DOCSLIB.ORG

21. the Milky Way Galaxy

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
21. the Milky Way Galaxy 4/12/12 21. The Milky Way Galaxy Take a giant step outside the Milky Way The Milky Way Galaxy c Artist's Conception Example (not to scale) b d a 1 4/12/12 6 Supermassive (3x10 M) Black Hole in the Perseus arm Galactic Center from above ("face-on") Orion arm see disk and Sun bulge Cygnus arm Carina arm from the side ("edge-on") Another galaxy: NGC 4414. The Milky Way roughly resembles it. M51 2 4/12/12 The Tree Main Structural Components of the Milky Way 3. Bulge • About 4 kpc across 1. Disk • 30,000 pc diameter (30 kpc) • Old stars, some gas, dust • Contains young and old stars, gas, dust. Has spiral structure. 6 • Central black hole of 3x10 M • Vertical thickness roughly 100 pc -2 kpc (depending on component). • Spherical Most gas and dust in thinner layer, most stars in thicker layer. 2. Halo • At least 30 kpc across • Contains globular clusters, old stars, little gas and dust, much ‘dark matter’ • Roughly spherical Shapley (1917) found that Sun was not at center of Milky Way Precise Distance to Galactic Center Distance = 7.94 +/- 0.42 kpc SgrA* Shapley used distances to variable “RR Lyrae” stars (a kind of Horizontal Branch star) in Globular Clusters to determine that Sun was 16 kpc from center of Milky Way. Modern value 8 kpc. Eisenhauer et al. 2003 Orbital motion 6.37 mas/yr 3 4/12/12 Stellar Orbits Clicker Question Where is out solar system located? A. Near the center of the milky Way Galaxy in the bulge. B. 4 kpc from the center of the Milky Way in the halo. C. 8 kpc from the center of the Milky Way in the disk. D. 20 kpc from the center of the Milky Way in the Halo: stars and globular clusters swarm around center of Milky Way. Very elliptical disk. orbits with random orientations. They also cross the disk. Bulge: similar to halo. Disk: rotates. Rotation of the Disk Clicker Question Sun moves at 220 km/sec around center. An orbit takes 240 million years. Stars closer to center take less time to orbit. Stars further from center take What lurks at the center of our galaxy? longer. A. A 3 million solar mass black hole. => rotation not rigid like a phonograph record or a merry-go-round. Rather, "differential rotation". B. A giant star cluster. Over most of disk, rotation velocity is roughly constant. C. A 30 solar mass black hole. D. Darth Vader The "rotation curve" of the Milky Way 4 4/12/12 Spiral Structure of Disk Spiral arms best traced by: Young stars and clusters Emission Nebulae HI Molecular Clouds (old stars to a lesser extent) Disk not empty between arms, just less material there. Problem: How do spiral arms survive? The spiral should end up like this: Given differential rotation, arms should be stretched and smeared out after a few revolutions (Sun has made 20 already): The Winding Dilemma Real structure of Milky Way (and other spiral galaxies) is more loosely wrapped. 5 4/12/12 Now replace cars by stars and gas Proposed solution: Traffic jam on a loop caused by merging clouds. The traffic jams are actually due to the stars' collective Arms are not material moving together, but mark peak of a compressional gravity. The higher gravity of the wave circling the disk: jams keeps stars in them for A Spiral Density Wave longer. Calculations and computer simulations show this Traffic-jam analogy: situation can be maintained for a long time. 90% of Matter in Milky Way is Dark Matter Gives off no detectable radiation. Evidence is from rotation curve: 10 Solar System Rotation Curve: when almost all Rotation mass at center, velocity decreases with radius ("Keplerian") Velocity 5 (AU/yr) 1 1 30 10 R (AU) 20 observed curve Molecular gas clouds pushed together in arms too => high density of clouds => high Milky Way concentration of dust => dust lanes. Rotation Curve if Milky Also, squeezing of clouds initiates collapse within them => star formation. Bright young Curve Way ended massive stars live and die in spiral arms. Emission