126 research outputs found
The Lick-Carnegie Exoplanet Survey: A Saturn-Mass Planet in the Habitable Zone of the Nearby M4V Star HIP 57050
Precision radial velocities from Keck/HIRES reveal a Saturn-mass planet
orbiting the nearby M4V star HIP 57050. The planet has a minimum mass of 0.3
Jupiter-mass, an orbital period of 41.4 days, and an orbital eccentricity of
0.31. V-band photometry reveals a clear stellar rotation signature of the host
star with a period of 98 days, well separated from the period of the radial
velocity variations and reinforcing a Keplerian origin for the observed
velocity variations. The orbital period of this planet corresponds to an orbit
in the habitable zone of HIP 57050, with an expected planetary temperature of
approximately 230 K. The star has a metallicity of [Fe/H] = 0.32+/-0.06 dex, of
order twice solar and among the highest metallicity stars in the immediate
solar neighborhood. This newly discovered planet provides further support that
the well-known planet-metallicity correlation for F, G, and K stars also
extends down into the M-dwarf regime. The a priori geometric probability for
transits of this planet is only about 1%. However, the expected eclipse depth
is ~7%, considerably larger than that yet observed for any transiting planet.
Though long on the odds, such a transit is worth pursuing as it would allow for
high quality studies of the atmosphere via transmission spectroscopy with HST.
At the expected planetary effective temperature, the atmosphere may contain
water clouds.Comment: 20 pages, 5 figures, 3 tables, to appear in the May 20 issue of ApJ
The Lick-Carnegie Survey: A New Two-Planet System Around the Star HD 207832
Keck/HIRES precision radial velocities of HD 207832 indicate the presence of
two Jovian-type planetary companions in Keplerian orbits around this G star.
The planets have minimum masses of 0.56 and 0.73 Jupiter-masses with orbital
periods of ~162 and ~1156 days, and eccentricities of 0.13 and 0.27,
respectively. Stromgren b and y photometry reveals a clear stellar rotation
signature of the host star with a period of 17.8 days, well separated from the
period of the radial velocity variations, reinforcing their Keplerian origin.
The values of the semimajor axes of the planets suggest that these objects have
migrated from the region of giant planet formation to closer orbits. In order
to examine the possibility of the existence of additional (small) planets in
the system, we studied the orbital stability of hypothetical terrestrial-sized
objects in the region between the two planets and interior to the orbit of the
inner body. Results indicated that stable orbits exist only in a small region
interior to planet b. However, the current observational data offer no evidence
for the existence of additional objects in this system.Comment: 23 pages, 4 figures, 5 tables, accepted for publication in Ap
A 4-Planet System Orbiting the K0V Star HD 141399
We present precision radial velocity (RV) data sets from Keck-HIRES and from
Lick Observatory's new Automated Planet Finder Telescope and Levy Spectrometer
on Mt. Hamilton that reveal a multiple-planet system orbiting the nearby,
slightly evolved, K-type star HD 141399. Our 91 observations over 10.5 years
suggest the presence of four planets with orbital periods of 94.35, 202.08,
1070.35, and 3717.35 days and minimum masses of 0.46, 1.36, 1.22, and 0.69
Jupiter masses respectively. The orbital eccentricities of the three inner
planets are small, and the phase curves are well sampled. The inner two planets
lie just outside the 2:1 resonance, suggesting that the system may have
experienced dissipative evolution during the protoplanetary disk phase. The
fourth companion is a Jupiter-like planet with a Jupiter-like orbital period.
