ASTR 101 Introduction to Astronomy: Stars & Galaxies
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Astronomy, Astrophysics, and Cosmology
Astronomy, Astrophysics, and Cosmology Luis A. Anchordoqui Department of Physics and Astronomy Lehman College, City University of New York Lesson I February 2, 2016 arXiv:0706.1988 L. A. Anchordoqui (CUNY) Astronomy, Astrophysics, and Cosmology 2-2-2016 1 / 22 Table of Contents 1 Stars and Galaxies 2 Distance Measurements Stellar parallax Stellar luminosity L. A. Anchordoqui (CUNY) Astronomy, Astrophysics, and Cosmology 2-2-2016 2 / 22 Stars and Galaxies Night sky provides a strong impression of a changeless universe G Clouds drift across the Moon + on longer times Moon itself grows and shrinks G Moon and planets move against the background of stars G These are merely local phenomena caused by motions within our solar system G Far beyond planets + stars appear motionless L. A. Anchordoqui (CUNY) Astronomy, Astrophysics, and Cosmology 2-2-2016 3 / 22 Stars and Galaxies According to ancient cosmological belief + stars except for a few that appeared to move (the planets) where fixed on sphere beyond last planet The universe was self contained and we (here on Earth) were at its center L. A. Anchordoqui (CUNY) Astronomy, Astrophysics, and Cosmology 2-2-2016 4 / 22 Stars and Galaxies Our view of universe dramatically changed after Galileo’s telescopic observations: we no longer place ourselves at the center and we view the universe as vastly larger L. A. Anchordoqui (CUNY) Astronomy, Astrophysics, and Cosmology 2-2-2016 5 / 22 Stars and Galaxies Is the Earth flat? L. A. Anchordoqui (CUNY) Astronomy, Astrophysics, and Cosmology 2-2-2016 6 / 22 Stars and Galaxies Distances involved are so large that we specify them in terms of the time it takes the light to travel a given distance light second + 1 ls = 1 s 3 108 m/s = 3 108m = 300, 000 km × × light minute + 1 lm = 18 106 km × light year + 1 ly = 2.998 108 m/s 3.156 107 s/yr × · × = 9.46 1015 m 1013 km × ≈ How long would it take the space shuttle to go 1 ly? Shuttle orbits Earth @ 18,000 mph + it would need 37, 200 yr L. -
Plotting Variable Stars on the H-R Diagram Activity
Pulsating Variable Stars and the Hertzsprung-Russell Diagram The Hertzsprung-Russell (H-R) Diagram: The H-R diagram is an important astronomical tool for understanding how stars evolve over time. Stellar evolution can not be studied by observing individual stars as most changes occur over millions and billions of years. Astrophysicists observe numerous stars at various stages in their evolutionary history to determine their changing properties and probable evolutionary tracks across the H-R diagram. The H-R diagram is a scatter graph of stars. When the absolute magnitude (MV) – intrinsic brightness – of stars is plotted against their surface temperature (stellar classification) the stars are not randomly distributed on the graph but are mostly restricted to a few well-defined regions. The stars within the same regions share a common set of characteristics. As the physical characteristics of a star change over its evolutionary history, its position on the H-R diagram The H-R Diagram changes also – so the H-R diagram can also be thought of as a graphical plot of stellar evolution. From the location of a star on the diagram, its luminosity, spectral type, color, temperature, mass, age, chemical composition and evolutionary history are known. Most stars are classified by surface temperature (spectral type) from hottest to coolest as follows: O B A F G K M. These categories are further subdivided into subclasses from hottest (0) to coolest (9). The hottest B stars are B0 and the coolest are B9, followed by spectral type A0. Each major spectral classification is characterized by its own unique spectra. -
190 6Ap J 23. . 2 4 8C the LUMINOSITY of the BRIGHTEST
8C 4 2 . 23. J 6Ap 190 THE LUMINOSITY OF THE BRIGHTEST STARS By GEORGE C. COMSTOCK The prevailing opinion among astronomers admits the presence in the heavens of at least a few stars of extraordinary intrinsic bril- liancy. ‘ Gill, Kapteyn, and Newcomb have under differing forms announced the probable existence of stars having a luminosity exceeding that of the Sun by ten-thousand fold or more, possibly a hundred-thousand fold, and Canopus is cited as an example of such a star. It is the purpose of the present article to examine the evidence upon which this doctrine is based, and the extent to which that evidence is confirmed or refuted by other considerations. As respects Canopus, the case is presented by Gill, Researches on Stellar Parallax, substantially as follows. The measured par- allaxes of this star and of a Centauri are respectively ofoio and 0^762, and their stellar magnitudes are — 0.96 and+ 0.40; i. e., Canopus is 3.50 times brighter than a Centauri. The light of the one star, is therefore 3.50 times as great as that of the other. But since a Centauri has the same mass and the same spectrum as the Sun, and therefore presumably emits the same quantity of light, we may substitute the Sun in place of a Centauri in this com- parison, and find from the expression given above that Canopus is more than 20,000 times as bright as the Sun. I have sought for other cases of a similar character, using a method slightly different from that of Gill. -
