22,798 research outputs found
SPECIES I: Spectroscopic Parameters and atmosphEric ChemIstriEs of Stars
The detection and subsequent characterisation of exoplanets are intimately
linked to the characteristics of their host star. Therefore, it is necessary to
study the star in detail in order to understand the formation history and
characteristics of their companion(s). Our aims were to develop a community
tool that allows the automated calculation of stellar parameters for a large
number of stars, using high resolution echelle spectra and minimal photometric
magnitudes, and introduce the first results in this work. We measured the
equivalent widths of several iron lines and used them to solve the radiative
transfer equation assuming local thermodynamic equilibrium to obtain the
atmospheric parameters (, [Fe/H], logg and ). We used
these values to derive the abundance of 11 chemical elements in the stellar
photosphere (Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Ni, Cu and Zn). Rotation and
macroturbulent velocity were obtained using temperature calibrators and
synthetic line profiles to match the observed spectra of five absorption lines.
Finally, by interpolating in a grid of MIST isochrones, we derived the mass,
radius and age using a Bayesian approach. SPECIES obtains bulk parameters that
are in good agreement with measured values from different existing catalogues,
including when different methods are used to derive them. We find excellent
agreement with previous works that used similar methodologies. We find
discrepancies in the chemical abundances for some elements with respect to
other works, which could be produced by differences in , or in
the line list or the atomic line data used to derive them. We also obtained
analytic relations to describe the correlations between different parameters,
and we implemented new methods to better handle these correlations, which
provides a better description of the uncertainties associated with the
measurements.Comment: 28 pages, 26 figures, resubmitted to A&
Aspects of Nucleon Chiral Perturbation Theory
I review recent progress made in the calculation of nucleon properties in the
framework of heavy baryon CHPT. Topics include: Compton scattering,
scattering, the anatomy of a low-energy constant and the induced pseudoscalar
form factor.Comment: plain TeX (macro included), 12pp, lecture delivered at the workshop
on "Chiral Dynamics: Theory and Experiments", MIT, July 25-29, 199
Baryon magnetic moments in chiral perturbation theory
We consider the chiral expansion of the octet baryon magnetic moments in
heavy baryon chiral perturbation theory including all terms which are of order
. These terms are formally of quadratic order in the quark masses. We show
that despite the large non-analytic quark mass corrections to the
Coleman-Glashow relations at order , including all analytic and
non-analytic corrections at order , which in total are of moderate size,
allows for a fit to the measured magnetic moments due to the appearance of
counter terms with free coupling constants of natural size. In this scheme, the
transition moment is predicted to be .Comment: 20 pp, LaTeX file, 2 figures (uses epsf), corrected versio
Effective field theory and the quark model
We analyze the connections between the quark model (QM) and the description
of hadrons in the low-momentum limit of heavy-baryon effective field theory in
QCD. By using a three-flavor-index representation for the effective baryon
fields, we show that the ``nonrelativistic'' constituent QM for baryon masses
and moments is completely equivalent through O(m_s) to a parametrization of the
relativistic field theory in a general spin--flavor basis. The flavor and spin
variables can be identified with those of effective valence quarks. Conversely,
the spin-flavor description clarifies the structure and dynamical
interpretation of the chiral expansion in effective field theory, and provides
a direct connection between the field theory and the semirelativistic models
for hadrons used in successful dynamical calculations. This allows dynamical
information to be incorporated directly into the chiral expansion. We find, for
example, that the striking success of the additive QM for baryon magnetic
moments is a consequence of the relative smallness of the non-additive
spin-dependent corrections.Comment: 25 pages, revtex, no figure
Large N_c, Constituent Quarks, and N, Delta Charge Radii
We show how one may define baryon constituent quarks in a rigorous manner,
given physical assumptions that hold in the large-N_c limit of QCD. This
constituent picture gives rise to an operator expansion that has been used to
study large-N_c baryon observables; here we apply it to the case of charge
radii of the N and Delta states, using minimal dynamical assumptions. For
example, one finds the relation r_p^2 - r_{Delta^+}^2 = r_n^2 - r_{Delta^0}^2
to be broken only by three-body, O(1/N_c^2) effects for any N_c.Comment: 15 pages, 1 eps figure. Version to appear in Phys. Rev.
Electromagnetic Moments of the Baryon Decuplet
We compute the leading contributions to the magnetic dipole and electric
quadrupole moments of the baryon decuplet in chiral perturbation theory. The
measured value for the magnetic moment of the is used to determine
the local counterterm for the magnetic moments. We compare the chiral
perturbation theory predictions for the magnetic moments of the decuplet with
those of the baryon octet and find reasonable agreement with the predictions of
the large-- limit of QCD. The leading contribution to the quadrupole
moment of the and other members of the decuplet comes from one--loop
graphs. The pionic contribution is shown to be proportional to (and so
will not contribute to the quadrupole moment of nuclei), while the
contribution from kaons has both isovector and isoscalar components. The chiral
logarithmic enhancement of both pion and kaon loops has a coefficient that
vanishes in the limit. The third allowed moment, the magnetic octupole,
is shown to be dominated by a local counterterm with corrections arising at two
loops. We briefly mention the strange counterparts of these moments.Comment: Uses harvmac.tex, 15 pages with 3 PostScript figures packed using
uufiles. UCSD/PTH 93-22, QUSTH-93-05, Duke-TH-93-5
Data from tests of a R4 airfoil in the Langley 0.3-meter transonic cryogenic tunnel
Aerodynamic data for the DFVLR R4 airfoil are presented in both graphic and tabular form. The R4 was tested in the Langley 0.3-Meter Transonic Cryogenic Tunnel (TCT) at Mach number from 0.60 to 0.78 at angles of attack from -2.0 to 8.0 degrees. The airfoil was tested at Reynolds numbers of 4, 6, 10, 15, 30, and 40 million based on the 152.32 mm chord
Critical Analysis of Baryon Masses and Sigma-Terms in Heavy Baryon Chiral Perturbation Theory
We present an analysis of the octet baryon masses and the and
--terms in the framework of heavy baryon chiral perturbation theory. At
next-to-leading order, , knowledge of the baryon masses and
allows to determine the three corresponding finite
low--energy constants and to predict the the two --terms
. We also include the spin-3/2 decuplet in the
effective theory. The presence of the non--vanishing energy scale due to the
octet--decuplet splitting shifts the average octet baryon mass by an infinite
amount and leads to infinite renormalizations of the low--energy constants. The
first observable effect of the decuplet intermediate states to the baryon
masses starts out at order . We argue that it is not sufficient to retain
only these but no other higher order terms to achieve a consistent description
of the three--flavor scalar sector of baryon CHPT. In addition, we critically
discuss an SU(2) result which allows to explain the large shift of via intermediate states.Comment: 18 pp, TeX, BUTP-93/05 and CRN-93-0
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