Positional Coincidence Research Articles

Optical identifications of QSOs with flat radio spectra

Optical identifications of 35 “empty fields” in a radio sample with flat-spectra have been made by using TV and CCD camera at Kitt Peak National Observatory 4-m telescope. Based on close radio-optical position coincidence, 29 sources are identified with stellar objects. The new identified objects have more steep radio-optical spectra indices α ro. The statistical results suggest a correlation of the radio and optical luminosities.

Radio detection of a jet in the Crab Nebula

The jet-like feature in the Crab Nebula discovered by van den Bergh1 shows a tubular structure of 75 × 45 arc s with strikingly well-collimated sharp parallel boundaries in the recent deep O III image obtained by Gull and Fesen2. I now report detection of radio emission at 20cm from this faint optical jet, in the Very Large Array (VLA) map obtained with a resolution of 15 × 15 arc s. The radio emission is extremely faint at less than 1% of the peak brightness within the nebula, and its detection was possible because of the high dynamic range in this VLA map. Its positional coincidence and structural similarity to the optical jet are remarkable. The emission at 20 cm appears to be nonthermal, with strong linear polarization of ∼30%.

The Draco Nebula, a Molecular Cloud Associated with a High Velocity Cloud?

Extended and very faint bright nebulae are found in high (b≳ 30°) galactic latitudes at the Palomar Observatory Sky Survey (POSS) (Lynds, 1965) and even more pronounced at a very sensitive photographic survey of the galactic polar caps by Sandage (1976). Such a nebula, located in the constellation Draco and called “Draco Nebula” or “Dracula”, was found to be in detailed positional coincidence with a 21-cm emission line feature at a LSR velocity of VLSR ≈ -22 km s-1 by Goerigk et al. (1983).

Optical Identifications of Radio Sources with Accurate Positions Using the UKST IIIa-J Plates

SummaryThree radio identification programmes are described which are drawn from radio samples with accurate radio positions (< 2" arc rms). Optical identifications are being made on the basis of radio-optical positional coincidence alone, without regard to colour or morphology, using the UKST IIIa-J sky survey to a limiting magnitude of 22.5. Some preliminary results are presented.

A large molecular cloud toward the SNR W50 and SS 433

view Abstract Citations (34) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A large molecular cloud toward the SNR W50 and SS 433. Huang, Y. -L. ; Dame, T. M. ; Thaddeus, P. Abstract The CO 1 yields 0 transition at 115 GHz has been mapped over an area of more than 6 deg sq toward W50, the extended SNR surrounding the peculiar object SS 433. W50 is found to lie at the end of a filamentary molecular cloud 4 deg long and 1 deg wide that closely matches a conspicuous dust lane on the Palomar Sky Survey; the cloud's kinematic distance is within 0.7 of 2.2 kpc, in agreement with the distance 2-3.3 kpc estimated for the SNR, and its mass is about 120,000 solar masses. Though there is little evidence of star formation in the molecular filament, or evidence of an interaction between the filament and W50 (or SS 433), the positional coincidence of the two, their similar distance, and their displacement nearly two molecular scale heights from the plane all suggest a physical relationship or common origin. One possibility is that both the molecular filament and the stellar progenitor of W50 were ejected from a large active molecular complex lying in the plane at l = 40 deg. Publication: The Astrophysical Journal Pub Date: September 1983 DOI: 10.1086/161323 Bibcode: 1983ApJ...272..609H Keywords: Molecular Clouds; Nebulae; Radio Astronomy; Supernova Remnants; Carbon Monoxide; Sky Surveys (Astronomy); Stellar Evolution; Astrophysics full text sources ADS | data products SIMBAD (8)

A Redshift Survey of Very Faint (B≤22.5) Field Galaxies, Radio Sources, and Quasars

