40 research outputs found
Radial velocity planets de-aliased. A new, short period for Super-Earth 55 Cnc e
Radial velocity measurements of stellar reflex motion have revealed many
extrasolar planets, but gaps in the observations produce aliases, spurious
frequencies that are frequently confused with the planets' orbital frequencies.
In the case of Gl 581 d, the distinction between an alias and the true
frequency was the distinction between a frozen, dead planet and a planet
possibly hospitable to life (Udry et al. 2007; Mayor et al. 2009). To improve
the characterization of planetary systems, we describe how aliases originate
and present a new approach for distinguishing between orbital frequencies and
their aliases. Our approach harnesses features in the spectral window function
to compare the amplitude and phase of predicted aliases with peaks present in
the data. We apply it to confirm prior alias distinctions for the planets GJ
876 d and HD 75898 b. We find that the true periods of Gl 581 d and HD 73526
b/c remain ambiguous. We revise the periods of HD 156668 b and 55 Cnc e, which
were afflicted by daily aliases. For HD 156668 b, the correct period is 1.2699
days and minimum mass is (3.1 +/- 0.4) Earth masses. For 55 Cnc e, the correct
period is 0.7365 days -- the shortest of any known planet -- and minimum mass
is (8.3 +/- 0.3) Earth masses. This revision produces a significantly improved
5-planet Keplerian fit for 55 Cnc, and a self-consistent dynamical fit
describes the data just as well. As radial velocity techniques push to
ever-smaller planets, often found in systems of multiple planets,
distinguishing true periods from aliases will become increasingly important.Comment: Accepted by ApJ (in press); 19 pages, 22 figures. Fixed typos;
improved wording; added more extensive discussion of orbital eccentricity;
improved figure captions; additional reference
The architecture of the GJ876 planetary system. Masses and orbital coplanarity for planets b and c
We present a combined analysis of previously published high-precision radial
velocities and astrometry for the GJ876 planetary system using a
self-consistent model that accounts for the planet-planet interactions.
Assuming the three planets so far identified in the system are coplanar, we
find that including the astrometry in the analysis does not result in a
best-fit inclination significantly different than that found by Rivera and
collaborators from analyzing the radial velocities alone. In this unique case,
the planet-planet interactions are of such significance that the radial
velocity data set is more sensitive to the inclination of the system through
the dependence of the interactions on the true masses of the two gas giant
planets in the system (planets b and c). The astrometry does allow
determination of the absolute orbital inclination (i.e. distinguishing between
i and 180-i) and longitude of the ascending node for planet b, which allows us
to quantify the mutual inclination angle between its orbit and planet c's orbit
when combined with the dynamical considerations. We find that the planets have
a mutual inclination of 5.0 +3.9 -2.3 degrees. This result constitutes the
first determination of the degree of coplanarity in an exoplanetary system
around a normal star. That we find the two planets' orbits are nearly coplanar,
like the orbits of the Solar System planets, indicates that the planets likely
formed in a circumstellar disk, and that their subsequent dynamical evolution
into a 2:1 mean motion resonance only led to excitation of a small mutual
inclination. This investigation demonstrates how the degree of coplanarity for
other exoplanetary systems could also be established using data obtained from
existing facilities.Comment: 9 pages, accepted for publication in A&
Measurement of the Spin-Orbit Alignment in the Exoplanetary System HD 189733
We present spectroscopy of a transit of the exoplanet HD 189733b. By modeling
the Rossiter-McLaughlin effect (the anomalous Doppler shift due to the partial
eclipse of the rotating stellar surface), we find the angle between the sky
projections of the stellar spin axis and orbit normal to be lambda = -1.4 +/-
1.1 deg. This is the third case of a ``hot Jupiter'' for which lambda has been
measured. In all three cases lambda is small, ruling out random orientations
with 99.96% confidence, and suggesting that the inward migration of hot
Jupiters generally preserves spin-orbit alignment.Comment: ApJ Letters, in pres
The Kepler-10 planetary system revisited by HARPS-N: A hot rocky world and a solid Neptune-mass planet
Kepler-10b was the first rocky planet detected by the Kepler satellite and
con- firmed with radial velocity follow-up observations from Keck-HIRES. The
mass of the planet was measured with a precision of around 30%, which was
insufficient to constrain models of its internal structure and composition in
