211 results on '"Bruce Margon"'
Search Results
102. Extreme Ultraviolet Observations of White Dwarfs
- Author
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Bruce Margon, Michael Lampton, and Stuart Bowyer
- Subjects
Physics ,Stars ,X-ray astronomy ,Ultraviolet astronomy ,Extreme ultraviolet ,Stellar atmosphere ,Spectral energy distribution ,White dwarf ,Astrophysics ,Lyman limit - Abstract
Observations shortward of the hydrogen Lyman limit provide sensitive determinations of stellar temperatures and interstellar absorption. Such data are of particular value in studies of hot white dwarfs, for which a large fraction of the emission occurs in the extreme ultraviolet band (100-1000 Å). Observations of HZ 43 and Feige 24 have been obtained with the Apollo-Soyuz extreme ultraviolet telescope; both stars are copious EUV emitters, with 4 × 10−9 and 3 × 10−9 erg/cm2 sec in the 170-620 A band respectively. The EUV data combined with optical spectrophotometry, allow their temperatures to be estimated as 80, 000 and 60, 000 K respectively. The corresponding interstellar neutral hydrogen column densities are ~ 4 × 1018 cm−2.
- Published
- 1977
103. Relativistic Jets in SS 433
- Author
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Bruce Margon
- Subjects
Physics ,Multidisciplinary ,Radio galaxy ,Astrophysics::High Energy Astrophysical Phenomena ,Astronomy ,Quasar ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Astronomical spectroscopy ,Black hole ,Neutron star ,Astrophysical jet ,Binary star ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Stellar evolution ,Astrophysics::Galaxy Astrophysics - Abstract
A variety of recent optical, radio, and x-ray observation have confirmed the hypothesis that the peculiar star SS 433 is ejecting two narrow, opposed, highly collimated jets of matter at one-quarter the speed of light. This unique behavior is probably driven by mass exchange between a relatively normal star and a compact companion, either a neutron star or a black hole. However, numerous details regarding the energetics, radiation, acceleration, and collimation of the jets remain to be understood. This phenomenon may well be a miniature example of similar collimated ejection of gas by active extragalactic objects such as quasars and radio galaxies.
- Published
- 1982
104. The Bizarre Spectrum of SS 433
- Author
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Bruce Margon
- Subjects
Physics ,Multidisciplinary ,Astrophysics::High Energy Astrophysical Phenomena ,X-ray binary ,Astronomy ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Giant star ,Astronomical spectroscopy ,Neutron star ,Binary star ,Precession ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Emission spectrum ,Supernova remnant ,Astrophysics::Galaxy Astrophysics - Abstract
SS 433 is an emission-line star, a radio source, and an x-ray source centered in a supernova remnant, W50. Through observations and spectroscopic studies much has been learned of this object. The spectrum of SS 433 is characterized by Doppler-shifted emission lines of hydrogen and helium. This implies the presence of a gas. The wavelengths of these lines vary. Some of the moving lines of the spectrum are red-shifted and some are blue-shifted. Since the wavelengths of the Doppler-shifted features change rapidly with time, the velocity of both approaching gas and receding gas is changing. On any given night the average velocity is 12,000 km/sec. Also, the variations in velocity are periodic, with a 164-day period. These characteristics of the spectrum of SS 433 are explained by assuming the following hypothetical model. The object responsible for ejecting two jets in opposite directions is thought to be part of a binary system, consisting of a comparatively normal star bound in close orbit to a neutron star, which is in the process of pulling material away from the companion by virtue of its strong gravitational field. The gas streaming from the normal star forms a rotating accretion disk around the neutron star,more » and it is from the faces of this disk that the two jets are ejected in opposite directions. Precession of the plane of the disk is presumably what causes the axis of the jets to rotate, hence the 164-day period. (SC)« less
- Published
- 1980
105. The Origin of the Cosmic X-Ray Background
- Author
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Bruce Margon
- Subjects
Physics ,Multidisciplinary ,COSMIC cancer database ,media_common.quotation_subject ,X-ray background ,Astronomy ,Cosmic ray ,Quasar ,Astrophysics ,Universe ,Intergalactic travel ,Astrophysical plasma ,media_common ,Background radiation - Abstract
Since 1962, it has been known that every part of the sky emits a uniform glow of x-rays. After two decades of intense study the origin of this diffuse x-ray background is still a subject of controversy. The near perfect isotropy of the x-ray background is clearly a vital clue to its origin. A second clue to the origin of the x-ray background arises from the fact that it is x-radiation tha is generated, rather than some longer wavelength radiation. Two hypotheses of the origin of this x-ray background are discussed. One hypothesis is that the x-ray background can be attributed to bremsstrahlung from a hot intergalactic medium. The second hypothesis is that the x-ray background originates from a large number of quasars. Because there is no estimate independent of the intensity of the x-ray background of how much hot intergalactic medium exists (if any), there is a real possibility that both sources contribute to the observed x-rays. (SC)
- Published
- 1983
106. 4U0241+61: a luminous low-redshift QSO
- Author
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L. Maraschi, Giovanni F. Bignami, H. V. Bradt, Krishna M. V. Apparao, Bruce Margon, H. Helmken, R. M. Hjellming, and R. G. Dower
- Subjects
QSOS ,Physics ,Multidisciplinary ,Resolution (electron density) ,Astronomy ,Quasar ,Astrometry ,Astrophysics ,Redshift ,Radio astronomy ,Luminosity - Abstract
The faint (1.8 micro Jy, 2-11 keV) X-ray QSO 4U0241+61 is considered in terms of its celestial position (galactic latitude = +2.4 plus or minus 30 sec), luminosity (M sub v = -25.8 plus or minus 1.8), redshift (z = 0.0438), and radio emission (0.2-0.5 Jy). Counting rates in two energy channels are presented, and found comparable to the Type 1 Seyfert 3C120. Spectrophotometric calibration to an approximately 8 A resolution was also achieved. Attention is given to the close relation between X-ray emitting QSOs and Seyferts.
- Published
- 1978
107. Observations of SS 433
- Author
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Bruce Margon
- Subjects
Physics ,Space and Planetary Science ,Astronomy ,Astronomy and Astrophysics ,Astrophysics - Abstract
Observations de base a chaque longueur d'onde, observations recentes, progres theoriques et problemes relatifs a SS 433
- Published
- 1984
108. Simultaneous Photometry of X Persei and 3U 0352 + 30
- Author
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Stuart Bowyer, Bruce Margon, and G. Penegor
- Subjects
Physics ,Photometry (astronomy) ,Space and Planetary Science ,Flux ,Astronomy ,Proportional counter ,Astronomy and Astrophysics ,Astrophysics - Abstract
The suggested association of X Persei with the weak X-ray source 3U 0352+30 raises the possibility of detection of X-ray/optical covariability. The paper reports a successfully conducted simultaneous optical/X-ray observation utilizing ground-based photometry and a satellite-borne proportional counter. Photoelectric photometry of X Persei was obtained on five out of seven consecutive nights in January 1975. The observations yield the faintest and bluest photoelectric magnitudes and colors ever reported for X Per; this change apparently occurred relatively uniformly during 1973-74 and is reminiscent of behavior last observed in about 1900. On January 21, 7 hr of data were obtained simultaneously with OAO Copernicus X-ray observations of 3U 0352+30. The X-ray flux varied during this period by a factor of 2, but there is no obviously correspondent optical activity, to a level of 0.02 mag. The optical data are also used to limit the 0.01-mag variations coincident with the X-ray periodicity reported by White et al. (1976).
