Christopher Gordon De Pree

Christopher Gordon De Pree
Agnes Scott College · Physics & Astronomy

PhD, University of North Carolina at Chapel Hill

About

75
Publications
2,844
Reads
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1,298
Citations
Citations since 2017
6 Research Items
446 Citations
2017201820192020202120222023020406080
2017201820192020202120222023020406080
2017201820192020202120222023020406080
2017201820192020202120222023020406080
Additional affiliations
June 1996 - present
Agnes Scott College
Position
  • Charles A. Dana Professor of Physics & Astronomy
June 1994 - June 1996
National Radio Astronomy Observatory
Position
  • PhD Student

Publications

Publications (75)
Article
Full-text available
We present new Jansky Very Large Array (VLA) images of the central region of the W49A star-forming region at 3.6 cm and at 7 mm at resolutions of 015 (1650 au) and 004 (440 au), respectively. The 3.6 cm data reveal new morphological detail in the ultracompact H ii region population, as well as several previously unknown and unresolved sources. In p...
Preprint
We present new Jansky Very Large Array (VLA) images of the central region of the W49A star-forming region at 3.6~cm and at 7~mm at resolutions of 0\farcs15 (1650 au) and 0\farcs04 (440 au), respectively. The 3.6~cm data reveal new morphological detail in the ultracompact \ion{H}{2} region population, as well as several previously unknown and unreso...
Article
We report the discovery of the first ¹⁴NH3 (2,2) maser, seen in the Sgr B2 Main star-forming region near the center of the Milky Way, using data from the Very Large Array radio telescope. The maser is seen in both lower-resolution (3″ or ∼0.1 pc) data from 2012 and higher-resolution (0.″1 or ∼1000 au) data from 2018. In the higher-resolution data N...
Preprint
We report the discovery of the first 14NH3 (2,2) maser, seen in the Sgr B2 Main star forming region near the center of the Milky Way, using data from the Very Large Array radio telescope. The maser is seen in both lower resolution (3" or ~0.1 pc) data from 2012 and higher resolution (0''.1 or ~1000 AU) data from 2018. In the higher resolution data...
Article
Full-text available
A number of ultracompact H ii regions in Galactic star-forming environments have been observed to vary significantly in radio flux density on timescales of 10–20 years. Theory predicted that such variations should occur when the accretion flow that feeds a young massive star becomes unstable and clumpy. We have targeted the massive star-forming reg...
Preprint
A number of ultracompact H II regions in Galactic star forming environments have been observed to vary significantly in radio flux density on timescales of 10-20 years. Theory predicted that such variations should occur when the accretion flow that feeds a young massive star becomes unstable and clumpy. We have targeted the massive star-forming reg...
Article
Full-text available
We describe the remote facilities operated by the Southeastern Association for Research in Astronomy (SARA), a consortium of colleges and universities in the US partnered with Lowell Observatory, the Chilean National Telescope Allocation Committee, and the Instituto de Astrofisica de Canarias. SARA observatories comprise a 0.96m telescope at Kitt P...
Article
Full-text available
We have recently published observations of significant flux density variations at 1.3 cm in HII regions in the star forming regions Sgr B2 Main and North (De Pree et al. 2014). To further study these variations, we have made new 7 mm continuum and recombination line observations of Sgr B2 at the highest possible angular resolution of the Karl G. Ja...
Article
Full-text available
We have used Very Large Array (VLA) observations of the massive star-forming regions W49A and Sgr B2, obtained with resolutions from 2 .0 to 0 .04, to classify the morphologies of nearly 100 ultracompact (UC) H ii regions. These high-resolution, multifrequency, multiconfiguration VLA observations motivate us to make several modifications of the exi...
Article
Full-text available
W49N is a mini-starburst in the Milky Way and thus an ideal laboratory for high-mass star formation studies. Due to its large distance (11.1$_{-0.7}^{+0.9}$ kpc), the kinematics inside and between the dense molecular clumps in W49N are far from well understood. The SMA observations resolved the continuum into two clumps. The molecular line observat...
