Chris De Pree | Agnes Scott College (original) (raw)

Papers by Chris De Pree

Ultracompact H II Regions have diameters less than 0.1 pc and densities larger than 10 4 cm −3 st... more Ultracompact H II Regions have diameters less than 0.1 pc and densities larger than 10 4 cm −3 start expanding when the protostar reaches ∼10 M ⊙ are forming while the massive star is still accreting are closely connected to high-mass star formation

Transiting planets have greatly expanded and diversified the exoplanet field. These planets provi... more Transiting planets have greatly expanded and diversified the exoplanet field. These planets provide greater access to characterization of exoplanet atmospheres and structure. The Kepler mission has been particularly successful in expanding the exoplanet inventory, even to planets smaller than the Earth. The orbital period sensitivity of the Kepler data is now extending into the Habitable Zones of their host stars, and several planets larger than the Earth have been found to lie therein. Here we examine one such proposed planet, Kepler-69c. We provide new orbital parameters for this planet and an in-depth analysis of the Habitable Zone. We find that, even under optimistic conditions, this 1.7 R ⊕ planet is unlikely to be within the Habitable Zone of Kepler-69. Furthermore, the planet receives an incident flux of 1.91 times the solar constant, which is similar to that received by Venus. We thus suggest that this planet is likely a super-Venus rather than a super-Earth in terms of atmospheric properties and habitability, and we propose follow-up observations to disentangle the ambiguity.

A tactile/Braille exhibit for the visually impaired community in the USA was launched in July 200... more 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 Crab Nebula, the Whirlpool Galaxy and the electromagnetic spectrum, and was adapted from the tactile/Braille book Touch the Invisible Sky. We present some of the early observations and findings on the tactile/Braille FETTU exhibit. The new exhibit opens a wider door to experiencing and understanding astronomy for the underserved visually impaired population.

Publications of the Astronomical Society of the Pacific, 2021

Bill Gray of Project Pluto brought to our attention an error of 0.03°in the listed latitude of ou... more Bill Gray of Project Pluto brought to our attention an error of 0.03°in the listed latitude of our Kitt Peak telescope. While correcting the table where this occurred, we also take the opportunity to update the instrument properties and weather statistics of our remote telescopes.

Publications of the Astronomical Society of the Pacific, 2016

We describe the remote facilities operated by the Southeastern Association for Research in Astron... more 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 Astrofísica de Canarias. SARA observatories comprise a 0.96m telescope at Kitt Peak, Arizona; a 0.6m instrument on Cerro Tololo, Chile; and the 1m Jacobus Kapteyn Telescope at the Roque de los Muchachos, La Palma, Spain. All are operated using standard VNC or Radmin protocols communicating with on-site PCs. Remote operation offers considerable flexibility in scheduling, allowing long-term observational cadences difficult to achieve with classical observing at remote facilities, as well as obvious travel savings. Multiple observers at different locations can share a telescope for training, educational use, or collaborative research programs. Each telescope has a CCD system for optical imaging, using thermoelectric cooling to avoid the need for frequent local service, and a second CCD for offset guiding. The Arizona and Chile instruments also have fiber-fed echelle spectrographs. Switching between imaging and spectroscopy is very rapid, so a night can easily accommodate mixed observing modes. We present some sample observational programs. For the benefit of other groups organizing similar consortia, we describe the operating structure and principles of SARA, as well as some lessons learned from almost 20 years of remote operations.

