Magnetic field measurements at milliarcsecond resolution around massive young stellar objects

Magnetic fields have only recently been included in theoretical simulations of high-mass star formation. The simulations show that magnetic fields can play a crucial role not only in the formation and dynamics of molecular outflows, but also in the evolution of circumstellar disks. Therefore, new measurements of magnetic fields at milliarcsecond resolution close to massive young stellar objects (YSOs) are fundamental for providing new input for numerical simulations and for understanding the formation process of massive stars. The polarized emission of 6.7 GHz CH3OH masers allows us to investigate the magnetic field close to the massive YSO where the outflows and disks are formed. Recently, we have detected with the EVN CH3OH maser polarized emission towards 10 massive YSOs. From a first statistical analysis we have found evidence that magnetic fields are primarily oriented along the molecular outflows. To improve our statistics we are carrying on a large observational EVN campaign for a total of 19 sources, the preliminary results of the first seven sources are presented in this contribution. Furthermore, we also describe our efforts to estimate the Lande' g-factors of the CH3OH maser transition to determine the magnetic field strength from our Zeeman-splitting measurements.Comment: Accepted for publication in the proceeding of the "12th European VLBI Network Symposium and Users Meeting", eds Tarchi et al. PoS(EVN 2014)04

Optimization of liquid crystal structures for real time holography applications

In this paper we present results of experiments designed to increase our understanding of the photorefractive effect occurring during processes of dynamic hologram generation in Hybrid Photorefractive Liquid Crystal Structures (HPLCS). We also propose equivalent mathematical model which can be used to optimize those structures in order to obtain the highest diffraction efficiency in possibly shortest time. (C) 2011 Optical Society of Americ

EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions III. The flux-limited sample

Theoretical simulations and observations at different angular resolutions have shown that magnetic fields have a central role in massive star formation. Like in low-mass star formation, the magnetic field in massive young stellar objects can either be oriented along the outflow axis or randomly. Measuring the magnetic field at milliarcsecond resolution (10-100 au) around a substantial number of massive young stellar objects permits determining with a high statistical significance whether the direction of the magnetic field is correlated with the orientation of the outflow axis or not. In late 2012, we started a large VLBI campaign with the European VLBI Network to measure the linearly and circularly polarized emission of 6.7 GHz methanol masers around a sample of massive star-forming regions. This paper focuses on the first seven observed sources, G24.78+0.08, G25.65+1.05, G29.86-0.04, G35.03+0.35, G37.43+1.51, G174.20-0.08, and G213.70-12.6. For all these sources, molecular outflows have been detected in the past. We detected a total of 176 methanol masing cloudlets toward the seven massive star-forming regions, 19% of which show linearly polarized emission. The methanol masers around the massive young stellar object MM1 in G174.20-0.08 show neither linearly nor circularly polarized emission. The linear polarization vectors are well ordered in all the other massive young stellar objects. We measured significant Zeeman splitting toward both A1 and A2 in G24.78+0.08, and toward G29.86-0.04 and G213.70-12.6. By considering all the 19 massive young stellar objects reported in the literature for which both the orientation of the magnetic field at milliarcsecond resolution and the orientation of outflow axes are known, we find evidence that the magnetic field (on scales 10-100 au) is preferentially oriented along the outflow axes.Comment: 17 pages, 10 figures, 9 tables, accepted by Astronomy & Astrophysics. arXiv admin note: text overlap with arXiv:1306.633

Influence of temperature on dynamics of birefringence switching in photochromic nematic phase

We present results of dynamic and fast switching of birefringence in a photochromic liquid-crystalline system as a function of the sample temperature. The system consists of photochromic molecules of 4-heptyl-4-methoxyazobenzene showing a liquid-crystalline nematic state close to room temperature. An experiment of dynamic birefringence switching was done in optical Kerr-effect set-up, where for the sample excitation, a picosecond-pulsed laser was used. Measurements were done for different temperatures of the sample in the liquid-crystalline nematic phase. We have proposed a mathematical model of dynamic, fast, and fully reversible birefringence changes. Theoretical estimations and experimental results have shown very good agreement. (C) 2011 American Institute of Physics. [doi:10.1063/1.3665123

