43 research outputs found
Nucleosynthesis of 26Al in rotating Wolf-Rayet stars
The 26Al radionuclide can be detected through its decay emission line at
1.809 MeV, as was first observed by Mahoney et al. (1982). Since then, COMPTEL
on board of the CGRO satellite, performed a sky survey in this energy range,
and provided maps of the 26Al distribution in the Galaxy. These results
revealed that the main contributors to the synthesis of 26Al are most likely
the massive stars, which contribute through their winds (Wolf-Rayet stars) and
through their supernova explosion. Comparison between these observations (in
particular observations in localized regions such as the Vela region and the
Cygnus region) and the models available at that moment, showed however the need
for improvements from both theoretical and observational points of view, in
order to improve our understanding of the 26Al galactic distribution as well as
that of its synthesis. With the launch of the INTEGRAL satellite in October
2002, the observational part will hopefully be improved, and the construction
of better resolution maps at 1.809 MeV is one of the main aims of the mission.
From a theoretical point of view, we need the most up-to-date predictions in
order to be able to interpret the forthcoming data. In this paper, we address
this latter part, and present new results for 26Al production by rotating
Wolf-Rayet stars and their contribution to the total amount observed in the
Galaxy.Comment: 4 pages, 3 figures, replaced version with minor changes, refereed and
accepted for publication in the proceedings of the Fifth INTEGRAL Workshop :"
The INTEGRAL Universe
A multimodal real-time MRI articulatory corpus of French for speech research
In this work we describe the creation of ArtSpeechMRIfr: a real-time as well as static magnetic resonance imaging (rtMRI, 3D MRI) database of the vocal tract. The database contains also processed data: denoised audio, its phonetically aligned annotation, articulatory contours, and vocal tract volume information , which provides a rich resource for speech research. The database is built on data from two male speakers of French. It covers a number of phonetic contexts in the controlled part, as well as spontaneous speech, 3D MRI scans of sustained vocalic articulations, and of the dental casts of the subjects. The corpus for rtMRI consists of 79 synthetic sentences constructed from a phonetized dictionary that makes possible to shorten the duration of acquisitions while keeping a very good coverage of the phonetic contexts which exist in French. The 3D MRI includes acquisitions for 12 French vowels and 10 consonants, each of which was pronounced in several vocalic contexts. Ar-ticulatory contours (tongue, jaw, epiglottis, larynx, velum, lips) as well as 3D volumes were manually drawn for a part of the images
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses III. Redshift of the lensing galaxy in eight gravitationally lensed quasars
Aims: We measure the redshift of the lensing galaxy in eight gravitationally
lensed quasars in view of determining the Hubble parameter H_0 from the time
delay method.
Methods: Deep VLT/FORS1 spectra of lensed quasars are spatially deconvolved
in order to separate the spectrum of the lensing galaxies from the glare of the
much brighter quasar images. A new observing strategy is devised. It involves
observations in Multi-Object-Spectroscopy (MOS) which allows the simultaneous
observation of the target and of several PSF and flux calibration stars. The
advantage of this method over traditional long-slit observations is a much more
reliable extraction and flux calibration of the spectra.
Results: For the first time we measure the redshift of the lensing galaxy in
three multiply-imaged quasars: SDSS J1138+0314 (z=0.445), SDSS J1226-0006
(z=0.517), SDSS J1335+0118 (z=0.440), and we give a tentative estimate of the
redshift of the lensing galaxy in Q 1355-2257 (z=0.701). We confirm four
previously measured redshifts: HE 0047-1756 (z=0.407), HE 0230-2130 (z=0.523),
HE 0435-1223 (z=0.454) and WFI J2033-4723 (z=0.661). In addition, we determine
the redshift of the second lensing galaxy in HE 0230-2130 (z=0.526). The
spectra of all lens galaxies are typical for early-type galaxies, except for
the second lensing galaxy in HE 0230-2130 which displays prominent [OII]
emission.Comment: 9 pages, 19 figures, accepted for publication in A&
The luminosity of supernovae of type Ia from TRGB distances and the value of H_0
Distances from the tip of the red-giant branch (TRGB) in the halo Population
of galaxies - calibrated through RR Lyr stars as well as tied to Hipparcos
parallaxes and further supported by stellar models - are used to determine the
luminosity of six nearby type Ia supernovae (SN 2011fe, 2007sr, 1998bu, 1989B,
1972E, and 1937C). The result is M_V^corr = -19.41 +/- 0.05. If this value is
applied to 62 SNe Ia with 3000< v < 20,000 km/s a large-scale value of the
Hubble constant follows of H_0 = 64.0 +/- 1.6 +/- 2.0. The SN HST Project gave
H_0 = 62.3 +/- 1.3 +/- 5.0 from ten Cepheid-calibrated SNe Ia (Sandage et al.
2006). The agreement of young Population I (Cepheids) and old, metal-poor
Population II (TRGB) distance indicators is satisfactory. The combined weighted
result is H_0 = 63.7 +/- 2.3 (i.e. +/-3.6%). The result can also be reconciled
with WMAP5 data (Reid et al. 2010).Comment: 9 pages, 3 figures, 3 tables, accepted for publication in Astronomy
and Astrophysic
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses V. The time delay in SDSS J1650+4251
Aims: Our aim is to measure the time delay between the two gravitationally
lensed images of the z = 1.547 quasar SDSS J1650+4251, in order to estimate the
Hubble constant H_0.
