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List of talks given during the summer of 2009 by SAO scientists
Links to:
Program of the SAO Summer Intern Symposium, August 12, 2009
Abstracts for posters presented at the January, 2010 AAS meeting
INTERN: Ingrid Beerer (UC Berkeley)
ADVISOR: Dr. Joe Hora
PROJECT TITLE: Analyzing Optical Spectra of Massive Stars and Young Stellar Objects in Cygnus-X
Abstract:
We are conducting a Spitzer Legacy survey of the Cygnus-X complex, with the
following goals: 1) to analyze the evolution of high mass protostars with a
large and statistically robust sample at a single, known distance, 2) study
the role of clustering and triggering in high mass star formation, 3) sudy
low mass star formation in a massive molecular cloud complex dominated
by the energetics of ~100 O-stars, and 4) determine what fraction of all
young low mass stars in the nearest 2 kpc are forming in this one massive
complex. The data have been obtained during the past couple years,
preliminary catalogs and mosaics have been completed, and candidate young
stellar objects (YSOs) have been identified.
We obtained optical spectra using the FAST instrument during the fall of
2008 of two samples of objects in the 2x2 deg field near DR21 in Cygnus-X.
First, we observed the YSO candidates that are sufficiently optically
bright that have been identified by the IRAC and near-IR observations in
the DR 21 field. In addition, we observed another sample of stars
identified from optical surveys as being possible O or B type stars. Much
of the Cygnus region has not been adequately surveyed to sufficiently
characterize the population of the most massive stars that generate the
majority of the UV flux in the region. To understand the effects of these
massive stars on their environments and possible triggering of star
formation in the surrounding clouds, we must have a census of the massive
stars in the region. We obtained data on approximately 200 stars that
fall in the color-magnitude region consistent with O or B-type
stars. The summer project will involve using stellar classification
software to analyze the FAST data to determine the stellar types of
the candidate O and B stars, and to produce a catalog of the most
massive stars in the DR21 neighborhood. The spectra of the YSO stars
will also be analyzed, along with the IR photometry from the Spitzer
Cygnus-X survey, to verify the classification of these objects as
YSOs, and to determine the age and mass of the stars.
Reference websites:
INTERN: Ian Czekala
ADVISOR: Dr. Sean Andrews
PROJECT TITLE: SMA and Spitzer Study of the Protoplanetary Disk around HD 98800
Abstract:
ADVISOR: Dr. Alicia Soderberg
PROJECT TITLE: Diversity of Massive Stellar Explosions
Abstract:
While our understanding of some basic aspects of stellar death date
back several decades, recent findings are forcing us to fundamentally
rethink the ways in which massive stars die. In the basic picture,
the stellar core exhausts its nuclear fuel and collapses spherically
to a neutron star or black hole, thereby generating a shockwave that
explodes the star. About 99 percent of the explosion energy is
expected to be emitted in neutrinos, with the remaining energy
propelling several solar masses of ejecta to velocities of 10,000
km/s. The radioactive decay of freshly synthesized Nickel-56 gives
rise to bright optical emission that peaks days to weeks after the
explosion, the observed signpost for a new supernova.
This simple scenario, however, cannot explain the observed intimate
connection between relativistic gamma-ray burst jets and spherical supernova
explosions. To that end, I have designed a comprehensive observational
program for an REU student to map the diversity of supernova properties
and environments in comparison to those of gamma-ray bursts.
Project 1: An Optical Study of Type Ibc Supernovae and Comparison to Gamma-ray Burst Supernovae
Type Ibc supernovae represent the explosive death of the most massive
stars in the Universe. They represent 10 percent of all local
supernova discoveries. We now know that a small fraction of Type Ibc
supernovae (less than 1 percent) also produce gamma-ray burst jets during
the explosion. However, the burning question remains, why are only
some supernovae able to produce gamma-ray bursts? Possibilities
include the progenitor star properties: energy and/or metallicity.
Using optical data from the robotic Palomar 60-inch telescope for a
sample of two dozen local Type Ibc supernovae, the student will
perform photometry on the images and construct optical light-curves
for each supernova. Since the light-curve is powered by the
radioactive decay fo Nickel-56, the student will fit some simple analytic
models to estimate the mass of Nickel synthesized in the explosion
and compare to the light-curves for gamma-ray burst supernovae.
Through this statistical comparison we will answer the question of
whether gamma-ray burst supernovae are more energetic and hence
synthesize a larger mass of Nickel. This very important result will
result in a first author paper for the student by the end of the summer.
