DOCSLIB.ORG

1973Apj. . .185. .597D the Astrophysical Journal, 185:597-619

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
1973Apj. . .185. .597D the Astrophysical Journal, 185:597-619 .597D The Astrophysical Journal, 185:597-619, 1973 October 15 .185. © 1973. The American Astronomical Society. All rights reserved. Printed in U.S.A. 1973ApJ. NEW OBSERVATIONS OF RV TAURI STARS David L. DuPuy* David Dunlap Observatory, University of Toronto, Richmond Hill, Ontario, Canada Received 1973 March 27 ABSTRACT New photoelectric and spectroscopic observations of RV Tauri stars have been obtained, and mean visual magnitudes and characteristics of the light and color curves have been derived. Most RV Tauri stars show rather irregular light curves, with successive cycles showing deviations up to several tenths of a magnitude. An analysis of the color excesses in ( F — i?) indicates the existence of reddening due to circumstellar material. Revised periods are suggested in a number of cases. Attempts were made to determine absolute magnitudes of RV Tauri stars by the following methods: (i) globular-cluster RV Tauri stars; (ii) mean secular and statistical parallaxes; (iii) the application of Wesselink’s method (which was unsuccessful); and (iv) luminosity classification spectrograms. A period-luminosity relation is evident. Absolute magnitude methods which depend on observa- tions of apparent magnitudes yield results averaging about 1.5 mag fainter than those methods based on other arguments. This difference is attributed to mostly nonselective absorption in circumstellar material and leads to visual absolute magnitudes of —5 to —6 inside the circum- stellar shells. Subject headings: circumstellar shells — luminosities — RV Tauri stars I. INTRODUCTION The class of RV Tauri stars comprises about 100 supergiant stars with unique characteristics of variability. Their light curves display two unequal minima, making uncertain which is the more physically significant period : the interval between succes- sive maxima or minima (single period), or the interval between successive deep minima (double period). Superposed on the double period (50-100 days), long-term periodic- ities of the order of 1000 days are sometimes observed (RV6); other RV Tauri stars maintain an approximately constant mean brightness (RVa). Furthermore, some RV Tauri stars repeat their cyclic variation uniformly, while others display poor repeat- ability from cycle to cycle. Spectral types range from F5 to late K, although spectral peculiarities (e.g., TiO bands, or Ca n versus hydrogen lines) sometimes preclude self- consistent classification. Hydrogen lines sometimes appear in emission during rising light. An interchange of deep and shallow minima may occasionally occur in some variables, but is never observed in others. A summary of previous observations and known characteristics is given in the study by Preston et al. (1963), and these will not be repeated here. The present study was initiated with the intention of investigating these stars’ positions on the H-R diagram, in the hope of learning more about the evolutionary role these stars play in stellar structure and about their relation to other variable stars. For this purpose, mean intrinsic colors were obtained with new UBVR photoelectric observations and an investigation of the interstellar absorption. Absolute magnitudes were derived from (i) globular-cluster RV Tauri stars; (ii) mean secular and statistical parallaxes; (iii) Wesselink’s (1946) method of radius determination; and (iv) spectral luminosity classification. Recent investigations at infrared wavelengths (Gehrz 1972; * Present address: Burke-Gaffney Observatory, St. Mary’s University, Halifax, Nova Scotia, Canada. 597 © American Astronomical Society • Provided by the NASA Astrophysics Data System .597D .185. 