Lecture 5: Stellar Distances 10/2/19, 8 02 AM
Lecture 5: Stellar Distances 10/2/19, 802 AM Astronomy 162: Introduction to Stars, Galaxies, & the Universe Prof. Richard Pogge, MTWThF 9:30 Lecture 5: Distances of the Stars Readings: Ch 19, section 19-1 Key Ideas Distance is the most important & most difficult quantity to measure in Astronomy Method of Trigonometric Parallaxes Direct geometric method of finding distances Units of Cosmic Distance: Light Year Parsec (Parallax second) Why are Distances Important? Distances are necessary for estimating: Total energy emitted by an object (Luminosity) Masses of objects from their orbital motions True motions through space of stars Physical sizes of objects The problem is that distances are very hard to measure... The problem of measuring distances Question: How do you measure the distance of something that is beyond the reach of your measuring instruments? http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit1/distances.html Page 1 of 7 Lecture 5: Stellar Distances 10/2/19, 802 AM Examples of such problems: Large-scale surveying & mapping problems. Military range finding to targets Measuring distances to any astronomical object Answer: You resort to using GEOMETRY to find the distance. The Method of Trigonometric Parallaxes Nearby stars appear to move with respect to more distant background stars due to the motion of the Earth around the Sun. This apparent motion (it is not "true" motion) is called Stellar Parallax. (Click on the image to view at full scale [Size: 177Kb]) In the picture above, the line of sight to the star in December is different than that in June, when the Earth is on the other side of its orbit. -
Spectroscopy of Variable Stars
Spectroscopy of Variable Stars Steve B. Howell and Travis A. Rector The National Optical Astronomy Observatory 950 N. Cherry Ave. Tucson, AZ 85719 USA Introduction A Note from the Authors The goal of this project is to determine the physical characteristics of variable stars (e.g., temperature, radius and luminosity) by analyzing spectra and photometric observations that span several years. The project was originally developed as a The 2.1-meter telescope and research project for teachers participating in the NOAO TLRBSE program. Coudé Feed spectrograph at Kitt Peak National Observatory in Ari- Please note that it is assumed that the instructor and students are familiar with the zona. The 2.1-meter telescope is concepts of photometry and spectroscopy as it is used in astronomy, as well as inside the white dome. The Coudé stellar classification and stellar evolution. This document is an incomplete source Feed spectrograph is in the right of information on these topics, so further study is encouraged. In particular, the half of the building. It also uses “Stellar Spectroscopy” document will be useful for learning how to analyze the the white tower on the right. spectrum of a star. Prerequisites To be able to do this research project, students should have a basic understanding of the following concepts: • Spectroscopy and photometry in astronomy • Stellar evolution • Stellar classification • Inverse-square law and Stefan’s law The control room for the Coudé Description of the Data Feed spectrograph. The spec- trograph is operated by the two The spectra used in this project were obtained with the Coudé Feed telescopes computers on the left. -
Cosmic Distances
Cosmic Distances • How to measure distances • Primary distance indicators • Secondary and tertiary distance indicators • Recession of galaxies • Expansion of the Universe Which is not true of elliptical galaxies? A) Their stars orbit in many different directions B) They have large concentrations of gas C) Some are formed in galaxy collisions D) The contain mainly older stars Which is not true of galaxy collisions? A) They can randomize stellar orbits B) They were more common in the early universe C) They occur only between small galaxies D) They lead to star formation Stellar Parallax As the Earth moves from one side of the Sun to the other, a nearby star will seem to change its position relative to the distant background stars. d = 1 / p d = distance to nearby star in parsecs p = parallax angle of that star in arcseconds Stellar Parallax • Most accurate parallax measurements are from the European Space Agency’s Hipparcos mission. • Hipparcos could measure parallax as small as 0.001 arcseconds or distances as large as 1000 pc. • How to find distance to objects farther than 1000 pc? Flux and Luminosity • Flux decreases as we get farther from the star – like 1/distance2 • Mathematically, if we have two stars A and B Flux Luminosity Distance 2 A = A B Flux B Luminosity B Distance A Standard Candles Luminosity A=Luminosity B Flux Luminosity Distance 2 A = A B FluxB Luminosity B Distance A Flux Distance 2 A = B FluxB Distance A Distance Flux B = A Distance A Flux B Standard Candles 1. Measure the distance to star A to be 200 pc. -
Determining Pulsation Period for an RR Lyrae Star
