1. A massive disk around the intermediate-mass young star AFGL 490 ? 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) Ø100´´

2. Introduction – Motivation 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 2/9

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

4. AFGL 490 — General Properties 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) - 3mm cont.: 2500 x 1500 AU - 13 CO 1–0: 45000 x 14000 AU Motivation: study of this disk-like structure Our Observations: used JCMT, IRAM 30m, PdBI 13 CO 1 – 0 Texas telescope NMA OVRO 4/9 25000 AU box: 55´´x 55´´

5. AFGL 490 — Observational Results: CS 2–1 PdBI bar-like structure (2.5x0.4)10 4 AU different outflow systems an unvisible jet enters the denser cloud material ? disk-like system around AFGL 490 5/9

6. AFGL 490 — Comparison of the CS 2–1 line wings with : 6/9 Model of a typical disk of a Herbig Ae star (R = 400 AU) 4000 AU large-scale high- velocity CO outflow (a) 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 M disk = 7...9 M  inside R = 4000 AU ( M  = 8 M , i = 20°) - from the 3mm continuum (deconvolved point source): M gas = 3...6 M  inside R = 500 AU ( T kin = 100...150 K)  M   M disk  dynamical / self-gravitational stability ?  lifetime ? dynamical stability  Toomre´s Q parameter (e.g. Stone et al. 2000): with epicylce frequency  = (GM/r 3 ) 0.5 & surface density  = M disk /  R 2 disk when Q < 1: disk  locally graviationally unstable, fragmentation AFGL 490: R disk = 300…4000 AU, T disk = 50…200 K, M disk = 3…10 M  Q < 0.5

8. AFGL 490 — Estimate of the lifetime against: 8/9 Its known  more evolved Be stars ( t life = 10 5 …10 6 yrs) have no disks anymore (Natta et al. 1997)  speculation about the destruction mechanism: (a)photoevaporation: (weak wind model by Hollenbach et al. 1994): M  = 8 M , M disk = 6 M  Ly continuum flux = 3x10 44 s -1   t destruction = 10 8 yrs (b) accretion onto the star: t acc = M  / M, with M = 10 -5 M  /yr (Palla & Stahler 1992), M  = 8 M    t accrection = 8x10 5 yrs - large compared with t dyn (outflow) = 2x10 4 yrs (Churchwell 1999) - to build up a star with 8 M   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 (  t destruction = 10 3 –10 4 yrs)  most important destruction mechanism

9. AFGL 490 — Model Conclusions 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 9/9 25 000 AU

10. END

11. AFGL 490 — Our Observations Single-dish Observations Mapping in - CS J = 5 – 4, 7 – 6, C 18 O 2 – 1: JCMT 15m, 1994 - CS 3 – 2, 2 – 1, C 18 O 2 – 1: IRAM 30m, 1995 - Continuum 450  m & 870  m, SCUBA, 1999 - Set of molecular lines at [0,0] position Plateau de Bure Interferometer Observations Mapping in - CS 2 – 1 & continuum al = 97.98 GHz - clean beam size: 2.73´´  2.22´´ - primary beam 51´´

12. AFGL 490 — Observational Results CS 2–1 PdB Interferometer IRAM 30m primary beam Ø51 ´´ K-band image (Hodapp 1994) + CS 2–1  

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 - C 18 O maps: extended in north-south similar to the continuum for  800  m

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

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 - R disk = 4´´ = 4000 AU, M  = 8(  1) M  Fit parameters: M disk = 7...9 M , inclination angle i = 20°