J/A+A/616/A37 Close encounters to the Sun in Gaia DR2 (Bailer-Jones+, 2018)
New stellar encounters discovered in the second Gaia data release.
Bailer-Jones C.A.L., Rybizki J., Andrae R., Fouesneau M.
<Astron. Astrophys. 616, A37 (2018)>
=2018A&A...616A..37B 2018A&A...616A..37B (SIMBAD/NED BibCode)
ADC_Keywords: Positional data; Solar system; Stars, nearby
Keywords: Oort cloud - methods: analytical - methods: statistical -
solar neighbourhood - surveys
Abstract:
Passing stars may play an important role in the evolution of our solar
system. We search for close stellar encounters to the Sun among all
7.2 million stars in Gaia DR2 that have six-dimensional phase space
data. We characterize encounters by integrating their orbits through a
Galactic potential and propagating the correlated uncertainties via a
Monte Carlo resampling. After filtering to remove spurious data, we
find 694 stars that have median (over uncertainties) closest encounter
distances within 5pc, all occurring within 15Myr from now. 26 of these
have at least a 50% chance of coming closer than 1pc (and 7 within
0.5pc), all but one of which are newly discovered here. We confirm
some and refute several other previously-identified encounters,
confirming suspicions about their data. The closest encounter in the
sample is Gl 710, which has a 95% probability of coming closer than
0.08pc (17000AU). Taking mass estimates obtained from Gaia astrometry
and multiband photometry for essentially all encounters, we find that
Gl 710 also has the largest impulse on the Oort cloud. Using a Galaxy
model, we compute the completeness of the Gaia DR2 encountering sample
as a function of perihelion time and distance. Only 15% of encounters
within 5pc occurring within ±5Myr of now have been identified,
mostly due to the lack of radial velocities for faint and/or cool
stars. Accounting for the incompleteness, we infer the present rate of
encounters within 1pc to be 19.7±2.2 per Myr, a quantity expected to
scale quadratically with the encounter distance out to at least
several pc. Spuriously large parallaxes in our sample from imperfect
filtering would tend to inflate both the number of encounters found
and this inferred rate. The magnitude of this effect is hard to
quantify.
Description:
The tables give the perihelion (closest approach) parameters of stars
in the Gaia-DR2 catalogue which are found by numerical integration
through a Galactic potential to approach within 10pc of the Sun. These
parameters are the time (relative to the Gaia measurement epoch),
heliocentric distance, and heliocentric speed of the star at
perihelion. Uncertainties in these have been calculated by a Monte
Carlo sampling of the data to give the posterior probability density
function (PDF) over the parameters. For each parameter, three summary
values of this PDF are reported: the median, the 5% lower bound, the
95% upper bound. The latter two give a 90% confidence interval. The
table also reports the measured parallax, proper motion, radial
velocity (plus uncertainties), and mass of the stars. A second table
reports additional data, in particular astrometric quality metrics,
from the Gaia-DR2 catalogue. Tables 2 and 3 in the article list the
first 31 lines of these data tables (stars with median perihelion
distances below 1pc). Stars with problematic data have not been
removed, so some encounters are not reliable.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 173 3379 Perihelion parameters for all objects with a
median perihelion distance below 10pc, in order
of increasing median perihelion distance
table3.dat 72 3379 Additional information on the objects in
table2.dat
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/A+A/575/A35 : Close star encounters (Bailer-Jones, 2015)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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2- 20 I19 --- ID Gaia source identifier (Source)
22- 30 F9.1 kyr tphmed Median perihelion time (tphmed)
32- 40 F9.1 kyr b_tph 5% bound on perihelion time distribution
(tphlo)
42- 50 F9.1 kyr B_tph 95% bound on perihelion time distribution
(tphup)
52- 60 F9.4 pc dphmed Median perihelion distance (dphmed)
62- 70 F9.4 pc b_dph 5% bound on perihelion distance distribution
(dphlo)
72- 80 F9.4 pc B_dph 95% bound on perihelion distance distribution
(dphup)
82- 89 F8.2 km/s vphmed Median perihelion speed (vphmed)
91- 98 F8.2 km/s b_vph 5% bound on perihelion speed distribution
(vphlo)
100-107 F8.2 km/s B_vph 95% bound on perihelion speed distribution
(vphup)
109-117 F9.3 mas plx Parallax (par)
119-127 F9.3 mas e_plx parallax uncertainty (1 sigma) (epar)
129-137 F9.3 mas/yr pm Total proper motion (pm)
139-147 F9.3 mas/yr e_pm Total proper motion uncertainty (1 sigma)
(epm)
149-156 F8.2 km/s RV Radial velocity (rv)
158-165 F8.2 km/s e_RV Radial velocity uncertainty (1 sigma) (erv)
167-173 F7.3 Msun Mass ? Mass (mass)
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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2- 20 I19 --- ID Gaia source identifier (Source)
22- 26 F5.2 mag Gmag G band magnitude (gmag)
28- 32 F5.2 mag BP-RP ? BP-RP colour (bprp)
34- 39 F6.2 --- u Astrometric unit weight error (u)
41- 43 I3 --- Nvis Number of visibility periods (nvis)
45- 52 F8.2 mas aen Astrometric excess noise (aen)
54- 61 F8.2 mas s_aen Astrometric excess noise sigma (aensig)
63- 64 I2 --- NRVS Number of RVS transits (nrvs)
66- 68 I3 deg GLON Galactic longitude (glon)
70- 72 I3 deg GLAT Galactic latitude (glat)
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Acknowledgements:
Coryn Bailer-Jones, calj(at)mpia.de
(End) Coryn Bailer-Jones [MPIA, Heidelberg], Patricia Vannier [CDS] 26-Jun-2018