RUI: Dynamic UC HII regions in Sgr B2: Flickering and Ionized Flows
I. Introduction & Motivation
Massive stars impact their environments in dramatic and fundamental ways: forming
deep in molecular cloud cores, depositing energy through molecular outflows, ionizing
their surroundings, and injecting vast amounts of energy and material into their
environments when they explode as supernovae (Zinnecker & Yorke 2007; Peters et al.
2011). Because of their short formation times (~105 years) and their location in high
density regions, the youngest massive objects can be more difficult to observe and to
understand than their low mass counterparts. The physical processes involved in the
formation of massive stars are actively debated in the literature (Zinnecker & Yorke
2007; McKee & Ostriker 2007; Mac Low & Klessen 2004). Two current models seek to
explain the formation process of high mass stars: either they form from the collision of
multiple lower mass stars in a stellar cluster (e.g. Bonnell et al. 1998), or they form like
low mass stars, by the infall of material through an accretion disk (McKee & Tan 2003).
Such disks have been observed around high mass protostars (e.g. Davies et al. 2010),
and their presence can solve some outstanding problems in massive star formation.
Recent modeling of the accretion process has also given insight into a number of other
outstanding issues in massive star formation.
The most massive stars in the Galaxy emit large amounts of ultraviolet radiation that
ionize their environments, creating HII regions. The first HII regions studied (“classical”
HII regions) were relatively large (D~100 pc). The advent of high-resolution radio
interferometers revealed that the ionized gas surrounding many young massive stars is
highly confined, and early studies (reviewed in Churchwell 2002) identified what were
called ultracompact (UC) HII regions (D~0.1 pc) and hypercompact (HC) HII regions
(D~0.01 pc). The earliest models to explain UC and HC HII regions assumed that they
were similar to classical HII regions, only smaller. That is, that they were steadily
expanding into their environments and that the ionizing star was fully formed (GalvánMadrid et al. 2011). These assumptions led to an apparent difficulty, dubbed the “lifetime
problem” (Wood & Churchwell 1989; Kurtz et al. 1994). The problem was that these
regions lasted longer than they should if they were simply expanding into their local
environments. A number of recent observations have led to a revision of these
assumptions. These include observations that (1) hot molecular cores are rotating and
infalling (e.g. Keto 1990), (2) resolved small-scale ionized gas and shows accretion
dynamics (e.g. Galván-Madrid et al 2009), (3) some UC and HC HII regions have rising
spectral indices (e.g. De Pree et al. 2004) and (4) a sample of UC and HC HII regions
have measured flux variations on timescales of years (e.g. Galván-Madrid et al. 2008).
These observations strongly suggest that the morphology and characteristics of UC and
HII regions may be related to the accretion processes that form massive stars.
II. Predictions and Detections of Flickering in Ionized Flows
It is only in the past few years that three-dimensional radiation-hydrodynamic numerical
simulations of the formation of HII regions in accretion flows have become possible.
These studies show that the dense, rotating, accretion flows required to form massive
stars quickly become gravitationally unstable. Recent high-resolution simulations (Peters
et al. 2010a) show that when accretion continues in the presence of ionizing radiation,
the UC HII region can be gravitationally trapped, and fluctuate over time between
trapped and extended states as infalling massive filaments of material interact with the
radiation field of the young massive star. As these “flickering” UC HII regions expand
and contract, they take on the shapes defined by the morphological classifications of
Wood & Churchwell (1989), Kurtz et al (1994) and De Pree et al. (2005). Magnetic fields
do not change the morphology of UC HII regions significantly. The resulting HII region
flickers between HC and UC sizes throughout the main accretion phase, rather than
monotonically expanding. Peters et al. (2010c) show that this behavior also solves the
UC HII lifetime problem (Wood & Churchwell 1989), since accretion continues for a
Figure 1 Figure 10 from Peters et al. (2010a), which shows UC HII region size and flux
variations resulting from large amounts of molecular gas accreting onto an HII region. The
figure shows the 2 cm continuum flux (green), the characteristic size of the HII region (blue),
and the rate of accretion to the star (red).
period ten times longer than the free expansion timescale for an HII region. The model
predicts that UC HII regions can experience scale length and flux variations of 5% per
year (Figure 1).
In a related paper, Galván-Madrid et al.
(2011) estimate that ~10% of observed UC
and HC HII regions should have significant,
detectable flux variations (of 10%) on
timescales of ~10 years. Indeed, such
fluctuations have been convincingly seen in
a few sources with multi-epoch VLA
observations (e.g. Cep A, Hughes 1988;
NGC~7358~IRS1, Franco-Hernandez &
Rodriguez 2004; G24.78+0.08, GalvánMadrid et al. 2008). Figure 2 shows one
such fluctuation detected by Galván-Madrid
et al. (2008). The primary scientific goals of
this proposal are to search for size and flux
variations in a large sample of UC and HC
HII regions, and to examine the properties
of the radio recombination line (RRL)
emission arising from those flickering
regions.
Figure 2 From Galván-Madrid et al. 2008. The
crosses indicate the positions of the components
A1 and B from Gaussian fits to the 1984.36
image. The negative residuals observed in the
difference image indicate a decrease of ~45% in
the flux density of component A1.
