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The mission of the Harvard-Smithsonian Center for Astrophysics (CfA) is to advance our knowledge and understanding of the universe through research and education in astronomy and astrophysics.
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2008 CfA Postdoc Science Symposium
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A day long event for the entire CfA community!
Phillips Auditorium
Tuesday Oct 7
9:40 am - 5:15 pm
Free coffee and snack breaks
Free lunch provided with RSVP to knoeske@cfa.harvard.edu by Sept 30th
Preliminary symposium schedule:
9:40-10:15: Orientation for incoming CfA Postdocs
- welcoming remarks by Charles Alcock
- Library introduction by Michael Blake
- CF orientation by Van McGlasson
- A working introduction to the CfA by current postdocs
10:15-10:30: Coffee Break
10:30-12:30: Science Session I: Stars & Planets
12:30-1:40: Lunch (Free with RSVP to knoeske@cfa.harvard.edu by Sept. 25th)
1:40-3:00: Science Session II: Clusters & Galaxies
3:00-3:20: Coffee Break II
3:20-5:00: Science Session III: Cosmology & Fundamental Physics
5:30-7:30: Postdoc Party
Talk Abstracts
Title: Star Formation: The Young and the Youngest
Abstract: IR photometry is a tool of excellence in studies of star formation.
In the first part of this talk I will summarize the most interesting results
obtained recently from deep, high-resolution NIR photometry of the embedded
clusters RCW 38, Westerlund 2, and Trumpler 14, and address the issue of
measuring mass segregation in young, massive clusters. For the second part, I
will focus on the Spitzer's view of the first stages of star formation, from
cores to protostars to the pre-main-sequence, as I outline the project to be
carried out at the CfA.
Title: Coronal "Wave": Magnetic Footprint of a CME?
Abstract: The Solar Heliospheric Observatory's Extreme ultra-violet Imaging
Telescope (EIT) brought us the first direct observations of large-scale
transient wave-like phenomena in the solar corona. Appearing as a diffuse
front of enhanced emission, these "EIT waves" are observed to expand
quasi-radially away from a source region, and can cover the entire face of the
Sun in tens of minutes. Initially identified as the predicted coronal
counterpart of a flare-induced near-surface blast wave, subsequent work showed
them to be preferentially associated with coronal mass ejections (CMEs) rather
than flares. Recent research on these "EIT waves" has shown them to exhibit
properties which are difficult to reconcile with existing interpretations of
plasma compression, or as magnetohydrodynamic waves. Developed within the
context of the recently discovered observational constraints, a new
understanding of these enigmatic "EIT waves" is presented, where the diffuse
bright front is identified as the magnetic footprint of a CME.
Title: Boiling Halos
Abstract: When heating the gas near the center of cluster halos (by AGN,
gravitational energy, dark matter, etc.) conditions for convection might
occur. Convection naturally explains entropy cores, turbulence, and perhaps
the observed temperature drop near the center. I will suggest yet another
possible mechanism for cluster heating (by gravitational energy), and will
present 1D spherical hydrodynamic simulation with convection (by mixing length
theory) that indicate that convection could be an important ingredient for
understanding the ICM gas.
Title: Monte Carlo Simulations of Ultracold Bosons in Optical Lattices
Abstract: Lattice boson systems, which can be realized by ultracold gases in
optical lattices, are interesting both theoretically (they allow studying
quantum phase transitions and exotic states of matter), and experimentally
(they can be used as optical lattice emulators of solid state systems and have
possible applications in quantum computation). Under certain conditions, such
systems can be described by the Bose-Hubbard model. I will present results of
extensive Quantum Monte Carlo simulations both at zero and finite temperature.
Title: The Age of B59 and the Pipe Nebula: Implications for the Timescale of Star Formation
Abstract: The Pipe Nebula is a valuable new laboratory for studying the
earliest stages of star formation. Containing only one small cluster (B59) of
~20 young stars, until recently, the Pipe has escaped detailed scrutiny despite
its proximity (~130 pc) and size (~10^4 M_sun). Detailed studies of dense
cores in the Pipe (Rathborne et al. 2008, Muench et al. 2007, Lada et al. 2008)
find that thermal pressure provides the dominant source of support against
collapse, and that non-thermal support is constrained to sub-sonic flows.
These cores are also found to be stable, with minimum ages of 1 million years,
suggesting that they are evolving quasi-statically counter to the more rapid
evolution predicted by theoretical models of turbulent star formation provides
the dominant means of support against collapse. Unferstanding the nature of
this seeming conflict between observations and theory is essential to ensuring
a proper description of time scale of star formation, and thus the limit to
which stellar populations can be considered co-eval.
