Publications (45)63.9 Total impact
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Article: Early Science with SOFIA, the Stratospheric Observatory For Infrared Astronomy
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ABSTRACT: The Stratospheric Observatory For Infrared Astronomy (SOFIA) is an airborne observatory consisting of a specially modified Boeing 747SP with a 2.7 m telescope, flying at altitudes as high as 13.7 km (45,000 ft). Designed to observe at wavelengths from 0.3 μm to 1.6 mm, SOFIA operates above 99.8% of the water vapor that obscures much of the infrared and submillimeter. SOFIA has seven science instruments under development, including an occultation photometer, near-, mid-, and far-infrared cameras, infrared spectrometers, and heterodyne receivers. SOFIA, a joint project between NASA and the German Aerospace Center Deutsches Zentrum für Luft und-Raumfahrt, began initial science flights in 2010 December, and has conducted 30 science flights in the subsequent year. During this early science period three instruments have flown: the mid-infrared camera FORCAST, the heterodyne spectrometer GREAT, and the occultation photometer HIPO. This Letter provides an overview of the observatory and its early performance.The Astrophysical Journal Letters 03/2012; 749(2):L17. · 5.53 Impact Factor -
Article: Ices in the Quiescent IC 5146 Dense Cloud
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ABSTRACT: This paper presents spectra in the 2 to 20 μm range of quiescent cloud material located in the IC 5146 cloud complex. The spectra were obtained with NASA's Infrared Telescope Facility SpeX instrument and the Spitzer Space Telescope's Infrared Spectrometer. We use these spectra to investigate dust and ice absorption features in pristine regions of the cloud that are unaltered by embedded stars. We find that the H2O-ice threshold extinction is 4.03 ± 0.05 mag. Once foreground extinction is taken into account, however, the threshold drops to 3.2 mag, equivalent to that found for the Taurus dark cloud, generally assumed to be the touchstone quiescent cloud against which all other dense cloud and embedded young stellar object observations are compared. Substructure in the trough of the silicate band for two sources is attributed to CH3OH and NH3 in the ices, present at the ~2% and ~5% levels, respectively, relative to H2O-ice. The correlation of the silicate feature with the E(J – K) color excess is found to follow a much shallower slope relative to lines of sight that probe diffuse clouds, supporting the previous results by Chiar et al.The Astrophysical Journal 03/2011; 731(1):9. · 6.02 Impact Factor -
Article: Status of the Stratospheric Observatory for Infrared Astronomy (SOFIA)
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ABSTRACT: The Stratospheric Observatory for Infrared Astronomy (SOFIA), a joint U.S./German project, is a 2.5-meter infrared airborne telescope carried by a Boeing 747-SP that flies in the stratosphere at altitudes as high as 45,000 feet (13.72 km). This facility is capable of observing from 0.3 {\mu}m to 1.6 mm with an average transmission greater than 80 percent. SOFIA will be staged out of the NASA Dryden Flight Research Center aircraft operations facility at Palmdale, CA. The SOFIA Science Mission Operations (SMO) will be located at NASA Ames Research Center, Moffett Field, CA. First science flights began in 2010 and a full operations schedule of up to one hundred 8 to 10 hour flights per year will be reached by 2014. The observatory is expected to operate until the mid 2030's. SOFIAs initial complement of seven focal plane instruments includes broadband imagers, moderate-resolution spectrographs that will resolve broad features due to dust and large molecules, and high-resolution spectrometers capable of studying the kinematics of atomic and molecular gas at sub-km/s resolution. We describe the SOFIA facility and outline the opportunities for observations by the general scientific community and for future instrumentation development. The operational characteristics of the SOFIA first-generation instruments are summarized. The status of the flight test program is discussed and we show First Light images obtained at wavelengths from 5.4 to 37 \"im with the FORCAST imaging camera. Additional information about SOFIA is available at http://www.sofia.usra.edu and http://www.sofia.usra.edu/Science/docs/SofiaScienceVision051809-1.pdf02/2011; -
Article: SpS1-SOFIA studies of stellar evolution
