Aperture Synthesis Maps Research Articles

Formaldehyde in Comets C/1995 O1 (Hale‐Bopp), C/2002 T7 (LINEAR), and C/2001 Q4 (NEAT): Investigating the Cometary Origin of H2CO

Observations of formaldehyde (H2CO) have been conducted toward comets C/1995 O1 (Hale-Bopp), C/2001 Q4 (NEAT), and C/2002 T7 (LINEAR) using the Arizona Radio Observatory (ARO) 12 m telescope at 1.2 and 2 mm. Aperture synthesis maps of H2CO at 3 mm were made using the Berkeley-Illinois-Maryland Association (BIMA) interferometer toward comet Hale-Bopp. These data indicate that the production rate of H2CO is ~3.7 × 1028 s-1 at ~1 AU in comet Hale-Bopp, using a simple Monte Carlo model, if a nuclear origin for the molecule is assumed. However, maps of H2CO in Hale-Bopp, in comparison with CO, show an extended distribution (rs ~ 15,000 km) with small-scale structure oriented roughly along the comet-Sun direction. This result suggests a source of H2CO other than the comet nucleus. The extended source of formaldehyde is probably grains composed of a mixture of silicates and organic material. The production rate for H2CO increases to Q ~ 1.4 × 1029 s-1 assuming such an extended grain source. This value implies a Q/Q(H2O) ~ 1.4%, which is similar to the production rate ratio of Q/Q(H2O) ~ 4% derived from in situ measurements of H2CO in comet Halley. Production rates for H2CO toward comets C/2002 T7 (LINEAR) and C/2001 Q4 (NEAT) are 1.4 × 1027 and 5.6 × 1026 s-1, respectively, modeled using the extended grain source. The spectra of H2CO measured toward comet C/2002 T7 (LINEAR) show evidence for a second velocity component, most likely arising from comet fragmentation.

Millimeter-Wave Aperture Synthesis Imaging of Vega: Evidence for a Ring Arc at 95 AU

We present the first millimeter-wave aperture synthesis map of dust around a main sequence star. A 3'' resolution image of 1.3 mm continuum emission from Vega reveals a clump of emission 12'' from the star at PA 45 deg, consistent with the location of maximum 850 micron emission in a lower resolution JCMT/SCUBA map. The flux density is 4.0+/-0.9 mJy. Adjacent 1.3 mm peaks with flux densities 3.4+/-1.0 mJy and 2.8+/-0.9 mJy are located 14'' and 13'' from the star at PA 67 deg and 18 deg, respectively. An arc-like bridge connects the two strongest peaks. There is an additional 2.4 +/-0.8 mJy peak to the SW 11'' from the star at PA 215 deg and a marginal detection, 1.4+/-0.5 mJy, at the stellar position, consistent with photospheric emission. An extrapolation from the 850 micron flux, assuming F_{1.3mm-0.85mm} proportional to lambda^{-2.8}, agrees well with the total detected flux for Vega at 1.3 mm, and implies a dust emissivity index, beta, of 0.8. We conclude that we have detected all but a very small fraction of the dust imaged by SCUBA in our aperture synthesis map and that these grains are largely confined to segments of a ring of radius 95 AU.

A Circumstellar Dust Disk around T Tauri N: Subarcsecond Imaging at λ = 3 Millimeters

