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Formation and Early Evolution of Intermediate-Mass Stars

Formation and Early Evolution of Intermediate-Mass Stars. Intermediate-Mass Stars in the Context Clustering and the Formation of “Early”-Type Systems Disks as a probe of the Formation Mechanism Evolution of Circumstellar Material. Leonardo Testi (INAF--Osservatorio Astrofisico di Arcetri).

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Formation and Early Evolution of Intermediate-Mass Stars

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  1. Formation and Early Evolution of Intermediate-Mass Stars • Intermediate-Mass Stars in the Context • Clustering and the Formation of “Early”-Type Systems • Disks as a probe of the Formation Mechanism • Evolution of Circumstellar Material Leonardo Testi (INAF--Osservatorio Astrofisico di Arcetri) Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  2. 2M/M15 B3 Log10(NLy) A0 B0 A0 Palla & Stahler 1993 Teff What are “Intermediate” Mass Stars? • Less massive than O-type stars • More massive than TTauri systems Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  3. NGC2023: B1 star, PDR HH 111: low-mass disk-jet system (Reipurth et al 1999) HD100546: B9 star with disk (Augereau et al 2001) Why “Intermediate” Mass? • Intermediate-Mass Stars allow one to study the transition from “quiet” low-mass and “violent” high-mass star-formation M17: O-stars, cluster and HII region Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  4. Clustering • Low-mass stars in nearby associations are found in isolation or loose groups (~ few /pc3) Dots: Ttauri Stars Grey: 13CO(1-0) Thin Con: C18O(1-0) Thick Con: 12CO(1-0) TTS groups in Taurus: Gomez et al. (1993) 13CO/C18O: NANTEN Mizuno et al. (1995) 12CO: Dame et al. (2001) Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  5. Clustering • Low-mass stars in nearby associations are found in isolation or loose groups (~ few /pc3) Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  6. Intermediate-mass stars Clustering • Low-mass stars in nearby associations are found in isolation or loose groups (~ few /pc3) • High-mass stars are foundin dense and well populated stellar clusters (~ 104 /pc3) Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  7. Search for Clusters around HAeBe • NIR imaging surveys for embedded clusters K band images Stellar surface density Radial density profile Testi et al. 1997-03 Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  8. Clustering properties • Clear dependence of the clusters richness with the spectral type of the Herbig Ae/Be star (the most luminous - massive - member) • No clusters and no evidence for dynamical dissipation around HAe stars (as expected) • Increase in cluster density with Sp. type It is tempting to speculate that there is a physical connection between clusters and massive stars, but available data is insufficient to claim this conclusion. Testi et al. 1997-1999 Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  9. CoD –40o MWC 137 MWC 1080 LkH 198 V645 Cyg LkH 234 AB Aur HD 200775 Elias 1 BD+40 MWC297 LkH 198 PV Cep R Mon R CrA The disks/envelopes debate • Extended emission detected at 50/100 m (KAO) • Models require Disk+Envelope Di Francesco et al. 1994/1998 Natta et al. 1993 Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  10. Disks around HAe Systems • Evidence for disks similar to the ones found around TTauri systems has been searched by means of mm interferometry • The presence of circumstellar disks have been demonstrated in many HAe systems Mannings & Sargent 1997/2000 Mannings et al. 1997 Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  11. HAe Disks vs. TTS Disks • Infrared interferometric observations are not consistent with standard disk models. Inner bright ring. Binary Disk Ring Gaussian Dullemond et al. 2001 Millan-Gabet et al. 1999 Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  12. Disk Evolution in Ae Systems • There is evidence that disk evolution and planet formation in HAe systems may occur on timescales of a few million years MWC 480 Young gaseous disk – 6 Myrs CO(2-1): Mannings et al 1997 HR 4796 A Evacuated inner disk – 15Myr MID-IR: Koerner et al. 1998  Pic Debris disk – 100 Myrs Scattered light: Burrows et al. 1995 Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  13. CQ Tau VLA 7mm Evolved dust in HAe disks • Search for the presence of large (cm-size) grains • The basic idea is to search for mm spectra that approach the black body spectrum  this limiting case is reached only if the disk is optically thick or the dust opacity is grey (size>>). • Very small, optically thick, ISM grains disk • Large disk with very large (few cm size) grains VLA 7mm and 3.6cm a  10cm (Testi et al. 2001; 2003) Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  14. More .... a small survey using mm interferometers (PdB and VLA) Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  15. Early-type Late-type Fuente et al. 1998/2002 Disks around HBe Systems? • Very little evidence for disks around HBe stars • mm-interferometers confirm KAO-FIR observations • Most of the circumstellar material is in envelopes Compilation by Natta et al. 2000 Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  16. PdBI+VLA Search for Hbe Disks • 3.6, 1.3 & 0.7 cm + 2.7 & 1.3mm • Dusty disks are detected in 2 out of four objects • Dusty disks around HBe stars are less massive and have short lifetimes compared with lower mass systems Fuente et al. 2003 Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  17. Disks and High-Mass Protostars • There is evidence that some high-mass protostars may be surrounded by massive (accretion??) disks • Best examples: • G192 (Shepherd et al. 2001) • IRAS 20126+4104 (Cesaroni et al. 1999) G192: 7mm cont 40 mas resol VLA+PT I20126: CH3CN PdBI Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  18. Disks and High-Mass (Proto)stars • Very common • Keplerian • Selfgravitating Cesaroni & Co. Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

  19. Summary • “Late”-type intermediate mass stars show similar formation and disk properties as lower mass TTS. They represent an ideal laboratory to study disk evolution processes • HBe stars are not associated with massive disks, this could be due to a faster evolution or a different formation process as many massive protostellar systems appears to be associated with disk-like structures • Richness and density of clusters are correlated with the mass of the most massive member. However, the indication of possible coalescence processes is not yet conclusive Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003

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