Quote from: Star One on 09/15/2016 07:55 amAre systematic errors those errors introduced into the results by Gaia itself?No, the parallax error listed in the database doesn't include the systematic error. This is said clearly in, for instance, the main paper presenting the data release (near the beginning of section 3):QuoteThe typical uncertainty for the parallaxes is 0.3 mas, where it should be noted that a systematic component of 0.3 mas should be added (see Sect. 6).I've seen a number of people online criticise ESA for the failure to get across clearly matters such as this and that their public outreach leaves a lot to be desired.
Are systematic errors those errors introduced into the results by Gaia itself?
The typical uncertainty for the parallaxes is 0.3 mas, where it should be noted that a systematic component of 0.3 mas should be added (see Sect. 6).
I've seen a number of people online criticise ESA for the failure to get across clearly matters such as this and that their public outreach leaves a lot to be desired.
The recommendation is to consider the quoted uncertainties on the parallaxes as ±σϖ (random) ±0.3 mas (systematic). Furthermore, averaging parallaxes over small regions of the sky will not reduce the uncertainty on the mean below the 0.3 mas level.
Quote from: Star One on 09/15/2016 08:46 amI've seen a number of people online criticise ESA for the failure to get across clearly matters such as this and that their public outreach leaves a lot to be desired.I don't know about public outreach, but I don't know how they could've been more clear about the systematics. The data release page even has this sentence bolded:QuoteThe recommendation is to consider the quoted uncertainties on the parallaxes as ±σϖ (random) ±0.3 mas (systematic). Furthermore, averaging parallaxes over small regions of the sky will not reduce the uncertainty on the mean below the 0.3 mas level.It seems that a lot of people just rushed into looking at data without bothering to read any of the release notes.
Further article on Gaia.Interesting comment underneath that if it keeps going for ten years it could discover 70,000 gas giants alone.http://www.centauri-dreams.org/?p=36391
We provide a revised assessment of the number of exoplanets that should be discovered by Gaia astrometry, extending previous studies to a broader range of spectral types, distances, and magnitudes. Our assessment is based on a large representative sample of host stars from the TRILEGAL Galaxy population synthesis model, recent estimates of the exoplanet frequency distributions as a function of stellar type, and detailed simulation of the Gaia observations using the updated instrument performance and scanning law. We use two approaches to estimate detectable planetary systems: one based on the S/N of the astrometric signature per field crossing, easily reproducible and allowing comparisons with previous estimates, and a new and more robust metric based on orbit fitting to the simulated satellite data. With some plausible assumptions on planet occurrences, we find that some 21,000 (+/-6000) high-mass (1-15M_J) long-period planets should be discovered out to distances of ~500pc for the nominal 5-yr mission (including at least 1000-1500 around M dwarfs out to 100pc), rising to some 70,000 (+/-20,000) for a 10-yr mission. We indicate some of the expected features of this exoplanet population, amongst them ~25-50 intermediate-period (P~2-3yr) transiting systems.
Congratulations to the Gaia craft and team!Wondering if Gaia data can confirm if Proxima b transits its star as seen from our solar system's vantage point.Also wondering if exoplanets (large gas giants of course) will be found in the Magellanic Cloud dwarf galaxies as a result of this data. (Extragalactic exoplanets!)Edit: I looked up the distance to the LMC after reviewing the post above mine. LMC is 50 kilo parsecs away and the arXiv article says Gaia can discover planets up to 500 parsecs away (0.5 kilo parsecs). So the answer would appear to be "no" for question 2 (no extragalactic exoplanets from Gaia)And can this data be used to find ring systems or exomoons?
Congratulations to the Gaia craft and team!
And can this data be used to find ring systems or exomoons?
We test the parallaxes reported in the Gaia first data release using the sample of eclipsing binaries with accurate, empirical distances from Stassun & Torres (2016). We find a clear average offset of −0.25±0.05 mas in the sense of the Gaia parallaxes being too small (i.e., the distances too long). The documented Gaia systematic uncertainty is 0.3 mas, which the eclipsing binary sample corroborates. The offset does not depend strongly on obvious parameters such as color, brightness, or spatial position. However, with a statistical significance of 99.7%, nearer stars possibly exhibit larger offsets according to Δπ≈−0.16−0.02×π mas.
There is a search page, the use of which is presumably self-evident to professional astronomers etc, but which is far from clear to me, and possibly most laymen. There's no how-to-use guide available, for instance. Or at least I couldn't find one! Given BBC news showed some schoolchildren who found a supernova, it's presumably not that difficult to use once you know how. Was there some material given to teachers by ESA, or did this school just happen to have contact with somehow who's familiar with such database search engines? A local university outreach perhaps?
We infer distances and their asymmetric uncertainties for two million stars using the parallaxespublished in the Gaia DR1 (GDR1) catalogue....except to remind readers that inverting parallaxes to estimate distances is only appropriate in the absence ofnoise. As parallax measurements have uncertainties— and for many TGAS stars very large uncertainties—distance estimation should always be treated as an inference problem.
The Gaia team has applied a renormalization to their internally-derived parallax errors σint(π)σtgas(π)=[Aσint(π)]2+σ20−−−−−−−−−−−−−√; (A,σ0)=(1.4,0.20 mas)based on comparison to Hipparcos astrometry. We use a completely independent method based on the RR Lyrae K-band period-luminosity relation to derive a substantially different result, with smaller ultimate errors(A,σ0)=(1.1,0.12 mas) (this paper).We argue that our estimate is likely to be more accurate and therefore that the reported TGAS parallax errors should be reduced according to the prescription:σtrue(π)=(0.79σtgas(π))2−(0.10 mas)2−−−−−−−−−−−−−−−−−−−−−−−√.
Concerning distances, from reading various tweets it seems computing distance from parallax is a complex problem and simply taking the inverse of the parallax is good only if the parallax error is small (< 1% I saw somewhere). I assume this is why DPAC provides parallax measurements and not directly distance, such that various science groups can estimate distances based on different techniques.For example, one article concerning converting Gaia's DR1 parallaxes into distances:https://arxiv.org/pdf/1609.07369v1.pdfQuoteWe infer distances and their asymmetric uncertainties for two million stars using the parallaxespublished in the Gaia DR1 (GDR1) catalogue....except to remind readers that inverting parallaxes to estimate distances is only appropriate in the absence ofnoise. As parallax measurements have uncertainties— and for many TGAS stars very large uncertainties—distance estimation should always be treated as an inference problem.
The DPAC project office and ESA are working on the longer term data release schedule. The release planned at three years after the end of the nominal mission lifetime (called 'final release' below) will be maintained, while the number of releases between Gaia DR2 and the final release remains to be decided.