Updated: 2 April 2012

MIT Kavli Institute for Astrophysics and Space Research

2012 Postdoc Symposium

April 18−20, 2012	11:45 AM−1:30 PM	BLDG 37-252 (MARLAR ROOM)

General Information

This annual event features the MKI-affiliated postdocs presenting 20 minute talks (with 5-10 minutes of questions) on their past, present, and/or future research to the MKI community. Lunch will be provided, and the talks will promptly begin at noon. There will be three speakers each day; the full schedule with abstracts is below.

Speaker Schedule

April 18, 2012

Moderator: Daniel Castro

Speaker: Michael McDonald

Title: "Reverse-Engineering Cooling Flows in Galaxy Clusters"

Abstract: The low temperature and high density of the intracluster medium in the cores of some galaxy clusters implies that 100-1000 Msun/yr of cool gas should be deposited on the central galaxy at the bottom of the potential well. The fact that central cluster galaxies appear "red and dead" is evidence that some form of feedback is offsetting this rapid cooling. Rather than studying the interaction between the hot phase and various feedback mechanisms, we have taken a different approach focused on tracking down the cooling byproducts and extrapolating backwards in time. We find that, in the densest regions of galaxy clusters, there is sufficient mass in the cold and warm phases, combined with young stellar populations, to match the predicted cooling rates, suggesting that the feedback mechanism responsible for the "cooling flow problem" may be most efficient in lower density regions.

Speaker: Joey Neilsen

Title: "High-Resolution X-ray Spectra: A Probe of Black Hole Accretion/Ejection Physics"

Abstract: In the last decade, high-resolution X-ray spectroscopy has revolutionized our understanding of the role of accretion disk winds in black hole X-ray binaries. Carrying away as much as 25x more matter than reaches the black hole, these ubiquitous, highly-ionized outflows exert a powerful influence on the dynamics of the accretion flow: they may quench relativistic jets and may facilitate or even cause state transitions. I will review a few major developments from the last decade, and then I will present some brand new results from our multiwavelength observing campaigns on several X-ray binaries, which reveal some of the deepest iron absorption lines ever observed with Chandra, as well as some of the fastest line variability. I will show how these observations highlight the intricate links between the inner accretion flow, relativistic jets, and accretion disk winds. Comparing to X-ray observations of other microquasars, I will argue that massive winds are truly a driving force in black hole X-ray binaries.

Speaker: Manu Linares

Title: "Thermonuclear burning on rapidly accreting neutron stars"

Abstract: I will present recent results on thermonuclear bursts from accreting neutron stars, focusing on the discovery of millihertz quasi-periodic oscillations and four distinct burning regimes in the 11 Hz X-ray pulsar located in the globular cluster Terzan 5. This unusual neutron star, with higher magnetic field and slower rotation than any other known burster, showed copious bursting activity when the mass accretion rate was high (between 10% and 50% of the Eddington limit). I will discuss the role of fuel composition, magnetic field and spin in setting the burst properties of this system, and the possible implications for the rest of thermonuclear bursters.

April 19, 2012

Moderator: Michael McDonald

Speaker: Daniel Castro

Title: "Exploring Cosmic Ray Acceleration in Supernova Remnants"

Abstract: The origin of cosmic rays continues to be puzzling. Observational evidence increasingly supports the scenario where the Galactic subset of these are accelerated at supernova remnant (SNR) shocks. Both thermal and non-thermal emission from these objects, in a wide range of wavelengths, indicate the presence of extremely energetic particles in SNRs, and the development of analytical and semi-analytical models of SNR evolution where diffusive shock acceleration (DSA) is efficient allow for constraining the nature of cosmic ray production. I will outline some of my most recent work on observations of SNRs in X-rays and gamma-rays, and how simulations have allowed me to build consistent morphological and spectral pictures of these objects and to understand their role as accelerating sites of cosmic rays.

