The physics of the accretion process in the formation and evolution of Young Stellar Objects Carlo Felice Manara München 2014 The physics of the accretion process in the formation and evolution of Young Stellar Objects Carlo Felice Manara Dissertation an der Fakultät für Physik der Ludwig--Maximilians--Universität München vorgelegt von Carlo Felice Manara aus Mailand, Italien München, den 22. Maj 2014 Erstgutachter: Prof. Dr. Barbara Ercolano Zweitgutachter: Prof. Dr. Andreas Burkert Tag der mündlichen Prüfung: 8. Juli 2014 To my two girls This work has been carried out at the European Southern Observatory (ESO) under the su- pervision of Leonardo Testi and within the ESO/International Max Planck Research School (IMPRS) student fellowship programme. The members of the Thesis Committee were: Barbara Ercolano, Leonardo Testi, Thomas Preibisch, and Antonella Natta. vi Contents Abstract xvii Zusammenfassung xvii List of Acronyms xxi 1 Introduction 1 1.1 Setting the scene: the evolutionary path from molecular cloud cores to stars and planets ................................... 1 1.2 Star-disk interaction: accretion ......................... 5 1.2.1 Magnetospheric accretion ....................... 5 1.3 Accretion as a tracer of protoplanetary disk evolution ............ 7 1.3.1 Evolution of accretion rates with time in a viscous disk ....... 7 1.3.2 Evolution of accretion rates with time due to photoevaporation ... 13 1.3.3 The dependence of accretion rates with the mass of the central star . 15 1.4 The role of this Thesis .............................. 20 1.4.1 The state of the art at the beginning of this Thesis ........... 20 1.4.2 Open issues at the beginning of this Thesis .............. 24 1.4.3 The structure of this Thesis ....................... 25 2 Modeling the accretion spectrum 29 2.1 Accretion spectrum models in the literature .................. 29 2.2 The slab model ................................. 31 2.2.1 The hydrogen emission ......................... 32 2.2.2 The H− emission ............................ 35 2.2.3 The total emission of the slab model .................. 37 2.3 Dependence of selected features on the input parameters .......... 37 2.3.1 Contribution of H and H− to the total emission ............ 38 2.3.2 Balmer jump .............................. 39 2.3.3 Balmer and Paschen continua ..................... 40 3 Photospheric templates of young stellar objects and the impact of chromospheric emission on accretion rate estimates 43 3.1 Introduction ................................... 44 3.2 Sample, observations, and data reduction ................... 45 3.3 Spectral type classification ........................... 48 3.3.1 Spectral typing from depth of molecular bands ............ 48 3.3.2 Spectral indices for M3-M8 stars .................... 49 3.4 Stellar parameters ................................ 56 3.4.1 Stellar luminosity ............................ 56 3.4.2 Stellar mass and age .......................... 58 vii CONTENTS 3.5 Line classification ................................ 58 3.5.1 Emission lines identification ...................... 58 3.5.2 Hα equivalent width and 10% width ................. 60 3.5.3 Line luminosity ............................. 60 3.6 Implications for mass accretion rates determination ............. 62 3.6.1 Accretion luminosity noise ....................... 66 3.6.2 Mass accretion rate noise ........................ 69 3.7 Conclusion ................................... 72 3.A Comments on individual objects ........................ 73 3.B NIR spectral indices ............................... 74 3.C On-line material ................................ 78 4 Accurate determination of accretion and photospheric parameters in young stellar objects 85 4.1 Introduction ................................... 86 4.2 Sample, observations, and data reduction ................... 87 4.2.1 Targets selection and description ................... 87 4.2.2 Observations and data reduction ................... 88 4.3 Method ..................................... 89 4.3.1 Parameters of the multicomponent fit ................. 90 4.3.2 Determination of the best fit ...................... 91 4.3.3 Comparison to synthetic spectra .................... 93 4.3.4 Stellar parameters ............................ 94 4.4 Results ...................................... 95 4.4.1 OM1186 ................................ 95 4.4.2 OM3125 ................................ 97 4.5 Discussion .................................... 97 4.5.1 Age related parameters ......................... 100 4.5.2 Sources of error in the previous classifications ............ 100 4.5.3 Implications of our findings ...................... 102 4.6 Conclusion ................................... 