F. Markwick-Kemper

The University of Manchester, Manchester, ENG, United Kingdom

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Publications (27)49.91 Total impact

  • G. C. Sloan · A. A. Zijlstra · K. E. Kraemer · F. Markwick-Kemper · J. M. Leisenring
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    ABSTRACT: We review the five programs to observe evolved stars in the Magellanic Clouds using the Infrared Spectrometer during the first half of the Spitzer Space Telescope mission. These programs have left a legacy of 176 spectra in the Large Magellanic Cloud and 63 in the Small Magellanic Cloud, and they have led to the publication of 12 refereed papers, with several more in preparation.
    No preview · Conference Paper · Sep 2009
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    ABSTRACT: We present empirical relations describing excess emission from evolved stars in the Large Magellanic Cloud (LMC) using data from the Spitzer Space Telescope Surveying the Agents of a Galaxy's Evolution (SAGE) survey which includes the Infrared Array Camera (IRAC) 3.6, 4.5, 5.8, and 8.0 μm and Multiband Imaging Photometer (MIPS) 24, 70, and 160 μm bands. We combine the SAGE data with the Two Micron All Sky Survey (2MASS; J, H, and K s) and the optical Magellanic Cloud Photometric Survey (MCPS; U, B, V, and I) point source catalogs in order to create complete spectral energy distributions (SEDs) of the asymptotic giant branch (AGB) star candidates in the LMC. AGB star outflows are among the main producers of dust in a galaxy, and this mass loss results in an excess in the fluxes observed in the 8 and 24 μm bands. The aim of this work is to investigate the mass loss return by AGB stars to the interstellar medium of the LMC by studying the dependence of the infrared excess flux on the total luminosity. We identify oxygen-rich, carbon-rich, and extreme AGB star populations in our sample based on their 2MASS and IRAC colors. The SEDs of oxygen- and carbon-rich AGB stars are compared with appropriate stellar photosphere models to obtain the excess flux in all the IRAC bands and the MIPS 24 μm band. Extreme AGB stars are dominated by circumstellar emission at 8 and 24 μm; thus we approximate their excesses with the flux observed in these bands. We find about 16,000 O-rich, 6300 C-rich, and 1000 extreme sources with reliable 8 μm excesses, and about 4500 O-rich, 5300 C-rich, and 960 extreme sources with reliable 24 μm excesses. The excesses are in the range 0.1 mJy to 5 Jy. The 8 and 24 μm excesses for all three types of AGB candidates show a general increasing trend with luminosity. The color temperature of the circumstellar dust derived from the ratio of the 8 and 24 μm excesses decreases with an increase in excess, while the 24 μm optical depth increases with excess. The extreme AGB candidates are the major contributors to the mass loss, and we estimate the total AGB mass loss return to the LMC to be (5.9-13) × 10–3M ☉ yr–1.
    Full-text · Article · Apr 2009 · The Astronomical Journal

  • No preview · Article · Mar 2009
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    ABSTRACT: Early results from the SAGE-SMC (Surveying the Agents of Galaxy Evolution in the tidally-disrupted, low-metallicity Small Magellanic Cloud) Spitzer legacy program are presented. These early results concentrate on the SAGE-SMC MIPS observations of the SMC Tail region. This region is the high H i column density portion of the Magellanic Bridge adjacent to the SMC Wing. We detect infrared dust emission and measure the gas-to-dust ratio in the SMC Tail and find it similar to that of the SMC Body. In addition, we find two embedded cluster regions that are resolved into multiple sources at all MIPS wavelengths.
    No preview · Conference Paper · Mar 2009
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    ABSTRACT: We present spectra of four Herbig Ae/Be stars obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. All four of the sources show strong emission from polycyclic aromatic hydrocarbons (PAHs), with the 6.2 μm emission feature shifted to 6.3 μm and the strongest C–C skeletal-mode feature occurring at 7.9 μm instead of at 7.7 μm, as is often seen. Remarkably, none of the four stars has silicate emission. The strength of the 7.9 μm feature varies with respect to the 11.3 μm feature among the sources, indicating that we have observed PAHs with a range of ionization fractions. The ionization fraction is higher for systems with hotter and brighter central stars. Two sources, HD 34282 and HD 169142, show emission features from aliphatic hydrocarbons at 6.85 and 7.25 μm. The spectrum of HD 141569 shows a previously undetected emission feature at 12.4 μm that may be related to the 12.7 μm PAH feature. The spectrum of HD 135344, the coolest star in our sample, shows an unusual profile in the 7-9 μm region, with the peak emission to the red of 8.0 μm and no 8.6 μm PAH feature.
    Full-text · Article · Dec 2008 · The Astrophysical Journal

