A gas density drop in the inner 6 AU of the transition disk around the Herbig Ae star HD 139614
Further evidence for a giant planet inside the disk?⋆
1 Université de Toulouse, UPS-OMP, IRAP, 14 avenue E. Belin, Toulouse, 31400, France
2 Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, PO Box 67, 1525 Budapest, Hungary
3 Departamento de Física Teórica, Universidad Autónoma de Madrid, Campus Cantoblanco, 28049 Madrid, Spain
4 Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching bei München, Germany
5 Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, The Netherlands
6 Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Boulevard de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France.
7 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
8 UMI-FCA, CNRS/INSU, France (UMI 3386), and Dept. de Astronomía, Universidad de Chile, 1058 Santiago, Chile
9 Univ. Grenoble Alpes, IPAG; CNRS, IPAG, 38000 Grenoble, France
10 Department of Astronomy, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix, Switzerland
11 University of Vienna, Department of Astronomy, Türkenschanzstrasse 17, 1180 Vienna, Austria
12 SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS, UK
13 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
14 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
15 Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, 1058 Santiago, Chile
16 Unidad Asociada Astro-UAM/CSIC, 28850 Madrid, Spain
Received: 9 March 2016
Accepted: 15 September 2016
Context. Quantifying the gas surface density inside the dust cavities and gaps of transition disks is important to establish their origin.
Aims. We seek to constrain the surface density of warm gas in the inner disk of HD 139614, an accreting 9 Myr Herbig Ae star with a (pre-)transition disk exhibiting a dust gap from 2.3 ± 0.1 to 5.3 ± 0.3 AU.
Methods. We observed HD 139614 with ESO/VLT CRIRES and obtained high-resolution (R ~ 90 000) spectra of CO ro-vibrational emission at 4.7 μm. We derived constraints on the disk’s structure by modeling the CO isotopolog line-profiles, the spectroastrometric signal, and the rotational diagrams using grids of flat Keplerian disk models.
Results. We detected υ = 1 → 0 12CO, 2→1 12CO, 1→0 13CO, 1→0 C18O, and 1→0 C17O ro-vibrational lines. Lines are consistent with disk emission and thermal excitation. 12CO υ = 1 → 0 lines have an average width of 14 km s-1, Tgas of 450 K and an emitting region from 1 to 15 AU. 13CO and C18O lines are on average 70 and 100 K colder, 1 and 4 km s-1 narrower than 12CO υ = 1 → 0, and are dominated by emission at R ≥ 6 AU. The 12CO υ = 1 → 0 composite line-profile indicates that if there is a gap devoid of gas it must have a width narrower than 2 AU. We find that a drop in the gas surface density (δgas) at R < 5–6 AU is required to be able to simultaneously reproduce the line-profiles and rotational diagrams of the three CO isotopologs. Models without a gas density drop generate 13CO and C18O emission lines that are too broad and warm. The value of δgas can range from 10-2 to 10-4 depending on the gas-to-dust ratio of the outer disk. We find that the gas surface density profile at 1 < R < 6 AU is flat or increases with radius. We derive a gas column density at 1 < R < 6 AU of NH = 3 × 1019−1021 cm-2 (7 × 10-5−2.4 × 10-3 g cm-2) assuming NCO = 10-4NH. We find a 5σ upper limit on the CO column density NCO at R ≤ 1 AU of 5 × 1015 cm-2 (NH ≤ 5 × 1019 cm-2).
Conclusions. The dust gap in the disk of HD 139614 has molecular gas. The distribution and amount of gas at R ≤ 6 AU in HD 139614 is very different from that of a primordial disk. The gas surface density in the disk at R ≤ 1 AU and at 1 < R < 6 AU is significantly lower than the surface density that would be expected from the accretion rate of HD 139614 (10-8 M⊙ yr-1) assuming a standard viscous α-disk model. The gas density drop, the non-negative density gradient in the gas inside 6 AU, and the absence of a wide (>2 AU) gas gap, suggest the presence of an embedded <2 MJ planet at around 4 AU.
Key words: protoplanetary disks / stars: pre-main sequence / planets and satellites: formation / techniques: spectroscopic / stars: variables: T Tauri, Herbig Ae/Be
Based on CRIRES observations collected at the VLTI and VLT (European Southern Observatory, Paranal, Chile) with program 091.C-0671(B).
Part of this research has been done by A. Carmona under the frame of ESO’s scientist visitor program during November 2013 and at Université Grenoble Alpes, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 38000 Grenoble, France. Current address: Institut de Recherche en Astrophysique et Planétologie (IRAP), 14 avenue E. Belin, Toulouse, 31400, France.
© ESO, 2017