- Published
- 1976
109. On the nature of Wx Ceti
- Author
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Ronald A. Downes and Bruce Margon
- Subjects
Physics ,Space and Planetary Science ,Astronomy and Astrophysics ,Astrophysics - Published
- 1981
110. Discovery of a Rare Late-type, Low-mass Wolf–Rayet Star in the LMC.
- Author
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Bruce Margon, Catherine Manea, Robert Williams, Howard E. Bond, J. Xavier Prochaska, Michał K. Szymański, and Nidia Morrell
- Subjects
- *
WOLF-Rayet stars , *PLANETARY nebulae , *ION recombination , *PARALLAX , *MOLECULAR spectra - Abstract
We report the serendipitous discovery of an object, UVQS J060819.93−715737.4, with a spectrum dominated by extremely intense, narrow C ii emission lines. The spectrum is similar to those of the very rare, late-type [WC11] low-mass Wolf–Rayet stars. Despite the recognition of these stars as a distinct class decades ago, there remains barely a handful of Galactic members, all of which are also planetary-nebula central stars. Although no obvious surrounding nebulosity is present in J0608, [O ii], [N ii], and [S ii] emission suggest the presence of an inconspicuous, low-excitation nebula. There is low-amplitude incoherent photometric variability on timescales of days to years, as well as numerous prominent P Cygni profiles, implying mass loss. There are indications of a binary companion. The star is located on the outskirts of the LMC, and the observed radial velocity (∼+250 km s−1) and proper motion strongly suggest membership. If indeed an LMC member, this is the first extragalactic late [WC] star, and the first with an accurately determined luminosity, as the Galactic examples are too distant for precise parallax determinations. A high-quality, broad-coverage spectrum of the prototype of the late [WC] class, CPD −56° 8032, is also presented. We discuss different excitation mechanisms capable of producing the great strength of the C ii emission. Numerous autoionizing levels of C ii are definitely populated by processes other than dielectronic recombination. Despite the spectacular emission spectra, observational selection makes objects such as these difficult to discover. Members of the [WC11] class may in fact be considerably more common than the handful of previously known late [WC] stars. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
111. Synchronous extreme spectral variability of BE Ursae Majoris
- Author
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Ronald A. Downes, J. I. Katz, and Bruce Margon
- Subjects
Physics ,G-type main-sequence star ,Multidisciplinary ,Binary star ,Flare star ,Astronomy ,White dwarf ,Contact binary ,Ursa Minor ,Astrophysics ,Variable star ,Light curve - Abstract
BE Ursae Majoris is a 15-mag variable star of period 2.29 days, with a sinusoidal light curve of ∼1 mag amplitude1. Recently, Ferguson et al.2 have drawn attention to this object, also known as PG1155 + 492, because of its UV excess and unusual spectrum, which they observed to vary between absorption and strong emission on a time scale of months. Here we report observations which demonstrate that the spectrum of BE UMa is dramatically variable on a time scale of hours and days, in synchrony with the 2.29-day periodic light variations. We interpret the system as a detached binary consisting of an extremely hot (T∼105K) white dwarf and a cool M star, whose upper layers are irradiated by the intense ionizing flux of the hot companion. This unique system should prove invaluable for measurements of the mass, luminosity and bolometric correction of the hottest white dwarfs.
- Published
- 1981
112. A kinematic model for SS433
- Author
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George O. Abell and Bruce Margon
- Subjects
Physics ,Multidisciplinary ,chemistry.chemical_element ,Astrophysics ,Redshift ,Blueshift ,Radial velocity ,symbols.namesake ,chemistry ,symbols ,Emission spectrum ,Acoustic Doppler velocimetry ,Doppler effect ,Helium ,Doppler broadening - Abstract
THE bizarre object SS433, first noted because of its Hα emission1 and most recently because it is the optical counterpart of a variable radio and X-ray source2–4, exhibits an extraordinary optical spectrum5. Three sets of emission lines of hydrogen and helium appear: one is near zero radial velocity (less than 180 km s−1), and the other two show large and variable shifts to the blue and red. These shifts are almost unquestionably due to the Doppler effect, as multiple lines with constant z ≡ Δλ/λ have been identified in both the red and blue systems6–8. The observed range of shifts5,8 corresponds to velocities from 0 to −30,000 km s−1 in the blueshift system, and 11,000 to 48,000 km s−1 in the redshift system, with the two sets of lines moving −180° out of phase with each other. At present the redand blueshift variations seem periodic, with a period of about 164 d, based on the observation of parts of three cycles7,8.
- Published
- 1979
113. Surface density of faint high-redshift quasi-stellar objects
- Author
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Scott F. Anderson and Bruce Margon
- Subjects
Red shift ,QSOS ,Surface (mathematics) ,Physics ,Multidisciplinary ,Young stellar object ,Dispersion (optics) ,Quasar ,Astrophysics ,Redshift ,Astronomical spectroscopy - Abstract
The majority of known very high-redshift (z>=3.4) quasi-stellar objects (QSOs) have relatively bright apparent magnitudes1,2, R = 21, R ˜ 19) at z = 3.56, selected by 'traditional' low dispersion spectroscopic methods. The surface density of very faint, high-redshift QSOs may not be negligible, with a variety of lines of evidence suggesting that there are at least ˜ 0.2 deg−2 objects with z>= 3.4.
- Published
- 1987
114. A Search for the Cygnus X-3 Infra-Red Candidate at One Micron
- Author
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John E. Gaustad, Bruce Margon, and Harold F. Weaver
- Subjects
Physics ,Space and Planetary Science ,Infrared ,Cosmic infrared background ,Astronomy ,Astronomy and Astrophysics ,Astrophysics - Published
- 1973
115. Infrared-Selected 'Warm' Galaxies Observed in X-Rays
- Author
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Paul J. Green, Martin Ward, Scott F. Anderson, Bruce Margon, M. H. K. Degrijp, and George K. Miley
- Published
- 1989
116. The Use of Diamond Turned & Replicated Wolter 1 Telescopes for High Sensitivity X-Ray Astronomy
- Author
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Ken Pounds, A. C. Fabian, de P. Korte, J. L. Culhane, Gordon P. Garmire, R. C. Catura, Bruce Margon, and A. Franks
- Subjects
Physics ,X-ray astronomy ,business.industry ,Reflecting telescope ,Astrophysics::Instrumentation and Methods for Astrophysics ,Astronomy ,Diamond ,X-ray telescope ,Diamond turning ,engineering.material ,law.invention ,Telescope ,Optics ,Wolter telescope ,law ,engineering ,Angular resolution ,business - Abstract
Following the siicces of Einstein, it is clear that telescopes of very large area ( ~ 104 cm2) with angular resolution (⪝20″) are needed for deep X-ray surveys and other observations. After a discussion of these objectives, which form the basis of the NASA LAMAR mission, the design & performance of a five mirror telescope is described. The system was studied for possible flight on Spacelab to undertake observations & to act as a prototype module for LAMAR. Both diamond turning & replication methods of mirror production are discussed. The performance of a single Wolter I telescope with diamond turned mirrors will be described.
