arXiv subjects

C. R. Kerton

Publications and source records attributed to C. R. Kerton.

At least 19 recordsLinked to original sources

arXiv2026

A Modified Conveyor Belt Model: Implications for Surface Density Thresholds for Massive Star Formation

Recent models and simulations of cluster formation within molecular clumps consider multi-scale, hierarchical accretion, which leads to clump mass growth over time. This mode of mass accumulation could have implications regarding the evolution of observable properties such as mass and radius, bringing into question the interpretation of commonly cited thresholds for high-mass star formation. In this paper, we use the conveyor belt model of cluster formation to create synthetic cores/clumps and derive physical and observational properties. We show that while this model successfully predicts many observed trends, modifications are required to match properties of high-mass prestellar clumps. When the model clumps are observationally classified as intermediate- or high-mass star-forming, the threshold delineating these two groups agrees with those found in the literature; however, results show that high-mass clumps at early evolutionary stages can be misclassified using standard surface density thresholds. Our logistic regression analysis reveals the quantity of material to ever enter a star-forming region is the most important factor in differentiating intermediate- and high-mass star-forming regions. This implies observations characterising the environment surrounding star-forming regions are crucial, especially at early evolutionary stages.

astro-ph.GA↗

arXiv2025

The Milky Way Project: Bridging Intermediate- and High-Mass Star Formation with the MIRION Catalog of Yellowballs

We describe the construction and use of the Mid-InfraRed Interstellar Objects and Nebulae (MIRION) catalog, which was compiled from 6176 objects identified as "yellowballs" (YBs) by participants in the Milky Way Project. The majority of YBs are compact photodissociation regions generated by intermediate- and high-mass young stellar objects that are embedded in star-forming clumps ranging in mass from ten to one million solar masses and luminosity from ten to ten thousand solar luminosities. The MIRION catalog increases the number of candidate intermediate-mass star-forming regions (SFRs) by nearly two orders of magnitude, providing an extensive database with which to explore the transition from isolated low-mass to clustered high-mass star formation. The catalog comprises five tables that include mid- and far-infrared photometry; velocities of source-associated molecular clouds; distances to these molecular clouds; physical properties of source-associated star-forming clumps; and source crossmatches with other catalogs. The structure of the catalog enables users to easily sort objects for further study based on distance or environmental properties. Our preliminary analysis extends our earlier findings that indicate a relationship between IR colors and the physical properties and evolutionary stages of SFRs. Photometry will be periodically updated online to incorporate measurements from volunteers participating in a classroom activity known as the People Enabling Research: a Yellowball Survey of the Colors Of Protostellar Environments (PERYSCOPE) Project. These updates will continue to refine the IR flux measurements and reduce photometric errors. A follow-up paper will present a detailed analysis of how IR colors can be used to predict the properties of star-forming environments.

astro-ph.GA↗

arXiv2024

Long-Term Monitoring of the Oe Star VES 735: Ope! Not So Quiet After All

Only 3-4 per cent of galactic O stars are observed to display the emission features representative of the OBe phenomenon, compared to galactic B stars, which display these characteristics in 25-35 per cent of B0 and B1 stars. We present new observations of the high-mass O star, VES 735, which confirms its classification as one of these rare emission-line stars. These are its first recorded observations that display strong spectroscopic variations in nearly 30 years of monitoring, with the H$α$ profile exhibiting a tenfold increase in emission compared to observations taken between 1996 and 2014 and having variations which show episodes of inflowing and outflowing material. These observations, coupled with photometric variations in the visible and infrared, show behavior that is consistent with the mass reservoir effect for viscous decretion discs. We propose that in 2015 VES 735 began an approximately three year event in which mass was being injected into the circumstellar environment followed by re-accretion towards the star. We also find evidence that the re-accretion may have been interrupted with another, smaller, mass-injection event based on observations in 2022 and 2023. Observational cadences ranging from hours to months show no evidence that VES 735 is part of a binary system, making it an ideal candidate for future observations to further investigate the evolution of high-mass stars and the OBe phenomenon as it pertains to their circumstellar environment.

