Observations of field and cluster RR Lyræ with Spitzer. Towards high precision distances with Population II stellar tracers

Indexación: Scopus.We present our project to calibrate the RR Lyræ period-luminosity-metallicity relation using a sample of Galactic calibrators in the halo and globular clusters.https://www.epj-conferences.org/articles/epjconf/pdf/2017/21/epjconf_puls2017_07004.pd

On a New Theoretical Framework for RR Lyrae Stars. II. Mid-infrared Period-Luminosity-Metallicity Relations

We present new theoretical period-luminosity-metallicity (PLZ) relations for RR Lyrae stars (RRL) at Spitzer and WISE wavelengths. The PLZ relations were derived using nonlinear, time-dependent convective hydrodynamical models for a broad range in metal abundances (Z=0.0001 to 0.0198). In deriving the light curves, we tested two sets of atmospheric models (Brott & Hauschildt 2005, Castelli & Kurucz 2003) and found no significant difference between the resulting mean magnitudes. We also compare our theoretical relations to empirical relations derived from RRL in both the field and in the globular cluster M4. Our theoretical PLZ relations were combined with multi-wavelength observations to simultaneously fit the distance modulus, mu_0, and extinction, Av, of both the individual Galactic RRL and of the cluster M4. The results for the Galactic RRL are consistent with trigonometric parallax measurements from Gaia's first data release. For M4, we find a distance modulus of $\mu_0=11.257 \pm 0.035$ mag with $A_V = 1.45 \pm 0.12$ mag, which is consistent with measurements from other distance indicators. This analysis has shown that when considering a sample covering a range of iron abundances, the metallicity spread introduces a dispersion in the PL relation on the order of 0.13 mag. However, if this metallicity component is accounted for in a PLZ relation, the dispersion is reduced to ~0.02 mag at MIR wavelengths

Data analysis and simulations of VIRTIS venus spectra

VIRTIS, a bordo di Venus Express, è uno spettrometro in grado di operare da 0.25 a 5 µm. Nel periodo 2006-2011 ha ricavato un'enorme mole di dati ma a tutt'oggi le osservazioni al lembo sono poco utilizzate per lo studio delle nubi e delle hazes, specialmente di notte. Gli spettri al lembo a quote mesosferiche sono dominati dalla radianza proveniente dalle nubi e scatterata in direzione dello strumento dalle hazes. L'interpretazione degli spettri al lembo non può quindi prescindere dalla caratterizzazione dell'intera colonna atmosferica. L'obiettivo della tesi è di effettuare un’analisi statistica sulle osservazioni al nadir e proporre una metodologia per ricavare una caratterizzazione delle hazes combinando osservazioni al nadir e al lembo. La caratterizzazione delle nubi è avvenuta su un campione di oltre 3700 osservazioni al nadir. È stato creato un ampio dataset di spettri sintetici modificando, in un modello iniziale, vari parametri di nube quali composizione chimica, numero e dimensione delle particelle. Un processo di fit è stato applicato alle osservazioni per stabilire quale modello potesse descrivere gli spettri osservati. Si è poi effettuata una analisi statistica sui risultati del campione. Si è ricavata una concentrazione di acido solforico molto elevata nelle nubi basse, pari al 96% in massa, che si discosta dal valore generalmente utilizzato del 75%. Si sono poi integrati i risultati al nadir con uno studio mirato su poche osservazioni al lembo, selezionate in modo da intercettare nel punto di tangenza la colonna atmosferica osservata al nadir, per ricavare informazioni sulle hazes. I risultati di un modello Monte Carlo indicano che il numero e le dimensioni delle particelle previste dal modello base devono essere ridotte in maniera significativa. In particolare si osserva un abbassamento della quota massima delle hazes rispetto ad osservazioni diurne

Retrieval of Venus' cloud parameters from VIRTIS nightside spectra in the latitude band 25\ub0-55\ub0N

Two years of data from the M-channel of the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS), on board the European Space Agency mission Venus Express operating around the planet Venus, are analysed. Nocturnal data from a nadir viewpoint in the latitude band 25\ub0N-55\ub0N are selected for their configuration advantages and maximisation of the scene homogeneity. A reference model, and radiance spectrum, is defined based on average accepted values of the Venus main atmospheric and cloud parameters found in the literature. Extensive radiative transfer simulations are performed to provide a synthetic database of more than 10 000 VIRTIS radiances representing the natural variability of the system parameters (atmospheric temperature profile, cloud H2OH2SO4 solution concentration and vertical distribution, particle size distribution density and modal radius). A simulated-observed fitting algorithm of spectral radiances in window channels, based on a weighting procedure accounting for the latitudinal observed radiance variations, is used to derive the best atmosphere-cloud configuration for each observation.Results show that the reference Venus model does not adequately reproduce the observed VIRTIS spectra. In particular, the model accounting for a constant sulphuric acid concentration along the vertical extent of the clouds is never selected as a best fit. The 75%/96% and 84%/96% concentrations (the first values refer to the upper cloud layers and the second values to the lower ones) are the most commonly retrieved models representing more than 85% of the retrieved cases for any latitudinal band considered. It is shown that the assumption of stratified concentration of aqueous sulphuric acid allows to adequately fit the observed radiance, in particular the peak at 1.74 \u3bcm and around 4 \u3bcm.The analysis of the results concerning the microphysics suggests larger radii for the upper cloud layers in conjunction with a large reduction of their number density with respect to the reference standard. Considerable variation of the particle concentration in the Venus' atmosphere is retrieved for altitudes between 60 and 70 km. The retrieved models also suggest that lower cloud layers have smaller particle radii and larger number density than expected from the reference model. Latitudinal variations of microphysical and chemical parameters are also analysed

