Author Topic: ESA - Gaia updates  (Read 54388 times)

Offline Star One

  • Senior Member
  • *****
  • Posts: 9579
  • UK
  • Liked: 1776
  • Likes Given: 183
Re: ESA - Gaia updates
« Reply #40 on: 08/26/2015 04:36 PM »
I can't wait to see the intermediary results. I am assuming the stray light problem is no longer an issue.

Offline denis

  • Full Member
  • *
  • Posts: 124
  • EU
  • Liked: 24
  • Likes Given: 9
Re: ESA - Gaia updates
« Reply #41 on: 08/28/2015 06:15 PM »
I can't wait to see the intermediary results. I am assuming the stray light problem is no longer an issue.

Neither can I!
The stray light problem is still there (there is nothing that can be done to remove it), but affects mostly the Radial Velocity Spectrometer and less so the astrometry and photometry measurements. For the RVS, they have tweaked a bit the on-board software to try to limit the impact, but they are going to measure less stars than anticipated.
For the main instrument (astrometry), it's probably not too bad as they are actually going down to magnitude 20.5 instead of 20, but possibly it's a bit noisier than expected (for some aspects, this could be compensated by a mission extension, assuming the spacecraft is fine after the nominal one).


Offline philw1776

  • Full Member
  • ****
  • Posts: 1080
  • Seacoast NH
  • Liked: 700
  • Likes Given: 305
Re: ESA - Gaia updates
« Reply #42 on: 08/28/2015 06:26 PM »
Anyone know if the summer 2016 release will have items such as the distance to the Hyades cluster & to standard candles like well known Cepheids so that metrics like the Hubble constant and stellar evolutionary models can be better calibrated?
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

Offline denis

  • Full Member
  • *
  • Posts: 124
  • EU
  • Liked: 24
  • Likes Given: 9
Re: ESA - Gaia updates
« Reply #43 on: 08/28/2015 06:37 PM »
Anyone know if the summer 2016 release will have items such as the distance to the Hyades cluster & to standard candles like well known Cepheids so that metrics like the Hubble constant and stellar evolutionary models can be better calibrated?

There is a Data release scenario on ESA's website:
http://www.cosmos.esa.int/web/gaia/release

Assuming this is still up-to-date, we'll have to wait for early2017 for distances:

Quote
First release: summer 2016   
 Potentially, the catalogue will be consisting of:

- Positions (α, δ) and G-magnitudes for all stars with acceptable formal standard errors of positions. For this release, it is assumed that at least 90% of the sky can be covered. The release is for all objects with single-star behavior.
...

Quote
Second release: early 2017   
Potentially, the catalogue will be consisting of:

- Five-parameter astrometric solutions of objects with single-star behavior will be released under the assumption that at least 90% of the sky can be covered.
...

Offline Star One

  • Senior Member
  • *****
  • Posts: 9579
  • UK
  • Liked: 1776
  • Likes Given: 183
Re: ESA - Gaia updates
« Reply #44 on: 08/28/2015 08:12 PM »
Thanks for that link. So no exo-planet list until 2022.

Offline denis

  • Full Member
  • *
  • Posts: 124
  • EU
  • Liked: 24
  • Likes Given: 9
Re: ESA - Gaia updates
« Reply #45 on: 08/28/2015 08:56 PM »
Thanks for that link. So no exo-planet list until 2022.

Maybe. It's all TBC. I guess it could change one way or another, depending on how the data processing goes (2022 is 3 years after end of nominal mission)

Offline Burninate

  • Full Member
  • ****
  • Posts: 1134
  • Liked: 351
  • Likes Given: 73
Re: ESA - Gaia updates
« Reply #46 on: 08/28/2015 11:53 PM »
Thanks for that link. So no exo-planet list until 2022.
Data releases will proceed year by year to build a better astrometric picture of the galaxy.  SNR will be very low to start with, it's only with successive observations that a better picture is built up.  Strong bias in this observation program towards nearer stars, larger planets, and longer periods.
http://arxiv.org/pdf/1411.1173v1.pdf
« Last Edit: 08/28/2015 11:53 PM by Burninate »

Offline bolun

  • Senior Member
  • *****
  • Posts: 2785
  • Europe
  • Liked: 231
  • Likes Given: 69
Re: ESA - Gaia updates
« Reply #47 on: 11/04/2015 05:04 PM »
Rosetta comet seen by Gaia

A Gaia image of Comet 67P/Churyumov–Gerasimenko, obtained on 14 September 2015.

At that time, the ESA Rosetta spacecraft was about 300 km from the nucleus of the comet, while Gaia was over 260 million kilometres away. The comet had reached the closest point to the Sun on its orbit about a month earlier, on 13 August.