astro-ph.SR↗

arXiv2022

BFS 10: A nascent bipolar H II region in a filamentary molecular cloud

We present a study of the compact blister HII region BFS 10 and its highly filamentary molecular cloud. We utilize 12CO observations from the Five College Radio Astronomy Observatory to determine the distance, size, mass, and velocity structure of the molecular cloud. Infrared observations obtained from the UKIRT Infrared Deep Sky Survey and the Spitzer Infrared Array Camera, as well as radio continuum observations from the Canadian Galactic Plane Survey, are used to extract information about the central HII region. This includes properties such as the ionizing photon rate and infrared luminosity, as well as identifying a rich embedded star cluster associated with the central O9 V star. Time-scales regarding the expansion rate of the HII region and lifetime of the ionizing star reveal a high likelihood that BFS 10 will develop into a bipolar HII region. Although the region is expected to become bipolar, we conclude from the clouds velocity structure that there is no evidence to support the idea that star formation at the location of BFS 10 was triggered by two colliding clouds. A search for embedded young stellar objects (YSOs) within the molecular cloud was performed. Two distinct regions of YSOs were identified; one region associated with the rich embedded cluster and another sparse group associated with an intermediate mass YSO.

astro-ph.GA↗

arXiv2021

The Milky Way Project: Probing Star Formation with First Results on Yellowballs from DR2

Yellowballs (YBs) were first discovered during the Milky Way Project citizen-science initiative (MWP; Simpson et al. 2012). MWP users noticed compact, yellow regions in Spitzer Space Telescope mid-infrared (MIR) images of the Milky Way plane and asked professional astronomers to explain these "yellow balls." Follow-up work by Kerton et al. (2015) determined that YBs likely trace compact photo-dissociation regions associated with massive and intermediate-mass star formation. YBs were included as target objects in a version of the Milky Way Project launched in 2016 (Jayasinghe et al. 2016), which produced a listing of over 6000 YB locations. We have measured distances, cross-match associations, physical properties, and MIR colors of ~500 YBs within a pilot region covering the l= 30 - 40 degrees, b= +/- 1 degree region of the Galactic plane. We find 20-30% of YBs in our pilot region contain high-mass star formation capable of becoming expanding H II regions that produce MIR bubbles. A majority of YBs represent intermediate-mass star-forming regions whose placement in evolutionary diagrams suggest they are still actively accreting, and may be precursors to optically-revealed Herbig Ae/Be nebulae. Many of these intermediate-mass YBs were missed by surveys of massive star-formation tracers and thus this catalog provides information for many new sites of star formation. Future work will expand this pilot region analysis to the entire YB catalog.

astro-ph.GA↗

arXiv2020

Revealing the Double Nucleus of NGC 4490

NGC 4490/85 (UGC 7651/48) or Arp 269 is well known for being one of the closest interacting/merging galactic systems. NGC 4490 has a high star formation rate (SFR) and is surrounded by an enormous HI feature stretching about 60 kpc north and south of the optically visible galaxies. Both the driver for the high SFR in NGC 4490 and the formation mechanism of the HI structure are puzzling aspects of this system. We have used mid-infrared Spitzer data to show that NGC 4490 has a double nucleus morphology. One nucleus is visible in the optical, while the other is only visible at infrared and radio wavelengths. We find the optical nucleus and the potential infrared visible nucleus have similar sizes, masses, and luminosities. Both are comparable in mass and luminosity to other nuclei found in interacting galaxy pairs and much more massive and luminous compared with typical non-nuclear star-forming complexes. We examine possible origin scenarios for the infrared feature, and conclude that it is likely that NGC 4490 is itself a merger remnant, which is now interacting with NGC 4485. This earlier encounter provides both a possible driver for extended star formation in NGC 4490, and multiple pathways for the formation of the extended HI plume.

astro-ph.GA↗

arXiv2019

High-Resolution Observations of the Molecular Clouds Associated with the Huge HII Region CTB 102

We report the first high-resolution (sub-arcminute) large-scale mapping $^{12}$CO and $^{13}$CO observations of the molecular clouds associated with the giant outer Galaxy HII region CTB~102 (KR 1). These observations were made using a newly commissioned receiver system on the 13.7-m radio telescope at the Taeduk Radio Astronomy Observatory. Our observations show that the molecular clouds have a spatial extent of $60 \times 35$ pc and a total mass of $10^{4.8} - 10^{5.0}$ M$_\odot$. Infrared data from WISE and 2MASS were used to identify and classify the YSO population associated with ongoing star formation activity within the molecular clouds. We directly detect 18 class I/class II YSOs and six transition disk objects. Moving away from the HII region, there is an age/class gradient consistent with sequential star formation. The infrared and molecular-line data were combined to estimate the star formation efficiency (SFE) of the entire cloud as well as the SFE for various sub-regions of the cloud. We find that the overall SFE is between $\sim5 - 10$%, consistent with previous observations of giant molecular clouds. One of the sub-regions, region 1a, is a clear outlier, with a SFE of 17 $-$ 35% on a 5 pc spatial scale. This high SFE is more typical for much smaller (sub-pc scale) star-forming cores, and we think region 1a is likely an embedded massive protocluster.

