1,054 research outputs found
Gaia view of low-mass star formation
Understanding how young stars and their circumstellar disks form and evolve
is key to explain how planets form. The evolution of the star and the disk is
regulated by different processes, both internal to the system or related to
their environment. The former include accretion of material onto the central
star, wind emission, and photoevaporation of the disk due to high-energy
radiation from the central star. These are best studied spectroscopically, and
the distance to the star is a key parameter in all these studies. Here we
present new estimates of the distance to a complex of nearby star-forming
clouds obtained combining TGAS distances with measurement of extinction on the
line of sight. Furthermore, we show how we plan to study the effects of the
environment on the evolution of disks with Gaia, using a kinematic modelling
code we have developed to model young star-forming regions.Comment: 4 pages, 1 figure. To appear in the Proceedings of IAU Symposium 330:
Astrometry and Astrophysics in the Gaia Sk
Searching for physics beyond the Standard Model in the decay B+ -> K+K+pi-
The observation potential of the decay B+ -> K+K+pi- with the ATLAS detector
at LHC is described in this paper. In the Standard Model this decay mode is
highly suppressed, while in models beyond the Standard Model it could be
significantly enhanced. To improve the selection of the K+K+pi- final state, a
charged hadron identification using Time-over-Threshold measurements in the
ATLAS Transition Radiation Tracker was developed and used.Comment: 12 pages, 4 figures, 1 tabl
X-Shooter spectroscopy of young stellar objects in Lupus. Atmospheric parameters, membership and activity diagnostics
A homogeneous determination of basic stellar parameters of young stellar
object (YSO) candidates is needed to confirm their evolutionary stage,
membership to star forming regions (SFRs), and to get reliable values of the
quantities related to chromospheric activity and accretion. We used the code
ROTFIT and synthetic BT-Settl spectra for the determination of the atmospheric
parameters (Teff and logg), the veiling, the radial (RV) and projected
rotational velocity (vsini), from X-Shooter spectra of 102 YSO candidates in
the Lupus SFR. We have shown that 13 candidates can be rejected as Lupus
members based on their discrepant RV with respect to Lupus and/or the very low
logg values. At least 11 of them are background giants. The spectral
subtraction of inactive templates enabled us to measure the line fluxes for
several diagnostics of both chromospheric activity and accretion. We found that
all Class-III sources have H fluxes compatible with a pure
chromospheric activity, while objects with disks lie mostly above the boundary
between chromospheres and accretion. YSOs with transitional disks displays both
high and low H fluxes. We found that the line fluxes per unit surface
are tightly correlated with the accretion luminosity () derived
from the Balmer continuum excess. This rules out that the relationships between
and line luminosities found in previous works are simply due to
calibration effects. We also found that the CaII-IRT flux ratio,
, is always small, indicating an optically thick emission
source. The latter can be identified with the accretion shock near the stellar
photosphere. The Balmer decrement reaches instead, for several accretors, high
values typical of optically thin emission, suggesting that the Balmer emission
originates in different parts of the accretion funnels with a smaller optical
depth.Comment: 28 pages, 26 figures, accepted by A&
Mapping young stellar populations towards Orion with Gaia DR1
We use the first data release of the Gaia mission to explore the three
dimensional arrangement and the age ordering of the many stellar groups towards
the Orion OB association, aiming at a new classification and characterization
of the stellar population. We make use of the parallaxes and proper motions
provided in the Tycho Gaia Astrometric Solution (TGAS) sub-set of the Gaia
catalogue, and of the combination of Gaia and 2MASS photometry. In TGAS we find
evidence for the presence of a young population, at a parallax , loosely distributed around some known clusters: 25 Ori,
Ori and Ori, and NGC 1980 ( Ori). The low mass
counterpart of this population is visible in the color-magnitude diagrams
constructed by combining Gaia and 2MASS photometry. We study the density
distribution of the young sources in the sky. We find the same groups as in
TGAS, and also some other density enhancements that might be related to the
recently discovered Orion X group, the Orion dust ring, and to the
Ori complex. We estimate the ages of this population and we infer the presence
of an age gradient going from 25 Ori (13-15 Myr) to the ONC (1-2 Myr). We
confirm this age ordering by repeating the Bayesian fit using the Pan-STARRS1
data. The estimated ages towards the NGC 1980 cluster span a broad range of
values. This can either be due to the presence of two populations coming from
two different episodes of star formation or to a large spread along the line of
sight of the same population. Our results form the first step towards using the
Gaia data to unravel the complex star formation history of the Orion region in
terms of the different star formation episodes, their duration, and their
effects on the surrounding interstellar medium.Comment: 17 pages, 17 figure
