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1. THE DISK IMAGING SURVEY OF CHEMISTRY WITH SMA. I. TAURUS PROTOPLANETARY DISK DATA

Author

Karin I. Öberg, Chunhua Qi, Jeffrey K. J. Fogel, Edwin A. Bergin, Sean M. Andrews, Catherine Espaillat, Tim A. van Kempen, David J. Wilner, and Ilaria Pascucci

Subjects
Physics, 010308 nuclear & particles physics, Astronomy and Astrophysics, Astrophysics, Protoplanetary disk, 01 natural sciences, Submillimeter Array, Luminosity, Stars, T Tauri star, Deuterium, 13. Climate action, Space and Planetary Science, Planet, 0103 physical sciences, 010303 astronomy & astrophysics, Chemical composition
Abstract

Chemistry plays an important role in the structure and evolution of protoplanetary disks, with implications for the composition of comets and planets. This is the first of a series of papers based on data from DISCS, a Submillimeter Array survey of the chemical composition of protoplanetary disks. The six Taurus sources in the program (DM Tau, AA Tau, LkCa 15, GM Aur, CQ Tau and MWC 480) range in stellar spectral type from M1 to A4 and offer an opportunity to test the effects of stellar luminosity on the disk chemistry. The disks were observed in 10 different lines at ~3" resolution and an rms of ~100 mJy beam-1 at ~0.5 km s-1. The four brightest lines are CO 2-1, HCO+ 3-2, CN 2_3-1_2 and HCN 3-2 and these are detected toward all sources (except for HCN toward CQ Tau). The weaker lines of CN 2_2-1_1, DCO+ 3-2, N2H+ 3-2, H2CO 3_03-2_02 and 4_14-3_13 are detected toward two to three disks each, and DCN 3-2 only toward LkCa 15. CH3OH 4_21-3_12 and c-C3H2 are not detected. There is no obvious difference between the T Tauri and Herbig Ae sources with regard to CN and HCN intensities. In contrast, DCO+, DCN, N2H+ and H2CO are detected only toward the T Tauri stars, suggesting that the disks around Herbig Ae stars lack cold regions for long enough timescales to allow for efficient deuterium chemistry, CO freeze-out, and grain chemistry.

Published
2010
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2. Transition disk chemistry and future prospects with ALMA

Author

Edwin A. Bergin, L. Ilsedore Cleeves, Jeffrey K. J. Fogel, Sebastian Wolf, Thomas Bethell, Nuria Calvet, and Juergen Sauter

Subjects
Physics, Void (astronomy), Opacity, 010308 nuclear & particles physics, FOS: Physical sciences, Astronomy and Astrophysics, Observable, Astrophysics, Radiation, medicine.disease_cause, 01 natural sciences, Submillimeter Array, Astrophysics - Solar and Stellar Astrophysics, 13. Climate action, Space and Planetary Science, Excited state, 0103 physical sciences, medicine, Millimeter, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Ultraviolet
Abstract

We explore the chemical structure of a disk that contains a large central gap of R ~ 45 AU, as is commonly seen in transitional disk systems. In our chemical model of a disk with a cleared inner void, the midplane becomes revealed to the central star so that it is directly irradiated. The midplane material at the truncation radius is permissive to reprocessed optical heating radiation, but opaque to the photo-dissociating ultraviolet, creating an environment abundant in gas-phase molecules. Thus the disk midplane, which would otherwise for a full disk be dominated by near complete heavy element freeze-out, should become observable in molecular emission. If this prediction is correct this has exciting prospects for observations with the Atacama Large Millimeter/Submillimeter Array (ALMA), as the inner transition region should thus be readily detected and resolved, especially using high-J rotational transitions excited in the high density midplane gas. Therefore such observations will potentially provide us with a direct probe of the physics and chemistry at this actively evolving interface., 6 pages, 4 figures. Accepted to ApJ Letters

