Past Interns and Projects: Summer 2009
 
 SAO Summer Intern Program Projects, 2009


Links to:

    List of colloquium talks given during the summer of 2009
    Program of the SAO Summer Intern Symposium, August 12, 2009
    2009 Summer Program Calendars for June , July , and August
    Abstracts for posters presented at the January, 2010 AAS meeting

 



INTERN: Ingrid Beerer (UC Berkeley)

ADVISOR: Dr. Joe Hora (OIR Division)

PROJECT TITLE: Analyzing Optical Spectra of Massive Stars and Young Stellar Objects in Cygnus-X

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.

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:
Home page of the Spitzer Cygnus-X Legacy Survey project
Spitzer Space Telescope homepage


INTERN: Ian Czekala (University of Virginia)

ADVISOR: Dr. Sean Andrews

PROJECT TITLE: SMA and Spitzer Study of the Protoplanetary Disk around HD 98800

Abstract:
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 (University of Iowa)

ADVISOR: Dr. Alicia Soderberg

PROJECT TITLE: Diversity of Massive Stellar Explosions

Abstract:
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.

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:
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.

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:
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.

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:
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.


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:
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.

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:
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.

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:
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 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:
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.

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:
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.

 
 

Clay Fellow Warren Brown