Abstract by Javier Rodríguez-Zaurín
During the first part of my talk I will summarize the results of our recent work in Luminous and Ultraluminous infrared galaxies (LIRGs and ULIRGs). These objects are much more numerous at higher redshifts than locally, dominating the star formation rate density at redshifts >~2. Therefore, they are important objects in order to understand how galaxies form and evolve through cosmic time. Local samples provide a unique opportunity to study these objects in detail. With that in mind, we did undertake a program of spectroscopic observations of over 40 objects involving both, long-slit and integral field spectroscopic datasets. Our aim is to investigate the distributions of the parameters associated with the stellar populations (i.e. age, reddening and percentage contribution), and also, whether the properties of the stellar populations correlate with other properties of (U)LIRGs (such as the spectral classification, infrared luminosity, etc...). In the second part of the talk I will present an undergoing, follow up project involving high resolution imaging and spectroscopy observed with the 10.4 m Gran Telescopio Canario (GTC) at La Palma, Spain. Our aim is to study the kinematics of young star clusters (< 10 Myr) in the halo of star forming galaxies, such as ULIRGs, in order to investigate what is the main mode of star formation in this rapidly evolving systems.
Relevant Papers
Rodríguez et al. 2010
Talk Slides
pdf
Friday, September 2, 2011
Tidal Warping of Be Star Decretion Discs
Abstract by Rebecca Martin
Rapidly rotating Be stars are observed as shell stars when the decretion disc is viewed edge on. Transitions between the two implies that the discs may be warped and precessing. Type II X-ray outbursts are thought to occur when the warped disc interacts with the fast stellar wind. We suggest that tides from a misaligned companion neutron star can cause the observed effects. We make numerical models of a Be star decretion disc in which the spin of the Be star is misaligned with the orbital axis of a neutron star companion. Tidal torques from the neutron star truncate the disc at a radius small enough that the neutron star orbit does not intersect the disc unless the eccentricity or misalignment is very large. A magnetic torque from the Be star that is largest at the equator, where the rotation is fastest, is approximated by an inner boundary condition. There are large oscillations in the mass and inclination of the disc as it moves towards a steady state. These large variations may explain the observed changes from Be star to Be shell star and vice-versa and also the Type II X-ray outbursts. We find the tidal timescale on which the disc warps, precesses and reaches a steady state to be around a year up to a few hundred years. If present, the oscillations in mass and disc inclination occur on a fraction of this timescale depending on the orbital parameters of the binary. The timescales associated with the tidal torque for observed Be star binaries suggest that these effects are important in all but the longest period binaries.
Relevant Papers
"Tidal Warping of Be Star Decretion Discs"
Martin et al. 2011
Talk Slides
pdf
Rapidly rotating Be stars are observed as shell stars when the decretion disc is viewed edge on. Transitions between the two implies that the discs may be warped and precessing. Type II X-ray outbursts are thought to occur when the warped disc interacts with the fast stellar wind. We suggest that tides from a misaligned companion neutron star can cause the observed effects. We make numerical models of a Be star decretion disc in which the spin of the Be star is misaligned with the orbital axis of a neutron star companion. Tidal torques from the neutron star truncate the disc at a radius small enough that the neutron star orbit does not intersect the disc unless the eccentricity or misalignment is very large. A magnetic torque from the Be star that is largest at the equator, where the rotation is fastest, is approximated by an inner boundary condition. There are large oscillations in the mass and inclination of the disc as it moves towards a steady state. These large variations may explain the observed changes from Be star to Be shell star and vice-versa and also the Type II X-ray outbursts. We find the tidal timescale on which the disc warps, precesses and reaches a steady state to be around a year up to a few hundred years. If present, the oscillations in mass and disc inclination occur on a fraction of this timescale depending on the orbital parameters of the binary. The timescales associated with the tidal torque for observed Be star binaries suggest that these effects are important in all but the longest period binaries.
Relevant Papers
"Tidal Warping of Be Star Decretion Discs"
Martin et al. 2011
Talk Slides
Friday, August 19, 2011
Young, UV-bright Stars Dominate Dust Heating in Star Forming Galaxies
Abstract by Ka-Hei Law
In star forming galaxies, dust plays a significant role in shaping the ultraviolet (UV) through infrared (IR) spectrum. Dust attenuates the radiation from stars, and re-radiates the energy through equilibrium and non-equilibrium emission. Polycyclic aromatic hydrocarbons (PAH), graphite, and silicates contribute to different features in the spectral energy distribution; however, they are all highly opaque in the same spectral region - the UV. Compared to old stellar populations, young populations release a higher fraction of their total luminosity in the UV, making them a good source of the energetic UV photons that can power dust emission. However, given their relative abundance, the question of whether young or old stellar populations provide most of these photons that power the infrared emission is an interesting question. Using three samples of galaxies observed with the Spitzer Space Telescope and our dusty radiative transfer model, we find that young stellar populations (on the order of 100 million years old) dominate the dust heating in star forming galaxies, and old stellar populations (13 billion years old) generally contribute less than 20% of the far-IR luminosity.
