10Subscribe to:  iCal 


 Astronomy Colloquia at Caltech for 2013-14


Colloquia are held every Wednesday during the academic year at 4pm in the Cahill Hameetman auditorium.
Wine and cheese will be served in the Cahill Foyer from 5-6pm.

 

 

Date

Speaker

                                                   Talk Title

OCTOBER

2

Anna Frebel
MIT
Host: Branimir Sesar

From building blocks to large galaxies: towards understanding the formation of
the Milky Way:

The early chemical evolution of the Galaxy and the Universe is vital to our understanding of a host of astrophysical phenomena.  Since the oldest, most metal-poor stars are relics from the high-redshift universe, they probe the chemical and dynamical conditions of a time when large galaxies first began to assemble.  Recent works have shown that the ultra-faint dwarf galaxies (with L<10^5Lsun) contain a relatively large fraction of extremely metal-poor stars and are devoid of solar-metallicity stars. This reflects a rather short or truncated star formation history similar to what one would expect to occur in a first/early galaxy. The chemical signatures of these dwarfs furthermore support the concept that small systems analogous to the surviving ultra-faint galaxies were the building blocks of the Milky Way's low-metallicity halo.  This opens a new window for studying galaxy formation with the means of stellar chemical analyses. I will also include some information on our newly discovered [Fe/H]<-7.0 star.

9

James Bullock
UC Irvine
Host: Branimir Sesar

A Cold Dark Matter Controversy in Dwarf Galaxies:

The cold dark matter (CDM) cosmological model has been very successful in explaining cosmic structure on large scales and over a vast span of cosmic time, but it has faced persistent challenges from observations that probe the innermost regions of dwarf galaxies in the local universe.  Cosmological simulations that incorporate only gravity and collisionless CDM predict central densities that are too high to match constraints from galaxy dynamics.   The solution could lie in baryonic physics: gravitational potential fluctuations associated with supernova feedback can lower central densities.  However, it is not clear that this solution can work for the faintest galaxies, where basic energetic arguments suggest that feedback alone cannot solve the problem.  Alternatively, the anomalous dark matter densities could be evidence of more complex physics in the dark sector itself. For example, elastic scattering from strong dark matter self-interactions can alter predicted halo mass profiles, leading to good agreement with observations across a wide range of galaxy mass.   I will discuss ways forward for discriminating between these scenarios.

16

Alexandra Pope
UMass
Host: Lisa Storrie-Lombardi

Dust-Obscured Activity in High Redshift Galaxies:

We now know that the majority of the star formation activity at high redshift occurs behind dust. Building on the sucess of the first extragalactic submm surveys over a decade ago, I will discuss observations with Spitzer and Herschel that have advanced our understanding of dust emission in high redshift galaxies. These observations constrain how intense star formation and active galactic nuclei growth are linked in major mergers and turbulent gas-rich disks that are orchestrating massive galaxy formation. I will present evidence for evolution in dust properties suggesting different interstellar medium conditions at high redshift. I'll discuss how future large dish (sub)millimeter facilities will directly detect the majority of the sources contributing to the infrared background allowing us to make a complete census of dust-obscured activity in the Universe.

23

Joan Najita
NOAO

Host: Lisa Storrie-Lombardi
From Planetesimals to Giant Planets: Chemical and Dynamical Probes of Planet Formation:

Work with the Spitzer Space Telescope revealed that emission from water and organic molecules is commonly present in the mid-infrared spectra of disks surrounding young stars. I will describe how these features might be used to help lift the veil on a very early stage of planet formation, the formation of planetesimals, those theoretically fundamental but observationally elusive building blocks of planets in core accretion theory. I will also describe some results from high resolution spectroscopy that suggest that forming high-mass giant planets may reveal themselves through non-axisymmetric signatures of their presence, e.g., circumplanetary disks and eccentric inner rims.

















