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Far-infrared observations of GL 915, 618, 2688 and OH 0739-14 are presented. The data provide information on the total flux arising in each of these sources, and on the wavelength-dependence of the emissivity of the associated dust. Two sources, GL 618 and GL 2688, have far-infrared continua similar to those recently observed in planetary nebulae.
During the past 15 years considerable progress in observational techniques has been achieved in the middle infrared, the spectral region most diagnostic of molecular vibrations. Spectra of many different astronomical infrared sources are now available. By comparing these astronomical spectra with the spectra of lab ices, one can determine the composition and abundance of the icy materials frozen on the cold dust grains present in the interior of molecular clouds. In the experiments described, the assumption is made that cometary ices are similar to interstellar ices. As an illustration of the processes which can take place as an ice is irradiated and subsequently warmed, the infrared spectra is presented of the mixture H2O:CH3OH:CO:NH3:C6H14 (100:50:10:10:10). Apart from the last species, the ratio of these compounds is representative of the simplest ices found in interstellar clouds.
During the past 15 years considerable progress in observational techniques has been achieved in the middle infrared (5000 to 500 cm(-1), 2 to 20 microns m), the spectral region most diagnostic of molecular vibrations. Spectra of many different astronomical infrared sources, some deeply embedded in dark molecular clouds, are now available. These spectra provide a powerful probe, not only for the identification of interstellar molecules in both the gas solid phases, but also of the physical and chemical conditions which prevail in these two very different domains. By comparing these astronomical spectra with the spectra of laboratory ices one can determine the composition and abundance of the icy materials frozen on the cold (10K) dust grains present in the interior of molecular clouds. These grains and their ice mantles may well be the building blocks from which comets are made. As an illustration of the processes which can take place as an ice is irradiated and subsequently warmed, researchers present the infrared spectra of the mixture H2O:CH3OH:CO:NH3:C6H14 (100:50:10:10:10). Apart from the last species, the ratio of these compounds is representative of the simplest ices found in interstellar clouds. The last component was incorporated into this particular experiment as a tracer of the behavior of a non-aromatic hydrocarbon. The change in the composition that results from ultraviolet photolysis of this ice mixture using a UV lamp to simulate the interstellar radiation field is shown. Photolysis produces CO, CO2, CH4, HCO, H2CO, as well as a family of moderately volatile hydrocarbons. Less volatile carbonaceous materials are also produced. The evolution of the infrared spectrum of the ice as the sample is warmed up to room temperature is illustrated. Researchers believe that the changes are similar to those which occur as ice is ejected from a comet and warmed up by solar radiation. The warm-up sequence shows that the nitrile or iso-nitrile bearing compound produced during photolysis evaporates between 200 and 250K, suggesting that it is carried by a small molecular species. These molecules could be similar to the source material in Comet Halley that is ejected in grains into the coma, freed by sublimation, and photolyzed by solar radiation to produce the observed jets.
Spectra of infrared sources associated with molecular clouds have shown absorption features at wavelengths of 6.0 and 6.8 microns. It is suggested that the 6.0 micron feature can be identified with the stretching vibration of C = 0 and the 6.8 micron feature with the bending vibrations of CH2 and CH3. The amount of carbon in the form of hydrocarbon molecules may be comparable to the amount in CO. This abundance of hydrocarbons is probably too large to be consistent with radio observations if the molecules are gaseous, but large abundances of hydrocarbons on the surfaces of grains may explain the infrared features, and yet be unobservable in the radio.
The molecular cloud associated with the S235 H II region has been studied by means of molecular lines and near-infrared observations. The cloud consists of two components, one of which partly surrounds the S235 H II region. The other component contains a dense, hot region of active star formation, marked by self-reversed CO profiles, compact H II regions, masers, and infrared sources. From the molecular line data, the size and mass of the two components are estimated to be 6-8 pc and 3000-4000 solar masses. More detailed studies near the region of active star formation yield estimates of density (approximately 200,000-500,000/cu cm) and the abundances of H2CO, HCO(+), HCN, and (C-13)O. Analysis of the energetics suggests that the cloud is heated by the exciting star of S235 and by the exciting stars of the compact H II regions. Assuming that the gas is heated by collisions with warm dust grains, the far-infrared luminosity has been predicted. The observations of far-infrared emission are in reasonable agreement with predictions.