nebulae mostly in spiral arms. where visible matter pretty So arms always contain same types of objects, but individual objects come and go. much runs out. 6 4/12/12 Not enough radiating matter at large R to explain rotation curve => "dark" matter! Dark matter must be about 90% of the mass! Composition unknown. Probably mostly exotic particles that don't interact with ordinary matter at all (except gravity). Some may be brown dwarfs, dead white dwarfs … Most likely it's a dark halo surrounding the Milky Way. Mass of Milky Way 6 x 1011 solar masses within 40 kpc of center. More Evidence for Dark Matter - Abell 1689 • Dark Matter halos At large radii there is little starlight. There is 5-10 times as much dark matter associated with galaxies, as ordinary matter. 7 4/12/12 Dark Matter candidates Clicker Question • MACHOs (Massive compact halo objects) • Brown dwarfs (low mass stars) How long does it take our solar system to orbit once around • White dwarfs (burn-out stars) the Milky Way? • Neutron stars (dead stars) A. 1 year. • Stellar black holes (dead stars) B. 2 million years. • mini (primordial) black holes C. 240 million years. • massive (primordial) black holes D. 250 billion years (longer than the age of the • WIMPS (Weakly interacting massive particles: neutrons, axions, etc). Universe). Clicker Question What makes up most of the mass (90%) of the Milky Way Galaxy? A. Hydrogen gas. B. Stars. C. Dead stars (white dwarfs, neutron stars and black holes). D. We don’t know. 8 4/12/12 The Galactic Center • Up to 30 mag extinction in the optical (only 1 in 1012 photons reaches us!)" •! Solar motion up through the disk will give us a clear view in 15 Myrs" •! Meanwhile, forced to work at radio, IR, X-ray and gamma ray wavelengths." Seeing into the center of the Milky Way Most information we have about the Galactic Center region is thus from IR and radio: •! 1kpc: expanding gas at 100km/s (explosive event 10Myr ago?) •! GC is about 8 kpc away, at a declination •! 100 pc: Sgr A (strongest radio source on the sky). of -29°, well in the southern hemisphere. •! 10 pc: pinwheel gas structure •! <1 pc: Sgr A*, pointlike radio/X-ray/IR source •! It is very busy, as 6 •! Nucleus: Supermassive black hole ~3x10 M shown by this 1x1 kpc VLA map. •! Stars are very tightly packed in the central region, reaching densities of up 7 -3 to 10 M pc -3 –! near the Sun the density is only about 0.05 M pc 4 -3 –! in globular clusters the central density reaches 10 M pc => Stellar collisions probably frequent (1 every 106 yrs). 9 4/12/12 Seeing into the center of the Milky Way •! Moving closer to the center, the picture gets more complex. •! The center-most source is called Sgr A, divides up into –! Sgr A West –! Sgr A East –! Sgr A* •! SgrA* is extremely compact, and is almost certainly due to the central black hole itself. •! Sgr A West appears like a mini spiral in an image at 6cm - complicated structure in the ionized gas. •! Consequently, IR stars can be observed very close to thecenter of the •! Scale of central region about 0.3 Galaxy. pc, IR (1.6, 2.2 and 3.8 microns). •! They move so fast (500 to 1000 km/s) that their proper motions are •! Sgr A* located near the center of measurable even after a few years. image (not bright in IR). •! In recent years even their orbits around the central massive source has •! Most of these stars are very young been detected. and massive and heavily reddened so they don't appear blue. •! Spectroscopic studies indicate that 1992-2008 the stars are luminous super giants and only a few 10s of millions years old. 10 4/12/12 4/17: Reading Assignment •! Is the black hole the dynamical center? Supporting evidence comes from the proper motion of Sgr A*. •! Chapter 15.1-15.3: Galaxies –! At 8 kpc from us its proper motion is very small, about 10 mas/yr. It moves at a straight line across the sky. –! The amount turns out to exactly reflect the motion of the Sun around the Galaxy => Sgr A* is clearly the Milky Way's dynamical heart. 11 .