astro-ph.GA↗

arXiv2018

A Refined Sample of Lyman Excess H II Regions

A large number (67) of the compact/ultra-compact H II regions identified in the Coordinated Radio and Infrared Survey for High-Mass Star Formation catalogue were determined to be powered by a Lyman continuum flux in excess of what was expected given their corresponding luminosity. In this study we attempt to reasonably explain the Lyman excess phenomenon in as many of the 67 H II regions as possible through a variety of observational and astrophysical means including new luminosity estimates, new Herschel photometry, new distance determinations, the use of different models for dust and ionized gas covering factors, and the use of different stellar calibrations. This phenomenon has been observed before; however, the objects shown to exhibit this behaviour in the literature have decidedly different physical properties than the regions in our sample, and thus the origin of the excess is not the same. We find that the excess can be reproduced using OB stellar atmosphere models that have been slightly modified in the extreme ultraviolet. Though the exact mechanism producing the excess is still uncertain, we do find that a scaled up magnetospheric accretion model, often used to explain similar emission from T Tauri stars, is unable to match our observations. Our results suggest that the Lyman excess may be associated with younger H II regions, and that it is more commonly found in early B-type stars. Our refined sample of 24 Lyman excess H II regions provides an ideal sample for comparative studies with regular H II regions, and can act as the basis for the further detailed study of individual regions.

astro-ph.SR↗

arXiv2015

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.

astro-ph.SR↗

arXiv2013

Massive Star Formation at the Periphery of the Evolved Giant HII 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.

astro-ph.GA↗

arXiv2012

IRAS 01202+6133 : A Possible Case of Protostellar Collapse Triggered by a Small HII Region

We present an analysis of HCO+ (J=3-2) and H13CO+ (J=3-2) observations of the massive (M ~ 20 Msun) submm/IR source IRAS 01202+6133 located on the periphery of the HII region KR 120 (Sh 2-187). The HCO+ line profile has a classic blue-asymmetric shape with the optically thin H13CO+ line peaking at the position expected if the HCO+ line arises from a combination of self-absorption and infall motion. We have modified existing analytic radiative transfer models to allow for the fitting of submm/mm line profiles that have both self-absorption features and optically thin wings and applied these models to our HCO+ spectrum of IRAS 01202+6133. We conclude that it is a young Class I YSO with a substantial envelope undergoing slow infall and having some outflow motions. The young age of the HII region rules out a "collect and collapse" scenario. While we cannot eliminate the possibility that IRAS 01202+6133 formed spontaneously at its current location, considering its early evolutionary state and its proximity to the HII region we think that the formation of IRAS 01202+6133 was triggered by the expansion of KR 120 (Sh 2-187).

astro-ph.SR↗

arXiv2012

GASKAP -- The Galactic ASKAP Survey

A survey of the Milky Way disk and the Magellanic System at the wavelengths of the 21-cm atomic hydrogen (HI) line and three 18-cm lines of the OH molecule will be carried out with the Australian Square Kilometre Array Pathfinder telescope. The survey will study the distribution of HI emission and absorption with unprecedented angular and velocity resolution, as well as molecular line thermal emission, absorption, and maser lines. The area to be covered includes the Galactic plane (|b|< 10deg) at all declinations south of delta = +40deg, spanning longitudes 167deg through 360deg to 79deg at b=0deg, plus the entire area of the Magellanic Stream and Clouds, a total of 13,020 square degrees. The brightness temperature sensitivity will be very good, typically sigma_T ~ 1 K at resolution 30arcsec and 1 km/s. The survey has a wide spectrum of scientific goals, from studies of galaxy evolution to star formation, with particular contributions to understanding stellar wind kinematics, the thermal phases of the interstellar medium, the interaction between gas in the disk and halo, and the dynamical and thermal states of gas at various positions along the Magellanic Stream.

