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Results for “Dust continuum emission”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
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NASA NTRS1991

Origins of the 12-200 micron flux in NGC 6946 - Starlight and continuum dust emission from AN Sc galaxy

Infrared maps and optical CCD images of NGC 6946, a nearly face-on spiral with evidence of active star formation, are presented. Consideration is given, at 1-3 kpc spatial scales, to the relationship of the infrared continuum to spiral and radial structure, tracers of the interstellar medium, and ionizing and nonionizing sources of stellar radiation. Two infrared components were revealed - one with surface brightnesses of 20-60 Jy per 45 arcsec aperture at 160 microns, and the other with a surface brightness of less than 20 Jy. Various continuum distributions show discrete sources coinciding with giant H II regions superposed on a smooth unresolved disk background which decreases exponentially with the radius. The optical and spectral properties of the nuclear source and the disk are described. Dust properties and heating conditions, and far-infrared emitting phases are discussed.

Engargiola, G.↗
NASA NTRS1992

The structure of NGC at 100, 160, and 200 microns - Continuum dust emission in a quiescent Sb galaxy

Observations of NGC 4565 at 100, 160, and 200 microns with the University of Chicago Far-Infrared Camera and the NASA-Kuiper Airborne Observatory are reported. In order to examine the dependence of FIR emission on spiral structure and star formation activity, these observations of NGC 4565, a quiescent Sb galaxy, are compared with observations of NGC 6946, an active Sc galaxy, made by Engargiola (1991) using the same instruments. Warm dust (30 K) in a bisymmetric spiral pattern superposed on an exponential disk of cool dust (20 K) can account for the FIR morphology of NGC 4565. Optical and IR data suggest that there are more embedded sources heating dust locally in the southeast arm region and more UV radiation from unobscured young stellar associations heating the cool, neutral medium in the northeast arm region.

Engargiola, G.↗
NASA NTRS2018

The Complex Morphology of the Young Disk MWC 758: Spirals and Dust Clumps around a Large Cavity

We present Atacama Large Millimeter Array observations at an angular resolution of 0 1 - 0 2 of the disk surrounding the young Herbig Ae star MWC758. The data consist of images of the dust continuum emission recorded at 0.88 millimeter, as well as images of the 13CO and C18O J = 3-2 emission lines. The dust continuum emission is characterized by a large cavity of roughly 40 au in radius which might contain a mildly inner warped disk. The outer disk features two bright emission clumps at radii of ~47 and 82 au that present azimuthal extensions and form a double-ring structure. The comparison with radiative transfer models indicates that these two maxima of emission correspond to local increases in the dust surface density of about a factor 2.5 and 6.5 for the south and north clumps, respectively. The optically thick 13CO peak emission, which traces the temperature, and the dust continuum emission, which probes the disk mid plane, additionally reveal two spirals previously detected in near-IR at the disk surface. The spirals seen in the dust continuum emission present, however, a slight shift of a few au toward larger radii and one of the spirals crosses the south dust clump. Finally, we present different scenarios to explain the complex structure of the disk.

Atacama Large Millimeter Array↗
NASA NTRS1996

Evidence for the Evolution of Grain Properties in the NGC 2024 Star Forming Ridge

High-resolution images of the NGC 2024 molecular ridge in CS(2-1) and 3 mm continuum emission have been obtained using the Owens Valley millimeter array. The data are used to determine the temperature and dynamics of the ridge, and to ascertain the evolutionary state of the embedded protostars FIR2-7. Dust continuum emission is detected from all six FIR sources. The CS(2-1) follows the ridge closely, but does not always coincide with the FIR sources. Direct comparison of column density estimates derived from the CS and the dust emission in the ridge shows that for all FIR sources except FIR5 both methods are in agreement to within a factor of two, assuming a dust opacity k(sub 3 mm) = 0.01 cm(exp 2)/g. However, away from the FIR sources strong CS(1-0) emission is observed in several compact clumps which, with the above dust opacity, should have been detected in 3 mm dust continuum. The brightness temperature of the CS, approx. 40 K, rules out the possibility that the high line-to-continuum ratio is due to low gas temperatures; the discrepancy can be resolved if k(sub 3 mm) is a factor of 10 lower away from the FIR sources. A new high-resolution image of the 450-micron dust continuum emission obtained using the James Clerk Maxwell Telescope supports this hypothesis. These results suggest an evolution in the physical properties of the dust grains, possibly grain size, between quiescent regions in the ridge and the sites of active star formation.

