Search results for "astrometry"
showing 10 items of 38 documents
The Star Formation Region NGC 6530: distance, ages and Initial Mass Function
2005
We present astrometry and $BVI$ photometry, down to $V\simeq22$, of the very young open cluster NGC6530, obtained from observations taken with the Wide Field Imager camera at the MPG/ESO 2.2 m Telescope. Both the $V$ vs. $B-V$ and the $V$ vs. $V-I$ color-magnitude diagrams (CMD) show the upper main sequence dominated by very bright cluster stars, while, due to the high obscuration of the giant molecular cloud surrounding the cluster, the blue envelopes of the diagrams at $V\gtrsim 14$ are limited to the main sequence stars at the distance of NGC6530. This particular structure of the NGC6530 CMD allows us to conclude that its distance is about $d \simeq 1250$ pc, significantly lower than the…
High Precision Differential Astrometry in Large Angular Separation Pairs of Radiosources
1994
We show preliminary results of three of the four radiosource pairs with angular separations ranging from 0.01° to 6° where we have determined such a separation with a typical fractional precision of 10-8using phase delays corrected for structural and ionospheric contributions. In the radiosource 4C39.25 we measure a motion with respect to an external radiosource which is compatible with previously reported internal superluminal motion.
Geodetic data analysis of VGOS experiments
2021
Very Long Baseline Interferometry (VLBI) serves as one of the common geodetic methods to define the global reference frames and monitor Earth's orientation variations. The technical upgrade of the VLBI method known as the VLBI Global Observing System (VGOS) includes a critical re-design of the observed frequencies from the dual band mode (S and X band, i.e. 2 GHz and 8 GHz) to observations in a broadband (2 – 14 GHz). Since 2019 the first VGOS experiments are available for the geodetic analysis in free access at the International VLBI service for Geodesy and Astrometry (IVS). Also regional-only subnetworks such as European VLBI stations have succeeded already in VGOS mode. Based on these br…
Multi-beam capabilities for high precision astrometry at low frequencies using VLBI
2011
We are carrying out a simulation study to characterise the advantages of VLBI with multiple beams, which will be a feature of the next generation of instruments. We will focus on VLBI astrometric measurements at lower frequencies (1.4 GHz and below). For our simulations, we have selected a network consisting of ASKAP, the Australian SKA precursor, plus existing Australian antennas from the LBA (Long Baseline Array) and the new antenna in New Zealand (figure 1a). We have used different models to represent the ionospheric turbulences and frequencies. The preliminary results show an improvement of an order of magnitude in the astrometric precision achieved using multiple calibrators with angul…
Parameters for automated star identification
2014
The determination of parameters for identifying stars sensed by charge-coupled device (CCD) is discussed. Numerical experiments are summarized which support the parameter space bound estimation practicality of the proposed star pattern recognition and identification by matching with coordinate list in star catalogue. The parameter analysis performed to apply them for proper identification algorithm which is developed and used at the Institute of Geodesy and Geoinformatics. This algorithm is applied for identification of large volume star sets.
Differential astrometry over 15°
1999
Abstract We observed the pair of radio sources 1150+812 and 1803+784 in November 1993 with a VLBI array, simultaneously recording at 8.4 and 2.3 GHz. We determined the angular separation between the two sources with submilliarcsecond accuracy by using differential techniques. This result demonstrates the feasibility of high precision differential astrometry for radio sources separated in the sky by almost 15°, and opens the avenue to its application to larger samples of radio sources.
Astrometric detection of a low-mass companion orbiting the star AB Doradus
1997
International audience; We report submilliarcsecond-precise astrometric measurements for the late-type star AB Doradus via a combination of VLBI (very long baseline interferometry) and HIPPARCOS data. Our astrometric analysis results in the precise determination of the kinematics of this star, which reveals an orbital motion readily explained as caused by gravitational interaction with a low-mass companion. From the portion of the reÑex orbit covered by our data and using a revised mass of the primary star (0.76 M _) derived from our new value of the parallax (66.3 mas \ n \ 67.2 mas), we Ðnd the dynamical mass of the newly discovered companion to be between 0.08 and 0.11 If accurate photom…
Phase Reference VLBI Astrometry for Mira-Type Stars
2003
We carried out phase reference VLBI observations at 43 GHz between SiO masers in Mira type variables and adjacent extragalactic continuum source with VLBA. Main aim of this observation is determination of spatial distribution between SiO maser spots at v = 1 and v = 2, J=l→0 transition. Although the standard calibration was successful for each source, the phase reference calibration have not been successful. However, we will determine the absolute positional difference of each SiO maser spot within about 1 milli arcsecond due to the structure effect of reference source if the phase reference VLBI is successful
Young, active radio stars in the AB Doradus moving group
2017
Context. Precise determination of stellar masses is necessary to test the validity of pre-main-sequence (PMS) stellar evolutionary models, whose predictions are in disagreement with measurements for masses below 1.2 M. To improve such a test, and based on our previous studies, we selected the AB Doradus moving group (AB Dor-MG) as the best-suited association on which to apply radio-based high-precision astrometric techniques to study binary systems. Aims. We seek to determine precise estimates of the masses of a set of stars belonging to the AB Dor-MG using radio and infrared observations. Methods. We observed in phase-reference mode with the Very Large Array (VLA) at 5 GHz and with the Eur…
Absolute kinematics of radio source components in the complete S5 polar cap sample
2008
We report on the first wide-field, high-precision astrometric analysis of the 13 extragalactic radio sources of the complete S5 polar cap sample at 15.4 GHz. We describe new algorithms developed to enable the use of differenced phase delays in wide-field astrometric observations and discuss the impact of using differenced phase delays on the precision of the wide-field astrometric analysis. From this global fit, we obtained estimates of the relative source positions with precisions ranging from 14 to 200 μas at 15.4 GHz, depending on the angular separation of the sources (from ∼1.6 to ∼20.8 degrees). These precisions are ∼10 times higher than the achievable precisions using the phase-refere…