DOCSLIB.ORG

Physical Processes in the Interstellar Medium

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Physical Processes in the Interstellar Medium Physical Processes in the Interstellar Medium Ralf S. Klessen and Simon C. O. Glover Abstract Interstellar space is filled with a dilute mixture of charged particles, atoms, molecules and dust grains, called the interstellar medium (ISM). Understand- ing its physical properties and dynamical behavior is of pivotal importance to many areas of astronomy and astrophysics. Galaxy formation and evolu- tion, the formation of stars, cosmic nucleosynthesis, the origin of large com- plex, prebiotic molecules and the abundance, structure and growth of dust grains which constitute the fundamental building blocks of planets, all these processes are intimately coupled to the physics of the interstellar medium. However, despite its importance, its structure and evolution is still not fully understood. Observations reveal that the interstellar medium is highly tur- bulent, consists of different chemical phases, and is characterized by complex structure on all resolvable spatial and temporal scales. Our current numerical and theoretical models describe it as a strongly coupled system that is far from equilibrium and where the different components are intricately linked to- gether by complex feedback loops. Describing the interstellar medium is truly a multi-scale and multi-physics problem. In these lecture notes we introduce the microphysics necessary to better understand the interstellar medium. We review the relations between large-scale and small-scale dynamics, we con- sider turbulence as one of the key drivers of galactic evolution, and we review the physical processes that lead to the formation of dense molecular clouds and that govern stellar birth in their interior. arXiv:1412.5182v1 [astro-ph.GA] 16 Dec 2014 Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Straße 2, 69120 Heidelberg, Germany e-mail: [email protected],[email protected] 1 Contents Physical Processes in the Interstellar Medium ................ 1 Ralf S. Klessen and Simon C. O. Glover 1 Introduction . .4 2 Composition of the ISM . .8 2.1 Gas . .8 2.2 Dust . 11 2.3 Interstellar radiation field . 13 2.4 Cosmic rays . 18 3 Heating and cooling of interstellar gas . 21 3.1 Optically-thin two-level atom . 21 3.2 Effects of line opacity . 26 3.3 Multi-level systems . 29 3.4 Atomic and molecular coolants in the ISM . 31 3.5 Gas-grain energy transfer . 41 3.6 Computing the dust temperature . 44 3.7 Photoelectric heating . 47 3.8 Other processes responsible for heating . 50 4 ISM Turbulence . 55 4.1 Observations . 55 4.2 Simple theoretical considerations . 65 4.3 Scales of ISM Turbulence . 71 4.4 Decay of ISM turbulence . 75 4.5 Sources of ISM turbulence: gravity and rotation. 77 4.6 Sources of ISM turbulence: stellar feedback . 82 5 Formation of molecular clouds . 90 5.1 Transition from atomic to molecular gas . 90 5.2 Importance of dust shielding . 101 5.3 Molecular cloud formation in a galactic context . 104 6 Star formation . 110 6.1 Molecular cloud cores as sites of star formation . 110 6.2 Statistical properties of stars and star clusters . 116 3 4 Introduction 6.3 Gravoturbulent star formation . 120 6.4 Theoretical models for the origin of the IMF . 123 6.5 Massive star formation . 137 6.6 Final stages of star and planet formation . 139 7 Summary . 142 References . 146 1 Introduction Understanding the physical processes that govern the dynamical behavior of the interstellar medium (ISM) is central to much of modern astronomy and astrophysics. The ISM is the primary galactic repository out of which stars are born and into which they deposit energy, momentum and enriched material as they die. It constitutes the anchor point of the galactic matter cycle, and as such is the key to a consistent picture of galaxy formation and evolution. The dynamics of the ISM determines where and when stars form. Similarly, the properties of the planets and planetary systems around these stars are intimately connected to the properties of their host stars and the details of their formation process. When we look at the sky on a clear night, we can notice dark patches of obscuration along the band of the Milky Way. These are clouds of dust and gas that block the light from distant stars. With the current set of telescopes and satellites we can observe dark clouds at essentially all frequencies possi- ble, ranging from low-energy radio waves all the way up to highly energetic γ-rays. We have learned that all star formation occurring in the Milky Way and other galaxies is associated with these dark clouds that mostly consist of cold molecular hydrogen and dust. In general, these dense clouds are embed- ded in and dynamically connected to the larger-scale and less dense atomic component. Once stellar birth sets in, feedback becomes important. Massive stars emit copious amounts of ionizing photons and create bubbles