Leisa K. Townsley
Ph.D. Physics, University of Wyoming, 1994
Office: 405 Davey
Mailing Address: 525 Davey Laboratory, University
Park, PA 16802
Phone: (814) 863-7946
Fax: (814) 863-3399
Star formation, massive young stellar clusters, giant HII regions,
X-ray astronomy instrumentation.
My CV gives further details, including a list of publications.
My primary Penn State collaborators are Patrick Broos, Matthew Povich, and Eric Feigelson.
I am a member of the Penn State High Energy Astrophysics Group and the Chandra
X-ray Observatory Advanced CCD Imaging
Spectrometer (ACIS) Instrument Team. The ACIS
Principal Investigator is Penn State Professor Gordon Garmire.
The Chandra instrument teams provide expertise and support to
the Chandra X-ray Center.
Some of our current efforts on the ACIS Team at PSU include
developing methods to analyze faint diffuse X-ray emission pervading fields of point sources, developing
new techniques for photometry in extremely crowded ACIS fields, and
reconstructing ACIS point source spectra and lightcurves that have been
corrupted by photon pile-up.
Star Formation Science:
The above project website is
password-protected -- please contact me if you need access.
~~~We have submitted 16 papers to ApJS for a
Special Issue on the CCCP.~~~
The CCCP is a 1.2 Ms Cycle 9 Chandra Very Large Project to study the Great
Nebula in Carina, consisting of 22 ACIS-I pointings and covering ~1.4
square degrees on the sky, to a depth of ~60 ks. There are ~57
co-investigators divided into 7 science groups, with overall management
provided by myself as Principal Investigator.
Science groups and group leaders:
Data Products, Patrick Broos
Massive Stars, Marc Gagne' and Mike Corcoran
Revealed Stellar Populations, Eric Feigelson
Obscured Stellar Populations, Thierry Montmerle
Diffuse Emission, Leisa Townsley
Multiwavelength Studies, Nathan Smith
Global Synthesis, Sally Oey
The proposal abstract:
"The Great Nebula in Carina is a superb site to study the violent
massive star formation and feedback that typifies giant HII regions and
starburst galaxies. We propose to map the Carina star-forming complex
with a mosaic of 20 new 60-ks ACIS-I pointings as a testbed for
understanding recent and ongoing star formation and to probe its
regions of bright diffuse X-ray emission. We will provide a catalog of
multiwavelength properties of ~12,000 X-ray-selected stars. We will
explore superbubble confinement, shocks, cloud evaporation,
mass-loading of winds, ISM enrichment, and HII region energetics. We
will also examine Carina as a surrogate environment for our Solar
System's formation, where protoplanetary disks are bathed in harsh
winds and radiation from nearby massive stars."
My contributed talk on the CCCP from the Sept 2009 conference Chandra's First Decade of Discovery is available here as both a PDF file and video.
The Giant Extragalactic HII Region 30 Doradus
30 Doradus was observed very early in the Chandra mission using the
17'x17' ACIS-I array, for just 20 ks. Our two papers on those
early data described the extensive diffuse X-ray emission across the
field and the X-ray point sources.
We re-observed 30 Dor with ACIS-I in Chandra Cycle 6, with a 70+30 ks
GO+GTO program titled "30~Doradus: Our Starburst Microscope," PI
Townsley, co-I's E. Feigelson, P. Broos, K. Getman, M. Tsujimoto, B.
Brandl, and G. Garmire.
The proposal abstract:
The Giant Extragalactic HII Region 30 Doradus in the LMC
provides us with a unique view of the fundamental building block of the
starburst phenomenon in galaxies. It contains several extremely
rich stellar clusters 1--10 million years old and a new generation of
deeply embedded high-mass stars just now forming. HST and Spitzer
data show that the combined actions of stellar winds and supernovae
have carved the ISM into an amazing display of arcs, shells, pillars,
voids, and bubbles, ranging over spatial scales of 1--100 pc.
This is the GO contribution to a joint GTO+GO, 100-ksec observation of
30 Doradus. We will exploit Chandra's fine spatial resolution to
study the diffuse X-ray morphology on 1--10 pc scales and to study the
highest-mass O and Wolf-Rayet stars that shape it.
