LECTURE 15 – Jerome Fang
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Arxiv:1612.03165V3 [Astro-Ph.HE] 12 Sep 2017 – 2 –
The second catalog of flaring gamma-ray sources from the Fermi All-sky Variability Analysis S. Abdollahi1, M. Ackermann2, M. Ajello3;4, A. Albert5, L. Baldini6, J. Ballet7, G. Barbiellini8;9, D. Bastieri10;11, J. Becerra Gonzalez12;13, R. Bellazzini14, E. Bissaldi15, R. D. Blandford16, E. D. Bloom16, R. Bonino17;18, E. Bottacini16, J. Bregeon19, P. Bruel20, R. Buehler2;21, S. Buson12;22, R. A. Cameron16, M. Caragiulo23;15, P. A. Caraveo24, E. Cavazzuti25, C. Cecchi26;27, A. Chekhtman28, C. C. Cheung29, G. Chiaro11, S. Ciprini25;26, J. Conrad30;31;32, D. Costantin11, F. Costanza15, S. Cutini25;26, F. D'Ammando33;34, F. de Palma15;35, A. Desai3, R. Desiante17;36, S. W. Digel16, N. Di Lalla6, M. Di Mauro16, L. Di Venere23;15, B. Donaggio10, P. S. Drell16, C. Favuzzi23;15, S. J. Fegan20, E. C. Ferrara12, W. B. Focke16, A. Franckowiak2, Y. Fukazawa1, S. Funk37, P. Fusco23;15, F. Gargano15, D. Gasparrini25;26, N. Giglietto23;15, M. Giomi2;59, F. Giordano23;15, M. Giroletti33, T. Glanzman16, D. Green13;12, I. A. Grenier7, J. E. Grove29, L. Guillemot38;39, S. Guiriec12;22, E. Hays12, D. Horan20, T. Jogler40, G. J´ohannesson41, A. S. Johnson16, D. Kocevski12;42, M. Kuss14, G. La Mura11, S. Larsson43;31, L. Latronico17, J. Li44, F. Longo8;9, F. Loparco23;15, M. N. Lovellette29, P. Lubrano26, J. D. Magill13, S. Maldera17, A. Manfreda6, M. Mayer2, M. N. Mazziotta15, P. F. Michelson16, W. Mitthumsiri45, T. Mizuno46, M. E. Monzani16, A. Morselli47, I. V. Moskalenko16, M. Negro17;18, E. Nuss19, T. Ohsugi46, N. Omodei16, M. Orienti33, E. -
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. -
A Fuse Survey of the Rotation Rates of Very Massive Stars in the Small and Large Magellanic Clouds
The Astrophysical Journal, 700:844–858, 2009 July 20 doi:10.1088/0004-637X/700/1/844 C 2009. The American Astronomical Society. All rights reserved. Printed in the U.S.A. A FUSE SURVEY OF THE ROTATION RATES OF VERY MASSIVE STARS IN THE SMALL AND LARGE MAGELLANIC CLOUDS Laura R. Penny1 and Douglas R. Gies2 1 Department of Physics and Astronomy, The College of Charleston, Charleston, SC 29424, USA; [email protected] 2 Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106, USA; [email protected] Received 2009 February 3; accepted 2009 May 26; published 2009 July 6 ABSTRACT We present projected rotational velocity values for 97 Galactic, 55 SMC, and 106 LMC O-B type stars from archival FUSE observations. The evolved and unevolved samples from each environment are compared through the Kolmogorov–Smirnov test to determine if the distribution of equatorial rotational velocities is metallicity dependent for these massive objects. Stellar interior models predict that massive stars with SMC metallicity will have significantly reduced angular momentum loss on the main sequence compared to their Galactic counterparts. Our results find some support for this prediction but also show that even at Galactic metallicity, evolved and unevolved massive stars have fairly similar fractions of stars with large V sin i values. Macroturbulent broadening that is present in the spectral features of Galactic evolved massive stars is lower in the LMC and SMC samples. This suggests the processes that lead to macroturbulence are dependent upon metallicity. -
Astro 404 Lecture 30 Nov. 6, 2019 Announcements
Astro 404 Lecture 30 Nov. 6, 2019 Announcements: • Problem Set 9 due Fri Nov 8 2 3/2 typo corrected in L24 notes: nQ = (2πmkT/h ) • Office Hours: Instructor – after class or by appointment • TA: Thursday noon-1pm or by appointment • Exam: grading elves hard at work Last time: low-mass stars after main sequence Q: burning phases? 