- Published
- 1981
117. High Resolution Large Area Modular Array Of Reflectors (LAMAR) Wolter Type I X-Ray Telescope For Spacelab
- Author
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P. H. Sheather, R. C. Catura, J. R. Vieira, K. Lindsey, T. J. Patrick, W. A. Brown, Ken Pounds, M. Stedman, A. Franks, J. L. Culhane, John P. Pye, K. D. Evans, O. Siegmund, Alan A. Wells, Bruce Margon, A. C. Fabian, J. E. Spragg, Gordon P. Garmire, C. H. Whitford, L. W. Acton, C. W. Gilbreth, B. Gale, Geoffrey Smith, L. A. Springer, B. A. Cooke, and I. W. Mason
- Subjects
Physics ,Galactic astronomy ,Einstein Telescope ,business.industry ,Reflecting telescope ,Astrophysics::High Energy Astrophysical Phenomena ,Astrophysics::Instrumentation and Methods for Astrophysics ,Astronomy ,X-ray telescope ,law.invention ,Telescope ,Primary mirror ,Optics ,Observational astronomy ,law ,Angular resolution ,business - Abstract
A Wolter type I X-ray telescope, intended both for astronomical observations and to serve as a prototype module for the Large Area Modular Array of Reflectors (LAMAR) mission, is now in definition study under NASA's Spacelab program. The 5 mirror telescope presently being designed is to have a,blur circle radius of 20 arc sec rd an effective area of about 400 cm at 1/4 keV, 200 cm4 in the 0.5-2 keV range and 50 cm between 2 and 5 keV. Future expansion to a full 10 mirror telescope will approximately double these effective areas. A rotary interchange mechanism will allow either of two imaging proportional counters (IPCs) to be placed at the telescope focus; one operating between 0.15 and 2 keV and the other optimized for the 0.6 - 6 keV energy range. During flight, the telescope will utilize an instrument pointing system for a series of observations lasting from 6 minutes to several hours. This investigation has dual objectives: the primary objective is scientific and involves observational study of galactic and extragalactic X-ray sources, extending the work of the Einstein Observatory to much fainter sources and to higher energies. The second objective is to provide an assessment of the cost and improved performance of utilizing Wolter Type I X-ray optics for the LAMAR mission and to extend the technology for producing these optics to still higher angular resolution and toward lower cost.
- Published
- 1982
118. High Resolution Large Area Modular Array Of Reflectors (LAMAR) Wolter Type I X-Ray Telescope For Spacelab
- Author
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J. L. Culhane, I. W. Mason, P. H. Sheather, Ken Pounds, T. J. Patrick, K. Evans, L. A. Springer, R. C. Catura, B. A. Cooke, J. R. Vieira, Geoffrey Smith, Bruce Margon, Christopher H. Whitford, Andrew C. Fabian, J. E. Spragg, L. W. Acton, Alan A. Wells, C. W. Gilbreth, John P. Pye, Gordon P. Garmire, O. Siegmund, and W. A. Brown
- Subjects
Physics ,Einstein Telescope ,business.industry ,Astrophysics::High Energy Astrophysical Phenomena ,Astrophysics::Instrumentation and Methods for Astrophysics ,General Engineering ,X-ray optics ,X-ray telescope ,Radius ,Atomic and Molecular Physics, and Optics ,law.invention ,Telescope ,Primary mirror ,Optics ,law ,Angular resolution ,Focus (optics) ,business - Abstract
A Wolter Type I x-ray telescope, intended both for astronomical observations and to serve as a prototype module for the large area modular array of reflectors (LAMAR) mission, is now in definition study under NASA's Spacelab program. The five mirror telescope presently being designed is to have a blur circle radius of 20 arc sec and an effective area of about 400 cm2 at 1/4 keV, 200 cm2 in the 0.5 to 2 keV range, and 50 cm2 between 2 and 5 keV. Future expansion to a full ten mirror telescope will approximately double these effective areas. A rotary interchange mechanism will allow either of two imaging proportional counters (IPCs) to be placed at the telescope focus; one operating between 0.15 and 2 keV and the other optimized for the 0.6 to 6 keV energy range. During flight, the telescope will utilize an instrument pointing system for a series of observations lasting from six minutes to several hours. This investigation has dual objectives: The primary objective is scientific and involves observational study of galactic and extragalactic x-ray sources, extending the work of the Einstein Observatory to much fainter sources and to higher energies. The second objective is to provide an assessment of the cost and improved performance of utilizing Wolter Type l x-ray optics for the LAMAR mission and to extend the technology for producing these optics to still higher angular resolution and toward lower cost.
- Published
- 1983
119. Faint Object Spectrograph (FOS) Calibration
- Author
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James Roger P. Angel, L. Ripp, Bruce Margon, E. M. Burbidge, Arthur F. Davidsen, H. Ford, R. Bohlin, R. J. Harms, F. Bartko, J. Mccoy, and E. A. Beaver
- Subjects
Physics ,Faint Object Spectrograph ,Physics::Instrumentation and Detectors ,business.industry ,Detector ,Astrophysics::Instrumentation and Methods for Astrophysics ,Faint Object Camera ,Astronomical spectroscopy ,Optics ,Spitzer Space Telescope ,Calibration ,Spectral resolution ,Optical filter ,business ,Remote sensing - Abstract
The Faint Object Spectrograph (FOS) designed for use with The Space Telescope (ST), is currently preparing for instrument assembly, integration, alignment, and calibration. Nearly all optical and detector elements have been completed and calibrated, and selection of flight detectors and all but a few optical elements has been made. Calibration results for the flight detectors and optics are presented, and plans for forthcoming system calibration are briefly described.
- Published
- 1982
120. Editorials, Forum and Book Reviews
- Author
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Christopher H. Whitford, Geoffrey Smith, C. W. Gilbreth, J. R. Vieira, Gordon P. Garmire, A. C. Fabian, J. L. Culhane, Ken Pounds, Alan A. Wells, T. J. Patrick, I. W. Mason, K. D. Evans, R. C. Catura, Bruce Margon, W. A. Brown, M. Stedman, A. Franks, J. E. Spragg, O. Siegmund, P. H. Sheather, L. W. Acton, L. A. Springer, B. A. Cooke, K. Lindsey, John P. Pye, and B. Gale
- Subjects
Style (visual arts) ,Blame ,Computer science ,Field (Bourdieu) ,Reading (process) ,media_common.quotation_subject ,Wish ,General Engineering ,Media studies ,Space (commercial competition) ,Atomic and Molecular Physics, and Optics ,media_common ,Trepidation - Abstract
It is with some trepidation that I undertake the use of the editorial as a means to express something of my individual approach to doing science. I will share the blame for my decision to "go public" with these thoughts with some outstanding researchers around the world who have urged me to do so. In addition, I will make this space available to credible scientists who wish to express other approaches. Part of the joy and charm of science is that, as a human activity, it is a highly individualized affair. All contributors with long careers develop a style of thinking that is unique and readily recognizable by their colleagues. I feel certain I could recognize the author of a paper by one of the "old timers" in my field without reading his or her name. Thus, rny remarks are of a personal nature and may not be useful to most readers. With all of these caveats expressed, I will delay no longer.
