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Northeastern Illinois University Surveying Stars Greg Anderson Department of Physics & Astronomy Northeastern Illinois University Fall 2018 c 2012-2018G. Anderson Universe: Past, Present & Future – slide 1 / 102 Northeastern Illinois Overview University The Night Sky Luminosity & Brightness Distance & Parallax Stellar Temperatures HR Diagrams Binary Systems Stellar Masses Star Clusters Review c 2012-2018G. Anderson Universe: Past, Present & Future – slide 2 / 102 Northeastern Illinois University The Night Sky Cassiopeia Stars in the Night Sky Star Trails Lower Canyons Luminosity & Brightness Distance & Parallax Stellar The Night Sky Temperatures HR Diagrams Binary Systems Stellar Masses Star Clusters Review c 2012-2018G. Anderson Universe: Past, Present & Future – slide 3 / 102 c T. Credner & S. Kohle, AlltheSky.com Northeastern Illinois Stars in the Night Sky University • Outside of the city, on very clear nights you can see thousands of stars. • Of the 25 brightest stars, the furthest away is Deneb (≈ 800 pc). • Under the best conditions the furthest star we can see with the naked eye is a few thousand light years away. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 5 / 102 G. Anderson: Star Trails in the Lower Canyons Northeastern Illinois University The Night Sky Luminosity & Brightness Luminosity Q: L Units Stellar L η Carinae Blackbody Rad. Relative L Luminosity & Q: Star L Motorcycle Q: b vs L b vs. d Brightness App Brightness Bulbs Q: L vs r Q: Units for b Magnitude Sys Apparent Magnitude m chart Bright Stars Q: Visible limit Stars vs. Limiting Magnitude Darks Sky Abs Mag (M) Q: c Vega2012-2018G. Anderson Universe: Past, Present & Future – slide 7 / 102 Distance & Northeastern Illinois Luminosity University Luminosity: The total amount of power (energy per unit time) emitted by a star or other object. Units: watts. • A 100-watt light-bulb emits half the power of a 200-watt light-bulb. It is half as bright. • The Sun has a luminosity of 26 L⊙ ≈ 4 × 10 watts 26 L⊙ ≈ 4 × 10 watts Lbulb = 100watts c 2012-2018G. Anderson Universe: Past, Present & Future – slide 8 / 102 Northeastern Illinois Q: Luminosity Units University What are the standard units for luminosity? A) Watts B) Joules C) Newtons D) kilograms E) Watts per second c 2012-2018G. Anderson Universe: Past, Present & Future – slide 9 / 102 Northeastern Illinois Q: Luminosity Units University What are the standard units for luminosity? A) Watts B) Joules C) Newtons D) kilograms E) Watts per second c 2012-2018G. Anderson Universe: Past, Present & Future – slide 9 / 102 Northeastern Illinois Stellar Luminosities University Solar Luminosity: 26 L⊙ ≈ 4 × 10 watts Eddington Limit: Upper limit for stellar luminosity. Above this, radiation pressure exceeds gravity. 6 L . 10 L⊙ Least luminous stars: −4 L ≈ 10 L⊙ Dim stars are much more common than bright stars. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 10 / 102 Northeastern Illinois η Carinae University Eta Carinae (η Car): Binary system less than 3 million years old, located in the Homuncu- lus Nebula in Carinae. One of the most massive stars studied in great detail. M = 150M⊙ −→ 120M⊙ 6 L ≈ 10 L⊙ R ≈ 24R⊙ c 2012-2018G. Anderson Universe: Past, Present & Future – slide 11 / 102 Northeastern Illinois Blackbody Radiation University Blackbody radiation: thermal radiation emitted by opaque bodies. (perfect absorbers) Stefan-Boltzmann law for Luminosity: 4 L = σAT Stefan-Boltzmann constant σ =5.67 × 10−8 W/m2 · K4 T = Temperature A = Area c 2012-2018G. Anderson Universe: Past, Present & Future – slide 12 / 102 Northeastern Illinois Relative Luminosity University Stefan-Boltzmann Law: radiated power L = = σT 4 area A eff Stefan-Boltzmann constant: σ =5.67 × 10−8 W/m2 · K4 Relative luminosity for stars with radius R and temperature T L R 2 T 4 star = star star Lsun Rsun Tsun c 2012-2018G. Anderson Universe: Past, Present & Future – slide 13 / 102 Northeastern Illinois Q: Star Luminosity University The luminosity of a star is the: A) apparent brightness of the star in our sky. B) surface temperature of the star. C) lifetime of the star. D) total amount of energy that the star will radiate over its entire lifetime. E) total amount of energy that the star radiates each second. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 14 / 102 Northeastern Illinois Q: Star Luminosity University The luminosity of a star is the: A) apparent brightness of the star in our sky. B) surface temperature of the star. C) lifetime of the star. D) total amount of energy that the star will radiate over its entire lifetime. E) total amount of energy that the star radiates each second. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 14 / 102 b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b
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  • Cosmic Distances