We present high-resolution imaging of the young binary T Tauri in continuum emission at ? = 3 mm. Compact dust emission with integrated flux density 50 ? 6 mJy is resolved in an aperture synthesis map at 05 resolution and is centered at the position of the optically visible component, T Tau N. No emission above a 3 ? level of 9 mJy is detected 07 south of T Tau N at the position of the infrared companion, T Tau S. We interpret the continuum detection as arising from a circumstellar disk around T Tau N, and estimate its properties by fitting a flat-disk model to visibilities at ? = 1 and 3 mm, and to the flux density at ? = 7 mm. Given the data, probability distributions are calculated for values of the free parameters, including the temperature, density, dust opacity, and disk outer radius. The radial variation in temperature and density is not narrowly constrained by the data. The most likely value of the frequency dependence of the dust opacity, ?=0.53 -->?0.17+0.27, is consistent with that of disks around other single T Tauri stars in which grain growth is believed to have taken place. The outer radius, R=41 -->?14+26 AU, is smaller than the projected separation between T Tau N and T Tau S, and may indicate tidal or resonance truncation of the disk by T Tau S. The total mass estimated for the disk, log (MD/M?) = -2.4 -->?0.6+0.7, is similar to masses observed around many single pre-main-sequence sources and, within the uncertainties, is similar to the minimum nebular mass required to form a planetary system like our own. This observation strongly suggests that the presence of a binary companion does not rule out the possibility of formation of a sizable planetary system.

A frequency-agile hybrid spectral correlator for mm-wave radio interferometry

A correlation spectrometer for the IRAM Plateau de Bure radio astronomy observatory is presented. It can process up to 960 MHz wide IF signals coming from the 4-antenna connected array. An IF processor selects the frequency window of interest, both in width and central frequency. A digital correlator produces channelized amplitude and phase information for the six pairs of antennas, which is later used for aperture synthesis mapping. Some original technical features are detailed. Some improvements suggested by observing results are discussed.

CO (2-1) in IC 342

AbstractWe present aperture synthesis maps of the CO J=2-1 emission in the central region of the spiral galaxy IC 342. The 4” resolution maps reveal emission that is a factor of two brighter than the CO (1-0) emission mapped at the same resolution. Since the CO (2-1) emission is likely to be optically thick, the high ratio is probably due to the fact that the two transitions sample different cloud layers in externally heated clouds. The high signal to noise of the maps indicates that CO (2-1) will be a powerful tool in the study of gas in galaxies.

Disks Around T Tauri Stars

AbstractA variety of evidence suggests that at least 50% of T Tauri stars are surrounded by disks of gas and dust. Inferred disk properties are compatible with those generally attributed to the solar nebula, before the formation of planets. Millimeter-wave aperture synthesis mapping of molecular line and dust continuum emission from T Tauri stars provides a direct way to ascertain if disks are present. The technique enables detailed studies of disk temperature and density distributions, chemical properties and velocity fields. These results inform our understanding of both star formation and solar system evolution. We review the observations to date and discuss directions for future research.

The small-scale structure and kinematics of B335

High-resolution (2″.8-5″) aperture synthesis maps of the 13 CO, C 18 O J=1→0, and continuum emission at 2.7 mm from the Bok globule B335 trace bipolar, high-velocity emission to within 250 AU of its source, and delineate a core which is elongated on scales of 1000 AU perpendicular to the outflow but unresolved along its minor axis. Our images in the optically thick 13 CO line show well-separated blue- and redshifted outflow lobes, and imply the presence of limb-brightened shells. The outflow opening angle close to its origin is the same as at distances of ∼5', suggesting that its morphology is determined primarily by a collimated driving wind

Aperture synthesis mapping of CO (2-1) in IC 342

view Abstract Citations (29) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Aperture Synthesis Mapping of CO (2--1) in IC 342 Turner, Jean L. ; Hurt, Robert L. ; Hudson, David Y. Abstract We present aperture synthesis maps of CO J = 2-1 emission in the central region of the spiral galaxy IC 342. The 3" resolution maps reveal emission with implied excitation temperatures of 5-30 K. This emission is significantly brighter than the CO (1-0) emission mapped at the same resolution. Since the CO (2-1) emission is likely to be optically thick, the high ratio is probably due to the fact that the CO preferentially traces the outer, warmer cloud layers in externally heated clouds. The locations of the peak values of the CO (2-1)/CO (1-0) intensity ratio appear to occur at the interfaces between regions of high molecular column density and ionized gas. The high signal to noise of these maps indicates that CO (2-1) will be a powerful tool in the study of dense, warm gas associated with recent star formation in galaxies. Publication: The Astrophysical Journal Pub Date: August 1993 DOI: 10.1086/186949 Bibcode: 1993ApJ...413L..19T Keywords: Astronomical Maps; Carbon Monoxide; Spiral Galaxies; Synthetic Apertures; H Ii Regions; Interferometry; Microwave Interferometers; Molecular Clouds; Signal To Noise Ratios; Astrophysics; GALAXIES: INDIVIDUAL ALPHANUMERIC: IC 342; GALAXIES: NUCLEI; GALAXIES: SPIRAL; GALAXIES: STARBURST; RADIO LINES: GALAXIES full text sources ADS | data products SIMBAD (2) NED (1)

