Spokes cluster: The search for the quiescent gas

Context. Understanding the role of fragmentation is one of the most important current questions of star formation. To better understand the process of star and cluster formation, we need to study in detail the physical structure and properties of the parental molecular cloud. The Spokes cluster, or NGC 2264 D, is a rich protostellar cluster where previous N2H+(1-0) observations of its dense cores presented linewidths consistent with supersonic turbulence. However, the fragmentation of the most massive of these cores appears to have a scale length consistent with that of the thermal Jeans length, suggesting that turbulence was not dominant. Aims. These two results probe different density regimes. Our aim is to determine if there is subsonic or less-turbulent gas (than previously reported) in the Spokes cluster at higher densities. Methods. We present APEX N2H+(3-2) and N2D+(3-2) observations of the NGC2264-D region to measure the linewidths and the deuteration fraction of the higher density gas. The critical densities of the selected transitions are more than an order of magnitude higher than that of N2H+(1-0). Results. We find that the N2H+(3-2) and N2D+(3-2) emission present significantly narrower linewidths than the emission from N2H+(1-0) for most cores. In two of the spectra, the nonthermal component is close (within 1-sigma) to the sound speed. In addition, we find that the three spatially segregated cores, for which no protostar had been confirmed show the highest levels of deuteration. Conclusions. These results show that the higher density gas, probed with N2H+ and N2D+(3-2), reveals more quiescent gas in the Spokes cluster than previously reported. More high-angular resolution interferometric observations using high-density tracers are needed to truly assess the kinematics and substructure within NGC2264-D. (Abridged)Comment: 8 pages, 4 figures. Accepted in A&

Fold-Saddle Bifurcation in Non-Smooth Vector Fields on the Plane

This paper presents results concerning bifurcations of 2D piecewise-smooth dynamical systems governed by vector fields. Generic three parameter families of a class of Non-Smooth Vector Fields are studied and its bifurcation diagrams are exhibited. Our main result describes the unfolding of the so called Fold-Saddle singularity

Mapping prior information onto LMI eigenvalue-regions for discrete-time subspace identification

In subspace identification, prior information can be used to constrain the eigenvalues of the estimated state-space model by defining corresponding LMI regions. In this paper, first we argue on what kind of practical information can be extracted from historical data or step-response experiments to possibly improve the dynamical properties of the corresponding model and, also, on how to mitigate the effect of the uncertainty on such information. For instance, prior knowledge regarding the overshoot, the period between damped oscillations and settling time may be useful to constraint the possible locations of the eigenvalues of the discrete-time model. Then, we show how to map the prior information onto LMI regions and, when the obtaining regions are non-convex, to obtain convex approximations.Comment: Under revie

Linear Invariant Systems Theory for Signal Enhancement

This paper discusses a linear time invariant (LTI) systems approach to signal enhancement via projective subspace techniques. It provides closed form expressions for the frequency response of data adaptive finite impulse response eigenfilters. An illustrative example using speech enhancement is also presented.Este artigo apresenta a aplicação da teoria de sistemas lineares invariantes no tempo (LTI) na análise de técnicas de sub-espaço. A resposta em frequência dos filtros resultantes da decomposição em valores singulares é obtida aplicando as propriedades dos sistemas LTI

Upper limit on mh in the MSSM and M-SUGRA vs. prospective reach of LEP

The upper limit on the lightest CP-even Higgs boson mass, mh, is analyzed within the MSSM as a function of tan(beta) for fixed mtop and Msusy. The impact of recent diagrammatic two-loop results on this limit is investigated. We compare the MSSM theoretical upper bound on mh with the lower bound obtained from experimental searches at LEP. We estimate that with the LEP data taken until the end of 1999, the region mh < 108.2 GeV can be excluded at the 95% confidence level. This corresponds to an excluded region 0.6 <= tan(beta) <= 1.9 within the MSSM for mtop = 174.3 GeV and Msusy <= 1 TeV. The final exclusion sensitivity after the end of LEP, in the year 2000, is also briefly discussed. Finally, we determine the upper limit on mh within the Minimal Supergravity (M-SUGRA) scenario up to the two-loop level, consistent with radiative electroweak symmetry breaking. We find an upper bound of mh \approx 127 GeV for mtop = 174.3 GeV in this scenario, which is slightly below the bound in the unconstrained MSSM.Comment: 10 pages, 3 figure

A dense micro-cluster of Class 0 protostars in NGC 2264 D-MM1

We present sensitive and high angular resolution (~1") 1.3 mm continuum observations of the dusty core D-MM1 in the Spokes cluster in NGC 2264 using the Submillimeter Array. A dense micro-cluster of seven Class 0 sources was detected in a 20" x 20" region with masses between 0.4 to 1.2 solar masses and deconvolved sizes of about 600 AU. We interpret the 1.3 mm emission as arising from the envelopes of the Class 0 protostellar sources. The mean separation of the 11 known sources (SMA Class 0 and previously known infrared sources) within D-MM1 is considerably smaller than the characteristic spacing between sources in the larger Spokes cluster and is consistent with hierarchical thermal fragmentation of the dense molecular gas in this region.Comment: Accepted for publication in the Astrophysical Journal Letter