DOCSLIB.ORG

1985Aj 90.22210 the Astronomical Journal

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
1985Aj 90.22210 the Astronomical Journal THE ASTRONOMICAL JOURNAL VOLUME 90, NUMBER 11 NOVEMBER 1985 90.22210 THE URSA MINOR DWARF GALAXY: STILL AN OLD STELLAR SYSTEM Edward W. Olszewski^ Steward Observatory, University of Arizona, Tucson, Arizona 85721 1985AJ and Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, Victoria, British Columbia V8X 4M6, Canada Marc AARONSONa) Steward Observatory, University of Arizona, Tucson, Arizona 85721 Received 25 March 1985; revised 5 August 1985 ABSTRACT We have constructed a color-magnitude diagram of the Ursa Minor dwarf spheroidal to = 24.8 mag from charged-coupled device (CCD) observations with the Kitt Peak 4 m telescope. The main-sequence turnoff is easily visible. Fits to evolutionary isochrones and the globular M92 indicate that Ursa Minor has an age and metal abundance very similar to that of the latter cluster. No evidence for stars younger than about 16 billion years is seen, with the possible exception of approximately 20 stars believed to be blue stragglers. Ursa Minor is therefore an extreme-age galaxy, unlike superficially similar objects such as the Carina dwarf. Indeed, Ursa Minor may be the only outer-halo spheroidal whose stellar content lives up to the classical ideals of a Population II system. A distance modulus of (m — Af )0 = 19.0 mag is derived from a sliding fit to the M92 ridge lines. However, this modulus is uncertain by ~0.1 mag, for the horizontal branch in our color-magnitude diagram is poorly populated. The ratio of blue stragglers to anomalous Cepheids in Ursa Minor is estimated to be ~ 100, a number that may provide an impor- tant constraint on binary models for the origin of these stars. A surprising result of our study is the discovery of dumpiness in the distribution of stars. This finding may give more weight to the idea that dwarf spheroidal galaxies were previously dwarf irregular galaxies, although clearly, if so, Ursa Minor must have lost its gaseous content very soon after formation. I. INTRODUCTION to accumulate (Zinn 1978; Demers, Kunkel, and Hardy The dwarf spheroidal galaxies have in the last few years 1979; Kinman, Kraft, and Suntzeff 1981; Suntzeff et al. become intensely studied objects, and deservedly so, for they 1984; and Buonanno et al. 1985; but see Bell 1985). This provide an outstanding laboratory in which to investigate latter result is possibly not unexpected in systems such as evolutionary processes in the Milky Way’s outer halo. Excel- Fornax, where enrichment processes should have had suffi- lent reviews of these systems have been written by Hodge cient time to occur, but it perhaps does present difficulties in (1971) and Zinn (1980, 1985; see also Carney 1984). Since galaxies such as Draco and Ursa Minor, where there is little Zinn’s earlier review, a number of major developments have evidence as yet for an extended period of star formation. occurred. Some rather speculative ideas concerning the dwarf spher- To begin with, the presence of stars younger than those oidals have also been recently raised. First, Lin and Faber found in galactic globular clusters has now been firmly es- (1983) and Kormendy (1985) have argued that the spheroi- tablished for many of the spheroidals. This came about first dals are closer in kinship to dwarf irregulars rather than to through identification of luminous asymptotic-giant-branch dwarf ellipticals. Second, the possibility that the spheroidals (AGB) carbon stars (see Aaronson and Mould 1985), and may contain substantial amounts of dark matter has been more directly by deep color-magnitude diagrams (CMDs) suggested (see Aaronson 1983; Faber and Lin 1983; Lin and that have now been published for Carina (Mould and Aaron- Faber 1983). son 1983) and Sculptor (Da Costa 1984), which reach the Ursa Minor and Draco form a pair of galaxies whose con- level of the main-sequence turnoff. Such age effects seem to trasts may illuminate many of the remaining problems in account naturally for the prevalence of red horizontal understanding the stellar content of the dwarf galaxies. branches in the spheroidal systems. Furthermore, these sys- These systems are the two lowest-luminosity halo dwarfs tems not only appear to differ from each other in mean age, (Mv = — 8.8 mag and — 8.5 mag for Ursa Minor and Dra- but a considerable age range may be present within some of co, respectively, after Zinn 1985), and in this regard are most them. The most striking case in point is Fornax, whose stars comparable to galactic globulars. Both contain RR Lyrae appear to span an age from ~ 3 X109 to ~ 15 X 109 yr (Aar- variables and anomalous Cepheids, while neither are known onson and Mould 1985; and Buonanno etal. 1985). to possess red giant variables, which have occasionally Reasonably accurate metal abundances for all seven halo cropped up in several of the other spheroidals (Baade and spheroidals are now also available, and a mean metallicity- Swope 1961; van Agt 1973). Both have mean abundances absolute magnitude relation has been shown to exist (see similar to M92, but have some stars of very different metalli- Aaronson and Mould 1985; Buonanno etal. 1985, and refer- city, and both have stars that show enhanced CNO (e.g., ences therein). Furthermore, evidence that within a given Kinman eiû/. 