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
Friday, January 20, 2012
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
Monday, October 10, 2011
The Hunt for Massive Stars Hiding in the Milky Way
Abstract by Matthew Povich
The failure to achieve a clear picture of the formation mechanism(s) and properties of massive stars remains one of the most persistent problems in astrophysics. An underlying cause for this lack of clarity is that massive stars are difficult to observe. They are relatively rare, generally located at large (often unknown) heliocentric distances and behind significant extinction. Ironically, simple color-magnitude diagrams yield a far better census of the highest-mass stars in Magellanic Clouds than is possible in the Milky Way, where overwhelming field star contamination conspires with uncertain stellar distances and differential reddening to foil well-intentioned observers. I will discuss the curious case of the missing OB stars in the Great Nebula in Carina, the nearest Galactic analog to extragalactic starburst regions. We have developed a new methodology for identifying candidate luminous stars using X-ray emission and infrared spectral energy distributions. First results from applying this methodology to Carina indicate that the population massive stars in this well-studied region may actually be twice as large as previously thought, with profound implications for the energy budget and stellar initial mass function in the region. I will also highlight the Milky Way Project (http://www.milkywayproject.org), our latest effort to map massive star-forming regions throughout the Galaxy by enlisting >20,000 "citizen scientists" to search Spitzer Space Telescope images for bubbles.
Figure. Image of the central 1° of the Great Nebula in Carina. The color code is blue=visible light (Digitized Sky Survey), green=near-IR (2MASS), and red=8.0 micron mid-IR (Spitzer Space Telescope). Regions that appear blue suffer little obscuration by interstellar dust, while regions that appear red have high obscuration. Previously cataloged massive stars are marked by diamonds, and new candidate massive stars identified by Povich et al. (2011) are marked by circles. Note that the candidate massive stars tend to be found in regions of higher dust obscuration.
Relevant Papers
"Candidate X-ray-emitting OB Stars in the Carina Nebula Identified Via Infrared Spectral Energy Distributions."
Povich et al. 2011
"The Bubbling Galactic Disk"
Churchwell et al. 2006
Talk Slides
pdf
The failure to achieve a clear picture of the formation mechanism(s) and properties of massive stars remains one of the most persistent problems in astrophysics. An underlying cause for this lack of clarity is that massive stars are difficult to observe. They are relatively rare, generally located at large (often unknown) heliocentric distances and behind significant extinction. Ironically, simple color-magnitude diagrams yield a far better census of the highest-mass stars in Magellanic Clouds than is possible in the Milky Way, where overwhelming field star contamination conspires with uncertain stellar distances and differential reddening to foil well-intentioned observers. I will discuss the curious case of the missing OB stars in the Great Nebula in Carina, the nearest Galactic analog to extragalactic starburst regions. We have developed a new methodology for identifying candidate luminous stars using X-ray emission and infrared spectral energy distributions. First results from applying this methodology to Carina indicate that the population massive stars in this well-studied region may actually be twice as large as previously thought, with profound implications for the energy budget and stellar initial mass function in the region. I will also highlight the Milky Way Project (http://www.milkywayproject.org), our latest effort to map massive star-forming regions throughout the Galaxy by enlisting >20,000 "citizen scientists" to search Spitzer Space Telescope images for bubbles.
Figure. Image of the central 1° of the Great Nebula in Carina. The color code is blue=visible light (Digitized Sky Survey), green=near-IR (2MASS), and red=8.0 micron mid-IR (Spitzer Space Telescope). Regions that appear blue suffer little obscuration by interstellar dust, while regions that appear red have high obscuration. Previously cataloged massive stars are marked by diamonds, and new candidate massive stars identified by Povich et al. (2011) are marked by circles. Note that the candidate massive stars tend to be found in regions of higher dust obscuration.
Relevant Papers
"Candidate X-ray-emitting OB Stars in the Carina Nebula Identified Via Infrared Spectral Energy Distributions."
Povich et al. 2011
"The Bubbling Galactic Disk"
Churchwell et al. 2006
Talk Slides
Tuesday, September 27, 2011
Properties of Galactic early-type O-supergiants: A combined FUV-UV and optical analysis
Abstract by Jean-Claude Bouret
Early type O supergiants (from O4 to O7) present conspicuous wind profiles. Therefore, they are excellent targets to study wind clumping and its consequences on measured mass-loss rates. These stars are also
expected to be on a rather advanced evolutionary stage.
We have analyzed the spectra from FUV to optical of 8 galactic supergiants, using the NLTE wind code CMFGEN. We derived the effective temperatures, luminosities, surface gravities and surface abundances, mass loss rates, wind terminal velocities and filling factors associated to clumping.
