Thomas L. Roellig
Ames Research Center
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Featured researches published by Thomas L. Roellig.
Astrophysical Journal Supplement Series | 2004
M. Werner; Thomas L. Roellig; Frank J. Low; G. H. Rieke; Marcia J. Rieke; William F. Hoffmann; Erick T. Young; J. R. Houck; Bernhard R. Brandl; Giovanni G. Fazio; Joseph L. Hora; Robert D. Gehrz; George Helou; B. T. Soifer; John R. Stauffer; Jocelyn Keene; Peter R. M. Eisenhardt; D.B Gallagher; Thomas N. Gautier; William R. Irace; C. R. Lawrence; L. Simmons; J. Van Cleve; Michael Jura; Edward L. Wright; Dale P. Cruikshank
The Spitzer Space Telescope, NASAs 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 | 2008
Michael C. Cushing; Mark S. Marley; Didier Saumon; Brandon C. Kelly; William D. Vacca; John T. Rayner; Richard S. Freedman; Katharina Lodders; Thomas L. Roellig
We present an analysis of the 0.95-14.5 ?m spectral energy distributions of nine field ultracool dwarfs with spectral types ranging from L1 to T4.5. Effective temperatures, gravities, and condensate cloud sedimentation efficiencies are derived by comparing the data to synthetic spectra computed from atmospheric models that self-consistently include the formation of condensate clouds. Overall, the model spectra fit the data well, although the agreement at some wavelengths remains poor due to remaining inadequacies in the models. Derived effective temperatures decrease steadily through the L1-T4.5 spectral types, and we confirm that the effective temperatures of ultracool dwarfs at the L/T transition are nearly constant, decreasing by only ~200 K from spectral types L7.5 to T4.5. The condensate cloud properties vary significantly among the L dwarfs in our sample, ranging from very thick clouds to relatively thin clouds with no particular trend with spectral type. The two objects in our sample with very red -->J ? Ks colors are, however, best fitted with synthetic spectra that have thick clouds, which hints at a possible correlation between the near-infrared colors of L dwarfs and the condensate cloud properties. The fits to the two T dwarfs in our sample (T2 and T4.5) also suggest that the clouds become thinner in this spectral class, in agreement with previous studies. Restricting the fits to narrower wavelength ranges (i.e., individual photometric bands) almost always yields excellent agreement between the data and models. Limitations in our knowledge of the opacities of key absorbers such as FeH, VO, and CH4 at certain wavelengths remain obvious, however. The effective temperatures obtained by fitting the narrower wavelength ranges can show a large scatter compared to the values derived by fitting the full spectral energy distributions; deviations are typically ~200 K and, in the worst cases, up to 700 K.
The Astrophysical Journal | 1986
R. Landau; B. Golisch; Terry Jay Jones; T. W. Jones; J. A. Pedelty; Lawrence Rudnick; Michael L. Sitko; J. Kenney; Thomas L. Roellig; Erkki Salonen
IRAS, IUE, and ground-based optical, NIR, mm and submm, and radio observations obtained mainly on Apr. 9-23, 1983, are reported for 19 active extragalactic sources and eight control sources. The overall spectra of the compact active sources are shown to be well represented by continuous-curvature functions such as parabolas. The spectra are found to be consistent with models involving continuous particle injection (with synchrotron losses) or first-order Fermi acceleration (with escape and synchrotron losses), but not with models using relativistic Maxwellian electron distributions.
The Astrophysical Journal | 2008
Dagny L. Looper; J. Davy Kirkpatrick; Roc Michael Cutri; Travis S. Barman; Adam J. Burgasser; Michael C. Cushing; Thomas L. Roellig; Mark R. McGovern; Ian S. McLean; Emily L. Rice; Brandon J. Swift; Steven D. Schurr
We present the discovery of two nearby L dwarfs from our 2MASS proper-motion search, which uses multiepoch 2MASS observations covering ~4700 deg^2 of sky. 2MASS J18212815+1414010 and 2MASS J21481628+4003593 were overlooked by earlier surveys due to their faint optical magnitudes and their proximity to the Galactic plane (10° ≤ | b | ≤ 15°). Assuming that both dwarfs are single, we derive spectrophotometric distances of ~10 pc, thus increasing the number of known L dwarfs within 10 pc to 10. In the near-infrared, 2MASS J21481628+4003593 shows a triangular H-band spectrum, strong CO absorption, and a markedly red J − K_s color (2.38 ± 0.06) for its L6 optical spectral type. 2MASS J18212815+1414010 also shows a triangular H-band spectrum and a slightly red J − K_s color (1.78 ± 0.05) for its L4.5 optical spectral type. Both objects show strong silicate absorption at 9-11 μm. Cumulatively, these features imply an unusually dusty photosphere for both of these objects. We examine several scenarios to explain the underlying cause for their enhanced dust content and find that a metal-rich atmosphere or a low surface gravity are consistent with these results. 2MASS J18212815+1414010 may be young (and therefore have a low surface gravity) based on its low tangential velocity of 10 km s^−1. On the other hand, 2MASS J21481628+4003593 has a high tangential velocity of 62 km s^−1 and is therefore likely old. Hence, high metallicity and low surface gravity may lead to similar effects.