1981; Stetson 1984; Suntzeff ei a/. 1984). Both spheroidal the stars exhibit a dispersion in [Fe/H] continues contain carbon stars (Aaronson, Liebert, and Stocke 1982; Aaronson, Olszewski, and Hodge 1983), but these are of the a)Visting Astronomer at Kitt Peak National Observatory, a division of low-luminosity, blue-color variety also found in co Cen and NO AO operated by AURA, Inc., under contract with the National Science several other galactic globulars. Foundation. On the other hand, Ursa Minor and Draco differ in two 2221 Astron. J. 90 (11), November 1985 0004-6256/85/112221-18$00.90 © 1985 Am. Astron. Soc. 2221 © American Astronomical Society • Provided by the NASA Astrophysics Data System 2222 E. W. OLSZEWSKI AND M. AARONSON: URSA MINOR 2222 90.22210 important respects. First, the characteristics of the Ursa Mi- III. DATA REDUCTIONS AND CALIBRATIONS nor RR Lyraes are very similar to those in OosterhofFType a) The Standard-Star Frames II clusters, while those in Draco cannot be readily placed in either of the Oosterhoff classes (e.g., Zinn 1980). This differ- Short exposures, ranging from 5 to 30 s, were taken of the 1985AJ ence may be related to Draco’s having a larger and slightly M92 CCD standard field (Davis 1984; Christian 1980; see more metal-rich abundance spread. Perhaps more signifi- also Christian et al. 1985; other photometry found in San- cant is the fact that Ursa Minor is the only spheroidal to have dage 1969) and the NGC 7790 videocamera field (Christian a blue horizontal branch. Draco, in contrast, has a red hori- 1980; Christian et al. 1985; photoelectric photometry also zontal branch like the other spheroidals, and given its mean available and used from Sandage 1958). All standard-star abundance exhibits perhaps the most extreme case known of observations were secured during photometric conditions. the famous “second-parameter” problem. In each case, two short and two longer exposures were made Although there are other possible ways to account for dif- for each observation of each object in each filter. M92 was ference in horizontal-branch type, it is very tempting to spec- observed at two different times during the night. The B —V ulate that Draco is a few billion years younger than Ursa colors of the observed standards cover a wide color base line Minor. The primary purpose of the present paper is to help from — 0.1 to 1.7. Twenty individual standard stars were test this hypothesis by providing a very deep color-magni- measured, 12 at two different airmasses. tude diagram for Ursa Minor. Two groups (Carney and Aperture photometry was then performed for each frame, Seitzer 1985; Stetson, VandenBerg, and McClure 1985) are yielding up to four observations of each standard star for currently supplying the companion data for Draco. Current each color at a given airmass. The instrumental total magni- detector technology readily enables the main sequence to be tudes were then determined by growing the radius until 1 reached in both systems, so that the crucial test can be made. pixel change in stellar magnitude was approximately equal The organization of the paper is as follows: A brief de- to the rms error in determining that quantity. This corre- scription of the observations is presented in Sec. II. The data sponded to a 7 pixel aperture, the last magnitude growth reduction, performed entirely with Peter Stetson’s dao from pixel 6 to pixel 7 being of order 0.005 mag (with the phot program, is fully described in Sec. III. Because this is scale — 0.6" per pixel). The total instrumental magnitudes one of the first papers to make extensive use of daophot, the and errors, and the standard-star magnitude with its asso- discussion in Sec. Ill has been made rather lengthy and de- ciated error, were then typed into two computer files. (Note tailed. The uninterested reader is invited to skip directly to that all instrumental magnitudes were derived using rou- Sec. IV, where the final color-mangitude diagram is present- tines in Stetson’s daophot program, and all transforma- ed, along with isochrone fits and the derivation of age and tions were made using daophot subsidiary programs, all distance modulus. A summary of our findings is given in Sec. also written by Stetson. The etymology of daophot is de- V. In Sec. VI we present and discuss the implications of a scribed in Stetson 1985.) A minor variation of the program startling and unexpected result pertaining to the presence of CCDSTD was then used to calculate the transformation to apparent stellar subclustering in the Ursa Minor field.
