Calendar

Sep
26
Mon
Pizza Lunch: Keith Hawkins (Cambridge/Columbia)
Sep 26 @ 12:30 pm – 1:30 pm
Pizza Lunch: Keith Hawkins (Cambridge/Columbia) @ AY 119

Title: TBD

Keith Hawkins (Columbia/Cambridge)

 

Oct
10
Mon
Pizza Lunch: Laura Mayorga
Oct 10 @ 12:30 pm – 1:30 pm
Pizza Lunch: Laura Mayorga @ AY 119

Title: Proto-BD disks and the Kavli Summer Program in Astrophysics

Laura Mayorga

 

Oct
17
Mon
Pizza Lunch: Caitlin Doughty
Oct 17 @ 12:30 pm – 1:30 pm
Pizza Lunch: Caitlin Doughty @ AY 119

Title: Probing the z~6 UVB with Aligned Metal Absorbers

Caitlin Doughty

 

Oct
28
Fri
Colloquium: Mark Wardle
Oct 28 @ 3:15 pm – 4:15 pm
Colloquium: Mark Wardle @ Biology Annex 102

Star formation in the vicinity of the supermassive black hole at the Galactic Centre

Dr. Mark Wardle, Macquarie University

The disruptive tidal field near supermassive black holes overcomes the self-gravity of objects that are less dense than the Roche density.  This was once expected to suppress star formation within several parsecs of  Sgr A*, the four million solar mass black hole at the centre of the Galaxy.   It has since become apparent that things are not this simple:  Sgr A* is surrounded by a sub-parsec-scale orbiting disk of massive stars, indicating a star formation event occurred a few million years ago.    And on parsec scales,  star formation seems to be happening now:  there are proplyd candidates and protostellar outflow candidates,  as well as methanol and water masers that in the galactic disk would be regarded as sure-fire signatures of star formation.  In this talk, I shall consider how star formation can occur so close to Sgr A*.

The stellar disk may be created through the partial capture of a molecular cloud as it swept through the inner few parsecs of the galaxy and temporarily engulfed Sgr A*.  This rather naturally creates a disk of gas with the steep surface density profile of the present stellar disk.  The inner 0.04 pc  is so optically thick that it cannot fragment, instead accreting onto Sgr A* in a few million years; meanwhile the outer disk fragments and creates the observed stellar disk.   The isolated young stellar objects found at larger distances, on the other hand,  can be explained by stabilisation of clouds or cloud cores by the high external pressure that permeates the inner Galaxy.   A virial analysis shows that clouds are indeed tidally disrupted within 0.5 pc of Sgr A*, but outside this the external pressure allows self-gravitating clouds to survive, providing the raw material for ongoing star formation.

 

Nov
11
Fri
Colloquium: Amy Simon (Host: Nancy Chanover)
Nov 11 @ 3:15 pm – 4:15 pm
Colloquium: Amy Simon (Host: Nancy Chanover) @ Biology Annex 102

Outer Planets Update

Dr. Amy Simon, NASA

The Hubble Outer Planet Atmospheres Legacy (OPAL) program is a yearly program for observing each of the outer planets over two full rotations. Observations began with Uranus in 2014, adding Neptune and Jupiter in 2015 (Saturn will be included in 2018, after the end of the Cassini mission). These observations have provided interesting new discoveries in their own right, but are also now being combined with observations from a number of facilities, including NASA’s IRTF, Keck, the VLA, as well as the Kepler and Spitzer missions to further expand the breadth of science they contain.  This talk will cover the latest observations for each of these planets and what we are learning from these data sets.

 

Nov
14
Mon
Pizza Lunch: Drew Chojnowski
Nov 14 @ 12:30 pm – 1:30 pm
Pizza Lunch: Drew Chojnowski @ AY 119

Title: H-band Spectral Variability of Classical Be Stars

Drew Chojnowski

 

Nov
18
Fri
Colloquium: Karen Olsen
Nov 18 @ 3:15 pm – 4:15 pm
Colloquium: Karen Olsen @ Biology Annex 102

Simulations of the interstellar medium at high redshift: What does [CII] trace?