- Published
- 1983
121. An X-Ray Selected List of QSOs: Implications for the QSO Luminosity Function and the Origin of the Diffuse X-Ray Background
- Author
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Ronald A. Downes, Bruce Margon, and G. A. Chanan
- Subjects
QSOS ,Physics ,Active galactic nucleus ,Einstein Telescope ,X-ray background ,Astronomy ,Quasar ,Astrophysics ,Redshift ,Luminosity function (astronomy) ,Luminosity - Abstract
For the past two years we have conducted a program aimed at optical identification of x-ray sources discovered serendipitously by the Einstein Observatory. We obtain spectroscopy of all visible objects in the positional error boxes of the new sources, and have thus far examined about 120 such boxes to a limiting flux of V=18.5 and.010 Einstein IPC counts/sec. Among our findings are the discovery of 50 previously unreported active galactic nuclei (QSOs or compact Seyferts), ranging in redshift from z=0.03 through z=1.40. This list of identifications has a distribution of red-shift with flux quite different from an optically or radio selected sample. The implications of these differences are twofold. First, new constraints are available on the form and evolution of the luminosity function of quasars. Secondly, there are interesting inferences regarding the contribution of QSOs to the diffuse x-ray background radiation. Previous studies of radio-selected QSOs have shown a strong correlation between radio and x-ray luminosity, thus providing a warning that conclusions regarding the composition of the background radiation based on such studies of preselected objects must be regarded with extreme caution. Our program avoids this basic selection effect, and provides new insight into the problem of the contribution of discrete sources to the background radiation.
- Published
- 1981
122. Infrared properties of serendipitous X-ray quasars
- Author
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Bruce Margon, G. A. Chanan, G. Neugebauer, B. T. Soifer, and Keith Matthews
- Subjects
Physics ,Infrared ,Astrophysics::High Energy Astrophysical Phenomena ,Astronomy ,Astronomy and Astrophysics ,Quasar ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Galactic nuclei ,Space and Planetary Science ,OVV quasar ,X ray spectra ,Astrophysics::Galaxy Astrophysics ,Radio astronomy - Abstract
Near-infrared measurements have been obtained of 30 quasars originally found serendipitously as x-ray sources in fields of other objects. The observations show that the infrared characteristics of these quasars do not differ significantly from those of quasars selected by other criteria. Because this x-ray-selected sample is subject to different selection biases than previous radio and optical surveys, this conclusion is useful in validating previous inferences regarding the infrared colors of “typical” quasars.
- Published
- 1982
123. The X-Ray Properties of High Redshift Quasi-Stellar Objects
- Author
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Scott F. Anderson and Bruce Margon
- Published
- 1986
124. Extreme Ultraviolet Observations of White Dwarfs
- Author
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Michael Lampton, Bruce Margon, and Stuart Bowyer
- Subjects
Interstellar medium ,Physics ,X-ray astronomy ,Ultraviolet astronomy ,Extreme ultraviolet lithography ,Extreme ultraviolet ,Stellar atmosphere ,White dwarf ,Astronomy ,Astrophysics ,Lyman limit - Abstract
Observations shortward of the hydrogen Lyman limit provide sensitive determinations of stellar temperatures and interstellar absorption. Such data are of particular value in studies of hot white dwarfs, for which a large fraction of the emission occurs in the extreme ultraviolet band (100–1000 A). Observations of HZ 43 and Feige 24 have been obtained with the Apollo-Soyuz extreme ultraviolet telescope; both stars are copious EUV emitters, with 4 × 10-9 and 3 × 10-9 erg/cm2 sec in the 170–620 A band respectively. The EUV data combined with optical spectrophotometry, allow their temperatures to be estimated as 80,000 and 60,000 K respectively. The corresponding interstellar neutral hydrogen column densities are ~ 4 × 1018 cm-2.
- Published
- 1977
125. High-redshift quasars found in sloan digital sky survey commissioning data. II. The spring equatorial stripe
- Author
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Xiaohui Fan, Michael A. Strauss, Donald P. Schneider, James E. Gunn, Robert H. Lupton, Scott F. Anderson, Wolfgang Voges, Bruce Margon, James Annis, Neta A. Bahcall, J. Brinkmann, Robert J. Brunner, Michael A. Carr, István Csabai, Mamoru Doi, Joshua A. Frieman, Masataka Fukugita, G. S. Hennessy, Robert B. Hindsley, Željko Ivezić, G. R. Knapp, D. Q. Lamb, Timothy A. McKay, Jeffrey A. Munn, Heidi Jo Newberg, A. George Pauls, Jeffrey R. Pier, Ron Rechenmacher, Gordon T. Richards, Constance M. Rockosi, Chris Stoughton, Alexander S. Szalay, Aniruddha R. Thakar, Douglas L. Tucker, Patrick Waddell, and Donald G. York
- Subjects
Physics ,Absolute magnitude ,Celestial equator ,media_common.quotation_subject ,Astrophysics::High Energy Astrophysical Phenomena ,Astrophysics (astro-ph) ,Astrophysics::Instrumentation and Methods for Astrophysics ,FOS: Physical sciences ,Astronomy and Astrophysics ,Quasar ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Redshift ,Spectral line ,Photometry (astronomy) ,Space and Planetary Science ,Sky ,Emission spectrum ,Astrophysics::Galaxy Astrophysics ,media_common - Abstract
This is the second paper in a series aimed at finding high-redshift quasars from five-color (u'g'r'i'z') imaging data taken along the Celestial Equator by the Sloan Digital Sky Survey (SDSS) during its commissioning phase. In this paper, we present 22 high-redshift quasars (z>3.6) discovered from ~250 deg^2 of data in the spring Equatorial Stripe, plus photometry for two previously known high-redshift quasars in the same region of sky. Our success rate of identifying high-redshift quasars is 68%. Five of the newly discovered quasars have redshifts higher than 4.6 (z=4.62, 4.69, 4.70, 4.92 and 5.03). All the quasars have i* < 20.2 with absolute magnitude -28.8 < M_B < -26.1 (h=0.5, q_0=0.5). Several of the quasars show unusual emission and absorption features in their spectra, including an object at z=4.62 without detectable emission lines, and a Broad Absorption Line (BAL) quasar at z=4.92., 28 pages, AJ in press (Jan 2000), final version with minor changes; high resolution finding charts available at http://www.astro.princeton.edu/~fan/paper/qso2.html
126. The sloan digital sky survey quasar catalog. II. First data release
- Author
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Donald P. Schneider, Xiaohui Fan, Patrick B. Hall, Sebastian Jester, Gordon T. Richards, Chris Stoughton, Michael A. Strauss, Mark SubbaRao, Daniel E. Vanden Berk, Scott F. Anderson, W. N. Brandt, James E. Gunn, Jim Gray, Jonathan R. Trump, Wolfgang Voges, Brian Yanny, Neta A. Bahcall, Michael R. Blanton, William N. Boroski, J. Brinkmann, Robert Brunner, Scott Burles, Francisco J. Castander, Mamoru Doi, Daniel Eisenstein, Joshua A. Frieman, Masataka Fukugita, Timothy M. Heckman, G. S. Hennessy, eljko Ivezi, Stephen Kent, Gillian R. Knapp, Donald Q. Lamb, Brian C. Lee, Jon Loveday, Robert H. Lupton, Bruce Margon, Avery Meiksin, Jeffrey A. Munn, Heidi Jo Newberg, R. C. Nichol, Martin Niederste-Ostholt, Jeffrey R. Pier, Michael W. Richmond, Constance M. Rockosi, David H. Saxe, David J. Schlegel, Alexander S. Szalay, Aniruddha R. Thakar, Alan Uomoto, and Donald G. York
