DOCSLIB.ORG

1 Globular Cluster Systems

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
1 Globular Cluster Systems Globular Cluster Systems William E Harris Department of Physics Astronomy McMaster University Hamilton ON LS M Canada Abstract The basic features of the globular cluster system of the Milky Way are summarized the total p opulation sub division of the clusters into the classic metalp o or and metalrich comp onents and rst ideas on formation mo dels The distance to the Galactic center is derived from the spatial distribution of the inner bulge clusters giving R kp c 0 The calibration of the fundamental distance scale for globular clusters is re viewed Dierent ways to estimate the zero p oint and metallicity dep endence of the RR Lyrae stars include statistical parallax and BaadeWesselink measurements of eld RR Lyraes astrometric parallaxes white dwarf cluster sequences and eld sub dwarfs and main sequence tting The results are compared with other distance measurements to the Large Magellanic Cloud and M Radial velo cities of the Milky Way clusters are used to derive the kinematics of various subsamples of the clusters the mean rotation sp eed ab out the Galactic center and the lineofsight velo city disp ersion The inner metalrich clusters b e have kinematically and spatially like a attened rotating bulge p opulation while the outer metalrich clusters resemble a thickdisk p opulation more closely The 1 metalp o or clusters have a signicant prograde rotation to km s in the R No identiable inner halo and bulge declining smo othly to nearzero for R 0 subgroups are found with signicant retrograde motion The radial velo cities of the globular clusters are used along with the spheri cally symmetric collisionless Boltzmann equation to derive the mass prole of the 11 Milky Way halo The total mass of the Galaxy is near M for r kp c Extensions to still larger radii with the same formalism are extremely uncertain b e cause of the small numb ers of outermost satellites and the p ossible correlations of their motions in orbital families The luminosity functions GCLF of the Milky Way and M globular clus ters are dened and analyzed We search for p ossible trends with cluster metallicity or radius and investigate dierent analytic tting functions such as the Gaussian and p owerlaw forms The global prop erties of GCSs in other galaxies are reviewed Measureable distributions include the total cluster p opulation quantied as the sp ecic fre quency S the metallicity distribution function MDF the luminosity and space N distributions and the radial velo city distribution W E Harris The GCLF is evaluated as a standard candle for distance determination For giant E galaxies the GCLF turnover has a mean luminosity of M on a V distance scale where Virgo has a distance mo dulus of and Fornax is at with galaxytogalaxy scatter M mag Applying this calibration to more V 1 1 remote galaxies yields a Hubble constant H km s Mp c 0 The observational constraints on globular cluster formation mo dels are sum 5 6 marized The appropriate host environments for the formation of M clusters are suggested to b e kiloparsecsized gas clouds SearleZinn fragments or 89 sup ergiant molecular clouds of M A mo del for the growth of proto cluster clouds by collisional agglomeration is presented and matched with observed mass distribution functions The issue of globular cluster formation eciency in dierent galaxies is discussed the sp ecic frequency problem Other inuences on galaxy formation are discussed including mergers accre tions and starbursts Mergers of disk galaxies almost certainly pro duce elliptical galaxies of low S while the highS ellipticals are more likely to have b een N N pro duced through in situ formation Starburst dwarfs and large active galaxies in which current globular cluster formation is taking place are compared with the key elements of the formation mo del App endix Some basic principles of photometric metho ds are gathered to gether and summarized the fundamental signaltonoise formula ob jective star nding ap erture photometry PSF tting articialstar testing detection com pleteness and photometric uncertainty Lastly we raise the essential issues in pho tometry of nonstellar ob jects including image moment analysis total