III. The Candidate Source: Sgr B2
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The Sgr B2 star forming region, located near the Galactic center is one of the most
luminous in the Galaxy, and is associated with a 106 MO giant molecular cloud (GMC). It
is an ideal source to search for flickering of UC and HC HII regions, because of the large
number of sources with a variety of morphologies located in a single field of view. The
region is highly extincted at optical and infrared wavelengths, but has been extensively
studied at radio wavelengths (Qiu et al. 2011, De Pree et al. 1998, Gaume et al. 1995).
Gaume et al. (1995) published the first high-resolution (beam = 0.25”, ~2000 AU) radio
images of the Sgr B2 Main, South and North star-forming regions. These original 1.3 cm
Very Large Array (VLA) continuum images were followed by H66 (1.3 cm) radio
recombination line (RRL) observations at the same resolution, lower resolution (beam =
2.5”) H52 (7 mm) RRL observations (De Pree et al. 1996) and high resolution (beam =
0.65”, ~600 AU) 7 mm continuum observations (De Pree et al. 1998). These final 7 mm
continuum observations revealed complex morphologies for a number of the sources
first imaged at 1.3 cm. Our previous H52 line observations (De Pree et al. 1996) had
insufficient spatial resolution and sensitivity to determine RRL parameters for the
individual 7 mm continuum sources discussed in De Pree et al. (1998). Higher resolution
H52a (7 mm) observations are presented in De Pree et al. (2011). The Sgr B2 Main
massive star forming region is shown in Figure 3.
Figure 3 The Sgr B2 Main 7-mm continuum image (left) and the 7 mm RRL profiles (right) from De
Pree et al. (2011). There are several peculiar sources with multiple-peaked profiles, and others that
show no clear line emission at all, possibly due to the limited bandwidth of the VLA correlator. These
line data have a bandwidth of 25 MHz and a velocity coverage of 150 km/s.
Galactic UC HII regions typically have high frequency recombination line widths of less
than 25 km/s (Osterbrock 1989). For example, the thermal width, assuming a constant
temperature inside an HII region of 8000 K, is 19.1 km/s (Keto et al. 2008). Jaffe &
Martin-Pintado (1999) found in a survey of Galactic UC HII regions that a substantial
fraction of the surveyed sources (~30%) had both radio recombination lines that were
significantly broader than the typical thermal profiles VFWHM > 50 km/s), and rising
spectral indices ( > 0.4, where S = ). They designated such objects broad
De Pree - 3
recombination line objects, or BRLOs. De Pree et al. (2004) found a similar fraction of
BRLOs in their 7 mm recombination line and continuum study of W49A. The exact
physical process that accounts for the presence of BRLOs is unclear, though the
combination of kinematically broadened lines and rising spectral indices is consistent
with ionized outflow, perhaps from a circumstellar disk, several examples of which have
been detected, e.g. K3-50A (De Pree et al. 1994).
IV. Observations of Sgr B2 with the VLA and EVLA
In 1989, the VLA was used to image the source-rich Sgr B2 massive star forming region
in the DnC, CnB and BnA configurations at 1.3 cm in the continuum and the H66 radio
recombination line (Gaume et al. 1995; De Pree et al. 1995, 1996). These data were
combined to produce high resolution 0.25” (2000~AU) images of the Sgr B2 Main and
Sgr B2 North regions, which together contain ~50 individual UC and HC HII regions.
My graduate work (1992-1996) focused on the origin and evolution of ultracompact (UC)
HII regions. As a graduate student and soon thereafter as an early career professor, I
made some of the first high resolution 7 mm observations of UC HII regions (e.g. Carral
et al. 1997, De Pree et al. 1996, De Pree et al. 2004), and worked to identify and
catalogue the 100+ sources in the Sgr B2 and W49A galactic star forming regions (De
Pree et al. 2005). Even when the 7 mm system was installed on all 27 VLA antennas (by
2000), high frequency work with the VLA was limited by the bandwidth and spectral
resolution of the old VLA correlator, and the advent of the EVLA (with its new correlator)
has opened up new vistas in observing high frequency radio recombination lines.
We have been awarded 20 hours of EVLA time to re-image this large sample of UC HII
regions in Sgr B2 at 1.3 cm with the three hybrid arrays (BnA, CnB and DnC) in the
continuum and H66 and H68 lines. At this wavelength, the Sgr B2 region contains 49
detected regions, 25 of which are hypercompact (HC), with physical diameters <5000
AU. The image from these combined data will have a beam of 0.25”. This work presents
one of the first attempts to carry out time domain astronomy in a massive star-forming
region, and detect the “flickering” of UC HII regions over a 22-year time baseline.
Specifically, these new 1.3 cm EVLA observations of the Sgr B2 will allow us to:
1. Determine the frequency and magnitude of UC HII flux and size fluctuations over
a 22 year time baseline (1989 to 2011) in one of the most source-rich massive
star forming regions in the Milky Way.
2. Constrain the theoretical models described in Peters et al. (2010a, 2010b, 2010c,
2011) and Galván-Madrid et al (2011).
