Infrared Imaging Survey Research Articles

Dust Extinction and Molecular Cloud Structure: L977

We report results of a near--infrared imaging survey of L977, a dark cloud in Cygnus seen in projection against the plane of the Milky Way. We use measurements of the near--infrared color excess and positions of the 1628 brightest stars in our survey to measure directly dust extinction through the cloud following the method described by Lada et al. (1994). We spatially convolve the individual extinction measurements with a square filter 90 in size to construct a large-scale map of extinction in the cloud. We derive a total mass of M(L977)= (660 +/- 30)(D/500 pc)^2 Msun and, via a comparison of source counts with predictions of a galactic model, estimate a distance to L977 of 500 +/- 100 pc. We find a correlation between the measured dispersion in our extinction determinations and the extinction. We interpret this as evidence for the presence of structure on scales smaller than the 90 resolution of our extinction map. To further investigate the structure of the cloud we construct the frequency distribution of the 1628 individual extinction measurements in the L977 cloud. The shape of the distribution is similar to that of the IC 5146 cloud. Monte Carlo modeling of this distribution suggests that between 2 < Av < 40 mag (or roughly 1 < r < 0.1 pc) the material inside L977 is characterized by a density profile n(r) \propto r^(-2). Direct measurement of the radial profile of a portion of the cloud confirms this result. (more...)

Joint effort results in first infrared survey of Kamchatka volcanoes

Scientists from the United States and the former Soviet Union (FSU) have performed a joint airborne infrared imaging survey of active volcanoes on the remote and politically sensitive Kamchatka Peninsula. The temperature map of Bezymyanny Volcano (Figure 1), revealing slow lava dome growth and collapse on the northwestern slope, shows the excellent quality of the images. The collaborative effort, which yielded thermal infrared multispectral scanner (TIMS) images of some of the 29 active volcanoes of the Eastern Range of the Kamchatka Peninsula (see Figure 2) provided new information on the ages, extent, and morphologies of volcanic deposits and quantitative data on thermal flux for active volcanoes and geothermal areas throughout the volcanic range. These data also provided a baseline against which changes caused by future eruptions can be gauged.

Supersonic Turbulence in the Interstellar Medium: Stellar Extinction Determinations as Probes of the Structure and Dynamics of Dark Clouds

Lada et al. have described a method for studying the distribution of dust in dark clouds using infrared imaging surveys. In particular, they show that the method provides some information about the structure of the gas (dust) on scales smaller than their resolution. In the present work we clarify the nature of the information provided by their method. We show that: 1. The three-dimensional density field of the gas is well described by a lognormal distribution down to very small scales. 2. The power spectrum and the standard deviation of the three-dimensional density field can be constrained. 3. Such a structure of the density field is likely to be the effect of random supersonic motions present in the gas. In fact, we find a qualitative and quantitative agreement between the predictions based on recent numerical simulations of randomly forced supersonic flows by Nordlund & Padoan and by Padoan, Nordlund, & Jones and the constraints given by the infrared dust extinction measurements.

The IR and sub-mm program in Japan

Infrared and sub-millimeter observations are shifting from balloons and sounding rockets to satellite observations in Japan. The first satellite mission, the Infrared Telescope in Space (IRTS), will be performed in early 1995. It is a 15cm cooled telescope. It will observe diffuse infrared sources over almost the entire infrared/sub-millimeter region and give information on a variety of sources such as interplanetary dust, interstellar matter and infrared cosmic background radiation. The next satellite mission agter the IRTS is under feasibility study for launch in the beginning of the next century. The basic concept of this mission, the Infrared Imaging Surveyor (IRIS), is a cooled survey telescope. The major objective is the birth and evolution of galaxies. Here, a brief description of these two mission is given.

Infrared Imaging Surveyor: IRIS

Based on the experience of the IRTS, a new infrared satellite mission, Infrared Imaging Surveyor:IRIS is now being proposed to ISAS. The IRIS will be thrown into the sun synchronous orbit at 900km altitude by the MV rocket which is now under development in ISAS. With use of new cryogenic technologies, considerably light weight with large aperture telescope is designed. Owing to the large format states-of-art array detectors, the IRIS has an enormous capability for the survey observation, and will provide new discoveries on the formation and evolution of galaxies, brown dwarfs, protoplanetary disk, interstellar matter and so on.

The evolutionary status of the stellar population in the rho Ophiuchi cloud core

This contribution reports the results of an infrared imaging survey aimed at characterizing the stellar populations associated with the three densest star-forming cores in the Ophiuchus molecular cloud complex. The survey has sufficient sensitivity at J, H, and K (at 5 sigma limits of 16.5, 15.4, and 14.2) to provide a complete census of embedded young stellar objects (YSOs) with masses greater than the hydrogen-burning limit, provided that their ages are less than 3 Myr and that they are obscured by no more than approximately 18 mag of visual extinction. Our data suggest (1) a large fraction (greater than 70%) of the sources located within the cores are still surrounded by circumstellar disks and/or envelopes; and (2) the shape of the initial mass function for masses, M less than 1 solar mass, appears to be consistent with that derived from the solar neighborhood. We also report the results of a deeper imaging survey of centimeter continuum sources (14 sources) in these star-forming cores and in the larger Ophiuchus complex (eight sources). A large fraction (11/14) of the radio sources associated with the cores appear to have infrared excesses diagnostic of circumstellar accretion disks and/or infalling circumstellar envelopes. In these cases, the centimeter continuum radiation most likely diagnoses the ionized component of energetic winds or jets which characterizes YSOs during the disk accretion phase. By contrast, of the eight radio sources located outside dense cores, only two show infrared excesses.