Its orbital eccentricity is consistent with zero, but more data will be
required for an accurate eccentricity determination.Comment: 11 pages, 13 figures, To appear in the Astrophysical Journa
A Super-Earth Orbiting the Nearby Sun-like Star HD 1461
We present precision radial velocity data that reveal a Super-Earth mass
planet and two probable additional planets orbiting the bright nearby G0V star
HD 1461. Our 12.8 years of Keck HIRES precision radial velocities indicate the
presence of a 7.4M_Earth planet on a 5.77-day orbit. The data also suggest, but
cannot yet confirm, the presence of outer planets on low-eccentricity orbits
with periods of 446.1 and 5017 days, and projected masses (M sin i) of 27.9 and
87.1M_Earth, respectively. Test integrations of systems consistent with the
radial velocity data suggest that the configuration is dynamically stable. We
present a 12.2-year time series of photometric observations of HD 1461, which
comprise 799 individual measurements, and indicate that it has excellent
long-term photometric stability. However, there are small amplitude variations
with periods comparable to those of the suspected 2nd and 3rd signals in the
radial velocities near 5000 and 446 days, thus casting some suspicion on those
periodicities as Keplerian signals. If the 5.77-day companion has a
Neptune-like composition, then its expected transit depth is of order ~0.5
millimags. The geometric a priori probability of transits is ~8%. Phase-folding
of the ground-based photometry shows no indication that transits of the
5.77-day companion are occurring, but high-precision follow-up of HD 1461
during upcoming transit phase windows will be required to definitively rule out
or confirm transits. This new system joins a growing list of solar-type stars
in the immediate galactic neighborhood that are accompanied by at least one
Neptune- (or lower) mass planets having orbital periods of 50 days or less.Comment: 33 pages, 7 figure
Formation and Detectability of Terrestrial Planets Around Alpha Centauri B
We simulate the formation of planetary systems around Alpha Centauri B. The
N-body accretionary evolution of a 1/r disk populated with 400-900 lunar-mass
protoplanets is followed for 200 Myr. All simulations lead to the formation of
multiple-planet systems with at least one planet in the 1-2 MEarth mass range
at 0.5-1.5 AU. We examine the detectability of our simulated planetary systems
by generating synthetic radial velocity observations including noise based on
the radial velocity residuals to the recently published three planet fit to the
nearby K0V star HD 69830. Using these synthetic observations, we find that we
can reliably detect a 1.8 MEarth planet in the habitable zone of Alpha Centauri
B after only three years of high cadence observations. We also find that the
planet is detectable even if the radial velocity precision is 3 m/s, as long as
the noise spectrum is white. Our results show that the greatest uncertainty in
our ability to detect rocky planets in the Alpha Centauri system is the unknown
magnitude of ultra-low frequency stellar noise.Comment: 17 pages, 5 figures; accepted for publication in the Astrophysical
Journa
The Lick-Carnegie Survey: Four New Exoplanet Candidates
We present new precise HIRES radial velocity (RV) data sets of five nearby
stars obtained at Keck Observatory. HD 31253, HD 218566, HD 177830, HD 99492
and HD 74156 are host stars of spectral classes F through K and show radial
velocity variations consistent with new or additional planetary companions in
Keplerian motion. The orbital parameters of the candidate planets in the five
planetary systems span minimum masses of M sin i = 27.43 M_{earth} to M sin i =
8.28 M_{jup}, periods of 17.05 to 4696.95 days and eccentricities ranging from
circular to extremely eccentric (e ~ 0.63). The 5th star, HD 74156, was known
to have both a 52-day and a 2500-day planet, and was claimed to also harbor a
3rd planet at 336d, in apparent support of the "Packed Planetary System"
hypothesis. Our greatly expanded data set for HD 74156 provides strong
confirmation of both the 52-day and 2500-d planets, but strongly contradicts
the existence of a 336-day planet, and offers no significant evidence for any
other planets in the system.Comment: 13 pages, 15 figures. Accepted for publication in ApJ. Fixed typos in
Table 2. Additional material at http://www.ucolick.org/~smeschia/4planet.ph
Planets in Mean-Motion Resonances and the System Around HD45364
In some planetary systems, the orbital periods of two of its members present
a commensurability, usually known by mean-motion resonance. These resonances
greatly enhance the mutual gravitational influence of the planets. As a
consequence, these systems present uncommon behaviors, and their motions need
to be studied with specific methods. Some features are unique and allow us a
better understanding and characterization of these systems. Moreover,
mean-motion resonances are a result of an early migration of the orbits in an
accretion disk, so it is possible to derive constraints on their formation.
Here we review the dynamics of a pair of resonant planets and explain how their
orbits evolve in time. We apply our results to the HD 45365 planetary system.Comment: invited review, 17 pages, 6 figure
Synthesis and functionalization of biocompatible Tb:CePO4 nanophosphors with spindle-like shape
Monoclinic Tb:CePO4 nanophosphors with a spindle-like morphology and tailored size (in the nanometer and micrometer range) have been prepared through a very simple procedure, which consists of aging, at low temperature (120 C), ethylene glycol solutions containing only cerium and terbium acetylacetonates and phosphoric acid, not requiring the addition of surfactants or capping agents. The influence of the heating mode (conventional convection oven or microwave oven) and the Tb doping level on the luminescent, structural and morphological features of the precipitated nanoparticles have also been analyzed. This study showed that microwave-assisted heating resulted in an important beneficial effect on the luminescent properties of these nanophosphors. Finally, a procedure for the functionalization of the Tb:CePO4 nanoparticles with asparticdextran is also reported. The functionalized nanospindles presented negligible toxicity for Verocells, which along with theirs excellent luminescent properties, make them suitable for biomedical applications.Junta de Andalucía FQM6090España CICYT MAT2011-2359
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