598 DAVID L. DUPUY Vol. 185 . Gehrz and Ney 1972) indicate that a strong infrared excess exists for most RV Tauri stars. This is new, strong evidence for cimcumstellar material, agreeing with earlier 1973ApJ. spectroscopic results (Preston 1962, 1972a). The absolute magnitudes obtained here confirm the existence of visual absorption in these circumstellar shells. II. OBSERVATIONAL DATA Photoelectric UBVR photometry has been obtained for about 25 stars, over two observing seasons. Only those stars listed in the second edition of the General Catalog of Variable Stars (GCVS; Kukarkin et al 1958) were considered for observation. A list of the stars observed is given in table 1, along with the GCVS periods and approxi- mate mean colors and magnitudes. A practical limit of 14 mag was chosen because of sky brightness difficulties, and only stars north of S = — 20° could be observed. All photoelectric observations were made with the 24-inch (61-cm) reflector of the David Dunlap Observatory in Richmond Hill, Ontario, using a~d.c. photometer of conven- tional design with an ITT FW-130 (S-20 photocathode) photomultiplier. The £/, B, and V filters were Schott filters UG2, BG12, and GG14, each sandwiched with a BG18 filter for red leak suppression. The R filter was an interference filter with maxi- mum transmission at 6931 Â and a half-width of 750 Â. Observations of 20 to 30 standard stars on 30 high-quality nights were used to investigate the characteristics of the transformations to the standard Johnson system. These transformations proved to be slightly nonlinear (to the extent of about 0.02 mag), but the final residuals show no systematic effect and the expected errors of TABLE 1 RV Tauri Stars Observed Star «(1950) S(1950) Period V (U - B) (B - V) {V - R) (1) (2) (3) (4) (5) (6) (7) (8) AD Aql... 18h56r l02s — 08°15'1 65H U™5 0.5: 0.6: 0.6: DY Aql... 19 43 45 -11 04.2 131.42 10.5: 1.60 1.35 CO Aur... 05 57 07 4-35 19.3 7.8 0.35 0.70 0.65 TW Cam. 04 16 33 + 57 19.2 85.6 9.6 0.95 1.38 1.15 EQ Cas... 23 50 19 + 54 44.1 58.31 12.0 1.10 0.95 PY Cas... 23 40 57 + 60 49.5 111 13.0 1.4: 1.2: V360 Cyg. 21 08 22 + 30 27.7 70.45 11.4 0.30 1.00 0.85 SS Gem... 06 05 32 + 22 37.8 89.31 8.9 0.80 1.10 1.00 SU Gem.. 06 10 48 + 27 43.8 50.12 11.4 0.30 1.10 1.20 AC Her... 18 28 07 + 21 50.1 75.46 7.5 0.50 0.80 0.65 EG Lyr... 19 09 04 + 38 29.7 136.7 11.6: 1.5: 1.7: 2.2: EP Lyr..., 19 16 17 + 27 45.0 83.32 10.5 0.20 0.75 0.65 UMon. .. 07 28 21 -09 40.4 92.26 6.3 0.75 1.15 0.90 TT Oph... 16 47 02 + 03 43.1 61.08 10.0 0.80 1.10 0.85 TX Oph.. 17 01 29 + 05 03.1 135 10.2 0.9: 1.00 0.84 UZ Oph. 17 19 28 + 06 57.4 87.44 10.7 0.75 1.10 0.90 V564 Oph. 17 49 33 + 07 57.0 70.6 9.9 1.60 1.60 1.25 CT Ori.... 06 07 07 + 09 52.5 135.52 10.5 0.47 1.00 0.90 DY Ori... 06 03 17 + 13 53.6 60.26 11.9 0.2: 1.2: 0.9 DW Peg. 21 29 58 + 24 15.1 10.1 0.9 1.65 2.30 El Peg.... 23 19 14 + 12 19.2 6Í.15 9.9 1.0: 1.50 1.85 R Sge 20 11 45 + 16 34.7 70.59 9.2 0.70 1.0 0.75 R Set 18 44 43 -05 45.6 140.2 5.8 1.45 1.45 1.10 Z Sex 10 08 24 + 02 48.7 57 9.4 1.45 1.50 1.75 RV Tau... 04 43 58 + 26 05.2 78.70 9.2 1.35 1.70 1.27 V Vul 20 34 27 + 26 25.6 75.72 8.4 0.80 1.10 0.77 M2 #11... 21 30 14 -01 02 67.0 11.5 0.50 0.50 © American Astronomical Society • Provided by the NASA Astrophysics Data System .597D No. 2, 1973 NEW OBSERVATIONS OF RV TAURI STARS 599 .185. TABLE 2 Comparison Stars 1973ApJ. Comparison Star for: (U - B) (B — V) (V-Jt) Identification TW Cam.. 7 11.25 0.09: 0.72 0.58 Figure 1 V360 Cyg. 12 11.34 0.07 0.58 0.44 Preston et al. (1963) SS Gem... 6 9.20 -0.39: 0.00 0.09 Figure 1 SU Gem.. 7 10.45 0.06 0.48 0.42 Figure 1 AC Her... 16 7.37 0.83 1.06 0.77 BD + 21°3465 EP Lyr.... 17 9.55 0.02 0.44 0.38 BD + 27°3336 TT Oph... 13 10.88 0.06 0.54 0.47 Preston et al. (1963) TX Oph.. 6 9.49 1.16 1.32 0.98 BD + 05°3312* UZ Oph. 5 10.86 0.86 1.12: 0.85 Preston et al. (1963) V564 Oph. 10 9.68 1.43 1.35 0.99 BD + 07°3495 CT Ori.... 3 9.36 -0.37 0.04 0.07 Figure 1 DY Ori... 6 10.08 0.82 1.06 0.78 Figure 1 DW Peg. 10 10.89 1.68 1.69: 1.30: Figure 1 El Peg:... 7 9.92 0.19 0.59 0.51 Figure 1 R Sge 10 8.87 0.39 0.88 0.68 BD+16°4192 Z Sex a... 4 10.88 1.44 1.30 0.99 Figure 1 ZSexb... 5 10.87 0.06 0.53 0.44 Figure 1 RV Tau... 6 7.71 -0.04: 0.34 0.31 BD + 25°0731 V Vul 11 8.60 0.83 1.06 0.75 BD + 25°4301 * Preston et al.