Load more

Recommended publications
  • Constructing a Galactic Coordinate System Based on Near-Infrared and Radio Catalogs
    A&A 536, A102 (2011) Astronomy DOI: 10.1051/0004-6361/201116947 & c ESO 2011 Astrophysics Constructing a Galactic coordinate system based on near-infrared and radio catalogs J.-C. Liu1,2,Z.Zhu1,2, and B. Hu3,4 1 Department of astronomy, Nanjing University, Nanjing 210093, PR China e-mail: [jcliu;zhuzi]@nju.edu.cn 2 key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210093, PR China 3 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, PR China 4 Graduate School of Chinese Academy of Sciences, Beijing 100049, PR China e-mail: [email protected] Received 24 March 2011 / Accepted 13 October 2011 ABSTRACT Context. The definition of the Galactic coordinate system was announced by the IAU Sub-Commission 33b on behalf of the IAU in 1958. An unrigorous transformation was adopted by the Hipparcos group to transform the Galactic coordinate system from the FK4-based B1950.0 system to the FK5-based J2000.0 system or to the International Celestial Reference System (ICRS). For more than 50 years, the definition of the Galactic coordinate system has remained unchanged from this IAU1958 version. On the basis of deep and all-sky catalogs, the position of the Galactic plane can be revised and updated definitions of the Galactic coordinate systems can be proposed. Aims. We re-determine the position of the Galactic plane based on modern large catalogs, such as the Two-Micron All-Sky Survey (2MASS) and the SPECFIND v2.0. This paper also aims to propose a possible definition of the optimal Galactic coordinate system by adopting the ICRS position of the Sgr A* at the Galactic center.
    [Show full text]
  • Eclipse Newsletter
    ECLIPSE NEWSLETTER The Eclipse Newsletter is dedicated to increasing the knowledge of Astronomy, Astrophysics, Cosmology and related subjects. VOLUMN 2 NUMBER 1 JANUARY – FEBRUARY 2018 PLEASE SEND ALL PHOTOS, QUESTIONS AND REQUST FOR ARTICLES TO [email protected] 1 MCAO PUBLIC NIGHTS AND FAMILY NIGHTS. The general public and MCAO members are invited to visit the Observatory on select Monday evenings at 8PM for Public Night programs. These programs include discussions and illustrated talks on astronomy, planetarium programs and offer the opportunity to view the planets, moon and other objects through the telescope, weather permitting. Due to limited parking and seating at the observatory, admission is by reservation only. Public Night attendance is limited to adults and students 5th grade and above. If you are interested in making reservations for a public night, you can contact us by calling 302-654- 6407 between the hours of 9 am and 1 pm Monday through Friday. Or you can email us any time at [email protected] or [email protected]. The public nights will be presented even if the weather does not permit observation through the telescope. The admission fees are $3 for adults and $2 for children. There is no admission cost for MCAO members, but reservations are still required. If you are interested in becoming a MCAO member, please see the link for membership. We also offer family memberships. Family Nights are scheduled from late spring to early fall on Friday nights at 8:30PM. These programs are opportunities for families with younger children to see and learn about astronomy by looking at and enjoying the sky and its wonders.
    [Show full text]
  • The Gould Belt
    Astrophysics, Vol. 57, No. 4, pp. 583-604, December, 2014. REVIEWS THE GOULD BELT V.V. Bobylev1,2 1Pulkovo Astronomical Observatory, St. Petersburg, Russia 2Sobolev Astronomical Institute, St. Petersburg State University, Russia AbstractThis review is devoted to studies of the Gould belt and the Local system. Since the Gould belt is the giant stellar-gas complex closest to the sun, its stellar component is characterized, along with the stellar associations and diffuse clusters, cold atomic and molecular gas, high-temperature coronal gas, and dust contained in it. Questions relating to the kinematic features of the Gould belt are discussed and the most interesting scenarios for its origin and evolution are examined. 1 Historical information Stars of spectral classes O and B that are visible to the naked eye define two large circles in the celestial sphere. One of them passes near the plane of the Milky Way, while the second is slightly inclined to it and is known as the Gould belt. The minimum galactic latitude of the Gould belt is in the region of the constellation Orion, and the maximum, in the region of Scorpio-Centaurus. Herschel noted [1] that some of the bright stars in the southern sky appear to be part of a separate structure from the Milky Way with an inclination to the galactic equator of about 20◦. Commenting on the features of the distribution of stars in the Milky Way, Struve [2] independently noted that the stars that form the largest densifications on the celestial sphere can lie in two planes with a mutual inclination of about 10◦.