3. Observe recombination lines with the improved spectral resolution and bandwidth
of the new EVLA correlator, and characterize line profiles and velocity gradients,
and
4. Examine the dynamics of sources with especially broad or multiply peaked line
profiles discussed in De Pree et al. (2011), and compare the RRL properties of
flickering sources with the predictions of Peters et al (2011b). We will
systematically look for kinematic signatures of H II region flickering. These
signatures could be shocks of ionized gas, line broadening or asymmetric line
profiles.
We will also make continuum and RRL observations at 7 mm in only the BnA
configuration to obtain morphological information in the continuum and RRLs at a short
De Pree - 4
wavelength recombination line at the highest available angular resolution of 0.06” (650
AU). These observations will allow us to:
1. Provide recombination line data at additional wavelengths (H52 and H53) to
diagnose the role of pressure broadening in the most compact sources as
described in Keto et al. (2008) and De Pree et al. (2011), and
2. Better resolve the dynamics of the ionized gas – which can result from a
combination of rotation of the evaporating accretion flow and outflow – to test the
predictions of Peters et al. 2011b
Details: Continuum Observations of Sgr B2
We will use the EVLA to observe Sgr B2 in the 1.3 cm continuum in the DnC, CnB and
BnA configurations between January-September 2012. We expect a continuum rms
noise of 10.3 microJy/beam (20.46 GHz) and 14.1 microJy/beam (22.36 GHz) and a
continuum rms noise of 22-24 microJy/beam (45.45 GHz) and 17-19 microJy/beam
(42.95 GHz). While noise characteristics are better away from the H2O line near H66
the observations are planned in order to match frequencies exactly to the 1989 VLA
observations. We will observe the 7 mm continuum in the BnA configuration only. At 1.3
cm, we were awarded 4 hour tracks in each configuration, resulting in 3 hours on source,
and one hour for bandpass and phase calibration. For the 7 mm observations, we were
awarded 8 hours total in BnA, to be split between Sgr B2 Main and Sgr B2 North, with 4
hours per pointing. The size of the primary beam at Q band will require separate
pointings for Sgr B2 Main and Sgr B2 North.
To search for the predicted brightness fluctuations in the sources in Sgr B2 Main and
Sgr B2 North, we will make 1.3 cm images using the DnC, CnB, and BnA observations.
Since the original 1.3 cm multi-configuration observations were made in 1989, the
proposed observations (to be made over a 9 month cycle from January to September
2012) will provide us with a 22 year time baseline over which to search for source
"flickering". Based on the predictions of Peters et al. (2010c) and Galván-Madrid et al.
(2011), at least two HII regions are expected to have variations larger than 50%. Other
sources are likely to show smaller changes, so that ~5-7 of the ~50 sources should have
flux variations above 10%.
We will compare the EVLA data with the archival 1989 VLA data to detect any
differences in the flux densities and sizes of the sources. The re-expansion of other
(previously undetected) sources, which is predicted to occur on ~100 year timescales,
could lead to the detection of new HC HII regions. One advantage of looking for
``flickering'' in the Sgr B2 region (as opposed to an isolated source) is that we do not
have to depend on the absolute flux calibrations of two observations separated by 22years. We should be able to easily detect any changes in the relative brightness
between sources imaged in the same field, since all of the sources in each field are
imaged simultaneously. With the weakest detected sources having source brightnesses
of 3-5 mJy/beam, and continuum rms noise measurements of approximately 10
microJy/beam, 10% fluctuations will be easily measurable.
Details: Radio Recombination Line Observations of Sgr B2
From January-September 2012, we will also carry out Dnc, CnB and BnA configuration
EVLA 1.3 cm observations of the H66(20.46 GHz) and H68 (22.36 GHz) lines and 7
mm observations of the H52 (45.45 GHz) and H53 lines (42.95 GHz). At 1.3 cm, we
will use 32 MHz sub bands for each recombination line (128 channels) giving 250 kHz-
De Pree - 5
wide channels. With 8 contiguous 32 MHz channels (in each RRL), we will have 512
MHz bandwidth in the continuum. In the DnC configuration, we expect rms channel
noise of 0.5 mJy/beam (H66 - smoothed over 2 channels), and 0.3 mJy/beam (H68).
Of course, the final noise will be improved considerably since we will combine three
arrays in the final image. At 7 mm, we will use 64 MHz sub bands for each
recombination line (128 channels) giving 500 kHz-wide channels. With 8 contiguous 64
MHz channels (in each RRL), we will have 1 GHz bandwidth in the continuum. In the
BnA configuration, we expect rms channel noise of 0.8-0.9 mJy/beam (H 53 and 1.01.1 mJy/beam (H 52). The proposed line observations will give ~420 km/s velocity
coverage and 3.25 km/s channel separation at 1.3 cm, and similar velocity coverage and
channel separation at 7 mm. This velocity coverage and spectral resolution is sufficient
to span the broadest known line sources and reveal details in the line profiles.