1 Q: shell burning “mirror” principle? Low-Mass Stars After Main Sequence unburnt H ⋆ helium core contracts H He H burning in shell around core He outer layers expand → red giant “mirror” effect of shell burning: • core contraction, envelope expansion • total gravitational potential energy Ω roughly conserved core becomes more tightly bound, envelope less bound ⋆ helium ignition degenerate core unburnt H H He runaway burning: helium flash inert He → 12 He C+O 2 then core helium burning 3α C and shell H burning “horizontal branch” star unburnt H H He ⋆ for solar mass stars: after CO core forms inert He He C • helium shell burning begins inert C • hydrogen shell burning continues Q: star path on HR diagram during these phases? 3 Low-Mass Post-Main-Sequence: HR Diagram ⋆ H shell burning ↔ red giant ⋆ He flash marks “tip of the red giant branch” ⋆ core He fusion ↔ horizontal branch ⋆ He + H shell burning ↔ asymptotic giant branch asymptotic giant branch H+He shell burn He flash core He burn L main sequence horizontal branch red giant branch H shell burning Sun Luminosity 4 Temperature T iClicker Poll: AGB Star Intershell Region in AGB phase: burning in two shells, no core fusion unburnt H H He inert He He C Vote your conscience–all -
Cfa in the News ~ Week Ending 3 January 2010
Wolbach Library: CfA in the News ~ Week ending 3 January 2010 1. New social science research from G. Sonnert and co-researchers described, Science Letter, p40, Tuesday, January 5, 2010 2. 2009 in science and medicine, ROGER SCHLUETER, Belleville News Democrat (IL), Sunday, January 3, 2010 3. 'Science, celestial bodies have always inspired humankind', Staff Correspondent, Hindu (India), Tuesday, December 29, 2009 4. Why is Carpenter defending scientists?, The Morning Call, Morning Call (Allentown, PA), FIRST ed, pA25, Sunday, December 27, 2009 5. CORRECTIONS, OPINION BY RYAN FINLEY, ARIZONA DAILY STAR, Arizona Daily Star (AZ), FINAL ed, pA2, Saturday, December 19, 2009 6. We see a 'Super-Earth', TOM BEAL; TOM BEAL, ARIZONA DAILY STAR, Arizona Daily Star, (AZ), FINAL ed, pA1, Thursday, December 17, 2009 Record - 1 DIALOG(R) New social science research from G. Sonnert and co-researchers described, Science Letter, p40, Tuesday, January 5, 2010 TEXT: "In this paper we report on testing the 'rolen model' and 'opportunity-structure' hypotheses about the parents whom scientists mentioned as career influencers. According to the role-model hypothesis, the gender match between scientist and influencer is paramount (for example, women scientists would disproportionately often mention their mothers as career influencers)," scientists writing in the journal Social Studies of Science report (see also ). "According to the opportunity-structure hypothesis, the parent's educational level predicts his/her probability of being mentioned as a career influencer (that ism parents with higher educational levels would be more likely to be named). The examination of a sample of American scientists who had received prestigious postdoctoral fellowships resulted in rejecting the role-model hypothesis and corroborating the opportunity-structure hypothesis. -
The Core Helium Flash Revisited
A&A 520, A114 (2010) Astronomy DOI: 10.1051/0004-6361/201014461 & c ESO 2010 Astrophysics The core helium flash revisited III. From Population I to Population III stars M. Mocák1,S.W.Campbell2,3,E.Müller4, and K. Kifonidis4 1 Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, CP 226, 1050 Brussels, Belgium e-mail: [email protected] 2 Departament de Física i Enginyeria Nuclear, EUETIB, Universitat Politécnica de Catalunya, C./Comte d’Urgell 187, 08036 Barcelona, Spain e-mail: [email protected] 3 Centre for Stellar and Planetary Astrophysics, School of Mathematical Sciences, Monash University, Melbourne 3800, Australia 4 Max-Planck-Institut für Astrophysik, Postfach 1312, 85741 Garching, Germany Received 18 March 2010 / Accepted 13 June 2010 ABSTRACT Context. Degenerate ignition of helium in low-mass stars at the end of the red giant branch phase leads to dynamic convection in their helium cores. One-dimensional (1D) stellar modeling of this intrinsically multi-dimensional dynamic event is likely to be inadequate. Previous hydrodynamic simulations imply that the single convection zone in the helium core of metal-rich Pop I stars grows during the flash on a dynamic timescale. This may lead to hydrogen injection into the core and to a double convection zone structure as known from one-dimensional core helium flash simulations of low-mass Pop III stars. Aims. We perform hydrodynamic simulations of the core helium flash in two and three dimensions to better constrain the nature of these events. To this end we study the hydrodynamics of convection within the helium cores of a 1.25 M metal-rich Pop I star (Z = 0.02), and, for the first time, a 0.85 M metal-free Pop III star (Z = 0) near the peak of the flash. -