Load more

Recommended publications
  • Information Bulletin on Variable Stars
    COMMISSIONS AND OF THE I A U INFORMATION BULLETIN ON VARIABLE STARS Nos November July EDITORS L SZABADOS K OLAH TECHNICAL EDITOR A HOLL TYPESETTING K ORI ADMINISTRATION Zs KOVARI EDITORIAL BOARD L A BALONA M BREGER E BUDDING M deGROOT E GUINAN D S HALL P HARMANEC M JERZYKIEWICZ K C LEUNG M RODONO N N SAMUS J SMAK C STERKEN Chair H BUDAPEST XI I Box HUNGARY URL httpwwwkonkolyhuIBVSIBVShtml HU ISSN COPYRIGHT NOTICE IBVS is published on b ehalf of the th and nd Commissions of the IAU by the Konkoly Observatory Budap est Hungary Individual issues could b e downloaded for scientic and educational purp oses free of charge Bibliographic information of the recent issues could b e entered to indexing sys tems No IBVS issues may b e stored in a public retrieval system in any form or by any means electronic or otherwise without the prior written p ermission of the publishers Prior written p ermission of the publishers is required for entering IBVS issues to an electronic indexing or bibliographic system to o CONTENTS C STERKEN A JONES B VOS I ZEGELAAR AM van GENDEREN M de GROOT On the Cyclicity of the S Dor Phases in AG Carinae ::::::::::::::::::::::::::::::::::::::::::::::::::: : J BOROVICKA L SAROUNOVA The Period and Lightcurve of NSV ::::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::: W LILLER AF JONES A New Very Long Period Variable Star in Norma ::::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::::: EA KARITSKAYA VP GORANSKIJ Unusual Fading of V Cygni Cyg X in Early November :::::::::::::::::::::::::::::::::::::::
    [Show full text]
  • Spectroscopy of Variable Stars
    Spectroscopy of Variable Stars Steve B. Howell and Travis A. Rector The National Optical Astronomy Observatory 950 N. Cherry Ave. Tucson, AZ 85719 USA Introduction A Note from the Authors The goal of this project is to determine the physical characteristics of variable stars (e.g., temperature, radius and luminosity) by analyzing spectra and photometric observations that span several years. The project was originally developed as a The 2.1-meter telescope and research project for teachers participating in the NOAO TLRBSE program. Coudé Feed spectrograph at Kitt Peak National Observatory in Ari- Please note that it is assumed that the instructor and students are familiar with the zona. The 2.1-meter telescope is concepts of photometry and spectroscopy as it is used in astronomy, as well as inside the white dome. The Coudé stellar classification and stellar evolution. This document is an incomplete source Feed spectrograph is in the right of information on these topics, so further study is encouraged. In particular, the half of the building. It also uses “Stellar Spectroscopy” document will be useful for learning how to analyze the the white tower on the right. spectrum of a star. Prerequisites To be able to do this research project, students should have a basic understanding of the following concepts: • Spectroscopy and photometry in astronomy • Stellar evolution • Stellar classification • Inverse-square law and Stefan’s law The control room for the Coudé Description of the Data Feed spectrograph. The spec- trograph is operated by the two The spectra used in this project were obtained with the Coudé Feed telescopes computers on the left.