magnitudes and ob ject classication techniques INTRODUCTION When the storm rages and the state is threatened by shipwreck we can do nothing more noble than to lower the anchor of our peaceful studies into the ground of eternity Johannes Kepler Why do we do astronomy It is a dicult frustrating and often p erverse business and one which is sometimes costly for so ciety to supp ort Moreover if we are genuinely serious ab out wanting to prob e Nature we might well employ ourselves b etter in other disciplines like physics chemistry or biology where at least we can exert exp erimental controls over the things we are studying and where progress is usually less ambiguous Kepler seems to have understo o d why It is often said that we pursue astronomy b ecause of our inb orn curiosity and the need to understand our place and origins True enough but there is something more Exploring the Globular Cluster Systems universe is a unique adventure of profound b eauty and exhilaration lifting us far b eyond our normal selfcentered concerns to a degree that no other eld can do quite as p owerfully Every human generation has found that the world b eyond the Earth is a vast and astonishing place In these chapters we will b e taking an allto obrief tour through just one small area of mo dern astronomy one which has ro ots extending back more than a century but which has reinvented itself again and again with the advance of b oth astrophysics and observational technology It is also one which draws intricate and sometimes surprising connections among stellar p opulations star formation the earliest history of the galaxies the distance scale and cosmology Fig Left panel Palomar a globular cluster ab out kiloparsecs from the Sun in the outer halo of the Milky Way The picture shown is an I band image taken with the CanadaFranceHawaii Telescop e see Harris et al c The eld size is arcmin or parsecs across and the image resolution seeing is arcsec Right panel A globular cluster in the halo of the giant elliptical galaxy NGC kiloparsecs from the Milky Way The picture shown is an I band image taken with the Hubble Space Telescop e see G Harris et al the eld size is arcmin or parsecs across and the resolution is arcsec This is the most distant globular cluster for which a colormagnitude diagram has b een obtained The sections to follow are organized in the same way as the lectures given at the SaasFee Advanced Course held in Les Diablerets Each one represents a well dened theme which could in principle stand on its own but all of them link together to build up an overview of what we currently know ab out globular cluster systems in galaxies It will I hop e b e true as in any active eld that much of the material will already b e sup erseded by newer insights by the time it is in print Wherever p ossible I have tried to preserve in the text the conversational style of the lectures in which lively W E Harris interchanges among the sp eakers and audience were p ossible The literature survey for this pap er carries up to the early part of A globular cluster system GCS is the collection of all globular star clus ters within one galaxy viewed as a subp opulation of that galaxys stars The essential questions addressed by each section of this review are in sequence What are the size and structure of the Milky Way globular cluster system and what are its denable subp opulations What should we use as the fundamental Population II distance scale What are the kinematical characteristics of the Milky Way GCS Do its subp opulations show traces of dierent formation ep o chs How can the velo city distribution of the clusters b e used to derive a mass prole for the Milky Way halo What is the luminosity mass distribution function for the Milky Way GCS Are there detectable trends with subp opulation or galacto centric distance What are the overall characteristics of GCSs in other galaxies total numb ers metallicity distributions correlations with parent galaxy typ e How can the luminosity distribution function GCLF b e used as a stan dard candle for estimation of the Hubble constant Do we have a basic understanding of how globular clusters formed within protogalaxies in the early universe How do we see globular cluster p opulations changing to day due to such phenomena