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
Friday, July 8, 2011
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
Friday, May 27, 2011
Young Stellar Objects in the Magellanic Clouds: Identification based on the Spitzer and Herschel Observations
Abstract by Marta Sewilo
The Surveying the Agents of a Galaxy's Evolution (SAGE) Spitzer Legacy Programs provide a comprehensive picture of the current star formation activity in the Large (SAGE-LMC, Meixner et al. 2006) and Small (SAGE-SMC, Gordon et al. 2011) Magellanic Clouds which is traced by the IRAC (3.6, 4.5, 5.8, and 8.0 microns) and MIPS (24, 70, and 160 microns) bands. It allowed for the first time a global study of star formation in the Magellanic Clouds (MCs) at high enough resolution to resolve individual cores and protostars at a range of mid-IR wavelengths. The methods for searching and identifying Young Stellar Objects (YSOs) in the MCs will be discussed. These methods involve color-magnitude selections, inspection of the multi-wavelength images, and fitting of the spectral energy distributions of the YSO candidates using the 2D radiative transfer models (Robitaille et al. 2006).
The most recent data from the "HERschel Inventory of the Agents of Galaxy Evolution” (HERITAGE; Meixner et al. 2010) survey provided reliable longwave (100 - 500 microns) SEDs of large samples of Spitzer-identified high-mass YSOs, thus constraining their physical properties and evolutionary stages more precisely than was previously possible. Herschel also discovers the youngest YSOs whose SEDs peak in Herschel bands.
Relevant Papers
"Spitzer Sage Survey of the Large Magellanic Cloud. III. Star Formation and ~1000 New Candidate Young Stellar Objects"
Whitney et al. 2008
"High- and Intermediate-Mass Young Stellar Objects in the Large Magellanic Cloud"
Gruendl and Chu 2009
"The youngest massive protostars in the Large Magellanic Cloud"
Sewilo et al. 2010
Talk Slides
pdf
The Surveying the Agents of a Galaxy's Evolution (SAGE) Spitzer Legacy Programs provide a comprehensive picture of the current star formation activity in the Large (SAGE-LMC, Meixner et al. 2006) and Small (SAGE-SMC, Gordon et al. 2011) Magellanic Clouds which is traced by the IRAC (3.6, 4.5, 5.8, and 8.0 microns) and MIPS (24, 70, and 160 microns) bands. It allowed for the first time a global study of star formation in the Magellanic Clouds (MCs) at high enough resolution to resolve individual cores and protostars at a range of mid-IR wavelengths. The methods for searching and identifying Young Stellar Objects (YSOs) in the MCs will be discussed. These methods involve color-magnitude selections, inspection of the multi-wavelength images, and fitting of the spectral energy distributions of the YSO candidates using the 2D radiative transfer models (Robitaille et al. 2006).
The most recent data from the "HERschel Inventory of the Agents of Galaxy Evolution” (HERITAGE; Meixner et al. 2010) survey provided reliable longwave (100 - 500 microns) SEDs of large samples of Spitzer-identified high-mass YSOs, thus constraining their physical properties and evolutionary stages more precisely than was previously possible. Herschel also discovers the youngest YSOs whose SEDs peak in Herschel bands.
Relevant Papers
"Spitzer Sage Survey of the Large Magellanic Cloud. III. Star Formation and ~1000 New Candidate Young Stellar Objects"
Whitney et al. 2008
"High- and Intermediate-Mass Young Stellar Objects in the Large Magellanic Cloud"
Gruendl and Chu 2009
"The youngest massive protostars in the Large Magellanic Cloud"
Sewilo et al. 2010
Talk Slides
Friday, May 13, 2011
Not Your Grandmother's HII Regions: An X-ray Tour of Massive Star-forming Regions
Abstract by Leisa Townsley
The Chandra X-ray Observatory is providing remarkable new views of massive star-forming regions, revealing all stages in the life cycle of high-mass stars and their effects on their surroundings. We will tour several such regions, highlighting physical processes that characterize the life of a cluster of massive stars, from deeply-embedded cores too young to have established an HII region to superbubbles so large that they shape our views of galaxies. Along the way we see that X-ray observations reveal hundreds of pre-main sequence stars accompanying the massive stars that power great HII region complexes. The most massive stars themselves are often anomalously hard X-ray emitters; this may be a new indicator of close binarity or strong magnetic fields. These complexes are sometimes suffused by diffuse X-ray structures, signatures of multi-million-degree plasmas created by fast O-star winds. In older regions we see the X-ray remains of the deaths of massive stars that stayed close to their birthplaces, exploding as cavity supernovae within the superbubbles that these clusters created.
