1,031 research outputs found
The IAG spectral atlas of the spatially resolved Sun: Centre-to-limb observations
Solar surface magneto-convection appears as granulation pattern that impacts
spectral lines in terms of both shape and wavelength. Such induced effects also
tend to vary over the observed solar disc because of the changing observation
angle and, thus, the changing observation height as well. Centre-to-limb
observations of the resolved Sun offer an insight into the variable spectral
behaviour across different heliocentric observing positions, providing crucial
information about limb darkening, convective velocities, and line profile
variability relevant to radial velocity (RV) calculations. Thus, RV
measurements and exoplanet transit spectroscopy depend on precise reference
templates. We want to provide a spectroscopic centre-to-limb solar atlas at
high spectral resolution and high-frequency accuracy. The atlas shall help
improve the understanding of the solar atmosphere and convection processes. We
performed high-resolution observations of the resolved quiet Sun with a Fourier
transform spectrograph at the Institut f\"ur Astrophysik und Geophysik in
G\"ottingen. Our dataset contains a wavelength range from 4200\r{A} to
8000\r{A}. We obtained 165 spectra in total, with a spectral resolution of
= 0.024cm, corresponding to a resolving power of
700,000 at 6000\r{A}. We present a centre-to-limb solar atlas containing
14 heliocentric positions. To check for consistency, we investigated the FeI
~6175\r{A} absorption line and compared our line profiles with previous
centre-to-limb observations and also with simulations. The line profile and
also the bisector profiles are generally consistent with previous observations,
but we have identified differences to model line profiles, especially close to
the solar limb
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
Comparison of different exoplanet mass detection limit methods using a sample of main-sequence intermediate-type stars
The radial velocity (RV) technique is a powerful tool for detecting
extrasolar planets and deriving mass detection limits that are useful for
constraining planet pulsations and formation models. Detection limit methods
must take into account the temporal distribution of power of various origins in
the stellar signal. These methods must also be able to be applied to large
samples of stellar RV time series We describe new methods for providing
detection limits. We compute the detection limits for a sample of ten main
sequence stars, which are of G-F-A type, in general active, and/or with
detected planets, and various properties. We use them to compare the
performances of these methods with those of two other methods used in the
litterature. We obtained detection limits in the 2-1000 day period range for
ten stars. Two of the proposed methods, based on the correlation between
periodograms and the power in the periodogram of the RV time series in specific
period ranges, are robust and represent a significant improvement compared to a
method based on the root mean square of the RV signal. We conclude that two of
the new methods (correlation-based method and local power analysis, i.e. LPA,
method) provide robust detection limits, which are better than those provided
by methods that do not take into account the temporal sampling.Comment: 18 pages, 15 figures Accepted in Astronomy & Astrophysic
Three planets around HD 27894. A close-in pair with a 2:1 period ratio and an eccentric Jovian planet at 5.4 AU
Aims. Our new program with HARPS aims to detect mean motion resonant
planetary systems around stars which were previously reported to have a single
bona fide planet, often based only on sparse radial velocity data. Methods.
Archival and new HARPS radial velocities for the K2V star HD 27894 were
combined and fitted with a three-planet self-consistent dynamical model. The
best-fit orbit was tested for long-term stability. Results. We find clear
evidence that HD 27894 is hosting at least three massive planets. In addition
to the already known Jovian planet with a period 18 days
we discover a Saturn-mass planet with 36 days, likely in
a 2:1 mean motion resonance with the first planet, and a cold massive planet
( 5.3 ) with a period 5170
days on a moderately eccentric orbit ( = 0.39). Conclusions. HD
27894 is hosting a massive, eccentric giant planet orbiting around a tightly
packed inner pair of massive planets likely involved in an asymmetric 2:1 mean
motion resonance. HD 27894 may be an important milestone for probing planetary
formation and evolution scenarios.Comment: 4 pages, 2 tables, 3 figures. Accepted for publication in A&A Letters
to the Edito
High-cadence spectroscopy of M-dwarfs – II. Searching for stellar pulsations with HARPS
Stellar oscillations appear all across the Hertzsprung–Russell diagram. Recent theoretical studies support their existence also in the atmosphere of M dwarfs. These studies predict for them short periodicities ranging from 20 min to 3 h. Our Cool Tiny Beats (CTB) programme aims at finding these oscillations for the very first time. With this goal, CTB explores the short time domain of M dwarfs using radial velocity data from the High Accuracy Radial velocity Planet Searcher (HARPS)-European Southern Observatory and HARPS-N high-precision spectrographs. Here we present the results for the two most long-term stable targets observed to date with CTB, GJ 588 and GJ 699 (i.e. Barnard's star). In the first part of this work we detail the correction of several instrumental effects. These corrections are especially relevant when searching for subnight signals. Results show no significant signals in the range where M dwarfs pulsations were predicted. However, we estimate that stellar pulsations with amplitudes larger than ∼0.5 m s−1 can be detected with a 90 per cent completeness with our observations. This result, along with the excess of power regions detected in the periodograms, opens the possibility of non-resolved very low amplitude pulsation signals. Next generation more precise instrumentation would be required to detect such oscillations. However, the possibility of detecting pulsating M-dwarf stars with larger amplitudes is feasible due to the short size of the analysed sample. This motivates the need for completeness of the CTB survey
Crisis, Charisma and Consequences: Evidence from the 2004 US Presidential Election
We investigate how conditions of crisis affect perceptions of charisma and how these, in turn, affect blame attribution and self-sacrificial behavior. Our data are from a 2004 experimental study that preceded the U.S. presidential election, in which we manipulated concerns of a terrorist attack. The results show that those in the Crisis condition rated Bush higher on perceptions of charisma compared to those in the Good Times condition. The Crisis condition also directly and indirectly, via perceptions of charisma, affected whether Bush was blamed for failures in Iraq and our subjects’ willingness to sacrifice their personal resources for his candidacy
Convective blueshift strengths for 242 evolved stars
Context. Extreme precision radial velocity (RV) surveys seeking to detect
planets at RV semi-amplitudes of 10 cm/s are facing numerous challenges. One of
those challenges is convective blueshift caused by stellar granulation and its
suppression through magnetic activity which plays a significant role in hiding
planetary signals in stellar jitter. Aims. Previously we found that for main
sequence stars, convective blueshift as an observational proxy for the strength
of convection near the stellar surface strongly depends on effective
temperature. In this work we investigate 242 post main sequence stars, covering
the subgiant, red giant, and asymptotic giant phases and empirically determine
the changes in convective blueshift with advancing stellar evolution. Methods.