New recombination line observations will provide a marked improvement over the
existing VLA data. In particular, the previous VLA 7 mm observations of Sgr B2 Main (De
Pree et al. 2011) do not have sufficient bandwidth (150 km/s) or channel spacing (5.5
km/s) to show detailed line profile shapes or to fully explain the nature of the detected
BRLOs. The EVLA correlator will allow us to improve on the VLA's original velocity
coverage and velocity resolution by factors of ~2-3. With the synthetic recombination line
observations of Peters et al. (2011b), we will be able to compare the kinematics of the
ionized gas in the observed H II regions with the numerical models. We will
systematically look for kinematic signatures of H II region flickering. These signatures
could be shocks of ionized gas, line broadening or asymmetric line profiles. A
comparison between observations and simulations will allow a better interpretation of the
observed data, as well as constrain the validity of the numerical models.
Pressure Broadening: These new models have consequences for the dynamics of the
UC HII regions probed by radio recombination lines. Some of the Broad Recombination
Line Objects (BRLOs) with highly supersonic linewidths, first described by Jaffe &
Martin-Pintado (1999) and also detected by De Pree et al (2004) may be explained by a
combination of steep density gradients and pressure broadening within accretion flows
(Keto et al. 2008). The effects of pressure broadening may be important even at
wavelengths as short as 7 mm. However, there are also BRLOs where multi-wavelength
recombination line observations suggest that dynamical flows must play a role in the
detected linewidth (De Pree et al., 2011). These broad lines may result from a process
analogous to a low-mass protostellar bipolar outflow, or perhaps a fast, massive star
wind.
Keto et al. (2008) suggest that some of the broad lines in Jaffe & Martin-Pintado (1999)
are the result of pressure broadening, and that pressure broadening can have a
significant effect, even at frequencies as high as 45 GHz. However, Keto et al. (2008)
conclude that some sources certainly have broad lines related to gas motions, and that
multifrequency RRL observations can be used to determine the relative contributions of
thermal, pressure and kinematic broadening processes. Whether the broadening is due
to high densities (pressure broadening) or gas motions, this subset of UC HII regions
represents a distinct phase in the early lifetime of a forming massive star.
Even given the limitations of the older recombination line data, it is clear that some UC
HII regions in Sgr B2 show decreases in line width from 1.3 cm to 7 mm that are
plausibly explained by pressure broadening (e.g. F4, De Pree et al. 2011), while there
De Pree - 6
are others that show similarly broad lines at both wavelengths (e.g. F3 with V > 50
km/s or multiply peaked lines (e.g. F1) more consistent with an origin in dynamical flows
within the ionized gas. The new EVLA RRL observations will allow us to characterize the
line shapes, to search for correlations of line shapes with morphology, and to probe the
resolved dynamics of some of the sources. This kinematic information could be
especially important for the bipolar sources that may harbor outflows or winds,
processes that are not yet incorporated in the models.
With the available bandwidth, we will also be able to detect the He and C recombination
lines associated with the H66 and H68 lines. Previous observations (De Pree et al.
1995) detected the He66 line in 9 sources, and we expect that number will increase
with improved EVLA sensitivity. The proposed observations will allow us to determine
more accurate helium abundances, and perform a first search for carbon RRL emission
in the Sgr B2 region.
V. Results of Previous NSF Support
The PI of this proposal was awarded an NSF RUI grant in 2002 (AST-0206103,
“Ultracompact HII Region Evolution in Extreme Environments”). The work on AST0206103 resulted in the involvement of 9 undergraduate women in data reduction,
analysis, conference presentation, publications and outreach. The grant-supported work
led to 3 direct publications and 6 related publications (described below). The primary
scientific and educational goals of the proposal were all fulfilled, and are described in
detail below. The project successfully involved a significant number of women in both
science and directly related education and public outreach. Many of the participants in
the PI’s previous NSF grant have pursued careers in astrophysics and science
education and outreach. The PI’s previous NSF support had a significant impact on his
career, on his ability to collaborate with researchers in related fields, and on his success
in publishing and reporting his results at national meetings. Below are listed the goals of
the previous NSF(RUI) proposal and the related outcomes.
De Pree - 7
Scientific Goals
1.
To determine and tabulate the morphologies and physical characteristics of the
nearly 100 UC HII regions in the W49A, Sgr B2 and W51 star forming regions. This
tabulation will provide new statistics as to the various morphological types detected in
these regions. These statistics will provide the starting point for hydrodynamic models to
explain the source morphologies.
Result: The morphology paper was
published in May 2005 as an ApJ Letter
(De Pree et al. 2005). Several students
(J. DeBlasio, L. Davis, and A. Mercer)
were involved in this analysis and work.
The preliminary morphology tabulations
were presented at AAS conferences in
preceding years.
2.
To gauge the impact of extreme
environments (high density, high
temperature) on the evolution of UC HII
regions. Such environments are known
to exist (e.g. de Vicente et al. 1997), and
the physical parameters from these
regions will be used as initial conditions
in the simulations.
