- ID:
- ivo://CDS.VizieR/J/AJ/148/72
- Title:
- Photometry & interferometry of nearby secondaries
- Short Name:
- J/AJ/148/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To improve the statistics of hierarchical multiplicity, secondary components of wide nearby binaries with solar-type primaries were surveyed at the SOAR telescope for evaluating the frequency of subsystems. Images of 17 faint secondaries were obtained with the SOAR Adaptive Module that improved the seeing; one new 0.2'' binary was detected. For all targets, photometry in the g', i', z' bands is given. Another 46 secondaries were observed by speckle interferometry, resolving 7 close subsystems. Adding literature data, the binarity of 95 secondary components is evaluated. We found that the detection-corrected frequency of secondary subsystems with periods in the well-surveyed range from 10^3^ to 10^5^ days is 0.21+/-0.06--same as the normal frequency of such binaries among solar-type stars, 0.18. This indicates that wide binaries are unlikely to be produced by dynamical evolution of N-body systems, but are rather formed by fragmentation.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/395/907
- Title:
- PISCO speckle observations in 2007
- Short Name:
- J/MNRAS/395/907
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present relative astrometric measurements of visual binaries made during the first semester of 2007, with the Pupil Interferometry Speckle camera and COronagraph (PISCO) at the 102-cm Zeiss telescope of Brera Astronomical Observatory, in Merate. Our sample contains orbital couples as well as binaries whose motion is still uncertain. We obtained 226 new measurements of 214 objects, with angular separations in the range 0.15-4.5arcsec, and an average accuracy of 0.013arcsec. The mean error on the position angles is. Most of the position angles could be determined without the usual 180{deg} ambiguity with the application of triple-correlation techniques and/or by inspection of the long integration files. We also present the new orbits we have computed for ADS 7871, 7982 and 8128, for which our measurements lead to large residuals and/or for which the revision is justified by the significant number of observations made since the publication of the previous orbit.
- ID:
- ivo://CDS.VizieR/J/AN/330/55
- Title:
- PISCO speckle observations in 2006
- Short Name:
- J/AN/330/55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present relative astrometric measurements of visual binaries made during the second semester of 2006, with the speckle camera PISCO at the 102cm Zeiss telescope of Brera Astronomical Observatory, in Merate. Our sample contains orbital couples as well as binaries whose motion is still uncertain. We obtained 175 new measurements of 169 objects, with angular separations in the range 0.1"-4.2", and an average accuracy of 0.01". The mean error on the position angles is 0.6{deg}. Most of the position angles could be determined without the usual 180{deg} ambiguity with the application of triple-correlation techniques and/or by inspection of the long integration files.We also present the new orbits we have computed for ADS 11479, 11584 and 16538, for which our measurements lead to large residuals and/or for which the revision was justified by the significant number of observations made since the last orbit computation.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A64
- Title:
- Position difference vectors and of the jets
- Short Name:
- J/A+A/651/A64
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We aim to study the relative positions of quasar emission centers at different wavelengths in order to help link the various realizations of the International Celestial Reference System (ICRS), and to unveil systematic uncertainties and individual source behavior at different wavelengths. We based our study on four catalogs representing the ICRS, the ICRF3 positions in the three VLBI bands X, K, and Ka, and the Gaia EDR3 catalog in optical wavelengths. We complemented radio source positions with jet kinematics results from the MOJAVE team, allowing us to obtain jet directions on the sky. A six-parameter deformation model was used to remove systematic uncertainties present in the different catalogs. For a set of 194 objects common to the four catalogs and to the objects whose jet kinematics was studied by the MOJAVE team, we computed the orientation between positions at the different wavelengths and with respect to the directions of the jets. We find that the majority of these objects have their radio-to-optical vector along the jet, with the optical centroid downstream from the radio centroids, and that the K and Ka centroids are preferably upstream in the jet with respect to the X centroid, which is consistent with the paradigm of a simple core-jet model. For a population of multiwavelength positions aligned along the jet, astrometric information can therefore be used to measure the direction of the jet independently of imaging. In addition, we find several sources for which the optical centroid coincides with stationary radio features with a relatively high fraction of polarization, indicating optical emission dominated by a synchrotron process in the jet.
