DOCSLIB.ORG

The Physics of the Accretion Process in the Formation and Evolution of Young Stellar Objects

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Physics of the Accretion Process in the Formation and Evolution of Young Stellar Objects 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
Load more

Recommended publications
  • HI Balmer Jump Temperatures for Extragalactic HII Regions in the CHAOS Galaxies
    HI Balmer Jump Temperatures for Extragalactic HII Regions in the CHAOS Galaxies A Senior Thesis Presented in Partial Fulfillment of the Requirements for Graduation with Research Distinction in Astronomy in the Undergraduate Colleges of The Ohio State University By Ness Mayker The Ohio State University April 2019 Project Advisors: Danielle A. Berg, Richard W. Pogge Table of Contents Chapter 1: Introduction ............................... 3 1.1 Measuring Nebular Abundances . 8 1.2 The Balmer Continuum . 13 Chapter 2: Balmer Jump Temperature in the CHAOS galaxies .... 16 2.1 Data . 16 2.1.1 The CHAOS Survey . 16 2.1.2 CHAOS Balmer Jump Sample . 17 2.2 Balmer Jump Temperature Determinations . 20 2.2.1 Balmer Continuum Significance . 20 2.2.2 Balmer Continuum Measurements . 21 + 2.2.3 Te(H ) Calculations . 23 2.2.4 Photoionization Models . 24 2.3 Results . 26 2.3.1 Te Te Relationships . 26 − 2.3.2 Discussion . 28 Chapter 3: Conclusions and Future Work ................... 32 1 Abstract By understanding the observed proportions of the elements found across galaxies astronomers can learn about the evolution of life and the universe. Historically, there have been consistent discrepancies found between the two main methods used to measure gas-phase elemental abundances: collisionally excited lines and optical recombination lines in H II regions (ionized nebulae around young star-forming regions). The origin of the discrepancy is thought to hinge primarily on the strong temperature dependence of the collisionally excited emission lines of metal ions, principally Oxygen, Nitrogen, and Sulfur. This problem is exacerbated by the difficulty of measuring ionic temperatures from these species.
    [Show full text]
  • An Analysis of the Shapes of Interstellar Extinction Curves. VII
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Ghent University Academic Bibliography The Astrophysical Journal, 886:108 (24pp), 2019 December 1 https://doi.org/10.3847/1538-4357/ab4c3a © 2019. The American Astronomical Society. All rights reserved. An Analysis of the Shapes of Interstellar Extinction Curves. VII. Milky Way Spectrophotometric Optical-through-ultraviolet Extinction and Its R-dependence* E. L. Fitzpatrick1 , Derck Massa2 , Karl D. Gordon3,4 , Ralph Bohlin3 , and Geoffrey C. Clayton5 1 Department of Astrophysics & Planetary Science, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085, USA 2 Space Science Institute 4750 Walnut Street, Suite 205 Boulder, CO 80301, USA; [email protected] 3 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA 4 Sterrenkundig Observatorium, Universiteit Gent, Gent, Belgium 5 Department of Physics & Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA Received 2019 September 20; revised 2019 October 7; accepted 2019 October 8; published 2019 November 26 Abstract We produce a set of 72 NIR-through-UV extinction curves by combining new Hubble Space Telescope/STIS optical spectrophotometry with existing International Ultraviolet Explorer spectrophotometry (yielding gapless coverage from 1150 to 10000 Å) and NIR photometry. These curves are used to determine a new, internally consistent NIR-through-UV Milky Way mean curve and to characterize how the shapes of the extinction curves depend on R(V ). We emphasize that while this dependence captures much of the curve variability, considerable variation remains that is independent of R(V ). We use the optical spectrophotometry to verify the presence of structure at intermediate wavelength scales in the curves.
    [Show full text]
  • Rest-Frame Ultraviolet-To-Optical Spectral Characteristics of Extremely Metal-Poor and Metal-Free Galaxies Akio K
    Mon. Not. R. Astron. Soc. 415, 2920–2931 (2011) doi:10.1111/j.1365-2966.2011.18906.x Rest-frame ultraviolet-to-optical spectral characteristics of extremely metal-poor and metal-free galaxies Akio K. Inoue College of General Education, Osaka Sangyo University, 3-1-1 Nakagaito, Daito, Osaka 574-8530, Japan Accepted 2011 April 12. Received 2011 March 31; in original form 2011 January 28 Downloaded from https://academic.oup.com/mnras/article/415/3/2920/1054046 by guest on 29 September 2021 ABSTRACT Finding the first generation of galaxies in the early Universe is the greatest step forward towards understanding galaxy formation and evolution. For a strategic survey of such galaxies and the interpretation of the obtained data, this paper presents an ultraviolet-to-optical spectral model of galaxies with a great care of the nebular emission. In particular, we present a machine- readable table of intensities of 119 nebular emission lines from Lyα to the rest-frame 1 µmas a function of metallicity from zero to the solar one. Based on the spectral model, we present criteria of equivalent widths of Lyα,HeII λ1640, Hα,Hβ and [O III] λ5007 to select extremely metal-poor and metal-free galaxies although these criteria have uncertainty caused by the Lyman continuum escape fraction and the star formation duration. We also present criteria of broad-band colours which will be useful to select candidates for spectroscopic follow-up from drop-out galaxies. We propose the line intensity ratio of [O III] λ5007 to Hβ<0.1 as the most robust criterion for <1/1000 of the solar metallicity.