- Subjects
Astrophysics::High Energy Astrophysical Phenomena ,media_common.quotation_subject ,FOS: Physical sciences ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Astronomy & Astrophysics ,01 natural sciences ,Omega ,Spectral line ,Photometry (optics) ,surveys ,0103 physical sciences ,Emission spectrum ,Spectral resolution ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,media_common ,Physics ,general [quasars] ,010308 nuclear & particles physics ,Astrophysics (astro-ph) ,Astrophysics::Instrumentation and Methods for Astrophysics ,Astronomy and Astrophysics ,Quasar ,Redshift ,13. Climate action ,Space and Planetary Science ,Sky ,astro-ph.CO ,catalogs ,Astronomical and Space Sciences - Abstract
We present the second edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog consists of 16713 objects in the SDSS First Data Release (DR1) that have luminosities larger than M_i=-22 (H_0=70 km/s, Omega_M=0.3, Omega_Lambda=0.7), have at least one emission line with FWHM larger than 1000 km/s, and have highly reliable redshifts. The area covered is ~1360 deg^2 and the redshifts range from 0.08 to 5.41, with a median value of 1.43. Each object has positions accurate to better than 0.2" rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method, in addition to radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large area surveys. Calibrated digital spectra covering 3800-9200 Angstroms at a spectral resolution 1800-2100, are available. This publication supersedes the first SDSS Quasar Catalog, which was based on material from the SDSS Early Data Release. A summary of corrections to current quasar databases is provided. The majority of the objects were found in SDSS commissioning data using a multicolor selection technique. Since the quasar selection algorithm was undergoing testing during the entire DR1 observational period, care must be taken when assembling samples for use in statistical studies. A total of 15786 objects (94%) in the catalog were discovered by the SDSS; 12,173 of which are reported here for the first time, including five quasars brighter than i=16.0 and 17 quasars with redshifts larger than 4.5., Comment: 41 pages, 9 figures, 4 tables; accepted by AJ. FITS and ASCII versions of the catalog can be obtained from http://www.sdss.org/dr1/products/value_added/qsocat_dr1.html
127. A QSO in a rich, distant cluster of galaxies
- Author
-
Ronald A. Downes, Bruce Margon, and Hyron Spinrad
- Subjects
QSOS ,Physics ,Multidisciplinary ,Galaxy groups and clusters ,Cluster (physics) ,Astronomy ,Quasar ,Astrophysics ,Galaxy ,Redshift ,Galaxy cluster ,Luminosity - Abstract
The detection of a 'classical' QSO in a previously studied, distant rich cluster of visible galaxies is reported. The blue and red/IR spectra of the QSO are shown. The QSO occurs at a redshift essentially identical to that of the cluster 0016+16, colocated on the 0.01 of the plate which contains the cluster. The simplest explanation of this association is that the QSO is a member of the cluster. The consequences of the finding are discussed. The QSO-cluster association is further confirmation of the cosmological nature of QSO-cluster association is further confirmation of the cosmological nature of QSOs, and it suggests that QSOs do not necessarily avoid the environment of rich clusters. The fact that this QSO is not well centered adds credence to the suggestion that 3C345 and QSO 1641+3998 constitute an additional case of QSOs in high redshift cluster. The location of this QSO could make it a unique probe to study the physical state of the intracluster gas that is common in rich clusters.
- Published
- 1983
128. A companion quasar to 3C345
- Author
-
Bruce Margon, G. A. Chanan, and Ronald A. Downes
- Subjects
Physics ,QSOS ,X-ray astronomy ,Multidisciplinary ,Astrophysics::High Energy Astrophysical Phenomena ,Astronomy ,Quasar ,X-ray telescope ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Redshift ,Galaxy groups and clusters ,Emission spectrum ,Astrophysics::Galaxy Astrophysics ,Galaxy cluster - Abstract
The discovery of a new quasistellar object (QSO) which presents the strongest evidence to date for the membership of quasars in rich clusters is reported. During X-ray observations of quasar 3C345, a serendipitous X-ray source located 8 arcmin northeast of the quasar was discovered. The observed flux of the new source is 3.2 x 10 to the -13th erg/sq cm/sec in the 0.5-4.5 keV band. Three separate observations over a six-month period failed to show intensity variability in excess of the statistical uncertainty in the count rate. The spectrum shows a modest signal-to-noise ratio but four strong emission lines. It is suggested that the redshift agreement between the two QSOs indicates a common membership in a cluster of galaxies which may well be a rich cluster.
- Published
- 1981
129. Molecular hydrogen in X-ray astronomy
- Author
-
Bruce Margon
- Subjects
Physics ,Interstellar medium ,X-ray astronomy ,Multidisciplinary ,Quality (physics) ,Crab Nebula ,Hydrogen molecule ,Resolution (electron density) ,Astronomy ,Astrophysics - Abstract
THERE is a serious discrepancy between determinations of the column density of interstellar matter in the direction of the Crab Nebula. Virtually every soft X-ray observation1–5 with sufficient energy resolution to derive this column density yields a result substantially in excess of determinations based on 21-cm absorption6–8. The quality of the X-ray and radio data is now such that this disagreement must represent a genuine physical effect rather than an artefact of the data analysis.
- Published
- 1974
130. The nature of Aquila X-1
- Author
-
J. I. Katz, Bruce Margon, and Larry Petro
- Subjects
Physics ,Multidisciplinary ,Astrophysics::High Energy Astrophysical Phenomena ,Stellar atmosphere ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Stellar classification ,Spectral line ,Photometry (optics) ,Stars ,Supernova ,Crab Nebula ,Roche limit ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
Photometry in the UBV spectra was used to observe Aquila X-1. This X-ray source, usually producing flux on the order of 1-10% that of the Crab Nebula, often behaves in a manner resembling the behavior of galactic X-ray stars. A description of the calibration methods used in the observations is presented, with attention to photoelectric-photographic methods. These observations suggest a quiescent spectral class near Ko, i.e., a dwarf at a distance of 1.6 kpc. The more intense X-ray emissions are said to be generated from internal heating of the stellar atmosphere, with additional energy supplied by a low-mass companion star. This explaination is at variance with the semi-detached Roche model.
