C. R. Kerton

A Sample of Intermediate-mass Star-forming Regions: Making Stars at Mass Column Densities <1?g?cm?2

In an effort to understand the factors that govern the transition from low- to high-mass star formation, for the first time we identify a sample of intermediate-mass star-forming regions (IM SFRs) where stars up to (but not exceeding) ~8 M ? are being produced. We use IRAS colors and Spitzer Space Telescope mid-IR images, in conjunction with millimeter continuum and 13CO maps, to compile a sample of 50 IM SFRs in the inner Galaxy. These are likely to be precursors to Herbig AeBe stars and their associated clusters of low-mass stars. IM SFRs constitute embedded clusters at an early evolutionary stage akin to compact H II regions, but they lack the massive ionizing central star(s). The photodissociation regions that demarcate IM SFRs have typical diameters of ~1 pc and luminosities of ~104 L ?, making them an order of magnitude less luminous than (ultra-)compact H II regions. IM SFRs coincide with molecular clumps of mass ~103 M ? which, in turn, lie within larger molecular clouds spanning the lower end of the giant molecular cloud mass range, 104-105 M ?. The IR luminosity and associated molecular mass of IM SFRs are correlated, consistent with the known luminosity-mass relationship of compact H II regions. Peak mass column densities within IM SFRs are ~0.1-0.5?g?cm?2, a factor of several lower than ultra-compact H II regions, supporting the proposition that there is a threshold for massive star formation at ~1?g?cm?2.

AN ALL-SKY SAMPLE OF INTERMEDIATE-MASS STAR-FORMING REGIONS

We present an all-sky sample of 984 candidate intermediate-mass Galactic star-forming regions that are color selected from the Infrared Astronomical Satellite (IRAS) Point Source Catalog and morphologically classify each object using mid-infrared Wide-field Infrared Survey Explorer (WISE) images. Of the 984 candidates, 616 are probable star-forming regions (62.6%), 128 are filamentary structures (13.0%), 39 are point-like objects of unknown nature (4.0%), and 201 are galaxies (20.4%). We conduct a study of four of these regions, IRAS 00259+5625, IRAS 00420+5530, IRAS 01080+5717, and IRAS 05380+2020, at Galactic latitudes |b| > 5° using optical spectroscopy from the Wyoming Infrared Observatory, along with near-infrared photometry from the Two-Micron All Sky Survey, to investigate their stellar content. New optical spectra, color-magnitude diagrams, and color-color diagrams reveal their extinctions, spectrophotometric distances, and the presence of small stellar clusters containing 20-78 M ☉ of stars. These low-mass diffuse star clusters contain ~65-250 stars for a typical initial mass function, including one or more mid-B stars as their most massive constituents. Using infrared spectral energy distributions we identify young stellar objects near each region and assign probable masses and evolutionary stages to the protostars. The total infrared luminosity lies in the range 190-960 L ☉, consistent with the sum of the luminosities of the individually identified young stellar objects.

The Milky Way Project: What are Yellowballs?

Yellowballs are a collection of approximately 900 compact, infrared sources identified and named by volunteers participating in the Milky Way Project (MWP), a citizen-science project that uses GLIMPSE/MIPSGAL images from Spitzer to explore topics related to Galactic star formation. In this paper, through a combination of catalog cross-matching and infrared color analysis, we show that yellowballs are a mix of compact star-forming regions, including ultra-compact and compact HII regions, as well as analogous regions for less massive B-type stars. The resulting MWP yellowball catalog provides a useful complement to the Red MSX Source (RMS) survey. It similarly highlights regions of massive star formation, but the selection of objects purely on the basis of their infrared morphology and color in Spitzer images identifies a signature of compact star-forming regions shared across a broad range of luminosities, and by inference, masses. We discuss the origin of their striking mid-infrared appearance, and suggest that future studies of the yellowball sample will improve our understanding of how massive and intermediate-mass star-forming regions transition from compact to more extended bubble-like structures.