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ABSTRACT: The U.S./German Stratospheric Observatory for Infrared Astronomy (SOFIA, Figure 1) is a 2.5-meter infrared airborne telescope in a Boeing 747-SP flying in the stratosphere at altitudes as high as 45,000 feet where the atmospheric transmission averages ≥ 80% throughout the 0.3 - 1600 μm spectral region. SOFIA's first-generation instruments include broadband imagers, moderate resolution spectrographs capable of resolving broad features due to dust and large molecules, and high resolution spectrometers suitable for kinematic studies of molecular and atomic gas lines at km s−1 resolution. These and future instruments will enable SOFIA to make unique contributions to studies of the physics and chemistry of stellar evolution for many decades. Science flights will begin in 2010. A full operations schedule of at least 100 flights per year will begin in 2014 and will continue for 20 years. The SOFIA Guest Investigator (GI) program, open to investigators worldwide, will constitute the major portion of the SOFIA observing program.Proceedings of the International Astronomical Union 10/2009; 5:529 - 530. -
Article: The Science Vision for the Stratospheric Observatory for Infrared Astronomy (SOFIA)
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ABSTRACT: An updated Science Vision for the SOFIA project is presented, including an overview of the characteristics and capabilities of the observatory and first generation instruments. A primary focus is placed on four science themes: 'The Formation of Stars and Planets', 'The Interstellar Medium of the Milky Way', 'Galaxies and the Galactic Center' and 'Planetary Science'. Comment: 128 pages pdf format Version 2 corrects: Attribution for Figure 5-1 Definition of "SIS" Affiliation of one of the contributors to the Science Vision05/2009; -
Article: The Physical Properties of Four ~600 K T Dwarfs
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ABSTRACT: We present Spitzer 7.6-14.5 μm spectra of ULAS J003402.77–005206.7 and ULAS J133553.45+113005.2, two T9 dwarfs with the latest spectral types currently known. We fit synthetic spectra and photometry to the near- through mid-infrared energy distributions of these dwarfs and that of the T8 dwarf 2MASS J09393548–2448279. We also analyze near-infrared data for another T9, CFBD J005910.82–011401.3. We find that the ratio of the mid- to near-infrared fluxes is very sensitive to effective temperature at these low temperatures, and that the 2.2 μm and 4.5 μm fluxes are sensitive to metallicity and gravity; increasing gravity has a similar effect to decreasing metallicity, and vice versa, and there is a degeneracy between these parameters. The 4.5 μm and 10 μm fluxes are also sensitive to vertical transport of gas through the atmosphere, which we find to be significant for these dwarfs. The full near- through mid-infrared spectral energy distribution allows us to constrain the effective temperature (K)/gravity (ms–2)/metallicity ([m/H] dex) of ULAS J0034–00 and ULAS J1335+11 to 550-600/100-300/0.0-0.3 and 500-550/100-300/0.0-0.3, respectively. These fits imply low masses and young ages for the dwarfs of 5-20 M Jupiter and 0.1-2 Gyr. The fits to 2MASS J0939–24 are in good agreement with the measured distance, the observational data, and the earlier T8 near-infrared spectral type if it is a slightly metal-poor 4-10 Gyr old system consisting of a 500 K and 700 K, ~25 M Jupiter and ~40 M Jupiter, pair, although it is also possible that it is an identical pair of 600 K, 30 M Jupiter, dwarfs. As no mid-infrared data are available for CFBD J0059–01 its properties are less well constrained; nevertheless it appears to be a 550-600 K dwarf with g= 300-2000 ms–2 and [m/H] = 0-0.3 dex. These properties correspond to mass and age ranges of 10-50 M Jupiter and 0.5-10 Gyr for this dwarf.The Astrophysical Journal 04/2009; 695(2):1517. · 6.02 Impact Factor -
Article: The Physical Properties of Four ~600K T Dwarfs
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ABSTRACT: We present Spitzer 7.6-14.5um spectra of ULAS J003402.77-005206.7 and ULAS J133553.45+113005.2, two T9 dwarfs with the latest spectral types currently known. We fit synthetic spectra and photometry to the near- through mid-infrared energy distributions of these dwarfs and that of the T8 dwarf 2MASS J09393548-2448279. We also analyse near-infrared data for another T9, CFBD J005910.82-011401.3. We find that the ratio of the mid- to near-infrared fluxes is very sensitive to effective temperature at these low temperatures, and that the 2.2 and 4.5um fluxes are sensitive to metallicity and gravity; there is a degeneracy between these parameters. The 4.5 and 10um fluxes are also sensitive to vertical transport of gas through the atmosphere, which we find to be significant for these dwarfs. The full near- through mid-infrared spectral energy distribution allows us to constrain the effective temperature (K)/gravity (m/s2)/metallicity ([m/H] dex) of ULAS J0034-00 and ULAS J1335+11 to 550-600/ 100-300/ 0.0-0.3 and 500-550/ 100-300/ 0.0-0.3, respectively. These fits imply low masses and young ages for the dwarfs of 5-20 M(Jup) and 0.1-2 Gyr. The fits to 2MASS J0939-24 are in good agreement with the measured distance, the observational data, and the earlier T8 near-infrared spectral type if it is a slightly metal-poor 4-10 Gyr old system consisting of a 500 and 700K, ~25 and ~40 M(Jup), pair, although it is also possible that it is an identical pair of 600K, 30 M(Jup), dwarfs. As no mid-infrared data are available for CFBD J0059-01 its properties are less well constrained; nevertheless it appears to be a 550-600K dwarf with g= 300-2000 m/s2 and [m/H]= 0-0.3 dex. These properties correspond to mass and age ranges of 10-50 M(Jup) and 0.5-10 Gyr for this dwarf.01/2009; -