Chandler, C. J.↗
NASA NTRS1998

Dust Emission and Molecular Depletion in L1498

The dust continuum emission provides information aboiut the chemical depletion and the properties of cold cores where there is a lack of gas tracers.

molecular cloud L1498 dust continuum emission gas-↗
NASA NTRS1993

Gas and dust in the pre-main-sequence multiple system GG Tauri

We present 1.4 and 2.7 mm aperture synthesis maps of the gas and dust continuum emission around GG Tauri, a very young component of a premain-sequence multiple star system; both GG Tau and its apparent companion, GG Tau/c, at 1500 AU separation, are themselves binaries. At 1.4 mm, dust continuum emission of about 750 AU in extent is associated with GG Tau, and a secondary peak is near GG Tau/c. Spectral line images reveal gaseous structure around GG Tau, elongated along the GG Tau-GG Tau/c axis. There is some suggestion that the gas associated with GG Tau/c alone is extended in a different direction. Marked changes in the morphology and velocity structure of the molecular emission near GG Tau/c also indicate that this system is differently oriented. Clumps between the two systems may be vestiges of a connecting bar. GG Tau and GG Tau/c appear to have originated in a common cloud; their different systemic orientations suggest that they formed from an initially prolate cloud rather than from an extensive and highly flattened disk.

Koerner, D. W.↗
NASA NTRS1998

Investigating the Near-Infrared Properties of Planetary Nebulae II. Medium Resolution Spectra: Medium Resolution Spectra - 2

We present medium-resolution (R approximately 700) near-infrared (lambda = 1 - 2.5 micrometers) spectra of a sample of planetary nebulae (PNe). A narrow slit was used which sampled discrete locations within the nebulae; observations were obtained at one or more positions in the 41 objects included in the survey. The PN spectra fall into one of four general categories: H1 emission line-dominated PNe, H1 and H2 emission line PNe, H2 emission line-dominated PNe, and continuum-dominated PNe. These categories correlate with morphological type, with the elliptical PNe falling into the first group, and the bipolar PNe primarily in the H2 and continuum emission groups. The categories also correlate with C/O ratio, with the O-rich objects falling into the first group and the C-rich objects in the groups. Other spectral features were observed in all catagories, such as continuum emission from the central star, and warm dust continuum emission towards the long wavelength end of the spectra. H2 was detected in four PNe in this survey for the first time. An analysis was performed using the H2 line ratios in all of the PN spectra in the survey where a sufficient number of lines were observed to determine the ortho-to-para ratio and the rotational and vibrational excitation temperatures of the H-2 in those objects. One unexpected result from this analysis is that the H-2 is excited by absorption of ultraviolet photons in most of the PNe, although there are several PNe in which collisional excitation plays an important role. The correlation between bipolar morphology and H2 emission has been strengthened with the new detections of H2 in this survey.

Hora, Joseph L.↗
NASA NTRS1997

Mid- and Far-IR Spectroscopy of the Nebular Phase of SN1987A

The mid- and far-infrared (IR) spectra of the nebular phase of SM 987A spans 250 days through more than 1000 days after the event. Analysis of the spectra, largely obtained from the Kuiper Airborne Observatory, leads to a rich picture of the structure of the supernebula. The evidence for dust grain formation. In the nebula after about 580 days will be reviewed. The dust continuum emission spectrum was gray and dust appears to have condensed in optically thick 'clumps' throughout a significant fraction of the nebula. Additional information is contained in the original extended abstract.

