Information about my research

A few recent images from theNational Radio Astronomy Observatory 12m radiotelescope. (NRAO).

Radio Astronomy Image Gallery

Meet the Molecules of C/1996 B2 Hyakutake

This image shows, in false color, the emission from carbon monoxide molecules in Comet C/1996 B2 Hyakutake shortly before it passed the Earth. The emission shows up as reddish/white here. The image was made on 21 March 1996, with the NRAO 12m radiotelescope atop Kitt Peak, Arizona, by Jeff Mangum using the newly implemented `on-the-fly' mapping technique. The spectral line here is very narrow, but emission has been integrated over all velocity channels to construct this image. The nominal telescope beam is 30" at 1.3mm wavelength, but the image was convolved to 40" resolution to improve the signal to noise ratio. As a comet warms on its journey around the sun, molecules boil off of the icy nucleus. CO boils off particularly far from the sun, when the nuclear temperature is only about 20 K, and powers activity in the comet's coma far from the sun. As the comet approaches the sun, the evaporation of other molecules powers increasingly violent activity. Three days after this image was taken, emission from ammonia molecules was detected with the NRAO 43m telescope in Green Bank, West Virginia. The ammonia emission suggested that the temperature of the gas near the nucleus was 67 K at that time, sufficiently warm for many molecules to leave the nucleus.

Destruction of a molecular cloud.

This image shows, in red, the emission from carbon monoxide molecules in a gas cloud in Ophiuchus called R12. The image was made with the NRAO 12m radiotelescope in September, 1995 using the newly implemented `on-the-fly' mapping technique. The spectral line here is very narrow, but emission has been integrated over all velocity channels to construct this image. The hot B star rho Ophiuchi is located to the southeast, and its ionizing radiation is penetrating the cloud, heating the dust, which in turn heats the gas. Additionally, the ultraviolet radiation is destroying the CO molecules. In blue, we see the IRAS image at 100 microns, showing the cooler dust. In green, the IRAS image at 12 microns is displayed, showing the warmer dust on the eastern edge of R12. The offset of the hot dust toward the star clearly shows that in the eastern and southern boundary regions, all CO molecules have been destroyed already, but the dust remains. This work is in collaboration with Jeff Mangum (Submillimeter Telescope Observatory, University of Arizona) and Bill Latter (NASA Ames Research Center).

Formation of a young star.

Earlier on another page was shown the striking molecular flow emanating from the very young source VLA1623. This image shows a spatially smaller flow powered by a somewhat more luminous source in the dark cloud L1157. This image was obtained in September 1995 at the NRAO 12m telescope, using the newly implemented `on-the-fly' imaging mode. The dense clump of material at the protostar is not shown in this view, but it lies between the lobe of redshifted CO molecules (shown, naturally, in red) and the lobe of blueshifted gas (in blue). The ambient gas in the surrounding cloud is shown in green. In August 1995, powerful redshifted emission from water molecules was detected at the position of the protostar for the first time with the NRAO 43m telescope. An image of the water maser was soon made with the NRAO Very Large Array, which showed that the emission arose within a few dozen astronomical units of the protostar itself, indicating that the forces which power the flow are set in motion close to the central object. Presumably, matter is still falling onto the protostar from the ambient cloud through a flattened, disklike structure. As the star struggles to achieve hydrostatic equilibrium, matter and energy are expelled from the poles, resulting in the flow illustrated here. This work is in collaboration with Mark Claussen (NRAO) and Bruce Wilking (University of Missouri at St. Louis).

Optical and radio views of a dark molecular cloud.

In the infrared image (in the `J' band at 1.2 microns) in the this panel, the dark cloud L483 stands out against a Scutum starfield. Deep within, a purple glow locates one lobe of a flow emanating from the densest part of the cloud, completely hidden from view at even the longest infrared wavelengths accessible from the Earth's surface. At these wavelengths, we could never peer into the cloud and uncover the mechanisms of star formation. Radio techniques remedy this situation. Image courtesy of Gary Fuller.

