U. Heiter: Comparative Modelling of the Spectra of Cool Giants
Talk: Stellar parameters determined by analysis of high-resolution spectra have great potential but are suffering from systematic uncertainties due to inadequate physics of model spectra and different approaches used for the analysis methods. We present a comparison of a wide variety of model codes attempting to analyse the spectra of cool giants. These are the results of an experiment conducted for a GREAT-ESF workshop held in August 2010. Participants were provided with a specific set of spectroscopic and photometric data for four unidentified giant stars. We discuss their findings, possible causes for the apparent differences and possible strategies for abundance analyses of cool giant stars.
P. Hauschildt: The PHOENIX Model Atmosphere Package
Talk: I will discuss some of the features of and results obtained with the PHOENIX general-purpose model atmosphere code. This will include both cool model atmospheres with PHOENIX/1D, in particular models which include non-equilibrium dust formation for L and M dwarfs and an overview over the PHOENIX/3D mode to compute spectra and spectro-images for 3D atmospheres.
M. Bergemann: Non-LTE Line Formation of Fe-peak Elements and Application to Large-scale Stellar Surveys
Talk: Chemical composition of late-type (FGK) stars provides major observational constraints to the evolution of the Galaxy. Still, calculation of element abundances from observed stellar spectra is a challenging task due to the difficulties of incorporating various physical aspects of radiative transfer theory, such as non-local thermodynamic equilibrium (NLTE), into spectrum analysis codes. The codes used for automated analysis of large sets of high- and low-resolution spectra obtained in various Galactic star surveys (i.e. SDSS/SEGUE, HERES) rely on a simplifying LTE assumption. Application of existing NLTE-capable codes to such surveys is computationally prohibitive; NLTE studies are often limited to a handful of stars.
Still, significant improvement over standard LTE analyses can be made by utilizing so-called NLTE abundance corrections. I will describe our project aimed at large-scale calculations of NLTE corrections for various chemical elements. I will focus on transition metals with 22 < Z < 28 and show some results for a grid of stellar parameters including very metal-poor dwarfs and giants. Particular attention will be given to iron, which is a proxy of stellar metallicity and is commonly used to derive effective temperature and gravity. The Fe model atom has been updated to include quantum-mechanical photoionisation cross-sections and new theoretically predicted energy levels and transitions. I will demonstrate that these NLTE abundance corrections can be easily implemented in other spectroscopic studies, such as follow-up spectroscopy for Gaia targets, enabling accurate derivation of element abundances from lines of various excitation potentials and strengths.
R. Collet: The StaggerGrid Project: a Grid of 3D Model Atmospheres for High-precision Spectroscopy
Talk: I will present the StaggerGrid project, a collaborative effort for the construction of a comprehensive grid of time-dependent, three-dimensional, hydrodynamic model atmospheres of solar- and late-type stars with different effective temperatures, surface gravities, and chemical compositions. The three-dimensional model atmospheres are being generated using the MPI-parallel radiation-hydrodynamic Stagger-Code and realistic input micro-physics, including a state-of-the-art equation-of-state and up-to-date opacity data. In this contribution, I will report about the progress of the StaggerGrid project and discuss the application of three-dimensional model atmospheres to spectral line-formation calculations and high-precision spectroscopy. I will illustrate the main effects of three-dimensional model atmospheres on the predicted strengths, wavelength-shifts, and shapes of spectral lines, highlighting the differences with respect to calculations based on classical, one-dimensional, hydrostatic models. I will focus in particular on the application of StaggerGrid models to the analysis and interpretation of data from the Gaia Radial Velocity Spectrometer (RVS) for the determination of accurate stellar parameters, elemental abundances, and radial velocities.
T. Aparicio Villegas: Stellar Physics with the ALHAMBRA Photometric System
Talk: The ALHAMBRA photometric system (Aparicio Villegas et al. 2010) was specifically designed to perform a tomography of the Universe in some selected areas (Moles et al. 2008). Although mainly designed for extragalactic purposes, it's 20 contiguous, equal-width, medium-band photometric system in the optical wavelength range, shows a great capacity for stellar classification. In this contribution we proposed a stellar classification and physical parameter estimation based on the 18 independent reddening-free Q values derived from the ALHAMBRA photometry. Based on the theoretical spectral library BaSeL 2.2 (Lejeuneet al. 1998) and applied to 288 stars from the Next Generation spectral Library (NGSL, Gregg et al. 2004), we discuss the reliability of the method and its dependence on the extinction law used.