    [Show full text]
  • Introduction to Astronomy from Darkness to Blazing Glory
    Introduction to Astronomy From Darkness to Blazing Glory Published by JAS Educational Publications Copyright Pending 2010 JAS Educational Publications All rights reserved. Including the right of reproduction in whole or in part in any form. Second Edition Author: Jeffrey Wright Scott Photographs and Diagrams: Credit NASA, Jet Propulsion Laboratory, USGS, NOAA, Aames Research Center JAS Educational Publications 2601 Oakdale Road, H2 P.O. Box 197 Modesto California 95355 1-888-586-6252 Website: http://.Introastro.com Printing by Minuteman Press, Berkley, California ISBN 978-0-9827200-0-4 1 Introduction to Astronomy From Darkness to Blazing Glory The moon Titan is in the forefront with the moon Tethys behind it. These are two of many of Saturn’s moons Credit: Cassini Imaging Team, ISS, JPL, ESA, NASA 2 Introduction to Astronomy Contents in Brief Chapter 1: Astronomy Basics: Pages 1 – 6 Workbook Pages 1 - 2 Chapter 2: Time: Pages 7 - 10 Workbook Pages 3 - 4 Chapter 3: Solar System Overview: Pages 11 - 14 Workbook Pages 5 - 8 Chapter 4: Our Sun: Pages 15 - 20 Workbook Pages 9 - 16 Chapter 5: The Terrestrial Planets: Page 21 - 39 Workbook Pages 17 - 36 Mercury: Pages 22 - 23 Venus: Pages 24 - 25 Earth: Pages 25 - 34 Mars: Pages 34 - 39 Chapter 6: Outer, Dwarf and Exoplanets Pages: 41-54 Workbook Pages 37 - 48 Jupiter: Pages 41 - 42 Saturn: Pages 42 - 44 Uranus: Pages 44 - 45 Neptune: Pages 45 - 46 Dwarf Planets, Plutoids and Exoplanets: Pages 47 -54 3 Chapter 7: The Moons: Pages: 55 - 66 Workbook Pages 49 - 56 Chapter 8: Rocks and Ice:
    [Show full text]
  • Arxiv:1907.03763V1 [Astro-Ph.GA] 8 Jul 2019 Keywords: Galaxy: Disk — Galaxy: Kinematics and Dynamics — Galaxy: Solar Neighborhood — Galaxy: Structure
    Draft version July 10, 2019 Typeset using LATEX twocolumn style in AASTeX62 Stellar Overdensity in the Local Arm in Gaia DR2 Yusuke Miyachi,1 Nobuyuki Sakai,2, 3 Daisuke Kawata,4 Junichi Baba,5 Mareki Honma,2, 6, 7 Noriyuki Matsunaga,8 and Kenta Fujisawa1 1Department of Physics, Faculty of Science, Yamaguchi University, Yoshida 1677-1, Yamaguchi-city, Yamaguchi 753-8512, Japan 2Mizusawa VLBI observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan 3Korea Astronomy & Space Science Institute, 776, Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Korea 4Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK 5National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan 6Mizusawa VLBI observatory, National Astronomical Observatory of Japan, 2-12 Hoshi-ga-oka-cho, Mizusawa-ku, Oshu, Iwate 023-0861, Japan 7The Graduate University for Advanced Studies (Sokendai), Mitaka, Tokyo 181-8588, Japan 8Department of Astronomy, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan (Received March 31, 2019; Revised June 17, 2019; Accepted July 2, 2019) Submitted to ApJ ABSTRACT Using the cross-matched data of Gaia DR2 and 2MASS Point Source Catalog, we investigated the surface density distribution of stars aged 1 Gyr in the thin disk in the range of 90◦ l 270◦. We ∼ ≤ ≤ selected 4,654 stars above the turnoff corresponding to the age 1 Gyr, that fall within a small box ∼ region in the color{magnitude diagram, (J K ) versus M(K ), for which the distance and reddening − s 0 s are corrected.
