83 research outputs found
Planetary systems across different niches: Synergies between Kepler and Calar Alto observatories
Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica. Fecha de lectura: 02-07-2015Since the discovery of the first extrasolar planets around two decades ago, more than a thousand
of these worlds have been confirmed and characterized. The wide and unexpected diversity of
properties shown by these planetary systems suggest the complexity of the planet formation and
evolution processes. Apart from providing indications on the formation of the Solar System,
these discoveries have opened many others. Step-by-step, we are providing observational hints
to answer them. In particular, the Kepler mission has provided an impressive sample of planet
candidates of any kind that can be fully characterized thanks to the technique used and the
subsequent ground-based follow-up. This full characterization is important in order to analyze
their origin and evolution history.
In this thesis, we present our contribution to complete the picture of the evolution of planetary
systems. We have performed a comprehensive follow-up of the Kepler candidates by making
use of ground-based instrumentation at Calar Alto Observatory. Due to the characteristics of the
Kepler mission, the detected transits (due to the pass of an object in front of a star) could be due
to other blended configurations mimicking a planetary-like transit. Our work has been centered
on ruling out these configurations, confirming the planetary-nature of the transiting objects,
and analyzing their properties. To that end, we have carried out a two-phases project making
use of different datasets and techniques. The two phases consisted on i) obtaining high-spatial
resolution images of a large sample of Kepler candidates owing to unveil possible companions
and ii) obtaining high-resolution spectroscopy of a smaller carefully selected sub-sample to
monitor the radial velocity of the host star and characterize the physical and orbital properties
of the planet. In addition, we have analyzed the Kepler light curve looking for modulations
induced by the presence of a planetary-mass or substellar object.
The results of this follow-up have yielded to the confirmation of five planets in four host stars.
Among them, we have found the closest-in planet orbiting a giant star (Kepler-91 b), being
the first confirmed planet known to transit one of these evolved stars. Additionally, we confirmed
other close-in giant planet around another giant star (Kepler-432 b), the planet having the
most grazing transit known to date (Kepler-447 b), and a two-planet system revolving around
a young solar-analog (KOI-372). Besides, our high-resolution images of more than 170 planet
host candidates have improved the candidacy of tens of planets and have reported close blended
companions in around 18% of the sample. In this dissertation we present the observations and
analysis that lead to these results and discuss their relevance in the exoplanetary fiel
Detection of the secondary eclipse of Qatar-1b in the Ks band
Qatar-1b is a close-orbiting hot Jupiter ( , ) around a metal-rich K-dwarf, with orbital separation and period of
0.023 AU and 1.42 days. We have observed the secondary eclipse of this
exoplanet in the Ks band with the objective of deriving a brightness
temperature for the planet and providing further constraints to the orbital
configuration of the system. We obtained near-infrared photometric data from
the ground by using the OMEGA2000 instrument at the 3.5 m telescope at Calar
Alto (Spain) in staring mode, with the telescope defocused. We have used
principal component analysis (PCA) to identify correlated systematic trends in
the data. A Markov chain Monte Carlo analysis was performed to model the
correlated systematics and fit for the secondary eclipse of Qatar-1b using a
previously developed occultation model. We adopted the prayer bead method to
assess the effect of red noise on the derived parameters. We measured a
secondary eclipse depth of , which indicates a
brightness temperature in the Ks band for the planet of K.
We also measured a small deviation in the central phase of the secondary
eclipse of , which leads to a value for
of . However, this last result
needs to be confirmed with more data.Comment: 6 pages, 6 figures, accepted for publication in A&
Magnetic activity and accretion on FU Tau A: Clues from variability
FU Tau A is a young very low mass object in the Taurus star forming region
which was previously found to have strong X-ray emission and to be anomalously
bright for its spectral type. In this study we discuss these characteristics
using new information from quasi-simultaneous photometric and spectroscopic
monitoring. From photometric time series obtained with the 2.2m telescope on
Calar Alto we measure a period of ~4d for FU Tau A, most likely the rotation
period. The short-term variations over a few days are consistent with the
rotational modulation of the flux by cool, magnetically induced spots. In
contrast, the photometric variability on timescales of weeks and years can only
be explained by the presence of hot spots, presumably caused by accretion. The
hot spot properties are thus variable on timescales exceeding the rotation
period, maybe due to long-term changes in the accretion rate or geometry. The
new constraints from the analysis of the variability confirm that FU Tau A is
affected by magnetically induced spots and excess luminosity from accretion.