As part of a three year program to study the evolution of galaxies, quasars, and radio sources (in collaborations with R. Kron and R. Windhorst), we will use over 30 nights on the KPNO 4-m CCD Cryogenic Camera System, in the multi-aperture mode, to measure the redshifts of several hundred very faint objects. These will be selected from four fields (SA68 00h+15; Lynx 08h+45; SA57 13h+30; Herc 17h+50); for each we possess 4-m plates in four bandpasses (limits: U≃23, B≃24, V≃23, I≃21) as well as Westerbork interferometer maps to 1 mJy at 21cm (a 50cm survey is in progress). Galaxies are selected randomly by their apparent red magnitudes as measured with a PDS; quasar candidates to B≈22.5 by stellar objects which lie apart from Galactic stars in the multi-color diagram; and radio sources by their positional coincidence with optical images (∼50% of the 300 radio sources are identified). To date, 10 nights have produced spectra of ∼250 field galaxies, ∼20 radio sources, and ∼40 quasar candidates.

2.3-GHz accurate positions and optical identifications for selected Parkes radio sources

Accurate radio positions of 74 extragalactic radio sources contained in the Parkes 2.7-GHz survey were measured at 2.3 GHz with the Tidbinbilla interferometer, located near Canberra, Australia. The radio sources, most of which lie between declinations -30 deg and -35 deg, were measured to an rms positional accuracy of about 3 arcsec relative to a grid of previously identified radio sources. Optical identifications have been made on the basis of positional coincidence alone, without regard to color or morphology, using the UK Schmidt telescope deep IIIa-J sky survey plates. Identifications are suggested and accurate optical positions have been measured for 62 objects brighter than magnitude 22.5 on the IIIa-J plates.

A confusion-limited extragalactic source survey at 4.755 GHz. III - Accurate positions and optical identifications

Accurate positions of sources stronger than 15 mJy at 4.755 GHz from a survey covering almost 0.01 sr of extragalactic sky were measured with the VLA. Optical identifications were made from the PSS prints on the basis of position coincidence alone. The spectral index ..cap alpha..(1.415,4.755) distributions of the identified QSO's and galaxies are significantly different from the corresponding distributions of strong-source identifications. The relative scarcity of faint flat-spectrum (..cap alpha.. 3) redshift, while the lack of faint galaxies with ..cap alpha..> or =+0.8 results from the spectral index--luminosity correlation of radio galaxies and the limited sensitivity of the PSS prints. The areal densities of optically selected and radio-selected QSO's brighter than m/sub b/ = +19.5 were compared, and both can be represented by a single, smoothly varying function of flux density.

RESEAU ASTROMETRY WITH PALOMAR SCHMIDT PLATES - POSITION-COINCIDENCE OPTICAL IDENTIFICATION OF RADIO SOURCES

ABSTRACT The simple, inexpensive method for determining celestial coordinates on original Palomar Schmidt plates developed previously is here inverted and shown to be a useful way of finding and identifying objects with known celestial coordinates. The method is especially suited for rapidly identifying large numbers of radio sources having accurate radio positions which are found in surveys made with large aperture-synthesis instruments. The average position error (approximately 0.9 arc sec) for stellar objects, galaxies, and faint objects near the plate limit is sufficient for making reliable optical identifications of objects as faint as J magnitude = +24 on the basis of position coincidence alone, without regard to color or morphology.

The Ophiuchus cluster - A bright X-ray cluster of galaxies at low galactic latitude

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.

Multifrequency radio observations of optically selected quasars

view Abstract Citations (26) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multifrequency radio observations of optically selected quasars. Condon, J. J. ; Condon, M. A. ; Jauncey, D. L. ; Smith, M. G. ; Turtle, A. J. ; Wright, A. E. Abstract A complete sample of 12 radio sources stronger than 10 mJy at 5.0 GHz are identified with optically selected quasars (discovered with the Curtis-Schmidt telescope) on the basis of precise radio-optical position coincidence. Radio spectra determined from flux densities at 0.408, 1.465, 2.29, 5.0, and 14.5 GHz indicate synchrotron self-absorption in 11 cases. The only steep-spectrum source is resolved by the VLA at 1.465 GHz. It is shown that the spectral-index distributions of radio sources identified with optically selected quasars can vary only weakly with radio finding frequency since the radio number-flux-density relation of these identifications is so flat. The number-magnitude distributions of radio-selected and optically selected quasars are compared and interpreted in terms of a radio-optical core-flux correlation. Finally, physical differences between radio-selected and optically selected quasars are considered. It is found that differing orientations of relativistically beamed radio jets cannot explain the differences between the radio luminosity functions of radio-selected and optically selected quasars. Publication: The Astrophysical Journal Pub Date: February 1981 DOI: 10.1086/158677 Bibcode: 1981ApJ...244....5C Keywords: Quasars; Radio Sources (Astronomy); Statistical Analysis; Astronomical Catalogs; Data Sampling; Magnitude; Astronomy full text sources ADS | data products SIMBAD (12) NED (12)