We have used the VLA A-configuration at lambda 20 cm to obtain new high-resolution (1\farcs5) flu... more We have used the VLA A-configuration at lambda 20 cm to obtain new high-resolution (1\farcs5) flux and polarization images of the large-scale, twisted jets in NGC 4258, a galaxy of particular interest because its nucleus houses the best observed case of an accretion disk around a supermassive black hole. We have also analyzed recently archived long-exposure ROSAT PSPC spectra of the jets. We have excluded the AGN itself, which is a highly obscured, hard-spectrum X-ray source. The jets are prominent in radio synchrotron, emission-lines, and X-rays because of their strong interaction with the dense galaxy ISM. Previously, we showed from the visible emission-line spectrum (Cecil, Morse, & Veilleux 1995, ApJ, 452, 613) that the jets are convincing examples of photoionizing shocks. The 5x deeper X-ray spectrum confirms our findings (Cecil, Wilson, & De Pree 1995, ApJ, 440, 181) that the SE jet has a thermal spectrum (kT = 0.3 keV) consistent with a ~400 km s(-1) shock. However, the NW jet exhibits a harder spectrum that suggests a higher shock velocity (kT ~ 0.5 keV) and non-thermal contribution. In both cases, the extragalactic photoelectric-absorption is small. We will discuss models of the X-ray spectrum based on the MAPPINGS II code described by Dopita & Sutherland (1995, ApJ, in press). Our radio image shows striking inversion symmetry across the nucleus, with several abrupt changes in ouflow direction. It is very unlikely that these arise from localized jet/ISM deflections; they may instead reflect past feasts of the currently starved nucleus. The jets within 25'' (800 pc) radius are projected along the spin axis of the accretion disk. The new images and spectra will be combined with existing datasets, including Fabry-Perot Hα and [O III] datacubes, to better constrain the history and driving mechanism of the outflow.

As part of the "From Earth to the Universe" (FETTU) project, a NASA-funded tactile exhi... more As part of the "From Earth to the Universe" (FETTU) project, a NASA-funded tactile exhibit for the visually impaired community was launched in July 2009 at the Martin Luther King Library in D.C. The exhibit is part of the global FETTU exhibit, a project of the International Year of Astronomy 2009. The science content of the exhibit includes explanations of our Sun, Eta Carinae, Crab Nebula, Whirlpool Galaxy, and the electromagnetic spectrum, and was adapted from the NASA-funded Braille/tactile book Touch the Invisible Sky. Multiple geographic locations and venue types have been targeted for the displays. The FETTU-tactile exhibit opens a wider door to experiencing and understanding astronomy, bridging a gap in learning. This exhibit is based upon work supported by the National Aeronautics and Space Administration under proposal 08-EPO08-0068 issued through the Science Mission Directorate.

The Astrophysical Journal, 2011

The discovery of transiting planets around bright stars holds the potential to greatly enhance ou... more The discovery of transiting planets around bright stars holds the potential to greatly enhance our understanding of planetary atmospheres. In this work

Monthly Notices of the Royal Astronomical Society, 2009

We present high spatial resolution mid-infrared (IR) images of the ring of ultracompact H ii regi... more We present high spatial resolution mid-infrared (IR) images of the ring of ultracompact H ii regions in W49A obtained at Gemini North, allowing us to identify the driving source of its powerful H 2 O maser outflow. These data also confirm our previous report that several radio sources in the ring are undetected in the mid-IR because they are embedded deep inside the cloud core. We locate the source of the water maser outflow at the position of the compact mid-IR peak of source G (source G:IRS1) to within 0. ′′ 07. This IR source is not coincident with any identified compact radio continuum source, but is coincident with a hot molecular core, so we propose that G:IRS1 is a hot core driving an outflow analogous to the wide-angle bipolar outflow in OMC-1. G:IRS1 is at the origin of a larger bipolar cavity and CO outflow. The water maser outflow is orthogonal to the bipolar CO cavity, so the masers probably reside near its waist in the thin cavity walls. Models of the IR emission require a massive protostar with M * ≃45 M ⊙ , L * ≃3×10 5 L ⊙ , and an effective envelope accretion rate of ∼10 −3 M ⊙ yr −1. Feedback from the central star could potentially drive the small-scale H 2 O maser outflow, but it has insufficient radiative momentum to have driven the largescale bipolar CO outflow, requiring that this massive star had an active accretion disk over the past 10 4 yr. Combined with the spatialy resolved morphology in IR images, G:IRS1 in W49 provides compelling evidence for a massive protostar that formed by accreting from a disk, accompanied by a bipolar outflow.