of hot ionized plasma, thus converting ISM material into a hot and very tenuous state. We shall see in this lecture that we cannot understand the large-scale dynamics of the ISM without profound knowledge of the underlying micro- physics. And vice versa, we will argue that dynamical processes on large galactic scales determine the local properties of the different phases of the ISM, such as their ability to cool and collapse, and to give birth to new stars. ISM dynamics spans a wide range of spatial scales, from the extent of the galaxy as a whole down to the local blobs of gas that collapse to form individual stars or binary systems. Similarly, it covers many decades in tem- poral scales, from the hundreds of millions of years it takes to complete one galactic rotation down to the hundreds of years it takes an ionization front to travel through a star-forming cloud. This wide range of scales is intricately Ralf Klessen & Simon Glover 5 linked by a number of competing feedback loops. Altogether, characterizing the ISM is truly a multi-scale and multi-physics problem. It requires insights from quantum physics and chemistry, as well as knowledge of magnetohy- drodynamics, plasma physics, and gravitational dynamics. It also demands a deep understanding of the coupling between matter and radiation, together with input from high-resolution multi-frequency and multi-messenger astro- nomical observations. By mass, the ISM consists of around 70% hydrogen (H), 28% helium (He), and 2% heavier elements. The latter are generally termed metals in the some- times very crude astronomical nomenclature. We give a detailed account of the composition of the ISM in Section 2. Because helium is chemically inert, it is customary, and indeed highly practical, to distinguish the different phases of the ISM by the chemical state of hydrogen. Ionized bubbles are called Hii regions, while atomic gas is often termed Hi gas, in both cases referring to the spectroscopic notation. Hii regions are best observed by looking at hydrogen recombination lines or the fine structure lines of ionized heavy atoms. The properties of Hi gas are best studied via the 21cm hyperfine structure line of hydrogen. Dark clouds are sufficiently dense and well-shielded against the dissociating effects of interstellar ultraviolet radiation to allow H atoms to bind together to form molecular hydrogen (H2). They are therefore called molecular clouds. H2 is a homonuclear molecule. Its dipole moment vanishes and it radiates extremely weakly under normal Galactic ISM conditions. Direct detection of H2 is therefore generally possible only through ultraviolet absorption studies. Due to atmospheric opacity these studies can only be done from space, and are limited to pencil-beam measurements of the absorption of light from bright stars or active galactic nuclei (AGN). We note that rotational and ro- vibrational emission lines from H2 have indeed been detected in the infrared, both in the Milky Way and in other galaxies. However, this emission comes from gas that has been strongly heated by shocks or radiation, and it traces only a small fraction of the overall amount of molecular hydrogen. Due to these limitations, the most common tool for studying the molecular ISM is radio and sub-millimeter emission either from dust grains or from other molecules that tend to be found in the same locations as H2. By far the most commonly used molecular tracer is carbon monoxide with its various isotopologues. The most abundant, and hence easiest to observe is 12C16O, usually referred to simply as 12CO or just CO. However, this isotopologue is often so abundant that its emission is optically thick, meaning that it only traces conditions reliably in the surface layers of the dense substructure found within most molecular clouds. The next most abundant isotopologues are 13C16O (usually written simply as 13CO) and 12C18O (usually just C18O). Their emission is often optically thin and can freely escape the system. This allows us to trace the full volume of the cloud. As CO has a relatively low critical density and also freezes out on dust grains at very high densities, other + tracers such as HCN or N2H need to be used to study conditions within 6 Introduction high density regions such as prestellar cores. We discuss the microphysics of the interaction between radiation and matter and the various heating and cooling processes that determine the thermodynamic response of the various phases of the ISM in Section 3. A key physical agent controlling the dynamical evolution of the ISM is turbulence. For a long time it was thought that supersonic turbulence in the interstellar gas could not produce significant compressions, since this would result in a rapid dissipation of the turbulent kinetic energy. In order to avoid this rapid dissipation of energy, appeal was made to the presence of strong magnetic fields in the clouds, which were thought to greatly reduce the dissipation rate.
