135 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 Kepler-19 System: A Thick-envelope Super-Earth with Two Neptune-mass Companions Characterized Using Radial Velocities and Transit Timing Variations
We report a detailed characterization of the Kepler-19 system. This star was previously known to host a transiting planet with a period of 9.29 days, a radius of 2.2 R_â, and an upper limit on the mass of 20 M_â. The presence of a second, non-transiting planet was inferred from the transit time variations (TTVs) of Kepler-19b over eight quarters of Kepler photometry, although neither the mass nor period could be determined. By combining new TTVs measurements from all the Kepler quarters and 91 high-precision radial velocities obtained with the HARPS-N spectrograph, using dynamical simulations we obtained a mass of 8.4 ± 1.6 M â for Kepler-19b. From the same data, assuming system coplanarity, we determined an orbital period of 28.7 days and a mass of 13.1 ± 2.7 M_â for Kepler-19c and discovered a Neptune-like planet with a mass of 20.3 ± 3.4 M_â on a 63-day orbit. By comparing dynamical simulations with non-interacting Keplerian orbits, we concluded that neglecting interactions between planets may lead to systematic errors that can hamper the precision in the orbital parameters when the data set spans several years. With a density of 4.32 ± 0.87 g cm^(â3) (0.78 ± 0.16 Ï_â) Kepler-19b belongs to the group of planets with a rocky core and a significant fraction of volatiles, in opposition to low-density planets characterized only by transit time variations and an increasing number of rocky planets with Earth-like density. Kepler-19 joins the small number of systems that reconcile transit timing variation and radial velocity measurements
An Ultra-short Period Rocky Super-Earth with a Secondary Eclipse and a Neptune-like Companion around K2-141
Ultra-short period (USP) planets are a class of low-mass planets with periods shorter than one day. Their origin is still unknown, with photo-evaporation of mini-Neptunes and in situ formation being the most credited hypotheses. Formation scenarios differ radically in the predicted composition of USP planets, and it is therefore extremely important to increase the still limited sample of USP planets with precise and accurate mass and density measurements. We report here the characterization of a USP planet with a period of 0.28 days around K2-141 (EPIC 246393474), and the validation of an outer planet with a period of 7.7 days in a grazing transit configuration. We derived the radii of the planets from the K2 light curve and used high-precision radial velocities gathered with the HARPS-N spectrograph for mass measurements. For K2-141b, we thus inferred a radius of 1.51 ± 0.05 R_â and a mass of 5.08 ± 0.41 M_â, consistent with a rocky composition and lack of a thick atmosphere. K2-141c is likely a Neptune-like planet, although due to the grazing transits and the non-detection in the RV data set, we were not able to put a strong constraint on its density. We also report the detection of secondary eclipses and phase curve variations for K2-141b. The phase variation can be modeled either by a planet with a geometric albedo of 0.30 ± 0.06 in the Kepler bandpass, or by thermal emission from the surface of the planet at ~3000 K. Only follow-up observations at longer wavelengths will allow us to distinguish between these two scenarios
TRADES: A new software to derive orbital parameters from observed transit times and radial velocities. Revisiting Kepler-11 and Kepler-9
Aims. With the purpose of determining the orbital parameters of exoplanetary
systems from observational data, we have developed a software, named TRADES
(TRAnsits and Dynamics of Exoplanetary Systems), to simultaneously fit observed
radial velocities and transit times data. Methods. We implemented a dynamical
simulator for N-body systems, which also fits the available data during the
orbital integration and determines the best combination of the orbital
parameters using grid search, minimization, genetic algorithms,
particle swarm optimization, and bootstrap analysis. Results. To validate
TRADES, we tested the code on a synthetic three-body system and on two real
systems discovered by the Kepler mission: Kepler-9 and Kepler-11. These systems
are good benchmarks to test multiple exoplanet systems showing transit time
variations (TTVs) due to the gravitational interaction among planets. We have
found that orbital parameters of Kepler-11 planets agree well with the values
proposed in the discovery paper and with a a recent work from the same authors.
We analyzed the first three quarters of Kepler-9 system and found parameters in
partial agreement with discovery paper. Analyzing transit times (T0s) covering
12 quarters of Kepler data, that we have found a new best-fit solution. This
solution outputs masses that are about 55% of the values proposed in the
discovery paper; this leads to a reduced semi-amplitude of the radial
velocities of about 12.80 m/s.Comment: 14 pages, 13 figures, 6 tables; accepted for publication in Astronomy
& Astrophysics, and corrected by the Language Edito
Data reduction, radial velocities and stellar parameters from spectra in the very low signal-to-noise domain
Large astronomical facilities usually provide data reduction pipeline designed to deliver ready-to-use scientific data, and too often as- tronomers are relying on this to avoid the most difficult part of an astronomer job Standard data reduction pipelines however are usu- ally designed and tested to have good performance on data with av- erage Signal to Noise Ratio (SNR) data, and the issues that are related with the reduction of data in the very low SNR domain are not taken int account properly. As a result, informations in data with low SNR are not optimally exploited.