  • No preview · Article · Aug 2008 · Astronomy and Astrophysics
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    ABSTRACT: We propose a comprehensive spectroscopic survey of the Small Magellanic Cloud (SMC), using the IRS and MIPS-SED. The SMC has a metallicity similar to high-redshift galaxies, and its proximity makes it a spatially resolved proxy for star-forming galaxies in the distant, early Universe. The sensitivity of the Spitzer Space Telescope allows us to to observe dust in nearly every stage of its life cycle in the SMC so that we can study how the interactions of dust and its host galaxy differ from more metal-rich systems like the Galaxy and the LMC. Our proposed observations concentrate on important classes underrepresented in the archive of SMC spectra such as young stellar objects, compact H II regions, objects in transition to and from the asymptotic giant branch, and supergiants. These observations, in combination with those already in the archive, will give us a complete picture of the dust in a metal-poor star-forming galaxy similar to those in the early Universe. We request 116 hours, 62 as IRS GTO time and 54 as GO time.
    No preview · Article · Mar 2008
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    G. Zasowski · F. Markwick-Kemper · Dan M. Watson · E. Furlan · C. J. Bohac · C. Hull · J. D. Green
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    ABSTRACT: We present observations of Taurus-Auriga Class I/II protostars obtained with the Spitzer InfraRed Spectrograph. Detailed spectral fits to the 6 and 15 micron features are made, using publicly-available laboratory data, to constrain the molecular composition, abundances, and levels of thermal processing along the lines of sight. We provide an inventory of the molecular environments observed, which have an average composition dominated by water ice with ~12% CO_2 (abundance relative to H_2O), >~2-9% CH_3OH, <~14% NH_3, ~4% CH_4, ~2% H_2CO, ~0.6% HCOOH, and ~0.5% SO_2. We find CO_2/H_2O ratios nearly equivalent to those observed in cold clouds and lines of sight toward the galactic center. The unidentified 6.8 micron profile shapes vary from source to source, and it is shown to be likely that even combinations of the most common candidates (NH_4+ and CH_3OH) are inadequate to explain the feature fully. We discuss correlations among SED spectral indices, abundance ratios, and thermally-processed ice fractions and their implications for CO_2 formation and evolution. Comparison of our spectral fits to cold molecular cloud sight-lines indicate abundant prestellar ice environments made even richer by the radiative effects of protostars. Our results add additional constraints and a finer level of detail to current full-scale models of protostellar and protoplanetary systems.
    Full-text · Article · Jan 2008