    [Show full text]
  • Detecting Differential Rotation and Starspot Evolution on the M Dwarf GJ 1243 with Kepler James R
    Western Washington University Masthead Logo Western CEDAR Physics & Astronomy College of Science and Engineering 6-20-2015 Detecting Differential Rotation and Starspot Evolution on the M Dwarf GJ 1243 with Kepler James R. A. Davenport Western Washington University, [email protected] Leslie Hebb Suzanne L. Hawley Follow this and additional works at: https://cedar.wwu.edu/physicsastronomy_facpubs Part of the Stars, Interstellar Medium and the Galaxy Commons Recommended Citation Davenport, James R. A.; Hebb, Leslie; and Hawley, Suzanne L., "Detecting Differential Rotation and Starspot Evolution on the M Dwarf GJ 1243 with Kepler" (2015). Physics & Astronomy. 16. https://cedar.wwu.edu/physicsastronomy_facpubs/16 This Article is brought to you for free and open access by the College of Science and Engineering at Western CEDAR. It has been accepted for inclusion in Physics & Astronomy by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. The Astrophysical Journal, 806:212 (11pp), 2015 June 20 doi:10.1088/0004-637X/806/2/212 © 2015. The American Astronomical Society. All rights reserved. DETECTING DIFFERENTIAL ROTATION AND STARSPOT EVOLUTION ON THE M DWARF GJ 1243 WITH KEPLER James R. A. Davenport1, Leslie Hebb2, and Suzanne L. Hawley1 1 Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195, USA; [email protected] 2 Department of Physics, Hobart and William Smith Colleges, Geneva, NY 14456, USA Received 2015 March 9; accepted 2015 May 6; published 2015 June 18 ABSTRACT We present an analysis of the starspots on the active M4 dwarf GJ 1243, using 4 years of time series photometry from Kepler.
    [Show full text]
  • Formation and Evolution of Galaxies and Black Holes
    Journal of Physical Science and Application 8 (1) (2018) 23-29 doi: 10.17265/2159-5348/2018.01.003 D DAVID PUBLISHING Formation and Evolution of Galaxies and Black Holes Cui-xiang Zhong Department of Science and Technology, Jiangxi Normal University, Nanchang 330022, China Abstract: In the past, people did not realize the formation and structure of galaxies. They even mistook the black holes hidden in the center of a galaxy as independent celestial objects, making black holes mysterious and unbelievable. It was only after the author studied and discovered the laws of the formation and evolution of satellites, planets and stars that he put forward the scientific theory of galaxy formation and evolution, therefore revealing the hierarchical structure of galaxy and the existence and characteristics of black holes as the main nodes of galactic structure. Key words: Galactic structure, galaxy formation, galaxy evolution, black holes, black hole area. 1. Introduction achievements in the research field of black holes. In 2005, the working group led by Zhiqiang Shen of As early as 1930s, it has been recognized that Shanghai Astronomical Observatory of Chinese galaxies in the universe are not randomly distributed, Academy of Sciences found some conclusive evidence but because of the lack of two dimensional supporting that there exists a super massive black observational data, there has been no breakthrough in holes in the center of Milky Way. In 2015, the the understanding of large-scale structures. Only until international team led by astronomers from Peking 1980s, with the continuous deepening of red-shift University in China and from the University of survey, could one clearly describe the Arizona announces their findings of a quasar, with its three-dimensional distribution of galaxies in large central black hole mass of 12 billion solar masses and scale structure, and found that galaxies have lumpy the luminosity of 420 trillion suns is at a distance of structures.