Download Version of Record (PDF / 6MB)
Open Research Online The Open University’s repository of research publications and other research outputs The Formation and Evolution of Cataclysmic Variables Thesis How to cite: Davis, Philip (2009). The Formation and Evolution of Cataclysmic Variables. PhD thesis The Open University. For guidance on citations see FAQs. c 2009 The Author https://creativecommons.org/licenses/by-nc-nd/4.0/ Version: Version of Record Link(s) to article on publisher’s website: http://dx.doi.org/doi:10.21954/ou.ro.0000f236 Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyright owners. For more information on Open Research Online’s data policy on reuse of materials please consult the policies page. oro.open.ac.uk e-p> Faculty of Science, The Open University The Formation and Evolution of Cataclysmic Variables Philip Davis MPhys. Submitted for the degree of Doctor of Philosophy June 2009 T>ecr€ <yf Suamission ; i=i Jotoe 2 ^rr£ op B S ProQuest Number: 13837663 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 13837663 Published by ProQuest LLC(2019). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. -
Expanding Space
ASK ASTRO Astronomy’s experts from around the globe answer your cosmic questions. cosmologists call “dark energy,” burn not only hydrogen, but also helium. But after about produces repulsive gravitational 1 to 2 billion years, it will exhaust its supply of nuclear effects that cause the average fuel entirely and its core will contract into a white dwarf distance between galaxies to made of carbon and oxygen, while the outer layers of its increase faster and faster over atmosphere drift away as a planetary nebula. time. Determining dark energy’s White dwarfs are roughly the size of Earth, but the true nature remains one of the Sun as a white dwarf will be about 200,000 times denser greatest mysteries in theoretical than our planet. These objects no longer burn fuel to physics today. generate light or heat, but because they start out hot So, does the existence of dark — 10,000 kelvins or more — and have immensely high energy in our accelerating density, they continue shining with residual heat and universe mean that space is cool slowly. It takes a white dwarf roughly 10 trillion expanding everywhere, even on years (nearly 730 times the current age of the universe, small scales such as those inside which is 13.7 billion years) to cool off enough that it no of an atom, where most of the longer gives off visible light and becomes what astrono- volume is effectively “empty” mers term a black dwarf. On March 7, 2004, space? The short answer is no! So, the Sun won’t become a black dwarf for trillions We do know that meteorites exist on the surface of NASA’s Mars rover Spirit captured a And we should all count ourselves of years — and, in fact, no black dwarfs exist yet, simply Mars. -
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. -
Stellar Evolution
AccessScience from McGraw-Hill Education Page 1 of 19 www.accessscience.com Stellar evolution Contributed by: James B. Kaler Publication year: 2014 The large-scale, systematic, and irreversible changes over time of the structure and composition of a star. Types of stars Dozens of different types of stars populate the Milky Way Galaxy. The most common are main-sequence dwarfs like the Sun that fuse hydrogen into helium within their cores (the core of the Sun occupies about half its mass). Dwarfs run the full gamut of stellar masses, from perhaps as much as 200 solar masses (200 M,⊙) down to the minimum of 0.075 solar mass (beneath which the