283 research outputs found
Interpolating sequences of 3D-data with C2 quintic PH B-spline curves
The goal of this paper is to present an effective method for interpolating sequences of 3D-data by means of C2 quintic Pythagorean-Hodograph (PH) B-spline curves. The strategy we propose works successfully with both open and closed sequences of 3D-points. It relies on calculations that are mostly explicit thanks to the fact that the interpolation conditions can explicitly be solved in dependence of the coefficients of the pre-image PH B-spline curve. In order to select a more suitable interpolant a functional is minimized in two remaining free coefficients of the pre-image PH B-spline curve and some angular parameters
Correction to: Fundamental functions for local interpolation of quadrilateral meshes with extraordinary vertices
The StEllar Counterparts of COmpact high velocity clouds (SECCO) survey. II. Sensitivity of the survey and an Atlas of Synthetic Dwarf Galaxies
SECCO is a survey devoted to the search for stellar counterparts within Ultra
Compact High Velocity Clouds. In this contribution we present the results of a
set of simulations aimed at the quantitative estimate of the sensitivity of the
survey as a function of the total luminosity, size and distance of the stellar
systems we are looking for. For all our synthetic galaxies we assumed an
exponential surface brightness profile and an old and metal-poor population.
The synthetic galaxies are simulated both on the images and on the photometric
catalogs, taking into account all the observational effects. In the fields
where the available observational material is of the top quality we detect
synthetic galaxies as >=5 sigma over-densities of resolved stars down to
muV,h=30.0 mag/arcsec2, for D<=1.5 Mpc, and down to muV,h~29.5 mag/arcsec2, for
D<=2.5 Mpc. In the field with the worst observational material of the whole
survey we detect synthetic galaxies with muV,h<=28.8 mag/arcsec2 out to D<=1.0
Mpc, and those with muV,h<=27.5 mag/arcsec2 out to D<=2.5 Mpc. Dwarf galaxies
with MV=-10, with sizes in the range spanned by known dwarfs, are detected by
visual inspection of the images up to D=5 Mpc independently of the image
quality. In the best quality images dwarfs are partially resolved into stars up
to D=3.0 Mpc, and completely unresolved at D=5 Mpc. As an independent test of
the sensitivity of our images to low surface brightness galaxies we report on
the detection of several dwarf spheroidal galaxies probably located in the
Virgo cluster with MV<=-8.0 and muV,h<=26.8 mag/arcsec2. The nature of the
previously discovered SECCO 1 stellar system, also likely located in the Virgo
cluster, is re-discussed in comparison with these dwarfs. While specific for
the SECCO survey, our study may also provide general guidelines for detection
of faint stellar systems with 8m class telescopes.Comment: accepted for publication on A&
The extended structure of the dwarf irregular galaxy Sagittarius
We present a detailed study of the stellar and HI structure of the dwarf
irregular galaxy Sagittarius. We use new deep and wide field photometry to
trace the surface brightness profile of the galaxy out to ~5.0' (corresponding
to ~1600 pc) and down to mag/arcsec, thus showing that
the stellar body of the galaxy is much more extended than previously believed,
and it is similarly (or more) extended than the overall HI distribution. The
whole major-axis profile is consistent with a pure exponential, with a scale
radius of pc. The surface density maps reveal that the
distribution of old and intermediate-age stars is smooth and remarkably
flattened out to its edges, while the associated HI has a much rounder shape,
is off-centred and presents multiple density maxima and a significant hole. No
clear sign of systemic rotation is detectable in the complex HI velocity field.
No metallicity gradient is detected in the old and intermediate age population
of the galaxy, and we confirm that this population has a much more extended
distribution than young stars (age Gyr).Comment: 11 pages, 14 figures, accepted for publication on A&A. arXiv admin
note: text overlap with arXiv:1404.169
The extended structure of the dwarf irregular galaxies Sextans A and Sextans B. Signatures of tidal distortion in the outskirts of the Local Group
We present a detailed study of the stellar and HI structure of the dwarf
irregular galaxies SextansA and SextansB, members of the NGC3109 association.
We use newly obtained deep (r~26.5) and wide field g,r photometry to extend the
Surface Brightness (SB) profiles of the two galaxies down to mu_V~ 31.0
mag/arcsec^2. We find that both galaxies are significantly more extended than
what previously traced with surface photometry, out to ~4 kpc from their
centers along their major axis. Older stars are found to have more extended
distribution with respect to younger populations. We obtain the first estimate
of the mean metallicity for the old stars in SexB, from the color distribution
of the Red Giant Branch, =-1.6. The SB profiles show significant
changes of slope and cannot be fitted with a single Sersic model. Both galaxies
have HI discs as massive as their respective stellar components. In both cases
the HI discs display solid-body rotation with maximum amplitude of ~50 km/s
(albeit with significant uncertainty due to the poorly constrained
inclination), implying a dynamical mass ~10^{9}~M_sun, a mass-to-light ratio
M/L_V~25 and a dark-to-barionic mass ratio of ~10. The distribution of the
stellar components is more extended than the gaseous disc in both galaxies. We
find that the main, approximately round-shaped, stellar body of Sex~A is
surrounded by an elongated low-SB stellar halo that can be interpreted as a
tidal tail, similar to that found in another member of the same association
(Antlia). We discuss these, as well as other evidences of tidal disturbance, in
the framework of a past passage of the NGC3109 association close to the Milky
Way, that has been hypothesized by several authors and is also supported by the
recently discovered filamentary configuration of the association itself.Comment: Accepted for publication by A&A. PdfLateX, 16 pages, 11 figures, 2
appendice
Assessment of Natural Resources Use for Sustainable Development - DPSIR Framework for Case Studies in Portsmouth and Thames Gateway, U.K.