    [Show full text]
  • Variable Star Classification and Light Curves Manual
    Variable Star Classification and Light Curves An AAVSO course for the Carolyn Hurless Online Institute for Continuing Education in Astronomy (CHOICE) This is copyrighted material meant only for official enrollees in this online course. Do not share this document with others. Please do not quote from it without prior permission from the AAVSO. Table of Contents Course Description and Requirements for Completion Chapter One- 1. Introduction . What are variable stars? . The first known variable stars 2. Variable Star Names . Constellation names . Greek letters (Bayer letters) . GCVS naming scheme . Other naming conventions . Naming variable star types 3. The Main Types of variability Extrinsic . Eclipsing . Rotating . Microlensing Intrinsic . Pulsating . Eruptive . Cataclysmic . X-Ray 4. The Variability Tree Chapter Two- 1. Rotating Variables . The Sun . BY Dra stars . RS CVn stars . Rotating ellipsoidal variables 2. Eclipsing Variables . EA . EB . EW . EP . Roche Lobes 1 Chapter Three- 1. Pulsating Variables . Classical Cepheids . Type II Cepheids . RV Tau stars . Delta Sct stars . RR Lyr stars . Miras . Semi-regular stars 2. Eruptive Variables . Young Stellar Objects . T Tau stars . FUOrs . EXOrs . UXOrs . UV Cet stars . Gamma Cas stars . S Dor stars . R CrB stars Chapter Four- 1. Cataclysmic Variables . Dwarf Novae . Novae . Recurrent Novae . Magnetic CVs . Symbiotic Variables . Supernovae 2. Other Variables . Gamma-Ray Bursters . Active Galactic Nuclei 2 Course Description and Requirements for Completion This course is an overview of the types of variable stars most commonly observed by AAVSO observers. We discuss the physical processes behind what makes each type variable and how this is demonstrated in their light curves. Variable star names and nomenclature are placed in a historical context to aid in understanding today’s classification scheme.
    [Show full text]
  • 121012-AAS-221 Program-14-ALL, Page 253 @ Preflight
    221ST MEETING OF THE AMERICAN ASTRONOMICAL SOCIETY 6-10 January 2013 LONG BEACH, CALIFORNIA Scientific sessions will be held at the: Long Beach Convention Center 300 E. Ocean Blvd. COUNCIL.......................... 2 Long Beach, CA 90802 AAS Paper Sorters EXHIBITORS..................... 4 Aubra Anthony ATTENDEE Alan Boss SERVICES.......................... 9 Blaise Canzian Joanna Corby SCHEDULE.....................12 Rupert Croft Shantanu Desai SATURDAY.....................28 Rick Fienberg Bernhard Fleck SUNDAY..........................30 Erika Grundstrom Nimish P. Hathi MONDAY........................37 Ann Hornschemeier Suzanne H. Jacoby TUESDAY........................98 Bethany Johns Sebastien Lepine WEDNESDAY.............. 158 Katharina Lodders Kevin Marvel THURSDAY.................. 213 Karen Masters Bryan Miller AUTHOR INDEX ........ 245 Nancy Morrison Judit Ries Michael Rutkowski Allyn Smith Joe Tenn Session Numbering Key 100’s Monday 200’s Tuesday 300’s Wednesday 400’s Thursday Sessions are numbered in the Program Book by day and time. Changes after 27 November 2012 are included only in the online program materials. 1 AAS Officers & Councilors Officers Councilors President (2012-2014) (2009-2012) David J. Helfand Quest Univ. Canada Edward F. Guinan Villanova Univ. [email protected] [email protected] PAST President (2012-2013) Patricia Knezek NOAO/WIYN Observatory Debra Elmegreen Vassar College [email protected] [email protected] Robert Mathieu Univ. of Wisconsin Vice President (2009-2015) [email protected] Paula Szkody University of Washington [email protected] (2011-2014) Bruce Balick Univ. of Washington Vice-President (2010-2013) [email protected] Nicholas B. Suntzeff Texas A&M Univ. suntzeff@aas.org Eileen D. Friel Boston Univ. [email protected] Vice President (2011-2014) Edward B. Churchwell Univ. of Wisconsin Angela Speck Univ. of Missouri [email protected] [email protected] Treasurer (2011-2014) (2012-2015) Hervey (Peter) Stockman STScI Nancy S.
