Astronomy 1 – Fall 2019
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White Dwarfs
Chandra X-Ray Observatory X-Ray Astronomy Field Guide White Dwarfs White dwarfs are among the dimmest stars in the universe. Even so, they have commanded the attention of astronomers ever since the first white dwarf was observed by optical telescopes in the middle of the 19th century. One reason for this interest is that white dwarfs represent an intriguing state of matter; another reason is that most stars, including our sun, will become white dwarfs when they reach their final, burnt-out collapsed state. A star experiences an energy crisis and its core collapses when the star's basic, non-renewable energy source - hydrogen - is used up. A shell of hydrogen on the edge of the collapsed core will be compressed and heated. The nuclear fusion of the hydrogen in the shell will produce a new surge of power that will cause the outer layers of the star to expand until it has a diameter a hundred times its present value. This is called the "red giant" phase of a star's existence. A hundred million years after the red giant phase all of the star's available energy resources will be used up. The exhausted red giant will puff off its outer layer leaving behind a hot core. This hot core is called a Wolf-Rayet type star after the astronomers who first identified these objects. This star has a surface temperature of about 50,000 degrees Celsius and is A composite furiously boiling off its outer layers in a "fast" wind traveling 6 million image of the kilometers per hour. -
SHELL BURNING STARS: Red Giants and Red Supergiants
SHELL BURNING STARS: Red Giants and Red Supergiants There is a large variety of stellar models which have a distinct core – envelope structure. While any main sequence star, or any white dwarf, may be well approximated with a single polytropic model, the stars with the core – envelope structure may be approximated with a composite polytrope: one for the core, another for the envelope, with a very large difference in the “K” constants between the two. This is a consequence of a very large difference in the specific entropies between the core and the envelope. The original reason for the difference is due to a jump in chemical composition. For example, the core may have no hydrogen, and mostly helium, while the envelope may be hydrogen rich. As a result, there is a nuclear burning shell at the bottom of the envelope; hydrogen burning shell in our example. The heat generated in the shell is diffusing out with radiation, and keeps the entropy very high throughout the envelope. The core – envelope structure is most pronounced when the core is degenerate, and its specific entropy near zero. It is supported against its own gravity with the non-thermal pressure of degenerate electron gas, while all stellar luminosity, and all entropy for the envelope, are provided by the shell source. A common property of stars with well developed core – envelope structure is not only a very large jump in specific entropy but also a very large difference in pressure between the center, Pc, the shell, Psh, and the photosphere, Pph. Of course, the two characteristics are closely related to each other. -
Brown Dwarf: White Dwarf: Hertzsprung -Russell Diagram (H-R
Types of Stars Spectral Classifications: Based on the luminosity and effective temperature , the stars are categorized depending upon their positions in the HR diagram. Hertzsprung -Russell Diagram (H-R Diagram) : 1. The H-R Diagram is a graphical tool that astronomers use to classify stars according to their luminosity (i.e. brightness), spectral type, color, temperature and evolutionary stage. 2. HR diagram is a plot of luminosity of stars versus its effective temperature. 3. Most of the stars occupy the region in the diagram along the line called the main sequence. During that stage stars are fusing hydrogen in their cores. Various Types of Stars Brown Dwarf: White Dwarf: Brown dwarfs are sub-stellar objects After a star like the sun exhausts its nuclear that are not massive enough to sustain fuel, it loses its outer layer as a "planetary nuclear fusion processes. nebula" and leaves behind the remnant "white Since, comparatively they are very cold dwarf" core. objects, it is difficult to detect them. Stars with initial masses Now there are ongoing efforts to study M < 8Msun will end as white dwarfs. them in infrared wavelengths. A typical white dwarf is about the size of the This picture shows a brown dwarf around Earth. a star HD3651 located 36Ly away in It is very dense and hot. A spoonful of white constellation of Pisces. dwarf material on Earth would weigh as much as First directly detected Brown Dwarf HD 3651B. few tons. Image by: ESO The image is of Helix nebula towards constellation of Aquarius hosts a White Dwarf Helix Nebula 6500Ly away. -
The Potential of Planets Orbiting Red Dwarf Stars to Support Oxygenic Photosynthesis and Complex Life
