Systematic study of AGB stars in the intermediate-age globular clusters in the Magellanic Clouds

We performed systematic infrared observations of the intermediate-age Magellanic Clouds clusters NGC 419, NGC 1783 and NGC 1978. Mid-infrared stars discovered in NGC 419 and NGC 1978 are very red and must be undergoing intense mass loss (comparable to superwinds). They are probably carbon stars but do not seem to show any FIR excesses. Three optically visible carbon stars as well as (at least) 2 near-infrared carbon stars observed with ISOPHOT show 60 μm excesses which may indicate mass loss in the past. It seems that the MIR stars are fainter than the AGB tip luminosity and that their Mbols are close to those of the transition luminosity from M type to C stars. Therefore, these MIR stars may not be in the final stage of the AGB phase. This may suggest that AGB stars lose mass heavily at some other time, possibly during the transition from M type to C stars.

Discovery of Infrared Stars in Globular Clusters in the Magellanic Clouds and Their Light Variations

A systematic near-infrared survey was made for globular clusters in the Magellanic Clouds. Two infrared stars were discovered in NGC419 (SMC) and NGC1783 (LMC). NGC419 and NGC1783 are well-studied rich globular clusters whose turn-off masses and ages are estimated MTO ~ 2.0 Mʘ and т ~1.2 Gyr for NGC419, and MT0 ~ 2.0 Mʘ and т ʘ 0.9 Gyr for NGC1783, respectively. The periods of the infrared light variations were determined to be 540 dfor NGC419IR1 and to be 480 d for NGC1783IR1, respectively. Comparison of the measurements with the period—if magnitude relation for carbon Miras in the LMC by Groenewegen and Whitelock(1996) revealed that the Kmagnitudes of the infrared stars were fainter by about 0.3 — 0.8 magnitude than those predicted by the P — K relation. This deviation can be explained if the infrared stars are surrounded by thick dust shells and are obscured even in the K band. The positions of NGC419IR1and NGC1783IR1 on the P — K diagram suggest that AGB stars with the main sequence masses of about 2 Mʘ start their heavy mass-loss when P ʘ 500 d.

Harlow Shapley and Red Giant Stars

In five papers written between 1951 and 1955 Shapley considers the topic of red giant stars and reddish variable stars in the Magellanic Clouds. These works coincide with Shapley's final year as Director at Harvard and the first years of his retirement which extended a full score of years before his death in 1972. They include the following: Magellanic Clouds II (Supergiants/Red Variable Stars in the Small Cloud; January 1951); Magellanic Clouds IV (On Period Frequency Anomalies; February 1952); Magellanic Clouds VII (Star Colors and Luminosities in Five Constellations; March 1953); Magellanic Clouds VIII (On the Populations Characteristics of the Two Clouds; October 1953); and Magellanic Clouds XVI (Infrared Stars and Stellar Evolution; July 1955). These five papers, which appeared originally in the Proceedings of the National Academy of Science, may be found in the Harvard Reprint Series I as numbers 346, 360, 373, 376, and 425.

A Historical Review of Star Formation: Observation and Theory

We present a historical review of evidence for ongoing star formation in our Galaxy beginning with the discovery that interstellar space is not empty. The discoveries of interstellar dust, interstellar hydrogen and molecular clouds are reviewed. Observational investigations of dark clouds are then traced from the photographs of Edward Emerson Barnard to contemporary studies of their molecular constituents. A historical overview of observational evidence for new-born stars includes T-Tauri stars, young stellar clusters, sequential star birth and infrared stars beginning with Alfred Joy, Merle Walker, Becklin, and Neugebauer, and Adrian Blaauw and continuing to giant molecular clouds and IRAS. Theoretical studies of gravitational collapse and the early stages of stellar evolution are also placed within a historical context.

Small telescopes and research from space

The number of artificial satellites dedicated to astrophysical research is increasing rapidly. Nearly 30 satellites currently under development or in the early planning stages will be in orbit within 10–12 years and will have more sensitive detectors and better data-processing technology as a result of current research. Many of the galactic and extragalactic objects discovered by the new technology are variable on surprisingly short time scales ranging from sub-seconds to many months. The new variable objects include but are not confined to: neutron and binary stars; quasars (and associated active centers of galaxies); newborn infrared stars and associated clouds; the coronal activity of main sequence stars; cataclysmic variables (white dwarfs in binaries); and novae, supernovae and remnants. We now realize that the short time-scale variations of many unusual stars and active galactic nuclei demand that ground and space data be taken as close in time as possible and that they be carefully planned and coordinated.