3,805 research outputs found
Synthetic Stellar Photometry - I. General considerations and new transformations for broad-band systems
After a pedagogical introduction to the main concepts of synthetic
photometry, colours and bolometric corrections in the Johnson-Cousins, 2MASS,
and HST-ACS/WFC3 photometric systems are generated from MARCS synthetic fluxes
for various [Fe/H] and [alpha/Fe] combinations, and virtually any value of
reddening E(B-V) < 0.7. The successes and failures of model fluxes in
reproducing the observed magnitudes are highlighted. Overall, extant synthetic
fluxes predict quite realistic broad-band colours and bolometric corrections,
especially at optical and longer wavelengths: further improvements of the
predictions for the blue and ultraviolet spectral regions await the use of
hydrodynamic models where the microturbulent velocity is not treated as a free
parameter. We show how the morphology of the colour-magnitude diagram (CMD)
changes for different values of [Fe/H] and [alpha/Fe]; in particular, how
suitable colour combinations can easily discriminate between red giant branch
and lower main sequence populations with different [alpha/Fe], due to the
concomitant loops and swings in the CMD. We also provide computer programs to
produce tables of synthetic bolometric corrections as well as routines to
interpolate in them. These colour-Teff-metallicity relations may be used to
convert isochrones for different chemical compositions to various bandpasses
assuming observed reddening values, thus bypassing the standard assumption of a
constant colour excess for stars of different spectral type. We also show how
such an assumption can lead to significant systematic errors. The MARCS
transformations presented in this study promise to provide important
constraints on our understanding of the multiple stellar populations found in
globular clusters (e.g., the colours of lower main sequence stars are predicted
to depend strongly on [alpha/Fe]) and of those located towards/in the Galactic
bulge.Comment: MNRAS, accepted. Tables and programs to generate synthetic colours
and bolometric corrections in various photometric systems and for different
combination of E(B-V), [Fe/H], [alpha/Fe], Teff and logg available via CDS at
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/MNRAS/444/39
On the use of Gaia magnitudes and new tables of bolometric corrections
The availability of reliable bolometric corrections and reddening estimates,
rather than the quality of parallaxes will be one of the main limiting factors
in determining the luminosities of a large fraction of Gaia stars. With this
goal in mind, we provide Gaia G, BP and RP synthetic photometry for the entire
MARCS grid, and test the performance of our synthetic colours and bolometric
corrections against space-borne absolute spectrophotometry. We find indication
of a magnitude-dependent offset in Gaia DR2 G magnitudes, which must be taken
into account in high accuracy investigations. Our interpolation routines are
easily used to derive bolometric corrections at desired stellar parameters, and
to explore the dependence of Gaia photometry on Teff, log(g), [Fe/H],
alpha-enhancement and E(B-V). Gaia colours for the Sun and Vega, and
Teff-dependent extinction coefficients, are also provided.Comment: MNRAS Letter. Solar colours: BP-G = 0.33, G-RP = 0.49, BP-RP = 0.82.
Mean extinction coefficients at turn-off: R_G = 2.740 , R_BP = 3.374, R_RP =
2.035. Interpolation routines available at
https://github.com/casaluca/bolometric-correction
Strongly-Driven One-Atom Laser and Decoherence Monitoring
We propose the implementation of a strongly-driven one-atom laser, based on
the off-resonant interaction of a three-level atom in -configuration
with a single cavity mode and three laser fields. We show that the system can
be described equivalently by a two-level atom resonantly coupled to the cavity
and driven by a strong effective coherent field. The effective dynamics can be
solved exactly, including a thermal field bath, allowing an analytical
description of field statistics and entanglement properties. We also show the
possible generation of Schr\"odinger cat states for the whole atom-field system
and for the field alone after atomic measurement. We propose a way to monitor
the system decoherence by measuring atomic population. Finally, we confirm the
validity of our model through numerical solutions.Comment: 9 pages, 7 figures Accepted in Phys. Rev.
Estimating Parasitism of Colorado Potato Beetle Eggs, \u3ci\u3eLeptinotarsa Decemlineata\u3c/i\u3e (Coleoptera: Chrysomelidae), by \u3ci\u3eEdovum Puttleri\u3c/i\u3e (Hymenoptera: Eulophidae)
A computer simulation was used to evaluate methods for estimating parasitism of Colorado potato beetle egg mass populations by Edovum puttleri. The algorithm incorporated the specific attack behavior of E. puttleri, and a development time for parasitized egg masses of ca. 2.9 times that of healthy egg masses. Of the methods compared, a modification of Southwood\u27s graphical technique was found to be most accurate in relation to the true parasitism derived from the algorithm. A regression equation is presented to correct the error in this method at high levels of parasitism. A second simulation was used to test the accuracy of this correcter where in a jacknife procedure was used to generate a mean and variance for estimates of parasitism
Clusters and Groups of Galaxies in the Simulated Local Universe
We compare the properties of galaxy groups extracted from the Updated Zwicky
Catalogue (UZC) with those of groups extracted from N-body simulations of the
local Universe, in a LambdaCDM and a tauCDM cosmology. In the simulations, the
initial conditions of the dark matter density field are set to reproduce the
present time distribution of the galaxies within 80 Mpc/h from the Milky Way.
These initial conditions minimize the uncertainty originated by cosmic
variance, which has affected previous analyses of this small volume of the
Universe. The simulations also model the evolution of the photometric
properties of the galaxy population with semi-analytic prescriptions. The
models yield a galaxy luminosity function sensibly different from that of the
UZC and are unable to reproduce the distribution of groups and their luminosity
content. The discrepancy between the model and the UZC reduces substantially,
if we redistribute the luminosity among the galaxies in the simulation
according to the UZC luminosity function while preserving the galaxy luminosity
rank. The modified LambdaCDM model provides the best match to the UZC: the
abundances of groups by harmonic radius, velocity dispersion, mass and
luminosity are consistent with observations. We find that this model also
reproduces the halo occupation number of groups and clusters. However, the
large-scale distribution of groups is marginally consistent with the UZC and
the redshift-space correlation function of galaxies on scales larger than 6
Mpc/h is still more than 3-sigma smaller than observed. We conclude that
reproducing the properties of the observed groups certainly requires a more
sophisticated treatment of galaxy formation, and possibly an improvement of the
dark matter model.Comment: 20 pages, 18 figures, accepted by MNRAS. Minor revisions according to
referee's comments. Conclusions unchange
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