The image shows the comet’s coma and tail. The nucleus and Rosetta, which was some 300 km from the surface at the time, are both hidden in the innermost pixel. A number of background stars are also sprinkled around the image, which measures about 4.5 arc minutes across – about one-seventh of the Moon’s diameter.

Related article: Celebrity comet spotted among Gaia's stars

http://www.esa.int/spaceinimages/Images/2015/11/Rosetta_comet_seen_by_Gaia

Image credit: ESA/Gaia/DPAC. Acknowledgement: F. Mignard & P. Tanga, Observatoire de la Côte d’Azur, France

Offline philw1776

  • Full Member
  • ****
  • Posts: 1080
  • Seacoast NH
  • Liked: 700
  • Likes Given: 305
Re: ESA - Gaia updates
« Reply #48 on: 01/11/2016 09:05 PM »
Any info on 1st catalog release date set in 2016?
Any informed speculation?
And finally what content would the 1st catalog contain?
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

Offline as58

  • Full Member
  • ****
  • Posts: 802
  • Liked: 276
  • Likes Given: 179
Re: ESA - Gaia updates
« Reply #49 on: 01/11/2016 09:45 PM »
Any info on 1st catalog release date set in 2016?
Any informed speculation?
And finally what content would the 1st catalog contain?

The link to the official data release scenario is http://www.cosmos.esa.int/web/gaia/release.  The scenario tells what to expect and when. I don't know anything more about the exact date for the first release and it may not have been even decided yet. There's a big European astronomy conference in early July, so maybe they're planning to release something there.

There has been a recent addition to the first release, according to the current plans it'll include the five-parameter astrometric solution (position, proper motion and parallax) for stars in the Hipparcos Tycho-2 catalogue (~2.5 million stars with m~<11.5)

Offline bolun

  • Senior Member
  • *****
  • Posts: 2785
  • Europe
  • Liked: 231
  • Likes Given: 69
Re: ESA - Gaia updates
« Reply #50 on: 06/29/2016 10:33 AM »

Offline as58

  • Full Member
  • ****
  • Posts: 802
  • Liked: 276
  • Likes Given: 179
Re: ESA - Gaia updates
« Reply #51 on: 07/04/2016 09:44 AM »
The first Gaia data release will be on the 14th of September.

http://sci.esa.int/gaia/58042-mark-your-calendar-gaia-data-release-set-for-14-september/
« Last Edit: 07/04/2016 09:45 AM by as58 »

Offline Star One

  • Senior Member
  • *****
  • Posts: 9579
  • UK
  • Liked: 1776
  • Likes Given: 183
ESA - Gaia updates
« Reply #52 on: 07/29/2016 07:04 PM »
Cross posting.

Can the Gaia mission find planet nine?

Quote
ESA’s Gaia satellite is scanning the entire sky, detecting objects as faint as 20.7 magnitudes, but Planet Nine is likely to be fainter. Even if Gaia did see it, it probably would not be immediately recognized as a Solar System object, as its apparent motion (about 0.2 arcsecs per hour) is also below the current threshold for the Gaia data processing to immediately recognize it as a moving solar system object, but large enough to cause the planet to appear as a new “star” at a different position of the sky during subsequent Gaia observations. 

But Gaia might not need to see Planet Nine to find it.

Like all massive objects, an otherwise invisible planet hiding in the outer reaches of the Solar System deforms the fabric of space-time around it, and the light from distant stars passing by the planet would be ever-so-slightly deflected.  Measuring this deflection as the hidden planet passes in front of distant stars could reveal its presence, even if the planet itself is too faint to be seen. (See the animation below.)  This temporary deflection is the less-well-known astrometric aspect of a phenomenon called microlensing, which also causes a temporary brightening of background sources (not shown in the animation).

Quote
Unfortunately it appears from their study that such a detection by Gaia is also unlikely. The expected deviation of a star’s direction for a 10 Earth mass planet at about 700 AU is incredibly tiny: about 3 milliarcsecs if the star is within 10 milliarcsecs of the planet’s position. (One milliarcsec is 1/1000 of an arcsecond, which is 1/3600 of a degree: That’s about the apparent height of Neil Armstrong standing on the Moon as seen from Earth.) Not only that, given the apparent motion of Planet Nine on the sky, such microlensing events would have a very short duration.  Essentially a star would have to be within about 10 milliarcsecs of Planet Nine at the moment that Gaia observes it.

Regardless of how Planet Nine is found (if it exists), measurements of microlensing events by the planet will likely be the only means to directly measure its mass, as any moons revolving around Planet Nine will be far too faint even for our most powerful telescopes.  And while such microlensing events might be observable with other telescopes, only Gaia will be able to provide an accurate enough map of the sky to be able to accurately foresee such microlensing events.

https://www.linkedin.com/pulse/gaia-points-planet-nine-ronald-drimmel
« Last Edit: 07/29/2016 07:06 PM by Star One »

Online hop

  • Senior Member
  • *****
  • Posts: 3322
  • Liked: 455
  • Likes Given: 809
Re: ESA - Gaia updates
« Reply #53 on: 08/02/2016 02:46 AM »
A status update on the various issues encountered after launch.
tl;dr seems to be they are being managed acceptably.

