68 research outputs found
Evaluating the stability of atmospheric lines with HARPS
Context: In the search for extrasolar systems by radial velocity technique, a
precise wavelength calibration is necessary for high-precision measurements.
The choice of the calibrator is a particularly important question in the
infra-red domain, where the precision and exploits still fall behind the
achievements of the optical.
Aims: We investigate the long-term stability of atmospheric lines as a
precise wavelength reference and analyze their sensitivity to different
atmospheric and observing conditions.
Methods: We use HARPS archive data on three bright stars, Tau Ceti, Mu Arae
and Epsilon Eri, spanning 6 years and containing high-cadence measurements over
several nights. We cross-correlate this data with an O2 mask and evaluate both
radial velocity and bisector variations down to a photon noise of 1 m/s.
Results: We find that the telluric lines in the three data-sets are stable
down to 10 m/s (r.m.s.) over the 6 years. We also show that the radial velocity
variations can be accounted for by simple atmospheric models, yielding a final
precision of 1-2 m/s.
Conclusions: The long-term stability of atmospheric lines was measured as
being of 10 m/s over six years, in spite of atmospheric phenomena. Atmospheric
lines can be used as a wavelength reference for short-time-scales programs,
yielding a precision of 5 m/s "out-of-the box". A higher precision, down to 2
m/s can be reached if the atmospheric phenomena are corrected for by the simple
atmospheric model described, making it a very competitive method even on long
time-scales.Comment: 7 pages, accepted for publication in A&
Decellularized skeletal muscles display neurotrophic effects in threeâdimensional organotypic cultures
Skeletal muscle decellularization allows the generation of natural scaffolds that retain the extracellular matrix (ECM) mechanical integrity, biological activity, and threeâdimensional (3D) architecture of the native tissue. Recent reports showed that in vivo implantation of decellularized muscles supports muscle regeneration in volumetric muscle loss models, including nervous system and neuromuscular junctional homing. Since the nervous system plays pivotal roles during skeletal muscle regeneration and in tissue homeostasis, support of reinnervation is a crucial aspect to be considered. However, the effect of decellularized muscles on reinnervation and on neuronal axon growth has been poorly investigated. Here, we characterized residual protein composition of decellularized muscles by mass spectrometry and we show that scaffolds preserve structural proteins of the ECM of both skeletal muscle and peripheral nervous system. To investigate whether decellularized scaffolds could per se attract neural axons, organotypic sections of spinal cord were cultured three dimensionally in vitro, in presence or in absence of decellularized muscles. We found that neural axons extended from the spinal cord are attracted by the decellularized muscles and penetrate inside the scaffolds upon 3D coculture. These results demonstrate that decellularized scaffolds possess intrinsic neurotrophic properties, supporting their potential use for the treatment of clinical cases where extensive functional regeneration of the muscle is required
Radial Velocities with CRIRES: Pushing precision down to 5-10 m/s
With the advent of high-resolution infrared spectrographs, Radial Velocity
(RV) searches enter into a new domain. As of today, the most important
technical question to address is which wavelength reference is the most
suitable for high-precision RV measurements.
In this work we explore the usage of atmospheric absorption features. We make
use of CRIRES data on two programs and three different targets. We re-analyze
the data of the TW Hya campaign, reaching a dispersion of about 6 m/s on the RV
standard in a time scale of roughly 1 week. We confirm the presence of a
low-amplitude RV signal on TW Hya itself, roughly 3 times smaller than the one
reported at visible wavelengths. We present RV measurements of Gl 86 as well,
showing that our approach is capable of detecting the signal induced by a
planet and correctly quantifying it.
Our data show that CRIRES is capable of reaching a RV precision of less than
10 m/s in a time-scale of one week. The limitations of this particular approach
are discussed, and the limiting factors on RV precision in the IR in a general
way. The implications of this work on the design of future dedicated IR
spectrographs are addressed as well.Comment: 9 pages, accepted for publication in A&
Cepheid Period-Radius and Period-Luminosity Relations and the Distance to the LMC
We have used the infrared Barnes-Evans surface brightness technique to derive
the radii and distances of 34 Galactic Cepheid variables. Radius and distance
results obtained from both versions of the technique are in excellent
agreement. The radii of 28 variables are used to determine the period-radius
relation. This relation is found to have a smaller dispersion than in previous
studies, and is identical to the period-radius relation found by Laney & Stobie
from a completely independent method, a fact which provides persuasive evidence
that the Cepheid period-radius relation is now determined at a very high
confidence level. We use the accurate infrared distances to determine
period-luminosity relations in the V, I, J, H and K passbands from the Galactic
sample of Cepheids. We derive improved slopes of these relations from updated
LMC Cepheid samples and adopt these slopes to obtain accurate absolute
calibrations of the PL relation. By comparing these relations to the ones
defined by the LMC Cepheids, we derive strikingly consistent and precise values
for the LMC distance modulus in each of the passbands which yield a mean value
of DM (LMC) = 18.46 +- 0.02.
