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1081. Astrometric Grid Giant Star Survey. I.
ID:
ivo://CDS.VizieR/J/AJ/131/1784
Title:
Astrometric Grid Giant Star Survey. I.
Short Name:
J/AJ/131/1784
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from a campaign of multiple-epoch echelle spectroscopy of relatively faint (V=9.5-13.5mag) red giants observed as potential astrometric grid stars for the Space Interferometry Mission (SIM PlanetQuest). Data are analyzed for 775 stars selected from the Grid Giant Star Survey, spanning a wide range of effective temperatures (Teff), gravities, and metallicities. The spectra are used to determine these stellar parameters and to monitor radial velocity (RV) variability at the 100m/s level.
1082. Astrometric Grid Giant Star Survey. III.
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.
1083. Astrometric Microlensing Events Predicted from Gaia DR2
ID:
ivo://org.gavo.dc/amlensing/q2/q
Title:
Astrometric Microlensing Events Predicted from Gaia DR2
Short Name:
am lensing 2
Date:
27 Dec 2024 08:31:01
Publisher:
The GAVO DC team
Description:
From the Gaia DR2 catalogue we predict astrometric microlensing events by foreground stars with high proper motion (µ_tot >150mas/yr) passing a background source in the next decades. Using Gaia DR2 photometry we determine an approximate mass of the lens, which we use to calculate the expected microlensing effects. This yields 3914 microlensing events by 2875 different lenses between 2010 and 2065 with expected shifts larger than 0.1 mas between the lensed and unlensed positions of the source. 513 of those are expected to happen between 2014.5 - 2026.5 and might be measured by Gaia. For 127 events we also expect a magnification between 1 mmag and 3 mag.
1084. Astrometric Microlensing Events Predicted from Gaia eDR3
ID:
ivo://org.gavo.dc/amlensing/q3/q
Title:
Astrometric Microlensing Events Predicted from Gaia eDR3
Short Name:
am lensing 2
Date:
27 Dec 2024 08:31:05
Publisher:
The GAVO DC team
Description:
From the Gaia eDR3 catalogue we predict astrometric microlensing events by foreground stars with high proper motion (μ > 100 mas/yr) passing a background source in the next decades. Using Gaia DR3 photometry we determine an approximate mass of the lens, which we use to calculate the expected microlensing effects. This yields 4842 microlensing events by 3791 different lenses between 2010 and 2066 with expected shifts larger than 0.1 mas between the lensed and unlensed positions of the source. The past events might be interested when analyzing the individual Gaia measurements). 685 of those are expected to happen within the next decade (2021-2031). For 140 events we also expect a magnification between 1 mmag and 0.6 mag.
1085. Astrometric monitoring of ultracool dwarf binaries
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.
1086. Astrometric observations of Deimos
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.
1087. Astrometric observations of Phobos
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.
1088. Astrometric observations of radio stars
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.
1089. Astrometric obs. of Phobos and Deimos in 1971
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.
1090. Astrometric orbits of SB9 stars
ID:
ivo://CDS.VizieR/J/A+A/442/365
Title:
Astrometric orbits of SB9 stars
Short Name:
J/A+A/442/365
Date:
21 Oct 2021
Publisher:
CDS
Description:
Hipparcos Intermediate Astrometric Data (IAD) have been used to derive astrometric orbital elements for spectroscopic binaries from the newly released Ninth Catalogue of Spectroscopic Binary Orbits (S_B^9^_). This endeavour is justified by the fact that (i) the astrometric orbital motion is often difficult to detect without the prior knowledge of the spectroscopic orbital elements, and (ii) such knowledge was not available at the time of the construction of the Hipparcos Catalogue for the spectroscopic binaries which were recently added to the S_B^9^_ catalogue. Among the 1374 binaries from S_B^9^_ which have an HIP entry (excluding binaries with visual companions, or DMSA/C in the Double and Multiple Stars Annex), 282 have detectable orbital astrometric motion (at the 5% significance level). Among those, only 70 have astrometric orbital elements that are reliably determined (according to specific statistical tests), and for the first time for 20 systems. This represents a 8.5% increase of the number of astrometric systems with known orbital elements (The Double and Multiple Systems Annex contains 235 of those DMSA/O systems).

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