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Copyright by Robert Michael Quimby 2006 the Dissertation Committee for Robert Michael Quimby Certifies That This Is the Approved Version of the Following Dissertation
Copyright by Robert Michael Quimby 2006 The Dissertation Committee for Robert Michael Quimby certifies that this is the approved version of the following dissertation: The Texas Supernova Search Committee: J. Craig Wheeler, Supervisor Peter H¨oflich Carl Akerlof Gary Hill Pawan Kumar Edward L. Robinson The Texas Supernova Search by Robert Michael Quimby, A.B., M.A. DISSERTATION Presented to the Faculty of the Graduate School of The University of Texas at Austin in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY THE UNIVERSITY OF TEXAS AT AUSTIN December 2006 Acknowledgments I would like to thank J. Craig Wheeler, Pawan Kumar, Gary Hill, Peter H¨oflich, Rob Robinson and Christopher Gerardy for their support and advice that led to the realization of this project and greatly improved its quality. Carl Akerlof, Don Smith, and Eli Rykoff labored to install and maintain the ROTSE-IIIb telescope with help from David Doss, making this project possi- ble. Finally, I thank Greg Aldering, Saul Perlmutter, Robert Knop, Michael Wood-Vasey, and the Supernova Cosmology Project for lending me their image subtraction code and assisting me with its installation. iv The Texas Supernova Search Publication No. Robert Michael Quimby, Ph.D. The University of Texas at Austin, 2006 Supervisor: J. Craig Wheeler Supernovae (SNe) are popular tools to explore the cosmological expan- sion of the Universe owing to their bright peak magnitudes and reasonably high rates; however, even the relatively homogeneous Type Ia supernovae are not intrinsically perfect standard candles. Their absolute peak brightness must be established by corrections that have been largely empirical. -
Stellar Magnetic Activity – Star-Planet Interactions
EPJ Web of Conferences 101, 005 02 (2015) DOI: 10.1051/epjconf/2015101005 02 C Owned by the authors, published by EDP Sciences, 2015 Stellar magnetic activity – Star-Planet Interactions Poppenhaeger, K.1,2,a 1 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambrigde, MA 02138, USA 2 NASA Sagan Fellow Abstract. Stellar magnetic activity is an important factor in the formation and evolution of exoplanets. Magnetic phenomena like stellar flares, coronal mass ejections, and high- energy emission affect the exoplanetary atmosphere and its mass loss over time. One major question is whether the magnetic evolution of exoplanet host stars is the same as for stars without planets; tidal and magnetic interactions of a star and its close-in planets may play a role in this. Stellar magnetic activity also shapes our ability to detect exoplanets with different methods in the first place, and therefore we need to understand it properly to derive an accurate estimate of the existing exoplanet population. I will review recent theoretical and observational results, as well as outline some avenues for future progress. 1 Introduction Stellar magnetic activity is an ubiquitous phenomenon in cool stars. These stars operate a magnetic dynamo that is fueled by stellar rotation and produces highly structured magnetic fields; in the case of stars with a radiative core and a convective outer envelope (spectral type mid-F to early-M), this is an αΩ dynamo, while fully convective stars (mid-M and later) operate a different kind of dynamo, possibly a turbulent or α2 dynamo. These magnetic fields manifest themselves observationally in a variety of phenomena. -
Arxiv:0709.0302V1 [Astro-Ph] 3 Sep 2007 N Ro,M,414 USA 48104, MI, Arbor, Ann USA As(..Mcayne L 01.Sc Aeilcudslow Could Material Such Some 2001)