The bottom panel shows an image of C18O J=1-->0 emission taken by the NRAO 12m radiotelescope. Here the interstellar gas glows with emission from the carbon monoxide molecules, which, mixed with dust, completely obscured the star-forming interior of the cloud in the previous image. Note how the gas glows most brightly where accretion onto a protostar warms the cloud. Only a dozen or so objects in the sky are thought to be as young as this protostar, which appears to be growing into a young star of about the same mass as the Sun. At this stage in its evolution, however, most of the matter which will eventually be incorporated into the star and its planets still lies in the surrounding cloud. Thus the L483 protostar offers us a chance to understand how interstellar gas and dust clouds form stars and planets.

Optical and radio views of a dark molecular cloud.

In some molecular clouds, whole clusters of stars form. In this cloud in Serpens, there are at least 50 young stars; three stars are thought to be in their `protostellar' stage. In blue tones, we see an infrared image taken at a wavelength of 2.2 microns by Casali, Eiroa and Duncan. In red tones, we see an image of emission from formaldehyde molecules at 72 GHz, taken with the NRAO 12m radiotelescope. Note that the stars, visible in the infrared image, avoid the gas and dust cloud, which glows red in this false color image, obscuring background objects. Deep within the clump at bottom center lies a protostar known as Serpens Submillimeter Source 4, or SMM4. Thus named owing to its brilliance at wavelengths shorter than one millimeter, it does not appear striking in this image. The very dense dust associated with a new star emits a continuous spectrum which increases rapidly in brightness at shorter wavelengths, and submillimeter maps have provided a useful tool for locating the youngest stars. In an image made at the Caltech Submillimeter Observatory, in the light of much warmer formaldehyde gas, SMM4 is pinpointed by the hot gas warmed by the nascent star. In this image, however, made in the light of cold formaldehyde gas at 4.5 mm wavelength, the location of the star is not easily noted. At the upper right, a short linear feature locates a second, quite luminous, young star called SMM1. A bipolar flow can be seen driving outward from this star in images made in the light of the carbon monoxide molecule, similar to what is seen in L1157 or VLA1623 images elsewhere on this page. Just to the north of it lies an enigmatic double object, called S68N or SMM9 which may be the youngest of the young stars in the image. It is the subject of intense current investigation.

Molecules escape a dying star, carrying new atoms into space.

False color image of molecular emission around the star AFGL2688, the Egg Nebula, from VLA and optical telescope data. The HC3N J=5->4 emission (45.5 GHz) is in red, in a velocity slice at line center, so that we see the distribution in the plane of the sky for this expanding envelope, as if we were to slice an onion and examine one of its layers. Superimposed, in a southwestern turquoise, is the 2 micron H2 image which NRAO Jansky Fellow Bill Latter published last year. Molecular hydrogen requires high temperatures for its excitation, probably provided here by shocks in a fast wind emanating from the poles of the star. The H2 is four-lobed, with the brightest lobe in the north, where the pole is tipped toward us slightly; the lobe lies just beyond the brightest knot of HC3N J=5-4 emission. There is a second lobe symmetrically placed in the south, lying just beyond the southern HC3N emission. There are also east and west H2 knots, though there is apparently no HC3N near those points--cyanoacetylene is produced from photodissociation byproducts of parent molecules, including HCN, and apparently photodissociating light does not penetrate into the equator of the system far enough for much HC3N to be produced, though excitation might have something to do with the way we see the emission. The UV does penetrate in the (thinner?) polar direction, so we see a broken ring of emission at 3" radius from the star. The ring in IRC+10216 would lie at a radius of 1" at the 1 kpc (?) distance of the Egg, but the mass loss rate in the Egg is about an order of magnitude higher than in IRC. For many more stunning pictures of gracefully aging stars, see Bill Latter's home page.

Further study is under way. Authors: Al Wootten, Bill Latter , Truong-Bach, and Nguyen-Q-Rieu.

Back to myHome Page