A. Quirrenbach: Spectroscopic Instrumentation in the GAIA Era
Talk: I will discuss some concepts and plans for massively parallel spectroscopic instruments, which can provide huge numbers of stellar spectra. It is obviously important to match the properties and capabilities of such instruments to the requirements of quantitative modeling efforts.
B. Plez: Model Atmospheres and Spectra for Cool Stars: Comparisons of MARCS and Other Brands of Models
Talk: I will detail similarities and differences between codes used for the modeling of cool star atmospheres. I will compare models and spectra, and discuss both SEDs and spectra in the RVS domain.
R. Sordo: Libraries of Synthetic Spectra in the Gaia Mission
Talk: Gaia will observe up to a billion stellar sources. Automated algorithms are under developement to derive the atmospheric parameters of all observed spectra, from low resolution optical spectra alone or in synergy with high resolution spectra in the Calcium IR triplet region. To do so, a large database of state-of-the-art stellar libraries have been produced and given to the Gaia community, computed using different codes optimized for specific purposes. The choice to use different spectral codes in different regions of the HR diagram raises the problem of the coherence of the different spectra, specifically in the transition zones. I will present comparison between the libraries from the point of view of the spectra simulations used to train the Gaia algorithms. I will also present the implementation of these libraries into a Simple Stellar Population code.
A. Recio-Blanco: Automatic Stellar Spectra Parametrisation in the IR Ca II Triplet Region
Talk: The presentation will show what astrophysical information can be retrieved from spectra observed around the IR Ca II triplet, as the Gaia/RVS ones. We investigate the performances of two methods of automated estimation of the values of stellar parameters, based on very different mathematical approaches, allowing us to describe the main problems encountered in this spectral region.
G. Pace: The Metallicity Scale of Dwarf and Giant Stars
Talk: Differences between metallicity measurements of dwarfs and giants belonging to the same open clusters, as envisaged, for instance, by Santos et al (2009), would have tremendous implications, among the other things, on the planet formation theory and on the stellar populations in the Milky Way. They also have a tremendous importance on their own right, as they would point to possible problems in atmosphere modelling of evolved stars. However, they have not yet been evaluated based on solid and conclusive data. We analyse and review literature and available archive data, using different models and line lists, in order to investigate the extent, the origin, and the nature of the aforementioned differences.
N. Gorlova:Abundance Analysis of Post-AGB Stars
Talk: We describe our analysis of the spectra of post-AGB stars (SpTs F-K, luminosity types I-II, [Fe/H]=-2.0..+0.5), obtained with the echelle spectrograph HERMES on the 1.2m Mercator telescope. We obtain atmospheric parameters and atomic abundances using hydrogen line profiles and the equivalent width (EW) of weak metal lines. Our oscillator strengths and solar abundances for the majority of elements have been consistently adjusted to match the observed solar spectrum. The EW analysis is performed with Atlas9 models using both R. Kurucz's WIDTH9 and C. Sneden's MOOG radiative transfer codes. The outlined procedure can be employed for spectroscopic analyses of high-resolution spectra in the ground-based follow-up programs of Gaia.
D. Montes: High-resolution Spectroscopy of FGK Nearby Stars: Stellar Parameters and Chemical Tagging
Talk: During the last years our group has undertaken several high resolution spectroscopic surveys of nearby FGK stars. A large number of stars have already been observed and we have already determined spectral types, rotational velocities as well as radial velocities, Lithium abundance and several chromospheric activity indicators. We are working now on an homogeneous determination of the fundamental stellar parameters (Teff, log g, metallicity, [Fe/H], and microturbulent velocity) and differential abundance analysis (chemical tagging) of all these stars. All this information will allow us to ascribe these stars to moving groups and associations of different ages, and could lead to a better understanding of the star formation history in the solar neighborhood discerning between field-like stars (associated with dynamical resonances (bar) or spiral structure) and young coeval stars (debris of star-forming aggregates in the disk). In addition, all this work and methods will be very useful for preparing for the huge amount of data that will be available with Gaia.
