524 research outputs found
The M dwarf planet search programme at the ESO VLT + UVES. A search for terrestrial planets in the habitable zone of M dwarfs
We present radial velocity (RV) measurements of our sample of 40 M dwarfs
from our planet search programme with VLT+UVES begun in 2000. Although with our
RV precision down to 2 - 2.5 m/s and timebase line of up to 7 years, we are
capable of finding planets of a few Earth masses in the close-in habitable
zones of M dwarfs, there is no detection of a planetary companion. To
demonstrate this we present mass detection limits allowing us to exclude
Jupiter-mass planets up to 1 AU for most of our sample stars. We identified 6 M
dwarfs that host a brown dwarf or low-mass stellar companion. With the
exception of these, all other sample stars show low RV variability with an rms
< 20 m/s. Some high proper motion stars exhibit a linear RV trend consistent
with their secular acceleration. Furthermore, we examine our data sets for a
possible correlation between RVs and stellar activity as seen in variations of
the Halpha line strength. For Barnard's star we found a significant
anticorrelation, but most of the sample stars do not show such a correlation.Comment: 13 pages, 12 figures, 5 tables, accepted by A&
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A Precise Radial Velocity Search for Giant Planets orbiting polluted White Dwarfs
The 21st European Workshop on White Dwarfs was held in Austin, TX from July 23rd to 27th of 2018We present a feasibility study for extending the
well-known radial velocity technique to search for
planetary companions around white dwarfs. Typically,
the spectra of white dwarfs contain only a
few pressure-broadened hydrogen and/or helium
lines, which do not permit to measure the radial
velocity with sufficient precision to detect planets.
A small subset of white dwarfs do also show sharp
metal lines, presumably from infalling circumstellar
material. We suggest to search these “polluted”
white dwarfs for possible giant planets using the
Doppler reflex motion technique. We show here
first results to estimate the Doppler information content
from simulated spectra of the metal-polluted
WD GD 362.Astronom
Toward detection of terrestrial planets in the habitable zone of our closest neighbor: Proxima Centauri
The precision of radial velocity (RV) measurements to detect indirectly
planetary companions of nearby stars has improved to enable the discovery of
extrasolar planets in the Neptune and Super-Earth mass range. Discoveries of
Earth-like planets by means of ground-based RV programs will help to determine
the parameter Eta_Earth, the frequency of potentially habitable planets around
other stars. In search of low-mass planetary companions we monitored Proxima
Centauri (M5V) as part of our M dwarf program. In the absence of a significant
detection, we use these data to demonstrate the general capability of the RV
method in finding terrestrial planets. For late M dwarfs the classic liquid
surface water habitable zone (HZ) is located close to the star, in which
circumstances the RV method is most effective. We want to demonstrate that late
M dwarfs are ideal targets for the search of terrestrial planets with the RV
technique. We obtained differential RV measurements of Proxima Cen over a time
span of 7 years with the UVES spectrograph at the ESO VLT. We determine upper
limits to the masses of companions in circular orbits by means of numerical
simulations. The RV data of Proxima Cen have a total rms scatter of 3.1 m/s and
a period search does not reveal any significant signals. As a result of our
companion limit calculations, we find that we successfully recover all test
signals with RV amplitudes corresponding to planets with m sin i > 2 - 3
M_Earth residing inside the HZ of Proxima Cen with a statistical significance
of >99%. Over the same period range, we can recover 50% of the test planets
with masses of m sin i > 1.5 - 2.5 M_Earth. Based on our simulations, we
exclude the presence of any planet in a circular orbit with m sin i > 1
M_Neptune at separations of a < 1 AU.Comment: 8 pages, 4 figures, accepted for publication in Astronomy &
Astrophysic
A Planetary Companion to gamma Cephei A
We report on the detection of a planetary companion in orbit around the
primary star of the binary system Cephei. High precision radial
velocity measurements using 4 independent data sets spanning the time interval
1981--2002 reveal long-lived residual radial velocity variations superimposed
on the binary orbit that are coherent in phase and amplitude with a period or
2.48 years (906 days) and a semi-amplitude of 27.5 m s. We performed a
careful analysis of our Ca II H & K S-index measurements, spectral line
bisectors, and {\it Hipparcos} photometry. We found no significant variations
in these quantities with the 906-d period. We also re-analyzed the Ca II
8662 {\AA} measurements of Walker et al. (1992) which showed possible
periodic variations with the ``planet'' period when first published. This
analysis shows that periodic Ca II equivalent width variations were only
present during 1986.5 -- 1992 and absent during 1981--1986.5. Furthermore, a
refined period for the Ca II 8662 {\AA} variations is 2.14 yrs,
significantly less than residual radial velocity period. The most likely
explanation of the residual radial velocity variations is a planetary mass
companion with sin = 1.7 and an orbital semi-major axis
of 2.13 AU. This supports the planet hypothesis for the residual
radial velocity variations for Cep first suggested by Walker et al.
(1992). With an estimated binary orbital period of 57 years Cep is the
shortest period binary system in which an extrasolar planet has been found.
This system may provide insights into the relationship between planetary and
binary star formation.Comment: 19 pages, 15 figures, accepted in Ap. J. Includes additional data and
improved orbital solutio
The planet search programme at the ESO CES and HARPS. IV. The search for Jupiter analogues around solar-like stars
In 1992 we began a precision radial velocity (RV) survey for planets around
solar-like stars with the Coude Echelle Spectrograph and the Long Camera (CES
LC) at the 1.4 m telescope in La Silla (Chile). We have continued the survey
with the upgraded CES Very Long Camera (VLC) and HARPS, both at the 3.6 m
telescope, until 2007. The observations for 31 stars cover a time span of up to
15 years and the RV precision permit a search for Jupiter analogues. We perform
a joint analysis for variability, trends, periodicities, and Keplerian orbits
and compute detection limits. Moreover, the HARPS RVs are analysed for
correlations with activity indicators (CaII H&K and CCF shape). We achieve a
long-term RV precision of 15 m/s (CES+LC, 1992-1998), 9 m/s (CES+VLC,
1999-2006), and 2.8 m/s (HARPS, 2003-2009, including archive data), resp. This
enables us to confirm the known planets around Iota Hor, HR 506, and HR 3259. A
steady RV trend for Eps Ind A can be explained by a planetary companion. On the
other hand, we find previously reported trends to be smaller for Beta Hyi and
not present for Alp Men. The candidate planet Eps Eri b was not detected
despite our better precision. Also the planet announced for HR 4523 cannot be
confirmed. Long-term trends in several of our stars are compatible with known
stellar companions. We provide a spectroscopic orbital solution for the binary
HR 2400 and refined solutions for the planets around HR 506 and Iota Hor. For
some other stars the variations could be attributed to stellar activity. The
occurrence of two Jupiter-mass planets in our sample is in line with the
estimate of 10% for the frequency of giant planets with periods smaller than 10
yr around solar-like stars. We have not detected a Jupiter analogue, while the
detections limits for circular orbits indicate at 5 AU a sensitivity for
minimum mass of at least 1 M_Jup (2 M_Jup) for 13% (61%) of the stars.Comment: 63 pages, 24 figures (+33 online figures), 13 Tables, accepted for
publication in A&A (2012-11-13
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