A 13CO SURVEY OF INTERMEDIATE-MASS STAR-FORMING REGIONS

We have conducted a 13CO survey of a sample of 128 infrared color-selected intermediate-mass star-forming region (IM SFR) candidates. We utilized the Onsala 20 m telescope to observe 13CO (1–0) toward 67 northern IM SFRs, used the 12 m Atacama Pathfinder Experiment telescope to observe 13CO (2–1) toward 22 southern IM SFRs, and incorporated an additional 39 sources from the Boston University Five College Radio Astronomy Observatory Galactic Ring Survey which observed 13CO (1–0). We detect 13CO (1–0) in 58 of the 67 northern sources and 13CO (2–1) in 20 of the 22 southern sources. The mean molecular column densities and 13CO linewidths in the inner Galaxy are higher by factors of 3.4 and 1.5, respectively, than the outer Galaxy. We attribute this difference to molecular clouds in the inner Galaxy being more massive and hosting star forming regions with higher luminosities on average than the outer Galaxy. IM SFRs have mean a molecular column density of 7.89 × 1021 cm−2, a factor of 3.1 lower than that for a sample of high-mass regions, and have a mean 13CO linewidth of 1.84 km s−1, a factor of 1.5 lower than that for high-mass regions. We demonstrate a correlation between 13CO linewidth and infrared luminosity as well as between molecular column density and infrared luminosity for the entire sample of intermediate-mass and high-mass regions. IM SFRs appear to form in distinctly lower-density environments with mean linewidths and beam-averaged column densities a factor of several lower than high-mass star-forming regions.

THE ENORMOUS OUTER GALAXY H II REGION CTB 102

We present new radio recombination line observations of the previously unstudied H II region CTB 102. Line parameters are extracted and physical parameters describing the gas are calculated. We estimate the distance to CTB 102 to be 4.3 kpc. Through comparisons with H I and 1.42 GHz radio continuum data, we estimate the size of CTB 102 to be 100-130 pc, making it one of the largest H II regions known, comparable to the W4 complex. A stellar wind blown bubble model is presented as the best explanation for the observed morphology, size, and velocities.

Revealing the Galactic H II Region G84.9+0.5 through 5 GHz Continuum and Polarization Emission and a Voigt Profile Analysis of Radio Recombination Line Observations

We present new λ = 6 cm radio observations (Stokes I, Q, and U and hydrogen recombination line) of the Galactic object G84.9+0.5, previously classified as a supernova remnant. Radio recombination line (RRL) emission near 6 cm is detected in deep GBT observations, and we are able to separate the 7.6 mK line detected from this object (appearing at vLSR = -40 km s-1) from the line emitted by ionized gas of W80 in the foreground (Tl = 5.4 mK; vLSR ~ 0 km s-1) along the same line of sight (LOS). Detection of RRL emission from G84.9+0.5 and the absence of polarized emission at 6 cm imply that this object is an H II region. Rather than a Gaussian, a Voigt function better describes the extended line profile of G84.9+0.5, which has a low-level wing extending into its negative-velocity end. A Monte Carlo analysis of noisy synthetic spectra is presented, and it is concluded the wing is not spurious. Two physical explanations for the wing (pressure broadening and an outflow of gas) are considered. We favor that of a champagne-type outflow in the gas flowing along the inside wall of a known molecular cloud in the vicinity of the nebula (at -40 km s-1), making G84.9+0.5 a blister type H II region viewed face-on. We find Te = 9900 K and ne = 20 cm-3 from a non-LTE analysis of the peak toward the RRL, and a total H II mass of 440 M☉. A distance of 4.9 kpc is determined for this object. An IR analysis using MSX and 2MASS data is presented, showing H II region colors for G84.9+0.5 and identifying a possible exciting star for this H II region.

