NOAO: Dr. Arlo Landolt
55 years of Observing at the National Observatories
6 July 2014
Dr. Arlo Landolt, Ball Family Professor Emeritus of physics and astronomy at Louisiana State University, was recently celebrated for his 55 years of observing at Kitt Peak National Observatory (KPNO), almost all of which were devoted to service to the astronomical community. In the summer of 1959, Dr. Landolt was the first guest observer at KPNO when the only telescope on the mountain was the 16-inch site survey telescope. Today, KPNO operates three major nighttime telescopes and hosts the facilities that operate 22 optical telescopes and two radio telescopes on the mountain.
Dr. Landolt is known best for his photometric standard star lists. “Landolt standards” is a term familiar to the entire astronomical community. Astronomers must observe through the Earth’s atmosphere, which, as anyone who watches the weather knows, can vary greatly with the date and location. Therefore, astronomical data must be calibrated; just as your bathroom scale may not reflect the accurate weight measured at your doctor’s office and require a correction, so measurements of stellar brightness must be corrected to keep everyone’s results on the same scale. So astronomers observe the same standard stars, along with their own observations, in order to correct for differences in the sky, the telescope, and the instruments on the telescope. Almost all of Dr. Landolt’s observations have been made at the national observatories: Kitt Peak National Observatory in Arizona, and Cerro Tololo Inter-American Observatory in Chile, where Dr. Landolt was also one of the first observers in March 1965.
Photometric calibration stars are needed around the sky, so they can be observed in either the Northern or Southern Hemisphere, at any season of the year, from any observatory. Landolt standards have been extended to fainter stars, to stars located at both 50 degrees north and south declination, as well as those located around the celestial equator. His most quoted paper, published in 1992, has been cited in the professional astronomical literature over 3800 times—an average of 172 times per year. For comparison, the number of times a typical astronomical paper is cited is in the single digits per year, and rarely, if at all, after 20 years. To compile the necessary data for the standard stars, Dr. Landolt has spent at least 1500 nights observing at different telescopes over the years since 1958: possibly an all-time record for any astronomer! Nor has formal retirement slowed him down; over half of these nights have been in the last 15 years.
Dr. Landolt, in late 1964, was the first to discover that white dwarf stars can pulsate, varying in brightness with a period of just a few minutes. This has allowed astronomers to probe the interior structure of these stars and study this end stage of a star’s life. But as the authors of a recent review article wrote, “…the story really begins with the accidental discovery of rapid luminosity variations in the DA white dwarf HL Tau 76 by Arlo Landolt….” (Fontaine & Brassard, 2008, PASP).
In 1995, he received the George van Biesbroeck award, which honors a living individual for long-term extraordinary or unselfish service to astronomy, often beyond the requirements of his or her paid position.
Born in 1935, Dr. Landolt grew up in a farming community in Illinois, east of St. Louis. He and his three siblings were the first in their family to go to high school. He continued on to college at Miami University in Ohio, then to Indiana University (IU) for graduate work (1955–1963), during which time he spent two years at the South Pole as part of the International Geophysical Year, studying aurora and air glow. Dr. John Irwin, his PhD thesis advisor at IU, interested him in binary stars; so he was able to secure time to observe the eclipsing binary V382 Cygni on KPNO in the summer of 1959. He observed at night; during the daytime, blasting was taking place for the construction of the 2.1- and 0.9-m telescopes.
Dr. Landolt has most recently been using the KPNO 2.1-m telescope to continue his work. But this may be his last observing run with this telescope; its future availability to astronomers in the community is not clear. The National Science Foundation (NSF) has determined that it can no longer provide operational support for this KPNO telescope after September 2014. Therefore, NSF and the National Optical Astronomy Observatory are accepting proposals for the operation of the KPNO 2.1-m.
KPNO is a division of the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the National Science Foundation.
Dr. Arlo Landolt
Department of Physics and Astronomy, Louisiana State University
202 Nicholson Hall, Baton Rouge, LA