Fine-structure infrared lines from the Cassiopeia A knots

Aims: Archival observations of infrared fine-structure lines of the young Galactic supernova remnant Cassiopeia A allow us to test existing models and determine the physical parameters of various regions of the fast-moving knots (FMKs), which are metal-dominated clouds of material ejected by the supernova explosion. Methods: The fluxes of the far-infrared [O i] and [O iii] lines are extracted from the previously unpublished archival ISO data. The archival Spitzer data are used to determine the fluxes of the O, Ne, Si, S, Ar and Fe ion fine-structure lines originating in the FMKs. The ratios of these line fluxes are used for the plasma diagnostics. We also determine the infrared line flux ratios to the optical [O iii] 5007 A line in the knots having previously measured reddening. Additionally, we analyze several optical and near-infrared observations of the FMKs to obtain clearer insight into the post-shock photoionized region (PIR) structure. Results: We show that the infrared oxygen line flux predictions of all existing theoretical models are correct only to within a factor of several. For the models to reproduce the observations it is essential to include the electron conductivity and effects of the dust. Detailed analysis of the diagnostic line flux ratios allows us to qualitatively confirm the general model of the FMK emission and to determine observationally the physical conditions in the PIR after the shock front. We infer that the pre-shock cloud densities most probably constitute several hundred particles per cm^3. We also determine the Cas A luminosities in the infrared continuum and lines. We show that accounting for the charge exchange processes in the post-shock PIR allows us to reproduce most of the relevant spectral line ratios even in the frame of a single-temperature model of this region. We also estimate its plasma parameters, thickness, and carbon abundance.Comment: Version accepted by A&A, 21 page, 10 figures. v2: major changes, Section 5 added with analysis of charge-exchange process influence

Nuclear de-excitation line spectrum of Cassiopeia A

The supernova remnant Cassiopeia A is a prime candidate for accelerating cosmic ray protons and ions. Gamma rays have been observed at GeV and TeV energies, which indicates hadronic interactions, but they could also be caused by inverse-Compton scattering of low-energy photons by accelerated electrons. We seek to predict the flux of nuclear de-excitation lines from Cas A through lower-energy cosmic rays and to compare it with COMPTEL measurements. Assuming a hadronic origin of the high-energy emission, we extrapolate the cosmic ray spectrum down to energies of 10 MeV, taking into account an equilibrium power-law momentum spectrum with a constant slope. We then calculate the nuclear line spectrum of Cassiopeia A, considering the most prominent chemical elements in the MeV band and their abundances as determined by X-ray spectroscopy. We show that the predicted line spectrum is close to the level of the COMPTEL sensitivity and agrees with conservative upper limits.Comment: 4 pages, 1 figure, accepted for publication by A&

Dark resonances for ground state transfer of molecular quantum gases

One possible way to produce ultracold, high-phase-space-density quantum gases of molecules in the rovibronic ground state is given by molecule association from quantum-degenerate atomic gases on a Feshbach resonance and subsequent coherent optical multi-photon transfer into the rovibronic ground state. In ultracold samples of Cs_2 molecules, we observe two-photon dark resonances that connect the intermediate rovibrational level |v=73,J=2> with the rovibrational ground state |v=0,J=0> of the singlet $X^1\Sigma_g^+$ ground state potential. For precise dark resonance spectroscopy we exploit the fact that it is possible to efficiently populate the level |v=73,J=2> by two-photon transfer from the dissociation threshold with the stimulated Raman adiabatic passage (STIRAP) technique. We find that at least one of the two-photon resonances is sufficiently strong to allow future implementation of coherent STIRAP transfer of a molecular quantum gas to the rovibrational ground state |v=0,J=0>.Comment: 7 pages, 4 figure

Formation of ultracold RbCs molecules by photoassociation

The formation of ultracold metastable RbCs molecules is observed in a double species magneto-optical trap through photoassociation below the ^85Rb(5S_1/2)+^133Cs(6P_3/2) dissociation limit followed by spontaneous emission. The molecules are detected by resonance enhanced two-photon ionization. Using accurate quantum chemistry calculations of the potential energy curves and transition dipole moment, we interpret the observed photoassociation process as occurring at short internuclear distance, in contrast with most previous cold atom photoassociation studies. The vibrational levels excited by photoassociation belong to the 5th 0^+ or the 4th 0^- electronic states correlated to the Rb(5P_1/2,3/2)+Cs(6S_1/2) dissociation limit. The computed vibrational distribution of the produced molecules shows that they are stabilized in deeply bound vibrational states of the lowest triplet state. We also predict that a noticeable fraction of molecules is produced in the lowest level of the electronic ground state