DRAFT VERSION NOVEMBER 4, 2018 Preprint typeset using LATEX style emulateapj v. 03/07/07 SN 2005AP: A MOST BRILLIANT EXPLOSION ROBERT M. QUIMBY1,GREG ALDERING2,J.CRAIG WHEELER1,PETER HÖFLICH3,CARL W. AKERLOF4,ELI S. RYKOFF4 Draft version November 4, 2018 ABSTRACT We present unfiltered photometric observations with ROTSE-III and optical spectroscopic follow-up with the HET and Keck of the most luminous supernova yet identified, SN 2005ap. The spectra taken about 3 days before and 6 days after maximum light show narrow emission lines (likely originating in the dwarf host) and absorption lines at a redshift of z =0.2832, which puts the peak unfiltered magnitude at −22.7 ± 0.1 absolute. Broad P-Cygni features corresponding to Hα, C III,N III, and O III, are further detected with a photospheric velocity of ∼ 20,000kms−1. Unlike other highly luminous supernovae such as 2006gy and 2006tf that show slow photometric evolution, the light curve of SN 2005ap indicates a 1-3 week rise to peak followed by a relatively rapid decay. The spectra also lack the distinct emission peaks from moderately broadened (FWHM ∼ 2,000kms−1) Balmer lines seen in SN 2006gyand SN 2006tf. We briefly discuss the origin of the extraordinary luminosity from a strong interaction as may be expected from a pair instability eruption or a GRB-like engine encased in a H/He envelope. Subject headings: Supernovae, SN 2005ap 1. INTRODUCTION the ultra-relativistic flow and thus mask the gamma-ray bea- Luminous supernovae (SNe) are most commonly associ- con announcing their creation, unlike their stripped progeni- ated with the Type Ia class, which are thought to involve tor cousins. -
Are Superluminous Supernovae Powered by Collision Or By
Are Superluminous Supernovae Powered By Collision Or By Millisecond Magnetars? Shlomo Dado1 and Arnon Dar1 ABSTRACT Using our previously derived simple analytic expression for the bolometric light curves of supernovae, we demonstrate that the collision of the fast de- bris of ordinary supernova explosions with relatively slow-moving shells from pre-supernova eruptions can produce the observed bolometric light curves of su- perluminous supernovae (SLSNe) of all types. These include both, those which can be explained as powered by spinning-down millisecond magnetars and those which cannot. That and the observed close similarity between the bolometric light-curves of SLSNe and ordinary interacting SNe suggest that SLSNe are pow- ered mainly by collisions with relatively slow moving circumstellar shells from pre-supernova eruptions rather than by the spin-down of millisecond magnetars born in core collapse supernova explosions. Subject headings: supernovae: general 1. Introduction For a long time, it has been widely believed that the observed luminosity of all known types of supernova (SN) explosions is powered by one or more of the following sources: radioactive decay of freshly-synthesized elements, typically 56Ni (Colgate and McKee 1969; Colgate et al. 1980), heat deposited in the envelope of a supergiant star by the explosion arXiv:1312.5273v1 [astro-ph.HE] 18 Dec 2013 shock (Grassberg et al. 1971), and interaction between the SN debris and the circumstellar wind environment (Chevalier 1982). Recently, however, a new type of SNe, superluminous SNe (SLSNe) whose peak luminosity exceeds 1044 ergs per second, much brighter than that of the brightest normal thermonuclear supernovae (type Ia) and core collapse supernova (types Ib/c and II) was discovered by modern supernova surveys. -
Chapter 11 SOLAR RADIO EMISSION W
Chapter 11 SOLAR RADIO EMISSION W. R. Barron E. W. Cliver J. P. Cronin D. A. Guidice Since the first detection of solar radio noise in 1942, If the frequency f is in cycles per second, the wavelength radio observations of the sun have contributed significantly X in meters, the temperature T in degrees Kelvin, the ve- to our evolving understanding of solar structure and pro- locity of light c in meters per second, and Boltzmann's cesses. The now classic texts of Zheleznyakov [1964] and constant k in joules per degree Kelvin, then Bf is in W Kundu [1965] summarized the first two decades of solar m 2Hz 1sr1. Values of temperatures Tb calculated from radio observations. Recent monographs have been presented Equation (1 1. 1)are referred to as equivalent blackbody tem- by Kruger [1979] and Kundu and Gergely [1980]. perature or as brightness temperature defined as the tem- In Chapter I the basic phenomenological aspects of the perature of a blackbody that would produce the observed sun, its active regions, and solar flares are presented. This radiance at the specified frequency. chapter will focus on the three components of solar radio The radiant power received per unit area in a given emission: the basic (or minimum) component, the slowly frequency band is called the power flux density (irradiance varying component from active regions, and the transient per bandwidth) and is strictly defined as the integral of Bf,d component from flare bursts. between the limits f and f + Af, where Qs is the solid angle Different regions of the sun are observed at different subtended by the source. -
