Recursos de colección

Caltech Authors (147.820 recursos)

Repository of works by Caltech published authors.

Group = Owens Valley Radio Observatory

Mostrando recursos 1 - 20 de 28

  1. A Comparison of the Determination of Closure Phase in Optical Interferometry with Fully Filled Apertures and Non-Redundant Aperture Masks

    Readhead, A. C. S.

  2. Timing Observations of the SMC Binary PSR J0045-7319

    Kaspi, V. M.; Manchester, R. N.; Bailes, M.; Bell, J. F.
    We describe radio timing observations of the binary pulsar PSR J0045-7319 made over the past 3.3 yr. We show that a simple timing model involving a standard Keplerian orbit well-describes the data, however significant lowlevel systematic residuals never before seen in other binary pulsars remain. We consider various possible origins of the residuals.

  3. A luminous companion to SGR 1806-20

    van Kerkwijk, M. H.; Kulkarni, S. R.; Matthews, K.; Neugebauer, G.
    We have obtained infrared spectra of the star suggested to be the counterpart of the soft gamma-ray repeater (SGR) 1806-20. We found strong emission lines similar to those seen in the spectra of the rare luminous blue variables and B(e) stars. A He I absorption line is also seen, from which we infer a spectral type O9-B2. This classification, in combination with the minimum distance of greater than or approximately = 6 kpc inferred from its extinction, makes the star one of the most luminous in the Galaxy. We infer that it is a companion to SGR 1806-20 and suggest...

  4. The Nature of the Galactic Center Arc

    Serabyn, E.
    Ever since the Galactic Center Arc was resolved into its component filaments a decade ago, it has been clear that its linear structure arises from the influence of a strong magnetic field. However, the origin and nature of the contributory phenomena have remained elusive. Since what is seen is synchrotron emission from relativistic particles, of prime interest is a knowledge of the acceleration mechanism involved. Interferometric imaging of the molecular gas in the vicinity of the Arc has now provided a tantalizing clue to the Arc’s origin: molecular clumps coinciding with the endpoints of a number of the Arc’s filaments...

  5. Images of HCO(+) (1-0) emission in a molecular cloud near 1E 1740.7 - 2942

    Phillips, J. A.; Lazio, T. Joseph W.
    We have observed the hard X-ray source 1E 1740.7 - 2942 in the HCO(+) (1-0) line using the Owens Valley millimeter interferometer. Previous single-dish observations have found HCO(+) emission coincident with the location of the radio continuum hot spots of the radio source associated with 1E 1740.7 - 2942. Our higher resolution observations show a 15 sec offset between the HCO(+) emission and the location of the radio hot spots. We propose that the lack of emission results from a large ionization rate, exceeding 10-15/s, in the neighborhood of 1E 1740.7 - 2942.

  6. Imaging the Small-Scale Circumstellar Gas Around T Tauri Stars

    Koerner, D. W.; Sargent, A. I.
    We have detected circumstellar molecular gas around a small sample of T Tauri stars through aperture synthesis imaging of CO(2→1) emission at ˜2"-3" resolution. RY Tauri, DL Tauri, DO Tauri, and AS 209 show resolved and elongated gaseous emission. For RY Tau, the deconvolved, half-maximum radius along the direction of elongation, P.A. ˜48°, is 110 AU. Corresponding radii and orientations for the other sources are: DL Tau-250 AU at P.A. ˜84°; DO Tau-350 AU at P.A. ˜160°; AS 209-290 AU at P.A. ˜138°. RY Tau, DL Tau, and AS 209 show velocity gradients parallel to the elongation, suggesting that the...

  7. Infrared CO Emission from Young Stars: Accretion Disks and Neutral Winds

    Chandler, C. J.; Carlstrom, J. E.; Scoville, N. Z.
    We have modeled the emission in the first-overtone rotation-vibration bands of CO from accretion disks and neutral winds. We compare our models with high-resolution spectra of five objects: DG Tau, SVS 13, WL 16, NGC 2024 IRS 2, and S106 IRS 4. The emission from accretion disks with accretion rates of ˜10^(-8) to 10^(-7) M_(sun) yr^(-1) successfully reproduce the fluxes, the profiles, and the optical depths of the observed spectra. We also find for several objects that the data are best reproduced by the disk model, with higher K-band extinctions to the central star than those measured by other methods....

  8. Caltech SIS Receivers

    Woody, David P.
    This paper describes the superconductor-insulator-superconductor (SIS) receivers which are being used in the Owens Valley Radio Observatory Millimeter Interferometer. These receivers operate over the frequency range from 85 to 115 GHz using a simple circular waveguide mixer block design and have achieved double sideband noise temperatures as low as 70 K. They have been in use since 1981 and have proven to be reliable and easy to operate.