as mergers tidal encounters and starbursts The study of globular cluster systems is a genuine hybrid sub ject mixing elements of star clusters stellar p opulations and the structure and history of all typ es of galaxies Over the past two decades it has grown rapidly along with the sp ectacular advances in imaging technology The rst review article in the sub ject Harris Racine sp ent its time almost entirely on the globular clusters in Lo cal Group galaxies and only briey discussed the little we knew ab out a few Virgo ellipticals Other reviews Harris ab b demonstrate the growth of the sub ject into one which can put a remarkable variety of constraints on issues in galaxy formation and evolution Students of this sub ject will also want to read the recent b o ok Globular Cluster Systems by Ashman Zepf which gives another comprehensive overview in a dierent style and with dierent em phases on certain topics I have kept abbreviations and acronyms in the text to a minimum Here is a list of the ones used frequently CMD colormagnitude diagram
Load more

Recommended publications
  • The Messenger
    10th anniversary of VLT First Light The Messenger The ground layer seeing on Paranal HAWK-I Science Verification The emission nebula around Antares No. 132 – June 2008 –June 132 No. The Organisation The Perfect Machine Tim de Zeeuw a ground­based spectroscopic comple­ thousand each semester, 800 of which (ESO Director General) ment to the Hubble Space Telescope. are for Paranal. The User Portal has Italy and Switzerland had joined ESO in about 4 000 registered users and 1981, enabling the construction of the the archive contains 74 TB of data and This issue of the Messenger marks the 3.5­m New Technology Telescope with advanced data products. tenth anniversary of first light of the Very pioneering advances in active optics, Large Telescope. It is an excellent occa­ crucial for the next step: the construction sion to look at the broader implications of the Very Large Telescope, which Winning strategy of the VLT’s success and to consider the received the green light from Council in next steps. 1987 and was built on Cerro Paranal in The VLT opened for business some five the Atacama desert between Antofagasta years after the Keck telescopes, but the and Taltal in Northern Chile. The 8.1­m decision to take the time to build a fully Mission Gemini telescopes and the 8.3­m Subaru integrated system, consisting of four telescope were constructed on a similar 8.2­m telescopes and providing a dozen ESO’s mission is to enable scientific dis­ time scale, while the Large Binocular Tele­ foci for a carefully thought­out comple­ coveries by constructing and operating scope and the Gran Telescopio Canarias ment of instruments together with four powerful observational facilities that are now starting operations.
    [Show full text]
  • THE 1000 BRIGHTEST HIPASS GALAXIES: H I PROPERTIES B
    The Astronomical Journal, 128:16–46, 2004 July A # 2004. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE 1000 BRIGHTEST HIPASS GALAXIES: H i PROPERTIES B. S. Koribalski,1 L. Staveley-Smith,1 V. A. Kilborn,1, 2 S. D. Ryder,3 R. C. Kraan-Korteweg,4 E. V. Ryan-Weber,1, 5 R. D. Ekers,1 H. Jerjen,6 P. A. Henning,7 M. E. Putman,8 M. A. Zwaan,5, 9 W. J. G. de Blok,1,10 M. R. Calabretta,1 M. J. Disney,10 R. F. Minchin,10 R. Bhathal,11 P. J. Boyce,10 M. J. Drinkwater,12 K. C. Freeman,6 B. K. Gibson,2 A. J. Green,13 R. F. Haynes,1 S. Juraszek,13 M. J. Kesteven,1 P. M. Knezek,14 S. Mader,1 M. Marquarding,1 M. Meyer,5 J. R. Mould,15 T. Oosterloo,16 J. O’Brien,1,6 R. M. Price,7 E. M. Sadler,13 A. Schro¨der,17 I. M. Stewart,17 F. Stootman,11 M. Waugh,1, 5 B. E. Warren,1, 6 R. L. Webster,5 and A. E. Wright1 Received 2002 October 30; accepted 2004 April 7 ABSTRACT We present the HIPASS Bright Galaxy Catalog (BGC), which contains the 1000 H i brightest galaxies in the southern sky as obtained from the H i Parkes All-Sky Survey (HIPASS). The selection of the brightest sources is basedontheirHi peak flux density (Speak k116 mJy) as measured from the spatially integrated HIPASS spectrum. 7 ; 10 The derived H i masses range from 10 to 4 10 M .
    [Show full text]
  • Giant H II Regions in the Merging System NGC 3256: Are They the Birthplaces of Globular Clusters?
