Abstract by Marc Gagné et al.
In the standard picture of radiatively driven winds, X-rays from single, massive stars are produced in shocks generated throughout the wind. While colliding wind binaries like η Carinae and magnetic O stars like θ1 Ori C show hard, time-variable X-ray emission, most OB stars produce relatively soft, steady X-ray emission (kT ≈ 0.5 keV). Two massive stars however have exhibited unusual X-ray flares: the magnetic B2 Vp star σ Ori E (Sanz-Forcada et al. 2004) and the spectroscopic binary O9.5 V system θ2 Ori A (Schulz et al. 2006). ud-Doula et al. (2006) suggested that the events on σ Ori E were evidence of centrifugal breakout of magnetically confined wind shocks, while Schulz et al. (2006) suggested that the flares on θ2 Ori A might be caused by magnetospheric interactions between the A1/A2 components near periastron.
In this talk we present new spectropolarimetric observations of θ2 Ori A that show a broad He I absorption line from the A2 secondary, and no evidence of strong magnetic fields in the Stokes-V profiles. Via a careful sub-pixel reconstruction of the Chandra X-ray images we also show that the hard, time variable X-ray emission is offset from the soft, steady X-ray source by 0.3”. The X-ray flare position is coincident with the position of the infrared A3 companion reported by Preibisch et al. (1999). Similarly, our sub-pixel reconstruction of the Chandra High-Resolution Camera image of σ Ori E shows that the flaring emission is offset by 0.4” from the magnetic primary, coincident with an infrared speckle companion discovered by Buoy et al. (2009). Thus, intermediate-mass young stellar objects produce the hard X-ray flares in both systems.
Background Papers
“The magnetic field of Sigma Orionis E”
Landstreet, J. D. & Borra, E. F.
“Multiplicity of the massive stars in the Orion Nebula cluster”
Preibisch, T. et al.
“XMM-Newton observations of the σ Ori cluster. I. The complex RGS spectrum of the hot star σ Ori AB”
Sanz-Forcada et al.
“X-Ray Variability in the Young Massive Triple θ2 Orionis A”
Schulz, N., et al.
“Centrifugal Breakout of Magnetically Confined Line-driven Stellar Winds”
ud-Doula, A., Townsend, R. H. D., & Owocki, S. P.
“A deep look into the cores of young clusters. I. σ Orionis”
Bouy, H. et al.
Talk Slides
pdf
Friday, February 17, 2012
Friday, February 3, 2012
Mass loss from the structured winds of hot, massive stars
Abstract by Jon Sundqvist
It is observationally as well as theoretically well-established that
the winds of hot, massive stars are highly structured on a broad range
of spatial scales. This talk first discusses consequences of the
small-scale structures associated with the strong instability inherent
to the line-driving of these winds. We demonstrate the importance of a
proper treatment of such wind clumping (including effects of optically
thick clumps and a non-monotonic velocity field) to accurately
interpret wind diagnostics and obtain reliable estimates of mass-loss
rates. But a growing subset of massive stars has also been found to
possess strong surface magnetic fields, which may channel the star's
wind outflow and so induce also large-scale structures and cyclic
behaviour of spectral diagnostics. The talk concludes by presenting
our recent result showing that multi-dimensional
magneto-hydrodynamical wind simulations together with detailed
radiative-transfer modeling remarkably well reproduce the periodic
Balmer emission observed in slowly rotating magnetic O stars.
Background Papers
"The nature and consequences of clumping in hot,
massive star winds"
Sundvist, Owocki, & Puls, 2011arXiv1110.0485S
It is observationally as well as theoretically well-established that
the winds of hot, massive stars are highly structured on a broad range
of spatial scales. This talk first discusses consequences of the
small-scale structures associated with the strong instability inherent
to the line-driving of these winds. We demonstrate the importance of a
proper treatment of such wind clumping (including effects of optically
thick clumps and a non-monotonic velocity field) to accurately
interpret wind diagnostics and obtain reliable estimates of mass-loss
rates. But a growing subset of massive stars has also been found to
possess strong surface magnetic fields, which may channel the star's
wind outflow and so induce also large-scale structures and cyclic
behaviour of spectral diagnostics. The talk concludes by presenting
our recent result showing that multi-dimensional
magneto-hydrodynamical wind simulations together with detailed
radiative-transfer modeling remarkably well reproduce the periodic
Balmer emission observed in slowly rotating magnetic O stars.
