307 research outputs found
A possibly inflated planet around the bright, young star DS Tuc A
The origin of the observed diversity of planetary system architectures is one
of the main topic of the exoplanetary research. The detection of a
statistically significant sample of planets around young stars allows us to
study the early stages of planet formation and evolution, but only a handful of
them is known so far. In this regard, a considerable contribution is expected
from the NASA TESS satellite, which is now performing a survey of
of the sky to search for short-period transiting planets In its first month of
operations, TESS found a planet candidate with an orbital period of 8.14 days
around a member of the Tuc-Hor young association ( 40 Myr), the G6V main
component of the binary system DS\,Tuc. If confirmed, it would be the first
transiting planet around a young star suitable for radial velocity and/or
atmospheric characterization. We aim to validate the planetary nature of this
companion and to measure its orbital and physical parameters. We obtain
accurate planet parameters by coupling an independent reprocessing of the TESS
light curve with improved stellar parameters and the dilution caused by the
binary companion; we analyse high precision archival radial velocities to
impose an upper limit of about 0.1 M on the planet mass; we finally
rule out the presence of external companions beyond 40 au with adaptive optics
images. We confirm the presence of a young, giant ( R) planet having a not negligible possibility to be inflated (theoretical
mass M) around DS\,Tuc~A. We discuss the feasibility
of mass determination, Rossiter-McLaughlin analysis and atmosphere
characterization, allowed by the brightness of the star.Comment: 12 pages, 11 figures. Accepted for publication in A&
The Asymptotic Giant Branches of GCs: Selective Entry Only
The handful of available observations of AGB stars in Galactic Globular
Clusters suggest that the GC AGB populations are dominated by cyanogen-weak
stars. This contrasts strongly with the distributions in the RGB (and other)
populations, which generally show a 50:50 bimodality in CN band strength. If it
is true that the AGB populations show very different distributions then it
presents a serious problem for low mass stellar evolution theory, since such a
surface abundance change going from the RGB to AGB is not predicted by stellar
models. However this is only a tentative conclusion, since it is based on very
small AGB sample sizes. To test whether this problem really exists we have
carried out an observational campaign specifically targeting AGB stars in GCs.
We have obtained medium resolution spectra for about 250 AGB stars across 9
Galactic GCs using the multi-object spectrograph on the AAT (2df/AAOmega). We
present some of the preliminary findings of the study for the second parameter
trio of GCs: NGC 288, NGC 362 and NGC 1851. The results indeed show that there
is a deficiency of stars with strong CN bands on the AGB. To confirm that this
phenomenon is robust and not just confined to CN band strengths and their
vagaries, we have made observations using FLAMES/VLT to measure elemental
abundances for NGC 6752.We present some initial results from this study also.
Our sodium abundance results show conclusively that only a subset of stars in
GCs experience the AGB phase of evolution. This is the first direct, concrete
confirmation of the phenomenon.Comment: 4 pages, to appear in conference proceedings of "Reading the book of
globular clusters with the lens of stellar evolution", Rome, 26-28 November
201
Glucose restriction induces cell death in parental but not in homeodomain-interacting protein kinase 2-depleted RKO colon cancer cells: molecular mechanisms and implications for tumor therapy.
Tumor cell tolerance to nutrient deprivation can be an important factor for tumor progression, and may depend on deregulation of both oncogenes and oncosuppressor proteins. Homeodomain-interacting protein kinase 2 (HIPK2) is an oncosuppressor that, following its activation by several cellular stress, induces cancer cell death via p53-dependent or -independent pathways. Here, we used genetically matched human RKO colon cancer cells harboring wt-HIPK2 (HIPK2(+/+)) or stable HIPK2 siRNA interference (siHIPK2) to investigate in vitro whether HIPK2 influenced cell death in glucose restriction. We found that glucose starvation induced cell death, mainly due to c-Jun NH2-terminal kinase activation, in HIPK2(+/+)cells compared with siHIPK2 cells that did not die. (1)H-nuclear magnetic resonance quantitative metabolic analyses showed a marked glycolytic activation in siHIPK2 cells. However, treatment with glycolysis inhibitor 2-deoxy-D-glucose induced cell death only in HIPK2(+/+) cells but not in siHIPK2 cells. Similarly, siGlut-1 interference did not re-establish siHIPK2 cell death under glucose restriction, whereas marked cell death was reached only after zinc supplementation, a condition known to reactivate misfolded p53 and inhibit the pseudohypoxic phenotype in this setting. Further siHIPK2 cell death was reached with zinc in combination with autophagy inhibitor. We propose that the metabolic changes acquired by cells after HIPK2 silencing may contribute to induce resistance to cell death in glucose restriction condition, and therefore be directly relevant for tumor progression. Moreover, elimination of such a tolerance might serve as a new strategy for cancer therapy
A study of the prevalence and genotypes of Giardia duodenalis infecting kennelled dogs
Giardia duodenalis is a protozoan parasite of animals that is zoonotic. Given the capacity of this organism to spread via the faecal–oral
route, animals held in overcrowded and unhygienic conditions are at high risk of infection. Faecal samples from dogs in three kennels in
Rome were examined by microscopy and PCR for G. duodenalis, and the prevalence data generated were correlated with variables such
as kennel identity, age of dog, length of time the dog had been kennelled and clinical signs.