    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.
  • Arxiv:2009.02409V1

    Arxiv:2009.02409V1

    Draft version September 8, 2020 Typeset using LATEX preprint style in AASTeX63 Spectroscopic Detection of the Pre-White Dwarf Companion of Regulus Douglas R. Gies,1 Kathryn V. Lester,1 Luqian Wang,1 Andrew Couperus,1 Katherine Shepard,1 Coralie Neiner,2 Gregg A. Wade,3 David W. Dunham,4 and Joan B. Dunham4 1Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P. O. Box 5060, Atlanta, GA 30302-5060, USA 2LESIA, Observatoire de Paris, PSL University, CNRS, Sorbonne Universit´e, Univ. Paris Diderot, Sorbonne Paris Cit´e, 5 place Jules Janssen, F-92195 Meudon, France 3 Department of Physics and Space Science, Royal Military College of Canada, P.O. Box 17000 Station Forces, Kingston, ON K7K 0C6, Canada 4IOTA, 7913 Kara Court, Greenbelt, MD 20770, USA ABSTRACT Mass transfer in an interacting binary will often strip the mass donor of its entire envelope and spin up the mass gainer to near critical rotation. The nearby B-type star Regulus represents a binary in the post-mass transfer stage: it is a rapid rotator with a very faint companion in a 40 d orbit. Here we present the results of a search for the spectral features of the stripped-down star in an extensive set of high S/N and high resolution spectra obtained with the CFHT/ESPaDOnS and TBL/NARVAL spectrographs. We first determine revised orbital elements in order to set accurate estimates of the orbital Doppler shifts at the times of observation. We then calculate cross-correlation functions of the observed and model spectra, and we search for evidence of the companion signal in the residuals after removal of the strong primary component.
  • Diameter and Photospheric Structures of Canopus from AMBER/VLTI Interferometry�,

    Diameter and Photospheric Structures of Canopus from AMBER/VLTI Interferometry,

    A&A 489, L5–L8 (2008) Astronomy DOI: 10.1051/0004-6361:200810450 & c ESO 2008 Astrophysics Letter to the Editor Diameter and photospheric structures of Canopus from AMBER/VLTI interferometry, A. Domiciano de Souza1, P. Bendjoya1,F.Vakili1, F. Millour2, and R. G. Petrov1 1 Lab. H. Fizeau, CNRS UMR 6525, Univ. de Nice-Sophia Antipolis, Obs. de la Côte d’Azur, Parc Valrose, 06108 Nice, France e-mail: [email protected] 2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany Received 23 June 2008 / Accepted 25 July 2008 ABSTRACT Context. Direct measurements of fundamental parameters and photospheric structures of post-main-sequence intermediate-mass stars are required for a deeper understanding of their evolution. Aims. Based on near-IR long-baseline interferometry we aim to resolve the stellar surface of the F0 supergiant star Canopus, and to precisely measure its angular diameter and related physical parameters. Methods. We used the AMBER/VLTI instrument to record interferometric data on Canopus: visibilities and closure phases in the H and K bands with a spectral resolution of 35. The available baselines (60−110 m) and the high quality of the AMBER/VLTI observations allowed us to measure fringe visibilities as far as in the third visibility lobe. Results. We determined an angular diameter of / = 6.93 ± 0.15 mas by adopting a linearly limb-darkened disk model. From this angular diameter and Hipparcos distance we derived a stellar radius R = 71.4 ± 4.0 R. Depending on bolometric fluxes existing in the literature, the measured / provides two estimates of the effective temperature: Teff = 7284 ± 107 K and Teff = 7582 ± 252 K.