Article
Full-text available
Accretion flows onto massive stars must transfer mass so quickly that they are themselves gravitationally unstable, forming dense clumps and filaments. These density perturbations interact with young massive stars, emitting ionizing radiation, alternately exposing and confining their HII regions. As a result, the HII regions are predicted to flicke...
Article
Full-text available
The Multi-scale Continuum and Line Exploration of W49 is a comprehensive gas and dust survey of the giant molecular cloud (GMC) of W49A, the most luminous star-formation region in the Milky Way. The project covers, for the first time, the entire GMC at different scales and angular resolutions. In this paper, we present (1) an all-configuration Subm...
Article
The Sgr B2 star forming region contains a large sample of ultracompact (UC) and hypercompact (HC) HII regions. The diversity of morphologies and number of unusual broad line sources make it an ideal laboratory for testing theories of UC HII region evolution. Recent high-resolution simulations that include heating from ionizing and non-ionizing radi...
Article
Full-text available
We have imaged the Sgr B2 Main region with the Very Large Array in the BnA configuration (θbeam = 013) in both the H52α (45.453 GHz) radio recombination line and 7 mm continuum emission. At a distance of 8500 pc, this spatial resolution corresponds to a physical scale of 0.005 pc (~1100 AU). The current observations detect H52α emission in 12 indiv...
Article
Full-text available
A tactile/Braille exhibit for the visually impaired community in the USA was launched in July 2009. The exhibit is part of the global From Earth to the Universe (FETTU) project, a Cornerstone of the International Year of Astronomy 2009. The science content of the travelling tactile/Braille exhibit includes explanations of our Sun, Eta Carinae, the...
Article
The Metro Atlanta Solar System (MASS) is a scale model solar system centered at the Bradley Observatory plaza on the campus of Agnes Scott College, a liberal arts women's college located in Decatur, GA. The MASS model was dedicated on September 11, 2009 in celebration of the International Year of Astronomy (IYA). One of the planets (Uranus) was ins...
Article
The greater Atlanta metropolitan area has been able to participate in the International Year of Astronomy in a number of ways, through local and national funding. The Hartsfield-Atlanta International airport has hosted a 7 month exhibition of over 50 images in From Earth to the Universe (FETTU), and the Atlanta Center for the Visually Impaired (CVI...
Article
Full-text available
We have used the VLA to observe SiO(v = 0, J = 1-0) at 43.4 GHz in the IRc2 region of Orion with 2'' resolution. Both a thermal component and a maser component are detected, making IRc2 the only known star-forming region with an SiO vibrational ground-state maser. The maser emission is double peaked and is extended over ~900 AU with the same positi...
Article
Full-text available
We have carried out a multifrequency, multiconfiguration VLA observational program of the massive Galactic star-forming region W49A (D = 11.4 kpc). Radio continuum observations were carried out at 0.7, 1.3, and 3.6 cm. In the highest sensitivity 3.6 cm images, we have detected 45 distinct continuum sources (located within a ~4' [13 pc] diameter reg...
Article
Using the Very Large Array, we have observed the H66α radio recombination line (RRL) emission at 1.3 cm and the H52α RRL emission at 7 mm toward the ultracompact H II region M17-UC1 and the nearby arc-shaped structure to the east. The angular resolution of the data is 1''-2''. The compact H II region (deconvolved size ~06 or 0.006 pc) is one of a n...
Article
Full-text available
The ionized gas in the Sagittarius B2 Main star-forming region has been imaged with ~65 mas (600 AU) resolution using the Very Large Array (VLA) at 7 mm in the A configuration. These observations have ~4-5 times the resolution of the previous highest resolution images of this source. These VLA observations show that the central four ultracompact H...
