Carl Alvar Wirtanen (1910–1990)

BACKGROUND

The name of Carl Alvar Wirtanen will always be recognized as the second member of the hyphenated name pair "Shane-Wirtanen" designating the well-known Lick survey for galaxies. He was born on 11 November 1910 in Kenosha, Wisconsin, where he attended the local public schools. He was attracted to astronomy at age 12 when his violin teacher brought him to a local observatory to view stars through a telescope. This led him to make his own reflecting telescope and deepen further his interest in astronomy.

Wirtanen completed his undergraduate and graduate studies at the University of Virginia, where he was awarded the B.S. (1936) and A.M. (1939) degrees. He majored in astronomy, mathematics, and physics.

Wirtanen's association with Lick Observatory began 1 October 1941 as an observing assistant. One year later, responding to the need for technically trained personel during World War II, he was granted leave to participate in ballistics research conducted at the Naval Ordnance Test Station at China Lake, California. After the war Wirtanen resumed his position at Lick Observatory on 1 October 1946 with advancement to Senior Observing Assistant. For the next 32 years Wirtanen remained at the Lick Observatory as observer and research assistant participating successively in the research programs of several staff astronomers until his retirement in 1978. In 1966 he, along with many Lick staff members residing on Mt. Hamilton, transferred to the new Santa Cruz campus of the University of California.

With the move to the Santa Cruz area in 1966, his personal interests expanded to sailing in Monterey Bay, an activity he pursued well into his retirement years. Following a lengthy period of progressively deteriorating health, he passed away on 7 March 1990, at the age of 79 years. He was survived by his wife Edith, a daughter Jean Hines, and son Alan, all of Santa Cruz.

RESEARCH

During his graduate and postgraduate years at the McCormick Observatory (1936-1941) Wirtanen, as an observing assistant, contributed to measurements of trigonometric parallaxes, photographic photometry for Nova Herculis 1936, and other astrometric and photometric studies.

During his long astronomical career at Lick Observatory Wirtanen was fortunate in participating as a team member in several large programs, the major one being the Northern Proper Motion (NPM) program initiated by W.H. Wright. In 1934 Wright obtained funds to construct the Carnegie 51-cm astrograph for photographing the sky accessible from Mt. Hamilton for a massive program of measuring absolute proper motions of stars to faint magnitudes using distant galaxies as a fixed reference frame. Discontinuity in the program caused by the Second World War and Wright's retirement in 1942 was solved when Shane assumed directorship of the Lick Observatory and control of the Wright program. Wirtanen, after a four-year absence, returned to Mt. Hamilton on 1 October 1946, in time to help Shane in the final adjustments of the astrograph and to participate in the first epoch photography (1947-1954). This consisted of 1246 two-hour exposures made on 17x17-in plates, covering the sky northward of declination –23°. Later Shane added a Southern Supplement of 144 fields to cover the sky down to –33°, as well as the 163 Kapteyn Selected Areas with centers northward from –30° for possible astrometry.

Several years before the completion of the observational phase, Shane decided to exploit the valuable NPM plate collection for a program of galaxy counts, This was to clarify the details of the surface distribution of galaxies, already hinted at from small-field results by others using large reflecting telescopes during previous decades. To this end during the 1950's both Shane and Wirtanen, independently and in duplicate, undertook the massive task of counting galaxies in each of the 1.6 million 10x10 arcmin squares on these 1246 plates covering the sky to declination –23°. Compared to the massive funding expended today for research equipment, the viewing frame used by Shane and Wirtanen represented simplicity in the extreme— a device easily made in a day or two in a woodshop. From this simple viewing frame resulted the famous Shane-Wirtanen Galaxy Survey— exploited even today by astronomers.

No doubt satisfying to Wirtanen were the discoveries of several comets and asteroids based on astrograph plates taken for the NPM and other programs. He discovered a total of five comets, for the first four of which he received Donohue Comet Medal Awards of the Astronomical Society of the Pacific. These included the periodic comet P/Wirtanen (1948b), as well as comets 1947h, 1948k, 1948h, and 1956c.

Wirtanen discovered three asteroids which passed within several million miles of the Earth, (1685) Toro = 1948 OA, 1948 EA, and 1950 DA, as well as the main-belt asteroid (1600) Vyssotsky = 1947 UC. Near the time of his retirement in 1918 an asteroid designated (2044) Wirt was named in his honor.

During the 1960's Wirtanen joined T. Kinman in his photographic survey with the astrograph for the discovery of faint RR Lyrae stars in the remote galactic halo. He participated in the intensive photography of several fields and in the blinking of these plates to discover the RR Lyrae stars, used to construct a clearer picture of their distribution in the distant halo.

Wirtanen also participated in observing and plate measurement for a new program of trigonometric parallaxes initiated in 1961 by S. Vasilevskis using the Lick 93-cm refractor.

During the final decade (1968-1978) of his professional career Wirtanen once again returned to the Lick NPM program, initiated decades earlier by Wright, to participate in the second-epoch photography at Mt. Hamilton and astrometric measurements at Santa Cruz under the direction of Vasilevskis. A major part of this program is now approaching completion,

Wirtanen's contribution to several large-scale research programs was that of performing the essential routine work needed to ensure their successful conclusions. This he did with great care and willingness. Already in his early professional years he had been described as "especially capable of handling apparatus and a first class observer," an assessment valid throughout his career.

The author wishes to thank Mrs. Dorothy Schaumberg for assistance in the use of the Mary Lea Shane Archives of Lick Observatory.