  • No preview · Conference Paper · Jan 2008
  • Adam G. Jensen · F. Markwick-Kemper · Theodore P. Snow
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    ABSTRACT: The oxygen that is observed in the Solar System today is a remnant of the interstellar oxygen that was in the dense molecular cloud that collapsed to form the Solar System. While the chemical evolution of the Galaxy has progressed since then, processes in the interstellar medium (ISM) that involve oxygen are relevant to the origins of oxygen in the Solar System. Oxygen in the ISM can be found as neutral or ionized atomic gas and as a constituent of molecular gas, volatile ices, and refractory minerals in dust, with the dominant state depending on the specific environment. The gas-phase abundance of atomic oxygen is well-known in the diffuse ISM that fills most of the Galaxy's volume, but the state of oxygen in denser environments is poorly understood. The ISM abundances of isotopes of oxygen other than 160 cannot be easily determined due to observational constraints. Oxygen in interstellar dust is primarily found in the form of silicates that are created in evolved stars and then ejected into the ISM before being incorporated into the formation of new solar systems. Some of the important unknowns concerning oxygen in the ISM include the "cosmic" (i.e., total) abundance of oxygen, the abundance of oxygen in dust, and the details of dust grain processing in the ISM.
    No preview · Article · Jan 2008 · Reviews in Mineralogy and Geochemistry
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    F. Markwick-Kemper · S. C. Gallagher · D. C. Hines · J. Bouwman
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    ABSTRACT: We have determined the mineralogical composition of dust in the broad absorption line (BAL) quasar PG 2112+059 using mid-infrared spectroscopy obtained with the Spitzer Space Telescope. From spectral fitting of the solid state features, we find evidence for Mg-rich amorphous silicates with olivine stoichiometry, as well as the first detection of corundum (Al 2O3) and periclase (MgO) in quasars. This mixed composition provides the first direct evidence for a clumpy density structure of the grain-forming region. The silicates in total encompass 56.5% +/- 1.4% of the identified dust mass, while corundum takes up 38+/-3 wt.%. Depending on the choice of continuum, a range of mass fractions is observed for periclase ranging from 2.7% +/- 1.7% in the most conservative case to 9% +/- 2% in a less-constrained continuum. In addition, we identify a feature at 11.2 mum as the crystalline silicate forsterite, with only a minor contribution from polycyclic aromatic hydrocarbons. The 5% +/- 3% crystalline silicate fraction requires high temperatures such as those found in the immediate quasar environment in order to counteract rapid destruction from cosmic rays.
    Full-text · Article · Oct 2007 · The Astrophysical Journal
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    L. Decin · S. Hony · A. de Koter · Geert MOLENBERGHS · S. Dehaes · F. Markwick-Kemper
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    ABSTRACT: Low and intermediate mass stars lose a significant fraction of their mass through a dust-driven wind during the Asymptotic Giant Branch (AGB) phase. Recent studies show that winds from late-type stars are far from being smooth. Mass-loss variations occur on different time scales, from years to tens of thousands of years. The variations appear to be particularly prominent towards the end of the AGB evolution. The occurrence, amplitude and time scale of these variations are still not well understood. The goal of our study is to gain insight into the structure of the circumstellar envelope (CSE) of WX Psc and map the possible variability of the late-AGB mass-loss phenomenon. We have performed an in-depth analysis of the extreme infrared AGB star WX Psc by modeling (1) the CO J=1-0 through 7-6 rotational line profiles and the full spectral energy distribution (SED) ranging from 0.7 to 1300 micron. We hence are able to trace a geometrically extended region of the CSE. Both mass-loss diagnostics bear evidence of the occurrence of mass-loss modulations during the last ~2000 yr. In particular, WX Psc went through a high mass-loss phase (Mdot~5e-5 Msun/yr) some 800 yr ago. This phase lasted about 600 yr and was followed by a long period of low mass loss (Mdot~5e-8 Msun/yr). The present day mass-loss rate is estimated to be ~6e-6 Msun/yr. The AGB star WX Psc has undergone strong mass-loss rate variability on a time scale of several hundred years during the last few thousand years. These variations are traced in the strength and profile of the CO rotational lines and in the SED. We have consistently simulated the behaviour of both tracers using radiative transfer codes that allow for non-constant mass-loss rates. Comment: 12 pages, accepted for publication in A&A
    Full-text · Article · Aug 2007 · Astronomy and Astrophysics
