Giants In Open Clusters Research Articles

Mass-losing red giants in open clusters

Mass-losing stars in open clusters with main-sequence turn-offs at intermediate mass have been searched for by using the IRAS data base. The absence of many strong 60 micron sources in open clusters implies that intermediate-mass stars lose much of their mass during an intense wind phase of rather short duration. For stars of about seven solar masses, this phase, if it exists at all, lasts for not much more than 100,000 yr. For stars of about four solar masses, the intense wind phase appears to last considerably less than 10 million yr; it may well last for less than a million yr.

SPECTRAL TYPES AND LUMINOSITIES OF SUPERGIANTS IN OPEN CLUSTERS.

ABSTRACT Revised MK spectral types of supergiants and bright giants in open clusters are combined with published cluster moduli to calibrate the luminosity classes in terms of visual absolute magnitudes.

DDO photometry of giants in the open cluster IC 4651

DDO photometry has been obtained for 14 stars in the open cluster IC 4651. The reddening and distance modulus derived from these data are in good agreement with the results obtained from UBV photometry by Eggen. The cluster appears to have a heavy-element abundance slightly less than that of the Hyades, although one giant shows an anomalously strong 4216-A CN band comparable to those seen in the SMR giants. A comparison is made between this star and CN-enhanced giants in eight other open clusters. It is suggested that the CN-strong phenomenon among open cluster giants is the result of nonstandard stellar evolution, the occurrence of which is supported by the presence of blue stragglers in five out of the eight comparison clusters, as well as in IC 4651 itself.

Membership and Binarity of Red Giants in Open Clusters Determined by Photoelectric Radial Velocities

An observing programme was started in the summer of 1977 to measure radial velocities of red giants in open clusters with the spectrovelocimeter “Coravel” (Baranne et al. 1979) attached to the 1 m telescope of the Geneva Observatory installed at the O.H.P. (France). 750 measurements for 160 stars in 30 open clusters north of −20°, with ages ranging from those of NGC 752 to Pleidades, have been obtained. The limiting magnitude is B = 12.5.

The Clump Giants: A Spectroscopic Survey of G and K Giants in Open Clusters

The clump giants in old and middle-aged open clusters provide a sample of stars whose evolutionary state can be clearly identified as core helium burning (Cannon 1970). The evolutionary state of the Ba II stars, on the other hand, is at present undetermined. The enrichment of s-process elements in the atmospheres of these peculiar stars suggests that the stars have at least passed through double shell burning, where the heavy elements may be produced and mixed to the surface. The Ba II stars are, however, too faint to be associated with this phase of stellar evolution; the absolute magnitudes and temperatures are consistent with the core helium burning phase. The barium stars should then occur in the clumps of Population I clusters in similar proportion to their numbers among the field giants.

The David Dunlap Observatory (DDO) Photometric System for Classification of Late-Type Stars

An intermediate bandpass filter system is described that is useful for classification of G and K stars in terms of effective temperature (spectral type), surface gravity (luminosity class), heavy element abundance, and interstellar reddening. The system measures the strength of the cyanogen band in the region shortward of λ4216, the break in the continuum at the G band, and a colour index in the λ4500–λ4900 region of the spectrum. The surface gravity parameter is independent of the cyanogen index, and the cyanogen band strength, after a surface gravity correction, is used as a measure of heavy element abundance.Application of the system to the determination of the atmospheric parameters of open cluster giants, as well as of field stars, is discussed. The system has been used to isolate stellar populations among field stars without any prior knowledge of their distances. From observations on this system, the only open cluster found so far to have giants with stronger cyanogen band absorption than the Hyades giants is the intermediate age southern cluster NGC 2477.

Population I Helium Burning Red Giants. Observations

The basic observational evidence for helium-burning red giants in open clusters has been given elsewhere, and I shall give here only a summary and then describe in more detail new results for one cluster, NGC 2477.