Relevant Papers
"The Integrated Diffuse X-ray Emission of the Carina Nebula Compared to Other Massive Star-forming Regions", Townsley et al. 2011
Talk Slides
pdf
The Chandra X-ray Observatory is providing remarkable new views of massive star-forming regions, revealing all stages in the life cycle of high-mass stars and their effects on their surroundings. We will tour several such regions, highlighting physical processes that characterize the life of a cluster of massive stars, from deeply-embedded cores too young to have established an HII region to superbubbles so large that they shape our views of galaxies. Along the way we see that X-ray observations reveal hundreds of pre-main sequence stars accompanying the massive stars that power great HII region complexes. The most massive stars themselves are often anomalously hard X-ray emitters; this may be a new indicator of close binarity or strong magnetic fields. These complexes are sometimes suffused by diffuse X-ray structures, signatures of multi-million-degree plasmas created by fast O-star winds. In older regions we see the X-ray remains of the deaths of massive stars that stayed close to their birthplaces, exploding as cavity supernovae within the superbubbles that these clusters created.
 |
| 30 Doradus (Chandra soft X-rays in red, MCELS H-alpha in green, Spitzer 8 microns in blue) |
Relevant Papers
"The Integrated Diffuse X-ray Emission of the Carina Nebula Compared to Other Massive Star-forming Regions", Townsley et al. 2011
Talk Slides
Friday, April 29, 2011
Against the Wind: How Extremely Massive Stars Lose Weight
Abstract by Michael F. Corcoran
Extremely massive stars (50 solar masses and above) are exceedingly rare in the local Universe but are believed to compose the entire first generation of stars, which lived fast, died young and left behind the first generation of black holes and set the stage for the formation of lower mass stars suitable to support life. For most of their lives, extremely massive stars give mass back to the ISM out of which they formed via strong radiatively-driven winds, though sporadic eruptions may play an important role too. This mass loss plays an important role in the chemical and dynamical evolution of the local interstellar medium prior to the supernova explosion. I'll discuss how high energy thermal (and, in some cases, non-thermal) emission, along with modern simulations in 2 and 3 dimensions, can be used to help determine a physically realistic picture of mass loss in some well-studied systems.
Relevant Papers
cv_corcoran.pdf
Talk Slides
pdf
Extremely massive stars (50 solar masses and above) are exceedingly rare in the local Universe but are believed to compose the entire first generation of stars, which lived fast, died young and left behind the first generation of black holes and set the stage for the formation of lower mass stars suitable to support life. For most of their lives, extremely massive stars give mass back to the ISM out of which they formed via strong radiatively-driven winds, though sporadic eruptions may play an important role too. This mass loss plays an important role in the chemical and dynamical evolution of the local interstellar medium prior to the supernova explosion. I'll discuss how high energy thermal (and, in some cases, non-thermal) emission, along with modern simulations in 2 and 3 dimensions, can be used to help determine a physically realistic picture of mass loss in some well-studied systems.