We used the third signature scaling approach to fit a solar model for the
convective blueshift to absorption-line shift measurements from a sample of
coadded HARPS spectra, ranging in temperature from 3750 K to 6150 K. We compare
the results to main sequence stars of comparable temperatures but with a higher
surface gravity. Results. We show that convective blueshift becomes
significantly stronger for evolved stars compared to main sequence stars of a
similar temperature. The difference increases as the star becomes more evolved,
reaching a 5x increase below 4300 K for the most evolved stars. The large
number of stars in the sample, for the first time, allowed for us to
empirically show that convective blueshift remains almost constant among the
entire evolved star sample at roughly solar convection strength with a slight
increase from the red giant phase onward. We discover that the convective
blueshift shows a local minimum for subgiant stars, presenting a sweet spot for
exoplanet searches around higher mass stars, by taking advantage of their
spin-down during the subgiant transition.Comment: 16 pages, 14 figures; accepted for publication in A&
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&
Indoor monitoring of heavy metals and NO2 using active monitoring by moss and palmes diffusion tubes
Background; : Indoor pollution is a real threat to human health all over the world. Indoor pollution derives from indoor sources (e.g. smoking, gas stoves, coated furniture) as well as from outdoor sources (e.g. industries, vehicles). Long-term monitoring measurements in indoor environments are missing to a large extent due to a lack of simple to operate measuring devices. Mosses proved well as biomonitors in hundreds of studies. Nevertheless, indoor use has been extremely scarce. Therefore, this study aimed to determine indoor and outdoor pollution by active biomonitoring using moss as well as NO2 samplers to analyse outdoor and indoor levels of pollution. We exposed moss (Pleurozium schreberi) for 8 weeks indoors and outdoors in 20 households in the city of Girona, Spain. Al, Cr, Cu, Zn, Sn, Cd, Pb, Mo, and Sb were analysed by moss-samplers. Additionally, NO2 was measured with Palmes diffusion tubes.; Results; : Compared to the pre-exposure analysis, concentrations of almost all elements both on indoor and outdoor mosses increased. Except for Cd, all metals and NO2 had, on average, higher concentrations in outdoor mosses than at corresponding indoor sites. However, some 20% of the samples showed inverse patterns, thus, indicating both indoor and outdoor sources. Indoor/outdoor correlations of elements were not significant, but highest for markers of traffic-related pollution, such as Sn, Sb, and NO2. The wide range of indoor-outdoor ratios of NO2 exemplified the relevance of indoor sources such as smoking or gas cooking. Though mostly excluded in this study, a few sites had these sources present.; Conclusions; : The study at hand showed that moss exposed at indoor sites could be a promising tool for long-time biomonitoring. However, it had also identified some drawbacks that should be considered in future indoor studies. Increments of pollutants were sometimes really low compared to the initial concentration and therefore not detectable. This fact hampers the investigation of elements with low basic element levels as, e.g. Pt. Therefore, moss with real low basic levels is needed for active monitoring, especially for future studies in indoor monitoring. Cloned material could be a proper material for indoor monitoring yet never was tested for this purpose
Physical modeling of echelle spectrographs: the CARMENES case study
We have developed a generic physical modeling scheme for high resolution spectroscopy based on simple optical principles. This model predicts the position of centroids for a given set of spectral features with high accuracy. It considers off-plane grating equations and rotations of the different optical elements in order to properly account for tilts in the spectral lines and order curvature. In this way any astronomical spectrograph can be modeled and controlled without the need of commercial ray tracing software. The computations are based on direct ray tracing applying exact corrections to certain surfaces types. This allows us to compute the position on the detector of any spectral feature with high reliability. The parameters of this model, which describe the physical properties of the spectrograph, are continuously optimized to ensure the best possible fit to the observed spectral line positions. We present the physical modeling of CARMENES as a case study. We show that our results are in agreement with commercial ray tracing software. The model prediction matches the observations at a pixel size level, providing an efficient tool in the design, construction and data reduction of high resolution spectrographs. © 2018 SPIE
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