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Star Formationin the Local Group
Nino PanagiaSTScI
INAF/NASupernova Ltd
Orion Nebula Cluster Workshop16 October 2012
… as seen by low mass stars
Part 1
16 October 2013Low Mass PMS Stars
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Guido De Marchi (ESA)
Nino Panagia (STScI)
Martino Romaniello (ESO)
Giacomo Beccari (ESO)
Francesco Paresce (INAF)
Loredana Spezzi (ESAESO)
Elena Sabbi (ESA/STScI)
Marco Sirianni (ESA)
Morten Andersen (ESA)
www.starformation.eu
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• Solar mass stars account for most of the star formation in a galaxy
• Low mass stars can form in small clouds as well as in big ones
• Low mass stars are forming both near massive stars and in isolated groups
In order to understandhow star formation proceeds
We have to study
Many young stars
In diverse environments
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Stellar Evolution Mass-loss/Rotation [Metallicity] Extinction
Stellar Properties Age [Metallicity] Initial Mass Function [?]
Star Formation History
Input
Output
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Crowding Limits for MS stars
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Scaled LF for SN 1987A fieldB) ~ 21 mags/arcsec2
star
s/A
CS
PSF
are
a
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PMS stars: How to find them?Low-mass stars grow in mass over time through accretion of matter from a circumstellar disc (e.g. Lynden-Bell & Pringle 1974; Bertout 1989)
Typical signature:
UV, IR and Hα excess emission
How to measure it?
1- Spectroscopy
2- Photometry (De Marchi et al. 2010)
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Spectroscopy made easy…
New simple method combines broad-band (V, I) and narrow-band (H ) photometry and allows us to:
identify all objects with H excess emission derive their accretion luminosity and mass
accretion rates for hundreds of stars simultaneously!
(De Marchi, Panagia & Romaniello 2010, ApJ, 715, 1)
PMS stars and photometry
IV
Hα
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H photometry
SMC(NGC 346)
LMC(SN 1987A)
9,300 K 5,000 K 3,500 K 9,300 K 5,000 K 3,500 K
De Marchi, Panagia & Romaniello 2010 De Marchi et al. 2011
gives L(H)
( )0 ( )0
(
)
0
(
)
0
Stars physical parameters
H luminosity LH gives accretion luminosity Lacc via a relationship based on simple physics and calibrated using spectroscopic data
Log (Lacc) = Log (LH) + 1.72
We can study how star formation has proceeded in space and time
Mass M radius R and age t from PMS isochrones in HR diagram
Free fall equation gives mass accretion rate M •
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NGC 1850 Neighborhood
NGC1850 A & B
The second brightest stellar cluster in the Large Magellanic Cloud
NGC 1850A Globular-like 50 Myrs old Flat IMF: 0.4
NGC 1850B Spatially diffuse 4 Myrs old “Normal” IMF: 1.6
Gilmozzi et al. 1994, ApJ 435, L43
A
B
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NGC 1850
First detection of
Pre-Main-Sequence stars
outside the Milky Way
Gilmozzi et al 1994
4 Myrs
50 Myrs
1 GyrsPMS PMS
A
B
NGC 1850 - H Excess Stars
50Myrs
T Tau
Be-Ae
(Romaniello et al. 2013, in preparation) -Weq(H)>10Å
4Myrs4Myrs50Myrs
Be-Ae
PMS
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NGC 1850 - Spatial Distribution
Markedly different spatial distributions for O type and PMS stars
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O type starBe-Ae starPMS star
NGC1850 - Conclusions
Different spatial distributions for massive (>10M) and low mass (<2M) stars of the same generation imply different star formation processes
IMF meaningful only in a statistical sense, i.e. averaged over a large volume and large number of stars
Similar results obtained in the field of SN1987A and other LMC/SMC star forming regions
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The Field around SN 1987A Stars with Hexcess (-Weq>10A)
Panagia et al. 2000
SN 1987A FieldMassive Stars vs PMS Stars
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Panagia et al. 2000
24
De Marchi et al 2010
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HLuminosity
L(H) > 0.020 L
L(H) < 0.020 L
> 0.008 L
L(H) < 0.008 L
Evidence for Disk Photo-Evaporation
PMS stars far from UV sources have higher L(H)
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Star Formationin the Local Group
Guido De MarchiESA
Orion Nebula Cluster Workshop16 October 2012
… as seen by low mass stars
Part 2