Radioactive Decay), Chapter 7 (SN 1987A), Background: Sections 3.1, 3.2, 3.3, 3.4, 3.5, 3.8, 3.10, 4.1, 4.2, 4.3, 4.4, 5.2, 5.4 (Binary Stars and Accretion Disks)
Friday, March 10, 2017 Reading for Exam 3: Chapter 6, end of Section 6 (binary evolution), Section 6.7 (radioactive decay), Chapter 7 (SN 1987A), Background: Sections 3.1, 3.2, 3.3, 3.4, 3.5, 3.8, 3.10, 4.1, 4.2, 4.3, 4.4, 5.2, 5.4 (binary stars and accretion disks). Plus superluminous supernovae, not in the book. Astronomy in the news? Potatoes can grow just about anywhere, including Mars, according to researchers who tested the idea put forth in the movie "The Martian." Scientists are growing potatoes in Mars-like soil from a Peruvian desert inside a CubeSat under extreme conditions, and the findings could not only benefit future Mars colonists but also help undernourished populations here on Earth. Goal: To understand the nature and importance of SN 1987A for our understanding of massive star evolution and iron core collapse. Chapter 7 Image of SN 1987A and environs in Large Magellanic Cloud, taken by Hubble Space Telescope, January 2017 One Minute Exam What was the most important thing about SN 1987A in terms of the basic physics of core collapse? It exploded in a blue, not a red supergiant It was surrounded by three rings It produced radioactive nickel and cobalt Neutrinos were detected from it Saw neutrinos! Neutron star must have formed and survived for at least 10 seconds. If a black hole had formed in the first instants, neither light nor neutrinos could have been emitted. No sign of neutron star since, despite looking hard for 30 years. Whatever is in the center of Cas A, most likely a neutron star, is too dim to be seen at the distance of the LMC, so SN 1987A might have made one of those (probably a neutron star, but not bright like the one in the Crab Nebula). -
ASTRONOMICAL IMAGE SUBTRACTION by CROSS-CONVOLUTION Fang Yuan1 and Carl W
The Astrophysical Journal, 677:808–812, 2008 April 10 # 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A. ASTRONOMICAL IMAGE SUBTRACTION BY CROSS-CONVOLUTION Fang Yuan1 and Carl W. Akerlof1 Received 2007 November 20; accepted 2008 January 1 ABSTRACT In recent years, there has been a proliferation of wide-field sky surveys to search for a variety of transient objects. Using relatively short focal lengths, the optics of these systems produce undersampled stellar images often marred by a variety of aberrations. As participants in such activities, we have developed a new algorithm for image subtraction that no longer requires high-quality reference images for comparison. The computational efficiency is comparable with similar procedures currently in use. The general technique is cross-convolution: two convolution kernels are generated to make a test image and a reference image separately transform to match as closely as possible. In analogy to the optimization technique for generating smoothing splines, the inclusion of an rms width penalty term constrains the diffusion of stellar images. In addition, by evaluating the convolution kernels on uniformly spaced subimages across the total area, these routines can accommodate point-spread functions that vary considerably across the focal plane. Subject headinggs: methods: statistical — techniques: photometric 1. INTRODUCTION and was quite familiar with the SN discovery process. Quimby adapted the SCP image-subtraction code (Perlmutter et al. 1999) The advent of low-noise megapixel electronic image sensors, for use as the basic tool for finding 30 SNe over a period of 2 years cheap fast computers, and terabyte data storage systems has en- abled searches for rare astrophysical phenomena that would from observations with the University of Texas 30% allocation of ROTSE-IIIb time at the McDonald Observatory. -
Stellar Atmospheres I – Overview
