K Gordon

Publications (60)33.57 Total impact

• Article: Hubble Tarantula Treasury Project: Unraveling Tarantula's Web. I. Observational overview and first results

  E. Sabbi, J. Anderson, D. J. Lennon, R. P. van der Marel, A. Aloisi, M. L. Boyer, M. Cignoni, G. de Marchi, S. E. de Mink, C. J. Evans, [......], K. Gordon, D. A. Gouliermis, E. K. Grebel, A. M. Koekemoer, S. S. Larsen, N. Panagia, J. E. Ryon, L. J. Smith, M. Tosi, D. Zaritsky
  [show abstract] [hide abstract]
  ABSTRACT: The Hubble Tarantula Treasury Project (HTTP) is an ongoing panchromatic imaging survey of stellar populations in the Tarantula Nebula in the Large Magellanic Cloud that reaches into the sub-solar mass regime (< 0.5 Mo). HTTP utilizes the capability of HST to operate the Advanced Camera for Surveys (ACS) and the Wide Field Camera 3 (WFC3) in parallel to study this remarkable region in the near-ultraviolet, optical, and near-infrared spectral regions, including narrow band H$\alpha$ images. The combination of all these bands provides a unique multi-band view. The resulting maps of the stellar content of the Tarantula Nebula within its main body provide the basis for investigations of star formation in an environment resembling the extreme conditions found in starburst galaxies and in the early Universe. Access to detailed properties of individual stars allows us to begin to reconstruct the evolution of the stellar skeleton of the Tarantula Nebula over space and time with parcsec-scale resolution. In this first paper we describe the observing strategy, the photometric techniques, and the upcoming data products from this survey and present preliminary results obtained from the analysis of the initial set of near-infrared observations.
  04/2013;
• Article: The CO-to-H2 Conversion Factor and Dust-to-Gas Ratio on Kiloparsec Scales in Nearby Galaxies

  K. M. Sandstrom, A. K. Leroy, F. Walter, A. D. Bolatto, K. V. Croxall, B. T. Draine, C. D. Wilson, M. Wolfire, D. Calzetti, R. C. Kennicutt, [......], L. Armus, B. Brandl, K. Gordon, J. Hinz, O. Krause, E. Montiel, M. Sauvage, A. Schmiedeke, J. D. T. Smith, L. Vigroux
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  ABSTRACT: We present maps of the CO-to-H2 conversion factor (alpha_co) and dust-to-gas ratio (DGR) in 26 nearby, star-forming galaxies with ~kiloparsec spatial resolution. We have simultaneously solved for alpha_co and DGR by assuming that the DGR is approximately constant on kpc scales. With this assumption, we can combine maps of dust mass surface density, CO integrated intensity and HI column density to solve for both alpha_co and DGR with no assumptions about their value or dependence on metallicity or other parameters. Such a study has just become possible with the availability of high resolution far-IR maps from the Herschel key program KINGFISH, 12CO J=(2-1) maps from the IRAM 30m large program HERACLES and HI 21-cm line maps from THINGS. We use a fixed ratio between the (2-1) and (1-0) lines to present our alpha_co results on the more typically used 12CO J=(1-0) scale and show using literature measurements that variations in the line ratio do not effect our results. In total, we derive 782 individual solutions for alpha_co and DGR. On average, alpha_co = 3.1 Msun pc^-2 (K km s^-1)^-1 for our sample with a standard deviation of 0.3 dex. Within galaxies we observe a generally flat profile of alpha_co as a function of galactocentric radius. However, most galaxies exhibit a lower alpha_co in the central kiloparsec---a factor of ~2 below the galaxy mean, on average. In some cases, the central alpha_co value can be factors of 5 to 10 below the standard MW value of alpha_co,MW = 4.4 Msun pc^-2 (K km s^-1)^-1. While for alpha_co we find only weak correlations with metallicity, DGR is well-correlated with metallicity, with an approximately linear slope. Finally, we present several recommendations for choosing an appropriate alpha_co for studies of nearby galaxies.
  12/2012;
• Article: Fundamental stellar parameters in 47 Tucanae (Mcdonald+, 2011)