Published
2011

3. Disk Imaging Survey of Chemistry with SMA: II. Southern Sky Protoplanetary Disk Data and Full Sample Statistics

Author

Sean M. Andrews, Jeffrey K. J. Fogel, Catherine Espaillat, Edwin A. Bergin, Ilaria Pascucci, Joel H. Kastner, Karin I. Öberg, David J. Wilner, and Chunhua Qi

Subjects
Physics, 010308 nuclear & particles physics, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Radius, Stellar classification, Protoplanetary disk, Astrophysics - Astrophysics of Galaxies, 01 natural sciences, Submillimeter Array, Accretion (astrophysics), Stars, T Tauri star, 13. Climate action, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), 0103 physical sciences, Statistics, 010303 astronomy & astrophysics, Line (formation)
Abstract

This is the second in a series of papers based on data from DISCS, a Submillimeter Array observing program aimed at spatially and spectrally resolving the chemical composition of 12 protoplanetary disks. We present data on six Southern sky sources - IM Lup, SAO 206462 (HD 135344b), HD 142527, AS 209, AS 205 and V4046 Sgr - which complement the six sources in the Taurus star forming region reported previously. CO 2-1 and HCO+ 3-2 emission are detected and resolved in all disks and show velocity patterns consistent with Keplerian rotation. Where detected, the emission from DCO+ 3-2, N2H+ 3-2, H2CO 3-2 and 4-3,HCN 3-2 and CN 2-1 are also generally spatially resolved. The detection rates are highest toward the M and K stars, while the F star SAO 206462 has only weak CN and HCN emission, and H2CO alone is detected toward HD 142527. These findings together with the statistics from the previous Taurus disks, support the hypothesis that high detection rates of many small molecules depend on the presence of a cold and protected disk midplane, which is less common around F and A stars compared to M and K stars. Disk-averaged variations in the proposed radiation tracer CN/HCN are found to be small, despite two orders of magnitude range of spectral types and accretion rates. In contrast, the resolved images suggest that the CN/HCN emission ratio varies with disk radius in at least two of the systems. There are no clear observational differences in the disk chemistry between the classical/full T Tauri disks and transitional disks. Furthermore, the observed line emission does not depend on measured accretion luminosities or the number of infrared lines detected, which suggests that the chemistry outside of 100 AU is not coupled to the physical processes that drive the chemistry in the innermost few AU., Comment: accepted for publication in ApJ, 41 pages including 7 figures

Published
2011
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4. Detection of the Water Reservoir in a Forming Planetary System

Author

Gary J. Melnick, Umut A. Yildiz, Lars E. Kristensen, Christian Brinch, L. Ilsedore Cleeves, Ewine F. van Dishoeck, Jeffrey K. J. Fogel, Edwin A. Bergin, Michiel R. Hogerheijde, David A. Neufeld, Olja Panić, Geoffrey A. Blake, Carsten Dominik, Dariusz C. Lis, John C. Pearson, Low Energy Astrophysics (API, FNWI), Leiden Observatory, Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA, California Institute of Technology, Division of Geological and Planetary Sciences, Astronomical Institute Anton Pannekoek, University of Amsterdam, California Institute of Technology, Department of Astronomy (CALTECH), Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique (LERMA), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université de Cergy Pontoise (UCP), Université Paris-Seine-Université Paris-Seine-Centre National de la Recherche Scientifique (CNRS), Dynamique des milieux interstellaires et plasmas stellaires, Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique et Atmosphères = Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres (LERMA), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-CY Cergy Paris Université (CY)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-CY Cergy Paris Université (CY), Harvard-Smithsonian Center for Astrophysics, Department of Physics and Astronomy, University of Missouri, European Southern Observatory (ESO), and Jet Propulsion Laboratory, California Institute of Technology (JPL)