Leah Fabrizio Dr. Mitchell 06/10/2010 Determining Pulsation Period for an RR Lyrae Star As children we used to sing in wonderment of the twinkling stars above and many of us asked, “Why do stars twinkle?” All stars twinkle because their emitted light travels through the Earth’s atmosphere of turbulent gas and clouds that move and shift causing the traversing light to fluctuate. This means that the actual light output of the star is not changing. However there are a number of stars called Variable Stars that actually produce light of varying brightness before it hits the Earth’s atmosphere. There are two categories of variable stars: the intrinsic, where light fluctuation is due from the star physically changing and producing different luminosities, and extrinsic, where the amount of starlight varies due to another star eclipsing or blocking the star’s light from reaching earth (AAVSO 2010). Within the category of intrinsic variable stars are the pulsating variables that have a periodic change in brightness due to the actual size and light production of the star changing; within this group are the RR Lyrae stars (“variable star” 2010). For my research project, I will observe an RR Lyrae and find the period of its luminosity pulsation. The first RR Lyrae star was named after its namesake star (Strobel 2004). It was first found while astronomers were studying the longer period variable stars Cepheids and stood out because of its short period. In comparison to Cepheids, RR Lyraes are smaller and therefore fainter with a shorter period as well as being much older. -
Cepheid Variable Stars Cepheid Variable Stars As Distance Indicators
Cepheid Variable Stars Cepheid variable stars as distance indicators. Certain stars that have used up their main supply of hydrogen fuel are unstable and pulsate. RR Lyrae variables have periods of about a day. Their brightness doubles from dimest to brightest. Typical light curve for a Cepheid variable star. Cepheid variables have longer periods, from one day up to about 50 days. Their brightness also doubles from dimest to brightest. From the shape of the ``light curve'' of a Cepheid variable star, one can tell that it is a Cepheid variable. The period is simple to measure, as is the apparent brightness at maximum brightness. Cepheids as distance indicators Cepheids are important beyond their intrinsic interest as pulsating stars. Astronomomers have found that their is a relation between the period of a Cepheid and its luminosity. http://zebu.uoregon.edu/~soper/MilkyWay/cepheid.html (1 of 3) [5/25/1999 10:34:08 AM] Cepheid Variable Stars This enables astronomers to determine distances: ● Find the period. ● This gives the luminosity. ● Measure the apparent brightness. ● Determine the distance from the luminosity and brightness. The same applies to RR Lyrae variable stars. Once you know that a star is an RR Lyrae variable (eg. from the shape of its light curve), then you know its luminosity. Where did this period-luminosity relation come from? ● American astronomer Henrietta Leavitt looked at many Cepheid variables in the Small Magellanic Cloud (a satellite galaxy to ours.) ● She found the period luminosity relation (reported in 1912). ● One needs a distance measurement from some other method for at least one Cepheid. -
A Comprehensive Study of Cepheid Variables in the Andromeda Galaxy Period Distribution, Blending, and Distance Determination
A&A 473, 847–855 (2007) Astronomy DOI: 10.1051/0004-6361:20077960 & c ESO 2007 Astrophysics A comprehensive study of Cepheid variables in the Andromeda galaxy Period distribution, blending, and distance determination F. Vilardell1,C.Jordi1,3, and I. Ribas2,3 1 Departament d’Astronomia i Meteorologia, Universitat de Barcelona, c/ Martí i Franquès, 1, 08028 Barcelona, Spain e-mail: [francesc.vilardell;carme.jordi]@am.ub.es 2 Institut de Ciències de l’Espai-CSIC, Campus UAB, Facultat de Ciències, Torre C5-parell-2a, 08193 Bellaterra, Spain e-mail: [email protected] 3 Institut d’Estudis Espacials de Catalunya (IEEC), Edif. Nexus, c/ Gran Capità, 2-4, 08034 Barcelona, Spain Received 28 May 2007 / Accepted 18 July 2007 ABSTRACT Extragalactic Cepheids are the basic rungs of the cosmic distance scale. They are excellent standard candles, although their lumi- nosities and corresponding distance estimates can be affected by the particular properties of the host galaxy. Therefore, the accurate analysis of the Cepheid population in other galaxies, and notably in the Andromeda galaxy (M 31), is crucial to obtaining reliable distance determinations. We obtained accurate photometry (in B and V passbands) of 416 Cepheids in M 31 over a five year campaign within a survey aimed at the detection of eclipsing binaries. The resulting Cepheid sample is the most complete in M 31 and has almost the same period distribution as the David Dunlap Observatory sample in the Milky Way. The large number of epochs (∼250 per filter) has permitted the characterisation of the pulsation modes of 356 Cepheids, with 281 of them pulsating in the fundamental mode and 75 in the first overtone. -
Appendix: Spectroscopy of Variable Stars