Article: Spitzer Infrared Spectrograph (IRS) Observations of M, L, and T Dwarfs
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ABSTRACT: We present the first mid-infrared spectra of brown dwarfs, together with observations of a low-mass star. Our targets are the M3.5 dwarf GJ 1001A, the L8 dwarf DENIS-P J0255-4700, and the T1/T6 binary system Indi Ba/Bb. As expected, the mid-infrared spectral morphology of these objects changes rapidly with spectral class because of the changes in atmospheric chemistry resulting from their differing effective temperatures and atmospheric structures. By taking advantage of the unprecedented sensitivity of the Infrared Spectrograph on the Spitzer Space Telescope, we have detected the 7.8 μm methane and 10 μm ammonia bands for the first time in brown dwarf spectra.The Astrophysical Journal Supplement Series 12/2008; 154(1):418. · 13.46 Impact Factor -
Article: The Spitzer Space Telescope Mission
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ABSTRACT: The Spitzer Space Telescope, NASA's Great Observatory for infrared astronomy, was launched 2003 August 25 and is returning excellent scientific data from its Earth-trailing solar orbit. Spitzer combines the intrinsic sensitivity achievable with a cryogenic telescope in space with the great imaging and spectroscopic power of modern detector arrays to provide the user community with huge gains in capability for exploration of the cosmos in the infrared. The observatory systems are largely performing as expected, and the projected cryogenic lifetime is in excess of 5 years. This paper summarizes the on-orbit scientific, technical, and operational performance of Spitzer. Subsequent papers in this special issue describe the Spitzer instruments in detail and highlight many of the exciting scientific results obtained during the first 6 months of the Spitzer mission.The Astrophysical Journal Supplement Series 12/2008; 154(1):1. · 13.46 Impact Factor -
Article: The Infrared Spectrograph (IRS) on the Spitzer Space Telescope
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ABSTRACT: The Infrared Spectrograph (IRS) is one of three science instruments on the Spitzer Space Telescope. The IRS comprises four separate spectrograph modules covering the wavelength range from 5.3 to 38 μm with spectral resolutions, R = λ/Δλ ≈ 90 and 600, and it was optimized to take full advantage of the very low background in the space environment. The IRS is performing at or better than the prelaunch predictions. An autonomous target acquisition capability enables the IRS to locate the mid-infrared centroid of a source, providing the information so that the spacecraft can accurately offset that centroid to a selected slit. This feature is particularly useful when taking spectra of sources with poorly known coordinates. An automated data-reduction pipeline has been developed at the Spitzer Science Center.The Astrophysical Journal Supplement Series 12/2008; 154(1):18. · 13.46 Impact Factor -
Article: Abundances of Planetary Nebula NGC2392
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ABSTRACT: The spectra of the planetary nebula NGC2392 is reanalysed using spectral measurements made in the mid-infrared with the Spitzer Space Telescope. The aim is to determine the chemical composition of this object. We also make use of IUE and ground based spectra. Abundances determined from the mid-infrared lines, which are insensitive to electron temperature, are used as the basis for the determination of the composition, which are found to differ somewhat from earlier results. The abundances found, especially the low value of helium and oxygen, indicate that the central star was originally of rather low mass. Abundances of phosphorus, iron, silicon and chlorine have been determined for the first time in this nebula. The variation of electron temperature in this nebula is very clear reaching quite high values close to the center. The temperature of the central star is discussed in the light of the high observed stages of ionization. The nebular information indicates the spectrum of the star deviates considerably from a blackbody. Comment: 9 pages, 7 tables, 3 figures. Accepted for publication in A&A01/2008; -
Article: Abundances of Planetary Nebula M1-42
