<<Since the first successful parallax measurement by Friedrich Bessel in 1838, astronomers have been puzzled by Betelgeuse's apparent distance. Knowledge of the star's distance improves the accuracy of other stellar parameters, such as luminosity that, when combined with an angular diameter, can be used to calculate the physical radius and effective temperature; luminosity and isotopic abundances can also be used to estimate the stellar age and mass. In 1920, when the first interferometric studies were performed on the star's diameter, the assumed parallax was 0.0180 arcseconds. This equated to a distance of 56 parsecs (pc) or roughly 180 light-years (ly), producing not only an inaccurate radius for the star but every other stellar characteristic. Since then, there has been ongoing work to measure the distance of Betelgeuse, with proposed distances as high as 400 pc or about 1300 ly.
Before the publication of the Hipparcos Catalogue (1997), there were two conflicting parallax measurements for Betelgeuse. The first, in 1991, gave a parallax of π = 9.8 ± 4.7 mas, yielding a distance of roughly 102 pc or 330 ly. The second was the Hipparcos Input Catalogue (1993) with a trigonometric parallax of π = 5 ± 4 mas, a distance of 200 pc or 650 ly. Given this uncertainty, researchers were adopting a wide range of distance estimates, leading to significant variances in the calculation of the star's attributes.
The results from the Hipparcos mission were released in 1997. The measured parallax of Betelgeuse was π = 7.63 ± 1.64 mas, which equated to a distance of 131 pc or roughly 430 ly, and had a smaller reported error than previous measurements. However, later evaluation of the Hipparcos parallax measurements for variable stars like Betelgeuse found that the uncertainty of these measurements had been underestimated. In 2007, an improved figure of π = 6.55±0.83 was calculated, hence a much tighter error factor yielding a distance of roughly 152±20 pc or 520±73 ly.
In 2008, using the Very Large Array (VLA), produced a radio solution of π = 5.07±1.10 mas, equalling a distance of 197±45 pc or 643±146 ly. As the researcher, Harper, points out: "The revised Hipparcos parallax leads to a larger distance (152±20 pc) than the original; however, the astrometric solution still requires a significant cosmic noise of 2.4 mas. Given these results it is clear that the Hipparcos data still contain systematic errors of unknown origin." Although the radio data also have systematic errors, the Harper solution combines the datasets in the hope of mitigating such errors. The European Space Agency's current Gaia mission may not improve over the measurements of Betelgeuse by the earlier Hipparcos mission as Betelgeuse is brighter than the approximately V=6 saturation limit of the mission's instruments.>>
The new data release of the RAdial Velocity Experiment (RAVE) is the fifth spectroscopic release of a survey of stars in the southern celestial hemisphere. It contains radial velocities for 520 781 spectra of 457 588 unique stars that were observed over ten years. With these measurements RAVE complements the first data release of the Gaia survey published by the European Space Agency ESA last week by providing radial velocities and stellar parameters, like temperatures, gravities and metallicities of stars in our Milky Way.
The velocities and spatial distributions of stars define the galaxy we live in, allowing the characterisation of the formation of the Milky Way. Large spectroscopic surveys provide definitive measurements of fundamental structural and dynamical parameters for a statistical sample of galactic stars and have been very successful in advancing the understanding of our galaxy. RAVE started in 2003 and was the first survey designed to provide necessary stellar parameters to complement missions that focus on astrometric information like Gaia. ...
The four previous data releases have been the foundation for a number of studies, which have especially advanced our understanding of the disk of the Milky Way. The fifth RAVE data release includes not only the culminating RAVE observations taken in 2013, but also also earlier discarded observations recovered from previous years, resulting in an additional 30,000 RAVE spectra. ...
The Radial Velocity Experiment (RAVE): Fifth Data Release - Andrea Kunder et al
RAVE observed nearly half a million stars of our Galaxy. The Sun is located at the
centre of the coordinate system. Credit: AIP/K. Riebe, the RAVE Collaboration;
Milky Way image (background): R. Hurt (SSC); NASA/JPL-Caltech
How do the stars in our Milky Way move? For more than a decade [ur=https://www.rave-survey.org/l]RAVE[/url], one of the first and largest systematic spectroscopic surveys, studied the motion of Milky Way stars. The RAVE collaboration now published the results for over half a million observations in its 6th and final data release. RAVE succeeded in measuring the velocities, temperatures, compositions and distances for different types of stars. The unique database enables scientists to systematically disentangle the structure and evolution history of our Galaxy.
The RAdial Velocity Experiment RAVE is a spectroscopic survey of stars in the southern hemisphere. RAVE was designed to get a representative census of the movements and of the atmospheric properties of stars in the wider neighbourhood of the Sun. By means of spectroscopy, the light of a star is decomposed into its rainbow colours. By analysing the spectra, the radial velocity of a star – the movement of the stars in the direction of the observer's view, can be determined. Furthermore, stellar spectra also enable scientists to determine stellar parameters like temperatures, surface gravities, and composition. In order to trace the structure and shape of our galaxy, RAVE successfully measured 518,387 spectra for 451,783 Milky Way stars.
Astronomers are not only used to think in long time scales – their projects also are often many-year endeavours. RAVE observed the sky for almost every clear night between 2003 and 2013 at the 1.2-metre UK Schmidt telescope of the Anglo-Australian Observatory in Siding Spring, Australia. RAVE utilized a dedicated fibre-optical setup to simultaneously take spectra of up to 150 stars in a single observation. Only with this massive multiplexing such a large number of targets was achievable – the largest spectroscopic survey before RAVE featured only some 14000 targets. In this way the survey obtained a representative sample of the stars around our Sun that are located roughly in a volume 15000 light years across.
Over the past 15 years, an increasing number of stars and refined data products have been released. The final RAVE data release not only provides for the first time the spectra of all stars in the RAVE sample; the stars were also matched with stars from the DR2 catalogue of the satellite mission Gaia. Thanks to the exquisite distances and proper motions measured by Gaia, considerably improved stellar temperatures, surface gravities and the chemical composition of the stellar atmospheres could be derived. ...
The Sixth Data Release of the Radial Velocity Experiment (RAVE).
I. Survey Description, Spectra, and Radial Velocities ~ Matthias Steinmetz et al