385 research outputs found
High-resolution imaging of planet host candidates. A comprehensive comparison of different techniques
The Kepler mission has discovered thousands of planet candidates. Currently,
some of them have already been discarded; more than 200 have been confirmed by
follow-up observations, and several hundreds have been validated. However, most
of them are still awaiting for confirmation. Thus, priorities (in terms of the
probability of the candidate being a real planet) must be established for
subsequent observations. The motivation of this work is to provide a set of
isolated (good) host candidates to be further tested by other techniques. We
identify close companions of the candidates that could have contaminated the
light curve of the planet host. We used the AstraLux North instrument located
at the 2.2 m telescope in the Calar Alto Observatory to obtain
diffraction-limited images of 174 Kepler objects of interest. The lucky-imaging
technique used in this work is compared to other AO and speckle imaging
observations of Kepler planet host candidates. We define a new parameter, the
blended source confidence level (BSC), to assess the probability of an object
to have blended non-detected eclipsing binaries capable of producing the
detected transit. We find that 67.2% of the observed Kepler hosts are isolated
within our detectability limits, and 32.8% have at least one visual companion
at angular separations below 6 arcsec. We find close companions (below 3
arcsec) for the 17.2% of the sample. The planet properties of this sample of
non-isolated hosts are revised. We report one possible S-type binary
(KOI-3158). We also report three possible false positives (KOIs 1230.01,
3649.01, and 3886.01) due to the presence of close companions. The BSC
parameter is calculated for all the isolated targets and compared to both the
value prior to any high-resolution image and, when possible, to observations
from previous high-spatial resolution surveys in the Kepler sample.Comment: Accepted for publication in A&A on April 29, 2014; 32 pages, 11
figures, 11 table
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
Eclipsing binaries and fast rotators in the Kepler sample. Characterization via radial velocity analysis from Calar Alto
The Kepler mission has provided high-accurate photometric data in a long time
span for more than two hundred thousands stars, looking for planetary transits.
Among the detected candidates, the planetary nature of around 15% has been
established or validated by different techniques. But additional data is needed
to characterize the rest of the candidates and reject other possible
configurations. We started a follow-up program to validate, confirm, and
characterize some of the planet candidates. In this paper we present the radial
velocity analysis (RV) of those presenting large variations, compatible with
being eclipsing binaries. We also study those showing large rotational
velocities, which prevents us from obtaining the necessary precision to detect
planetary-like objects. We present new RV results for 13 Kepler objects of
interest (KOIs) obtained with the CAFE spectrograph at the Calar Alto
Observatory, and analyze their high-spatial resolution images and the Kepler
light curves of some interesting cases. We have found five spectroscopic and
eclipsing binaries. Among them, the case of KOI-3853 is of particular interest.
This system is a new example of the so-called heartbeat stars, showing dynamic
tidal distortions in the Kepler light curve. We have also detected duration and
depth variations of the eclipse. We suggest possible scenarios to explain such
effect, including the presence of a third substellar body possibly detected in
our RV analysis. We also provide upper mass limits to the transiting companions
of other six KOIs with large rotational velocities. This property prevents the
RV method to obtain the necessary precision to detect planetary-like masses.
Finally, we analyze the large RV variations of other two KOIs, incompatible
with the presence of planetary-mass objects. These objects are likely to be
stellar binaries but a longer timespan is still needed.Comment: Accepted for publication in A&A. 18 pages, 9 figures, 17 tables. This
version fixes an error affecting the values of tables A.1-A.13. The text
remains unaltere
Kepler-447b: a hot-Jupiter with an extremely grazing transit
We present the radial velocity confirmation of the extrasolar planet
Kepler-447b, initially detected as a candidate by the Kepler mission. In this
work, we analyze its transit signal and the radial velocity data obtained with
the Calar Alto Fiber-fed Echelle spectrograph (CAFE). By simultaneously
modeling both datasets, we obtain the orbital and physical properties of the
system. According to our results, Kepler-447b is a Jupiter-mass planet
(), with an estimated radius of
(uncertainties provided in this work are
unless specified). This translates into a sub-Jupiter density. The
planet revolves every days in a slightly eccentric orbit
() around a G8V star with detected activity in the
Kepler light curve. Kepler-447b transits its host with a large impact parameter
(), being one of the few planetary grazing transits
confirmed so far and the first in the Kepler large crop of exoplanets. We
estimate that only around 20% of the projected planet disk occults the stellar
disk. The relatively large uncertainties in the planet radius are due to the
large impact parameter and short duration of the transit. Planets with such an
extremely large impact parameter can be used to detect and analyze interesting
configurations such as additional perturbing bodies, stellar pulsations,
rotation of a non-spherical planet, or polar spot-crossing events. All these
scenarios would periodically modify the transit properties (depth, duration,
and time of mid-transit), what could be detectable with sufficient accurate
photometry. Short-cadence photometric data (at the 1 minute level) would help
in the search for these exotic configurations in grazing planetary transits
like that of Kepler-447b.Comment: Accepted for publication in A&A. 13 pages, 8 figures, 4 tables. This
version replaces an earlier version of the pape
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-539: a young extrasolar system with two giant planets on wide orbits and in gravitational interaction
We confirm the planetary nature of Kepler-539b (aka Kepler object of interest
K00372.01), a giant transiting exoplanet orbiting a solar-analogue G2 V star.