During the last decade our group has collected thousands of spec- tra using the GIRAFFE spectrograph at Very Large Telescope (Chile) of the European Southern Observatory (ESO) to determine the ge- ometrical distance and dynamical state of several Galactic Globular Clusters but ultimately the analysis has been hampered by system- atics in data reduction, calibration and radial velocity measurements. Moreover these data has never been exploited to get other informa- tions like temperature and metallicity of stars, because considered too noisy for these kind of analyses.
In this thesis we focus our attention on data reduction and analysis of spectra with very low SNR.
The dataset we analyze in this thesis comprises 7250 spectra for 2771 stars of the Globular Cluster M 4 (NGC 6121) in the wavelength region 5145 â 5360AÌ obtained with GIRAFFE. Stars from the upper Red Giant Branch down to the Main Sequence have been observed in very different conditions, including nights close to full moon, and reaching SNR â 10 for many spectra in the dataset.
We will first review the basic steps of data reduction and spec- tral extraction, adapting techniques well tested in other field (like photometry) but still under-developed in spectroscopy. We improve the wavelength dispersion solution and the correction of radial veloc- ity shift between day-time calibrations and science observations by following a completely different approach with respect to the ESO pipeline. We then analyze deeply the best way to perform sky sub- traction and continuum normalization, the most important sources respectively of noise and systematics in radial velocity determination and chemical analysis of spectra. The huge number of spectra of our dataset requires an automatic but robust approach, which we do not fail to provide. We finally determine radial velocities for the stars in the sample with unprecedented precision with respect to previous works with similar data and we recover the same stellar atmosphere parameters of other studies performed on the same cluster but on brighter stars, with higher spectral resolution and wavelength range ten times larger than our data.
In the final chapter of the thesis we face a similar problem but from a completely different perspective. High resolution, high SNR data from the High Accuracy Radial Velocity Planet Searcher spectro- graph (HARPS) in La Silla (Chile) have been used to calibrate the at- mospheric stellar parameters as functions of the main characteristics of Cross-Correlation Functions, specifically built by including spec- tral lines with different sensitivity to stellar atmosphere parameters. These tools has been designed to be quick and to be easy to imple- ment in a instrument pipeline for a real-time determination, neverthe- less they provide accurate parameters even for lower SNR spectra
Atmospheric Parameters and Metallicities for 2191 stars in the Globular Cluster M4
We report new metallicities for stars of Galactic globular cluster M4 using
the largest number of stars ever observed at high spectral resolution in any
cluster. We analyzed 7250 spectra for 2771 cluster stars gathered with the VLT
FLAMES+GIRAFFE spectrograph at VLT. These medium resolution spectra cover by a
small wavelength range, and often have very low signal-to-noise ratios. We
attacked this dataset by reconsidering the whole method of abundance analysis
of large stellar samples from beginning to end. We developed a new algorithm
that automatically determines the atmospheric parameters of a star. Nearly all
data preparation steps for spectroscopic analyses are processed on the
syntheses, not the observed spectra. For 322 Red Giant Branch stars with we obtain a nearly constant metallicity, ( = 0.02). No difference in the metallicity at the level of
is observed between the two RGB sequences identified by
\cite{Monelli:2013us}. For 1869 Subgiant and Main Sequence Stars we
obtain ( = 0.09) after fixing the
microturbulent velocity. These values are consistent with previous studies that
have performed detailed analyses of brighter RGB stars at higher spectroscopic
resolution and wavelength coverage. It is not clear if the small mean
metallicity difference between brighter and fainter M4 members is real or is
the result of the low signal-to-noise characteristics of the fainter stars. The
strength of our approach is shown by recovering a metallicity close to a single
value for more than two thousand stars, using a dataset that is non-optimal for
atmospheric analyses. This technique is particularly suitable for noisy data
taken in difficult observing conditions.Comment: 17 pages, 20 figures, 3 tables. Accepted for publication in The
Astronomical Journa
An Ultra-short Period Rocky Super-Earth with a Secondary Eclipse and a Neptune-like Companion around K2-141
Ultra-short period (USP) planets are a class of low-mass planets with periods shorter than one day. Their origin is still unknown, with photo-evaporation of mini-Neptunes and in situ formation being the most credited hypotheses. Formation scenarios differ radically in the predicted composition of USP planets, and it is therefore extremely important to increase the still limited sample of USP planets with precise and accurate mass and density measurements. We report here the characterization of a USP planet with a period of 0.28 days around K2-141 (EPIC 246393474), and the validation of an outer planet with a period of 7.7 days in a grazing transit configuration. We derived the radii of the planets from the K2 light curve and used high-precision radial velocities gathered with the HARPS-N spectrograph for mass measurements. For K2-141b, we thus inferred a radius of 1.51 ± 0.05 R_â and a mass of 5.08 ± 0.41 M_â, consistent with a rocky composition and lack of a thick atmosphere. K2-141c is likely a Neptune-like planet, although due to the grazing transits and the non-detection in the RV data set, we were not able to put a strong constraint on its density. We also report the detection of secondary eclipses and phase curve variations for K2-141b. The phase variation can be modeled either by a planet with a geometric albedo of 0.30 ± 0.06 in the Kepler bandpass, or by thermal emission from the surface of the planet at ~3000 K. Only follow-up observations at longer wavelengths will allow us to distinguish between these two scenarios