- Published
- 1978
131. Infrared-Selected 'Warm' Galaxies Observed in X-rays
- Author
-
Martin Ward, Bruce Margon, George K. Miley, M. H. K. de Grijp, Paul J. Green, and Scott F. Anderson
- Subjects
Luminous infrared galaxy ,Physics ,H II region ,Active galactic nucleus ,Infrared ,Astrophysics::High Energy Astrophysical Phenomena ,Astronomy ,Astronomy and Astrophysics ,Quasar ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Disc galaxy ,Galaxy ,Spectral line ,Space and Planetary Science ,ROSAT ,Satellite ,Astrophysics::Galaxy Astrophysics - Abstract
Infrared, optical, and X-ray observations are presented for a sample of 'warm' infrared selected galaxies listed in the IRAS Point Source Catalog. These galaxies have also been observed serendipitously in X-rays by the Einstein Observatory. From low-resolution optical spectra, it is found that all have emission lines, indicating a Seyfert or H II region type nucleus. Many of these galaxies were previously uncataloged. Based on the X-ray detection rate of this sample, it is concluded that large numbers of warm IRAS Seyfert 1-1.9 galaxies may be detectable in X-rays by future surveys such as Rosat.
- Published
- 1989
132. SS433 continues to perplex
- Author
-
Bruce Margon
- Subjects
Physics ,Multidisciplinary ,Astronomy ,Astrophysics - Abstract
Etude de raies d'emission dans le spectre radio, IR, visible et RX de cet objet nouvellement decouvert
- Published
- 1987
133. Data from a Satellite: X-Ray Astronomy . Proceedings of an institute, Erice, Sicily, July 1979. Riccardo Giacconi and Giancarlo Setti, Eds, Reidel, Boston, 1980 (distributor, Kluwer Boston, Hingham, Mass.). viii, 406 pp., illus. $47.50. NATO Advanced Study Institutes Series C, vol. 60
- Author
-
Bruce Margon
- Subjects
Multidisciplinary ,biology ,Computer science ,DORIS (geodesy) ,Satellite (biology) ,biology.organism_classification ,Remote sensing - Published
- 1981
134. On Identifying New Kinds of Astronomical Objects
- Author
-
Stuart Bowyer, Michael Lampton, Bruce Margon, and R. Cruddace
- Subjects
Physics ,Neutron star ,Uniform distribution (continuous) ,Bremsstrahlung ,Range (statistics) ,General Medicine ,Interval (mathematics) ,Astrophysics ,Table (information) ,Power law ,Random variable - Abstract
WE agree that our results are not compelling and accordingly we claimed “evidence for” rather than “a discovery of” a compact X-ray object, but we believe the evidence for a black-body source1 is stronger than Bahcall and Yahil2 imply. These authors have assumed that the confidences of the three spectral fits to GX 340+0 are independent random variables with a uniform distribution on the interval (0, 1). Under these assumptions, the validity of which we consider subsequently, the formula they state is indeed correct. We contend, however, that in the application of this formula one should not use n=10. In Table 1 (extracted from ref. 3) we list the confidences derived for the three model photon distributions for all ten sources observed on this flight. In three of the sources observed, no model had confidence ≳0.02 and thus according to commonly applied criteria* the models do not fit the data. For these sources, none of the three photon distributions is possible. Thus, if we wish to use the formula cited to compute probabilities, we must set n=7, which yields P (bremsstrahlung)=0.455 and P (power law)=0.238. These are appreciable probabilities, but if GX 340+0 is in fact a bremsstrahlung source, two effects must have occurred simultaneously. First, the analysis of the “correct” bremsstrahlung hypothesis has yielded quite a low confidence—one that does not usually permit the conclusion that the proposed model fits the data. Second, the “incorrect” blackbody model has returned a remarkably high confidence, in fact the fifth highest of any listed in Table 1. The probability for the simultaneous occurrence of these two events would clearly be substantially less than 0.455. In addition the blackbody hypothesis combined with the intensity and distance estimates of the source gives a physically reasonable a priori source size. Only 60% of the sources listed in Table 1 have best-fit blackbody radii lying in the range of commonly accepted5 neutron star radii, 5 to 20 km.
- Published
- 1972
135. An X-ray-selected white dwarf of intermediate luminosity
- Author
-
Scott F. Anderson, Michael Bolte, and Bruce Margon
- Subjects
Physics ,Photosphere ,Wavelength ,Space and Planetary Science ,Magnitude (astronomy) ,Stellar atmosphere ,Astronomy ,White dwarf ,Astronomy and Astrophysics ,Astrophysics ,Spectral line ,Visible spectrum ,Luminosity - Abstract
Spectrophotometric observations of a previously uncataloged 17th magnitude hot DA white dwarf are reported. Simple models can reproduce the visible spectrum if the star has log g = 8.0 + or - 0.5 and T(eff) = 22,500 + or - 2000 K. The implied distance is about 200 pc. It is plausible that photospheric emission from this star is responsible for the observed X-ray source. Identification of this object with the X-ray source would imply a photosphere free of traces of helium inferred in other X-ray-emitting DAs, and would support previous suggestions that current DA model atmospheres are in need of revision at X-ray wavelengths.
- Published
- 1987
136. Spectrophotometry and image analysis of the nebulosity around the low-redshift quasar 0241 + 622
- Author
-
Robin Ciardullo, Holland C. Ford, W. Romanishin, and Bruce Margon
- Subjects
Physics ,Barred spiral galaxy ,Space and Planetary Science ,Elliptical galaxy ,Astronomy ,Astronomy and Astrophysics ,Quasar ,Astrophysics ,Interacting galaxy ,Irregular galaxy ,Lenticular galaxy ,Redshift ,Astronomical spectroscopy - Published
- 1984
137. Precession instablity in SS 433
- Author
-
S. A. Grandi, Bruce Margon, and Scott F. Anderson
- Subjects
Physics ,Stellar rotation ,X-ray binary ,Astronomy ,Astronomy and Astrophysics ,Astrophysics ,Instability ,Spectral line ,symbols.namesake ,Space and Planetary Science ,Binary star ,symbols ,Precession ,Emission spectrum ,Doppler effect - Published
- 1983
138. Two X-ray selected BL Lacertae candidates
- Author
-
D. Chance, Bruce Margon, Ronald A. Downes, G. A. Chanan, and David J. Helfand
- Subjects
Physics ,Einstein Telescope ,Astrophysics::High Energy Astrophysical Phenomena ,X-ray ,Astronomy ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Astronomical spectroscopy ,Spectral line ,Luminosity ,Space and Planetary Science ,Astrophysics::Galaxy Astrophysics ,Order of magnitude ,BL Lac object - Abstract
Two serendipitous Einstein Observatory X-ray sources with faint (V approximately 19) optical counterparts having the featureless spectra characteristic of BL Lacertae objects are identified. Observations with the VLA at 6 cm establish that these sources have radio to optical luminosity ratios which are lower than the mean for BL Lac objects by one to two orders of magnitude but which are not extreme when compared with those of the known X-ray bright BL Lac objects. It is therefore suggested that these two objects are among the first examples of radio-quiet BL Lac objects.
