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 Physics , 1999, DOI: 10.1086/312200 Abstract: A group of young, active stars in the vicinity of TW Hydrae has recently been identified as a possible physical association with a common origin. Given its proximity ($\sim$50 pc), age ($\sim$10 Myr) and abundance of binary systems, the TW Hya Association is ideally suited to studies of diversity and evolution of circumstellar disks. Here we present mid-infrared observations of 15 candidate members of the group, 11 of which have no previous flux measurements at wavelengths longer than 2$\mu$m. We report the discovery of a possible 10$\mu$m excess in CD -33$^{\circ}$7795, which may be due to a circumstellar disk or a faint, as yet undetected binary companion. Of the other stars, only TW Hya, HD 98800, Hen 3-600A, and HR 4796A -- all of which were detected by IRAS -- show excess thermal emission. Our 10$\mu$m flux measurements for the remaining members of the Association are consistent with photospheric emission, allowing us to rule out dusty inner disks. In light of these findings, we discuss the origin and age of the TW Hya Association as well as implications for disk evolution timescales.
 Physics , 2002, DOI: 10.1051/0004-6361:20020992 Abstract: We present results of our diffraction-limited mid-infrared imaging of the massive star-forming region W3(OH) with SpectroCam-10 on the 5-m Hale telescope at wavelengths of 8.8, 11.7, and 17.9 micron. The thermal emission from heated dust grains associated with the ultracompact HII region W3(OH) is resolved and has a spatial extent of ~2 arcsec in the N band. We did not detect the hot core source W3(H_2O) which implies the presence of at least 12 mag of extinction at 11.7 micron towards this source. These results together with other data were used to constrain the properties of W3(OH) and W3(H_2O) and their envelopes by modelling the thermal dust emission.
 Physics , 2014, DOI: 10.1088/0004-637X/791/2/99 Abstract: The massive star forming region W49A represents one of the largest complexes of massive star formation present in the Milky Way and contains at least fifty young massive stars still enshrouded in their natal molecular cloud. We employ Spitzer/IRS spectral mapping observations of the northern part of W49A to investigate the mid-infrared (MIR) spatial appearance of the polycyclic aromatic hydrocarbon (PAH) bands, PAH plateau features, atomic lines and continuum emission. We examine the spatial variations of the MIR emission components in slices through two of the ultra compact-HII (UC-HII) regions. We find that the PAH bands reproduce known trends, with the caveat that the 6.2 $\mu$m PAH band seems to decouple from the other ionized PAH bands in some of the UC-HII regions -- an effect previously observed only in one other object: the giant star forming region N66 in the LMC. Furthermore, we compare the nature of the emission surrounding W49A to that of diffuse' sightlines. It is found that the surrounding emission can be explained by line of sight emission, and does not represent true diffuse' material. Additionally, we examine the MIR appearance of star formation on various scales from UC-HII regions to starburst galaxies, including a discussion of the fraction of PAH emission in the 8 $\mu$m IRAC filter. We find that the MIR appearance of W49A is that of a starburst on large scales yet its individual components are consistent with other galactic HII regions.
 Physics , 2009, DOI: 10.1111/j.1365-2966.2010.16206.x Abstract: We present near-IR VLT/ISAAC and mid-IR Spitzer/IRS spectroscopy of the young massive cluster in the W31 star-forming region. H-band spectroscopy provides refined classifications for four cluster members O stars with respect to Blum et al. In addition, photospheric features are detected in the massive Young Stellar Object (mYSO) #26. Spectroscopy permits estimates of stellar temperatures and masses, from which a cluster age of ~0.6 Myr and distance of 3.3 kpc are obtained, in excellent agreement with Blum et al. IRS spectroscopy reveals mid-infrared fine structure line fluxes of [Ne II-III] and [S III-IV] for four O stars and five mYSOs. In common with previous studies, stellar temperatures of individual stars are severely underestimated from the observed ratios of fine-structure lines, despite the use of contemporary stellar atmosphere and photoionization models. We construct empirical temperature calibrations based upon the W31 cluster stars of known spectral type, supplemented by two inner Milky Way ultracompact (UC) HII regions whose ionizing star properties are established. Calibrations involving [NeIII] 15.5um/[NeII] 12.8um, [SIV] 10.5um/[NeII] 12.8um or [ArIII] 9.0um/[NeII] 12.8um have application in deducing the spectral types of early- to mid- O stars for other inner Milky Way compact and UCHII regions. Finally, evolutionary phases and timescales for the massive stellar content in W31 are discussed, due to the presence of numerous young massive stars at different formation phases in a `coeval' cluster.
