Spectroastrometric Imaging of Molecular Gas within Protoplanetary Disk Gaps

By K. Pontoppidan, G. Blake, E. V. van Dishoeck, A. Smette, Michael J. Ireland, Joanna M. Brown. 2008

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We present velocity-resolved spectroastrometric imaging of the 4.7 μm rovibrational lines of CO gas in protoplanetary disks using the CRIRES high-resolution infrared spectrometer on the Very Large Telescope (VLT). The method as applied to three disks with known dust gaps or inner holes out to 4-45 AU (SR 21, HD 135344B, and TW Hya) achieves an unprecedented spatial resolution of 0.1-0.5 AU. While one possible gap formation mechanism is dynamical clearing by giant planets, other equally good explanations (stellar companions, grain growth, photoevaporation) exist. One way of distinguishing between different scenarios is the presence and distribution of gas inside the dust gaps. Keplerian disk models are fit to the spectroastrometric position-velocity curves to derive geometrical parameters of the molecular gas. We determine the position angles and inclinations of the inner disks with accuracies as good as 1°-2°, as well as the radial extent of the gas emission. Molecular gas is detected well inside the dust gaps in all three disks. The gas emission extends to within a radius of 0.5 AU for HD 135344B and to 0.1 AU for TW Hya, supporting partial clearing by a <1-10 MJup planetary body as the cause of the observed dust gaps, or removal of the dust by extensive grain coagulation and planetesimal formation. The molecular gas emission in SR 21 appears to be truncated within ~7 AU, which may be caused by complete dynamical clearing by a more massive companion. We find a smaller inclination angle of the inner disk of TW Hya than that determined for the outer disk, suggestive of a disk warp. We also detect significant azimuthal asymmetries in the SR 21 and HD 135344B inner disks.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/30e3439dcc6291c338998b06c591dc78b1982e61

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Citations in the corpus

Astrochemistry and compositions of planetary systems (2020, background): “Figure 8 shows ice spectra observed towards protostars in ρ-Oph F, and how the ice composition changes with distance from the central dense core (Pontoppidan et al. 2008b).”
The Inner Regions of Protoplanetary Disks (2010, background): “Breakthrough results by Pontoppidan et al. (2008) show Keplerian motion in the fundamental CO band with evidence for strong departures of symmetry in some sources, demonstrating that even single telescopes can access information at the sub-milli-arcsecond level in some cases.”
Protoplanetary Disks and Their Evolution (2011, background): “However, Pontoppidan et al. (2008) found mid-infrared CO emission from well inside the dust gaps in SR 21, HD 135344, and TW Hya.”
Gas density drops inside dust cavities of transitional disks around young stars observed with ALMA (2015, background): “(L⊙) (M⊙) (R⊙) (K) (M⊙ s−1) (pc) (mag) SR21 G3 10 1.0 3.2 5830 < 1 · 10−9 120 6.3 1,2,3 HD135344B F4 7.8 1.6 2.2 6590 6· 10−9 140 0.3 4,5,6 LkCa15 K3 1.2 1.0 1.7 4730 2· 10−9 140 1.5 6,7,8 RXJ1615-3255 K5 1.3 1.1 2.0 4400 4· 10−10 185 0.4 5,9 SR24S K2 2.5 0.7 2.7 4170 7· 10−8 120 7.0 5,10,11 J1604-2”
A SPITZER SURVEY OF MID-INFRARED MOLECULAR EMISSION FROM PROTOPLANETARY DISKS. I. DETECTION RATES (2010, background): “In contrast, LkHa 330, SR 21 and HD135344B show CO in emission in the fundamental rovibrational band at 4.7µm (Pontoppidan et al. 2008; Salyk et al. 2009).”
TRANSITIONAL DISKS AS SIGNPOSTS OF YOUNG, MULTIPLANET SYSTEMS (2011, background): “…of this inner disk material, even “traditional” transitional disk sources typically have measurable excess dust emission (e.g. Eisner et al. 2006; Espaillat et al. 2010) as well as emission from hot CO gas (Rettig et al. 2004; Pontoppidan et al. 2008; Salyk et al. 2009) originating at r < 1 AU.”
LARGE-SCALE ASYMMETRIES IN THE TRANSITIONAL DISKS OF SAO 206462 AND SR 21 (2014, unknown): “The dustdepleted cavity (Rcav = 36 AU, Andrews et al. 2011) in this transition disk (Brown et al. 2007, 2009) is not completely devoid of material, as rovibrational CO line observations reveal the presence of inner disk gas (Pontoppidan et al. 2008; Brown et al. 2013).”
Survival of molecular gas in cavities of transition disks - I. CO (2013, background): “…page 1 of 26 pioneering observations at near-IR wavelengths have detected rovibrational emission of CO at 4.7 μm in some sources indicating the presence of hot molecular gas inside their dust cavities (Salyk et al. 2007, 2009, 2011; Pontoppidan et al. 2008; Brittain et al. 2007; Brown et al. 2012).”
Possible planet-forming regions on submillimetre images (2011, background): “…et al. (2009) contain significant amount of gas – supported by Hα (Fernandez et al. 1995), [OI] (van der Plas et al. 2008) and fundamental band CO emissions (Pontoppidan et al. 2008; Salyk et al. 2009) –, these vortices can be imaged in submillimetre wavelengths as overdense regions in the dust.”
RESOLVED IMAGES OF LARGE CAVITIES IN PROTOPLANETARY TRANSITION DISKS (2011, background): “Also, some of these transition disks emit CO rovibrational spectra that attest to the presence of warm molecular gas in their inner few AU (Najita et al. 2003; Salyk et al. 2007, 2009; Pontoppidan et al. 2008).”
PROTOPLANETARY DISK STRUCTURES IN OPHIUCHUS (2009, background): “On the contrary, Pontoppidan et al. (2008) find infrared emission lines from molecular gas inside the SR 21 disk cavity.”
Resolved gas cavities in transitional disks inferred from CO isotopologs with ALMA (2015, methodology): “Rovibrational CO emission suggests a gas cavity of 7 AU radius (Pontoppidan et al. 2008) that remains unresolved at the ALMA spatial resolution (14 AU diameter ∼ 0.12′′).”
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, background): “Curiously, the position of this bump is consistent with that of the azimuthal asymmetry shown by CO lines in the inner 25 AU (at PA∼ 240◦, Pontoppidan et al. 2008).”
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◦).”