The supergiants define a very clear evolutionary sequence, in terms of ages and masses, from younger and more massive to older stars with lower initial masses.
The surface chemical composition are typical of evolved O supergiant (nitrogen-rich, carbon and oxygen-poor).
The observed span for carbon and nitrogen mass-fractions are compatible with those expected from the models, for the measured stellar masses but the [N/C] ratios as a function of age is inconsistent with
the theoretical predictions for the four earliest (O4 spectral type) stars of the sample. The efficiency of rotational mixing as a function of age is questioned for these stars and other mechanism might be needed to explain the observed patterns. Mass-loss rates derived using clumped models range within factors up to three with theoretical mass-loss rates. This difference is actually very reasonable given the known uncertainty on both estimates. The corresponding filling-factors associated to small-scale clumping are 0.05$\pm 0.02$. Clumping is found to start close to the photosphere for all but three stars, two of which are fast rotators.
Talk Slides
pdf
Early type O supergiants (from O4 to O7) present conspicuous wind profiles. Therefore, they are excellent targets to study wind clumping and its consequences on measured mass-loss rates. These stars are also
expected to be on a rather advanced evolutionary stage.
We have analyzed the spectra from FUV to optical of 8 galactic supergiants, using the NLTE wind code CMFGEN. We derived the effective temperatures, luminosities, surface gravities and surface abundances, mass loss rates, wind terminal velocities and filling factors associated to clumping.
The supergiants define a very clear evolutionary sequence, in terms of ages and masses, from younger and more massive to older stars with lower initial masses.
The surface chemical composition are typical of evolved O supergiant (nitrogen-rich, carbon and oxygen-poor).
The observed span for carbon and nitrogen mass-fractions are compatible with those expected from the models, for the measured stellar masses but the [N/C] ratios as a function of age is inconsistent with
the theoretical predictions for the four earliest (O4 spectral type) stars of the sample. The efficiency of rotational mixing as a function of age is questioned for these stars and other mechanism might be needed to explain the observed patterns. Mass-loss rates derived using clumped models range within factors up to three with theoretical mass-loss rates. This difference is actually very reasonable given the known uncertainty on both estimates. The corresponding filling-factors associated to small-scale clumping are 0.05$\pm 0.02$. Clumping is found to start close to the photosphere for all but three stars, two of which are fast rotators.
Talk Slides
Friday, September 16, 2011
Is the young star cluster NGC 376 dissolving in the field of the SMC?
Abstract by Elena Sabbi
We use deep images acquired with the Advanced Camera for Surveys (ACS) on board of the Hubble Space Telescope (HST) in the filters F555W and F814W to characterize the properties of NGC 376, a young star cluster located in the wing of the Small Magellanic Cloud (SMC). Using isochrone fitting we derive for NGC 376 an age of 28+/-7 Myr, in good agreement with previous studies. The high spatial resolution ACS data allow us to determine the center of gravity of the cluster and to construct extended surface brightness and radial density profiles. Neither of these profiles can be fitted with a theoretical model, suggesting that the cluster is not in virial equilibrium. Considering the young age of the cluster, we speculate that the distortion of the radial profiles may be the result of the rapid gas dispersal that follows the initial phase of star formation. The cluster shows clear evidence of dynamical mass segregation. From the properties of the radial profiles and the present day mass function (PDMF) we conclude that NGC 376 appears to have already lost nearly 90% of its initial stellar mass, probably as a consequence of the sudden gas dispersal that follows the early phase of star formation (SF).
Relevant Papers
"Is the young star cluster NGC 376 dissolving in the field of the SMC?"
Sabbi et al. 2011
Talk Slides
We use deep images acquired with the Advanced Camera for Surveys (ACS) on board of the Hubble Space Telescope (HST) in the filters F555W and F814W to characterize the properties of NGC 376, a young star cluster located in the wing of the Small Magellanic Cloud (SMC). Using isochrone fitting we derive for NGC 376 an age of 28+/-7 Myr, in good agreement with previous studies. The high spatial resolution ACS data allow us to determine the center of gravity of the cluster and to construct extended surface brightness and radial density profiles. Neither of these profiles can be fitted with a theoretical model, suggesting that the cluster is not in virial equilibrium. Considering the young age of the cluster, we speculate that the distortion of the radial profiles may be the result of the rapid gas dispersal that follows the initial phase of star formation. The cluster shows clear evidence of dynamical mass segregation. From the properties of the radial profiles and the present day mass function (PDMF) we conclude that NGC 376 appears to have already lost nearly 90% of its initial stellar mass, probably as a consequence of the sudden gas dispersal that follows the early phase of star formation (SF).
Relevant Papers
"Is the young star cluster NGC 376 dissolving in the field of the SMC?"
Sabbi et al. 2011
Talk Slides
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