64 research outputs found
Planets around active stars
We present the results of radial velocity measurements of two samples of
active stars. The first sample contains field G and K giants across the Red
Giant Branch, whereas the second sample consists of nearby young stars (d < 150
pc) with ages between 10 - 300 Myrs. The radial velocity monitoring program has
been carried out with FEROS at 1.52 m ESO telescope (1999 - 2002) and continued
since 2003 at 2.2 m MPG/ESO telescope. We observed stellar radial velocity
variations which originate either from the stellar activity or the presence of
stellar/substellar companions. By means of a bisector technique we are able to
distinguish the sources of the radial velocity variation. Among them we found
few candidates of planetary companions, both of young stars and G-K giants
sample.Comment: 4 pages, 5 figures, to appear in the Proceedings of the ESO Workshop
"Precision Spectroscopy in Astrophysics", eds. L. Pasquini, M. Romaniello,
N.C. Santos, A. Correi
Noise Sources in Photometry and Radial Velocities
The quest for Earth-like, extrasolar planets (exoplanets), especially those
located inside the habitable zone of their host stars, requires techniques
sensitive enough to detect the faint signals produced by those planets. The
radial velocity (RV) and photometric transit methods are the most widely used
and also the most efficient methods for detecting and characterizing
exoplanets. However, presence of astrophysical "noise" makes it difficult to
detect and accurately characterize exoplanets. It is important to note that the
amplitude of such astrophysical noise is larger than both the signal of
Earth-like exoplanets and state-of-the-art instrumentation limit precision,
making this a pressing topic that needs to be addressed. In this chapter, I
present a general review of the main sources of noise in photometric and RV
observations, namely, stellar oscillations, granulation, and magnetic activity.
Moreover, for each noise source I discuss the techniques and observational
strategies which allow us to mitigate their impact.Comment: 11 pages, 2 tables, Lecture presented at the IVth Azores
International Advanced School in Space Sciences on "Asteroseismology and
Exoplanets: Listening to the Stars and Searching for New Worlds"
(arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in
July 201
Super-Earths: A New Class of Planetary Bodies
Super-Earths, a class of planetary bodies with masses ranging from a few
Earth-masses to slightly smaller than Uranus, have recently found a special
place in the exoplanetary science. Being slightly larger than a typical
terrestrial planet, super-Earths may have physical and dynamical
characteristics similar to those of Earth whereas unlike terrestrial planets,
they are relatively easier to detect. Because of their sizes, super-Earths can
maintain moderate atmospheres and possibly dynamic interiors with plate
tectonics. They also seem to be more common around low-mass stars where the
habitable zone is in closer distances. This article presents a review of the
current state of research on super-Earths, and discusses the models of the
formation, dynamical evolution, and possible habitability of these objects.
Given the recent advances in detection techniques, the detectability of
super-Earths is also discussed, and a review of the prospects of their
detection in the habitable zones of low-mass stars is presented.Comment: A (non-technical) review of the literature on the current state
ofresearch on super-Earths. The topics include observation, formation,
dynamical evolution, habitability, composition, interior dynamics, magnetic
field, atmosphere, and propsect of detection. The article has 44 pages, 27
figures, and 203 references. It has been accepted for publication in the
journal Contemporary Physics (2011
Against all odds? Forming the planet of the HD196885 binary
HD196885Ab is the most "extreme" planet-in-a-binary discovered to date, whose
orbit places it at the limit for orbital stability. The presence of a planet in
such a highly perturbed region poses a clear challenge to planet-formation
scenarios. We investigate this issue by focusing on the planet-formation stage
that is arguably the most sensitive to binary perturbations: the mutual
accretion of kilometre-sized planetesimals. To this effect we numerically
estimate the impact velocities amongst a population of circumprimary
planetesimals. We find that most of the circumprimary disc is strongly hostile
to planetesimal accretion, especially the region around 2.6AU (the planet's
location) where binary perturbations induce planetesimal-shattering of
more than 1km/s. Possible solutions to the paradox of having a planet in such
accretion-hostile regions are 1) that initial planetesimals were very big, at
least 250km, 2) that the binary had an initial orbit at least twice the present
one, and was later compacted due to early stellar encounters, 3) that
planetesimals did not grow by mutual impacts but by sweeping of dust (the
"snowball" growth mode identified by Xie et al., 2010b), or 4) that HD196885Ab
was formed not by core-accretion but by the concurent disc instability
mechanism. All of these 4 scenarios remain however highly conjectural.Comment: accepted for publication by Celestial Mechanics and Dynamical
Astronomy (Special issue on EXOPLANETS
Biosignatures from Earth-Like Planets Around M Dwarfs
Coupled one-dimensional photochemical-climate calculations have been
performed for hypothetical Earth-like planets around M dwarfs. Visible,
near-infrared and thermal-infrared synthetic spectra of these planets were
generated to determine which biosignature gases might be observed by a future,
space-based telescope. Our star sample included two observed active M dwarfs,
AD Leo and GJ 643, and three quiescent model stars. The spectral distribution
of these stars in the ultraviolet generates a different photochemistry on these
planets. As a result, the biogenic gases CH4, N2O, and CH3Cl have substantially
longer lifetimes and higher mixing ratios than on Earth, making them
potentially observable by space-based telescopes. On the active M-star planets,
an ozone layer similar to Earth's was developed that resulted in a
spectroscopic signature comparable to the terrestrial one. The simultaneous
detection of O2 (or O3) and a reduced gas in a planet's atmosphere has been
suggested as strong evidence for life. Planets circling M stars may be good
locations to search for such evidence.Comment: 34 pages, 10 figures, Astrobiology, in pres
Discovery of an inflated hot Jupiter around a slightly evolved star TOI-1789
Stars and planetary system
K2-60b and K2-107b. A Sub-Jovian and a Jovian Planet from the K2 Mission
FWN – Publicaties zonder aanstelling Universiteit LeidenStars and planetary system
A tentative detection of He I in the atmosphere of GJ 1214 b
Stars and planetary system
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