    [Show full text]
  • Gaia Data Release 2 Special Issue
    A&A 623, A110 (2019) Astronomy https://doi.org/10.1051/0004-6361/201833304 & © ESO 2019 Astrophysics Gaia Data Release 2 Special issue Gaia Data Release 2 Variable stars in the colour-absolute magnitude diagram?,?? Gaia Collaboration, L. Eyer1, L. Rimoldini2, M. Audard1, R. I. Anderson3,1, K. Nienartowicz2, F. Glass1, O. Marchal4, M. Grenon1, N. Mowlavi1, B. Holl1, G. Clementini5, C. Aerts6,7, T. Mazeh8, D. W. Evans9, L. Szabados10, A. G. A. Brown11, A. Vallenari12, T. Prusti13, J. H. J. de Bruijne13, C. Babusiaux4,14, C. A. L. Bailer-Jones15, M. Biermann16, F. Jansen17, C. Jordi18, S. A. Klioner19, U. Lammers20, L. Lindegren21, X. Luri18, F. Mignard22, C. Panem23, D. Pourbaix24,25, S. Randich26, P. Sartoretti4, H. I. Siddiqui27, C. Soubiran28, F. van Leeuwen9, N. A. Walton9, F. Arenou4, U. Bastian16, M. Cropper29, R. Drimmel30, D. Katz4, M. G. Lattanzi30, J. Bakker20, C. Cacciari5, J. Castañeda18, L. Chaoul23, N. Cheek31, F. De Angeli9, C. Fabricius18, R. Guerra20, E. Masana18, R. Messineo32, P. Panuzzo4, J. Portell18, M. Riello9, G. M. Seabroke29, P. Tanga22, F. Thévenin22, G. Gracia-Abril33,16, G. Comoretto27, M. Garcia-Reinaldos20, D. Teyssier27, M. Altmann16,34, R. Andrae15, I. Bellas-Velidis35, K. Benson29, J. Berthier36, R. Blomme37, P. Burgess9, G. Busso9, B. Carry22,36, A. Cellino30, M. Clotet18, O. Creevey22, M. Davidson38, J. De Ridder6, L. Delchambre39, A. Dell’Oro26, C. Ducourant28, J. Fernández-Hernández40, M. Fouesneau15, Y. Frémat37, L. Galluccio22, M. García-Torres41, J. González-Núñez31,42, J. J. González-Vidal18, E. Gosset39,25, L. P. Guy2,43, J.-L. Halbwachs44, N. C. Hambly38, D.
    [Show full text]
  • A High Contrast Survey for Extrasolar Giant Planets with the Simultaneous Differential Imager (SDI)
    A High Contrast Survey for Extrasolar Giant Planets with the Simultaneous Differential Imager (SDI) Item Type text; Electronic Dissertation Authors Biller, Beth Alison Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 03/10/2021 23:58:44 Link to Item http://hdl.handle.net/10150/194542 A HIGH CONTRAST SURVEY FOR EXTRASOLAR GIANT PLANETS WITH THE SIMULTANEOUS DIFFERENTIAL IMAGER (SDI) by Beth Alison Biller A Dissertation Submitted to the Faculty of the DEPARTMENT OF ASTRONOMY In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA 2 0 0 7 2 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE As members of the Dissertation Committee, we certify that we have read the dis- sertation prepared by Beth Alison Biller entitled “A High Contrast Survey for Extrasolar Giant Planets with the Simultaneous Differential Imager (SDI)” and recommend that it be accepted as fulfilling the dissertation requirement for the Degree of Doctor of Philosophy. Date: June 29, 2007 Laird Close Date: June 29, 2007 Don McCarthy Date: June 29, 2007 John Bieging Date: June 29, 2007 Glenn Schneider Final approval and acceptance of this dissertation is contingent upon the candi- date's submission of the final copies of the dissertation to the Graduate College. I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fulfilling the dissertation requirement.
    [Show full text]
  • Pulsating Variable Stars and the Hertzsprung-Russell Diagram
    - !% ! $1!%" % Studying intrinsically pulsating variable stars plays a very important role in stellar evolution under- standing. The Hertzsprung-Russell diagram is a powerful tool to track which stage of stellar life is represented by a particular type of variable stars. Let's see what major pulsating variable star types are and learn about their place on the H-R diagram. This approach is very useful, as it also allows to make a decision about a variability type of a star for which the properties are known partially. The Hertzsprung-Russell diagram shows a group of stars in different stages of their evolution. It is a plot showing a relationship between luminosity (or abso- lute magnitude) and stars' surface temperature (or spectral type). The bottom scale is ranging from high-temperature blue-white stars (left side of the diagram) to low-temperature red stars (right side). The position of a star on the diagram provides information about its present stage and its mass. Stars that burn hydrogen into helium lie on the diagonal branch, the so-called main sequence. In this article intrinsically pulsating variables are covered, showing their place on the H-R diagram. Pulsating variable stars form a broad and diverse class of objects showing the changes in brightness over a wide range of periods and magnitudes. Pulsations are generally split into two types: radial and non-radial. Radial pulsations mean the entire star expands and shrinks as a whole, while non- radial ones correspond to expanding of one part of a star and shrinking the other. Since the H-R diagram represents the color-luminosity relation, it is fairly easy to identify not only the effective temperature Intrinsic variable types on the Hertzsprung–Russell and absolute magnitude of stars, but the evolutionary diagram.