The Astrophysical Journal, 2018

We report ALMA observations with resolution ≈ 0.5 at 3 mm of the extended Sgr B2 cloud in the Cen... more We report ALMA observations with resolution ≈ 0.5 at 3 mm of the extended Sgr B2 cloud in the Central Molecular Zone (CMZ). We detect 271 compact sources, most of which are smaller than 5000 AU. By ruling out alternative possibilities, we conclude that these sources consist of a mix of hypercompact H ii regions and young stellar objects (YSOs). Most of the newly-detected sources are YSOs with gas envelopes which, based on their luminosities, must contain objects with stellar masses M * 8 M. Their spatial distribution spread over a ∼ 12 × 3 pc region demonstrates that Sgr B2 is experiencing an extended star formation event, not just an isolated 'starburst' within the protocluster regions. Using this new sample, we examine star formation thresholds and surface density relations in Sgr B2. While all of the YSOs reside in regions of high column density (N (H 2) 2 × 10 23 cm −2), not all regions of high column density contain YSOs. The observed column density threshold for star formation is substantially higher than that in solar vicinity clouds, implying either that high-mass star formation requires a higher column density or that any star formation threshold in the CMZ must be higher than in nearby clouds. The relation between the surface density of gas and stars is incompatible with extrapolations from local clouds, and instead stellar densities in Sgr B2

Citizen Sky is a citizen science project organized by the AAVSO and supported by a 3-year Nationa... more Citizen Sky is a citizen science project organized by the AAVSO and supported by a 3-year National Science Foundation (NSF) ISE grant focusing on the variable star, epsilon Aurigae. The source epsilon Aurigae is ideal for this project because of the timing of its transit (coinciding with the International Year of Astronomy 2009), and the brightness of the source (allowing for naked eye observing). The overall goals of the project are to: help answer open questions about the epsilon Aurigae system, stimulate new interest in astronomy, allow citizen scientists to experience teamwork and scientific collaboration, and fully participate in the scientific method. The project and its web site provide ways for citizen scientists to practice observing variable sources, acquire and analyze data, and present results.

The Astrophysical …, 1997

We present 7 mm VLA observations of five ultracompact H II regions of cometary morphology that ha... more We present 7 mm VLA observations of five ultracompact H II regions of cometary morphology that have H2O masers near their cometary arcs. We detect 7 mm sources near two of these, NGC 6334F and G75.780.34. In the latter case, the emission coincides with the ...

This Seyfert galaxy has a helically twisted, bisymmetric nuclear jet that flows mostly in the gas... more This Seyfert galaxy has a helically twisted, bisymmetric nuclear jet that flows mostly in the gas disk. Our ROSAT results are: 1) The jet dominates the soft x-ray emission. After correcting pointing-errors of up to ±6″ in our 25 ksec HRL exposure, we find that the SE jet branch is spatially unresolved in width along much of its 2″5 length. The NW branch is more diffuse, and the extensive radio ‘‘plateaus’’ also emit x-rays. 2) The jet spectrum from the 6.5 ksec PSPC archival exposure is noisy, but is best fit as a Raymond-Smith plasma with kT=0.30 keV, log NH&ape;20.0 cm−2, and luminosity 1.6×1040 ergs s−1 between 0.1 and 2.4 keV.Gas at this temperature can arise from shock speeds of 350–500 km s−1 (depending on preshock excitation), and may have been entrained as the jet scrapes along molecular clouds. The gaseous excitation and radial velocities from our published optical, emission-line spectra of the jet are consistent with these shock speeds if gas flows along helical paths. The PSPC spectral fit is poor above 0.6 keV. An additional hard component is required that peaks near the nucleus.

Publications of the Astronomical Society of the Pacific, 2021

Publications of the Astronomical Society of the Pacific, 2016

The Astrophysical Journal, 2011

Monthly Notices of the Royal Astronomical Society, 2009

The Astrophysical Journal, 2018

The Astrophysical …, 1997