Dust extinction and molecular gas in the dark cloud IC 5146

In this paper we describe a powerful method for mapping the distribution of dust through a molecular cloud using data obtained in large-scale, multiwavelength, infrared imaging surveys. This method combines direct measurements of near-infrared color excess and certain techniques of star counting to derive mean extinctions and map the dust column density distribution through a cloud at higher angular resolutions and greater optical depths than those achieved previously by optical star counting. We report the initial results of the application of this method to a dark cloud complex near the cluster IC 5146, where we have performed coordinated, near-infrared, JHK imaging and (13)CO, C(18)O, and CS millimeter-wave, molecular-line surveys of a large portion of the complex. More than 4000 stars were detected in our JHK survey of the cloud. Of these, all but about a dozen appear to be field stars not associated with the cloud. Star count maps at J band show a striking and detailed anticorrelation between the surface density of J-band sources and CO and CS molecular-line emission. We used the (H-K) colors and positions of nearly 1300 sources to directly measure and map the extinction and thus trace the dust column density through the cloud at an effective angular resolution of 1 min .5. We report an interesting correlation between the measured dispersion in our extinction determinations and the extinction. Modeling this relation indicates that effects of small-scale cloud structure dominate the uncertainties in our measurements. Moreover, we demonstrate that such observations can be used to place constraints on the nature of the spatial distribution of extinction on scales smaller than our resolution. In particular, we show that models in which the dust is distributed uniformly or in discrete high-extinction clumps on scales smaller than (1 min .5) are inconsistent with the observations. We have derived extinctions at the same positions and at the same angular resolution (1 min .7) as our molecular-line observations. This enabled a direct comparison of (13)CO, C(18)O, and CS integrated intensities and column densities with A(sub V) for more than 500 positions in the cloud, corresponding to a range in A(sub V) between 0 to 32 mag of extinction. We found the integrated intensities of (13)CO, C(18)O, and CS to be roughly linearly correlated with extinction over different ranges of extinction. However, for all three molecules we find the scatter in the observed relations to be larger than can be accounted for by instrumental error, suggesting that there are large intrinsic variations in the abundances or excitation of the molecules through the cloud. Mean abundances for all the molecules relative to hydrogen were directly derived from the data. The ratio of (13)CO to C(18)O abundances was found to be significantly higher than the terrestrial ratio in regions where extinction is less than 10 mag. In the same region, the dispersion in the abundance ratio is also found to be very large, suggesting that the abundances of one or both molecules are very unstable even at relatively large cloud optical depths. Beyond 10 mag of extinction the abundances of both species appear very stable with their ratio close to the terrestrial value.

Infrared observations of highly variable radio sources in the galactic plane

We have performed a comprehensive infrared imaging survey of 29 radio sources which were first detected by the UBC radio patrol survey of the galactic plane. The sources in our sample are the subset of variable and non-variable «control» objects which were mapped with the VLA by Duric & Gregory. Since other sources in the original variability survey have been shown to be associated with unusual galactic X-ray and gamma-ray sources, the aim of the present work was to make the first steps towards discovering whether the remaining radio variables represent a hitherto undetected sample of faint, unusual X-ray binary stars

An Infrared Imaging Survey of the ρ Oph and R CrA Dark Cloud Cores

AbstractWe report on an initial survey of the cores of the Rho Ophiuchus and R Coronae Australis clouds, made with the AAT’s new IR array camera, IRIS. No turnover is seen in the initial luminosity function for ρ Oph to the sensitivity limit of the survey. Some implications for the low mass end of the initial mass function are discussed.

OPERATIONAL AIRBORNE THERMAL IMAGING SURVEYS

This paper reviews the methodology and significant parameters which experience has shown to be required in the conduct of airborne infrared imaging surveys using optical‐mechanical line scanning systems in the three to five and eight to fourteen micron spectral regions. For nonrectilinearized infrared imagery to be compatible with uncontrolled mosaicking, all flight lines should be in the same direction, flight lines must be spaced to allow matching of only the central seventy degrees of each strip, and surveys must be flown parallel to the prevailing wind direction. High‐resolution detectors are recommended for most geological terranes, and high‐sensitivity detectors for imaging hydrological and certain geothermal terranes. Nighttime data collection has proven superior to daytime data collection for most applications and little difference is found between the interpretability of imagery resulting from longwave and that from shortwave infrared detectors. Automatic gain control (AGC) and attendant ac averaging effects are minimal over homogeneous terranes exhibiting low infrared emittance variations. Amplification circuitry using dc restoration and manual level and gain controls is necessary when imaging land/water contacts or terranes with large variations in infrared emittance. A signal differentiation capability proved useful in coal fire and thermal pollution surveys.