The overall prevalence of the parasite in the faecal samples was 20.5% and was higher in samples from the largest kennel, which had
the greatest turnover of dogs, and in faecal samples from younger animals. Giardia cysts were found more frequently in diarrhoeic animals
but were also found in dogs with no clinical signs. Although the finding that the majority of isolates were dog-specific rather than
zoonotic genotypes suggests that the zoonotic risk from this pathogen is less than previously thought, the higher prevalence of infection
in younger dogs may pose a specific public health issue as such animals are more frequently re-homed with families.
2008 Elsevier Ltd. All rights reserved
The origin of R CrA variability: A complex triple system hosting a disk
R~CrA is the brightest member of the Coronet star forming region and it is
the closest Herbig AeBe star with a spectrum dominated by emission lines. Its
luminosity has been monitored since the end of the 19th century, but the origin
of its variability, which shows a stable period of ~days, is
still unknown. We studied photometric and spectroscopic data for this star to
investigate the nature of the variability of R~CrA. We exploited the fact that
near infrared luminosity of the Herbig AeBe stars is roughly proportional to
the total luminosity of the stars to derive the absorption, and then mass and
age of R~CrA. In addition, we model the periodic modulation of the light curve
as due to partial attenuation of a central binary by a circumbinary disk. This
model reproduces very well the observations. We found that the central object
in R~CrA is a very young (~Myr), highly absorbed (~mag) binary; we obtain masses of ~M and
~M for the two components. We propose that the
secular decrease of the R~CrA apparent luminosity is due to a progressive
increase of the disk absorption. This might be related to precession of a
slightly inclined disk caused by the recently discovered M-dwarf companion.
Thus, R~CrA may be a triple system hosting a disk.Comment: Accepted for publication in A&A. 14 pages, 11 figure
AF Lep b: the lowest mass planet detected coupling astrometric and direct imaging data
Aims. Using the direct imaging technique we searched for low mass companions
around the star AF Lep that presents a significant proper motion anomaly (PMa)
signal obtained from the comparison of Hipparcos and Gaia eDR3 catalogs.
Methods. We observed AF Lep in two epochs with VLT/SPHERE using its subsystems
IFS and IRDIS in the near-infrared (NIR) covering wavelengths ranging from the
Y to the K spectral bands (between 0.95 and 2.3 {\mu}m). The data were then
reduced using the high-contrast imaging techniques angular differential imaging
(ADI) and spectral differential imaging (SDI) to be able to retrieve the signal
from low mass companions of the star. Results. A faint companion was retrieved
at a separation of ~0.335" from the star and with a position angle of ~70.5 deg
in the first epoch and with a similar position in the second epoch. This
corresponds to a projected separation of ~9 au. The extracted photometry
allowed us to estimate for the companion a mass between 2 and 5 MJup. This mass
is in good agreement with what is expected for the dynamic mass of the
companion deduced using astrometric measures (5.2-5.5 MJup). This is the first
companion with a mass well below the deuterium burning limit discovered
coupling direct imaging with PMa measures. Orbit fitting done using the orvara
tool allowed to further confirm the companion mass and to define its main
orbital parameters.Comment: 10 pages, 8 Figures, accepted for publication on A&
A new white dwarf companion to the star GJ 3346
We present the discovery of a white dwarf companion at 3.6" from GJ3346, a
nearby (42 mas) K star observed with SPHERE@VLT as part of an open
time survey for faint companions to objects with significant proper motion
discrepancies () between Gaia DR1 and Tycho-2. Syrius-like systems
like GJ3346AB, which include a main sequence star and a white dwarf, can be
difficult to detect because of the intrinsic faintness of the latter. They
have, however, been found to be common contaminants for direct imaging
searches. White dwarfs have in fact similar brightness to sub-stellar
companions in the infrared, while being much brighter in the visible bands like
those used by Gaia. Combining our observations with Gaia DR2 and with several
additional archival data sets, we were able to fully constrain the physical
properties of GJ3346B, such as its effective temperature
(1110500 K) as well as the cooling age of the system (64858
Myrs). This allowed us to better understand the system history and to partially
explains the discrepancies previously noted in the age indicators for this