Relevant Papers
cv_corcoran.pdf
Talk Slides
Friday, April 15, 2011
Dust in the extremely metal poor galaxy I Zw 18
Abstract by Rodrigo Herrera Camus
The blue compact dwarf galaxy I Zw18 is one of the most metal poor systems in the local Universe, with a nebular metallicity of 12 + log(O/H) = 7.2. Because of this, I Zw18 can provide crucial information about the relation between dust-to-gas mass ratio and metallicity in galaxies. In this work we use Spitzer MIPS observations at 70 and 160 micrometer combined with empirical fits from Muñoz-Mateos et al. (2009) to Draine et al. (2007) dust emission models to derive a dust mass upper limit for I Zw 18 of M_Dust = 3 * 10^4 solar masses and a upper limit to the dust-to-gas mass ratio of M_Dust / M_gas = 9.1 * 10^{-4} (3 sigma limits). This upper limit for the dust-to-gas mass ratio is similar to the Milky Way value after scaling by their respective metallicities, and suggests that a linear scaling law could be compatible with metal-poor systems. The upper limit to the dust mass is driven by the confusion limit of Spitzer at 160 micrometer, and we expect it to be significantly improved by future Herschel observations.
Relevant papers
"Dust in I Zw 18 from Hubble Space Telescope Narrowband Imaging" Cannon et al. 2002
"Dust in the Extremely Metal-Poor Blue Compact Dwarf Galaxy I Zw 18: The Spitzer Mid-infrared View" Wu et al. 2007
Talk slides
pdf
The blue compact dwarf galaxy I Zw18 is one of the most metal poor systems in the local Universe, with a nebular metallicity of 12 + log(O/H) = 7.2. Because of this, I Zw18 can provide crucial information about the relation between dust-to-gas mass ratio and metallicity in galaxies. In this work we use Spitzer MIPS observations at 70 and 160 micrometer combined with empirical fits from Muñoz-Mateos et al. (2009) to Draine et al. (2007) dust emission models to derive a dust mass upper limit for I Zw 18 of M_Dust = 3 * 10^4 solar masses and a upper limit to the dust-to-gas mass ratio of M_Dust / M_gas = 9.1 * 10^{-4} (3 sigma limits). This upper limit for the dust-to-gas mass ratio is similar to the Milky Way value after scaling by their respective metallicities, and suggests that a linear scaling law could be compatible with metal-poor systems. The upper limit to the dust mass is driven by the confusion limit of Spitzer at 160 micrometer, and we expect it to be significantly improved by future Herschel observations.
Relevant papers
"Dust in I Zw 18 from Hubble Space Telescope Narrowband Imaging" Cannon et al. 2002
"Dust in the Extremely Metal-Poor Blue Compact Dwarf Galaxy I Zw 18: The Spitzer Mid-infrared View" Wu et al. 2007
Talk slides
Friday, April 1, 2011
The VLT-FLAMES Tarantula survey of Massive Stars
Abstract
This survey is an ESO Large Programme that has obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud. It is by far the largest homogeneous spectroscopic study of extragalactic early-type stars undertaken to date. The 30 Dor region is the only ‘super star-cluster’ at a well-known distance in which individual objects can be resolved spatially in optical light. This makes it the perfect target for the comprehensive studies required to address some of the fundamental questions that remain in our understanding of massive-star evolution, relying on the analysis of a statistically-significant and unbiased sample. Authors Danny Lennon, Selma E. de Mink, and Nolan Walborn will lead the discussion.
Relevant Papers
"The VLT-FLAMES Tarantula Survey I: Introduction and observational overview" Evans et al. 2011
"The VLT-FLAMES Tarantula Survey II: R139 revealed as a massive binary system" Taylor et al. 2011
This survey is an ESO Large Programme that has obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud. It is by far the largest homogeneous spectroscopic study of extragalactic early-type stars undertaken to date. The 30 Dor region is the only ‘super star-cluster’ at a well-known distance in which individual objects can be resolved spatially in optical light. This makes it the perfect target for the comprehensive studies required to address some of the fundamental questions that remain in our understanding of massive-star evolution, relying on the analysis of a statistically-significant and unbiased sample. Authors Danny Lennon, Selma E. de Mink, and Nolan Walborn will lead the discussion.
Relevant Papers
"The VLT-FLAMES Tarantula Survey I: Introduction and observational overview" Evans et al. 2011
"The VLT-FLAMES Tarantula Survey II: R139 revealed as a massive binary system" Taylor et al. 2011
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