1 The Potential of Planets Orbiting Red Dwarf Stars to Support Oxygenic Photosynthesis and Complex Life Joseph Gale1 and Amri Wandel2 The Institute of Life Sciences1and The Racach Institute of Physics2, The Hebrew University of Jerusalem, 91904, Israel. [email protected] [email protected] Accepted for publication in the International Journal of Astrobiology Abstract We review and reassess the latest findings on the existence of extra-solar system planets and their potential of having environmental conditions that could support Earth-like life. Within the last two decades, the multi-millennial question of the existence of extra-Solar- system planets has been resolved with the discovery of numerous planets orbiting nearby stars, many of which are Earth-sized (and some even with moderate surface temperatures). Of particular interest in our search for clement conditions for extra-solar system life are planets orbiting Red Dwarf (RD) stars, the most numerous stellar type in the Milky Way galaxy. We show that including RDs as potential life supporting host stars could increase the probability of finding biotic planets by a factor of up to a thousand, and reduce the estimate of the distance to our nearest biotic neighbor by up to 10. We argue that multiple star systems need to be taken into account when discussing habitability and the abundance of biotic exoplanets, in particular binaries of which one or both members are RDs. Early considerations indicated that conditions on RD planets would be inimical to life, as their Habitable Zones (where liquid water could exist) would be so close as to make planets tidally locked to their star. -
Chapter 16 the Sun and Stars
Chapter 16 The Sun and Stars Stargazing is an awe-inspiring way to enjoy the night sky, but humans can learn only so much about stars from our position on Earth. The Hubble Space Telescope is a school-bus-size telescope that orbits Earth every 97 minutes at an altitude of 353 miles and a speed of about 17,500 miles per hour. The Hubble Space Telescope (HST) transmits images and data from space to computers on Earth. In fact, HST sends enough data back to Earth each week to fill 3,600 feet of books on a shelf. Scientists store the data on special disks. In January 2006, HST captured images of the Orion Nebula, a huge area where stars are being formed. HST’s detailed images revealed over 3,000 stars that were never seen before. Information from the Hubble will help scientists understand more about how stars form. In this chapter, you will learn all about the star of our solar system, the sun, and about the characteristics of other stars. 1. Why do stars shine? 2. What kinds of stars are there? 3. How are stars formed, and do any other stars have planets? 16.1 The Sun and the Stars What are stars? Where did they come from? How long do they last? During most of the star - an enormous hot ball of gas day, we see only one star, the sun, which is 150 million kilometers away. On a clear held together by gravity which night, about 6,000 stars can be seen without a telescope. -
Pulsating Red Giant Stars in Eccentric Binary Systems Discovered from Kepler Space-Based Photometry a Sample Study and the Analysis of KIC 5006817 P
A&A 564, A36 (2014) Astronomy DOI: 10.1051/0004-6361/201322477 & c ESO 2014 Astrophysics Pulsating red giant stars in eccentric binary systems discovered from Kepler space-based photometry A sample study and the analysis of KIC 5006817 P. G. Beck1,K.Hambleton2,1,J.Vos1, T. Kallinger3, S. Bloemen1, A. Tkachenko1, R. A. García4, R. H. Østensen1, C. Aerts1,5,D.W.Kurtz2, J. De Ridder1,S.Hekker6, K. Pavlovski7, S. Mathur8,K.DeSmedt1, A. Derekas9, E. Corsaro1, B. Mosser10,H.VanWinckel1,D.Huber11, P. Degroote1,G.R.Davies12,A.Prša13, J. Debosscher1, Y. Elsworth12,P.Nemeth1, L. Siess14,V.S.Schmid1,P.I.Pápics1,B.L.deVries1, A. J. van Marle1, P. Marcos-Arenal1, and A. Lobel15 1 Instituut voor Sterrenkunde, KU Leuven, 3001 Leuven, Belgium e-mail: [email protected] 2 Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK 3 Institut für Astronomie der Universität Wien, Türkenschanzstr. 17, 1180 Wien, Austria 4 Laboratoire AIM, CEA/DSM-CNRS – Université Denis Diderot-IRFU/SAp, 91191 Gif-sur-Yvette Cedex, France 5 Department of Astrophysics, IMAPP, University of Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands 6 Astronomical Institute Anton Pannekoek, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands 7 Department of Physics, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia 8 Space Science Institute, 4750 Walnut street Suite #205, Boulder CO 80301, USA 9 Konkoly Observ., Research Centre f. Astronomy and Earth Sciences, Hungarian Academy of Sciences, 1121 Budapest, Hungary 10 LESIA, CNRS, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, 92195 Meudon Cedex, France 11 NASA Ames Research Center, Moffett Field CA 94035, USA 12 School of Physics and Astronomy, University of Birmingham, Edgebaston, Birmingham B13 2TT, UK 13 Department of Astronomy and Astrophysics, Villanova University, 800 East Lancaster avenue, Villanova PA 19085, USA 14 Institut d’Astronomie et d’Astrophysique, Univ. -