WINERED as a Stepping Stone for the Cosmic Distance Scale

We present the Oscillating Stars with wIneRed near-Infrared Spectroscopy (OSIRIS) project, aimed at deriving accurate chemical abundances of primary distance indicators covering a wide age range from young Classical Cepheids to intermediate-age Anomalous Cepheids and Miras, old RR Lyrae stars, and Type-II Cepheids. High-resolution near-infrared spectra will be collected with WINERED, a Japanese instrument with the highest available throughput in the range 0.9-1.35 \u3bcm. We summarize here the characteristics of the instrument, the data acquisition and reduction, and preliminary results

The use of Far InfraRed high spectral resolution data for cloud identification and classification

An innovative methodology for Cloud Identification and Classification (CIC) is presented. The CIC algorithm is a machine-learning technique, based on Principal Component Analysis, performing binary classification for clear/cloudy scene detection and classification (i.e. liquid/ice cloud phase). Firstly, CIC is tested on a wide synthetic dataset of high spectral resolution radiances in the far and mid infrared (FIR and MIR) part of the spectrum simulating measurements from the ESA Earth Explorer Fast Track 9 competing mission FORUM (Far Infrared Outgoing Radiation Understanding and Monitoring) that is currently (2018/19) undergoing the industrial and scientific Phase-A studies. Simulated spectra represent observations covering many diverse climatic areas, ranging from the tropical to polar regions. Secondly, CIC is applied to a small dataset of high spectral resolution radiance observations taken from aircraft on the 13th March 2015 off the north-east coast of Scotland, UK, during the Cirrus Coupled Cloud-Radiation Experiment (CIRCCREX). Measurements in the FIR are made by the Tropospheric Airborne Fourier Transform Spectrometer, TAFTS, (Canas et al. 1997) and in the MIR by the Airborne Research Interferometer Evaluation System, ARIES, (Wilson et al. 1999). The main result demonstrates the high information content of spectral radiance in the FIR region of the electromagnetic spectrum which is exploited here to improve the detection performance in identifying cloudy scenes, specifically thin cirrus clouds

Observations of field and cluster RR Lyræ with Spitzer. Towards high precision distances with Population II stellar tracers

We present our project to calibrate the RR Lyræ period-luminosity-metallicity relation using a sample of Galactic calibrators in the halo and globular clusters

Characterization of the Far Infrared Properties and Radiative Forcing of Antarctic Ice and Water Clouds Exploiting the Spectrometer-LiDAR Synergy

Optical and microphysical cloud properties are retrieved from measurements acquired in 2013 and 2014 at the Concordia base station in the Antarctic Plateau. Two sensors are used synergistically: a Fourier transform spectroradiometer named REFIR-PAD (Radiation Explorer in Far Infrared-Prototype for Applications and Developments) and a backscattering-depolarization LiDAR. First, in order to identify the cloudy scenes and assess the cloud thermodynamic phase, the REFIR-PAD spectral radiances are ingested by a machine learning algorithm called Cloud Identification and Classification (CIC). For each of the identified cloudy scenes, the nearest (in time) LiDAR backscattering profile is processed by the Polar Threshold (PT) algorithm that allows derivation of the cloud top and bottom heights. Subsequently, using the CIC and PT results as external constraints, the Simultaneous Atmospheric and Clouds Retrieval (SACR) code is applied to the REFIR-PAD spectral radiances. SACR simultaneously retrieves cloud optical depth and effective dimensions and atmospheric vertical profiles of water vapor and temperature. The analysis determines an average effective diameter of 28 \u3bcm with an optical depth of 0.76 for the ice clouds. Water clouds are only detected during the austral Summer, and the retrieved properties provide an average droplet diameter of 9 \u3bcm and average optical depth equal to four. The estimated retrieval error is about 1% for the ice crystal/droplet size and 2% for the cloud optical depth. The sensitivity of the retrieved parameters to the assumed crystal shape is also assessed. New parametrizations of the optical depth and the longwave downwelling forcing for Antarctic ice and water clouds, as a function of the ice/liquid water path, are presented. The longwave downwelling flux, computed 2 from the top of the atmosphere to the surface, ranges between 70 and 220 W/m . The estimated cloud longwave forcing at the surface is (31 \ub1 7) W/m2 and (29 \ub1 6) W/m2 for ice clouds and (64 \ub1 12) and (62 \ub1 11) W/m2 for water clouds, in 2013 and 2014, respectively. The total average cloud forcing 2 for the two years investigated is (46 \ub1 9) W/m2

Rubin Observatory LSST Transients and Variable Stars Roadmap

International audienceThe Vera C. Rubin Legacy Survey of Space and Time (LSST) holds the potential to revolutionize time domain astrophysics, reaching completely unexplored areas of the Universe and mapping variability time scales from minutes to a decade. To prepare to maximize the potential of the Rubin LSST data for the exploration of the transient and variable Universe, one of the four pillars of Rubin LSST science, the Transient and Variable Stars Science Collaboration, one of the eight Rubin LSST Science Collaborations, has identified research areas of interest and requirements, and paths to enable them. While our roadmap is ever-evolving, this document represents a snapshot of our plans and preparatory work in the final years and months leading up to the survey’s first light