20 research outputs found
The Magellanic Bridge as a Damped Lyman Alpha System: Physical Properties of Cold Gas Toward PKS 0312-770
We measure the physical properties of a local multicomponent absorption-line system at V-circle dot similar to 200 km s(-1) toward the quasar PKS 0312-770 behind the Magellanic Bridge (MB) using Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) spectroscopy in conjunction with photoionization modeling. At an impact parameter of similar to 10 kpc from the Small Magellanic Cloud (SMC), this sightline provides a unique opportunity to probe the chemical properties and ionization structure in a nearby absorption line system with a column density of log N-H I similar to 20.2, at the transition between damped Ly alpha (DLA) and sub-DLA systems. We find that metallicity of -1.0 < log(Z/Z(circle dot)) < -0.5 and ionization parameter of -6 < logU < -5 for three low-ionization components and logU similar to -2.6 for one high-ionization component. One component at V-circle dot = 207 km s(-1) shows an alpha-element abundance log( Si/H) similar to -5.0, making it similar to 0.2 dex more metal-rich than both SMC HII regions and stars within the MB and the SMC. The N/Si ratio in this component is log( N/Si)= -0.3 +/- 0.1, making it comparable to other N-poor dwarf galaxies and similar to 0.2 dex lower than Hii regions in the SMC. Another component at V-circle dot = 236 km s(-1) shows a similar Si/H ratio but has log(N/Si) = -1.0 +/- 0.2, indicating a nitrogen deficiency comparable to that seen in the most N-poor DLA systems. These differences imply different chemical enrichment histories between components along the same sightline. Our results suggest that if these absorbers are representative some fraction of DLA systems, then (1) DLA systems along single sightlines do not necessarily represent the global properties of the absorbing cloud, and (2) the chemical composition within a given DLA cloud may be inhomogeneous.ArticleThe Astrophysical Journal. 695:1382-1398 (2009)journal articl
Long gamma-ray bursts and core-collapse supernovae have different environments
When massive stars exhaust their fuel they collapse and often produce the
extraordinarily bright explosions known as core-collapse supernovae. On
occasion, this stellar collapse also powers an even more brilliant relativistic
explosion known as a long-duration gamma-ray burst. One would then expect that
long gamma-ray bursts and core-collapse supernovae should be found in similar
galactic environments. Here we show that this expectation is wrong. We find
that the long gamma-ray bursts are far more concentrated on the very brightest
regions of their host galaxies than are the core-collapse supernovae.
Furthermore, the host galaxies of the long gamma-ray bursts are significantly
fainter and more irregular than the hosts of the core-collapse supernovae.
Together these results suggest that long-duration gamma-ray bursts are
associated with the most massive stars and may be restricted to galaxies of
limited chemical evolution. Our results directly imply that long gamma-ray
bursts are relatively rare in galaxies such as our own Milky Way.Comment: 27 pages, 4 figures, submitted to Nature on 22 August 2005, revised 9
February 2006, online publication 10 May 2006. Supplementary material
referred to in the text can be found at
http://www.stsci.edu/~fruchter/GRB/locations/supplement.pdf . This new
version contains minor changes to match the final published versio
Morphological Mutations of Dwarf Galaxies
Dwarf galaxies (DGs) are extremely challenging objects in extragalactic
astrophysics. They are expected to originate as the first units in Cold
Dark-Matter cosmology. They are the galaxy type most sensitive to environmental
influences and their division into multiple types with various properties have
invoked the picture of their variant morphological transformations. Detailed
observations reveal characteristics which allow to deduce the evolutionary
paths and to witness how the environment has affected the evolution. Here we
review peculiarities of general morphological DG types and refer to processes
which can deplete gas-rich irregular DGs leading to dwarf ellipticals, while
gas replenishment implies an evolutionary cycling. Finally, as the less
understood DG types the Milky Way satellite dwarf spheroidal galaxies are
discussed in the context of transformation.Comment: 17 pages, 7 figures, Proceedings of Symposium 3 of JENAM 2010 "Dwarf
Galaxies: Key to Galaxy Formation and Evolution", Polychronis Papaderos,
Simone Recchi, Gerhard Hensler (Eds.), Springer Publisher, Heidelberg, ISBN
978-3-642-22017-
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star
Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining1. Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability2,3,4,5. That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required
Relativistic Binaries in Globular Clusters
Galactic globular clusters are old, dense star systems typically containing
10\super{4}--10\super{7} stars. As an old population of stars, globular
clusters contain many collapsed and degenerate objects. As a dense population
of stars, globular clusters are the scene of many interesting close dynamical
interactions between stars. These dynamical interactions can alter the
evolution of individual stars and can produce tight binary systems containing
one or two compact objects. In this review, we discuss theoretical models of
globular cluster evolution and binary evolution, techniques for simulating this
evolution that leads to relativistic binaries, and current and possible future
observational evidence for this population. Our discussion of globular cluster
evolution will focus on the processes that boost the production of hard binary
systems and the subsequent interaction of these binaries that can alter the
properties of both bodies and can lead to exotic objects. Direct {\it N}-body
integrations and Fokker--Planck simulations of the evolution of globular
clusters that incorporate tidal interactions and lead to predictions of
relativistic binary populations are also discussed. We discuss the current
observational evidence for cataclysmic variables, millisecond pulsars, and
low-mass X-ray binaries as well as possible future detection of relativistic
binaries with gravitational radiation.Comment: 88 pages, 13 figures. Submitted update of Living Reviews articl
Proper-motion age dating of the progeny of Nova Scorpii AD 1437.
'Cataclysmic variables' are binary star systems in which one star of the pair is a white dwarf, and which often generate bright and energetic stellar outbursts. Classical novae are one type of outburst: when the white dwarf accretes enough matter from its companion, the resulting hydrogen-rich atmospheric envelope can host a runaway thermonuclear reaction that generates a rapid brightening. Achieving peak luminosities of up to one million times that of the Sun, all classical novae are recurrent, on timescales of months to millennia. During the century before and after an eruption, the 'novalike' binary systems that give rise to classical novae exhibit high rates of mass transfer to their white dwarfs. Another type of outburst is the dwarf nova: these occur in binaries that have stellar masses and periods indistinguishable from those of novalikes but much lower mass-transfer rates, when accretion-disk instabilities drop matter onto the white dwarfs. The co-existence at the same orbital period of novalike binaries and dwarf novae-which are identical but for their widely varying accretion rates-has been a longstanding puzzle. Here we report the recovery of the binary star underlying the classical nova eruption of 11 March AD 1437 (refs 12, 13), and independently confirm its age by proper-motion dating. We show that, almost 500 years after a classical-nova event, the system exhibited dwarf-nova eruptions. The three other oldest recovered classical novae display nova shells, but lack firm post-eruption ages, and are also dwarf novae at present. We conclude that many old novae become dwarf novae for part of the millennia between successive nova eruptions
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