Applying HR Diagrams: Spectroscopic Parallax & Stellar Sizes Version: 1.0 Author: Sean S
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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. -
• Classifying Stars: HR Diagram • Luminosity, Radius, and Temperature • “Vogt-Russell” Theorem • Main Sequence • Evolution on the HR Diagram
Stars • Classifying stars: HR diagram • Luminosity, radius, and temperature • “Vogt-Russell” theorem • Main sequence • Evolution on the HR diagram Classifying stars • We now have two properties of stars that we can measure: – Luminosity – Color/surface temperature • Using these two characteristics has proved extraordinarily effective in understanding the properties of stars – the Hertzsprung- Russell (HR) diagram If we plot lots of stars on the HR diagram, they fall into groups These groups indicate types of stars, or stages in the evolution of stars Luminosity classes • Class Ia,b : Supergiant • Class II: Bright giant • Class III: Giant • Class IV: Sub-giant • Class V: Dwarf The Sun is a G2 V star Luminosity versus radius and temperature A B R = R R = 2 RSun Sun T = T T = TSun Sun Which star is more luminous? Luminosity versus radius and temperature A B R = R R = 2 RSun Sun T = T T = TSun Sun • Each cm2 of each surface emits the same amount of radiation. • The larger stars emits more radiation because it has a larger surface. It emits 4 times as much radiation. Luminosity versus radius and temperature A1 B R = RSun R = RSun T = TSun T = 2TSun Which star is more luminous? The hotter star is more luminous. Luminosity varies as T4 (Stefan-Boltzmann Law) Luminosity Law 2 4 LA = RATA 2 4 LB RBTB 1 2 If star A is 2 times as hot as star B, and the same radius, then it will be 24 = 16 times as luminous. From a star's luminosity and temperature, we can calculate the radius. -
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. -
ASTR 545 Module 2 HR Diagram 08.1.1 Spectral Classes: (A) Write out the Spectral Classes from Hottest to Coolest Stars. Broadly
ASTR 545 Module 2 HR Diagram 08.1.1 Spectral Classes: (a) Write out the spectral classes from hottest to coolest stars. Broadly speaking, what are the primary spectral features that define each class? (b) What four macroscopic properties in a stellar atmosphere predominantly govern the relative strengths of features? (c) Briefly provide a qualitative description of the physical interdependence of these quantities (hint, don’t forget about free electrons from ionized atoms). 08.1.3 Luminosity Classes: (a) For an A star, write the spectral+luminosity class for supergiant, bright giant, giant, subgiant, and main sequence star. From the HR diagram, obtain approximate luminosities for each of these A stars. (b) Compute the radius and surface gravity, log g, of each luminosity class assuming M = 3M⊙. (c) Qualitative describe how the Balmer hydrogen lines change in strength and shape with luminosity class in these A stars as a function of surface gravity. 10.1.2 Spectral Classes and Luminosity Classes: (a,b,c,d) (a) What is the single most important physical macroscopic parameter that defines the Spectral Class of a star? Write out the common Spectral Classes of stars in order of increasing value of this parameter. For one of your Spectral Classes, include the subclass (0-9). (b) Broadly speaking, what are the primary spectral features that define each Spectral Class (you are encouraged to make a small table). How/Why (physically) do each of these depend (change with) the primary macroscopic physical parameter? (c) For an A type star, write the Spectral + Luminosity Class notation for supergiant, bright giant, giant, subgiant, main sequence star, and White Dwarf. -
Ptrsa, 365, 1307, 2007
Phil. Trans. R. Soc. A (2007) 365, 1307–1313 doi:10.1098/rsta.2006.1998 Published online 9 February 2007 Giant flares in soft g-ray repeaters and short GRBs BY S. ZANE* Mullard Space Science Laboratory, University College of London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK Soft gamma-ray repeaters (SGRs) are a peculiar family of bursting neutron stars that, occasionally, have been observed to emit extremely energetic giant flares (GFs), with energy release up to approximately 1047 erg sK1. These are exceptional and rare events. It has been recently proposed that GFs, if emitted by extragalactic SGRs, may appear at Earth as short gamma-ray bursts. Here, I will discuss the properties of the GFs observed in SGRs, with particular emphasis on the spectacular event registered from SGR 1806-20 in December 2004. I will review the current scenario for the production of the flare, within the magnetar model, and the observational implications. Keywords: soft gamma-ray repeaters; short gamma-ray bursts; stars: neutron 1. Introduction Soft gamma-ray repeaters (SGRs) are a small group (four known sources and one candidate) of neutron stars (NSs) discovered as bursting gamma-ray sources. During the quiescent state (i.e. outside bursts events), these sources are detected as persistent emitters in the soft X-ray range (less than 10 keV), with a luminosity of approximately 1035 erg sK1 and with a typical blackbody plus power law spectrum. Their NS nature is probed by the detection of periodic X-ray pulsations at a few seconds in three cases. Very recently, a hard and pulsed emission (20–100 keV) has been discovered in two sources (Mereghetti et al. -