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.

A completely sampled aperture synthesis map of the CO emission in M51

view Abstract Citations (55) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Completely Sampled Aperture Synthesis Map of the CO Emission in M51 Adler, David S. ; Lo, K. Y. ; Wright, Melvyn C. H. ; Rydbeck, Gustav ; Plante, Raymond L. ; Allen, Ronald J. Abstract Interferometric observations from the Berkeley-Illinois-Maryland Association millimeter interferometer are combined with single-dish observations from the Onsala Space Observatory to create high-resolution fully sampled maps of CO (J = 1-0) emission from two 2' fields in the spiral galaxy M51. In previous interferometer CO maps of M51, >= 65% of the CO flux density in each field is missing but assumed to be uniformly distributed through the field of view. In contrast, our maps recover all of the flux density and show directly that 75% of the CO flux density from the inner few kiloparsecs of M51 come from the spiral arms. The CO arms are wider (<~1.3 kpc) and more extended than the CO arms presented in previous interferometer maps. The CO arm is clumpy along the arm with a linear scale ~1 kpc. The average arm-to-interarm intensity contrast over the two fields is >=4.6:1 peak arm-to-interarm CO integrated intensity contrasts of >= 20:1 are seen in the inner arms. Some large "clumps" of interarm CO emission are seen. Streaming motions of up to 70 km s^-1^ (in the plane of the galaxy) are seen in the arms; these motions are consistent with those expected from the spiral density wave theory. Both the intensity contrast and streaming motions are consistent with numerical simulations which show that orbit crowding is the dominant physical mechanism for gathering the molecular clouds into the arms. Dissipative cloud-cloud collisions and gaseous self-gravity must be included in the numerical models to account for the observed clumpiness along the spiral arms. Adopting the Galactic conversion ratio of H_2_ to CO integrated intensity, we find that the inferred gas mass of the molecular cloud complexes in the spiral arms of M51 is systematically larger than the virial mass. An H_2_-to-CO conversion ratio in the inner spiral arms of M51 2.5 times smaller than the Galactic value will correct the discrepancy. Publication: The Astrophysical Journal Pub Date: June 1992 DOI: 10.1086/171450 Bibcode: 1992ApJ...392..497A Keywords: Carbon Monoxide; Emission Spectra; Interstellar Matter; Spiral Galaxies; Astronomical Models; H Ii Regions; Interferometry; Astrophysics; GALAXIES: INDIVIDUAL MESSIER NUMBER: M51; GALAXIES: INTERSTELLAR MATTER; TECHNIQUES: INTERFEROMETRIC full text sources ADS | data products SIMBAD (2) NED (1)

Orion B (NGC 2024). III - BIMA SO J(K) = 2(2)-1(1) observations - Evidence for peculiar sulfur chemistry

Aperture synthesis maps are presented of SO J(K) = 2(2)-1(1) emission at 86.093938 GHz of the molecular cloud Orion B obtained from combined BIMA/NRAO 12-m data. The spatial resolution is 11 x 7 arcsec and the velocity resolution is 0.54 km/s. The maps show fine structure in the dense molecular core, the main features being two relatively compact components aligned with the long quiescent NS-oriented ridge of previous maps. Most notable, however, is the approximately 1-2 km/s blueshift of this line with respect to other high-density tracers of the main core. Implications of these data for the chemistry of SO in dense clouds are discussed.