Indo-German Winter School on Astrophysics Stellar atmospheres I { overview Hans-G. Ludwig ZAH { Landessternwarte, Heidelberg ZAH { Landessternwarte 0.1 Overview What is the stellar atmosphere? • observational view Where are stellar atmosphere models needed today? • ::: or why do we do this to us? How do we model stellar atmospheres? • admittedly sketchy presentation • which physical processes? which approximations? • shocking? Next step: using model atmospheres as \background" to calculate the formation of spectral lines •! exercises associated with the lecture ! Linux users? Overview . TOC . FIN 1.1 What is the atmosphere? Light emitting surface layers of a star • directly accessible to (remote) observations • photosphere (dominant radiation source) • chromosphere • corona • wind (mass outflow, e.g. solar wind) Transition zone from stellar interior to interstellar medium • connects the star to the 'outside world' All energy generated in a star has to pass through the atmosphere Atmosphere itself usually does not produce additional energy! What? . TOC . FIN 2.1 The photosphere Most light emitted by photosphere • stellar model atmospheres often focus on this layer • also focus of these lectures ! chemical abundances Thickness ∆h, some numbers: • Sun: ∆h ≈ 1000 km ? Sun appears to have a sharp limb ? curvature effects on the photospheric properties small solar surface almost ’flat’ • white dwarf: ∆h ≤ 100 m • red super giant: ∆h=R ≈ 1 Stellar evolution, often: atmosphere = photosphere = R(T = Teff) What? . TOC . FIN 2.2 Solar photosphere: rather homogeneous but ::: What? . TOC . FIN 2.3 Magnetically active region, optical spectral range, T≈ 6000 K c Royal Swedish Academy of Science (1000 km=tick) What? . TOC . FIN 2.4 Corona, ultraviolet spectral range, T≈ 106 K (Fe IX) c Solar and Heliospheric Observatory, ESA & NASA (EIT 171 A˚ ) What? . -
What Do We See on the Face of the Sun? Lecture 3: the Solar Atmosphere the Sun’S Atmosphere
What do we see on the face of the Sun? Lecture 3: The solar atmosphere The Sun’s atmosphere Solar atmosphere is generally subdivided into multiple layers. From bottom to top: photosphere, chromosphere, transition region, corona, heliosphere In its simplest form it is modelled as a single component, plane-parallel atmosphere Density drops exponentially: (for isothermal atmosphere). T=6000K Hρ≈ 100km Density of Sun’s atmosphere is rather low – Mass of the solar atmosphere ≈ mass of the Indian ocean (≈ mass of the photosphere) – Mass of the chromosphere ≈ mass of the Earth’s atmosphere Stratification of average quiet solar atmosphere: 1-D model Typical values of physical parameters Temperature Number Pressure K Density dyne/cm2 cm-3 Photosphere 4000 - 6000 1015 – 1017 103 – 105 Chromosphere 6000 – 50000 1011 – 1015 10-1 – 103 Transition 50000-106 109 – 1011 0.1 region Corona 106 – 5 106 107 – 109 <0.1 How good is the 1-D approximation? 1-D models reproduce extremely well large parts of the spectrum obtained at low spatial resolution However, high resolution images of the Sun at basically all wavelengths show that its atmosphere has a complex structure Therefore: 1-D models may well describe averaged quantities relatively well, although they probably do not describe any particular part of the real Sun The following images illustrate inhomogeneity of the Sun and how the structures change with the wavelength and source of radiation Photosphere Lower chromosphere Upper chromosphere Corona Cartoon of quiet Sun atmosphere Photosphere The photosphere Photosphere extends between solar surface and temperature minimum (400-600 km) It is the source of most of the solar radiation. -
Superluminous Supernovae 56 I H Neato Ewe Uenv Jcaaddense and Ejecta Supernova Between Interaction the Ni, ⋆ − ∼ · · Ln .Sorokina I
SSRv manuscript No. (will be inserted by the editor) Superluminous supernovae Takashi J. Moriya⋆ · Elena I. Sorokina · Roger A. Chevalier Received: 25 December 2017 / Accepted: 5 March 2018 Abstract Superluminous supernovae are a new class of supernovae that were recognized about a decade ago. Both observational and theoretical progress has been significant in the last decade. In this review, we first briefly summarize the observational properties of superluminous super- novae. We then introduce the three major suggested luminosity sources to explain the huge luminosities of superluminous supernovae, i.e., the nu- clear decay of 56Ni, the interaction between supernova ejecta and dense circumstellar media, and the spin down of magnetars. We compare these models and discuss their strengths and weaknesses. Keywords supernovae · superluminous supernovae · massive stars 1 Introduction Superluminous