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ABSTRACT: The spectra of the planetary nebula M1-42 is reanalysed using spectral measurements made in the mid-infrared with the Spitzer Space Telescope. The aim is to determine the chemical composition of this object. We also make use of ISO, IUE and ground based spectra. Abundances determined from the mid- and far-infrared lines, which are insensitive to electron temperature, are used as the basis for the determination of the composition, which are found to substantially differ from earlier results. High values of neon, argon and sulfur are found. They are higher than in other PN, with the exception of NGC6153, a nebula of very similar abundances. The high values of helium and nitrogen found indicate that the second dredge-up and hot bottom burning has occurred in the course of evolution and that the central star was originally more massive than 4Msun. The present temperature and luminosity of the central star is determined and at first sight may be inconsistent with such a high mass. Comment: 9 pages, 8 tables, 1 figure. Accepted for publication in A&A06/2007; -
Article: The Spitzer/IRS Infrared Spectrum and Abundances of the Planetary Nebula IC 2448
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ABSTRACT: We present the mid-infrared spectrum of the planetary nebula IC 2448. In order to determine the chemical composition of the nebula, we use the infrared line fluxes from the Spitzer spectrum along with optical line fluxes from the literature and ultraviolet line fluxes from archival IUE spectra. We determine an extinction of C(H-beta) = 0.27 from hydrogen recombination lines and the radio to H-beta ratio. Forbidden line ratios give an electron density of 1860 cm-3 and an average electron temperature of 12700 K. The use of infrared lines allows us to determine more accurate abundances than previously possible because abundances derived from infrared lines do not vary greatly with the adopted electron temperature and extinction, and additional ionization stages are observed. Elements left mostly unchanged by stellar evolution (Ar, Ne, S, and O) all have subsolar values in IC 2448, indicating that the progenitor star formed out of moderately metal deficient material. Evidence from the Spitzer spectrum of IC 2448 supports previous claims that IC 2448 is an old nebula formed from a low mass progenitor star.04/2007; -
Article: The NASA Spitzer Space Telescope.
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ABSTRACT: The National Aeronautics and Space Administration's Spitzer Space Telescope (formerly the Space Infrared Telescope Facility) is the fourth and final facility in the Great Observatories Program, joining Hubble Space Telescope (1990), the Compton Gamma-Ray Observatory (1991-2000), and the Chandra X-Ray Observatory (1999). Spitzer, with a sensitivity that is almost three orders of magnitude greater than that of any previous ground-based and space-based infrared observatory, is expected to revolutionize our understanding of the creation of the universe, the formation and evolution of primitive galaxies, the origin of stars and planets, and the chemical evolution of the universe. This review presents a brief overview of the scientific objectives and history of infrared astronomy. We discuss Spitzer's expected role in infrared astronomy for the new millennium. We describe pertinent details of the design, construction, launch, in-orbit checkout, and operations of the observatory and summarize some science highlights from the first two and a half years of Spitzer operations. More information about Spitzer can be found at http://spitzer.caltech.edu/.Review of Scientific Instruments 02/2007; 78(1):011302. · 1.37 Impact Factor -
Article: Spitzer Space Telescope Observations of M, L, and T Dwarfs
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ABSTRACT: We present the first mid-infrared spectra of very low-mass stars and brown dwarfs obtained with the Infrared Spectrograph onboard the Spitzer Space Telescope. We observed GJ 1001 A (M3.5 V), DENIS 0255-4700 (L8), and ɛ Ind Ba/Bb (T1/T6). As expected from the predictions of model atmospheres, the spectra show absorption features of H2O, CH4 at 7.8 μm, and NH3 at 10.5 μm. This is the first detection of the 7.8 μm CH4 band in the spectrum of a brown dwarf and the first detection of NH3 in the atmosphere of a brown dwarf.11/2006; 357:66. -
Article: Ammonia as a tracer of chemical equilibrium in the T7.5 dwarf Gliese 570D
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ABSTRACT: We present the first analysis of an optical to mid-infrared spectrum of the T7.5 dwarf Gliese 570D with model atmospheres, synthetic spectra, and brown dwarf evolution sequences. We obtain precise values for the basic parameters of Gl 570D: Teff=800 - 820K, log g (cm/s^2)=5.09 - 5.23, and log L/Lsun= -5.525 to -5.551. The Spitzer IRS spectrum shows prominent features of ammonia (NH3) that can only be fitted by reducing the abundance of NH3 by about one order of magnitude from the value obtained with chemical equilibrium models. We model departures from chemical equilibrium in the atmosphere of Gl 570D by considering the kinetics of nitrogen and carbon chemistry in the presence of vertical mixing. The resulting model spectrum reproduces the data very well.06/2006; -