Relevant Papers
"Young, UV-bright Stars Dominate Dust Heating in Star Forming Galaxies"
Law et al. 2011
Talk Slides
pdf
In star forming galaxies, dust plays a significant role in shaping the ultraviolet (UV) through infrared (IR) spectrum. Dust attenuates the radiation from stars, and re-radiates the energy through equilibrium and non-equilibrium emission. Polycyclic aromatic hydrocarbons (PAH), graphite, and silicates contribute to different features in the spectral energy distribution; however, they are all highly opaque in the same spectral region - the UV. Compared to old stellar populations, young populations release a higher fraction of their total luminosity in the UV, making them a good source of the energetic UV photons that can power dust emission. However, given their relative abundance, the question of whether young or old stellar populations provide most of these photons that power the infrared emission is an interesting question. Using three samples of galaxies observed with the Spitzer Space Telescope and our dusty radiative transfer model, we find that young stellar populations (on the order of 100 million years old) dominate the dust heating in star forming galaxies, and old stellar populations (13 billion years old) generally contribute less than 20% of the far-IR luminosity.
Relevant Papers
"Young, UV-bright Stars Dominate Dust Heating in Star Forming Galaxies"
Law et al. 2011
Talk Slides
Friday, August 5, 2011
Star formation in 30 Doradus
Abstract by De Marchi et al.
Using observations obtained with the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope (HST), we have studied the properties of the stellar populations in the central regions of 30 Dor, in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterise and quantify this effect using young massive main sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main sequence (PMS) stars by looking for objects with a strong (> 4 sigma) Halpha excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one third of these objects are younger than ~4Myr, compatible with the age of the massive stars in the central ionising cluster R136, whereas the rest have ages up to ~30Myr, with a median age of ~12Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very centre of the cluster. We attribute this latter effect to photoevaporation of the older circumstellar discs caused by the massive ionising members of R136.
Relevant Papers
"Star formation in 30 Doradus"
De Marchi et al.
Talk Slides
pdf
Using observations obtained with the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope (HST), we have studied the properties of the stellar populations in the central regions of 30 Dor, in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterise and quantify this effect using young massive main sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main sequence (PMS) stars by looking for objects with a strong (> 4 sigma) Halpha excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one third of these objects are younger than ~4Myr, compatible with the age of the massive stars in the central ionising cluster R136, whereas the rest have ages up to ~30Myr, with a median age of ~12Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very centre of the cluster. We attribute this latter effect to photoevaporation of the older circumstellar discs caused by the massive ionising members of R136.
Relevant Papers
"Star formation in 30 Doradus"
De Marchi et al.
Talk Slides
Friday, July 22, 2011
Highlights of Four Decades of Research on Massive Stars: A Scientific Meeting in the Honour of Anthony F.J. Moffat
Abstract
We are organizing a meeting to celebrate four decades of contributions of Professor Anthony F.J. Moffat to massive-star research. Since his first papers on open clusters in the early 70’s, Tony’s research interests have expanded in many directions to cover a multitude of aspects of massive stars. The meeting will encompass the following main subjects on which he has worked during his career:
* Young open star clusters: keys to understanding massive stars
* Galactic structure and dynamics; runaway stars
* Massive binaries: orbits, masses, mass-loss rates, binary frequency, colliding winds, dust formation
* The most massive stars
* The true nature of clumping in hot stellar winds and its consequences
* Rotation and magnetic fields
* Pulsations (e.g. MOST and soon BRITE-Constellation)
* WR surveys (Galactic and extra-galactic)
Talk Slides
pdf
We are organizing a meeting to celebrate four decades of contributions of Professor Anthony F.J. Moffat to massive-star research. Since his first papers on open clusters in the early 70’s, Tony’s research interests have expanded in many directions to cover a multitude of aspects of massive stars. The meeting will encompass the following main subjects on which he has worked during his career:
* Young open star clusters: keys to understanding massive stars
* Galactic structure and dynamics; runaway stars
* Massive binaries: orbits, masses, mass-loss rates, binary frequency, colliding winds, dust formation
* The most massive stars
* The true nature of clumping in hot stellar winds and its consequences
* Rotation and magnetic fields
* Pulsations (e.g. MOST and soon BRITE-Constellation)
* WR surveys (Galactic and extra-galactic)
Talk Slides
Friday, July 8, 2011
The Most Massive Stars in the Universe
Abstract by Jorick Vink
The recent detection of a gamma-ray burst just a few hundred millions years after the Big Bang provides strong evidence that massive stars can form and die when the Universe was not yet enriched. Recent studies also reveal the existence and deaths of stars up to 300 solar masses in our local Universe. Might such objects produce superluminous supernovae, or even pair-instability supernovae? Do they suffer extreme mass loss ending their lives as "normal" Wolf-Rayet stars instead? Could they explode prematurely as Luminous Blue Variables? In order to address these issues, I discuss the latest developments in mass loss and evolution modelling - as a function of host galaxy metallicity.