supernovae (SLSNe) are supernovae (SNe) that become more luminous than ∼ −21 mag in optical. They are more than 1 mag more luminous than broad-line Type Ic SNe, or the so-called “hypernovae,” ⋆ NAOJ Fellow T. J. Moriya Division of Theoretical Astronomy, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan E-mail: [email protected] E. I. Sorokina Sternberg Astronomical Institute, M.V. Lomonosov Moscow State University, Uni- versitetski pr. 13, 119234 Moscow, Russia E-mail: [email protected] arXiv:1803.01875v2 [astro-ph.HE] 9 Mar 2018 R. A. Chevalier Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325, USA E-mail: [email protected] 2 which have kinetic energy of more than ∼ 1052 erg and are the most lumi- nous among the classical core-collapse SNe. -
First Firm Spectral Classification of an Early-B Pre-Main-Sequence Star: B275 in M
A&A 536, L1 (2011) Astronomy DOI: 10.1051/0004-6361/201118089 & c ESO 2011 Astrophysics Letter to the Editor First firm spectral classification of an early-B pre-main-sequence star: B275 in M 17 B. B. Ochsendorf1, L. E. Ellerbroek1, R. Chini2,3,O.E.Hartoog1,V.Hoffmeister2,L.B.F.M.Waters4,1, and L. Kaper1 1 Astronomical Institute Anton Pannekoek, University of Amsterdam, Science Park 904, PO Box 94249, 1090 GE Amsterdam, The Netherlands e-mail: [email protected]; [email protected] 2 Astronomisches Institut, Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany 3 Instituto de Astronomía, Universidad Católica del Norte, Antofagasta, Chile 4 SRON, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands Received 14 September 2011 / Accepted 25 October 2011 ABSTRACT The optical to near-infrared (300−2500 nm) spectrum of the candidate massive young stellar object (YSO) B275, embedded in the star-forming region M 17, has been observed with X-shooter on the ESO Very Large Telescope. The spectrum includes both photospheric absorption lines and emission features (H and Ca ii triplet emission lines, 1st and 2nd overtone CO bandhead emission), as well as an infrared excess indicating the presence of a (flaring) circumstellar disk. The strongest emission lines are double-peaked with a peak separation ranging between 70 and 105 km s−1, and they provide information on the physical structure of the disk. The underlying photospheric spectrum is classified as B6−B7, which is significantly cooler than a previous estimate based on modeling of the spectral energy distribution. This discrepancy is solved by allowing for a larger stellar radius (i.e. -
Resolving the Radio Photospheres of Main Sequence Stars
Astro2020 Science White Paper Resolving the Radio Photospheres of Main Sequence Stars Thematic Areas: Resolved Stellar Populations and their Environments Principal Author: Name: Chris Carilli Institution: NRAO, Socorro, NM, 87801 Email: [email protected] Phone: 1-575-835-7306 Co-authors: B. Butler, K. Golap (NRAO), M.T. Carilli (U. Colorado), S.M. White (AFRL) Abstract We discuss the need for spatially resolved observations of the radio photospheres of main sequence stars. Such studies are fundamental to determining the structure of stars in the key transition region from the cooler optical photosphere to the hot chromosphere – the regions powering exo-space weather phenomena. Future large area radio facilities operating in the tens to 100 GHz range will be able to image directly the larger main sequence stars within 10 pc or so, possibly resolving the large surface structures, as might occur on eg. active M-dwarf stars. For more distant main sequence stars, measurements of sizes and brightnesses can be made using disk model fitting to the uv data down to stellar diameters of ∼ 0:4 mas. This size would include M0 V stars to a distance of 15 pc, A0 V stars to 60 pc, and Red Giants to 2.4 kpc. Based on the Hipparcos catalog, we estimate that there are at least 10,000 stars that will be resolved by the ngVLA. While the vast majority of these (95%) are giants or supergiants, there are still over 500 main sequence stars that can be resolved, with ∼ 50 to 150 in each spectral type (besides O stars). 1 Main Sequence Stars: Radio Photospheres The field of stellar atmospheres, and atmospheric activity, has taken on new relevance in the context of the search for habitable planets, due to the realization of the dramatic effect ’space weather’ can have on the development of life (Osten et al.