    [Show full text]
  • 198 6Apj. . .309. .7 32J the Astrophysical Journal, 309:732-736
    32J .7 The Astrophysical Journal, 309:732-736,1986 October 15 kf 1986. The American Astronomical Society. All rights reserved. Printed in U.S.A. .309. 6ApJ. 198 RV TAURI STARS AS POST-ASYMPTOTIG GIANT BRANCH OBJECTS M.Jura Department of Astronomy, University of California, Los Angeles Received 1986 February 5 ; accepted 1986 April 8 ABSTRACT RV Tau stars are rare, luminous pulsators of spectral types F, G, and K. Analysis of the IRAS data shows that the mass-loss rates from RV Tau stars have apparently significantly decreased during the past ~500 yr -5 -1 from about 10 M0 yr , depending upon the metallicity of the stars and the grain emissivity at 60 /mi. It seems likely that these stars have just evolved from the phase of rapid mass loss, characteristic of the last stages of the asymptotic giant branch (AGB). The birthrate of RV Tau stars in the solar neighborhood is very roughly 6 x 10"4 kpc-3 yr-1, about a tenth of the birthrate of all planetary nebulae, and this is consistent with the view that we are witnessing the subset of stars undergoing post-AGB evolution that are low mass and at least in some cases of low metallicity. Most RV Tau stars will probably become planetary nebulae; others, however, may evolve sufficiently slowly that their envelopes will dissipate before being photoionized. Subject headings: infrared: sources — stars: evolution — stars: mass loss — stars: RV Tauri — stars : stellar statistics I. INTRODUCTION and a small bolometric correction, then, from equation (1), 3 The evolution of stars from the asymptotic giant branch again, L ~ 10 L0.
    [Show full text]
  • Among the Intrinsic Variables, the RV Tauri Stars Days
    496 ASTRONOMY: PA YNE-GAPOSCHKIN AND BRENTON PROC. N. A. S. A STUDY OF THE RV TAURI VARIABLES By CECILIA PAYNE-GAPOSCHKIN AND VIRGINIA K. BRENTON HARVARD COLLEGE OBSERVATORY Communicated October 16, 1942 1. Definitions.-Among the intrinsic variables, the RV Tauri stars stand out with rather definite characteristics. Three principal criteria may be used for assigning stars to the class. (a) Successive minima differ in depth. Deep and shallow minima are conventionally called "primary" and "secondary." (b) Primary and secondary minima interchange phases at intervals. (c) The stars are variable in spectrum and in radial velocity. The spectrum is of Class F, G or K at maximum. The shortest known period is 38 days (EZ Aquilae), the longest is 146 days (R Scuti). Although the period usually assigned to these stars is that from one primary minimum to the next, a comparison with the velocity curve shows that the star undergoes a type of pulsation with one-half that period. The brighter RV Tauri stars have recently been studied on the Harvard collection of stellar photographs. Of the twenty-nine stars now assigned to the class, fourteen proved to be bright enough for intensive study. A discussion of about sixteen thousand observations of these stars has been completed,' and the present note is intended to summarize some of the physical results. 2. The Secondary Characteristics.-Many RV Tauri stars show rather marked irregularities in period, and though over a long interval a mean period can always be assigned, instantaneous elements for short intervals may require periods differing by one or two per cent.