NOVEMBER

30
  Jean Brodie
 
UCO Lick Observatory
  Host: Branimir Sesar
  Globular Clusters and Halo Stars: Chemodynamical tracers of galaxy assembly:

  Since more than 90% of the total mass and angular momentum in galaxies resides beyond
  one effective radius, wide field observations are crucial for understanding the assembly
  histories of galaxies. The SLUGGS survey is producing 2-dimensional kinematic and
  metallicity maps for globular clusters (GCs) out to 10 effective radii and galaxy starlight
  out  to 3 effective radii in 28 nearby early-type galaxies.   Data obtained with Suprime-Cam
  on  Subaru and DEIMOS on Keck are being compared to a variety of simulations of galaxy
  build-up and are found to support and constrain two-phase galaxy formation scenarios.
  Early "in situ" formation and subsequent minor mergers appear to be the dominant
  mechanisms for building galaxies and their GC systems. Later major mergers may have
  been  important only in a small minority of cases. We find that the behavior of galaxies in
  their central regions  is a surprisingly poor predictor of large scale trends. I will also
  explore  the relationships between the different types of compact stellar systems, including
  a newly discovered class of faint ultra compact dwarfs (UCDs) that may be markers of the
  halo assembly process.

6

Xuening Bai
Harvard
Host: Sterl Phinney

The microphysics of astrophysics: adventures in computational magnetohydrodynamics:

Astronomical observations yield rich data of phenomenology on macroscopic scales, while they are typically consequences of microphysical processes on much smaller scales. Many of such processes involve magnetic fields, instabilities and turbulence, and are the subject of computational magnetohydrodynamics (MHD). By properly incorporating the microphysics, I will draw three examples which show that MHD simulations can greatly improve our understandings towards reality, and sometimes lead to surprises. First, I show that the recent simulations on the magneto-rotational instability (MRI) imply that the evolution of accretion disks is likely controlled by the global distribution and transport of magnetic flux. Second, I discuss the gas dynamics in protoplanetary disks and show that non-ideal MHD effects completely suppress the MRI in the inner disk (<10AU), leading to a laminar flow with accretion driven by magneto-centrifugal wind. Finally, I describe a preliminary study of particle acceleration in non-relativistic shocks, which is enabled by capturing the cosmic-ray driven instabilities using charged particles.

13

Pieter van Dokkum
Yale
Host: Richard Ellis

The build-up of galaxies since z~2:


Owing to large surveys such as the 3D-HST Treasury program we now have high resolution snapshots of the Universe over most of its history. The challenge now is to use this wealth of data to figure out how galaxies assembled, and what physical processes drove their evolution. The talk will highlight recent results on the evolution of galaxies with the present-day mass of the Milky Way and higher, linking galaxies across cosmic time by their number density. We find that the most massive galaxies were assembled in a very different way than Milky Way-like galaxies, which may explain their different present-day morphologies and their apparently different stellar initial mass functions.

20

Chris Carilli
NRAO, Socorro

Host: Gregg Hallinan

Cosmic Reionization:

Cosmic reionization corresponds to the epoch when light from the first stars and black holes reionized the neutral InterGalactic Medium (IGM) that pervade the Universe following recombination. This epoch of 'first new light' in the Universe, remains the last epoch of cosmic structure formation to be tested and explored.  I will summarize the latest constraints on cosmic reionization, with a focus on observations of the Gunn-Peterson effect in the spectra of the highest z quasars (z > 6), and related techniques. I will then focus on the PAPER experiment to detect HI 21cm emission directly from the neutral IGM at low frequencies (120MHz to 180MHZ). PAPER has produced unprecedented wide field, low frequency images of the southern sky, and we have set the best (statistical) limits on the HI 21cm signal from reionization to date.  I will conclude by presenting plans for the Hydrogen Epoch of Reionization Array, a 568 element array in South Africa that will provide a detailed characterization of the HI 21cm power spectrum and its evolution, as well as the potential for direct imaging of the largest scale structures during reionization.
     27   Thanksgiving

  No Colloquium

DECEMBER

4   Christoph Baranec
  Univ of Hawaii
  Host: Gregg Hallinan

  Scientific highlights from the Palomar Robo-AO system and plans for a Mauna Kea Robo-AO:


