144 research outputs found
Evidence for Variable, Correlated X-ray and Optical/IR Extinction toward the Nearby, Pre-main Sequence Binary TWA 30
We present contemporaneous XMM-Newton X-ray and ground-based optical/near-IR
spectroscopic observations of the nearby ( pc), low-mass (mid-M)
binary system TWA 30A and 30B. The components of this wide (separation
3400 AU) binary are notable for their nearly edge-on disk viewing
geometries, high levels of variability, and evidence for collimated stellar
outflows. We obtained XMM-Newton X-ray observations of TWA 30A and 30B in 2011
June and July, accompanied (respectively) by IRTF SpeX (near-IR) and VLT
XSHOOTER (visible/near-IR) spectroscopy obtained within 20 hours of the
X-ray observations. TWA 30A was detected in both XMM-Newton observations at
relatively faint intrinsic X-ray luminosities (
) compared to stars of similar mass and age . The intrinsic
(0.15-2.0 keV) X-ray luminosities measured in 2011 had decreased by a factor
20-100 relative to a 1990 (ROSAT) X-ray detection. TWA 30B was not detected,
and we infer an upper limit of ( 3.0 erg
s). We measured a large change in visual extinction toward TWA 30A (from
to ) between the two 2011 observing epochs,
and we find evidence for a corresponding significant decrease in X-ray
absorbing column (). The apparent correlated change in and is
suggestive of variable obscuration of the stellar photosphere by disk material
composed of both gas and dust. However, in both observations, the inferred
to ratio is lower than that typical of the ISM, suggesting that
the disk is either depleted of gas or is deficient in metals in the gas phase.Comment: 10 pages, 7 figures, Accepted for publication in MNRA
X-shooter spectroscopy of young stellar objects: I - Mass accretion rates of low-mass T Tauri stars in \sigma Orionis
We present high-quality, medium resolution X-shooter/VLT spectra in the range
300-2500 nm for a sample of 12 very low-mass stars in the \sigma Orionis
cluster. The sample includes stars with masses ranging from 0.08 to 0.3
M. The aim of this first paper is to investigate the reliability of the
many accretion tracers currently used to measure the mass accretion rate in
low-mass, young stars. We use our spectra to measure the accretion luminosity
from the continuum excess emission in the UV and visual; the derived mass
accretion rates range from 10 M yr down to
5 M yr, allowing us to investigate the
behavior of the accretion-driven emission lines in very-low mass accretion rate
regimes. We compute the luminosity of ten accretion-driven emission lines, from
the UV to the near-IR, obtained simultaneously. Most of the secondary tracers
correlate well with the accretion luminosity derived from the continuum excess
emission. We confirm the validity of the correlations between accretion
luminosities and line luminosities given in the literature, with the possible
exception of H\alpha. When looking at individual objects, we find that the
Hydrogen recombination lines, from the UV to the near-IR, give good and
consistent measurements of accretion luminosities, often in better agreement
than the uncertainties introduced by the adopted correlations. The average
accretion luminosity derived from several Hydrogen lines, measured
simultaneously, have a much reduced error. This suggests that some of the
spread in the literature correlations may be due to the use of non-simultaneous
observations of lines and continuum. Three stars in our sample deviate from
this behavior, and we discuss them individually.Comment: 15 pages, 14 figure
Confirming Accretion in Mylupi with UV-HST Observations