Figure 4 Velocity flow of ionized gas in the
Result: The presence of high density
proximity of a B0 star, generated with the VH-1
molecular material is sufficient to confine
code (A Mercer & J. Blondin). Gas velocities
UC HII regions, as shown in the 2-D
range up to a few tens of kilometers per second
simulations presented at the January
and could account for some of the broad lines in
2005 AAS meeting (Mercer et al. 2005).
Broad Recombination Line Objects (BRLOs).
Sarah Scoles and Katy Means also
worked on this computational project and
presented the results at a conference in January 2006.
3.
To formulate and execute computer simulations of the evolution of UC HII
regions in extreme environments. These models can be compared with the highresolution images and spectroscopy that have been gathered and will continue to be
gathered in the coming year in preparation for this project cycle. These models will be
run in collaboration with J. Blondin (NC State) from existing VH-1 codes to produce 2-D
and 3-D models of the evolution of UC HII regions in high-density environments and
density gradients.
Result: The modeling work was carried out inFigure
conjunction
withflow
John
(NCinState),
2: Velocity
ofBlondin
ionized gas
the
and A. Mercer received valuable computational
experience
atstar,
NC generated
State in the
summer
of
proximity
of a B0
with
the VH-1
2003. Figure 4 shows ionized gas velocity in the
star. These
results
codeproximity
(A Mercerof&aJ.B0
Blondin).
Gas velocities
were presented at two AAS meetings, but notrange
published.
is the
only part ofper
this
up to aThis
few tens
of kilometers
second
and could
account
formake
some of
the broad lines in
project that was not completed to my satisfaction,
though
we did
significant
Broad Recombination Line Objects (BRLOs).
progress in the modeling and forged new collaborations.
4.
To arrive at a plausible explanation of the nature of UC HII regions that
encompasses the observable morphologies, velocity fields and spectral indices of the
regions in these three giant star-forming clusters.
Result: This was an ambitious long-term goal of the project. The 2-D hydrodynamic
simulations, in addition to the continuum and radio recombination line results from both
the W49A and Sgr B2 results indicate the importance of outflows in a significant
percentage of ultracompact HII regions. The importance of kinematic effects was
explored in two papers, one related to the W49A data (De Pree et al. 2004), and one
De Pree - 8
related to the Sgr B2 data (De Pree et al. 2011). The line and continuum data were also
used in the analysis of data in a number of related projects, namely McGrath et al.
(2004), Qiu et al. (2008) and Smith et al. (2009).
Educational and Other Goals
1.
To continue to involve advanced undergraduate women in the process of data
acquisition, data reduction, computer modeling, data analysis, scientific writing, and
publication and presentation of results.
Result: Nine undergraduates (all women) worked
on this project over its lifetime. In the final year of
the project Katy Means (Vassar College), Sarah
Scoles (ASC ’07), and Jill Carson (ASC ’05) all
contributed to the success of the project. Katy
and Sarah carried out computational work, and
Jill Carson completed the web site design and
implementation, and the educational poster. The
involvement of students in the acquisition,
analysis and presentation of scientific data was
Figure 5 The Bradley Observatory
one of the great successes of this project. Sarah
logo was designed by Jill Carson
('05), who worked on the PI’s NSF
Scoles now works for the National Radio
(RUI) project in 2005. Jill was also
Astronomy Observatory in Green Bank, WV and
the designer of the web site in
writes a popular astronomy blog.
support of that project. She made
this logo for the observatory after
her graduation.
2.
To provide an easily accessible, FITS
format database of high-resolution imaging and
spectroscopy of these star-forming regions,
openly available to all astronomers.
Result: The Web site was designed, completed and implemented by Jill Carson, an
Agnes Scott College graduate who is now a professional
graphic
designer.
Jill later
Figure
1: Bradley
Observatory
designed the logo for Bradley Observatory, shown in Fig.
The site
all('05)
of the
logo 5.
designed
bycontains
Jill Carson
research and outreach information originally planned. who
The worked
FITS format
data
is
also
on the PI’s NSF (RUI)
available at the site, and has been since the end of the
project
in 2005.
The the
PI receives
project
in 2005.
She was
regular requests for use of these data.
designer of the web site for the
3.
To produce a pilot “white paper” on radio studies
of massive
star formation
for
project,
and designed
this logo for
the National Radio Astronomy Observatory (NRAO) as
model for aafter
series
thea observatory
herof such
papers to be used for NRAO Education and Public Outreach
(EPO).
graduation.
Result: These white papers were produced and are still available under the White
Papers tab on the web site. These white papers were shared with NRAO at the
completion of the project (2005).
4.
To maintain an openly available web site on the progress of this project.
Results: All data related to the project are still available on line. Since the conclusion of
the project, several requests were made for the FITS data, and colleagues have been
referred to this site to retrieve the data. Several publications (e.g. Harper-Clark & Murray
2009, Aulicino 2009) have resulted from the public availability of these data.
5.
By the end of the third summer, we will have submitted the final of the three
papers to be published. Aspects of the drafts of these papers will be the honors thesis
projects of the seniors involved in the project during the project cycle.
De Pree - 9
Results: The first paper related to this
research was published in January 2004 in
the Astrophysical Journal. The second paper
(on morphologies) was published as an ApJ
Letter in 2005. The final paper on the analysis
of the Sgr B2 line data was published in AJ in
2011. While the computational results were
not published, they were presented at two
AAS meetings, and their results led to other
valuable collaborations (e.g. this project).