The infrared source R CrA IRS 5 in the R CrA dark cloud has been mapped, and it is found that it is extended at H (1.6 micron) and at K (2.2 micron). The geometry of the data suggest that this object consists of a disk and polar reflection lobe surrounding a star, similar to GSS 30 in the Ophiuchus dark cloud and to SGS 1 in the NGC 1333 dark cloud. The illuminating star has an effective temperature below 8000 K, a luminosity less than 9 solar luminosities, and lies above the main sequence. The luminosity of this star is smaller than the luminosity of any other known star which illuminates an infrared reflection nebula.
Young stars are formed out of the interstellar medium (ISM) which is replenished by mass loss rates from evolved stars. Circumstellar matter around young and evolved stellar objects usually emits energy in the infrared (IR) wavelength range as the matter is heated by the central star. Surveys of the Magellanic Clouds with the Spitzer Space Telescope in the 3.6-160 micron range have previously been completed. These surveys have led to catalogs of infrared sources: which include HII regions, young stars, super giants, asymptotic giant branch (AGB) stars, post-asymptotic giant branch (post-AGB) stars, and planetary nebulae. The utility of such surveys can be improved upon by using Hubble Space Telescope (HST) data. HST provides higher angular resolution than Spitzer and has allowed for more detailed investigation of these luminous IR objects. This project used previously obtained HST archival data to examine luminous IR objects at optical wavelengths. This allows for the reclassification of stellar objects previously thought as one type of object or in a particular stage of their stellar evolution. An overall objective of this project included looking for extended nebulosity around evolved stars to better understand the life cycle of such objects and classify these nebulae by shape.
We report the first detection of galactic spiral structure by means of thermal emission from magnetically aligned dust grains. Our 89μm polarimetric imaging of NGC 1068 with the High-resolution Airborne Wideband Camera/Polarimeter(HAWC+)on NASAs Stratospheric Observatory for Infrared Astronomy(SOFIA)also sheds light on magnetic field structure in the vicinity of the galaxyʼs inner-bar and active galactic nucleus(AGN).We find correlations between the 89μm magnetic field vectors and other tracers of spiral arms, and a symmetric polarization pattern as a function of the azimuthal angle arising from the projection and inclination of the disk field component in the plane of the sky. The observations can befit with a logarithmic spiral model with pitch angle of-+16.92.82.7and a disk inclination of 48°±2°. We infer that the bulk of the interstellar medium from which the polarized dust emission originates is threaded by a magnetic field that closely follows the spiral arms. Inside the central starburst disk(<1.6 kpc), the degree of polarization is found to be lower than for far-infrared sources in the Milky Way, and has minima at the locations of most intense star formation near the outer ends of the inner-bar. Inside the starburst ring, the field direction deviates from the model, becoming more radial along the leading edges of the inner-bar. The polarized flux and dust temperature peak∼3′′–6′′NE of the AGN at the location of a bow shock between the AGN outflow and the surrounding interstellar medium, but the AGN itself is weakly polarized(<1%)at both 53 and 89μm.
We present new methodology to use cosmic infrared background (CIB) fluctuations to probe sources at 10 less than or approx. equal to z less than or approx. equal to 30 from a James Webb Space Telescope (JWST) NIRCam configuration that will isolate known galaxies to 28 AB mag at 0.55 m. At present significant mutually consistent source-subtracted CIB fluctuations have been identified in the Spitzer and AKARI data at 25 m, but we demonstrate internal inconsistencies at shorter wavelengths in the recent CIBER data. We evaluate CIB contributions from remaining galaxies and show that the bulk of the high-z sources will be in the confusion noise of the NIRCam beam, requiring CIB studies. The accurate measurement of the angular spectrum of the fluctuations and probing the dependence of its clustering component on the remaining shot noise power would discriminate between the various currently proposed models for their origin and probe the flux distribution of its sources. We show that the contribution to CIB fluctuations from remaining galaxies is large at visible wavelengths for the current instruments precluding probing the putative Lyman-break of the CIB fluctuations. We demonstrate that with the proposed JWST configuration such measurements will enable probing the Lyman-break. We develop a Lyman-break tomography method to use the NIRCam wavelength coverage to identify or constrain, via the adjacent two-band subtraction, the history of emissions over 10 less than or approx. equal to z less than or approx. equal to 30 as the universe comes out of the Dark Ages. We apply the proposed tomography to the current SpitzerIRAC measurements at 3.6 and 4.5 m, to find that it already leads to interestingly low upper limit on emissions at z greater than or approx. equal to 30.
Preregulator feedback circuit employing a Light Actuated Switch /LAS/ provides a simple and efficient feedback device in a power supply preregulator which maintains dc isolation between input and output grounds. The LAS consists of a diode PN junction infrared source close to, but electrically isolated from, a photodetector.