  9. Aperture Synthesis Maps of CO Emission from M51

    Lo, K. Y.; Berge, G.; Claussen, M.; Heiligman, G.; Keene, J.; Masson, C.; Phillips, T.; Sargent, A.; Scoville, N.; Watson, D.; Woody, D.
    7"-resolution maps of CO emission from the central 2' of M51 have been made with the Owens Valley millimeter-wave interferometer. Relative warm gas from giant molecular clouds is seen largely confined to arms coincident with the dust lanes, forming coherent structure on the scale of ~3 Kpc. There is a minimum of CO emission within 400 pc of the center. Integrated CO intensity maps are presented. Non-circular motion of the CO gas is evident from the velocity field.

  10. The Caltech Millimeter Wave Interferometer

    Masson, C. R.; Berge, G. L.; Claussen, Mark J.; Heiligman, G. M.; Leighton, R. B.; Lo, K. Y.; Moffett, A. T.; Phillips, T. G.; Sargent, Anneila I.; Scott, S. L.; Woody, David P.; Young, A.
    The Caltech Millimeter-Wave Interferometer has recently begun observations at a wavelength of 2.6 mm. We describe the instrument and some of the first results from it.

  11. Gamma rays from the quasar PKS 1441+25: story of an escape

    Abeysekara, A. U.; Archambault, S.; Archer, A.; Aune, T.; Barnacka, A.; Benbow, W.; Bird, R.; Biteau, J.; Buckley, J. H.; Bugaev, V.; Cardenzana, J. V.; Cerruti, M.; Chen, X.; Christiansen, J. L.; Ciupik, L.; Connolly, M. P.; Coppi, P.; Cui, W.; Dickinson, H. J.; Dumm, J.; Eisch, J. D.; Errando, M.; Falcone, A.; Feng, Q.; Finley, J. P.; Fleischhack, H.; Flinders, A.; Fortin, P.; Fortson, L.; Furniss, A.; Gillanders, G. H.; Griffin, S.; Grube, J.; Gyuk, G.; Hütten, M.; Håkansson, N.; Hanna, D.; Holder, J.; Humensky, T. B.; Johnson, C. A.; Kaaret, P.; Kar, P.; Kelley-Hoskins, N.; Khassen, Y.; Kieda, D.; Krause, M.; Krennrich, F.; Kumar, S.; Lang, M. J.; Maier, G.; McArthur, S.; McCann, A.; Meagher, K.; Moriarty, P.; Mukherjee, R.; Nieto, D.; O’Faoláin de Bhróithe, A.; Ong, R. A.; Otte, A. N.; Park, N.; Perkins, J. S.; Petrashyk, A.; Pohl, M.; Popkow, A.; Pueschel, E.; Quinn, J.; Ragan, K.; Ratliff, G.; Reynolds, P. T.; Richards, G. T.; Roache, E.; Rousselle, J.; Santander, M.; Sembroski, G. H.; Shahinyan, K.; Smith, A. W.; Staszak, D.; Telezhinsky, I.; Todd, N. W.; Tucci, J. V.; Tyler, J.; Vassiliev, V. V.; Vincent, S.; Wakely, S. P.; Weiner, O. M.; Weinstein, A.; Wilhelm, A.; Williams, D. A.; Zitzer, B.; Smith, P. S.; Holoien, T. W.-S.; Prieto, J. L.; Kochanek, C. S.; Stanek, K. Z.; Shappee, B.; Hovatta, T.; Max-Moerbeck, W.; Pearson, T. J.; Reeves, R. A.; Richards, J. L.; Readhead, A. C. S.; Madejski, G. M.; Djorgovski, S. G.; Drake, A. J.; Graham, M. J.; Mahabal, A.
    Outbursts from gamma-ray quasars provide insights on the relativistic jets of active galactic nuclei and constraints on the diffuse radiation fields that fill the Universe. The detection of significant emission above 100 GeV from a distant quasar would show that some of the radiated gamma rays escape pair-production interactions with low-energy photons, be it the extragalactic background light (EBL), or the radiation near the supermassive black hole lying at the jet's base. VERITAS detected gamma-ray emission up to 200 GeV from PKS 1441+25 (z=0.939) during April 2015, a period of high activity across all wavelengths. This observation of PKS 1441+25...

  12. Accurate Measurement of the Declinations of Radio Sources

    Read, Richard Bradley
    The two 90-foot steerable paraboloids of the Owens Valley Radio Observatory were used as a two-element interferometer at 960 Mc/s with various separations along a north-south baseline to measure accurately the declinations of a number of radio sources, most of which were of small diameter. The measured values of declination are tabulated for 110 sources with right ascensions between 0 hours and 14 hours 10 minutes. The standard errors of the measured values range from ± 2.6 seconds of arc to ± 46 seconds of arc with an average of ± 13 seconds of arc. A discussion of the sources of error is included.

