Category: Uncategorized

Tuesday Lunch April 12th, 2016 Talk: Illuminating the First X-ray sources with Low Frequency Radio Observations.

April 11th, 2016 in Uncategorized

Title: Illuminating the First X-ray sources with Low Frequency Radio Observations.

Aaron Ewall-Wice

April 12th, 2016
CAS 500

Observations of the 21 cm power spectrum at high redshift will allow us to characterize the sources that heated the intergalactic medium including the first stellar mass black holes and hot interstellar medium. Most current power spectrum experiments are targeting reionization; however, the best constraints on heating will come from redshifts higher than those of the reionization epoch.

I present forecasts on our ability to determine the astrophysics of X-ray heating from power spectrum measurements along with results from a recent observational campaign on the Murchison Widefield Array (MWA) carried out to explore the systematics present at higher redshift and lower frequencies (75-112 MHz, corresponding to the redshifts between 18 and 12).  We find that while next generation experiments will be sensitive enough to deliver 10% or better constraints on the spectral properties and X-ray efficiencies of the first galaxies, sub-percent spectral structure in the MWA data, that are challenging to calibrate, prevent us, so far, from reaching our design sensitivity. I describe the design and calibration features in future experiments such as the Hydrogen Epoch of Reionization Array (HERA) that will allow us to obtain precision measurements of X-ray heating in the coming decade.

Feb 24 Silas Peirce Lecture: Following the Water on Mars

February 24th, 2014 in Uncategorized

Join Bethany Elhmann, Assistant Professor of Planetary Science at California Institute of Technology, as she presents the first annual College of Arts & Sciences Silas Peirce Lecture.

The Curiosity rover represents the latest chapter in NASA’s exploration of Mars. It was designed to assess whether Mars ever had an environment able to support small life forms called microbes. The rover’s onboard laboratory is studying the rocks and soil it encounters to search for the chemical building blocks of life on Mars, revealing what the Martian environment was like in the past. Professor Ehlmann, a member of the intrepid rover’s science team, will describe why Curiosity was sent to Mars and what it has found since landing 18 months ago.

When: Monday, February 24, 2014 7pm
Where: Tsai Auditorium, 685 Commonwealth Ave.

Tsai Auditorium is easily accessible by public transportation: Green Line B, BU Central stop. This event is free and open to the public. For additional information, contact Paul Withers.

Studying the Venusian Atmosphere on a Surface-to-Air Missile

January 31st, 2014 in Uncategorized

On Nov. 26, 2013, The Venus Spectral Rocket Experiment (VeSpR) launched successfully  from White Sands Missile Range.  VeSpR is a sounding rocket experiment designed to study the ultraviolet light emitted in the upper atmosphere of Venus, led by principal investigator and BU Astronomy Professor John Clarke.  VeSpR was loaded into a two-stage rocket, consisting of a Black Brant model Mk1 sounding rocket and a modified Terrier surface-to-air missile.  Please see the NASA press release for more details:

Pictured below is the VeSpR launch and subsequent retrieval at White Sands.


VeSpR_Launchpad VeSpR_Launch VeSpR_Recovery VeSpR_recovery_27nov13

11/19 Lunch Talk: Protoplanetary Disks

November 18th, 2013 in Uncategorized

Spatial Variation of Dust Evolution in Protoplanetary Disks

Dr. Melissa McClure
University of Michigan

CAS 500
12:30 pm
November 19, 2013


Within circumstellar disks, the properties of the dust dictate the structure of the disk, and the variation in these properties as a function of vertical height and radius can be used to probe dynamical processes such as settling, turbulence, and radial transport. These processes affect the ability to form a proto-planet at a given disk location, while the variety of dust species at each location impacts the final composition of planets formed there. By comparing data from spectroscopic programs using Magellan, Spitzer, and Herschel with physical models of irradiated accretion disks, I aim to characterize the spatial variations in mineralogy, grain size, and dust/gas mass ratio within circumstellar disks and identify how early they occur.