A PSF-based approach to Kepler/K2data â III. Search for exoplanets and variable stars within the open cluster MÂ 67 (NGCÂ 2682)
In the third paper of this series we continue the exploitation of Kepler/K2
data in dense stellar fields using our PSF-based method. This work is focused
on a ~720-arcmin^2 region centred on the Solar-metallicity and Solar-age open
cluster M 67. We extracted light curves for all detectable sources in the
Kepler channels 13 and 14, adopting our technique based on the usage of a
high-angular-resolution input catalogue and target-neighbour subtraction. We
detrended light curves for systematic errors, and searched for variables and
exoplanets using several tools. We found 451 variables, of which 299 are new
detection. Three planetary candidates were detected by our pipeline in this
field. Raw and detrended light curves, catalogues, and K2 stacked images used
in this work will be released to the community.Comment: 14 pages, 9 figures (1 at low resolution), 3 tables. Accepted for
publication in MNRAS on August 24, 2016. Electronic materials are available
at http://groups.dfa.unipd.it/ESPG/Kepler-K2.htm
Clodronate in the management of different musculoskeletal conditions
INTRODUCTION: Clodronic acid is a non-nitrogen-containing bisphosphonate largely used from some decades in the prevention and treatment of postmenopausal and secondary osteoporosis. in addition to antiresorptive activity, clodronate has shown anti-inflammatory and analgesic properties, and modulatory effects on bone and cartilage metabolism. EVIDENCE ACQUISITION: A literature review has been conducted to characterize the mechanism of action of clodronate and to retrieve available evidence about the use of clodronate in primary and secondary osteoporosis, and its potential role in other musculoskeletal conditions and orthopedic surgery. EVIDENCE SYNTHESIS: The efficacy and safety of the available clodronate formulations (oral, intravenous and intramuscular) in the prevention and treatment of postmenopausal and secondary osteoporosis, including corticosteroid-induced osteoporosis and bone mass loss secondary to endocrine, gastrointestinal and neoplastic diseases, have been demonstrated in a variety of clinical trials. The analgesic, anti-inflammatory, bone- and chondro-modulating properties of clodronate have allowed to expand its use in other musculoskeletal conditions to those currently approved. clodronate has proven to be beneficial in the treatment of osteoarthritis of the knee and of the hand, in the management of complex regional pain syndrome, and in the peri- and postoperative phase in subjects undergoing arthroplasty. CONCLUSIONS: The analysis of the available literature has shown that clodronate has relevant musculoskeletal effects beyond the antiresorptive activity. Further research is needed to better position clodronate therapy in the management of these conditions and to define the optimal formulation and dose regimen in any of the tested new indications
JavaScript Dead Code Identification, Elimination, and Empirical Assessment
Web apps are built by using a combination of HTML, CSS, and JavaScript. While
building modern web apps, it is common practice to make use of third-party
libraries and frameworks, as to improve developers' productivity and code
quality. Alongside these benefits, the adoption of such libraries results in
the introduction of JavaScript dead code, i.e., code implementing unused
functionalities. The costs for downloading and parsing dead code can negatively
contribute to the loading time and resource usage of web apps. The goal of our
study is two-fold. First, we present Lacuna, an approach for automatically
detecting and eliminating JavaScript dead code from web apps. The proposed
approach supports both static and dynamic analyses, it is extensible and can be
applied to any JavaScript code base, without imposing constraints on the coding
style or on the use of specific JavaScript constructs. Secondly, by leveraging
Lacuna we conduct an experiment to empirically evaluate the run-time overhead
of JavaScript dead code in terms of energy consumption, performance, network
usage, and resource usage in the context of mobile web apps. We applied Lacuna
four times on 30 mobile web apps independently developed by third-party
developers, each time eliminating dead code according to a different
optimization level provided by Lacuna. Afterward, each different version of the
web app is executed on an Android device, while collecting measures to assess
the potential run-time overhead caused by dead code. Experimental results,
among others, highlight that the removal of JavaScript dead code has a positive
impact on the loading time of mobile web apps, while significantly reducing the
number of bytes transferred over the network
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