Radiation astronomy/Continua

The 15" refractor at Comanche Springs Astronomy Campus had its finder scope (a Stellarvue 80/9D achromat) equipped with a Baader Herschel Solar Wedge and a Solar Continuum Filter for today's transit of Venus. Credit: Jeff Barton from Richardson, TX, USA.{{free media}}

Lyc photon or Ly continuum photon or Lyman continuum photon are a kind of photon emitted from stars. Hydrogen is ionized by absorption of Lyc photons. Lyc photons are in the ultraviolet portion of the electromagnetic spectrum of the hydrogen atom and immediately next to the limit of the Lyman series of the spectrum with wavelengths that are shorter than 91.1267 nanometres and with energy above 13.6 eV.

NeutronsEdit

"The weakening of the neutron shell structure for the nuclei near the neutron drip results from the coupling of the bound neutron states to the particle continuum, which is explicitly taken into account in our [Hartree-Fock-Bogolyubov] HFB calculation (see DFT [Dobaczewski, Flocard and Treiner 1984]). Since the neutron Fermi energy λn is small for such nuclei, the neutron continuum is close in energy to the occupied levels and hence the shell gap cannot be greater than |λn|."[1]

Beta particlesEdit

"The annihilation of positrons with electrons gives rise to two spectral features, a line emission at 511 keV and a positronium continuum emission (which increases in intensity with energy roughly as a power law up to 511 keV and falls abruptly to zero above 511 keV)[4]."[2]

NeutrinosEdit

In the solar neutrino spectrum predicted by the standard solar model, "The neutrino fluxes from the continuum sources (like pp and 8Be) are given in the units of number per cm2 per second per MeV at one astronomical unit."[3]

Gamma raysEdit

Continuum "radiation ... diffuse gamma rays with energies above 10 MeV. In the galaxy these are produced primarily by bremsstrahlung from cosmic ray electrons and from decay in flight of π0's produced by interactions of cosmic ray protons."[4]

X-raysEdit

The X-ray continuum can arise from bremsstrahlung, black-body radiation, synchrotron radiation, or what is called inverse Compton scattering of lower-energy photons by relativistic electrons, knock-on collisions of fast protons with atomic electrons, and atomic recombination, with or without additional electron transitions.[5]

UltravioletsEdit

A "detection of, or a significant upper limit to, the Lyman continuum can constrain the fraction of photons escaping absorption within the galaxy and ionizing the surrounding intergalactic medium."[6]

VisualsEdit

 
This is a typical supercontinuum spectrum. Credit: Burlyc.
 
Spectrum of light emitted by a deuterium lamp, shows a discrete part (tall sharp peaks) and a continuous part (smoothly varying between the peaks). Credit: Deglr6328.

Black and white images are not ordinarily starkly contrasted black and white but combine black and white in a continuum producing a range of shades of gray.

In physics, a continuous spectrum usually means a set of values for some physical quantity (such as energy or wavelength) that is best described as an interval of real numbers. It is opposed to discrete spectrum, a set of values that is discrete in the mathematical sense, where there is a positive gap between each value and the next one.

At left is a continuous spectrum from a deuterium lamp. The tall sharp peaks are discrete emissions and the continuous part is the smoothly varying part between the peaks. The smaller peaks and valleys may be due to measurement errors rather than discrete spectral lines.

"[W]ith Scorpius X-1 ... the visible continuum is roughly what would be expected from a hot plasma fitting the observed X-ray flux.[5] The plasma could be a coronal cloud of a central object or a transient plasma, where the energy source is unknown, but could be related to the idea of a close binary.[5]

A spectrum (plural spectra or spectrums[7]) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum.

In the continuum of colors of visible light [green] is located between yellow and blue.

Continuum light is linearly polarized at different locations across the face of the Sun (limb polarization) though taken as a whole, this polarization cancels.

In optics, a supercontinuum is formed when a collection of nonlinear processes act together upon a pump beam in order to cause severe spectral broadening of the original pump beam. The result is a smooth spectral continuum.

The figure at right shows a typical supercontinuum spectrum about an emission-line source. The blue line shows the spectrum of the source launched into a photonic crystal fiber while the red line shows the resulting supercontinuum spectrum generated after propagating through the fiber.

The inverse Raman effect[8] in optics ... which deals with the properties and behavior of light) is a form of Raman scattering.

If a material is simultaneously irradiated by intense monochromatic light of frequency νL (typically a laser beam) and light of a continuum of higher frequencies, among the possibilities for light scattering are scattering:

  • from the monochromatic beam at νL to the continuum at νLM (anti-Stokes Raman scattering)
  • from the continuum at νLM to the monochromatic beam at νL (Stokes Raman scattering)

where νM is a Raman frequency of the material.