Dr. Karen Olsen, Arizona State University

We are in an exciting era were simulations on large, cosmological scales meet modeling of the interstellar medium (ISM) on sub-parsec scales. This gives us a way to predict and interpret observations of the ISM, and in particular the star-forming gas, in high-redshift galaxies, useful for ongoing and future ALMA/VLA projects.

In this talk, I will walk you though the current state of simulations targeting the the fine structure line of [CII] at 158 microns, which has now been observed in several z>6 galaxies. [CII] can arise throughout the interstellar medium (ISM), but the brightness of the [CII] line depends strongly on local environment within a galaxy, meaning that the ISM phase dominating the [CII] emission can depend on galaxy type. This complicates the use of [CII] as a tracer of either SFR or ISM mass and calls for detailed modeling following the different ways in which [CII] can be excited.

I will present SÍGAME (Simulator of GAlaxy Millimeter/submillimeter emission) – a novel method for predicting the origin and strength of line emission from galaxies. Our method combines data from cosmological simulations with sub-grid physics that carefully calculates local radiation field strength, pressure, and ionizational/thermal balance. Preliminary results will be shown from recent modeling of [CII] emission from z~6 star-forming galaxies with SÍGAME. We find strong potential for using the total [CII] luminosity to derive the ISM and molecular gas mass of galaxies during the Epoch of Reionization (EoR).

 

Mar
3
Fri
Colloquium: Bart De Pontieu
Mar 3 @ 3:15 pm – 4:15 pm
Colloquium: Bart De Pontieu @ BX 102

Interface Region Imaging Spectrograph Views of How the Solar Atmosphere is Energized

Dr. Bart De Pontieu, Lockheed Martin

At the interface between the Sun’s surface and million-degree outer atmosphere or corona lies the chromosphere. At 10,000K it is much cooler than the corona, but also many orders of magnitude denser. The chromosphere processes all magneto-convective energy that drives the heating of the million-degree outer atmosphere or corona, and requires a heating rate that is at least as large as that required for the corona. Yet many questions remain about what drives the chromospheric dynamics and energetics and how these are connected to the transition region and corona.

The Interface Region Imaging Spectrograph (IRIS) is a NASA small explorer satellite that was launched in 2013 to study these questions. I will review recent results from IRIS in which observations and models are compared to study the onset of fast magnetic reconnection in the solar atmosphere, the generation of violent jets and how they feed plasma into the hot corona, and the role of nanoflares in heating the corona.

Mar
10
Fri
Colloquium: Hazel Bain
Mar 10 @ 3:15 pm – 4:15 pm
Colloquium: Hazel Bain @ BX 102

Antarctic high altitude balloon observations of solar flares: Life and work on the ice

Dr. Hazel Bain, University of California, Berkeley

 

The Gamma-Ray Imager/Polarimeter for solar flares (GRIPS) instrument is a balloon-borne telescope designed to study particle acceleration in solar flares. The process through which stored magnetic energy is released and particles are accelerated to high energies in solar flares is not well understood. Hard x-rays and gamma-rays are direct signatures of these accelerated particles and can be used as a proxy to investigate particle acceleration mechanisms in these explosive events.

In the austral summer of 2016, GRIPS began its inaugural flight from NASA’s Long Duration Balloon (LDB) facility just outside McMurdo, Antarctica. During the 12 day flight, the balloon was carried around the Antarctic continent by the seasonal stratospheric polar vortex. At the end of the 2016 season, the data vaults were recovered however due to the lateness of the season a full recovery was scheduled for the following year.

In this talk I will discuss the GRIPS instrument design and science goals, the process of testing and integration leading up to a balloon launch, the inaugural flight and subsequent instrument recovery this year from the GRIPS landing site out in Antarctica’s “flat white”. I’ll also talk a little bit about life and work on the ice.

Apr
24
Mon
Pizza Lunch: Laurel Farris
Apr 24 @ 12:30 pm – 1:30 pm
Pizza Lunch: Laurel Farris @ AY 119

Determining the size of coronal bright points using cross-correlation methods

Laurel Farris