 Physics , 2009, DOI: 10.1051/0004-6361/200913209 Abstract: The circumstellar structure on 100 AU scales of the massive young stellar object W33A is probed using the VLTI and the MIDI instrument. N-band visibilities on 4 baselines are presented which are inconsistent with a spherically symmetric geometry. The visibility spectra and SED are simultaneously compared to 2D axi-symmetric dust radiative transfer models with a geometry including a rotationally flattened envelope and outflow cavities. We assume an O7.5 ZAMS star as the central source, consistent with the observed bolometric luminosity. The observations are also compared to models with and without (dusty and gaseous) accretion disks. A satisfactory model is constructed which reproduces the visibility spectra for each (u,v) point. It fits the silicate absorption, the mid-IR slope, the far-infrared peak, and the (sub)mm of the SED. It produces a 350 micron morphology consistent with observations. The 10 micron emission on 100 AU scales is dominated by the irradiated walls of the cavity sculpted by the outflow. The visibilities rule out the presence of dust disks with total (gas and dust) masses more than 0.01 Msun. However, optically thick accretion disks, interior to the dust sublimation radius, are allowed to accrete at rates equalling the envelope's mass infall rate (up to 10^(-3) Msun/yr) without substantially affecting the visibilities due to the extinction by the extremely massive envelope of W33A.
 中国物理 B , 2008, Abstract: In this paper a high-repetition-rate mid-infrared (mid-IR) optical parametric oscillator based on periodically poled MgO-doped LiNbO红外线 光学仪器 振荡器 周期性温度optical parametric oscillator, mid-infrared, periodically poled MgO-doped LiNbO_{3}, room temperatureProject supported by the National Natural Science Foundation of China (Grant Nos 60637010 and 10471071), the Ministry of Education of China, the National Research Foundation for the Doctoral Program of Ministry of Education of China (Grant No 20040056010), and Tianjin Application Bases and Advanced Technology Plan (Grant No 07JCYBJC06200).2007-04-106/4/2007 12:00:00 AMIn this paper a high-repetition-rate mid-infrared （mid-IR） optical parametric oscillator based on periodically poled MgO-doped LiNbO3 （PPMgLN） at room temperature was demonstrated. The maximum average mid-IR output power at 3.63μm was 1.02 W with the repetition rate of 60kHz and corresponding efficiency from the pump to the idler was 26.7%. The temperature tuning and the period tuning characteristics were also discussed.Institute of Laser and Opto-electronics, College of Precision Instrument and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China;Cooperated Institute of Nankai University and Tianjin University, Tianjin 300072, China;Key Laboratory o;Institute of Laser and Opto-electronics, College of Precision Instrument and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China;Institute of Laser and Opto-electronics, College of Precision Instrument and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China;Institute of Laser and Opto-electronics, College of Precision Instrument and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China;Institute of Laser and Opto-electronics, College of Precision Instrument and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China;Institute of Laser and Opto-electronics, College of Precision Instrument and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China;Cooperated Institute of Nankai University and Tianjin University, Tianjin 300072, China;Key Laboratory oCorresponding author. E-mail：terry_tju@163.com/qk/85823A/200802/26433263.html4265K, 4270, 4260FIn this paper a high-repetition-rate mid-infrared (mid-IR) optical parametric oscillator based on periodically poled MgO-doped LiNbO红外线 光学仪器 振荡器 周期性温度optical parametric oscillator, mid-infrared, periodically poled MgO-doped LiNbO_{3}, room temperatureProject supported by the National Natural Science Foundation of China (Grant Nos 60637010 and 10471071), the Ministry of Education of China, the National Research Foundation for the Doctoral Program of Ministry of Education of China (Grant No 20040056010), and Tianjin Application Bases and Advanced Technology Plan (Grant No 07JCYBJC06200).2007-04-106/4/2007 12:00:00 AMIn this paper a high-repetition-rate mid-infrared （mid-IR） optical parametric oscillator based on periodically poled MgO-doped LiNbO3
 Physics , 2012, DOI: 10.1051/0004-6361/201118150 Abstract: Mid-IR (8 - 13 micron) interferometric data of four oxygen-rich AGB stars (R Aql, R Aqr, R Hya, and W Hya) and one carbon-rich AGB star (V Hya) were obtained with MIDI/VLTI between April 2007 and September 2009. The spectrally dispersed visibility data are analyzed by fitting a circular fully limb-darkened disk (FDD). Results. The FDD diameter as function of wavelength is similar for all oxygen-rich stars. The apparent size is almost constant between 8 and 10 micron and gradually increases at wavelengths longer than 10 micron. The apparent FDD diameter in the carbon-rich star V Hya essentially decreases from 8 to 12 micron. The FDD diameters are about 2.2 times larger than the photospheric diameters estimated from K-band observations found in the literature. The silicate dust shells of R Aql, R Hya and W Hya are located fairly far away from the star, while the silicate dust shell of R Aqr and the amorphous carbon (AMC) and SiC dust shell of V Hya are found to be closer to the star at around 8 photospheric radii. Phase-to-phase variations of the diameters of the oxygen-rich stars could be measured and are on the order of 15% but with large uncertainties. From a comparison of the diameter trend with the trends in RR Sco and S Ori it can be concluded that in oxygen-rich stars the overall larger diameter originates from a warm molecular layer of H2O, and the gradual increase longward of 10 micron can be most likely attributed to the contribution of a close Al2O3 dust shell. The chromatic trend of the Gaussian FWHM in V Hya can be explained with the presence of AMC and SiC dust. The observations suggest that the formation of amorphous Al2O3 in oxygen- rich stars occurs mainly around or after visual minimum. However, no firm conclusions can be drawn concerning the mass-loss mechanism.
