- ID:
- ivo://CDS.VizieR/J/AJ/140/1911
- Title:
- Astrometric Grid Giant Star Survey. III.
- Short Name:
- J/AJ/140/1911
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of high-resolution (~55000) spectral observations of 830 photometrically pre-selected candidate red giants in the magnitude range of V=9-12. We develop a pipeline for automated determination of the stellar atmospheric parameters from these spectra and estimate Teff, logg, [Fe/H], microturbulence velocity, and projected rotational velocities, vsin i, for the stars. The analysis confirms that the candidate selection procedure yielded red giants with very high success rate. We show that most of these stars are G and K giants with slightly subsolar metallicity ([Fe/H]~-0.3dex). An analysis of Mg abundances in the sample results in consistency of the [Mg/Fe] vs [Fe/H] trend with published results.
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- ID:
- ivo://CDS.VizieR/J/AJ/160/141
- Title:
- Astrometric measurements of * bet LMi
- Short Name:
- J/AJ/160/141
- Date:
- 09 Mar 2022
- Publisher:
- CDS
- Description:
- bet LMi is a double-lined visual binary with an orbital period of ~39yr. Via a simultaneous fitting to both astrometric and radial velocity measurements, we give a complete and improved orbit solution with high precision. Then, the component masses are precisely determined as 2.98{+/-}0.10M{sun} and 1.92{+/-}0.04M{sun} with a relative precision of ~3%, respectively. The orbital parallax is determined to be 19.6{+/-}0.2mas, which is two times more precise than Hipparcos parallax. With the known apparent magnitudes and magnitude difference of the components, we derive the luminosity of the components as 50.7{+/-}1.8L{sun} and 9.1{+/-}4.1L{sun}. The estimated radii of the components are 9.4{+/-}0.3R{sun} and 3.7{+/-}1.5R{sun}.
- ID:
- ivo://CDS.VizieR/J/ApJ/757/29
- Title:
- Astrometric measurements of HD 143275
- Short Name:
- J/ApJ/757/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The highly eccentric Be binary system {delta} Sco reached periastron during early 2011 July, when the distance between the primary and secondary was a few times the size of the primary disk in the H band. This opened a window of opportunity to study how the gaseous disks around Be stars respond to gravitational disturbance. We first refine the binary parameters with the best orbital phase coverage data from the Navy Precision Optical Interferometer. Then we present the first imaging results of the disk after the periastron, based on seven nights of five telescope observations with the MIRC combiner at the CHARA array. We found that the disk was inclined 27{deg}.6+/-6{deg}.0 from the plane of the sky, had a half-light radius of 0.49mas (2.2 stellar radii), and consistently contributed 71.4%+/-2.7% of the total flux in the H band from night to night, suggesting no ongoing transfer of material into the disk during the periastron. The new estimation of the periastron passage is UT 2011 July 3 07:00+/-4:30. Re-analysis of archival VLTI-AMBER interferometry data allowed us to determine the rotation direction of the primary disk, constraining it to be inclined either ~119{deg} or ~171{deg} relative to the orbital plane of the binary system. We also detect inner disk asymmetries that could be explained by spot-like emission with a few percent of the disk total flux moving in Keplerian orbits, although we lack sufficient angular resolution to be sure of this interpretation and cannot yet rule out spiral density waves or other more complicated geometries.
- ID:
- ivo://CDS.VizieR/J/ApJS/231/15
- Title:
- Astrometric monitoring of ultracool dwarf binaries
- Short Name:
- J/ApJS/231/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the full results of our decade-long astrometric monitoring programs targeting 31 ultracool binaries with component spectral types M7-T5. Joint analysis of resolved imaging from Keck Observatory and Hubble Space Telescope and unresolved astrometry from CFHT/WIRCam yields parallactic distances for all systems, robust orbit determinations for 23 systems, and photocenter orbits for 19 systems. As a result, we measure 38 precise individual masses spanning 30-115M_Jup_. We determine a model-independent substellar boundary that is ~70M_Jup_ in mass (~L4 in spectral type), and we validate Baraffe et al. evolutionary model predictions for the lithium-depletion boundary (60M_Jup_ at field ages). Assuming each binary is coeval, we test models of the substellar mass-luminosity relation and find that in the L/T transition, only the Saumon & Marley (2008ApJ...689.1327S) "hybrid" models accounting for cloud clearing match our data. We derive a precise, mass-calibrated spectral type-effective temperature relation covering 1100-2800K. Our masses enable a novel direct determination of the age distribution of field brown dwarfs spanning L4-T5 and 30-70M_Jup_. We determine a median age of 1.3Gyr, and our population synthesis modeling indicates our sample is consistent with a constant star formation history modulated by dynamical heating in the Galactic disk. We discover two triple-brown-dwarf systems, the first with directly measured masses and eccentricities. We examine the eccentricity distribution, carefully considering biases and completeness, and find that low-eccentricity orbits are significantly more common among ultracool binaries than solar-type binaries, possibly indicating the early influence of long-lived dissipative gas disks. Overall, this work represents a major advance in the empirical view of very low-mass stars and brown dwarfs.
