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451. Radio reference frame
ID:
ivo://CDS.VizieR/J/AJ/110/880
Title:
Radio reference frame
Short Name:
J/AJ/110/880
Date:
21 Oct 2021
Publisher:
CDS
Description:
A catalogue is presented based on the radio positions of 436 extragalactic sources distributed over the entire sky. The positional accuracy of the sources is better than 3 milliarcsec (mas) in both coordinates, with the majority of the sources having errors better than 1mas. This catalogue is based upon a general solution of all applicable dual frequency 2.3 and 8.4GHz Mark-III VLBI data available through the end of 1993 consisting of 1,015,292 pairs of group delay and phase delay rate observations. Details and positions are also given for an additional 124 objects that either need further observation or are currently unsuitable for the definition of a reference frame. The final orientation of the catalogue has been obtained by a rotation of the positions into the system of the International Earth Rotation Service and is consistent with the FK5 J2000.0 optical system, within the limits of the link accuracy.
452. Radio source distribution
ID:
ivo://CDS.VizieR/J/A+A/506/1477
Title:
Radio source distribution
Short Name:
J/A+A/506/1477
Date:
21 Oct 2021
Publisher:
CDS
Description:
Information on physical characteristics of astrometric radio sources, such as magnitude and redshift, is of great importance for many astronomical studies. However, data usually used in radio astrometry is often incomplete and outdated. Our purpose is to study the optical characteristics of more than 4000 radio sources observed by the astrometric VLBI technique since 1979. We also studied the effect of the asymmetry in the distribution of the reference radio sources on the correlation matrices between vector spherical harmonics of the first and second degrees. The radio source characteristics were mainly taken from the NASA/IPAC Extragalactic Database (NED). Characteristics of the gravitational lenses were checked with the CfA-Arizona Space Telescope LEns Survey. SIMBAD and HyperLeda databases were also used to clarify the characteristics of some objects. Also we simulated and investigated a list of 4000 radio sources evenly distributed around the celestial sphere. We estimated the correlation matrices between the vector spherical harmonics using the real as well as modelled distribution of the radio sources.
453. Radio source selection for the ICRF
ID:
ivo://CDS.VizieR/J/A+A/493/317
Title:
Radio source selection for the ICRF
Short Name:
J/A+A/493/317
Date:
21 Oct 2021
Publisher:
CDS
Description:
The most accurate realization of a quasi inertial reference frame, the International Celestial Reference Frame (ICRF), is made of 212 defining extragalactic radio sources whose coordinates are determined using VLBI observations. Recent studies demonstrated however that using other sets of sources could improve the frame stability. This study examines a simple radio source selection scheme to define celestial reference frame axes more stable than the ones as currently defined by the ICRF. After having derived source coordinate time series from 26 years of VLBI observations, we select the most suitable sources on the basis of their positional variability (rms and slope), and observational history. We determine the axis stability of the frame defined by the selection, as well as its suitability for global geodetic VLBI analyses, i.e., determination of Earth orientation parameters and source and station coordinates.
454. Radio star proper motions
ID:
ivo://CDS.VizieR/J/AJ/133/906
Title:
Radio star proper motions
Short Name:
J/AJ/133/906
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have used the Very Large Array, linked with the Pie Town Very Long Baseline Array antenna, to determine astrometric positions of 46 radio stars in the International Celestial Reference Frame (ICRF). Positions were obtained in the ICRF directly through phase referencing of the stars to nearby ICRF quasars whose positions are accurate at the 0.25mas level. Radio star positions are estimated to be accurate at the 10mas level, with position errors approaching a few milliarcseconds for some of the stars observed. Our measured positions were combined with previous measurements taken from as early as 1978 to obtain proper-motion estimates for all 46 stars with average uncertainties of ~1.7mas/yr.
455. Redshift of 97 spirals
ID:
ivo://CDS.VizieR/J/A+A/310/353
Title:
Redshift of 97 spirals
Short Name:
J/A+A/310/353
Date:
21 Oct 2021
Publisher:
CDS
Description:
Persistent claims have been made over the last ~15yr that extragalactic redshifts, when corrected for the Sun's motion around the Galactic centre, occur in multiples of ~24 or ~36km/s. A recent investigation by us of 40 spiral galaxies out to 1000km/s, with accurately measured redshifts, gave evidence of a periodicity ~37.2-37.7km/s. Here we extend our enquiry out to the edge of the Local Super cluster (~2600km/s), applying a simple and robust procedure to a total of 97 accurately determined redshifts. We find that, when corrected for related vectors close to recent estimates of the Sun's galactocentric motion, the redshifts of spirals are strongly periodic (P~37.6km/s). The formal confidence level of the result is extremely high, and the signal is seen independently with different radio telescopes. We also examine a further sample of 117 spirals observed with the 300-foot Green Bank telescope alone. The periodicity phenomenon appears strongest for the galaxies linked by group membership, but phase coherence probably holds over large regions of the Local Supercluster.