Speaker: Laura Lopez

Title: "Under Pressure: Assessing the Role of Stellar Feedback in HII Regions"

Abstract: The role of stellar feedback in the star formation process in an open issue of debate. Although it is understood that massive stars inject energy and deposit momentum to surrounding gas, the dominant modes of this feedback and their relative role in regulating star formation is uncertain. In this talk, I will discuss how one can measure the pressures associated with several stellar feedback processes using multiwavelength data (radio, infrared, optical, and X-ray). I will present the results from applying these techniques to a large sample of HII regions in the Large and Small Magellanic Clouds, and I will consider the implications of our findings regarding the dynamics and the regulation of star formation in these regions.

Speaker: Kathy Cooksey

Title: "Precious Metals in SDSS QSOs: The Hunt for Intergalactic CIV in DR7"

Abstract: The CIV doublet has proven to be an important tracer of the IGM and its evolution from z = 6 to 0. These transitions have been well-studied at high redshifts because: they are strong transitions of common metals; they are observable outside the Ly-alpha forest, where they become easier to identify; they redshift into optical passbands for 1.5 < z < 4.5; and they are resonant doublets, which give them distinctive characteristics and enable the survey to be largely automated. However, the 1.5 < z < 4.5 results can be vastly improved by surveying the thousands of SDSS DR7 QSOs. Having done this, we now present early results on the over 15,000 CIV systems that we identified. We are constructing a uniform 0 < z < 6 dataset by combining the SDSS survey with the z < 1 HST results (Cooksey et al. 2010) and the new z > 5 FIRE results (Simcoe et al. 2011). Thus, we can compare apples-to-apples: the absorber line density over time and the CIV mass density evolution. This is the first in a series on our surveys for various metal-line absorption systems in SDSS DR7 QSOs.

April 20, 2012

Moderator: Laura Lopez

Speaker: Bryce Croll

Title: "Observations of the atmosphere of the super-Earth GJ 1214b"

Abstract: The super-Earth GJ 1214b is the most Earth-like planet that we can well characterize its atmospheric features to date. With a radius of ~2.7 Earth radii and with a mass of ~6.5 Earth masses, this planet should have a composition either of a water-world, or a rocky core enshrouded by a hydrogen-helium envelope. A hydrogen-helium envelope would result in detectable atmospheric features, while a water-world's features would be too small to likely be detectable. There have been a wealth of observations for this planet, most showing a lack of detectable features, while others (namely my own) display signs of atmospheric features that would favour the scenario of a hydrogen-helium dominated planet enveloping a rocky core. I'll summarize the latest observations of this planet, including showing some of my own more recent observations, in the hopes of determining the true nature of this intriguing exoplanet.

Speaker: Jeff Kissel

Title: "Commissioning Advanced LIGO Suspensions"

Abstract: The upgrades to the interferometers for Advanced LIGO are well underway, which can only mean one thing: we've finally got parts of the interferometer to play with! In this talk I'll focus on a particular part of the interferometers, the optic suspensions, and walk through the rigorous amounts of testing and commissioning we must do before/during/after any particular competent is installed. You'll definitely come away from the talk with appreciation of how difficult it is to built the worlds most sensitive gravitational wave interferometers!

Speaker: Ruslan Vaulin

Title: "Searching for Gravitational-Wave Transients and Their Electromagnetic Counterparts"

Abstract: Gravitational waves (GW) produced in mergers of compact objects (e.g. neutron stars and black holes) or other gravitationally driven phenomena (e.g. supernova, gravitational collapse etc) are expected to be accompanied by emission of electromagnetic (EM) radiation covering wide range of frequencies from radio and optical to X-ray and Gamma rays. Joint observations of GW and EM signals will provide us with complete picture of the underlying physical processes as well as improve our ability to robustly detect these signals. I will overview the most recent searches for transient GW-EM signals with the LIGO-Virgo detector network and partner optical/X-ray telescopes. In particular, I will present latest results of the joint analysis of GW and EM data acquired during prompt follow-up observations by Swift of candidate GW transient events identified in two observational periods during 2009-2010 LIGO and Virgo science run. I will conclude with discussion of sensitivity of the joint search and prospects of such multi-wavelength observations in the era of advanced gravitational-wave detectors.