Project 2: A Detailed Study of the Host Galaxies of Type Ibc Supernovae
We will test whether metallicity is the key parameter that enables
some Type Ibc supernova progenitors to produce gamma-ray bursts while
most cannot. Unfortunately we can't measure the metallicity of the
dying star after the explosion. However, low metallicity stars are
likely to be found in low metallicity galaxies. Therefore, by
studying the properties of the host galaxies of Type Ibc supernovae we
can learn about the properties of the progenitors. The student will
analyze a sample of spectra for two dozen Type Ibc supernovae and
extract the metallicity and star-formation rates. Through comparison
with models, we will extract information about the stellar population
in each host galaxy. These diagostics will be compared with the
properties of gamma-ray burst host galaxies as compiled from the
literature. Through this effort we will shed light on whether
gamma-ray burst progenitor stars are lower metallicity than those of
ordinary supernovae. This is a longer term project but we aim to
at least start it during the summer if the student is interested.
INTERN: Dan Gifford (University of Western Washington)
ADVISORS: Dr. Matt Ashby, Dr. Joe Hora
PROJECT TITLE: Deep Infrared Galaxy Counts
Abstract:
Hora and Ashby have already reduced and coadded the 100+ IRAC mosaics of
the field. Instead of basic data crunching, the student will be asked
to use SExtractor to generate the deepest-ever IRAC source count
measurements, to address quantitatively the effects of source confusion
in the field via simulations, and to interpret/compare the outcomes to
an abundant literature on this topic. We will investigate the use of
HST/ACS F814W counts as priors; we are also hoping to have available a
deep MMT/MMIRS K-band image of the field that may prove more useful for
this purpose by virtue of being a better match to the IRAC
wavelengths.
INTERN: Derek Huelsman (University of Cincinnati)
ADVISORS: Dr. Massimo Marengo, Dr. Nancy Evans
PROJECT TITLE: The Mysterious Case of the Cepheid Missing Mass
Abstract:
One would think that after 100 years of intense study, we should know
everything there is to know about Cepheids. That is not so. There is a
lingering mystery about their life, that even the most advanced
observations and theoretical works have not yet been able to solve.
This mystery concerns their mass. Whenever we have been able to
directly measure the mass of Cepheid stars, we surprisingly found a
number significantly smaller that the mass predicted by the most
advanced models of stellar evolution. Take Polaris, the nearest
Cepheid: its measured mass is as much as 10-15% smaller than the mass
theoreticians can account for. Where has this missing mass gone?
One possibility is that this mass has been lost along the way, blown
away by stellar winds as the star aged and entered the Cepheid phase
(Cepheid stars are not born as variables, they become Cepheids once
they reach their middle age). If that's what happened, then the
evidence of such event may be found by searching for the ejected
material still lurking in the neighborhood of these stars. The
infrared Spitzer Space Telescope, thanks to its unchallenged
sensitivity to the faint emission from the ghostly matter dispersed
in the interstellar medium, is the perfect tool to investigate this
hypothesis. To this aim, we have observed a sample of 29 nearby
Cepheids with the Spitzer's InfraRed Array Camera (IRAC). In this
dataset, we may find the missing clue to solve the long standing
mystery of the Cepheid mass discrepancy.
The summer intern:
INTERN: Li-Wei Hung (Ohio State University)
ADVISORS: Dr. Saeqa Vrtilek, Dr. Ryan Hickox, Dr. Bram Boronson
PROJECT TITLE: Suzaku X-Ray Spectra and Pulse Profile Variations during the Superorbital Cycle of LMC X-4
Abstract:
In this project the student will study the X-ray binary LMC X-4,
consisting of a 1.25 solar mass neutron star accreting from a 14.5
solar mass O8III companion. In addition to the pulse period and
orbital period, LMC X-4 has been observed to have a long-term period
(the superorbital period) caused by a precessing accretion disk that
periodically obscures the neutron star. The student will determine an
improved value for the superorbital period of LMC X-4 based on 13
years of RXTE and ASM data, and use it to accurately determine the
superorbital phase of three new Suzaku observations. The student will
analyze the phase-averaged X-ray spectra and energy-resolved pulse
profiles for the Suzaku observations, and interpret them in terms of
as simple model based on the reprocessing of hard X-rays by the
precessing accretion disk. This should result in a journal-worthy
paper.
INTERN: Nathan Sanders (Michigan State University)
ADVISORS: Dr. Nelson Caldwell, Dr. Jonathan McDowell
PROJECT TITLE: HII Regions and Planetary Nebulae in M31
Abstract:
With the MMT, I have collected spectra of over 3000 objects of
those various objects in M31. The spectra of HII regions and planetary
nebulae in particular can be used to measure gas-phase abundances, and thus
determine the radial abundance distribution in that galaxy,
something that was last done over 25 years ago, and even then using very
little data. The abundance distribution can then be used to determine
the galaxy's formation history and map out evidence of mergers. The
work will involve measuring the emission lines of the spectra,
developing programs to use line ratios to determine electron densities,
electron temperatures and then the Oxygen to Hydrogen abundance ratios.