Load more

Recommended publications
  • Astronomie in Theorie Und Praxis 8. Auflage in Zwei Bänden Erik Wischnewski
    Astronomie in Theorie und Praxis 8. Auflage in zwei Bänden Erik Wischnewski Inhaltsverzeichnis 1 Beobachtungen mit bloßem Auge 37 Motivation 37 Hilfsmittel 38 Drehbare Sternkarte Bücher und Atlanten Kataloge Planetariumssoftware Elektronischer Almanach Sternkarten 39 2 Atmosphäre der Erde 49 Aufbau 49 Atmosphärische Fenster 51 Warum der Himmel blau ist? 52 Extinktion 52 Extinktionsgleichung Photometrie Refraktion 55 Szintillationsrauschen 56 Angaben zur Beobachtung 57 Durchsicht Himmelshelligkeit Luftunruhe Beispiel einer Notiz Taupunkt 59 Solar-terrestrische Beziehungen 60 Klassifizierung der Flares Korrelation zur Fleckenrelativzahl Luftleuchten 62 Polarlichter 63 Nachtleuchtende Wolken 64 Haloerscheinungen 67 Formen Häufigkeit Beobachtung Photographie Grüner Strahl 69 Zodiakallicht 71 Dämmerung 72 Definition Purpurlicht Gegendämmerung Venusgürtel Erdschattenbogen 3 Optische Teleskope 75 Fernrohrtypen 76 Refraktoren Reflektoren Fokus Optische Fehler 82 Farbfehler Kugelgestaltsfehler Bildfeldwölbung Koma Astigmatismus Verzeichnung Bildverzerrungen Helligkeitsinhomogenität Objektive 86 Linsenobjektive Spiegelobjektive Vergütung Optische Qualitätsprüfung RC-Wert RGB-Chromasietest Okulare 97 Zusatzoptiken 100 Barlow-Linse Shapley-Linse Flattener Spezialokulare Spektroskopie Herschel-Prisma Fabry-Pérot-Interferometer Vergrößerung 103 Welche Vergrößerung ist die Beste? Blickfeld 105 Lichtstärke 106 Kontrast Dämmerungszahl Auflösungsvermögen 108 Strehl-Zahl Luftunruhe (Seeing) 112 Tubusseeing Kuppelseeing Gebäudeseeing Montierungen 113 Nachführfehler
    [Show full text]
  • 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.
    [Show full text]
  • Naming the Extrasolar Planets
    Naming the extrasolar planets W. Lyra Max Planck Institute for Astronomy, K¨onigstuhl 17, 69177, Heidelberg, Germany [email protected] Abstract and OGLE-TR-182 b, which does not help educators convey the message that these planets are quite similar to Jupiter. Extrasolar planets are not named and are referred to only In stark contrast, the sentence“planet Apollo is a gas giant by their assigned scientific designation. The reason given like Jupiter” is heavily - yet invisibly - coated with Coper- by the IAU to not name the planets is that it is consid- nicanism. ered impractical as planets are expected to be common. I One reason given by the IAU for not considering naming advance some reasons as to why this logic is flawed, and sug- the extrasolar planets is that it is a task deemed impractical. gest names for the 403 extrasolar planet candidates known One source is quoted as having said “if planets are found to as of Oct 2009. The names follow a scheme of association occur very frequently in the Universe, a system of individual with the constellation that the host star pertains to, and names for planets might well rapidly be found equally im- therefore are mostly drawn from Roman-Greek mythology. practicable as it is for stars, as planet discoveries progress.” Other mythologies may also be used given that a suitable 1. This leads to a second argument. It is indeed impractical association is established. to name all stars. But some stars are named nonetheless. In fact, all other classes of astronomical bodies are named.