detail. In addition to Kepler-10b, a second planet transiting the same star
with a period of 45 days was sta- tistically validated, but the radial
velocities were only good enough to set an upper limit of 20 Mearth for the
mass of Kepler-10c. To improve the precision on the mass for planet b, the
HARPS-N Collaboration decided to observe Kepler-10 intensively with the HARPS-N
spectrograph on the Telescopio Nazionale Galileo on La Palma. In to- tal, 148
high-quality radial-velocity measurements were obtained over two observing
seasons. These new data allow us to improve the precision of the mass
determina- tion for Kepler-10b to 15%. With a mass of 3.33 +/- 0.49 Mearth and
an updated radius of 1.47 +0.03 -0.02 Rearth, Kepler-10b has a density of 5.8
+/- 0.8 g cm-3, very close to the value -0.02 predicted by models with the same
internal structure and composition as the Earth. We were also able to determine
a mass for the 45-day period planet Kepler-10c, with an even better precision
of 11%. With a mass of 17.2 +/- 1.9 Mearth and radius of 2.35 +0.09 -0.04
Rearth, -0.04 Kepler-10c has a density of 7.1 +/- 1.0 g cm-3. Kepler-10c
appears to be the first strong evidence of a class of more massive solid
planets with longer orbital periods.Comment: 44 pages, 8 figures, accepted for publication in Ap
The Solar Twin Planet Search. V. Close-in, low-mass planet candidates and evidence of planet accretion in the solar twin HIP 68468
[Methods]. We obtained high-precision radial velocities with HARPS on the ESO
3.6 m telescope and determined precise stellar elemental abundances (~0.01 dex)
using MIKE spectra on the Magellan 6.5m telescope. [Results]. Our data indicate
the presence of a planet with a minimum mass of 26 Earth masses around the
solar twin HIP 68468. The planet is a super-Neptune, but unlike the distant
Neptune in our solar system (30 AU), HIP 68468c is close-in, with a semi-major
axis of 0.66 AU, similar to that of Venus. The data also suggest the presence
of a super-Earth with a minimum mass of 2.9 Earth masses at 0.03 AU; if the
planet is confirmed, it will be the fifth least massive radial velocity planet
discovery to date and the first super-Earth around a solar twin. Both
isochrones (5.9 Gyr) and the abundance ratio [Y/Mg] (6.4 Gyr) indicate an age
of about 6 billion years. The star is enhanced in refractory elements when
compared to the Sun, and the refractory enrichment is even stronger after
corrections for Galactic chemical evolution. We determined a NLTE Li abundance
of 1.52 dex, which is four times higher than what would be expected for the age
of HIP 68468. The older age is also supported by the low log(R'HK) (-5.05) and
low jitter. Engulfment of a rocky planet of 6 Earth masses can explain the
enhancement in both lithium and the refractory elements. [Conclusions]. The
super-Neptune planet candidate is too massive for in situ formation, and
therefore its current location is most likely the result of planet migration
that could also have driven other planets towards its host star, enhancing thus
the abundance of lithium and refractory elements in HIP 68468. The intriguing
evidence of planet accretion warrants further observations to verify the
existence of the planets that are indicated by our data and to better constrain
the nature of the planetary system around this unique star.Comment: A&A, in pres
Trumpeting M Dwarfs with CONCH-SHELL: a Catalog of Nearby Cool Host-Stars for Habitable ExopLanets and Life
We present an all-sky catalog of 2970 nearby ( pc), bright
() M- or late K-type dwarf stars, 86% of which have been confirmed by
spectroscopy. This catalog will be useful for searches for Earth-size and
possibly Earth-like planets by future space-based transit missions and
ground-based infrared Doppler radial velocity surveys. Stars were selected from
the SUPERBLINK proper motion catalog according to absolute magnitudes, spectra,
or a combination of reduced proper motions and photometric colors. From our
spectra we determined gravity-sensitive indices, and identified and removed
0.2% of these as interloping hotter or evolved stars. Thirteen percent of the
stars exhibit H-alpha emission, an indication of stellar magnetic activity and
possible youth. The mean metallicity is [Fe/H] = -0.07 with a standard
deviation of 0.22 dex, similar to nearby solar-type stars. We determined
stellar effective temperatures by least-squares fitting of spectra to model
predictions calibrated by fits to stars with established bolometric
temperatures, and estimated radii, luminosities, and masses using empirical
relations. Six percent of stars with images from integral field spectra are
resolved doubles. We inferred the planet population around M dwarfs using
data and applied this to our catalog to predict detections by future
exoplanet surveys.Comment: Accepted to MNRAS 22 figures, 3 tables, 2 electronic tables.