However, accretion is not sufficient to explain its anomalous position in the
HR diagram. In addition, suppressed convection due to magnetic activity and/or
an early evolutionary stage need to be invoked to fully account for the
observed properties. These factors cause considerable problems in estimating
the mass of FU Tau A and other objects in this mass/age regime, to the extent
that it appears questionable if it is feasible to derive the Initial Mass
Function for young low-mass stars and brown dwarfs.Comment: 10 pages, 7 figures, accepted for publication in MNRAS, 'Note added
in proof' include
Kepler-432 b: a massive planet in a highly eccentric orbit transiting a red giant
We report the first disclosure of the planetary nature of Kepler-432 b (aka
Kepler object of interest KOI-1299.01). We accurately constrained its mass and
eccentricity by high-precision radial velocity measurements obtained with the
CAFE spectrograph at the CAHA 2.2-m telescope. By simultaneously fitting these
new data and Kepler photometry, we found that Kepler-432 b is a dense
transiting exoplanet with a mass of Mp = 4.87 +/- 0.48 MJup and radius of Rp =
1.120 +/- 0.036 RJup. The planet revolves every 52.5 d around a K giant star
that ascends the red giant branch, and it moves on a highly eccentric orbit
with e = 0.535 +/- 0.030. By analysing two NIR high-resolution images, we found
that a star is located at 1.1 from Kepler-432, but it is too faint to cause
significant effects on the transit depth. Together with Kepler-56 and
Kepler-91, Kepler-432 occupies an almost-desert region of parameter space,
which is important for constraining the evolutionary processes of planetary
systems.Comment: 4 pages, 5 figures, accepted for publication in A&A Letters. Also see
the companion paper by Ortiz et a
Detection of the secondary eclipse of WASP-10b in the Ks-band
WASP-10b, a non-inflated hot Jupiter, was discovered around a K-dwarf in a
near circular orbit (). Since its discovery in 2009, different
published parameters for this system have led to a discussion about the size,
density, and eccentricity of this exoplanet. In order to test the hypothesis of
a circular orbit for WASP-10b, we have observed its secondary eclipse in the
Ks-band, where the contribution of planetary light is high enough to be
detected from the ground. Observations were performed with the OMEGA2000
instrument at the 3.5-meter telescope at Calar Alto (Almer\'ia, Spain), in
staring mode during 5.4 continuous hours, with the telescope defocused,
monitoring the target during the expected secondary eclipse. A relative light
curve was generated and corrected from systematic effects, using the Principal
Component Analysis (PCA) technique. The final light curve was fitted using a
transit model to find the eclipse depth and a possible phase shift. The best
model obtained from the Markov Chain Monte Carlo analysis resulted in an
eclipse depth of of and a phase
offset of of . The eclipse phase
offset derived from our modeling has systematic errors that were not taken into
account and should not be considered as evidence of an eccentric orbit. The
offset in phase obtained leads to a value for of .
The derived eccentricity is too small to be of any significance.Comment: 8 pages, 10 figure
Tentative co-orbital submillimeter emission within the Lagrangian region L5 of the protoplanet PDS 70 b
Context: High-spatial resolution Atacama Large Millimeter/submillimeter Array
(ALMA) data have revealed a plethora of substructures in protoplanetary disks.
Some of those features are thought to trace the formation of embedded planets.
One example is the gas and dust that accumulated in the co-orbital Lagrangian
regions /, which were tentatively detected in recent years and might
be the pristine material for the formation of Trojan bodies. Aims: This work is
part of the TROY project, whose ultimate goal is to find robust evidence of
exotrojan bodies and study their implications in the exoplanet field. Here, we
focus on the early stages of the formation of these bodies by inspecting the
iconic system PDS 70, the only confirmed planetary system in formation.
