Abstract
Abstract
We present the discoveries of two giant plants orbiting the red-giant-branch star HD 112570 and the red-clump star HD 154391, based on the radial-velocity (RV) measurements from the Xinglong station and Okayama Astrophysical Observatory. Spectroscopic and asteroseismic analyses suggest that HD 112570 has a mass of 1.15 ± 0.12 M
☉, a radius of 9.85 ± 0.23 R
☉, a metallicity [Fe/H] of −0.46 ± 0.1, and
log
g
of 2.47 ± 0.1. With the joint analysis of RV and Hipparcos-Gaia astrometry, we obtain a dynamical mass of
M
p
=
3.42
−
0.84
+
1.4
M
Jup
, a period of
P
=
2615
−
77
+
85
days, and a moderate eccentricity of
e
=
0.20
−
0.14
+
0.16
for the Jovian planet HD 112570 b. For HD 154391, it has a mass of 2.07 ± 0.03 M
☉, a radius of 8.56 ± 0.05 R
☉, a metallicity [Fe/H] of 0.07 ± 0.1, and
log
g
of 2.86 ± 0.1. The super-Jupiter HD 154391 b has a mass of
M
p
=
9.1
−
1.9
+
2.8
M
Jup
, a period of
P
=
5163
−
57
+
60
days, and an eccentricity of
e
=
0.20
−
0.04
+
0.04
. We found that HD 154391 b has one of the longest orbital periods among those ever discovered orbiting evolved stars, which may provide a valuable case in our understanding of planetary formation at wider orbits. Moreover, while a mass gap at 4 M
Jup seems to be present in the population of giant stars, there appear to be no significant differences in the distribution of metallicity among giant planets with masses above or below this threshold. Finally, the origin of the abnormal accumulation near 2 au for planets around large evolved stars (R
⋆ > 21 R
☉), remains unclear.
Funder
MOST ∣ National Key Research and Development Program of China
MOST ∣ National Natural Science Foundation of China
MEXT ∣ Japan Society for the Promotion of Science
Publisher
American Astronomical Society
Subject
Space and Planetary Science,Astronomy and Astrophysics