6.
In the third year of the project, we will
Figure 6 The 30 foot diameter
produce a color poster of the W49A region
observing plaza at Bradley Observatory
that will be similar in size and format to the
represents the Sun in the Metro Atlanta
Solar System (MASS). Students also
recently produced 90 cm image of the
carry out night lab observations on this
Galactic center of N. Kassim (NRL) (poster
plaza.
was produced in a 24”x36” format). Result:
The final poster was designed and produced.
The poster layout was also done by Jill Carson, who was one of the students who
worked on the grant. The logo that she later designed for the Observatory is shown in
Figure 5.
Previous support from the NSF had a huge impact on this small Department, and on the
PI’s ability to both involve students in research, and maintain a viable research program
of his own. The results of previous NSF support definitely increased the PI’s visibility
among star formation colleagues, and led to a widening circle of collaborators.
VI. Project Goals and Timeline
The current project has a number of specific scientific and educational goals which are
listed below. In order to build on the success of our previous NSF grant, we hope to
increase the representation of minorities in the women who participate in this research
and outreach work.
Scientific Goals
1. To observe and image the Sgr B2 region (Main and North) at 1.3 cm and the Sgr
B2 Main region at 7 mm. The observations are scheduled for January, May and
August 2012.
2. To use the new 1.3 cm and 7 mm images to determine the frequency and
magnitude of UC HII flux and size fluctuations over the 22-year time baseline
(1989 to 2011) in one of the most source-rich massive star forming regions in the
Milky Way (Sgr B2, including both Sgr B2 Main and Sgr B2 North).
3. To use these new data (and our earlier continuum data) to constrain the
theoretical models described in Peters et al. (2010a, 2010b, 2010c). This work
will be carried out with Mordecai-Mark Mac Low and collaborators.
4. To observe and image the Sgr B2 region (Main and North) in 1.3 cm and 7 mm
recombination lines with the improved spectral resolution and bandwidth of the
new EVLA correlator. To characterize line profiles and velocity gradients. To use
these recombination line data to determine the relative contribution of kinematic
broadening in the UC and HC sources in Sgr B2 Main.
5. To use the new RRL data to explore the dynamics of sources with especially
broad or multiply peaked line profiles discussed in De Pree et al. (2011) and to
use recombination line data at an additional wavelength (H53) to diagnose the
De Pree - 10
role of pressure broadening in the most compact sources in Sgr B2 Main and
North. These RRL data will also be used to test RRL numerical predictions from
the modeling of Peters et al. (2011b).
Educational and other Goals
1. Involve 2 undergraduate women per year in the reduction, analysis and
presentation of EVLA data. Students will do most of their work in the summer
months (2013-2015), but will also do some work during the academic year as
part of the upper level course Astronomy 300 (Radiation) which will be taught in
the Fall of 2013 and 2015 according to our normal rotation.
2. Work with the Department of Art & Art History faculty member and graphic
designer Nell Ruby to improve the presentation of scientific the line and
continuum data to a popular audience in ways that have high impact.
3. Employ a student from the Agnes Scott College graphic design program to
design and maintain a web site that will convey the results of this project.
4. Produce an educational poster about massive star formation that will feature the
new 1.3 cm and 7 mm continuum images of Sgr B2. This image will be the result
of the 3 hybrid configuration imaging carried out over the period JanuarySeptember 2012.
5. To increase the diversity of majors in our Department by actively recruiting
incoming majors with the possibility of summer research internships at the
College.
Project Timeline
The project timeline will be built around my teaching load during the academic year
(typically 5 courses), the observing schedule for the EVLA data, and the increased
availability of students during summer months. The schedule is set on the basis of the
availability of NSF funding of this project in Fall 2012.
Year 0 (before the start of NSF funding)
Twenty (20) hours of EVLA time awarded for observations of Sgr B2 in the DnC, CnB
and BnA configurations will be scheduled in the 2012 calendar year during the three
hybrid arrays. The following dates are from the EVLA science site. Data will be available
no later than the end of the listed period.
a. DnC: 30 December 2011 – 17 January 2012 (1.3 cm) – 6h
b. CnB: 27 April 2012 – 14 May 2012 (1.3 cm) – 6h
c. BnA: 31 August 2012 – 17 September 2012 (1.3 cm and 7 mm) – 2x4h
During the summer of 2012, the PI will begin work on the continuum data reduction of
the DnC and CnB data. Because these are smaller arrays, and the Sgr B2 region has a
large number of bright sources, the imaging of these first data should be straightforward.
I will be applying to the Professional Development Committee (PDC) at Agnes Scott
College for funds to support a summer student who will help in the early analysis of
these DnC and BnC data. The full dataset will not be available until September 2012.
During the spring and summer of 2012, I will be starting the training of two
undergraduate students in the reduction of radio data using AIPS and CASA with
existing datasets. The PI will apply for internal (Agnes Scott College) funding to attend a
CASA data reduction workshop with students in February 2012. We will also make use
of the EVLA CASA high frequency spectral line tutorial available online.
