15,738 research outputs found
A New Method to Calibrate the Magnitudes of Type Ia Supernovae at Maximum Light
We present a new empirical method for fitting multicolor light curves of Type
Ia supernovae. Our method combines elements from two widely used techniques in
the literature: the delta_m15 template fitting method and the Multicolor
Light-Curve Shape method. An advantage of our technique is the ease of adding
new colors, templates, or parameters to the fitting procedure. We use a large
sample of published light curves to calibrate the relations between the
absolute magnitudes at maximum and delta_m15 in BVRI filters. We find that
individual subsamples from a given survey or publication have significantly
tighter relationships between light curve shape and luminosity than the
relationship derived from the sum of all the samples, pointing to uncorrected
systematic errors in the photometry, mainly in BV filters. Using our method, we
calculate luminosity distances and host galaxy reddening to 89 SNe in the
Hubble flow and construct a low-z Hubble diagram. The dispersion of the SNe in
the Hubble diagram is 0.20 mag, or an error of ~9% in distance to a single SN.
Our technique produces similar or smaller dispersion in the low-z Hubble
diagram than other techniques in the literature.Comment: 43 pages, 16 figures, 6 tables, accepted by ApJ. For additional
material go to
http://www.astronomy.ohio-state.edu/~prieto/paper_dm15/dm15.htm
Convective line shifts for the Gaia RVS from the CIFIST 3D model atmosphere grid
To derive space velocities of stars along the line of sight from wavelength
shifts in stellar spectra requires accounting for a number of second-order
effects. For most stars, gravitational redshifts, convective blueshifts, and
transverse stellar motion are the dominant contributors. We provide theoretical
corrections for the net velocity shifts due to convection expected for the
measurements from the Gaia Radial Velocity Spectrometer (RVS). We used a set of
three-dimensional time-dependent simulations of stellar surface convection
computed with CO5BOLD to calculate spectra of late-type stars in the Gaia RVS
range and to infer the net velocity offset that convective motions will induce
in radial velocities derived by cross-correlation. The net velocity shifts
derived by cross-correlation depend both on the wavelength range and spectral
resolution of the observations. Convective shifts for Gaia RVS observations are
less than 0.1 km/s for late-K-type stars, and they increase with stellar mass,
reaching about 0.3 km/s or more for early F-type dwarfs. This tendency is the
result of an increase with effective temperature in both temperature and
velocity fluctuations in the line-forming region. Our simulations also indicate
that the net RVS convective shifts can be positive (i.e. redshifts) in some
cases. Overall, the blueshifts weaken slightly with increasing surface gravity,
and are enhanced at low metallicity. Gravitational redshifts amount up to 0.7
km/s and dominate convective blueshifts for dwarfs, but become much weaker for
giants.Comment: 13 pages, to appear in A&A; model fluxes available from
ftp://leda.as.utexas.edu/pub/callende/Gaia3D and soon from CD
TIGER Capacity Building Facility - Phase 1, lessons learnt
The TIGER Capacity Building Facility focused on
closing the technological gap between the users and the
earth observation community within the TIGER
programme. Thirteen projects participated in different
aspects of the capacity building facility:
1. - Basic education, provided via distance learning.
2. - Tailored short courses, selected according to the
research interest and technical background of the
participants.
3. - Research topic oriented supervision, provided by
specialists of the research fields of the participants.
4. - Advanced short courses focusing on selected
earth observation techniques.
Distance education turned to be efficient and cost
effective in the programme - but only for those, who
followed the courses completely. There was a relatively
large percentage that could not complete the studies. The
second and the third type of education were carried out in
ITC, in the Netherlands. The participants evaluated the
courses and the supervision very effective and adequate.
Nevertheless, the follow-up was not always possible.
