Nan Dieter Conklin: A Life in Science

AFCRL

At the Air Force Cambridge Research Laboratory I found two jobs - one with the new Space Track (charged with figuring out how to keep track of the growing number of satellites) and one with the Astronomy Section (charged in part with the same mission but also with some freedom for basic research). The satellite tracking plan involved setting up very wide angle (Schmidt) telescopes that would be used to record the presence of satellites and to carry out astronomical research as well. The idea was to locate the telescopes at observatories around the world where they could be managed by astronomers, and used as well for astronomical research. The plan seems quaint now, but no one foresaw the magnitude of the task.

For my first research project I used published observational material to look at the interstellar neutral hydrogen in special groups of very young stars -- known as OB associations. A few had already been studied in detail, but I chose to look at a large sample in less detail. In 31 out of the 40 I observed there was hydrogen at the position and velocity of the stellar group (within the limits of error of both the radio and optical measurements). This coincidence strongly suggests that they are associated and that the separate observations used together could yield some insight. In particular the distance of the stars can be estimated independently of any model of galactic rotation (on the basis of the difference between their absolute and observed brightness). The distance of the interstellar hydrogen not associated with an optical feature can be deduced only by the use of a model of the rotation of the galaxy. Thus the connection of the optical and radio measurements can provide a check on the model itself.

This program illustrates the pitfalls in astronomical research. The results were published in the Astrophysical Journal where all contributions are examined by a referee (someone familiar with the topic). Although I do not now remember the details, a colleague pointed out to me that my work was fundamentally flawed, because of a difference in the two kinds of observations. Apparently the optical observations of stellar velocities are based on a different zero point from that of the radio observations. I was unaware of this, although I should have been.

As a research associate at Harvard I was able to continue my 21 cm studies of nearby galaxies. They now seem horribly dated because they were so limited by the available instruments. Not so obviously "antique" are studies of hydrogen clouds in the interstellar medium of our own galaxy. I chose to study the gas in directions of least complex structure - the north and south galactic poles. Since all the neutral hydrogen along the line of sight of a given observation contributes to the observed profile, observations in the plane of the galaxy include gas at a wide range of distances and velocities. Their interpretation is therefore complicated compared to observations perpendicular to the plane. Along with evidence of gas at rest with respect to the sun in the form of clouds similar to those observed elsewhere, I found gas approaching the sun and therefore the galactic plane at about 50 km/sec. This was among the first observations supporting the theory of what is picturesquely called a "galactic fountain." The picture consists of hot gas thrown out of the galactic plane by active stars and cold (neutral hydrogen) gas falling back to the plane. It is that cold gas that I observed.

In early 1963 the 84-foot radio telescope of the Air Force Cambridge Research Laboratory was completed. Since in the same year scientists at the Lincoln Laboratory of MIT had found the first evidence at radio wavelengths of another constituent of the interstellar gas, OH (the hydroxyl radical), we equipped the telescope to pursue the discovery. They had found the OH molecule absorbing radiation at 18 cm from the direction of Cassiopeia A, the brightest radio source at this wavelength. We, along with two other groups, were able to confirm and extend the observation. The time is memorable for me, however, for reasons that have little to do with science.

On the afternoon of Friday, November 22, 1963 we were planning our observations for the weekend when we heard the news of President Kennedy’s assassination. We decided despite the shock to go on with them. As a result the weekend had a surreal quality. The receiver was housed within the large conical mount of the telescope where there were no windows, and only the presence of continuous reports over the radio kept us in touch with the real world. Something else, however, led me to a closer touch with real events. Just around this time I had been conferring with the producer of a television show called "Science All Stars", and taping for the show that included both young hopeful and established scientists was scheduled in New York for the following weekend. I met there Dr. Jerry Wiesner, Presidential Science Advisor. Over dinner he told me of the scene in the White House that day. He and other members of the administration were meeting in the Cabinet Room when the Secretary of Defense was called out of the room. Dr. Wiesner said that on his return the look on his face made many guess that an atomic bomb had been dropped somewhere. No one guessed the truth.