    [Show full text]
  • Life Cycle of Stars Script Edited by SJ on 29Th June 2011
    Life Cycle of Stars Script Edited by SJ on 29th June 2011. This first show is based loosely on the Life Cycle of Stars. It is aimed at students studying GCSE Astronomy. If the kids are younger than GCSE or below, nicer to start with Planets and Ecliptic and star signs stuff, detailed in Optional Start, leaving out more complex stuff on Neutron Stars and Black Holes. Stellarium commands are in blue Red notes are optional facts to add, and depend on age of audience and time. The talk should take 20-30 mins depending on how much science/mythology you elaborate on. Suggest that it is nice to do this show condensed into 20 mins at the end of We are Astronomers… to give a 40-45minute show. Optional easing-in start Do this if audience have no real knowledge of the stars and planets - best starting point for younger kids, if GCSE probably not needed can jump straight in at Finding North, but check! In stellarium start with sky as it is with sun (a for atmosphere) and ground, g. and at current time 8 . Ask ‘Can we see any stars in the night sky?’ Expect responses such as ‘Only the Sun, no because it’s too bright’- Ask ‘so why can’t we see the other stars in the day?’ - Get response cos our star the sun, too bright, light bounces off atmosphere, stops us seeing the other stars. Mention the light pollution in cities bouncing off the inner atmosphere stopping us seeing stars even at Night! Speed up time <L> and see sun moving across the sky, ask why the sun is moving? Explain that sun is not actually moving it’s us that is moving about on our axis and this makes the sun appear to rise in the East and set in the West.
    [Show full text]
  • Elements of Astronomy and Cosmology Outline 1
    ELEMENTS OF ASTRONOMY AND COSMOLOGY OUTLINE 1. The Solar System The Four Inner Planets The Asteroid Belt The Giant Planets The Kuiper Belt 2. The Milky Way Galaxy Neighborhood of the Solar System Exoplanets Star Terminology 3. The Early Universe Twentieth Century Progress Recent Progress 4. Observation Telescopes Ground-Based Telescopes Space-Based Telescopes Exploration of Space 1 – The Solar System The Solar System - 4.6 billion years old - Planet formation lasted 100s millions years - Four rocky planets (Mercury Venus, Earth and Mars) - Four gas giants (Jupiter, Saturn, Uranus and Neptune) Figure 2-2: Schematics of the Solar System The Solar System - Asteroid belt (meteorites) - Kuiper belt (comets) Figure 2-3: Circular orbits of the planets in the solar system The Sun - Contains mostly hydrogen and helium plasma - Sustained nuclear fusion - Temperatures ~ 15 million K - Elements up to Fe form - Is some 5 billion years old - Will last another 5 billion years Figure 2-4: Photo of the sun showing highly textured plasma, dark sunspots, bright active regions, coronal mass ejections at the surface and the sun’s atmosphere. The Sun - Dynamo effect - Magnetic storms - 11-year cycle - Solar wind (energetic protons) Figure 2-5: Close up of dark spots on the sun surface Probe Sent to Observe the Sun - Distance Sun-Earth = 1 AU - 1 AU = 150 million km - Light from the Sun takes 8 minutes to reach Earth - The solar wind takes 4 days to reach Earth Figure 5-11: Space probe used to monitor the sun Venus - Brightest planet at night - 0.7 AU from the
    [Show full text]
  • Differential Rotation of Kepler-71 Via Transit Photometry Mapping of Faculae and Starspots
    MNRAS 484, 618–630 (2019) doi:10.1093/mnras/sty3474 Advance Access publication 2019 January 16 Differential rotation of Kepler-71 via transit photometry mapping of faculae and starspots Downloaded from https://academic.oup.com/mnras/article-abstract/484/1/618/5289895 by University of Southern Queensland user on 14 November 2019 S. M. Zaleski ,1‹ A. Valio,2 S. C. Marsden1 andB.D.Carter1 1University of Southern Queensland, Centre for Astrophysics, Toowoomba 4350, Australia 2Center for Radio Astronomy and Astrophysics, Mackenzie Presbyterian University, Rua da Consolac¸ao,˜ 896 Sao˜ Paulo, Brazil Accepted 2018 December 19. Received 2018 December 18; in original form 2017 November 16 ABSTRACT Knowledge of dynamo evolution in solar-type stars is limited by the difficulty of using active region monitoring to measure stellar differential rotation, a key probe of stellar dynamo physics. This paper addresses the problem by presenting the first ever measurement of stellar differential rotation for a main-sequence solar-type star using starspots and faculae to provide complementary information. Our analysis uses modelling of light curves of multiple exoplanet transits for the young solar-type star Kepler-71, utilizing archival data from the Kepler mission. We estimate the physical characteristics of starspots and faculae on Kepler-71 from the characteristic amplitude variations they produce in the transit light curves and measure differential rotation from derived longitudes. Despite the higher contrast of faculae than those in the Sun, the bright features on Kepler-71 have similar properties such as increasing contrast towards the limb and larger sizes than sunspots. Adopting a solar-type differential rotation profile (faster rotation at the equator than the poles), the results from both starspot and facula analysis indicate a rotational shear less than about 0.005 rad d−1, or a relative differential rotation less than 2 per cent, and hence almost rigid rotation.