My work thus far finds that even in young star-forming regions (like Ophiuchus at ~ 0.8-1 Myr), disks show signs of significant dust processing and settling. However, grains in the innermost ~0.2 AU may be prevented from growing beyond several microns in disks with high mass accretion, likely a sign of turbulent fragmentation due to viscous dissipation through the midplane. Based on the large solid angle required to fit these disks’ emission excess over their stellar photospheres and comparison against models with a variety of dust opacities, the midplane dust in the highly accreting systems may be rich in FeO while the upper layers are depleted of it, suggesting a vertical gradient in the gas phase oxygen abundance. In the outer regions of the disk, oxygen-rich ices appear to be sequestered in the millimeter sized grains in the midplane due to settling; in less settled systems where we do see ice emission, it appears at radii consistent with a proto-Kuiper belt, sometimes in conjunction with flash-heated silicates. Further work to examine variation in grain size distributions at intermediate radii with updated disk models and spatially resolved data is underway.

11/18 seminar: Star Formation in Galaxies

November 18th, 2013 in Uncategorized

Astrophysics Seminar Series

“Cold Gas Content and Star Formation in Galaxies”

Min Yun

University of Massachusetts

Monday, November 18, 2013
Refreshments at 3:15pm in CAS 500
Talk begins at 3:30pm in CAS 502


Cosmological simulations of large scale structures and mass assembly have shown that the gas accretion rate onto DM halos broadly tracks the observationally established cosmic star formation density evolution, and semi-analytic incorporation of baryon physics has been applied to these simulations to model the build up of ISM and stellar mass in galaxies.  I will examine the current data on cold gas content in present day galaxies and their relation to other physical properties such as stellar mass, color, and star formation rate, in the context of understanding the limitations and utilities of such modeling as a tool for studying the mass assembly history of galaxies.

Nov. 12 Tuesday Lunch Talk: The New Heliosphere

November 12th, 2013 in Uncategorized

Please note our new time of 12:30!

The New Heliosphere

Prof. Merav Opher
BU Astronomy

CAS 500
12:30 pm
November 12, 2013

“As the Sun moves through the interstellar medium it carves a bubble called the heliosphere. A fortunate confluence of missions has provided a treasury of data that will likely not be repeated for decades The measurements in-situ by the Voyager spacecrafts, combined with the all-sky images of the heliospheric boundaries by the Interstellar Boundary Explorer mission have transformed our understanding of heliosphere. In particular one of the first surprises was that both Voyager spacecrafts found no evidence for the acceleration of the anomalous cosmic rays (ACRs) at the termination shock as expected for approximately 25 years. Another challenge are the energetically particles intensities and the plasma flows that are dramatically different at Voyager 1 and 2. There are several other observations that are key challenges to the heliospheric models such as a) Why the azimuthal magnetic flux is not conserved along the Voyager 1 trajectory? b) What causes the flow stagnation region seen at Voyager 1? c) What causes the unexpected observation of a depletion-region beginning in 2012 at Voyager 1? These observations point to the need to move past the standard description of the heliosphere. In this talk I will review the state-of-the art of our understanding of this “new heliosphere”. I will review our model that proposes that collisionless reconnection is happening within the sector region (the region where the solar magnetic field reverses polarity) and can explain the different observational puzzles. I will review our model as well as describe its consequences for the transport, acceleration of particles as well as for the flows and fields in the heliosheath. Finally, recent observations indicate a magnetic connectivity between the heliosheath magnetic field and the interstellar medium magnetic field; where the energetic particles of the heliosheath leaked out while the galactic cosmic rays penetrated the heliosheath. I will comment on our current effort of understanding the nature of the heliopause. We argue that these observations can be explained by Voyager 1 being in the last layer of the heliosheath where the heliosheath magnetic field reconnect with the interstellar magnetic field, what we call the “porous heliosheath”. The knowledge gain from the edge of the heliosphere will have consequences for other astrospheres and astrosheaths where the magnetic nature of the winds could be much more complex that previously thought.”

