J/A+A/609/A8 Close encounters to the Sun in Gaia DR1 (Bailer-Jones, 2018)
The completeness-corrected rate of stellar encounters with the Sun from the
first Gaia data release.
Bailer-Jones C.A.L.
<Astron. Astrophys. 609, A8 (2018)>
=2018A&A...609A...8B 2018A&A...609A...8B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, nearby ; Positional data ; Solar system
Keywords: Oort cloud - solar neighbourhood - stars: kinematics and dynamics -
surveys - methods: statistical - methods: analytical
Abstract:
I report on close encounters of stars to the Sun found in the first
Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I
integrate orbits in a Galactic potential to identify those stars which
pass within a few parsecs. Such encounters could influence the solar
system, for example through gravitational perturbations of the Oort
cloud. 16 stars are found to come within 2pc (although a few of
these have dubious data). This is fewer than were found in a similar
study based on Hipparcos data, even though the present study has many
more candidates. This is partly because I reject stars with large
radial velocity uncertainties (>10km/s), and partly because of
missing stars in GDR1 (especially at the bright end). The closest
encounter found is Gl 710, a K dwarf long-known to come close to the
Sun in about 1.3Myr. The Gaia astrometry predict a much closer
passage than pre-Gaia estimates, however: just 16000AU (90%
confidence interval: 10000-21000AU), which will bring this
star well within the Oort cloud. Using a simple model for the spatial,
velocity, and luminosity distributions of stars, together with an
approximation of the observational selection function, I model the
incompleteness of this Gaia-based search as a function of the time and
distance of closest approach. Applying this to a subset of the
observed encounters (excluding duplicates and stars with implausibly
large velocities), I estimate the rate of stellar encounters within
5pc averaged over the past and future 5Myr to be 545±59Myr-1.
Assuming a quadratic scaling of the rate within some encounter
distance (which my model predicts), this corresponds to 87±9Myr-1
within 2pc. A more accurate analysis and assessment will be possible
with future Gaia data releases.
Description:
The table gives the perihelion (closest approach) parameters of stars
in the Gaia-DR1 TGAS 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 probability that each star
approaches the Sun within 0.5, 1.0, and 2.0pc, as well as the
measured parallax, proper motion, and radial velocity (plus
uncertainties) of the stars.
Table 3 in the article lists the first 20 lines of this data table
(stars with median perihelion distances below 2pc). Some stars are
duplicated in this table, i.e. there are rows with the same ID, but
different data. Stars with problematic data have not been removed, so
some encounters are not reliable. Most IDs are Tycho, but in a few
cases they are Hipparcos.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
encount.dat 166 646 Perihelion parameters for all objects with a
median perihelion distance below 10pc, in order
of increasing median perihelion distance (table3)
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See also:
I/239 : The Hipparcos and Tycho Catalogues (ESA 1997)
I/259 : The Tycho-2 Catalogue (Hog+ 2000)
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
Byte-by-byte Description of file: encount.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- ID Tycho or Hipparcos identifier
14- 15 I2 --- Cat [1/10] Radial velocity catalogue identifier (1)
17- 25 F9.1 kyr tphmed Median perihelion time
27- 35 F9.1 kyr tphlo 5% bound on perihelion time distribution
37- 45 F9.1 kyr tphup 95% bound on perihelion time distribution
47- 53 F7.3 pc dphmed Median perihelion distance
55- 61 F7.3 pc dphlo 5% bound on perihelion distance distribution
63- 69 F7.3 pc dphup 95% bound on perihelion distance distribution
71- 78 F8.2 km/s vphmed Median perihelion speed
80- 87 F8.2 km/s vphlo 5% bound on perihelion speed distribution
89- 96 F8.2 km/s vphup 95% bound on perihelion speed distribution
98-100 I3 --- f0.5 Probability star approaches within 0.5pc
102-104 I3 --- f1.0 Probability star approaches within 1.0pc
106-108 I3 --- f2.0 Probability star approaches within 2.0pc
110-118 F9.3 mas plx Parallax
120-128 F9.3 mas e_plx Parallax uncertainty (1 sigma)
130-138 F9.3 mas/yr pm Proper motion
140-148 F9.3 mas/yr e_pm Proper motion uncertainty (1 sigma)
150-157 F8.2 km/s RV Radial velocity
159-166 F8.2 km/s e_RV Radial velocity uncertainty (1 sigma)
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Note (1): Catalogs as follows:
1 = RAVE-DR5, Kunder et al. (2017, Cat. III/279)
2 = GCS2001, Casagrande et al. (2011,Cat. J/A+A/530/A138)
3 = Pulkovo, Gontcharov, 2006, Cat. III/252
4 = Famey et al., 2005, Cat. J/A+A/430/165
5 = Duflot et al., 1995, Cat. III/190
6 = Barbier-Brossat & Figon, 2000, Cat. III/213
7 = Maladora et al., 2000, Cat. III/249
8 = Maldonado et al., 2010, Cat. J/A+A/521/A12
9 = Fehrenbach et al., 1997, Cat. J/A+AS/124/255
10 = APOGEE2, SDSS Collaboration (2016, in prep.)
11 = Gaia-ESO-DR2, https://www.gaia-eso.eu
12 = GALAH, Martell et al., 2010, Cat. J/MNRAS/465/3203
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Acknowledgements:
Coryn Bailer-Jones, calj(at)mpia.de
(End) Coryn Bailer-Jones [MPIA, Heidelberg], Patricia Vannier [CDS] 17-Aug-2017