    [Show full text]
  • UV EXCESS MEASURES of ACCRETION ONTO YOUNG VERY LOW MASS STARS and BROWN DWARFS Gregory J
    The Astrophysical Journal, 681:594Y625, 2008 July 1 # 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A. UV EXCESS MEASURES OF ACCRETION ONTO YOUNG VERY LOW MASS STARS AND BROWN DWARFS Gregory J. Herczeg1 and Lynne A. Hillenbrand1 Received 2007 November 6; accepted 2008 January 16 ABSTRACT Low-resolution spectra from 3000 to 9000 8 of young low-mass stars and brown dwarfs were obtained with LRIS on Keck I. The excess UVand optical emission arising in the Balmer and Paschen continua yields mass accretion rates ; À12 À8 À1 ranging from 2 10 to 10 M yr . These results are compared with HST STIS spectra of roughly solar-mass ; À10 ; À8 À1 accretors with accretion rates that range from 2 10 to 5 10 M yr . The weak photospheric emission from M dwarfs at <4000 8 leads to a higher contrast between the accretion and photospheric emission relative to higher mass counterparts. The mass accretion rates measured here are systematically 4Y7 times larger than those from H emission line profiles, with a difference that is consistent with but unlikely to be explained by the uncertainty in both methods. The accretion luminosity correlates well with many line luminosities, including high Balmer and many He i lines. Correlations of the accretion rate with H 10% width and line fluxes show a large amount of scatter. Our results and previous accretion rate measurements suggest that M˙ / M 1:87Æ0:26 for accretors in the Taurus molecular cloud. Subject headinggs: planetary systems: protoplanetary disks — stars: preYmain-sequence 1. INTRODUCTION observed previously.
    [Show full text]
  • Glossary/Print.Php?Id=322668&Mode=Lett
    http://learn.open.ac.uk/mod/glossary/print.php?id=322668&mode=lett... Tuesday, 3 August 2010, 17:04 Site: OU online Course: Astrophysics (S382-10B) Glossary: Glossary 1 1 micron minimum: A local minimum in the continuum spectrum of most AGN occurring around a wavelength of 1 micron (1 µm). It is thought to represent the minimum between a hot thermal spectrum (the big blue bump) possibly due to emission from an accretion disc, and a cool thermal spectrum due to emission in the infrared by warm dust grains. 2 2dF: The 2 degree field multi-object spectrometer on the Anglo Australian Telescope. Used to conduct the 2dF galaxy redshift survey and the 2dF quasar survey. 2MASS: The 2 Micron All Sky Survey. A survey of the complete sky using two telescopes (one at Mount Hopkins, Arizona and one at Cerro-Tololo, Chile) in three infrared wavebands: J-band (1.25 µm), H-band (1.65 µm) and K-band (2.17 µm). 3 3C273: One of the closest quasars to us (redshift = 0.158), the optically brightest (magnitude = 12.9) and the first quasar to be identified, in the 3C radio source catalogue. 4 4000 angstrom break: A break, or absorption feature, at a wavelength of 4000Å in the spectra of galaxies caused by Balmer continuum absorption in the atmospheres of stars. A aberration of light: The phenomenon whereby the observed direction of a star changes with time, due to the combined effect of the motion of the observer and the finite speed of light. If the relative speed of the observer and star is small compared to the speed of light, the aberration is small: tan α = (v/c)sin θ, where α is the aberration angle, v is the speed of motion, c is the speed of light and θ is the angle between the direction of motion and the direction of the star.