  I McDonald, M ~L Boyer, J ~T Loon, A ~A Zijlstra, J ~L Hora, B Babler, M Block, K Gordon, M Meade, M Meixner, K Misselt, T Robitaille, M Sewilo, B Shiao, B Whitney
  VizieR Online Data Catalog. 05/2011; 219:30023.
• Article: Fundamental Parameters, Integrated Red Giant Branch Mass Loss, and Dust Production in the Galactic Globular Cluster 47 Tucanae

  I McDonald, M ~L Boyer, J ~T Loon, A ~A Zijlstra, J ~L Hora, B Babler, M Block, K Gordon, M Meade, M Meixner, K Misselt, T Robitaille, M Sewilo, B Shiao, B Whitney
  apjs. 04/2011; 193:23.
• Source

  Available from: A. Pasquali

  Article: A Panchromatic View OF NGC 602: Time-Resolved Star Formation with the Hubble and Spitzer Space Telescopes

  Lynn Redding Carlson, Marta Sewilo, Margaret Meixner, Krista A. Romita, Barbara Whitney, Joseph L. Hora, M. Cignoni, E. Sabbi, A. Nota, M. Sirianni, L. J. Smith, K Gordon, B. Babler, S. Bracker, J. S. Gallagher III, M. Meade, K. Misselt, A. Pasquali, B. Shiao
  [show abstract] [hide abstract]
  ABSTRACT: We present the photometric catalogs for the star-forming cluster NGC 602 in the wing of the Small Magellanic Cloud covering a range of wavelengths from optical HST/ACS (F555W, F814W) and SMARTS/ANDICAM (V, I) to infrared (Spitzer/IRAC 3.6, 4.5, 5.8, and 8 micron and MIPS 24 micron). Combining this with IRSF (InfraRed Survey Facility) near-infrared photometry (J, H, Ks), we compare the young main sequence (MS) and pre-main sequence (PMS) populations prominent in the optical with the current young stellar object (YSO) populations revealed by the infrared (IR). We analyze the MS and PMS population with isochrones in color-magnitude diagrams to derive ages and masses. The optical data reveal ~565 PMS candidates, low mass Stage III YSOs. We characterize ~40 YSOs by fitting their spectral energy distributions (SEDs) to a grid of models (Robitaille et al. 2007) to derive luminosities, masses and evolutionary phase (Stage I-III). The higher resolution HST images reveal that ~70% of the YSO candidates are either multiples or protoclusters. For YSOs and PMS sources found in common, we find a consistency in the masses derived. We use the YSO mass function to derive a present-day star-formation rate of ~0.2-1.0 Msun/yr/kpc^2, similar to the rate derived from the optical star formation history suggesting a constant star formation rate for this region. We demonstrate a progression of star formation from the optical star cluster center to the edge of the star forming dust cloud. We derive lifetimes of a few 10^5 years for the YSO Stages I and II. Comment: 55 pages, 18 Figures; High resolution images available form author Accepted to ApJ
  12/2010;
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  Available from: ArXiv

  Article: The Infrared Properties of Massive Stars in the Magellanic Clouds

  A. Z. Bonanos, D. J. Lennon, D. L. Massa, M. Sewilo, F. Köhlinger, N. Panagia, J. Th. van Loon, C. J. Evans, L. J. Smith, M. Meixner, K Gordon, the SAGE teams
  [show abstract] [hide abstract]
  ABSTRACT: We present results of our study of the infrared properties of massive stars in the Large and Small Magellanic Clouds, which are based on the Spitzer SAGE surveys of these galaxies. We have compiled catalogs of spectroscopically confirmed massive stars in each galaxy, as well as photometric catalogs for a subset of these stars that have infrared counterparts in the SAGE database, with uniform photometry from 0.3 to 24 microns in the UBVIJHKs+IRAC+MIPS24 bands. These catalogs enable a comparative study of infrared excesses of OB stars, classical Be stars, yellow and red supergiants, Wolf-Rayet stars, Luminous Blue Variables and supergiant B[e] stars, as a function of metallicity, and provide the first roadmaps for interpreting luminous, massive, resolved stellar populations in nearby galaxies at infrared wavelengths. Comment: 5 pages, 1 figure, contribution to 39th Liege Astrophysical Colloquium, 'The multi-wavelength view of hot, massive stars'
  10/2010;
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  Available from: ArXiv