The mass accretion rate is a crucial parameter for the study of the evolution of accretion discs around young low-mass stellar and substellar objects (YSOs), because it sets important constraints for disc evolution models and disc clearing mechanisms, and is a key quantity for the studies of Pre-Main Sequence (PMS) stellar evolution and planet formation. Low-mass PMS stars with transitional discs accreting at very low rates are likely in the final stages of inner disc evolution, and probably have already formed protoplanets. Hence, identifying and investigating such low accretors may help understanding planet formation. However, measurements of low accretion rates are challenging. In this work, we use UV-HST spectra to unambiguously confirm and investigate the accretion rate in the transitional YSO MYLup, an object previously classified as a weak or non-accretor based on optical spectra. The puzzle here is that the HST data provide a Macc value an orde
Thermorresponsive magnetic nanoparticles as target drug delivery for cancer treatment
In this research, temperature sensitive microgels with magnetic core for controlled release of 5-fluoruracil was synthesized. Magnetic nanoparticles (Fe3O4) were prepared by coprecipitation method and the surface was functionalized by acrylic acid. Polymer poly(N-isopropylacrylamide) (PNIPAM) were grown by free radical polymerization in presence of cross-liker and initiator. The size of the polymer was manipulated by changing the mole percent of the crosslinker and evaluated for their morphology (TEM), particle size, zeta potential, loading efficiency, drug content and drug release. Furthermore, microgels were tagged with FITC, a fluorochrome which could be applied for cell imaging. Cytotoxicity studies revealed that the microgels were not toxic. These complex nanoparticles (Fe3O4/pNIPAM/FITC/5-Fu) appear to be a great promise to be used in controlled drug delivery and tumor targeting.Universidad de Málaga. Campus de Excelencia Internacional AndalucÃa Tech
Synthesis of New Analogues of the Bengamides to encapsulate in magnetic nanoparticles
The development and identification of new antitumoral has become a research area of great interest and maximum priority due to secondary effects of current antitumoral and the appearance of tumours resistant to these agents. Marine sponges corresponding to the Jaspidae family have proved to be a prolific source of bioactive natural products. Among these, the Bengamides have showed an important biological profile, including antitumor, antibiotic and anthelmintic properties. Due to the interest of theses natural products, we describe a study directed towards the total synthesis of this class of compounds. Then we encapsulate Bengamides in temperature sensitive microgels with a magnetic core. Magnetic nanoparticles (Fe3O 4) were prepared by coprecipitation method and the surface was functionalized by acrylic acid. Polymer poly(N-isopropylacrylamide) (PNIPAM) were grown by free radical polymerization in presence of cross-liker and initiator.Universidad de Málaga. Campus de Excelencia Internacional AndalucÃa Tec
Search for young stars among ROSAT All-Sky Survey X-ray sources in and around the R CrA dark cloud
We present the ROSAT All-Sky Survey data in a 126 deg^2 area in and around
the CrA star forming region. With low-resolution spectroscopy of unidentified
ROSAT sources we could find 19 new pre-main sequence stars, two of which are
classical T Tauri stars, the others being weak-lined. The spectral types of
these new T Tauri stars range from F7 to M6. The two new classical T Tauri
stars are located towards two small cloud-lets outside of the main CrA cloud.
They appear to be ~10 Myrs old, by comparing their location in the H-R diagram
with isochrones for an assumed distance of 130 pc, the distance of the main CrA
dark cloud. The new off-cloud weak-line T Tauri stars may have formed in
similar cloud-lets, which have dispersed recently. High-resolution spectra of
our new T Tauri stars show that they have significantly more lithium absorption
than zero-age main-sequence stars of the same spectral type, so that they are
indeed young. From those spectra we also obtained rotational and radial
velocities. For some stars we found the proper motion in published catalogs.
