leonardo testi: intermediate-mass star formation, iau symp 221, sydney, july 23, 2003 formation and...
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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
Log10(NLy)
Teff
B0
A0
B3
A0
Palla & Stahler 1993
2M/M15
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 (Reipurth 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 /pc3)
TTS groups in Taurus: Gomez et al. (1993)13CO/C18O: NANTEN Mizuno et al. (1995)12CO: Dame et al. (2001)
Dots: Ttauri StarsGrey: 13CO(1-0)Thin Con: C18O(1-0)Thick Con: 12CO(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 /pc3)
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 /pc3)
High-mass stars are found in dense and well populated stellar clusters (~ 104 /pc3)
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. 1997-03
K band images
Stellar 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. 1997-1999
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. 1994/1998Natta et al. 1993
AB Aur
Elias 1
R CrA
PV Cep
LkH 198
R Mon
LkH 198LkH 234
HD 200775BD+40
MWC297
CoD –40o
MWC 137MWC 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 1997/2000Mannings 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. 2001Millan-Gabet et al. 1999
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 480Young gaseous disk – 6 MyrsCO(2-1): Mannings et al 1997
HR 4796 AEvacuated inner disk – 15MyrMID-IR: Koerner et al. 1998
PicDebris disk – 100 MyrsScattered 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 3.6cma 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. 2000
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 + 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
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
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