Subjects
Solar System, Extraterrestrial Environment, Planets, FOS: Physical sciences, 01 natural sciences, Physics::Geophysics, Astrobiology, Stars, Celestial, Planet, 0103 physical sciences, TW Hydrae, Astrophysics::Solar and Stellar Astrophysics, 010306 general physics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics::Atmospheric and Oceanic Physics, Solar and Stellar Astrophysics (astro-ph.SR), Physics, Earth and Planetary Astrophysics (astro-ph.EP), Multidisciplinary, Ice, Astronomy, Planetary system, Early Earth, Steam, Stars, Astrophysics - Solar and Stellar Astrophysics, 13. Climate action, Physics::Space Physics, Astrophysics::Earth and Planetary Astrophysics, Formation and evolution of the Solar System, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Evolution, Planetary, Water vapor, Astrophysics - Earth and Planetary Astrophysics
Abstract

Icy bodies may have delivered the oceans to the early Earth, yet little is known about water in the ice-dominated regions of extra-solar planet-forming disks. The Heterodyne Instrument for the Far-Infrared on-board the Herschel Space Observatory has detected emission from both spin isomers of cold water vapor from the disk around the young star TW Hydrae. This water vapor likely originates from ice-coated solids near the disk surface hinting at a water ice reservoir equivalent to several thousand Earth Oceans in mass. The water's ortho-to-para ratio falls well below that of Solar System comets, suggesting that comets contain heterogeneous ice mixtures collected across the entire solar nebula during the early stages of planetary birth., Comment: 18 pages, 2 figures. Corrected typo in reported mass (in g) of detected water vapor reservoir. All conclusions are unchanged

Published
2011
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5. Sensitive limits on the abundance of cold water vapor in the DM Tau protoplanetary disk

Author

T. A. Bell, Per Bjerkeli, A. Baudry, E. F. van Dishoeck, Friedrich Wyrowski, J. Santiago-Garcia, Jeffrey K. J. Fogel, Christian Brinch, D. Johnstone, Rene Plume, Fabien Daniel, Christophe Risacher, S. Bruderer, David A. Neufeld, Steven D. Doty, R. Shipman, J. Stutzki, Paola Caselli, Olja Panić, G. J. Herczeg, A. Fuente, Aggm Tielens, J. R. Goicoechea, Michael Olberg, G. A. Blake, C. Codella, E. A. Bergin, M. Fich, Bengt Larsson, Th. de Graauw, Berengere Parise, René Liseau, Rafael Bachiller, M. Benedettini, Paul Hartogh, Brunella Nisini, J. C. Pearson, Ryszard Szczerba, Mario Tafalla, Jes K. Jørgensen, F. F. S. van der Tak, Umut A. Yildiz, Michiel R. Hogerheijde, T. A. van Kempen, M. Marseille, Carsten Dominik, Frank Helmich, J. Braine, P. J. Encrenaz, Arnold O. Benz, Sylvain Bontemps, Susanne F. Wampfler, Fabrice Herpin, C. McCoey, P. Saraceno, Lars E. Kristensen, R. Visser, Teresa Giannini, José Cernicharo, T. Jacq, Willem Jellema, Gary J. Melnick, A. M. di Giorgio, Dariusz C. Lis, Low Energy Astrophysics (API, FNWI), Astronomy, Kapteyn Astronomical Institute, Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University [Cambridge]-Smithsonian Institution, Laboratoire Optimisation de la Conception et Ingénierie de l'Environnement (LOCIE), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Centro de Investigaciones Biológicas (CSIC), Consejo Superior de Investigaciones Científicas [Madrid] (CSIC), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), Laboratoire d'Astrophysique de Grenoble (LAOG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Sciences et Technologies - Bordeaux 1, Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Civilisations atlantiques & Archéosciences (C2A), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Ministère de la Culture et de la Communication (MCC)-Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Nantes - UFR Histoire, Histoire de l'Art et Archéologie (UFR HHAA), Université de Nantes (UN)-Université de Nantes (UN), INAF - Osservatorio Astrofisico di Arcetri (OAA), Istituto Nazionale di Astrofisica (INAF), Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique (LERMA), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université de Cergy Pontoise (UCP), Université Paris-Seine-Université Paris-Seine-Centre National de la Recherche Scientifique (CNRS), SRON Netherlands Institute for Space Research (SRON), INAF - Osservatorio Astronomico di Roma (OAR), Onsala Space Observatory, Chalmers University of Technology [Göteborg], Centre d'étude spatiale des rayonnements (CESR), Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées, ESO, European Southern Observatory (ESO), Istituto di Fisica dello Spazio Interplanetario (IFSI), Consiglio Nazionale delle Ricerche (CNR), Max-Planck-Institut für Radioastronomie (MPIFR), Max Planck Institute for Solar System Research (MPS), Max-Planck-Gesellschaft, Harvard University-Smithsonian Institution, Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Sciences et Technologies - Bordeaux 1 (UB), École normale supérieure - Paris (ENS-PSL), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), National Research Council of Italy | Consiglio Nazionale delle Ricerche (CNR), Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research (MPS), Smithsonian Institution-Harvard University [Cambridge], Université de Nantes - UFR Histoire, Histoire de l'Art et Archéologie (UFR HHAA), and Université de Nantes (UN)-Université de Nantes (UN)-Centre National de la Recherche Scientifique (CNRS)-Ministère de la Culture et de la Communication (MCC)