Wooden, Diane↗
NASA NTRS1993

The contribution of disks and envelopes to the millimeter continuum emission from very young low-mass stars

We investigate the question of disk formation during the protostar phase. We model the dust continuum emission from the dense cloud core using the cloud-collapse models of Terebey et al. (1984) and show that dust emission from the dense core is important when measured with large single-dish telescopes at 1.3 mm, but nearly negligible with interferometers at 2.7 mm. From published and new data, we conclude that massive disks are also seen toward a number of other sources including L1448 IRS 3, whose disk mass is estimated to be 0.5 solar mass. However, 1.3 mm data show that massive disks are relatively rare, occurring around perhaps 5 percent of young embedded stars. This implies that either massive disks occur briefly during the embedded phase or that relatively few young stars form massive disks. The median 1.3 mm flux density of IRAS-Dense cores in our sample is nearly the same as T Tauri stars in the sample of Beckwith et al. (1990). We conclude that the typical disk mass is not significantly higher during the embedded phase than during the later T Tauri phase.

Terebey, S.↗
NASA NTRS1986

The infrared spectrum of M8 E - Evidence for circumstellar CO

High-resolution spectroscopic observations of the compact infrared source M8 E are reported in the region from 3 to 5 microns. Very prominent CO absorption lines are observed in the v = 1-0 band at 4.7 microns. The velocity width and rotational temperature suggest that this CO absorption occurs in a highly excited region. The high background continuum flux level and the prominent appearance of the CO features suggest that the CO line-forming region must be in front of the dust emission region. A blister model for M8 E, which places most of the dust continuum emission behind the source, satisfies this requirement. According to this picture, the observed circumstellar CO spectrum shows a high rotational temperature and a large velocity dispersion because of the combined effects of the strong stellar wind and possible shock heating near the dust zone as the wind encounters the ambient molecular cloud.

Larson, H. P.↗
NASA NTRS1994

(abstract) The Circumstellar Environment of the Extremely Young Protostellar Source L1448IRS3

The class 0 sources form an interesting new category of protostellar objects. Many have strong millimeter continuum emission and exhibit jetlike outflows. There are suggestions that these objects are systematically younger than typical embedded (class I) sources. We are investigating the properties of class 0 sources to determine whether they are indeed very young or perhaps represent extreme physical conditions, such as rapid rotation. We present millimeter interferometric data for the class 0 object known as L1448 IRS3. This young low-mass star has extremely strong millimeter continuum emission. The interferometer data show the emission is resolved on a scale of a few arcseconds (1000 AU) This suggests the bulk of the dust continuum emission originates in an 'infall' envelope rather than a protostar disk. In addition, the C180 line data display a strong velocity gradiant which indicates the dense core is rapidly rotating. We compare our data with the predictions of protostellar collapse models.

protostellar objects young protostellar sources mi↗
NASA NTRS2003

High Resolution Imaging of Circumstellar Disks at Millimeter Wavelengths

Our program uses the techniques of millimeter interferometry to make high resolution observations of dust continuum emission to study the structure of protoplanetary disks and debris disks around nearby stars. Observations of dust emission at these wavelengths are advantageous because the dust emission is generally optically thin and directly proportional to mass, and contrast with stellar photospheres is not a problem. We are using of several observational facilities, including (1) the Very Large Array (VLA) of the National Radio Astronomy Observatories, (2) the Plateau de Bure Interferometer (PdBI) of the Institut de RadioAstronomie Millimetrique, and (3) the Submillimeter Array (SMA), now under construction by the Smithsonian Astrophysical Observatory and Academia Sinica (Taiwan). In the past year, we have accomplished the following (more details below): (1) We continued work on our 'low resolution' VLA survey of disks in Herbig Ae star and binary systems, primarily to identify candidates for higher resolution follow-up. We have submitted a paper for publication on the detailed analysis of the structure of the disk around CQ Tauri; (2) We completed analysis of our PdBI observations of the debris disk around Vega, and we presented these results at (1) the 199th AAS meeting in Washington, DC, and (2) a symposium in memory of Fred Gillett on Debris Disks and the Formation of Planets, in Tucson, AZ; (3) We continue commissioning observations with the SMA, which include the first ever interferometric images in the 850 micron wavelength band, in preparation for eventually imaging debris disks.