    [Show full text]
  • Variable Stars
    VARIABLE STARS RONALD E. MICKLE Denver, Colorado 80211 ©2001 Ronald E. Mickle ABSTRACT The objective of this paper is to research the causes for variability and identify selected stars within telescope reach. In addition, individual observations of the magnitudes (Mv) of selected variable stars were made and a plan designed for more extensive work on variable stars was developed. Variable stars are stars that vary in brightness. They can range from a thousandth of a magnitude to as much as 20 magnitudes. This range of magnitudes, referred to as amplitude variation, can have periods of variability ranging from a fraction of a second to years. Algol, one of the oldest know variables, was known to ancient astronomers to vary in brightness. Today over 30,000 variable stars are known and catalogued, and thousands more are suspected. Variable stars change their brightness for several reasons. Pulsating variables swell and shrink due to internal forces, while an eclipsing binary will dim when it is eclipsed by its binary companion. (Universe 1999; The Astrophysical Journal) Today measurements of the magnitudes of variable stars are made through visual observations using the naked eye, or instruments such as a charge- coupled device (CCD). The observations made for this paper were reported to the American Association of Variable Star Observers (AAVSO) via their website. The AAVSO website lists variable star organizations in 17 countries to which observations can be reported (AAVSO). 1. IDENTIFICATION OF STAR FIELDS Observations were made from Denver, Colorado, United States. Latitude and longitude coordinates are 40ºN, 105ºW. 1.1. EYEPIECE FIELD-OF-VIEW (FOV) AAVSO charts aid in locating the target variable.
    [Show full text]
  • Basic Astronomy Labs
    Astronomy Laboratory Exercise 31 The Magnitude Scale On a dark, clear night far from city lights, the unaided human eye can see on the order of five thousand stars. Some stars are bright, others are barely visible, and still others fall somewhere in between. A telescope reveals hundreds of thousands of stars that are too dim for the unaided eye to see. Most stars appear white to the unaided eye, whose cells for detecting color require more light. But the telescope reveals that stars come in a wide palette of colors. This lab explores the modern magnitude scale as a means of describing the brightness, the distance, and the color of a star. The earliest recorded brightness scale was developed by Hipparchus, a natural philosopher of the second century BCE. He ranked stars into six magnitudes according to brightness. The brightest stars were first magnitude, the second brightest stars were second magnitude, and so on until the dimmest stars he could see, which were sixth magnitude. Modern measurements show that the difference between first and sixth magnitude represents a brightness ratio of 100. That is, a first magnitude star is about 100 times brighter than a sixth magnitude star. Thus, each magnitude is 100115 (or about 2. 512) times brighter than the next larger, integral magnitude. Hipparchus' scale only allows integral magnitudes and does not allow for stars outside this range. With the invention of the telescope, it became obvious that a scale was needed to describe dimmer stars. Also, the scale should be able to describe brighter objects, such as some planets, the Moon, and the Sun.
    [Show full text]
  • A Catalog of Variable Stars Based on the New Name List
    ISSN 1063-7729, Astronomy Reports, 2009, Vol. 53, No. 11, pp. 1013–1019. c Pleiades Publishing, Ltd., 2009. Original Russian Text c E.V. Kazarovets, N.N. Samus’, O.V. Durlevich, N.N. Kireeva, E.N. Pastukhova, G. Pojmanski, 2009, published in Astronomicheski˘ı Zhurnal, 2009, Vol. 86, No. 11, pp. 1088–1094. A Catalog of Variable Stars Based on the New Name List E. V. Kazarovets1, N.N.Samus’1, 2*, O.V.Durlevich2, N. N. Kireeva1, E.N.Pastukhova1,andG.Pojmanski3 1Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya ul. 48, Moscow, 119017 Russia 2Sternberg Astronomical Institute, Universitetskii pr. 13, Moscow, 119992 Russia 3Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, Warsaw, 00-478 Poland Received April 30, 2009; in final form, June 25, 2009 Abstract—We present a new electronic version of the General Catalog of Variable Stars (GCVS) based on thenewIAUnamelistofconfirmed variable stars. The catalog contains 1270 stars, most of them contained earlier in the New Catalog of Suspected Variable Stars or its supplement. A number of recent studies— including those by authors of the catalog, who investigated many stars using data from modern automatic surveys, determined light-curve elements for periodic stars, and plotted numerous light curves—have made it possible to move these stars to the GCVS. Among the catalog objects, 24 stars are novae or other unusual variable stars that acquired their GCVS names out of the usual order, upon communication from the Bureau of Astronomical Telegrams of the International Astronomical Union. We present the GCVS names, coordinates, classifications (in two forms: the GCVS system and a new, proposed system), brightness- variation limits, and light-curve elements for the catalog stars, as well as bibliographic references and remarks when necessary.
    [Show full text]