Load more

Recommended publications
  • Selective Production of Phase-Separable Product from a Mixture of Biomass-Derived Aqueous Oxygenates
    ARTICLE DOI: 10.1038/s41467-018-07593-0 OPEN Selective production of phase-separable product from a mixture of biomass-derived aqueous oxygenates Yehong Wang 1, Mi Peng2, Jian Zhang1, Zhixin Zhang1, Jinghua An1,3, Shuyan Du1, Hongyu An1,3, Fengtao Fan1, Xi Liu 4,5, Peng Zhai2, Ding Ma 2 & Feng Wang1 1234567890():,; Selective conversion of an aqueous solution of mixed oxygenates produced by biomass fermentation to a value-added single product is pivotal for commercially viable biomass utilization. However, the efficiency and selectivity of the transformation remains a great challenge. Herein, we present a strategy capable of transforming ~70% of carbon in an aqueous fermentation mixture (ABE: acetone–butanol–ethanol–water) to 4-heptanone (4- HPO), catalyzed by tin-doped ceria (Sn-ceria), with a selectivity as high as 86%. Water (up to 27 wt%), detrimental to the reported catalysts for ABE conversion, was beneficial for producing 4-HPO, highlighting the feasibility of the current reaction system. In a 300 h continuous reaction over 2 wt% Sn-ceria catalyst, the average 4-HPO selectivity is main- tained at 85% with 50% conversion and > 90% carbon balance. This strategy offers a route for highly efficient organic-carbon utilization, which can potentially integrate biological and chemical catalysis platforms for the robust and highly selective production of value-added chemicals. 1 State Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China. 2 College of Chemistry and Molecular Engineering and College of Engineering, BIC-ESAT, Peking University, Beijing 100871, China.
    [Show full text]
  • 145, September 2010
    British Astronomical Association VARIABLE STAR SECTION CIRCULAR No 145, September 2010 Contents EG Andromedae Light Curve ................................................... inside front cover From the Director ............................................................................................... 1 Letter Page. Visual Observing ............................................................................ 4 Epsilon Aurigae Spectroscopically at Mid Eclipse .......................................... 5 Eclipsing Binary News ...................................................................................... 7 AO Cassiopeiae Phase Diagram ............................................................ 9 PV Cephei and Gyulbudaghian’s Nebula ........................................................ 10 WR140 Periastron Campaign Update .............................................................. 12 VSS Meeting, Pendrell Hall. The Central Stars of Planetary Nebulae ............ 14 RR Coronae Borealis 1993-2004 ...................................................................... 16 TU Cassiopeiae Phase Diagram 2005-2010 ..................................................... 18 Binocular Priority List ..................................................................................... 19 Eclipsing Binary Predictions ............................................................................ 20 Charges for Section Publications .............................................. inside back cover Guidelines for Contributing to the Circular .............................
    [Show full text]
  • John J. Cowan Date of Birth: April 3, 1948 Place of Birth: Washington, D.C
    VITA NAME: John J. Cowan Date of Birth: April 3, 1948 Place of Birth: Washington, D.C. EDUCATION: 1970 B.A. George Washington University, Washington, D.C. 1972 M.S. Case Institute of Technology, Cleveland, OH 1976 Ph.D. University of Maryland, College Park, MD PROFESSIONAL EXPERIENCE: 2002–present David Ross Boyd Professor, University of Oklahoma, 2002–2002 Research Fellow, University of Texas, Austin, TX 1998–2002 Samuel Roberts Noble Foundation Presidential Professor, University of Oklahoma, Norman, OK 1997–1998 Big XIIFaculty Fellow,University ofOklahoma 1991–1992 Visiting Professor, Department of Astronomy, Columbia University, New York, NY 1989–present Professor, Department of Physics and Astronomy, University of Oklahoma, Norman, OK 1988–1994 Consultant and Participating Guest, Lawrence Livermore National Laboratory, Livermore, CA 1987–1988 Visiting Research Associate, Harvard-Smithsonian Center for Astrophysics, Harvard University, Cambridge, MA 1984–1989 Associate Professor, University of Oklahoma 1979–1984 Assistant Professor, University of Oklahoma 1976–1979 Postdoctoral Research Fellow, Harvard-Smithsonian Center for Astrophysics, Harvard University PROFESSIONAL AND HONORARY SOCIETIES: American Astronomical Society International Astronomical Union Phi Beta Kappa RESEARCH INTERESTS: Stellar evolution, supernovae, nucleosynthesis and abundances Radio observations of supernovae and galaxies JOHN J. COWAN Page 2 PUBLICATIONS J. J. Cowan and W. K. Rose, “Production of 17O and 18O by Means of the Hot CNO Tri-Cycle,” Astrophys. J. (Letters) 201, L45 (1975) J. J. Cowan, M. Kafatos, and W. K. Rose, “Sources of Excitation of the Interstellar Gas and Galactic Structure,” Astrophys. J. 195, 47 (1975) M. F. A’Hearn and J. J. Cowan, “Molecular Production Rates in Comet Kohoutek,” As- tron.
