Author Topic: ESA - Gaia updates  (Read 51665 times)

Offline Star One

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Re: ESA - Gaia updates
« Reply #160 on: 05/03/2018 07:53 PM »
Evidence for Unresolved Exoplanet-hosting Binaries in Gaia DR2

Quote
This note describes an effort to detect additional stellar sources in known transiting exoplanet (TEP) systems, which are unresolved or barely resolved in the Gaia Data Release 2 (DR2) catalog (Gaia Collaboration et al. 2016, 2018). The presence of multiple unresolved stars in photometric and spectroscopic observations of a transiting planetary system biases measurements of the planet's radius, mass, and atmospheric conditions (e.g., Buchhave et al. 2011; Evans et al. 2016; Southworth & Evans 2016). In addition to the effect on individual planetary systems, the presence of unresolved stars across the sample of known exoplanets biases our overall understanding of planetary systems, due to the systematic underestimation of both masses and radii (Ciardi et al. 2015).

http://iopscience.iop.org/article/10.3847/2515-5172/aac173/meta

Offline Star One

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Re: ESA - Gaia updates
« Reply #161 on: 05/07/2018 07:45 PM »
Gaia Reveals Evidence for Merged White Dwarfs

We use Gaia Data Release 2 to identify 13,928 white dwarfs within 100 pc of the Sun. The exquisite astrometry and photometry from Gaia reveals for the first time a bifurcation in the observed white dwarf sequence in both Gaia and the Sloan Digital Sky Survey passbands. The latter is easily explained by a helium atmosphere (DB) white dwarf fraction of 36%. However, the bifurcation in the Gaia passbands cannot be explained by DB white dwarfs. We simulate theoretical color-magnitude diagrams for single and binary white dwarfs using a population synthesis approach and demonstrate that the only way to explain the bifurcation in the Gaia data is through a significant contribution from single white dwarfs that formed through mergers. This is the first direct detection of such a population in the solar neighborhood.

https://arxiv.org/abs/1805.01227

Offline AegeanBlue

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Re: ESA - Gaia updates
« Reply #162 on: 05/10/2018 09:09 PM »
Spain's contribution to Gaia DPAC:

https://www.res.es/en/news/gaia-creates-richest-star-map-our-galaxy-participation-two-res-nodes

There is also a large number of discoveries coming out of GaiaDR2. A twitter search for the hashtag #GaiaDR2 reveals quite a number of papers out. New stellar streams, new open star clusters, error margins in the DR2 parallaxes and other stuff. The typical method seems to be run a script on DR2, pull out interesting stars, cross check with other catalogs or at best a couple of days of observations and then publish your findings.

Offline philw1776

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Re: ESA - Gaia updates
« Reply #163 on: 05/15/2018 04:45 PM »
Generic public article on early Gaia papers & results...
https://www.sciencenews.org/article/gaia-delivers-trove-data-revealing-secrets-milky-way

Couple of favorites interesting to me...

Improved radii for Kepler stars & exoplanets
https://arxiv.org/abs/1805.00231


Better Cepheid distances and problems with cosmic expansion rates
https://arxiv.org/abs/1804.10655

"Including the DR2 parallaxes with all prior distance ladder data raises the current tension between the late and early Universe route to the Hubble constant to 3.8 sigma (99.99 %)."
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

Offline Star One

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Re: ESA - Gaia updates
« Reply #164 on: 05/18/2018 03:42 PM »
ESA Euronews: Gaia’s revolution in astronomy


Offline AegeanBlue

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Re: ESA - Gaia updates
« Reply #165 on: 06/11/2018 06:55 PM »
The amount of research coming out of DR2 is just amazing. Last week there was a Gaia sprint in New York, and I found amazing just what they are trying to pull out of the data. The pitch slides are here:

https://docs.google.com/presentation/d/19_Un3VQrB9d7Ftczf9yNxoJkW6BDe-EtDbrjSR6mMHY/edit#slide=id.p

On Gaia news, as I read them on twitter, they are trying to pull out binaries misclassified as single stars out of the spectra based on their position on the H-R diagram. Also it seems that in DR2 galaxies were misclassified as variable stars because of the way Gaia scans: Galaxies are, for the most part, not spherical. Since Gaia sees the star in different angles, it passes a different cross section of the galaxy with a different brightness leading to the misclassification. As someone who measured classification error in land cover datasets for the first part of his dissertation, I feel empathy for the researchers.