    CORE Metadata, citation and similar papers at core.ac.uk Provided by CERN Document Server Paper I: To be submitted to A.J. Giant H II regions in the merging system NGC 3256: Are they the birthplaces of globular clusters? J. English University of Manitoba K.C. Freeman Research School of Astronomy and Astrophysics, The Australian National University ABSTRACT CCD images and spectra of ionized hydrogen in the merging system NGC3256 were acquired as part of a kinematic study to investigate the formation of globular clusters (GC) during the interactions and mergers of disk galaxies. This paper focuses on the proposition by Kennicutt & Chu (1988) that giant H II regions, with an Hα luminosity > 1:5 1040 erg s 1, are birthplaces of young populous clusters (YPC’s ). × − Although NGC 3256 has relatively few (7) giant H II complexes, compared to some other interacting systems, these regions are comparable in total flux to about 85 30- Doradus-like H II regions (30-Dor GHR’s). The bluest, massive YPC’s (Zepf et al. 1999) are located in the vicinity of observed 30-Dor GHR’s, contributing to the notion that some fraction of 30-Dor GHR’s do cradle massive YPC’s, as 30 Dor harbors R136. If interactions induce the formation of 30-Dor GHR’s, the observed luminosities indi- cate that almost 900 30-Dor GHR’s would form in NGC 3256 throughout its merger epoch. In order for 30-Dor GHR’s to be considered GC progenitors, this number must be consistent with the specific frequencies of globular clusters estimated for elliptical galaxies formed via mergers of spirals (Ashman & Zepf 1993).
    [Show full text]
  • Winter Constellations
    Winter Constellations *Orion *Canis Major *Monoceros *Canis Minor *Gemini *Auriga *Taurus *Eradinus *Lepus *Monoceros *Cancer *Lynx *Ursa Major *Ursa Minor *Draco *Camelopardalis *Cassiopeia *Cepheus *Andromeda *Perseus *Lacerta *Pegasus *Triangulum *Aries *Pisces *Cetus *Leo (rising) *Hydra (rising) *Canes Venatici (rising) Orion--Myth: Orion, the great ​ ​ hunter. In one myth, Orion boasted he would kill all the wild animals on the earth. But, the earth goddess Gaia, who was the protector of all animals, produced a gigantic scorpion, whose body was so heavily encased that Orion was unable to pierce through the armour, and was himself stung to death. His companion Artemis was greatly saddened and arranged for Orion to be immortalised among the stars. Scorpius, the scorpion, was placed on the opposite side of the sky so that Orion would never be hurt by it again. To this day, Orion is never seen in the sky at the same time as Scorpius. DSO’s ● ***M42 “Orion Nebula” (Neb) with Trapezium A stellar ​ ​ ​ nursery where new stars are being born, perhaps a thousand stars. These are immense clouds of interstellar gas and dust collapse inward to form stars, mainly of ionized hydrogen which gives off the red glow so dominant, and also ionized greenish oxygen gas. The youngest stars may be less than 300,000 years old, even as young as 10,000 years old (compared to the Sun, 4.6 billion years old). 1300 ly. ​ ​ 1 ● *M43--(Neb) “De Marin’s Nebula” The star-forming ​ “comma-shaped” region connected to the Orion Nebula. ● *M78--(Neb) Hard to see. A star-forming region connected to the ​ Orion Nebula.
    [Show full text]
  • The Most Massive Star Cluster in the Local Group
    This is a repository copy of A 'super' star cluster grown old: the most massive star cluster in the Local Group. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/144713/ Version: Published Version Article: Ma, J., De Grijs, R., Yang, Y. et al. (5 more authors) (2006) A 'super' star cluster grown old: the most massive star cluster in the Local Group. Monthly Notices of the Royal Astronomical Society , 368 (3). pp. 1443-1450. ISSN 0035-8711 https://doi.org/10.1111/j.1365-2966.2006.10231.x This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2006 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Reuse Items deposited in White Rose Research Online are protected by copyright, with all rights reserved unless indicated otherwise. They may be downloaded and/or printed for private study, or other acts as permitted by national copyright laws. The publisher or other rights holders may allow further reproduction and re-use of the full text version. This is indicated by the licence information on the White Rose Research Online record for the item. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ Mon. Not. R. Astron. Soc. 368, 1443–1450 (2006) doi:10.1111/j.1365-2966.2006.10231.x A ‘super’ star cluster grown old: the most massive star cluster in the Local Group J.
