DOCSLIB.ORG

Interstellar Medium, Star and Planet Formation

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Interstellar Medium, Star and Planet Formation Robi Banerjee Hamburger Sternwarte [email protected] General Information Get your points: • Tutorials (2 weeks) • Exam: 19/20. January ? • Credit Points: 6 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 2 Literature • Frank Shu The Physical Universe, Univ Science Books, 1982 • Weigert, Wendker & Wisotzki Astronomie und Astrophysik, Wiley-VCH, 2009 • Bruce Draine Physics of the Interstellar and Intergalactic Medium, Princeton Univ. Press 2011 • Lyman Spitzer Physical Processes in the Interstellar Medium, John Wiley & Sons, 1998 • Steven Stahler & Francesco Palla The Formation of Stars, Wiley-VCH, 2004 • Peter Bodenheimer Prinicples of Star Formation, Springer, 2011 • Derek Ward-Thomson & Anthony Whitworth An Introduction to Star Formation, Cambridge Univ. Press, 2011 • Norbert Schulz The Formation and Early Evolution of Stars, Springer, 2012 • Eds. Hubert Klahr & Wolfgang Brandner Planet Formation, Cambridge University Press, 2011 • Philip Armitage The Physics of Planet Formation, Cambridge University Press, 2009 • ... ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 3 Overview • ISM (three phases + physical properties) • Molecular clouds (observations + physical properties) • Conditions for star formation (i.e. cold dense regions, Jeans criterion, BE spheres) • Turbulence (Larson’s relation, Kolmogorov turbulence) • Fragmentation • Initial mass function (reconstruction from observations) • IMF (theoretical ideas, conversion from CMF to IMF) • The collapse (1D calculations: Larson/Penston, Shu) • Magnetic fields: mass-to-flux ratio, ambipolar diffusion • Magnetic fields: observational techniques (polarisation, Zeeman, RM) • 3D collapse: disc formation, Jets • Jet launching • Observations of Jets • Formation of Massive stars • Feedback (HII-Regions, SN) + triggered star formation • Protostellar evolution (Hayashi track, classes) • Evolution of protoplanetary discs • Planet formation (grav. instability, core accretion models) ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 4 Overview • Stars have a finite life time e.g. Sun ~ 10 Gyrs but massive stars live only a few Myrs ⟹ stars must have a beginning ⟹ star formation • star formation rate in the Milky Way: 3 - 5 stars / year (cf. SNe: ~ one/50 years) • young scientific branch of Astronomy & Astrophysics (~ 1950er) ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 5 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 6 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 7 Star Formation Questions: • Where do stars form? (galaxies, molecular clouds, dark clouds, Bok-Globules) •Under which conditions do stars form? (gravitational instability) • How do molecular clouds form and evolve? • What determines the star formation rate? • What determines the stellar mass distribution (initial mass function, ISM)? • ... ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 8 Sites of Galactic Star Form • Milky Way consists of ~ 100 billion stars and gas + dust = Interstellar Medium (ISM) (+ radiation, cosmic rays, magnetic fields, ...) • Stars form in dark/molecular clouds (only few % of the galactic volume) ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 9 Edward Barnard 1920: discovery of dark cloudsISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 10 Star Formation sites example: Orion-Nebula • emission nebula • D ~ 500 pc • R ~ 9 pc ESO: VLT ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 11 Hubble Teleskop: Sternentstehungsgebiet NGCISM, 604 Star- inand M33Planet Formation,Galaxie WS (Dreiecksnebel) 14/15 Robi Banerjee 12 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 13 ESA Herschel Teleskop: SternentstehungsgebietISM, Star- and Planet Formation, WS 14/15 Rosetta Robi Banerjee Nebel14 Hubble Teleskop: “Pillars of Creation” Sternbild: Adler ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 15 Star Formation sites Taurus molecular cloud • infrared observations: ⟹ young proto-stars become visible in dark clouds proto-stars ESO: APEX ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 16 Interstellar Medium Phases of the ISM: 3-phase model (McKee & Ostriker 1977) • regions with various temperatures and densities Weigert, Wendker Wisotzki ⟹ cold, warm and hot phase ⟹ determined by cooling and heating processes ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 17 Star Formation sites Properties of clouds/nebulas: • emission nebula: • emit light: mainly by ionising radiation of massive stars • hot: T ~ 10.000 K • mean densities: 10 − 100 cm-3 • dark clouds / Bok Globule: • dense and compact regions, absorb light (mainly dust): • mean densities: 103 − 105 cm-3 • cold: 6 − 20 K • reflection nebula: • visible by reflecting light • don’t contain ionising stars Merope-Nebel ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 19 Magnetic Fields M51 Galaktisches B-Feld (e.g. R.Beck 2001) Polarisationkarte des Pfeifennebels großskalige Komponente: ~ 4µG F.O.Alves, Franco, Girart 2008 Gesamtstärke: ~ 10µG ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 20 Bok* Globule * Bartholomeus Bok (1906-1983) • localised star forming regions • often protostars visible in IR radial density profile • hydrostatic equilibrium? ⟹ Bonnor-Ebert sphere (1956/55) (William Bonnor, 1920, Rolf Ebert, 1926) Bok Globule: Barnard 68 absorption measurements by Alves, Lada & Lada 2001 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 21 Gravitational Collapse critical mass: Jeans Masse MJ • warm neutral interstellar Medium: • T ≈ 5000 K ⟹ cs ≈ 5.7 km/sec • n ≈ 1 cm-3 ⟹ ρ ~ 10-24 g cm-3 7 • ⟹ MJ ≈ 10 M⨀ • ⟹ no collapse / no star formation • Bok Globule: • T ≈ 10 K ⟹ cs ≈ 0.2 km/sec • n ≈ 105 cm-3 ⟹ ρ ~ 4×10-19 g cm-3 • ⟹ MJ ≈ 1 M⨀ • ⟹ sites of individual star formation ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 22 Protostellar Phases • collapse proceeds quickly: 5 dynamical time scales tff ~ 10 yr ⟹ free-fall time • gravitational energy can be released until gas becomes optically thick isothermer Kollaps ⟹ gas core heats up Larson 1969 ⟹ contracts adiabatically ⟹ Hayashi-Track pre main sequence star, PMS ⟹ birth of a proto-star ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 23 Hayashi Track credits: CSIRO Australia ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 24 Protostellar Evolution ISM, Star- and Planet Formation,Bachiller, WS 14/15 RobiARAA Banerjee 199625 Disc evolution Bachiller, ARAA 1996 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 26 Protostars Tobin et al., Nature 2012 • L1527 IRS: youngest protostar at that time t < 300.000 yr M ~ 0.2 M⨀ −7 dM/dt ~ 6.6×10 M⨀/yr ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 27 Protostars • protostars are deeply embedded in dusty envelopes ⟹ re-emission of infrared radiation NICMOS: near infrared camera: 0.8 − 2.5 µm ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 28 Herbig-Haro Objekte 1000 AU ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 29 Herbig-Haro Objects ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 30 1000 AU NGC 1333, Spitzer Telescope, IRAC, NASA, JPL ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 31 1000 AU “Mysitc Mountain” in ISM,Carina Star- and PlanetNebula, Formation, HST,WS 14/15 NASA, Robi Banerjee ESA32 Jets Pudritz & Norman 1986 • Jet launching? ⟹ Lorentz force ⟹ Magnetic fields + disc ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 33 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 34 Turbulence and Fragmentation ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 35 Mass distribution of stars ⟹ Initial Mass Function (IMF) Munch et al. 2002: Orion Trapezium Cluster ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 36 Formation of Massive Stars Radiation • Problem: most of the mass gets accreted while the star is on the main sequence ⟹ strong radiation pressure ⟹ Eddington Limit ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 37 Entstehung massereicher Sterne Hubble Space Telescope: R 136 in LMC ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 38 Protostellar/Protoplanetary discs ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 39 Extrasolar Planets • list of extrasolar planets: The ExtrasolarPlanets Encyclopaedia http://exoplanet.eu ⟹ by October 2014: ~ 1800 planets • Kepler Mission / NASA: • space telescope main mission: March 2009 - Aug. 2013 since K2-mission (reduced capabilities) • search for extrasolar planets by transit method ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 40 Formation of Planets • coeval formation of stars and planets ⟹ from protoplanetary disc around young star • growth of dust particles to planetesimals d ~ few km → “Core Accretion” (Safronov 1969) → further growth by gravitational focusing • gas giants (like Jupiter)? ⟹ accretion by gravitational attraction ⟹ gravitational instability in the disc (Toomre instability) ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 41.
Recommended publications
  • Plasma Physics and Pulsars

