343 research outputs found
A PSF-based approach to Kepler/K2 data. I. Variability within the K2 Campaign 0 star clusters M 35 and NGC 2158
Kepler and K2 data analysis reported in the literature is mostly based on
aperture photometry. Because of Kepler's large, undersampled pixels and the
presence of nearby sources, aperture photometry is not always the ideal way to
obtain high-precision photometry and, because of this, the data set has not
been fully exploited so far. We present a new method that builds on our
experience with undersampled HST images. The method involves a point-spread
function (PSF) neighbour-subtraction and was specifically developed to exploit
the huge potential offered by the K2 "super-stamps" covering the core of dense
star clusters. Our test-bed targets were the NGC 2158 and M 35 regions observed
during the K2 Campaign 0. We present our PSF modeling and demonstrate that, by
using a high-angular-resolution input star list from the Asiago Schmidt
telescope as the basis for PSF neighbour subtraction, we are able to reach
magnitudes as faint as Kp~24 with a photometric precision of 10% over 6.5
hours, even in the densest regions. At the bright end, our photometric
precision reaches ~30 parts-per-million. Our method leads to a considerable
level of improvement at the faint magnitudes (Kp>15.5) with respect to the
classical aperture photometry. This improvement is more significant in crowded
regions. We also extracted raw light curves of ~60,000 stars and detrended them
for systematic effects induced by spacecraft motion and other artifacts that
harms K2 photometric precision. We present a list of 2133 variables.Comment: 27 pages (included appendix), 2 tables, 25 figures (5 in low
resolution). Accepted for publication in MNRAS on November 05, 2015. Online
materials will be available on the Journal website soo
Hubble Space Telescope astrometry of the closest brown dwarf binary system -- I. Overview and improved orbit
Located at ~2pc, the L7.5+T0.5 dwarfs system WISE J104915.57-531906.1
(Luhman16AB) is the third closest system known to Earth, making it a key
benchmark for detailed investigation of brown dwarf atmospheric properties,
thermal evolution, multiplicity, and planet-hosting frequency. In the first
study of this series -- based on a multi-cycle Hubble Space Telescope (HST)
program -- we provide an overview of the project and present improved estimates
of positions, proper motions, annual parallax, mass ratio, and the current best
assessment of the orbital parameters of the A-B pair. Our HST observations
encompass the apparent periastron of the binary at 220.5+/-0.2 mas at epoch
2016.402. Although our data seem to be inconsistent with recent ground-based
astrometric measurements, we also exclude the presence of third bodies down to
Neptune masses and periods longer than a year.Comment: 19 pages, 9 figures, 9 tables. Accepted for publication in MNRAS on
2017 May
High-precision astrometry with VVV. I. An independent reduction pipeline for VIRCAM@VISTA
We present a new reduction pipeline for the VIRCAM@VISTA detector and
describe the method developed to obtain high-precision astrometry with the
VISTA Variables in the V\'ia L\'actea (VVV) data set. We derive an accurate
geometric-distortion correction using as calibration field the globular cluster
NGC 5139, and showed that we are able to reach a relative astrometric precision
of about 8 mas per coordinate per exposure for well-measured stars over a field
of view of more than 1 square degree. This geometric-distortion correction is
made available to the community. As a test bed, we chose a field centered
around the globular cluster NGC 6656 from the VVV archive and computed proper
motions for the stars within. With 45 epochs spread over four years, we show
that we are able to achieve a precision of 1.4 mas/yr and to isolate each
population observed in the field (cluster, Bulge and Disk) using proper
motions. We used proper-motion-selected field stars to measure the motion
difference between Galactic disk and bulge stars. Our proper-motion
measurements are consistent with UCAC4 and PPMXL, though our errors are much
smaller. Models have still difficulties in reproducing the observations in this
highly-reddened Galactic regions.Comment: 11 pages, 10 figures (some in low res), 1 table. Accepted for
publication in MNRAS on March 25, 2015. The FORTRAN routine will be soon made
available at http://groups.dfa.unipd.it/ESPG/ , and via email request to the
first autho
Variable stars in one open cluster within the Kepler/K2-Campaign-5 field: M 67 (NGC 2682)
In this paper we continue the release of high-level data products from the
multiyear photometric survey collected at the 67/92 cm Schmidt Telescope in
Asiago. The primary goal of the survey is to discover and to characterise
variable objects and exoplanetary transits in four fields containing five
nearby open clusters spanning a broad range of ages. This second paper releases
a photometric catalogue, in five photometric bands, of the Solar-age,
Solar-metallicity open cluster M 67 (NGC 2682). Proper motions are derived
comparing the positions observed in 2013 at the Asiago's Schmidt Telescope with
those extracted from [email protected] MPG/ESO images in 2000. We also analyse the
variable sources within M 67. We detected 68 variables, 43 of which are new
detection. Variable periods and proper-motion memberships of a large majority
of sources in our catalogue are improved with respect to previous releases. The
entire catalogue will be available in electronic format. Besides the general
interest on an improved catalogue, this work will be particularly useful
because of: (1) the imminent release of Kepler/K2 Campaign-5 data of this
cluster, for which our catalogue will provide an excellent, high spatial
resolution input list, and (2) characterisation of the M 67 stars which are
targets of intense HARPS and HARPS-N radial-velocity surveys for planet search.Comment: 8 pages, 6 figures (2 at low resolution), 2 tables. Accepted for