INTERN: Evan Schneider (Bryn Mawr)
ADVISORS: Dr. Andrea Dupree, Dr. Nancy Brickhouse
PROJECT TITLE: Optical and Xray Signatures of Accretion in TW Hya
Abstract:
We carried out a world-wide ground based campaign simutaneously
with a long CHANDRA observation of the X-ray spectrum of TW Hya.
High resolution optical spectra were obtained of TW Hya with MIKE
on the Magellan telescopes that can be used to evaluate the presence of
'optical veiling' thought to be produced by the accretion continuum.
We want to know whether the amount of veiling and its variation are
related (or not) to the X-ray line emission. This will help to identify
the contributions of both accretion and coronal activity to the X-ray
emission, and determine the characteristics (steady or impulsive)
of the accretion process.
The data (both X-ray and optical) are in hand and are reduced and
ready for analysis. Software required includes IDL, and IRAF and possibly
specialized routines developed for this analysis. IDL will be used in
analysis mode as well as for developing plotting routines. Simple
statistics of means and variations will be used.
INTERN: Allison Strom (University of Arizona)
ADVISOR: Dr. Aneta Siemiginowska
PROJECT TITLE: Emission processes in parsec scale jets: sub-millimeter and X-ray connection
Abstract:
The sub-millimeter and millimeter wavelengths probed by the SMA are
critical to understanding the spectrum of relativistic particles that
are being accelerated within the core of the blazar source. The
particles that are responsible for the observed synchrotron emission
at ~300~GHz have Lorentz factors ~10^4 (for the expected magnetic
field of ~mGauss). These particles are responsible for upscattering
the IR and optical photons to GeV energies and are directly
responsible for the observed gamma-ray emission. Thus the variability
observed in the millimeter wavelengths gives the immediate information
about a change in the population of relativistic particles in the
emitting region. Any increase in the total flux in the millimeter band
must be related to a fresh population of newly accelerated
particles. The variability in the spectral shape gives us additional
measure of the particle energy distribution that is important for
inverse Compton modeling of the high energy emission observed in
X-rays and gamma-rays.
A sample of quasars that are bright in the sub-millimeter band has been
monitored with SMA and there is a set of lightcurves available in the
archive. We will characterize these lightcurves for each source and
study the sub-mm properties of these quasars. Do they all vary? Is
there any characteristic timescale? Are there any similarities between
different type of sources in their variability? We will also collect
the available archival X-ray and gamma-ray data to construct the
spectral energy distribution for the observed sources. This will allow
us to study correlations between different wave bands and also
discriminate between different classes of sources. We will estimate
basic physical parameters that are required to generate the observed
SED for the sources in the SMA sample.
INTERN: Anthony Wong (Ohio Wesleyan University)
ADVISOR: Dr. Soeren Meibom
PROJECT TITLE: A study of rich clusters of stars in our Galaxy through high-resolution multi-object spectroscopy
Abstract:
The Cygnus-X region is one of the brightest regions of the sky
at all wavelengths and one of the richest known regions of star formation
of the Galaxy. It contains as many as 800 distinct HII regions, a number of
Wolf-Rayet and OIII stars and several OB associations. Cygnus-X also
contains one of the most massive molecular complexes of the nearby Galaxy,
significantly larger than other nearby molecular clouds with OB
associations such as Orion A, M17, or Carina.
Home page of the Spitzer Cygnus-X Legacy Survey project
Spitzer Space Telescope homepage
With the growing number of planets found orbiting Sun-like stars, there is
increasing attention on the origins of our Solar System and others like
it. Direct observations of the reservoirs of planet-building material- the
disks around young stars - play a critical role in testing planet
formation theories. This project will use data from the Smithsonian's
Submillimeter Array (SMA), located on Mauna Kea, Hawaii, and the Spitzer
Space Telescope, to characterize the physical conditions in the unique
protoplanetary disk around the young multiple star system HD 98800. At an
age of 5-10 Myr, this system probes a critical time period in the
evolution of disk material and the potential birth of a planetary system.
Moreover, the HD 98800 system is an interesting test case to explore how
disks are affected by dynamical interactions with stellar companions.
The student working on this project will learn the basic tools and
techniques used to analyze millimeter interferometer data and infrared
spectral energy distributions. He/she will also gain valuable experience
comparing these data to theoretical models of protoplanetary disks and
interpreting the results. If time permits, there are opportunities to
extend the project to other disk targets. The project report should lead
to journal publication.