The mass of Kepler-539b was accurately derived thanks to a series of precise
radial velocity measurements obtained with the CAFE spectrograph mounted on the
CAHA 2.2m telescope. A simultaneous fit of the radial-velocity data and Kepler
photometry revealed that Kepler-539b is a dense Jupiter-like planet with a mass
of Mp = 0.97 Mjup and a radius of Rp = 0.747 Rjup, making a complete circular
revolution around its parent star in 125.6 days. The semi-major axis of the
orbit is roughly 0.5 au, implying that the planet is at roughly 0.45 au from
the habitable zone. By analysing the mid-transit times of the 12 transit events
of Kepler-539b recorded by the Kepler spacecraft, we found a clear modulated
transit time variation (TTV), which is attributable to the presence of a planet
c in a wider orbit. The few timings available do not allow us to precisely
estimate the properties of Kepler-539c and our analysis suggests that it has a
mass between 1.2 and 3.6 Mjup, revolving on a very eccentric orbit (0.4<e<0.6)
with a period larger than 1000 days. The high eccentricity of planet c is the
probable cause of the TTV modulation of planet b. The analysis of the CAFE
spectra revealed a relatively high photospheric lithium content, A(Li)=2.48
dex, which, together with both a gyrochronological and isochronal analysis,
suggests that the parent star is relatively young.Comment: 11 pages, 14 figures, accepted for publication in Astronomy &
Astrophysic
A new look inside Planetary Nebula LoTr 5: A long-period binary with hints of a possible third component
LoTr 5 is a planetary nebula with an unusual long-period binary central star.
As far as we know, the pair consists of a rapidly rotating G-type star and a
hot star, which is responsible for the ionization of the nebula. The rotation
period of the G-type star is 5.95 days and the orbital period of the binary is
now known to be 2700 days, one of the longest in central star of
planetary nebulae. The spectrum of the G central star shows a complex H
double-peaked profile which varies with very short time scales, also reported
in other central stars of planetary nebulae and whose origin is still unknown.
We present new radial velocity observations of the central star which allow us
to confirm the orbital period for the long-period binary and discuss the
possibility of a third component in the system at 129 days to the G star.
This is complemented with the analysis of archival light curves from SuperWASP,
ASAS and OMC. From the spectral fitting of the G-type star, we obtain a
effective temperature of = 5410250 K and surface gravity of
= 2.70.5, consistent with both giant and subgiant stars. We also
present a detailed analysis of the H double-peaked profile and conclude
that it does not present correlation with the rotation period and that the
presence of an accretion disk via Roche lobe overflow is unlikely.Comment: 12 pages, 12 figures, accepted for publication in MNRA
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
Kepler-91b: a planet at the end of its life. Planet and giant host star properties via light-curve variations
The evolution of planetary systems is intimately linked to the evolution of
their host star. Our understanding of the whole planetary evolution process is
based on the large planet diversity observed so far. To date, only few tens of
planets have been discovered orbiting stars ascending the Red Giant Branch.
Although several theories have been proposed, the question of how planets die
remains open due to the small number statistics. In this work we study the
giant star Kepler-91 (KOI-2133) in order to determine the nature of a
transiting companion. This system was detected by the Kepler Space Telescope.
However, its planetary confirmation is needed. We confirm the planetary nature
of the object transiting the star Kepler-91 by deriving a mass of and a planetary radius of
. Asteroseismic analysis produces a
stellar radius of and a mass of
. We find that its eccentric orbit
() is just away
from the stellar atmosphere at the pericenter. Kepler-91b could be the previous
stage of the planet engulfment, recently detected for BD+48 740. Our
estimations show that Kepler-91b will be swallowed by its host star in less
than 55 Myr. Among the confirmed planets around giant stars, this is the
planetary-mass body closest to its host star. At pericenter passage, the star
subtends an angle of , covering around 10% of the sky as seen from
the planet. The planetary atmosphere seems to be inflated probably due to the
high stellar irradiation.Comment: 21 pages, 8 tables and 11 figure
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