Background Papers
"The nature and consequences of clumping in hot,
massive star winds"
Sundvist, Owocki, & Puls, 2011arXiv1110.0485S
Iron-line diagnostics in the extreme colliding-wind binary Eta Carinae
Abstract by Jean-Christophe Leyder
Eta Carinae, one of the most peculiar objects in our Galaxy, was the second brightest object in the sky during its eruption in 1843. The large quantities of matter that were ejected at that time are now forming an extended nebula, while Eta Car is still ejecting matter through energetic stellar winds. Eta Car is a colliding-wind binary system: the dense stellar wind coming from the massive luminous blue variable primary star collides with the higher-velocity, lower-density wind from the hotter and luminous (and otherwise unseen) companion star in a highly eccentric orbit. Monitoring observations in the radio, UV, optical, and X-ray domains all indicate an orbital period of 5.5 years.
X-ray observations of a colliding-wind binary system such as Eta Carinae provide numerous clues as to the shock physics and mechanisms responsible for particle acceleration and emission in the hydrodynamical shocks that form between the stellar winds. Furthermore, Eta Carinae's long period and high eccentricity provides varying physical conditions, and allow to probe a large parameter space of densities and wind speeds, especially when observing periastron passages where strong variations occur over a short timescale.
In this talk, I will present a set of 23 high-resolution X-ray spectra of Eta Carinae obtained by the Chandra satellite, with a particularly detailed coverage around the X-ray minima of 2003.5 and 2009. I will focus on the variations and peculiarities observed in the Fe K line region. First noticed by Hamaguchi et al. 2007, the existence of a variable “red wing” in the profile of the Fe XXV triplet is puzzling. I will discuss possible hypothesis for the unexpected presence of such a "red wing" : the presence of an extremely bright, relatively cool, and heavily absorbed equilibrium plasma; emission due to unshocked photoionized wind material; or the possibility that a fraction of the thermal plasma is not in ionization equilibrium.
Background Papers
"X-Ray Spectral Variation of Eta Carinae through the 2003 X-Ray Minimum"
Hamaguchi K. et al. 2007
"Recent X-ray Variability of Eta Carinae: The Quick Road to Recovery"
Corcoran M.F. et al. 2010
"Chandra X-Ray Grating Spectrometry of Eta Carinae near X-Ray Minimum. I. Variability of the Sulfur and Silicon Emission Lines"
Henley D.B. et al. 2008
"Bulk Velocities, Chemical Composition, and Ionization Structure of the X-Ray Shocks in WR 140 near Periastron as Revealed by the Chandra Gratings"
Pollock A.M.T. et al. 2005
Eta Carinae, one of the most peculiar objects in our Galaxy, was the second brightest object in the sky during its eruption in 1843. The large quantities of matter that were ejected at that time are now forming an extended nebula, while Eta Car is still ejecting matter through energetic stellar winds. Eta Car is a colliding-wind binary system: the dense stellar wind coming from the massive luminous blue variable primary star collides with the higher-velocity, lower-density wind from the hotter and luminous (and otherwise unseen) companion star in a highly eccentric orbit. Monitoring observations in the radio, UV, optical, and X-ray domains all indicate an orbital period of 5.5 years.
X-ray observations of a colliding-wind binary system such as Eta Carinae provide numerous clues as to the shock physics and mechanisms responsible for particle acceleration and emission in the hydrodynamical shocks that form between the stellar winds. Furthermore, Eta Carinae's long period and high eccentricity provides varying physical conditions, and allow to probe a large parameter space of densities and wind speeds, especially when observing periastron passages where strong variations occur over a short timescale.
