Infrared Astronomy ’ s Delayed Development George Rieke June 28, 2017 at

1. Infrared Astronomy’s Delayed Development George Rieke June 28, 2017 at Science Enabled by Novel Infrared Instrumentation in honor of Jim Houck

2. Prior to 1910, the best that had been done in infrared astronomy was barely detecting Vega and Arcturus. That was not sufficient to open up many possibilities. Better detectors were needed. Coblentz developed the vacuum thermocouple (thus reducing the heat losses and substantially improving both the stability and the sensitivity). In 1914, he measured the infrared fluxes of more than 100 stars and a few planets. He used these measurements to derive temperatures of the stars, a “hot” topic at the time!

3. I tried to promote this important benchmark in astronomy by inventing a celebration for the 100th anniversary of infrared astronomy. But I had little success.

4. As Jim would have appreciated, there was great activity in developing novel infrared detectors all through the 1920s. “The vanes of the radiometer system were 0.4 mm wide and 1.0 mm tall, and but 1.2 mm between centers. Each vane had three parallel laminae of houseflies’ wings, of which the front one was painted dead black, the two rear ones being unpainted. “Abbot, C. G. 1929, ApJ, 69, 293

5. Pettit and Nicholson built on Coblentz’s work and developed their own high-performance thermocouples. Comparing their measurements with modern, commercial thermopiles suggests the historic ones were an order of magnitude more sensitive! A device with a pair of thermocouples was placed on the plate holder of the 100-Inch so the star image could be switched from one detector to the other by turning the guide screw.

6. The output wires went to the basement of the telescope, where there was a sensitive galvanometer arranged so a continuously driven photographic plate could record the signals.

7. The photometry looks quite good. They used a water cell to block the infrared, so its strength was deduced by the amount by which this cell reduced the signal. (Coblentz had introduced this approach) As an example, compare the behavior of Vega (top) with that of R Hydrae (bottom).

8. The photometry looks quite good. They used a water cell to block the infrared, so its strength was deduced by the amount by which this cell reduced the signal. (Coblentz had introduced this approach) As an example, compare the behavior of Vega (top) with that of R Hydrae (bottom). Also note that even with the infrared blocked, they got a nice signal on R Hydrae at 8th magnitude visually!

9. The work of Pettit and Nicholson was used by Kuiper (1938) in a classic derivation of stellar temperatures and bolometric corrections.

10. …….but nothing more happened. Fellgett tried infrared photometry with a PbS cell in 1951 …….but nothing more happened.

11. Modern infrared astronomy started in the 1960s led by Harold Johnson, Frank Low, Gerry Neugebauer, Martin Harwit, and Ed Ney. Here is Harold “maintaining the photometric system” at the Catalina 28-Inch telescope of the UA Lunar and Planetary Laboratory

12. Why did the field not take off until the 60s and 70s??

13. It wasn’t because astronomers got interested: Early infrared astronomy was dominated by physicists: Physicists: 11 Astronomers: 1 As was early X-ray astronomy: Physicists: 9 Astronomers: 0

14. Non-astronomers had opened up radio astronomy also Jarrell (2005)* summarizes a study of citation rates: “To be sure, several important optical and theoretical astronomers….showed interest in the early radio work. But, for most of their colleagues, radio data were simply irrelevant to their research. In fact, radio results were as likely to be of as much value to atmospheric scientists as to astronomers.” * “’Radio astronomy, whatever that may be’: The marginalization of early radio astronomy,”Jarrell, R., Astrophysics and Space Science Library, 2005, p. 191 Physicists and engineers: 82 Astronomers: 11

15. It wasn’t because of an advance in accuracy: Fellgett’s PbS Index agreed with Pettit & Nicholson’s Heat Index with a scatter of only 8%!!! Both sets of measurements were quite accurate. Nor a breakthrough in sensitivity: Because Pettit and Nicholson had a large telescope (100”), their measurements were just as sensitive as Johnson’s (28”).

16. Nor was it the opening of the non-stellar Universe with radio astronomy: Vasilii Ivanovich Moroz started an infrared program in the USSR at the same time almost exclusively on non-stellar targets, but it died out and he migrated to planetary studies.

17. Any ideas???

18. The secret seems to be the formation of a number of groups competing and exchanging ideas.

19. Jim was, of course, one of those physicist-pioneers. photo by Greg Sloan