    [Show full text]
  • Alyssa Goodman, Naomi Ridge, Scott Wolk, Scott Schnee, Di Li & Bryan
    COMPLET(E)ING THE STAR-FORMATION HISTORY OF THE RHO-OPH REGION Alyssa Goodman, Naomi Ridge, Scott Wolk, Scott Schnee, Di Li & Bryan Gaensler Background The interaction of newly formed stars with their parent cloud, particularly in the case of massive stars, can have significant consequences for the subsequent development of the cloud. Hot, massive stars will cause cloud disruption through their ionizing flux as well as through the momentum in their stellar winds. Alternatively, given the right conditions in the cloud, stellar winds may also cause the collapse of cloud cores and induce further star formation. Located only 160pc from the Sun, the Ophiuchus molecular cloud is one of the most conspicuous nearby regions where low- and intermediate-mass star formation is taking place (e.g. Wilking 1992 for a review). The Ophiuchus cloud consists of two massive, centrally condensed cores, L1688 and L1689, from each of which a filamentary system of streamers extends to the north-east over tens of parsecs (e.g. Loren 1989). While little star formation activity is observed in the streamers, the westernmost core, L1688 (figure 1), harbors a rich cluster of young stellar objects (YSOs) at various evolutionary stages and is distinguished by a high star-formation efficiency (Wilking & Lada 1983 - hereafter WL83). This young stellar cluster and the cloud core in which it resides are commonly referred to as the ρ-Oph star-forming region. Both the gas/dust content and the embedded stellar population of ρ−Oph have been extensively studied for more than two decades. The distribution of the low-density molecular gas was mapped in C18O(1-0) by WL83, revealing a ridge of high column density gas.
    [Show full text]
  • Winter Constellations
    Winter Constellations *Orion *Canis Major *Monoceros *Canis Minor *Gemini *Auriga *Taurus *Eradinus *Lepus *Monoceros *Cancer *Lynx *Ursa Major *Ursa Minor *Draco *Camelopardalis *Cassiopeia *Cepheus *Andromeda *Perseus *Lacerta *Pegasus *Triangulum *Aries *Pisces *Cetus *Leo (rising) *Hydra (rising) *Canes Venatici (rising) Orion--Myth: Orion, the great ​ ​ hunter. In one myth, Orion boasted he would kill all the wild animals on the earth. But, the earth goddess Gaia, who was the protector of all animals, produced a gigantic scorpion, whose body was so heavily encased that Orion was unable to pierce through the armour, and was himself stung to death. His companion Artemis was greatly saddened and arranged for Orion to be immortalised among the stars. Scorpius, the scorpion, was placed on the opposite side of the sky so that Orion would never be hurt by it again. To this day, Orion is never seen in the sky at the same time as Scorpius. DSO’s ● ***M42 “Orion Nebula” (Neb) with Trapezium A stellar ​ ​ ​ nursery where new stars are being born, perhaps a thousand stars. These are immense clouds of interstellar gas and dust collapse inward to form stars, mainly of ionized hydrogen which gives off the red glow so dominant, and also ionized greenish oxygen gas. The youngest stars may be less than 300,000 years old, even as young as 10,000 years old (compared to the Sun, 4.6 billion years old). 1300 ly. ​ ​ 1 ● *M43--(Neb) “De Marin’s Nebula” The star-forming ​ “comma-shaped” region connected to the Orion Nebula. ● *M78--(Neb) Hard to see. A star-forming region connected to the ​ Orion Nebula.