    [Show full text]
  • The Milky Way Almost Every Star We Can See in the Night Sky Belongs to Our Galaxy, the Milky Way
    The Milky Way Almost every star we can see in the night sky belongs to our galaxy, the Milky Way. The Galaxy acquired this unusual name from the Romans who referred to the hazy band that stretches across the sky as the via lactia, or “milky road”. This name has stuck across many languages, such as French (voie lactee) and spanish (via lactea). Note that we use a capital G for Galaxy if we are talking about the Milky Way The Structure of the Milky Way The Milky Way appears as a light fuzzy band across the night sky, but we also see individual stars scattered in all directions. This gives us a clue to the shape of the galaxy. The Milky Way is a typical spiral or disk galaxy. It consists of a flattened disk, a central bulge and a diffuse halo. The disk consists of spiral arms in which most of the stars are located. Our sun is located in one of the spiral arms approximately two-thirds from the centre of the galaxy (8kpc). There are also globular clusters distributed around the Galaxy. In addition to the stars, the spiral arms contain dust, so that certain directions that we looked are blocked due to high interstellar extinction. This dust means we can only see about 1kpc in the visible. Components in the Milky Way The disk: contains most of the stars (in open clusters and associations) and is formed into spiral arms. The stars in the disk are mostly young. Whilst the majority of these stars are a few solar masses, the hot, young O and B type stars contribute most of the light.
    [Show full text]
  • Arxiv:1307.0569V1
    IAUS 298 Setting the scence for Gaia and LAMOST Proceedings IAU Symposium No. 298, 2014 c 2014 International Astronomical Union S. Feltzing, G. Zhao, N. A. Walton & P. A. Whitelock, eds. DOI: 00.0000/X000000000000000X The Milky Way thin disk structure as revealed by stars and young open clusters Giovanni Carraro Alonso de Cordova 3107, 19001, Santiago de Chile, Chile email: [email protected] Abstract. In this contribution I shall focus on the structure of the Galactic thin disk. The evolution of the thin disk and its chemical properties have been discussed in detail by T. Bensby’s contribution in conjunction with the properties of the Galactic thick disk, and by L.Olivia in conjunction with the properties of the Galactic bulge. I will review and discuss the status of our understanding of three major topics, which have been the subject of intense research nowadays, after long years of silence: (1) the spiral structure of the Milky Way, (2) the size of the Galactic disk, and (3) the nature of the Local arm (Orion spur), where the Sun is immersed. The provisional conclusions of this discussion are that : (1) we still have quite a poor knowledge of the Milky Way spiral structure, and the main dis-agreements among various tracers are still to be settled; (2) the Galactic disk does clearly not have an obvious luminous cut-off at about 14 kpc from the Galactic center, and next generation Galactic models need to be updated in this respect, and (3) the Local arm is most probably an inter-arm structure, similar to what we see in several external spirals, like M 74.
    [Show full text]