Two advanced short courses were held in Africa (Cape
Town and Nairobi). One of them addressed the 'scientific
elite' of the EO community, whilst the second focused on
the users of this technology
A Wire Position Monitor System for the 1.3 GHZ Tesla-Style Cryomodule at the Fermilab New-Muon-Lab Accelerator
The first cryomodule for the beam test facility at the Fermilab New-Muon-Lab
building is currently under RF commissioning. Among other diagnostics systems,
the transverse position of the helium gas return pipe with the connected 1.3
GHz SRF accelerating cavities is measured along the ~15 m long module using a
stretched-wire position monitoring system. An overview of the wire position
monitor system technology is given, along with preliminary results taken at the
initial module cool down, and during further testing. As the measurement system
offers a high resolution, we also discuss options for use as a vibration
detector.Comment: 4 pp. 15th International Conference on RF Superconductivity
(SRF2011). 25-29 Jul 2011. Chicago, Illinois, US
Ground state and constrained domain walls in Gd/Fe multilayers
The magnetic ground state of antiferromagnetically coupled Gd/Fe multilayers
and the evolution of in-plane domain walls is modelled with micromagnetics. The
twisted state is characterised by a rapid decrease of the interface angle with
increasing magnetic field. We found that for certain ratios M(Fe):M(Gd), the
twisted state is already present at low fields. However, the magnetic ground
state is not only determined by the ratio M(Fe):M(Gd) but also by the
thicknesses of the layers, that is the total moments of the layer. The
dependence of the magnetic ground state is explained by the amount of overlap
of the domain walls at the interface. Thicker layers suppress the Fe aligned
and the Gd aligned state in favour of the twisted state. Whereas ultrathin
layers exclude the twisted state, since wider domain walls can not form in
these ultrathin layers
Velocities from Cross-Correlation: A Guide for Self-Improvement
The measurement of Doppler velocity shifts in spectra is a ubiquitous theme
in astronomy, usually handled by computing the cross-correlation of the
signals, and finding the location of its maximum. This paper addresses the
problem of the determination of wavelength or velocity shifts among multiple
spectra of the same, or very similar, objects. We implement the classical
cross-correlation method and experiment with several simple models to determine
the location of the maximum of the cross-correlation function. We propose a new
technique, 'self-improvement', to refine the derived solutions by requiring
that the relative velocity for any given pair of spectra is consistent with all
others. By exploiting all available information, spectroscopic surveys
involving large numbers of similar objects may improve their precision
significantly. As an example, we simulate the analysis of a survey of G-type
stars with the SDSS instrumentation. Applying 'self-improvement' refines
relative radial velocities by more than 50% at low signal-to-noise ratio. The
concept is equally applicable to the problem of combining a series of
spectroscopic observations of the same object, each with a different Doppler
velocity or instrument-related offset, into a single spectrum with an enhanced
signal-to-noise ratio.Comment: 7 pages, 3 figures, uses emulateapj.cls; to appear in the
Astronomical Journal; see http://hebe.as.utexas.edu/stools/ to obtain the
companion softwar
Medida de la eficacia de dos hidrofugantes aplicados a rocas graníticas
We evaluated the efficacy of two water-repellents applied to three types of granitic rock widely used in building construction and restoration in Galicia (NW Spain). The depth of penetration of the water-repellents was determined by measuring capillary absorption by the treated rock. The efficacies of the water-repellent were evaluated in terms of two parameters characteristic of surface wet: water-rock contact angle and the time taken for absorption of microgroplets. The effects of the treatments on the rocks' surface color and permeability to water vapor were also determined. The results indicate that neither water-repellent effectively penetrates the rock surface, and both induce undesirably high reductions in vapor permeability. Notwithstanding, both agents effectively improved the rocks' resistance to surface wetting, without altering its surface color. Overall, determination of water-rock contact angle and the time taken for absorption of microdroplets, together with colorimetric characterization of the treated rock, constitutes an useful approach to evaluation of the effects of water-repellents on granitic rocks. Nonetheless, it should be borne in mind that the marked heterogeneity of this type of rock, and the associated mineralogy and dominant type of fissuration are sources of considerable variation in the measurement parameters.Se presentan los resultados de la aplicación de dos tratamientos hidrofugantes a tres rocas graníticas ampliamente utilizadas en la construcción y restauración en Galicia. Se ha determinado la profundidad de penetración de los hidrofugantes a través de la absorción capilar, la eficacia de los tratamientos comparando dos parámetros relacionados con el mojado superficial (ángulo de contacto roca-agua y tiempo de absorción de microgotas), y las variaciones en el color y en la permeabilidad al vapor. Se comprueba que si bien ambos tratamientos penetran deforma muy escasa en las rocas graníticas y reducen significativamente la permeabilidad al vapor, mejoran sensiblemente su comportamiento frente al mojado superficial sin modificar el color original. El ángulo de contacto, el tiempo de absorción de microgotas y la determinación colorimétrica utilizada, constituyen una buena metodología en la evaluación de los efectos de tratamientos hidrofugantes en rocas graníticas; sin embargo, el fuerte carácter heterogéneo este tipo de rocas, la mineralogía y el tipo de fisuración predominante, suponen un factor de variación significativo en la determinación de estos parámetros
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