- ID:
- ivo://CDS.VizieR/J/A+A/545/A144
- Title:
- Astrometric observations of Deimos
- Short Name:
- J/A+A/545/A144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Between July 2005 and July 2011 Mars Express performed 50 Deimos approaches. 156 SRC images were acquired and used for astrometric (positional) measurements of the small Martian satellite. For this study, we have developed a new technique, where the center-of-figure of the odd-shaped Deimos was determined by fitting the predicted to the observed satellite limb. The prediction of the limb was made based on the moon's known shape model. The camera pointing was verified and corrected by means of background star observations. We obtained a set of spacecraft- centered Deimos coordinates with accuracies between 0.6 and 3.6km (1 sigma). Comparisons with current orbit models indicate that Deimos is ahead or falling behind its predicted position along its track by as much as +3.7km or -4.4km, respectively, depending on the chosen model. Our data may be used to improve the orbit models of the satellite.
- ID:
- ivo://CDS.VizieR/J/A+AS/143/405
- Title:
- Astrometric observations of Helene
- Short Name:
- J/A+AS/143/405
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Astrometric photographic positions of the Saturnian satellite Helene obtained from 22 plates taken in 6 nights are presented. The observations are distributed between 5 missions in 1985 and 1987. All positions are compared with those calculated by Jacobson (1999, personal communication). The residuals have mean and standard deviation smaller than 0.25" and 0.30" respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/580/A28
- Title:
- Astrometric observations of Phobos
- Short Name:
- J/A+A/580/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Mars Express (MEX) carried out 74 Phobos flybys at distances between 669 and 5579km from April 2008 to August 2011. Images taken with the Super Resolution Channel (SRC) were used to determine the Martian moon's spacecraft-centered right ascension and declination. Image positions of Phobos were measured using the control point and limb fit measurement techniques. Camera pointing and pointing drift were controlled by means of background star observations that were compared to the corresponding positions from the Tycho-2 catalog. Blurred and noisy images were restored by applying an image-based point spread function in a Richardson-Lucy deconvolution. Altogether, we provide 158 astrometric observations of Phobos with estimated uncertainties between 0.224 and 3.405km circular about the direction to the satellite. Control point measurements yield more accurate results than limb fit observations.
- ID:
- ivo://CDS.VizieR/J/other/PBeiO/32.87
- Title:
- Astrometric observations of radio stars
- Short Name:
- J/other/PBeiO/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the data observed in San Juan with the photoelectric Astrolabe Mark II of the Beijing Astronomical Observatory from February, 1992 through March, 1997, the radio stars catalogue in San Juan (RSSJ95) has been compiled. There are 69 radio stars in this catalogue. The Positions of the radio stars are for the epoch of observation and the equinox J2000.0 and a system close that of the system FK5. The mean precisions are +/-2.2ms and +/-0.035" in right ascensions and declinations, respectively. The magnitudes of stars are from 0.9 to 10.7. The declinations are from -2.5{deg} to -60{deg}. The mean epoch is 1995.1. Finally, the comparison results with Hipparcos catalogue and CAMC are given.
- ID:
- ivo://CDS.VizieR/J/A+A/572/A104
- Title:
- Astrometric obs. of Phobos and Deimos in 1971
- Short Name:
- J/A+A/572/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate positional measurements of planets and satellites are used to improve our knowledge of their dynamics and to infer the accuracy of planet and satellite ephemerides. In the framework of the FP7 ESPaCE project, we provide positions of Mars, Phobos and Deimos taken with the U.S. Naval Observatory 26-inch refractor during the 1971 opposition of the planet. These plates were measured with the digitizer of the Royal Observatory of Belgium and reduced through an optimal process that includes image, instrumental and spherical corrections to provide the most accurate data.
- ID:
- ivo://CDS.VizieR/J/A+A/556/A133
- Title:
- Astrometric orbit of DENIS-P J082303.1-49120
- Short Name:
- J/A+A/556/A133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Little is known about the existence of extrasolar planets around ultracool dwarfs. Furthermore, binary stars with Sun-like primaries and very low-mass binaries composed of ultracool dwarfs show differences in the distributions of mass ratio and orbital separation that can be indicative of distinct formation mechanisms. Using FORS2/VLT optical imaging for high precision astrometry we are searching for planets and substellar objects around ultracool dwarfs to investigate their multiplicity properties for very low companion masses. Here we report astrometric measurements with an accuracy of one tenth of a milli-arcsecond over two years that reveal orbital motion of the L1.5 dwarf DENIS-P J082303.1-491201 (having 7.5+/-1% of the Sun's mass) caused by a companion with a mass of 28+/-2 Jupiter masses that revolves about its host on an eccentric orbit in 246.4+/-1.4days. This new system is nearby at 20.77+/-0.08pc and has the smallest mass ratio (0.36+/-0.02) of known very low-mass binaries with a characterised orbit. With this discovery we demonstrate 100 micro-arcsecond astrometry over an arc-minute field and over several years that is sufficient to discover sub-Jupiter mass planets around ultracool dwarfs. We also show that the achieved parallax accuracy of <0.4% makes it possible to remove distance as a dominant source of uncertainty in the modelling of ultracool dwarfs.
