12 research outputs found
Radial velocities from the N2K Project: 6 new cold gas giant planets orbiting HD 55696, HD 98736, HD 148164, HD 203473, and HD 211810
The N2K planet search program was designed to exploit the planet-metallicity
correlation by searching for gas giant planets orbiting metal-rich stars. Here,
we present the radial velocity measurements for 378 N2K target stars that were
observed with the HIRES spectrograph at Keck Observatory between 2004 and 2017.
With this data set, we announce the discovery of six new gas giant exoplanets:
a double-planet system orbiting HD 148164 ( of 1.23 and 5.16 M) and single planet detections around HD 55696 ( = 3.87 M), HD 98736 ( = 2.33 M), HD 203473 ( = 7.8
M), and HD 211810 ( = 0.67 M). These gas
giant companions have orbital semi-major axes between 1.0 and 6.2 AU and
eccentricities ranging from 0.13 to 0.71. We also report evidence for three
gravitationally bound companions with between 20 to 30 M, placing them in the mass range of brown dwarfs, around HD 148284, HD
214823, and HD 217850, and four low mass stellar companions orbiting HD 3404,
HD 24505, HD 98630, and HD 103459. In addition, we present updated orbital
parameters for 42 previously announced planets. We also report a nondetection
of the putative companion HD 73256 b. Finally, we highlight the most promising
candidates for direct imaging and astrometric detection, and find that many hot
Jupiters from our sample could be detectable by state-of-the-art telescopes
such as Gaia.Comment: Accepted by the Astronomical Journal. 75 pages, 49 figure
Radial Velocities from the N2K Project: Six New Cold Gas Giant Planets Orbiting HD 55696, HD 98736, HD 148164, HD 203473, and HD 211810
The N2K planet search program was designed to exploit the planet-metallicity correlation by searching for gas giant planets orbiting metal-rich stars. Here, we present the radial velocity measurements for 378 N2K target stars that were observed with the HIRES spectrograph at Keck Observatory between 2004 and 2017. With this data set, we announce the discovery of six new gas giant exoplanets: a double-planet system orbiting HD 148164 (M sin i of 1.23 and 5.16 M_(JUP)) and single planet detections around HD 55696 (M sin i = 3.87 M_(JUP)), HD 98736 (M sin i = 2.33 M_(JUP)), HD 203473 ( M sin i = 7.8 M_(JUP)), and HD 211810 (M sin i = 0.67 M_(JUP)). These gas giant companions have orbital semimajor axes between 1.0 and 6.2 au and eccentricities ranging from 0.13 to 0.71. We also report evidence for three gravitationally bound companions with M sin i between 20 and 30 M_(JUP), placing them in the mass range of brown dwarfs, around HD 148284, HD 214823, and HD 217850, and four low-mass stellar companions orbiting HD 3404, HD 24505, HD 98630, and HD 103459. In addition, we present updated orbital parameters for 42 previously announced planets. We also report a nondetection of the putative companion HD 73256 b. Finally, we highlight the most promising candidates for direct imaging and astrometric detection, and we find that many hot Jupiters from our sample could be detectable by state-of-the-art telescopes such as Gaia
TOI 540 b: A Planet Smaller than Earth Orbiting a Nearby Rapidly Rotating Low-mass Star
We present the discovery of TOI 540 b, a hot planet slightly smaller than
Earth orbiting the low-mass star 2MASS J05051443-4756154. The planet has an
orbital period of days ( 170 ms) and a radius of , and is likely terrestrial based on the observed
mass-radius distribution of small exoplanets at similar insolations. The star
is 14.008 pc away and we estimate its mass and radius to be and , respectively. The
star is distinctive in its very short rotational period of hours and correspondingly small Rossby number of 0.007 as
well as its high X-ray-to-bolometric luminosity ratio of based on a serendipitous XMM-Newton detection during a slew operation.