The angular size of the infrared source associated with the peculiar optical object Eta Carinae was measured at wavelengths from 2.2 to 18 microns. The angular diameter, which is 2 arc sec at 2.2 microns, is found to increase with increasing wavelength to 6 arc sec at 10 to 18 microns. The solid materials responsible for the thermal radiation have a temperature of roughly 425 K in the inner shell, and 250 K in the outer region. The observed bolometric magnitude of -11.5 is mostly produced by the cool shell, which in turn must be powered by absorption of shortwave radiation emitted by a central object of corresponding bolometric magnitude.
The interaction of graphite grains with a hot gas is investigated. Detailed computations, based on experimental data and simple theoretical models are presented of the energy transfer by gas particle collisions and of the sputtering rates and grain lifetimes, as functions of gas temperature and grain radius. The electric charge on the grains is calculated, and the effect of electric forces on mechanical stability is discussed. The rate at which the gas cools by this mechanism is evaluated. The results of the work on gas-grain cooling and sputtering rates are applied to various astrophysical environments where dust and hot gas may coexist. The effect is studied of swept-up interstellar grains on the evolution of young supernova remnants, and the infrared luminosity is computed as a function of the age of the remnant. An interpretation is proposed of far-infrared sources embedded in compact H II regions or dense clouds, in terms of the supernova phenomenon, with specific application to eta Carinae. The question of the existence of dust in intergalactic matter in galaxy clusters is also reexamined.
The expected polarization of far infrared sources is discussed, and it is shown that the observed degree of polarization generally depends on two factors: (1) the availability of a mechanism that can produce polarization, and (2) the gain in polarization which absorption or stimulated emission can produce within a source. It is pointed out that stimulated emission could produce sizeable gain changes in compact dust clouds such as those associated with H2 regions and possibly also in dense regions exhibiting OH and H2O masers. Whether such a gain can actually become positive (maser-like behavior) is not clear, but this would in any case depend on the chemical structure of the grain material and the spectral range of interest.
The performance characteristics of a widely tunable infrared source that can be rapidly and conveniently angle tuned over the entire 1.4-4.4 micron range are reported. It is significant that the source requires only one set of optics and a single LiNbO3 crystal to tune the entire range. Conversion efficiencies of 15% and an operating amplitude stability of better than 3% have been demonstrated. The availability of large 15-mm-diam by 5-cm-long 47-deg cut LiNbO3 crystals makes possible oscillator operation at up to 2 J of 1.06-micron input pulse energy.
The paper reports high-sensitivity observations of (C-12)O and (C-13)O in the infrared source IRC + 10216, which were made with the NRAO 11-m telescope at frequencies of 115.2712 and 110.2014 GHz, respectively. The emission-line profiles are found to be in good qualitative agreement with model profiles predicted for a spherically symmetric and uniformly expanding envelope. Analysis of the profile shapes indicates that the (C-12)O line is optically thick, while the (C-13)O line is both optically thin and double-peaked. It is shown that the shape of the (C-12)O line is determined largely by the motion of the gas and that the expansion velocity at the edges of the CO cloud is 15 km/s, in contrast to 12 km/s for more centrally confined molecules. Based on the estimated (C-13)O content, the envelope mass is estimated to be 0.5 solar mass.
Spectrophotometric observations from 2 to 4 microns and from 8 to 13 microns of several infrared sources associated with molecular clouds are reported. Narrow absorption features at 3.08 microns, attributed to interstellar ices, appear in all sources with a molecular cloud in the intervening line of sight. All sources showing ice absorptions also show broad absorption features, attributed to cold silicates, from 8 to 13 microns. The observed ice absorption profiles are all quite similar; however, they do not fit in detail Mie theory predictions of extinction for pure H2O or NH3 ices. The ratio of ice-to-silicate optical depths is found to vary, with most sources showing a ratio in the range 0.1-0.4. The ratio of visual extinction to ice absorption is found to increase rapidly from inside to outside the molecular cloud in NGC 2024.
A far-infrared map of M20 shows a total flux of 26 kJy at an effective wavelength of 69 microns and a size of 8 arcmin FWHM. In the region near M20, two compact far-infrared sources were also detected; one source coincides with W28 C, and the other is not identified with any radio source.
The Lambda Orionis association has the photometric properties of a typical young cluster with an age of about 4 million yr. Its distance is 400 + or - 40 pc. Attention is drawn to the lack of a dense molecular cloud and associated infrared sources in this young grouping