The direction and velocity of the 3D space motion - south relative to the
galatic plane - of the CrA T Tauri stars is consistent with the dark cloud
being formed originally by a high-velocity cloud impact onto the galactic
plane, which triggered the star formation in CrA. We also present VRIJHK
photometry for most of the new T Tauri stars to derive their luminosities,
ages, and masses.Comment: A&A Suppl. in pres
The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. XI. Lupus Observed With IRAC and MIPS
We present c2d Spitzer/IRAC observations of the Lupus I, III and IV dark
clouds and discuss them in combination with optical and near-infrared and c2d
MIPS data. With the Spitzer data, the new sample contains 159 stars, 4 times
larger than the previous one. It is dominated by low- and very-low mass stars
and it is complete down to M 0.1M. We find 30-40 % binaries
with separations between 100 to 2000 AU with no apparent effect in the disk
properties of the members. A large majority of the objects are Class II or
Class III objects, with only 20 (12%) of Class I or Flat spectrum sources. The
disk sample is complete down to ``debris''-like systems in stars as small as M
0.2 M and includes sub-stellar objects with larger IR
excesses. The disk fraction in Lupus is 70 -- 80%, consistent with an age of 1
-- 2 Myr. However, the young population contains 20% optically thick accretion
disks and 40% relatively less flared disks. A growing variety of inner disk
structures is found for larger inner disk clearings for equal disk masses.
Lupus III is the most centrally populated and rich, followed by Lupus I with a
filamentary structure and by Lupus IV, where a very high density core with
little star-formation activity has been found. We estimate star formation rates
in Lupus of 2 -- 10 M Myr and star formation efficiencies of a
few percent, apparently correlated with the associated cloud masses.Comment: Accepted for publication in the ApJS. Contains 101 pages, 23 figures,
and 13 tables. A version with full resolution figures can be found at
http://peggysue.as.utexas.edu/SIRTF/PAPERS/pap102.pub.pd
ReForm: A Tool for Rapid Requirements Formalization
Formal methods practices can sometimes be challenging to adopt in industrial environments. On the other hand, the need for formalization and verification in the design of complex systems is now more evident than ever. To the end of easing integration of formal methods in industrial model based system engineering workflows, UTRC Ireland has developed a tool aiming to render requirements formalization as effortless as possible to the industrial engineer. The developed approach is an end-to-end solution, starting with natural language requirements as input and going all the way down to auto-generated monitors in MATLAB / Simulink. We employ natural language processing and machine learning techniques for (semi-)automatic pattern extraction from requirements, which drastically reduces the required formalization workload for both legacy and new requirements. For monitor generation, we provide our own approach which outperforms existing state-of-the-art tools by orders of magnitude in some cases
Effect of Y2O3 addition on the microstructure and mechanical properties of an Al1.8CoCrCu0.5FeNi BCC HEA
The present study investigated the influence of Y2O3 addition by mechanical alloying (MA) on the microstructure evolution of a BCC High Entropy Alloy (HEA). The characterisation and mechanical properties of the alloy were explored using X-ray diffraction, SEM, EBSD, and nano-indentation. The sintered Al1.8CoCrCu0.5FeNi HEA shows a microstructure formed by an ordered BCC phase (Al-rich) and a second disordered BCC (Cr-rich), while a minor FCC (Cu-rich) appears. These BCC phases show a wide morphology evolution from cuboidal and wave-like structures to irregular shapes. The minor FCC phase also adopts several morphologies as the MA is performed. The introduction of oxide reinforcements and microstructure refinement through mechanical alloying yields a change in phase quantification and grain structure. In accordance with the hardness and elastic modulus values from ordered/disordered BCC phases, the disordered BCC shows higher values than the ordered one. The grain size reduction as well as the solid solution strengthening from the microstructure evolution consequence of the MA are shown to be the main contributors to the increase in hardness and elastic modulus in the consolidated samples.This research was supported by the Regional Government of Madrid under the programme S2018/NMT-4381-MAT4.0-CM project. Funding from PID2019-109334RB-C32 awarded by the Spanish Ministry of Science, Innovation and Universities is also acknowledged. J. Cornide also acknowledges funding from the Spanish Ministry of Science and Innovation (IJCI-2017-31348) and TED2021-130831B-I00 funded by MCIN/AEI/10.13039/501100011033 and NextGenerationEU/PRTR. Funding for APC: Universidad Carlos III de Madrid (Read & Publish Agreement CRUE-CSIC 2023)
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