This chapter reports on the uses of the DPSIR framework to assess the sustainability of the intertidal environments within the two UK case study areas, Portsmouth and Thames Gateway. It focuses on statutory conservation areas dominated by intertidal habitats. Two are located in Portsmouth (Portsmouth and Langstone Harbours) and four in the Thames Gateway (Benfleet Marshes, South Thames Estuary, Medway Estuary and the Swale in the Thames Gateway). Based on the reduction of a number of pressures and impacts observed in recent decades and the improvement of overall environmental quality, all six SSSIs are considered to be sustainable in the short and medium term. In the future, it is possible that the impacts of climate change, especially sea-level rise, might result in further reduction in the area and/or quality of intertidal habitats. Further integration between conservation and planning objectives (both for urban development and management of flood risk) at local level is needed to support the long-term sustainability of intertidal habitats
Lithium abundances in globular cluster giants: NGC 1904, NGC 2808, and NGC 362
The presence of multiple populations in globular clusters has been well
established thanks to high-resolution spectroscopy. It is widely accepted that
distinct populations are a consequence of different stellar generations:
intra-cluster pollution episodes are required to produce the peculiar chemistry
observed in almost all clusters. Unfortunately, the progenitors responsible
have left an ambiguous signature and their nature remains unresolved. To
constrain the candidate polluters, we have measured lithium and aluminium
abundances in more than 180 giants across three systems: NGC~1904, NGC~2808,
and NGC~362. The present investigation along with our previous analysis of M12
and M5 affords us the largest database of simultaneous determinations of Li and
Al abundances. Our results indicate that Li production has occurred in each of
the three clusters. In NGC~362 we detected an M12-like behaviour, with first
and second-generation stars sharing very similar Li abundances favouring a
progenitor that is able to produce Li, such as AGB stars. Multiple progenitor
types are possible in NGC~1904 and NGC~2808, as they possess both an
intermediate population comparable in lithium to the first generation stars and
also an extreme population, that is enriched in Al but depleted in Li. A simple
dilution model fails in reproducing this complex pattern. Finally, the internal
Li variation seems to suggest that the production efficiency of this element is
a function of the cluster's mass and metallicity - low-mass or relatively
metal-rich clusters are more adept at producing Li.Comment: Accepted for publication in MNRAS. 10 pages, 8 figure
HII regions within a compact high velocity cloud. A nearly star-less dwarf galaxy?
Within the SECCO survey we identified a candidate stellar counterpart to the
Ultra Compact High Velocity Cloud (UCHVC) HVC274.68+74.70-123, that was
suggested by Adams et al. (2013) as a possible mini-halo within the Local Group
of galaxies. The spectroscopic follow-up of the brightest sources within the
candidate reveals the presence of two HII regions whose radial velocity is
compatible with physical association with the UVHVC. The available data does
not allow us to give a definite answer on the nature of the newly identified
system. A few alternative hypotheses are discussed. However, the most likely
possibility is that we have found a new faint dwarf galaxy residing in the
Virgo cluster of galaxies, which we name SECCO-1. Independently of its actual
distance, SECCO-1 displays a ratio of neutral hydrogen mass to V luminosity of
M_{HI}/L_V>= 20, by far the largest among local dwarfs. Hence, it appears as a
nearly star-less galaxy and it may be an example of the missing links between
normal dwarfs and the dark mini halos that are predicted to exist in large
numbers according to the currently accepted cosmological model.Comment: Accepted for publication in ApJ Letters. Pdflatex, emulateapj.cls. 6
pages, 3 figures, 2 table
The StEllar Counterparts of COmpact high velocity clouds (SECCO) survey. I. Photos of ghosts
We present an imaging survey aimed at searching for the stellar counterparts
of recently discovered ultra-compact high-velocity HI clouds (UCHVC). Adams et
al. (2013) proposed these clouds to be candidate mini-haloes in the Local Group
and/or its surroundings, within a distance range of 0.25-2.0 Mpc. Using the
Large Binocular Telescope we obtain wide-field (~ 23' X 23') g- and r-band
images of the twenty-five most promising and most compact clouds among the
fifty-nine identified by Adams et al. Careful visual inspection of all the
images does not reveal any stellar counterpart even slightly resembling LeoP,
the only local dwarf galaxy that was found as a counterpart to a previously
detected high velocity cloud. Only a possible distant (D>3.0 Mpc) counterpart
to HVC274.68+74.70-123 has been identified on our images. The point source
photometry in the central 17.3' X 7.7' chips reaches r<= 26.5, and is expected
to contain most of the stellar counterparts to the UCHVCs. However, no obvious
stellar over-density is detected in any of our fields, in marked contrast to
our comparison LeoP field in which the dwarf galaxy is detected at a >30 sigma
significance level. Only HVC352.45+59.06+263 may be associated with a weak
over-density, whose nature cannot be ascertained with our data. Sensitivity
tests shows that our survey would have detected any dwarf galaxy dominated by
an old stellar population, with an integrated absolute magnitude M_V<= -8.0, a
half-light radius r_h<= 300 pc, and lying within 1.5 Mpc from us, thereby
confirming that it is unlikely that the observed UCHVCs are associated with
stellar counterparts typical of known Local Group dwarf galaxies.Comment: Accepted for publication by A&A. PdfLaTex. 24 pages, 27 figures.
Minor changes; A&A language editin
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