2,980 research outputs found
Star Formation from Spitzer (Lyman) to Spitzer (Space Telescope) and Beyond
A summary of JENAM 2008 Symposium 9 "Star Formation from Spitzer (Lyman) to
Spitzer (Space Telescope) and Beyond", held in Vienna, 10-12 September 2008.Comment: 6 page
Estimating Extinction using Unsupervised Machine Learning
Dust extinction is the most robust tracer of the gas distribution in the
interstellar medium, but measuring extinction is limited by the systematic
uncertainties involved in estimating the intrinsic colors to background stars.
In this paper we present a new technique, PNICER, that estimates intrinsic
colors and extinction for individual stars using unsupervised machine learning
algorithms. This new method aims to be free from any priors with respect to the
column density and intrinsic color distribution. It is applicable to any
combination of parameters and works in arbitrary numbers of dimensions.
Furthermore, it is not restricted to color space. Extinction towards single
sources is determined by fitting Gaussian Mixture Models along the extinction
vector to (extinction-free) control field observations. In this way it becomes
possible to describe the extinction for observed sources with probability
densities. PNICER effectively eliminates known biases found in similar methods
and outperforms them in cases of deep observational data where the number of
background galaxies is significant, or when a large number of parameters is
used to break degeneracies in the intrinsic color distributions. This new
method remains computationally competitive, making it possible to correctly
de-redden millions of sources within a matter of seconds. With the
ever-increasing number of large-scale high-sensitivity imaging surveys, PNICER
offers a fast and reliable way to efficiently calculate extinction for
arbitrary parameter combinations without prior information on source
characteristics. PNICER also offers access to the well-established NICER
technique in a simple unified interface and is capable of building extinction
maps including the NICEST correction for cloud substructure. PNICER is offered
to the community as an open-source software solution and is entirely written in
Python.Comment: Accepted for publication in A&A, source code available at
http://smeingast.github.io/PNICER
A new method to unveil embedded stellar clusters
In this paper we present a novel method to identify and characterize stellar
clusters deeply embedded in a dark molecular cloud. The method is based on
measuring stellar surface density in wide-field infrared images using star
counting techniques. It takes advantage of the differing -band luminosity
functions (HLFs) of field stars and young stellar populations and is able to
statistically associate each star in an image as a member of either the
background stellar population or a young stellar population projected on or
near the cloud. Moreover, the technique corrects for the effects of
differential extinction toward each individual star. We have tested this method
against simulations as well as observations. In particular, we have applied the
method to 2MASS point sources observed in the Orion A and B complexes, and the
results obtained compare very well with those obtained from deep Spitzer and
Chandra observations where presence of infrared excess or X-ray emission
directly determines membership status for every star. Additionally, our method
also identifies unobscured clusters and a low resolution version of the Orion
stellar surface density map shows clearly the relatively unobscured and diffuse
OB 1a and 1b sub-groups and provides useful insights on their spatial
distribution.Comment: A&A, in press; 13 pages, multi-layer figures can be displayed with
Adobe Acrobat Reade
Symmetry Constrained Two Higgs Doublet Models
We study Two-Higgs-Doublet Models (2HDM) where Abelian symmetries have been
introduced, leading to a drastic reduction in the number of free parameters in
the 2HDM. Our analysis is inspired in BGL models, where, as the result of a
symmetry of the Lagrangian, there are tree-level scalar mediated
Flavour-Changing-Neutral-Currents, with the flavour structure depending only on
the CKM matrix. A systematic analysis is done on the various possible schemes,
which are classified in different classes, depending on the way the extra
symmetries constrain the matrices of couplings defining the flavour structure
of the scalar mediated neutral currents. All the resulting flavour textures of
the Yukawa couplings are stable under renormalisation since they result from
symmetries imposed at the Lagrangian level. We also present a brief
phenomenological analysis of the most salient features of each class of
symmetry constrained 2HDM.Comment: 30 pages, 5 Table
ECONOMIC TRADEOFF ANALYSIS OF A PRODUCT LINE ARCHITECTURE APPROACH THROUGH MODEL-BASED SYSTEMS ENGINEERING: A CASE STUDY OF FUTURE MINE COUNTERMEASURES UNMANNED UNDERWATER VEHICLES
The defense sector often develops systems to operate for at least 15 years, which can reach 40 or even 50 years. Those systems tend to be cheaper, more rapidly developed, and reliable when developed on product lines (PL). Product line architecture surges with potential to improve the acquisition process, resulting in a more rapid insertion of cost-effective warfighting capabilities. This thesis investigates the impact of the PL approach by analyzing the future generation of mine countermeasure (MCM) unmanned underwater vehicle (UUV) architecture alternatives, employing a detailed reuse model based on the COPLIMO framework. The research integrates parametric cost modeling with model-based systems engineering (MBSE), feeding the existing baseline knowledge regarding PL architecture. Furthermore, this can improve systems acquisition processes, deliver more agile capability, and reduce total life cycle costs (LCC). The integration of models highlights significant differences among the architectural variations considered early in the acquisition process before substantial financial commitments. Early decisions determine most of the total LCC and establish a baseline for long-term system performance. Hence, the choice of favorable design alternatives is crucial to program success. The results demonstrate that up-front investments in product lines generate a significant return on investment (ROI).Capitao-Tenente, Brazilian NavyApproved for public release. Distribution is unlimited