- ID:
- ivo://CDS.VizieR/J/AJ/121/1192
- Title:
- Proper-motion measurements with the VLA
- Short Name:
- J/AJ/121/1192
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The pulsar velocity distribution provides information about the binary history of pulsar progenitors, as well as the asymmetries of the supernova events in which pulsars are born. Studies of local pulsars present a biased view of this distribution, because they preferentially select low-velocity pulsars that have remained near their birthplaces in the Galactic plane. Using the VLA, we have studied the proper motions of a large sample of distant pulsars. These pulsars are generally faint, and the expected proper motions are small. In this paper, we describe the data analysis techniques that we have developed to allow precise astrometric measurements of faint sources with the VLA. These techniques include "gating" the VLA correlator to increase the signal-to-noise ratio of the pulsar by gathering data only during the pulse. Wide-field imaging techniques, including multiband imaging to account for bandwidth smearing, were used to allow identification of multiple in-beam background sources for astrometric calibration. We present the analysis of three pulsars and demonstrate that astrometric accuracy of about 10 mas can be obtained for individual sources with our technique, allowing measurement of proper motions with errors of only a few milliarcseconds per year over our 7 year baseline.
- ID:
- ivo://CDS.VizieR/J/A+A/529/A91
- Title:
- Proper motions of 555 quasars from VLBI
- Short Name:
- J/A+A/529/A91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- While analyzing decades of very long baseline interferometry (VLBI) data, we detected the secular aberration drift of the extragalactic radio source proper motions caused by the rotation of the Solar System barycenter around the Galactic center. Our results agree with the predicted estimate to be 4-6 micro arcseconds per year (uas/yr) towards RA=266{deg} and DE=-29{deg}. In addition, we tried to detect the quadrupole systematics of the velocity field. The analysis method consisted of three steps. First, we analyzed geodetic and astrometric VLBI data to produce radio source coordinate time series. Second, we fitted proper motions of 555 sources with long observational histories over the period 1990-2010 to their respective coordinate time series. Finally, we fitted vector spherical harmonic components of degrees 1 and 2 to the proper motion field.
- ID:
- ivo://CDS.VizieR/J/ApJS/176/276
- Title:
- PTI calibrator catalog
- Short Name:
- J/ApJS/176/276
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Palomar Testbed Interferometer (PTI) archive of observations between 1998 and 2005 is examined for objects appropriate for calibration of optical long-baseline interferometer observations - stars that are predictably pointlike and single. Approximately 1400 nights of data on 1800 objects were examined for this investigation. We compare those observations to an intensively studied object that is a suitable calibrator, HD 217014, and statistically compare each candidate calibrator to that object by computing both a Mahalanobis distance and a principal component analysis. Our hypothesis is that the frequency distribution of visibility data associated with calibrator stars differs from noncalibrator stars such as binary stars. Spectroscopic binaries resolved by PTI, objects known to be unsuitable for calibrator use, are similarly tested to establish detection limits of this approach. From this investigation, we find more than 350 observed stars suitable for use as calibrators (with an additional ~140 being rejected), corresponding to >~95% sky coverage for PTI.
- ID:
- ivo://CDS.VizieR/J/ApJ/775/45
- Title:
- PTI carbon star angular size survey
- Short Name:
- J/ApJ/775/45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report new interferometric angular diameter observations of 41 carbon stars observed with the Palomar Testbed Interferometer. Two of these stars are CH carbon stars and represent the first such measurements of this subtype. Of these, 39 have Yamashita spectral classes and are of sufficiently high quality that we can determine the dependence of effective temperature on spectral type. We find that there is a tendency for the effective temperature to increase with increasing temperature index by ~120K per step, starting at T_eff_=~2500K for C3, y, although there is a large amount of scatter in this relationship. Overall, the median effective temperature of the carbon star sample is 2800+/-270 K and the median linear radius is 360+/-100R_{sun}_. We also find agreement, on average within 15K, with the T_eff_ determinations of Bergeat et al. (J/A+A/369/178) and a refinement of the carbon star angular size prediction based on V & K magnitudes is presented that is good to an rms of 12%. A subsample of our stars have sufficient {u, v} coverage to permit non-spherical modeling of their photospheres, and a general tendency for detection of statistically significant departures from sphericity with increasing interferometric signal-to-noise is seen. The implications of most -and potentially all- carbon stars being non-spherical is considered in the context of surface inhomogeneities and a rotation-mass-loss connection.