  Article: Infrared properties of Active OB stars in the Magellanic Clouds from the Spitzer SAGE Survey

  A. Z. Bonanos, D. J. Lennon, D. L. Massa, M. Sewilo, F. Köhlinger, N. Panagia, J. Th. van Loon, C. J. Evans, L. J. Smith, M. Meixner, K Gordon, the SAGE teams
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  ABSTRACT: We present a study of the infrared properties of 4922 spectroscopically confirmed massive stars in the Large and Small Magellanic Clouds, focusing on the active OB star population. Besides OB stars, our sample includes yellow and red supergiants, Wolf-Rayet stars, Luminous Blue Variables (LBVs) and supergiant B[e] stars. We detect a distinct Be star sequence, displaced to the red, and find a higher fraction of Oe and Be stars among O and early-B stars in the SMC, respectively, when compared to the LMC, and that the SMC Be stars occur at higher luminosities. We also find photometric variability among the active OB population and evidence for transitions of Be stars to B stars and vice versa. We furthermore confirm the presence of dust around all the supergiant B[e] stars in our sample, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs. Comment: 5 pages, 1 figure, to appear in the proceedings of the IAUS 272 on "Active OB stars: structure, evolution, mass loss and critical limits" (Paris, July 19-23, 2010), Cambridge University Press. Editors C. Neiner, G. Wade, G. Meynet and G. Peters
  10/2010;
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  Available from: Marco Marengo

  Article: The mass-loss return from evolved stars to the Large Magellanic Cloud III. Dust properties for carbon-rich asymptotic giant branch stars

  Sundar Srinivasan, B. A. Sargent, M Matsuura, M. Meixner, F. Kemper, A. G. G. M. Tielens, K. Volk, A. K. Speck, Paul M. Woods, K Gordon, M. Marengo, G. C. Sloan
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  ABSTRACT: We present a 2Dust model for the dust shell around a LMC long-period variable (LPV) previously studied as part of the OGLE survey. OGLE LMC LPV 28579 (SAGE J051306.40-690946.3) is a carbon-rich asymptotic giant branch (AGB) star for which we have photometry and spectra from the Spitzer SAGE and SAGE-Spec programs along with UBVIJHK_s photometry. By modeling this source, we obtain a baseline set of dust properties to be used in the construction of a grid of models for carbon stars. We reproduce its spectral energy distribution using a mixture of AmC and SiC (15% by mass). The grain sizes are distributed according to the KMH model. The best-fit model has an optical depth of 0.28 for the shell at the peak of the SiC feature, with R_in~1430 R_sun or 4.4 R_star. The temperature at this inner radius is 1310 K. Assuming an expansion velocity of 10 km s^-1, we obtain a dust mass-loss rate of 2.5x10^-9 M_sun yr-1. We calculate a 15% variation in this rate by testing the fit sensitivity against variation in input parameters. We also present a simple model for the molecular gas in the extended atmosphere that could give rise to the 13.7 \mu m feature seen in the spectrum. We find that a combination of CO and C_2H_2 gas at an excitation temperature of about 1000 K and column densities of 3x10^21 cm^-2 and 10^19 cm^-2 respectively are able to reproduce the observations. Given that the excitation temperature is close to T_dust(R_in), most of the molecular contribution probably arises from the inner shell region. The luminosity corresponding to the first epoch of SAGE observations is 6580 L_sun. For an effective temperature of about 3000 K, this implies a stellar mass of 1.5-2 M_sun and an age of 1-2.5 Gyr. For a gas:dust ratio of 200, we obtain a gas mass-loss rate of 5.0x10^-7 M_sun yr^-1, consistent with the gas mass-loss rates estimated from the period, color and 8 \mu m flux of the source. Comment: 14 pages, 5 figures, accepted for publication in Astronomy & Astrophysics
  09/2010;
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  Available from: Frank P. Israel