Article
We present high spatial resolution Gemini mid-infrared images of the ring of ultracompact (UC) HII regions in W49A, and use the images to identify the driving source of the powerful H$_2$O maser outflow. We locate the origin of the outflow at the position of the compact mid-IR peak to within 0$\farcs$07. This IR source is not coincident with any of...
Article
Full-text available
We report here on a survey of carbon recombination lines (RLs) near 8.5 GHz toward 17 ultracompact H II regions (UCHs). Carbon RLs are detected in 11 directions, indicating the presence of dense photodissociation regions (PDRs) associated with the UCHs. In this paper, we show that the carbon RLs provide important, complementary information on the k...
Article
Full-text available
We present 7 mm observations of the W49 North (W49N) massive star forming region, made with the Very Large Array, that detect recombination line emission from individual ultracompact H II regions on 50 mas (600 AU) scales. These recombination line observations, together with multifrequency continuum imaging, indicate that 5-7 of the 18 ultracompact...
Article
Full-text available
We present subarcsecond resolution observations of the star-forming region W49N made with the Berkeley-Illinois-Maryland Association array at 1.4 mm wavelength in the continuum and CH3CN J = 12-11 lines. The continuum image, at a resolution of 018 (2000 AU), shows many of the previously identified ultracompact H II regions and at least one new sour...
Article
Full-text available
We have observed the ionized gas in the star-forming region W49N with the National Radio Astronomy Observatory Very Large Array (VLA) at 13 mm and 7 mm, and with the Berkeley Illinois Maryland Association (BIMA) Array at 3.3 mm. These observations vary in resolution from 0045 to 035 (500 AU to 4000 AU at a distance of 11.4 kpc). In addition, we hav...
Article
Full-text available
Using the Very Large Array (VLA) of the National Radio Astronomy Observatory in the A and B configurations, we have obtained simultaneous high-resolution observations of both the 22 GHz H2O maser lines as well as the 22 GHz continuum for the H II regions W49N and Sagittarius B2. The angular resolution of both observations is ~ 01, which at the dist...
Article
Full-text available
We present Spitzer Space Telescope IRAC and MIPS observations toward a sample of nine high-mass star forming regions at a distance of around 2 kpc. Based on IRAC and MIPS 24 mum photometric results and 2MASS JHKs data, we carry out a census of young stellar objects (YSOs) in a 5'×5' field toward each region. Toward seven out of the nine regions, w...
Article
Full-text available
Absorption in the J = 211–212 transition of formaldehyde at 2 cm toward the ultracompact H II regions C1 and C2 of W58 has been observed with the Very Large Array with an angular resolution of ~02 and a velocity resolution of ~1 km s-1. The high-resolution continuum image of C1 (also known as ON) shows a partial shell that opens to the northeast. S...
Article
Full-text available
We have carried out 8.3 GHz hydrogen and helium radio recombination line and continuum observations of three Galactic H II regions with the NRAO 140 Foot Telescope and the Very Large Array. These observations measure the spatial variations in the singly ionized helium-to-hydrogen abundance ratio, 4He+/H+ (y+), and probe for any localized enhancemen...
Article
Observations of W49N and Sgr B2 were carried out with the VLA in both A and B configurations using the correlator in line mode with two intermediate frequencies (IFs) at 22GHz, in 1998 and 1999. (1 data file).
Article
The IYA 2009 working group on Research Experience for Students, Teachers, and Citizen-Scientists is planning a multi-year project involving occulting systems. The project will include both observing and data analysis components. It begins with training programs of several types of binary and transient variable stars that are easy to observe from su...
Article
Spitzer IRAC and MIPS observations toward high-mass star forming regions are presented. With the photometry from the IRAC and 2MASS, we derive the magnitude-color and color-color diagrams to investigate evolutionary stages of the YSOs in the fields. Toward sources well resolved in MIPS 24mum and/or 70mum, we fit their SEDs combining the (sub)mm dat...