Offline AegeanBlue

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Re: ESA - Gaia updates
« Reply #166 on: 06/23/2018 07:41 AM »
Another new Gaia discovery that popped up on twitter today: there is a gap in the HR main sequence stars. This seems to correspond to where dwarfs transition to partial to fully convective. The Gaia team members have weighed in on twitter and do not believe that this is a systematic error, rather a real effect.

arXiv paper: https://arxiv.org/abs/1806.07792

A Gap in the Lower Main Sequence Revealed by Gaia Data Release 2

Synopsis: We present the discovery of a gap near MG≈10 in the main sequence on the Hertzsprung-Russell Diagram (HRD) based on measurements presented in Gaia Data Release 2 (DR2). Using an observational form of the HRD with MG representing luminosity and GBP−GRP representing temperature, the gap presents a diagonal feature that dips toward lower luminosities at redder colors. The gap is seen in samples extracted from DR2 with various distances, and is not unique to the {\it Gaia} photometry --- it also appears when using near-IR photometry (J−Ks vs MKs). The gap is very narrow (∼0.05 mag) and is near the luminosity-temperature regime where M dwarf stars transition from partially to fully convective, i.e., near spectral type M3.0V. This gap provides a new feature in the H-R Diagram that hints at an underlying astrophysical cause and we propose that it is linked to the onset of full convection in M dwarfs.

Offline CuddlyRocket

Re: ESA - Gaia updates
« Reply #167 on: 06/24/2018 01:19 AM »
Another new Gaia discovery that popped up on twitter today: there is a gap in the HR main sequence stars.

So, who's this gap going to be named after? :)

Offline Ben the Space Brit

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Re: ESA - Gaia updates
« Reply #168 on: 06/24/2018 07:35 AM »
That's interesting. Might there be a 'threshold energy' required to jump into full convection that's lower than the linear energy increase just below M3?
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Offline jebbo

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Re: ESA - Gaia updates
« Reply #169 on: 06/25/2018 07:54 AM »
I think you have that the wrong way around: dwarfs *later* (smaller) than M3V are fully convective.

So it seems to imply an energy threshold for developing an outer radiative zone.

--- Tony

Offline AegeanBlue

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Re: ESA - Gaia updates
« Reply #170 on: 06/25/2018 09:36 PM »
Another new Gaia discovery that popped up on twitter today: there is a gap in the HR main sequence stars.

So, who's this gap going to be named after? :)

How about Van Ness gap? In downtown Fresno, the next street over from Fulton Street is Van Ness Street. And sure, Fulton is a person and Fresno is pretty obscure as a place, but that doesn't mean we should have fun :)

On a more serious note there was a Gaia workshop in Heidelberg last week, not to be confused with the one in Barcelona taking place this week, and the presentations are up at:
http://gaia.ari.uni-heidelberg.de/gaia-workshop-2018/programme.html

Most interestingly in the very first presentation by Biermann there is the last slide (attached)



Offline AegeanBlue

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Re: ESA - Gaia updates
« Reply #171 on: 07/03/2018 07:10 AM »
Speaking of gaps, this paper, based on Gaia and Kepler claims that there are gaps at 2 Earth radii (rocky planets), 4 Earth radii (water worlds) and 10 Earth radii (transition worlds to gas giants above 10)

https://arxiv.org/abs/1806.11234

Abstract:
<quote> Applying the survival function analysis to the planet radius distribution of the Kepler confirmed/candidate planets, we have identified two natural divisions of planet radius at 4 Earth radii and 10 Earth radii. These divisions place constraints on planet formation and interior structure model. The division at 4 Earth radii separates small exoplanets from large exoplanets above. When combined with the recently-discovered radius gap at 2 Earth radii, it supports the treatment of planets 2-4 Earth radii as a separate group, likely water worlds. For planets around solar-type FGK main-sequence stars, we argue that 2 Earth radii is the separation between water-poor and water-rich planets, and 4 Earth radii is the separation between gas-poor and gas-rich planets. We confirm that the slope of survival function in between 4 and 10 Earth radii to be shallower compared to either ends, indicating a relative paucity of planets in between 4-10 Earth radii, namely, the sub-Saturnian desert there. We name them transitional planets, as they form a bridge between the gas-poor small planets and gas giants. Accordingly, we propose the following classification scheme: (<2 Earth radii) rocky planets, (2-4 Earth radii) water worlds, (4-10 Earth radii) transitional planets, and (>10 Earth radii) gas giants.  </quote>

Offline AegeanBlue

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Re: ESA - Gaia updates
« Reply #172 on: 07/05/2018 07:40 AM »
Discovery of the day: the Milky Way collided early in its history with a galaxy dubbed "the Gaia Sausage" and this is visible in radial velocities:

https://www.simonsfoundation.org/2018/07/04/gaia-sausage-galaxy/

Now usually when scientists want to say something more elegantly than their mother tongue and obfuscate a colloquialism, they use ancient Greek. Ancient Greek for sausage is "άλλας", or allas to spell it in the Latin alphabet. Could it be that in the future this progenitor galaxy will be known as the Allas Galaxy rather than the Gaia sausage?

Tags: gaia