  Article: Herschel Inventory of The Agents of Galaxy Evolution (HERITAGE): the Large Magellanic Cloud dust

  M. Meixner, F. Galliano, S. Hony, J. Roman-Duval, T. Robitaille, P. Panuzzo, M. Sauvage, K Gordon, C. Engelbracht, K. Misselt, [......], B. Sargent, M. Sewiło, J. D. Simon, R. Skibba, L. J. Smith, S. Srinivasan, A. G. G. M. Tielens, J. Th. van Loon, B. Whitney, P. M. Woods
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  ABSTRACT: The HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) of the Magellanic Clouds will use dust emission to investigate the life cycle of matter in both the Large and Small Magellanic Clouds (LMC and SMC). Using the Herschel Space Observatory's PACS and SPIRE photometry cameras, we imaged a 2x8 square degree strip through the LMC, at a position angle of ~22.5 degrees as part of the science demonstration phase of the Herschel mission. We present the data in all 5 Herschel bands: PACS 100 and 160 {\mu}m and SPIRE 250, 350 and 500 {\mu}m. We present two dust models that both adequately fit the spectral energy distribution for the entire strip and both reveal that the SPIRE 500 {\mu}m emission is in excess of the models by 6 to 17%. The SPIRE emission follows the distribution of the dust mass, which is derived from the model. The PAH-to-dust mass (f_PAH) image of the strip reveals a possible enhancement in the LMC bar in agreement with previous work. We compare the gas mass distribution derived from the HI 21 cm and CO J=1-0 line emission maps to the dust mass map from the models and derive gas-to-dust mass ratios (GDRs). The dust model, which uses the standard graphite and silicate optical properties for Galactic dust, has a very low GDR = 65(+15,-18) making it an unrealistic dust model for the LMC. Our second dust model, which uses amorphous carbon instead of graphite, has a flatter emissivity index in the submillimeter and results in a GDR = 287(+25,-42) that is more consistent with a GDR inferred from extinction. Comment: To be published in Astronomy & Astrophysics, Herschel First Results Issue
  06/2010;
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  Available from: Frank P. Israel

  Article: The Herschel revolution: unveiling the morphology of the high mass star formation sites N44 and N63 in the LMC

  S. Hony, F. Galliano, S. C. Madden, P. Panuzzo, M. Meixner, C. Engelbracht, K. Misselt, M. Galametz, M. Sauvage, J. Roman-Duval, [......], A. Bolatto, K Okumura, C. -H. R. Chen, R. Indebetouw, F. P. Israel, E. Kwon, A. Li, F. Kemper, M. S. Oey, M. Rubio
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  ABSTRACT: We study the structure of the medium surrounding sites of high-mass star formation to determine the interrelation between the HII regions and the environment from which they were formed. The density distribution of the surroundings is key in determining how the radiation of the newly formed stars interacts with the surrounds in a way that allows it to be used as a star formation tracer. We present new Herschel/SPIRE 250, 350 and 500 mum data of LHA 120-N44 and LHA 120-N63 in the LMC. We construct average spectral energy distributions (SEDs) for annuli centered on the IR bright part of the star formation sites. The annuli cover ~10-~100 pc. We use a phenomenological dust model to fit these SEDs to derive the dust column densities, characterise the incident radiation field and the abundance of polycyclic aromatic hydrocarbon molecules. We see a factor 5 decrease in the radiation field energy density as a function of radial distance around N63. N44 does not show a systematic trend. We construct a simple geometrical model to derive the 3-D density profile of the surroundings of these two regions. Herschel/SPIRE data have proven very efficient in deriving the dust mass distribution. We find that the radiation field in the two sources behaves very differently. N63 is more or less spherically symmetric and the average radiation field drops with distance. N44 shows no systematic decrease of the radiation intensity which is probably due to the inhomogeneity of the surrounding molecular material and to the complex distribution of several star forming clusters in the region. Comment: Accepted for publication in A&A letters (Herschel special issue)
  05/2010;
• Article: Youngest massive protostars in the LMC (Sewilo+, 2010)