full proton-proton chain does not operate). They occupy the spectral sequence from class O (maximum effective temperature nearly 50,000 K or 90,000◦F, maximum luminosity 5 × 10,6 solar), through classes B, A, F, G, K, and M, to the new class L (2400 K or 3860◦F and under, typical luminosity below 10,−4 solar). Within the main sequence, they break into two broad groups, those under 1.3 solar masses (class F5), whose luminosities derive from the proton-proton chain, and higher-mass stars that are supported principally by the carbon cycle. Below the end of the main sequence (masses less than 0.075 M,⊙) lie the brown dwarfs that occupy half of class L and all of class T (the latter under 1400 K or 2060◦F). These shine both from gravitational energy and from fusion of their natural deuterium. Their low-mass limit is unknown. -
Population Parameters of Intermediate-Age Star Clusters in the Large Magellanic Cloud
The Astrophysical Journal, 737:4 (10pp), 2011 August 10 doi:10.1088/0004-637X/737/1/4 C 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A. POPULATION PARAMETERS OF INTERMEDIATE-AGE STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD. III. DYNAMICAL EVIDENCE FOR A RANGE OF AGES BEING RESPONSIBLE FOR EXTENDED MAIN-SEQUENCE TURNOFFS∗ Paul Goudfrooij1, Thomas H. Puzia2, Rupali Chandar3, and Vera Kozhurina-Platais1 1 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA; [email protected], [email protected] 2 Department of Astronomy and Astrophysics, Pontificia Universidad Catolica´ de Chile, Av. Vicuna˜ Mackenna 4860, Macul 7820436, Santiago, Chile; [email protected] 3 Department of Physics and Astronomy, The University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606, USA; [email protected] Received 2011 March 29; accepted 2011 May 13; published 2011 July 20 ABSTRACT We present a new analysis of 11 intermediate-age (1–2 Gyr) star clusters in the Large Magellanic Cloud based on Hubble Space Telescope imaging data. Seven of the clusters feature main-sequence turnoff (MSTO) regions that are wider than can be accounted for by a simple stellar population, whereas their red giant branches (RGBs) indicate a 4 5 single value of [Fe/H]. The star clusters cover a range in present-day mass from about 1 × 10 M to 2 × 10 M. We compare radial distributions of stars in the upper and lower parts of the MSTO region, and calculate cluster masses and escape velocities from the present time back to a cluster age of 10 Myr. -
A FUSE Survey of Interstellar Molecular Hydrogen in the Small
DRAFT VERSION OCTOBER 25, 2018 Preprint typeset using LATEX style emulateapj v. 04/03/99 A FUSE SURVEY OF INTERSTELLAR MOLECULAR HYDROGEN IN THE SMALL AND LARGE MAGELLANIC CLOUDS1 JASON TUMLINSON 2, J. MICHAEL SHULL2,3, BRIAN L. RACHFORD2, MATTHEW K. BROWNING2, THEODORE P. SNOW2, ALEX W. FULLERTON4,5, EDWARD B. JENKINS6, BLAIR D. SAVAGE7, PAUL A. CROWTHER8, H. WARREN MOOS5, KENNETH R. SEMBACH5, GEORGE SONNEBORN9, & DONALD G. YORK10 Draft version October 25, 2018 ABSTRACT We describe a moderate-resolution FUSE survey of H2 along 70 sight lines to the Small and Large Magellanic Clouds, using hot stars as background sources. FUSE spectra of 67% of observed Magellanic Cloud sources (52% of LMC and 92% of SMC) exhibit absorption lines from the H2 Lyman and Werner bands between 912 and 14 −2 1120 Å. Our survey is sensitive to N(H2) ≥ 10 cm ; the highest column densities are log N(H2) = 19.9 in the LMC and 20.6 in the SMC. We find reduced H2 abundances in the Magellanic Clouds relative to the Milky Way, +0.005 +0.006 with average molecular fractions h fH2i =0.010−0.002 for the SMC and h fH2i =0.012−0.003 for the LMC, compared with h fH2i =0.095 for the Galactic disk over a similar range of reddening. The dominant uncertainty in this measurement results from the systematic differences between 21 cm radio emission and Lyα in pencil-beam sight 6 lines as measures of N(H I). These results imply that the diffuse H2 masses of the LMC and SMC are 8 × 10 M⊙ 6 and 2 × 10 M⊙, respectively, 2% and 0.5% of the H I masses derived from 21 cm emission measurements.