To shed light on the true age of the dense core population in the Pipe, we have
made spectroscopic observations of the stellar content of B59, the most evolved
core in the Pipe. Measuring stellar temperatures from these spectra, we have
created an observational HR diagram for B59; comparing this HR diagram to
theoretical pre-main sequence evolutionary tracks, we have derived the mean
stellar age of B59, providing a first estimate of the ages of dense cores in
the Pipe, and constrained the characteristic time scale of the star formation
process in the Pipe Nebula.
Title: The Last Gasp of Gas Giant Planet Formation: A Spitzer Study of the 5 Myr-old Cluster NGC 2362
Abtract: Constraining the timescale for primordial circumstellar disks, which
comprise the building blocks of planets, evolve into debris disks sets an
empirical upper limit for the formation timescale of gas giant planets. In
this talk, I discuss results from a comprehensive Spitzer/Chandra/ground-based
study of the massive 5 Myr-old open cluster NGC 2362, which investigates the
primordial-to-debris disk transition in detail. We find evidence for two
different morphologies of disks evolving from the primordial disk phase to the
debris disk phase: so-called 'transition' disks, whose SEDs show inner
holes/gaps consistent with gas giant planet formation, and 'homologously
depleted' disks, whose SEDs are consistent with a steady loss of disk mass at
all radii simultaneously. These two types of disks outnumber primordial disks
by as much as 8 to 1. Therefore, these results refute the two-decade old
arguments in favor of a rapid, < 0.1 Myr transition timescale based on
observations of Taurus-Auriga and rule out UV photoevaporation as the physical
process by which most primordial disks disperse. Finally, we find that gas
giant planets must form prior to 5 Myr around nearly all stars with masses >
1.4 solar masses and around the majority of solar/subsolar-mass stars.
Title: Astrophysical Consequences of Particle Dark Matter: From Microwaves to Gamma Rays
Abtract: Though the evidence for the existence of dark matter has been firmly
established for some time, the nature of the dark matter remains elusive.
Recent developments provide mounting evidence that the dark matter is composed
of heavy particles (~ 500-1000 GeV) which self-annihilate producing copious
amounts of electrons and positrons in regions where the dark matter density is
high. The injection of these electrons and positrons into the ISM has
potentially interesting astrophysical consequences including synchrotron
radiation towards the Galactic center which may have already been seen by WMAP
as well as inverse Compton gamma rays which may be observable by GLAST/Fermi.
In this talk I will describe the excess microwaves towards the Galactic center
in the WMAP data (the WMAP "haze") and show that this signal is consistent with
electron/positron injection by a self-annihilating DM particle with mass ~800
GeV. I will discuss this interpretation in the context of present local cosmic
ray measurements as well as upcoming gamma ray observations.
Title: Small Dwarf Galaxies within Larger Dwarfs: Why Some are Luminous while Most Go Dark
Abstract: We consider a scenario in which the LMC, SMC, and those dwarfs whose
orbits are similar to those of the Magellanic Clouds were all originally part
of a group of dwarfs that was accreted by the Milky Way (MW) and tidally
disrupted. Our theory addresses a number of outstanding problems in galaxy
formation, particularly those associated with dwarf galaxies. First, it can
explain the planar orbital configuration population by some dSphs in the MW.
Second, it provides a mechanism for lighting up dwarf galaxies and reproduces
the bright end of the cumulative circular velocity distribution of the
satellites in the MW. Finally, our model predicts that other isolated dwarfs
will be found to have companions down to this mass limit. The recent
discovery of Leo V (Belokurov et al. 2008), a dwarf spheroidal companion of Leo
IV and the nearby dwarf associations supports our hypothesis.
Title: Low Frequency Radio Observations of Galaxy Groups
Abstract: I will present preliminary results of a low frequency radio survey of
a sample of galaxy groups using the Giant Metrewave Radio Telescope at 610,
327, and 235 MHz. The survey aims to study the morphological and spectral
properties of the central radio galaxy, correlate the radio data with extant
X-ray data, and investigate the AGN effects on the thermal intragroup medium at
various phases of its activity.
Title: Clustering of Obscured and Unobscured Quasars
Abstract: Recent observations (particularly with Spitzer) have uncovered a
significant population of the long sought-after dust obscured quasars.
However, the mechanisms that produce the obscuration in these sources are still
unclear. I will present the angular cross-correlation of IR-selected quasars
and galaxies 0.7 < z < 2 from the Bootes multiwavelength survey. We find that
dust-obscured quasars are more strongly clustered with galaxies than unobscured
quasars on scales smaller than ~500 h^-1 kpc. This result has implications for
the applicability of unified models AGN obscuration at high redshifts, and may
place constraints on merger-driven models of quasar evolution.