  M Sewilo, R Indebetouw, L ~R Carlson, B Whitney, C -H ~R Chen, M Meixner, T Robitaille, J ~T Loon, J ~M Oliveira, E Churchwell, [......], P Panuzzo, M Sauvage, J Roman-Duval, K Gordon, C Engelbracht, K Misselt, K Okumura, T Beck, J Hora, P ~M Woods
  VizieR Online Data Catalog. 04/2010; 351:89073.
• Conference Proceeding: Two Magellanic Cloud Star-Forming Clusters from Optical to Infrared

  K Romita, L ~R Carlson, M Sewilo, M Meixner, E Sabbi, K Gordon, A Nota, M Sirianni, L ~J Smith, C Leither, [......], R Indebetouw, D Kato, J ~S Gallagher, B Babler, M Meade, M ~S Oey, M Cignoni, M Tosi, U Vijh, R Walterbos
  American Astronomical Society Meeting Abstracts #215; 01/2010
• Conference Proceeding: Infrared Variable Stars in the Small Magellanic Cloud Using the Spitzer SAGE-SMC Survey

  M Terrazas, B Whitney, M Meade, B Babler, R Indebetouw, J Hora, S Bracker, C Engelbracht, K Gordon, M Block, K Misselt, M Meixner, M Sewilo, B Shiao
  American Astronomical Society Meeting Abstracts #215; 01/2010
• Conference Proceeding: HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) in the Magellanic Clouds

  M Meixner, S Hony, S Madden, K Gordon, C Engelbracht, A ~G ~G ~M Tielens, A Bolatto, J Duval, B Babler, K Misselt, [......], M Sauvage, S Srinivasan, T Robitaille, J Loon, B Whitney, J Oliveira, J Hora, C Bot, R Skibba, HERITAGE Team
  American Astronomical Society Meeting Abstracts #215; 01/2010
• Article: Discovery of 21 Micron Sources in the Magellanic Clouds

  Kevin Volk, M. Matsuura, J. Bernard-Salas, G. C. Sloan, R. Szczerba, F. Kemper, P. M. Woods, B. J. Hrivnak, X. Tielens, M. Meixner, K. Gordon, R. Indebetouw, J. van Loon, M. Marengo
  [show abstract] [hide abstract]
  ABSTRACT: We report the detection of the unidentified emission feature at 21 microns in infrared spectra of eight post-AGB objects in the Magellanic Clouds. This is the first detection of the feature in extragalactic objects. The observations were made by the IRS instrument on the Spitzer Space Telescope, as part of multiple observing programs. The eight new detections are considerable, given that only 15 post-AGB objects in the Galaxy have been identified with 21-micron features. The infrared spectra with 21-micron features in the Magellanic Clouds tend to show stronger emission from the accompanying aromatic hydrocarbon (PAH) features than those in the Galaxy do. The dust in the new objects also generally appears to be hotter, which might imply that they have not evolved as far from the AGB as their Galactic analogues. The 21-micron features are weaker on average than in the Galactic objects, although two of the objects do show strong features. We present the Spitzer spectra of these objects as well as the available ground-based optical and near-infrared photometry and some preliminary results from radiative transfer models.
  12/2009; 42:486.
• Conference Proceeding: Spatial Distribution and Variations of Dust Abundances in the Large Magellanic Cloud

  D Paradis, W ~T Reach, J Bernard, M Block, C ~W Engelbracht, K Gordon, J ~L Hora, R Indebetouw, A Kawamura, M Meade, M Meixner, M Sewilo, U ~P Vijh, K Volk
  American Astronomical Society Meeting Abstracts #214; 05/2009
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  Available from: Joseph L. Hora