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    ABSTRACT: We will present empirical relations for excess emission from evolved stars in the Large Magellanic Cloud (LMC) using data from the Spitzer Space Telescope SAGE (Surveying the Agents of a Galaxy's Evolution) survey. Combined with the 2MASS survey and the optical Magellanic Cloud Photometric Survey (MCPS) catalog, these data enable multiband analysis of evolved stars, and can help probe the life cycle of dust in the LMC. Outflows from evolved asymptotic giant branch (AGB) stars and supergiants are the main producers of dust in a galaxy, and the aim of this work is to investigate the mass loss return by AGBs and supergiants to the interstellar medium of the LMC. The spectral energy distributions (SEDs) are compared with plane-parallel (for Carbon-rich AGBs) and spherical (for Oxygen-rich AGBs) atmosphere models to obtain the excess flux in the 8 and 24 micron bands, which is plotted against the total integrated flux. We will show that this excess emission increases with total integrated flux, and the 24 micron flux for heavily obscured AGBs is entirely due to excess emission from dust. The SAGE Project is supported by NASA/Spitzer grant 1275598 and NASA NAG5-12595.
    No preview · Conference Paper · Dec 2006
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    ABSTRACT: The Spitzer photometric survey of the Large Magellanic Cloud (SAGE) has the sensitivity to detect all evolved stars of luminosity 1000 L &sun; or higher. In order to estimate the global mass return to the interstellar medium for these stars we will need to (a) classify the type of object based upon the available photometry from Spitzer, and 2MASS where available; and (b) estimate the dust shell properties directly from these observations. This will require calculating a grid of dust radiative transfer models to cover the range of parameters suitable for stars in the LMC and having an automatic algorithm for selecting the best fit model for each observed object. Given the lower metallicity of the LMC compared to the Galaxy we need to study some of the brighter objects in detail including fitting of spectroscopy observations to understand the basic dust properties for both oxygen-rich objects with silicate dust and carbon-rich objects with amorphous carbon and silicon-carbide dust. The dust to gas mass ratio must also be estimated, as it is expected to be somewhat higher than the values derived for galactic objects. We will show some preliminary results of the modelling work for a small number of the brighter AGB stars or M-type supergiants in the LMC, as well as discussing the identification of groups of objects in the multi-color space defined by the Spitzer IRAC, Spitzer MIPS, and 2MASS observations. The SAGE Project is supported by NASA/Spitzer grant 1275598 and NASA NAG5-12595.
    No preview · Conference Paper · Dec 2006
  • Francisca Markwick-Kemper · C. Dijkstra
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    ABSTRACT: We present 5-40 micron spectroscopy obtained with the Infrared Spectrograph on board Spitzer of a sample of oxygen-rich Asymptotic Giant Branch stars. The spectra of these dust-enshrouded objects all show the characteristic resonances at 9.7 and 18 micron due to 'amorphous' silicates. In addition, several of the spectra show the finer substructure that is ascribed to crystalline silicates, in particular crystalline forsterite. We will explore the range in physical conditions at which these crystalline silicates are found, and compare those to the crystalline fraction seen in Galactic post-main sequence stars in the same evolutionary stage.
    No preview · Conference Paper · Dec 2006
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    ABSTRACT: I will present preliminary results for Evolved Star properties and their mass--loss contribution to the Large Magellanic Cloud (LMC) as viewed from color--magnitude diagrams (CMDs) obtained with the Spitzer space telescope SAGE (Surveying the Agents of a Galaxy's Evolution) survey. These data represent the deepest, widest mid--infrared CMDs of their kind ever produced in the LMC. Combined with the 2MASS survey, the diagrams are used to delineate the evolved stellar populations in the LMC from which we can deduce the relative contributions to the complete mass--loss budget. I will show initial fits to the spectral energy distributions of the LMC stars using dust radiative transfer models and assumptions about the evolved star envelopes guided by existing observations of luminous stars. Owing to the high angular resolution and sensitivity of Spitzer, we can identify essentially all the important mass--loss sources in the galaxy. Indeed, there is strong evidence from the 24 micron channel of Spitzer that previously unexplored, lower luminosity oxygen--rich AGB stars contribute significantly to the mass loss budget. This work has been funded by generous grants from the NASA SST program.
    No preview · Conference Paper · Dec 2006