INTERN: Maria Drout
Massive stars end their short lives in spectacular explosions that are
visible to the far reaches of the Universe. These explosions give
birth to extreme compact objects -- black holes and neutron stars --
and play a crucial role in galaxy evolution through the injection of
metals and mechanical energy into their environments. Equally
important, through the synthesis of new elements, massive stars help
to fuel the formation of stars, planets, and ultimately life.
The student will analyze deep/faint galaxy counts at 3.6, 4.5, 5.8, and
8.0 microns in a uniquely deep Spitzer/IRAC survey field, the so-called
IRAC Calibration Field (IRAC-CF). This field is the deepest IRAC survey
field in existence in the four IRAC bands, and the deepest portion
covers four times as much area as the next-deepest survey, GOODS
Ultra-Deep. What's more, we anticipate an additional integration at 3.6
and 4.5 um this April that will be the equivalent of the total of all
existing data to date. These data make it possible to measure the
source counts in the IRAC bands at the very faintest levels, where they
suffer heavily from confusion.
Astronomers think that Cepheids are among the coolest stars. It all
started exactly 100 years ago, at the Harvard College Observatory,
when Henrietta Leavitt found one of the most widely used laws in
astronomy. By monitoring the brightness variations of Cepheid stars,
she discovered that the period of such variations was directly related
to their average brightness. This relation, once properly calibrated,
allows Cepheids to be used as powerful "standard candles", the first
step in a sequence of distance indicators that we still use today
to measure the size of the cosmo.
1) will reduce the already available Spitzer data using our data
reduction pipeline;
2) will remove the light of the central star (using our PSF
subtraction routines) to uncover the faint emission from diffuse
matter that may have been ejected from the star;
3) will measure with high precision the brightness of each star, and
derive the (still poorly characterized) period-luminosity relation
(the Leavitt Law) of the sample in the IRAC bands.
The results will be presented available to the community at the
January 2010 AAS meeting and will be the base for a refereed
publication.
An X-ray binary is a system containing a normal star orbiting a
compact object, where the compact object is either a neutron star of a
black hole, and the normal star fills its Roche lobe. In particular,
X-ray pulsars are rotating neutron stars that are powered by material
accreted from the normal companion. Because X-ray publsars have strong
magnetic fields, the matter follows the fields and falls into the
magnetic poles, generating pulses as themagnetic poles rotate in and
out of our line-of-sight. While the general picture of the accretion
mechanism is well known, the physics of the accretion near the
magnetosphere, where the neutron star's magnetic field begins to
dominate the flow, is not fully understood. By studying individual
X-ray pulsars in detail, we hope to gain a better understanding of the
accretion mechanism.
M31 is the nearest galaxy similar to our own, and the advent
of large ground based telescopes and the Hubble telescope has
recently made it possible to study individual parts of that
galaxy with nearly the same level of detail as has been done in the
Milky Way. Specifically, star clusters, HII regions, planetary nebulae
and individual bright stars have been cataloged, and observed via direct
imaging and optical spectroscopy. These data sets can be used in
studies of ages, abundances and velocities of various components.
A fundamental characteristic of low mass star formation is the accretion
of material from a circumstellar disk, channeled by magnetic fields, to the
stellar surface. One nearby star, TW Hya is the closest accreting T Tauri
type star. This object presents a unique opportunity to relate accretion
signatures in the optical spectrum to the high energy emissions in the
X-ray regime to understand the physics of the accretion process and its
relation to a magnetically-active stellar corona.
We will study non-thermal emission processes in quasars monitored by
SMA (sub-millimeter array). The observed non-thermal spectral energy
distribution from radio-gamma-rays is typically associated with the
parsec scale jet emission. In such model the observed radio spectrum
is due to the synchrotron emission from relativistic particles. The
main emission processes contributing to X-rays and gamma-rays are
related to the Inverse Compton scattering of the ``soft'' photons by
the relativistic particles. In the Synchrotron Self-Compton (SSC)
process the synchrotron photons emitted by the relativistic particles
are Compton scattered by the same population of particles. In the
External Radiation Compton (ERC) process the seed photons are located
outside a jet/shock region.
Clusters of stars born together in the same time and space, are critical
to our understanding of how stars form and evolve, and lay the foundation
for a wide range of studies in astrophysics. The intern working with me
will learn about stars and star clusters, and how to use high-resolution
spectra of stars to determine their properties, whether they are members
of a cluster or not, and if they have any close unseen companions. There
will be several possibilities for astrophysical study upon completion of
the data analysis - incl. stellar evolution, the evolution of stellar
rotation, comparative studies of single and binary stars, and stellar and
cluster dynamics. The intern will not have to write new computer code,
but will work with existing codes running on the Center for Astrophysics
super-computer cluster. The intern will not have to acquire new data for
his/her project, but if observing is scheduled during the summer period,
the intern will be included in the preparations for the observations, and
possibly in the observing.