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M Emission (m + emission)
Selected AbstractsEnergy Transfer and Population Inversion in Heavy Metal Oxide Glasses Doped with Tm3+ and Tb3+JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2004Jay Hyok Song Emission properties and energy transfer of PbO,Bi2O3,Ga2O3,GeO2 glasses codoped with Tm3+ and Tb3+ ions were investigated. The 1.48-,m emission due to the Tm3+:3H4,3F4 transition can be used to amplify the S-band (1460,1530-nm) signal light. With Tb3+ addition, the lifetime and emission intensity of the Tm3+:3F4 level decreased sharply via the Tm3+:3F4,Tb3+:7F0,1,2 energy transfer. Population densities of the 3F4 and 3H4 levels in Tm3+ calculated from rate equations clearly verified that population inversion in Tm3+ ions became possible with as little as 0.1 mol% of Tb3+ addition. [source] The haloes of planetary nebulae in the mid-infrared: evidence for interaction with the interstellar mediumMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009G. Ramos-Larios ABSTRACT The motion of planetary nebulae through the interstellar medium (ISM) is thought to lead to a variety of observational consequences, including the formation of bright rims, deformation and fragmentation of the shells, and a shift of the central stars away from the geometric centres of the envelopes. These and other characteristics have been noted through imaging in the visual wavelength regime. We report further observations of such shells taken in the mid-infrared (MIR), acquired through programmes of Infrared Array Camera imaging undertaken using the SpitzerSpace Telescope. NGC 2440 and NGC 6629 are shown to possess likely interacting haloes, together with ram-pressure-stripped material to one side of their shells. Similarly, the outer haloes of NGC 3242 and NGC 6772 appear to have been fragmented through Rayleigh,Taylor (RT) instabilities, leading to a possible flow of ISM material towards the inner portions of their envelopes. If this interpretation is correct, then it would suggest that NGC 3242 is moving towards the NE, a suggestion which is also supported through the presence of a 60 ,m tail extending in the opposite direction, and curved bands of H, emission in the direction of motion , components which may arise through RT instabilities in the magnetized ISM. NGC 2438 possesses strong scalloping at the outer limits of its asymptotic giant branch (AGB) halo, probably reflecting RT instabilities at the nebular/ISM interface We also note that the interior structure of the source has been interpreted in terms of a recombining shell, a hypothesis which may not be consistent with the central star luminosities. Finally, we point out that two of the rims (and likely shock interfaces) appear to have a distinct signature in the MIR, whereby relative levels of 8.0 ,m emission are reduced. This may imply that the grain emission agents are depleted in the post-shock AGB regimes. [source] A census of the Carina Nebula , II.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007Energy budget, global properties of the nebulosity ABSTRACT The first paper in this series took a direct census of energy input from the known OB stars in the Carina Nebula, and in this paper we study the global properties of the surrounding nebulosity. This detailed comparison may prove useful for interpreting observations of extragalactic giant H ii regions and ultraluminous infrared (IR) galaxies. We find that the total IR luminosity of Carina is about 1.2 × 107 L,, accounting for only about 50,60 per cent of the known stellar luminosity from Paper I. Similarly, the ionizing photon luminosity derived from the integrated radio continuum is about 7 × 1050 s,1, accounting for ,75 per cent of the expected Lyman continuum from known OB stars. The total kinetic energy of the nebula is about 8 × 1051 erg, or ,30 per cent of the mechanical energy from stellar winds over the lifetime of the nebula, so there is no need to invoke a supernova (SN) explosion based on energetics. Warm dust grains residing in the H ii region interior dominate emission at 10,30 ,m, but cooler grains at 30,40 K dominate the IR luminosity and indicate a likely gas mass of ,106 M,. We find an excellent correlation between the radio continuum and 20,25 ,m emission, consistent with the idea that the ,80-K grain population is heated by trapped Ly, photons. Similarly, we find a near perfect correlation between the far-IR optical depth map of cool grains and 8.6-,m hydrocarbon emission, indicating that most of the nebular mass resides as atomic gas in photodissociation regions and not in dense molecular clouds. Synchronized star formation around the periphery of Carina provides a strong case that star formation here was indeed triggered by stellar winds and ultraviolet radiation. This second generation appears to involve a cascade toward preferentially intermediate- and low-mass stars, but this may soon change when , Carinae and its siblings explode. If the current reservoir of atomic and molecular gas can be tapped at that time, massive star formation may be rejuvenated around the periphery of Carina much as if it were a young version of Gould's Belt. Furthermore, when these multiple SNe occur, the triggered second generation will be pelted repeatedly with SN ejecta bearing short-lived radioactive nuclides. Carina may therefore represent the most observable analogue to the cradle of our own Solar system. [source] ISO observations of 3,200 ,m emission by three dust populations in an isolated local translucent cloudMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2005M. G. Rawlings ABSTRACT We present isophot spectrophotometry of three positions within the isolated high-latitude cirrus cloud G 300.2,16.8, spanning from the near- to far-infrared (NIR to FIR). The positions exhibit contrasting emission spectrum contributions from the unidentified infrared bands (UIBs), very small grains (VSGs) and large classical grains, and both semi-empirical and numerical models are presented. At all three positions, the UIB spectrum shapes are found to be similar and the large grain emission may be fitted by an equilibrium temperature of ,17.5 K. The energy requirements of both the observed emission spectrum and optical scattered light are shown to be satisfied by the incident local interstellar radiation field (ISRF). The FIR emissivity of dust in G 300.2,16.8 is found to be lower than in globules or dense clouds and is even lower than model predictions for dust in the diffuse interstellar medium (ISM). The results suggest physical differences in the ISM mixtures between positions within the cloud, possibly arising from grain coagulation processes. [source] Limits on the Short Term Variability of Sagittarius A* in the Near-InfraredASTRONOMISCHE NACHRICHTEN, Issue S1 2003S. D. Hornstein Abstract The detection of X-ray flares by the Chandra X-ray Observatory and XMM-Newton has raised the possibility of enhanced emission over a broad range of wavelengths from Sagittarius A*, the suspected 2.6 × 106 M, black hole at the Galactic center, during a flaring event. We have, therefore, reconstructed 3,4 hr data sets from 2 ,m speckle and adaptive optics images (,core = 50,100 mas) obtained with the W. M. Keck 10 m telescopes between 1995 and 2002. The results for 25 of these observations were reported by Hornstein et al. (2002) and an additional 11 observations are presented here. In the 36 separate observations, no evidence of any significant excess emission associated with Sgr A* was detected. The lowest of our detection limits gives an observed limit for the quiescent state of Sgr A* of 0.09 ± 0.005 mJy, or, equivalently, a dereddened value of 2.0 ± 0.1 mJy. Under the assumption that there are random 3 hr flares producing both enhanced X-ray and near-infrared emission, our highest limit constrains the variable state of Sgr A* to ,0.8 mJy (observed) or 19 mJy (dereddened). These results suggest that the early model favored by Markoff et al. (2002), in which the flare is produced through local heating of relativistic particles surrounding Sgr A* (e.g., a sudden magnetic reconnection event), is unlikely because it predicts peak 2 ,m emission of ,300 mJy, well above our detection limit. [source] | ||||||||||