm our previous predictions,
suggesting that changes in the jet orientation likely occurred in the last few
years. The historical multiwavelength behaviour indicates that a significant
variation in the viewing angle may have happened around year 2000. Colour
analysis reveals a complex spectral behaviour, which is due to the interplay of
different emission components. All the near-IR spectra show a prominent Halpha
emission line, whose flux appears nearly constant. The analysis of the
XMM-Newton data indicates a correlation between the UV excess and the
soft-X-ray excess, which may represent the head and the tail of the big blue
bump, respectively. The X-ray flux correlates with the optical flux, suggesting
that in the inverse-Compton process either the seed photons are synchrotron
photons at IR-optical frequencies or the relativistic electrons are those that
produce the optical synchrotron emission. The X-ray radiation would thus be
produced in the jet region from where the IR-optical emission comes.Comment: 10 pages, 12 figures (7 included in the text, 5 in GIF format),
accepted for publication in A&
Radio-to-UV monitoring of AO 0235+164 by the WEBT and Swift during the 2006--2007 outburst
The blazar AO 0235+164 was claimed to show a quasi-periodic behaviour in the
radio and optical bands. Moreover, an extra emission component contributing to
the UV and soft X-ray flux was detected, whose nature is not yet clear. A
predicted optical outburst was observed in late 2006/early 2007. We here
present the radio-to-optical WEBT light curves during the outburst, together
with UV data acquired by Swift in the same period. We found the optical
outburst to be as strong as the big outbursts of the past: starting from late
September 2006, a brightness increase of 5 mag led to the outburst peak in
February 19-21, 2007. We also observed an outburst at mm and then at cm
wavelengths, with an increasing time delay going toward lower frequencies
during the rising phase. Cross-correlation analysis indicates that the 1 mm and
37 GHz flux variations lagged behind the R-band ones by about 3 weeks and 2
months, respectively. These short time delays suggest that the corresponding
jet emitting regions are only slightly separated and/or misaligned. In
contrast, during the outburst decreasing phase the flux faded contemporaneously
at all cm wavelengths. This abrupt change in the emission behaviour may suggest
the presence of some shutdown mechanism of intrinsic or geometric nature. The
behaviour of the UV flux closely follows the optical and near-IR one. By
separating the synchrotron and extra component contributions to the UV flux, we
found that they correlate, which suggests that the two emissions have a common
origin.Comment: 9 pages, 7 figures, in press for Astronomy and Astrophysic
WEBT and XMM-Newton observations of 3C 454.3 during the post-outburst phase. Detection of the little and big blue bumps
The blazar 3C 454.3 underwent an unprecedented optical outburst in spring
2005. This was first followed by a mm and then by a cm radio outburst, which
peaked in February 2006. We report on follow-up observations by the WEBT to
study the multiwavelength emission in the post-outburst phase. XMM-Newton
observations on July and December 2006 added information on the X-ray and UV
fluxes. The source was in a faint state. The radio flux at the higher
frequencies showed a fast decreasing trend, which represents the tail of the
big radio outburst. It was followed by a quiescent state, common at all radio
frequencies. In contrast, moderate activity characterized the NIR and optical
light curves, with a progressive increase of the variability amplitude with
increasing wavelength. We ascribe this redder-when-brighter behaviour to the
presence of a "little blue bump" due to line emission from the broad line
region, which is clearly visible in the source SED during faint states.
Moreover, the data from the XMM-Newton OM reveal a rise of the SED in the UV,
suggesting the existence of a "big blue bump" due to thermal emission from the
accretion disc. The X-ray spectra are well fitted with a power-law model with
photoelectric absorption, possibly larger than the Galactic one. However, the
comparison with previous X-ray observations would imply that the amount of
absorbing matter is variable. Alternatively, the intrinsic X-ray spectrum
presents a curvature, which may depend on the X-ray brightness. In this case,
two scenarios are possible.Comment: 9 pages, 7 figures, accepted for publication in A&
Meshalkin National Medical Research Center
We present three cases of successful transatrial transcatheter valve-in-valve implantation in patients with bioprosthetic mitral valve dysfunction. Patients with a high surgical risk, with severe heart failure due to bioprosthetic mitral valve dysfunction, were implanted with transcatheter prostheses using the transatrial approach.Transesophageal echocardiography and fluoroscopy-guided transcatheter mitral prosthetic valve positioning was performed. With a cardiac pacing at 180 bpm, a transcatheter valve was implanted. The transcatheter valves functioned properly after surgery. The patients were discharged in satisfactory condition
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