Electronic tables are available as links on this pag
The Mass of Kepler-93b and The Composition of Terrestrial Planets
Kepler-93b is a 1.478 +/- 0.019 Earth radius planet with a 4.7 day period
around a bright (V=10.2), astroseismically-characterized host star with a mass
of 0.911+/-0.033 solar masses and a radius of 0.919+/-0.011 solar radii. Based
on 86 radial velocity observations obtained with the HARPS-N spectrograph on
the Telescopio Nazionale Galileo and 32 archival Keck/HIRES observations, we
present a precise mass estimate of 4.02+/-0.68 Earth masses. The corresponding
high density of 6.88+/-1.18 g/cc is consistent with a rocky composition of
primarily iron and magnesium silicate. We compare Kepler-93b to other dense
planets with well-constrained parameters and find that between 1-6 Earth
masses, all dense planets including the Earth and Venus are well-described by
the same fixed ratio of iron to magnesium silicate. There are as of yet no
examples of such planets with masses > 6 Earth masses: All known planets in
this mass regime have lower densities requiring significant fractions of
volatiles or H/He gas. We also constrain the mass and period of the outer
companion in the Kepler-93 system from the long-term radial velocity trend and
archival adaptive optics images. As the sample of dense planets with
well-constrained masses and radii continues to grow, we will be able to test
whether the fixed compositional model found for the seven dense planets
considered in this paper extends to the full population of 1-6 Earth mass
planets.Comment: 8 pages, 4 figures. Accepted for publication in Ap
The Kepler-10 Planetary System Revisited by HARPS-N: A Hot Rocky World and a Solid Neptune-Mass Planet
Kepler-10b was the first rocky planet detected by the Kepler satellite and
con- firmed with radial velocity follow-up observations from Keck-HIRES. The
mass of the planet was measured with a precision of around 30%, which was
insufficient to constrain models of its internal structure and composition in
detail. In addition to Kepler-10b, a second planet transiting the same star
with a period of 45 days was sta- tistically validated, but the radial
velocities were only good enough to set an upper limit of 20 Mearth for the
mass of Kepler-10c. To improve the precision on the mass for planet b, the
HARPS-N Collaboration decided to observe Kepler-10 intensively with the HARPS-N
spectrograph on the Telescopio Nazionale Galileo on La Palma. In to- tal, 148
high-quality radial-velocity measurements were obtained over two observing
seasons. These new data allow us to improve the precision of the mass
determina- tion for Kepler-10b to 15%. With a mass of 3.33 +/- 0.49 Mearth and
an updated radius of 1.47 +0.03 -0.02 Rearth, Kepler-10b has a density of 5.8
+/- 0.8 g cm-3, very close to the value -0.02 predicted by models with the same
internal structure and composition as the Earth. We were also able to determine
a mass for the 45-day period planet Kepler-10c, with an even better precision
of 11%. With a mass of 17.2 +/- 1.9 Mearth and radius of 2.35 +0.09 -0.04
Rearth, -0.04 Kepler-10c has a density of 7.1 +/- 1.0 g cm-3. Kepler-10c
appears to be the first strong evidence of a class of more massive solid
planets with longer orbital periods.Comment: 44 pages, 8 figures, accepted for publication in Ap
Three’s Company: An Additional Non-transiting Super-Earth in the Bright HD 3167 System, and Masses for All Three Planets
HD 3167 is a bright (V = 8.9), nearby K0 star observed by the NASA K2 mission (EPIC 220383386), hosting two small, short-period transiting planets. Here we present the results of a multi-site, multi-instrument radial velocity campaign to characterize the HD 3167 system. The masses of the transiting planets are 5.02±0.38 MEarth for HD 3167 b, a hot super-Earth with a likely rocky composition (ρb = 5.60+2.15-1.43g cm-3), and 9.80+1.30-1.24 MEarth for HD 3167 c, a warm sub-Neptune with a likely substantial volatile complement (ρc = 1.97+0.94-0.59 g cm-3). We explore the possibility of atmospheric composition analysis and determine that planet c is amenable to transmission spectroscopy measurements, and planet b is a potential thermal emission target. We detect a third, non-transiting planet, HD 3167 d, with a period of 8.509+/-0.045 d (between planets b and c) and a minimum mass of 6.90±0.71 MEarth. We are able to constrain the mutual inclination of planet d with planets b and c: we rule out mutual inclinations below 1.3 degrees as we do not observe transits of planet d. From 1.3-40 degrees, there are viewing geometries invoking special nodal configurations which result in planet d not transiting some fraction of the time. From 40-60 degrees, Kozai-Lidov oscillations increase the system's instability, but it can remain stable for up to 100Myr. Above 60 degrees, the system is unstable. HD 3167 promises to be a fruitful system for further study and a preview of the many exciting systems expected from the upcoming NASATESS mission.Publisher PDFPeer reviewe
Recommended from our members