objects. Although further investigation is still needed, it seems that GJ3346,
which was previously classified as young, is in fact most likely to be older
than 4 Gyrs. Finally, given that the mass (0.580.01)} and
separation (85 au) of GJ3346B are compatible with the observed ,
this discovery represents a further confirmation of the potential of this kind
of dynamical signatures as selection methods for direct imaging surveys
targeting faint, sub-stellar companions.Comment: 10 pages, 7 figure
Prevalence and genotyping of human isolates of Giardia duodenalis from Albania
Microscopical and PCR-based techniques were performed in order to investigate the prevalence of infection and the genotypes of Giardia duodenalis from 125 stool samples collected from children living in the urban and the rural areas of Tirana (Albania) and hospitalized with acute gastroenteritis. 7 out of 125 samples resulted positive for Giardia at the microscopic examination (5.6%). In 50 selected samples including the 7 samples positive for Giardia by microscopy, 3 and 15 additional positive samples were detected by immunofluorescence and PCR, respectively. Seasonality appeared as an important parameter to be evaluated in order to better understand the prevalence of infection. Sequence analysis revealed both human Assemblage A and B. This result represents the first data on G. duodenalis genotypes in Albania. (c) 2006 Elsevier Ireland Ltd. All rights reserved
Characterizing HR3549B using SPHERE
Aims. In this work, we characterize the low mass companion of the A0 field
star HR3549. Methods. We observed HR3549AB in imaging mode with the the NIR
branch (IFS and IRDIS) of SPHERE@VLT, with IFS in YJ mode and IRDIS in the H
band. We also acquired a medium resolution spectrum with the IRDIS long slit
spectroscopy mode. The data were reduced using the dedicated SPHERE GTO
pipeline, purposely designed for this instrument. We employed algorithms such
as PCA and TLOCI to reduce the speckle noise. Results. The companion was
clearly visible both with IRDIS and IFS.We obtained photometry in four
different bands as well as the astrometric position for the companion. Based on
our astrometry, we confirm that it is a bound object and put constraints on its
orbit. Although several uncertainties are still present, we estimate an age of
~100-150 Myr for this system, yielding a most probable mass for the companion
of 40-50MJup and T_eff ~300-2400 K. Comparing with template spectra points to a
spectral type between M9 and L0 for the companion, commensurate with its
position on the color-magnitude diagram.Comment: Accepted by A&A, 13 pages, 10 Figures (Figures 9 and 10 degraded to
reduce the dimension
The VLT/NaCo Large program to probe the occurrence of exoplanets and brown dwarfs in wide orbits: I- Sample definition and characterization
Young, nearby stars are ideal targets to search for planets using the direct
imaging technique. The determination of stellar parameters is crucial for the
interpretation of imaging survey results particularly since the luminosity of
substellar objects has a strong dependence on system age. We have conducted a
large program with NaCo at the VLT in order to search for planets and brown
dwarfs in wide orbits around 86 stars. A large fraction of the targets observed
with NaCo were poorly investigated in the literature. We performed a study to
characterize the fundamental properties (age, distance, mass) of the stars in
our sample. To improve target age determinations, we compiled and analyzed a
complete set of age diagnostics. We measured spectroscopic parameters and age
diagnostics using dedicated observations acquired with FEROS and CORALIE
spectrographs at La Silla Observatory. We also made extensive use of archival
spectroscopic data and results available in the literature. Additionally, we
exploited photometric time-series, available in ASAS and Super-WASP archives,
to derive rotation period for a large fraction of our program stars. We
provided updated characterization of all the targets observed in the VLT NaCo
Large program, a survey designed to probe the occurrence of exoplanets and
brown dwarfs in wide orbits. The median distance and age of our program stars
are 64 pc and 100 Myr, respectively. Nearly all the stars have masses between
0.70 and 1.50sun, with a median value of 1.01 Msun. The typical metallicity is
close to solar, with a dispersion that is smaller than that of samples usually
observed in radial velocity surveys. Several stars are confirmed or proposed
here to be members of nearby young moving groups. Eight spectroscopic binaries
are identified.Comment: 64 pages with Appendix, 15 figures, accepted to A&
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