M17, Our Closest Giant HII Region
This Chandra Large Project from Cycle 7 was another combination of GO
and ACIS GTO programs (280 ks on the main cluster NGC 6618 + 92 ks on
an eastern pointing) and added to the original 40-ks GTO observation of
NGC 6618 from Cycle 2. This was the first clear discovery of soft
diffuse X-rays, probably from massive star winds, in the Chandra
project (see Townsley et al. 2003). The Cycle 2 data yielded ~900
X-ray point sources (Broos et al. 2007); the combined Cycle 2+7 data
show ~2700 point sources and the extensive diffuse hot plasma shown in
blue here (our Fire-breathing Dragon).
The Cycle 7 Large Project was called "Winds, OB Populations, and Young
Stars: New Science from M17," PI Townsley, co-I's P. Broos, Y-H.
Chu, E. Churchwell, E. Feigelson, G. Garmire, K. Getman, N. Grosso, T.
Montmerle, A. Tielens, M. Tsujimoto, and B. Whitney.
The proposal abstract:
We propose to use two ACIS-I pointings centered on the young, massive
OB cluster in M17 (the Omega Nebula) and on its powerful X-ray outflow
as a testbed for understanding recent and ongoing star formation in the
M17 complex and its environmental impact. This rich field is
perfect for studying X-ray emission from high-mass as well as
intermediate/low-mass stars and for comparing the X-ray luminosity
function in a high-mass complex to that in the closer, less powerful
Orion Nebula Cluster, recently established by a long Chandra exposure.
M17 is ideal for exploring the properties of diffuse X-ray emission to
elucidate wind/wind and wind/cloud shock physics in HII regions and for
studying embedded stellar clusters and massive protostars forming as
M17 interacts with its molecular cloud.
M17's O4-O4 Binary: The Eyes of the Dragon
The two O4 stars at the center of NGC 6618, separated by 1.8", are
clearly resolved in the Chandra data; both are bright X-ray sources and
one of them is highly variable. Their hard X-ray spectral
components are unusual for massive stars.
This image shows the ACIS event data binned up into an image with 0.25"
pixels. Point sources are marked by blue +'s. Their
extraction regions are outlined by red polygons. Source-finding
was performed on a maximum-likelihood reconstruction of this image,
enabling us to find close pairs and faint sources in the PSF wings of
Analysis of the two O4 stars proved to be quite the circus: one
of them is constant and always piled up, the other is unpiled until it
brightens, with the pile-up fraction changing as the source gets
brighter (corrupting its lightcurve as well as its spectrum).
Annular spectral extraction is impossible due to surrounding sources
and the fact that the region of overlap between the PSF wings of the
two O4 stars is also variably piled up (so I call it the Bowtie of
Death). Using our ACIS CCD simulator and the MARX Chandra
ray-tracing code, Patrick Broos built a tool to reconstruct an unpiled
spectrum as a way of handling these two O4 stars. Using the CCD
simulator, this tool makes a spatio-spectral model of the two O4 stars
to try to recover pile-up-free spectra and lightcurves. We are
testing this pile-up corrector on a number of Chandra targets.
X-ray study of these O4 stars is underway by Townsley, Broos, and our
colleague Marc Gagne' from West Chester University.
Spontaneous or Triggered Formation of a Giant HII Region?
These two ACIS-I pointings were obtained as separate GO programs, NGC
3576 (the lower pointing) in Cycle 5, followed by the upper pointing in
Cycle 9 to follow up the diffuse emission seen in the original dataset
-- that proposal included joint Spitzer time (the Spitzer data are in
the capable hands of Remy Indebetouw). An added bonus in the
Cycle 9 ACIS data was the discovery of a pulsar wind nebula around PSR
J1112-6103 and hard diffuse emission pervading a large cavity outlined
by heated dust, as seen in MSX, Spitzer, and now WISE data.
We have recently completed the point source extraction and validation
from these two pointings and find 1559 X-ray point sources -- a very
large number for a partially-embedded complex at 2.8 kpc.
For both observations I serve as PI; co-I's are P. Broos, Y-H. Chu, E. Feigelson, K. Getman, R. Indebetouw, and T. Montmerle.