Pengaruh Tata Ruang Kelas dan Media Visual terhadap Minat Belajar Fisika Peserta Didik Kelas VIII MTs Madani Alauddin Paopao
Penelitian ini bertujuan untuk menggambarkan pengaruh tata ruang kelas dan media visual terhadap minat belajar fisika peserta didik kelas VIII MTs Madani Alauddin Paopao. Populasi dalam penelitian ini adalah peserta didik kelas VIII MTs Madani Alauddin Pao-pao sebanyak 49 orang dan sampel pada penelitian ini berjumlah 49 orang. Instrumen pengumpulan data yang digunakan adalah lembar observasi untuk penataan ruang kelas dan media visual dan angket untuk minat belajar fisika. Data tersebut kemudian di analisis dengan menggunakan regresi berganda. Berdasarkan hasil penelitian dan analisis deskriptif diperoleh skor rata-rata tata ruang kelas adalah 62 termasuk dalam kategori cukup dan skor rata-rata penggunaan media visual adalah 56 termasuk dalam kategori cukup,serta skor rata-rata minat belajar fisika adalah 61 termasuk dalam kategori tinggi. Adapun hasil analisis inferensial menunjukkan nilai Fhitung adalah 585,9 sedangkan Ftabel pada taraf signifikansi 5% adalah 3,20. Dengan demikian, nilai Fhitung lebih besar dari pada nilai Ftabel dan hipotesis nol ditolak, artinya terdapat pengaruh yang signifikan antara tata ruang kelas dan media visual teradap minat belajar fisika peserta didik kelas VIII MTs Madani Alauddin Paopao
Pengaruh Gaya Kepemimpinan Transformasional Dan Iklim Organisasi Terhadap Komitmen Organisasi
This study aimed to determine the effect of transformational leadership style and organizational climate on organizational commitment. Subjects were employees and lecturers at the University of Setia Budi Surakarta as many as 65 people. Data analysis used regression analysis techniques. Analisisis results showed a correlation coefficient (R) of 0.760 with F of 42.386 p = 0.000 (p <0.01) which means that there was a highly significant correlation between transformational leadership and organizational climate on organizational commitment. Determinant coefficient (R2) of 57.8%, this indicates that the variables of transformational leadership and organizational commitment affected organizational climate by 57.8% and 42.2% were influenced by other variables
DNA sequencing with MspA: molecular dynamics simulations reveal free-energy differences between sequencing and non-sequencing mutants
MspA has been identified as a promising candidate protein as a component of a nanopore-based DNA-sequencing device. However the wildtype protein must be engineered to incorporate all of the features desirable for an accurate and efficient device. In the present study we have utilized atomistic molecular dynamics to perform umbrella-sampling calculations to calculate the potential of mean force (PMF) profiles for translocation of the four DNA nucleotides through MspA. We show there is an energetic barrier to translocation of individual nucleotides through a mutant that closely resembles the wildtype protein, but not through a mutant engineered for the purpose of sequencing. Crucially we are able to quantify the change in free energy for mutating key residues. Thus providing a quantitative characterisation of the energetic impact of individual amino acid sidechains on nucleotide translocation through the pore of MspA
X-shooter spectroscopy of young stellar objects in Lupus: Lithium, iron, and barium elemental abundances
With the purpose of performing a homogeneous determination of elemental
abundances for members of the Lupus T association, we analyzed three chemical
elements: lithium, iron, and barium. The aims were: to derive the Li abundance
for ~90% of known class II stars in the Lupus I, II, III, IV clouds; to perform
chemical tagging of a region where few Fe abundance measurements have been
obtained in the past, and no determination of the Ba content has been done up
to now. We also investigated possible Ba enhancement, as this element has
become increasingly interesting in the last years following the evidence of Ba
over-abundance in young clusters, the origin of which is still unknown. Using
X-shooter@VLT, we analyzed the spectra of 89 cluster members, both class II and
III stars. We measured the strength of the Li line and derived the abundance of
this element through equivalent width measurements and curves of growth. For
six class II stars we also measured the Fe and Ba abundances using the spectral
synthesis and the code MOOG. The veiling contribution was taken into account
for all three elements. We find a dispersion in the strength of the Li line at
low Teff and identify three targets with severe Li depletion. The nuclear age
inferred for these highly Li-depleted stars is around 15 Myr, which exceeds the
isochronal one. As in other star-forming regions, no metal-rich members are
found in Lupus, giving support to a recent hypothesis that the Fe abundance
distribution of most of the nearby young regions could be the result of a
common and widespread star formation episode involving the Galactic thin disk.
We find that Ba is over-abundant by ~0.7 dex with respect to the Sun. Since
current theoretical models cannot reproduce this Ba abundance pattern, we
investigated whether this unusually large Ba content might be related to
effects due to stellar parameters, stellar activity, and accretion.Comment: 15 pages, 14 figures, 3 tables; accepted for publication in A&A;
abstract shortene
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