    [Show full text]
  • Time-Resolved Properties and Global Trends in Dme Flares From
    Time-Resolved Properties and Global Trends in dMe Flares from Simultaneous Photometry and Spectra1 Adam F. Kowalski2,8, Suzanne L. Hawley2, John P. Wisniewski3, Rachel A. Osten4, Eric J. Hilton5, Jon A. Holtzman6, Sarah J. Schmidt7, James R. A. Davenport2 Received ; accepted 2University of Washington, Astronomy Department, Box 351580, U.W. Seattle, WA 98195-1580, USA 3HL Dodge Department of Physics & Astronomy, University of Oklahoma, 440 W Brooks St, Norman, OK 73019 USA 4Space Telescope Science Institute, 3700 San Martin Drive Baltimore, MD 21218, USA arXiv:1307.2099v1 [astro-ph.SR] 8 Jul 2013 5Universe Sandbox, Seattle, WA, USA 6New Mexico State University, Department of Astronomy, Box 30001, Las Cruces, NM 88003, USA 7Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 8current address: NASA Postdoctoral Program Fellow, NASA Goddard Space Flight Center, Code 671, Greenbelt, MD 20771, USA; email: [email protected] –2– ABSTRACT We present a homogeneous analysis of line and continuum emission from si- multaneous high-cadence spectra and photometry covering near-ultraviolet and optical wavelengths for twenty M dwarf flares. These data were obtained to study the white-light continuum components at bluer and redder wavelengths than the Balmer jump. Our goals were to break the degeneracy between emission mecha- nisms that have been fit to broadband colors of flares and to provide constraints for radiative-hydrodynamic (RHD) flare models that seek to reproduce the white- light flare emission. The main
    [Show full text]
  • Analysis and Interpretation of Astronomical Spectra 1
    Analysis and Interpretation of Astronomical Spectra 1 Analysis and Interpretation of Astronomical Spectra Theoretical Background and Practical Applications for Amateur Astronomers Richard Walker Version 5.1, May 2012 Analysis and Interpretation of Astronomical Spectra 2 Analysis and Interpretation of Astronomical Spectra 2 Table of Contents 1 Introduction .................................................................................................................. 3 2 Photons – Messengers from the Universe ............................................................... 4 3 The Continuum ............................................................................................................. 6 4 Spectroscopic Wavelenght Domains......................................................................... 9 5 Typology of the spectra ............................................................................................. 11 6 Form and Intensity of the Spectral Lines ................................................................ 15 7 The measurement of the spectral lines ................................................................... 17 8 Calibration and Normalisation of Spectra ............................................................... 21 9 Visible Effects of Quantum Mechanics.................................................................... 25 10 Wavelength and Energy ............................................................................................ 28 11 Ionisation Stage and Degree of Ionisation .............................................................
    [Show full text]
  • Stellar and Emission Line Spectra Laboratory Exercise - Astrophysical Spectra
    Stellar and emission line spectra Laboratory exercise - Astrophysical Spectra Magnus Gålfalk Stockholm Observatory 2007 1 1 Introduction Almost everything we know about the universe outside our solar system comes from informa- tion provided by light, or more precisely, electromagnetic radiation. The science of astronomy is thus intimately connected to the science of analysing and interpreting light. The purpose of this exercise is to provide some insight into how information can be extracted from observations of spectra. Several spectra are studied; first from stars of various types, then a spectrum from the nebula surrounding the supernova remnant SN1987A (in the Large Magellanic Cloud). Sect. 2 introduces some background theory and general concepts that are used in the exercises. Sect. 3 gives some preparatory exercises. Sect. 4 shortly describes the functionality of the program Spectrix, a tool to assist in the analysis of the spectra. In the final section, the exercises to be solved during the lab are detailed. 1.1 The report To pass the lab you must write a report, preferably to be handed in within two weeks of the lab. Regarding the level of detail in the report, a good rule of thumb is that the report should be comprehensible to yourself even in five years from now. Answer every exercise fully, including the preparatory exercises, and be careful to estimate errors in your figures when asked to. If you wish, you may write in English, although not a requirement, it is always a good practice. 2 Background theory 2.1 Radiation processes Radiation can be both emitted and absorbed in a number of processes.
    [Show full text]
  • Non-Thermal Hydrogen Balmer and Paschen Emission in Solar Flares
    A&A 610, A68 (2018) Astronomy DOI: 10.1051/0004-6361/201731053 & c ESO 2018 Astrophysics HYDRO2GEN: Non-thermal hydrogen Balmer and Paschen emission in solar flares generated by electron beams M. K. Druett and V. V. Zharkova Northumbria University, Department of Mathematics, Physics and Electrical Engineering, 2 Ellison Pl, Newcastle upon Tyne, NE1 8ST, UK e-mail: [email protected] Received 26 April 2017 / Accepted 26 September 2017 ABSTRACT Aims. Sharp rises of hard X-ray (HXR) emission accompanied by Hα line profiles with strong red-shifts up to 4 Å from the central wavelength, often observed at the onset of flares with the Specola Solare Ticinese Telescope (STT) and the Swedish Solar Telescope (SST), are not fully explained by existing radiative models. Moreover, observations of white light (WL) and Balmer continuum emission with the Interface Region Imaging Spectrograph (IRISH) reveal strong co-temporal enhancements and are often nearly co- spatial with HXR emission. These effects indicate a fast effective source of excitation and ionisation of hydrogen atoms in flaring atmospheres associated with HXR emission. In this paper, we investigate electron beams as the agents accounting for the observed hydrogen line and continuum emission. Methods. Flaring atmospheres are considered to be produced by a 1D hydrodynamic response to the injection of an electron beam defining their kinetic temperatures, densities, and macro velocities. We simulated a radiative response in these atmospheres using a fully non-local thermodynamic equilibrium (NLTE) approach for a 5-level plus continuum hydrogen atom model, considering its excitation and ionisation by spontaneous, external, and internal diffusive radiation and by inelastic collisions with thermal and beam electrons.
    [Show full text]