  Robo-AO is the world's first fully automated laser adaptive optics instrument. The prototype
  system, fielded at the Palomar Observatory 60-inch telescope, went live in June 2012 and has
  since executed ~10,000 observations at the ~0.1" visible diffraction limit. Among these
  observations are the largest diffraction limited surveys of stellar multiplicity in the local solar
  neighborhood and of nearby companions to Kepler exoplanet host candidates. The Palomar
  system will be augmented with two new infrared camera next summer which will both widen
  the spectral bandwidth of observations and enable deeper visible-light imaging using
  adaptive-optics-sharpened infrared tip-tilt guide sources - necessary for completion of the
  Kepler survey by the fall of 2014. I am planning on bringing an upgraded facility-class
  Robo-AO system to the University of Hawai'i's 2.2-m telescope on Mauna Kea to exploit the
  excellent native seeing and enable imaging approaching that of HST. This new system will be
  used for high-cadence monitoring of solar-system weather, characterization of asteroids and
  supernovae discovered by Pan-STARRS and ATLAS, and for validating the potentially tens of
  thousands of exoplanet host candidates discovered by the future Transiting Exoplanet Survey
  Satellite.
      11   Andrea Isella
  Caltech
  Host: Nick Scoville
 From Circumstellar Disks to Extrasolar Planets: Observational Insights:
 
  The transformational imaging capabilities offered by the Atacama Large Millimeter Array (ALMA) and the
  Karl Jansky  Very Large Array (VLA), as well as 
high-contrast near-infrared cameras, are opening an
  unprecedented window on the planet formation region in nearby young stellar objects. This enables us to
  investigate how gas-rich disks around young stars evolve and form planetary systems. This is a key step to
  understand
the origins of our Solar System and the puzzling diversity in the demographics of known
  exoplanetary systems.  I will summarize the current understanding of the planet formation process and 
present
  the most recent results from observations that spatially resolve 
the planet formation region in nearby disks.
  I will discuss the constraints
 on the initial conditions for planet formation, such as the radial distribution of the
  circumstellar material and the properties of the circumstellar dust, which inform about 
the location and time
  scale for the formation of  planets. 
I will then present ALMA, VLA, and CARMA observations that reveal spiral
  structures and asymmetries in the disk structure possibly caused by the interaction with planetary systems in
  the act of forming
.  I will conclude by presenting future plans that combine the ALMA capabilities with those of
  present and future 
high-contrast near-infrared cameras to study the formation and evolution of
  planetary systems  on spatial scales of a few AUs.
       18   Matteo Cantiello
  Kavli Inst
  Host: Sterl Phinney
  Angular momentum transport in stars:

  Stars are born rotating. Understanding how the angular velocity profile changes during their evolution is key to
  unravel the details of explosive stellar deaths (Supernovae and Gamma Ray Bursts) and the properties of
  stellar remnants (White Dwarfs, Neutron Stars and Black Holes).  I will quickly introduce the different classes of
  angular momentum transport mechanisms discussed in the literature and included in stellar evolution calculations. 
  I will then describe the new exciting results obtained by the KEPLER satellite, which through asteroseismology
  provided a measure of the degree of radial differential rotation in many evolved low-mass stars.  These observations
  can be used to test current theories for angular momentum transport. I will show results of such comparisons performed
  with the state-of-the-art open source stellar evolution code MESA.
      25
  Christmas
   No Colloquium

JANUARY

1

New Year's day

  No Colloquium

8

Andrea Comastri
Bologna
Host: Fiona Harrison

The evolution of obscured accretion probed by deep and hard X-ray surveys:

According to the recent models for the joint growth of Super Massive Black Holes and their Host Galaxies, heavy, possibly Compton thick, obscuration represents a key phase in their evolution and is expected to play a fundamental role in the feedback mechanisms linking SMBH activity with host galaxy properties. The smoking gun signature of heavily obscured accreting SMBH is the presence of a strong iron line on top of a flat/reflected hard X-ray spectrum. X-ray spectroscopy thus represents the most efficient method to obtain an almost unbiased view of the accretion history evolution from the early stages (i.e. z > 3) to the present days. I will review the key results obtained by extragalactic X-ray surveys with Chandra and XMM in the last 10+ years and the current hard X-ray (3-80 keV) observations with NuSTAR complemented by multi-wavelength follow up. I will also discuss the perspectives for future observations in the X-ray band and the expected breakthroughs in the study of SMBH evolution, with particular emphasis on the recent ESA recommendation for the next Large mission in 2028: The hot and energetic Universe.