astro-ph.GA↗

arXiv2011

IRAS03063+5735: A Bowshock Nebula Powered by an Early B Star

Mid-infrared images from the Spitzer Space Telescope Galactic Legacy Infrared MidPlane Survey Extraordinaire program reveal that the infrared source IRAS 03063+5735 is a bowshock nebula produced by an early B star, 2MASS 03101044+5747035. We present new optical spectra of this star, classify it as a B1.5 V, and determine a probable association with a molecular cloud complex at V_LSR=-38 -- -42 km/s in the outer Galaxy near l=140.59 degr, b=-0.250 degr. On the basis of spectroscopic parallax, we estimate a distance of 4.0 +/-1 kpc to both the bowshock nebula and the molecular complex. One plausible scenario is that this a high-velocity runaway star impinging upon a molecular cloud. We identify the HII region and stellar cluster associated with IRAS 03064+5638 at a projected distance of 64 pc as one plausible birth site. The spectrophotometric distance and linkage to a molecular feature provides another piece of data helping to secure the ill-determined rotation curve in the outer Galaxy. As a by-product of spectral typing this star, we present empirical spectral diagnostic diagrams suitable for approximate spectral classification of O and B stars using He lines in the little-used yellow-red portion of the optical spectrum.

astro-ph.GA↗

arXiv2009

The enormous outer Galaxy HII region CTB 102

We present new radio recombination line observations of the previously unstudied HII 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 HI 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 HII 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.

astro-ph.GA↗

arXiv2008

Sequential and Spontaneous Star Formation Around the Mid-Infrared Halo HII Region KR 140

We use 2MASS and MSX infrared observations, along with new molecular line (CO) observations, to examine the distribution of young stellar objects (YSOs) in the molecular cloud surrounding the halo HII region KR 140 in order to determine if the ongoing star-formation activity in this region is dominated by sequential star formation within the photodissociation region (PDR) surrounding the HII region. We find that KR 140 has an extensive population of YSOs that have spontaneously formed due to processes not related to the expansion of the HII region. Much of the YSO population in the molecular cloud is concentrated along a dense filamentary molecular structure, traced by C18O, that has not been erased by the formation of the exciting O star. Some of the previously observed submillimetre clumps surrounding the HII region are shown to be sites of recent intermediate and low-mass star formation while other massive starless clumps clearly associated with the PDR may be the next sites of sequential star formation.

astro-ph↗

arXiv2007

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 reexamine radio sources listed in the Kallas and Reich (1980) 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 vs. compact, Galactic vs. extragalactic) of all of these bright radio sources. A number of large HII 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.

astro-ph↗

arXiv2007

A sharper view of the outer Galaxy at 1420 and 408 MHz from the Canadian Galactic Plane Survey II: The catalogue of extended radio sources

A new catalogue of extended radio sources has been prepared based on arcminute-resolution 1420 MHz images from the Canadian Galactic Plane Survey (CGPS). The new catalogue provides both 1420 MHz and 408 MHz flux density measurements on sources found near the Galactic plane in the second quadrant of our Galaxy. In addition cross-identifications are made with other major radio catalogues and information is provided to facilitate the recovery of CGPS image data associated with each catalogued source. Numerous new radio sources are identified and the catalogue provides a comprehensive summary of both newly discovered and previously known HII regions and supernova remnants in the outer Galaxy. The catalogue should be of use both for synoptic studies of Galactic structure and for placing higher resolution observations, at radio and other wavelengths, in context.

astro-ph↗

arXiv2001

A Submillimeter View of Star Formation Near the HII Region KR 140

We present the results of 450 and 850 micron continuum mapping of the HII region KR 140 using the SCUBA instrument on the JCMT. KR 140 is a small (5.7 pc diameter) HII region at a distance of 2.3+/-0.3 kpc. Five of the six IRAS point sources near KR 140 were mapped in this study. Our analysis shows that two of these IRAS sources are embedded late B type stars lying well outside the HII region, two are a part of the dust shell surrounding the HII region, and one is the combined emission from an ensemble of smaller sources unresolved by IRAS. We have discovered a number of relatively cold submillimeter sources not visible in the IRAS data, ranging in size from 0.2 to 0.7 pc and in mass from 0.5 to 130 Msun. The distribution of masses for all sources is well characterized by a power law N(>M) ~ M^{-alpha} with alpha = 0.5 +/- 0.04, in agreement with the typical mass function for clumped structures of this scale in molecular clouds. Several of the submillimeter sources are found at the HII-molecular gas interface and have probably been formed as the result of the expansion of the HII region. Many of the submillimeter sources we detect are gravitationally bound and most of these follow a mass-size relationship expected for objects in virial equilibrium with non-thermal pressure support. Upon the loss of non-thermal support they could be sites of star formation. Along with the two B stars that we have identified as possible cluster members along with VES 735, we argue that five nearby highly-reddened stars are in a pre-main-sequence stage of evolution.

astro-ph↗