    [Show full text]
  • Správa O Činnosti Organizácie SAV Za Rok 2017
    Astronomický ústav SAV Správa o činnosti organizácie SAV za rok 2017 Tatranská Lomnica január 2018 Obsah osnovy Správy o činnosti organizácie SAV za rok 2017 1. Základné údaje o organizácii 2. Vedecká činnosť 3. Doktorandské štúdium, iná pedagogická činnosť a budovanie ľudských zdrojov pre vedu a techniku 4. Medzinárodná vedecká spolupráca 5. Vedná politika 6. Spolupráca s VŠ a inými subjektmi v oblasti vedy a techniky 7. Spolupráca s aplikačnou a hospodárskou sférou 8. Aktivity pre Národnú radu SR, vládu SR, ústredné orgány štátnej správy SR a iné organizácie 9. Vedecko-organizačné a popularizačné aktivity 10. Činnosť knižnično-informačného pracoviska 11. Aktivity v orgánoch SAV 12. Hospodárenie organizácie 13. Nadácie a fondy pri organizácii SAV 14. Iné významné činnosti organizácie SAV 15. Vyznamenania, ocenenia a ceny udelené organizácii a pracovníkom organizácie SAV 16. Poskytovanie informácií v súlade so zákonom o slobodnom prístupe k informáciám 17. Problémy a podnety pre činnosť SAV PRÍLOHY A Zoznam zamestnancov a doktorandov organizácie k 31.12.2017 B Projekty riešené v organizácii C Publikačná činnosť organizácie D Údaje o pedagogickej činnosti organizácie E Medzinárodná mobilita organizácie F Vedecko-popularizačná činnosť pracovníkov organizácie SAV Správa o činnosti organizácie SAV 1. Základné údaje o organizácii 1.1. Kontaktné údaje Názov: Astronomický ústav SAV Riaditeľ: Mgr. Martin Vaňko, PhD. Zástupca riaditeľa: Mgr. Peter Gömöry, PhD. Vedecký tajomník: Mgr. Marián Jakubík, PhD. Predseda vedeckej rady: RNDr. Luboš Neslušan, CSc. Člen snemu SAV: Mgr. Marián Jakubík, PhD. Adresa: Astronomický ústav SAV, 059 60 Tatranská Lomnica http://www.ta3.sk Tel.: 052/7879111 Fax: 052/4467656 E-mail: [email protected] Názvy a adresy detašovaných pracovísk: Astronomický ústav - Oddelenie medziplanetárnej hmoty Dúbravská cesta 9, 845 04 Bratislava Vedúci detašovaných pracovísk: Astronomický ústav - Oddelenie medziplanetárnej hmoty prof.
    [Show full text]
  • The Tritium Beta-Ray Induced Reactions in Deuterium Oxide Vapor and Hydrogen Or Carbon Monoxide and the Exchange of H-Atoms with Water Molecules
    This dissertation has been microfilmed exactly as received 66-6232 BIBLER, Ned Eugene, 1937- THE TRITIUM BETA-RAY INDUCED REACTIONS IN DEUTERIUM OXIDE VAPOR AND HYDROGEN OR CARBON MONOXIDE AND THE EXCHANGE OF H-ATOMS WITH WATER MOLECULES. The Ohio State University, Ph.D., 1965 Chemistry, physical University Microfilms, Inc., Ann Arbor, Michigan THE TRITIUM 3ETA-RAY INDUCED REACTIONS IN DEUTERIUM OXIDE VAPOR AND HYDROGEN OR CARBON MONOXIDE AND THE EXCHANGE OF H-ATOMS WITH WATER MOLECULES DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Ned Eugene B ib le r , B .S ., M.S * * * * * The Ohio S ta te U n iversity 1965 Approved by Adviser Department of Chemistry ACKNOWLEDGMENTS Several groups were influential in the completion of this work and the culmination of my graduate career at the Ohio State University. I have singled out two who deserve special acknowledg­ ment. I wish to express my appreciation to the members of my family for their understanding and sympathetic guidance during this demanding period. In particular, I thank my wife, Jane, who was a source of encouragement, for her devotion, scientific advice, and unswervingly honest criticism ; and my mother in law, Mrs. Pauline Pycraft, who typed a major portion of the first draft of this thesis. I am indebted to the stimulating research group headed by Dr. R. F. Firestone for many fruitful discussions and altercations on an array of subjects, including the radiation chemistry of water vapor. Specifically, I thank Dr. Firestone for his keen interest and set of high scientific standards which, when applied to the course and completion of this study, made it a maturing and g r a tify in g experience.