    Plasma Physics and Pulsars

    Plasma Physics and Pulsars On the evolution of compact o bjects and plasma physics in weak and strong gravitational and electromagnetic fields by Anouk Ehreiser supervised by Axel Jessner, Maria Massi and Li Kejia as part of an internship at the Max Planck Institute for Radioastronomy, Bonn March 2010 2 This composition was written as part of two internships at the Max Planck Institute for Radioastronomy in April 2009 at the Radiotelescope in Effelsberg and in February/March 2010 at the Institute in Bonn. I am very grateful for the support, expertise and patience of Axel Jessner, Maria Massi and Li Kejia, who supervised my internship and introduced me to the basic concepts and the current research in the field. Contents I. Life-cycle of stars 1. Formation and inner structure 2. Gravitational collapse and supernova 3. Star remnants II. Properties of Compact Objects 1. White Dwarfs 2. Neutron Stars 3. Black Holes 4. Hypothetical Quark Stars 5. Relativistic Effects III. Plasma Physics 1. Essentials 2. Single Particle Motion in a magnetic field 3. Interaction of plasma flows with magnetic fields – the aurora as an example IV. Pulsars 1. The Discovery of Pulsars 2. Basic Features of Pulsar Signals 3. Theoretical models for the Pulsar Magnetosphere and Emission Mechanism 4. Towards a Dynamical Model of Pulsar Electrodynamics References 3 Plasma Physics and Pulsars I. The life-cycle of stars 1. Formation and inner structure Stars are formed in molecular clouds in the interstellar medium, which consist mostly of molecular hydrogen (primordial elements made a few minutes after the beginning of the universe) and dust.
  • Midterm Results the Milky Way in the Infrared

    Midterm Results the Milky Way in the Infrared

    3/2/10 Lecture 13 : Midterm Results The Interstellar Medium and Cosmic Recycling A2020 Prof. Tom Megeath The Milk The Milky Way in the Infrared Way from Above (artist conception) The Milky Way appears to have a bar and four spiral arms. Star formation and hot blue stars concentrated in arms. View from the Earth: Edge On Infrared light penetrates the clouds and shows the entire galaxy 1 3/2/10 NGC 7331: the Milky Way’s Twins The Interstellar Medium The space between the stars is not empty, but filled with a very low density of matter in the form of: •Atomic hydrogen •Ionized hydrogen •Molecular Hydrogen •Cosmic Rays •Dust grains •Many other molecules (water, carbon monoxide, formaldehyde, methanol, etc) •Organic molecules like polycyclic aromatic hydrocarbons How do we know the gas is there? Review: Kirchoff Laws Remainder of the Lecture Foreground gas cooler, absorption 1. How we observe and study the interstellar medium 2. The multiwavelength Milky Way Absorbing gas hotter, 3. Cosmic Recycling emission lines (and (or cooler blackbody) blackbody) If foreground gas and emitting blackbody the same temperature: perfect blackbody (no lines) Picture from Nick Strobel’s astronomy notes: www.astronomynotes.com 2 3/2/10 Observing the ISM through Absorption Lines • We can determine the composition of interstellar gas from its absorption lines in the spectra of stars • 70% H, 28% He, 2% heavier elements in our region of Milky Way Picture from Nick Strobel’s astronomy notes: www.astronomynotes.com Emission Lines Emission Line Nebula M27 Emitted by atoms and ions in planetary and HII regions.
  • TESTING MODELS of LOW-EXCITATION PHOTODISSOCIATION REGIONS with FAR-INFRARED OBSERVATIONS of REFLECTION NEBULAE Rolaine C

    TESTING MODELS of LOW-EXCITATION PHOTODISSOCIATION REGIONS with FAR-INFRARED OBSERVATIONS of REFLECTION NEBULAE Rolaine C

