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