N. Przybilla: A Comprehensive Test of Common Hydrostatic LTE and non-LTE Model Atmosphere/Line-formation Codes for Quantitative Spectroscopy of Early-type Dwarfs and Giants
Talk: It is generally accepted that the atmospheres of cool/luke stars of spectral types A and later are described well by LTE model atmospheres, while the O-type stars require a detailed treatment of non-LTE effects. Exemplary for the two different approaches, model atmosphere structures, SEDs and synthetic spectra computed with ATLAS9/SYNTHE and TLUSTY/SYNSPEC are compared and verified for their ability to reproduce observed spectra in the transition region 15000< Teff < 35000 K. Strengths and weaknesses of both approaches are identified. Recommendations are given how to improve the models in order to derive unbiased stellar parameters and chemical abundances for future applications, with special emphasis on Gaia science.
N. Walton: VAMDC: The Virtual Atomic and Molecular Data Centre
Talk: This talk will describe the EU FP7 research infrastructure : VAMDC: The Virtual Atomic and Molecular (A+M) Data Centre (see http://www.vamdc.eu). This project is building an open framework to enable seamless access to an inclusive range of A+M data - with the first public portal due to be released for use in July 2011. Key data providers participating in VAMDC include amongst others those responsible for: VALD, BASECOL, HITRAN, CHIANTI, CDMS. I will describe how use of VAMDC offers advantages in obtaining complete and current fundamental data (e.g. atomic data as input to spectral synthesis analysis systems) which in turn improves the accuracy of detailed abundance analyses of stars to be observed in the large spectroscopic surveys to be carried out by, or in support of, Gaia.
T. Dall: Modeling Rotating Geometrically Distorted Stars with Inhomogeneous Surface Features
Talk: Simple spherical, non-rotating stellar models are inadequate when describing real stars in the limit of very fast rotation: Both the observable spectrum and the geometrical shape of the star deviate strongly from simple models. We attempt to approach the problem of modeling geometrically distorted, rapidly rotating stars from a new angle: By constructing distorted geometrical models and integrating standard stellar models with varying temperature, gravity, and abundances, over the entire surface, we attempt a semi-empirical approach to modeling. We will present our models and the methodology, and present simple examples of applications.
F. Nieva: High-precision Stellar Parameter and Abundance Determinations of OB Dwarfs and BA Supergiants
Talk: We present a self-consistent spectrum analysis technique employing non-LTE line formation, which allows precise atmospheric parameters and chemical abundances of massive stars to be derived: 1sigma-uncertainties as low as ~1% in effective temperature, ~0.05-0.10 dex in surface gravity and ~20% in abundances can be achieved. Special emphasis is given to the minimization of the main sources of systematic errors in the quantitative spectral analysis. Examples of applications are discussed for OB-type stars near the main sequence and their evolved progeny, the BA-type supergiants, covering masses of ~6 to 25 Msun and a range in effective temperature from ~8000 to 35000 K.
We show results for a sample of 30 stars analyzed with a semi-automatic fitting routine, achieving high accuracy and precision at the same time. We are making efforts to implement all critical steps that are handled interactively in our current approach into an fully automated line-fitting routine that will allow larger samples of stars to be analyzed at the same precision than our control sample.
R. Hudec: Tests of Simulated Gaia Bp/Rp Spectra with LDS (Low Dispersion Spectroscopy) Photographic Sky Surveys
Talk: The LDS (Low Dispersion Spectroscopy) performed in various extended sky surveys with optical telescopes with objective prisma and photographic plates offers an interesting possibility to test simulated low-dispersion spectra for Gaia Bp/Rp photometers and compare them with real data, especially for objects with strong emission lines. I will give a review of astrophysics with LDS performed in the past, as well as an overview of existing extended sky surveys (with photographic plates) providing LDS data. Some of them give almost complete coverage of either the northern or southern hemisphere (e.g. the Northern and Southern Mt Wilson ~V Michigan H-alpha surveys or the German La Paz Bolivia Southern Spectral Sky Survey). I will show examples of these data and will discuss a comparison of existing LDS plate data with expected/simulated Bp/Rp data. I will show examples of real data for objects with very strong and wide emission, confirming that such emissions will be detectable with Bp/Rp. I will also discuss the importance of Gaia Rp/Bp low-dispersion spectroscopy for astrophysical studies.