Speaker:	Michael McDonald
Title:	"Reverse-Engineering Cooling Flows in Galaxy Clusters"
Abstract:	The low temperature and high density of the intracluster medium in the cores of some galaxy clusters implies that 100-1000 Msun/yr of cool gas should be deposited on the central galaxy at the bottom of the potential well. The fact that central cluster galaxies appear "red and dead" is evidence that some form of feedback is offsetting this rapid cooling. Rather than studying the interaction between the hot phase and various feedback mechanisms, we have taken a different approach focused on tracking down the cooling byproducts and extrapolating backwards in time. We find that, in the densest regions of galaxy clusters, there is sufficient mass in the cold and warm phases, combined with young stellar populations, to match the predicted cooling rates, suggesting that the feedback mechanism responsible for the "cooling flow problem" may be most efficient in lower density regions.

Speaker:	Joey Neilsen
Title:	"High-Resolution X-ray Spectra: A Probe of Black Hole Accretion/Ejection Physics"
Abstract:	In the last decade, high-resolution X-ray spectroscopy has revolutionized our understanding of the role of accretion disk winds in black hole X-ray binaries. Carrying away as much as 25x more matter than reaches the black hole, these ubiquitous, highly-ionized outflows exert a powerful influence on the dynamics of the accretion flow: they may quench relativistic jets and may facilitate or even cause state transitions. I will review a few major developments from the last decade, and then I will present some brand new results from our multiwavelength observing campaigns on several X-ray binaries, which reveal some of the deepest iron absorption lines ever observed with Chandra, as well as some of the fastest line variability. I will show how these observations highlight the intricate links between the inner accretion flow, relativistic jets, and accretion disk winds. Comparing to X-ray observations of other microquasars, I will argue that massive winds are truly a driving force in black hole X-ray binaries.

Speaker:	Manu Linares
Title:	"Thermonuclear burning on rapidly accreting neutron stars"
Abstract:	I will present recent results on thermonuclear bursts from accreting neutron stars, focusing on the discovery of millihertz quasi-periodic oscillations and four distinct burning regimes in the 11 Hz X-ray pulsar located in the globular cluster Terzan 5. This unusual neutron star, with higher magnetic field and slower rotation than any other known burster, showed copious bursting activity when the mass accretion rate was high (between 10% and 50% of the Eddington limit). I will discuss the role of fuel composition, magnetic field and spin in setting the burst properties of this system, and the possible implications for the rest of thermonuclear bursters.

Speaker:	Daniel Castro
Title:	"Exploring Cosmic Ray Acceleration in Supernova Remnants"
Abstract:	The origin of cosmic rays continues to be puzzling. Observational evidence increasingly supports the scenario where the Galactic subset of these are accelerated at supernova remnant (SNR) shocks. Both thermal and non-thermal emission from these objects, in a wide range of wavelengths, indicate the presence of extremely energetic particles in SNRs, and the development of analytical and semi-analytical models of SNR evolution where diffusive shock acceleration (DSA) is efficient allow for constraining the nature of cosmic ray production. I will outline some of my most recent work on observations of SNRs in X-rays and gamma-rays, and how simulations have allowed me to build consistent morphological and spectral pictures of these objects and to understand their role as accelerating sites of cosmic rays.