A FEROS Survey of Hot Subdwarf Stars
Open Astron. 2018; 27: 7–13 Research Article Stéphane Vennes*, Péter Németh, and Adela Kawka A FEROS Survey of Hot Subdwarf Stars https://doi.org/10.1515/astro-2018-0005 Received Oct 02, 2017; accepted Nov 07, 2017 Abstract: We have completed a survey of twenty-two ultraviolet-selected hot subdwarfs using the Fiber-fed Extended Range Optical Spectrograph (FEROS) and the 2.2-m telescope at La Silla. The sample includes apparently single objects as well as hot subdwarfs paired with a bright, unresolved companion. The sample was extracted from our GALEX cat- alogue of hot subdwarf stars. We identified three new short-period systems (P = 3.5 hours to 5 days) and determined the orbital parameters of a long-period (P = 62d.66) sdO plus G III system. This particular system should evolve into a close double degenerate system following a second common envelope phase. We also conducted a chemical abundance study of the subdwarfs: Some objects show nitrogen and argon abundance excess with respect to oxygen. We present key results of this programme. Keywords: binaries: close, binaries: spectroscopic, subdwarfs, white dwarfs, ultraviolet: stars 1 Introduction ing a mass transfer event, i.e., comparable to the observed fraction (≈70%) of short period binaries (P < 10 d, Maxted et al. 2001; Morales-Rueda et al. 2003), while the remain- The properties of extreme horizontal branch (EHB) stars, ing single objects are formed by the merger of two helium i.e., the hot, hydrogen-rich (sdB) and helium-rich subd- white dwarfs which would also result in a thin hydrogen warf (sdO) stars, located at the faint blue end of the hori- layer. -
Massive Fast Rotating Highly Magnetized White Dwarfs: Theory and Astrophysical Applications
Massive Fast Rotating Highly Magnetized White Dwarfs: Theory and Astrophysical Applications Thesis Advisors Ph.D. Student Prof. Remo Ruffini Diego Leonardo Caceres Uribe* Dr. Jorge A. Rueda *D.L.C.U. acknowledges the financial support by the International Relativistic Astrophysics (IRAP) Ph.D. program. Academic Year 2016–2017 2 Contents General introduction 4 1 Anomalous X-ray pulsars and Soft Gamma-ray repeaters: A new class of pulsars 9 2 Structure and Stability of non-magnetic White Dwarfs 21 2.1 Introduction . 21 2.2 Structure and Stability of non-rotating non-magnetic white dwarfs 23 2.2.1 Inverse b-decay . 29 2.2.2 General Relativity instability . 31 2.2.3 Mass-radius and mass-central density relations . 32 2.3 Uniformly rotating white dwarfs . 37 2.3.1 The Mass-shedding limit . 38 2.3.2 Secular Instability in rotating and general relativistic con- figurations . 38 2.3.3 Pycnonuclear Reactions . 39 2.3.4 Mass-radius and mass-central density relations . 41 3 Magnetic white dwarfs: Stability and observations 47 3.1 Introduction . 47 3.2 Observations of magnetic white dwarfs . 49 3.2.1 Introduction . 49 3.2.2 Historical background . 51 3.2.3 Mass distribution of magnetic white dwarfs . 53 3.2.4 Spin periods of isolated magnetic white dwarfs . 53 3.2.5 The origin of the magnetic field . 55 3.2.6 Applications . 56 3.2.7 Conclusions . 57 3.3 Stability of Magnetic White Dwarfs . 59 3.3.1 Introduction . 59 3.3.2 Ultra-magnetic white dwarfs . 60 3.3.3 Equation of state and virial theorem violation . -
PS 224, Fall 2014 HW 4
PS 224, Fall 2014 HW 4 1. True or False? Explain in one or two short sentences. a. Scientists are currently building an infrared telescope designed to observe fusion reactions in the Sun’s core. False. Infrared telescopes cannot see through the Sun. b. Two stars that look very different must be made of different kinds of elements. False. What a star looks like depends on many different properties like mass, age, and size. c. Two stars that have the same apparent brightness in the sky must also have the same luminosity. False. How bright a star appears depends on the luminosity of a stars and its distance away from us. d. Some of the stars on the main sequence of the H-R diagram are not converting hydrogen into helium. False. The main-seuqence is defined as the phase of a star’s life when it burns hydrogen into helium. e. Stars that begin their lives with the most mass live longer than less massive stars because they have so much more hydrogen fuel. False. Massive stars live have shorter lifetimes as they burn through their fuel faster. f. All giants, supergiants, and white dwarfs were once main-sequence stars. True. Main-sequence stars evolve to become giants and supergiants based on their mass and eventually end up as white dwarfs. g. The iron in my blood came from a star that blew up more than 4 billion years ago. True. All elements except hydrogen and helium were produced in stars. h. If the Sun had been born 4½ billion years ago as a high-mass star rather than as a low- mass star, Jupiter would have Earth-like conditions today, while Earth would be hot like Venus. -
Earth-Deadly-Future.Pdf