The Cycle 9 proposal abstract:
Our understanding of massive star formation is uncertain at all levels,
from individual stars to massive stellar clusters to OB
associations. Our first Chandra observation of the Galactic giant
HII region NGC 3576 addressed one example of the first of these
problems: because hard X-rays penetrate even very large columns
of obscuring material, we were able to pinpoint massive, young,
embedded stars that remained undetected even at 3.5 microns, solving
the mystery of NGC 3576's missing ionizing sources. With a new
ACIS-I pointing and the first Spitzer observation of this target, we
will address the second two of these problems: how massive
clusters form and how they are related to the formation and evolution
of the larger-scale, unbound populations known as OB associations.
The Embedded Massive Cluster Powering NGC 3576
These ACIS images show the ionizing cluster powering the NGC 3576 giant
HII region. They have 0.25" pixels and show soft X-rays (0.5-2
keV) in red, hard X-rays (2-8 keV) in green. Point source
extraction regions from ACIS Extract are shown as blue polygons.
The rightmost image is ~1.5' x 1.5' and shows the bulk of the
cluster. The near image (~30"x30") shows the deeply-embedded
bright X-ray sources at the western edge of the cluster; many of them
are closely-spaced pairs or multiples. These are some of the massive stars responsible for the ionization of this
region. They are extraordinarily hard X-ray emitters -- the only
reason we detect them behind such large absorbing columns.
The Cycle 5 proposal abstract:
We propose a 60-ksec ACIS observation of the Galactic giant HII region
NGC 3576, to image and confirm a soft X-ray bubble suggested by ROSAT
data and likely due to flows created by the winds of OB stars powering
the HII region. This observation will also reveal the massive
stellar engine powering NGC 3576, shredding the molecular cloud from
which it formed, and triggering a new generation of massive star
formation. This target bears many similarities to the edge-on `blister'
HII region M 17 (the Omega Nebula), where such soft X-ray flows were
first confidently detected by Chandra. We hope to establish
whether these wind-blown bubbles, filled with hot X-ray-emitting gas,
are ubiquitous in blister HII regions (given O stars of sufficient wind
power) or unique to M 17 for some reason.
My Other Chandra Targets and Projects
The examples above are just a few of the massive star-forming regions
for which I have obtained Chandra data. Some of my other projects
are listed below.
- An ACIS-I mosaic of W3 North, Main, (OH), and IC 1795, plus a
mosaic of XMM pointings on HB3, a large supernova remnant just to the
west (this is a Chandra Large Project with joint XMM time)
- IC 1805 with two XMM pointings on the W4 superbubble (Chandra GO project with joint XMM time)
- Diffuse X-ray emission in the Orion Nebula Cluster
- G333.6-0.2, an embedded giant HII region in the G333 (RCW106) giant molecular cloud
- A Chandra Large Project on the Galactic starburst cluster NGC 3603
- An ACIS-I mosaic of the Rosette Nebula, including its ionizing cluster NGC 2244 and the Rosette Molecular Cloud
- RCW 49
- An ACIS-I mosaic of NGC 6357, including G353.2+0.9, G353.2+0.7, and G353.1+0.6
I am co-PI (with Eric Feigelson) on a multi-year NSF Astrophysics
project to link Chandra observations of young stellar clusters with
international groups developing theories and models of star
formation and evolution.
I am co-I (PI Eric Feigelson) on a multi-year NASA ADP project to study
20 young stellar clusters with Chandra, XMM, Spitzer, and 2MASS.
We are working with several groups around the world to include
high-quality ground-based imaging and spectroscopy in this effort.
I am working with NSF Postdoctoral Fellow Matthew Povich and University
of Wisconsin Professor Ed Churchwell to obtain near-IR imaging of
northern young stellar clusters with the WHIRC camera on WIYN.
ACIS is used for most Chandra observations. We typically
with the 2x2-CCD ACIS-I array, covering ~17'x17' on the sky. I
recently gathered up a short sampler of some ACIS Instrument Team science activities and software projects.
The Penn State ACIS Team has developed data and science analysis tools
and recipes, many of which are publicly available (others may be
supplied upon request because they change often). Please visit Tools for ACIS Data Analysis
to see what's available. Note that most of this software is in
IDL and was written by Patrick Broos. For an overview, please see
Pat's recent ApJ paper, Broos et al. 2010.
