Formation and Early Evolution of Intermediate-Mass Stars

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)


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


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)


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)







High-mass stars are found in dense and well populated stellar clusters (~ 104 /pc3)

Intermediate-mass stars


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


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.


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


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


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


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


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


More .... a small survey using mm interferometers

(PdB and VLA)


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


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


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


Disks and High-Mass (Proto)stars

Very common Keplerian Selfgravitating

Cesaroni & Co.


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

Documents

Formation and Early Evolution of Intermediate-Mass Stars