Year I (September 2012 – August 2013)
De Pree - 11
Fall 2012: I will be teaching a normal academic schedule in Fall 2012, so it will be
difficult to make significant progress during the fall. The goal of my work that fall will
simply to integrate the BnA 1.3 cm continuum image into the existing continuum data. To
that end, David Wilner (CfA) will travel to Agnes Scott College for a week in order to
work on data reduction and analysis. He will deliver an Open House lecture at the end of
that week (October or November).
With Nell Ruby (Department of Art and Art History), the PI will identify a student who will
begin work on the design and development of a web site that will share the process and
the results of this grant with the public.
Winter 2012-13: I will plan to attend the January 2013 AAS meeting and at that meeting,
present the early results of the Sgr B2 1.3 cm continuum imaging. These results will be
preliminary to my summer 2013 work with two students on the comparison of the
continuum data to the models of Peters et al. (2010a).
Spring 2013: I will begin the continuum data analysis with the imaging of the 7 mm Sgr
B2 Main and Sgr B2 North data with undergraduate students. The early analysis of these
data will comprise the senior thesis of one student.
Summer 2013: The goal of the first summer will be to prepare for publication the
continuum 1.3 cm and 7 mm data sets with two students. This will comprise Paper I of
the three paper sequence that will come out of this proposal. The paper will be submitted
for publication in August 2013. The PI will also employ a design student who will prepare
web and print versions of the continuum data of the Sgr B2 star forming region. The print
version of the poster will be shared with local, regional and national middle and high
school science teachers for use in their classrooms. The PI will work with his existing
contacts with Decatur middle and high school teachers to both develop and share the
materials.
Year II (September 2013 – August 2014)
Fall 2013: The PI is eligible for a sabbatical leave in the Fall of 2013, and I will apply for
sabbatical for that semester. I will use my sabbatical time for collaborative visits to CfA
(Wilner) and the Museum of Natural History (Mac Low). These visits will be used to
make detailed analysis of the continuum data in comparison with the flickering UC HII
region models of Peters et al. (2010a).
Winter 2013-14: I will attend the January 2014 AAS meeting and present the preliminary
results of the comparison of the continuum images to the models. These results will be
preliminary to the summer 2014 work of preparing Paper II for publication.
Spring 2014: I will do preliminary writing of Paper II, comparing the continuum data to
the flickering models. The early analysis of these data will comprise the senior thesis of
one student.
Summer 2014: I will spend this summer preparing Paper II for submission with two
students. Co-I Mac Low will visit Agnes Scott College, or alternately I will visit the
Museum of Natural History in New York City. We will submit the paper for publication in
August 2014.
Year III (September 2014 – August 2015)
Fall 2014: The PI will finish reduction and begin analysis of the radio recombination line
data. David Wilner (CfA) will make a second visit to Agnes Scott College for work on
these recombination line data.
De Pree - 12
Winter 2014-15: I will attend the January 2015 AAS meeting and present the preliminary
results of recombination line data. These results will be preliminary to the summer 2015
work of preparing Paper III for publication.
Spring 2015: I will continue the reduction and analysis of the recombination line data.
This work will comprise the senior thesis of one student.
Summer 2015: I will spend this summer preparing Paper III for publication with two
students. Paper III will be the analysis of the multifrequency recombination line data.
These data will be compared with the models of Peters et al. (2011) that specifically deal
with predictions about recombination line emission. Paper III will be submitted for
publication in August 2015.
VII. Project Outcomes
The project outcomes will span the period of this grant, Fall 2012 – Fall 2015. Below we
list the specific outcomes of the scientific and educational programs, outcome
summaries, and dates. Students will be expected to be active participants in the
preparation of the poster, and the presentation of the results.
Scientific Outcomes
1. Poster I (AAS) – January 2013
This poster will be presented at the AAS meeting, and two students will
accompany the PI for the presentation. This poster will present the preliminary
reduction of the continuum data in Sgr B2 at 1.3 cm and 7 mm.
2. Paper I: Continuum Images– August 2013
This paper will present the continuum 1.3 cm and 7 mm data for Sgr B2 Main and
Sgr B2 North. Comprehensive tabulations will be made of the source positions
and flux densities for comparison with the archival Sgr B2 1.3 cm data.
3. Poster II – January 2014
This poster will be presented at the AAS meeting, and two students will
accompany the PI for the presentation. This poster will present the preliminary
comparisons of the continuum data in Sgr B2 to the flickering UC HII region
models of Peters et al. (2010a).
4. Paper II: Comparison of Continuum Data to Flickering Models – August 2014
This paper will present the comparison of the 1.3 cm continuum images to the
models of Peters et al. (2010a). The paper will be written in close coordination
with Peters, Wilner & Mac Low.
5. Poster III – January 2015
This poster will be presented at the AAS meeting, and two students will
accompany the PI for the presentation. This poster will present the preliminary
comparisons of the 1.3 cm and 7 mm recombination line data in Sgr B2 to the
line predictions for flickering UC HII regions in the models of Peters et al.
(2011b).