The Astrophysical Journal | 2012
Erick T. Young; Eric E. Becklin; Pamela M. Marcum; Thomas L. Roellig; J. M. De Buizer; Terry L. Herter; R. Güsten; Edward W. Dunham; P. Temi; B. G. Andersson; Dana E. Backman; M. J. Burgdorf; Lawrence John Caroff; Sean C. Casey; Jacqueline A. Davidson; Edwin F. Erickson; Robert D. Gehrz; D. A. Harper; Paul M. Harvey; L. A. Helton; S. D. Horner; C. D. Howard; Randolf Klein; Alfred Krabbe; Ian S. McLean; A. W. Meyer; J. W. Miles; Mark R. Morris; William T. Reach; Jeonghee Rho
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 fur 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 | 2007
Thomas N. Gautier; G. H. Rieke; J. A. Stansberry; G. Bryden; Karl R. Stapelfeldt; M. Werner; Charles A. Beichman; C. H. Chen; Kate Su; David E. Trilling; Brian M. Patten; Thomas L. Roellig
We report the mid- and far-infrared properties of nearby M dwarfs. Spitzer MIPS measurements were obtained for a sample of 62 stars at 24 μm, with subsamples of 41 and 20 stars observed at 70 and 160 μm, respectively. We compare the results with current models of M star photospheres and look for indications of circumstellar dust in the form of significant deviations of K-[24 μm] colors and 70 μm/24 μm flux ratios from the average M star values. At 24 μm, all 62 of the targets were detected; 70 μm detections were achieved for 20 targets in the subsample observed, and no detections were seen in the 160 μm subsample. No clear far-infrared excesses were detected in our sample. The average far-infrared excess relative to the photospheric emission of the M stars is at least 4 times smaller than the similar average for a sample of solar-type stars. However, this limit allows the average fractional infrared luminosity in the M-star sample to be similar to that for more massive stars. We have also set low limits (10-4 to 10-9 M⊕ depending on location) for the maximum mass of dust possible around our stars.
The Astrophysical Journal | 1985
R.J. Sopka; Roger H. Hildebrand; D.T. Jaffe; Ian Gatley; Thomas L. Roellig; M. Werner; M. Jura; B. Zuckerman
Broad-band submillimeter observations of the thermal emission from evolved stars have been obtained with the United Kingdom Infrared Telescope on Mauna Kea, Hawaii. These observations, at an effective wavelength of 400 ..mu..m, provide the most direct method for estimating the mass loss rate in dust from these stars and also help to define the long-wavelength thermal spectrum of the dust envelopes. The mass loss rates in dust that we derive range from 10/sup -9/ to 10/sup -6/ M/sub sun/ yr/sup -1/ and are compared with mass loss rates derived from molecular line observations to estimate gas-to-dust ratios in outflowing envelopes. These values are found to be generally compatible with the interstellar gas-to-dust ratio of approx.100 if submillimeter emissivities appropriate to amorphous grain structures are assumed. Our analysis of the spectrum of IRC+10216 confirms previous suggestions that the grain emissivity varies as lambda/sup -1.2/ rather than as lambda/sup -2/ for 10
Review of Scientific Instruments | 2007
Robert D. Gehrz; Thomas L. Roellig; M. Werner; Giovanni G. Fazio; J. R. Houck; Frank J. Low; G. H. Rieke; B. T. Soifer; Deborah A. Levine; E. A. Romana
The National Aeronautics and Space Administrations 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 Spitzers 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/.
The Astrophysical Journal | 2009
S. K. Leggett; Michael C. Cushing; Didier Saumon; Mark S. Marley; Thomas L. Roellig; S. J. Warren; B. Burningham; Hugh R. A. Jones; J. D. Kirkpatrick; N. Lodieu; P. W. Lucas; A. Mainzer; Eduardo L. Martin; Mark J. McCaughrean; D. J. Pinfield; G. C. Sloan; R. L. Smart; Motohide Tamura; J. Van Cleve
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 Astronomical Journal | 2006
Tea Temim; Robert D. Gehrz; Charles E. Woodward; Thomas L. Roellig; Nathan Smith; Lawrence Rudnick; Elisha F. Polomski; Kris Davidson; Lunming Yuen; Takashi Onaka
We present 3.6, 4.5, 5.8, 8.0, 24, and 70 μm images of the Crab Nebula obtained with the Spitzer Space Telescope IRAC and MIPS cameras, low- and high-resolution Spitzer IRS spectra of selected positions within the nebula, and a near-infrared ground-based image made in the light of [Fe II] 1.644 μm. The 8.0 μm image, made with a bandpass that includes [Ar II] 7.0 μm, resembles the general morphology of visible Hα and near-IR [Fe II] line emission, while the 3.6 and 4.5 μm images are dominated by continuum synchrotron emission. The 24 and 70 μm images show enhanced emission that may be due to line emission or the presence of a small amount of warm dust in the nebula on the order of less than 1% of a solar mass. The ratio of the 3.6 and 4.5 μm images reveals a spatial variation in the synchrotron power-law index ranging from approximately 0.3 to 0.8 across the nebula. Combining this information with optical and X-ray synchrotron images, we derive a broadband spectrum that reflects the superposition of the flatter spectrum of the jet and torus with the steeper spectrum of the diffuse nebula. We also see suggestions of the expected pileup of relativistic electrons just before the exponential cutoff in the X-ray. The pulsar, and the associated equatorial toroid and polar jet structures seen in Chandra and Hubble Space Telescope images (Hester et al. 2002), can be identified in all of the IRAC images. We present the IR photometry of the pulsar. The forbidden lines identified in the high-resolution IR spectra are all double due to Doppler shifts from the front and back of the expanding nebula and give an expansion velocity of ≈1264 km s-1.