VLA observations of 21 centimeter H I absorption toward Cassiopeia A

A multiconfiguration aperture synthesis mapping of the Perseus arm H I absorption line toward Cas A has been performed using the VLA. The sensitivity achieved was sufficient to detect optical depths as low as 0.03 and as large as about 5 over a region about 5 arcmin in diameter. Optical depth images are presented as gray scale with contours superposed for 41 spectral channels showing H I absorption. Representative optical depth spectra are shown as a function of position over Cas A. The images represent a significant improvement in angular resolution over earlier aperture synthesis work. The H I images show much structure in the absorbing gas, with the morphology dominated by elongated structures. 22 refs.

Orion B (NGC 2024). II - Hat Creek synthesis observations of the molecular core in the J = 1 to 0 line of HCO(+)

Aperture synthesis maps of HCO(+) J = 1 to 0 emission at 89 GHz for the molecular cloud Orion B were obtained with the Hat Creek Array. The spatial resolution is 11 x 8 arcsec and the velocity resolution is 0.53 km/s. The maps show much fine structure in the dense molecular core, including a centrally located broad-line region with an elliptical velocity distribution and apparently centered on the FIR source FIR 6, a long-quiescent, NS-oriented ridge at a PA of -10 deg with a similar appearance to the cold dust emission, an EW ridge exactly abuts the ioniztaion front of the adjacent H II region, and a possible one-sided high-density outflow to the south with an region apparently not near any of the NIR sources but instead close to FIR 5. FIR 5 and 6 therefore seem to indicate two different centers of activity in the molecular core. 32 refs.

Aperture Synthesis Observations of NH3 and CS in Orion-KL

ABSTRACT.We have made aperture synthesis maps of Orion-KL in NH3(1,1),(2,2) and CS(J=l-0) emissions using the Nobeyama Millimeter Array. Both NH3 and CS maps show new detailed structures that have not been recognized before. Two NH3 filaments in the size of ~0.45 pc x0.04 pc are found extending to the northwest direction of Orion-KL. These filaments are associated with the HH objects and the finger-like H2 emissions; they are probably formed through the interaction with high velocity, highly channeled winds from the KL region. The CS maps show, on the other hand, shell structures around IRc2 as well as the well-known rotating disk. These shells coincide with the two lobes of the shock-excited H2 emission, being interpreted as the shock-compressed shells of ambient molecular gas interacting with the outflow from IRc2.

Aperture synthesis observations of individual molecular clouds in M33

Aperture synthesis maps of six fields in the nearby spiral galaxy M33 have revealed the presence of a population of molecular clouds whose masses, sizes, velocity widths, and brightness temperatures are similar to Galactic giant molecular clouds. The masses of the clouds obtained from the virial theorem and from the integrated CO flux are in relatively good agreement, suggesting that the conversion factor from CO flux to molecular mass in M33 is unlikely to be much different from the value measured in our own Galaxy. The star formation properties of these regions are under study with deep optical CCD imaging and near-infrared data.

Evidence for ion-molecular chemistry in the envelope of IRC +10216

Results of aperture synthesis mapping of line emission from the molecules HNC, C/sub 2/H, and HC/sub 3/N in the envelope of the carbon star IRC +10216 are presented. The observations of the molecules clearly show the shell-like structure predicted by model calculations. It is argued that the results constitute strong evidence for the importance of ion-molecule reactions and photochemical processes in the circumstellar envelope of IRC +10216. 24 references.