- ID:
- ivo://CDS.VizieR/J/AJ/144/150
- Title:
- QCAL-1 43 GHz Calibrator Survey
- Short Name:
- J/AJ/144/150
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the catalog of correlated flux densities in three ranges of baseline projection lengths of 637 sources from a 43GHz (Q band) survey observed with the Korean VLBI Network. Of them, 14 objects used as calibrators were previously observed, but 623 sources have not been observed before in the Q band with very long baseline interferometry (VLBI). The goal of this work in the early science phase of the new VLBI array is twofold: to evaluate the performance of the new instrument that operates in a frequency range of 22-129GHz and to build a list of objects that can be used as targets and as calibrators. We have observed the list of 799 target sources with declinations down to -40{deg}. Among them, 724 were observed before with VLBI at 22GHz and had correlated flux densities greater than 200mJy. The overall detection rate is 78%. The detection limit, defined as the minimum flux density for a source to be detected with 90% probability in a single observation, was in the range of 115-180mJy depending on declination. However, some sources as weak as 70mJy have been detected. Of 623 detected sources, 33 objects are detected for the first time in VLBI mode. We determined their coordinates with a median formal uncertainty of 20mas. The results of this work set the basis for future efforts to build the complete flux-limited sample of extragalactic sources at frequencies of 22GHz and higher at 3/4 of the celestial sphere.
- ID:
- ivo://CDS.VizieR/J/A+A/602/A29
- Title:
- QSO 1308+326 at 15GHz modelfit results
- Short Name:
- J/A+A/602/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Despite numerous and detailed studies of the jets of Active Galactic Nuclei (AGN) on pc-scales, many questions are still debated. The physical nature of the jet components is one of the most prominent unsolved problems as is the launching mechanism of jets in AGN. The Quasar 1308+326 (z=0.997) allows detailed studies of the overall properties of the jet and to derive a more physical understanding of the nature and origin of jets in general. The long-term data provided by the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) survey permit tracing out the structural changes in 1308+326 presented here. The long-lived jet features in this source can be followed for about two decades. We investigate the VLBI morphology and kinematics of the jet of 1308+326 to understand the physical nature of this jet and jets in general, the role of magnetic fields, and the causal connection between jet features and the launching process. 50 VLBA observations performed at 15GHz from the MOJAVE survey have been re-modeled with Gaussian components and re-analyzed (the time covered: 1995.05-2014.07). The analysis is supplemented by multi-wavelength radio-data (UMRAO, at 4.8, 8.0, and 14.5GHz) in polarization and total intensity. We fit the apparent motion of the jet features with the help of a model of a precessing nozzle. The jet features seem to be emitted with varying viewing angles and launched into an ejection cone. Tracing the component paths yields evidence for rotational motion. Radio flux-density variability can be explained as a consequence of enhanced Doppler boosting corresponding to the motion of the jet relative to the line of sight. Based on the presented kinematics and other indicators, such as electric-vector polarization position angle (EVPA)-rotation we conclude that the jet of 1308+326 has a helical structure, i.e. the components are moving along helical trajectories, while the trajectories themselves are experiencing a precessing motion as well. A model of a precessing nozzle (Qian et al., 2014RAA....14..249Q) was applied to the data and a subset of the observed jet feature paths can be modeled successfully within this model. The data through 2012 are consistent with a swing period of 16.9 years. We discuss several scenarios to explain the observed motion phenomena, including a binary black hole model. It seems unlikely that the accretion disk around the primary black hole, that is disturbed by tidal forces of the secondary black hole, is able to launch a persistent axisymmetric jet. We conclude that we are observing a rotating helix. In particular, the observed EVPA swings can be explained by a shock moving through a straight jet pervaded by a helical magnetic field. We compare our results for 1308+326 with other astrophysical scenarios where similar, wound up filamentary structures are found. They all are related to accretion-driven processes. A helically moving or wound up object is often explained by filamentary features moving along magnetic field lines of magnetic flux tubes. It seems that a "component" is plasma tracing the magnetic field which guides the motion of the radiating radio-band plasma. Further investigations and modeling are in preparation.