In this talk, I will present a set of 23 high-resolution X-ray spectra of Eta Carinae obtained by the Chandra satellite, with a particularly detailed coverage around the X-ray minima of 2003.5 and 2009. I will focus on the variations and peculiarities observed in the Fe K line region. First noticed by Hamaguchi et al. 2007, the existence of a variable “red wing” in the profile of the Fe XXV triplet is puzzling. I will discuss possible hypothesis for the unexpected presence of such a "red wing" : the presence of an extremely bright, relatively cool, and heavily absorbed equilibrium plasma; emission due to unshocked photoionized wind material; or the possibility that a fraction of the thermal plasma is not in ionization equilibrium.
Background Papers
"X-Ray Spectral Variation of Eta Carinae through the 2003 X-Ray Minimum"
Hamaguchi K. et al. 2007
"Recent X-ray Variability of Eta Carinae: The Quick Road to Recovery"
Corcoran M.F. et al. 2010
"Chandra X-Ray Grating Spectrometry of Eta Carinae near X-Ray Minimum. I. Variability of the Sulfur and Silicon Emission Lines"
Henley D.B. et al. 2008
"Bulk Velocities, Chemical Composition, and Ionization Structure of the X-Ray Shocks in WR 140 near Periastron as Revealed by the Chandra Gratings"
Pollock A.M.T. et al. 2005
Friday, January 20, 2012
Revealing the secrets of star-forming galaxies through studies of young stellar clusters
Abstract by Angela Adamo
Star formation, the process that converts gas in stars, is a key mechanism regulating the galaxy evolution process. It is thought that the vast majority of stars in galaxies are formed in clustered systems. A fraction of these systems survive gravitationally bound as star clusters, making them bright tracers of their host galaxy properties. The physical properties of clusters retain key information about the nature of the star formation event (i.e. its intensity), the environment, and the physical condition of their hosts at the moment they formed. In the first part of the talk, I will present some recent results based on studies of star clusters in irregular starburst galaxies, the so-called blue compact galaxies (BCGs). I will mainly focus on the properties of the very young star clusters (age smaller than 10 Myr), and how cluster properties scale with the global properties of their hosts (e.g. star formation rate). In the second part, I will present some highlights of the Snapshot Hubble U-band Cluster Survey (SHUCS), an ongoing deep U-band imaging survey of nearby star-forming galaxies. Thanks to the information provided by the U band, together with archival HST optical data, we are able to constrain reliable ages, masses, and extinctions of the cluster populations in these galaxies. I will show some preliminary results from the study of one of the SHUCS galaxies, NGC 2146. From the cluster properties, we can reconstruct the starburst propagation history in the different galaxy components and understand how diverse galactic environments affect cluster formation.
Background Papers
"Super star clusters in Haro 11: properties of a very young starburst and evidence for a near-infrared flux excess", Adamo, A., et al. 2010a
"On the Origin of the Red Excess in Very Young Super Star Clusters: The Case of SBS 0335-052E", Adamo, A., et al. 2010b,
"The massive star clusters in the dwarf merger ESO 185-IG13: is the red excess ubiquitous in starbursts?", Adamo, A., et al. 2011a
"Star cluster formation and evolution in Mrk 930: properties of a metal-poor starburst", Adamo, A, et al. 2011b
"Probing cluster formation under extreme conditions: massive star clusters in blue compact galaxies", Adamo, A., et al. 2011c
"Probing the near-IR flux excess in young star clusters", Adamo, A., Ostlin, G., & Zackrisson, E. 2011d
Talk Slides
pdf
Star formation, the process that converts gas in stars, is a key mechanism regulating the galaxy evolution process. It is thought that the vast majority of stars in galaxies are formed in clustered systems. A fraction of these systems survive gravitationally bound as star clusters, making them bright tracers of their host galaxy properties. The physical properties of clusters retain key information about the nature of the star formation event (i.e. its intensity), the environment, and the physical condition of their hosts at the moment they formed. In the first part of the talk, I will present some recent results based on studies of star clusters in irregular starburst galaxies, the so-called blue compact galaxies (BCGs). I will mainly focus on the properties of the very young star clusters (age smaller than 10 Myr), and how cluster properties scale with the global properties of their hosts (e.g. star formation rate). In the second part, I will present some highlights of the Snapshot Hubble U-band Cluster Survey (SHUCS), an ongoing deep U-band imaging survey of nearby star-forming galaxies. Thanks to the information provided by the U band, together with archival HST optical data, we are able to constrain reliable ages, masses, and extinctions of the cluster populations in these galaxies. I will show some preliminary results from the study of one of the SHUCS galaxies, NGC 2146. From the cluster properties, we can reconstruct the starburst propagation history in the different galaxy components and understand how diverse galactic environments affect cluster formation.
