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- ID:
- ivo://CDS.VizieR/J/A+A/355/398
- Title:
- Celestial Ephemeris Origin definition
- Short Name:
- J/A+A/355/398
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The adoption of the International Celestial Reference System ICRS, and of the corresponding Frame, ICRF, by the 23rd General Assembly of the International Astronomical Union, calls for a redefinition of the departure point on the true equator. Several possibilities have been suggested. This paper considers the use of the non-rotating origin (Guinot, 1979, In: McCarthy D.D., Pilkington J.D. (eds.) Time and the Earth's Rotation. D. Reidel Pub. Co, p. 7). The ``Celestial Ephemeris Origin'' (CEO) is defined here as the non-rotating origin on the equator of the Celestial Ephemeris Pole (CEP). Developments valid at the microarcsecond, based on the best model for precession, nutation and pole offset at J2000.0 with respect to the pole of ICRF, are provided for computing the CEP coordinates and the position of the CEO. It is shown that an operational definition of UT1 based on the CEO leads to values which are insensitive at the microarcsecond level to future improvements of this model.
- ID:
- ivo://CDS.VizieR/J/A+A/400/1145
- Title:
- Celestial Intermediate Pole & Ephemeris Origin
- Short Name:
- J/A+A/400/1145
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Expressions for the position of the Celestial Intermediate Pole (CIP) and the Celestial Ephemeris Origin (CEO) in the Geocentric Celestial Reference System (GCRS) have been computed using the IAU 2000A precession-nutation. These expressions are for use in the new transformation between the GCRS and the International Terrestrial Reference System (ITRS) which is recommended by IAU Resolution B1.8. Various comparisons and numerical checks have been performed between the classical and the new transformations based on the IAU 2000A precession-nutation. These comparisons revealed necessary improvements to be applied to the classical form of the transformation in order to achieve the required level of accuracy. Once these improvements are applied, the consistency between the positions of the CIP in the GCRS corresponding to the classical and the new transformations is at a level of a few microarcseconds after one century. This work has demonstrated that the new method, in addition to providing an explicit separation between precession-nutation of the equator from Earth rotation, is more simple, compact and direct than the classical one, achieving accuracies at the level of a few microarcseconds with greatly reduced scope for accidental misuse. The resulting expressions for X, Y and s have been included in the IERS Conventions 2000.
- ID:
- ivo://CDS.VizieR/J/AJ/139/1695
- Title:
- Celestial Reference Frame at 24 and 43 GHz
- Short Name:
- J/AJ/139/1695
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present astrometric results for compact extragalactic objects observed with the Very Long Baseline Array at radio frequencies of 24 and 43GHz. Data were obtained from ten 24-hr observing sessions made over a five-year period. These observations were motivated by the need to extend the International Celestial Reference Frame (ICRF) to higher radio frequencies to enable improved deep space navigation after 2016 and to improve state-of-the-art astrometry. Source coordinates for 268 sources were estimated at 24GHz and for 131 sources at 43GHz.
- ID:
- ivo://CDS.VizieR/J/AJ/139/1713
- Title:
- Celestial Reference Frame at 24 and 43GHz. II
- Short Name:
- J/AJ/139/1713
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have measured the submilliarcsecond structure of 274 extragalactic sources at 24 and 43 GHz in order to assess their astrometric suitability for use in a high-frequency celestial reference frame (CRF). Ten sessions of observations with the Very Long Baseline Array have been conducted over the course of ~5 years, with a total of 1339 images produced for the 274 sources. There are several quantities that can be used to characterize the impact of intrinsic source structure on astrometric observations including the source flux density, the flux density variability, the source structure index, the source compactness, and the compactness variability.
- ID:
- ivo://CDS.VizieR/J/A+A/581/A22
- Title:
- 67 CEMP-s stars model analysis
- Short Name:
- J/A+A/581/A22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Many of the carbon-enhanced metal-poor (CEMP) stars that we observe in the Galactic halo are found in binary systems and show enhanced abundances of elements produced by the slow neutron-capture process (s-elements). The origin of the peculiar chemical abundances of these CEMP-s stars is believed to be accretion in the past of enriched material from a primary star in the asymptotic giant branch (AGB) phase of its evolution. We investigate the mechanism of mass transfer and the process of nucleosynthesis in low-metallicity AGB stars by modelling the binary systems in which the observed CEMP-s stars were formed. For this purpose we compare a sample of 67 CEMP-s stars with a grid of binary stars generated by our binary evolution and nucleosynthesis model. We classify our sample CEMP-s stars in three groups based on the observed abundance of europium. In CEMP-s/r stars the europium-to-iron ratio is more than ten times higher than in the Sun, whereas it is lower than this threshold in CEMP-s/nr stars. No measurement of europium is currently available for CEMP-s/ur stars. On average our models reproduce the abundances observed in CEMP-s/nr stars well, whereas in CEMP-s/r stars and CEMP-s/ur stars the abundances of the light-s elements (strontium, yttrium, zirconium) are systematically overpredicted by our models, and in CEMP-s/r stars the abundances of the heavy-s elements (barium, lanthanum) are underestimated. In all stars our modelled abundances of sodium overestimate the observations. This discrepancy is reduced only in models that underestimate the abundances of most of the s-elements. Furthermore, the abundance of lead is underpredicted in most of our model stars, independent of the metallicity. These results point to the limitations of our AGB nucleosynthesis model, particularly in the predictions of the element-to-element ratios. In our models CEMP-s stars are typically formed in wide systems with periods above 10000-days, while most of the observed CEMP-s stars are found in relatively close orbits with periods below 5000-days. This evidence suggests that either the sample of CEMP-s binary stars with known orbital parameters is biased towards short periods or that our wind mass-transfer model requires more efficient accretion in close orbits.