Speaker:	Laura Lopez
Title:	"Under Pressure: Assessing the Role of Stellar Feedback in HII Regions"
Abstract:	The role of stellar feedback in the star formation process in an open issue of debate. Although it is understood that massive stars inject energy and deposit momentum to surrounding gas, the dominant modes of this feedback and their relative role in regulating star formation is uncertain. In this talk, I will discuss how one can measure the pressures associated with several stellar feedback processes using multiwavelength data (radio, infrared, optical, and X-ray). I will present the results from applying these techniques to a large sample of HII regions in the Large and Small Magellanic Clouds, and I will consider the implications of our findings regarding the dynamics and the regulation of star formation in these regions.

Speaker:	Kathy Cooksey
Title:	"Precious Metals in SDSS QSOs: The Hunt for Intergalactic CIV in DR7"
Abstract:	The CIV doublet has proven to be an important tracer of the IGM and its evolution from z = 6 to 0. These transitions have been well-studied at high redshifts because: they are strong transitions of common metals; they are observable outside the Ly-alpha forest, where they become easier to identify; they redshift into optical passbands for 1.5 < z < 4.5; and they are resonant doublets, which give them distinctive characteristics and enable the survey to be largely automated. However, the 1.5 < z < 4.5 results can be vastly improved by surveying the thousands of SDSS DR7 QSOs. Having done this, we now present early results on the over 15,000 CIV systems that we identified. We are constructing a uniform 0 < z < 6 dataset by combining the SDSS survey with the z < 1 HST results (Cooksey et al. 2010) and the new z > 5 FIRE results (Simcoe et al. 2011). Thus, we can compare apples-to-apples: the absorber line density over time and the CIV mass density evolution. This is the first in a series on our surveys for various metal-line absorption systems in SDSS DR7 QSOs.

Speaker:	Bryce Croll
Title:	"Observations of the atmosphere of the super-Earth GJ 1214b"
Abstract:	The super-Earth GJ 1214b is the most Earth-like planet that we can well characterize its atmospheric features to date. With a radius of ~2.7 Earth radii and with a mass of ~6.5 Earth masses, this planet should have a composition either of a water-world, or a rocky core enshrouded by a hydrogen-helium envelope. A hydrogen-helium envelope would result in detectable atmospheric features, while a water-world's features would be too small to likely be detectable. There have been a wealth of observations for this planet, most showing a lack of detectable features, while others (namely my own) display signs of atmospheric features that would favour the scenario of a hydrogen-helium dominated planet enveloping a rocky core. I'll summarize the latest observations of this planet, including showing some of my own more recent observations, in the hopes of determining the true nature of this intriguing exoplanet.

Speaker:	Jeff Kissel
Title:	"Commissioning Advanced LIGO Suspensions"
Abstract:	The upgrades to the interferometers for Advanced LIGO are well underway, which can only mean one thing: we've finally got parts of the interferometer to play with! In this talk I'll focus on a particular part of the interferometers, the optic suspensions, and walk through the rigorous amounts of testing and commissioning we must do before/during/after any particular competent is installed. You'll definitely come away from the talk with appreciation of how difficult it is to built the worlds most sensitive gravitational wave interferometers!

Speaker:	Ruslan Vaulin
Title:	"Searching for Gravitational-Wave Transients and Their Electromagnetic Counterparts"
Abstract:	Gravitational waves (GW) produced in mergers of compact objects (e.g. neutron stars and black holes) or other gravitationally driven phenomena (e.g. supernova, gravitational collapse etc) are expected to be accompanied by emission of electromagnetic (EM) radiation covering wide range of frequencies from radio and optical to X-ray and Gamma rays. Joint observations of GW and EM signals will provide us with complete picture of the underlying physical processes as well as improve our ability to robustly detect these signals. I will overview the most recent searches for transient GW-EM signals with the LIGO-Virgo detector network and partner optical/X-ray telescopes. In particular, I will present latest results of the joint analysis of GW and EM data acquired during prompt follow-up observations by Swift of candidate GW transient events identified in two observational periods during 2009-2010 LIGO and Virgo science run. I will conclude with discussion of sensitivity of the joint search and prospects of such multi-wavelength observations in the era of advanced gravitational-wave detectors.