15

Simon Lilly
ETH, Zurith
Host: Nick Scoville
Reverse engineering galaxies:

Using large data sets like SDSS and COSMOS we can now study the evolving galaxy population with unprecedented statistical precision over a wide range of cosmic time.  This has opened up new approaches to the study of galaxy evolution.   Key simplicities, or even symmetries, can be identified within the evolving galaxy population, the implications of which can then be developed, often analytically, to give new insights into the physical evolution of individual galaxies.  I will review some of the new perspectives that have been gained in this way, focusing mostly on the control and eventual quenching of star-formation, but also touching on the merging of galaxies and their structural morphologies, as well as the links with other phenomenological approaches to this topic.

22

Dimitri Mawet
ESO
Host: Shri Kulkarni

Extra-solar planetary system formation and evolution in the golden age of high contrast imaging:

After outlining the basics of our current understanding of the formation and evolution of extra-solar planetary systems, I briefly describe the three pathways used so far to tackle remaining open questions: the 'top-down' brown dwarf and the 'bottom-up' disk sciences, both bracketing the indirect/direct exoplanet detection/characterization efforts. As an illustration of a hybrid bottom-up/direct approach, I present the status of our adaptive optics (AO) survey of Spitzer/WISE debris disk stars with NIRC2@Keck, NACO@VLT, and PHARO@Palomar. This survey is as ambitious as it gets provided the current capabilities of AO instruments. Direct imaging has indeed up to now only scratched the surface of a huge parameter space, orthogonal to the very successful, yet indirect techniques. With the advent of extreme AO/wavefront control technologies and modern coronagraphy, second-generation facilities such as GPI, SPHERE, P3K, SCExAO are poised to break through the current contrast and inner working angle (IWA) wall. However, first-generation instruments still have a lot of untapped potential, that savvy upgrades can unleash, especially in the mid-IR (L/M/N bands), a scientifically key wavelength regime neglected by second-generation instruments. As a case in point, I present the development, deployment, and first science results of small IWA mid-IR vector vortex coronagraphs (VVC) at the VLT (NACO & VISIR), and LBT (LMIRCAM). I also review the scientific achievements of the P3K-PHARO near-IR VVCs (available since 2010), the status of on-going Palomar upgrades, and proposed plans for Keck, paving the way towards the extremely large telescopes (TMT, European ELT, and GMT). Finally, I discuss the results and implications of the successful 2-year VVC test campaign on the JPL high contrast imaging testbed (HCIT), performed within NASA's technology demonstration for exoplanet space-based missions (TDEM) framework. The VVC demonstrated contrast levels and inner working angles sufficient for imaging Earth-like and Super-Earth planets around M dwarfs with ELTs, as well as old Jupiter in reflected light with, e.g. a space-based coronagraphic probe, or explorer.
       29
  Selma de Mink
  CIT/Carnegie

  Host: Phil Hopkins
  Live Fast Die Young: The Evolution of Massive Stars towards their Death:

  Massive stars are rare and short-lived. Nevertheless, through their extreme brightness, strong
  outflows and powerful explosions, they heat and stir their surroundings, drive outflows on galactic
  scales, and are responsible for the main production the heavy elements in the Universe.  
Because of
  their large impact, 
evolutionary models of massive stars are an essential ingredient for a wide variety
  of astrophysical problems.
 

  New insight —in particular concerning the importance of binarity and rotation— is raising severe
  questions about the validity of the widely-used classic stellar models. I will discuss advances on the
  modeling side as well as ongoing surveys that are providing for the first time large and homogenous
  data sets, including stars with estimated masses up to a few hundred solar masses.   I will show
  examples of the potentially drastic effects on the properties of both stars (brightness, color, ionizing
  flux, chemical yields, X-rays etc.) as well as their final fate as core-collapse and pair-instability
  supernovae and gamma-ray bursts.