This is consistent with the X-ray emission being observed at a maximum value of
as predicted for the most rapidly rotating M
dwarfs. TOI 540 b may be an alluring target to study atmospheric erosion due to
the strong stellar X-ray emission. It is also among the most accessible targets
for transmission and emission spectroscopy and eclipse photometry with JWST,
and may permit Doppler tomography with high-resolution spectroscopy during
transit. This discovery is based on precise photometric data from TESS and
ground-based follow-up observations by the MEarth team.Comment: 18 pages, 7 figures. Accepted for publication in The Astronomical
Journa
TESS Discovery of an ultra-short-period planet around the nearby M dwarf LHS 3844
Data from the newly-commissioned \textit{Transiting Exoplanet Survey
Satellite} (TESS) has revealed a "hot Earth" around LHS 3844, an M dwarf
located 15 pc away. The planet has a radius of and
orbits the star every 11 hours. Although the existence of an atmosphere around
such a strongly irradiated planet is questionable, the star is bright enough
(, ) for this possibility to be investigated with transit and
occultation spectroscopy. The star's brightness and the planet's short period
will also facilitate the measurement of the planet's mass through Doppler
spectroscopy.Comment: 10 pages, 4 figures. Submitted to ApJ Letters. This letter makes use
of the TESS Alert data, which is currently in a beta test phase, using data
from the pipelines at the TESS Science Office and at the TESS Science
Processing Operations Cente
A Super-Earth and Sub-Neptune Transiting the Late-type M Dwarf LP 791-18
Planets occur most frequently around cool dwarfs, but only a handful of specific examples are known to orbit the latest-type M stars. Using TESS photometry, we report the discovery of two planets transiting the low-mass star called LP 791-18 (identified by TESS as TOI 736). This star has spectral type M6V, effective temperature 2960 K, and radius 0.17 R o, making it the third-coolest star known to host planets. The two planets straddle the radius gap seen for smaller exoplanets; they include a 1.1R ⊕ planet on a 0.95 day orbit and a 2.3R ⊕ planet on a 5 day orbit. Because the host star is small the decrease in light during these planets' transits is fairly large (0.4% and 1.7%). This has allowed us to detect both planets' transits from ground-based photometry, refining their radii and orbital ephemerides. In the future, radial velocity observations and transmission spectroscopy can both probe these planets' bulk interior and atmospheric compositions, and additional photometric monitoring would be sensitive to even smaller transiting planets
TESS Discovery of an Ultra-short-period Planet around the Nearby M Dwarf LHS 3844
Data from the newly commissioned Transiting Exoplanet Survey Satellite has revealed a 'hot Earth' around LHS 3844, an M dwarf located 15 pc away. The planet has a radius of R ⊕ and orbits the star every 11 hr. Although the existence of an atmosphere around such a strongly irradiated planet is questionable, the star is bright enough (I = 11.9, K = 9.1) for this possibility to be investigated with transit and occultation spectroscopy. The star's brightness and the planet's short period will also facilitate the measurement of the planet's mass through Doppler spectroscopy
The Occurrence Rate of Terrestrial Planets Orbiting Nearby Mid-to-late M Dwarfs from TESS Sectors 1-42
We present an analysis of a volume-complete sample of 363 mid-to-late M
dwarfs within 15 pc of the Sun with masses between 0.1 and 0.3 M
observed by TESS within Observation Sectors 1 to 42. The median mass of the
stars in this sample is 0.17 M. We search the TESS 2-minute cadence
light curves for transiting planets with orbital periods below 7 days using a
modified Box-Least Squares (BLS) algorithm and recover all 6 known planets
within the sample as well as a likely planet candidate orbiting LHS 475 (TESS
Object of Interest 910.01). Each of these planets is consistent with a
terrestrial composition, with planet radii ranging from 0.91 R to 1.31
R. In addition, we perform a transit injection and recovery analysis
for each of the 363 stars to characterize the transit detection sensitivity as
a function of planet radius, insolation, and orbital period. We obtain a
cumulative occurrence rate of terrestrial planets per M
dwarf with radii above 0.5 R and orbital periods between 0.4-7 days.
We find that for comparable insolations, planets larger than 1.5 R
(sub-Neptunes and water worlds) are significantly less abundant around
mid-to-late M dwarfs compared to earlier-type stars, while the occurrence rate
of terrestrial planets is comparable to that of more massive M dwarfs. We
estimate that overall, terrestrials outnumber sub-Neptunes around mid-to-late M
dwarfs at a ratio of 14 to 1, in contrast to GK dwarfs where they are roughly
equinumerous. We place a upper limit of 0.07 planets larger than 1.5
R per mid-to-late M dwarf, within the orbital period range of 0.5-7
days. We find evidence for a downturn in occurrence rates for planet radii
below 0.9 R, suggesting that Earth-sized and larger terrestrials may
be more common around mid-to-late M dwarfs.Comment: 25 pages, 8 figures, 9 tables. Accepted for publication in the
Astronomical Journa
The Occurrence Rate of Terrestrial Planets Orbiting Nearby Mid-to-late M Dwarfs from TESS Sectors 1–42
We present an analysis of a volume-complete sample of 363 mid-to-late M dwarfs within 15 pc of the Sun with masses between 0.1 and 0.3 M _⊙ observed by TESS within sectors 1–42. The median stellar mass of the sample is 0.17 M _⊙ . We search the TESS light curves for transiting planets with orbital periods below 7 days and recover all six known planets within the sample, as well as a likely planet candidate orbiting LHS 475. Each of these planets is consistent with a terrestrial composition, with planet radii between 0.91 and 1.31 R _⊕ . We characterize the transit detection sensitivity for each star as a function of planet radius, insolation, and orbital period. We obtain a cumulative occurrence rate of terrestrial planets per star with radii above 0.5 R _⊕ and orbital periods between 0.4 and 7 days. We find that for comparable insolations, planets larger than 1.5 R _⊕ (sub-Neptunes) are significantly less abundant around mid-to-late M dwarfs compared to earlier-type stars, while the occurrence rate of terrestrial planets is comparable to that of more massive M dwarfs. We estimate that overall, terrestrials outnumber sub-Neptunes around mid-to-late M dwarfs by 14 to 1, in contrast to GK dwarfs, where they are roughly equinumerous. We place a 1 σ upper limit of 0.07 planets larger than 1.5 R _⊕ per star within the orbital period range of 0.5–7 days. We find evidence for a downturn in occurrence rates for planet radii below 0.9 R _⊕ , suggesting that Earth-sized and larger terrestrials may be more common around mid-to-late M dwarfs