Wilner, David J.↗
NASA NTRS1993

IRAS 21391 + 5802 - A study in intermediate mass star formation

We present infrared and millimeter wavelength observations of the cold IRAS source 21391 + 5802 and its associated molecular core. Infrared observations at lambda = 3.5 microns reveal a heavily obscured, central point source which is coincident with a compact lambda = 2.7 mm continuum and C18O emission region. The source radiates about 310 solar luminosities, primarily at FIR wavelengths, suggesting that it is a young stellar object of intermediate mass. The steeply rising spectral energy distribution and the large fraction of the system mass residing in circumstellar material imply that IRAS 21391 + 5802 is in an early stage of evolution. The inferred dust temperature indicates a temperature gradient in the core. A comprehensive model for the surrounding core of dust and gas is devised to match the observed dust continuum emission and multitransition CS emission from this and previous studies. We find a r exp -1.5 +/- 0.2 density gradient consistent with that of a gravitationally evolved core and a total core mass of 380 solar masses. The observed dust emission is most consistent with a lambda exp -1.5 - lambda exp -2 dust emissivity law; for a lambda exp -2 law, the data are best fit by a mass opacity coefficient of 3.6 x 10 exp -3 sq cm/g at lambda = 1.25 mm.

Wilking, Bruce↗
NASA NTRS2003

High Resolution Imaging of Circumstellar Disks at Millimeter Wavelengths

We update progress on our research program to use high angular resolution imaging of thermal dust continuum emission at millimeter and submillimeter wavelengths to probe the structure of protoplanetary disks and debris disks around nearby stars. Observations at these wavelengths are advantageous because the dust emission is generally optically thin and directly proportional to mass, contrast with stellar photospheres is not problematic, and the wavelength dependence provides information on an important regime of grain sizes. We employ several facilities for state-of-the-art high resolution observations, including the Very Large Array (VLA), the Australia Telescope Compact Array (ATCA), the Plateau de Bure Interferometer (PdBI) of the Institut de RadioAstronomie Millimetrique, the Submillimeter Array (SMA) of the Smithsonian Astrophysical Observatory, and the Caltech Submillimeter Observatory (CSO). Many recent highlights of our program were presented in an invited review on High Angular Resolution Studies of Disks- the Millimetre at IAU Symposium 221, Star Formation at High Angular Resolution, in July 2003.

Wilner, David J.↗
NASA NTRS2003

The [C II] 158 Micron Line in Ultraluminous Infrared Galaxies Revisited

We present a study of the [C II] 157.74 micron fine-structure line in a sample of 15 ultraluminous infrared (IR) galaxies (IR luminosity L(sub IR greater than or equal to 10(exp 12)L.; ULIRGs) using the Long Wavelength Spectrometer (LWS) on the Infrared Space Observatory (ISO). We confirm the observed order of magnitude deficit (compared to normal and starburst galaxies) in the strength of the [C II] line relative to the far-infrared (FIR) dust continuum emission found in our initial report, but here with a sample that is twice as large. This result suggests that the deficit is a general phenomenon affecting 4 out of 5 ULIRGs. We present an analysis using observations of generally acknowledged photodissociation region (PDR) tracers ([C II], [OI] 63 and 145 micron, and FIR continuum emission), which suggests that a high ultraviolet flux G(sub 0) incident on a moderate density n PDR could explain the deficit. However, comparisons with other ULIRG observations, including CO (1-0), [C I] (1-0), and 6.2 micron polycyclic aromatic hydrocarbon (PAH) emission, suggest that high G(sub 0)/n PDRs alone cannot produce a self-consistent solution that is compatible with all of the observations. We propose that non-PDR contributions to the FIR continuum can explain the apparent [C II] deficiency. Here, unusually high G(sub 0) and/ or n physical conditions in ULIRGs as compared to those in normal and starburst galaxies are not required to explain the [C II] deficit. Dust-bounded photoionization regions, which generate much of the FIR emission but do not contribute significant [C II] emission, offer one possible physical origin for this additional non-PDR component. Such environments may also contribute to the observed suppression of FIR fine-structure emission from ionized gas and PAHs, as well as the warmer FIR colors found in ULIRGs. The implications for observations at higher redshifts are also revisited.

