archive-ca.com » CA » Q » QUEENSU.CA

Total: 401

Choose link from "Titles, links and description words view":

Or switch to "Titles and links view".
  • QUARG - Stéphane Courteau - Research
    puzzles in extragalactic astronomy My research also involves assembling extensive data bases for structural parameters of nearby galaxies and applying devising numerical methods for their analysis Through observing programs that I lead or via collaborations my students have access to some of the best observational research facilities worldwide Research Opportunities I am always keen to add more driven and talented students to my research group Feel free to contact me by email courteau astro queensu ca if my research is of interest to you I welcome applications from students interested in exploring topics in Galactic and Extragalactic Astronomy at the MSc or PhD levels Research topics range from stellar populations in globular clusters and nearby galaxies to the dynamical modelling of galaxies and the distribution of dark matter in the universe and involve a mix of observational projects data modeling numerical analysis and simulations My students travel all over the world to present their research at conferences and workshops or to attend winter summer schools or for astronomical observations I typically supervise highly motivated students and care very much about their future career I am proud that all my former graduate students are employed in astronomy Students are encouraged to

    Original URL path: http://www.astro.queensu.ca/people/Stephane_Courteau/research.php?pf=yes&pf=yes&pf=yes (2016-02-13)
    Open archived version from archive


  • QUARG - Stéphane Courteau - Teaching
    Current and Past Students Selected Publications Gallery Personal Links Home General Information Meet the people Seminars Journals Club Queen s Observatory Astro Links Back to Department Back to QUARG People Stéphane Courteau Teaching Fall 2015 PHYS 814 Graduate Extragalactic Astronomy Winter 2016 PHYS 216 Undergraduate Introduction to Astrophysics RMC PHYS 593 Astronomical Instrumentation co taught by David Hanes Kristine Spekkens Gregg Wade and myself 2007 Department of Physics Engineering Physics

    Original URL path: http://www.astro.queensu.ca/people/Stephane_Courteau/teaching.php?pf=yes&pf=yes&pf=yes (2016-02-13)
    Open archived version from archive

  • Untitled
    Coordinate Systems

    Original URL path: http://www.astro.queensu.ca/~courteau/Phys216/201review.html (2016-02-13)
    Open archived version from archive



  • Untitled
    eg Johnson Cousins UBVRI system Common visual filter system IR extensions JHKLMN Filter Characteristics Band eff nm FWHM nm Visual U B V R I 365 445 551 658 806 66 94 88 138 149 IR J H K L M 1220 1630 2190 3450 4750 213 307 390 472 460 Data published in Binney and Merrifield 1998 Galactic Astronomy Princeton University Press 53 How are photometric systems defined Constant relates magnitude scale with flux calibration Traditionally we use the star Vega bright A0 star to define systems m 0 for all filters ie V Vega 0 B Vega R Vega V Sun 26 74 V Sirius 1 45 Absolute magnitude M Define as m at a distance d 10 parsecs 1 pc 3 09 times 10 18 cm 3 26 ly m 1 M 2 2 5 log F 1 F 2 m M 10 2 5 log 10pc d 2 note F 1 d 2 Distance modulus m M 5 log d 5 very often used Similarly F L thus M bol 1 M bol 2 2 5 log L 1 L 2 Bolometric magnitude M bol flux from all energy emitted by object Typically define terms in a particular eg in V Often use M V as a measure of Luminosity of object To convert to observed quantities use bolometric correction BC BC bol M bol M NOTE often quote L of an object based on M V any potential problems Colour indices Not just interested in brightness luminosity but also colour The colour index is a crude look at spectral energy distribution SED This is related to the physical mechanism responsible for the radiation In the case of stars this is generally thermal or blackbody radiation and is controlled almost entirely by the surface temperature of the star Colour index magnitude difference or flux ratio in different bandpasses eg B V 2 5 log F B F V C B C V C B and C V are constants of calibration If F B F V then blue light dominates over yellow and the object looks blue also B V is small even negative eg consider SED of hot blue star Note lack of sensitivity at large small T Back to distance modulus In reality measured m M is dependant eg m M V V M V in V band Why Flux can be attenuated by dust interstellar extinction m M 5 log d 5 A A extinction at strong dependence Thus m M o m M A m M o TRUE distance modulus 5 log d 5 m M observed distance modulus A can be very important Dust grains effectively absorb scatter small larger less affected Cardelli et al 1989 ApJ 345 245 NOTE R I are in a different system slightly than commonly used IR less extinction UV much extinction DUST makes objects REDDER and FAINTER As extinction varies with so will the colours of objects colours ratio of flux from different filters Reddening

    Original URL path: http://www.astro.queensu.ca/~courteau/Phys216/intro.html (2016-02-13)
    Open archived version from archive