    The Astrophysical Journal, 578:885–896, 2002 October 20 # 2002. The American Astronomical Society. All rights reserved. Printed in U.S.A. TESTING MODELS OF LOW-EXCITATION PHOTODISSOCIATION REGIONS WITH FAR-INFRARED OBSERVATIONS OF REFLECTION NEBULAE Rolaine C. Young Owl Department of Physics and Astronomy, University of California at Los Angeles, Mail Code 156205, Los Angeles, CA 90095-1562 Margaret M. Meixner1 and David Fong Department of Astronomy, University of Illinois, Urbana, IL 61801; [email protected], [email protected] Michael R. Haas NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035-1000; [email protected] Alexander L. Rudolph1 Department of Physics, Harvey Mudd College, 301 East 12th Street, Claremont, CA 91711; [email protected] and A. G. G. M. Tielens Kapteyn Astronomical Institute, P.O. Box 800, 9700 AV Groningen, Netherlands; [email protected] Received 2001 August 2; accepted 2002 June 24 ABSTRACT This paper presents Kuiper Airborne Observatory observations of the photodissociation regions (PDRs) in nine reflection nebulae. These observations include the far-infrared atomic fine-structure lines of [O i]63 and 145 lm, [C ii] 158 lm, and [Si ii]35lm and the adjacent far-infrared continuum to these lines. Our analysis of these far-infrared observations provides estimates of the physical conditions in each reflection nebula. In our sample of reflection nebulae, the stellar effective temperatures are 10,000–30,000 K, the gas densities are 4 Â 102 2 Â 104 cmÀ3, the gas temperatures are 200–690 K, and the incident far-ultraviolet intensities are 300–8100 times the ambient interstellar radiation field strength (1:2 Â 10À4 ergs cmÀ2 sÀ1 srÀ1).
  • 1 the XMM-NEWTON SURVEY of the TAURUS MOLECULAR CLOUD: ACCRETION, JETS, and FLUORESCENCE M. Audard1, Manuel Güdel2, Kevin Brigg

    1 the XMM-NEWTON SURVEY of the TAURUS MOLECULAR CLOUD: ACCRETION, JETS, and FLUORESCENCE M. Audard1, Manuel Güdel2, Kevin Brigg

    1 THE XMM-NEWTON SURVEY OF THE TAURUS MOLECULAR CLOUD: ACCRETION, JETS, AND FLUORESCENCE M. Audard1, Manuel G¨udel2, Kevin Briggs2, and the XEST Team3 1Columbia Astrophysics Laboratory, 550 West 120th Street, NC 5247, New York, NY 10027, USA 2Paul Scherrer Institut, 5232 Villigen PSI, Switzerland ABSTRACT 1031 The Taurus Molecular Cloud (TMC) is one of the best studied star forming regions. It is close (140 pc) and represents the mode of isolated, non-clustered star for- mation. XMM-Newton has surveyed the richer 5 square degrees of the TMC in X-rays and has obtained high- 30 quality photometric and spectroscopic data of young stars 10 LX and brown dwarfs in their early stages of formation. We present results of the X-ray Emission Survey of TMC (XEST) on the following topics: i) Accretion. The ori- gin of X-rays in young, accreting stars is controversial, as accretion appears to be the dominant emission mech- 1029 anism in some classical T Tauri stars, whereas magnetic activity is the preferred explanation for others. The TMC 10-10 10-9 10-8 10-7 10-6 10-5 Mdot contains several accreting stars whose spectra help us un- derstand the importance of accretion for the production of X-rays. ii) Jets. Young, accreting stars display jets detected in the optical, near-infrared, and radio domains. There is now evidencethat jets are also detected in X-rays in some TMC targets. iii) Fluorescence. The detection of 7.5 an emission feature at 6.4 keV indicates that fluorescence of Fe in a cool environment,e.g., the accretion disk, takes place due to photoionization by hard X-rays or collisions logTav with electron beams.
  • Statistics of Superimposed Flares in the Taurus Molecular Cloud

    Statistics of Superimposed Flares in the Taurus Molecular Cloud

    A&A 468, 477–484 (2007) Astronomy DOI: 10.1051/0004-6361:20066551 & c ESO 2007 Astrophysics The XMM-Newton extended survey of the Taurus molecular cloud Special feature Statistics of superimposed flares in the Taurus molecular cloud K. Arzner1, M. Güdel1, K. Briggs1, A. Telleschi1, and M. Audard2, 1 Paul Scherrer Institut, CH 5232 Villigen, Switzerland e-mail: [email protected] 2 Columbia Astrophysics Laboratory, 550 West 120th St., MC 5247, New York, NY 10027, USA Received 12 October 2006 / Accepted 19 February 2007 ABSTRACT Context. Stochastically occurring flares provide a possible mechanism of coronal heating in magnetically active stars such as T Tauri objects in star-forming regions. Aims. We investigate the statistics of stellar X-ray light curves from the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST). Methods. To this end, the light curve is modeled as superimposed flares occurring at random times and with random amplitudes. The flare shape is estimated non-parametrically from the observations, while the flare amplitude distribution is modeled as a truncated power law, and the flare times are assumed as uniformly distributed. From these model assumptions, predictions on the binned counts are derived and compared with the observations. Results. From a sample of 22 XEST observations matching the above model assumptions we find that the majority of cases have flare amplitude distributions with slopes steeper than two. This favours the role of small flares in coronal heating for 5 targets, of which, however, 4 are foreground or background main-sequence stars. Key words. methods: statistical – stars: coronae – stars: pre-main sequence – X-rays: stars 1.
  • A Joint Chandra and Swift View of the 2015 X-Ray Dust Scattering Echo of V404 Cygni S