    [Show full text]
  • Wynyard Planetarium & Observatory a Autumn Observing Notes
    Wynyard Planetarium & Observatory A Autumn Observing Notes Wynyard Planetarium & Observatory PUBLIC OBSERVING – Autumn Tour of the Sky with the Naked Eye CASSIOPEIA Look for the ‘W’ 4 shape 3 Polaris URSA MINOR Notice how the constellations swing around Polaris during the night Pherkad Kochab Is Kochab orange compared 2 to Polaris? Pointers Is Dubhe Dubhe yellowish compared to Merak? 1 Merak THE PLOUGH Figure 1: Sketch of the northern sky in autumn. © Rob Peeling, CaDAS, 2007 version 1.2 Wynyard Planetarium & Observatory PUBLIC OBSERVING – Autumn North 1. On leaving the planetarium, turn around and look northwards over the roof of the building. Close to the horizon is a group of stars like the outline of a saucepan with the handle stretching to your left. This is the Plough (also called the Big Dipper) and is part of the constellation Ursa Major, the Great Bear. The two right-hand stars are called the Pointers. Can you tell that the higher of the two, Dubhe is slightly yellowish compared to the lower, Merak? Check with binoculars. Not all stars are white. The colour shows that Dubhe is cooler than Merak in the same way that red-hot is cooler than white- hot. 2. Use the Pointers to guide you upwards to the next bright star. This is Polaris, the Pole (or North) Star. Note that it is not the brightest star in the sky, a common misconception. Below and to the left are two prominent but fainter stars. These are Kochab and Pherkad, the Guardians of the Pole. Look carefully and you will notice that Kochab is slightly orange when compared to Polaris.
    [Show full text]
  • 1 Kepler's Third
    Astronomy 114 { Summary of Important Concepts #1 1 1 Kepler's Third Law Kepler discovered that the size of a planet's orbit (the semi-major axis of the ellipse) is simply related to sidereal period of the orbit. If the size of the orbit (a) is expressed in astronomical units (1 AU equals the average distance between the Earth and Sun) and the period (P) is measured in years, then Kepler's Third Law says P 2 = a3: After applying Newton's Laws of Motion and Newton's Law of Gravity we find that Kepler's Third Law takes a more general form: 4π2 P 2 = a3 "G(m1 + m2)# in MKS units where m1 and m2 are the masses of the two bodies. Let's assume that one body, m1 say, is always much larger than the other one. Then m1 + m2 is nearly equal to m1. We can then use our technique of dividing two instances of this equation derive a general form of Kepler's Third Law: MP 2 = a3 where P is in Earth years, a is in AU and M is the mass of the central object in units of the mass of the Sun. So M = 1 whenever we talk about planets orbiting the Sun. Examples: Q: The Earth orbits the Sun at a distance of 1AU with a period of 1 year. 12 = 13. Suppose a new asteroid is discovered which orbits the Sun at a distance of 9AU. How long does it take this object to orbit the Sun? A: MP 2 = a3 (1)(P 2) = 93 P 2 = 729 P = p729 = 27 years Astronomy 114 { Summary of Important Concepts #1 2 2 Newton's Law of Gravitation Any two objects, no matter how small, attract one another gravitationally.
    [Show full text]
  • Apparent and Absolute Magnitudes of Stars: a Simple Formula
    Available online at www.worldscientificnews.com WSN 96 (2018) 120-133 EISSN 2392-2192 Apparent and Absolute Magnitudes of Stars: A Simple Formula Dulli Chandra Agrawal Department of Farm Engineering, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi - 221005, India E-mail address: [email protected] ABSTRACT An empirical formula for estimating the apparent and absolute magnitudes of stars in terms of the parameters radius, distance and temperature is proposed for the first time for the benefit of the students. This reproduces successfully not only the magnitudes of solo stars having spherical shape and uniform photosphere temperature but the corresponding Hertzsprung-Russell plot demonstrates the main sequence, giants, super-giants and white dwarf classification also. Keywords: Stars, apparent magnitude, absolute magnitude, empirical formula, Hertzsprung-Russell diagram 1. INTRODUCTION The visible brightness of a star is expressed in terms of its apparent magnitude [1] as well as absolute magnitude [2]; the absolute magnitude is in fact the apparent magnitude while it is observed from a distance of . The apparent magnitude of a celestial object having flux in the visible band is expressed as [1, 3, 4] ( ) (1) ( Received 14 March 2018; Accepted 31 March 2018; Date of Publication 01 April 2018 ) World Scientific News 96 (2018) 120-133 Here is the reference luminous flux per unit area in the same band such as that of star Vega having apparent magnitude almost zero. Here the flux is the magnitude of starlight the Earth intercepts in a direction normal to the incidence over an area of one square meter. The condition that the Earth intercepts in the direction normal to the incidence is normally fulfilled for stars which are far away from the Earth.
