Nicola Da Rio HST Orion Treasury Science Meeting II Baltimore, September 12-13, 2011 A Multi-color optical survey of the Orion Nebula Cluster

Nicola Da Rio Age: 28 Nationality: Italian Education: 2005 B.Sc. in Physics, University of Trieste, Italy M.Sc. in Astrophysics and Space Physics, University of Trieste, Italy – Summer Student, STScI, Baltimore, USA 2010 PhD in Astronomy, Max Planck Institute for Astronomy, Heidelberg, Germany Career: 2011 Post doctoral researcher at the Space Telescope Science Inst., Baltimore, USA 2011 ESA Fellowship, ESTEC, The Netherlands. Scientific Interests: Pre-main Sequence Stars and Clusters Stellar evolutionary models Statistical analysis applied to stellar data Dynamics of stellar systems Nicola Da Rio Age: 28 Nationality: Italian Education: 2005 B.Sc. in Physics, University of Trieste, Italy M.Sc. in Astrophysics and Space Physics, University of Trieste, Italy – Summer Student, STScI, Baltimore, USA 2010 PhD in Astronomy, Max Planck Institute for Astronomy, Heidelberg, Germany Career: 2011 Post doctoral researcher at the Space Telescope Science Inst., Baltimore, USA 2011 ESA Fellowship, ESTEC, The Netherlands. Scientific Interests: Pre-main Sequence Stars and Clusters Stellar evolutionary models Statistical analysis applied to stellar data Dynamics of stellar systems

The Orion HST Treasury program Orion HST Treasury Program 104 HST orbits, ACS+WFPC2+NIC3 UBVIZJHK Ground based simultaneous follow-up 2.2 ESO-MPG/WFI UBVI+H  +620nm 4m CTIO/ISPI JHK 0.9m CTIO UBVRI Goal of the ground-based observations 1)Cover the bright end of the population 2)Account for stellar variability 3)Characterize the ONC stellar population Orion HST Treasury Program 104 HST orbits, ACS+WFPC2+NIC3 UBVIZJHK Ground based simultaneous follow-up 2.2 ESO-MPG/WFI UBVI+H  +620nm 4m CTIO/ISPI JHK 0.9m CTIO UBVRI Goal of the ground-based observations 1)Cover the bright end of the population 2)Account for stellar variability 3)Characterize the ONC stellar population

Da Rio et al. (2009), ApJS, 183, 261 Da Rio et al. (2010), ApJ, 722, 1092

A multi-band, large field optical catalog 2612 stars detected in I, 58% in V, 58% in V, 43% in B, 43% in B, 17% U 17% U ~1000 sources in H Wide-Field Imager (WFI) 2.2m ESO/MPG telescope La Silla (Chile) 33’x34’ Field of view 1 pointing1 pointing 6 filters6 filters 2 nights2 nights

Photospheric colors of PMS dwarfs ≠ MS stars for the same Teff Question: what are the intrinsic (photospheric) colors of young PMS stars? do the intrinsic colors depend on age? do the intrinsic colors depend on age? WFI photometric system: The computed ZAMS locus in incompatible with the observed sequence, which is bluer as predicted by atmosphere models The synthetic ZAMS is in agreement empirical colors of dwarfs For young M-type stars photospheric colors are significantly different than dwarf colors MS 2Myr isoch Av = 2

Analysis of the stellar colors Question: what are the intrinsic (photospheric) colors of young PMS stars? do the intrinsic colors depend on age? do the intrinsic colors depend on age? WFI photometric system: The computed ZAMS locus in incompatible with the observed sequence, which is bluer as predicted by atmosphere models The synthetic ZAMS is in agreement empirical colors of dwarfs For young M-type stars photospheric colors are significantly different than dwarf colors MS 2Myr isoch Av = 2

Accretion DOES alter 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 L accr to a star of given temperature 3)Solution for L accr and A V from multi-band photometry and known spectral type. UNBIASED ESTIMATE OF INDIVIDUAL EXTINTIONS UNBIASED ESTIMATE OF INDIVIDUAL EXTINTIONS