Software engineer Patrick Broos and I have developed Monte Carlo
simulations in IDL to understand the
of photons and particles with different types of X-ray CCD devices.
these simulations, we developed a technique to derive subpixel
of astronomical targets using the distribution of multiple-pixel
For some photon energies, this may result in a 10-fold improvement in
position estimation for ACIS. We are also using the IDL simulation code
model photon pile-up from bright point sources. In our ACIS
calibration efforts over the years, we used the CCD simulator to
of photon events by particle events, to derive the best split-event
threshold, and as a basis for a model of the entire ACIS instrument
The PSU ACIS CCD Simulator, developed by Patrick Broos and
and written in IDL, is available from our Simulator
Webpage. A detailed description of our methods is available in Townsley et al. 2002, NIMPA, 486, 716.
The back-illuminated (BI) chips in ACIS (S1 and S3) always
marked charge transfer inefficiency (CTI) due to their manufacturing
process. We worked on amelioration techniques for this kind of CTI
for several years before the Chandra launch. At the beginning of on-orbit operations
ACIS chips were damaged by radiation, so now they also exhibit CTI,
to a more severe degree than the BI chips.
Patrick Broos and I subsequently developed a technique to
energies and grades from CTI-corrupted data. Our IDL code
available and there is an ApJ
Letter (Townsley et al. 2000) giving a brief description of our
method. More details and results are on our old CTI
Corrector Webpage. A detailed description of our methods is available in Townsley et al. 2002, NIMPA, 486, 751.
As part of the ACIS Team's pre-launch calibration efforts, in
1995-1997 we spatially and spectrally mapped the transmissivity of the
(OBFs) at the University of Wisconsin Synchrotron
Radiation Center (SRC) as part of their
flight calibration. I managed a team of scientists, engineers, and
technicians at Penn State and MIT and worked with high-energy physicist
James MacKay and
the SRC staff to design and carry out suites of measurements on several
sets of these aluminized Lexan and Polyimide unsupported thin films (made by Luxel
that block UV and visual radiation. We developed specialized
procedures for handling this extremely delicate space hardware and
constructed a Class 100 cleanroom over the SRC beamline to adhere to
NASA requirements for X-ray mission flight units. Our
transmissivity uniformity measurements provided the
basic criterion for choosing the filters to be installed in the ACIS
in front of the focal
plane, to ensure that only X-radiation is detected by the CCDs. This
calibration effort involved five major institutions and produced the
spatial maps ever obtained on such films. The OBFs are
single-point failures for the ACIS camera (if they rupture Chandra+ACIS
turns into a really bad UV/visual telescope).
ACIS Spectroscopy Array Filter, actual size ~1"x6"
ACIS Imaging Array Filter, actual size ~2"x2"
Some Conference Presentations:
The Chandra Carina Complex Project
Contributed talk at "Chandra’s First Decade of Discovery," 22-25 September 2009, Boston, MA
Remarkable X-ray Emission from the Young O4-O4 Binary in M17
Poster at Contifest, a workshop honoring Peter Conti: "Hot Massive Stars... A Lifetime of Influence," 12-15 October 2008, Lowell Observatory
X-ray observations of massive star formation and feedback
Contributed talk at the 2008 ALMA Workshop
"Transformational Science with ALMA: the Birth and Feedback of
Massive Stars, Within and Beyond the Galaxy," 25-27 September 2008,
Chandra's X-ray View of Massive Star-forming Regions
Poster at "Eight Years of Science with Chandra" Symposium, 23-24 October 2007, Huntsville, AL
An X-ray Tour of Massive Star-forming Regions with Chandra
Contributed talk at the 2006 May Symposium, "Massive Stars: From Pop III and GRBs to the Milky Way," 8-11 May 2006, STScI
Parsec-scale X-ray Flows in High Mass Star Forming Regions
Contributed talk at IAU Symposium 227, "Massive Star Birth: A Crossroads of Astrophysics," 16-20 May 2005, Acireale, Italy
Spectra of the 30 Doradus Star Forming Region
Observations of 30 Doradus
Poster from the January 2001 AAS meeting in San
It reviews some of our preliminary spectral analysis of the ACIS
GTO observation of 30 Doradus and updates our work on CTI and response
matrices for ACIS front-illuminated CCDs.
Poster from the January 2000 AAS meeting in
It shows some of the early images of the ACIS data on 30 Doradus and
outlines our early attempts to correct CTI on ACIS front-illuminated
Image Releases and other Public Outreach:
Our friends in the Chandra X-ray Center E/PO group have done a great job over the years of publicizing my research.
Web page by Leisa Townsley (
Astronomy and Astrophysics
Penn State University