Article
Full-text available
We have detected C91alpha (8.5891 GHz) emission toward four ultracompact H II regions (UCHs; W49G, J, L, and C) in the W49 North massive star-forming region with the Very Large Array (VLA) at 3" resolution. No carbon line emission was detected toward UCHs W49F, A, O, S, and Q at this frequency to a 3 sigma level of 2 mJy. We also observed the same...
Article
The distribution and density of molecular material strongly influences the evolution of ultracompact (UC) HII regions. We have modified the Virginia Hydrodynamics code (VH-1) to simulate the evolution of UC HII regions in a variety of densities . We have verified the results of analytical investigations (e.g. De Pree, et al. 1995) of the dynamic in...
Article
We have recently imaged the Sgr B2 Main region with the Very Large Array in the BnA configuration in both H52alpha line and 7 mm continuum emission. This study is part of a larger effort to characterize high frequency recombination lines in ultracompact and hypercompact HII regions in the Galaxy. In particular, these observations supplement lower r...
Article
The research on massive star formation has advanced significant over the last decade via ground-based observations at the near-infrared and mm wavelengths. However, the important mid-infrared regime has been largely neglected. We propose to observe eight carefully selected regions of massive star formation, which have been studied extensively with...
Article
We have developed a code to simulate the evolution of ultracompact (UC) HII regions using the Virginia Hydrodynamics code (VH-1), a numerical inviscid code built on the piecewise parabolic method (PPM) developed by Collela and Woodward (1984). We have investigated the dynamic interaction of the photo-ionized Stromgren region with the young massive...
Article
We present completed morphological classifications and physical parameters for a sample of approximately 100 compact and ultracompact (UC) HII regions in the W49A, Sgr B2 and W51 massive star forming regions. These classifications and parameters are based on VLA 7 mm and 3.6 cm images of W49A, 7 mm and 1.3 cm images of Sgr B2, and 7 mm images of W5...
Article
Full-text available
Using the VLBA and the phase VLA, the extragalactic source 3C138 has been re-observed in the Galactic HI absorption line on December 2, 1999. These new observations are compared with the previous HI absorption line data of Faison et al. (1998). For both epochs, the spatial resolution is 20 mas and the velocity resolution is 0.49 km/s. The new d...
Article
Full-text available
Recent 7 mm observations of the W49A North massive star-forming region have detected radio recombination line (RRL) emission from ultracompact HII regions on 50 milliarcsecond scales. These observations, combined with multifrequency, high-resolution continuum imaging of the region at 7 mm with the VLA and at 3 mm with BIMA, indicate that several of...
Article
Spectral line observations of the W49A North massive star forming region made with the Very Large Array (VLA) have detected H52alpha (7 mm) radio recombination line (RRL) emission from 15 ultracompact HII regions on 50 milliarcsecond (600 AU) scales. Seven of the sources were unresolved in previous spectroscopic observations of the region. These sp...
Article
Absorption in the J_{K_-,K_+} = 211-212 transition of formaldehyde at 2 cm towards the ultracompact HII regions C1 and C2 of W 58 has been observed with the Very Large Array with an angular resolution of 0.2'' and a velocity resolution of 1 km/s. The high resolution continuum image of C1 (also known as ON 3) shows a partial shell which opens to the...
Conference Paper
We present several laboratory exercises used with a commercially available optical/IR spectometer. The room-temperature spectrometer, produced by OceanOptics, has an optical fiber feed and provides 0.3 nm/pixel resolution with good sensitivity. Students are able to use a PC to obtain spectra of black body sources, gas discharge tubes, and the solar...
Article
Full-text available
We have observed the ionized gas in W49N with the Very Large Array (VLA) at 13 mm and 7 mm, and with the Berkeley Illinois Maryland Association (BIMA) Array at 3.3 mm. These observations vary in resolution from 0.35\arcsec to 0.045\arcsec (0.019 to 0.0025 pc at a distance of 11.4 kpc). In addition, we have used the VLA to observe water maser emissi...