Title: The L1448 Molecular Cloud: Where (and Why) Do Stars Form?
Abstract: We apply a novel hierarchical structure identification approach
(i.e., dendrograms) to the L1448 molecular cloud. This reveals that a network
of dense filaments pervades the L1448 cloud and constitutes about 1/4 of the
cloud's mass. Within the filaments, dense cores and stars form only in
unusually massive and dense regions of high pressure that are typically
influenced by strong self-gravity. Thus, one may expect that the evolution of
dense cores in L1448 is primarily set by these boundary conditions (e.g.,
pressure and density). We find, however, that further agents matter. Dense
cores seem to be also shaped the the impact of "winds" (e.g., from stars).
Most interestingly, all of the dense core and star formation in L1448 might
have been triggered by the collision of filaments within the cloud.
Title: The X-ray Extended Structure in 3C 17 and 3C 305
Abtract: The X-ray radiation observed from radio jets and hotspots is generally
interpreted to be from non-thermal processes, even if the choice between
inverse Compton and synchrotron emission has to be decided on a case-by-case
basis. Recently, during a Chandra snapshot survey of 3C sources at redshift
lower than 0.3, several jets and hotspots have been detected; among these
cases, two interesting radio galaxies has been found: 3C 17 and 3C 305. With
only 8 ksec of exposure it has been possible to detect extended X-ray structure
in these two sources. The first, 3C 17, contains a bent radio jet with an
X-ray detection from two knots, while the second, 3C 305, shows an extended
X-ray structure. For 3C 17, we compare the X-rays emission with the radio maps
in the VLA archive and with the optical-IR-UV archival images of the Hubble
Space Telescope derived during the HST snapshot program of the 3CR sample. We
found that the X-ray detection of the radio jet has counterparts in the
optical, IR and UV. We give source parameters required for the various X-ray
emission models. A peculiar object has been found at the beginning of the
radio jet of 3C 17, with no counterpart in the radio and in the X-ray band. We
will propose some interpretations to understand the nature of this object. For
the other soruce, 3C 305, the comparison with the HST images and the MERLIN-VLA
radio maps revealed an unexpected association between the X-ray emission and
the lower frequency radiation from the radio to the optical band. Two
different scenarios will be presented to interpret this new behavior. The
multiwavelenght image of this radio galaxy has been entered in this year's NRAO
image contest.
Title: Atmospheric Escape from Highly Irradiated Planets
Abstract: About 1 in 5 of the more than 200 extrasolar planets observed to date
are located less than 0.1 AU from the host stars. Observations of HD 209458b,
the first highly irradiated "hot Jupiter" discovered on an orbit transiting its
host star, suggest that the planet may be losing atomic hydrogen.
Photoionization heating from stellar UV radiation can drive planetary mass
loss in the form of hydrodynamic winds. I will demonstrate that Jupiter-mass
planets at 0.05 AU lose at most 1% of their mass over the main sequence
lifetimes of their host stars. I will discuss the stability of hydrogen
atmospheres on highly irradiated planets as a function of planetary mass,
stellocentric distance, and the age and type of the host star.
Title: Measurements of Atmospheric Trace Gases from Space
Abstract: Over the last half-century, the use of satellite-based
instrumentation to measure the terrestrial atmosphere has enabled global remote
sounding of atmospheric constituents. These global observations are important
for the study of the Earth's climate, weather, and for information on air
quality and pollution sources. In the remote sounding group of AMP, we use
spectroscopic measurements of the atmosphere from several satellite instruments
working in the ultraviolet, visible and infrared regions of the spectrum to
derive information on the distribution of trace gases in the Earth's
atmosphere, with a particular focus on tropospheric pollution. These trace
gases include ozone, BrO, formaldehyde, glyoxal and SO2, and have both
anthropogenic and natural sources.
Title: A Wide Field Narrowband Survey for Star Forming Galaxies at Different Eopchs: Lyman Alapha Emitters at Redshift 5.7
Abstract: Narrowband surveys are a well-established tool for finding
star-forming galaxies at different epochs. I will present the Wide Field
Imager Lyman Alpha Search (WFILAS). This survey was designed to find
Lyman-alpha (Lya) emission line galaxies at a redshift of 5.7. I will present
the WFILAS sample of seven Lya emitters. I will show spectra of two of the
sources and show evidence for a second line component redward of Lya.
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