Gaia: focus, straylight and basic angle
Quote
The Gaia all-sky astrometric survey is challenged by several issues affecting the spacecraft stability. Amongst them, we find the focus evolution, straylight and basic angle variations
Contrary to pre-launch expectations, the image quality is continuously evolving, during commissioning and the nominal mission. Payload decontaminations and wavefront sensor assisted refocuses have been carried out to recover optimum performance. An ESA-Airbus DS working group analysed the straylight and basic angle issues and worked on a detailed root cause analysis. In parallel, the Gaia scientists have also analysed the data, most notably comparing the BAM signal to global astrometric solutions, with remarkable agreement.
In this contribution, a status review of these issues will be provided, with emphasis on the mitigation schemes and the lessons learned for future space missions where extreme stability is a key requirement.

Some indication of the sensitivity to subtle thermal effects:
Quote
The 24 hours period was later identified as an effect of the way the downlink is operated. Even though the phased array antenna is never switched-off, the signal coding scheme changed between ground station contacts (complex signal encoding only when downlink was active). This meant the transponders consumed more power during the contacts, which are typically scheduled according to a 24 hour logic. It was decided to force signal encoding without data transmission in the antenna outside contacts (except when spacecraft ranging is needed). This action reduced the impact of the 24 hours basic variation by more than half.
Quote
The correlation with the number of stars was puzzling at first glance, due to the negligible brightness of stellar sources. However, many service module components are affected by a bigger data rate, most notably the computers and the on-board data storage. A clear correlation thus exists between e.g. VPU5 and the peak basic angle variations, giving further support to the thermoelastic hypothesis.
« Last Edit: 08/02/2016 05:25 AM by hop »

Online redliox

  • Full Member
  • ****
  • Posts: 1927
  • Arizona USA
  • Liked: 372
  • Likes Given: 64
Re: ESA - Gaia updates
« Reply #54 on: 08/02/2016 05:18 AM »
Gaia isn't malfunctioning thermally is it?
"Let the trails lead where they may, I will follow."
-Tigatron

Online hop

  • Senior Member
  • *****
  • Posts: 3322
  • Liked: 455
  • Likes Given: 809
Re: ESA - Gaia updates
« Reply #55 on: 08/02/2016 05:40 AM »
Gaia isn't malfunctioning thermally is it?
The paper I quoted above provides some details of issues that were noticed in commissioning. The issues seem to be pretty well understood now, and AFIAK the impact on the final results is expected to be relatively minor.

Just another reminder that space is hard...

Offline as58

  • Full Member
  • ****
  • Posts: 802
  • Liked: 276
  • Likes Given: 179
Re: ESA - Gaia updates
« Reply #56 on: 08/02/2016 05:46 AM »
Gaia isn't malfunctioning thermally is it?

Gaia not malfunctioning, it's just that there are some very subtle effects (for instance due to higher heat output generated by on-board computers when scanning areas of high stellar density) that were not expected. Gaia is very sensitive to such variations, but they seem to have been able to mitigate them quite well.

Offline baldusi

  • Senior Member
  • *****
  • Posts: 7437
  • Buenos Aires, Argentina
  • Liked: 1445
  • Likes Given: 4499
Re: ESA - Gaia updates
« Reply #57 on: 08/03/2016 05:15 PM »
When the thermal variations due to excess or reduced processing affect your stability, you know you have a reaaaaaally extreme requirement. I'm amazed at this level of sensitivity.

Offline jebbo

  • Full Member
  • ****
  • Posts: 610
  • Cambridge, UK
  • Liked: 246
  • Likes Given: 238
Re: ESA - Gaia updates
« Reply #58 on: 08/17/2016 08:35 AM »
A new blog post on the current status and the unexpected problems they've had to overcome:

http://sci.esa.int/gaia/58135-gaia-s-second-anniversary-marked-by-successes-and-challenges/

--- Tony

Offline Nomadd

  • Senior Member
  • *****
  • Posts: 3226
  • Boca Chica, Texas
  • Liked: 5339
  • Likes Given: 333
Re: ESA - Gaia updates
« Reply #59 on: 08/17/2016 04:36 PM »
 The positions of faint stars seems to be the biggest issue. Stray light from the edge of the shield has cut accuracy almost in half. (Planned 300 microarcseconds to 500)
 Still a whole lot better than anything else.
« Last Edit: 08/17/2016 04:40 PM by Nomadd »

Tags: gaia