  • Untitled
    Shapley Curtis Debate April 20 1920 NAS Washington Debate on the state of the universe More info Harlow Shapley Mt Wilson Observatory Galactic interpretations Large model of the Milky Way Sun far from centre Spiral nebulae likely gas clouds within MW Galaxy too big for them to be external Nebulae too small to be galaxies eg rotation of M101 Nebulae disrupted by Galaxy zone of avoidance Used Cepheids to get distances to globulars large Galaxy Heber Curtis 1872 1932 Lick Observatory Extragalactic interpretations Small eg Kapteyn MW Sun near centre Spiral nebulae seperate entities ie island universes outside the MW Sizes similar to MW also Not fond of Cepheids as distance indicators Who was right discussion Summary of the Debate What are the distances to the spirals Shapley small distance Von Maanen s measurements of proper motion of rotation in M101 0 02 yr M101 must be small or v rot high Brightness of S Andromedae a supernova thought to be an ordinary nova in M31 compared to Nova Persei Curtis large distance Proper motion measurements may be in error Brightness of nova outbursts in M31 compared to those in Milky Way Are spirals composed of stars or gas Shapley not stars Milky Way in neighbourhood of Sun has much less surface brightness than central parts of most spirals Outer regions of spirals are bluer than their central portions Why do spirals avoid the plane of the Milky Way Shapley MW not an island universe Avoidance suggests influence as do large velocities of recession Both could be explained by postulating a new force of repulsion ejecting nebulae from the zone Nebulae have been observed with high redshifts also Curtis MW is an island universe Many edge on spirals exhibit central belt of obscuring material around them eg NGC 4565 If

    Original URL path: http://www.astro.queensu.ca/~courteau/Phys216/hist.html (2016-02-13)
    Open archived version from archive

  • Untitled
    f fraction in the core f 0 1 Rate of consumption L the Luminosity Therefore For the Sun L 4 10 26 W m 2 10 30 kg X 0 75 f 0 1 7 10 3 c 2 3 10 8 m s 2 Thus 8 10 9 yr 10 10 yr 10 Gyr For any star Observationally Thus For example if m m 10 then 10 7 yr

    Original URL path: http://www.astro.queensu.ca/~courteau/Phys216/stellarev.html (2016-02-13)
    Open archived version from archive

  • Untitled
    stars and star clusters are found in dusty regions Dust and gas is confined to a very thin layer in the Galaxy The scale height z t 160 pc Simple model uniform slab with density n particles cm 3 Look at the propagation of radiation in this slab see theory of radiative transfer in ch 9 of Carroll Ostlie I intensity k L 1 absorption coefficient where l is the mean free path of the radiation n is the density and is the cross section to absorption scattering of radiation at optical wavelengths volume emissivity at visible wavelengths the emissivity of the dust 0 Thus Integrate from the source through the medium Therefore The observed flux from the source is obtained by integrating the intensity over the solid angle subtended by the source Convert to magnitudes Empirically we write Note Extinction and the Distance Modulus V M V m M V V o A V M V V o M V A V m M o A V m M V m M o A V The apparent distance modulus m M V is always larger than or equal to the true distance modulus m M o So stars in the MW appear to be farther away than they really are The true distance modulus is the same at all bands m M o 5 log d 5 Extinction and Colour For Johnson photometric bands A A reddening function or curve extinction function or curve The SHAPE of the reddening curve can be fairly easily determined by comparing the spectrum of a reddened star say f with that of an unreddened star of the same spectral type say f o The constant C depends on the distance ratio between the pair of stars This constant can be determined by requiring A 0 as in practice 2 2 m Traditionally the zero point of the reddening curve is set by specifying Two methods to get R V single stars reddened of known spectral type the true colours are known Plot Example Extinction curves for 3 stars Cardelli et al 1989 ApJ 345 245 The same graph extended to smaller wavelengths Gordan Clayton 1998 ApJ 500 816 Extinction curves for the SMC LMC and MW R V 3 1 typical common value but variable ie can be quite different along some lines of sight This also allows one to determine the reddening curve from photometry Drawback need IR photometry in order to properly normalize the curve R V directly from observations of open Galactic star clusters For each star i 1 2 n E B V i B V photometry which gives the apparent color and spectral type which gives the true color and requires spectroscopy alternatively more common U B V photometry 3 colour photometry 2 colours U B B V colours From reddening curve Colour Colour diagram Extinction in mag optical depth of the dust What is Q g where Q is the efficiency factor Mie theory and g is

    Original URL path: http://www.astro.queensu.ca/~courteau/Phys216/ism.html (2016-02-13)
    Open archived version from archive

  • Untitled
    3 10 8 M Diameter 28 kpc Distance 1 Mpc no direct way to measure distances Blitz et al 1999 ApJ 514 818 Few thousand detected in emission absorption against distant extragalactic radio sources difficult No detection of molecular material eg CO HVCs associated with Magellanic Stream Matthewson et al 1974 tidal debris from interaction with LMC Magellanic Stream and C complex contiguous structures covering thousands of square degrees on the sky Most HVCs few square degrees on the sky Individual clouds separated by several tens of degrees often separated in velocity by hundreds of km s Except for Magellanic Stream largest cloud complexes lie at positive latitudes eg A C M complexes Some images Distance measurements difficult Complex A M 5 kpc Low dust gas ratios 3 below normal Galactic clouds if temperature similar to interstellar clouds Typical internal velocity v 13 km s Galactic Fountain Model Bregman 1980 Material ejected from Supernovae HI gas driven to large values of z Clouds cool and rain back down on Galactic plane Pros HI supershells have been detected Explain predominance of negative velocity HVCs at high latitudes Cons Cannot explain substantial assymetries in the overall distribution of HVCs Cannot explain vertical

    Original URL path: http://www.astro.queensu.ca/~courteau/Phys216/hvc.html (2016-02-13)
    Open archived version from archive