The strength of these two scatterings depends (among other things) on the energy levels of the material, their occupancy, and the intensity of the continuum. In some circumstances Stokes scattering can exceed anti-Stokes scattering; in these cases the continuum (on leaving the material) is observed to have an absorption line (a dip in intensity) at νLM. This phenomenon is referred to as the inverse Raman effect; the application of the phenomenon is referred to as inverse Raman spectroscopy, and a record of the continuum is referred to as an inverse Raman spectrum.

Both absorption from a continuum of higher frequencies and absorption from a continuum of lower frequencies [can occur]. Absorption from a continuum of lower frequencies will not be observed if the Raman frequency of the material is vibrational in origin and if the material is in thermal equilibrium.

Reverberation mapping is an astrophysical technique for measuring the structure of the broad emission-line region (BLR) around a supermassive black hole at the center of an active galaxy and estimating the hole's mass. It is considered a "primary" mass estimation technique, i.e., the mass is measured directly from the motion that its gravitational force induces in the nearby gas.[9]

The black hole mass is measured from the formula

 

In this formula, ΔV is the rms velocity of gas moving near the black hole in the broad emission-line region, measured from the Doppler broadening of the gaseous emission lines; RBLR is the radius of the broad-line region; G is the constant of gravitation; and f is a poorly-known "form factor" that depends on the shape of the BLR.

The biggest difficulty with applying this formula is the measurement of RBLR. One standard technique[10] is based on the fact that the emission-line fluxes vary strongly in response to changes in the continuum, i.e., the light from the accretion disk near the black hole ("reverberation"). Furthermore, the emission-line response is found to be delayed with respect to changes in the continuum. Assuming that the delay is due to light travel times, the size of the broad emission-line region can be measured.

Only a small handful of AGN (less than 40) have been accurately "mapped" in this way. An alternative approach is to use an empirical correlation between RBLR and he continuum luminosity.[9]

Another uncertainty is the value of f. In principle, the response of the BLR to variations in the continuum could be used to map out the three-dimensional structure of the BLR. In practice, the amount and quality of data required to carry out such a deconvolution is prohibitive. Until about 2004, f was estimated ab initio based on simple models for the structure of the BLR. More recently, the value of f has been determined so as to bring the M-sigma relation for active galaxies into the best possible agreement with the M-sigma relation for quiescent galaxies.[9] When f is determined in this way, reverberation mapping becomes a "secondary", rather than "primary," mass estimation technique.

PolarizationsEdit

 
This image of the Crab Nebula is the result of long exposures in the Red, Blue, Green. Credit: Chris Schur.

"This unusual image [at right of the Crab Nebula] is the result of long exposures in the Red, Blue, Green [including Hα], and a separate set of exposures on the inner continuum radiation with RGB and polarizers crossed 120 degrees for each color. The result is an inner region that is mapped in polarization according to color. The outer filaments are primarily HII and OIII regions and have no polarization. The Object: The Crab Nebula in Taurus is a super nova remnant that exploded in the year 1084 AD and has been rapidly expanding ever since. It is located a degree from the easternmost star in the Bulls horns, and glows dimly at a magnitude of 8.4. While small at 6 arc minutes, it is typical of the [telescope image] size of many galaxies".[11]

VioletsEdit

"[T]he blue-violet continuum of some S and C-S stars is greatly depressed similar to that observed for N stars."[12] "Depending upon the polytype, temperature, and concentration of various possible impurities, SiC exhibits a fundamental absorption edge lying between about 2.2 and 3.0 eV."[12]

BluesEdit

"[T]he diffuse blue region [of the Crab nebula] is predominantly produced by synchrotron radiation, which is radiation given off by the curving motion of electrons in a magnetic field. The radiation corresponded to electrons moving at speeds up to half the speed of light."[13]

GreensEdit

"[H]igh-resolution (0.1") observations of the Seyfert 2 galaxy NGC 5728 with the Hubble Space Telescope [have produced images in the] green and red continua."[14]

YellowsEdit

"A density tracing of the spectrum of θ Lyr, K0 II. Straight chords through the yellow continuum toward the blue and from λ 4750 along the green depression to the Mg I "b" triplet lines define the break-angle α (α here is about 12°)."[15]

SubmillimetersEdit

Notation: let the symbol JCMT stand for the 15 m James Clerk Maxwell Telescope.

Notation: let the symbol IRAM stand for the 30 m Institute for Radio Astronomy in the Millimeter Range telescope.

The "submillimeter continuum emission from the rich star-forming core, ρ Oph A, at 350, 450,800, and 1300 μm using the JCMT and IRAM 30 m telescopes [has been mapped]."[16]

RadiosEdit

 
This is a Hubble Space Telescope image of the Crab Nebula showing the diffuse blue region. Credit: NASA, ESA, J. Hester and A. Loll (Arizona State University).