The 3D Structure of N132D in the LMC: A Late-Stage Young Supernova Remnant

We have used the Wide Field Spectrograph (WiFeS) on the 2.3m telescope at Siding Spring Observatory to map the [O III] 5007{\AA} dynamics of the young oxygen-rich supernova remnant N132D in the Large Magellanic Cloud. From the resultant data cube, we have been able to reconstruct the full 3D structure of the system of [O III] filaments. The majority of the ejecta form a ring of ~12pc in diameter inclined at an angle of 25 degrees to the line of sight. We conclude that SNR N132D is approaching the end of the reverse shock phase before entering the fully thermalized Sedov phase of evolution. We speculate that the ring of oxygen-rich material comes from ejecta in the equatorial plane of a bipolar explosion, and that the overall shape of the SNR is strongly influenced by the pre-supernova mass loss from the progenitor star. We find tantalizing evidence of a polar jet associated with a very fast oxygen-rich knot, and clear evidence that the central star has interacted with one or more dense clouds in the surrounding ISM.Comment: Accepted for Publication in Astrophysics & Space Science, 18pp, 8 figure

Hydrogen-like nitrogen radio line from hot interstellar and warm-hot intergalactic gas

Hyperfine structure lines of highly-charged ions may open a new window in observations of hot rarefied astrophysical plasmas. In this paper we discuss spectral lines of isotopes and ions abundant at temperatures 10^5-10^7 K, characteristic for warm-hot intergalactic medium, hot interstellar medium, starburst galaxies, their superwinds and young supernova remnants. Observations of these lines will allow to study bulk and turbulent motions of the observed target and will broaden the information about the gas ionization state, chemical and isotopic composition. The most prospective is the line of the major nitrogen isotope having wavelength 5.65 mm (Sunyaev and Churazov 1084). Wavelength of this line is well-suited for observation of objects at z=0.15-0.6 when it is redshifted to 6.5-9 mm spectral band widely-used in ground-based radio observations, and, for example, for z>=1.3, when the line can be observed in 1.3 cm band and at lower frequencies. Modern and future radio telescopes and interferometers are able to observe the absorption by 14-N VII in the warm-hot intergalactic medium at redshifts above z=0.15 in spectra of brightest mm-band sources. Sub-millimeter emission lines of several most abundant isotopes having hyperfine splitting might also be detected in spectra of young supernova remnants.Comment: 12 pages, 5 figures, accepted by Astronomy Letters; v3: details added; error fixe

Formation and interactions of cold and ultracold molecules: new challenges for interdisciplinary physics

Progress on researches in the field of molecules at cold and ultracold temperatures is reported in this review. It covers extensively the experimental methods to produce, detect and characterize cold and ultracold molecules including association of ultracold atoms, deceleration by external fields and kinematic cooling. Confinement of molecules in different kinds of traps is also discussed. The basic theoretical issues related to the knowledge of the molecular structure, the atom-molecule and molecule-molecule mutual interactions, and to their possible manipulation and control with external fields, are reviewed. A short discussion on the broad area of applications completes the review.Comment: to appear in Reports on Progress in Physic

Optical and near-infrared recombination lines of oxygen ions from Cassiopeia A knots

Context. Fast-moving knots (FMK) in the Galactic supernova remnant Cassiopeia A consist mainly of metals and allow to study element production in supernovae and shock physics in great detail. Aims. We work out theoretically and suggest to observe previously unexplored class of spectral lines -- metal recombination lines in optical and near-infrared bands -- emitted by the cold ionized and cooling plasma in the fast-moving knots. Methods. By tracing ion radiative and dielectronic recombination, collisional $l$-redistribution and radiative cascade processes, we compute resulting oxygen, silicon and sulphur recombination line emissivities. It allows us to determine the oxygen recombination line fluxes, based on the fast-moving knot model of Sutherland and Dopita (1995b), that predicts existence of highly-ionized ions from moderate to very low plasma temperatures. Results. The calculations predict oxygen ion recombination line fluxes detectable on modern optical telescopes in the wavelength range from 0.5 to 3 microns. Line ratios to collisionally-excited lines will allow to probe in detail the process of rapid cloud cooling after passage of a shock front, to test high abundances of O V and O VI ions at low temperatures and measure them, to test existing theoretical models of a FMK and to build more precise ones.Comment: 18 pages, 22 figures, version accepted by A&A. Electronic supplement available at http://www.mpa-garching.mpg.de/~dima/CasA_ORL/e-sup

Dust in Supernovae and Supernova Remnants II: Processing and survival

Observations have recently shown that supernovae are efficient dust factories, as predicted for a long time by theoretical models. The rapid evolution of their stellar progenitors combined with their efficiency in precipitating refractory elements from the gas phase into dust grains make supernovae the major potential suppliers of dust in the early Universe, where more conventional sources like Asymptotic Giant Branch (AGB) stars did not have time to evolve. However, dust yields inferred from observations of young supernovae or derived from models do not reflect the net amount of supernova-condensed dust able to be expelled from the remnants and reach the interstellar medium. The cavity where the dust is formed and initially resides is crossed by the high velocity reverse shock which is generated by the pressure of the circumstellar material shocked by the expanding supernova blast wave. Depending on grain composition and initial size, processing by the reverse shock may lead to substantial dust erosion and even complete destruction. The goal of this review is to present the state of the art about processing and survival of dust inside supernova remnants, in terms of theoretical modelling and comparison to observations