Background Papers
"Super star clusters in Haro 11: properties of a very young starburst and evidence for a near-infrared flux excess", Adamo, A., et al. 2010a
"On the Origin of the Red Excess in Very Young Super Star Clusters: The Case of SBS 0335-052E", Adamo, A., et al. 2010b,
"The massive star clusters in the dwarf merger ESO 185-IG13: is the red excess ubiquitous in starbursts?", Adamo, A., et al. 2011a
"Star cluster formation and evolution in Mrk 930: properties of a metal-poor starburst", Adamo, A, et al. 2011b
"Probing cluster formation under extreme conditions: massive star clusters in blue compact galaxies", Adamo, A., et al. 2011c
"Probing the near-IR flux excess in young star clusters", Adamo, A., Ostlin, G., & Zackrisson, E. 2011d
Talk Slides
Friday, November 18, 2011
Eta Carinae--a demanding mistress
Abstract by Ted Gull
Over the past 15 years, a number of observers and modelers have increasingly focused on this massive system that is approaching its end stage, a supernova? a hypernova? When?
The discovery by Augusto Damineli that Eta Carinae had a 5.5-year period proved timely as the newly-installed STIS was primed to observe its properties in the visible and ultraviolet. Initial observations occurred on January 1998, and through multiple programs, including the multi-cycle Hubble Treasury program, have sampled changes across two cycles. Now a multi-cycle program, focused on mapping variations in the extended wind-wind collision zones through early 2015, will test 3-D models of the interacting winds.
In parallel, studies have been accomplished in X-rays with RXTE and CHANDRA, now in the far infrared with Herschel and from the ground with VLT.
Each new observation is helping to peel back the veil of mystery on this massive binary system, but also opening up more questions to be answered. Timely inclusion of laboratory studies and models have greatly enhanced the observational results. We will summarize the latest results including submitted papers and very recent results with Herschel.
Relevant Papers
"Constraining the Absolute Orientation of Eta Carinae's Binary Orbit: A 3-D Dynamical Model for the Broad [Fe III] Emission"
Madura et al. 2011
"Multi-Wavelength Implications of the Companion Star in Eta Carinae"
Madura et al. 2011
"Imaging with HST the time evolution of Eta Carinae's colliding winds"
Gull et al. 2011
Talk Slides
pdf
Over the past 15 years, a number of observers and modelers have increasingly focused on this massive system that is approaching its end stage, a supernova? a hypernova? When?
The discovery by Augusto Damineli that Eta Carinae had a 5.5-year period proved timely as the newly-installed STIS was primed to observe its properties in the visible and ultraviolet. Initial observations occurred on January 1998, and through multiple programs, including the multi-cycle Hubble Treasury program, have sampled changes across two cycles. Now a multi-cycle program, focused on mapping variations in the extended wind-wind collision zones through early 2015, will test 3-D models of the interacting winds.
In parallel, studies have been accomplished in X-rays with RXTE and CHANDRA, now in the far infrared with Herschel and from the ground with VLT.
Each new observation is helping to peel back the veil of mystery on this massive binary system, but also opening up more questions to be answered. Timely inclusion of laboratory studies and models have greatly enhanced the observational results. We will summarize the latest results including submitted papers and very recent results with Herschel.