    [Show full text]
  • Apparent and Absolute Magnitudes of Stars: a Simple Formula
    Available online at www.worldscientificnews.com WSN 96 (2018) 120-133 EISSN 2392-2192 Apparent and Absolute Magnitudes of Stars: A Simple Formula Dulli Chandra Agrawal Department of Farm Engineering, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi - 221005, India E-mail address: [email protected] ABSTRACT An empirical formula for estimating the apparent and absolute magnitudes of stars in terms of the parameters radius, distance and temperature is proposed for the first time for the benefit of the students. This reproduces successfully not only the magnitudes of solo stars having spherical shape and uniform photosphere temperature but the corresponding Hertzsprung-Russell plot demonstrates the main sequence, giants, super-giants and white dwarf classification also. Keywords: Stars, apparent magnitude, absolute magnitude, empirical formula, Hertzsprung-Russell diagram 1. INTRODUCTION The visible brightness of a star is expressed in terms of its apparent magnitude [1] as well as absolute magnitude [2]; the absolute magnitude is in fact the apparent magnitude while it is observed from a distance of . The apparent magnitude of a celestial object having flux in the visible band is expressed as [1, 3, 4] ( ) (1) ( Received 14 March 2018; Accepted 31 March 2018; Date of Publication 01 April 2018 ) World Scientific News 96 (2018) 120-133 Here is the reference luminous flux per unit area in the same band such as that of star Vega having apparent magnitude almost zero. Here the flux is the magnitude of starlight the Earth intercepts in a direction normal to the incidence over an area of one square meter. The condition that the Earth intercepts in the direction normal to the incidence is normally fulfilled for stars which are far away from the Earth.
    [Show full text]
  • Variable Star Section Circular
    British Astronomical Association Variable Star Section Circular No 82, December 1994 CONTENTS A New Director 1 Credit for Observations 1 Submission of 1994 Observations 1 Chart Problems 1 Recent Novae Named 1 Z Ursae Minoris - A New R CrB Star? 2 The February 1995 Eclipse of 0¼ Geminorum 2 Computerisation News - Dave McAdam 3 'Stella Haitland, or Love and the Stars' - Philip Hurst 4 The 1994 Outburst of UZ Bootis - Gary Poyner 5 Observations of Betelgeuse by the SPA-VSS - Tony Markham 6 The AAVSO and the Contribution of Amateurs to VS Research Suspected Variables - Colin Henshaw 8 From the Literature 9 Eclipsing Binary Predictions 11 Summaries of IBVS's Nos 4040 to 4092 14 The BAA Instruments and Imaging Section Newsletter 16 Light-curves (TZ Per, R CrB, SV Sge, SU Tau, AC Her) - Dave McAdam 17 ISSN 0267-9272 Office: Burlington House, Piccadilly, London, W1V 9AG Section Officers Director Tristram Brelstaff, 3 Malvern Court, Addington Road, READING, Berks, RG1 5PL Tel: 0734-268981 Section Melvyn D Taylor, 17 Cross Lane, WAKEFIELD, Secretary West Yorks, WF2 8DA Tel: 0924-374651 Chart John Toone, Hillside View, 17 Ashdale Road, Cressage, Secretary SHREWSBURY, SY5 6DT Tel: 0952-510794 Computer Dave McAdam, 33 Wrekin View, Madeley, TELFORD, Secretary Shropshire, TF7 5HZ Tel: 0952-432048 E-mail: COMPUSERV 73671,3205 Nova/Supernova Guy M Hurst, 16 Westminster Close, Kempshott Rise, Secretary BASINGSTOKE, Hants, RG22 4PP Tel & Fax: 0256-471074 E-mail: [email protected] [email protected] Pro-Am Liaison Roger D Pickard, 28 Appletons, HADLOW, Kent TN11 0DT Committee Tel: 0732-850663 Secretary E-mail: [email protected] KENVAD::RDP Eclipsing Binary See Director Secretary Circulars Editor See Director Telephone Alert Numbers Nova and First phone Nova/Supernova Secretary.
    [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]
  • Planetary Companions Around the K Giant Stars 11 Ursae Minoris and HD 32518
    A&A 505, 1311–1317 (2009) Astronomy DOI: 10.1051/0004-6361/200911702 & c ESO 2009 Astrophysics Planetary companions around the K giant stars 11 Ursae Minoris and HD 32518 M. P. Döllinger1, A. P. Hatzes2, L. Pasquini1, E. W. Guenther2, and M. Hartmann2 1 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany e-mail: [email protected] 2 Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany Received 22 January 2009 / Accepted 10 August 2009 ABSTRACT Context. 11 UMi and HD 32518 belong to a sample of 62 K giant stars that has been observed since February 2004 using the 2m Alfred Jensch telescope of the Thüringer Landessternwarte (TLS) to measure precise radial velocities (RVs). Aims. The aim of this survey is to investigate the dependence of planet formation on the mass of the host star by searching for plane- tary companions around intermediate-mass giants. Methods. An iodine absorption cell was used to obtain accurate RVs for this study. Results. Our measurements reveal that the RVs of 11 UMi show a periodic variation of 516.22 days with a semiamplitude of −1 −7 K = 189.70 m s . An orbital solution yields a mass function of f (m) = (3.608 ± 0.441) × 10 solar masses (M) and an eccentricity of e = 0.083 ± 0.03. The RV curve of HD 32518 shows sinusoidal variations with a period of 157.54 days and a semiamplitude of −1 −8 K = 115.83 m s . An orbital solution yields an eccentricity, e = 0.008 ± 0.03 and a mass function, f (m) = (2.199 ± 0.235) × 10 M.
