- ID:
- ivo://CDS.VizieR/J/AJ/151/160
- Title:
- 1103 parallaxes and proper motions from URAT
- Short Name:
- J/AJ/151/160
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 1103 trigonometric parallaxes and proper motions from the United States Naval Observatory Robotic Astrometric Telescope (URAT) observations taken at the Naval Observatory Flagstaff Station (NOFS) over a three-year period from 2012 April to 2015 June covering the entire sky north of about -10{deg} decl. We selected two samples: previously suspected nearby stars from known photometric distances and stars showing a large, significant parallax signature in URAT epoch data without any prior selection criteria. All systems presented in this paper have an observed parallax {>=}40mas with no previous published trigonometric parallax. The formal errors on these weighted parallax solutions are mostly between 4 and 10mas. This sample gives a significant (of the order of 50%) increase to the number of known systems having a trigonometric parallax to be within 25pc of the Sun (without applying Lutz-Kelker bias corrections). A few of these are found to be within 10pc. Many of these new nearby stars display a total proper motion of less than 200mas/yr. URAT parallax results have been verified against Hipparcos and Yale data for stars in common. The publication of all significant parallax observations from URAT data is in preparation for CDS.
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Search Results
- ID:
- ivo://CDS.VizieR/I/129
- Title:
- Parallaxes and Proper Motions near SGP
- Short Name:
- I/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The catalog contains 6125 stars brighter than B=17.5, V=17.0 in the south galactic cap. The data have been obtained using the UK Schmidt telescope between 1975 and 1981. The plates were measured on the GALAXY machine at RGO. External errors of the parallaxes range between -/+0.012 and -/+0.017 arcsec according to magnitude. Internal proper motion errors range from -/+0.006 and -/+0.008 arcsec. In addition to the positions, proper motions, and parallaxes, the photometric data include B and V.
- ID:
- ivo://CDS.VizieR/J/A+A/616/L15
- Title:
- Parallaxes and Proper Motions of OB stars
- Short Name:
- J/A+A/616/L15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Gaia mission has released the second data set (Gaia DR2), which contains parallaxes and proper motions for a large number of massive, young stars. We investigate the spiral structure in the solar neighborhood revealed by Gaia DR2 and compare it with that depicted by VLBI maser parallaxes. We examined three samples with different constraints on parallax uncertainty and distance errors and stellar spectral types: (1) all OB stars with parallax errors less than 10%; (2) only O-type stars with 0.1mas errors imposed and with parallax distance errors less than 0.2kpc; (3) only O-type stars with 0.05 mas errors imposed and with parallax distance errors less than 0.3kpc. In spite of the significant distance uncertainties for stars in DR2 beyond 1.4kpc,the spiral structure in the solar neighborhood demonstrated by Gaia agrees well with that illustrated by VLBI maser results. The O-type stars available from DR2 extend the spiral arm models determined from VLBI maser parallaxes into the fourth Galactic quadrant, and suggest the existence of a new spur between the Local and Sagittarius arms.
- ID:
- ivo://CDS.VizieR/J/ApJ/784/156
- Title:
- Parallaxes for 1507 nearby mid-to-late M dwarfs
- Short Name:
- J/ApJ/784/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The MEarth survey is a search for small rocky planets around the smallest, nearest stars to the Sun as identified by high proper motion with red colors. We augmented our planetary search time series with lower cadence astrometric imaging and obtained two million images of approximately 1800 stars suspected to be mid-to-late M dwarfs. We fit an astrometric model to MEarth's images for 1507 stars and obtained trigonometric distance measurements to each star with an average precision of 5mas. Our measurements, combined with the Two Micron All Sky Survey photometry, allowed us to obtain an absolute K_s_ magnitude for each star. In turn, this allows us to better estimate the stellar parameters than those obtained with photometric estimates alone and to better prioritize the targets chosen to monitor at high cadence for planetary transits. The MEarth sample is mostly complete out to a distance of 25pc for stars of type M5.5V and earlier, and mostly complete for later type stars out to 20pc. We find eight stars that are within 10pc of the Sun for which there did not exist a published trigonometric parallax distance estimate. We release with this work a catalog of the trigonometric parallax measurements for 1507 mid-to-late M dwarfs, as well as new estimates of their masses and radii.
