153 research outputs found
Atmospheric Stellar Parameters from Cross-Correlation Functions
The increasing number of spectra gathered by spectroscopic sky surveys and
transiting exoplanet follow-up has pushed the community to develop automated
tools for atmospheric stellar parameters determination. Here we present a novel
approach that allows the measurement of temperature (),
metallicity () and gravity () within a few seconds
and in a completely automated fashion. Rather than performing comparisons with
spectral libraries, our technique is based on the determination of several
cross-correlation functions (CCFs) obtained by including spectral features with
different sensitivity to the photospheric parameters. We use literature stellar
parameters of high signal-to-noise (), high-resolution HARPS
spectra of FGK Main Sequence stars to calibrate , and as a function of CCFs parameters. Our technique is validated
using low spectra obtained with the same instrument. For FGK
stars we achieve a precision of K, and at , while the precision for observation with
and the overall accuracy are constrained by the
literature values used to calibrate the CCFs. Our approach can be easily
extended to other instruments with similar spectral range and resolution, or to
other spectral range and stars other than FGK dwarfs if a large sample of
reference stars is available for the calibration. Additionally, we provide the
mathematical formulation to convert synthetic equivalent widths to CCF
parameters as an alternative to direct calibration. We have made our tool
publicly available.Comment: Accepted by MNRAS. 12 pages, 12 figures. The code to retrieve the
atmospheric stellar parameters from HARPS and HARPS-N spectra is available
"at this url, https://github.com/LucaMalavolta/CCFpams
The "missing link": a 4-day period transiting exoplanet around OGLE-TR-111
We report the discovery of a transiting hot Jupiter around OGLE-TR-111, from
our radial velocity follow-up of OGLE transiting candidates in Carina. The
planet has a mass of 0.53 +- 0.11 M_J and a radius of 1.0 +0.13-0.06 R_J. Three
transiting exoplanets have already been found among OGLE candidates, all with
periods near 1.5 days. The planet presented here, with P=4.0 days, is the first
exoplanet detected by transits with the characteristics of a "normal" hot
Jupiter, as found in abundance by radial velocity surveys The radius of
OGLE-TR-111b and the scarcity of hot Jupiters detected among OGLE transit
candidates tend to indicate that the case of HD209458b, with a radius of 1.4
R_J, is exceptional, with most hot Jupiters being smaller.Comment: 4 pages, 4 figures, to be published in A&A Letter
Stellar noise and planet detection. II. Radial-velocity noise induced by magnetic cycles
For the 451 stars of the HARPS high precision program, we study correlations between the radial-velocity (RV) variation and other parameters of the Cross Correlated Function (CCF). After a careful target selection, we found a very good correlation between the slope of the RV-activity index (log(R'HK)) correlation and the Teff for dwarf stars. This correlation allow us to correct RV from magnetic cycles given the activity index and the Tef
A New Analysis of the Exoplanet Hosting System HD 6434
The current goal of exoplanetary science is not only focused on detecting but
characterizing planetary systems in hopes of understanding how they formed,
evolved, and relate to the Solar System. The Transit Ephemeris Refinement and
Monitoring Survey (TERMS) combines both radial velocity (RV) and photometric
data in order to achieve unprecedented ground-based precision in the
fundamental properties of nearby, bright, exoplanet-hosting systems. Here we
discuss HD 6434 and its planet, HD 6434b, which has a M_p*sin(i) = 0.44 M_J
mass and orbits every 22.0170 days with an eccentricity of 0.146. We have
combined previously published RV data with new measurements to derive a
predicted transit duration of ~6 hrs, or 0.25 days, and a transit probability
of 4%. Additionally, we have photometrically observed the planetary system
using both the 0.9m and 1.0m telescopes at the Cerro Tololo Inter-American
Observatory, covering 75.4% of the predicted transit window. We reduced the
data using the automated TERMS Photometry Pipeline, developed to ensure
consistent and accurate results. We determine a dispositive null result for the
transit of HD 6434b, excluding the full transit to a depth of 0.9% and grazing
transit due to impact parameter limitations to a depth of 1.6%Comment: 9 pages, 5 figures, 3 tables, accepted to A
The HARPS search for southern extra-solar planets. IX. Exoplanets orbiting HD 100777, HD 190647, and HD 221287
The HARPS high-resolution high-accuracy spectrograph is offered to the
astronomical community since the second half of 2003. Since then, we have been
using this instrument for monitoring radial velocities of a large sample of
Solar-type stars (~1400 stars) in order to search for their possible low-mass
companions. Amongst the goals of our survey, one is to significantly increase
the number of detected extra-solar planets in a volume-limited sample to
improve our knowledge of their orbital elements distributions and thus obtain
better constraints for planet-formation models.
In this paper, we present the HARPS radial-velocity data and orbital
solutions for 3 Solar-type stars: HD 100777, HD 190647, and HD 221287. The
radial-velocity data of HD 100777 is best explained by the presence of a 1.1
M_Jup planetary companion on a 384--day eccentric orbit (e=0.36). The orbital
fit obtained for the slightly evolved star HD 190647 reveals the presence of a
long-period (P=1038 d) 1.9 M_Jup planetary companion on a moderately eccentric
orbit (e=0.18). HD 221287 is hosting a 3.1 M_Jup planet on a 456--day orbit.