    A Joint Chandra and Swift View of the 2015 X-Ray Dust Scattering Echo of V404 Cygni S

    Draft version July 20, 2021 Preprint typeset using LATEX style emulateapj v. 5/2/11 A JOINT CHANDRA AND SWIFT VIEW OF THE 2015 X-RAY DUST SCATTERING ECHO OF V404 CYGNI S. Heinz1, L. Corrales2, R. Smith3, W.N. Brandt4,5,6, P.G. Jonker7,8, R.M. Plotkin9,10, and J. Neilsen2,11 Draft version July 20, 2021 Abstract We present a combined analysis of the Chandra and Swift observations of the 2015 X-ray echo of V404 Cygni. Using stacking analysis, we identify eight separate rings in the echo. We reconstruct the soft X-ray lightcurve of the June 2015 outburst using the high-resolution Chandra images and cross-correlations of the radial intensity profiles, indicating that about 70% of the outburst fluence occurred during the bright flare at the end of the outburst on MJD 57199.8. By deconvolving the intensity profiles with the reconstructed outburst lightcurve, we show that the rings correspond to eight separate dust concentrations with precise distance determinations. We further show that the column density of the clouds varies significantly across the field of view, with the centroid of most of the clouds shifted toward the Galactic plane, relative to the position of V404 Cyg, invalidating the assumption of uniform cloud column typically made in attempts to constrain dust properties from light echoes. We present a new XSPEC spectral dust scattering model that calculates the differential dust scattering cross section for a range of commonly used dust distributions and compositions and use it to jointly fit the entire set of Swift echo data.
  • Classification of Planetary Nebulae Through Deep Transfer Learning

    Classification of Planetary Nebulae Through Deep Transfer Learning

    galaxies Article Classification of Planetary Nebulae through Deep Transfer Learning Dayang N. F. Awang Iskandar 1,2,*,† , Albert A. Zijlstra 2,† , Iain McDonald 2,3 , Rosni Abdullah 4 , Gary A. Fuller 2, Ahmad H. Fauzi 1 and Johari Abdullah 1 1 Faculty of Computer Science and Information Technology, Universiti Malaysia Sarawak, Sarawak 94300, Malaysia; [email protected] (A.H.F.); [email protected] (J.A.) 2 Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, School of Natural Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, UK; [email protected] (A.A.Z.); [email protected] (I.M.); [email protected] (G.A.F.) 3 School of Physical Sciences, The Open University, Walton Hall, Kents Hill, Milton Keynes MK7 6AA, UK 4 School of Computer Sciences, Universiti Sains Malaysia, Pulau Pinang 11800, Malaysia; [email protected] * Correspondence: [email protected] † These authors contributed equally to this work. Received: 11 August 2020; Accepted: 7 December 2020; Published: 11 December 2020 Abstract: This study investigate the effectiveness of using Deep Learning (DL) for the classification of planetary nebulae (PNe). It focusses on distinguishing PNe from other types of objects, as well as their morphological classification. We adopted the deep transfer learning approach using three ImageNet pre-trained algorithms. This study was conducted using images from the Hong Kong/Australian Astronomical Observatory/Strasbourg Observatory H-alpha Planetary Nebula research platform database (HASH DB) and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). We found that the algorithm has high success in distinguishing True PNe from other types of objects even without any parameter tuning.
  • Gas and Dust in the Magellanic Clouds