- ID:
- ivo://CDS.VizieR/J/ApJ/783/130
- Title:
- Parallaxes of high mass star forming regions
- Short Name:
- J/ApJ/783/130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Over 100 trigonometric parallaxes and proper motions for masers associated with young, high-mass stars have been measured with the Bar and Spiral Structure Legacy Survey, a Very Long Baseline Array key science project, the European VLBI Network, and the Japanese VLBI Exploration of Radio Astrometry project. These measurements provide strong evidence for the existence of spiral arms in the Milky Way, accurately locating many arm segments and yielding spiral pitch angles ranging from about 7{deg} to 20{deg}. The widths of spiral arms increase with distance from the Galactic center. Fitting axially symmetric models of the Milky Way with the three-dimensional position and velocity information and conservative priors for the solar and average source peculiar motions, we estimate the distance to the Galactic center, R_0_, to be 8.34+/-0.16kpc, a circular rotation speed at the Sun, {Theta}_0_, to be 240+/-8km/s, and a rotation curve that is nearly flat (i.e., a slope of -0.2+/-0.4km/s/kpc) between Galactocentric radii of {approx}5 and 16kpc. Assuming a "universal" spiral galaxy form for the rotation curve, we estimate the thin disk scale length to be 2.44+/-0.16kpc. With this large data set, the parameters R_0_ and {Theta}_0_are no longer highly correlated and are relatively insensitive to different forms of the rotation curve. If one adopts a theoretically motivated prior that high-mass star forming regions are in nearly circular Galactic orbits, we estimate a global solar motion component in the direction of Galactic rotation, V_{sun}_=14.6+/-5.0km/s. While {Theta}_0_and V_{sun}_are significantly correlated, the sum of these parameters is well constrained, {Theta}_0_+V_{sun}_=255.2+/-5.1km/s, as is the angular speed of the Sun in its orbit about the Galactic center, ({Theta}_0_+V_{sun}_)/R_0_=30.57+/-0.43km/s/kpc. These parameters improve the accuracy of estimates of the accelerations of the Sun and the Hulse-Taylor binary pulsar in their Galactic orbits, significantly reducing the uncertainty in tests of gravitational radiation predicted by general relativity.
- ID:
- ivo://CDS.VizieR/J/ApJS/240/19
- Title:
- Parallaxes of late-T and Y dwarfs
- Short Name:
- J/ApJS/240/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present preliminary trigonometric parallaxes of 184 late-T and Y dwarfs using observations from Spitzer (143), the U.S. Naval Observatory (18), the New Technology Telescope (14), and the United Kingdom Infrared Telescope (9). To complete the 20pc census of >=T6 dwarfs, we combine these measurements with previously published trigonometric parallaxes for an additional 44 objects and spectrophotometric distance estimates for another 7. For these 235 objects, we estimate temperatures, sift into five 150K wide T_eff_ bins covering the range 300-1050K, determine the completeness limit for each, and compute space densities. To anchor the high-mass end of the brown dwarf mass spectrum, we compile a list of early- to mid-L dwarfs within 20pc. We run simulations using various functional forms of the mass function passed through two different sets of evolutionary code to compute predicted distributions in T_eff_. The best fit of these predictions to our L, T, and Y observations is a simple power-law model with {alpha}~0.6 (where dN/dM{propto}M^-{alpha}^), meaning that the slope of the field substellar mass function is in rough agreement with that found for brown dwarfs in nearby star-forming regions and young clusters. Furthermore, we find that published versions of the log-normal form do not predict the steady rise seen in the space densities from 1050 to 350K. We also find that the low-mass cutoff to formation, if one exists, is lower than ~5M_Jup_, which corroborates findings in young, nearby moving groups and implies that extremely low-mass objects have been forming over the lifetime of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/A+A/493/L27
- Title:
- Parallaxes of 10 ultracool subdwarfs
- Short Name:
- J/A+A/493/L27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We measure absolute trigonometric parallaxes and proper motions with respect to many background galaxies for a sample of ten ultracool subdwarfs. Observations were taken in the H-band with the OMEGA2000 camera on the 3.5 m-telescope at Calar Alto, Spain during a time period of 3.5-years. For the first time, the reduction of the astrometric measurements was carried out directly with respect to background galaxies. We obtained absolute parallaxes with mean errors ranging between 1 and 3mas.