A synchrotron model for the continuum spectrum of the Crab Nebula fits the radiation given off.[17]

In the Crab Nebula X-ray spectrum there are three features that differ greatly from Scorpius X-1: its spectrum is much harder, its source diameter is in light-years (ly)s, not astronomical units (AU), and its radio and optical synchrotron emission are strong.[5] Its overall X-ray luminosity rivals the optical emission and could be that of a nonthermal plasma. However, the Crab Nebula appears as an X-ray source that is a central freely expanding ball of dilute plasma, where the energy content is 100 times the total energy content of the large visible and radio portion, obtained from the unknown source.[5]

SpectroscopyEdit

"The CCD spectroscopic observations were performed with the 91-cm telescope at Okayama Astrophysical Observatory (OAO) and the 101-cm telescope at Bisei Astronomical Observatory (BAO) between July 23 and 27."[18]

"The averaged signal to noise ratios (S/N) at the continuum level were 60-100 for OAO data using exposure times of 180-300 s, and 25-40 for BAO data using exposure times of 120 s respectively, which depend on the brightness of the object and the sky condition."[18]

InertialsEdit

"The problem of formation of generic structures in the Universe is addressed, whereby first the kinematics of inertial continua for coherent initial data is considered. The generalization to self-gravitating continua is outlined focused on the classification problem of singularities and metamorphoses arising in the density field."[19]

TerrainsEdit

 
This chaotic terrain on Europa has areas consisting of densely packed blocks with fractures and narrow lanes of matrix between them. Credit: G. C. Collins, J. W. Head III, R. T. Pappalardo, and N. A. Spaun.{{fairuse}}
 
The image shows areas on Europa consisting of almost all matrix and no blocks. Credit: G. C. Collins, J. W. Head III, R. T. Pappalardo, and N. A. Spaun.{{fairuse}}
 
Conamara Chaos, the most intensely studied chaos area, lies near the middle of this continuum. Credit: G. C. Collins, J. W. Head III, R. T. Pappalardo, and N. A. Spaun.{{fairuse}}
 
High-resolution (10 m/pixel) image shows a plate surrounded by matrix material within Conamara Chaos. Credit: G. C. Collins, J. W. Head III, R. T. Pappalardo, and N. A. Spaun.{{fairuse}}
 
Image of Europa's Conamara Chaos taken by the Galileo spacecraft. This view is approximately 35 kilometers across. Credit: NASA.{{free media}}

"The morphology of chaotic terrain forms a continuum from areas consisting of densely packed blocks with fractures and narrow lanes of matrix between them ([first image at the right]), to areas consisting of almost all matrix and no blocks ([first image at the left]). Conamara Chaos, the most intensely studied chaos area ([second image at the right]), lies near the middle of this continuum, with -60% of its area consisting of matrix and the remainder consisting of blocks [Spaunet al., 1998]. In addition to these large chaos areas, chaotic terrain also occurs in the interiors of some small (-10 km diameter) features [Spaun et al., 1999] known as "lenticulae.""[20]

"In Conamara Chaos, where data with spatial resolution of up to ten meters per pixel were obtained, the hummocky matrix appears to be a jumbled collection of ice chunks of all sizes, from a kilometer to tens of meters across ([second image on the left])."[20]

CratersEdit

"Croft [3] called moat craters anomalous pit craters and also suggested a continuum between moat craters, craters, and palimpsests, even though morphometrically they appeared to be distinct."[21]