Mapping the interstellar dust with near-infrared observations: An optimized multi-band technique
We generalize the technique of Lada et al. (1994) to map dust column density
through a molecular cloud (NICE) to an optimized multi-band technique (NICER)
that can be applied to any multi-band survey of molecular clouds. We present a
first application to a ~625 deg^2 subset of the Two Micron All Sky Survey
(2MASS) data and show that when compared to NICE, the optimized NICER technique
(i) achieves the same extinction peak values, (ii) improves the noise variance
of the map by a factor of 2 and (iii) is able to reach 3 \sigma dust extinction
measurements as low as A_V = 0.5 magnitudes, better than or equivalent to
classical optical star count techniques and below the threshold column density
for the formation of CO, the brightest H2 tracer in radio-spectroscopy
techniques. The application of the NICER techniques to near-infrared data
obtained with a 8 meter-class telescope with a state-of-the-art NIR camera,
such as the VLT-ISAAC combination, will be able to achieve dynamic ranges from
below 10^21 protons cm^-2 to over 10^23 protons cm^-2 (A_V in the range [0.3,
60]) and spatial resolutions < 10'', making use of a single and straightforward
column density tracer, extinction by interstellar dust.Comment: 12 pages, 8 figures; A&A, in press. Full document with figures
available at http://www.astro.uni-bonn.de/~lombardi/ms1526.pd
Schmidt's Conjecture and Star Formation in Molecular Clouds
We investigate Schmidt's conjecture (i.e., that the star formation rate
scales in a power-law fashion with the gas density) for four well-studied local
molecular clouds (GMCs). Using the Bayesian methodology we show that a local
Schmidt scaling relation of the form Sigma*(A_K) = kappa x (A_K)^{beta}
(protostars pc^{-2}) exists within (but not between) GMCs. Further we find that
the Schmidt scaling law, by itself, does not provide an adequate description of
star formation activity in GMCs. Because the total number of protostars
produced by a cloud is given by the product of Sigma*(A_K) and S'(> A_K), the
differential surface area distribution function, integrated over the entire
cloud, the cloud's structure plays a fundamental role in setting the level of
its star formation activity. For clouds with similar functional forms of
Sigma*(A_K), observed differences in their total SFRs are primarily due to the
differences in S'(> A_K) between the clouds. The coupling of Sigma*(A_K) with
the measured S'(> A_K) in these clouds also produces a steep jump in the SFR
and protostellar production above A_K ~ 0.8 magnitudes. Finally, we show that
there is no global Schmidt law that relates the star formation rate and gas
mass surface densities between GMCs. Consequently, the observed
Kennicutt-Schmidt scaling relation for disk galaxies is likely an artifact of
unresolved measurements of GMCs and not a result of any underlying physical law
of star formation characterizing the molecular gas.Comment: 34 pages, 8 figures, and 2 tables; accepted for publication in ApJ on
Sept 23, 201
Controlled Flavour Changing Neutral Couplings in Two Higgs Doublet Models
We propose a class of Two Higgs Doublet Models where there are Flavour
Changing Neutral Currents (FCNC) at tree level, but under control due to the
introduction of a discrete symmetry in the full Lagrangian. It is shown that in
this class of models, one can have simultaneously FCNC in the up and down
sectors, in contrast to the situation encountered in BGL models. The intensity
of FCNC is analysed and it is shown that in this class of models one can
respect all the strong constraints from experiment without unnatural
fine-tuning. It is pointed out that the additional sources of flavour and CP
violation are such that they can enhance significantly the generation of the
Baryon Asymmetry of the Universe, with respect to the Standard Model.Comment: 29 pages, 3 figure
X Marks the Spot: Nexus of Filaments, Cores, and Outflows in a Young Star-Forming Region
We present a multiwavelength investigation of a region of a nearby giant
molecular cloud that is distinguished by a minimal level of star formation
activity. With our new 12CO(J=2-1) and 13CO(J=2-1) observations of a remote
region within the middle of the California molecular cloud, we aim to
investigate the relationship between filaments, cores, and a molecular outflow
in a relatively pristine environment. An extinction map of the region from
Herschel Space Observatory observations reveals the presence of two 2-pc-long
filaments radiating from a high-extinction clump. Using the 13CO observations,
we show that the filaments have coherent velocity gradients and that their
mass-per-unit-lengths may exceed the critical value above which filaments are
gravitationally unstable. The region exhibits structure with eight cores, at
least one of which is a starless, prestellar core. We identify a low-velocity,
low-mass molecular outflow that may be driven by a flat spectrum protostar. The
outflow does not appear to be responsible for driving the turbulence in the
core with which it is associated, nor does it provide significant support
against gravitational collapse.Comment: Accepted for publication in the Astrophysical Journa
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