11/7 seminar: Resolving Earth and Space Science Uncertainty

November 4th, 2013 in Uncategorized

Space Physics Seminar

Resolving Earth and Space Science Uncertainty:
One tiny satellite at a time

Lars Dyrud
Draper Laboratory

Thursday, November 7, 2013
725 Commonwealth Ave.
Refreshments at 3:30pm in CAS 500
Talk begins at 4:00pm in CAS 502

Two thematic drivers are motivating the science community towards constellations of small satellites, the revelation that many next generation system science questions are uniquely addressed with sufficient numbers of simultaneous space based measurements, and the realization that space is historically expensive, and in an environment of constrained costs, we must innovate to “do more with less”. We present analysis that answers many of the key questions surrounding constellations of scientific satellites, including research that resulted from the GEOScan community based effort originally intended as hosted payloads on Iridium NEXT. We present analysis that answers the question how many satellites does global system science require? Perhaps serendipitously, the analyses show that many of the key science questions independently converge towards similar results, i.e. that 20-40 satellites are needed for transformative, as opposed to incremental capability in system science. We focus on climate, carbon-cycle, and gravity science as demonstrations of these findings, including results from funded and proposed NASA missions, ERIS, RAVAN and EPIC. We conclude with a discussion on implementation plans and the new paradigms for community and international cooperation enabled by small satellite constellations.

11/4 seminar: the Epoch of Reionization

November 4th, 2013 in Uncategorized

Astrophysics Seminar Series

“Hydrogen and Heavy Element Measurements near the Epoch of Reionization”

Robert Simcoe

Monday, November 4, 2013
Refreshments at 3:15pm in CAS 500
Talk begins at 3:30pm in CAS 502

Infrared photometric surveys are now discovering quasars at z > 6.5, enabling investigation of neutral Hydrogen and its associated heavy elements at the tail end of the reionization epoch. I will discuss results from our earliest spectroscopic observations of these objects using FIRE on Magellan, and frame these results in the context of early circumgalactic metal pollution. I will also discuss limitations of the current measurements and ways that next-generation telescopes may help address these shortcomings. Finally, I will provide a high-level overview of selected new instrumentation concepts and technology development projects underway at MIT.

October 28 seminar: Dusty Galaxies

October 28th, 2013 in Uncategorized

Astrophysics Seminar Series

“The evolution of dusty galaxies as seen through their infrared spectral energy distributions”

Anna Sajina
Tufts University

Monday, October 28, 2013
Refreshments at 3:15pm in CAS 500
Talk begins at 3:30pm in CAS 502


I will present recent results on characterizing the infrared spectral energy distributions (SEDs) of mid-IR selected z~0.3-3.0 and L_IR~10^10-10^13Lsun galaxies, and study how their SEDs differ from those of local and high-z analogs. Infrared SEDs depend both on the power source (AGN or star-formation) and the dust distribution. Therefore, differences in the SEDs of high-z and local galaxies provide clues as to differences in their physical conditions. I will show that there is strong evolution in the SEDs between local and z~2 IR-luminous galaxies, as well as that there is a wide range of SEDs among high redshift IR-luminous sources. I will discuss possible explanations for this SED evolution as revealed in the morphology (based on HST NICMOS images) of our sources, and as revealed by theoretical SED models (based on GADGET+SUNRISE simulations).

10/30 lunch talk: Hot Jupiters

October 28th, 2013 in Uncategorized

Hot Jupiters and the Rotational History of their Host Stars

Dr. Katja Poppenhaeger
Sagan Fellow, CfA

noon to 1pm
CAS 500


‘Stellar rotation is the driver of magnetic dynamos. For cool stars, their thus generated magnetic fields lead to phenomena like flares, coronal mass ejections, and high-energy emission, generally summarized under the name “magnetic activity”. Magnetic activity shapes the environment of close-in exoplanets and can lead to the evaporation of exoplanetary atmospheres. To study this phenomenon, I have collected observations which yielded the first X-ray detection of an exoplanetary transit in front of its host star. These data show a surprisingly deep X-ray transit with three times the optical transit depth, which can be traced back to thin outer atmosphere layers of the planet that are transparent at optical wavelengths, but opaque to X-ray photons. With a larger sample of X-ray observations of such systems, there is now also accumulating evidence that Hot Jupiters may influence the rotation and activity of their host stars. Without external input of angular momentum, cool stars spin down over time due to magnetic breaking. However, if there is tidal interaction between a star and its Hot Jupiter, the spin-down of the host star does not necessarily follow the usual age/rotation/activity relations. I will present results from our ongoing observational campaign at X-ray wavelengths and in the optical, and present several outstanding systems which display significant age/activity discrepancies presumably caused by their Hot Jupiters.’