    [Show full text]
  • Spatial Distribution of Galactic Globular Clusters: Distance Uncertainties and Dynamical Effects
    Juliana Crestani Ribeiro de Souza Spatial Distribution of Galactic Globular Clusters: Distance Uncertainties and Dynamical Effects Porto Alegre 2017 Juliana Crestani Ribeiro de Souza Spatial Distribution of Galactic Globular Clusters: Distance Uncertainties and Dynamical Effects Dissertação elaborada sob orientação do Prof. Dr. Eduardo Luis Damiani Bica, co- orientação do Prof. Dr. Charles José Bon- ato e apresentada ao Instituto de Física da Universidade Federal do Rio Grande do Sul em preenchimento do requisito par- cial para obtenção do título de Mestre em Física. Porto Alegre 2017 Acknowledgements To my parents, who supported me and made this possible, in a time and place where being in a university was just a distant dream. To my dearest friends Elisabeth, Robert, Augusto, and Natália - who so many times helped me go from "I give up" to "I’ll try once more". To my cats Kira, Fen, and Demi - who lazily join me in bed at the end of the day, and make everything worthwhile. "But, first of all, it will be necessary to explain what is our idea of a cluster of stars, and by what means we have obtained it. For an instance, I shall take the phenomenon which presents itself in many clusters: It is that of a number of lucid spots, of equal lustre, scattered over a circular space, in such a manner as to appear gradually more compressed towards the middle; and which compression, in the clusters to which I allude, is generally carried so far, as, by imperceptible degrees, to end in a luminous center, of a resolvable blaze of light." William Herschel, 1789 Abstract We provide a sample of 170 Galactic Globular Clusters (GCs) and analyse its spatial distribution properties.
    [Show full text]
  • Young Globular Clusters and Dwarf Spheroidals
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server Young Globular Clusters and Dwarf Spheroidals Sidney van den Bergh Dominion Astrophysical Observatory Herzberg Institute of Astrophysics National Research Council of Canada 5071 West Saanich Road Victoria, British Columbia, V8X 4M6 Canada ABSTRACT Most of the globular clusters in the main body of the Galactic halo were formed almost simultaneously. However, globular cluster formation in dwarf spheroidal galaxies appears to have extended over a significant fraction of a Hubble time. This suggests that the factors which suppressed late-time formation of globulars in the main body of the Galactic halo were not operative in dwarf spheroidal galaxies. Possibly the presence of significant numbers of “young” globulars at RGC > 15 kpc can be accounted for by the assumption that many of these objects were formed in Sagittarius-like (but not Fornax-like) dwarf spheroidal galaxies, that were subsequently destroyed by Galactic tidal forces. It would be of interest to search for low-luminosity remnants of parental dwarf spheroidals around the “young” globulars Eridanus, Palomar 1, 3, 14, and Terzan 7. Furthermore multi-color photometry could be used to search for the remnants of the super-associations, within which outer halo globular clusters originally formed. Such envelopes are expected to have been tidally stripped from globulars in the inner halo. Subject headings: Globular clusters - galaxies: dwarf The galaxy is, in fact, nothing but a congeries of innumerable stars grouped together in clusters. Galileo (1610) –2– 1. Introduction The vast majority of Galactic globular clusters appear to have formed at about the same time (e.g.
    [Show full text]
  • A Basic Requirement for Studying the Heavens Is Determining Where In
    Abasic requirement for studying the heavens is determining where in the sky things are. To specify sky positions, astronomers have developed several coordinate systems. Each uses a coordinate grid projected on to the celestial sphere, in analogy to the geographic coordinate system used on the surface of the Earth. The coordinate systems differ only in their choice of the fundamental plane, which divides the sky into two equal hemispheres along a great circle (the fundamental plane of the geographic system is the Earth's equator) . Each coordinate system is named for its choice of fundamental plane. The equatorial coordinate system is probably the most widely used celestial coordinate system. It is also the one most closely related to the geographic coordinate system, because they use the same fun­ damental plane and the same poles. The projection of the Earth's equator onto the celestial sphere is called the celestial equator. Similarly, projecting the geographic poles on to the celest ial sphere defines the north and south celestial poles. However, there is an important difference between the equatorial and geographic coordinate systems: the geographic system is fixed to the Earth; it rotates as the Earth does . The equatorial system is fixed to the stars, so it appears to rotate across the sky with the stars, but of course it's really the Earth rotating under the fixed sky. The latitudinal (latitude-like) angle of the equatorial system is called declination (Dec for short) . It measures the angle of an object above or below the celestial equator. The longitud inal angle is called the right ascension (RA for short).