Subjects
DESORPTION, Abundance (chemistry), [PHYS.ASTR.EP]Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Astronomy, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], FOS: Physical sciences, DUST, Astrophysics, Protoplanetary disk, 01 natural sciences, ISM: abundances, MOLECULES, PLANET-FORMING REGION, CIRCUMSTELLAR DISKS, 0103 physical sciences, H2O, SPECTRA, Solar and Stellar Astrophysics, Emission spectrum, 010306 general physics, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Line (formation), Physics, Earth and Planetary Astrophysics (astro-ph.EP), Spectrometer, [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Research Programm of Institute for Mathematics, Astrophysics and Particle Physics, protoplanetary disks, Astronomy and Astrophysics, [PHYS.ASTR.SR]Physics [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], ISM: molecules, EVOLUTION, Astrophysics - Solar and Stellar Astrophysics, 13. Climate action, Space and Planetary Science, GAS, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Earth and Planetary Astrophysics, Water ice, Water vapor, Intensity (heat transfer), STARS, Astrophysics - Earth and Planetary Astrophysics
Abstract

We performed a sensitive search for the ground-state emission lines of ortho- and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI instrument. No strong lines are detected down to 3sigma levels in 0.5 km/s channels of 4.2 mK for the 1_{10}--1_{01} line and 12.6 mK for the 1_{11}--0_{00} line. We report a very tentative detection, however, of the 1_{10}--1_{01} line in the Wide Band Spectrometer, with a strength of T_{mb}=2.7 mK, a width of 5.6 km/s and an integrated intensity of 16.0 mK km/s. The latter constitutes a 6sigma detection. Regardless of the reality of this tentative detection, model calculations indicate that our sensitive limits on the line strengths preclude efficient desorption of water in the UV illuminated regions of the disk. We hypothesize that more than 95-99% of the water ice is locked up in coagulated grains that have settled to the midplane., 5 pages, 3 figures. Accepted for publication in the Herschel HIFI special issue of A&A

Published
2010
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6. Chemistry of a protoplanetary disk with grain settling and Lyman alpha radiation

Author

Dmitry Semenov, Jeffrey K. J. Fogel, Nuria Calvet, Edwin A. Bergin, and Thomas Bethell