Methods: We reanalyzed archival high-angular resolution Band 7 ALMA
observations from PDS 70 by doing an independent imaging process to look for
emission in the Lagrangian regions of the two detected gas giant protoplanets,
PDS 70 b and c. We then projected the orbital paths and visually inspected
emission features at the regions around the / locations as defined by
60 in azimuth from the planet position. Results: We found
emission at a 4- level (6- when correcting from a
cleaning effect) at the position of the region of PDS 70 b. This
emission corresponds to a dust mass in a range of 0.03- 2 M, which
potentially accumulated in this gravitational well. Conclusions: The tentative
detection of the co-orbital dust trap that we report requires additional
observations to be confirmed. We predict that we could detect the co-orbital
motion of PDS 70 b and the dust presumably associated with by observing
again with the same sensitivity and angular resolution as early as February
2026.Comment: 8 pages, 5 figures, 2 tables. Published in Astronomy & Astrophysic
Pleiades or Not? Resolving the Status of the Lithium-rich M Dwarfs HHJ 339 and HHJ 430
Oppenheimer et al. discovered two M5 dwarfs in the Pleiades with nearly primordial lithium. These stars are not low enough in mass to represent the leading edge of the lithium depletion boundary at Pleiades age (~125 Myr). A possible explanation for the enhanced lithium in these stars is that they are actually not members of the Pleiades but instead are members of a younger moving group seen in projection toward the Pleiades. We have used data from Gaia DR2 to confirm that these two stars, HHJ 339 and HHJ 430, are indeed not members of the Pleiades. Based on their space motions, parallaxes, and positions in a Gaia-based color–magnitude diagram, it is probable that these two stars are about 40 parsecs foreground to the Pleiades and have ages of ~25 Myr. Kinematically they are best matched to the 32 Ori moving group
Revisiting K2-233 spectroscopic time-series with multidimensional Gaussian Processes
Detecting planetary signatures in radial velocity time-series of young stars
is challenging due to their inherently strong stellar activity. However, it is
possible to learn information about the properties of the stellar signal by
using activity indicators measured from the same stellar spectra used to
extract radial velocities. In this manuscript, we present a reanalysis of
spectroscopic HARPS data of the young star K2-233, which hosts three transiting
planets. We perform a multidimensional Gaussian Process regression on the
radial velocity and the activity indicators to characterise the planetary
Doppler signals. We demonstrate, for the first time on a real dataset, that the
use of a multidimensional Gaussian Process can boost the precision with which
we measure the planetary signals compared to a one-dimensional Gaussian Process
applied to the radial velocities alone. We measure the semi-amplitudes of
K2-233 b, c, and d as 1.31(-0.74)(+0.81), 1.81(-0.67)(+0.71), and
2.72(-0.70)(+0.66) m/s, which translates into planetary masses of
2.4(-1.3)(+1.5), 4.6(-1.7)(+1.8), and 10.3(-2.6)(+2.4), respectively. These new
mass measurements make K2-233 d a valuable target for transmission spectroscopy
observations with JWST. K2-233 is the only young system with two detected inner
planets below the radius valley and a third outer planet above it. This makes
it an excellent target to perform comparative studies, to inform our theories
of planet evolution, formation, migration, and atmospheric evolution.Comment: Accepted for publication in MNRA
Precise radial velocities of giant stars XV. Mysterious nearly periodic radial velocity variations in the eccentric binary Cygni
Using the Hamilton Echelle Spectrograph at Lick Observatory, we have obtained
precise radial velocities (RVs) of a sample of 373 G- and K-giant stars over
more than 12 years, leading to the discovery of several single and multiple
planetary systems. The RVs of the long-period (~53 years) spectroscopic binary
Cyg (HIP 102488) are found to exhibit additional regular variations
with a much shorter period (~291 days). We intend to improve the orbital
solution of the Cyg system and attempt to identify the cause of the
nearly periodic shorter period variations, which might be due to an additional
substellar companion. We used precise RV measurements of the K-giant star
Cyg from Lick Observatory, in combination with a large set of RVs
collected more recently with the SONG telescope, as well as archival data sets.
Our Keplerian model to the RVs characterizes the orbit of the spectroscopic
binary to higher precision than achieved previously, resulting in a semi-major
axis of , an eccentricity of , and a minimum
mass of the secondary of . Additional short-period RV
variations closely resemble the signal of a Jupiter-mass planet orbiting the
evolved primary component with a period of , but the period and
amplitude of the putative orbit change strongly over time. Furthermore, in our
stability analysis of the system, no stable orbits could be found in a large
region around the best fit. Both of these findings deem a planetary cause of
the RV variations unlikely. Most of the investigated alternative scenarios,
such as an hierarchical triple or stellar spots, also fail to explain the
observed variability convincingly. Due to its very eccentric binary orbit, it
seems possible, however, that Cyg could be an extreme example of a
heartbeat system.Comment: 17 pages, 13 figures, accepted to A&
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