Using 766 compact objects found in a systematic survey of the Galactic plane in the 1612MHz masing OH line, new light is cast on the IR properties of evolved stars on the thermally pulsing asymptotic giant branch (AGB) and beyond. The usual mid-IR selection criteria for post-AGB, based on IRAS colors, largely fail to distinguish early post-AGB stages. A two-color diagram from much narrower band MSX flux densities, with bimodal distributions, provides a better tool for doing this. Four mutually consistent selection criteria for OH-masing red protoplanetary nebulae are given, as well as two for early post-AGB masers and one for all post-AGB masers including the earliest ones. All these criteria miss a group of blue, high-outflow post-AGB sources with 60{mu}m excess; these will be discussed in detail in Paper II (Sevenster, 2002AJ....123.2772S). The majority of post-AGB sources show regular double-peaked spectra in the OH 1612MHz line, with fairly low outflow velocities, although the fractions of single peaks and irregular spectra may vary with age and mass. The OH flux density shows a fairly regular relation with the stellar flux and the envelope optical depth, with the maser efficiency increasing with IRAS color R_21_. The OH flux density is linearly correlated with the 60{mu}m flux density.
Optical astrometry of Benchmark radio sources. III
Short Name:
J/A+AS/115/75
Date:
21 Oct 2021
Publisher:
CDS
Description:
Optical positions, relative to the International Reference Stars catalogue (IRS), and therefore in the system of the FK5, have been obtained for the optical counterparts of 35 extragalactic radio sources south of {delta}~+3deg. Many of these sources are being considered as possible Benchmark objects for the establishment of a quasi-inertial unified radio/optical reference frame. Precision levels better than 0.2" in both coordinates were achieved. A comparison with VLBI radio positions available for these sources is presented. We give evidence for a possible offset in RA between the radio and optical reference frames.
Results are presented of deep identifications of 40 steep spectrum radio sources detected on RATAN-600 in an area ~100deg in the 'Kholod' experiment and then studied using the VLA. Candidates for optical objects responsible for the radio emission were found for 32 sources. With the exception of a few quasars and objects with ill-defined morphology, a large fraction of the radio sources are associated either with gE galaxies or with galaxies of an unknown nature.
Two hundred and forty radio sources that are common for RC (RATAN-600) and UTRAO (VLA, Douglas J.N.+, 1980PAUTx..17....1D) catalogs were identified on the enlarged prints of the Palomar Sky Atlas. The number of identified radio sources with flux density between 15 and 300 mJy drops with decreasing flux density in the centimeter wavelength range.
Optical identifications, magnitudes, and redshifts have been compiled for the 185 radio sources of the S5 catalogue, representing its current optical identification status. Reliable optical counterparts are found for more than 75% of the sources, nearly 50% of which have measured redshifts. Our tabulation also includes radio positions, radio fluxes, and radio spectral indices. References to other catalogues and detailed supplementary notes are given for a large fraction of the sources.
An update of the optical identification status of the S4 radio source catalogue is presented. An extensive literature search has been made to gather the types of the optical counterparts, their magnitudes and redshifts. As far as possible, references to other optical catalogues are given for these data, which are often supplemented by more detailed notes on individual sources. Accurate radio positions taken from the literature are given for a large fraction of the sources.
Optical identifications have been sought for 304 radio sources from the declination -20{deg} region of the first Molonglo deep survey. Optical objects have been measured using the Palomar sky survey to an accuracy of 1 arcsec and magnitude estimates are to 0.4mag. Finding charts are given for all fields with optical objects within +/-2{sigma} of the radio position. Sixteen QSOs have been confirmed (details have been reported elsewhere) amongst the blue stellar-like objects and spectroscopy is complete to m_o_=19.5. The mean magnitude of the QSOs is 19.2 and the mean redshift is 1.34. A study of the background densities of objects indicates that about half of the remaining blue stellar-like objects are QSOs and about 80 per cent of the galaxies are associated with the radio emission. The QSOs are amongst the fainter and the bluer of the blue stellar-like objects. There is no evidence for any average offset between the radio and optical positions.
CCD images of the fields of 115 radio sources from the 1Jy, S4 and S5 catalogues are presented. New optical counterparts have been found for a total of 34 sources, a large fraction of which had as yet only been described as empty fields on Sky Survey Plates. Of the 54 radio sources with previously published identifications, 50 optical counterparts have been confirmed while for 4 sources new identifications are proposed. R band magnitudes, derived from the CCD images, are provided for all but a few identified optical counterparts. The fields at the positions of 27 radio sources are still empty down to a limiting magnitude of at least m_R_=22mag, requiring much deeper optical as well as additional infrared images for establishing their optical counterparts.
We present the coordinates, apparent magnitudes, and morphological types for 230 galaxies presumably identified with HIPASS (HI Parkes All-Sky Survey) sources. The new optical counterparts of the HIPASS sources follow the well-known statistical relationships between the hydrogen mass, luminosity, and type of galaxies. Low-surface-brightness galaxies constitute a significant fraction among these objects. The median value of the hydrogen mass-to-luminosity ratio for them is a factor of 2 or 3 higher than that for bright HIPASS galaxies, reaching 1.7M_{sun}_/L_{sun}_. A number of our objects are located near the boundary log (M(HI)/L(B))=0.2(M(B)+20) that defines the zone of gravitational stability of disk galaxies against large-scale star formation.