Appendix: Spectroscopy of Variable Stars As amateur astronomers gain ever-increasing access to professional tools, the science of spectroscopy of variable stars is now within reach of the experienced variable star observer. In this section we shall examine the basic tools used to perform spectroscopy and how to use the data collected in ways that augment our understanding of variable stars. Naturally, this section cannot cover every aspect of this vast subject, and we will concentrate just on the basics of this field so that the observer can come to grips with it. It will be noticed by experienced observers that variable stars often alter their spectral characteristics as they vary in light output. Cepheid variable stars can change from G types to F types during their periods of oscillation, and young variables can change from A to B types or vice versa. Spec troscopy enables observers to monitor these changes if their instrumentation is sensitive enough. However, this is not an easy field of study. It requires patience and dedication and access to resources that most amateurs do not possess. Nevertheless, it is an emerging field, and should the reader wish to get involved with this type of observation know that there are some excellent guides to variable star spectroscopy via the BAA and the AAVSO. Some of the workshops run by Robin Leadbeater of the BAA Variable Star section and others such as Christian Buil are a very good introduction to the field. © Springer Nature Switzerland AG 2018 M. Griffiths, Observer’s Guide to Variable Stars, The Patrick Moore 291 Practical Astronomy Series, https://doi.org/10.1007/978-3-030-00904-5 292 Appendix: Spectroscopy of Variable Stars Spectra, Spectroscopes and Image Acquisition What are spectra, and how are they observed? The spectra we see from stars is the result of the complete output in visible light of the star (in simple terms). -
Magisterarbeit
MAGISTERARBEIT Titel der Magisterarbeit BINARY AGB STARS OBSERVED WITH HERSCHEL Verfasser Klaus Kornfeld, Bakk.rer.nat. angestrebter akademischer Grad Magister der Naturwissenschaften (Mag.rer.nat.) Wien, 2012 Studienkennzahl lt. Studienblatt: A 066 861 Studienrichtung lt. Studienblatt: Astronomie Betreuer: Ao. Univ.-Prof. Mag. Dr. Franz Kerschbaum 2 Every atom in your body came from a star that ex- ploded. And the atoms in your left hand probably came from a different star than your right hand. It really is the most poetic thing I know about physics: You are all stardust. You couldn't be here if stars hadn't exploded, because the elements - the carbon, nitrogen, oxygen, iron, all the things that matter for evolution - weren't created at the beginning of time. They were created in the nuclear furnaces of stars, and the only way they could get into your body is if those stars were kind enough to explode. So, forget Jesus. The stars died so that you could be here today. - Lawrence Krauss 3 4 Contents Kurzbeschreibung/Abstract9 Danksagung/Acknowledgement 13 1 Introduction 17 1.1 The Herschel Space Observatory....................... 17 1.1.1 The satellite.............................. 18 1.1.2 On-board instrumentation...................... 18 1.1.3 The Herschel Interactive Processing Environment......... 21 1.1.4 The Herschel Key Program MESS.................. 22 1.2 The Asymptotic Giant Branch........................ 23 1.2.1 AGB stars............................... 25 1.3 The atmosphere and outer CSE....................... 29 1.3.1 Observational properties....................... 30 1.3.2 Mass loss............................... 32 1.3.3 Geometry of the CSE......................... 33 1.4 Outflow morphology............................ -
Variable Star
Variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) fluctuates. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either: Intrinsic variables, whose luminosity actually changes; for example, because the star periodically swells and shrinks. Extrinsic variables, whose apparent changes in brightness are due to changes in the amount of their light that can reach Earth; for example, because the star has an orbiting companion that sometimes Trifid Nebula contains Cepheid variable stars eclipses it. Many, possibly most, stars have at least some variation in luminosity: the energy output of our Sun, for example, varies by about 0.1% over an 11-year solar cycle.[1] Contents Discovery Detecting variability Variable star observations Interpretation of observations Nomenclature Classification Intrinsic variable stars Pulsating variable stars Eruptive variable stars Cataclysmic or explosive variable stars Extrinsic variable stars Rotating variable stars Eclipsing binaries Planetary transits See also References External links Discovery An ancient Egyptian calendar of lucky and unlucky days composed some 3,200 years ago may be the oldest preserved historical document of the discovery of a variable star, the eclipsing binary Algol.[2][3][4] Of the modern astronomers, the first variable star was identified in 1638 when Johannes Holwarda noticed that Omicron Ceti (later named Mira) pulsated in a cycle taking 11 months; the star had previously been described as a nova by David Fabricius in 1596. This discovery, combined with supernovae observed in 1572 and 1604, proved that the starry sky was not eternally invariable as Aristotle and other ancient philosophers had taught.