Methods: Our measurement is based on R-band light curves with 57 epochs
obtained at Maidanak Observatory, in Uzbekistan, from May 2004 to September
2005. The photometry is performed using simultaneous deconvolution of the data,
which provides the individual light curves of the otherwise blended quasar
images. The time delay is determined from the light curves using two very
different numerical techniques, i.e., polynomial fitting and direct
cross-correlation. The time delay is converted into H_0 following analytical
modeling of the potential well.
Results: Our best estimate of the time delay is Dt = 49.5 +/- 1.9 days, i.e.,
we reach a 3.8% accuracy. The R-band flux ratio between the quasar images,
corrected for the time delay and for slow microlensing, is F_A /F_B = 6.2 +/-
5%.
Conclusions: The accuracy reached on the time delay allows us to discriminate
well between families of lens models. As for most other multiply imaged
quasars, only models of the lensing galaxy that have a de Vaucouleurs mass
profile plus external shear give a Hubble constant compatible with the current
most popular value (H_0 = 72 +/- 8 km s-1 Mpc-1). A more realistic singular
isothermal sphere model plus external shear gives H_0 = 51.7 +4.0 -3.0 km s-1
Mpc-1.Comment: 8 pages, 12 figures, accepted by A&
Cosmological distance indicators
We review three distance measurement techniques beyond the local universe:
(1) gravitational lens time delays, (2) baryon acoustic oscillation (BAO), and
(3) HI intensity mapping. We describe the principles and theory behind each
method, the ingredients needed for measuring such distances, the current
observational results, and future prospects. Time delays from strongly lensed
quasars currently provide constraints on with < 4% uncertainty, and with
1% within reach from ongoing surveys and efforts. Recent exciting discoveries
of strongly lensed supernovae hold great promise for time-delay cosmography.
BAO features have been detected in redshift surveys up to z <~ 0.8 with
galaxies and z ~ 2 with Ly- forest, providing precise distance
measurements and with < 2% uncertainty in flat CDM. Future BAO
surveys will probe the distance scale with percent-level precision. HI
intensity mapping has great potential to map BAO distances at z ~ 0.8 and
beyond with precisions of a few percent. The next years ahead will be exciting
as various cosmological probes reach 1% uncertainty in determining , to
assess the current tension in measurements that could indicate new
physics.Comment: Review article accepted for publication in Space Science Reviews
(Springer), 45 pages, 10 figures. Chapter of a special collection resulting
from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in
the Space Ag
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses II. SDSS J0924+0219: the redshift of the lensing galaxy, the quasar spectral variability and the Einstein rings
(Abridged) We present our VLT/FORS1 deep spectroscopic observations of the
gravitationally lensed quasar SDSS J0924+0219, as well as archival HST/NICMOS
and ACS images of the same object. The two-epoch spectra, obtained in the Multi
Object Spectroscopy (MOS) mode, allow for very accurate flux calibration,
spatial deconvolution of the data, and provide the redshift of the lensing
galaxy z=0.394 +/- 0.001. These spectra, taken 15 days apart, show only slight
continuum variations, while the broad emission lines display obvious changes in
the red wing of the Mg II line, in the Fe II bands, and in the central part of
the C III] line. Even though variations in the line profiles are present, we do
not see any significant differences between the continuum and emission line
flux ratios of images A and B of the quasar. Spatial deconvolution of the HST
images reveals a double Einstein ring. One ring corresponds to the lensed
quasar host galaxy at z=1.524 and a second bluer one, is the image either of a
star-forming region in the host galaxy, or of another unrelated lower redshift
object. We find that a broad range of lens models gives a satisfactory fit to
the data. However, they predict very different time delays, making SDSS
J0924+0219 an object of particular interest for photometric monitoring. In
addition, the lens models reconstructed using exclusively the constraints from
the Einstein rings, or using exclusively the astrometry of the quasar images,
are not compatible. This suggests that substructures play an important role in
SDSS J0924+0219.Comment: 13 pages, 14 figures, accepted for publication in A&
The Hubble Constant
I review the current state of determinations of the Hubble constant, which
gives the length scale of the Universe by relating the expansion velocity of
objects to their distance. There are two broad categories of measurements. The
first uses individual astrophysical objects which have some property that
allows their intrinsic luminosity or size to be determined, or allows the
determination of their distance by geometric means. The second category
comprises the use of all-sky cosmic microwave background, or correlations
between large samples of galaxies, to determine information about the geometry
of the Universe and hence the Hubble constant, typically in a combination with
other cosmological parameters. Many, but not all, object-based measurements
give values of around 72-74km/s/Mpc , with typical errors of 2-3km/s/Mpc.
This is in mild discrepancy with CMB-based measurements, in particular those
from the Planck satellite, which give values of 67-68km/s/Mpc and typical
errors of 1-2km/s/Mpc. The size of the remaining systematics indicate that
accuracy rather than precision is the remaining problem in a good determination
of the Hubble constant. Whether a discrepancy exists, and whether new physics
is needed to resolve it, depends on details of the systematics of the
object-based methods, and also on the assumptions about other cosmological
parameters and which datasets are combined in the case of the all-sky methods.Comment: Extensively revised and updated since the 2007 version: accepted by
Living Reviews in Relativity as a major (2014) update of LRR 10, 4, 200