- ID:
- ivo://CDS.VizieR/J/A+A/645/L8
- Title:
- Parallaxes & proper motions of OB stars from Gaia EDR3
- Short Name:
- J/A+A/645/L8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The astrometric satellite Gaia is expected to significantly increase our knowledge as to the properties of the MilkyWay. The Gaia Early Data Release 3 (Gaia EDR3) provides the most precise parallaxes for many OB stars, which can be used to delineate the Galactic spiral structure. We investigate the local spiral structure with the largest sample of spectroscopically confirmed young OB stars available to date, and we compare it with what was traced by the parallax measurements of masers. A sample consisting of three different groups of massive young stars, including O-B2 stars, O-B0 stars and O-type stars with parallax accuracies better than 10% was compiled and used in our analysis. The local spiral structures in all four Galactic quadrants within ~5kpc of the Sun are clearly delineated in detail. The revealed Galactic spiral pattern outlines a clear sketch of nearby spiral arms, especially in the third and fourth quadrants where the maser parallax data are still absent. These O-type stars densify and extend the spiral structure constructed by using the Very Long Baseline Interferometry (VLBI) maser data alone. The clumped distribution of O-type stars also indicates that the Galaxy spiral structure is inhomogeneous.
- ID:
- ivo://CDS.VizieR/J/A+A/654/A20
- Title:
- Parallax zero-point offset from Gaia EDR3 data
- Short Name:
- J/A+A/654/A20
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The second data release of Gaia revealed a parallax zero-point offset of -0.029mas based on quasars. The value depended on the position on the sky, and also likely on magnitude and colour. The offset and its dependence on other parameters inhibited improvement in the local distance scale using for example the Cepheid and RR Lyrae period-luminosity relations. Analysis of the recent Gaia Early Data Release 3 (EDR3) reveals a mean parallax zero-point offset of -0.021 mas based on quasars. The Gaia team addresses the parallax zero-point offset in detail and proposes a recipe to correct for it based on ecliptic latitude, G-band magnitude, and colour information. This paper presents a completely independent investigation into this issue focusing on the spatial dependence of the correction based on quasars and the magnitude dependence based on wide binaries. The spatial and magnitude corrections are connected to each other in the overlap region in the range 17<G<19. The spatial correction is presented at several spatial resolutions based on the HEALPix formalism. The colour dependence of the parallax offset is unclear and in any case secondary to the spatial and magnitude dependence. The spatial and magnitude corrections are applied to two samples of brighter sources, namely a sample of approximately 100 stars with independent trigonometric parallax measurements from Hubble Space Telescope data, and a sample of 75 classical cepheids using photometric parallaxes. The mean offset between the observed GEDR3 parallax and the independent trigonometric parallax (excluding outliers) is about -39{mu}as, and after applying the correction it is consistent with being zero. For the classical cepheid sample the analysis presented here suggests that the photometric parallaxes may be underestimated by about 5%.
- ID:
- ivo://CDS.VizieR/J/AJ/159/174
- Title:
- Parameters & abundances for Hyades/Field G-K dwarfs
- Short Name:
- J/AJ/159/174
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has been suggested that Fe abundances of K dwarfs derived from FeI and FeII lines show considerable discrepancies, and oxygen abundances determined from high-excitation OI-7771-5 triplet lines are appreciably overestimated (the problem becoming more serious toward lower Teff), which, however, has not yet been widely confirmed. With the aim of clarifying this issue, we spectroscopically determined the atmospheric parameters of 148 G-K dwarfs (Hyades cluster stars and field stars) by assuming the classical FeI/FeII ionization equilibrium as usual, and determined their oxygen abundances by applying the non-local thermal equilibrium spectrum fitting analysis to OI-7771-5 lines. It turned out that the resulting parameters did not show any significant inconsistency with those determined by other methods (for example, the mean differences in Teff and logg from the well-determined solutions of Hyades dwarfs are mostly <~100K and <~0.1dex). Likewise, the oxygen abundances of Hyades stars are around [O/H]~+0.2dex (consistent with the metallicity of this cluster) without exhibiting any systematic Teff-dependence. Accordingly, we conclude that parameters can be spectroscopically evaluated to a sufficient precision in the conventional manner (based on the Saha-Boltzmann equation for FeI/FeII) and oxygen abundances can be reliably determined from the OI-7771-5 triplet for K dwarfs as far as stars of Teff>~4500K are concerned. We suspect that previously reported strongly Teff-dependent discrepancies may have stemmed mainly from overestimation of weak-line strengths and/or improper Teff scale.