    [Show full text]
  • Manganese Spread in Ursa Minor As a Proof of Sub-Classes of Type Ia
    Astronomy & Astrophysics manuscript no. paperMn6 c ESO 2018 September 22, 2018 Manganese spread in Ursa Minor as a proof of sub-classes of type Ia supernovae G. Cescutti1,3 ⋆ and C. Kobayashi2,3 1 INAF, Osservatorio Astronomico di Trieste, I-34131 Trieste, Italy 2 Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK 3 BRIDGCE UK Network (www.bridgce.net), UK Received xxxx / Accepted xxxx ABSTRACT Context. Recently, new sub-classes of Type Ia supernovae (SNe Ia) were discovered, including SNe Iax. The suggested progenitors of SNe Iax are relatively massive, possibly hybrid C+O+Ne white dwarfs, which can cause white dwarf winds at low metallicities. There is another class that can potentially occur at low or zero metallicities; sub-Chandrasekhar mass explosions in single and/or double degenerate systems of standard C+O white dwarfs. These explosions have different nucleosynthesis yields compared to the normal, Chandrasekhar mass explosions. Aims. We test these SN Ia channels using their characteristic chemical signatures. Methods. The two sub-classes of SNe Ia are expected to be rarer than normal SNe Ia and do not affect the chemical evolution in the solar neighbourhood; however, because of the shorter delay time and/or weaker metallicity dependence, they could influence the evolution of metal-poor systems. Therefore, we have included both in our stochastic chemical evolution model for the dwarf spheroidal galaxy Ursa Minor. Results. The model predicts a butterfly-shape spread in [Mn/Fe] in the interstellar medium at low metallicity and - at the same time - a decrease of [α/Fe] ratios at lower [Fe/H] than in the solar neighbourhood, both of which are consistent with the observed abundances in stars of Ursa Minor.
    [Show full text]
  • Arxiv:2001.10147V1
    Magnetic fields in isolated and interacting white dwarfs Lilia Ferrario1 and Dayal Wickramasinghe2 Mathematical Sciences Institute, The Australian National University, Canberra, ACT 2601, Australia Adela Kawka3 International Centre for Radio Astronomy Research, Curtin University, Perth, WA 6102, Australia Abstract The magnetic white dwarfs (MWDs) are found either isolated or in inter- acting binaries. The isolated MWDs divide into two groups: a high field group (105 − 109 G) comprising some 13 ± 4% of all white dwarfs (WDs), and a low field group (B < 105 G) whose incidence is currently under investigation. The situation may be similar in magnetic binaries because the bright accretion discs in low field systems hide the photosphere of their WDs thus preventing the study of their magnetic fields’ strength and structure. Considerable research has been devoted to the vexed question on the origin of magnetic fields. One hypothesis is that WD magnetic fields are of fossil origin, that is, their progenitors are the magnetic main-sequence Ap/Bp stars and magnetic flux is conserved during their evolution. The other hypothesis is that magnetic fields arise from binary interaction, through differential rotation, during common envelope evolution. If the two stars merge the end product is a single high-field MWD. If close binaries survive and the primary develops a strong field, they may later evolve into the arXiv:2001.10147v1 [astro-ph.SR] 28 Jan 2020 magnetic cataclysmic variables (MCVs). The recently discovered population of hot, carbon-rich WDs exhibiting an incidence of magnetism of up to about 70% and a variability from a few minutes to a couple of days may support the [email protected] [email protected] [email protected] Preprint submitted to Journal of LATEX Templates January 29, 2020 merging binary hypothesis.
