741 research outputs found
Early Spectra of the Gravitational Wave Source GW170817: Evolution of a Neutron Star Merger
On 2017 August 17, Swope Supernova Survey 2017a (SSS17a) was discovered as
the optical counterpart of the binary neutron star gravitational wave event
GW170817. We report time-series spectroscopy of SSS17a from 11.75 hours until
8.5 days after merger. Over the first hour of observations the ejecta rapidly
expanded and cooled. Applying blackbody fits to the spectra, we measure the
photosphere cooling from K to K,
and determine a photospheric velocity of roughly 30% of the speed of light. The
spectra of SSS17a begin displaying broad features after 1.46 days, and evolve
qualitatively over each subsequent day, with distinct blue (early-time) and red
(late-time) components. The late-time component is consistent with theoretical
models of r-process-enriched neutron star ejecta, whereas the blue component
requires high velocity, lanthanide-free material.Comment: 33 pages, 5 figures, 2 tables, Accepted to Scienc
The Absolute Magnitude of RRc Variables From Statistical Parallax
We present the first definitive measurement of the absolute magnitude of RR
Lyrae c-type variable stars (RRc) determined purely from statistical parallax.
We use a sample of 247 RRc selected from the All Sky Automated Survey (ASAS)
for which high-quality light curves, photometry and proper motions are
available. We obtain high-resolution echelle spectra for these objects to
determine radial velocities and abundances as part of the Carnegie RR Lyrae
Survey (CARRS). We find that M_(V,RRc) = 0.52 +/- 0.11 at a mean metallicity of
[Fe/H] = -1.59. This is to be compared with previous estimates for RRab stars
(M_(V,RRab) = 0.75 +/- 0.13 and the only direct measurement of an RRc absolute
magnitude (RZ Cephei, M_(V, RRc) = 0.27 +/- 0.17). We find the bulk velocity of
the halo to be (W_pi, W_theta, W_z) = (10.9,34.9,7.2) km/s in the radial,
rotational and vertical directions with dispersions (sigma_(W_pi),
sigma_(W_theta), sigma_(W_z)) = (154.7, 103.6, 93.8) km/s. For the disk, we
find (W_pi, W_theta, W_z) = (8.5, 213.2, -22.1) km/s with dispersions
(sigma_(W_pi), sigma_(W_theta), sigma_(W_z)) = (63.5, 49.6, 51.3) km/s.
Finally, we suggest that UCAC2 proper motion errors may be overestimated by
about 25%Comment: Submitted to ApJ. 11 pages including 6 figure
Lucky Imaging Adaptive Optics of the brown dwarf binary GJ569Bab
The potential of combining Adaptive Optics (AO) and Lucky Imaging (LI) to
achieve high precision astrometry and differential photometry in the optical is
investigated by conducting observations of the close 0\farcs1 brown dwarf
binary GJ569Bab. We took 50000 -band images with our LI instrument FastCam
attached to NAOMI, the 4.2-m William Herschel Telescope (WHT) AO facility. In
order to extract the most of the astrometry and photometry of the GJ569Bab
system we have resorted to a PSF fitting technique using the primary star
GJ569A as a suitable PSF reference which exhibits an -band magnitude of
. The AO+LI observations at WHT were able to resolve the binary
system GJ569Bab located at 4\farcs 92 \pm 0\farcs05 from GJ569A. We measure a
separation of mas and -band magnitudes of
and and colors of 2.720.08 and 2.830.08 for
the Ba and Bb components, respectively. Our study rules out the presence of any
other companion to GJ569A down to magnitude I 17 at distances larger than
1\arcsec. The colors measured are consistent with M8.5-M9 spectral types
for the Ba and Bb components. The available dynamical, photometric and
spectroscopic data are consistent with a binary system with Ba being slightly
(10-20%) more massive than Bb. We obtain new orbital parameters which are in
good agreement with those in the literature.Comment: 13 pages, 9 figures, 7 tables, in press in MNRA
The Distance to NGC 1316 (Fornax A) From Observations of Four Type Ia Supernovae
The giant elliptical galaxy NGC 1316 (Fornax A) is a well-studied member of
the Fornax Cluster and a prolific producer of Type Ia supernovae, having hosted
four observed events since 1980. Here we present detailed optical and
near-infrared light curves of the spectroscopically normal SN 2006dd. These
data are used, along with previously published photometry of the normal SN
1980N and SN 1981D, and the fast-declining, low-luminosity SN 2006mr, to
compute independent estimates of the host reddening for each supernova, and the
distance to NGC 1316. From the three normal supernovae, we find a distance of