The Maunder Minimum and the Variable Sun-Earth Connection
The Maunder Minimum and the Variable Sun-Earth Connection (Front illustration: the Sun without spots, July 27, 1954) By Willie Wei-Hock Soon and Steven H. Yaskell To Soon Gim-Chuan, Chua Chiew-See, Pham Than (Lien+Van’s mother) and Ulla and Anna In Memory of Miriam Fuchs (baba Gil’s mother)---W.H.S. In Memory of Andrew Hoff---S.H.Y. To interrupt His Yellow Plan The Sun does not allow Caprices of the Atmosphere – And even when the Snow Heaves Balls of Specks, like Vicious Boy Directly in His Eye – Does not so much as turn His Head Busy with Majesty – ‘Tis His to stimulate the Earth And magnetize the Sea - And bind Astronomy, in place, Yet Any passing by Would deem Ourselves – the busier As the Minutest Bee That rides – emits a Thunder – A Bomb – to justify Emily Dickinson (poem 224. c. 1862) Since people are by nature poorly equipped to register any but short-term changes, it is not surprising that we fail to notice slower changes in either climate or the sun. John A. Eddy, The New Solar Physics (1977-78) Foreword By E. N. Parker In this time of global warming we are impelled by both the anticipated dire consequences and by scientific curiosity to investigate the factors that drive the climate. Climate has fluctuated strongly and abruptly in the past, with ice ages and interglacial warming as the long term extremes. Historical research in the last decades has shown short term climatic transients to be a frequent occurrence, often imposing disastrous hardship on the afflicted human populations. -
Lithium Abundances in Fast Rotating Bright Giant Stars
Stellar Rotation Proceedings [AU Symposium No. 215, © 2003 [AU Andre Maeder & Philippe Eenens, eds. Lithium Abundances in Fast Rotating Bright Giant Stars J.D.Jr do NascimentoI, A. Lebre", R. Konstantinova-Antova' and J. R. De Medeiros! I-Departamento de Fisico Teorica e Experimental, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, R.N., Brazil; 2-GRAAL, UMR 5024 ISTEEM/CNRS, CC 072, Uniuersiie Montpellier II, F-34095 Montpellier Cedex, France; 3 Institute of Astronomy, 72 Tsarigradsko shose, BG-1784 Sofia, Bulgaria Abstract. We present the results of high resolution spectroscopic observations of Li I resonance doublet at A6707.8 A for fast rotating single stars of luminosity class II and lb. We present a discussion on the link between rotation and Li content in intermediate mass giant stars, with emphasis on their evolutionary status. At least one of the observed stars, HD 232862, a G8I1 with an unusual vsini of 20 km/s, present a Li-rich behavior. 1. The Problem and Observations This work brings the first results of a large observational campaign to deter- mine Li, rotation and CNO abundances for a sample of single bright giants and Ib supergiants, along the spectral region F, G and K. Measurements of Li and CNO surface content of evolved stars is of paramount importance to test quan- titative and qualitative theoretical predictions of the effects of nucleosynthesis and subsequent mixing events on the stellar surface abundances. A survey of bright giants and Ib supergiants along the spectral region F, G and K, has been carried out to study the possible link between the rotational be- havior and CNO abundances (do Nascimento & De Medeiros 2003). -
Arxiv:1703.10181V1 [Astro-Ph.SR] 29 Mar 2017 Ordo H G.W Alteesas“E Stragglers” “Red Stars These Call We Similar Found RGB
Draft version October 15, 2018 Preprint typeset using LATEX style emulateapj v. 01/23/15 ON THE ORIGIN OF SUB-SUBGIANT STARS II: BINARY MASS TRANSFER, ENVELOPE STRIPPING, AND MAGNETIC ACTIVITY Emily Leiner1, Robert D. Mathieu1, and Aaron M. Geller2,3 Draft version October 15, 2018 ABSTRACT Sub-subgiant stars (SSGs) lie to the red of the main-sequence and fainter than the red giant branch in cluster color-magnitude diagrams (CMDs), a region not easily populated by standard stellar evo- lution pathways. While there has been speculation on what mechanisms may create these unusual stars, no well-developed theory exists to explain their origins. Here we discuss three hypotheses of SSG formation: (1) mass transfer in a binary system, (2) stripping of a subgiant’s envelope, perhaps during a dynamical encounter, and (3) reduced luminosity due to magnetic fields that lower convective efficiency and produce large star spots. Using the stellar evolution code MESA, we develop evolu- tionary tracks for each of these hypotheses, and compare the expected stellar and orbital properties of these models with six known SSGs in the two open clusters M67 and NGC 6791. All three of these mechanisms can create stars or binary systems in the SSG CMD domain. We also calculate the frequency with which each of these mechanisms may create SSG systems, and find that the magnetic field hypothesis is expected to create SSGs with the highest frequency in open clusters. Mass transfer and envelope stripping have lower expected formation frequencies, but may nevertheless create occa- sional SSGs in open clusters. They may also be important mechanisms to create SSGs in higher mass globular clusters. -