R. Blomme: Hot Stars in the Gaia-ESO Public Survey
Talk: The Gaia-ESO Public Survey will produce spectra of about 200,000 stars, using the VLT FLAMES instrument. This includes hot, massive stars in a number of selected clusters. I describe the on-going cluster selection as well as the work package responsible for analyzing the hot-star spectra.
J. Groh: Modeling the Wind and Photosphere of Massive Stars with the Radiative Transfer Code CMFGEN
Talk: Massive stars are extremely luminous and characterized by mass loss through radiation-driven stellar winds. The radiation emitted at the stellar surface may interact with the wind, making the analysis of the emerging spectrum a very challenging task. In addition to the luminosity, effective temperature, and surface gravity, several other stellar parameters impact the spectral morphology of these objects, remarkably the mass-loss rate and the wind terminal velocity. That is generally the case for OB supergiants, Luminous Blue Variables, and WR stars. CMFGEN (Hillier and Miller 1998) comprises the state-of-the-art in non-LTE radiative transfer and has been successfully applied to the above classes of objects over the last decade. The code assumes spherical symmetry, stationary outflow, and both photospheric and wind lines can be treated in non-LTE. Full line blanketing due to hundreds of thousands of spectral lines is included, as well as wind clumping. In this talk I will discuss the assumptions behind CMFGEN and present examples of models and spectroscopic analyses that can be done with CMFGEN.
S. Simon-Diaz: The IACOB Project (WP3: Quantitative Spectroscopic Analysis of Galactic OB stars)
Talk: The IACOB spectroscopic survey of Northern Galactic OB stars is a long-term observational project aimed at building a multi-epoch, homogeneous spectroscopic database of high-resolution, high signal-to-noise ratio spectra of Galactic bright OB stars. At present, the database comprises more than 1000 spectra of about 200 stars with spectral types earlier than B2.
Associated to this unique spectroscopic dataset there are several working packages aimed at its scientific exploitation. Within the frame of WP3: Quantitative Spectroscopic Analysis, we may cite the development of a very powerful tool for the automatic analysis of optical spectra of OB stars based on a large grid of synthetic spectra computed with the FASTWIND stellar atmopshere code, and a line-profile fitting technique.
The tool, which provides a fast and objective way to determine the stellar parameters and the associated uncertainties of large samples of OB-type stars within a reasonable computational time, is not only being applied to Galactic stars, but also to other massive stars in external galaxies (for example, 30Dor/LMC - from the VLT-Tarantula FLAMES survey -, and IC1613).
In this talk I will present (1) the main characteristics of the FASTWIND grid and the automatic tool, and (2) some important outcomes from the IACOB project, with special emphasis in those results which will imply a mutual benefit between the IACOB and GAIA scientific projects (concerning Galactic Massive Stars).
A. de Koter: The VLT-FLAMES Tarantula Survey
Talk: The VLT-FLAMES Tarantula Survey (VFTS) is an ESO Large Programme that has obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud (LMC). Detailed spectral classification and quantitative analysis of the O- and B-type stars in the VFTS sample, paying particular attention to the effects of rotational mixing and binarity, will be carried out in the next years to address fundamental questions in both stellar and cluster evolution. Here we present our modeling strategy for the O stars, employing the latest version of FASTWIND and Genetic Algorithm based fitting techniques. Though these results are based on optical spectra, first results on applying this method to infrared spectra will be presented as well.
Y. Chen: XSL: The X-Shooter Stellar Library
Talk: We are building a new spectral library with the X-Shooter instrument on VLT telescope: XSL, the X-Shooter Spectral Library. We present here our progress in building XSL. XSL covers the wavelength range from the near-UV to the near-IR with a resolution of R~10000. At the present time we have collected spectra for nearly 400 stars. An important feature of XSL is that we have already collected spectra of more than 100 Asymptotic Giant Branch stars in the Galaxy and the Magellanic Clouds and of more than 100 hot stars in the disk of the Galaxy. I will discuss the current status and future plans for XSL.