Our results show that the infrared Barnes-Evans technique is very insensitive
to both Cepheid metallicity and adopted reddening, and therefore a very
powerful tool to derive accurate distances to nearby galaxies by a direct
application of the technique to their Cepheid variables, rather than by
comparing PL relations of different galaxies, which introduces much more
sensitivity to metallicity and absorption corrections which are usually
difficult to determine.Comment: LaTeX, AASTeX style, 9 Figures, 10 Tables, The Astrophysical Journal
in press (accepted Oct. 14, 1997). Fig. 3 replace
Radii and Distances of Cepheids, I., Method and Measurement Errors
We develop a formulation of the Baade-Wesselink method which uses the Fourier
coefficients of the observables. We derive an explicit, analytic expression to
determine the mean radius from each Fourier order. The simplicity of this
method allows us to derive the uncertainty in the mean radius due to
measurement errors.
Using simulations and a recent dataset we demonstrate that the precision of
the radius measurement with optical magnitudes is in most cases limited by the
accuracy of the measurement of the phase difference between the light and the
color index curve. In this case it is advantageous to determine the inverse
radius, because it has normal errors.Comment: 18 pages, postscript, accepted for publication in Ap
Optical spectroscopic variability of Herbig Ae/Be stars
We analysed 337 multi-epoch optical spectra of 38 Herbig Ae/Be (HAeBe) stars
to gain insights into the variability behaviour of the circumstellar (CS)
atomic gas. Equivalent widths (EWs) and line fluxes of the Halpha, [OI]6300,
HeI5876 and NaID lines were obtained for each spectrum; the Halpha line width
at 10% of peak intensity (W10) and profile shapes were also measured and
classified. The mean line strengths and relative variabilities were quantified
for each star. Simultaneous optical photometry was used to estimate the line
fluxes.
We present a homogeneous spectroscopic database of HAeBe stars. The lines are
variable in practically all stars and timescales, although 30 % of the objects
show a constant EW in [OI]6300, which is also the only line that shows no
variability on timescales of hours. The HeI5876 and NaID EW relative
variabilities are typically the largest, followed by those in [OI]6300 and
Halpha. The EW changes can be larger than one order of magnitude for the
HeI5876 line, and up to a factor 4 for Halpha. The [OI]6300 and Halpha EW
relative variabilities are correlated for most stars in the sample. The Halpha
mean EW and W10 are uncorrelated, as are their relative variabilities. The
Halpha profile changes in 70 % of the objects. The massive stars in the sample
usually show more stable Halpha profiles with blueshifted self-absorptions and
less variable 10% widths.
Our data suggest multiple causes for the different line variations, but the
[OI]6300 and Halpha variability must share a similar origin in many objects.
The physical mechanism responsible for the Halpha line broadening does not
depend on the amount of emission; unlike in lower-mass stars, physical
properties based on the Halpha luminosity and W10 would significantly differ.
Our results provide additional support to previous works that reported
different physical mechanisms in Herbig Ae and Herbig Be stars.Comment: 10 pages, 5 figures, 2 appendixe
High precision effective temperatures for 181 F--K dwarfs from line-depth ratios
Line depth ratios measured on high resolution (R=42000), high S/N echelle
spectra are used for the determination of precise effective temperatures of 181
F,G,K Main Sequence stars with about solar metallicity (-0.5 < [Fe/H] < +0.5).