Radio observations of O-type stars

Eight O-type giants and supergiants, selected for being relatively isolated in the sky, have been observed at 5 GHz with 17 antennae of the partially completed VLA (NRAO, Socorro, New Mexico: The National Radio Astronomy Observatory is operated by Associated Universities under contract with the National Science Foundation) on October 7 and 8, 1979. The integration times ranged between 38 and 187 minutes. The results are displayed in Table 1. Most of the stars (6 out of 8) were not detected. The upper limits given in Table 1 for these stars correspond to the 3σ noise level. Possible detection has been achieved for the two supergiants HD 225160 and HD 30614 both with a flux density of 0.15 mJy. Although this flux is equal to the 3a noise level, the detections can be considered to be real because 1) Excellent positional coincidence is found between stars and the radio peaks (better than 1”) 2) The observed source pattern corresponds very well to the expected response to a point-like source.

Search for X-Ray Sources in the COS-B Gamma-Ray Error Boxes

The publication of the first and preliminary second catalogue of the COS-B sources, has brought to the attention of the astronomical community the new reality of the high-energy Galactic Gamma-Ray Sources (GGRS). It is worth recalling here the definition of such objects, in the COS-B sense: “A GRS is a significant excess of photon counts, compatible with the instrument's angular resolution, or, more clearly, with the instrument's Point Spread Function”. This definition of an unresolved (as it is the case for the vast majority of the GGRS) GRS is, to some extent, dependent on the shape of the source spectrum; however a general shape of the PSF for the case of the source associated with 3C273 can be found in Bignami et al, 1980. Naturally, the absolute flux (i.e. the total number of photons) from a source is also important in determining the positional error, especially when usage is made of the cross-correlation method. Typical photon numbers (100 Mev) for GGRS range from 50 to few hundreds. The COS-B catalogue error boxes are defined taking into account both the PSF and the photon statistics; it is then apparent that the search for candidate counterparts of the GGRS should be carried out inside such boxes, or in their immediate vicinity, and that, for examples, such loose positional coincidences as obtainable by increasing a quoted error radius by 50%, let alone doubling it, are totally unacceptable. Systematic searches for counterparts at other wavelengths have not yet been carried out, except for a few cases of X-ray and radio observations, as for example in the case of CG 135+1 (the only COS-B GRS erbox compatible with a 4U erbox) which led to the discovery of a new X-ray QSO by Apparao et al, 1978.

X-ray observations of the supernova remnant MSH 11-54

Soft X-ray observations of the X-ray source H1122-59 in the 0.4-2 keV band made with the low-energy detector 1 of the HEAO A-2 experiment are described. Based on positional coincidence, the source is identified with the supernova remnant MSH-11-54, thus confirming the report of Share et al. (1980). The object is a bright source in the 0.4-2 keV band with an X-ray flux of 9 x 10 to the -11th ergs/sq cm s near the earth. The measured source spectrum implies a plasma temperature of 4 million K and X-ray luminosity in the 0.4-2 keV band of 10 to the 37th ergs/s using a distance of 10 kpc for MSH 11-54. The X-ray observations, interpreted in terms of an adiabatic shock wave model, give a shock velocity of about 560 km/s and a supernova age of about 2300 yr, in good agreement with the age derived from the radio observations.

