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Villanueva de la Cañada, Spain

Woitke P.,University of Vienna | Woitke P.,Astronomy Technology Center | Woitke P.,University of St. Andrews | Riaz B.,US Space Telescope Science Institute | And 17 more authors.
Astronomy and Astrophysics | Year: 2011

We present new continuum and line observations, along with modelling, of the faint (6-8) Myr old T Tauri star ET Cha belonging to the η Chamaeleontis cluster. We have acquired Herschel/PACS photometric fluxes at 70 μm and 160 μm, as well as a detection of the [OI] 63 μm fine-structure line in emission, and derived upper limits for some other far-IR OI, CII, CO and o-H2O lines. These observations were carried out in the frame of the open time key programme GASPS, where ET Cha was selected as one of the science demonstration phase targets. The Herschel data is complemented by new simultaneous ANDICAM B-K photometry, new HST/COS and HST/STIS UV-observations, a non-detection of CO J = 3 → 2 with APEX, re-analysis of a UCLES high-resolution optical spectrum showing forbidden emission lines like [OI] 6300Å, [SII] 6731Å and 6716Å, and [NII] 6583Å, and a compilation of existing broad-band photometric data. We used the thermo-chemical disk code ProDiMo and the Monte-Carlo radiative transfer code MCFOST to model the protoplanetary disk around ET Cha. The paper also introduces a number of physical improvements to the ProDiMo disk modelling code concerning the treatment of PAH ionisation balance and heating, the heating by exothermic chemical reactions, and several non-thermal pumping mechanisms for selected gas emission lines. By applying an evolutionary strategy to minimise the deviations between model predictions and observations, we find a variety of united gas and dust models that simultaneously fit all observed line and continuum fluxes about equally well. Based on these models we can determine the disk dustmass with confidence, Mdust â‰̂ (2-5) × 10-8 MâŠ(tm) whereas the total disk gas mass is found to be only little constrained, Mgas â‰̂ (5 × 10-5-3 × 10-3) MâŠ(tm). Both mass estimates are substantially lower than previously reported. In the models, the disk extends from 0.022 AU (just outside of the co-rotation radius) to only about 10 AU, remarkably small for single stars, whereas larger disks are found to be inconsistent with the CO J = 3 → 2 non-detection. The low velocity component of the [OI] 6300Å emission line is centred on the stellar systematic velocity, and is consistent with being emitted from the inner disk. The model is also consistent with the line flux of H2 v = 1 → 0 S(1) at 2.122 μm and with the [OI] 63 μm line as seen with Herschel/PACS. An additional high-velocity component of the [OI] 6300Å emission line, however, points to the existence of an additional jet/outflow of low velocity 40-65 km s-1 with mass loss rate â‰̂ 10 -9 M·/yr. In relation to our low estimations of the disk mass, such a mass loss rate suggests a disk lifetime of only ∼0.05-3 Myr, substantially shorter than the cluster age. If a generic gas/dust ratio of 100 was assumed, the disk lifetime would be even shorter, only ∼3000 yrs. The evolutionary state of this unusual protoplanetary disk is discussed. © 2011 ESO. Source

Maldonado J.,Autonomous University of Madrid | Mora A.,ESA ESAC Gaia SOC | Montesinos B.,CSIC - National Institute of Aerospace Technology | Villaver E.,Autonomous University of Madrid | Eiroa C.,Autonomous University of Madrid
Journal of Physics: Conference Series | Year: 2011

The question of the origin and evolution of planetary systems is of fundamental importance for astrophysics. Dusty debris discs are signatures of planetary systems and, therefore, constitute valuable tools to provide new light in our understanding of how planetary systems form and evolve. We present the first results of a spectroscopic programme of a sample of stars with debris discs. High-resolution echelle spectra are used to determine metallicities and abundances. Properties of stars with debris discs, are compared with those of stars hosting planets, as well as 'normal' stars. Source

Maldonado J.,National institute for astrophysics | Eiroa C.,Autonomous University of Madrid | Villaver E.,Autonomous University of Madrid | Montesinos B.,CSIC - National Institute of Aerospace Technology | Mora A.,ESA ESAC Gaia SOC
Astronomy and Astrophysics | Year: 2015