Article
Full-text available
NGC 3576 (G291.28-0.71; l=291.3o, b=-0.7o) and NGC 3603 (G291.58-0.43; l=291.6o, b=-0.5o) are optically visible, luminous HII regions located at distances of 3.0 kpc and 6.1 kpc, respectively. We present 3.4 cm Australian Telescope Compact Array (ATCA) observations of these two sources in the continuum and the H90a, He90a, C90a and H113b recombinat...
Article
We present observations from the Very Large Array (VLA) in A and B configuration at 43 GHz and 22 GHz of the energetic star forming region W49N. Maser features in this source extend between velocities -260 km/s and +270 km/s. Positions and fluxes were calculated for 312 H2O masers with resolutions between 0.045" and 0.30". The weak continuum was cr...
Article
Standard Big Bang Nucleosynthesis predicts that greater than 90% of the observed 4He in the Galaxy should have been produced during the era of primordial nucleosynthesis. Observations of the primordial 4He/H abundance ratio from metal poor galaxies vary from 0.0764 -- 0.0803 by number. Additional production of 4He comes from the evolution of stars....
Article
NGC 4258 (M106) is a nearby (7 Mpc, 0\farcs1 = 3.5 pc) active spiral galaxy, distinguished by long (5' projected extent), narrow (5\arcsec) radio jets. The jets are jointed, linear segments that are embedded in diffuse plateaux of radio and X-ray emission. They flow close to the galaxy gas disk, entraining and shocking the ISM; X-rays with a therma...
Article
We have observed ionized gas in the Sagittarius B2 Main (Sgr B2 M) star forming region with ~ 60 mas (500 AU) resolution using the Very Large Array (VLA) in ``fast-switching'' mode at 7 mm. These images have 40 times the resolution of the best published images at this wavelength. These high resolution observations have revealed extremely high emiss...
Article
The Galactic center star-forming region Sagittarius B2 Main [Sgr B2 (M)] has been observed with the Very Large Array in the continuum (7 mm and 1.3 cm) and in the radio recombination lines H52α, H66α, and He 66α. The H66α(˜0".25 resolution) and H52α(˜2".5 resolution) data provide high spatial resolution kinematics of the ionized gas associated with...
Article
In an ongoing study of high-mass star formation regions in the near infrared (1-5 μm), we present J (1.2 μm), H (1.65 μm), K (2.23 μm), and L" (3.81 μm) broadband images as well as Brγ (n = 7 4, → 2.166 μm) and Brα (n = 5 4, → 4.052 μm) hydrogen recombination line images, and 3.29 μm unidentified feature emission images of the K3-50 H II regions K3...
Article
The Galactic center star-forming region Sagittarius B2 Main [Sgr B2 (M)] has been observed with the Very Large Array in the continuum (7 mm and 1.3 cm) and in the radio recombination lines H52α, H66α, and He 66α. The H66α (∼0.″25 resolution) and H52α (∼2.″5 resolution) data provide high spatial resolution kinematics of the ionized gas associated wi...
Article
Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 1996. Bibliography: leaves 207-215.
Article
HII regions in the earliest stages of their evolution are typically embedded deep in molecular clouds and unobservable at optical frequencies. At radio frequencies, however, the ionized gas distribution and kinematics may be imaged with high spatial ( ~ 0\farcs5) and spectral ( ~ 5 km s(-1) ) resolution. We have undertaken an extensive, multi-frequ...
Article
We have observed the Sagittarius B2 (Sgr B2) North star-forming region with the Very Large Array in the continuum (1.3 cm) and in the radio recombination lines H66α and He66α. Sgr B2 North contains regions of ionized gas ranging in size from unresolved (d < 0.01 pc) to extended (d ˜ 0.5 pc) and thus presents an ideal laboratory to study the effects...