  The theoretical and observational developments in this field call for a critical reconsideration of our
  understanding of the role that massive stars play in the Universe as Cosmic Engines, i.e. through
  their chemical, mechanical and radiative feedback, as Cosmic Probes, i.e. as tracers of starformation
  nearby and at high redshift, and in the variety of Cosmic Transients they produce.

FEBRUARY

5

Martin Harwit
Cornell
Host: Richard Ellis

The Instability of Astrophysics Witnessed in the Twentieth Century:

Progress in astrophysics entails instabilities, some of which are beneficial in leading to unanticipated advances. Often these come about through the import of new tools developed in other sciences or for industry or the military.  Other instabilities, however, can be harmful and lead to setbacks.  The history of 20th century astronomy is replete with examples of both types, some of which I will recount.  One source of instability is astronomy’s inability, sometimes for decades at a time, to systematically pursue discoveries of rare events.  Such delays inject levels of uncertainty in our observational discipline that the experimental sciences seldom encounter.   Partial remedies for this difficulty may already be available.  Other instabilities arise as the complexity of the various disciplines constituting our field increases, the tools and vocabularies used by the disciplines begin to diverge, and misunderstandings arise to threaten a coherent, unified view of the Universe.   As historical examples show misinformation then cascades throughout astrophysics, with consequences akin to those of major failures of electrical power grids or financial meltdowns.  I will outline ways to retain beneficial instabilities while more readily thwarting damaging intrusions.  

12

Chuck Steidel
Caltech
Host: Tony Readhead
The Ecology of Galaxy Formation Within the "Cosmic Web"

I will discuss recent results from the ``Keck Baryonic Structure Survey'', a unique survey of the high redshift universe optimized for sensitivity to both forming galaxies and the surrounding gas-phase circumgalactic and intergalactic baryons (and the exchange between the two) at 2 < z < 3, when the relevant energetic processes (star formation, black hole accretion) were at their historical peak. I will emphasize how ``wholesale'' near-IR (rest-frame optical) spectroscopy of distant galaxies, made possible by the recent commissioning of the MOSFIRE imaging spectrometer on the Keck 1 telescope,  vastly improves measurements of metallicity, kinematics, and physical conditions-- both within galaxies and in the surrounding intergalactic gas.                    

19

Mariangela Lisanti
Princeton
Host: Judy Cohen
Bringing Dark Matter into Focus:

Although dark matter comprises the vast majority of the matter in the universe, its properties remain elusive.  Direct detection experiments are a promising avenue for discovering and characterizing the dark sector.  These experiments seek to identify dark matter particles as they scatter off nuclei in underground detectors.  The standard picture since the 1980s is that the scattering rate modulates annually due to the Earth's orbit around the Sun.  We have recently discovered a new modulation effect: Unbound dark-matter particles are focused by the Sun's gravitational potential, affecting their phase-space density in the lab frame.  This 'gravitational focusing' results in a significant overall shift in the phase of the annual modulation and provides a powerful new tool for characterizing the properties of the dark matter particle.

26

Andrew Pontzen
UC London
Host: Richard Ellis
The structure and evolution of dark matter halos:

The cold dark matter paradigm is being challenged by its apparent inability to explain the low density measured at the centre of cosmological systems, ranging from faint dwarf galaxies to massive clusters containing hundreds of galaxies the size of the Milky Way.  But before drawing conclusions one should carefully include the effect of gas and stars, which were historically seen as merely a passive component during the assembly of galaxies. We now understand that these can in fact significantly alter the dark matter component, through a coupling based on rapid gravitational potential fluctuations. I will review recent observational and theoretical developments and take a critical look at just how little we understand about the dynamics of dark matter in even the simplest scenarios.

MARCH

 

5

Evan Kirby
UC Irvine
Shri Kulkarni:
Dwarf Galaxies: The Nexus of Dark Matter and Chemical Evolution

The Local Group's dwarf galaxies are near enough for exquisitely detailed, resolved stellar spectroscopy and diverse enough to conduct controlled experiments on dark matter and chemical evolution.  I have collected medium-resolution spectra for thousands of stars in many Local Group dwarf galaxies, including satellites of the Milky Way and M31 as well as field dwarf galaxies.  Innovative techniques applied to these spectra recover velocities precise to a few km/s and detailed abundances precise to 0.1 dex.