  Article: Physical Conditions in the Ionized Gas of 30 Doradus

  R. Indebetouw, G. E. de Messières, S. Madden, C. Engelbracht, J. D. Smith, M. Meixner, B. Brandl, L. J. Smith, F. Boulanger, F. Galliano, K. Gordon, J. L. Hora, M. Sewilo, A. G. G. M. Tielens, M. Werner, and M. G. Wolfire
  [show abstract] [hide abstract]
  ABSTRACT: We present a mid-infrared spectroscopic data cube of the central part of 30 Doradus, observed with Spitzer's Infrared Spectrograph and Multiband Imaging Photometer for Spitzer/spectral energy distribution mode. Aromatic dust emission features and emission lines from molecular and atomic hydrogen are detected but they are not particularly strong. The dominant spectral features are emission lines from moderately ionized species of argon, neon, and sulfur, which are used to determine the physical conditions in the ionized gas. The ionized gas excitation shows strong variations on parsec scales, some of which can plausibly be associated with individual hot stars. We fit the ionic line strengths with photoionization and shock models, and find that photoionization dominates in the region. The ionization parameter U traces the rim of the central bubble, as well as highlighting isolated sources of ionization, and at least one quiescent clump. The hardness of the ionizing radiation field T rad reveals several "hot spots" that are either the result of individual very hot stars or trace the propagation of the diffuse ionizing field through the surrounding neutral cloud. Consistent with other measurements of giant H II regions, log(U) ranges between –3 and –0.75, and T rad between 30,000 and 85,000 K.
  The Astrophysical Journal 03/2009; 694(1):84. · 6.02 Impact Factor
• Article: A spatially resolved study of photoelectric heating and [C II] cooling in the LMC. Comparison with dust emission as seen by SAGE

  D Rubin, S Hony, S ~C Madden, A ~G ~G ~M Tielens, M Meixner, R Indebetouw, W Reach, A Ginsburg, S Kim, K Mochizuki, [......], C ~W Engelbracht, B -Q For, K Gordon, J ~L Hora, C Leitherer, M Meade, K Misselt, M Sewilo, U Vijh, B Whitney
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  ABSTRACT: Context. Photoelectric heating is a dominant heating mechanism for many phases of the interstellar medium. We study this mechanism throughout the Large Magellanic Cloud (LMC). Aims. We aim to quantify the importance of the [C II] cooling line and the photoelectric heating process of various environments in the LMC and to investigate which parameters control the extent of photoelectric heating. Methods. We use the BICE [C II] map and the Spitzer/SAGE infrared maps. We examine the spatial variations in the efficiency of photoelectric heating: photoelectric heating rate over power absorbed by grains, i.e. the observed [C II] line strength over the integrated infrared emission. We correlate the photoelectric heating efficiency and the emission from various dust constituents and study the variations as a function of H emission, dust temperatures, and the total infrared luminosity. The observed variations are interpreted in a theoretical framework. From this we estimate radiation field, gas temperature, and electron density. Results. We find systematic variations in photoelectric efficiency. The highest efficiencies are found in the diffuse medium, while the lowest coincide with bright star-forming regions (~1.4 times lower). The [C II] line emission constitutes 1.32% of the far infrared luminosity across the whole of the LMC. We find correlations between the [C II] emission and ratios of the mid infrared and far infrared bands, which comprise various dust constituents. The correlations are interpreted in light of the spatial variations of the dust abundance and by the local environmental conditions that affect the dust emission properties. As a function of the total infrared surface brightness, S_(TIR), the [C II] surface brightness can be described as: S_([C II]) = 1.25 S^(0.69)_(TIR)[10^(-3) erg s^(-1) cm^(-2) sr^(-1)], for S_(TIR) ≳ 3.2 x 10^(-4) erg s^(-1) cm^(-2) sr^(-1). We provide a simple model of the photoelectric efficiency as a function of the total infrared luminosity. We find a power-law relation between radiation field and electron density, consistent with other studies. The [C II] emission is well-correlated with the 8 µm emission, suggesting that the polycyclic aromatic hydrocarbons play a dominant role in the photoelectric heating process.
  åp. 02/2009; 494:647-661.
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  Available from: arxiv.org

