A massive disk around the intermediate-mass young star AFGL 490 ?

1. A massive disk around the intermediate-mass young star AFGL 490 ? Ø100´´ Katharina Schreyer (AIU Jena, Germany) Thomas Henning (MPIA Heidelberg, Germany) Floris van der Tak (MPIfR Bonn, Germany) Annemieke Boonman (Univ. Leiden, NL) Ewine F. van Dishoeck (Univ. Leiden, NL)

2. Introduction – Motivation 2/9 • formation of high-mass stars – one of the unresolved • mysteries of the present research • dominant formation process: disk accretion or coalesence ? • recent detections of disks around massive protostars: • IRAS 20126+4104 (1.7kpc, Cesaroni et al. 1999, Zhang et al. 1998, B2) & • G 192.16-3.82 (2.0kpc, Shepherd et al. 2001, B2...3) • _disks are more massive and larger than disks around T Tauri and Herbig Ae stars Search for high-mass objects in early evolutionary states • survey of bright IRAS sources(Klein, Posselt, Henning, Schreyer: Poster) • one of these targets: AFGL 490

3. AFGL 490 — General Properties 3/9 K-band image • optical: diffuse nebulosity, • NIR: luminous source • D = 1 kpc,L= 1.4 – 4·103L8 • early B2..3 star, M= 8...10 M8 typical properties of a Becklin Neugebauer Object: - weak continuum flux at l1cm - broad & strong Bra and Brg (Bunn et al. 1995) ionized region  100 AU (Simon et al. 1981, 1983) AFGL 490

4. Texas telescope AFGL 490 — General Properties 25000 AU 4/9 embedded in a dense cloud core (e.g Kawabe et al. 1984, Snell et al. 1984) poorly collimated high-velocity outflow (e.g. Lada & Harvey 1981) previous interferom. observations  presence of a huge disk ? (Mundy & Adelmann 1988, Nakamura et al. 1991) - l3mm cont.: 2500 x 1500 AU -13CO 1–0: 45000 x14000 AU Motivation: study of this disk-like structure Our Observations: used JCMT, IRAM 30m, PdBI OVRO 13CO 1 – 0 box: 55´´x 55´´ NMA

5. AFGL 490 — Observational Results: CS 2–1 PdBI 5/9 bar-like structure (2.5x0.4)104AU different outflow systems an unvisible jet enters the denser cloud material ? disk-like system around AFGL 490

6. large-scale high- velocity CO outflow 4000 AU Model of a typical disk of a Herbig Ae star (R = 400 AU) AFGL 490 — Comparison of the CS 2–1 linewings with : 6/9 • VLA 2cm continuum map (b) Speckle H-band image • (Campbell et al. 1986) (Hoare et al. 1996) - repeated 2cm + H band observations by Hoare (2001): at the moment a point source

7. A disk around AFGL 490 ? 7/9 Mass - from a Keplerian model – fit to the outer line wings: estimates Mdisk = 7...9 M8 inside R= 4000 AU(M=8 M8, i = 20°) - from the l3mmcontinuum (deconvolved point source): Mgas = 3...6 M8 inside R= 500 AU (Tkin = 100...150 K) M Mdisk dynamical / self-gravitational stability?  lifetime? dynamical stability  Toomre´s Q parameter (e.g. Stone et al. 2000): with epicylce frequency = (GM/r3)0.5 &surface density  = Mdisk/R2disk when Q < 1: disk  locally graviationally unstable, fragmentation AFGL 490:Rdisk= 300…4000 AU, Tdisk= 50…200 K, Mdisk= 3…10 M8  Q < 0.5

8. AFGL 490 — Estimate of the lifetime against: 8/9 Its known  more evolved Be stars (tlife = 105…106 yrs) have no disks anymore (Natta et al. 1997) speculation about the destruction mechanism: • photoevaporation: • (weak wind model by Hollenbach et al. 1994): M=8 M8, Mdisk=6 M8 • Ly continuum flux = 3x1044s-1 tdestruction=108 yrs • (b) accretion onto the star: • tacc=M/M, with M=10-5 M8/yr(Palla & Stahler 1992), • M= 8 M8taccrection=8x105 yrs • - large compared with tdyn(outflow) = 2x104 yrs(Churchwell 1999) • - to build up a star with 8 M8M must have been larger in the past • (c) self-gravitation: • e.g. Adams et al. (1989), Laughlin & Bodenheimer (1994) – evolution of • disk with Q  1 : fragmentation within the time of the orbital period • (tdestruction=103–104 yrs)  most important destruction mechanism • • •

9. AFGL 490 — Model Conclusions 9/9 inner free zone R = 50..100 AU a larger gas torus R  4000 AU feeds an inner (accrection) disk R  500 AU remnant of the flattened inner cloud core R  25000 AU further high- resolution observations and theoretical work are needed 25 000 AU

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11. AFGL 490 — Our Observations Single-dish Observations Mapping in - CS J = 5 – 4, 7 – 6, C18O 2 – 1: JCMT 15m, 1994 - CS 3 – 2, 2 – 1, C18O 2 – 1: IRAM 30m, 1995 - Continuum 450mm & 870 mm, SCUBA, 1999 - Set of molecular lines at [0,0] position Plateau de Bure Interferometer Observations Mapping in - CS 2 – 1 & continuum al l = 97.98 GHz - clean beam size: 2.73´´  2.22´´ - primary beam 51´´

12. AFGL 490 — Observational Results IRAM 30m CS 2–1 PdB Interferometer   K-band image (Hodapp 1994) + CS 2–1 primary beamØ51´´

13. AFGL 490 — Observational Results: CS 2–1 PdBI Spectra

14. AFGL 490 — Observational Results: Single-Dish • AFGL 490: • - embedded in a dense cloud core • CS maps: spherically symmetric • morphology • C18O maps: extended in north-south • similar to the continuum for • l 800m

15. AFGL 490 — Observational Results: l = 3mm PdBI Continuum green contours: > 3 s rms white contours: 1 s rms only one strong mm source

16. AFGL 490 — Position-velocity-maps • A simple model of Keplerian motion (Vogel et al. 1985) • Assumptions: • rotational equilibrium model: a central star + the • disk mass lineary increasing with the radius • Rdisk = 4´´ = 4000 AU, M = 8(1) M8 • Fit parameters: • Mdisk = 7...9 M8, inclination angle i = 20°