[Toronto] Using a novel method and data from the Gaia space telescope, astronomers from the University of Toronto have estimated that the speed of the Sun as it orbits the centre of the Milky Way Galaxy is approximately 240 kilometres per second.In turn, they have used that result to calculate that the Sun is approximately 7.9 kiloparsecs from the Galaxy’s centre—or almost twenty-six thousand light-years.Using data from the Gaia space telescope and the RAdial Velocity Experiment (RAVE) survey, Jason Hunt and his colleagues determined the velocities of over 200,000 stars relative to the Sun. Hunt is a Dunlap Fellow at the Dunlap Institute for Astronomy & Astrophysics, University of Toronto.
Context. The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and parallax are calculated using Hipparcos and Tycho-2 positions in 1991.25 as prior information. Aims. We investigate the scientific potential and limitations of the TGAS component by means of the astrometric data for open clusters. Methods. Mean cluster parallax and proper motion values are derived taking into account the error correlations within the astrometric solutions for individual stars, an estimate of the internal velocity dispersion in the cluster, and, where relevant, the effects of the depth of the cluster along the line of sight. Internal consistency of the TGAS data is assessed. Results. Values given for standard uncertainties are still inaccurate and may lead to unrealistic unit-weight standard deviations of least squares solutions for cluster parameters. Reconstructed mean cluster parallax and proper motion values are generally in very good agreement with earlier Hipparcos-based determination, although the Gaia mean parallax for the Pleiades is a significant exception. We have no current explanation for that discrepancy. Most clusters are observed to extend to nearly 15 pc from the cluster centre, and it will be up to future Gaia releases to establish whether those potential cluster-member stars are still dynamically bound to the clusters. Conclusions. The Gaia DR1 provides the means to examine open clusters far beyond their more easily visible cores, and can provide membership assessments based on proper motions and parallaxes. A combined HR diagram shows the same features as observed before using the Hipparcos data, with clearly increased luminosities for older A and F dwarfs.
With the help of software that mimics a human brain, ESA's Gaia satellite spotted six stars zipping at high speed from the centre of our Galaxy to its outskirts. This could provide key information about some of the most obscure regions of the Milky Way.
@ESAGaia and #DPAC are happy to announce the release date and expected contents of #GaiaDR2: https://www.cosmos.esa.int/web/gaia/dr2
05 April 2018As astronomers worldwide are preparing to explore the second data release of ESA's Gaia satellite, the Data Processing and Analysing Consortium announced just how many sources will be included in the new catalogue, which will be made public on 25 April.[/quote{http://sci.esa.int/gaia/60146-how-many-stars-to-expect-in-gaia-s-second-data-release/
14,000 Solar system objects are expected in DR2. Could Gaia detect Oort cloud objects microlensing a background star? What kinds of Ss objects is it detecting, Main belt asteroids, or NEAs?
Quote from: TakeOff on 04/06/2018 05:20 am14,000 Solar system objects are expected in DR2. Could Gaia detect Oort cloud objects microlensing a background star? What kinds of Ss objects is it detecting, Main belt asteroids, or NEAs?It should be mostly main-belt asteroids, possibly NEOs, depending on how good the algorithms are that they're using to match observations of fast moving things (connecting the dots, if you will).But a quick check shows Gaia should go down to 20th magnitude (probably in uncluttered areas only), whereas Pluto's more than 100x brighter. So, direct detection of some big KBOs/TNOs should be possible. But Oort Cloud... I'd say unlikely, because the reflected brightness scales like 1/r^4 (inverse square both ways) so Pluto would be visible out to about 3x, maybe a little more, than its current distance. You'd need something a lot bigger to be seen in the Oort cloud. Microlensing would simply look to be a transient, I'd suppose.The observing arcs should be long enough to give half decent prelim orbits for bright TNOs, could be very interesting to see what this does to statistics for the TNO orbits from which Planet 9 has been hypothesized.
What about detecting Planet 9 itself?
Quote from: Star One on 04/06/2018 11:14 amWhat about detecting Planet 9 itself?That's the million dollar question! But I believe, from Brown's website, it could be 22nd mag or fainter (and 22nd magnitude is about 6 times fainter than Gaia's limit of 20th mag). And Gaia's completeness at 20th magnitude won't be as high *in* the Galactic plane as *out* of the plane. My gut says Gaia probably won't see Putative Planet 9 (<50% chance), though I'd be happy to be wrong. However, I think it's more likely Gaia will discover a good number of TNOs, and if gets a bunch of the really high semi major axis ones, those might be sufficient to make (or break) the statistical case for Planet 9. We'll know soon!