861 research outputs found
Dynamics of wide binary stars: A case study for testing Newtonian dynamics in the low acceleration regime
Extremely wide binary stars represent ideal systems to probe Newtonian
dynamics in the low acceleration regimes (<10e-10 m/s/s) typical of the
external regions of galaxies. Here we present a study of 60 alleged wide binary
stars with projected separation ranging from 0.004 to 1 pc, probing
gravitational accelerations well below the limit were dark matter or modified
dynamics theories set in. Radial velocities with accuracy ~100 m/s were
obtained for each star, in order to constrain their orbital velocity, that,
together with proper motion data, can distinguish bound from unbound systems.
It was found that about half of the observed pairs do have velocity in the
expected range for bound systems, out to the largest separations probed here.
In particular, we identified five pairs with projected separation >0.15 pc that
are useful for the proposed test. While it would be premature to draw any
conclusion about the validity of Newtonian dynamics at these low accelerations,
our main result is that very wide binary stars seem to exist in the harsh
environment of the solar neighborhood. This could provide a tool to test
Newtonian dynamics versus modified dynamics theories in the low acceleration
conditions typical of galaxies. In the near future the GAIA satellite will
provide data to increase significantly the number of wide pairs that, with the
appropriate follow up spectroscopic observations, will allow the implementation
of this experiment with unprecedented accuracy.Comment: Accepted for publication on International Journal of Modern Physics
Spectroscopy of 10 gamma-ray BL Lac objects at high redshift
We present high S/N optical spectra of 10 BL Lac objects detected at GeV
energies by Fermi satellite (3FGL catalog), for which previous observations
suggested that they are at relatively high redshift. The new observations,
obtained at the 10 m Gran Telescopio Canarias, allowed us to find the redshift
for J0814.5+2943 (z = 0.703) and we can set spectroscopic lower limit for
J0008.0+4713 (z>1.659) and J1107.7+0222 (z>1.0735) on the basis of Mg II
intervening absorption features. In addition we confirm the redshifts for
J0505.5+0416 (z=0.423) and for J1450+5200 (z>2.470). Finally we contradict the
previous z estimates for five objects (J0049.7+0237, J0243.5+7119,
J0802.0+1005, J1109.4+2411, and J2116.1+3339).Comment: 10 pages, 2 figures, 4 tables; accepted for publication in Ap
On the redshift of the very high energy {\gamma}-ray BL Lac object S2 0109+22
The determination of the redshift of extragalactic gamma ray sources is of
fundamental importance for the interpretation of their emission models and
extragalactic population studies, AGN classification schemes, and to study the
interaction with the extragalactic background light. Here we focus on the BL
Lac S2 0109+22, recently detected at very high energies. We obtained a high
signal-to-noise optical spectrum at Gran Telescopio Canarias for the source
over the spectral range 4000-10000 Angstrom, to search for spectral features of
the host galaxy and/or of the nuclear source and it was compared with previous
observations in order to confirm and/or dispute its redshift determination. We
find the S2 0109+22 optical spectrum is well represented by a power law
continuum without any absorption or emission feature of Equivalent Width >0.1
Angstrom. Based on the new optical spectrum we are able to set a redshift lower
limit z>0.35, assuming the source is hosted by a massive elliptical galaxy
typical for this class of sources. The redshift z=0.265 proposed in the
literature for this object is most probably referred to a r=18.3 galaxy at 15"
from S2 0109. This galaxy could belong to a group of faint galaxies located at
z~0.26.Comment: 5 pages, 5 figures; accepted on MNRA
Preclinical Modelling of PDA: Is Organoid the New Black?