17.8 +/- 0.3 (random) +/- 0.3 (systematic) Mpc for Ho = 72. Distance moduli
derived from the "EBV" and Tripp methods give values that are mutually
consistent to 4 -- 8%. Moreover, the weighted means of the distance moduli for
these three SNe for three methods agree to within 3%. This consistency is
encouraging and supports the premise that Type Ia supernovae are reliable
distance indicators at the 5% precision level or better. On the other hand, the
two methods used to estimate the distance of the fast-declining SN 2006mr both
yield a distance to NGC 1316 which is 25-30% larger. This disparity casts doubt
on the suitability of fast-declining events for estimating extragalactic
distances. Modest-to-negligible host galaxy reddening values are derived for
all four supernovae. Nevertheless, two of them (SN 2006dd and SN 2006mr) show
strong NaID interstellar lines in the host galaxy system. The strength of this
absorption is completely inconsistent with the small reddening values derived
from the supernova light curves if the gas in NGC 1316 is typical of that found
in the interstellar medium of the Milky Way. In addition, the equivalent width
of the NaID lines in SN 2006dd appear to have weakened significantly some
100-150 days after explosion.Comment: 50 pages, 13 figures, 10 tables; constructive comments welcome.
Accepted for publication in A
Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis
On 2017 August 17, gravitational waves were detected from a binary neutron
star merger, GW170817, along with a coincident short gamma-ray burst,
GRB170817A. An optical transient source, Swope Supernova Survey 17a (SSS17a),
was subsequently identified as the counterpart of this event. We present
ultraviolet, optical and infrared light curves of SSS17a extending from 10.9
hours to 18 days post-merger. We constrain the radioactively-powered transient
resulting from the ejection of neutron-rich material. The fast rise of the
light curves, subsequent decay, and rapid color evolution are consistent with
multiple ejecta components of differing lanthanide abundance. The late-time
light curve indicates that SSS17a produced at least ~0.05 solar masses of heavy
elements, demonstrating that neutron star mergers play a role in r-process
nucleosynthesis in the Universe.Comment: Accepted to Scienc
Injectable alginate hydrogel loaded with GDNF promotes functional recovery in a hemisection model of spinal cord injury
We hypothesized that local delivery of GDNF in spinal cord lesion via an injectable alginate hydrogel gelifying in situ would support spinal cord plasticity and functional recovery. The GDNF release from the hydrogel was slowed by GDNF encapsulation in microspheres compared to non-formulated GDNF (free GDNF). When injected in a rat spinal cord hemisection model, more neurofilaments were observed in the lesion when the rats were treated with free GDNF-loaded hydrogels. More growing neurites were detected in the tissues surrounding the lesion when the animals were treated with GDNF microsphere-loaded hydrogels. Intense GFAP (astrocytes), low III tubulin (neural cells) and RECA-1 (endothelial cells) stainings were observed for non-treated lesions while GDNF-treated spinal cords presented less GFAP staining and more endothelial and nerve fiber infiltration in the lesion site. The animals treated with free GDNF-loaded hydrogel presented superior functional recovery compared with the animals treated with the GDNF microsphere-loaded hydrogels and non-treated animals
On the origin of [Ne II] emission in young stars: mid-infrared and optical observations with the Very Large Telescope
{Abridged version for ArXiv}. We provide direct constraints on the origin of
the [Ne II] emission in 15 young stars using high-spatial and spectral
resolution observations with VISIR at the VLT that allow us to study the
kinematics of the emitting gas. In addition we compare the [Ne II] line with
optical forbidden lines observed for three stars with UVES. The [Ne II] line
was detected in 7 stars, among them the first confirmed detection of [Ne II] in
a Herbig Be star, V892 Tau. In four cases, the large blueshifted lines indicate
an origin in a jet. In two stars, the small shifts and asymmetric profiles
indicate an origin in a photo-evaporative wind. CoKu Tau 1, seen close to
edge-on, shows a spatially unresolved line centered at the stellar rest
velocity, although cross-dispersion centroids move within 10 AU from one side
of the star to the other as a function of wavelength. The line profile is