  Article: Variable Evolved Stars and Young Stellar Objects Discovered in the Large Magellanic Cloud Using the SAGE Survey

  Uma P. Vijh, M. Meixner, B. Babler, M. Block, S. Bracker, C. W. Engelbracht, B. For, K. Gordon, J. Hora, R. Indebetouw, C. Leitherer, M. Meade, K. Misselt, M. Sewilo, S. Srinivasan, and B. Whitney
  [show abstract] [hide abstract]
  ABSTRACT: We present initial results and source lists of variable sources in the Large Magellanic Cloud (LMC) for which we detect thermal infrared variability from the Surveying the Agents of a Galaxy's Evolution (SAGE) survey, which had two epochs of photometry separated by 3 months. The SAGE survey mapped a 7° × 7° region of the LMC using the Infrared Array Camera (IRAC) and the MIPS instruments on board Spitzer. Variable sources are identified using a combination of the IRAC 3.6, 4.5, 5.8, 8.0 μ bands and the MIPS 24 μ bands. An error-weighted flux difference between the two epochs is used to assess the variability. Of the ~3 million sources detected at both epochs, we find ~2000 variable sources for which we provide electronic catalogs. Most of the variable sources can be classified as asymptotic giant branch (AGB) stars. A large fraction (>66%) of the extreme AGB stars are variable and only smaller fractions of carbon-rich (6.1%) and oxygen-rich (2.0%) stars are detected as variable sources. We also detect a population of variable young stellar object candidates.
  The Astronomical Journal 01/2009; 137(2):3139. · 4.03 Impact Factor
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  Available from: Joseph L. Hora

  Article: A spatially resolved study of photoelectric heating and [CII] cooling in the LMC

  D. Rubin, S. Hony, S. C. Madden, A. G. G. M. Tielens, M. Meixner, R. Indebetouw, W. Reach, A. Ginsburg, S Kim, K. Mochizuki, [......], C. W. Engelbracht, B. -Q. For, K Gordon, J. L. Hora, C. Leitherer, M. Meade, K. Misselt, M. Sewilo, U. Vijh, B. Whitney
  [show abstract] [hide abstract]
  ABSTRACT: (abridged) We study photoelectric heating throughout the Large Magellanic Cloud. We quantify the importance of the [CII] cooling line and the photoelectric heating process of various environments in the LMC and investigate which parameters control the extent of photoelectric heating. We use the BICE [CII] map and the Spitzer/SAGE infrared maps. We examine the spatial variations in the efficiency of photoelectric heating: photoelectric heating rate over power absorbed by grains. We correlate the photoelectric heating efficiency and the emission from various dust constituents and study the variations as a function of H\alpha emission, dust temperatures, and the total infrared luminosity. From this we estimate radiation field, gas temperature, and electron density. We find systematic variations in photoelectric efficiency. The highest efficiencies are found in the diffuse medium, while the lowest coincide with bright star-forming regions (~1.4 times lower). The [CII] line emission constitutes 1.32% of the far infrared luminosity across the whole of the LMC. We find correlations between the [CII] emission and ratios of the mid infrared and far infrared bands, which comprise various dust constituents. The correlations are interpreted in light of the spatial variations of the dust abundance and by the local environmental conditions that affect the dust emission properties. As a function of the total infrared surface brightness, S_{TIR}, the [CII] surface brightness can be described as: S_{[CII]}=1.25 S_{TIR}^{0.69} [10^{-3} erg s^{-1} cm^{-2} sr^{-1}]. The [CII] emission is well-correlation with the 8 micrometer emission, suggesting that the polycyclic aromatic hydrocarbons play a dominant role in the photoelectric heating process.
  01/2009;