publication in MNRAS on October 17, 2015. Electronic materials available at
the url http://groups.dfa.unipd.it/ESPG/M67.html , and later on the Journal
and at the CD
Super adsorbent bio-polymer additive to improve hygroscopic and acoustic properties of a conventional lime plaster
The paper introduces a new lime plaster composition, with a Super Bio-Polymeric Adsorbent (SABP), for interior applications to improve hygrothermal and acoustic comfort. Alginate SABP is added to a conventional lime plaster to improve hygroscopic and acoustic performance. The hygrothermal and acoustic properties of the modified plaster are compared with the ones of the original plaster with a preliminary moisture uptake test, the evaluation of the sorption isotherm, the moisture buffering value (MBV), and the acoustic absorption. The results show a significant increase in the equilibrium moisture contents and the MBV (from 0.7 to 6.2 g/(m2 ...%RH)). At the same time, the sound absorption coefficient is slightly improved, increasing 0.1-0.2 at frequencies higher than 500 Hz compared to the reference conventional lime plaster. The paper describes the material characterization: the sorption isotherm and the MBV are obtained using a dynamic vapor sorption (DVS) analyzer. The acoustic absorption is measured using the impedance tube method
Biodegradation of Plastics Induced by Marine Organisms: Future Perspectives for Bioremediation Approaches
Plastic pollution is a distinctive element of the globalized world. In fact, since the 1970s the expansion and use of plastics, particularly in the consumer and commercial sectors, has given this material a permanent place in our lives. The increasing use of plastic products and the wrong management of end-of-life plastic products have contributed to increasing environmental pollution, with negative impacts on our ecosystems and the ecological functions of natural habitats. Nowadays, plastic pollution is pervasive in all environmental compartments. As aquatic environments are the dumping points for poorly managed plastics, biofouling and biodegradation have been proposed as promising approaches for plastic bioremediation. Known for the high stability of plastics in the marine environment, this represents a very important issue to preserve marine biodiversity. In this review, we have summarized the main cases reported in the literature on the degradation of plastics by bacteria, fungi, and microalgae and the degradation mechanisms involved, to highlight the potential of bioremediation approaches to reduce macro and microplastic pollution
A bag of tricks: Using proper motions of Galactic stars to identify the Hercules ultra-faint dwarf galaxy members
Hercules is the prototype of the ultra-faint dwarf (UFD) galaxies. To date,
there are still no firm constraints on its total luminosity, due to the
difficulty of disentangling Hercules bona-fide stars from the severe Galactic
field contamination. In order to better constrain Hercules properties we aim at
removing foreground and background contaminants in the galaxy field using the
proper motions of the Milky Way stars and the colour-colour diagram. We have
obtained images of Hercules in the rSloan, BBessel and Uspec bands with the
Large Binocular Telescope (LBT) and LBC-BIN mode capabilities. The rSloan new
data-set combined with data from the LBT archive span a time baseline of about
5 yr, allowing us to measure for the first time proper motions of stars in the
Hercules direction. The Uspec data along with existing LBT photometry allowed
us to use colour-colour diagram to further remove the field contamination.
Thanks to a highly-accurate procedure to derive the rSloan-filter geometric
distortion solution for the LBC-red, we were able to measure stellar relative
proper motions to a precision of better than 5 mas yr^-1 down to rSloan=22 mag
and disentangle a significant fraction (\>90\%) of Milky Way contaminants. We
ended up with a sample of 528 sources distributed over a large portion of the
galaxy body (0.12 deg^2). Of these sources, 171 turned out to be background
galaxies and additional foreground stars, from the analysis of the Uspec -
BBessel vs. BBessel - rSloan colour-colour diagram. This leaves us with a
sample of 357 likely members of the Hercules UFD. We compared the cleaned
colour-magnitude diagram (CMD) with evolutionary models and synthetic CMDs,
confirming the presence in Hercules of an old population (t=12\pm 2 Gyr), with
a wide spread in metallicity (-3.3\<[Fe/H]\<-1.8).Comment: 16 pages, 15 figures, 3 tables, accepted for publication in A&
Biofilms: Novel strategies based on antimicrobial peptides
The problem of drug resistance is very worrying and ever increasing. Resistance is due not only to the reckless use of antibiotics but also to the fact that pathogens are able to adapt to different conditions and develop self-defense mechanisms such as living in biofilms; altogether these issues make the search for alternative drugs a real challenge. Antimicrobial peptides appear as promising alternatives but they have disadvantages that do not make them easily applicable in the medical field; thus many researches look for solutions to overcome the disadvantages and ensure that the advantages can be exploited. This review describes the biofilm characteristics and identifies the key features that antimicrobial peptides should have. Recalcitrant bacterial infections caused by the most obstinate bacterial species should be treated with a strategy to combine conventional peptides functionalized with nano-tools. This approach could effectively disrupt high density infections caused by biofilms. Moreover, the importance of using in vivo non mammalian models for biofilm studies is described. In particular, here we analyze the use of amphibians as a model to substitute the rodent model
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