John Ouellette - Academia.edu (original) (raw)

Papers by John Ouellette

We present a spectroscopic analysis of HST/STIS and FOS low- and intermediate-resolution spectros... more We present a spectroscopic analysis of HST/STIS and FOS low- and intermediate-resolution spectroscopy of 55 stars (turn-off stars, horizontal branch stars and blue stragglers) in four globular clusters (47 Tucanae, M3, NGC6752, and NGC6397). Stars were analyzed with non-Local Thermodynamic Equilibrium model atmospheres, and values for their effective temperatures and gravities and some rotation rates were obtained. Using photometric fluxes, we also obtained radii, luminosities and spectroscopic masses.

GSC 3505.677 turned out to be a new eclipsing variable.

Blue stragglers are enigmatic stars which appear to have undergone some form of rejuvenation, bri... more Blue stragglers are enigmatic stars which appear to have undergone some form of rejuvenation, bringing them near the zero-age main sequence of the cluster in which they reside. The most likely explanation for the existence of these stars is that they have formed recently, through the merger of two stars, either through a direct stellar collision, or through binary mass-transfer and coalescence. This thesis presents models of the remnants of these processes, and a comparison of the predictions of these models with observed blue stragglers in several dusters. The predictions of smoothed particle hydrodynamic simulations of colliding stars have been used to create models appropriate for input into a stellar evolution code. Since these models develop only thin, short-lived, convective envelopes, angular momentum loss via a magnetically driven stellar wind is unlikely to be a viable mechanism for slowing the rapidly rotating blue stragglers predicted by the collisional scenario. Angular ...

Software and Cyberinfrastructure for Astronomy, 2010

The Canadian Advanced Network For Astronomical Research (CANFAR) is a 2 1/2-year project that is ... more The Canadian Advanced Network For Astronomical Research (CANFAR) is a 2 1/2-year project that is delivering a network-enabled platform for the accessing, processing, storage, analysis, and distribution of very large astronomical datasets. The CANFAR infrastructure is being implemented as an International Virtual Observatory Alliance (IVOA) compliant web service infrastructure. A challenging feature of the project is to channel all survey

The JCMT Science archive has adopted an agile "reduce-often release-always" model that ... more The JCMT Science archive has adopted an agile "reduce-often release-always" model that continuously processes data and exposes it to the user. This paper describes the reasons for, and advantages of, this model.

The Astronomical Journal, 1998

We have used the results of recent smoothed particle hydrodynamic simulations of colliding stars ... more We have used the results of recent smoothed particle hydrodynamic simulations of colliding stars to create models appropriate for input into a stellar evolution code. In evolving these models, we find that little or no surface convection occurs, precluding angular momentum loss via a magnetically-driven stellar wind as a viable mechanism for slowing rapidly rotating blue stragglers which have been formed by collisions. Angular momentum transfer to either a circumstellar disk (possibly collisional ejecta) or a nearby companion are plausible mechanisms for explaining the observed low rotation velocities of blue stragglers Under the assumption that the blue stragglers seen in NGC 6397 and 47 Tuc have been created solely by collisions, we find that the majority of blue stragglers cannot have been highly mixed by convection or meridional circulation currents at anytime during their evolution. Also, on the basis of the agreement between the predictions of our non-rotating models and the observed blue straggler distribution, the evolution of blue stragglers is apparently not dominated by the effects of rotation.

The Canadian Advanced Network For Astronomical Research (CANFAR) is an operational system for the... more The Canadian Advanced Network For Astronomical Research (CANFAR) is an operational system for the delivery, processing, storage, analysis, and distribution of very large astronomical datasets. CANFAR combines the Canadian national research network (CANARIE), grid processing and storage resources (Compute Canada) and a data center (CADC) into a unified Platform-as-a-service (PaaS) cyberinfrastructure supporting Canadian astronomy projects. The CANFAR processing service is

The Astrophysical Journal, 2004

We present an analysis of optical HST/STIS and HST/FOS spectroscopy of 6 blue stragglers found in... more We present an analysis of optical HST/STIS and HST/FOS spectroscopy of 6 blue stragglers found in the globular clusters M 3, NGC 6752 and NGC 6397. These stars are a subsample of a set of ∼50 blue stragglers and stars above the main sequence turn-off in four globular clusters which will be presented in an forthcoming paper. All but the 6 stars presented here can be well fitted with non-LTE model atmospheres. The 6 misfits, on the other hand, possess Balmer jumps which are too large for the effective temperatures implied by their Paschen continua. We find that our data for these stars are consistent with models only if we account for extra absorption of stellar Balmer photons by an ionized circumstellar disk. Column densities of H i and Ca ii are derived as are the the disks' thicknesses. This is the first time that a circumstellar disk is detected around blue stragglers. The presence of magnetically-locked disks attached to the stars has been suggested as a mechanism to lose the large angular momentum imparted by the collision event at the birth of these stars. The disks implied by our study might not be massive enough to constitute such an angular momentum sink, but they could be the leftovers of once larger disks.