Bright galaxies in nearby Abell clusters

A list of galaxies possibly associated with nearby Abell clusters is presented. The galaxies have been chosen from the catalog of Zwicky et al. or that of Nilson, and are found within 1 Abell radius of the center of an Abell cluster. The effects of line-of-sight contamination have been considered. Because of the magnitude limitations of the galaxy catalogs, the present list is useful only for the nearer Abell clusters (distance class less than 4). While positional coincidence is not a sufficient criterion for the determination of cluster membership, it is likely that most of the cataloged galaxies are in fact associated with the clusters in which they appear to lie.

Optical and X-ray properties of the newly discovered BL Lacertae object PKS 2155-304 /= H2155-304/

The soft X-ray source H 2155-304 has been precisely located with the HEAO 1 scanning modulation collimator, and identified with an object of bolometric magnitude approximately 14. The linear polarization, variability, spectrum, and diffuse image of the optical flux, together with the positional coincidence of the radio source PKS 2155-304, indicate that this object is a new member of the BL Lacertae class. Its characteristics are compared with those of other X-ray-emitting BL Lacertae objects, particularly Mrk 421.

Evidence for supernova-induced star formation in the monoceros OB2 association

The Monoceros ring, a circular optical nebulosity ∼3°.5 in diameter and centred at R.A.=6h37m, Dec.=6°30′ (lii=205°.5,bii=0°.2) is in good structural agreement with radio observations. A neutral hydrogen shell is also accurately projected on the ring. These observations are consistent with the Monoceros ring being a supernova remnant 90–100 pc in diameter expanding at about 45 km s−1 and having an age of the order of a million years. Bright Hii regions containing early-type stars (e.g., galactic cluster NGC 2244 in the Rosette nebula) and extremely young stars of the OB association Mon OB2 lie at the edges of the ring. The positional and temporal coincidence of the Mon OB2 association with a supernova remnant suggests that probably the star formation in this region is induced or speeded up by the passage of a supernova shock wave through the clumpy interstellar medium.

Radio emission from flows

Many emission line stars are radio sources including early type stars such as ζ Pup and P Cyg, peculiar objects such as MWC 349 (a possible proto-planetary system) and V1016 Cyg, nebular variables such as T Tau, and at least one late M giant. These “radio stars” are characterized by (1) a rising spectrum with spectral index α = 0.6 to 1.1, (2) positional coincidence between star and radio source, and (3) no rapid (less than 107 sec) time variability. These characteristics are in contrast with the non-thermal spectrum and rapid variability of Algol type “radio stars” and the radio emission associated with x-ray sources. The radio component of the spectrum of emission line stars originates in the substantial mass loss flows which are a feature of their outer atmospheres and which, when ionized by stellar radiation, radiate by free-free electron thermal bremsstrahlung. These circumstellar H II regions are, in general, detectable with present radiotelescopes if the characteristic size of the optically thick region of the flow is greater than about 10−7 of the distance to the star.

A comparative study of G+C-rich satellite components of sheep and goat DNA

Restriction fragment patterns of G+C-rich satellites of sheep and goat DNA were compared. The 1,712 g/cm3 satellites of both species appear homologous, consisting of repeats 760 base pairs long and showing coincidence of position of primary+ EcoRI, BamHI and most BspRI restriction target sites. The EcoRI and BamHI endonucleases produce mostly monomers of the repeating unit, while oligomers prevail in the A1uI and Bg1II digests. Species-specific differences in the frequency, position and mode of distribution of secondary+ restriction target sites for EcoRI, Bg1II and A1uI were observed. Unlike the 1,712 g/cm3 satellites, the 1,723 g/cm3 component of sheep DNA and the 1,719 g/cm3 material from goat DNA appear species--specific, since no homologous material could ever be detected in the DNA of the other species.

Accurate Radio Positions with the Tidbinbilla Interferometer

Radio position measurements with an error of <2” arc rms allow reliable optical identifications of compact radio sources to be made solely on the basis of radio-optical position coincidence. In this way neutral or red stellar objects, faint compact galaxies and faint QSOs can be reliably identified. Such identifications are of particular interest because they are rich in BL Lac objects, high-redshift QSOs, QSOs with unusual optical emission or absorption spectra and galaxies with active nuclei (see Jaunceyet al. 1978).