    Gas and Dust in the Magellanic Clouds

    Gas and dust in the Magellanic clouds A Thesis Submitted for the Award of the Degree of Doctor of Philosophy in Physics To Mangalore University by Ananta Charan Pradhan Under the Supervision of Prof. Jayant Murthy Indian Institute of Astrophysics Bangalore - 560 034 India April 2011 Declaration of Authorship I hereby declare that the matter contained in this thesis is the result of the inves- tigations carried out by me at Indian Institute of Astrophysics, Bangalore, under the supervision of Professor Jayant Murthy. This work has not been submitted for the award of any degree, diploma, associateship, fellowship, etc. of any university or institute. Signed: Date: ii Certificate This is to certify that the thesis entitled ‘Gas and Dust in the Magellanic clouds’ submitted to the Mangalore University by Mr. Ananta Charan Pradhan for the award of the degree of Doctor of Philosophy in the faculty of Science, is based on the results of the investigations carried out by him under my supervi- sion and guidance, at Indian Institute of Astrophysics. This thesis has not been submitted for the award of any degree, diploma, associateship, fellowship, etc. of any university or institute. Signed: Date: iii Dedicated to my parents ========================================= Sri. Pandab Pradhan and Smt. Kanak Pradhan ========================================= Acknowledgements It has been a pleasure to work under Prof. Jayant Murthy. I am grateful to him for giving me full freedom in research and for his guidance and attention throughout my doctoral work inspite of his hectic schedules. I am indebted to him for his patience in countless reviews and for his contribution of time and energy as my guide in this project.
  • Protostars and Planets V

    Protostars and Planets V

    Protostars and Planets V Hilton Waikoloa Grand Ballroom Oral Program Speakers are listed in italics MONDAY October 24, 2005 6:45 a.m. - 8:00 a.m. Breakfast and Posters Chair morning session: Ewine van Dishoeck 8:00 a.m. - 8:15 a.m. Welcome I. CLOUDS AND CORES 8:15 a.m. - 8:50 a.m. Giant Molecular Clouds in Galaxies Leo Blitz, Yasuo Fukui, Akiko Kawamura, Adam Leroy, Norikazu Mizuno, Erik Rosolowsky 8:50 a.m. - 9:25 a.m. Near-Infrared Extinction and the Structure and Nature of Molecular Clouds Charles J. Lada, Joao F. Alves, Marco Lombardi, and Elizabeth A. Lada 9:25 a.m. - 10:00 a.m. Molecular Cloud Turbulence and Star Formation Javier Ballesteros-Paredes, Ralf S. Klessen, Mordecai-M. Mac Low, Enrique Vazquez-Semadeni 10:00 a.m. - 10:30 a.m. Break and Posters 10:30 a.m. - 11:05 a.m. Structure and Evolution of Low Mass Dense Cores: An Observational Perspective James Di Francesco, Philippe Andre´, Derek Ward-Thompson, Paola Caselli, Mario Tafalla, Philip C. Myers, Neal J. Evans, Yancy L. Shirley, Yuri Aikawa, Doug Johnstone, Richard M. Crutcher, Christine D. Wilson, and Toshikazu Onishi 11:05 a.m. - 11:40 a.m. Extreme Deuteration and Hot Corinos: The Earliest Signatures of Low-Mass Star Formation Cecilia Ceccarelli, Paola Caselli, Xander Tielens, Eric Herbst, and Emmanuel Caux 1 II. STAR FORMATION AND PROTOSTARS 11:40 a.m. - 12:15 p.m. Current Advances in the Computational Simulation of the Formation of Low-Mass Stars Richard I. Klein, Shu-ichiro Inutsuka, Paolo Padoan, Kohji Tomisaka 12:15 p.m.
  • X-Ray Super-Flares from Pre-Main Sequence Stars: Flare Energetics and Frequency

