54 research outputs found
The first all-sky view of the Milky Way stellar halo with Gaia+2MASS RR Lyrae
We exploit the first \gaia data release to study the properties of the
Galactic stellar halo as traced by RR Lyrae. We demonstrate that it is possible
to select a pure sample of RR Lyrae using only photometric information
available in the Gaia+2MASS catalogue. The final sample contains about 21600 RR
Lyrae covering an unprecedented fraction () of the volume of the
Galactic inner halo ( kpc). We study the morphology of the stellar
halo by analysing the RR Lyrae distribution with parametric and non-parametric
techniques. Taking advantage of the uniform all-sky coverage, we test halo
models more sophisticated than usually considered in the literature, such as
those with varying flattening, tilt and/or offset of the halo with respect to
the Galactic disc. A consistent picture emerges: the inner halo is well
reproduced by a smooth distribution of stars settled on triaxial ellipsoids.
The minor axis is perpendicular to the Milky Ways disc, while the major axis is
misaligned by from the Galactic Y axis. The elongation along
the major axis is mild (), and the vertical flattening is shown
to evolve from a squashed state with in the centre to a
more spherical at the outer edge of our dataset. The
density slope is well approximated by a single power-law with exponent
. Within the range probed, we see no significant evidence for a
change of the radial density slope, out of the plane tilt or an offset of the
halo with respect to the Galaxy's centre.Comment: Accepted for publication in MNRA
A deeper look at the GD1 stream::density variations and wiggles
Using deep photometric data from CFHT/Megacam, we study the morphology and
density of the GD-1 stream, one of the longest and coldest stellar streams in
the Milky Way. Our deep data recovers the lower main sequence of the stream
with unprecedented quality, clearly separating it from Milky Way foreground and
background stars. An analysis of the distance to different parts of the stream
shows that GD-1 lies at a heliocentric distance between 8 and 10 kpc, with only
a shallow gradient across 45 deg on the sky. Matched filter maps of the stream
density show clear density variations, such as deviations from a single orbital
track and tentative evidence for stream fanning. We also detect a clear
under-density in the middle of the stream track at =-45 deg
surrounded by overdense stream segments on either side. This location is a
promising candidate for the elusive missing progenitor of the GD-1 stream. We
conclude that the GD-1 stream has clearly been disturbed by interactions with
the Milky Way disk or other sub-halos.Comment: submitted to MNRAS, comments welcom
Deep Subaru Hyper Suprime-Cam Observations of Milky Way Satellites Columba I and Triangulum II
Dark Matter in the Milky Way's Dwarf Spheroidal Satellites
The Milky Way's dwarf spheroidal satellites include the nearest, smallest and
least luminous galaxies known. They also exhibit the largest discrepancies
between dynamical and luminous masses. This article reviews the development of
empirical constraints on the structure and kinematics of dSph stellar
populations and discusses how this phenomenology translates into constraints on
the amount and distribution of dark matter within dSphs. Some implications for
cosmology and the particle nature of dark matter are discussed, and some
topics/questions for future study are identified.Comment: A version with full-resolution figures is available at
http://www.cfa.harvard.edu/~mwalker/mwdsph_review.pdf; 70 pages, 22 figures;
invited review article to be published in Vol. 5 of the book "Planets, Stars,
and Stellar Systems", published by Springe
The Molecular Identification of Organic Compounds in the Atmosphere: State of the Art and Challenges
X-ray photoelectron spectroscopy characterization of composite TiO2–poly(vinylidenefluoride) films synthesised for applications in pesticide photocatalytic degradation
X-ray photoelectron spectroscopy (XPS) was adopted for the analytical characterization of composite titanium dioxide–
poly(vinylidenefluoride) (TiO2–PVDF) films developed for applications in the photocatalytic degradation of pollutants.
The composites were deposited on glass substrates by casting or spin coating from TiO2–PVDF suspensions in dimethylformamide
(DMF). XPS data on the TiO2–PVDF surface composition were used to optimize preparation conditions
(composition of the TiO2/PVDF suspension, deposition technique) in terms of titanium dioxide surface amount and film
stability.
The use of spin-coating deposition and the increase of TiO2 amount in the DMF suspensions were found to improve the
titanium surface content, although high TiO2/PVDF ratios led to film instability. PVDF–TiO2 films were also used in preliminary
photocatalytic degradation tests on isoproturon, a phenylurea herbicide, under solar UVirradiation; the results were compared to
direct photolysis to evaluate the catalytic efficiency of immobilized TiO2 and the role played by the PVDF film during the
degradation process
Simultaneous determination of phenyl- and sulfonyl-urea herbicides in river water at sub-parts-per-billion level by on-line preconcentration and liquid chromatography–tandem mass spectrometry
A method based on on-line preconcentration followed by liquid chromatography-electrospray ionization–tandem mass spectrometry (LCESI–
MS/MS) was developed for the determination of three sulfonyl-urea (thifensulfuron, metsulfuron, chlorsulfuron) and two phenyl-urea
(isoproturon and chlortoluron) herbicides in water at sub-ppb concentration ranges.
Preconcentration was accomplished using on-line enrichment on a C18 cartridge; the procedure was optimized by an evaluation of the breakthrough
volumes for the target analytes. Subsequently, LC-ESI–MS/MS was adopted for analytes separation and detection.
In particular, a selective reaction monitoring (SRM) approach, based on the detection of a peculiar fragment for each analyte, was chosen for
MS/MS analysis, in order to enhance selectivity. Normalization to the response of a phenyl-urea herbicide (chloroxuron), used as an internal
standard, was also adopted to achieve a reproducibility enhancement.
The described method was applied to the analysis of the target analytes in river water samples and LOD values ranging between 8 and 30 ppt
were obtained
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