    [Show full text]
  • Evolution of Star Clusters in Time-Variable Tidal Fields
    Evolution of Star Clusters in Time-Variable Tidal Fields A Thesis Submitted to the Faculty of Drexel University by Ernest N. Mamikonyan in partial fulfillment of the requirement for the degree of Doctor of Philosophy December 12, 2013 Contents 1 Introduction 1 1.1 TypesofStarClusters............................ 2 1.1.1 GlobularClusters .......................... 3 1.1.2 OpenClusters............................ 4 1.2 Mass Function: From Young to Globular . 5 2 Arbitrary Tidal Acceleration 8 2.1 ApproximatingTidalEffects. 9 2.1.1 Tidal Acceleration Tensor . 10 2.2 Stellar Dynamics with KIRA ........................ 11 2.2.1 CircularOrbitinPoint-MassPotential . 14 2.3 GalaxyMergerSimulations . 16 2.3.1 TidalHistories............................ 19 2.4 N-BodySimulations ............................ 24 2.4.1 N-BodyUnits ............................ 26 2.4.2 Scaling ................................ 26 3 Mass Loss Model 30 i 3.1 Accelerated Two-Body Relaxation . 30 3.2 FluctuationsintheJacobiRadius. 34 3.3 Results .................................... 36 3.4 Discussion.................................. 37 3.4.1 Limitations ............................. 40 4 Globular Cluster Mass Functions 44 4.1 MassFunctionEvolution . 47 4.2 Results .................................... 48 4.2.1 SinkParticles ............................ 48 4.2.2 DiskParticles ............................ 50 4.2.3 HaloParticles ............................ 55 5 Conclusions and Future Work 57 Appendix A Implementation of Tidal Fields in KIRA 63 Appendix B Computing Tidal Acceleration from GADGET Output 66 ii List of Figures 1.1 Infrared image of the globular cluster Omega Centauri. It is the most massive cluster in the Galaxy and thought to be a remnant of a dwarf galaxy absorbed by the Milky Way. (NASA/JPL-Caltech/ NOAO/AURA/NSF)............................. 3 1.2 The Pleiades open cluster in the infrared. It is one of the most well- known and spectacular objects in the Galaxy.
    [Show full text]
  • October 2006
    OCTOBER 2 0 0 6 �������������� http://www.universetoday.com �������������� TAMMY PLOTNER WITH JEFF BARBOUR 283 SUNDAY, OCTOBER 1 In 1897, the world’s largest refractor (40”) debuted at the University of Chica- go’s Yerkes Observatory. Also today in 1958, NASA was established by an act of Congress. More? In 1962, the 300-foot radio telescope of the National Ra- dio Astronomy Observatory (NRAO) went live at Green Bank, West Virginia. It held place as the world’s second largest radio scope until it collapsed in 1988. Tonight let’s visit with an old lunar favorite. Easily seen in binoculars, the hexagonal walled plain of Albategnius ap- pears near the terminator about one-third the way north of the south limb. Look north of Albategnius for even larger and more ancient Hipparchus giving an almost “figure 8” view in binoculars. Between Hipparchus and Albategnius to the east are mid-sized craters Halley and Hind. Note the curious ALBATEGNIUS AND HIPPARCHUS ON THE relationship between impact crater Klein on Albategnius’ southwestern wall and TERMINATOR CREDIT: ROGER WARNER that of crater Horrocks on the northeastern wall of Hipparchus. Now let’s power up and “crater hop”... Just northwest of Hipparchus’ wall are the beginnings of the Sinus Medii area. Look for the deep imprint of Seeliger - named for a Dutch astronomer. Due north of Hipparchus is Rhaeticus, and here’s where things really get interesting. If the terminator has progressed far enough, you might spot tiny Blagg and Bruce to its west, the rough location of the Surveyor 4 and Surveyor 6 landing area.
