CO emission from discs around isolated HAeBe and Vega-excess stars

By W. Dent, J. Greaves, I. Coulson. 2005

175 citations recorded by the source corpus.

We describe results from a survey for J = 3‐2 12 CO emission from visible stars classified as having an infrared excess. The line is clearly detected in 21 objects, and significant molecular gas (10 −3 Jupiter masses) is found to be common in targets with infrared excesses 0.01 (56 per cent of objects), but rare for those with smaller excesses (∼10 per cent of objects). A simple geometrical argument based on the infrared excess implies that disc opening angles are typically 12 ◦ for objects with detected CO; within this angle, the disc is optically thick to stellar radiation and shields the CO from photodissociation. Two or three CO discs have an unusually low infrared excess (0.01), implying the shielding disc is physically very thin (1 ◦ ). Around 50 per cent of the detected line profiles are double-peaked, while many of the rest have significantly broadened lines, attributed to discs in Keplerian rotation. Simple model fits to the line profiles indicate outer radii in the range 30‐300 au, larger than found through fitting continuum SEDs, but similar to the sizes of debris discs around main-sequence stars. As many as five have outer radii smaller than the Solar System (50 au), with a further four showing evidence of gas in the disc at radii smaller than 20 au. The outer disc radius is independent of the stellar spectral type (from K through to B9), but there is evidence of a correlation between radius and total dust mass. Also the mean disc size appears to decrease with time: discs around stars of age 3-7 Myr have a mean radius ∼210 au, whereas discs of age 7-20 Myr are a factor of three smaller. This shows that a significant mass of gas (at least 2 M⊕ )e xists beyond the region of planet formation for up to ∼7 Myr, and may remain for a further ∼10 Myr within this region. The only bona fide debris disc with detected CO is HD9672; this shows a double-peaked CO profile and is the most compact gas disc observed, with a modelled outer radius of 17 au. In the case of HD141569, detailed modelling of the line profile indicates gas may lie in two rings, with radii of 90 and 250 au, similar to the dust structure seen in scattered light and the mid-infrared. In both AB Aur and HD163296 we also find that the sizes of the molecular disc and the dust scattering disc are similar; this suggests that the molecular gas and small dust grains are closely co-located. Ke yw ords: planetary systems: proto planetary discs ‐ submillimetre.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/a365b7e9cf97a543e972b4786436b985cdf050c5

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In Astronomy and Astrophysics

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2. D. Wilner
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4. Anders Johansen
5. A. Hughes
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In Instrumentation

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7. R. Dong
8. T. Birnstiel

Citations in the corpus

• Spitzer IRS Spectroscopy of IRAS-discovered Debris Disks (2006, background): “Zuckerman et al. (1995) and Dent et al. (2005) estimate that between 2 and 30 M⊕ H2 exists in the disk, assuming a gas excitation temperature, Tex = 50 - 60 K, and an interstellar H2:CO number ratio between 1 - 2×104, significantly smaller than the <6000 M⊕ and <80 M⊕ that we infer assuming Tex =…”
• EMPIRICAL CONSTRAINTS ON TURBULENCE IN PROTOPLANETARY ACCRETION DISKS (2010, background): “These systems were selected on the basis of their bright CO(3-2) line emission (e.g., Kastner et al. 1997; Dent et al. 2005), to ensure adequate sensitivity for high-resolution spectroscopy.”
• DISCOVERY OF SMALL-SCALE SPIRAL STRUCTURES IN THE DISK OF SAO 206462 (HD 135344B): IMPLICATIONS FOR THE PHYSICAL STATE OF THE DISK FROM SPIRAL DENSITY WAVE THEORY (2012, background): “The observations of CO line profiles (Dent et al. 2005; Pontoppidan et al. 2008; Lyo et al. 2011) and stellar rotation (Müller et al. 2011) consistently indicate an almost face-on geometry (i ∼ 11◦).”
• Radiation thermo-chemical models of protoplanetary disks I. Hydrostatic disk structure and inner rim (2009, background): “However, the sensitivity of current radio telescopes allows only observations of small samples (Dent et al., 2005) and in a few cases detailed studies of individual objects (e.g. Qi et al., 2003; Semenov et al., 2005; Qi et al., 2008).”
• Cold Disks: Spitzer Spectroscopy of Disks around Young Stars with Large Gaps (2007, background): “T Cha isi ∼ 30 more edge-on, so was adopted (Alcala´ et l. 1993), and HDi ∼ 75 135344 is more face-on with (Dent et al. 2005).”
• Small vs. large dust grains in transitional disks: do different cavity sizes indicate a planet? - SAO 206462 (HD 135344B) in polarized light with VLT/NACO (2013, methodology): “The properties of the disk around SAO 206462 have been constrained via imaging (e.g. Grady et al. 2009; Muto et al. 2012), spectroscopy (e.g. Dent et al. 2005; Brown et al. 2007), and interferometry (e.g. Fedele et al. 2008; Andrews et al. 2011).”
• A PARAMETRIC MODELING APPROACH TO MEASURING THE GAS MASSES OF CIRCUMSTELLAR DISKS (2013, background): “CO is the most abundant molecule after H2 and its millimeter wavelength rotational lines are the strongest that are observable from the ground (Thi et al. 2004; Dent et al. 2005).”
• Forming the cores of giant planets from the radial pebble flux in protoplanetary discs (2014, background): “CO observations tracing the gas component of the disc suggest a mean outer disc radii larger than ro ≈ 210 AU, for stars with ages <∼7 Myr, nearly independent of the stellar spectral type (Dent et al. 2005).”