    [Show full text]
  • On the Detection of Exoplanets Via Radial Velocity Doppler Spectroscopy
    The Downtown Review Volume 1 Issue 1 Article 6 January 2015 On the Detection of Exoplanets via Radial Velocity Doppler Spectroscopy Joseph P. Glaser Cleveland State University Follow this and additional works at: https://engagedscholarship.csuohio.edu/tdr Part of the Astrophysics and Astronomy Commons How does access to this work benefit ou?y Let us know! Recommended Citation Glaser, Joseph P.. "On the Detection of Exoplanets via Radial Velocity Doppler Spectroscopy." The Downtown Review. Vol. 1. Iss. 1 (2015) . Available at: https://engagedscholarship.csuohio.edu/tdr/vol1/iss1/6 This Article is brought to you for free and open access by the Student Scholarship at EngagedScholarship@CSU. It has been accepted for inclusion in The Downtown Review by an authorized editor of EngagedScholarship@CSU. For more information, please contact [email protected]. Glaser: Detection of Exoplanets 1 Introduction to Exoplanets For centuries, some of humanity’s greatest minds have pondered over the possibility of other worlds orbiting the uncountable number of stars that exist in the visible universe. The seeds for eventual scientific speculation on the possibility of these "exoplanets" began with the works of a 16th century philosopher, Giordano Bruno. In his modernly celebrated work, On the Infinite Universe & Worlds, Bruno states: "This space we declare to be infinite (...) In it are an infinity of worlds of the same kind as our own." By the time of the European Scientific Revolution, Isaac Newton grew fond of the idea and wrote in his Principia: "If the fixed stars are the centers of similar systems [when compared to the solar system], they will all be constructed according to a similar design and subject to the dominion of One." Due to limitations on observational equipment, the field of exoplanetary systems existed primarily in theory until the late 1980s.
    [Show full text]
  • Astronomy 2008 Index
    Astronomy Magazine Article Title Index 10 rising stars of astronomy, 8:60–8:63 1.5 million galaxies revealed, 3:41–3:43 185 million years before the dinosaurs’ demise, did an asteroid nearly end life on Earth?, 4:34–4:39 A Aligned aurorae, 8:27 All about the Veil Nebula, 6:56–6:61 Amateur astronomy’s greatest generation, 8:68–8:71 Amateurs see fireballs from U.S. satellite kill, 7:24 Another Earth, 6:13 Another super-Earth discovered, 9:21 Antares gang, The, 7:18 Antimatter traced, 5:23 Are big-planet systems uncommon?, 10:23 Are super-sized Earths the new frontier?, 11:26–11:31 Are these space rocks from Mercury?, 11:32–11:37 Are we done yet?, 4:14 Are we looking for life in the right places?, 7:28–7:33 Ask the aliens, 3:12 Asteroid sleuths find the dino killer, 1:20 Astro-humiliation, 10:14 Astroimaging over ancient Greece, 12:64–12:69 Astronaut rescue rocket revs up, 11:22 Astronomers spy a giant particle accelerator in the sky, 5:21 Astronomers unearth a star’s death secrets, 10:18 Astronomers witness alien star flip-out, 6:27 Astronomy magazine’s first 35 years, 8:supplement Astronomy’s guide to Go-to telescopes, 10:supplement Auroral storm trigger confirmed, 11:18 B Backstage at Astronomy, 8:76–8:82 Basking in the Sun, 5:16 Biggest planet’s 5 deepest mysteries, The, 1:38–1:43 Binary pulsar test affirms relativity, 10:21 Binocular Telescope snaps first image, 6:21 Black hole sets a record, 2:20 Black holes wind up galaxy arms, 9:19 Brightest starburst galaxy discovered, 12:23 C Calling all space probes, 10:64–10:65 Calling on Cassiopeia, 11:76 Canada to launch new asteroid hunter, 11:19 Canada’s handy robot, 1:24 Cannibal next door, The, 3:38 Capture images of our local star, 4:66–4:67 Cassini confirms Titan lakes, 12:27 Cassini scopes Saturn’s two-toned moon, 1:25 Cassini “tastes” Enceladus’ plumes, 7:26 Cepheus’ fall delights, 10:85 Choose the dome that’s right for you, 5:70–5:71 Clearing the air about seeing vs.
    [Show full text]