Article
The radio continuum toward the Sgr B2 region of star formation has been imaged at a wavelength of 1.3 cm with a spatial resolution of ≍2000 AU (0".25) and a sensitivity of ≍0.4 mJy beam-1. These high-quality images show many newly detected continuum components and reveal remarkable features associated with several previously known H II regions. Cur...
Article
Full-text available
Two compact components of the NGC 6334 star-forming region have been imaged in molecular and ionized gas at high spatial and spectral resolution with the Very Large Array. The H II region NGC 6334A has been imaged in the radio continuum at 6, 3.6, and 2 cm, and in the recombination lines H76α (2 cm) and H92α (3.6 cm). NGC 6334F has been imaged at 6...
Article
Very Large Array (VLA) 20 cm continuum observations (2 sec x 1 sec resolution) of the Sgr B2 star-forming region have been carried out. The peak intensity, which occurs at the location of the Sgr B2 F complex of H II regions, corresponds to a brightness temperature of 23,000 K. The continuum spectrum appears to be thermal; thus the brightness tempe...
Article
Full-text available
Ultracompact H II regions (UCHIIs) are defined as regions of ionized gas with diameters smaller than ˜0.1 pc. H II regions are expected to expand at velocities of the order of the sound speed (10 km s-1) until reaching equilibrium at dimensions of a few pc. In regions with density of n0 ˜105cm-3, H II regions should remain ultracompact for ˜3000 ye...
Article
The ROSAT High Resolution Interferometer (HRI) and Position Sensitive Proportional Counter (PSPC) detectors have been used to study the soft X-ray emission of the nearby SABbc galaxy NGC 4258 (M106). The helically twisted, nuclear jets, previously detected in radio continuum and visual emission-line studies, are found to dominate the X-ray images....
Article
The bipolar HII region K3-50A has been observed in the radio recombination lines (RRLs) H92alpha and He92alpha with the Very Large Array, and in the Bralpha recombination line with the United Kingdom Infrared Telescope. The spatial and spectral resolutions of the two observations are 2.3\arcsec and 7 km s(-1) for the RRLs and 1.3\arcsec and 19 km s...
Article
We correlate new HIFI Fabry-Perot (FP) and KPNO Goldcam long-slit spectra with VLA radio, BIMA CO, and ROSAT X-ray datasets to study the twisted jets in this nearby Seyfert. The multi-arcminute extent of the jet and the extensive wavelength coverage of its interaction with the multiphase ISM make this jet an important laboratory for studying the pr...
Article
Full-text available
The famous, large-scale, bisymmetric ``braided" jets are found to emit most of the X-rays from this nearby SABbc LINER/Seyfert galaxy. After removing wobble-related errors of up to +/-6('') in our 27 ksec ROSAT HRI image, we find that the SE branch of the jet is spatially unresolved across its width along much of its 2.5-arcmin length. The NW branc...
Article
Full-text available
The massive star-forming region Sgr B2 has been observed with the Very Large Array in all three hybrid configurations at 1.3 cm in the radio recombination lines (RRLs) H66alpha and He66alpha . The observations are sensitive to structures ranging in angular scales from 0\farcs08 to 60\arcsec, which is essential in a region containing ultracompact HI...
Article
We present the discovery of a synchrotron-emitting 'halo' of relativistic particles and magnetic fields in the inclined spiral galaxy NGC 253. This halo rises to a height of at least 9 kpc. The halo emission is substantially polarized. The spectral index of the radio continuum emission steepens considerably from the disk into the halo. Radio contin...
Article
We have observed the massive star forming regions W49A and Sgr B2 with the Very Large Array (VLA) at resolutions as high as 0.04 arcseconds, corresponding to a physical scale of a few hundred AU. We have assigned a morphological type to each of the 90+ compact and ultracompact (UC) HII regions in these regions using the classification scheme first...

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