Pulsed laser induced switching of birefringence in nematic phase of photochromic molecules

Fast and dynamic switching of liquid-crystalline photochromic system birefringence induced by pulsed laser has been observed. The system consisted of photochromic molecules of 4-heptyl-4-methoxyazobenzene showing liquid-crystalline nematic state close to the room temperature. Experiment of dynamic birefringence switching was done in optical Kerr effect (OKE) set-up, where for the sample excitation picosecond pulsed laser was used. Simultaneously, He-Ne laser was served as a probe beam source. Measurements were done for different voltages applied to the sample. Rise time constant was in the range of microseconds. Full reversibility of the OKE signal was observed. (C) 2011 American Institute of Physics. [doi:10.1063/1.3559613

6.7 GHz CH3OH masers polarization in massive star-forming regions: The Flux-Limited Sample

The formation process of high-mass stars (M > 8Msun) is still unclear; this is mainly due to their fast evolution and large distances that make difficult to observe them in details. The observational and theoretical efforts made in the last decades have shown that a common and essential component in the formation of high-mass stars is the presence of molecular outflows during the protostellar phase, similarly to what is observed during the formation of low-mass stars. Theoretically, it has been convincingly demonstrated that the magnetic field plays an important role in launching and shaping molecular outflows in massive young stellar objects (YSOs). Therefore, providing new observational measurements of magnetic fields close (10s-100s au) to massive YSOs is of great importance. More than 10 years ago we started a large EVN campaign to measure the magnetic field orientation and strength toward a sample of 30 massive star-forming regions, called the "Flux-Limited sample", by observing the polarized emission of 6.7 GHz CH3OH masers. Here, we present a summary of the final statistics of the Flux-Limited sample, extensively reported in [1], which are focused on the relative orientation of the outflows with the magnetic fields and on the polarized characteristics of 6.7 GHz CH3OH masers

Structural and optical properties of as-grown and annealed Alq3 thin films

International audienc

Amplified spontaneous emission in the spiropyran-biopolymer based system

Amplified spontaneous emission (ASE) phenomenon in the 6-nitro-1′,3′,3′-trimethylspiro[2H-1-benzopyran-2,2′-indolin] organic dye dispersed in a solid matrix has been observed. The biopolymer system deoxyribonucleic acid blended with cationic surfactant molecule cetyltrimethyl-ammonium chloride served as a matrix. ASE appeared under sample excitation by UV light pulses (λ=355 nm) coming from nanosecond or picosecond neodymium doped yttrium aluminum garnet lasers and has been reinforced with green (λ=532 nm) light excitation followed UV light pulse. The ASE characteristics in function of different excitation pulse energies as well as signal gain were measured

Amplified spontaneous emission of Rhodamine 6G embedded in pure deoxyribonucleic acid

Deoxyribonucleic acid (DNA) is commonly viewed as a genetic information carrier. However, now it is recognized as a nanomaterial, rather than as a biological material, in the research field of nanotechnology. Here, we show that using pure DNA, doped with rhodamine 6G, we are able to observe amplified spontaneous emission (ASE) phenomenon. Moderate ASE threshold, photodegradation, and reasonable gain coefficient observed in this natural host gives some perspectives for practical applications of this system in biophotonics. Obtained results open the way and will be leading to construction of truly bio-lasers using nature made luminophores, such as anthocyanins

Techniques for Accurate Parallax Measurements for 6.7-GHz Methanol Masers

The BeSSeL Survey is mapping the spiral structure of the Milky Way by measuring trigonometric parallaxes of hundreds of maser sources associated with high-mass star formation. While parallax techniques for water masers at high frequency (22 GHz) have been well documented, recent observations of methanol masers at lower frequency (6.7 GHz) have revealed astrometric issues associated with signal propagation through the ionosphere that could significantly limit parallax accuracy. These problems displayed as a "parallax gradient" on the sky when measured against different background quasars. We present an analysis method in which we generate position data relative to an "artificial quasar" at the target maser position at each epoch. Fitting parallax to these data can significantly mitigate the problems and improve parallax accuracy