We have measured spectral indices for ~ 2000 galaxies in the CNOC1 redshift survey of 15 X-ray luminous clusters at 0.2 < ≈ < 0.55. A detailed comparison is made between the star formation histories of galaxies in these clusters with an identically selected sample of galaxies in the lower density field population, to establish the effects these cluster environments have on galaxy evolution. We find that the mean star formation rate, as determined from the [OII]λ3727 emission line, is suppressed in all cluster galaxies, out to and even beyond the virial radius. The number of actively star forming galaxies, and the mean star formation rate among cluster galaxies, increases with increasing distance from the cluster centre. This correlation is not completely due to the morphology-radius relation, as cluster galaxies of a given physical size, fractional bulge luminosity and redshift have lower star formation rates than similar galaxies in the field environment. We find no evidence that the cluster environment induces star formation in its constituent galaxies. Galaxies with positive W₀(OII), of any strength, are more common in the field than they are in the clusters. In particular, the A+em galaxies, which have spectra that may reflect dust obscured starburst activity, make up only 6.3 ± 2.1% of the field population, and are twice as common there as they are in the cluster sample. If star formation is terminated in a galaxy after a short starburst, the spectrum will show strong Balmer absorption lines without [OII] emission; we find that less than ~5% of all galaxies have such a spectrum, and there is no evidence that they are preferentially found within the cluster sample. Spectrophotometric model results suggest that many of these galaxies may have had their star formation abruptly truncated without such a starburst. Alternatively, Hα observations of Abell 2390 cluster galaxies suggest that the lack of [OII] emission in some such galaxies may be due to dust obscuration, and not necessarily indicative of the absence of star formation activity. These results suggest that star formation is terminated in galaxies that are incorporated into these clusters. This termination need not be abrupt, and may take place over a period of several Gyr. Thus, the differential evolution of cluster galaxies may result because field galaxies are able to refuel their stellar disk with gas from an extended halo, thus perpetuating star formation, while such a halo would be disrupted within rich clusters, and star formation would gradually cease. / Graduate

An automated method of determining the relative line separations on digitized blended stellar spectra has been developed. A pair of standard profiles are fitted to the observed blended profile by allowing the standards to relax in position and amplitude until a least-square 'best fit' is obtained. The technique has been tested on numerous blends of known separation and it has been shown that with certain restrictions on the relative amplitudes it is not susceptible to systematic errors. Blended hydrogen and helium lines in two B-stars have been separated to < 100 km/sec at 30 A/mm with a probable error of 15 km/sec. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

We present new 6 cm observations of the binary radio, X-ray and ɿ -ray star GT0236+610 (LSI+61°303) obtained in August 1984 and September 1986. Ve calculate an improved period for the source's periodic radio outbursts of 26.50 ± 0.03 days. No significant period derivative was found. Based on an analysis of 201 flux density measurements from 1977 August to 1986 September, we find evidence for a possible 4 year modulation of the amplitude of the 26.50 day periodic radio outbursts. A precessing jet model for this long period modulation is discussed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Carbon stars are relatively uncommon, luminous, cool stars whose spectra exhibit exceptionally strong bands of carbon-containing molecules. This is direct evidence of extensive nucleosynthesis, as will occur in the late stages of stellar evolution. The two aspects investigated here are their luminosities and atmospheric carbon and nitrogen isotope ratios. The luminosities are derived through the study of those carbon stars which are members of double star systems. Since the companion star is apparently normal and thus of known luminosity, the carbon star luminosity is directly attainable. Photometry and spectroscopy of suspected binaries yield absolute visual magnitudes for a dozen stars as bright as -4.7, and bolo-metric magnitudes primarily in the range -4 to -8. This means they are slightly mere luminous than normal giants. The isotopic ratios have been deduced by a comparison of synthetic spectra with the observed near infrared stellar spectra. The synthetic spectra were calculated by direct integration of the flux emerging from an appropriate model atmosphere, and contain lines primarily of the Bed band system of the CN molecule. A new analysis technique, used in time series analysis, which is based on the mutual coherence of the spectra being compared and makes full use of the entire spectrum, has been employed. By varying the parameters describing the synthetic spectrum, including the isotopic ratio, the coherence can be maximized and the isotopic ratio of the stellar spectrum deduced. Results for five carbon stars yield ¹²C/¹³C ratios in the range 2.5 to 30. A search was also made for the isotopes ¹⁴C and ¹³N; ¹⁴C was not found, while a tentatively positive result is reported for ¹⁵N. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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New observations of the star formation region NGC 7538 are presented. Energetic outflows are commonly associated with regions of active star formation, despite the fact that the star formation process itself must be predominantly one of infall. This work shows how multi-wavelength observations can be used to study such phenomena on a variety of scales, in an attempt to infer their connection with star formation processes. Included are near-infrared spectroscopy of IRS 2; carbon monoxide J = 1-0 emission line mapping of the central regions of the NGC 7538 molecular cloud; and high spatial resolution maps of IRS 1 at 5 and 15 GHz. Other recent observational data are also considered, including far-infrared continua mapping, maser sources, and spectroscopy of numerous atomic and molecular species. A very large (r ≥ 1.5 pc) and massive (m ≥ 100 solar masses) distribution of high velocity (ΔV(FWHM) ≃ 35 - 40 km s⁻¹) molecular gas is identified in NGC 7538. The correspondence of far-infrared emission with the extent of the high velocity gas, along with the near-equality between the observed momentum flux of the gas and that which is available for radiation pressure L(*) /c (IRS 1-3) leads to the proposal of an in situ mechanism for radiative acceleration of the gas. This mechanism for radiative acceleration of the gas. This mechanism operates in cases where the optical depth of dust is insufficient to permit the "snowplow" outflow effect from strong radiation pressure. On the 1/2 - 1 pc minimum scale of these molecular observations, no obvious bipolarity or collimation is detected, consistent with the in situ mechanism. The highly luminous infrared source IRS 1 is identified as the probable source of this high velocity phenomenon. It is the most luminous source of the three (IRS 1-3) upon which the high velocity gas distribution is centered. The presence on a scale of 100 - 100 AU of a high density ridge perpendicular to a collimated distribution of ionized gas is strongly indicated in both mid-infrared and radio emission, and by anomalous optical and infrared extinctions. There is thus a startling discontinuity between collimation of gas on this scale and the lack of it observed at the arcminute scale of the molecular observations.