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    ABSTRACT: We investigate the composition and shape distribution of silicate dust grains in the interstellar medium. The effect of the amount of magnesium in the silicate lattice is studied. We fit the spectral shape of the interstellar 10 mu extinction feature as observed towards the galactic center. We use very irregularly shaped coated and non-coated porous Gaussian Random Field particles as well as a statistical approach to model shape effects. For the dust materials we use amorphous and crystalline silicates with various composition and SiC. The results of our analysis of the 10 mu feature are used to compute the shape of the 20 mu silicate feature and to compare this with observations. By using realistic particle shapes we are, for the first time, able to derive the magnesium fraction in interstellar silicates. We find that the interstellar silicates are highly magnesium rich (Mg/(Fe+Mg)>0.9) and that the stoichiometry lies between pyroxene and olivine type silicates. This composition is not consistent with that of the glassy material found in GEMS in interplanetary dust particles indicating that these are, in general, not unprocessed remnants from the interstellar medium. Also, we find a significant fraction of SiC (~3%). We discuss the implications of our results for the formation and evolutionary history of cometary and circumstellar dust. We argue that the fact that crystalline silicates in cometary and circumstellar grains are almost purely magnesium silicates is a natural consequence of our findings that the amorphous silicates from which they were formed were already magnesium rich. Comment: Accepted for publication in A&A
    Full-text · Article · Nov 2006 · Astronomy and Astrophysics
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    ABSTRACT: Color-magnitude diagrams (CMDs) are presented for the Spitzer SAGE (Surveying the Agents of a Galaxy's Evolution) survey of the Large Magellanic Cloud (LMC). IRAC and MIPS 24 um epoch one data are presented. These data represent the deepest, widest mid-infrared CMDs of their kind ever produced in the LMC. Combined with the 2MASS survey, the diagrams are used to delineate the evolved stellar populations in the Large Magellanic Cloud as well as Galactic foreground and extragalactic background populations. Some 32000 evolved stars brighter than the tip of the red giant branch are identified. Of these, approximately 17500 are classified as oxygen-rich, 7000 carbon-rich, and another 1200 as ``extreme'' asymptotic giant branch (AGB) stars. Brighter members of the latter group have been called ``obscured'' AGB stars in the literature owing to their dusty circumstellar envelopes. A large number (1200) of luminous oxygen--rich AGB stars/M supergiants are also identified. Finally, there is strong evidence from the 24 um MIPS channel that previously unexplored, lower luminosity oxygen-rich AGB stars contribute significantly to the mass loss budget of the LMC (1200 such sources are identified).
    Full-text · Article · Sep 2006 · The Astronomical Journal
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    ABSTRACT: We report spectra obtained with the Spitzer Space Telescope in the 5 to 35 micron range of HD 233517, an evolved K2 III giant with circumstellar dust. At wavelengths longer than 13 microns, the flux is a smooth continuum that varies approximately as frequency to the -5/3 power. For wavelengths shorter than 13 microns, although the star is oxygen-rich, PAH features produced by carbon-rich species at 6.3 microns, 8.2 microns, 11.3 microns and 12.7 microns are detected along with likely broad silicate emission near 20 microns. These results can be explained if there is a passive, flared disk orbiting HD 233517. Our data support the hypothesis that organic molecules in orbiting disks may be synthesized in situ as well as being incorporated from the interstellar medium. Comment: 11 pages, 2 figures, ApJ Letters, in press
    Preview · Article · Dec 2005 · The Astrophysical Journal
  • E. Peeters · F. Markwick-Kemper · L. J. Allamandola
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    ABSTRACT: We present Spitzer-IRS observations of 11 different positions within the vicinity of the Orion Bar. Together with ISO observations of the Orion Bar, we obtain a more complete infrared view on the spatial variations of the spectral characteristics observed towards Orion. On top of a strong dust continuum, we observe fine-structure lines, molecular hydrogen and PAH emission bands. We discuss the spatial variation of these emission components. In particular, we focus on the observed variations of the PAH bands in order to constrain the PAH family located in Orion and its distribution, and to probe the radiation field. In addition, these observations provide the opportunity to settle the question whether or not crystalline silicates are present in Orion. EP acknowledges the support of the National Research Council.
    No preview · Conference Paper · Nov 2005

Publication Stats

386 Citations
49.91 Total Impact Points

Institutions

  • 2007-2009
    • The University of Manchester
      • School of Physics and Astronomy
      Manchester, ENG, United Kingdom
  • 2008
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, MD, United States
  • 2005-2008
    • University of Virginia
      • Department of Astronomy
      Charlottesville, Virginia, United States
    • University of California, Los Angeles
      • Department of Physics and Astronomy
      Los Angeles, California, United States