    [Show full text]
  • 5. Cosmic Distance Ladder Ii: Standard Candles
    5. COSMIC DISTANCE LADDER II: STANDARD CANDLES EQUIPMENT Computer with internet connection GOALS In this lab, you will learn: 1. How to use RR Lyrae variable stars to measures distances to objects within the Milky Way galaxy. 2. How to use Cepheid variable stars to measure distances to nearby galaxies. 3. How to use Type Ia supernovae to measure distances to faraway galaxies. 1 BACKGROUND A. MAGNITUDES Astronomers use apparent magnitudes , which are often referred to simply as magnitudes, to measure brightness: The more negative the magnitude, the brighter the object. The more positive the magnitude, the fainter the object. In the following tutorial, you will learn how to measure, or photometer , uncalibrated magnitudes: http://skynet.unc.edu/ASTR101L/videos/photometry/ 2 In Afterglow, go to “File”, “Open Image(s)”, “Sample Images”, “Astro 101 Lab”, “Lab 5 – Standard Candles”, “CD-47” and open the image “CD-47 8676”. Measure the uncalibrated magnitude of star A: uncalibrated magnitude of star A: ____________________ Uncalibrated magnitudes are always off by a constant and this constant varies from image to image, depending on observing conditions among other things. To calibrate an uncalibrated magnitude, one must first measure this constant, which we do by photometering a reference star of known magnitude: uncalibrated magnitude of reference star: ____________________ 3 The known, true magnitude of the reference star is 12.01. Calculate the correction constant: correction constant = true magnitude of reference star – uncalibrated magnitude of reference star correction constant: ____________________ Finally, calibrate the uncalibrated magnitude of star A by adding the correction constant to it: calibrated magnitude = uncalibrated magnitude + correction constant calibrated magnitude of star A: ____________________ The true magnitude of star A is 13.74.
    [Show full text]
  • New Globular Cluster Age Estimates and Constraints on the Cosmic Equation of State and the Matter Density of the Universe
    1 New Globular Cluster Age Estimates and Constraints on the Cosmic Equation of State and The Matter Density of the Universe. Lawrence M. Krauss* & Brian Chaboyer *Departments of Physics and Astronomy, Case Western Reserve University, 10900 Euclid Ave., Cleveland OH USA 44106-7079; Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH. USA New estimates of globular cluster distances, combined with revised ranges for input parameters in stellar evolution codes and recent estimates of the earliest redshift of cluster formation allow us to derive a new 95% confidence level lower limit on the age of the Universe of 11 Gyr. This is now definitively inconsistent with the expansion age for a flat Universe for the currently allowed range of the Hubble constant unless the cosmic equation of state is dominated by a component that violates the strong energy condition. This solidifies the case for a dark energy-dominated universe, complementing supernova data and direct measurements of the geometry and matter density in the Universe. The best-fit age is consistent with a cosmological constant-dominated (w=pressure/energy density = -1) universe. For the Hubble Key project best fit value of the Hubble Ω Constant our age limits yields the constraints w < -0.4 and Ωmatter < 0.38 at the 68 Ω % confidence level, and w < -0.26 and Ωmatter < 0.58 at the 95 % confidence level. Age determinations of globular clusters provided one of the earliest motivations for considering the possible existence of a cosmological constant. By comparing a lower limit on the age of the oldest globular clusters in our galaxy--- estimated in the 1980 s to be 15-20 Gyr---with the expansion age, determined by measurements of the Hubble constant, an apparent inconsistency arose: globular clusters appeared to be older than 2 the Universe unless one allowed for a possible Cosmological Constant.
    [Show full text]