Although satellite and field dwarf galaxies are different in many ways, their velocity dispersions show that both types of galaxy pose a serious challenge to cold dark matter.  Both types also obey the same mass-metallicity relation despite the large diversity of star formation histories, detailed abundance ratios, and even metallicity distributions.  I will present one galaxy, Segue 2, in detail because it is the least massive galaxy known.  This data set is even rich enough to address stellar evolution.  I will close with a fascinating puzzle involving a great deal of lithium in red giants, which have no right to have any lithium.

12

Sam Skillman
Stanford/KIPAC
Sunil Golwala:
Radio Emission in Galaxy Clusters: Insights from Cosmological Simulations:

Galaxy clusters are unique astrophysical laboratories that contain many thermal and non-thermal phenomena that demand a coordinated effort from theory, numerical simulations, and observations.  After discussing a few of the major open questions in galaxy cluster formation and evolution, I’ll present our recent work in attempting to model the non-thermal cosmic-ray population present in clusters.  It is proposed that cosmic shocks that propagate through the intracluster medium form through the process of structure formation, and may be capable of accelerating charged particles through diffusive shock acceleration.  These relativistic particles decay and radiate through a variety of mechanisms, and have observational signatures in radio, hard X-ray, and Gamma-ray wavelengths.  Modelling these dynamics require a combination of cosmological hydrodynamics coupled with a model to follow the momentum-space distribution of cosmic ray electrons and protons. We have implemented such a model by combining Enzo, an Adaptive Mesh Refinement hydrodynamics + N-body particle-mesh gravity solver, with a numerical library for cosmic ray transport. I will end with a look to what future observatories in the radio, X-ray, and sub-mm may uncover and what new capabilities our simulations must have to understand fundamental physical processes present in galaxy clusters.

19

Daniel Eisenstein
Biard Lecturer, Harvard
Host: Richard Ellis 
Measuring the Cosmic Distance Scale with SDSS-III

I will discuss how sound waves racing through the cosmos during the first million years of the Universe provide a robust method formeasuring the low-redshift cosmologicaldistance scale and thereby the properties of dark energy. The distance that the sound can travel can be computed to high precision and creates a signature in the late-time clustering of matter that serves as a standard ruler. Galaxy clustering results from the Sloan Digital Sky Surveyand SDSS-III reveal this feature and allow us to measure distancesto high accuracy, including a new 1% measurement to z=0.57.

      26

 Sarah  Burke-Spolaor
Caltech
Host: Gregg Hallinan

  Fast Radio Bursts on the Horizon

  Several reports of intense radio pulses---lasting only milliseconds--have been fuelling a heated debate as to the origin
  of this emission. Until recently, it was widely hypothesized that such bursts were Earth-local, but a growing body of
  evidence is demonstrating that some may be arriving from extragalactic sources at redshifts up to z~2. As an
  extragalactic population, these bursts would be unprecedented probes of extragalactic baryons and hitherto unidentified
  physical processes.

  I will outline the entertaining state of radio burst research, and describe the emerging evidence that we are seeing
  several sub-populations that range from local to cosmic origins. I will discuss potential progenitors of extragalactic
  "Fast Radio Bursts", and describe ongoing work to identify where they are, and what they are. 

APRIL

 

2

Richard Bower
Durham

Host: Richard Ellis
The EAGLE Universe

The EAGLE (Evolution and Assembly of Galaxies and their Environments) project is a suite of hydrodynamic simulations of the Universe. The simulations, include the full range of baryonic physics including metal dependent gas cooling star formation, supernovae, black hole formation. The resolution of the simulations is sufficient to resolve the onset of the Jeans instability in galactic disks, allowing us to study the formation of galaxies in detail.  At the same time the largest calculation simulates a volume that is 100 Mpc on each side, allowing us to study galaxy formation across  the full range of galaxy environments from the isolated dwarves to rich galaxy clusters.