Subjects
Physics, 010504 meteorology & atmospheric sciences, Radiation field, Photodissociation, FOS: Physical sciences, Astronomy and Astrophysics, Penetration (firestop), Alpha particle, Astrophysics, Radiation, Protoplanetary disk, 01 natural sciences, Settling, Astrophysics - Solar and Stellar Astrophysics, 13. Climate action, Space and Planetary Science, 0103 physical sciences, Astrophysics::Earth and Planetary Astrophysics, 010303 astronomy & astrophysics, Order of magnitude, Astrophysics::Galaxy Astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), 0105 earth and related environmental sciences
Abstract

We present results from a model of the chemical evolution of protoplanetary disks. In our models we directly calculate the changing propagation and penetration of a high energy radiation field with Lyman alpha radiation included. We also explore the effect on our models of including dust grain settling. We find that, in agreement with earlier studies, the evolution of dust grains plays a large role in determining how deep the UV radiation penetrates into the disk. Significant grain settling at the midplane leads to much smaller freeze-out regions and a correspondingly larger molecular layer, which leads to an increase in column density for molecular species such as CO, CN and SO. The inclusion of Lyman alpha radiation impacts the disk chemistry through specific species that have large photodissociation cross sections at 1216 A. These include HCN, NH3 and CH4, for which the column densities are decreased by an order of magnitude or more due to the presence of Lyman alpha radiation in the UV spectrum. A few species, such as CO2 and SO, are enhanced by the presence of Lyman alpha radiation, but rarely by more than a factor of a few., Comment: 17 pages, 15 Figures. Accepted to ApJ

Published
2010
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7. Far-Ultraviolet H2 Emission from Circumstellar Disks

Author

Edwin A. Bergin, Cesar Briceno, Nuria Calvet, John M. Carpenter, Ashwin Yerasi, Laura Ingleby, Michael R. Meyer, Catherine Espaillat, Jesús Hernández, Jeffrey K. J. Fogel, Evelyne Roueff, Jon M. Miller, Melissa McClure, Hervé Abgrall, Gregory J. Herczeg, Lee Hartmann, Nathan R. Crockett, and Ilaria Pascucci

Subjects
010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Advanced Camera for Surveys, Luminosity, 0103 physical sciences, TW Hydrae, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Physics, Molecular cloud, Astronomy and Astrophysics, Accretion (astrophysics), Stars, T Tauri star, Astrophysics - Solar and Stellar Astrophysics, 13. Climate action, Space and Planetary Science, Astrophysics::Earth and Planetary Astrophysics, Formation and evolution of the Solar System
Abstract

We analyze the far-ultraviolet (FUV) spectra of 33 classical T Tauri stars (CTTS), including 20 new spectra obtained with the Advanced Camera for Surveys Solar Blind Channel (ACS/SBC) on the Hubble Space Telescope. Of the sources, 28 are in the ~1 Myr old Taurus-Auriga complex or Orion Molecular Cloud, 4 in the 8-10 Myr old Orion OB1a complex and one, TW Hya, in the 10 Myr old TW Hydrae Association. We also obtained FUV ACS/SBC spectra of 10 non-accreting sources surrounded by debris disks with ages between 10 and 125 Myr. We use a feature in the FUV spectra due mostly to electron impact excitation of \h2 to study the evolution of the gas in the inner disk. We find that the \h2 feature is absent in non-accreting sources, but is detected in the spectra of CTTS and correlates with accretion luminosity. Since all young stars have active chromospheres which produce strong X-ray and UV emission capable of exciting \h2 in the disk, the fact that the non-accreting sources show no \h2 emission implies that the \h2 gas in the inner disk has dissipated in the non-accreting sources, although dust (and possibly gas) remains at larger radii. Using the flux at 1600 {\AA}, we estimate that the column density of \h2 left in the inner regions of the debris disks in our sample is less than ~ 3x10^-6 g cm^-2, nine orders of magnitude below the surface density of the minimum mass solar nebula at 1 AU., Comment: 15 pages, 4 figures, accepted to ApJL

Published
2009

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