Intermediate-Velocity Gas in the Canadian Galactic Plane Survey

We present observations of intermediate-velocity clouds (IVCs) found at positive velocities in the Canadian Galactic Plane Survey Phase I region (74° < l < 148°, -35 < b < +56). A catalog of 138 distinct IVCs and 13 IVC complexes has been compiled. From the global characteristics of our sample we demonstrate that the majority of these IVCs are directly associated with energetic phenomena, such as supernova explosions and massive star-forming regions, within the disk of the Galaxy and thus form a different population than the high-velocity clouds and high-latitude IVCs. We report what we believe to be the first detection of H I 21 cm absorption of a background source by an IVC and attempt to determine its physical properties and distance. We discuss in some detail a few of the IVCs that illustrate the connection between the clouds and energetic phenomena in the Galaxy. We suggest that the velocity shift of these IVCs away from the bulk of the Galactic H I emission provides an opportunity to study the structure of the low-latitude H I emission in a relatively confusion-free environment and present two examples of large (degree-scale) complexes of H I emission particularly suitable for such studies.

A sharper view of the outer Galaxy at 1420 and 408 MHz from the Canadian Galactic Plane Survey – I. Revisiting the KR catalogue and new Gigahertz Peaked Spectrum sources

Arcminute-resolution radio continuum images at 408 and 1420 MHz from the Canadian Galactic Plane Survey (CGPS) have been used to re-examine radio sources listed in the Kallas & Reich catalogue. This catalogue is of particular interest to Galactic studies as it lists both extended and compact radio sources found in the second Galactic quadrant. We have determined the nature (extended versus compact, Galactic versus extragalactic) of all of these bright radio sources. A number of large H II regions with no optical counterparts are highlighted along with a sample of large radio galaxies. Many sources previously thought to be extended Galactic objects are shown to be point sources. A sample of point sources with flat or rising spectra between 408 and 1420 MHz has been compiled, and within this sample likely Gigahertz Peaked Spectrum sources have been identified.

The Big Crunch: A Hybrid Solution to Earth and Space Science Instruction for Elementary Education Majors

ABSTRACT We describe the rationale and process for the development of a new hybrid Earth and Space Science course for elementary education majors. A five-step course design model, applicable to both online and traditional courses, is presented. Assessment of the course outcomes after two semesters indicates that the intensive time invested in the development of the course results in a manageable workload during the semester for faculty with an already full teaching load. We also found that average scores in proctored online exams for this cohort of students are identical to the average scores of students from the same major enrolled in a face-to-face (F2F) course. Exam scores significantly improved in the second semester after adjustments to the workload and the introduction of explicit test-taking tips at the beginning of the semester. We found that our students, at all stages of their studies, were not used to the self-guided instruction required for success in online courses, and were often not as comfortable using Web-based technology for instruction as we expected.

MASSIVE STAR FORMATION AT THE PERIPHERY OF THE EVOLVED GIANT H II REGION W 39

We present the first detailed study of the large, ~30 pc diameter, inner-Galaxy HII region W 39. Radio recombination line observations combined with HI absorption spectra and Galactic rotation models show that the region lies at V(LSR) = +65.4+/-0.5 km/s corresponding to a near kinematic distance of 4.5+/-0.2 kpc. Analysis of radio continuum emission shows that the HII region is being powered by a cluster of OB stars with a combined hydrogen-ionizing luminosity of log(Q) >=50, and that there are three compact HII regions located on the periphery of W 39, each with log(Q)~48.5 (single O7 - O9 V star equivalent). In the infrared, W 39 has a hierarchical bubble morphology, and is a likely site of sequential star formation involving massive stars. Kinematic models of the expansion of W 39 yield timescales of order Myr consistent with a scenario where the formation of the smaller HII regions has been triggered by the expansion of W 39. Using Spitzer GLIMPSE and MIPSGAL data we show that star-formation activity is not distributed uniformly around the periphery of W 39 but is concentrated in two areas that include the compact HII regions as well as a number of intermediate-mass Class I and Class II YSOs.