Characterizing CO Fourth Positive Emission in Young Circumstellar Disks

Abstract

Carbon Monoxide is a commonly used IR/sub-mm tracer of gas in protoplanetary disks. We present an analysis of ultraviolet CO emission in {HST}-COS spectra for 12 Classical T Tauri stars. Several ro-vibrational bands of the CO A^1Π- X^1Σ^+ (Fourth Positive) electronic transition system are spectrally resolved from emission of other atoms and H_2. The CO A^1Πv'=14 state is populated by absorption of Lyαphotons, created at the accretion column on the stellar surface. For targets with strong CO emission, we model the Lyαradiation field as an input for a simple fluorescence model to estimate CO rotational excitation temperatures and column densities. Typical column densities range from N_{CO} = 10^{18} - 10^{19} cm^{-2}. Our measured excitation temperatures are mostly below T_{CO} = 600 K, cooler than typical M-band CO emission. These temperatures and the emission line widths imply that the UV emission originates in a different population of CO than that which is IR-emitting. We also find a significant correlation between CO emission and the disk accretion rate M_{acc} and age. Our analysis shows that ultraviolet CO emission can be a useful diagnostic of CTTS disk gas.

References in corpus (22)

• Resolved Images of Large Cavities in Protoplanetary Transition Disks
• LkCa 15: A Young Exoplanet Caught at Formation?
• On the Diversity of the Taurus Transitional Disks: UX Tau A & Lk Ca 15
• Accretion Rates in Herbig Ae stars
• Spectro-astrometric imaging of molecular gas within protoplanetary disk gaps
• H2O and OH gas in the terrestrial planet-forming zones of protoplanetary disks
• LkH$\alpha$ 330: Evidence for dust clearing through resolved submillimeter imaging
• A Spitzer Survey of Mid-Infrared Molecular Emission from Protoplanetary Disks II: Correlations and LTE Models
• Direct Measurement of the Ratio of Carbon Monoxide to Molecular Hydrogen in the Diffuse Interstellar Medium
• CO rovibrational emission as a probe of inner disk structure
• Tracing the inner edge of the disk around HD 100546 with Ro-vibrational CO Emission Lines
• The Origins of Fluorescent H2 Emission From T Tauri~Stars
• NUV Excess in Slowly Accreting T Tauri Stars: Limits Imposed by Chromospheric Emission
• The unusual protoplanetary disk around the T Tauri star ET Cha
• Multiwavelength Observations of A0620-00 in Quiescence
• The Fourth Positive System of Carbon Monoxide in the Hubble Space Telescope Spectra of Comets
• The Far-Ultraviolet "Continuum" in Protoplanetary Disk Systems II: CO Fourth Positive Emission and Absorption
• Molecules in the disk orbiting the twin young suns of V4046 Sgr
• Spitzer-MIPS Observations of the eta Cha Young Association
• Molecular Hydrogen emission from disks in the eta Chamaeleontis cluster
• CO and H2 Absorption in the AA Tauri Circumstellar Disk
• HST/COS Spectra of DF Tau and V4046 SGR: First Detection of Molecular Hydrogen Absorption Against the Ly$\alpha$ Emission Line

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• Constraining the structure of the transition disk HD 135344B (SAO 206462) by simultaneous modeling of multiwavelength gas and dust observations
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• HST spectra reveal accretion in MY Lupi
• The evolution of accretion in young stellar objects: Strong accretors at 3 - 10 Myr
• Using FUV to IR Variability to Probe the Star-Disk Connection in the Transitional Disk of GM Aur
• Direct Measurement of Interstellar Extinction Toward Young Stars Using Atomic Hydrogen Lyman-$\alpha$ Absorption
• The Evolution of Inner Disk Gas in Transition Disks
• HST FUV imaging of DG Tau: Fluorescent molecular hydrogen emission from the wide angle outflow
• A UV-to-NIR Study of Molecular Gas in the Dust Cavity Around RY Lupi
• Spectrally Resolved Mid-Infrared Molecular Emission from Protoplanetary Disks and the Chemical Fingerprint of Planetesimal Formation
• Probing the Inner Regions of Protoplanetary Disks with CO Absorption Line Spectroscopy
• Photochemical Heating of Dense Molecular Gas
• Probing UV-Sensitive Pathways for CN and HCN Formation in Protoplanetary Disks with the Hubble Space Telescope
• A model exploration of NIR ro-vibrational CO emission as a tracer of inner cavities in protoplanetary disks
• UV Fluorescence Traces Gas and LyA Evolution in Protoplanetary Disks
• Lyman-alpha Scattering Models Trace Accretion and Outflow Kinematics in T Tauri Systems
• The Mysterious Affair of the H${}_2$ in AU Mic