# Tag Info

## Hot answers tagged gaia

66

Well, you thought about the spatial aspect of a parallax measurement, but not about the temporal one. Gaia's intention is to measure 3D positions as well as 3D velocities. For the distance, you need accurate parallactic measurement, which come in with your orbital period. For a typical Gaia-star with several measurement per year, you'll get 5 values of the ...

52

I think it is to do with (a) orbital speed and (b) telemetry and (c) power. In order to measure Parallax you need to measure the position of the star from different locations in the solar system. The Parallax becomes more precise the greater the separation between those positions. At Earth-Sun L2 you get a difference of about 2 au in 6 months. i.e. the ...

21

The panels need to be about 2.3 times bigger to generate the same power. The telemetry requirements are limited by distance to some power, assuming that the communications beam cannot be infinitely narrow. Mars is much further away than the L2 point - somewhere between a factor of 50 and 250. It wouldn't necessarily make it possible to measure parallaxes ...

11

The Ca triplet in the near infrared are extremely strong resonance absorption lines. They are by far the strongest features in the near infrared spectra of cool G,K,M type dwarfs and giants, which will be the majority of the stars observed by the Gaia RVS. The Ca triplet lines are so strong that even in low metallicity halo stars, that have little Ca in ...

7

The ESA states it pretty clearly (although their figure of 855.2 nm is incorrect; it should be 866.2 nm): The RVS wavelength range, 847-874 nm, has been selected to coincide with the energy-distribution peaks of G- and K-type stars which are the most abundant RVS targets. For these late-type stars, the RVS wavelength interval displays, besides numerous ...

7

Did you read this section of the documentation? It suggests there are ways to deal with it, but I have not examined the paper it refers to. • For closely aligned sources (separated by 0.2–0.3 arcsec), which are only occasionally resolved in the Gaia observations, confusion in the observation-to-source matching can lead to spurious parallax values which ...

6

Gaia data release 1 was announced in September 2016. It has parallaxes for 2 million stars previously observed by the Hipparcos mission, a small fraction of the 1.1 billion positions recorded so far. Future releases will of course have more data and smaller errors. Gaia has ~600 light curves for Cepheids but probably not parallaxes for most of those. ...

6

According to Cropper and Katz 2011 part 2.2, the RVS working group considered other bands, but the ~850 nm band is relatively unaffected by absorption in the Earth's atmosphere, facilitating ground-based preparation and follow-up. In addition to the strong Ca II triplet, this band is rich in lines enabling study of astrophysical quantities other than radial ...

5

Am I naive to think that it is necessary to build up a nice, complete light curve with dense points in time in order to use the photometry for precision distance calculations? No, the more I read about it, the more difficult it seems to be. In principle, if you sample regularly and often, you should eventually get a light curve, unless the period is the ...

5

My query for stars north of +75° and brighter than magnitude 4 returns only 6 stars, brightest of which is γ Cephei. Polaris may be too bright for Gaia. Even if it doesn't saturate the detector, a bright star will probably have larger astrometric errors than a star between magnitudes 6 and 12. DR2 coverage of magnitude 5 and brighter stars is better than DR1 ...

5

3 problems. 1) Time. As previous answers say, to make use of the larger diameter around the sun at Neptune's L2 point, you need to wait for a full rotation which takes 168+ years. 2) Energy. Solar panels provide significantly less energy, potentially not enough. 3) Distance. Data from a probe around Neptune take a good 4h10min to earth on average, which ...

4

One could certainly send a Gaia-like spacecraft into deep space, and take parallax measures at all times along its orbit. This is unattractive for several reasons, however. In short the large baseline may get you only a factor of 10 accuracy at the cost of several expensive modifications. The money would be better spent making a more powerful telescope ...

4

Parallax and proper motion are determined from a series of position measurements taken over the course of (for Gaia DR2) 22 months. A "5-parameter" astrometric model is fitted to these position measurements, consisting of a sky position at some epoch, a parallax and a proper motion in each of the celestial coordinates. The precisions of each of these ...

4

I ended up making my own small code that you can find here: https://github.com/crhea93/AstronomyTools/blob/master/Astrometry/Correction.py Essentially, after inputting at least 3 matching target (found by eye in DS9 for example), the program will calculate the mean offset and apply it to the target image. The output is a new fits file of the target ...

4

I will throw out a suggestion that could hardly be considered an "answer", but it would be interesting if someone could put flesh on the bones of it. When I first read your question I thought you were asking whether gravitational perturbations from an unseen neutron star would cause a measurable effect on the positions of other stars. I think the answer to ...