Relevant Papers
"Constraining the Absolute Orientation of Eta Carinae's Binary Orbit: A 3-D Dynamical Model for the Broad [Fe III] Emission"
Madura et al. 2011
"Multi-Wavelength Implications of the Companion Star in Eta Carinae"
Madura et al. 2011
"Imaging with HST the time evolution of Eta Carinae's colliding winds"
Gull et al. 2011
Talk Slides
Tuesday, October 25, 2011
Extinction in Nebular Luminosities & Star Formation Rate of Disk Galaxies: Inclination Correction
Abstract by Ching-Wa Yip
Star formation is one of the most important processes in galaxy formation. The luminosity of Hα recombination and [O II]λ3728 forbidden emissions re- main to be most used in measuring formation rate of massive stars in galax- ies. Here we report the inclination dependency of continuum-subtracted and aperture-corrected nebular luminosities, including Hα, Hβ, Hγ, [O II], [N II], of disk-dominated galaxies in the local universe. Their luminosities decrease by a factor of three from face-on to edge-on (axis ratio limit = 0.17) orientations. This dependence is deduced to be caused by extinction due to diffuse dust within the disks with an amplitude of 1.2 mag. The line-luminosity–inclination rela- tion provides a novel way to remove extinction in emission lines and present star formation rate of disk galaxies out to redshift of 1.6.
Relevant Papers
"Extinction in Nebular Luminosities & Star Formation Rate of Disk Galaxies: Inclination Correction"
Yip & Szalay
Star formation is one of the most important processes in galaxy formation. The luminosity of Hα recombination and [O II]λ3728 forbidden emissions re- main to be most used in measuring formation rate of massive stars in galax- ies. Here we report the inclination dependency of continuum-subtracted and aperture-corrected nebular luminosities, including Hα, Hβ, Hγ, [O II], [N II], of disk-dominated galaxies in the local universe. Their luminosities decrease by a factor of three from face-on to edge-on (axis ratio limit = 0.17) orientations. This dependence is deduced to be caused by extinction due to diffuse dust within the disks with an amplitude of 1.2 mag. The line-luminosity–inclination rela- tion provides a novel way to remove extinction in emission lines and present star formation rate of disk galaxies out to redshift of 1.6.
Relevant Papers
"Extinction in Nebular Luminosities & Star Formation Rate of Disk Galaxies: Inclination Correction"
Yip & Szalay
Sunday, October 23, 2011
Nature of Starburst in Local Lyman Break Galaxy Analogs
Abstract by Sanch Borthakur
In this talk, I'll briefly describe the properties of local Lyman
break galaxy analogs (LBAs) and then go on to discuss our COS data for
a sample of LBAs. I'll primarily present our analysis of the spectra
focusing on various transitions in the UV. And finally I'll compare
these spectra with various Starburst99 models to understand the nature
of star formation in these systems.
Relevant Papers
"The Properties of Ultraviolet-luminous Galaxies at the Current Epoch"
Heckman et al. 2005
"Hubble Space Telescope Morphologies of Local Lyman Break Galaxy Analogs. I. Evidence for Starbursts Triggered by Merging"
Overzier et al. 2008
"Morphologies of Local Lyman Break Galaxy Analogs. II. A Comparison with Galaxies at z ~= 2-4 in ACS and WFC3 Images of the Hubble Ultra Deep Field"
Overzier et al. 2010
"Extreme Feedback and the Epoch of Reionization: Clues in the Local Universe"
Heckman et al. 2011
Talk Slides
In this talk, I'll briefly describe the properties of local Lyman
break galaxy analogs (LBAs) and then go on to discuss our COS data for
a sample of LBAs. I'll primarily present our analysis of the spectra
focusing on various transitions in the UV. And finally I'll compare
these spectra with various Starburst99 models to understand the nature
of star formation in these systems.
Relevant Papers
"The Properties of Ultraviolet-luminous Galaxies at the Current Epoch"
Heckman et al. 2005
"Hubble Space Telescope Morphologies of Local Lyman Break Galaxy Analogs. I. Evidence for Starbursts Triggered by Merging"
Overzier et al. 2008
"Morphologies of Local Lyman Break Galaxy Analogs. II. A Comparison with Galaxies at z ~= 2-4 in ACS and WFC3 Images of the Hubble Ultra Deep Field"
Overzier et al. 2010
"Extreme Feedback and the Epoch of Reionization: Clues in the Local Universe"
Heckman et al. 2011
Talk Slides
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