3257. Cen A 118MHz MWA image
- ID:
- ivo://CDS.VizieR/J/MNRAS/436/1286
- Title:
- Cen A 118MHz MWA image
- Short Name:
- J/MNRAS/436/1286
- Date:
- 07 Feb 2022 14:36:33
- Publisher:
- CDS
- Description:
- We present new wide-field observations of Centaurus A (Cen A) and the surrounding region at 118MHz with the Murchison Widefield Array (MWA) 32-tile prototype, with which we investigate the spectral-index distribution of Cen A's giant radio lobes. We compare our images to 1.4GHz maps of Cen A and compute spectral indices using temperature-temperature plots and spectral tomography. We find that the morphologies at 118MHz and 1.4GHz match very closely apart from an extra peak in the southern lobe at 118MHz, which provides tentative evidence for the existence of a southern counterpart to the northern middle lobe of Cen A. Our spatially averaged spectral indices for both the northern and southern lobes are consistent with previous analyses, however we find significant spatial variation of the spectra across the extent of each lobe. Both the spectral-index distribution and the morphology at low radio frequencies support a scenario of multiple outbursts of activity from the central engine. Our results are consistent with inverse-Compton modelling of radio and gamma-ray data that support a value for the lobe age of between 10 and 80Myr.
3258. Cen A MWA 154MHz image
- ID:
- ivo://CDS.VizieR/J/MNRAS/474/4056
- Title:
- Cen A MWA 154MHz image
- Short Name:
- J/MNRAS/474/4056
- Date:
- 07 Feb 2022 14:39:09
- Publisher:
- CDS
- Description:
- We present new radio and optical images of the nearest radio galaxy Centaurus A and its host galaxy NGC 5128. We focus our investigation on the northern transition region, where energy is transported from the ~5kpc (~5-arcmin) scales of the northern inner lobe (NIL) to the ~30kpc (~30-arcmin) scales of the northern middle lobe (NML). Our Murchison Widefield Array observations at 154MHz and our Parkes radio telescope observations at 2.3GHz show diffuse radio emission connecting the NIL to the NML, in agreement with previous Australia Telescope Compact Array observations at 1.4GHz. Comparison of these radio data with our wide-field optical emission-line images show the relationship between the NML radio emission and the ionized filaments that extend north from the NIL, and reveal a new ionized filament to the east, possibly associated with a galactic wind. Our deep optical images show clear evidence for a bipolar outflow from the central galaxy extending to intermediate scales, despite the non-detection of a southern radio counterpart to the NML. Thus, our observational overview of Centaurus A reveals a number of features proposed to be associated with active galactic nucleus feedback mechanisms, often cited as likely to have significant effects in galaxy evolution models. As one of the closest galaxies to us, Centaurus A therefore provides a unique laboratory to examine feedback mechanisms in detail.
- ID:
- ivo://CDS.VizieR/J/MNRAS/346/627
- Title:
- CENSORS (Combined EIS-NVSS Survey) catalog
- Short Name:
- J/MNRAS/346/627
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new sample of radio sources, with the designated name CENSORS (A Combined EIS-NVSS Survey Of Radio Sources), has been defined by combining the National Radio Astronomy Observatory Very Large Array Sky Survey (NVSS) at 1.4GHz with the ESO Imaging Survey (EIS) Patch D, a 3x2deg^2^ region of sky centred at RA = 09 51 36.0, DE = -21 00 00 (J2000). New radio observations of 199 NVSS radio sources with NVSS flux densities S_1.4GHz_>7.8mJy are presented, and are compared with the EIS I-band imaging observations which reach a depth of I~23; optical identifications are obtained for over two-thirds of the ~150 confirmed radio sources within the EIS field.
3260. CENSORS infrared imaging
- ID:
- ivo://CDS.VizieR/J/MNRAS/366/1265
- Title:
- CENSORS infrared imaging
- Short Name:
- J/MNRAS/366/1265
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Combined EIS-NVSS Survey of Radio Sources (CENSORS) is a 1.4-GHz radio survey selected from the National Radio Astronomy Observatories (NRAO) Very Large Array (VLA) Sky Survey (NVSS) and complete to a flux density of 7.2mJy. It targets the European Southern Observatory (ESO) Imaging Survey (EIS) Patch D, which is a 3x2{deg}^2^ field centred on right ascension 09:51:36.0 and declination 21:00:00 (J2000). This paper presents K-band imaging of 142 of the 150 CENSORS sources. The primary motivation for beginning infrared imaging of the sample was to identify the host galaxies of ~30 per cent of sources for which the EIS I-band imaging failed to produce a likely candidate. In addition, K-band magnitudes allow photometric redshift estimation and IK colours aid the identification of host galaxies (which are typically old, red ellipticals). Of the sources observed in the I and K bands, four remain undetected, possibly indicating high redshifts for the host galaxies, and eight involve complicated radio structures, or several candidate host galaxies, which have yet to be resolved. Thus, the host galaxy identifications are brought to 92 per cent completeness.