6. Paper III: Comparison of RRL data to Flickering Models – August 2015
This paper will present the comparisons of the 1.3 cm and 7 mm recombination
line data in Sgr B2 to the line predictions for flickering UC HII regions in the
models of Peters et al. (2011b). The paper will be written in close coordination
with Peters, Wilner & Mac Low.
Education and Public Outreach Outcomes
1. We will involve 2 undergraduate women per year in significant ways in the
research and outreach aspects of this grant.
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2. We will increase the diversity of our undergraduate major population by the end
of this grant in 2015 by actively recruiting minority students with an interest in
science. Students in the GEMS
program (see Impact Statement)
often come from
underrepresented minorities.
3. We will incorporate the research
of this grant into the regular
monthly Open House program
that is a 50-year tradition at
Bradley Observatory (Figure 7).
Students and faculty involved in
this grant will deliver a portion of
the Open House lectures in
2012-2015.
4. We will produce and distribute a
Figure 7 Bradley Observatory at Agnes Scott
high impact educational poster
College was built in 1949 and renovated in
on the topic of massive star
2000.
formation in the Milky Way
Galaxy, deigned by student, and
based on input from local middle and high school teachers.
VII. Intellectual Merit, Broader Impacts & Future Work
Intellectual Merit: This project endeavors to address significant outstanding questions in
massive star formation. If massive stars form via accretion, then accretion models (e.g.
Peters et al. 2010a) make specific predictions about the frequency of size and
brightness fluctuations that can be tested by the new EVLA observations. Line modeling
(e.g. Peters et al. 2011b) also makes predictions about line properties that will be tested
against high spectral resolution observations. The models of Peters et al. (2010c) predict
that accretion is stopped not by ionization, but by the fragmentation of the gravitationally
unstable accretion flow. Thus, testing the accretion model for massive stars can provide
insight into broader massive star formation issues.
The 1.3 cm continuum images will be compared with data taken in 1989, allowing for a
determination of how many of the nearly 50 regions have changed in size or brightness.
The EVLA observations will provide a definitive test of the flickering UC HII region model
(Peters et al. 2010a) and will be the first attempt to make time-domain (20 year baseline)
observations of a sample of UC HII regions. Time domain astronomy has been identified
in Astro2010 as Frontier Science. Whether or not flickering is detected, the new 1.3 cm
image will be the most sensitive, highest resolution radio frequency observation of the
prototype Sgr B2 massive star forming region. The previous 1.3 cm VLA image (Gaume
et al. 1995) has been used in a large number of studies of this region. The continuum
images will be made publicly available with the publication of Paper II (in year 2 of the
proposal). De Pree et al. (2011) discussed the broad RRLs in Sgr B2 Main detected at 7
mm. Only the EVLA has the spatial and the spectral resolution needed to properly
examine the Broad Line Recombination Objects (BLROs) in the crowded Sgr B2 starforming region.
Broader Impacts: Agnes Scott College is a small, liberal arts women’s college located in
the Atlanta metro area. The College has a long tradition in astronomy that stretches back
to the early part of the 20th century. The campus was established as a focal point for
De Pree - 14
astronomy outreach in 1949 with the construction of the on campus Bradley
Observatory. The monthly open house was started in 1949, and a portion of the lectures
during 2012-2015 will be delivered by faculty and students associated with this project.
The Observatory has a well-established outreach program, connecting it to area K-12
institutions and hosting over 1500 students each year. Agnes Scott is the only women’s
college in the SARA consortium, and the Department of Physics & Astronomy has a
record of success in sending women on to graduate work and careers in the sciences.
Agnes Scott College’s student population is 30% African American, 7% Hispanic and
45% Pell Grant recipients. This project will support the involvement of two
undergraduate students per year. Our experience with the PI’s previous NSF support
was that student involvement in observations, analysis, presentation and publication of
astronomical data led to success in graduate careers in astronomy.
This fall (2011), the College hosted the 10th Annual Georgia Regional Astronomy
Meeting (GRAM) with over 60 attendees from Georgia and South Carolina. This meeting
was established in 2002 by the PI and Loris Magnani, and the first two meetings were
held on the campus of Agnes Scott College. The PI and involved undergraduate
students will present progress on this research at the GRAM each year in addition to the
presentations described at national (AAS) meetings. Finally, Bradley Observatory is the
center of the Metro Atlanta Solar System (MASS). The MASS planets are located at high
visibility locations throughout Atlanta, including Hartsfield-Jackson International Airport
(85 million passengers/yr) and Sweetwater Creek State Park.
Future Work and Collaboration: During the course of this project, the PI will work with D.
Wilner, W. M. Goss and other collaborators to apply for time on ALMA. Our new 1.3 cm
and 7 mm EVLA data will motivate a search for high frequency RRL emission in the Sgr
B2 and W49A regions. These lines could potentially be used to trace accretion disks
around massive stars (Keto 2007).
VIII. Acknowledgements
The PI gratefully acknowledges the hard work of many colleagues in bringing this
proposal together, in particular Pamela Napier and Emily Kandetzski in the Office of
Sponsored Programs, and Jim Abbot for helpful edits to a draft of this document.
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