OBSERVATIONAL CONSTRAINTS ON
PLANETS IN THE ALPHA CENTAURI STAR SYSTEM
L. L. Zhao and D. A. Fischer | Yale University, 52 Hillhouse Ave., New Haven, CT 06511
ABSTRACT:
Using observations of α Centauri A and B with CHIRON, α Centauri B with HARPS, and Proxima Centauri with HARPS and UVES, we
place constraints on the extent to which undetected planetary companions may still exist around these stars. Orbital periods of two days to
nearly three years are investigated. Existing observations are sufficient to rule out planets with masses down to at least 15 MEarth at short (<100
days) periods. While more massive planets are excluded, the parameter space remains wide open for the discovery of more potentially
habitable, Earth-like planets. As the projected separation of α Centauri A and B increases beginning in 2019, high-precision, radial velocity measurements may well detect analogs to our Earth around α Centauri A and B in addition to Proxima Centauri b.
DATA:
Data from CHIRON, HARPS, and UVES
were used in this analysis[1,2,3]. The binary
trend was fit to a low-or and subtracted.
SIMULATIONS:
SIGNIFICANCE:
We maintain the time of observations to
retain any periodicities that could have arisen
due to the observing cadence.
Using the residuals from fitting out the binary
trend, we introduce error to our simulated data.
We simulate radial velocity measurements for
planets with different masses and periods.
Masses ranged from 0.1 to 1000 Earth masses;
periods ranged from 2 to 1000 days.
Observations were vetted for particularly bad
scatter based on the nightly standard deviation.
They were then binned by night.
This simulated data with errors is run through
a periodogram to identify periodicities.
Simulated data is compared to periodograms
of pure white noise to establish the significance of the signal
RESULTS:
A p-value
of
less
than
0.01
is
set
as
sufficient
to
detect
planets.
Our
2
Data Set
WNDT K [m/s] σ [m/s] Num Obs (N) χ /DOF
analysis
that Earth-mass
at78all periods
Censhows
A - CHIRON
2.942
0.822 planets
6.085
35.438 may still
Cen B - CHIRON
3.240
0.991
7.298
78
38.574
existCen
undetected
around
the
α
Centauri
Stars.
B - HARPS
6.809
0.897
3.787
218
25.265
Proxima - HARPS/UVES
45.466
1.729
0.308
213
4.302
white
noise
−1/3 detectability
We fit the 28.4329
border
of
−1 detection to a −2/3
m s mP sin(i) mS + mP P
√
K=
(1)
N
T
ABLE
1:
Fits
to
W
N
DT
=
K
∗
2
threshold
(WNDT)
curve,
MJup
MSun
1 yr
1−e
σ
W N DT = K
Data Set
WNDT
N
σ
K [m/s]
(2)
σ [m/s]
Num Obs (N)
where
the semi-major
velocities, N
CenK
A is
- CHIRON
2.942 amplitude
0.149
0.2of the radial
78
B - CHIRON
3.240
0.164
0.2the error.
78
is theCen
number
of
observations
and
σ
is
Cen B - HARPS
6.809
0.206
0.2
218
−1
HARPS/UVES
Proxima -28.4329 m s
Earth’s
−2/3 −1/3
mS + mP 0.2
P 213
mP1.393
sin(i) 1.728
√
K=
MJup
MSun
1 yr
1 − e2
TABLE 2: Achievable K values with 20 cm/s errors
NK value of 0.1m s-1.
orbit around theWSun
gives
a
N DT = K
σ
Data Set
WNDT
K [m s-1 ]
σ [m s-1 ]
N
Cen A - CHIRON
Cen B - CHIRON
Cen B - HARPS
Proxima - HARPS/UVES
2.942
3.240
6.809
45.466
0.822
0.991
0.897
1.729
6.085
7.298
3.787
0.308
78
78
218
213
(1)
(2)
CITATIONS:
[1] Tokovinin, A. et al. (2013) PASP, 125, 1336. | [2] Dumusque, X. et al. (2012) Nature, 491, 207. |
[3] Anglada-Escudé, G. et al. (2016) Nature, 536, 437.