A key philosophy of the simulations has been to use the simplest possible sub-grid models for star formation and black hole accretion, and for feedback from supernovae and AGN. Efficient feedback is achieved without hydrodynamic decoupling of particles. The small number of parameters in these models are calibrated by requiring that the simulations match key observed properties of local galaxies.  Having set the parameters using the local Universe, I will show that the simulations reproduce the observed evolution of galaxy properties extremely well.

The resulting universe provides us with deep insight into the formation of galaxies and black holes. In particular, we can use the simulations to understand the relationship between local galaxies and their progenitors at higher redshift and to understand the role of interactions between galaxies and the AGN that they host. I will present an overview of some of the most important results from the project.

9

Daniela Calzetti
UMass
Host: Lisa Storrie-Lombardi

Nearby Galaxies: Star Formation in Your Neighborhood

Despite many decades of progress in understanding the evolution of stellar populations in galaxies, we have still fundamental questions that have remained unanswered. These include: how do
stars cluster in galaxies, and how do these structures evolve in time? Do we actually have a `clustered' and `diffuse' mode of star formation? When structures remain bound (star clusters), how do their populations evolve? Is the stellar Initial Mass Function universal? How are popular star formation rate indicators affected by the recent star formation history of a galaxy? The answer to
these questions informs our theories for the evolution of galaxies through cosmic times. Many of these questions are being addressed by recent projects that combine UV and high-angular resolution with the Hubble Space Telescope, and which I will describe together with the results they have obtained so far.

16

Sun Kwok
Univ of Hong Kong
Host: Peter Goldreich
Synthesis of Complex Organics in the Late Stages of Stellar Evolution:

Infrared spectroscopic observations of the stretching and bending modes of aliphatic and aromatic compounds are now seen throughout the Universe, from the diffuse interstellar medium of the Galaxy to distant galaxies.  Observations of evolved stars have revealed a rapid and continuous synthesis of organic materials from the end of the asymptotic giant branch, to proto-planetary nebulae, to planetary nebulae.  These synthesized products are ejected into the interstellar medium through stellar winds and as a result enriching the Galaxy with complex organics. Over 70 gas-phase molecules, including rings, radicals, and molecular ions, as well as fullerene have been identified by millimeter-wave and infrared spectroscopic observations through their rotational and vibrational transitions.  Possible chemical pathways leading to the formation of complex organics will be discussed. Analysis of the infrared spectra suggests that the chemical structure of the carrier is consistent with that of mixed aromatic and aliphatic nanoparticles.  These structures are very similar to those of the insoluble organic matter found in meteorites, suggesting that the early solar system may have been enriched by stellar ejecta.


      23

  Davy Kirkpatrick
  IPAC/Caltech
  Host:  Gregg Hallinan

 Y Dwarfs and the Field Substellar Mass Function

 

 Nearby (sub)stellar astronomy is undergoing a renaissance. The Wide-field
 Infrared Survey Explorer (WISE) has discovered room-temperature Y-type brown
 dwarfs and has revealed over two dozen missing stellar and substellar members
 in the canonical 8-pc sample, which itself contains less than 200 total
 systems. One of these discoveries is the 2.0-pc distant L+T dwarf binary WISE
 1049-5319 (Luhman 16AB), now recognized as the third closest system to the Sun.
 In this talk I will give an update of our current knowledge of Y dwarfs,
 highlight what they and other nearby discoveries are telling us about the
 substellar mass function for field objects, and discuss how new motion surveys
 of the Solar Neighborhood are revealing previously missed objects not selected
 by traditional color searches.

       30   Nathan Smith
  Arizona
  Host:  Nick Scoville
 The Pre-Supernova Evolution of Massive Stars:

MAY

 

7

Tom Abel
Stanford
Host: Phil Hopkins



14

Vicki Kaspi
Greenstein Lecturer


No Colloquium

21

Alice Shapley
UCLA
Host: Richard Ellis

 

      28

  Karin Oberg
 
Harvard
  Host: Leslie Rogers


JUNE

4

James Miller-Jones
Curtin
Host: Gregg Hallinan



Information for Speakers

 

Previous Astronomy Colloquia:
1997
1998
1999
2000
2001
2002
2003
2004

2005

2006

2007

2008

2009

2010

2011
2012
2013

Updated: 9/18/13 aek