S. Van Eck: A Grid of MARCS Model Atmospheres for S Stars
Poster: S-type stars are late-type giants whose atmosphere is enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing AGB. A large grid of S-star model atmospheres has been computed covering the range 2700 <= Teff (K) <= 4000 with 0.5 <= C/O <= 0.99. ZrO and TiO band strength indices as well as VJHKL photometry are needed to disentangle Teff, C/O and [s/Fe]. A "best-model finding tool'' was developed using a set of well-chosen indices and checked against photometry as well as low- and high-resolution spectroscopy. It is found that applying M-star model atmospheres (i.e., with a solar C/O ratio) to S stars can lead to errors on Teff up to 400 K. We constrain the parameter space occupied by S stars of the vast sample of Henize stars in terms of Teff, [C/O] and [s/Fe].
T. Morel: Using CoRoT and Kepler Targets as Benchmarks for Spectroscopic Analyses of Cool Stars
Poster: The stellar surface gravity is one of the most difficult quantities to estimate from spectroscopic data, with errors of the order of 0.2-0.3 dex being typical. In contrast, the values derived from studying the pulsation properties of the CoRoT and Kepler targets are thought to be largely model independent and accurate to within 0.05 dex. Performing a spectroscopic analysis of these stars hence offers the opportunity to assess the reliability of the classical gravity diagnostics used in cool stars, such as the ionization balance of iron or fitting strong pressure-sensitive lines.
This issue is discussed for solar-like and red giant stars observed by the CoRoT and Kepler missions. A hybrid method whereby the spectroscopic analysis is carried out fixing logg to the much more precise seismic value can be used to substantially narrow down the errors in the other parameters and ultimately abundances. This is illustrated by the results of an abundance study of a sample of red giants observed in the seismo fields of the CoRoT satellite.
J. Maldonado: Spectroscopic Properties of Stars with Circumstellar Debris Discs
Poster: 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.
In this contribution we present the first results of an spectroscopic programme of a sample of stars with debris discs. High-resolution echelle spectra is used to determine metallicities, abundances, age (via lithium abundances, chromospheric activity) and kinematics (moving group membership).
A. Chiavassa: 3-D Hydrodynamical Model Atmospheres: A Tool to Correct Radial Velocities and Parallaxes
Poster: I will present time-dependent, three-dimensional, hydrodynamical simulations of the whole convective envelope of massive evolved stars carried out with the radiation-hydrodynamic code CO5BOLD. Big efforts have been done to include a better treatment of opacities as well as an extension of the stellar parameters with higher numerical resolution. The final aim is the construction of a comprehensive grid of 3D global hydrodynamical simulations. I will explore the impact of the granulation pattern in the Gaia-G band on high resolution spectroscopy and intensity maps. I will focus in particular on the application to the radial velocity and parallaxes corrections to Gaia measurements.
L. Mahy: Quantitative Study of the O Stars in NGC 2244
Poster: NGC 2244 located in the Rosette Nebula is a young open cluster composed of seven O-type stars. A first paper focused on the multiplicity of these stars, revealed only one binary system out of the six studied stars. The binary fraction of this cluster (~17 %) has nothing in comparison to the average fraction measured on the nearby clusters (~44%). In order to better constrain this discrepancy, an analysis based on the determination of the stellar and wind parameters of these stars with the CMFGEN atmosphere code was performed. The main results confirm that all the stars have an age between 1 and 5 Myr, and that the N surface abundance appears to be consistent with the evolutionary models for a population of stars of the same age. Moreover, this investigation exhibits the existence of dynamical interactions inside this young open cluster sufficiently strong to eject the hottest component from its centre.
F. A. Stap: Quantitative IR Spectroscopy of Massive Stars
Poster: Interest for NIR spectroscopy of massive stars has been dramatically increasing over the last decade. Because it allows one to observe objects inaccessible at optical wavelengths due to absorption, the IR domain offers a privileged window to study highly extinguished objects. Yet, detailed calibrations of the massive star properties at NIR wavelengths are still missing. In this context, we have acquired high resolution spectroscopy of several nearby massive stars using VLT/CRIRES, focusing on spectral lines of interest in the J, H, K and L bands. In this poster, we present the earliest results of our quantitative spectroscopic analysis. Using the unique combination of a genetic algorithm approach with the state-of-the-art non-LTE atmosphere model FASTWIND, we compare the stellar and wind properties as derived from the optical and the NIR regime. Future work and implications for NIR spectroscopy of massive stars are briefly discussed.