VLBI Mapping of 43 GHz SiO Emission Associated with IRc2 in Orion-KL

Information on the structure of the molecular flow within 1″ of IRC-2, in Orion-KL, is sparse. Measurements of the continuum at 7.8μ and 12.5μ show a disk of size and suggest that the center of the disk may be dust free (Lester et al. 1985). Aperture synthesis mapping of water maser shell features (Sylber 1986) has provided information on the scale. Smaller scales can be studied by mapping SiO maser emission. We observed the 43 GHz, v=1, J = 1 → 0, transition of SiO using a 2 station interferometer with a 74 km baseline between Haystack Observatory, Westford, MA and Five College Radio Observatory, New Salem, MA. The fringe spacing was 20 milliarcseconds (mas) and the velocity resolution was 0.25 km-s−1. Our results provide the highest resolution view to date of what is likely to be the inner of IRC-2.

Aperture synthesis mapping of molecular gas in high-luminosity IRAS galaxies

The Owens Valley millimeter-wave interferometer has been used for high-resolution mapping of the 2.6 mm CO emission from the high-luminosity infrared galaxies NGC 520 (Arp 157), NGC 7469 (Arp 298), and Arp 55. Assuming the same empirical relationship between CO brightness and molecular hydrogen surface mass density as has been found for giant molecular clouds in the Milky Way, it is found that the masses of H2 gas in these concentrations are 10 to the 9th - 10 to the 10th solar masses, typically one-third of the total molecular gas content of these galaxies. The interferometric sizes correspond to radii of 0.8 kpc (NGC 520), 1.4 kpc (NGC 7469), and less than 2.8 kpc (Arp 55). For the same regions the dynamical masses estimated from the CO line width and size of the emission region are only a factor of 3-5 higher. The mean molecular gas surface densities averaged over these regions are in the range 610-825 solar masses/sq pc, a factor of 10 brighter than those obtained for corresponding regions in the nucleus of the Milky Way. The high mass fractions obtained for the interstellar medium in the central regions of these three galaxies strongly suggest that large-scale gravitational instability in the gas may play an important role in the further concentration of the gas in the nucleus and in possibly precipitating a large-scale burst of star formation.

Aperture synthesis maps of HDO emission in Orion-KL

view Abstract Citations (72) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Aperture Synthesis Maps of HDO Emission in Orion-KL Plambeck, R. L. ; Wright, M. C. H. Abstract The 110-111 transition of deuterated water has been mapped toward the Kleinmann-Low nebula in Orion with the Hat Creek millimeter interferometer. The synthesized beamwidth is 3arcsec.4. The "hot core", "plateau", and "compact ridge" emission regions can be identified on the maps. The compact ridge appears to consist of streamers of gas which connect to the hot core clump and are directed away from the source IRc 2. The HDO/H2 abundance toward both hot core and compact ridge is inferred to be ≡10-7, unexpectedly high for such warm regions. Publication: The Astrophysical Journal Pub Date: June 1987 DOI: 10.1086/184920 Bibcode: 1987ApJ...317L.101P Keywords: Astronomical Maps; Heavy Water; Interstellar Gas; Orion Nebula; Abundance; Nebulae; Synthetic Apertures; Astrophysics; DEUTERIUM; NEBULAE: ORION NEBULA; INTERSTELLAR: MOLECULES full text sources ADS | data products SIMBAD (3)

Maximum Entropy Image Restoration in Astronomy

Imaging the two-dimensional intensity distribution of the sky has always been an important part of astronomy. This is particularly true at present, a time when aperture synthesis mapping is firmly established in radio astronomy, charge-coupled devices are revolutionizing optical imaging, and X-ray-imaging cameras are being flown in space. Atmospheric irregularities, instrument aberrations, detector noise, and the diffraction limit all cause the observed image to deviate from the ideal one. Image restoration techniques have therefore had a long history. The field owes much to the classic papers of Bracewell & Roberts ( 12) and Fellgett & Linfoot (35), which focused attention on the amount and nature of information about the image present in the measurements. These ideas have become increasingly relevant with the growth of interferometry, where the data correspond to the Fourier transform of the image. The Michelson stellar interferometer (82) was an early application in optical astronomy. However, it is at radio frequencies where interferometry has proved most fruitful and where astronomers have had to face the problem