A set of 105 relations is obtained which rely Teff on ratios of the strengths
of lines with high and low excitation potentials, calibrated against previously
published precise (1%) temperature estimates. The application range of the
calibrations is 4000--6150 K (F8V--K7V). The internal error of a single
calibration is less than 100 K, while the combination of all calibrations for a
spectrum of S/N=100 reduces uncertainty to only 5-10 K, and for S/N=200 or
higher, to better than 5 K. The zero point of the temperature scale is directly
defined from reflection spectra of the Sun with an uncertainty about 1 K. The
application of this method to investigation of the planet host stars properties
is discussed.Comment: 9 pages, accepted for publication in A&
Allogenic tissue-specific decellularized scaffolds promote long-term muscle innervation and functional recovery in a surgical diaphragmatic hernia model
Congenital diaphragmatic hernia (CDH) is a neonatal defect in which the diaphragm muscle does not develop properly, thereby raising abdominal organs into the thoracic cavity and impeding lung development and function. Large diaphragmatic defects require correction with prosthetic patches to close the malformation. This treatment leads to a consequent generation of unwelcomed mechanical stress in the repaired diaphragm and hernia recurrences, thereby resulting in high morbidity and significant mortality rates. We proposed a specific diaphragm-derived extracellular matrix (ECM) as a scaffold for the treatment of CDH. To address this strategy, we developed a new surgical CDH mouse model to test the ability of our tissue-specific patch to regenerate damaged diaphragms. Implantation of decellularized diaphragmatic ECM-derived patches demonstrated absence of rejection or hernia recurrence, in contrast to the performance of a commercially available synthetic material. Diaphragm-derived ECM was able to promote the generation of new blood vessels, boost long-term muscle regeneration, and recover host diaphragmatic function. In addition, using a GFPâŻ+âŻSchwann cell mouse model, we identified re-innervation of implanted patches. These results demonstrated for the first time that implantation of a tissue-specific biologic scaffold is able to promote a regenerating diaphragm muscle and overcome issues commonly related to the standard use of prosthetic materials
Modeling the Subsurface Structure of Sunspots
While sunspots are easily observed at the solar surface, determining their
subsurface structure is not trivial. There are two main hypotheses for the
subsurface structure of sunspots: the monolithic model and the cluster model.
Local helioseismology is the only means by which we can investigate
subphotospheric structure. However, as current linear inversion techniques do
not yet allow helioseismology to probe the internal structure with sufficient
confidence to distinguish between the monolith and cluster models, the
development of physically realistic sunspot models are a priority for
helioseismologists. This is because they are not only important indicators of
the variety of physical effects that may influence helioseismic inferences in
active regions, but they also enable detailed assessments of the validity of
helioseismic interpretations through numerical forward modeling. In this paper,
we provide a critical review of the existing sunspot models and an overview of
numerical methods employed to model wave propagation through model sunspots. We
then carry out an helioseismic analysis of the sunspot in Active Region 9787
and address the serious inconsistencies uncovered by
\citeauthor{gizonetal2009}~(\citeyear{gizonetal2009,gizonetal2009a}). We find
that this sunspot is most probably associated with a shallow, positive
wave-speed perturbation (unlike the traditional two-layer model) and that
travel-time measurements are consistent with a horizontal outflow in the
surrounding moat.Comment: 73 pages, 19 figures, accepted by Solar Physic
Generation of a Functioning and Self-Renewing Diaphragmatic Muscle Construct
Surgical repair of large muscular defects requires the use of autologous graft transfer or prosthetic material. Naturally derived matrices are biocompatible materials obtained by tissue decellularization and are commonly used in clinical practice. Despite promising applications described in the literature, the use of acellular matrices to repair large defects has been only partially successful, highlighting the need for more efficient constructs. Scaffold recellularization by means of tissue engineering may improve not only the structure of the matrix, but also its ability to functionally interact with the host. The development of such a complex construct is challenging, due to the complexity of the native organ architecture and the difficulties in recreating the cellular niche with both proliferative and differentiating potential during growth or after damage. In this study, we tested a mouse decellularized diaphragmatic extracellular matrix (ECM) previously described by our group, for the generation of a cellular skeletal muscle construct with functional features. The decellularized matrix was stored using different conditions to mimic the offâtheâshelf clinical need. Pediatric human muscle precursors were seeded into the decellularized scaffold, demonstrating proliferation and differentiation capability, giving rise to a functioning threeâdimensional skeletal muscle structure. Furthermore, we exposed the engineered construct to cardiotoxin injury and demonstrated its ability to activate a regenerative response in vitro promoting cell selfârenewal and a positive ECM remodeling. Functional reconstruction of an engineered skeletal muscle with maintenance of a stem cell pool makes this a promising tool toward future clinical applications in diaphragmatic regeneratio
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