The evolving solar system “BLACK SMOKERS” are bastions of life at hydrothermal vents in today’s oceans. They get their names from the soot-like look of Earth’s the mineral-rich material they eject. NOAA he first things to go will be A brightening Sun will boil the Earth’s glaciers and polar ice caps. Warming surface seas and bake the continents a temperatures will turn billion years from now. But that’s ice to water, leading to a deadly slow but steady rise in sea levels. But it Tdoesn’t stop there. Eventually, tempera- nothing compared with what tures will rise high enough for seawater to boil away, leaving Earth bereft of this we can expect further down vital substance. With that, life on our world will need to relocate underground the road. ⁄⁄⁄ BYCR RI HA D TALCOTT or emigrate from our home planet. This apocalyptic scenario is more than an inconvenient truth — it’s our inevitable destiny. And it has nothing future to do with changes humans may work on our fragile environment. The agent for this transformation is far beyond our control. The culprit: our current life-sustaining source of heat and energy, the Sun. Ask most people familiar with astronomy when to expect this coming apocalypse, and you’ll hear answers of around 5 billion years — once the Sun swells into a red giant. But the end is nearer than that. The Sun is currently growing brighter, and has been since the day it was born. Life on the main sequence A BILLION YEARS FROM NOW, the Sun’s When the Sun was a baby, it was rather increasing luminosity will have boiled off miserly by today’s standards. -
(NASA/Chandra X-Ray Image) Type Ia Supernova Remnant – Thermonuclear Explosion of a White Dwarf
Stellar Evolution Card Set Description and Links 1. Tycho’s SNR (NASA/Chandra X-ray image) Type Ia supernova remnant – thermonuclear explosion of a white dwarf http://chandra.harvard.edu/photo/2011/tycho2/ 2. Protostar formation (NASA/JPL/Caltech/Spitzer/R. Hurt illustration) A young star/protostar forming within a cloud of gas and dust http://www.spitzer.caltech.edu/images/1852-ssc2007-14d-Planet-Forming-Disk- Around-a-Baby-Star 3. The Crab Nebula (NASA/Chandra X-ray/Hubble optical/Spitzer IR composite image) A type II supernova remnant with a millisecond pulsar stellar core http://chandra.harvard.edu/photo/2009/crab/ 4. Cygnus X-1 (NASA/Chandra/M Weiss illustration) A stellar mass black hole in an X-ray binary system with a main sequence companion star http://chandra.harvard.edu/photo/2011/cygx1/ 5. White dwarf with red giant companion star (ESO/M. Kornmesser illustration/video) A white dwarf accreting material from a red giant companion could result in a Type Ia supernova http://www.eso.org/public/videos/eso0943b/ 6. Eight Burst Nebula (NASA/Hubble optical image) A planetary nebula with a white dwarf and companion star binary system in its center http://apod.nasa.gov/apod/ap150607.html 7. The Carina Nebula star-formation complex (NASA/Hubble optical image) A massive and active star formation region with newly forming protostars and stars http://www.spacetelescope.org/images/heic0707b/ 8. NGC 6826 (Chandra X-ray/Hubble optical composite image) A planetary nebula with a white dwarf stellar core in its center http://chandra.harvard.edu/photo/2012/pne/ 9. -
Announcements
Announcements • Next Session – Stellar evolution • Low-mass stars • Binaries • High-mass stars – Supernovae – Synthesis of the elements • Note: Thursday Nov 11 is a campus holiday Red Giant 8 100Ro 10 years L 10 3Ro, 10 years Temperature Red Giant Hydrogen fusion shell Contracting helium core Electron Degeneracy • Pauli Exclusion Principle says that you can only have two electrons per unit 6-D phase- space volume in a gas. DxDyDzDpxDpyDpz † Red Giants • RG Helium core is support against gravity by electron degeneracy • Electron-degenerate gases do not expand with increasing temperature (no thermostat) • As the Temperature gets to 100 x 106K the “triple-alpha” process (Helium fusion to Carbon) can happen. Helium fusion/flash Helium fusion requires two steps: He4 + He4 -> Be8 Be8 + He4 -> C12 The Berylium falls apart in 10-6 seconds so you need not only high enough T to overcome the electric forces, you also need very high density. Helium Flash • The Temp and Density get high enough for the triple-alpha reaction as a star approaches the tip of the RGB. • Because the core is supported by electron degeneracy (with no temperature dependence) when the triple-alpha starts, there is no corresponding expansion of the core. So the temperature skyrockets and the fusion rate grows tremendously in the `helium flash’. Helium Flash • The big increase in the core temperature adds momentum phase space and within a couple of hours of the onset of the helium flash, the electrons gas is no longer degenerate and the core settles down into `normal’ helium fusion. • There is little outward sign of the helium flash, but the rearrangment of the core stops the trip up the RGB and the star settles onto the horizontal branch.