  13. Brightness Distribution in Discrete Radio Sources III. The Structure of the Sources

    Maltby, P.; Moffett, A. T.
    The visibility functions of 195 radio sources are interpreted in terms of the structure of these sources. Of the 195 sources, 174 are known or presumed to be extragalactic. Seventy-five of these extragalactic sources are resolved with the interferometer spacings used, and complex structure is found in all but 13. In the sources showing complex structure, two similar components with nearly equal intensities are found in 15, 40 show two or more components of unequal intensities, while 7 appear to be a bright core surrounded by a halo. It is suggested that the majority of all extragalactic sources have complex structure. Data are also given on the brightness distributions in...

  14. The Radio Spectrum of Supernova Remnants

    Harris, D. E.
    960 Mc/s observations of thirteen galactic sources generally assumed to be supernova remnants, are coupled with previous observations at other frequencies to derive spectral indices. Although several values of spectral index are found in the neighborhood of zero, arguments are presented that free-free transitions are not the primary cause of the radio emission. An interpretation of the relatively large range of spectral indices is suggested on the basis of an evolutionary sequence in which young, bright objects with relatively steep spectra gradually evolve into old, faint objects with flat or inverted spectra.

  15. The Discrete Sources of Cosmic Radio Emission

    Bolton, J. G.
    One of the principal problems in the radio astronomy of the discrete sources is their identification with visible objects. Identification is necessary in . most instances to determine the distance of a source and thus its intrinsic luminosity. It is of assistance in deciding the probable mechanism for the radio emission. Identification of a reasonable sample of radio sources should be made prior to speculations from statistical studies of the radio sources as a class.

  16. Radio Source Measurements at 960 MC/S

    Harris, D. E.; Roberts, J. A.
    The major surveys of radio sources made at meter wavelengths have shown a disquieting lack of agreement, and an independent study of these sources using as simple an antenna as possible seems to be desirable. As a partial step in this direction, we report here a study of 106 radio sources made with one of the equatorially-mounted 90-foot paraboloids of the Owens Valley Radio Observatory. This investigation was made at a frequency of 960 Mc/s. The primary result of the study is a reliable catalog of sources which will be used as a 'finding list' for precise position measurements which are currently being undertaken with the two antennas operating as an...

  17. Brightness Distribution in Discrete Radio Sources. II Observations with a North-South Interferometer

    Maltby, P.
    Information about the brightness distribution in 165 radio sources has been obtained at a wavelength of 31. 3 cm. The measurements were made with the variable spacing interferometer at the Owens Valley Radio Observatory using a north-south baseline. Primary sets of observations, giving the visibility amplitude and the phase, were taken at transit at four different antenna spacings. Additional information about the brightness distribution was obtained from observations at large hour angles, using the same physical antenna separations. The results of the observations are given in tabular form and several visibility curves are show.

  18. Brightness Distribution in Discrete Radio Sources I. Observations with an East-West Interferometer

    Moffet, Alan T.
    The Caltech variable baseline interferometer has been used in a program of brightness distribution measurements on 195 discrete radio sources at a wave length of 31.3 cm. This paper reports measurements, made with an east- west interferometer baseline, of the complex visibility functions of 127 sources. The amplitude and phase of the visibility functions were measured at transit with antenna spacings of 195λ, 389λ, 779λ and 1557λ. Using these same basic spacings, and by observing at large hour angles, the visibility amplitude was measured at ten other effective spacings between 126λ and 1363λ. Not all sources are observed at all spacings. The data are presented in tabular...

  19. 7.960 MC/S Observations of Radio Sources in the Sydney Catalogue

    Kellermann, K. I.; Harris, D. E.
    During March and September 1960, observations were made with the Caltech interferometer of 739 sources listed in the two catalogues of Mills, Slee and Hill^1,^2. The primary purpose of the investigation was to provide this observatory with a 960 Mc/s "finding list" for future measurements of source sizes and precise positions. The area covered in these observations was: 0: -50° to -20° a: 17 to 5 hours o: -20° to +10° a: O to 24 hours. In general, the observations were restricted to sources in the MSH catalogues whose flux density at 86 Mc/s was greater than 15 x l0^(-26) watts m^-2 (c/s)^-l. All sources down to this level were examined with...

  20. A 10-Meter Telescope for Millimeter and Sub-Millimeter Astronomy

    Leighton, Robert B.
    The design and construction of a prototype 10.4 meter, f/0.4 telescope intended for millimeter- and submillimeter-wave astronomy is described, with particular emphasis on design features, fabrication techniques, and error sources. The surface accuracy attained on a prototype dish was about 50 µm rms; on the first of four "production" dishes, about 25 µm rms; the goal for at least one of the four dishes is to be 10 µm rms or less. The reflecting surface is sheet aluminum cemented to accurately machined honeycomb panels. The 84 demountable panels are supported on a tubular steel- framework which is itself disassemblable into a few easily transportable pieces. A notable feature is...

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