Article: A Spitzer Infrared Spectrograph (IRS) Spectral Sequence of M, L, and T Dwarfs
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ABSTRACT: We present a low-resolution (R = 90), 5.5-38 micron spectral sequence of a sample of M, L, and T dwarfs obtained with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. The spectra exhibit prominent absorption bands of H_2O at 6.27 microns, CH_4 at 7.65 microns, and NH_3 at 10.5 microns and are relatively featureless at lambda > 15 microns. Three spectral indices that measure the strengths of these bands are presented; H_2O absorption features are present throughout the MLT sequence while the CH_4 and NH_3 bands first appear at roughly the L/T transition. Although the spectra are, in general, qualitatively well matched by synthetic spectra that include the formation of spatially homogeneous silicate and iron condensate clouds, the spectra of the mid-type L dwarfs show an unexpected flattening from roughly 9 to 11 microns. We hypothesize that this may be a result of a population of small silicate grains that are not predicted in the cloud models. The spectrum of the peculiar T6 dwarf 2MASS J0937+2931 is suppressed from 5.5-7.5 microns relative to typical T6 dwarfs and may be a consequence of its mildly metal-poor/high surface gravity atmosphere. Finally, we compute bolometric luminosities of a subsample of the M, L, and T dwarfs by combining the IRS spectra with previously published 0.6-4.1 micron spectra and find good agreement with the values of Golimowski et al. who use L'- and M'-band photometry and to account for the flux emitted at lambda > 2.5 microns. Comment: Accepted for publication in the Astrophysical Journal05/2006; -
Article: Spitzer Spectroscopy of low-mass stars and brown dwarfs
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ABSTRACT: We present the first results of a spectroscopic survey of M, L, and T dwarfs being conducted with the Infrared Spectrograph onboard the Spitzer Space Telescope. We observed GJ 1001 A (M3.5 V), DENIS 0255-4700 (L8.0 V), and epsilon Ind Ba/Bb (T1/T6 V). As expected from the predictions of model atmospheres, the spectra show absorption features of H(sub 2)O, CH(sub 4) at 7.8 micron, and NH(sub 3) at 10.5 micron. This is the first detection of the 7.8 micron CH(sub 4) band and the first secure detection of NH(sub 3) in the spectra of brown dwarfs. Finally, we compute the bolometric luminosities of three of the dwarfs in our sample by combining 0.6-4.1 micron spectra with the Spitzer spectra and find good agreement with previous results that use L' -and M' -band photometry to account for the flux emitted between 2.5 and 5 micron.02/2005; -
Article: Spitzer Observations of SN 1987A
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ABSTRACT: We present new Spitzer observations of the well known supernova remnant, SN 1987A. Spitzer's milli-Jy spectroscopic sensitivity, paired with an imaging super-resolution of 0.3″ /pixel, offers a unique opportunity to study the thermal emission of SN 1987A across a large wavelength regime for the first time since its initial outburst. SN 1987A was the first supernova observed by naked eye in almost 400 years and has been intensely studied at all wavelengths with a wide array of telescopes and instrumentation. Hubble Space Telescope optical imaging of this object shows a triple-ringed structure spanning ≈5″ diameter (Burrows et al. 1995, ApJ 452, 680). These rings are believed to be material originating in an earlier stellar wind and mass-loss phase of the progenitor star and is now being heated by an expanding shock wave from the supernova remnant (SNR). Near-infrared imaging has shown that the remnant size is slowly increasing over time as the shock wave continues to expand outward. We present Spitzer IRAC imaging spanning the 3-8 μ m regime and IRS spectroscopy in the 5-25 μ m regime. Our observations are the first detections of the remnant in the 3-8 μ m regime since ISO observations in 1998 (Fischera et al. 2002, A&A 395, 189) and boad-band 10 μ m imaging in 2003 by Bouchet et al. (2004, ApJ 611, 394) and the first mid-IR spectroscopy since KAO measurements in 1988. We discuss the source of the IR emission and estimate a dust mass from our photometry. This work is suported in part by NASA (JPL/SSC-1256406, 1215746)11/2004; 36:1466. -
Conference Proceeding: The infrared spectrograph on the Spitzer Space Telescope
Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 10/2004
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2004
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University of Minnesota Duluth
Duluth, MN, USA
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