J. Zhang: Stellar Parameter Estimation for the LAMOST Survey
Poster: The LAMOST survey will observe millions of stars in the coming years to explore the origin, structure and evolution of the Milk Way. In order to derive the effective temperature, surface gravity, and metallicity from LAMOST spectra, our pipeline employed different synthetic stellar spectra libraries, which were calculated based on the newest MAFAGS atmospheric models and Kurucz 2003 atmospheric models. The validations with various tests on large empirical stellar spectral data sets with precisely calibrated parameters are presented in the paper. We will illustrate results from the spectra obtained during the LAMOST commissioning stage as well.
P. Koubsky: Gaia RVS Spectroscopy of Be Stars
Poster: It is expected that the RVS spectrograph on board the Gaia satellite will observe about 100,000 Be stars - early type non giant stars with emission lines - in the range 8470 - 8740 A. The RVS spectra of Be stars can show emission in Paschen lines (P16 - P13), in Ca II and N I lines with reasonable resolution (20,000). However, the H alpha line which is the primary indicator of disks or envelopes in Be stars will be covered with a very low resolution by the Gaia Bp/Rp instrument. The aim of the long-term ground-based project is to cover the H alpha and Paschen Gaia regions for many Be stars and check if a relation between properties of H alpha, Paschen and Ca II lines in Be stars could be established. No systematic study of such kind can be found in the literature.
P. Neyskens: Abundance Patterns in S-type AGB Stars to Set Constraints on Nucleosynthesis and Stellar Evolution Models
Poster: During their evolution on the AGB, S-type stars are the first objects to experience s-process nucleosynthesis and third dredge-ups, and therefore to exhibit s-process signatures in their atmospheres. Precise abundance determinations in S stars are of the utmost importance to set constraints on nucleosynthesis and stellar evolution models.
We present precise abundances of key s-process elements derived by using dedicated S-star model atmospheres. A special interest is paid to technetium (Tc), an element with no stable isotope. The detection of Tc is considered as the best signature that the S star is effectively populating the thermally-pulsing AGB phase of evolution.
The derived Tc/Zr abundances are compared, as a function of the derived [Zr/Fe] overabundances, with AGB stellar model predictions. The [Zr/Fe] overabundances are in good agreement with the model predictions, while the Tc/Zr abundances are slightly overpredicted. This discrepancy can help to set better constraints on nucleosynthesis and stellar evolution models of AGB stars.
A. Jorissen: Chemically Tagging the Hyades Stream: Does it Partly Originate from the Hyades Cluster?
Poster: The Hyades stream has long been thought to be a dispersed vestige of the Hyades cluster. However, recent analyses of the parallax distribution, of the mass function, and of the action-space distribution of stream stars have shown it to be rather composed of orbits trapped at a resonance of a density disturbance. This resonant scenario should leave a clearly different signature in the element abundances of stream stars than the dispersed cluster scenario, since the Hyades cluster is chemically homogeneous. Here, we study the metallicity as well as the element abundances of Li, Na, Mg, Fe, Zr, Ba, La, Ce, Nd, and Eu for a random sample of stars belonging to the Hyades stream, and compare them with those of stars from the Hyades cluster. From this analysis: (i) we independently confirm that the Hyades stream cannot be solely composed of stars originating in the Hyades cluster; (ii) we show that some stars from the Hyades stream nevertheless have abundances compatible with an origin in the cluster; (iii) we emphasize that the use of Li as a chemical tag of the cluster origin of main-sequence stars is very efficient in the range 5500 - 6200 K, since the Li sequence in the Hyades cluster is very tight; (iv) we show that, while this evaporated population has a metallicity excess of ~0.2 dex w.r.t. the local thin disk population, identical to that of the Hyades cluster, the remainder of the Hyades stream population has still a metallicity excess of ~0.06 to 0.15 dex, consistent with an origin in the inner Galaxy; (v) we show that the Hyades stream can be interpreted as an inner 4:1 resonance of the spiral pattern: this then also reproduces an orbital family compatible with the Sirius stream, and places the origin of the Hyades stream up to 1 kpc inwards from the solar radius, which might explain the observed metallicity excess of the stream population.