 Physics , 2001, DOI: 10.1086/320332 Abstract: We present ground-based near-infrared (H-band) imaging of the circumstellar disk around the nearby classical T Tauri star TW Hydrae. The scattered light image shows a face-on disk with radius 4 arcseconds (corresponding to 225 AU) and a morphology which agrees with recent images from the Hubble Space Telescope and the Very Large Array. The best fit power-law for the disk's radial surface brightness profile obeys the law r^{-3.3\pm0.3}. We use our image and published continuum flux densities to derive properties of the disk with a simple model of emission from an optically thick, flat disk. The best-fit values for disk mass and inner radius are 0.03 M_{\odot} and 0.3 AU; best-fit values for temperature, density, and grain opacity power law exponents (q, p, and \beta) are 0.7, 1.3, and 0.9, respectively. These properties are similar to those of disks around classical T Tauri stars located in more distant molecular clouds. Because of TW Hydrae's nearby location and pole-on orientation, it is a uniquely favorable object for future studies of radial disk structure at the classical T Tauri stage.
 Physics , 2012, DOI: 10.1088/2041-8205/749/2/L21 Abstract: The massive star forming region W3 was observed with the faint object infrared camera for the SOFIA telescope (FORCAST) as part of the Short Science program. The 6.4, 6.6, 7.7, 19.7, 24.2, 31.5 and 37.1 \um bandpasses were used to observe the emission of Polycyclic Aromatic Hydrocarbon (PAH) molecules, Very Small Grains and Big Grains. Optical depth and color temperature maps of W3A show that IRS2 has blown a bubble devoid of gas and dust of $\sim$0.05 pc radius. It is embedded in a dusty shell of ionized gas that contributes 40% of the total 24 \um emission of W3A. This dust component is mostly heated by far ultraviolet, rather than trapped Ly$\alpha$ photons. This shell is itself surrounded by a thin ($\sim$0.01 pc) photodissociation region where PAHs show intense emission. The infrared spectral energy distribution (SED) of three different zones located at 8, 20 and 25\arcsec from IRS2, show that the peak of the SED shifts towards longer wavelengths, when moving away from the star. Adopting the stellar radiation field for these three positions, DUSTEM model fits to these SEDs yield a dust-to-gas mass ratio in the ionized gas similar to that in the diffuse ISM. However, the ratio of the IR-to-UV opacity of the dust in the ionized shell is increased by a factor $\simeq$3 compared to the diffuse ISM.
 Physics , 2000, DOI: 10.1086/317317 Abstract: We construct a self-consistent model for the wind around W Hya by solving the coupled equations describing the hydrodynamics and dust radiative transfer problems. The model matches simultaneously the observed continuum radiation and wind velocity profile. The water line emission is calculated next using the water abundance as the only free parameter, fitted from the ISO observations of Neufeld et al. (1996) and Barlow et al. (1996). The gas temperature is determined from a thermal balance calculation that includes water as one of its main components. Our model successfully fits all the observed water lines, resolving a major discrepancy between the modeling results of the two observing teams. The mass loss rate is 2.3 x 10^{-6} M_solar yr^{-1}, the water abundance is 1.0 x 10^{-4} and the ortho:para ratio is 1:1.3.
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