[TiO]: a spectro-photometric index to classify M stars The 620nm medium band filter used is centered on a TiO spectral feature of M starsThe 620nm medium band filter used is centered on a TiO spectral feature of M stars Theoretical atmosphere models still show remarkable uncertainties in modeling such featureTheoretical atmosphere models still show remarkable uncertainties in modeling such feature Can we use such information to constrain the stellar parameter for the ONC members?Can we use such information to constrain the stellar parameter for the ONC members? Definition of a Spectro- photometric [TiO] index:Definition of a Spectro- photometric [TiO] index: “the difference, in magnitudes, between the measured flux at 620nm and the linear interpolation between V- and I-band fluxes”“the difference, in magnitudes, between the measured flux at 620nm and the linear interpolation between V- and I-band fluxes”

[TiO]: a spectro-photometric index to classify M stars Comparison with synthetic photometry: Poor agreement Comparison with known spectral classification: Determination of a [TiO] – Spt correlation for M-Type stars Classification of 217 new M-type stars in the ONC Causes of spread: dependence of [TiO] on log(g) The lower the gravity, the higher the predicted Spt

New spectral types from narrow-band photometry The 620nm medium band filter used is centered on a TiO spectral feature of M stars [TiO] index: measures the depth of the TiO 620nm band, and correlates with spectral type for M-type stars The index is poorly sensitive to extinction. Classification of 217 new M-type stars in the ONC based on photometry

The new, complete, unbiased H-R diagram for the ONC The new, complete, unbiased H-R diagram for the ONC Further improvements: Constraints on temperature scale Luhman (2000) Revised (lower) distance 414pc Menten+ (2007)

Spectral Type – vs Temperature relation For the M-type star, the measured colors are bluer than the intrinsic ones: Negative extinction? Solution: change the SpT vs T eff relation.Solution: change the SpT vs T eff relation. Luhman (‘99) – semi empirical relation imposing the members of the GC Tau quadruplet to lie on a single BCAH isochroneLuhman (‘99) – semi empirical relation imposing the members of the GC Tau quadruplet to lie on a single BCAH isochrone Spectral catalog of Hillenbrand (1997) 65 new types from unpublished spectroscopy ~200 new M-type stars from [TiO] index Wide field, deep sample of ~1000 members with known spectral type + +

The revised H-R diagram for the ONC corrected T eff, best determined A V - new intrinsic colors and BCs relevant for the ONC - correction for veiling - new revised distance MC simulation of the propagation of known uncertainties to T eff and L tot Simulated completeness (probabilistic) in the HRD accounting for differential A V and selection effects Differences in the derived L tot compared to previous works: Higher L for M- types stars (best intrinsic colors), lower L for early types (distance + BCs)

Conclusions: Orion is older: 2-3 Myr, The large age spread is still there: ~ dex. No evidence for a mass- age dependence: -In part it is a bias from selection effects and incompleteness - In part is a model dependent bias of the isochrones IMF -Model dependent flattening at ~0.2 M 

A catalog of calibrated H excesses H  fluxes for ~1000 ONC members. Determination of the photospheric continuum using 3 bands (V,I, TiO) improves the continuum subtraction accounting for color and T eff dependence. Absolute flux calibration – erg/s/cm 2 /Å ~1/3 of the sources shows H  excess of E.W.>50Å Data will be used for determining dM/d 

Conclusions 1.New H-R diagram for Orion: ~1000 sources 1.Older age than previously estimated (2Myr) 2.Mass-age correlation not confirmed: selection effect due to source detection 3.IMF peaks at ~ Msun. Shape down to the H-burning limit strongly model dependent. 2.Photospheric colors of young stars differ from those of MS dwarfs (and from predictions of atmosphere modeling). Empirical calibration in BVI. 3.Accretion excess affects the observed colors in the entire optical wavelength range. A modeling in a 2-color diagram can be used to disentangle L acc and A V. 4.Derivation of spectral types from medium band photometry.