Relevant Papers
"Wind modelling of very massive stars up to 300 solar masses"
Vink et al. 2011
"The VLT-FLAMES Tarantula Survey. III. A very massive star in apparent isolation from the massive cluster R136"
Bestenlehner et al. 2011
Talk Slides
pdf
The recent detection of a gamma-ray burst just a few hundred millions years after the Big Bang provides strong evidence that massive stars can form and die when the Universe was not yet enriched. Recent studies also reveal the existence and deaths of stars up to 300 solar masses in our local Universe. Might such objects produce superluminous supernovae, or even pair-instability supernovae? Do they suffer extreme mass loss ending their lives as "normal" Wolf-Rayet stars instead? Could they explode prematurely as Luminous Blue Variables? In order to address these issues, I discuss the latest developments in mass loss and evolution modelling - as a function of host galaxy metallicity.
Relevant Papers
"Wind modelling of very massive stars up to 300 solar masses"
Vink et al. 2011
"The VLT-FLAMES Tarantula Survey. III. A very massive star in apparent isolation from the massive cluster R136"
Bestenlehner et al. 2011
Talk Slides
Friday, June 10, 2011
Observations of Boron in Rapidly Rotating Early-B Stars
Abstract by Charles Proffitt
We discuss new HST/STIS observations of the B III resonance doublet in 26 early-B stars with projected rotational velocities between 50 and 220 km/s and compare the measured boron abundances with predictions of stellar evolution models that include rotationally induced mixing. Our results suggest that some stars show significantly less mixing than predicted by the models. When combined with previous results for stars with low projected rotational velocities (below 50 km/s) the distribution of [B/H] with V sin(i) bears a strong resemblance to that for nitrogen, the so-called Hunter diagram (Hunter et al 2008). Especially surprising is the apparent detection of substantial boron in two Be stars that are believed to be very rapid rotators viewed at small inclination angles for which the true rotational velocities are at 75 - 80% of the breakup limit.
Relevant Papers
"Testing Rotational Mixing Predictions with New Boron Abundances in Main-Sequence B-Type Stars"
Mendel et al 2006
"Nitrogen enrichment, boron depletion and magnetic fields in slowly-rotating B-type dwarfs"
Morel et al 2008
"Rotating Massive Main-Sequence Stars I: Grids of Evolutionary Models and Isochrones"
Bortt et al. 2011a
"Rotating Massive Main-Sequence Stars II: Simulating a Population of LMC early B-type Stars as a Test of Rotational Mixing"
Brott et al. 2011b
Talk Slides
pdf
We discuss new HST/STIS observations of the B III resonance doublet in 26 early-B stars with projected rotational velocities between 50 and 220 km/s and compare the measured boron abundances with predictions of stellar evolution models that include rotationally induced mixing. Our results suggest that some stars show significantly less mixing than predicted by the models. When combined with previous results for stars with low projected rotational velocities (below 50 km/s) the distribution of [B/H] with V sin(i) bears a strong resemblance to that for nitrogen, the so-called Hunter diagram (Hunter et al 2008). Especially surprising is the apparent detection of substantial boron in two Be stars that are believed to be very rapid rotators viewed at small inclination angles for which the true rotational velocities are at 75 - 80% of the breakup limit.
Relevant Papers
"Testing Rotational Mixing Predictions with New Boron Abundances in Main-Sequence B-Type Stars"
Mendel et al 2006
"Nitrogen enrichment, boron depletion and magnetic fields in slowly-rotating B-type dwarfs"
Morel et al 2008
"Rotating Massive Main-Sequence Stars I: Grids of Evolutionary Models and Isochrones"
Bortt et al. 2011a
"Rotating Massive Main-Sequence Stars II: Simulating a Population of LMC early B-type Stars as a Test of Rotational Mixing"
Brott et al. 2011b
Talk Slides
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