We present the Extended Hipparcos Compilation (XHIP), a database of all stars in the New Reduction of the Hipparcos Catalog extensively cross-referenced with data from a broad survey of presently available sources. The resulting collection uniquely assigns 116 096 spectral classifications, 46 392 radial velocities, and 18 549 homogenized iron abundances [Fe/H] to Hipparcos stars. Stellar classifications from SIMBAD, indications of multiplicity from CCDM or WDS, stellar ages from the Geneva-Copenhagen Survey III, supplemental photometry from 2MASS and SIMBAD, and identifications of exoplanet host stars are also included. Parameters for solar encounters and Galactic orbits are calculated for a kinematically complete subset. Kinetic bias is found to be minimal. Our compilation is available through the Centre de Donn´ees astronomiques de Strasbourg as Catalog V/137A.
Context. An accurate estimate of the local standard of rest (LSR) is required to determine key parameters used in approximate galactic mass models and to understand Galactic structure and evolution. However, authors are often forced to base dynamical analyses on potentially unreliable figures because recent determinations of the LSR have failed to reach agreement, especially with regard to the direction, V, of Galactic rotation. Aims. To explain why the traditional method for calculating the LSR fails, and to find alternative means of calculating the LSR with realistic error margins. Methods. We assemble and investigate the kinematic properties of 20 574 stars within 300 pc, with complete and accurate kinematic data. The traditional method of calculating the LSR assumes a well-mixed distribution. In fact, the velocity distribution is highly structured, invalidating calculations based on mean motions and asymmetric drift. We find other indicators in the distribution which we believe give a better estimate of circular motion. Results. We find good agreement between results and give as our best estimate of the LSR (U 0 , V 0 , W 0 ) = (7.5 ± 1.0, 13.5 ± 0.3, 6.8 ± 0.1) kms -1 . We calculate the slope of the circular speed curve at the solar radius, finding -9.3 ±0.9 kms -1 kpc -1 .
We use recently updated globular cluster distances to estimate the distance to the Galactic Centre, finding 7.4 ± 0.2| stat ± 0.2| sys kpc from symmetry considerations, including a trough at the Galactic Centre and peaks denoting the position of the bar. We recalibrate the red clump magnitude from Hipparcos stars, finding a skew distribution and a significant difference between peak and mean magnitudes. We find an estimate from stars in the periphery of the bulge using 2MASS, R 0 = 7.5 ± 0.3 kpc, in agreement with the figure from the halo centroid. We resolve discrepancies in the literature between estimates from the red clump. Our results are consistent with those found by different methodologies after taking systematic errors into account.
Context: Because of our viewing point within the Galactic disc, it is extremely difficult to observe the spiral structure of the Milky Way. Aims: To clarify the structure of the Galaxy by re-examination of gas distributions and data from 2MASS; to determine stream memberships among local stars and to show the relationship between streaming motions and spiral structure. Methods: We extend the spiral pattern found from neutral gas towards the Galactic centre using data from 2MASS. We select a population of 23 075 local disc stars for which complete kinematic data is available. We plot eccentricity against the true anomaly for stellar orbits and identify streams as dense regions of the plot. We reconstruct the spiral pattern by replacing each star at a random position of the inward part of its orbit. Results: We find evidence in 2MASS of a bar of length 4.2 \pm 0.1 kpc at angle 30 \pm 10\degree. We extend spiral structure by more than a full turn toward the Galactic centre, and confirm that the Milky Way is a two-armed grand-design bisymmetric spiral with pitch angle 5.56 \pm 0.06\degree. Memberships of kinematic groups are assigned to 98% of local disc stars and it is seen that the large majority of local stars have orbits aligned with this spiral structure.Comment: Accepted by MNRAS. 11 pages, 19 figure
The Lutz-Kelker correction is intended to give an unbiased estimate for stellar parallaxes and magnitudes, but it is shown explicitly that it does not. This paradox results from the application of an argument about sample statistics to the treatment of individual stars, and involves the erroneous use of a frequency distribution in the manner of a probability density function considered as a Bayesian prior. It is shown that the Bayesian probability distribution for true parallax given the observed parallax of a selected star is independent of the distribution of other stars. Consequently the Lutz-Kelker correction should not be used for individual stars. This result has important implications for the RR Lyrae scale and for the interpretation of results from Gaia and Hipparcos. The Lutz-Kelker correction is a poor treatment of the Trumpler-Weaver bias which affects parallax limited samples. A true correction is calculated using numerical integration and confirmed by a Monte Carlo method.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.