Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003 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 What are “Intermediate” Mass Stars?  Less massive than O-type stars  More massive than TTauri systems Log 10 (N L y ) T eff B0 A0 B3B3 A0A0 Palla & Stahler  M  /M   15

Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003 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 NGC2023: B1 star, PDR HH 111: low- mass disk-jet system (Reipurt h et al 1999) HD100546: B9 star with disk (Augereau et al 2001)

Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003 Clustering  Low-mass stars in nearby associations are found in isolation or loose groups (   ~ few  /pc 3 ) TTS groups in Taurus: Gomez et al. (1993) 13 CO/C 18 O: NANTEN Mizuno et al. (1995) 12 CO: Dame et al. (2001) Dots: Ttauri Stars Grey: 13 CO(1-0) Thin Con: C 18 O(1- 0) Thick Con: 12 CO(1- 0)

Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003 Clustering  Low-mass stars in nearby associations are found in isolation or loose groups (   ~ few  /pc 3 )

Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003 Clustering  Low-mass stars in nearby associations are found in isolation or loose groups (   ~ few  /pc 3 )  High-mass stars are found in dense and well populated stellar clusters (   ~ 10 4  /pc 3 ) Intermediate- mass stars

Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003 Search for Clusters around HAeBe  NIR imaging surveys for embedded clusters Testi et al K band imagesStellar surface density Radial density profile

Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003 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 Testi et al 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.

Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003 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 AB Aur Elias 1 R CrA PV Cep LkH  198 R Mon LkH  198 LkH  234 HD BD+40 MWC297 CoD – 40 o MWC 137 MWC 1080 V645 Cyg

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

Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003  There is evidence that disk evolution and planet formation in HAe systems may occur on timescales of a few million years Disk Evolution in Ae Systems 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  Pic Debris disk – 100 Myrs Scattered light: Burrows et al. 1995

Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003  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>> ). Evolved dust in HAe disks (Testi et al. 2001; 2003) VLA 7mm and 3.6cm a  10cm 1.Very small, optically thick, ISM grains disk 2.Large disk with very large (few cm size) grains CQ Tau VLA 7mm

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

Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003 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 Late- type Early- type Fuente et al. 1998/2002

Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003 PdBI+VLA Search for Hbe Disks  3.6, 1.3 & 0.7 cm & 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 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 (Cesaroni et al. 1999) G192: 7mm cont 40 mas resol VLA+PT I20126: CH 3 CN PdBI

Leonardo Testi: Intermediate-Mass Star Formation, IAU Symp 221, Sydney, July 23, 2003 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 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