Pancreatic ductal adenocarcinoma (PDA) is a malignancy of the exocrine pancreas with the worst prognosis among all solid tumours, and soon to become the second leading cause of cancer-related deaths. A more comprehensive understanding of the molecular mechanisms underlying this disease is crucial to the development of diagnostic tools as well as to the identification of more effective therapies. High-frequency mutations in PDA occur in "undruggable" genes, and molecular subtyping based on bulk transcriptome analysis does not yet nominate valid therapeutic intervention strategies. Genome-wide sequencing studies have also demonstrated a considerable intra- and inter-patient's genetic heterogeneity, which further complicate this dire scenario. More than in other malignancies, functionalization of the PDA genome and preclinical modelling at the individual patient level appear necessary to substantially improve survival rates for pancreatic cancer patients. Traditional human PDA models, including monolayer cell cultures and patient-derived xenografts, have certainly led to valuable biological insights in the past years. However, those model systems suffer from several limitations that have contributed to the lack of concordance between preclinical and clinical studies for PDA. Pancreatic ductal organoids have recently emerged as a reliable culture system to establish models from both normal and neoplastic pancreatic tissues. Pancreatic organoid cultures can be efficiently generated from small tissue biopsies, which opens up the possibility of longitudinal studies in individual patients. A proof-of-concept study has demonstrated that patient-derived PDA organoids are able to predict responses to conventional chemotherapy. The use of this three-dimensional culture system has already improved our understanding of PDA biology and promises to implement precision oncology by enabling the alignment of preclinical and clinical platforms to guide therapeutic intervention in PDA
The redshift of the BL Lac object TXS 0506+056
The bright BL Lac object TXS 0506+056 is a most likely counterpart of the
IceCube neutrino event EHE 170922A. The lack of this redshift prevents a
comprehensive understanding of the modeling of the source. We present high
signal-to-noise optical spectroscopy, in the range 4100-9000 ,
obtained at the 10.4m Gran Telescopio Canarias. The spectrum is characterized
by a power law continuum and is marked by faint interstellar features. In the
regions unaffected by these features, we found three very weak (EW 0.1
) emission lines that we identify with [O II] 3727
, [O III] 5007 , and [N II] 6583 ,
yielding the redshift z = 0.33650.0010.Comment: 7 pages, 3 figures, 2 tables; accepted for publication in ApJ
Circum-galactic medium in the halo of quasars
The properties of circum-galactic gas in the halo of quasar host galaxies are
investigated analyzing Mg II 2800 and C IV 1540 absorption-line systems along
the line of sight close to quasars. We used optical spectroscopy of closely
aligned pairs of quasars (projected distance 200 kpc, but at very
different redshift) obtained at the VLT and Gran Telescopio Canarias to
investigate the distribution of the absorbing gas for a sample of quasars at
z1. Absorption systems of EW 0.3 associated with the
foreground quasars are revealed up to 200 kpc from the centre of the host
galaxy, showing that the structure of the absorbing gas is patchy with a
covering fraction quickly decreasing beyond 100 kpc. In this contribution we
use optical and near-IR images obtained at VLT to investigate the relations
between the properties of the circum-galactic medium of the host galaxies and
of the large scale galaxy environments of the foreground quasars.Comment: 6 pages, 3 figures, proceedings of the conference "QUASARS at all
cosmic epochs", accepted for publication on Frontiers in Astronomy and Space
Scienc
Genetic abnormalities in pancreatic cancer
The incidence and mortality of pancreatic adenocarcinoma are nearly coincident having a five-year survival of less than 5%. Enormous advances have been made in our knowledge of the molecular alterations commonly present in ductal cancer and other pancreatic malignancies. One significant outcome of these studies is the recognition that common ductal cancers have a distinct molecular fingerprint compared to other nonductal or endocrine tumors. Ductal carcinomas typically show alteration of K-ras, p53, p16(INK4), DPC4 and FHIT, while other pancreatic tumor types show different aberrations. Among those tumors arising from the exocrine pancreas, only ampullary cancers have a molecular fingerprint that may involve some of the same genes most frequently altered in common ductal cancers. Significant molecular heterogeneity also exists among pancreatic endocrine tumors. Nonfunctioning pancreatic endocrine tumors have frequent mutations in MEN-1 and may be further subdivided into two clinically relevant subgroups based on the amount of chromosomal alterations. The present review will provide a brief overview of the genetic alterations that have been identified in the various subgroups of pancreatic tumors. These results have important implications for the development of genetic screening tests, early diagnosis, and prognostic genetic markers
HST Observations of the Optical Jets of PKS 0521-365, 3C371, and PKS 2201+044
HST observations have led to the discovery of the optical counterpart of the
radio jet of PKS 2201+044, and to a detailed analysis of the optical jets of
PKS 0521-365 and 3C371. At HST spatial resolution these jets are well resolved,
displaying knotty morphologies. When compared with radio maps of appropriate
resolution, a clear one-to-one correspondence between optical and radio
structures is found, showing that all detected optical structures are indeed
related to the radio synchrotron emission. Photometry of the brightest knots
shows that the radio-to-optical spectral index and the derived intensity of the
equipartition magnetic field are approximately constant along the jet. Thus,
present observations suggest that the electron energy distribution does not
change significantly all along the jet.Comment: Accepted for publications on the Astrphysical Journal. Contains 14
pages and 5 figure
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