symmetric with wings extending up to about +-80 km/s. The origin of the [Ne II]
line could either be due to the bipolar jet or to the disk. For the stars with
VLT-UVES observations, in several cases, the optical forbidden line profiles
and shifts are very similar to the profile of the [Ne II] line, suggesting that
the lines are emitted in the same region. A general trend observed with VISIR
is a lower line flux when compared with the fluxes obtained with Spitzer. We
found no correlation between the line full-width at half maximum and the line
peak velocity. The [Ne II] line remains undetected in a large part of the
sample, an indication that the emission detected with Spitzer in those stars is
likely extended.Comment: Accepted for publication in Astronomy & Astrophysics; revised
version: corrected minor typos, corrected center values (col 3) for CoKuTau1
in Table
PEGylated-PLGA microparticles containing VEGF for long term drug delivery
The potential of poly(lactic-co-glycolic) acid (PLGA) microparticles as carriers for vascular endothelial growth factor (VEGF) has been demonstrated in a previous study by our group, where we found improved angiogenesis and heart remodeling in a rat myocardial infarction model (Formiga et al., 2010). However, the observed accumulation of macrophages around the injection site suggested that the efficacy of treatment could be reduced due to particle phagocytosis.
The aim of the present study was to decrease particle phagocytosis and consequently improve protein delivery using stealth technology. PEGylated microparticles were prepared by the double emulsion solvent evaporation method using TROMS (Total Recirculation One Machine System). Before the uptake studies in monocyte-macrophage cells lines (J774 and Raw 264.7), the characterization of the microparticles developed was carried out in terms of particle size, encapsulation efficiency, protein stability, residual poly(vinyl alcohol) (PVA) and in vitro release. Microparticles of suitable size for intramyocardial injection (5 mu m) were obtained by TROMS by varying the composition of the formulation and TROMS conditions with high encapsulation efficiency (70-90%) and minimal residual PVA content (0.5%). Importantly, the bioactivity of the protein was fully preserved. Moreover, PEGylated microparticles released in phosphate buffer 50% of the entrapped protein within 4 h, reaching a plateau within the first day of the in vitro study. Finally, the use of PLGA microparticles coated with PEG resulted in significantly decreased uptake of the carriers by macrophages, compared with non PEGylated microparticles, as shown by flow cytometry and fluorescence microscopy.
On the basis of these results, we concluded that PEGylated microparticles loaded with VEGF could be used for delivering growth factors in the myocardium
Sustained release of VEGF through PLGA microparticles improves vasculogenesis and tissue remodeling in an acute myocardial ischemiaâreperfusion model
The use of pro-angiogenic growth factors in ischemia models has been associated with limited success in the
clinical setting, in part owing to the short lived effect of the injected cytokine. The use of a microparticle
system could allow localized and sustained cytokine release and consequently a prolonged biological effect
with induction of tissue revascularization. To assess the potential of VEGF165 administered as continuous
release in ischemic disease, we compared the effect of delivery of poly(lacticâco-glycolic acid) (PLGA)
microparticles (MP) loaded with VEGF165 with free-VEGF or control empty microparticles in a rat model of
ischemiaâreperfusion. VEGF165 loaded microparticles could be detected in the myocardium of the infarcted
animals for more than a month after transplant and provided sustained delivery of active protein in vitro and
in vivo. One month after treatment, an increase in angiogenesis (small caliber caveolin-1 positive vessels)
and arteriogenesis (α-SMA-positive vessels) was observed in animals treated with VEGF microparticles
(pb0.05), but not in the empty microparticles or free-VEGF groups. Correlating with this data, a positive
remodeling of the heart was also detected in the VEGF-microparticle group with a significantly greater LV
wall thickness (pb0.01). In conclusion, PLGA microparticle is a feasible and promising cytokine delivery
system for treatment of myocardial ischemia. This strategy could be scaled up and explored in pre-clinical
and clinical studies
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