    [Show full text]
  • Determination of Stellar Parameters for M-Dwarf Stars: the NIR Approach
    Determination of stellar parameters for M-dwarf stars: the NIR approach by Daniel Thaagaard Andreasen A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Graduate Department of Departamento de Fisica e Astronomia University of Porto c Copyright 2017 by Daniel Thaagaard Andreasen Dedication To Linnea, Henriette, Rico, and Else For always supporting me ii Acknowledgements When doing a PhD it is important to remember it is more a team effort than the work of an individual. This is something I learned quickly during the last four years. Therefore there are several people I would like to thank. First and most importantly are my two supervisors, Sérgio and Nuno. They were after me in the beginning of my studies because I was too shy to ask for help; something that I quickly learned I needed to do. They always had their door open for me and all my small questions. It goes without saying that I am thankful for all their guidance during my studies. However, what I am most thankful for is the freedom I have had to explorer paths and ideas on my own, and with them safely on the sideline. This sometimes led to failures and dead ends, but it make me grow as a researcher both by learning from my mistake, but also by prioritising my time. When I thank Sérgio and Nuno, my official supervisors, I also have to thank Elisa. She has been my third unofficial supervisor almost from the first day. Although she did not have any experience with NIR spectroscopy, she was never afraid of giving her opinion and trying to help.
    [Show full text]
  • Effects of the Galactic Winds on the Stellar Metallicity Distribution of Dwarf Spheroidal Galaxies
    A&A 468, 927–936 (2007) Astronomy DOI: 10.1051/0004-6361:20066576 & c ESO 2007 Astrophysics Effects of the galactic winds on the stellar metallicity distribution of dwarf spheroidal galaxies G. A. Lanfranchi1,2,3 and F. Matteucci3,4 1 Núcleo de Astrofísica Teórica, CETEC, Universidade Cruzeiro do Sul, R. Galvão Bueno 868, Liberdade, 01506-000, São Paulo, SP, Brazil e-mail: [email protected] 2 IAG-USP, R. do Matão 1226, Cidade Universitária, 05508-900 São Paulo, SP, Brazil 3 Dipartimento di Astronomia-Universitá di Trieste, via G. B. Tiepolo 11, 34131 Trieste, Italy 4 INAF Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy Received 16 October 2006 / Accepted 12 March 2007 ABSTRACT Aims. To study the effects of galactic winds on the stellar metallicity distributions and on the evolution of Draco and Ursa Minor dwarf spheroidal galaxies (dSphs), we compared the predictions of several chemical evolution models, adopting different prescriptions for the galactic winds (including a model with no wind), with the photometrically-derived stellar metallicity distributions (SMDs) of both galaxies. Methods. We adopted chemical evolution models for Draco and Ursa Minor, which are able to reproduce several observational features of these two galaxies, such as the [α/Fe], [Eu/Fe], [Ba/Fe] ratios and the present gas mass. The models take up-to-date nucleosynthesis into account for intermediate-mass stars and supernovae of both types, as well as the effect of these objects on the energetics of the systems. The predictions were compared to the photometric SMDs, which are accurate enough for a global comparison with general aspects such as metallicity range, shape, position of the peak, and high-metallicity tail, leaving aside minor details of the distributions.
    [Show full text]
  • The Angular Size of Objects in the Sky
    APPENDIX 1 The Angular Size of Objects in the Sky We measure the size of objects in the sky in terms of degrees. The angular diameter of the Sun or the Moon is close to half a degree. There are 60 minutes (of arc) to one degree (of arc), and 60 seconds (of arc) to one minute (of arc). Instead of including – of arc – we normally just use degrees, minutes and seconds. 1 degree = 60 minutes. 1 minute = 60 seconds. 1 degree = 3,600 seconds. This tells us that the Rosette nebula, which measures 80 minutes by 60 minutes, is a big object, since the diameter of the full Moon is only 30 minutes (or half a degree). It is clearly very useful to know, by looking it up beforehand, what the angular size of the objects you want to image are. If your field of view is too different from the object size, either much bigger, or much smaller, then the final image is not going to look very impressive. For example, if you are using a Sky 90 with SXVF-M25C camera with a 3.33 by 2.22 degree field of view, it would not be a good idea to expect impressive results if you image the Sombrero galaxy. The Sombrero galaxy measures 8.7 by 3.5 minutes and would appear as a bright, but very small patch of light in the centre of your frame. Similarly, if you were imaging at f#6.3 with the Nexstar 11 GPS scope and the SXVF-H9C colour camera, your field of view would be around 17.3 by 13 minutes, NGC7000 would not be the best target.
    [Show full text]