456. Relative proper motions in NGC 362
ID:
ivo://CDS.VizieR/J/A+AS/93/311
Title:
Relative proper motions in NGC 362
Short Name:
J/A+AS/93/311
Date:
22 Feb 2022
Publisher:
CDS
Description:
Relative proper motions are determined for stars brighter than B~=17mag in a 1.5{deg}x1.5{deg} field centered on the globular cluster NGC 362. Proper motions and membership probabilities are tabulated for 488 stars within 10.2' of the cluster center. 14 astrographic plates with epoch differences up to 92 years were completely scanned, and each detectable object was stored. Proper motions were computed with an iterative central-overlap technique. A modal proper motion accuracy of 0.9 milliarcsec/year (mas/a) was achieved. NGC 362 appears projected onto the Small Magellanic Cloud (SMC), allowing to measure the proper motion of the cluster relative to extragalactic background stars. SMC stars were identified by position, proper motion and colour; the mean proper motion of these SMC candidates agrees well with the proper motions of SMC members known from the literature. The proper motion of NGC 362 relative to the SMC is +3.5+/-0.8mas/a in right ascension and -2.6+/-0.8mas/a in declination. For reasonable assumptions on the absolute proper motion of the SMC, the absolute proper motion and space motion of NGC 362 are computed. NGC 362 exhibits a highly eccentric orbit, typical for a member of the halo subgroup of the galactic globular cluster system. The perigalactic distance of NGC 362 is very small (<~1kpc), which raises the interesting question of how the cluster can survive the many passages near the galactic bulge over its lifetime.
457. Results of obs with the 6-inch transit circle
ID:
ivo://CDS.VizieR/I/100A
Title:
Results of obs with the 6-inch transit circle
Short Name:
I/100A
Date:
21 Oct 2021
Publisher:
CDS
Description:
This catalog is a compilation of seven catalogs of positions derived from observations with the six-inch transit circle of the U. S. Naval Observatory. The observations were obtained between 1911 and 1971 and were published in the catalogs: W210, W025, W150, W250, W350, W450, and W550. Proper motions and, in most catalogs, spectral types were added from other sources.
458. Revised coordinates for SGC galaxies
ID:
ivo://CDS.VizieR/J/PASP/101/360
Title:
Revised coordinates for SGC galaxies
Short Name:
J/PASP/101/360
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have determined improved positions for 373 galaxies listed in the Southern Galaxy Catalogue of Corwin, de Vaucouleurs, and de Vaucouleurs (1985, Cat. VII/116) as having poor coordinates. The revised coordinates are expected to be good to 6 arcsec (rms) in each coordinate.
459. Revised Luyten Half-Second Catalogue
ID:
ivo://CDS.VizieR/I/279
Title:
Revised Luyten Half-Second Catalogue
Short Name:
I/279
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present refined coordinates and proper motion data for the high proper motion (HPM) stars in the Luyten Half-Second (LHS) catalogue. The positional uncertainty in the original Luyten catalogue is typically >10" and is often >30". We have used the digital scans of the Palomar Observatory Sky Survey (POSS) I and POSS II plates to derive more accurate positions and proper motions of the objects. Out of the 4470 candidates in the LHS catalogue, 4323 objects were manually re-identified in the POSS I and POSS II scans. A small fraction of the stars were not found due to the lack of finder charts and digitized POSS II scans. The uncertainties in the revised positions are typically ~2", but can be as high as ~8" in a few cases, which is a large improvement over the original data. Cross-correlation with the Tycho-2 and Hipparcos catalogues yielded 819 candidates (with m_R_<~12). For these brighter sources, the position and proper motion data were replaced with the more accurate Tycho/Hipparcos data. In total, we have revised proper motion measurements and coordinates for 4040 stars and revised coordinates for 4330 stars. In the printed version of the paper, we present the updated coordinates and proper motion information on 528 sources which represent the high proper motion subset ({mu}>1"/yr) of the LHS catalogue. The electronic version contains the updated information on all the 4470 stars in the LHS catalogue.
460. Revisiting the Cygnus OB associations
ID:
ivo://CDS.VizieR/J/MNRAS/508/2370
Title:
Revisiting the Cygnus OB associations
Short Name:
J/MNRAS/508/2370
Date:
24 Jan 2022 09:16:32
Publisher:
CDS
Description:
OB associations play an important role in Galactic evolution, though their origins and dynamics remain poorly studied, with only a small number of systems analysed in detail. In this paper we revisit the existence and membership of the Cygnus OB associations. We find that of the historical OB associations only Cyg OB2 and OB3 stand out as real groups. We search for new OB stars using a combination of photometry, astrometry, evolutionary models and an SED fitting process, identifying 4680 probable OB stars with a reliability of >90%. From this sample we search for OB associations using a new and flexible clustering technique, identifying 6 new OB associations. Two of these are similar to the associations Cyg OB2 and OB3, though the others bear no relationship to any existing systems. We characterize the properties of the new associations, including their velocity dispersions and total stellar masses, all of which are consistent with typical values for OB associations. We search for evidence of expansion and find that all are expanding, albeit anistropically, with stronger and more significant expansion in the direction of Galactic longitude. We also identify two large-scale (160pc and 25km/s) kinematic expansion patterns across the Cygnus region, each including three of our new associations, and attribute this to the effects of feedback from a previous generation of stars. This work highlights the need to revisit the existence and membership of the historical OB associations, if they are to be used to study their properties and dynamics.