4

These are spurious data points. They are likely genuine objects, but the parallax value is incorrect. There are a small number of these in the Gaia data set. There are 59 object with a parallax greater than Proxima Centuri. These don't represent genuine objects, instead they are when two sources are closely aligned (within about 0.2 arcsec). Most of these ...

4

There are 61,234 data files in the directory. There are three additional (non-data) files: MD5SUM.txt _citation.txt _disclaimer.txt If you include those, the total number is 61,237.

4

Although should not use the negative parallaxes, you should not ignore them either. If you are looking at populations of objects, removing those with negative parallaxes will lead to significant bias in your results, as Luri et al. 2018 has shown.

4

You can calculate the absolute magnitude of a star: $$M=m-5\log_{10}(\frac{d}{10\,\text{pc}})$$ where $M$ is absolute magnitude, $m$ is apparent magnitude and $d$ is the distance. Then you take a look at the HR diagram. One can easily see, that you need two data to obtain the third one, but we have only one data (absolute magnitude). That means, that you ...

3

It depends how negative the parallax is and what your "prior" knowledge is of the distance to the star is. As another answer suggests, there are some spurious large negative (and positive) parallaxes for faint, crowded sources. If possible, these should be removed. If this is not the case, and the parallax is negative, but close to zero within its ...

3

Casertano et al. used the period-luminosity (P-L) relation of Cepheid variables as a sanity check on Gaia DR1 parallaxes. They chose Cepheid variables within the Milky Way having parallaxes in TGAS (Tycho-Gaia astrometric solution, reusing Hipparcos data for a head start). The period and apparent magnitude come from ground-based photometry (van Leeuwen et al....

3

Two techniques immediately spring to mind. For the stars you detect, you can compare their colours and luminosities (Gaia provides photometric colours and distances) with what you expect for a star of that type at that distance. The difference between what you expect and what you observe tells you the reddening and extinction caused by interstellar dust, ...

3

The early 1990s Hipparcos mission yielded parallaxes for 118000 stars (Hipparcos catalog) and positions without parallax for another 2.4 million (Tycho-2 catalog). The Tycho-Gaia astrometric solution (TGAS) combines those data with preliminary Gaia observations to get 2 million parallaxes, "only" 17 times as many as Hipparcos, with better precision. If this ...

3

You can query TIC by Gaia ID. Using the MAST Portal, MAST Catalogs, TESS Input v7, Advanced Search form, I specified: GAIA ID: 4052922352453886976 and got a single result: TIC ID (ID): 50559830 RA (ra): 275.945292 (18:23:46.870) Dec (dec): -25.672353 (-25:40:20.47) TESS Mag. (Tmag): 13.579 Version (version): ...

3

But you demonstrate that you know the answer to this question! Fainter objects have larger magnitudes. So as the white dwarf becomes cooler and redder, its blue magnitude $(G_{BP})$ grows by more than its red magnitude $(G_{RP})$ and the colour-index $(G_{BP} - G_{RP})$ becomes larger. This is very similar to the commonly used $B-V$ colour, which is larger ...

3

Negative parallaxes can be interpreted as the observer (in this case Gaia satellite) going the "wrong way around the sun" as mentioned in this Jupyter Notebook by Anthony Brown. This notebook is meant to supplement the Luri+ 2018 paper that has been mentioned in other answers and comments here.

3

LORRI will be used in 4x4 mode, which yields 4-arcsec pixels. The error in positions is unlikely to be better than 1%, or 40 mas, about 200x larger than Gaia's error. NH has a baseline ~20x larger, but this means it still misses Gaia by ~10x. The date was selected for New Moon to help Earth observers find the two targets. There is no Earth analogue for ...

3

That is because what is measured is a flux and the flux errors are in the DR2 catalogue. Since magnitudes are based on the logarithm of the flux, then there is no straightforward correspondence (although it matters little if the error bars are less than a few hundredths if a magnitude). Simple error propagation formulae give |\Delta G| \simeq \frac{2.5}{\...

3

For Gaia EDR3： Note (G1): Note on magnitude errors: They are obtained with a simple propagation of errors with the formulas e_Gmag = sqrt((-2.5/ln(10)*e_FG/FG)**2 + sigmaG_0**2) e_GBPmag = sqrt((-2.5/ln(10)*e_FGBP/FGBP)**2 + sigmaGBP_0**2)) e_GRPmag = sqrt((-2.5/ln(10)*e_FGRP/FGRP)**2 + sigmaGRP_0**2)) with the G, G_BP, G_RP zero point uncertainties ...

Only top voted, non community-wiki answers of a minimum length are eligible