103 5 On the gas content of transitional disks 105 5.1 Introduction ................................... 106 5.2 Observations .................................. 108 5.2.1 Sample description ........................... 108 5.2.2 Observational strategy ......................... 110 5.2.3 Data reduction ............................. 111 5.3 Accretion and photospheric parameters .................... 114 5.3.1 Method description ........................... 114 5.3.2 Infrared color excess .......................... 123 5.4 Wind signatures ................................. 124 5.5 Discussion .................................... 125 viii Contents 5.5.1 Accretion properties .......................... 126 5.5.2 Wind properties ............................. 128 5.5.3 Accretion and wind properties in objects with inner disk emission . 132 5.5.4 Constraint on the gas content of the inner disk ............ 133 5.5.5 Discussion on the gas content of the inner disk ............ 137 5.6 Conclusions ................................... 139 5.A Comments on individual objects ........................ 140 5.A.1 Sample properties ............................ 140 5.B Additional literature data ............................ 141 6 Accretion as a function of stellar properties in nearby star forming regions 143 6.1 Introduction ................................... 143 6.2 Accretion in the Lupus clouds ......................... 144 6.2.1 Sample ................................. 145 6.2.2 Stellar and substellar properties .................... 146 6.2.3 Accretion rate determination ...................... 150 6.2.4 Accretion properties of stellar and substellar objects in Lupus .... 157 6.3 Accretion in the σ-Orionis region ....................... 159 6.4 New data in the ρ-Ophiucus embedded complex ............... 160 6.4.1 Sample, observations, and data reduction ............... 162 6.4.2 Stellar and substellar properties .................... 163 6.4.3 Accretion properties of ρ-Ophiucus young stellar objects ...... 174 6.5 New data in the Upper Scorpius association ................. 178 6.6 Discussion .................................... 180 6.6.1 Accretion luminosity and stellar luminosity relation ......... 181 6.6.2 Accretion as a function of stellar mass ................. 184 6.6.3 Accretion as a function of age ..................... 187 6.7 Conclusions ................................... 191 7 Conclusions 193 Acknowledgments 210 ix Contents x List of Figures 1.1 Evolutionary sequence of young stellar objects ................ 3 1.2 Fraction of young stellar objects surrounded by protoplanetary disks as a function of time ................................. 4 1.3 Scheme of the magnetospheric accretion scenario .............. 6 1.4 Evolution of the disk surface density in the spreading ring case ....... 9 1.5 Evolution of the disk surface density according to similarity solutions in the case where ν / R. ............................... 11 1.6 Evolution of mass accretion rates with time according to similarity solution viscous models ................................. 12 1.7 Evolution of mass accretion rates according to different photoevaporation models ...................................... 14 1.8 First observations of the mass accretion rate as a function of age ...... 21 1.9 Observation and modeling of the UV-excess of young stellar objects due to accretion .................................... 22 1.10 Observations of the mass accretion rates as a function of age in various regions 22 1.11 Observations of the mass accretion rates as a function of age and mass in the Orion Nebula Cluster ............................ 23 2.1 Scheme of the angular velocity as a function of the radius in the innermost region of a disk extending down to the stellar surface ............ 30 2.2 Example of the emission of a slab model ................... 38 2.3 Ratio of the emission due to H to that due to H− in the slab model ..... 39 2.4 Balmer jump obtained with the slab model as a function of the input pa- rameters ..................................... 40 2.5 Ratio of the emission from the Balmer and Paschen continua obtained with the slab model as a function of the input parameters ............. 41 2.6 Balmer continuum slope obtained with the slab model as a function of the input parameters ................................ 41 2.7 Paschen continuum slope obtained with the slab model as a function of the input parameters ................................ 42 3.1 Spectra of Class III YSOs with SpT earlier than M3 .............. 50 3.2 Spectra of Class III YSOs with SpT between M3 and M5 ........... 51 3.3 Spectra of Class III YSOs with SpT later than M5 ............... 52 3.4 Distribution of spectral types of the Class III YSOs discussed in this work .. 55 3.5 Example of the combination of a flux-calibrated and telluric