    X-Ray Super-Flares from Pre-Main Sequence Stars: Flare Energetics and Frequency

    Draft version May 12, 2021 Typeset using LATEX twocolumn style in AASTeX63 X-ray Super-Flares From Pre-Main Sequence Stars: Flare Energetics And Frequency Konstantin V. Getman1 and Eric D. Feigelson1, 2 1Department of Astronomy & Astrophysics Pennsylvania State University 525 Davey Laboratory University Park, PA 16802, USA 2Center for Exoplanetary and Habitable Worlds (Accepted for publication in ApJ, May 2021) ABSTRACT Solar-type stars exhibit their highest levels of magnetic activity during their early convective pre- main sequence (PMS) phase of evolution. The most powerful PMS flares, super-flares and mega-flares, −1 have peak X-ray luminosities of log(LX ) = 30:5−34:0 erg s and total energies log(EX ) = 34−38 erg. Among > 24; 000 X-ray selected young (t . 5 Myr) members of 40 nearby star-forming regions from our earlier Chandra MYStIX and SFiNCs surveys, we identify and analyze a well-defined sample of 1,086 X-ray super-flares and mega-flares, the largest sample ever studied. Most are considerably more powerful than optical/X-ray super-flares detected on main sequence stars. This study presents energy estimates of these X-ray flares and the properties of their host stars. These events are produced by young stars of all masses over evolutionary stages ranging from protostars to diskless stars, with the occurrence rate positively correlated with stellar mass. Flare properties are indistinguishable for disk- bearing and diskless stars indicating star-disk magnetic fields are not involved. A slope α ' 2 in the −α flare energy distributions dN=dEX / EX is consistent with those of optical/X-ray flaring from older stars and the Sun.
  • GEORGE HERBIG and Early Stellar Evolution

    GEORGE HERBIG and Early Stellar Evolution

    GEORGE HERBIG and Early Stellar Evolution Bo Reipurth Institute for Astronomy Special Publications No. 1 George Herbig in 1960 —————————————————————– GEORGE HERBIG and Early Stellar Evolution —————————————————————– Bo Reipurth Institute for Astronomy University of Hawaii at Manoa 640 North Aohoku Place Hilo, HI 96720 USA . Dedicated to Hannelore Herbig c 2016 by Bo Reipurth Version 1.0 – April 19, 2016 Cover Image: The HH 24 complex in the Lynds 1630 cloud in Orion was discov- ered by Herbig and Kuhi in 1963. This near-infrared HST image shows several collimated Herbig-Haro jets emanating from an embedded multiple system of T Tauri stars. Courtesy Space Telescope Science Institute. This book can be referenced as follows: Reipurth, B. 2016, http://ifa.hawaii.edu/SP1 i FOREWORD I first learned about George Herbig’s work when I was a teenager. I grew up in Denmark in the 1950s, a time when Europe was healing the wounds after the ravages of the Second World War. Already at the age of 7 I had fallen in love with astronomy, but information was very hard to come by in those days, so I scraped together what I could, mainly relying on the local library. At some point I was introduced to the magazine Sky and Telescope, and soon invested my pocket money in a subscription. Every month I would sit at our dining room table with a dictionary and work my way through the latest issue. In one issue I read about Herbig-Haro objects, and I was completely mesmerized that these objects could be signposts of the formation of stars, and I dreamt about some day being able to contribute to this field of study.
  • Reflection Nebula Visualization

    Reflection Nebula Visualization

    Reflection Nebula Visualization Marcus A. Magnor∗ Kristian Hildebrand Andrei Lintu Andrew J. Hanson† MPI Informatik MPI Informatik MPI Informatik Indiana University ABSTRACT Stars form in dense clouds of interstellar gas and dust. The residual dust surrounding a young star scatters and diffuses its light, making the star's “cocoon” of dust observable from Earth. The resulting structures, called reflection nebulae, are commonly very colorful in appearance due to wavelength-dependent effects in the scatter- ing and extinction of light. The intricate interplay of scattering and extinction cause the color hues, brightness distributions, and the ap- parent shapes of such nebulae to vary greatly with viewpoint. We describe here an interactive visualization tool for realistically ren- dering the appearance of arbitrary 3D dust distributions surround- ing one or more illuminating stars. Our rendering algorithm is based on the physical models used in astrophysics research. The tool can be used to create virtual fly-throughs of reflection nebulae for interactive desktop visualizations, or to produce scientifically accurate animations for educational purposes, e.g., in planetarium shows. The algorithm is also applicable to investigate on-the-fly the visual effects of physical parameter variations, exploiting visualiza- tion technology to help gain a deeper and more intuitive understand- ing of the complex interaction of light and dust in real astrophysical settings. CR Categories: I.3.3 [Computer Graphics]: Picture/Image Figure 1: Reflection nebulae: Recently formed, hot stars illuminate Generation—Viewing algorithms; I.3.7 [Computer Graphics]: the surrounding interstellar dust that scatters and absorbs the star Three-Dimensional Graphics and Realism—Color, shading, shad- light to give rise to a large range of color hues and brightness varia- owing, and texture; J.2 [Computer Applications]: Physical Sciences tions.