Strongly misaligned triple system in SR 24 revealed by ALMA

We report the detection of the 1.3 mm continuum and the molecular emission of the disks of the young triple system SR24 by analyzing ALMA (The Atacama Large Millimeter/Submillimter Array) subarcsecond archival observations. We estimate the mass of the disks (0.025 M ⊙ and 4 × 10‑5 M ⊕ for SR24S and SR24N, respectively) and the dynamical mass of the protostars (1.5 M ⊙ and 1.1 M ⊙). A kinematic model of the SR24S disk to fit its C18O (2-1) emission allows us to develop an observational method to determine the tilt of a rotating and accreting disk. We derive the size, inclination, position angle, and sense of rotation of each disk, finding that they are strongly misaligned (108^circ ) and possibly rotate in opposite directions as seen from Earth, in projection. We compare the ALMA observations with 12CO SMA archival observations, which are more sensitive to extended structures. We find three extended structures and estimate their masses: a molecular bridge joining the disks of the system, a molecular gas reservoir associated with SR24N, and a gas streamer associated with SR24S. Finally, we discuss the possible origin of the misaligned SR24 system, concluding that a closer inspection of the northern gas reservoir is needed to better understand it. Fil: Fernandez Lopez, Manuel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Zapata, L. A.. Universidad Nacional Autónoma de México; MéxicoFil: Gabbasov, R.. Universidad Autónoma del Estado de Hidalgo; Méxic

Ultrafast Insulator-Metal Phase Transition in VO2 Studied by Multiterahertz Spectroscopy

The ultrafast photoinduced insulator-metal transition in VO2 is studied at different temperatures and excitation fluences using multi-THz probe pulses. The spectrally resolved mid-infrared response allows us to trace separately the dynamics of lattice and electronic degrees of freedom with a time resolution of 40 fs. The critical fluence of the optical pump pulse which drives the system into a long-lived metallic state is found to increase with decreasing temperature. Under all measurement conditions we observe a modulation of the eigenfrequencies of the optical phonon modes induced by their anharmonic coupling to the coherent wave packet motion of V-V dimers at 6.1 THz. Furthermore, we find a weak quadratic coupling of the electronic response to the coherent dimer oscillation resulting in a modulation of the electronic conductivity at twice the frequency of the wave packet motion. The findings are discussed in the framework of a qualitative model based on an approximation of local photoexcitation of the vanadium dimers from the insulating state.Comment: 10 pages, 8 figures submitted to Physical Review