Nicola Da Rio Department of Astronomy, University of Florida
The pre-main sequence population of the Orion Nebula
Cluster.Optical studies
The pre-main sequence population of the Orion Nebula
Cluster.Optical studies
M. Robberto (STScI) – R. Jeffries (Keele) – J. Tan - L. Hillenbrand (Caltech) – D. Soderblom (STScI) – C. Manara (ESO) – G. Scandariato (INAF Catania) – M. Reggiani (ETH) – F. Palla (INAF Arcetri) – K. Stassun (Vanderbild) – L. Ricci (Caltech)
The Orion Nebula Cluster as a Paradigm of Star Formation
Space Telescope Science Institute, October 13-16 2013
Census of the ONC population• “Complete” census of the
PMS population in the Orion Nebula Cluster.
(Da Rio et al, 2009, 2010, 2012)
• Individual spectral types and AV for >1800 sources.
• 40’x40’ – 3pc x 3pc
2.2 ESO-MPG/WFI UBVI+Ha+620nm (2005)
I + 770nm + 753nm (2010)
Survey started as part of the HST Orion Treasury Program
Ongoing updates are being carried out.
Spectral types
1) Collection of spectral types from Hillenbrand (1997)
2) >200 new spectral types from 620nm narrow band photometry (Da Rio et al 2010)
Spectral types
1) Collection of spectral types from Hillenbrand (1997)
2) >200 new spectral types from 620nm narrow band photometry (Da Rio et al 2010)
3) >500 new spectral types from 770nm narrow band photometry (Da Rio et al 2012)
Empirical calibration of stellar colorswhat are the intrinsic (photospheric) colors of young PMS stars?do the intrinsic colors depend on age?
Intrinsic optical colors in Orion• differ from MS dwarfs• are not reproduced by current
atmosphere modelsMS2Myr isoch
Av =
2
Inaccurate calibration of colors and temperature
scale
systematic offsets in AV, masses, ages(see also Naylor et al works)
Accretion excess in the broad-band optical colors
Colors are shifted to the blue due to accretion hot spots on the stellar surface
Disentangling accretion and extinction for individual stars:
1) Simulation of an accretion spectrum, considering optically thick + thin emission.
2) Computation of the shifts in the colors adding Lacc to a star of given temperature
3) Solution for Lacc and AV from multi-band photometry and known spectral type.
Better estimate of AV
Not a good indicator for the determination of Lacc
Substellar IMF in Orion
Dramatic lack of brown dwarfs in Orion
-compared to canonical IMFs
-compared to other young stellar clusters
Chabrier system
Chabrier stellar Kroupa
Contamination of stellar samples and IMF
Andersen et al. (2011) NICMOS photometry• no deficiency of BDs • Brown dwarfs segregated
Previous works on BDs / substellar IMF in Orion also included under-luminous sources, likely background contaminants. (e.g. Slesnick et al 2004, Riddick et al 2007)
contamination
0.31 0.06 (0.2<r<0.4pc)(0.2 1.0 )
0.17 0.02 (0.2<r<1.0pc)(0.02 0.2 )
N M
N M
Rob Jeffries’ talk
Stellar ages
• Isochronal ages show a spread of ~0.4 dex around 2.5Myr (model dependent!)
• This spread is not produced by uncertainties (Reggiani+2012)
• Several pieces of evidence (Disk-age correlation Jeffries et al
2011, and mass accretion – age biases, Da Rio et al submitted) point to a 0.2 dex real age spread
• Bayesian estimate of allowed combinations of age spread, uncertainties and diversity of protostellar accretion to reproduce the observed HRD
CTIO ISPI JHK photometry
Meyer (1997)
Robberto et al. (2010)
CTIO ISPI JHK photometry
Meyer (1997)
Extinction map (Scandariato et al. 2011)
CTIO ISPI JHK photometryAvailable Teff and AV + near-infrared photometry
1) Calibration of intrinsic colors and consequences on the IMF (Scandariato et al 2012)
Meyer (1997)
2) CTTS NIR locus (Scandariato et al, in prep)
Accuracy of stellar parametersThe knowledge of the (in)accuracies severely impacts ours understanding of Orion
see Reggiani et al. (2011)
Meyer (1997)
Hillenbrand (2013)RMS=1.75 subtypes
Are we overestimating the accuracy of the stellar parameters?
How many sources have VERY wrong assigned stellar parameters (see Manara et al 2013)
RMS=2.25 subtypes
(Non uniform) incompleteness - Spatially variable extinction- Inhomogeneous detection limits
May cause Do cause selection effects when looking for correlations
Meyer (1997)
The Orion HST Treasury program
ACS
NICMOS
WFPC2
Robberto et al (2013)
104 orbits
Full coverage
ACS BVIZ H aWFPC2 UBI Ha
Partial coverege
NICMOS JH
The Orion HST Treasury program
Ricci et al (2009)catalog of proplyds
Robberto et al (2009)evidence for a circumbinary proplyd
and..
Manara et al. (2012) – accretion rates from WFPC2 U and Ha excess
Reggiani et al (2011) – role of stellar parameter uncertainties in age spread
Andersen et al (2011) – substellar IMF
Press release, credits NASA/ESA and L. Ricci (ESO)
The Orion HST Treasury program
The HST photometry is deep enough to reach down to planetary masses.
The NIR surveys probe into the embedded populations.
Lack of memberships or spectral types is limiting.
FIELD
0.5M0.5M
0.08M0.08M
0.02M0.02M
0.5M0.5M
0.08M0.08M
0.02M0.02M
ACS NICMOS
We keep on using only a fraction of the information available
Meyer (1997)
1) Spectral types collected by dozens of works
2) Multi band and multi-epoch photometry• Pan-Starrs
3) Membership estimators and other (circum)stellar properties:• Proper motions (Parenago 1954, Jones & Walker 1998, McNamara 1976, Tian et al. 1996)
• X-ray emission (Getman+2005)
• Disk excess (Megeath+2012, Morales-Caleron+2011)
• Accretion tracers (Rebull, Manara, Da Rio, Robberto, …)
• Stellar variability and rotation (Rodriguez-Ledesma+2009, Herbst+2002, Jeffries+)
• Radial velocity (Furesz+2008, Tobin+2009,.. )
A universal (inspected and reasoned) catalog
of all stellar information in the ONC?
Black: ACS photometry
• Increase the sample• Detect and correct for
problems• Improve estimates of
stellar properties
Extension of stellar census to the south
Meyer (1997)
Black: ACS photometry
• Identical observational setup as in Da Rio et al (2012)• Is NGC1980 a foreground older cluster (Alves & Bouy 2012)• How does average age and age spread vary along the filament?
In-Sync Orion survey
Meyer (1997)
Black: ACS photometry
APOGEE fiber spectrograph at the SDSS
• High resolution NIR spectra of 2700 candidate members down to H=12.5 (0.5M)
• Radial velocities with 0.3-0.5 km s-1 accuracy of nearly all known members
• Larger coverage than previous works• Less limited by extinction
Tobin 2009
Summary
• We have obtained the “full” census of the ONC stellar population. • Unpublished updates are and will be present.
• The accuracy of derived stellar parameters is un part unclear. • Beware of spatially non uniform incompleteness.
• IMF is deficient of brown dwarfs.• Future extension of the sample to the lowest masses is needed to settle the debate.
• The full potential of the Orion HST Treasury program has not been yet used.• We need deep surveys to get memberships and spectral types in the substellar
range.• A universal catalog of stellar properties in Orion could enable a number of new
studies
• Coming soon: extension of census along the Orion A filament and RV
Top Related