- Published
- 1982
139. The atmosphere of Sirius B. II - Extreme-ultraviolet observations
- Author
-
F. Paresce, H. L. Shipman, R. A. Stern, Stuart Bowyer, M. L. Lampton, and Bruce Margon
- Subjects
Atmosphere ,Physics ,Space and Planetary Science ,Thermal radiation ,Extreme ultraviolet ,Sirius ,Stellar atmosphere ,White dwarf ,Flux ,Astronomy ,Astronomy and Astrophysics ,Astrophysics ,Effective temperature - Abstract
The letter reports an observation of Sirius in the extreme-ultraviolet (100-1000 A) band, using a grazing-incidence telescope flown aboard the Apollo-Soyuz mission. No positive flux is detected; under the arbitrary assumption of flat incident spectrum, an upper limit to the flux in the 170-620 A band is 5 billion erg/sq cm per sec. A detailed model-atmosphere analysis, when combined with the EUV limits, places severe constraints on models which attribute the previously reported soft X-ray (44-60 A) flux to thermal radiation from deep layers of the atmosphere of the white dwarf Sirius B. EUV radiation should be detectable from Sirius B just below the sensitivity threshold of the current data, or a thermal origin for the X-ray flux is untenable. If the X-ray flux is thermal, the present results provide extremely sensitive constraints on the temperature and helium abundance of Sirius B: the white dwarf has an effective temperature of 32,000 K to 32,500 K and a helium abundance (relative to hydrogen) of 0.0001 to 0.0002.
- Published
- 1977
140. A spectrophotometric survey of the A0535+26 field
- Author
-
Stuart Bowyer, Jerry Nelson, Gary Chanan, Bruce Margon, and John R. Thorstensen
- Subjects
Physics ,Field (physics) ,Pulsar ,medicine.diagnostic_test ,Space and Planetary Science ,Spectrophotometry ,Continuous spectrum ,Binary star ,medicine ,Astronomy ,Astronomy and Astrophysics ,Emission spectrum ,Astrophysics - Published
- 1977
141. Nodding motions of accretion rings and disks - A short-term period in SS 433
- Author
-
Bruce Margon, J. I. Katz, Scott F. Anderson, and S. A. Grandi
- Subjects
Physics ,Orbital elements ,Astrophysics::High Energy Astrophysical Phenomena ,Nutation ,Astronomy ,Astronomy and Astrophysics ,Astrophysics ,Accretion (astrophysics) ,Astronomical spectroscopy ,symbols.namesake ,Amplitude ,Space and Planetary Science ,Binary star ,symbols ,Precession ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Doppler effect ,Astrophysics::Galaxy Astrophysics - Abstract
It is pointed out that accretion disks and rings in mass transfer binaries have been observed spectroscopically and calculated theoretically for many years. The present investigation is partly based on the availability of several years of spectroscopic observations of the Doppler shifts of the moving lines in SS433. A formalism is presented to compute frequencies and amplitudes of short-term 'nodding' motions in precessing accretion disks in close binary systems. This formalism is applied to an analysis of the moving-line Doppler shifts in SS433. The 35d X-ray cycle of Hercules X-1 is also discussed. In the considered model, the companion star exerts a gravitational torque on the disk rim. Averaged over the binary orbit, this yields a steady torque which results in the mean driven counterprecession of the disk.
- Published
- 1982
142. KPD 0005 + 5106 - A post-PG 1159 type object?
- Author
-
James Liebert, Ronald A. Downes, and Bruce Margon
- Subjects
Physics ,Milky Way ,Astronomy ,White dwarf ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Galactic plane ,Stellar classification ,Stars ,Space and Planetary Science ,Astrophysics::Solar and Stellar Astrophysics ,Spectral energy distribution ,Astrophysics::Earth and Planetary Astrophysics ,Emission spectrum ,Stellar evolution ,Astrophysics::Galaxy Astrophysics - Abstract
In a survey for galactic plane UV-excess objects, a very hot (T about 100,000 K) helium-rich white dwarf is discovered. The object is spectroscopically similar to the pulsating PG 1159 class of stars, with narrow emission lines of He II, probably C IV, and possibly C III/N III, although there is no trace of carbon absorptions. Not all features have positive identifications. This object appears to be an old PG 1159 star, having ceased pulsations during evolution toward a more typical DO white dwarf.
- Published
- 1985
143. An X-ray selected list of QSOs: Implications for the QSO luminosity function and the origin of the diffuse X-ray background
- Author
-
Bruce Margon, Gary Chanan, and Ronald Downes
- Subjects
Space and Planetary Science ,Astronomy and Astrophysics - Published
- 1981
144. On the nature of M28 V7
- Author
-
Bruce Margon and Scott F. Anderson
- Subjects
Physics ,Star cluster ,Mira variable ,Space and Planetary Science ,Globular cluster ,Binary star ,Cluster (physics) ,Astronomy ,Astronomy and Astrophysics ,Astrophysics ,Variable star ,Type (model theory) ,Blue straggler - Abstract
It has recently been suggested that V7 in NGC 6626 (M28) may be one of the few known cataclysmic variables in a globular cluster. The authors have obtained the spectrum of the object, and find it instead to be near type M5 III, and thus probably a normal Mira variable. However, if V7 is indeed a member of the cluster (which is far from certain), then it proves to be very interesting for an entirely different reason: it would represent the first high-amplitude Mira variable in a moderately metal-poor cluster.
- Published
- 1985
145. An atlas of X-ray-selected quasi-stellar objects
- Author
-
G. A. Chanan, Bruce Margon, and Ronald A. Downes
- Subjects
Physics ,QSOS ,Astrophysics::High Energy Astrophysical Phenomena ,Young stellar object ,Astronomy ,Astronomy and Astrophysics ,Quasar ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Redshift ,Galaxy ,Luminosity ,Photometry (astronomy) ,Galaxy groups and clusters ,Space and Planetary Science ,Astrophysics::Galaxy Astrophysics - Abstract
Coordinates, finding charts, photometry, and spectroscopy are presented for 55 X-ray selected QSOs. The selection technique, optical identification of X-ray sources observed serendipitously by the Einstein Observatory was used to find QSOs projected near bright galaxies, pairs of QSOs with similar redshifts; and low-redshift QSOs (z less than 0.5) which are well suited for imaging. Very luminous QSOs of more than 10 to the 46th ergs/s, and a very-high redshift X-ray-selected object were also found. It is suggested that most efforts to identify optically faint QSO counterparts to X-ray sources may yield intrinsically less luminous objects at redshifts less than 1 due to the weak influence of the limiting magnitude on the mean redshift of the sample. A complete list of the QSOs is given.