Luhman, M. L.↗
NASA NTRS2018

ALMA Reveals a Misaligned Inner Gas Disk inside the Large Cavity of a Transitional Disk

Pairs of azimuthal intensity decrements at near-symmetric locations have been seen in a number of protoplanetary disks. They are most commonly interpreted as the two shadows cast by a highly misaligned inner disk. Direct evidence of such an inner disk, however, remains largely illusive, except in rare cases. In 2012, a pair of such shadows were discovered in scattered-light observations of the near face-on disk around 2MASS J16042165- 2130284, a transitional object with a cavity ∼60 au in radius. The star itself is a “dipper,” with quasi-periodic dimming events on its light curve, commonly hypothesized as caused by extinctions by transiting dusty structures in the inner disk. Here, we report the detection of a gas disk inside the cavity using Atacama Large Millimeter/ submillimeter Array (ALMA) observations with ∼0".2 angular resolution. A twisted butterfly pattern is found in the moment 1 map of the CO (3–2) emission line toward the center, which is the key signature of a high misalignment between the inner and outer disks. In addition, the counterparts of the shadows are seen in both dust continuum emission and gas emission maps, consistent with these regions being cooler than their surroundings. Our findings strongly support the hypothesized misaligned inner disk origin of the shadows in the J1604-2130 disk. Finally, the inclination of the inner disk would be close to −45° in contrast with 45°; it is possible that its internal asymmetric structures cause the variations on the light curve of the host star.

azimuthal intensity decrements↗
NASA NTRS1979

Far infrared maps of the ridge between OMC-1 and OMC-2

Dust continuum emission from a 6 ft x 20 ft region surrounding OMC-1 and OMC-2 were mapped at 55 and 125 microns with 4 ft resolution. The dominant features of the maps are a strong peak at OMC-1 and a ridge of lower surface brightness between OMC-1 and OMC-2. Along the ridge the infrared flux densities and the color temperature decreases smoothly from OMC-1 to OMC-2. OMC-1 is heated primarily by several optical and infrared stars situated within or just at the boundary of the cloud. At the region of minimum column density between OMC-1 and OMC-2 the nearby B0.5 V star NU Ori may contribute significantly to the dust heating. Near OMC-2 dust column densities are large enough so that, in addition to the OMC-2 infrared cluster, the nonlocal infrared sources associated with OMC-1 and NU Ori can contribute to the heating.

Keene, J.↗
NASA NTRS1994

The detection and study of pre-planetary disks

A variety of evidence suggests that at least 50% of low-mass stars are surrounded by disks of the gas and dust similar to the nebula that surrounded the Sun before the formation of the planets. The properties of these disks may bear strongly on the way in which planetary systems form and evolve. As a result of major instrumental developments over the last decade, it is now possible to detect and study the circumstellar environments of the very young, solar-type stars in some detail, and to compare the results with theoretical models of the early solar system. For example, millimeter-wave aperture synthesis imaging provides a direct means of studying in detail the morphology, temperature and density distributions, velocity field and chemical constituents in the outer disks, while high resolution, near infrared spectroscopy probes the inner, warmer parts; the emergence of gaps in the disks, possibly reflecting the formation of planets, may be reflected in the variation of their dust continuum emission with wavelength. We review progress to date and discuss likely directions for future research.

Sargent, A. I.↗