The shape of this orbit is not very well constrained because of our non-optimal
temporal coverage and because of the presence of abnormally large residuals. We
find clues for these large residuals to result from spectral line profile
variations probably induced by stellar activity related processes.Comment: 7 pages, 4 figures, RV data added in paper. A&A in pres
ELODIE metallicity-biased search for transiting Hot Jupiters II. A very hot Jupiter transiting the bright K star HD189733
Among the 160 known exoplanets, mainly detected in large radial-velocity
surveys, only 8 have a characterization of their actual mass and radius thanks
to the two complementary methods of detection: radial velocities and
photometric transit. We started in March 2004 an exoplanet-search programme
biased toward high-metallicity stars which are more frequently host extra-solar
planets. This survey aims to detect close-in giant planets, which are most
likely to transit their host star. For this programme, high-precision radial
velocities are measured with the ELODIE fiber-fed spectrograph on the 1.93-m
telescope, and high-precision photometry is obtained with the CCD Camera on the
1.20-m telescope, both at the Haute-Provence Observatory. We report here the
discovery of a new transiting hot Jupiter orbiting the star HD189733. The
planetary nature of this object is confirmed by the observation of both the
spectroscopic and photometric transits. The exoplanet HD189733b, with an
orbital period of 2.219 days, has one of the shortest orbital periods detected
by radial velocities, and presents the largest photometric depth in the light
curve (~ 3%) observed to date. We estimate for the planet a mass of 1.15 +-
0.04 Mjup and a radius of 1.26 +- 0.03 RJup. Considering that HD189733 has the
same visual magnitude as the well known exoplanet host star HD209458, further
ground-based and space-based follow-up observations are very promising and will
permit a characterization of the atmosphere and exosphere of this giant
exoplanet.Comment: 5 pages, submitted to Astronomy & Astrophysic
A search for starlight reflected from HD 75289b
We have used a Doppler tomographic analysis to conduct a deep search for the starlight reflected from the planetary companion to HD 75289. In four nights on VLT(UT2)/UVES in 2003 January, we obtained 684 high-resolution echelle spectra with a total integration time of 26 h. We establish an upper limit on the geometric albedo of the planet p < 0.12 (to the 99.9 per cent significance level) at the most probable orbital inclination i≃ 60°, assuming a grey albedo, a Venus-like phase function and a planetary radius Rp= 1.6 RJup. We are able to rule out some combinations of the predicted planetary radius and atmospheric albedo models with high, reflective cloud deck
Rossiter-McLaughlin Observations of 55 Cnc e
We present Rossiter-McLaughlin observations of the transiting super-Earth 55
Cnc e collected during six transit events between January 2012 and November
2013 with HARPS and HARPS-N. We detect no radial-velocity signal above 35 cm/s
(3-sigma) and confine the stellar v sin i to 0.2 +/- 0.5 km/s. The star appears
to be a very slow rotator, producing a very low amplitude Rossiter-McLaughlin
effect. Given such a low amplitude, the Rossiter-McLaughlin effect of 55 Cnc e
is undetected in our data, and any spin-orbit angle of the system remains
possible. We also performed Doppler tomography and reach a similar conclusion.
Our results offer a glimpse of the capacity of future instrumentation to study
low amplitude Rossiter-McLaughlin effects produced by super-Earths.Comment: Accepted for publication in ApJ Letter
WASP-80b has a dayside within the T-dwarf range
AHMJT is a Swiss National Science Foundation (SNSF) fellow under grant number P300P2-147773. MG and EJ are Research Associates at the F.R.S-FNRS; LD received the support the support of the F.R.I.A. fund of the FNRS. DE, KH, and SU acknowledge the financial support of the SNSF in the frame of the National Centre for Competence in Research ‘PlanetS’. EH and IR acknowledge support from the Spanish Ministry of Economy and Competitiveness (MINECO) and the ‘Fondo Europeo de Desarrollo Regional’ (FEDER) through grants AYA2012-39612-C03-01 and ESP2013-48391-C4-1-R.WASP-80b is a missing link in the study of exo-atmospheres. It falls between the warm Neptunes and the hot Jupiters and is amenable for characterisation, thanks to its host star's properties. We observed the planet through transit and during occultation with Warm Spitzer. Combining our mid-infrared transits with optical time series, we find that the planet presents a transmission spectrum indistinguishable from a horizontal line. In emission, WASP-80b is the intrinsically faintest planet whose dayside flux has been detected in both the 3.6 and 4.5 m Spitzer channels. The depths of the occultations reveal that WASP-80b is as bright and as red as a T4 dwarf, but that its temperature is cooler. If planets go through the equivalent of an L-T transition, our results would imply this happens at cooler temperatures than for brown dwarfs. Placing WASP-80b's dayside into a colour-magnitude diagram, it falls exactly at the junction between a blackbody model and the T-dwarf sequence; we cannot discern which of those two interpretations is the more likely. Flux measurements on other planets with similar equilibrium temperatures are required to establish whether irradiated gas giants, like brown dwarfs, transition between two spectral classes. An eventual detection of methane absorption in transmission would also help lift that degeneracy. We obtained a second series of high-resolution spectra during transit, using HARPS. We reanalyse the Rossiter-McLaughlin effect. The data now favour an aligned orbital solution and a stellar rotation nearly three times slower than stellar line broadening implies. A contribution to stellar line broadening, maybe macroturbulence, is likely to have been underestimated for cool stars, whose rotations have therefore been systematically overestimated. [abridged]Publisher PDFPeer reviewe
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