- Published
- 1985
146. The early spectral phase of type Ib supernovae - Evidence for helium
- Author
-
John C Wheeler, Robert P. Harkness, H. L. Dinerstein, Robert P. Kirshner, Edwin S. Barker, R. M. Levreault, Anita L. Cochran, Alan Uomoto, Bruce Margon, R. A. Downes, and D. R. Garnett
- Subjects
Physics ,Stellar mass ,White dwarf ,Astronomy ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Light curve ,Spectral line ,Stars ,Supernova ,Space and Planetary Science ,Astrophysics::Solar and Stellar Astrophysics ,Emission spectrum ,Ejecta ,Astrophysics::Galaxy Astrophysics - Abstract
A near-infrared spectrum and several optical spectra of SN 1983N obtained over a period from 10 days before maximum light to about a week after maximum and of SN 1984L from about maximum light to about 60 days later are presented. On the basis of these spectra it is argued that the first definite identification of helium in supernova ejecta near maximum light has been made. The emergence of oxygen emission lines which presage the dramatic transition to the supernebular phase is identified. Supernova atmosphere models which are consistent with the observations are presented, and it is argued that a strong departure of helium level populations from LTE is necessary. The current status of SNe Ib, the arguments that they result from core collapse in moderately massive stars, and some of the immediate work necessary to further clarify the nature of these events are summarized.
- Published
- 1987
147. Spectroscopy of the extreme-ultraviolet source Feige 24 - The binary orbit and the mass of the white dwarf
- Author
-
P. A. Charles, Stuart Bowyer, John R. Thorstensen, and Bruce Margon
- Subjects
Physics ,Solar mass ,Astrophysics::High Energy Astrophysical Phenomena ,White dwarf ,Astronomy ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Astronomical spectroscopy ,Orbital inclination ,Radial velocity ,Space and Planetary Science ,Ultraviolet astronomy ,Binary star ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Emission spectrum ,Astrophysics::Galaxy Astrophysics - Abstract
Results are reported for coude spectroscopy of the extreme-ultraviolet white dwarf Feige 24. Radial velocities of the H-alpha, He I 5876-A, and He I 6678-A emission lines, and the underlying M-dwarf absorption features, were determined from spectrograms obtained with the Lick 3-m telescope. The velocities show a binary period of 4.239(+ or - 0.0015) days. The emission-line and absorption-line velocities agree in phase, which indicates that the emission lines originate in the atmosphere of the M-dwarf secondary as a result of reprocessing of the EUV radiation. This effect is modeled, and the observed amplitude of the emission-line variability is used to place a lower limit on the orbital inclination. From these and other data it is shown that the mass of the white dwarf lies between 0.46 and 1.24 solar masses. Some possible implications for the evolution of binary stars are briefly discussed.
- Published
- 1978
148. The X-ray properties of high-redshift quasi-stellar objects
- Author
-
Bruce Margon and Scott F. Anderson
- Subjects
QSOS ,Physics ,X-ray astronomy ,Space and Planetary Science ,Young stellar object ,X-ray ,Narrow range ,Astronomy ,Astronomy and Astrophysics ,Quasar ,Astrophysics ,Redshift ,Luminosity - Abstract
Sensitive X-ray information is presented for about 90 previously uncataloged high-redshift, optically selected QSOs. Two high-redshift subsets of this larger data base are emphasized: (1) a 'complete' sample of 37 objects with z = 1.8 - 3.0, and B of 19.5 or less and (2) a sample of 78 QSOs that span a narrow range in redshift and optical luminosity. From the complete sample, it is inferred that such QSOs contribute less than 3 percent to the diffuse X-ray background (XRB), and that the contribution of all QSOs with B of 19.5 or less to the XRB is 21 + or - 8 percent. For the narrow sample, it is found that the mean X-ray to optical luminosity ratio is characterized by alpha(eff)ox = 1.50 + or - 0.03. A variety of new, model-independent, empirical evidence is presented that the primary dependence of alpha(ox) is on optical luminosity rather than redshift. It is concluded that QSOs can supply as much as 70 percent of the XRB, with the typical contributor a moderate redshift QSO with B of roughly 19-21.
- Published
- 1987
149. The Ophiuchus cluster - A bright X-ray cluster of galaxies at low galactic latitude
- Author
-
H. V. Bradt, Bruce Margon, M. D. Johnston, R. E. Doxsey, F. E. Marshall, and David A. Schwartz
- Subjects
Physics ,Norma Cluster ,Astrophysics::High Energy Astrophysical Phenomena ,Astronomy ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Galaxy ,Luminosity ,Galaxy groups and clusters ,Space and Planetary Science ,Ophiuchus ,Surface brightness ,Brightest cluster galaxy ,Astrophysics::Galaxy Astrophysics ,Galaxy cluster - Abstract
The discovery of an extended X-ray source identified with a cluster of galaxies at low galactic latitude is reported. The source, designated the Ophiuchus cluster, was detected near 4U 1708-23 with the HEAO 1 Scanning Modulation Collimator, and identified with the cluster on the basis of extended X-ray size and positional coincidence on the ESO/SRC (J) plate of the region. An X-ray flux density in the region 2-10 keV of approximately 25 microJ was measured, along with an X-ray luminosity of 1.6 x 10 to the 45th ergs/sec and an X-ray core radius of approximately 4 arcmin (0.2 Mpc) for an assumed isothermal sphere surface brightness distribution. The X-ray spectrum in the range 2-10 keV obtained with the HEAO 1 A-2 instrument is well fit by a thermal bremsstrahlung model with kT = 8 keV and a 6.7-keV iron line of equivalent width 450 eV. The steep-spectrum radio source MSH 17-203 also appears to be associated with the cluster, which is the closest and brightest representative of the class of X-ray clusters with a dominant central galaxy.
- Published
- 1981
150. A lower limit on the magnitude of the companion to HDE 226868 /Cygnus X-1
- Author
-
Bruce Margon, Allen W. Shafter, R. Harms, and J. I. Katz
- Subjects
Physics ,Astrophysics::High Energy Astrophysical Phenomena ,Astronomy ,Astronomy and Astrophysics ,Astrophysics ,Astronomical spectroscopy ,Spectral line ,Photon counting ,Black hole ,Stars ,Apparent magnitude ,Space and Planetary Science ,Binary star ,Magnitude (astronomy) ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
High-precision digital spectra of the HDE 226868/Cygnus X-1 system have been obtained at a variety of orbital phases, using a Digicon photon counting array at the coude focus of the Lick Shane reflector. The spectra have been cross-correlated to search for evidence for the existence of a luminous stellar companion to HDE 226868, as has been suggested by several models where the secondary star is not a black hole. We find no evidence for such a star and place a lower limit on the difference between HDE 226868 and its companion of 4 magnitudes. This limit rules out all of the models for the Cygnus X-1 system calculated by Avni and Bahcall which include main-sequence stars as secondaries rather than black holes. A merit function generally useful for cross-correlation of digital spectra is described.
- Published
- 1980
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