F. Markwick-Kemper

The University of Manchester, Manchester, ENG, United Kingdom

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Publications (22)41.95 Total impact

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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.
    09/2009;
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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) × 10–3 M ☉ yr–1.
    The Astronomical Journal 04/2009; 137(6):4810. · 4.97 Impact Factor
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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.
    IAU Symposium; 03/2009
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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.
    The Astrophysical Journal 12/2008; 632(2):956. · 6.73 Impact Factor
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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.
    Spitzer Proposal. 03/2008;
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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.
    01/2008;
  • A. G. Jensen, F. Markwick-Kemper, T. P. Snow
    Reviews in Mineralogy & Geochemistry - REV MINERAL GEOCHEM. 01/2008; 68(1):55-72.
  • 12/2007: pages 333-334;
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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.
    The Astrophysical Journal 10/2007; · 6.73 Impact Factor
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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
    08/2007;
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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.
    12/2006;
  • 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.
    12/2006;
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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
    Astronomy and Astrophysics 11/2006; · 5.08 Impact Factor
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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).
    The Astronomical Journal 09/2006; · 4.97 Impact Factor
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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
    The Astrophysical Journal 12/2005; · 6.73 Impact Factor
  • 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.
    Proceedings of the International Astronomical Union 11/2005; 37:1302.
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    F. Markwick-Kemper, J. D. Green, E. Peeters
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    ABSTRACT: We present Spitzer high spectral resolution IRS spectroscopy of three positions in the carbon-rich outflow of post-AGB star HD 44179, better known as the Red Rectangle. Surprisingly, the spectra show some strong unknown mid-infrared resonances, in the 13-20 micron range. The shape and position of these resonances varies with position in the nebula, and are not correlated with the PAH features. We conclude these features are due to oxygen-rich minerals, located in a region which is believed to be predominantly carbon-rich. We provide possible explanations for the presence of oxygen-rich dust in the carbon-rich outflows. Simple Mg-Fe-oxides are suggested as carriers of these unidentified features. Comment: accepted by ApJL; 5 pages; 4 figures
    The Astrophysical Journal 06/2005; · 6.73 Impact Factor
  • E. Peeters, F. Markwick-Kemper
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    ABSTRACT: R CrB stars are evolved late-type (F-G) supergiants whose atmospheres are extremely hydrogen deficient and carbon- and nitrogen-rich. They suffer irregular periods of minimum light when the star has faded by several orders of magnitude. These minima are related to the formation of carbon-rich dust. However, the detailed identification of the dust particles and the dust formation process in these R CrB stars remain mysterious. In the outflow of C-rich AGB stars, acetylene (C2H2) and its radical derivatives are likely to be the dominant precursor molecules from which PAHs and soot are formed. However, this formation route does not apply to H-poor environments. Here, the formation process is based on the formation of C-chain radicals and subsequent monocyclic ring molecules followed by planar, carbon hexagon structures. The absence of hydrogen leads to dangling bonds at the peripheries. Incorporating pentagons and curling reduces the dangling bonds which can lead to the formation of fullerene molecules (e.g. C60). Therefore, the presence of PAH molecules or fullerenes can distinguish between these two different dust formation pathways. Here, we present Spitzer-IRS spectroscopic observations of three R CrB stars spanning a range in H abundances. These data allow to characterize the different dust components and probe their spatial distribution. In particular, this study focuses on presence or non-presence of PAH molecules and C60 and hence investigate the role of hydrogen in the dust formation process around R CrB stars.
    Proceedings of the International Astronomical Union 01/2005; 235.
  • 01/2005;
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    ABSTRACT: Cycling of matter between the ISM and stars drives the evolution of a galaxy's visible matter and its emission characteristics. To understand this recycling, the SAGE legacy project has surveyed the Large Magellanic Cloud with IRAC and MIPS to study the physical processes of the ISM, the formation of new stars and the injection of mass by evolved stars and their relationships on the galaxy-wide scale. Due to its proximity, favorable viewing angle, and multi-wavelength information, the LMC is uniquely suited to survey the agents of a galaxy's evolution, the ISM and stars. We propose to leverage the SAGE legacy program to conduct a comprehensive IRS and MIPS-SED spectroscopy program of dust with the goal to determine the composition, origin, evolution, and observational characteristics of interstellar dust and its role in the LMC. Analysis of the spectra will yield composition and abundance of the dust compounds in different LMC objects, including AGB stars, post-AGB, young stellar objects, HII regions and the general diffuse ISM and provide a quantitative picture of the dust lifecyle. Besides dust features, the spectra will also contain molecular and atomic emission and absorption lines, providing the diagnostics to determine physical parameters such as temperature, density and radiation field - all important to the formation and processing of dust, and understanding the life cycle of matter. The proposed spectroscopic survey will provide critical underpinning for the SAGE survey by linking observed IRAC and MIPS colors of LMC objects to the infrared spectral type of the object. We will to the maximum extent utilize the LMC spectroscopy available in the Spitzer archive. A subset of the IRS point sources from this proposal will also be surveyed in MIPS SED. Legacy data products that will be made available to the public include all reduced single point spectra and data cubes, feature maps, a spectral catalog, and a fully classified SAGE point source catalog.

Publication Stats

178 Citations
41.95 Total Impact Points

Institutions

  • 2007–2009
    • The University of Manchester
      • School of Physics and Astronomy
      Manchester, ENG, United Kingdom
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, MD, United States
  • 2006–2008
    • University of Virginia
      • Department of Astronomy
      Charlottesville, Virginia, United States
  • 2005
    • University of California, Los Angeles
      • Department of Physics and Astronomy
      Los Angeles, California, United States