Context. Tentative correlations between the presence of dusty circumstellar debris discs and low-mass planets have recently been presented. In parallel, detailed chemical abundance studies have reported different trends between samples of planet and non-planet hosts. Whether these chemical differences are indeed related to the presence of planets is still strongly debated. Aims. We aim to test whether solar-type stars with debris discs show any chemical peculiarity that could be related to the planet formation process. Methods. We determine in a homogeneous way the metallicity, [Fe/H], and abundances of individual elements of a sample of 251 stars including stars with known debris discs, stars harbouring simultaneously debris discs and planets, stars hosting exclusively planets, and a comparison sample of stars without known discs or planets. High-resolution échelle spectra (R ∼ 57 000) from 2-3 m class telescopes are used. Our methodology includes the calculation of the fundamental stellar parameters (Teff, log? g, microturbulent velocity, and metallicity) by applying the iron ionisation and equilibrium conditions to several isolated Fe I and Fe II lines, as well as individual abundances of C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn. Results. No significant differences have been found in metallicity, individual abundances or abundance-condensation temperature trends between stars with debris discs and stars with neither debris nor planets. Stars with debris discs and planets have the same metallicity behaviour as stars hosting planets, and they also show a similar 〈[X/Fe]〉 - TC trend. Different behaviour in the 〈[X/Fe]? - TC trends is found between the samples of stars without planets and the samples of planet hosts. In particular, when considering only refractory elements, negative slopes are shown in cool giant planet hosts, whilst positive ones are shown in stars hosting low-mass planets. The statistical significance of the derived slopes is low, however, probably because of the wide range of stellar parameters of our samples. Stars hosting exclusively close-in giant planets behave in a different way, showing higher metallicities and positive 〈[X/Fe]〉 - TC slope. A search for correlations between the 〈[X/Fe]〉 - TC slopes and the stellar properties reveals a moderate but significant correlation with the stellar radius and a weak correlation with the stellar age, which remain even if Galactic chemical evolution effects are considered. No correlation between the 〈[X/Fe]〉 - TC slopes and the disc/planet properties are found. Conclusions. The fact that stars with debris discs and stars with low-mass planets do not show either metal enhancement or a different 〈[X/Fe]〉 - TC trend might indicate a correlation between the presence of debris discs and the presence of low-mass planets. We extend results from previous works based mainly on solar analogues with reported differences in the 〈[X/Fe]〉 - TC trends between planet hosts and non-hosts to a wider range of parameters. However, these differences tend to be present only when the star hosts a cool distant planet and not in stars hosting exclusively low-mass planets. The interpretation of these differences as a signature of planetary formation should be considered with caution since moderate correlations between the TC-slopes with the stellar radius and the stellar age are found, suggesting that an evolutionary effect might be at work. © ESO, 2015. Source

Podio L.,Institute Of Planetologie Et Dastrophysique Of Grenoble | Podio L.,Kapteyn Institute | Kamp I.,Kapteyn Institute | Flower D.,Durham University | And 9 more authors.
Astronomy and Astrophysics | Year: 2012

Context. Observations of the atomic and molecular line emission associated with jets and outflows emitted by young stellar objects provide sensitive diagnostics of the excitation conditions, and can be used to trace the various evolutionary stages they pass through as they evolve to become main sequence stars. Aims. To understand the relevance of atomic and molecular cooling in shocks, and how accretion and ejection efficiency evolves with the evolutionary state of the sources, we will study the far-infrared counterparts of bright optical jets associated with Class I and II sources in Taurus (T Tau, DG Tau A, DG Tau B, FS Tau A+B, and RW Aur). Methods. We have analysed Herschel/PACS observations of a number of atomic ([O i]63 μm, 145 μm, [C ii]158 μm) and molecular (high-J CO, H 2O, OH) lines, collected within the open time key project GASPS (PI: W. R. F. Dent). To constrain the origin of the detected lines we have compared the obtained FIR emission maps with the emission from optical-jets and millimetre-outflows, and the measured line fluxes and ratios with predictions from shock and disk models. Results. All of the targets are associated with extended emission in the atomic lines; in particular, the strong [O≠i] 63 μm≠emission is correlated with the direction of the optical jet/mm-outflow. The line ratios suggest that the atomic lines can be excited in fast dissociative J-shocks occurring along the jet. The molecular emission, on the contrary, originates from a compact region, that is spatially and spectrally unresolved, and lines from highly excited levels are detected (e.g., the o-H 2O 8 18-7 07 line, and the CO J = 36-35 line). Disk models are unable to explain the brightness of the observed lines (CO and H 2O line fluxes up to 10 -15-6 × 10 -16 W m -2). Slow C-or J-shocks with high pre-shock densities reproduce the observed H 2O and high-J CO lines; however, the disk and/or UV-heated outflow cavities may contribute to the observed emission. Conclusions. Similarly to Class 0 sources, the FIR emission associated with Class I and II jet-sources is likely to be shock-excited. While the cooling is dominated by CO and H 2O lines in Class 0 sources, [O i] becomes an important coolant as the source evolves and the environment is cleared. The cooling and mass loss rates estimated for Class II and I sources are one to four orders of magnitude lower than for Class 0 sources. This provides strong evidence to indicate that the outflow activity decreases as the source evolves. © 2012 ESO. Source

Eiroa C.,Autonomous University of Madrid | Marshall J.P.,Autonomous University of Madrid | Mora A.,ESA ESAC Gaia SOC | Krivov A.V.,Friedrich - Schiller University of Jena | And 25 more authors.
Astronomy and Astrophysics | Year: 2011

We present Herschel PACS 100 and 160 μm observations of the solar-type stars α Men, HD 88230 and HD 210277, which form part of the FGK stars sample of the Herschel open time key programme (OTKP) DUNES (DUst around NEarby S tars). Our observations show small infrared excesses at 160 μm for all three stars. HD 210277 also shows a small excess at 100 μm, while the 100 μm fluxes of α Men and HD 88230 agree with the stellar photospheric predictions. We attribute these infrared excesses to a new class of cold, faint debris discs. Both ? Men and HD 88230 are spatially resolved in the PACS 160 μm images, while HD 210277 is point-like at that wavelength. The projected linear sizes of the extended emission lie in the range from ∼115 to ≤250 AU. The estimated black body temperatures from the 100 and 160 ?m fluxes are ≈22 K, and the fractional luminosity of the cold dust is L dust/Lz.ast ∼ 10?6, close to the luminosity of the solar-system's Kuiper belt. These debris discs are the coldest and faintest discs discovered so far around mature stars, so they cannot be explained easily invoking "classical" debris disc models. © 2011 ESO. Source

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