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تسجيل مستخدم جديدIdentification of New Near-Infrared DIBs in the Orion Nebula
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Large organic molecules and carbon clusters are basic building blocks of life, but their existence in the universe has not been confirmed beyond doubt. A number of unidentified absorption features (arising in the diffuse inter-stellar medium), usually called ``Diffuse Inter-stellar Bands (DIBs), are hypothesized to be produced by large molecules. Among these, buckminsterfullerene C_60 has gained much attention as a candidate for DIB absorbers because of its high stability in space. Two DIBs at ~9577A and 9632A have been reported as possible features of C_60^+. However, it is still not clear how their existence depends on their environment. We obtained high-resolution spectra of three stars in/around the Orion Nebula, to search for any correlations of the DIB strength with carriers physical conditions, such as dust-abundance and UV radiation field. We find three DIBs at ~9017A, 9210A, and 9258A as additional C_60^+ feature candidates, which could support this identification. These DIBs have asymmetric profiles similar to the longer wavelength features. However, we also find that the relative strengths of DIBs are close to unity and differ from laboratory measurements, a similar trend as noticed for the 9577/9632 DIBs.
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Using the United Kingdom Infrared Telescope on Mauna Kea, we have carried out a new near-infrared J, H, K monitoring survey of almost a square degree of the star-forming Orion Nebula Cluster with observations on 120 nights over three observing season
s, spanning a total of 894 days. We monitored ~15,000 stars down to J=20 using the WFCAM instrument, and have extracted 1203 significantly variable stars from our data. By studying variability in young stellar objects (YSOs) in the H-K, K color-magnitude diagram, we are able to distinguish between physical mechanisms of variability. Many variables show color behavior indicating either dust-extinction or disk/accretion activity, but we find that when monitored for longer periods of time, a number of stars shift between these two variability mechanisms. Further, we show that the intrinsic timescale of disk/accretion variability in young stars is longer than that of dust-extinction variability. We confirm that variability amplitude is statistically correlated with evolutionary class in all bands and colors. Our investigations of these 1203 variables have revealed 73 periodic AA Tau type variables, many large-amplitude and long-period (P > 15 day) YSOs, including three stars showing widely-spaced periodic brightening events consistent with circumbinary disk activity, and four new eclipsing binaries. These phenomena and others indicate the activity of long-term disk/accretion variability processes taking place in young stars. We have made the light curves and associated data for these 1203 variables available online.
Wide-field (~8 x 8) and deep near-infrared (JHKs bands) polarization images of the Orion nebulae (IRNe) around young stellar objects (YSOs), both massive and low-mass. We found the IRNe around both IRc2 and BN to be very extensive, suggesting that th
ere might be two extended (>0.7 pc) bipolar/monopolar IRNe in these sources. We discovered at least 13 smaller-scale (~0.01-0.1 pc) IRNe around less-massive YSOs including the famous source theta^2 Ori C. We also suggest the presence of many unresolved (<690 AU) systems around low-mass YSOs and young brown dwarfs showing possible intrinsic polarizations. Wide-field infrared polarimetry is thus demonstrated to be a powerful technique in revealing IRNe and hence potential disk/outflow systems among high-mass to substellar YSOs.
The existence of multiple layers in the inner Orion Nebula has been revealed using data from an Atlas of spectra at 2 and 12 km/s resolution. These data were sometimes grouped over Samples of 10x10to produce high Signal to Noise spectra and sometimes
grouped into sequences of pseudo-slit Spectra of 12.8--39 width for high spatial resolution studies. Multiple velocity systems were found: Vmif traces the Main Ionization Front (MIF), Vscat arises from back-scattering of Vmif emission by particles in the background Photon Dissociation Region (PDR), Vlow is an ionized layer in front of the MIF and if it is the source of the stellar absorption lines seen in the Trapezium stars, it must lie between the foreground Veil and those stars, Vnew may represent ionized gas evaporating from the Veil away from the observer. There are features such as the Bright Bar where variations of velocities are due to changing tilts of the MIF, but velocity changes above about 25arise from variations in velocity of the background PDR. In a region 25 ENE of the Orion-S Cloud one finds dramatic changes in the [OIII]components, including the signals from the Vlowoiii and Vmifoiii becoming equal, indicating shadowing of gas from stellar photons of >24.6 eV. This feature is also seen in areas to the west and south of the Orion-S Cloud.
In order to study the nature, origin, and impact of turbulent velocity fluctuations in the ionized gas of the Orion Nebula, we apply a variety of statistical techniques to observed velocity cubes. The cubes are derived from high resolving power ($R a
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