T. Allen

Lowell Observatory, Flagstaff, Arizona, United States

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Publications (5)11.7 Total impact

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    ABSTRACT: We present Spitzer mid-infrared and far-infrared images of the Mon OB1 giant molecular cloud, which contains the young star forming region NGC 2264 and several sub-clusters of young stellar objects (YSOs). With the Spitzer data, along with 2MASS photometry, we classify YSOs in the entire Mon OB1 giant molecular cloud (GMC) by their infrared-excess emission and study their distribution with respect to cloud material. We find that in regions with higher spatial YSO and molecular gas density there is a strong correlation between local surface density of YSOs and density of molecular gas as traced by dust. This correlation is roughly described as a power law in these quantities. We use a number counting technique to determine the fraction of cloud members which are YSOs for different portions of the cloud that have differing average extinctions. We find that this disk fraction differs between the NGC 2264 region alone and the other regions of the Mon OB1 GMC. We compare these results with other molecular clouds and contrast our results for the NGC 2264 region with other estimates in the literature which use a different YSO classification approach.
    The Astrophysical Journal 01/2012; 794(2). · 6.73 Impact Factor
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    ABSTRACT: We have conducted a detailed characterization of the structure of the CepOB3b young cluster using membership lists derived from space-based (Spitzer mid-IR and Chandra Xray) and ground-based (NEWFIRM near-IR) imaging. We currently estimate the CepOB3b cluster membership at roughly 2500 members; at a distance of 700 pc, CepOB3b is the second nearest large (>1000 members) young cluster after the Orion Nebula Cluster. Recent examination of the Spitzer-identified YSOs has revealed that the Cep B cluster (CepOB3b East) is significantly extended to the west, including a second overdense cluster core (CepOB3b West) near the Cep F molecular cloud core. We present radial and azimuthal surface density profiles of both cluster cores using the improved member list. We also examine the density contrast between the two cores, the intra-core region, and the exterior of the cluster, in order to constrain the probability that the cluster cores are either physically associated or spatially distinct structures that are associated only by projection.
    01/2011;
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    ABSTRACT: We have recently discovered over 1000 young stars in the Cep OB3b young cluster with the Spitzer Space Telescope; showing that CepOB3b is one of the two large (1000+ member), young (< 5 Myr), dense clusters within 1 Kpc of the Sun. It has largely dispersed its natal gas, suggesting it is more evolved than the Orion Nebula Cluster, and thus can provide a rare glimpse at the evolution of young large clusters. We have recently found that the stars in Cep OB3b closest to an O7V star preferentially lack disks, evidence that disk evaporation is ongoing in this cloud. We propose hectospec and hectochelle observations to measure the spectral types, accretion properties and radial velocities of the member stars. This will allow us to analyze the age and dynamics of the emerging cluster, and to study the photoevaporation of disks around stars orbiting in the cluster. These observations will also support 150 kiloseconds of Chandra Observations to study the X-ray properties of this young cluster.
    NOAO Proposal. 08/2009;
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    ABSTRACT: The giant molecular cloud G216-2.5, also known as Maddalena's cloud or the Maddalena-Thaddeus cloud, is distinguished by an unusual combination of high gas mass (1-6 x 10^5) solar masses, low kinetic temperatures (10 K), and the lack of bright far infrared emission. Although star formation has been detected in neighboring satellite clouds, little evidence for star formation has been found in the main body of this cloud. Using a combination of mid-infrared observations with the IRAC and MIPS instruments onboard the Spitzer space telescope, and near-IR images taken with the Flamingos camera on the KPNO 2.1-meter, we identify a population of 41 young stars with disks and 33 protostars in the center of the cloud. Most of the young stellar objects are coincident with a filamentary structure of dense gas detected in CS (2-1). These observations show that the main body of G216 is actively forming stars, although at a low stellar density comparable to that found in the Taurus cloud. Comment: Accepted to AJ. Full electronic version at: http://astro1.physics.utoledo.edu/~megeath/mt_stm.pdf tables on http://astro1.physics.utoledo.edu/~megeath/mt_stm_table.pdf
    The Astronomical Journal 04/2009; 137:4072-4082. · 4.97 Impact Factor
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    ABSTRACT: We present preliminary results from our Spitzer surveys of the active star-forming molecular clouds Cepheus OB3 and Monoceros R2. These clouds each have several clusters of forming young stellar objects, but the extent of lower number density star formation in these clouds has been largely unknown. With Spitzer, we have the sensitivity to efficiently survey these clouds, confidently detecting and classifying most young stellar objects forming there. With these data, we can now examine in detail distributed star formation within these clouds and compare it to the high density environments of their embedded clusters.
    06/2006;