ReferencesEdit

  1. P. Haensel, J.L. Zdunik, and J. Dobaczewski (1989). "Composition and equation of state of cold catalyzed matter below neutron drip". Astronomy and Astrophysics. 222 (1–2): 353–7. Bibcode:1989A&A...222..353H. Retrieved 2014-01-22. Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  2. P.A. Milne, J.D. Kurfess, R.L. Kinzer, M.D. Leising (2002). "Supernovae and Positron Annihilation Radiation". New Astronomy Reviews. 46 (8–10): 553–8. arXiv:astro-ph/0110442. Retrieved 2013-08-13. Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  3. John N. Bahcall, K. Lande, R. E. Lanou Jr, J. G. Learned, R. G. H. Robertson, L. Wolfenstein (1995). "Progress and prospects in neutrino astrophysics". Nature. 375 (6526): 29–34. Bibcode:1995Natur.375...29B. Retrieved 2013-11-07. Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  4. Thomas K. Gaisser (1990). Cosmic Rays and Particle Physics. Cambridge University Press. p. 279. ISBN 0521339316. Retrieved 2014-01-11.
  5. 5.0 5.1 5.2 5.3 5.4 P Morrison (1967). "Extrasolar X-ray Sources". Annual Review of Astronomy and Astrophysics. 5 (1): 325–50. Bibcode:1967ARA&A...5..325M. doi:10.1146/annurev.aa.05.090167.001545.
  6. Claus Leitherer, Henry C. Ferguson, Timothy M. Heckman and James D. Lowenthal (1995). "The Lyman continuum in starburst galaxies observed with the Hopkins ultraviolet telescope". The Astrophysical Journal. 454 (1): L19-22. Bibcode:1995ApJ...454L..19L. doi:10.1086/309760. Retrieved 2014-02-11. Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  7. Dictionary.com. The American Heritage Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. (accessed: January 25, 2008).
  8. W.J. Jones and B.P. Stoicheff, ‘Inverse Raman Spectra: Induced Absorption at Optical Frequencies’, Phys. Rev. Lett. 13, 657 - 9 (1964).
  9. 9.0 9.1 9.2 David Merritt (2013). Dynamics and Evolution of Galactic Nuclei. Princeton, NJ: Princeton University Press. ISBN 9781400846122.
  10. B.M. Peterson & K. Horne Reverberation Mapping of Active Galactic Nuclei (2004)
  11. Chris Schur (17 January 2011). The Crab Nebula in Taurus. Starship Asterisk. Retrieved 25 February 2014.
  12. 12.0 12.1 D.P. Gilra and A.D. Code (1971). "The Violet Opacity in S, C-S and N Stars and Circumstellar Silicon Carbide Grains". Bulletin of the American Astronomical Society. 3 (6): 379. Bibcode:1971BAAS....3..379G. Unknown parameter |month= ignored (help); |access-date= requires |url= (help)
  13. Iosif Shklovskii (1953). "On the Nature of the Crab Nebula's Optical Emission". Doklady Akademii Nauk SSSR. 90: 983. Bibcode:1957SvA.....1..690S.
  14. A. S. Wilson, J. A. Braatz, T. M. Heckman, J. H. Krolik, and G. K. Miley (1993). "The Ionization Cones in the Seyfert Galaxy NGC 5728". The Astrophysical Journal Letters. 419 (12): L61-4. Bibcode:1993ApJ...419L..61W. doi:10.1086/187137. Unknown parameter |month= ignored (help); |access-date= requires |url= (help)CS1 maint: multiple names: authors list (link)
  15. Hyron Spinrad and David B. Wood (January 1965). "Magnesium Hydride in Cool Stars and Galaxies". The Astrophysical Journal. 141 (01): 109–14. Bibcode:1965ApJ...141..109S. doi:10.1086/148092. Retrieved 2013-09-18.
  16. Philippe Andre, Derek Ward-Thompson and Mary Barsony (1993). "Submillimeter continuum observations of ρ Ophiuchi A - The candidate protostar VLA 1623 and prestellar clumps". The Astrophysical Journal. 406 (1): 122–41. Bibcode:1993apj...406..122a. Retrieved 2013-10-21. Unknown parameter |month= ignored (help)
  17. B. J. Burn (1973). "A synchrotron model for the continuum spectrum of the Crab Nebula". Monthly Notices of the Royal Astronomical Society. 165: 421. Bibcode:1973MNRAS.165..421B.
  18. 18.0 18.1 Hajime Baba, Kozo Sadakane, Yuji Norimoto, Kazuya Ayani, Masayuki Ioroi, Katsura Matsumoto, Daisaku Nogami, Makoto Makita, Taichi Kato (2002). "Spiral Structure in WZ Sagittae around the 2001 Outburst Maximum". Publications of the Astronomical Society of Japan. 54 (1): L7-10. Bibcode:2002PASJ...54L...7B. Retrieved 2013-12-10. Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  19. Thomas Buchert (1995). "Cosmogony of Generic Structures". Publications of the Beijing Astronomical Observatory. 1: 59–70. Bibcode:1995PBeiO...1...59B. Retrieved 2013-12-19.
  20. 20.0 20.1 G. C. Collins, J. W. Head III, R. T. Pappalardo, and N. A. Spaun (25 January 2000). "Evaluation of models for the formation of chaotic terrain on Europa" (PDF). Journal of Geophysical Research. 105 (E1): 1709–16. Retrieved 2014-08-26.CS1 maint: multiple names: authors list (link)
  21. B.K. Lucchitta and H.M. Ferguson (1988). "Ganymede: "Moat" Craters Compared with Palimpsests and Basins". Abstracts of the Lunar and Planetary Science Conference. 19 (03): 701. Bibcode:1988LPI....19..701L. Retrieved 2013-10-18. Unknown parameter |month= ignored (help)

External linksEdit