We present a spectroscopic analysis of HST/STIS and FOS low- and intermediate-resolution spectros... more We present a spectroscopic analysis of HST/STIS and FOS low- and intermediate-resolution spectroscopy of 55 stars (turn-off stars, horizontal branch stars and blue stragglers) in four globular clusters (47 Tucanae, M3, NGC6752, and NGC6397). Stars were analyzed with non-Local Thermodynamic Equilibrium model atmospheres, and values for their effective temperatures and gravities and some rotation rates were obtained. Using photometric fluxes, we also obtained radii, luminosities and spectroscopic masses.

GSC 3505.677 turned out to be a new eclipsing variable.

Blue stragglers are enigmatic stars which appear to have undergone some form of rejuvenation, bri... more Blue stragglers are enigmatic stars which appear to have undergone some form of rejuvenation, bringing them near the zero-age main sequence of the cluster in which they reside. The most likely explanation for the existence of these stars is that they have formed recently, through the merger of two stars, either through a direct stellar collision, or through binary mass-transfer and coalescence. This thesis presents models of the remnants of these processes, and a comparison of the predictions of these models with observed blue stragglers in several dusters. The predictions of smoothed particle hydrodynamic simulations of colliding stars have been used to create models appropriate for input into a stellar evolution code. Since these models develop only thin, short-lived, convective envelopes, angular momentum loss via a magnetically driven stellar wind is unlikely to be a viable mechanism for slowing the rapidly rotating blue stragglers predicted by the collisional scenario. Angular ...

Software and Cyberinfrastructure for Astronomy, 2010

The Canadian Advanced Network For Astronomical Research (CANFAR) is a 2 1/2-year project that is ... more The Canadian Advanced Network For Astronomical Research (CANFAR) is a 2 1/2-year project that is delivering a network-enabled platform for the accessing, processing, storage, analysis, and distribution of very large astronomical datasets. The CANFAR infrastructure is being implemented as an International Virtual Observatory Alliance (IVOA) compliant web service infrastructure. A challenging feature of the project is to channel all survey

The JCMT Science archive has adopted an agile "reduce-often release-always" model that ... more The JCMT Science archive has adopted an agile "reduce-often release-always" model that continuously processes data and exposes it to the user. This paper describes the reasons for, and advantages of, this model.

The Astronomical Journal, 1998

We have used the results of recent smoothed particle hydrodynamic simulations of colliding stars ... more We have used the results of recent smoothed particle hydrodynamic simulations of colliding stars to create models appropriate for input into a stellar evolution code. In evolving these models, we find that little or no surface convection occurs, precluding angular momentum loss via a magnetically-driven stellar wind as a viable mechanism for slowing rapidly rotating blue stragglers which have been formed by collisions. Angular momentum transfer to either a circumstellar disk (possibly collisional ejecta) or a nearby companion are plausible mechanisms for explaining the observed low rotation velocities of blue stragglers Under the assumption that the blue stragglers seen in NGC 6397 and 47 Tuc have been created solely by collisions, we find that the majority of blue stragglers cannot have been highly mixed by convection or meridional circulation currents at anytime during their evolution. Also, on the basis of the agreement between the predictions of our non-rotating models and the observed blue straggler distribution, the evolution of blue stragglers is apparently not dominated by the effects of rotation.

The Canadian Advanced Network For Astronomical Research (CANFAR) is an operational system for the... more The Canadian Advanced Network For Astronomical Research (CANFAR) is an operational system for the delivery, processing, storage, analysis, and distribution of very large astronomical datasets. CANFAR combines the Canadian national research network (CANARIE), grid processing and storage resources (Compute Canada) and a data center (CADC) into a unified Platform-as-a-service (PaaS) cyberinfrastructure supporting Canadian astronomy projects. The CANFAR processing service is

The Astrophysical Journal, 2004

We present an analysis of optical HST/STIS and HST/FOS spectroscopy of 6 blue stragglers found in... more We present an analysis of optical HST/STIS and HST/FOS spectroscopy of 6 blue stragglers found in the globular clusters M 3, NGC 6752 and NGC 6397. These stars are a subsample of a set of ∼50 blue stragglers and stars above the main sequence turn-off in four globular clusters which will be presented in an forthcoming paper. All but the 6 stars presented here can be well fitted with non-LTE model atmospheres. The 6 misfits, on the other hand, possess Balmer jumps which are too large for the effective temperatures implied by their Paschen continua. We find that our data for these stars are consistent with models only if we account for extra absorption of stellar Balmer photons by an ionized circumstellar disk. Column densities of H i and Ca ii are derived as are the the disks' thicknesses. This is the first time that a circumstellar disk is detected around blue stragglers. The presence of magnetically-locked disks attached to the stars has been suggested as a mechanism to lose the large angular momentum imparted by the collision event at the birth of these stars. The disks implied by our study might not be massive enough to constitute such an angular momentum sink, but they could be the leftovers of once larger disks.